Preamble for a TFI-OFDM communications system

Abstract

System and method for simplifying preamble detection and reducing power consumption in receivers. A preferred embodiment comprises a preamble made up of two sequences, a first sequence that is specified in the time domain and a second sequence that is specified in the frequency domain. The first sequence which comprises multiple copies of a time domain code sequence can allow easy detection of the preamble while the second sequence comprises multiple copies of a frequency domain code sequence and allows easy determination of the frequency response of the communications channel. A hierarchical sequence can be used to allow multi-stage correlation. This can result in a less complex correlator, hence lower power consumption. Piconets can use different code sequences to allow rapid determination of the source of a transmission without requiring the receiver to decode the entire transmission.

Description

TECHNICAL FIELD

[0003] The present invention relates generally to a system and method for digital communications, and more particularly to a system and method for simplifying preamble detection and reducing power consumption in receivers.

BACKGROUND

[0004] In a typical wireless communications system, in order to reduce power consumption, a receiver periodically wakes up from a sleep state to determine if there is a transmission for which it is the intended receiver. If there is not, then the receiver can go back to sleep. Since the amount of power consumed while the receiver is in the sleep state can be much less than when the receiver is operating in a normal mode and the amount of time the receiver spends determining if there is an incoming transmission is short, the average power consumption can be quite low. The low power consumption may lead to extended periods between recharging (or replacing) the batteries used in the receiver.

[0005] However, while the receiver is on for the determination if there is an incoming transmission, a comparatively large amount of power may still be consumed. Therefore, it can be desirable to reduce the amount of time that the receiver is active. One technique that can be used to reduce the amount of on-time for the receiver is to use a short preamble. The short preamble reduces the amount of time that is required to receive the transmission, therefore reducing the on-time. Another technique that can be used involves the use of a specific and easy-to-detect preamble.

[0006] One disadvantage of the prior art is that by shortening the preamble, the amount of time that the transmission is on the air is shortened. By shortening the air-time, it may be easier for a receiver to miss the transmission, which can lead to the receiver missing an incoming call or message.

[0007] A second disadvantage of the prior art is that by shortening the preamble, existing advantages of a particular wireless communications technique may not be fully exploited, such as making full use of available bandwidth, exploiting the frequency diversity available in a communications channel, complying to technical and regulatory requirements, operating in the presence of interferers, and so forth.

SUMMARY OF THE INVENTION

[0008] These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention which provides for a system and method for simplifying preamble detection and reducing power consumption in receivers of wireless communications systems.

[0009] In accordance with a preferred embodiment of the present invention, a preamble for a wireless communications system, the preamble comprising a sequence wherein the sequence comprises a concatenation of a first set of sub-sequences, with each sub-sequence containing a specified number of zeroes, and wherein each sub-sequence can differ depending upon its position in the preamble is provided.

[0010] In accordance with another preferred embodiment of the present invention, a method for distinguishing multiple piconets, wherein each piconet transmits a preamble with a unique code sequence, the method comprising determining the code sequence in the preamble, and identifying the piconet based on the code sequence, wherein the code sequence maps onto a unique piconet identifier is provided.

[0011] In accordance with another preferred embodiment of the present invention, a circuit to despread a hierarchical sequence made by spreading an M-length sequence with an N-length sequence, the circuit comprising a first despreader coupled to a signal input, the first despreader to despread a received signal provided by the signal input with a first sequence and a second despreader coupled to an output of the first despreader, the second despreader to despread the output of the first despreader with a second sequence is provided.

[0012] An advantage of a preferred embodiment of the present invention is that the amount of power consumed by a receiver when the receiver is determining if there is an incoming transmission can be significantly reduced. This can reduce the average power consumption for the receiver, therefore possibly extending the battery life of the receiver.

[0013] A further advantage of a preferred embodiment of the present invention is that performance specifications for circuitry in portions of the receiver can be relaxed. Therefore, lower performing (and hence lower cost) circuitry can be used and the overall cost of the receiver can be reduced.

[0014] Yet another advantage of a preferred embodiment of the present invention is that preamble detection may be more robust. This can allow for more electronic devices to operate in close proximity and/or at a higher data rate.

[0015] The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0017] FIG. 1 is a diagram of a physical layer convergence procedure (PLCP) frame that can be used in a wireless communications system;

[0018] FIGS. 2 a and 2b are diagrams of detailed views of preambles that can be used in the PLCP frame, according to a preferred embodiment of the present invention;

[0019] FIGS. 3 a and 3b are diagrams of detailed views of preambles that can be used in the PLCP frame, wherein the PLCP frame is for a communications system operating in a streaming mode, according to a preferred embodiment of the present invention;

[0020] FIGS. 4 a and 4b are diagrams of additional processing and manipulating that a time domain sequence may undergo prior to transmission, according to a preferred embodiment of the present invention;

[0021] FIG. 5 is a diagram of the creation of a code sequence by spreading one sequence with another sequence, according to a preferred embodiment of the present invention;

[0022] FIGS. 6 a and 6b are diagrams of algorithms for creating a code sequence and despreading a received signal with a hierarchical sequence, according to a preferred embodiment of the present invention;

[0023] FIG. 7 is a diagram of a despreader for use in removing a spreading sequence from a received signal;

[0024] FIGS. 8 a , 8b, and 8c are diagrams of a despreader for use in removing a spreading sequence from a received signal, wherein the spreading sequence is a hierarchical spreading sequence and the despreading is performed in multiple steps, according to a preferred embodiment of the present invention;

[0025] FIG. 9 is a diagram of a coverage area map of several piconets, according to a preferred embodiment of the present invention;

[0026] FIG. 10 is a diagram of a mapping of a piconet identifier to a unique sequence, according to a preferred embodiment of the present invention; and

[0027] FIG. 11 is a diagram of an algorithm for use in distinguishing transmissions from multiple piconets, according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0028] The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.

[0029] The present invention will be described with respect to preferred embodiments in a specific context, namely a time-frequency interleaved, orthogonal frequency division multiplexed (TFI-OFDM) wireless communications system, such as one that is adherent to IEEE 802.15.3a technical specifications. The IEEE 802.15.3a technical requirements can be found in a document entitled “TG3a Technical Requirements,” published Dec. 27, 2002, which is herein incorporated by reference. The invention may also be applied, however, to any wireless communications system that places its receivers into a sleep state and then periodically wakes them up to determine if there is an incoming transmission in order to reduce power consumption.

[0030] With reference now to FIG. 1, there is shown a diagram illustrating a physical layer convergence procedure (PLCP) frame 100 that can be used in a wireless communications system. The PLCP frame 100 can be made up of a PLCP preamble 105, a PLCP header 110 (which can include a physical layer header, a media access control layer header, a header check sequence, tail bits, and check bits), an optional extension sequence 115, a frame payload 120, a frame check sequence (FCS) 125, tail bits 130, and pad bits 135. The optional extension sequence 115 may carry additional information that can be used in the estimation of additional channels, beyond what is provided for in a transmission header. The frame payload 120 can be used to carry the data (if any) to be transmitted, while the FCS 120 can be used to protect the contents of the frame payload 120. The tail bits 130 may be used to return a convolutional encoder to a zero state, while the pad bits 135 can be used to align the transmission along symbol boundaries. The PLCP preamble 105 can be used to aid receivers in synchronizing, carrier-offset recovery, and channel estimation. A detailed discussion of the PLCP preamble 105 is presented below.

[0031] With reference now to FIG. 2a, there is shown a diagram illustrating a detailed view of the PLCP preamble 105, according to a preferred embodiment of the present invention. According to a preferred embodiment of the present invention, the PLCP preamble 105 can be transmitted prior to the PLCP header 110 to aid the receiver in performing tasks such as synchronization, carrier-offset recovery, and channel estimation. Note that in some communications, a preamble may actually be located in the middle of a transmission (in this case, it is referred to as a midamble) or at the end of a transmission (in this case, it is referred to as a postamble). However, in a majority of communications systems, especially asynchronous systems, the preamble is located at the beginning of a transmission.

[0032] As shown in FIG. 2a, the PLCP preamble 105 is for a communications system operating in a normal mode. The PLCP preamble 105 can be made up of three distinct sequences: a packet synchronization sequence 205, a frame synchronization sequence 215, and a channel estimation sequence 225. According to a preferred embodiment of the present invention, the packet synchronization sequence 205 can be used for packet detection and acquisition, coarse frequency estimation, and coarse symbol timing. The packet synchronization sequence 205 can be constructed from multiple periods, such as periods PS0 207 and PS, 209, of a time domain sequence (preferably 21 periods). The frame synchronization sequence 215 can be used to synchronize the receiver. The frame synchronization sequence 215 can be constructed from multiple periods, such as periods FSO 217 and FS, 219, of a time domain sequence (preferably three (3) periods). The channel estimation sequence 225 can be used to estimate the frequency response of the communications channel, for fine carrier frequency estimation, and fine symbol timing. The channel estimation sequence 225 can be constructed from multiple periods, such as periods CEO 227 and CE, 229, of an OFDM training symbol (preferably six (6) periods). Note that the number of periods for each sequence (21, 3, and 6) may have been chosen due to performance, regulatory, and technical constraints and that the selection of other values may result in an equally operable communications system. Therefore, the specific lengths of the sequences should not be construed as limiting the spirit of the present invention.

