I. Field
The following description relates generally to wireless communications and more particularly to properties of sets of frequency domain pseudo random/pseudo noise (PN) sequences.
II. Background
Wireless communication systems are widely deployed to provide various types of communication; for instance, voice and/or data can be provided via such wireless communication systems. A typical wireless communication system, or network, can provide multiple users access to one or more shared resources (e.g., bandwidth, transmit power, etc.). For instance, a system can use a variety of multiple access techniques such as Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), Orthogonal Frequency Division Multiplexing (OFDM), and others.
Generally, wireless multiple-access communication systems can simultaneously support communication for multiple access terminals. Each access terminal can communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to access terminals, and the reverse link (or uplink) refers to the communication link from access terminals to base stations. This communication link can be established via a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
MIMO systems commonly employ multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas can be decomposed into NS independent channels, which can be referred to as spatial channels, where NS≦{NT, NR}. Each of the NS independent channels corresponds to a dimension. Moreover, MIMO systems can provide improved performance (e.g., increased spectral efficiency, higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and received antennas are utilized.
MIMO systems can support various duplexing techniques to divide forward and reverse link communications over a common physical medium. For instance, frequency division duplex (FDD) systems can utilize disparate frequency regions for forward and reverse link communications. Further, in time division duplex (TDD) systems, forward and reverse link communications can employ a common frequency region so that the reciprocity principle allows estimation of the forward link channel from reverse link channel.
Wireless communication systems oftentimes employ one or more base stations that provide a coverage area. A typical base station can transmit multiple data streams for broadcast, multicast and/or unicast services, wherein a data stream may be a stream of data that can be of independent reception interest to an access terminal. An access terminal within the coverage area of such base station can be employed to receive one, more than one, or all the data streams carried by the composite stream. Likewise, an access terminal can transmit data to the base station or another access terminal.
A typical wireless communication network (e.g., employing frequency, time and code division techniques) can include one or more base stations that provide a coverage area and one or more mobile (e.g., wireless) terminals that can transmit and receive data within the coverage area. A typical base station can simultaneously transmit multiple data streams for broadcast, multicast, and/or unicast services, wherein a data stream is a stream of data that can be of independent reception interest to a mobile terminal. A mobile terminal within the coverage area of that base station can be interested in receiving one, more than one or all the data streams carried by the composite stream. Likewise, a mobile terminal can transmit data to the base station or another mobile terminal. Such communication between access points and mobile terminals or between mobile terminals can take place after a terminal has “acquired” a base station serving a coverage sector. Typically, in an acquisition process a terminal accesses the necessary system information to communicate with the serving base station. As terminals enter and leave a sector without a specific pattern, acquisition information is frequently transmitted by the sector. The latter imposes a significant overhead in a wireless system.
The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of such embodiments. This summary is not an extensive overview of all contemplated embodiments, and is intended to neither identify key or critical elements of all embodiments nor delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.
In one aspect, a method is provided for receiving wireless communication using a family of time domain pseudo-noise (PN) sequences based upon a frequency domain base PN sequence by employing a processor executing computer executable instructions stored on a computer readable storage medium to implement the following acts: A data packet communication signal is received that was transmitted on a plurality m of frequency domain available tones. A frequency domain binary pseudo-noise (PN) sequence ai, i=0, 1, . . . , m−1 is accessed comprising a binary maximum length shift register sequence (m-sequence) whose members are mapped to ±1 from {0, 1}. A family of total number k of time domain sequence spectrum is generated by cyclically shifting the frequency domain binary PN sequence within the plurality m of frequency domain available consecutive tones. A series p=1, 2, . . . , k of sequence spectrum of the received data packet communication sequence are demodulated using the family of time domain PN sequences. The family of frequency domain PN sequences provides a low time domain peak-to-average (PAR) ratio, each PN sequence provides perfect autocorrelation thus zero out-of-phase correlation, any pair of PN sequences has substantially perfect cross-correlation; and sequence correlation in frequency domain achieved with addition-only or addition and subtraction-only operations.
