The following description relates generally to communications systems, and more particularly to testing and monitoring transmitter performance.
Wireless networking systems have become a prevalent means to communicate with others worldwide. Wireless communication devices, such as cellular telephones, personal digital assistants, and the like have become smaller and more powerful in order to meet consumer needs and to improve portability and convenience. Consumers have become dependent upon these devices, demanding reliable service, expanded areas of coverage, additional services (e.g., web browsing capabilities), and continued reduction in size and cost of such devices.
A typical wireless communication network (e.g., employing frequency, time, and code division techniques) includes one or more base stations that provides coverage areas to subscribers as well as mobile (e.g., wireless) devices that can transmit and receive data within the coverage areas. A typical base station can simultaneously transmit multiple data streams to multiple devices 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 user device. A user device 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 user device can transmit data to the base station or another user device.
Forward Link Only (FLO) technology has been developed by an industry group of wireless communication service providers to utilize the latest advances in system design to achieve the highest-quality performance. FLO technology is intended for a mobile multimedia environment and is suited for use with mobile user devices. FLO technology is designed to achieve high quality reception, both for real-time (streaming) content and other data services. FLO technology can provide robust mobile performance and high capacity without compromising power consumption. In addition, the technology reduces the network cost of delivering multimedia content by decreasing the number of base station transmitters that are necessarily deployed. Furthermore, FLO technology based multimedia multicasting is complimentary to wireless operators' cellular network data and voice services, as cellular network data can be delivered to a same device that receives multimedia content by way of FLO technology.
Performance of transmitters, both within base stations and mobile devices, is crucial to success of a wireless system generally and in connection with FLO technology in particular. Additionally, as alluded to above, it is desirable to maintain low costs with respect to transmitters within wireless systems. Accordingly, wireless service providers may wish to determine performance of a transmitter designed and provided by a vendor prior to finalizing purchase of the transmitter. For instance, performance of channel estimation may be desirable to enable determination of signal-to-noise ratio, modulation error ratio, and various other performance metrics. More particularly, it may be desirable to perform phase correction with respect to transmitted signals and thereafter analyze particular parameters of a resultant signal to analyze transmitter performance. Conventional phase estimation and correction techniques, however, are computationally expensive or are not associated with sufficient accuracy to enable meaningful analysis of transmitter performance.
The following presents a simplified summary in order to provide a basic understanding of some aspects of the claimed subject matter. This summary is not an extensive overview, and is not intended to identify key/critical elements or to delineate the scope of the claimed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.
The claimed subject matter relates to testing performance of a transmitter. Such testing can be performed while the transmitter is in the field, within a factory, etc. In an example, modulation error ratio can be indicative of how a transmitter is performing, and accordingly, such ratio can be required to reside within a particular range. To determine modulation error ratio, phase estimation and correction with respect to a super frame may need to be undertaken. Estimating and correcting phase alteration over an entirety of a super frame, however, may not sufficiently cancel nonlinear noise associated with the transmitter/super frame, thereby not enabling determination of an accurate modulation error ratio. Accordingly, the claimed subject matter relates to segmenting the super frame with respect to time and thereafter performing phase estimation/correction over individual segments. For example, a first order and/or a second order phase correction algorithm can be employed.
In accordance with an aspect, a method for analyzing performance of a transmitter comprises partitioning a super frame into a plurality of segments and estimating and correcting phase with respect to at least one of the plurality of segments. The method can also include determining additive noise with respect to the at least one segment. For instance, the super frame can include several OFDM symbols. Additionally, first and/or second order phase correction algorithms can be employed.
With respect to another aspect, a wireless communications apparatus described herein includes a memory that retains instructions for segmenting a super frame with respect to time upon receipt of the super frame and further retains instructions for correcting phase alteration with respect to the super frame. The wireless communications apparatus can also include a processor, wherein the processor executes the instructions retained within memory to correct phase alteration with respect to at least one segment of the super frame.