[0033] Note that it is preferred that the packet synchronization sequence 205 and the frame synchronization sequence 215 be created from time domain sequences while the channel estimation sequence 225 be created from a frequency domain symbol. According to a preferred embodiment of the present invention, a period of the packet synchronization sequence 205, for example, period PS0 207, can be created from a 128-length sequence that is zero-padded by 32 samples (the 32 zero samples can be prepended to the 128-length sequence) and then a guard interval may be appended to the 160-length sequence (shown as sequence 211). The zero-padded sequence is displayed in the sequence 211 as “0 0 . . . 0”, while the 128-length sequence is represented as “C, C2. C127” and the guard interval is represented as “0 0 0 0 0.” Note that rather than being zero-padded by 32 samples, the 128-length sequence may have a 32-sample cyclic prefix that is prepended to the 128-length sequence. The guard interval can be used to ensure that the transmitter and receiver have adequate time to switch from a current channel to a subsequent channel. The guard interval may be made from a sequence of five zero samples. Note that other values may be used in place of the zero samples, such as one samples or five samples from the 128-length sequence. Refer to the tables at the end of the specification Oust before the claims), illustrating exemplary 128-length sequences that can be used in the creation of a packet synchronization sequence, such as Tables 1 through 4 and 7 through 10.

[0034] A period of the frame synchronization sequence 215, for example, period FSo 217, can also be created from a 128-length sequence that has been zero-padded by 32 samples with a five sample guard interval of zero values (shown as sequence 221). As discussed above, a 32 sample cyclic prefix may be prepended to the 128-length sequence in place of the zero-padding. Once again, other values may be used in the guard band, such as one values or actual values from the 128-length sequence. According to a preferred embodiment of the present invention, the 128-length sequence used to create the frame synchronization sequence 215 may be a 180-degree rotated version of the 128-length sequence used to create the packet synchronization sequence 205. A 180-degree rotation of the 128-length sequence may also be thought of as inverting the phase of the 128-length sequence. Once again, the particular values used in the generation of the sequences (such as the 128-length sequence, the 32 sample cyclic extension, and the five sample guard band) may have been chosen based on performance, regulatory, and technical specifications and can change without changing the spirit of the present invention.

[0035] While the packet synchronization sequence 205 and the frame synchronization sequence 215 may be created from time domain sequences, the channel estimation sequence 225 can be created from a frequency domain sequence. Refer to tables 11 and 12 for exemplary 128-length sequences that can be used in the creation of a channel estimation sequence. The use of a frequency domain sequence in place of a time domain sequence can permit the exploitation of the frequency diversity of the communications channel since the frequency domain sequence can be specified to take full use of the available frequency bandwidth. Additionally, by specifying the channel estimation sequence in the frequency domain, any regulatory restrictions can be readily met by simply changing the specifications of the frequency domain sequence. For example, if a portion of the frequency band of the communications channel needs to eliminated, perhaps due to a governmental restriction or the presence of an interferer, the frequency domain sequence can be modified to compensate for the particular portion. Similar changes to a time domain sequence may require significant work. Note that for both time domain and frequency domain sequences, a value commonly referred to as a peak-to-average ratio (PAR) is of concern. A large PAR value can have a detrimental effect upon the resolution of digital-to-analog and analog-to-digital converters. Therefore, the time domain and frequency domain sequences should be selected with minimum PAR in mind.

[0036] Once the frequency domain sequence is defined, it may be converted into a time domain sequence via the use of an inverse Fourier transform. It may be preferred that an inverse Fast Fourier transform (IFFT) be used, but other inverse Fourier transforms may also be used. Note that if the frequency domain sequence is conjugate symmetric, then the output of the inverse Fourier transform is real-valued. After the conversion, a zero-padded prefix and a guard band may be appended to the time domain sequence. According to a preferred embodiment of the present invention, the time domain sequence is a 128-length sequence, while the zero-padding may be 32 samples long and the guard band can be a five sample sequence of zero values. Alternatively, rather than the 32 sample zero-padding, a cyclic prefix that is 32 samples in length may be used. Once again, other values may be used in the guard band, such as one values or actual values from the 128-length sequence.

[0037] With reference now to FIG. 2b, there is shown a diagram illustrating a detailed view of the PLCP preamble 105, wherein the PLCP preamble can be used in a communications system using transmit frequency interleaving (TFI), according to a preferred embodiment of the present invention. In a communications system that is using TFI, a transmit pattern may be used to specify the frequency channels used, for example, a transmit pattern of [1 1 2 2 3 3] implies that frequency channel #1 is to be used to transmit-the-first two periods and then frequency channel #2 is used for the next two periods and frequency channel #3 is used for the fifth and sixth periods, with the pattern repeating. The term interleaving sequence may sometimes be used interchangeably with transmit pattern. Note that many different transmit patterns may be possible. Refer to a co-pending and co-assigned patent application entitled “Interleaving Sequences for Multiple Access,” Attorney Docket Number TI-36381 for a detailed discussion of different interleaving patterns.

[0038] In order to support boundary detection (for example, between the packet synchronization sequence 205 (FIG. 2a) and the frame synchronization sequence 210 (FIG. 2a)), the final periods of a packet synchronization sequence should be followed by the first periods of a frame synchronization sequence, with both periods appearing upon the same frequency channel. With the standard PLCP preamble 105 (as shown in FIG. 2a) and certain transmit patterns, such as [1 1 2 2 3 3], the periods of the frame synchronization sequence 215 do not appear in all three frequency channels. With the transmit pattern [1 1 2 2 3 3], the periods of the frame synchronization sequence 215 are transmitted on frequency channels 2 and 3, with two periods transmitted on frequency channel 3. One way to ensure that this occurs is to interleave the packet synchronization sequence 205 with the frame synchronization sequence 210. Rather than having disjoint packet and frame synchronization sequences as displayed in FIG. 2a, the PLCP preamble 105 displayed in FIG. 2b has an interleaved packet and frame synchronization sequence 255. Since the packet synchronization sequence may be significantly longer than the frame synchronization sequence, the frame synchronization sequence periods may be interleaved with the final few periods of the packet synchronization sequence. For example, period PS18 261 may be followed with period FS0 262 and period PS19 263 may be followed with period FS1 264.

[0039] The PLCP preamble 105 displayed in FIG. 2b, when used with certain transmit patterns, such as, [1 1 2 2 3 3] and [1 1 3 3 2 2], can permit a packet synchronization period (PS18 261) to be immediately followed by a frame synchronization period (FS0 262) on the same frequency channel. Note that other transmit patterns, such as [1 2 3 1 2 3] and [1 3 2 1 3 2] may perform better with the disjoint PLCP preamble 105 shown in FIG. 2a, since with the interleaved PLCP preamble, the periods of the frame synchronization sequence may not be present in each frequency channel. Therefore, depending upon the transmit pattern, the optimal PLCP preamble can be different. In fact, the PLCP preamble used may differ depending upon the transmit pattern. For example, if a piconet uses a certain transmit pattern, then it may elect to use a certain PLCP preamble (either disjoint or interleaved) to improve performance.

[0040] With reference now to FIG. 3a, there is shown a diagram illustrating a detailed view of the PLCP preamble 105, wherein the PLCP preamble 105 is for a communications system operating in a streaming mode, according to a preferred embodiment of the present invention. When operating in streaming mode, an initial packet can use a preamble that is identical to a normal mode PLCP preamble (FIG. 2a), while subsequent packets can use a different preamble. The streaming mode PLCP preamble 105 can be made up of three distinct sequences: a packet synchronization sequence 305, a frame synchronization sequence 315, and a channel estimation sequence 325. The three sequences in the streaming mode PLCP preamble 105 (the packet synchronization sequence 305, the frame synchronization sequence 315, and the channel estimation sequence 325) may be used for the same purposes as in a normal mode PLCP preamble. However, according to a preferred embodiment of the present invention, the packet synchronization sequence 305 can be made up of nine (9) periods, such as periods PS0 307 and PS1 309, of a time domain sequence. Note that the time domain sequence may be identical to the time domain sequence used in a normal mode PLCP preamble. The frame synchronization sequence 315 can be made up of three periods, such as periods FS0 317 and FS1 319, of a time domain sequence. The channel estimation sequence 325 can be created from six (6) periods, such as periods CEO 327 and CE, 329, of a frequency domain sequence. Refer to the tables at the end of the specification, illustrating exemplary 128-length sequences that can be used in the creation of packet synchronization, frame synchronization, and channel estimation sequences.

[0041] With reference now to FIG. 3b, there is shown a diagram illustrating a detailed view of the PLCP preamble 105, wherein the PLCP preamble 105 is for a communications system operating in a streaming mode and features transmit frequency interleaving (TFI), according to a preferred embodiment of the present invention. As discussed above, when the communications system uses TFI, it may be necessary to interleave the PLCP preamble 105. If the communications system uses a transmit pattern of [1 1 2 2 3 3], for example, then the PLCP preamble 105 may be scrambled as illustrated in FIG. 3b. The PLCP preamble 105 has an interleaved packet and frame synchronization sequence 355 that can be 12 OFDM symbols in length. The OFDM symbols in the interleaved packet and frame synchronization sequence 355 may be made up of additional packet synchronization sequence periods, such as period PS6 361 and PS7 363. Periods of the frame synchronization sequence, such as period FSo 362 and FS, 364 can be interleaved between these additional packet synchronization sequence periods.