In another aspect, a computer program product is provided for receiving wireless communication using a family of time domain pseudo-noise (PN) sequences based upon a frequency domain base PN sequence. At least one computer readable storage medium stores computer executable instructions that, when executed by at least one processor, implement components. A set of codes causes a computer to receive a data packet communication signal transmitted on a plurality m of frequency domain available tones. A set of codes causes the computer to access a frequency domain binary pseudo-noise (PN) sequence ai, i=0, 1, . . . , m−1 comprising a binary maximum length shift register sequence (m-sequence) whose members are mapped to ±1 from {0, 1}. A set of codes causes the computer to generate a family of total number k of time domain sequence spectrum by cyclically shifting the frequency domain binary PN sequence within the plurality m of frequency domain available consecutive tones. A set of codes causes the computer to demodulate a series p=1, 2, . . . , k of sequence spectrum of the received data packet communication sequence using the family of time domain PN sequences. The family of frequency domain PN sequences provides a low time domain peak-to-average (PAR) ratio, each PN sequence provides perfect autocorrelation thus zero out-of-phase correlation, any pair of PN sequences has substantially perfect cross-correlation; and sequence correlation in frequency domain achieved with addition-only or addition and subtraction-only operations.
In an additional aspect, an apparatus is provided for receiving wireless communication using a family of time domain pseudo-noise (PN) sequences based upon a frequency domain base PN sequence. At least one computer readable storage medium stores computer executable instructions that when executed by at least one processor implement components. Means are provided for receiving a data packet communication signal transmitted on a plurality m of frequency domain available tones. Means are provided for accessing a frequency domain binary pseudo-noise (PN) sequence ai, i=0, 1, . . . , m−1 comprising a binary maximum length shift register sequence (m-sequence) whose members are mapped to ±1 from {0, 1}. Means are provided for generating a family of total number k of time domain sequence spectrum by cyclically shifting the frequency domain binary PN sequence within the plurality m of frequency domain available consecutive tones. Means are provided for demodulating a series p=1, 2, . . . , k of sequence spectrum of the received data packet communication sequence using the family of time domain PN sequences. The family of frequency domain PN sequences provides low time domain peak-to-average (PAR) ratio, each PN sequence provides perfect autocorrelation thus zero out-of-phase correlation, any pair of PN sequences has substantially perfect cross-correlation; and sequence correlation in frequency domain achieved with addition-only or addition and subtraction-only operations.
In a further aspect, an apparatus is provided for receiving wireless communication using a family of time domain pseudo-noise (PN) sequences based upon a frequency domain base PN sequence. A receiver is for receiving a data packet communication signal transmitted on a plurality m of frequency domain available tones. A computer-readable storage medium is for accessing a frequency domain binary pseudo-noise (PN) sequence ai, i=0, 1, . . . , m−1 comprising a binary maximum length shift register sequence (m-sequence) whose members are mapped to ±1 from {0, 1}. A computing platform is for generating a family of total number k of time domain sequence spectrum by cyclically shifting the frequency domain binary PN sequence within the plurality m of frequency domain available consecutive tones. A demodulator is for demodulating a series p=1, 2, . . . , k of sequence spectrum of the received data packet communication sequence using the family of time domain PN sequences. The family of frequency domain PN sequences provides low time domain peak-to-average (PAR) ratio, each PN sequence provides perfect autocorrelation thus zero out-of-phase correlation, any pair of PN sequences has substantially perfect cross-correlation; and sequence correlation in frequency domain achieved with addition-only or addition and subtraction-only operations.