[0042] With reference now to FIGS. 4a and 4b, there are shown diagrams illustrating additional processing and manipulation that a time-domain sequence, such as a PLCP preamble, may undergo prior to transmission, according to a preferred embodiment of the present invention. As shown in FIG. 4a, the time-domain sequence may undergo a transformation, such as a time-domain filtering operation by a filter 405. An example of the filter 405 may be a pulse-shape filter implementing a square-root raised cosine pulse shape. The pulse shape filter may be used to place a spectral limit on the time-domain sequence, which may have infinite bandwidth prior to filtering. The spectral limit may be due to technical and/or regulatory requirements. A digital-to-analog converter (DAC) 410 may be used to convert the time-domain sequence into an analog signal that can be provided to transmit circuitry for transmission purposes.

[0043] In addition to being filtered, the time-domain sequence may undergo processing in alternate domain representations. As shown in FIG. 4b, the time-domain sequence may be converted into another domain by transform 455; For example, the time-domain sequence may be converted into a frequency domain sequence. After the transformation into another domain, a processor 460 may be used to provide desired processing of the sequence. Examples of the processing that can be performed upon the sequence may be magnitude clipping, shaping (such as to provide a shape to a flat sequence or to provide a desired roll-off), and pre-emphasis (to compensate for the behavior of circuitry or antennas, for example). After processing, an inverse transform 465 can be used to return the sequence back into the time-domain and the DAC 410 can be used to convert the time-domain sequence into an analog signal that can be provided to transmit circuitry.

[0044] According to a preferred embodiment of the present invention, the operations that the filter 405 or the transform 455, processor 460, and inverse transform 465 can perform to the PLCP preamble 105 can be performed while the communications system is not on-line and the results may be stored in memory for later use. Since there may be a limited number of PLCP preambles 105, off-line computation of the processing can be feasible since it can significantly reduce computational requirements during normal operations. Alternatively, if there are sufficient computational resources available, the processing can be performed in real-time to reduce storage requirements.

[0045] The complexity of a digital circuit can have an effect upon the amount of power consumed while the digital circuit is in operation. For example, a correlator that is correlating a short sequencewill tend to be less complex than a correlator designed to work with a long sequence. Therefore, it may be desirable to perform multiple correlations of short sequences as opposed to a single correlation of a long sequence.

[0046] The spreading of a bi-phase sequence with another bi-phase sequence can create a hierarchical sequence. A bi-phase sequence is a sequence that has the property of havirig the minimum peak side-lobe of all possible sequences for a given length. Note that besides from creating a longer sequence by spreading two shorter bi-phase sequences (which may not be guaranteed to produce a bi-phase sequence), another way to create a bi-phase sequence is to perform an exhaustive search. Note that more than two sequences can be used. However, the chances of having the result being a bi-phase sequence can be reduced greatly.

[0047] With reference now to FIG. 5, there is shown a diagram illustrating a circuit 500 for the spreading of one sequence with another sequence to create a code sequence for use in a PLCP preamble, according to a preferred embodiment of the present invention. The circuit 500 can be used for creating a code sequence by spreading two shorter length sequences. The code sequence, which can be a 128-length sequence, according to a preferred embodiment of the present invention, can be created by spreading a first sequence (M-length) by a second sequence (N-length), wherein M*N can be equal to 128. For example, M may be equal to 16 while N may be equal to eight (8).

[0048] As shown in FIG. 5, the first sequence (M-length) and the second sequence (N-length) may be provided to a spreader 505. Output of the spreader 505 may be the code sequence that can be used in the creation of a PLCP preamble. Let the M-length sequence be represented as {b0b1 . . . bl5} and the N-length sequence be represented as {a0a1 . . . a7}, then the M*N-length sequence (the output of the spreader 505) can be represented as {b0a0 b0a1 b0a2 . . . b0a7 b1a0 . . . b15a7}. For illustrative purposes, let the first sequence be {1, 1, 1, 1, −1, −1, 1, 1, −1, −1, 1, −1, 1, −1, 1, 1} and the second sequence be {1, −1, −1, −1, 1, 1, −1, 1}. With these two sequences as input, the output of the spreader 505 will be a 128-length sequence and may be found in Table 7. Please refer to Tables 5 and 6 for other M- and N-length sequences that can be used to create hierarchical sequences which may be used to create PLCP preambles. Note that it may be possible that more than two sequences can be spread to produce a code sequence that can be used as the time-domain packet synchronization sequence. However, significant improvement over the use of two sequences may not be present.

[0049] Note that even if each of the individual sequences (the 16-length and the 8-length sequences, for example) has the minimumpeak side-lobes, i.e., they are bi-phase sequences, this alone may not ensure that the resulting sequence (when one sequence is spread with another) has the minimum peak side-lobes. Therefore, hierarchical sequences can also be found through exhaustive search. Please refer to Tables 1 through 5 for five such sequences.

[0050] With reference now to FIGS. 6a and 6b, there are shown diagrams illustrating algorithms for creating a code sequence (algorithm 600, FIG. 6a) and despreading a hierarchical sequence (algorithm 650, FIG. 6b), according to a preferred embodiment of the present invention. With reference first to FIG. 6a, as discussed previously, the creation of a code sequence wherein the code sequence is a hierarchical sequence can involve the spreading of a first sequence, for example, an M-length sequence with a second sequence, for example, an N-length sequence (block 605). For example, if M and N were 16- and 8-length sequences respectively, the result would be a 128-length sequence.

[0051] With reference now to FIG. 6b, a hierarchical sequence can undergo two operations in order to remove the hierarchical sequence. A first operation may involve the removal of a first spreading sequence. For example, using the example discussed above wherein hierarchical sequence was created by spreading an M-length sequence with an N-length sequence, then the first despreading operation can involve despreading the received signal with the N-length spreading sequence (block 655). A second operation may then involve the despreading with an M-length spreading sequence. To ensure that the data stream is reconstructed properly, every N-th chip should be despread with the M-length spreading sequence in order to reconstruct a single bit of data rather than M consecutive chips (block 660).

[0052] The order in which the despreading occurs may not be important in the reconstruction of the data. For example, if the hierarchical sequence was created with an M-length sequence being spread with an N-length sequence, then the despreading could be performed with the N-length sequence first, followed by the M-length sequence, wherein the despreading with the M-length sequence should be applied to every N-th chip or with the M-length sequence first, followed by the N-length sequence, wherein the despreading with the M-length sequence should be applied to every N-th chip.

[0053] As discussed previously, the complexity of a digital circuit can have a direct impact on the amount of power consumed by the digital circuit when it is operating. The following discussion compares the complexity and power consumption of a correlator designed to be used with a hierarchical sequence and a correlator designed to be used with a 128-length sequence. Assuming the use of a 1-bit analog-to-digital converter (ADC), a first stage of the correlator with the hierarchical sequence, 16 1-bit numbers are added together. On average, each add could correspond to 10 gates. This implies a total of 160 gates to implement the first stage. For a second stage, eight 4-bit numbers could be added together. In the second stage, each add could correspond to 75 gates. This implies a total of 600 gates to implement the second stage. The power consumption for the correlator for the hierarchical sequence could then be 760 gates*528 MHz*5.2 nW per MHz=2.1 mW (assuming that the correlator operates at 528 MHz and each gate consumes 5.2 nW per MHz).

[0054] The correlator for the 128-length sequence could require 128 1-bit adds. On average, each add could correspond to 60 gates, for a total of 7680 gates. Note the difference in the number of gates per typical add may be due to a larger number of stages required to perform the correlation. Then, the power consumption for the correlator for the 128-length sequence could then be 7680 gates*528 MHz*5.2 nW per MHz=21 mW (again, assuming that the correlator operates at 528 MHz and each gate consumes 5.2 nW per MHz). Notice the ten-fold increase in power consumption by the correlator designed to operate on the 128-length sequence when compared with the correlator designed to operate on hierarchical sequences.

[0055] With reference now to FIG. 7, there is shown a diagram illustrating a despreader 700 for use in remove a spreading sequence from a received signal. The despreader 700 may also be used to detect a particular sequence in a preamble. As discussed above, the despreader 700 performs the despreading with the entire spreading sequence at one time, for example, the despreader 700 would despread received data that was originally spread with a spreading sequence of length 128 with the 128-length sequence. As displayed in FIG. 7, the despreader 700 can be implemented as a tapped delay line. Tapped delay lines are considered to be well understood by those of ordinary skill in the art of the present invention and will not be discussed in detail.

[0056] For discussion purposes, let rk denote the k-th chip of the received signal, yk denote the k-th chip of the despread data, and cj be the j-th coefficient of the spreading sequence. The received signal may be provided to a linear array of delay elements, for example, delay element 705 and 707. Note that the linear array of delay elements may be referred to as a tapped delay line. The delay elements may have a unity delay. Therefore, if rk is the input to the delay element 705, then rk−1 is the output of the delay element 705 while rk−2 is the output of the delay element 707. If the spreading sequence is of length q, then there can be q−1 delay elements in the tapped delay line. In addition to having an output coupled to the following delay element, the output of each delay element may also be coupled to a multiplier. For example, delay element 705 may have its output coupled to delay element 707 as well as multiplier 712. Note that an additional multiplier, multiplier 710, may have as its input, the received signal, rk.

[0057] Each multiplier has as a second input a coefficient of the spreading sequence, with a multiplier coupled to a first delay element in the tapped delay line having the last coefficient of the spreading sequence (cq). The second input to each of the subsequent multipliers are the remaining coefficients of the spreading sequence. For example, with the 128-length spreading sequence, then the second input to the multiplier 710 would be c127 and for multiplier 712, it would be c126. Output from each of the multipliers can then be provided to a summation unit 715 that can combine the outputs together to produce the despread data.

[0058] With reference now to FIG. 8a, there is shown a diagram illustrating a high-level view of a two-stage despreader 800 for use in removing a hierarchical spreading sequence from a received signal, according to a preferred embodiment of the present invention. The two-stage despreader 800 may also be used to detect a sequence in a preamble. When a hierarchical sequence is used as a spreading sequence, the despreading of the received signal may also be performed using a despreader similar to the despreader 700 (FIG. 7) wherein the despreading is performed in a single step with the full spreading sequence. However, as discussed above, the single step despreading can lead to a complex despreader that consumes a large amount of power. Therefore, when a hierarchical spreading sequence is used, the despreading can occur as a two-step operation. The resulting despreader may be smaller and therefore use less power.

[0059] The received signal may first be provided to a first despreader 805, which can perform a despreading operation with a second sequence, wherein the hierarchical spreading sequence may be the result of the first sequence being spread with a second-sequence. Note that if the first sequence is of length M and the second sequence is of length N, then the hierarchical spreading sequence is of length M*N. After being despread with the second sequence in the first despreader 805, the output of the first despreader 805 may then be provided to a second despreader 810, which can perform a despreading on the output of the first despreader 805 with the first sequence. Note that the second despreader 810 should despread every N-th output of the first despreader.

[0060] According to a preferred embodiment of the present invention, the order of the despreading can be independent of the order of the spreading. If the first despreader 805 were to despread the received signal with the first sequence (the M-length sequence), then the first despreader 805 should despread every N-th received signal. The output of the first despreader 805 may then be provided to the second despreader 810, which can despread every output of the first despreader 805 with the second sequence (the N-length sequence).

[0061] With reference now to FIG. 8b, there is shown a diagram illustrating a detailed view of the two-stage despreader 800 for use in removing a hierarchical spreading sequence from a received signal, according to a preferred embodiment of the present invention. As shown in FIG. 8b, the first despreader 805 will despread with the N-length spreading sequence and the second despreader 810 will despread with the M-length spreading sequence.

[0062] The design of the first and the second despreaders 805 and 810 uses the tapped delay line structure of the despreader 700 (FIG. 7), with differences mainly in the coefficients, the value of the delay elements, and the input signals. Since the first despreader 805 despreads the received signal with the N-length spreading sequence, the received signal, rk, can be the input to the first despreader 805 at the tapped delay line. As in the despreader 700, the number of delay elements should be one less than the length of the spreading sequence (N). According to a preferred embodiment of the present invention, each of the delay elements (for example, delay element 855) may have a unity delay. Coupled to each of the delay elements is a multiplier that can be used to multiply the output of the delay element with a coefficient of the spreading sequence, with an additional multiplier being coupled to the received signal, rk. For example, a multiplier 860 multiplies the received signal, rk, with an eight coefficient of the N-length spreading sequence, while a multiplier 862 multiplies the output of delay element 855 with a seventh coefficient of the N-length spreading sequence. A summation unit 865 combines the outputs of the multipliers to form an intermediate signal, sk.

[0063] The second despreader 810, which despreads every N-th output produced by the first despreader 805, has a design that differs slightly from the design of the first despreader 805. The second despreader 810 also makes use of a tapped delay line, but rather than the delay elements having unity delay, the delay elements (such as delay elements 870 and 872) have delays that can be equal to the length of the spreading sequence used in the first despreader 805, which in this discussion, is N=8. The number of delay elements in the tapped delay line is one less than the length of the spreading sequence (M) while the number of multipliers (such as multiplier 875) is equal to the length of the spreading sequence (M). As in the first despreader 805, the multipliers multiply the outputs of the delay elements with the coefficients of the spreading sequence. For example, the multiplier 875 multiplies the intermediate signal, sk, with a sixteenth coefficient of the spreading sequence. A summation unit 880 combines the outputs of the multipliers to produce the despread data, yk.

[0064] With reference now to FIG. 8c, there is shown a diagram illustrating a detailed view of the two-stage despreader 800 for use in removing a hierarchical spreading sequence from a received signal, according to a preferred embodiment of the present invention. As shown in FIG. 8c, the first despreader 805 will despread with the M-length spreading sequence and the second despreader 810 will despread with the N-length spreading sequence.

[0065] Since the received signal may have been originally an M-length sequence that was spread with an N-length sequence, the first despreader 805 may be configured to despread every N-th received signal. This may be accomplished by using a tapped delay line with delay elements, such as delay element 885, having a delay equal to N=8. Multipliers, such as multiplier 887 can multiply the outputs of the delay elements (or in the case of the multiplier 887, the received signal) with coefficients of the M-length spreading sequence. A summation unit 889 can combine the outputs of the multipliers to produce an intermediate value, tk.

[0066] The second despreader 810 may have a more conventional design, wherein its tapped delay line may have delay elements, such as delay element 890, with unity delay. Again, multipliers, such as multiplier 892 can multiply the outputs of the delay elements (or in the case of the multiplier 892, the intermediate signal) with the coefficients of the N-length spreading sequence. A summation unit 894 can combine the outputs of the multipliers to produce the despread data, yk.

[0067] Piconets, by their very nature, tend to have relatively small coverage areas. This can permit multiple piconets to operate within close vicinity of one another. When the piconets that are operating in close vicinity with one another are operating in a coordinated fashion, then transmissions from devices in the piconets can be arranged so that they do not interfere with one another (for example, transmissions from devices in different piconets can be made at different frequency bands or the transmissions could occur at different times). However, when the piconets are un-coordinated, then it may be possible that transmissions will interfere. For example, a transmission from a device in a first piconet can occur at the same time as a transmission from a device in a second piconet. If both transmissions use the same preamble, then a device that is in the operating range of the two piconets could lock onto the transmission from the first piconet and miss the transmission from the second piconet. This can then lead to a loss of any information contained in the transmission from the second piconet. This can also lead to a situation that can be referred to as a ‘false lock’ wherein the device locks onto one transmission thinking that it is from a desired transmitter when the transmission is in fact from a different transmitter. This may result in a higher than acceptable packet error rate (PER).

[0068] Another problem that can be associated with multiple uncoordinated piconets using a single preamble is that a device may not be able to distinguish which piconet a transmission that it has received originated from. The receiver may then be required to perform decoding of the transmission in order to determine the identity of the sender of the transmission. If the receiver did not wish to receive a transmission from this sender, then the receiver has just performed some unnecessary operations. For wireless devices, this can lead to shorter battery life due to the expenditure of power needed to decode the transmissions. Furthermore, the time spent in decoding the received transmissions can be spent in performing other tasks.

[0069] With reference now to FIG. 9, there is shown a diagram illustrating a coverage area map 900 of several piconets, according to a preferred embodiment of the present invention. The coverage area map 900 displays the operational range for devices in three piconets: piconet A 905, piconet B 910, and piconet C 915. The coverage area map 900 shows that the operational ranges for devices in the three piconets have some degree of overlap, for example, the operational range of piconet A 905 overlaps the operational range of both piconet B 910 and piconet C 915.

[0070] Located in the middle of the coverage area map 900 may be a device 920, such as a receiver, a multimedia device, a terminal, a printer, a storage device, a wireless device, or so forth. Note that the device 920 may lie within the operational range of all three piconets. Therefore, the device 920 may receive transmissions from other devices located in any (or all) three piconets. If devices in the three piconets all use the same preamble, it may be impossible for the device 920 to distinguish the originator of a transmission until it has decoded the transmission. Furthermore, the inability to distinguish the origin of a transmission may lead to the loss of desired transmissions due to confusion about the origination of transmissions.

[0071] A solution to these problems may be that transmissions from devices in different piconets use different preambles. The use of unique preambles can permit a receiver to identify which piconet a transmission is associated with, without needing to perform any decoding of the transmission itself. Furthermore, since transmissions associated with different piconets can be uniquely identified, ‘false lock’ may no longer be a problem. This can lead to an improved PER and therefore more robust communications may be a result.

[0072] Note that the use of unique preambles may apply to a preamble's packet synchronization sequence and frame synchronization sequence, but may not apply to the preamble's channel estimation sequence since the purpose of the channel estimation sequence may be to help estimate the frequency response of the communications channel. This may be true since in many cases by the time a receiver receives the channel estimation sequence, the uniqueness of the packet and frame synchronization sequences have already been detected and the source of the transmission has already been determined. Therefore, there may not be a need for as many unique sequences that can be used in the creation of channel estimation sequences.

[0073] With reference now to FIG. 10, there is shown a diagram illustrating a mapping of a piconet identifier to a unique sequence, according to a preferred embodiment of the present invention. In order to implement the use of unique preambles, there may be required a mechanism to uniquely associate a piconet with a unique sequence that may be used to create the unique preamble (or the unique preamble itself). According to a preferred embodiment of the present invention, a piconet may have a unique identifier, such as its name, identification number, access number, or so forth. This unique identifier may be assigned to a piconet during installation/configuration or it may be assigned during manufacture, wherein each piconet produced by a manufacturer may be given a unique identifier.