In yet one aspect, a method is provided for transmitting wireless communication using a family of time domain pseudo-noise (PN) sequences based upon a frequency domain base PN sequence by employing a processor executing computer executable instructions stored on a computer readable storage medium to implement the following acts: A frequency domain binary pseudo-noise (PN) sequence ai, i=0, 1, . . . , m−1 is accessed comprising a binary maximum length shift register sequence (m-sequence) whose members are mapped to ±1 from {0, 1}. A family of total number k of time domain sequence spectrum is generated by cyclically shifting the frequency domain binary PN sequence within the plurality m of frequency domain available consecutive tones. A data packet communication is modulated using the family of time domain PN sequences. The modulated data packet communication signal is transmitted on a plurality m of frequency domain available tones. The family of frequency domain PN sequences provides low time domain peak-to-average (PAR) ratio, each PN sequence provides perfect autocorrelation thus zero out-of-phase correlation, any pair of PN sequences has substantially perfect cross-correlation; and sequence correlation in frequency domain achieved with addition-only or addition and subtraction-only operations.
In yet another aspect, a computer program product is provided for transmitting wireless communication using a family of time domain pseudo-noise (PN) sequences based upon a frequency domain base PN sequence. At least one computer readable storage medium stores computer executable instructions that when executed by at least one processor implement components. A set of codes causes a computer to access a frequency domain binary pseudo-noise (PN) sequence ai, i=0, 1, . . . , m−1 comprising a binary maximum length shift register sequence (m-sequence) whose members are mapped to ±1 from {0, 1}. A set of codes causes the computer to generate a family of total number k of time domain sequence spectrum by cyclically shifting the frequency domain binary PN sequence within the plurality m of frequency domain available consecutive tones. A set of codes causes the computer to modulate a data packet communication using the family of time domain PN sequences. A set of codes causes the computer to transmit the modulated data packet communication signal transmitted on a plurality m of frequency domain available tones. The family of frequency domain PN sequences provides a low time domain peak-to-average (PAR) ratio, each PN sequence provides perfect autocorrelation thus zero out-of-phase correlation, any pair of PN sequences has substantially perfect cross-correlation; and sequence correlation in frequency domain achieved with addition-only or addition and subtraction-only operations.
In yet an additional aspect, an apparatus is provided for transmitting wireless communication using a family of time domain pseudo-noise (PN) sequences based upon a frequency domain base PN sequence. At least one computer readable storage medium stores computer executable instructions that when executed by the at least one processor implement components. Means are provided for accessing a frequency domain binary pseudo-noise (PN) sequence ai, i=0, 1, . . . , m−1 comprising a binary maximum length shift register sequence (m-sequence) whose members are mapped to ±1 from {0, 1}. Means for provided for generating a family of total number k of time domain sequence spectrum by cyclically shifting the frequency domain binary PN sequence within the plurality m of frequency domain available consecutive tones. Means are provided for modulating a data packet communication using the family of time domain PN sequences. Means are provided for transmitting the modulated data packet communication signal transmitted on a plurality m of frequency domain available tones. The family of frequency domain PN sequences provides low time domain peak-to-average (PAR) ratio, each PN sequence provides perfect autocorrelation thus zero out-of-phase correlation, any pair of PN sequences has substantially perfect cross-correlation; and sequence correlation in frequency domain achieved with addition-only or addition and subtraction-only operations.
In yet a further aspect, an apparatus is provided for transmitting wireless communication using a family of time domain pseudo-noise (PN) sequences based upon a frequency domain base PN sequence. A computer-readable storage medium is for accessing a frequency domain binary pseudo-noise (PN) sequence ai, i=0, 1, . . . , m−1 comprising a binary maximum length shift register sequence (m-sequence) whose members are mapped to ±1 from {0, 1}. The computing platform is further for generating a family of total number k of time domain sequence spectrum by cyclically shifting the frequency domain binary PN sequence within the plurality m of frequency domain available consecutive tones. A modulator is for modulating a data packet communication using the family of time domain PN sequences. A transmitter is for transmitting the modulated data packet communication signal transmitted on a plurality m of frequency domain available tones. The family of frequency domain PN sequences provides low time domain peak-to-average (PAR) ratio, each PN sequence provides perfect autocorrelation thus zero out-of-phase correlation, any pair of PN sequences has substantially perfect cross-correlation; and sequence correlation in frequency domain achieved with addition-only or addition and subtraction-only operations.