[0074] Through this unique identifier (block 1005), an association with a unique sequence can be made (block 1010). For example, if there may be three piconets operating within close proximity of one another, each of the three piconet's identifiers can be used to associate a unique sequence (or unique preamble). The piconet's identifier may also be used to associate a specific transmit pattern to the piconet. The piconet can use the transmit pattern associated with it in order to help reduce transmission collisions. Furthermore, depending upon the transmit pattern associated with the piconet, a PLCP preamble format may be selected. For example, if the transmit pattern has consecutive transmissions on the same transmission band, then an interleaved PLCP preamble (such as those shown in FIGS. 2b and 3b) may be used or if the transmit pattern does not have consecutive transmissions on the same transmission band, then a disjoint PLCP preamble (such as those shown in FIGS. 2a and 3a) may be used.

[0075] With reference now to FIG. 11, there is shown a diagram illustrating an algorithm 1100 for use in distinguishing transmissions from multiple piconets, according to a preferred embodiment of the present invention. As discussed above, when there are multiple piconets operating within a general area, it can be difficult to determine which piconet a transmission originated from if the piconets are not using unique preambles. When unique preambles are not being used, then a receiver of a transmission may not be able to determine the source of a transmission until it has decoded the contents of the transmission. However, when unique preambles are used, then the determination of the source of a transmission can be simpler.

[0076] According to a preferred embodiment of the present invention, the algorithm 1100 may execute within a controller, processing element, central processor, custom designed integrated circuit, or so forth of a receiver. The algorithm 1100 may be executed each time the receiver detects the presence of a transmission. The controller may begin by determining the code sequence that is in the preamble (block 1105). This code sequence should be unique to the piconet that originated the transmission. For example, using the PLCP preambles discussed above, the packet synchronization sequence 211 (FIG. 2a) may contain up to 21 copies of a sequence while the frame synchronization sequence 221 (FIG. 2a) may contain up to three copies of an inverse of the sequence. The determination of the presence of a code sequence in the PLCP preamble can be made by using a despreader, such as those shown in FIGS. 8a, 8b, and 8c.

[0077] Once the controller is able to determine the code sequence used in the creation of the preamble, the code sequence can be used to identify the piconet which is the source of the transmission (block 1110). Note that the identification process may be a reverse mapping of the mapping shown in FIG. 10. The identification of the piconet can be accomplished by looking up the identity of the piconet in a look-up table that can-be indexed by the code sequence, with the reverse mapping providing the piconet's identifier. Alternatively, since the number of piconets operating in an area may be small, a simple search in a list of piconets and their associated code sequence can be accomplished in short order without affecting the overall performance of the receiver. After identifying the source of the transmission, the controller may decide on a course of events depending upon its programming.

[0078] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, the above discussion discloses the structure of several preambles, specific lengths for the sequences used in the frame and packet synchronization sequences and the channel estimation sequence, the size of the guard bands, and so forth. Note that the structure of the preambles may change, the lengths of the sequences and guard bands may change, and the sequences themselves may change without affecting the present invention.

[0079] Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

TABLE 1
Time-domain packet synchronization sequence one
Sequence
Element Value
C0      0.6564
C1      −1.3671
C2      −0.9958
C3      −1.3981
C4      0.8481
C5      1.0892
C6      −0.8621
C7      1.1512
C8      0.9602
C9      −1.3581
C10     −0.8354
C11     −1.3249
C12     1.0964
C13     1.3334
C14     −0.7378
C15     1.3565
C16     0.9361
C17     −0.8212
C18     −0.2662
C19     −0.6866
C20     0.8437
C21     1.1237
C22     −0.3265
C23     1.0511
C24     0.7927
C25     −0.3363
C26     −0.1342
C27     −0.1546
C28     0.6955
C29     1.0608
C30     −0.1600
C31     0.9442
C32     −0.0844
C33     1.1974
C34     1.2261
C35     1.4401
C36     −0.5988
C37     −0.4675
C38     0.8520
C39     −0.8922
C40     −0.5603
C41     1.1886
C42     1.1128
C43     1.0833
C44     −0.9073
C45     −1.6227
C46     1.0013
C47     −1.6067
C48     0.3360
C49     −1.3136
C50     −1.4448
C51     −1.7238
C52     1.0287
C53     0.6100
C54     −0.9237
C55     1.2618
C56     0.5974
C57     −1.0976
C58     −0.9776
C59     −0.9982
C60     0.8967
C61     1.7640
C62     −1.0211
C63     1.6913
C64     −0.2095
C65     1.1640
C66     1.2334
C67     1.5338
C68     −0.8844
C69     −0.3857
C70     0.7730
C71     −0.9754
C72     −0.2315
C73     0.5579
C74     0.4035
C75     0.4248
C76     −0.3359
C77     −0.9914
C78     0.5975
C79     −0.8408
C80     0.3587
C81     −0.9604
C82     −1.0002
C83     −1.1636
C84     0.9590
C85     0.7137
C86     −0.6776
C87     0.9824
C88     −0.5454
C89     1.1022
C90     1.6485
C91     1.3307
C92     −1.2852
C93     −1.2659
C94     0.9435
C95     −1.6809
C96     0.4232
C97     −1.2684
C98     −1.8151
C99     −1.4829
C100    1.0302
C101    0.9419
C102    −1.1472
C103    1.4858
C104    −0.6794
C105    0.9573
C106    1.0807
C107    1.1445
C108    −1.2312
C109    −0.6643
C110    0.3836
C111    −1.1482
C112    −0.0353
C113    −0.6747
C114    −1.1653
C115    −0.8896
C116    0.2414
C117    0.1160
C118    −0.6987
C119    0.4781
C120    0.1821
C121    −1.0672
C122    −0.9676
C123    −1.2321
C124    0.5003
C125    0.7419
C126    −0.8934
C127    0.8391

[0080]

TABLE 2
Time-domain packet synchronization sequence two
Sequence
Element Value
C0      0.9679
C1      −1.0186
C2      0.4883
C3      0.5432
C4      −1.4702
C5      −1.4507
C6      −1.1752
C7      −0.0730
C8      −1.2445
C9      0.3143
C10     −1.3951
C11     −0.9694
C12     0.4563
C13     0.3073
C14     0.6408
C15     −0.9798
C16     −1.4116
C17     0.6038
C18     −1.3860
C19     −1.0888
C20     1.1036
C21     0.7067
C22     1.1667
C23     −1.0225
C24     −1.2471
C25     0.7788
C26     −1.2716
C27     −0.8745
C28     1.2175
C29     0.8419
C30     1.2881
C31     −0.8210
C32     −1.2905
C33     1.1040
C34     −1.2408
C35     −0.8062
C36     1.5425
C37     1.0955
C38     1.4284
C39     −0.4593
C40     −1.0408
C41     1.0542
C42     −0.4446
C43     −0.7929
C44     1.6733
C45     1.7568
C46     1.3273
C47     −0.2465
C48     1.6850
C49     −0.7091
C50     1.1396
C51     1.5114
C52     −1.4343
C53     −1.5005
C54     −1.2572
C55     0.8274
C56     −1.5140
C57     1.1421
C58     −1.0135
C59     −1.0657
C60     1.4073
C61     1.8196
C62     1.1679
C63     −0.4131
C64     1.5280
C65     −0.9193
C66     1.1246
C67     1.2622
C68     −1.4406
C69     −1.4929
C70     −1.1508
C71     0.4126
C72     −1.0462
C73     0.7232
C74     −1.1574
C75     −0.7102
C76     0.8502
C77     0.6260
C78     0.9530
C79     −0.4971
C80     −0.8633
C81     0.6910
C82     −0.3639
C83     −0.8874
C84     1.5311
C85     1.1546
C86     1.1935
C87     −0.2930
C88     1.3285
C89     −0.7231
C90     1.2832
C91     0.7878
C92     −0.8095
C93     −0.7463
C94     −0.8973
C95     0.5560
C96     0.5193
C97     −0.3439
C98     0.1428
C99     0.6251
C100    −1.0468
C101    −0.5798
C102    −0.8237
C103    0.2667
C104    −0.9563
C105    0.6016
C106    −0.9964
C107    −0.3541
C108    0.3965
C109    0.5201
C110    0.4733
C111    −0.2362
C112    −0.6892
C113    0.4787
C114    −0.2605
C115    −0.5887
C116    0.9411
C117    0.7364
C118    0.6714
C119    −0.1746
C120    1.1776
C121    −0.8803
C122    1.2542
C123    0.5111
C124    −0.8209
C125    −0.8975
C126    −0.9091
C127    0.2562

[0081]

TABLE 3
Time-domain packet synchronization sequence three
Sequence
Element Value
C0      0.4047
C1      0.5799
C2      −0.3407
C3      0.4343
C4      0.0973
C5      −0.7637
C6      −0.6181
C7      −0.6539
C8      0.3768
C9      0.7241
C10     −1.2095
C11     0.6027
C12     0.4587
C13     −1.3879
C14     −1.0592
C15     −1.4052
C16     −0.8439
C17     −1.5992
C18     1.1975
C19     −1.9525
C20     −1.5141
C21     0.7219
C22     0.6982
C23     1.2924
C24     −0.9460
C25     −1.2407
C26     0.4572
C27     −1.2151
C28     −0.9869
C29     1.2792
C30     0.6882
C31     1.2586
C32     −0.9671
C33     −0.9819
C34     0.7980
C35     −0.8158
C36     −0.9188
C37     1.5146
C38     0.8138
C39     1.3773
C40     0.2108
C41     0.9245
C42     −1.2138
C43     1.1252
C44     0.9663
C45     −0.8418
C46     −0.6811
C47     −1.3003
C48     −0.3397
C49     −1.1051
C50     1.2400
C51     −1.3975
C52     −0.7467
C53     0.2706
C54     0.7294
C55     0.7444
C56     −0.3970
C57     −1.0718
C58     0.6646
C59     −1.1037
C60     −0.5716
C61     0.9001
C62     0.7317
C63     0.9846
C64     −0.7298
C65     −0.9662
C66     0.9694
C67     −0.8053
C68     −0.9052
C69     1.5933
C70     0.8418
C71     1.5363
C72     0.3085
C73     1.3016
C74     −1.5546
C75     1.5347
C76     1.0935
C77     −0.8978
C78     −0.9712
C79     −1.3763
C80     −0.6360
C81     −1.2947
C82     1.6436
C83     −1.6564
C84     −1.1981
C85     0.8719
C86     0.9992
C87     1.4872
C88     −0.4586
C89     −0.8404
C90     0.6982
C91     −0.7959
C92     −0.5692
C93     1.3528
C94     0.9536
C95     1.1784
C96     0.2424
C97     0.5703
C98     −0.6381
C99     0.7861
C100    0.9175
C101    −0.4595
C102    −0.2201
C103    −0.7755
C104    −0.2965
C105    −1.1220
C106    1.7152
C107    −1.2756
C108    −0.7731
C109    1.0724
C110    1.1733
C111    1.4711
C112    0.4881
C113    0.7528
C114    −0.6417
C115    1.0363
C116    0.8002
C117    −0.0077
C118    −0.2336
C119    −0.4653
C120    0.6862
C121    1.2716
C122    −0.8880
C123    1.4011
C124    0.9531
C125    −1.1210
C126    −0.9489
C127    −1.2566

[0082]

TABLE 4
Time-domain packet synchronization sequence four
Sequence
Element Value
C0      1.1549
C1      1.0079
C2      0.7356
C3      −0.7434
C4      −1.3930
C5      1.2818
C6      −1.1033
C7      −0.2523
C8      −0.7905
C9      −0.4261
C10     −0.9390
C11     0.4345
C12     0.4433
C13     −0.3076
C14     0.5644
C15     0.2571
C16     −1.0030
C17     −0.7820
C18     −0.4064
C19     0.9034
C20     1.5406
C21     −1.4613
C22     1.2745
C23     0.3715
C24     1.8134
C25     0.9438
C26     1.3130
C27     −1.3070
C28     −1.3462
C29     1.6868
C30     −1.2153
C31     −0.6778
C32     −1.2385
C33     −0.7883
C34     −0.7954
C35     1.0874
C36     1.1491
C37     −1.4780
C38     0.8870
C39     0.4694
C40     1.5066
C41     1.1266
C42     0.9935
C43     −1.2462
C44     −1.7869
C45     1.7462
C46     −1.4881
C47     −0.4090
C48     −1.4694
C49     −0.7923
C50     −1.4607
C51     0.9113
C52     0.8454
C53     −0.8866
C54     0.8852
C55     0.4918
C56     −0.6096
C57     −0.4321
C58     −0.1327
C59     0.4953
C60     0.9702
C61     −0.8667
C62     0.6803
C63     −0.0244
C64     1.3095
C65     0.6675
C66     1.2587
C67     −0.9993
C68     −1.0052
C69     0.6601
C70     −1.0228
C71     −0.7489
C72     0.5086
C73     0.1563
C74     0.0673
C75     −0.8375
C76     −1.0746
C77     0.4454
C78     −0.7831
C79     −0.3623
C80     −1.3658
C81     −1.0854
C82     −1.4923
C83     0.4233
C84     0.6741
C85     −1.0157
C86     0.8304
C87     0.4878
C88     −1.4992
C89     −1.1884
C90     −1.4008
C91     0.7795
C92     1.2926
C93     −1.2049
C94     1.2934
C95     0.8123
C96     −1.0094
C97     −0.7598
C98     −1.0786
C99     0.6699
C100    0.9813
C101    −0.5563
C102    1.0548
C103    0.8925
C104    −1.3656
C105    −0.8472
C106    −1.3110
C107    1.1897
C108    1.5127
C109    −0.7474
C110    1.4678
C111    1.0295
C112    −0.9210
C113    −0.4784
C114    −0.5022
C115    1.2153
C116    1.5783
C117    −0.7718
C118    1.2384
C119    0.6695
C120    0.8821
C121    0.7807
C122    1.0537
C123    −0.0791
C124    −0.2845
C125    0.5790
C126    −0.4664
C127    −0.1097

[0083]

TABLE 5
Four M-length sequences, M = 16
Sequence
Number	Sequence A
1	1	1	1	1	−1	−1	1	1	−1	−1	1	−1	1	−1	1	1
2	1	−1	−1	−1	−1	−1	1	−1	1	−1	−1	1	1	−1	−1	1
3	1	1	−1	−1	−1	1	−1	−1	−1	1	−1	−1	1	−1	1	1
4	1	−1	−1	1	−1	1	−1	−1	1	1	−1	−1	−1	−1	−1	1

[0084]

TABLE 6
Four N-length sequences, N = 8
Sequence
Number	Sequence B
1	1	−1	−1	−1	1	1	−1	1
2	1	−1	1	1	−1	−1	−1	1
3	1	1	−1	1	1	−1	−1	−1
4	1	1	1	−1	−1	1	−1	−1

[0085]

TABLE 7
Time-domain packet synchronization sequence five
Sequence
Element Value
C0      1
C1      −1
C2      −1
C3      −1
C4      1
C5      1
C6      −1
C7      1
C8      1
C9      −1
C10     −1
C11     −1
C12     1
C13     1
C14     −1
C15     1
C16     1
C17     −1
C18     −1
C19     −1
C20     1
C21     1
C22     −1
C23     1
C24     1
C25     −1
C26     −1
C27     −1
C28     1
C29     1
C30     −1
C31     1
C32     −1
C33     1
C34     1
C35     1
C36     −1
C37     −1
C38     1
C39     −1
C40     −1
C41     1
C42     1
C43     1
C44     −1
C45     −1
C46     1
C47     −1
C48     1
C49     −1
C50     −1
C51     −1
C52     1
C53     1
C54     −1
C55     1
C56     1
C57     −1
C58     −1
C59     −1
C60     1
C61     1
C62     −1
C63     1
C64     −1
C65     1
C66     1
C67     1
C68     −1
C69     −1
C70     1
C71     −1
C72     −1
C73     1
C74     1
C75     1
C76     −1
C77     −1
C78     1
C79     −1
C80     1
C81     −1
C82     −1
C83     −1
C84     1
C85     1
C86     −1
C87     1
C88     −1
C89     1
C90     1
C91     1
C92     −1
C93     −1
C94     1
C95     −1
C96     1
C97     −1
C98     −1
C99     −1
C100    1
C101    1
C102    −1
C103    1
C104    −1
C105    1
C106    1
C107    1
C108    −1
C109    −1
C110    1
C111    −1
C112    1
C113    −1
C114    −1
C115    −1
C116    1
C117    1
C118    −1
C119    1
C120    1
C121    −1
C122    −1
C123    −1
C124    1
C125    1
C126    −1
C127    1

[0086]

TABLE 8
Time-domain packet synchronization sequence six
Sequence
Element Value
C0      1
C1      −1
C2      1
C3      1
C4      −1
C5      −1
C6      −1
C7      1
C8      −1
C9      1
C10     −1
C11     −1
C12     1
C13     1
C14     1
C15     −1
C16     −1
C17     1
C18     −1
C19     −1
C20     1
C21     1
C22     1
C23     −1
C24     −1
C25     1
C26     −1
C27     −1
C28     1
C29     1
C30     1
C31     −1
C32     −1
C33     1
C34     −1
C35     −1
C36     1
C37     1
C38     1
C39     −1
C40     −1
C41     1
C42     −1
C43     −1
C44     1
C45     1
C46     1
C47     −1
C48     1
C49     −1
C50     1
C51     1
C52     −1
C53     −1
C54     −1
C55     1
C56     −1
C57     1
C58     −1
C59     −1
C60     1
C61     1
C62     1
C63     −1
C64     1
C65     −1
C66     1
C67     1
C68     −1
C69     −1
C70     −1
C71     1
C72     −1
C73     1
C74     −1
C75     −1
C76     1
C77     1
C78     1
C79     −1
C80     −1
C81     1
C82     −1
C83     −1
C84     1
C85     1
C86     1
C87     −1
C88     1
C89     −1
C90     1
C91     1
C92     −1
C93     −1
C94     −1
C95     1
C96     1
C97     −1
C98     1
C99     1
C100    −1
C101    −1
C102    −1
C103    1
C104    −1
C105    1
C106    −1
C107    −1
C108    1
C109    1
C110    1
C111    −1
C112    −1
C113    1
C114    −1
C115    −1
C116    1
C117    1
C118    1
C119    −1
C120    1
C121    −1
C122    1
C123    1
C124    −1
C125    −1
C126    −1
C127    1

[0087]