To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth detail certain illustrative aspects of the one or more embodiments. These aspects are indicative, however, of but a few of the various ways in which the principles of various embodiments can be employed and the described embodiments are intended to include all such aspects and their equivalents.
The features, nature, and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:
In accordance with one or more aspects and corresponding disclosure thereof, various aspects are described in connection with employing a complete period of frequency domain pseudo random/pseudo noise (PN) sequences—(the binary maximum length shift register sequences referred to as m-sequences)—wherein the PN sequences satisfy predetermined requirements or relations. Such requirements or relations include:
(1) supplying substantially low time domain Peak-to-Average Ratio (PAR);
(2) supplying perfect periodic autocorrelation (zero out-of-phase correlation); 3—supplying substantially perfect cross correlation for any pair of sequences; and
(4) supplying sequence correlation in the frequency domain by performing additive operations only (as opposed to also using multiplicative operations). Taken together, such features in a family of sequences facilitate efficient signal transmission (e.g., substantially low power usage)—wherein different sequences in the family are generated as the frequency domain cyclic shift of each other. As such, for acquisition signals, aspects of the subject innovation supply a substantially large (relative to the sequence length) set of base sequences with a substantially low peak-to-average ratio, while maintaining autocorrelation/cross-correlation both with regards to zero and non-zero frequency offsets.
Various embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that such embodiment(s) may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more embodiments.
As used in this application, the terms “component,” “module,” “system,” and the like are intended to refer to a computer-related entity, either hardware, firmware, a combination of hardware and software, software, or software in execution. For example, a component can be, but is not limited to being, a process running on a processor, a processor, an object, an executable, a thread of execution, a program, and/or a computer. By way of illustration, both an application running on a computing device and the computing device can be a component. One or more components can reside within a process and/or thread of execution and a component can be localized on one computer and/or distributed between two or more computers. In addition, these components can execute from various computer readable media having various data structures stored thereon. The components can communicate by way of local and/or remote processes such as in accordance with a signal having one or more data packets (e.g., data from one component interacting with another component in a local system, distributed system, and/or across a network such as the Internet with other systems by way of the signal).
The techniques described herein can be used for various wireless communication systems such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), single carrier-frequency division multiple access (SC-FDMA) and other systems. The terms “system” and “network” are often used interchangeably. A CDMA system can implement a radio technology such as Universal Terrestrial Radio Access (UTRA), CDMA2000, etc. UTRA includes Wideband-CDMA (W-CDMA) and other variants of CDMA. CDMA2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA system can implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA system can implement a radio technology such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) is an upcoming release of UMTS that uses E-UTRA, which employs OFDMA on the downlink and SC-FDMA on the uplink.
Single carrier frequency division multiple access (SC-FDMA) utilizes single carrier modulation and frequency domain equalization. SC-FDMA has similar performance and essentially the same overall complexity as those of an OFDMA system. A SC-FDMA signal has lower peak-to-average power ratio (PAPR) because of its inherent single carrier structure. SC-FDMA can be used, for instance, in uplink communications where lower PAPR greatly benefits access terminals in terms of transmit power efficiency. Accordingly, SC-FDMA can be implemented as an uplink multiple access scheme in 3GPP Long Term Evolution (LTE) or Evolved UTRA.
Furthermore, various embodiments are described herein in connection with an access terminal. An access terminal can also be called a system, subscriber unit, subscriber station, mobile station, mobile, remote station, remote terminal, mobile device, user terminal, terminal, wireless communication device, user agent, user device, or user equipment (UE). An access terminal can be a cellular telephone, a cordless telephone, a Session Initiation Protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a handheld device having wireless connection capability, computing device, or other processing device connected to a wireless modem. Moreover, various embodiments are described herein in connection with a base station. A base station can be utilized for communicating with access terminal(s) and can also be referred to as an access point, Node B, Evolved Node B (eNodeB) or some other terminology.