TABLE 9
Time-domain packet synchronization sequence seven
Sequence
Element Value
C0      1
C1      1
C2      −1
C3      1
C4      1
C5      −1
C6      −1
C7      −1
C8      1
C9      1
C10     −1
C11     1
C12     1
C13     −1
C14     −1
C15     −1
C16     −1
C17     −1
C18     1
C19     −1
C20     −1
C21     1
C22     1
C23     1
C24     −1
C25     −1
C26     1
C27     −1
C28     −1
C29     1
C30     1
C31     1
C32     −1
C33     −1
C34     1
C35     −1
C36     −1
C37     1
C38     1
C39     1
C40     1
C41     1
C42     −1
C43     1
C44     1
C45     −1
C46     −1
C47     −1
C48     −1
C49     −1
C50     1
C51     −1
C52     −1
C53     1
C54     1
C55     1
C56     −1
C57     −1
C58     1
C59     −1
C60     −1
C61     1
C62     1
C63     1
C64     −1
C65     −1
C66     1
C67     −1
C68     −1
C69     1
C70     1
C71     1
C72     1
C73     1
C74     −1
C75     1
C76     1
C77     −1
C78     −1
C79     −1
C80     −1
C81     −1
C82     1
C83     −1
C84     −1
C85     1
C86     1
C87     1
C88     −1
C89     −1
C90     1
C91     −1
C92     −1
C93     1
C94     1
C95     1
C96     1
C97     1
C98     −1
C99     1
C100    1
C101    −1
C102    −1
C103    −1
C104    −1
C105    −1
C106    1
C107    −1
C108    −1
C109    1
C110    1
C111    1
C112    1
C113    1
C114    −1
C115    1
C116    1
C117    −1
C118    −1
C119    −1
C120    1
C121    1
C122    −1
C123    1
C124    1
C125    −1
C126    −1
C127    −1

[0088]

TABLE 10
Time-domain packet synchronization sequence eight
Sequence
Element Value
C0      1
C1      1
C2      1
C3      −1
C4      −1
C5      1
C6      −1
C7      −1
C8      −1
C9      −1
C10     −1
C11     1
C12     1
C13     −1
C14     1
C15     1
C16     −1
C17     −1
C18     −1
C19     1
C20     1
C21     −1
C22     1
C23     1
C24     1
C25     1
C26     1
C27     −1
C28     −1
C29     1
C30     −1
C31     −1
C32     −1
C33     −1
C34     −1
C35     1
C36     1
C37     −1
C38     1
C39     1
C40     1
C41     1
C42     1
C43     −1
C44     −1
C45     1
C46     −1
C47     −1
C48     −1
C49     −1
C50     −1
C51     1
C52     1
C53     −1
C54     1
C55     1
C56     −1
C57     −1
C58     −1
C59     1
C60     1
C61     −1
C62     1
C63     1
C64     1
C65     1
C66     1
C67     −1
C68     −1
C69     1
C70     −1
C71     −1
C72     1
C73     1
C74     1
C75     −1
C76     −1
C77     1
C78     −1
C79     −1
C80     −1
C81     −1
C82     −1
C83     1
C84     1
C85     −1
C86     1
C87     1
C88     −1
C89     −1
C90     −1
C91     1
C92     1
C93     −1
C94     1
C95     1
C96     −1
C97     −1
C98     −1
C99     1
C100    1
C101    −1
C102    1
C103    1
C104    −1
C105    −1
C106    −1
C107    1
C108    1
C109    −1
C110    1
C111    1
C112    −1
C113    −1
C114    −1
C115    1
C116    1
C117    −1
C118    1
C119    1
C120    1
C121    1
C122    1
C123    −1
C124    −1
C125    1
C126    −1
C127    −1

[0089]

TABLE 11
Frequency-domain OFDM training sequence one.
Tone
Number Value
−56    (1 − j)/{square root over (2)}
−55    (−1 + j)/{square root over (2)}
−54    (−1 + j)/{square root over (2)}
−53    (1 − j)/{square root over (2)}
−52    (1 − j)/{square root over (2)}
−51    (1 − j)/{square root over (2)}
−50    (−1 + j)/{square root over (2)}
−49    (1 − j)/{square root over (2)}
−48    (−1 + j)/{square root over (2)}
−47    (−1 + j)/{square root over (2)}
−46    (−1 + j)/{square root over (2)}
−45    (1 − j)/{square root over (2)}
−44    (−1 + j)/{square root over (2)}
−43    (−1 + j)/{square root over (2)}
−42    (−1 + j)/{square root over (2)}
−41    (−1 + j)/{square root over (2)}
−40    (−1 + j)/{square root over (2)}
−39    (−1 + j)/{square root over (2)}
−38    (1 − j)/{square root over (2)}
−37    (−1 + j)/{square root over (2)}
−36    (1 − j)/{square root over (2)}
−35    (−1 + j)/{square root over (2)}
−34    (−1 + j)/{square root over (2)}
−33    (−1 + j)/{square root over (2)}
−32    (1 − j)/{square root over (2)}
−31    (−1 + j)/{square root over (2)}
−30    (−1 + j)/{square root over (2)}
−29    (1 − j)/{square root over (2)}
−28    (1 − j)/{square root over (2)}
−27    (1 − j)/{square root over (2)}
−26    (−1 + j)/{square root over (2)}
−25    (−1 + j)/{square root over (2)}
−24    (−1 + j)/{square root over (2)}
−23    (1 − j)/{square root over (2)}
−22    (−1 + j)/{square root over (2)}
−21    (−1 + j)/{square root over (2)}
−20    (1 − j)/{square root over (2)}
−19    (−1 + j)/{square root over (2)}
−18    (−1 + j)/{square root over (2)}
−17    (−1 + j)/{square root over (2)}
−16    (−1 + j)/{square root over (2)}
−15    (1 − j)/{square root over (2)}
−14    (−1 + j)/{square root over (2)}
−13    (1 − j)/{square root over (2)}
−12    (−1 + j)/{square root over (2)}
−11    (1 − j)/{square root over (2)}
−10    (1 − j)/{square root over (2)}
−9     (1 − j)/{square root over (2)}
−8     (−1 + j)/{square root over (2)}
−7     (−1 + j)/{square root over (2)}
−6     (−1 + j)/{square root over (2)}
−5     (−1 + j)/{square root over (2)}
−4     (−1 + j)/{square root over (2)}
−3     (1 − j)/{square root over (2)}
−2     (−1 + j)/{square root over (2)}
−1     (1 − j)/{square root over (2)}
1      (1 + j)/{square root over (2)}
2      −(1 + j)/{square root over (2)}
3      (1 + j)/{square root over (2)}
4      −(1 + j)/{square root over (2)}
5      −(1 + j)/{square root over (2)}
6      −(1 + j)/{square root over (2)}
7      −(1 + j)/{square root over (2)}
8      −(1 + j)/{square root over (2)}
9      (1 + j)/{square root over (2)}
10     (1 + j)/{square root over (2)}
11     (1 + j)/{square root over (2)}
12     −(1 + j)/{square root over (2)}
13     (1 + j)/{square root over (2)}
14     −(1 + j)/{square root over (2)}
15     (1 + j)/{square root over (2)}
16     −(1 + j)/{square root over (2)}
17     −(1 + j)/{square root over (2)}
18     −(1 + j)/{square root over (2)}
19     −(1 + j)/{square root over (2)}
20     (1 + j)/{square root over (2)}
21     −(1 + j)/{square root over (2)}
22     −(1 + j)/{square root over (2)}
23     (1 + j)/{square root over (2)}
24     −(1 + j)/{square root over (2)}
25     −(1 + j)/{square root over (2)}
26     −(1 + j)/{square root over (2)}
27     (1 + j)/{square root over (2)}
28     (1 + j)/{square root over (2)}
29     (1 + j)/{square root over (2)}
30     −(1 + j)/{square root over (2)}
31     −(1 + j)/{square root over (2)}
32     (1 + j)/{square root over (2)}
33     −(1 + j)/{square root over (2)}
34     −(1 + j)/{square root over (2)}
35     −(1 + j)/{square root over (2)}
36     (1 + j)/{square root over (2)}
37     −(1 + j)/{square root over (2)}
38     (1 + j)/{square root over (2)}
39     −(1 + j)/{square root over (2)}
40     −(1 + j)/{square root over (2)}
41     −(1 + j)/{square root over (2)}
42     −(1 + j)/{square root over (2)}
43     −(1 + j)/{square root over (2)}
44     −(1 + j)/{square root over (2)}
45     (1 + j)/{square root over (2)}
46     −(1 + j)/{square root over (2)}
47     −(1 + j)/{square root over (2)}
48     −(1 + j)/{square root over (2)}
49     (1 + j)/{square root over (2)}
50     −(1 + j)/{square root over (2)}
51     (1 + j)/{square root over (2)}
52     (1 + j)/{square root over (2)}
53     (1 + j)/{square root over (2)}
54     −(1 + j)/{square root over (2)}
55     −(1 + j)/{square root over (2)}
56     (1 + j)/{square root over (2)}

[0090]

TABLE 12
Frequency-domain OFDM training sequence two
Tone
Number Value
−56    1
−55    −1
−54    −1
−53    1
−52    −1
−51    −1
−50    1
−49    1
−48    −1
−47    1
−46    −1
−45    −1
−44    −1
−43    1
−42    −1
−41    1
−40    1
−39    −1
−38    −1
−37    −1
−36    1
−35    −1
−34    −1
−33    −1
−32    1
−31    1
−30    1
−29    1
−28    1
−27    −1
−26    1
−25    1
−24    1
−23    −1
−22    1
−21    −1
−20    1
−19    −1
−18    −1
−17    1
−16    −1
−15    −1
−14    −1
−13    1
−12    1
−11    −1
−10    1
−9     1
−8     1
−7     −1
−6     −1
−5     1
−4     1
−3     1
−2     1
−1     1
1      1
2      1
3      1
4      1
5      1
6      −1
7      −1
8      1
9      1
10     1
11     −1
12     1
13     1
14     −1
15     −1
16     −1
17     1
18     −1
19     −1
20     1
21     −1
22     1
23     −1
24     1
25     1
26     1
27     −1
28     1
29     1
30     1
31     1
32     1
33     −1
34     −1
35     −1
36     1
37     −1
38     −1
39     −1
40     1
41     1
42     −1
43     1
44     −1
45     −1
46     −1
47     1
48     −1
49     1
50     1
51     −1
52     −1
53     1
54     −1
55     −1
56     1

Claims

1. A preamble for a wireless communications system, the preamble comprising a sequence wherein the sequence comprises a concatenation of a first set of sub-sequences, with each sub-sequence containing a specified number of zeroes, and wherein each sub-sequence can differ depending upon its position in the preamble.

2. The preamble of claim 1, wherein the sub-sequences may be specified in the time domain.

3. The preamble of claim 1 further comprising a second sequence wherein the second sequence comprises a concatenation of a second set of sub-sequences, wherein the second set of sub-sequences can differ from the first set of sub-sequences.

4. The preamble of claim 3, wherein the second sequence comprises a concatenation of multiple copies of a frequency domain sequence.

5. The preamble of claim 4, wherein the frequency domain sequence is converted into a time domain sequence prior to use in creating the second sequence.

6. The preamble of claim 5, wherein the second sequence comprises six (6) copies of the time domain sequence version of the frequency domain sequence.

7. The preamble of claim 4, wherein the frequency domain sequence is specified as follows:

8. The preamble of claim 4, wherein the frequency domain sequence is specified as follows:

9. The preamble of claim 1, wherein the first sequence comprises: a third sequence wherein the third sequence comprises a concatenation of multiple copies of a first sub-sequence; and a fourth sequence wherein the fourth sequence comprises a concatenation of multiple copies of a fifth sequence comprising 180-degree rotations of each member of the first sub-sequence.

10. The preamble of claim 9, wherein the first sub-sequence is a hierarchical sequence.

11. The preamble of claim 10, wherein the first sub-sequence is created by spreading a first hierarchical sequence with a second hierarchical sequence, wherein the two hierarchical sequences are shorter than the first sub-sequence.

12. The preamble of claim 11, wherein the first hierarchical sequence is a sequence selected from:

13. The preamble of claim 11, wherein the second hierarchical sequence is a sequence selected from:

14. The preamble of claim 11, wherein the time domain sequence is specified as follows:

15. The preamble of claim 11, wherein the time domain sequence is specified as follows:

16. The preamble of claim 11, wherein the time domain sequence is specified as follows:

17. The preamble of claim 11, wherein the time domain sequence is specified as follows:

18. The preamble of claim 9, wherein the third sequence comprises multiple copies of the first sub-sequence combined with a guard band.

19. The preamble of claim 18, wherein the third sequence comprises multiple copies of the first sub-sequence with a postpended guard band and a prepended sequence.

20. The preamble of claim 19, wherein the third sequence comprises twenty one (21) copies of the first sub-sequence with a postpended guard band and a prepended sequence.

21. The preamble of claim 19, wherein the third sequence comprises nine (9) copies of the first sub-sequence with a postpended guard band and a prepended sequence.

22. The preamble of claim 19, wherein the guard band comprises a sequence of five (5) zero samples.

23. The preamble of claim 19, wherein the prepended sequence is a zero-padded sequence.

24. The preamble of claim 19, wherein the prepended sequence is a cyclic prefix.

25. The preamble of claim 9, wherein the fourth sequence comprises multiple copies of the fifth sequence combined with a guard band.

26. The preamble of claim 25, wherein the fourth sequence comprises three (3) copies of the fifth sequence with a postpended guard band and a prepended sequence.

27. The preamble of claim 9, wherein the third sequence comprises multiple concatenated copies of the first sub-sequence, wherein the fourth sequence comprises multiple concatenated copies of the fifth sequence, and wherein the third and fourth sequences are interleaved.

28. The preamble of claim 27, wherein the preamble is used in a communications system that changes transmit frequency based on a transmit code, and wherein the length of the interleaved third and fourth sequence is an integer multiple of a period of the transmit code.

29. The preamble of claim 1, wherein the wireless communications system uses orthogonal frequency division multiple access.

30. The preamble of claim 29, wherein the wireless communications system is a time-frequency interleaved, orthogonal frequency division multiple access communications system.

31. The preamble of claim 1, wherein the preamble can be transformed prior to transmission.

32. The preamble of claim 31, wherein the transformation comprises a time-domain filtering.

33. The preamble of claim 31, wherein the transformation comprises: a first domain conversion; processing the domain converted preamble; and a second domain conversion.

34. The preamble of claim 33, wherein the processing comprises magnitude clipping, and wherein the time domain sequence after the second domain conversion is specified as follows:

35. The preamble of claim 33, wherein the processing comprises magnitude clipping, and wherein the time domain sequence after the second domain conversion is specified as follows:

36. The preamble of claim 33, wherein the processing comprises magnitude clipping, and wherein the time domain sequence after the second domain conversion is specified as follows:

37. The preamble of claim 33, wherein the processing comprises magnitude clipping, and wherein the time domain sequence after the second domain conversion is specified as follows:

38. The preamble of claim 31, wherein the preamble can be transformed prior to use and stored in a memory.

39. A method for distinguishing multiple piconets, wherein each piconet transmits a preamble with a unique code sequence, the method comprising: determining the code sequence in the preamble; and identifying the piconet based on the code sequence, wherein the code sequence maps onto a unique piconet identifier.

40. The method of claim 39, wherein the determining comprises extracting the code sequence used to create the preamble.

41. The method of claim 40, wherein the code sequence is a hierarchical code, wherein the code sequence can be created by spreading a first sequence with a second sequence, and wherein the extracting comprises: despreading the preamble with the second sequence; and despreading an output of the first despreading with the first sequence.

42. The method of claim 41, wherein the first sequence is an M-length sequence, wherein the second sequence is an N-length sequence, and wherein the second despreading comprises despreading every N-th chip produced by the first despreading with the first sequence.

43. The method of claim 40, wherein the code sequence is a hierarchical code, wherein the code sequence can be created by spreading a first sequence with a second sequence, and wherein the extracting comprises: despreading the preamble with the first sequence; and despreading an output of the first despreading with the second sequence.

44. The method of claim 43, wherein the first sequence is an M-length sequence, wherein the second sequence is an N-length sequence, and wherein the first despreading comprises despreading every N-th chip of the preamble with the first sequence.

45. The method of claim 39, wherein the identifying comprises using a look-up table indexed by the code sequence to find the source of the preamble.

46. The method of claim 39, wherein the identifying comprises searching a list of sources and their associated code sequences to find the source of the preamble.

47. A circuit to despread a hierarchical sequence made by spreading an M-length sequence with an N-length sequence, the circuit comprising: a first despreader coupled to a signal input, the first despreader to despread a received signal provided by the signal input with a first sequence; and a second despreader coupled to an output of the first despreader, the second despreader to despread the output of the first despreader with a second sequence.

48. The circuit of claim 47, wherein the first and second despreader comprises: a serially coupled chain of delay elements, wherein a first delay element is coupled to an input; a plurality of multipliers, wherein each multiplier having a first input coupled to an output of one delay element and a second input coupled to a coefficient of the first sequence; and a summation unit coupled to outputs of each multiplier, the summation unit to combine the outputs of each multiplier to produce a value.

49. The circuit of claim 48, wherein-a first multiplier in the plurality of multipliers has a first input coupled to the input.

50. The circuit of claim 48, wherein the first sequence is the N-length sequence and the second sequence is the M-length sequence, and wherein the first despreader has N−1 delay elements and N multipliers and the second despreader has M−1 delay elements and M multipliers.

51. The circuit of claim 50, wherein the delay elements of the second despreader have a delay of N and the delay elements of the first despreader have unity delay.

52. The circuit of claim 48, wherein the first sequence is the M-length sequence and the second sequence is the N-length sequence, and wherein the first despreader has M−1 delay elements and M multipliers and the second despreader has N−1 delay elements and N multipliers.

53. The circuit of claim 52, wherein the delay elements of the first despreader have a delay of N and the delay elements of the second despreader have unity delay.

54. The circuit of claim 47, wherein the circuit is used in a wireless receiver.

55. The circuit of claim 54, wherein the wireless receiver is part of a wireless communications system wherein transmissions include a preamble that makes use of a hierarchical sequence.

56. The circuit of claim 55, wherein the wireless receiver is part of a wireless communications system using orthogonal frequency division multiplexing.

57. The circuit of claim 55, wherein the wireless receiver is part of a wireless communications system using time frequency interleaved, orthogonal frequency division multiplexing.