In addition, various aspects or features described herein can be implemented as a method, apparatus, or article of manufacture using standard programming and/or engineering techniques. The term “article of manufacture” as used herein is intended to encompass a computer program accessible from any computer-readable device, carrier, or media. For example, computer-readable media can include but are not limited to magnetic storage devices (e.g., hard disk, floppy disk, magnetic strips, etc.), optical disks (e.g., compact disk (CD), digital versatile disk (DVD), etc.), smart cards, and flash memory devices (e.g., EPROM, card, stick, key drive, etc.). Additionally, various storage media described herein can represent one or more devices and/or other machine-readable media for storing information. The term “machine-readable medium” can include, without being limited to, wireless channels and various other media capable of storing, containing, and/or carrying instruction(s) and/or data.
In
A network controller 130 may couple to a set of base stations and provide coordination and control for these base stations. Network controller 130 may be a single network entity or a collection of network entities. Network controller 130 may communicate with base stations 110 via a backhaul. Backhaul network communication can facilitate point-to-point communication between base stations 110 employing such a distributed architecture. Base stations 110 may also communicate with one another, e.g., directly or indirectly via wireless or wireline backhaul.
In
In
In one aspect, it can be assumed that the transmit signal is generated by an N-point IFFT followed by cyclic prefix insertion, windowing, and the like. Moreover, it can be assumed that in an acquisition slot, one has m, m<N consecutive tones available for the acquisition sequence, where m=2l−1 for an l (m, N, l are integers.) The remainder of the tones can be employed for FDM data, or can be set to zero. One can also employ sequence repetition, which can require m=2(2l−1) tones, and every other tone would be used only. It is to be appreciated that even though the following discussion is primarily described in the case of no sequence repetition and no data FDM, the subject innovation is not so limited and other aspects are well within the realm of the subject innovation.
According to a further aspect, the frequency domain PN sequences can be described as follows: let ai, i=0, 1, . . . , m−1 be a binary PN sequence, whose elements are mapped to +/−1 (from {0, 1}). The m available consecutive tones are modulated with the consecutive elements of ai to obtain the first sequence spectrum. A total of k sequence spectrums can be generated, each of which is obtained by cyclically shifting the first spectrum within the m available tones. Therefore the pth sequence spectrum employs the same set of tones as the first sequence spectrum and the tones are modulated by amod(i+Δ(p−1),m), where p is the sequence index, p=1, 2, . . . , k, and Δ is an appropriately selected frequency increment. Typically, Δ should be sufficiently large to avoid frequency acquisition ambiguity problems. It is to be appreciated that a uniform step size Δ is not necessary. In particular, if k does not divide m evenly, then having a uniform Δ is not possible—yet such does not represent a practical problem.
The k time domain sequences can be achieved by obtaining the IFFT of each of the k frequency domain sequence spectra, followed by cyclic prefix insertion, windowing, interpolation, and the like. When calculating the correlation of sequences, the following identity can be employed:
Wherein, si and ri are arbitrary time domain sequences of length m, and S=FFT{s}, R=FFT{r} and where ƒ(t)|d signifies evaluating a function ƒ(t) at t=d.
Put differently, one can exploit the fact that time domain convolution (or correlation) is equivalent to frequency domain multiplication with the spectrum (or the conjugate spectrum). This holds even if the roles of FFT and IFFT are changed. (In general, lower case letters can denote time domain variables and upper case letters can denote frequency domain variables.)
Time Domain Peak-to-Average
Likewise, for the time domain peak-to-average the time domain envelope for a frequency domain PN sequence si can be determined based on Equation (1) as follows:
Therefore one can obtain
As indicated, the time domain signal has a constant envelope, except for a dip at i=0, which gives a negligible rise in PAR. Moreover, subsequent time domain interpolation (pulse shaping) can also increase the PAR but any significant increase is unlikely. It is to be appreciated that due to the short sequence length, statistical methods such as finding 0.1% or 0.01% CDF points become meaningless or of low importance. For the same reason, it is likely that different frequency domain PN sequences of the same length (corresponding to different generating polynomials) can result in slightly different PAR in the time domain.
Autocorrelation
Similarly, by employing Equation (1), one can obtain
Therefore one can obtain
and hence, the sequences demonstrate perfect auto-correlation.
Accordingly, and because of such perfect autocorrelation, the m cyclic shifts of si span a full orthogonal base. Therefore, any cyclic shift of any other sequence ri cannot be simultaneously orthogonal to all shifts of si. In particular, exactly because of the cyclic shifts of si being an orthogonal base, the following identity holds:
Put differently, the sum of all absolute squared correlation values with ri will be equal to the sum of absolute squared values of the time samples of ri: A perfect cross-correlation can then be obtained, if all correlation absolute values were equal, which would result in the maximum possible minimum distance between the time shifts of si and ri. One can determine the time domain cross-correlation of two frequency domain PN sequences, si and ri, where the second sequence is generated by the frequency domain cyclic shift of the first sequence. Equation (1) can then be employed to obtain:
Since the two spectra S and R are PN sequences, their elements are real and their element-wise product is just another shift of the same PN sequence. Therefore, the cross-correlation magnitude can be determined very similarly to the way the PAR was determined in the Time Domain Peak-to-Average described above.
Therefore, one can obtain:
Put differently, the sequences can demonstrate substantially perfect cross-correlation. Moreover, the fact that there exists a dip at time offset d=0 does not represent a practical problem. As such, for acquisition signals, aspects of the subject innovation supply a substantially large (relative to the sequence length) set of base sequences with substantially low peak-to-average ratio, while maintaining autocorrelation/cross correlation both with regards to zero and non-zero frequency offsets.
As illustrated in
Each base station 110 provides communication coverage for a respective geographic area. A base station and/or its coverage area may be referred to as a “cell”, depending on the context in which the term is used. To increase capacity, the coverage area of each base station may be partitioned into multiple (e.g., three) sectors. Each sector is served by a base transceiver subsystem (BTS). For a sectorized cell, the base station for that cell typically includes the BTSs for all sectors of that cell. For simplicity, in the following description, the term “base station” is used generically for both a fixed station that serves a cell and a fixed station that serves a sector. The terms “user” and “terminal” are also used interchangeably herein.
In a related aspect,
At terminal 120x, the modulated signal transmitted by base station 110x and possibly other base stations are received by an antenna 352. A receiver unit (RCVR) 354 processes (e.g., conditions and digitizes) the received signal from antenna 352 and provides received samples. A demodulator (Demod) 360 processes (e.g., demodulates and detects) the received samples and provides detected data symbols for terminal 120x. Each detected data symbol is a noisy estimate of a data symbol transmitted by base station 110x to terminal 120x. A receive (RX) data processor 362 processes (e.g., symbol demaps, deinterleaves, and decodes) the detected data symbols and provides decoded data.
For the reverse link, at terminal 120x, traffic data is processed by a TX data processor 368 to generate data symbols. A modulator 370 processes the data symbols, pilot symbols, and signaling from terminal 120x for the reverse link and provides an output chip stream, which is further conditioned by a transmitter unit 372 and transmitted from antenna 352. At base stations 110x, the modulated signals transmitted by terminal 120x and other terminals are received by antenna 324, conditioned and digitized by a receiver unit 328, and processed by a demodulator 330 to detect the data symbols and signaling sent by each terminal. An RX data processor 332 processes the detected data symbols for each terminal and provides decoded data for the terminal. Controller 340 receives the detected signaling data and controls the data transmissions on the forward and reverse links. Controllers 340 and 380 direct the operation at base station 110x and terminal 120x, respectively. Memory units 342 and 382 store program codes and data used by controllers 340 and 380, respectively.
Within data/pilot modulator 410, a multiplexer (Mux) 414 receives and multiplexes data symbols with pilot symbols. For each OFDM symbol period, a symbol-to-subband mapper 416 maps the multiplexed data and pilot symbols onto the subbands assigned for data and pilot transmission in that symbol period. Mapper 416 also provides a signal value of zero for each subband not used for transmission. For each symbol period, mapper 416 provides N transmit symbols for the N total subbands, where each transmit symbol may be a data symbol, a pilot symbol, or a zero-signal value. For each symbol period, an inverse fast Fourier transform (IFFT) unit 418 transforms the N transmit symbols to the time domain with an N-point IFFT and provides a “transformed” symbol that contains N time-domain chips. Each chip is a complex value to be transmitted in one chip period. A parallel-to-serial (P/S) converter 420 serializes the N time-domain chips. A cyclic prefix generator 422 repeats a portion of each transformed symbol to form an OFDM symbol that contains N+C chips, where C is the number of chips being repeated. The repeated portion is often called a cyclic prefix and is used to combat inter-symbol interference (ISI) caused by frequency selective fading. An OFDM symbol period corresponds to the duration of one OFDM symbol, which is N+C chip periods. Cyclic prefix generator 422 provides a stream of data/pilot chips. IFFT unit 418, P/S converter 420, and cyclic prefix generator 422 form an OFDM modulator.
Within signaling modulator 430, a multiplier 432 receives and multiplies signaling data with a PN sequence from a PN generator 434 and provides spread signaling data. The signaling data for each terminal is spread with the PN sequence assigned to the terminal. A symbol-to-subband mapper 436 maps the spread signaling data onto the subbands used for signaling transmission, which may be all or a subset of the N usable subbands. An IFFT unit 438, a P/S converter 440, and a cyclic prefix generator 442 perform OFDM modulation on the mapped and spread signaling data and provide a stream of signaling chips.
Within combiner 460, a multiplier 462a multiplies the data/pilot chips from modulator 410 with a gain of Gdata. A multiplier 462b multiplies the signaling chips from modulator 430 with a gain of Gsignal. The gains Gdata and Gsignal determine the amount of transmit power to use for traffic data and signaling, respectively, and may be set to achieve good performance for both. A summer 464 sums the scaled chips from multipliers 462a and 462b and provides the output chips for modulator 370a.
Data modulator 510 includes a symbol-to-subband mapper 516, an IFFT unit 518, a P/S converter 520, and a cyclic prefix generator 522 that operate in the manner described above for units 416, 418, 420, and 422, respectively, in
Signaling modulator 550 includes a multiplier 552 and a PN generator 554 that operate in the manner described above for units 432 and 434, respectively, in
Within combiner 560, multipliers 562a, 562b, and 562c multiply the chips from modulators 510, 530, and 550, respectively, with gains of Gdata, Gpilot, and Gsignal, respectively, which determine the amount of transmit power used for traffic data, pilot, and signaling, respectively. A summer 564 sums the scaled chips from multipliers 562a, 562b, and 562c and provides the output chips for modulator 550b.
Within data modulator 610, a multiplier 614 receives and scales data symbols with a gain of Gdata and provides scaled data symbols. A symbol-to-subband mapper 616 then maps the scaled data symbols onto the subbands used for data transmission. Within pilot modulator 620, a multiplier 624 receives and scales pilot symbols with a gain of Gpilot and provides scaled pilot symbols. A symbol-to-subband mapper 626 then maps the scaled pilot symbols onto the subbands used for pilot transmission. Within signaling modulator 630, a multiplier 632 spreads signaling data across the subbands used for signaling transmission with a PN sequence generated by a PN generator 634. A multiplier 635 scales the spread signaling data with a gain of Gsignal and provides scaled and spread signaling data, which is then mapped onto the subbands used for signaling transmission by a symbol-to-subband mapper 636. Combiner 660 includes N summers 662a through 662n for the N total subbands. For each symbol period, each summer 662 sums the scaled data, pilot, and signaling symbols for the associated subband and provides a combined symbol. OFDM modulator 670 includes an IFFT unit 672, a P/S converter 674, and a cyclic prefix generator 676 that operate in the manner described above for units 418, 420, and 422, respectively, in
Within OFDM demodulator 710, a cyclic prefix removal unit 712 obtains N+C received samples for each OFDM symbol period, removes the cyclic prefix, and provides N received samples for a received transformed symbol. A serial-to-parallel (S/P) converter 714 provides the N received samples in parallel form. An FFT unit 716 transforms the N received samples to the frequency domain with an N-point FFT and provides N received symbols for the N total subbands. Within signaling demodulator 740, a symbol-to-subband demapper 742 obtains the received symbols for all N total subbands from OFDM demodulator 710 and passes only the received symbols for the subbands used for signaling transmission. A multiplier 744 multiplies the received symbols from demapper 742 with the PN sequence used for signaling, which is generated by a PN generator 746. An accumulator 748 accumulates the output of multiplier 744 over the length of the PN sequence and provides detected signaling data.
Within data demodulator 720, a symbol-to-subband demapper 722 obtains the received symbols for all N total subbands and passes only the received symbols for the subbands used for traffic data and pilot. A demultiplexer (Demux) 724 provides received pilot symbols to a channel estimator 730 and received data symbols to a summer 734. Channel estimator 730 processes the received pilot symbols and derives a channel estimate Ĥdata for the subbands used for traffic data and a channel estimate Ĥsignal for the subbands used for signaling. An interference estimator 736 receives the detected signaling data and the Ĥsignal channel estimate, estimates the interference due to the detected signaling data, and provides an interference estimate to summer 734. Summer 734 subtracts the interference estimate from the received data symbols and provides interference-canceled symbols. The interference estimation and cancellation may be omitted, e.g., if the Ĥsignal channel estimate is not available. A data detector 738 performs data detection (e.g., matched filtering, equalization, and so on) on the interference-canceled symbols with the Ĥdata channel estimate and provides detected data symbols.
Within signaling demodulator 840, a multiplier 844 multiplies the data samples with the PN sequence used for signaling, which is generated by a PN generator 846. An accumulator 848 accumulates the output of multiplier 844 over the length of the PN sequence and provides the detected signaling data. Within data demodulator 820, a symbol-to-subband demapper 822 obtains the received symbols for all N total subbands from OFDM demodulator 710 and passes only the received pilot symbols for the subbands used for pilot transmission. A multiplier 824 and an accumulator 828 perform despreading on the received pilot symbols with the PN sequence used for the pilot, which is generated by a PN generator 826. The pilot despreading is performed in a manner complementary to the pilot spreading. A channel estimator 830 processes the despread pilot symbols and derives the Ĥdata channel estimate for the subbands used for traffic data and the Ĥsignal channel estimate for the subbands used for signaling.
A symbol-to-subband demapper 832 also obtains the received symbols for all N total subbands and passes only the received data symbols for the subbands used for traffic data. An interference estimator 836 estimates the interference due to the detected signaling and provides the interference estimate to a summer 834, which subtracts the interference estimate from the received data symbols and provides the interference-canceled symbols. A data detector 838 performs data detection on the interference-canceled symbols with the Ĥdata channel estimate and provides the detected data symbols. It is to be appreciated that other designs may also be used for the demodulator, and are well within the scope of the invention. In general, the processing by the demodulator at one entity is determined by, and is complementary to, the processing by the modulator at the other entity.
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What has been described above includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for the purposes of describing the aforementioned embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term “includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is interpreted when employed as a transitional word in a claim.
The present application for patent claims priority to Provisional Application No. 61/092,200 entitled “FREQUENCY DOMAIN PN SEQUENCE” filed Aug. 27, 2008, assigned to the assignee hereof and hereby expressly incorporated by reference herein in its entirety.
Number | Date | Country | |
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61092200 | Aug 2008 | US |