In accordance with still another aspect, a wireless communications apparatus described herein comprises means for partitioning a super frame received from a transmitter into a plurality of segments, and means for performing phase correction with respect to at least one of the segments. The wireless communications apparatus also includes means for determining a performance metric with respect to the transmitter based at least in part upon the phase correction. Additionally, the wireless communications apparatus can include means for performing channel estimation based at least in part upon the phase correction.
In accordance with still another aspect, a machine-readable medium is described herein, wherein the machine readable medium has stored thereon machine-executable instructions for receiving a first portion of a super frame and estimating and correcting phase alteration with respect to the first portion in connection with testing performance of a transmitter. The machine-readable medium can include additional machine-executable instructions for determining modulation error ratio based at least in part upon the corrected phase alteration.
In accordance with yet another aspect, a processor is described herein, wherein the processor executes instructions for determining timing information in connection with segmenting a received signal that includes multiple symbols. The processor can also execute instruction for segmenting the received signal in accordance with the determining timing information as well as instructions for correcting phase alteration with respect to at least one segment of the received signal, wherein the at least one segment comprises two or more symbols. The processor can additionally execute instructions for determining whether a transmitter is performing adequately based at least in part upon the corrected phase alteration.
To the accomplishment of the foregoing and related ends, certain illustrative aspects are described herein in connection with the following description and the annexed drawings. These aspects are indicative, however, of but a few of the various ways in which the principles of the claimed subject matter may be employed and the claimed subject matter is intended to include all such aspects and their equivalents. Other advantages and novel features may become apparent from the following detailed description when considered in conjunction with the drawings.
The claimed subject matter is 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 the claimed subject matter. It may be evident, however, that such subject matter 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 the claimed subject matter.
Furthermore, various aspects are described herein in connection with a user device. A user device can also be called a system, a subscriber unit, subscriber station, mobile station, mobile device, remote station, remote terminal, access terminal, user terminal, terminal, user agent, or user equipment. A user device can be a cellular telephone, a cordless telephone, a Session Initiation Protocol (SIP) phone, a wireless local loop (WLL) station, a PDA, a handheld device having wireless connection capability, or other processing device connected to a wireless modem.
Moreover, aspects of the claimed subject matter may be implemented as a method, apparatus, or article of manufacture using standard programming and/or engineering techniques to produce software, firmware, hardware, or any combination thereof to control a computer or computing components to implement various aspects of the claimed subject matter. 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 . . . ), optical disks (e.g., compact disk (CD), digital versatile disk (DVD) . . . ), smart cards, and flash memory devices (e.g., card, stick, key drive, . . . ). Additionally it should be appreciated that a carrier wave can be employed to carry computer-readable electronic data such as those used in transmitting and receiving voice mail or in accessing a network such as a cellular network. Of course, those skilled in the art will recognize many modifications may be made to this configuration without departing from the scope or spirit of what is described herein.
Base station transmitter performance is vital to the overall performance of a wireless system, particularly a wireless system utilizing FLO technology. Accordingly, prior to placing a transmitter in the field of use, it is desirable to test such transmitter to ensure that it is operating within certain specifications. In one example, it may be desirable to ascertain modulation error ratio (MER) with respect to a transmitter to ensure that MER falls within specifications. MER indicates mean or maximum deviation of I/Q values with respect to ideal signal states, and thus provides a measure of signal quality output by a transmitter. Computation of MER is described in greater detail below. In another example, group delay, frequency response (in-band and out-band), and other parameters can be determined to ensure that the transmitter accords to specifications. Still further, additive noise (e.g., noise that can be attributed to power amplifiers, filters, D/A converters, . . . ) can be computed to analyze transmitter performance. To enable determination of these and other parameters, channel estimations of each OFDM symbol within a super frame can be averaged to obtain a mean value—however, it is desirable to correct phase alterations due to frequency offset prior to undertaking the aforementioned averaging.
Referring now to
The system 100 includes a receiver 102 that receives the signal, wherein such receiver can be a test receiver that is utilized in connection with ensuring that a transmitter (not shown) is performing according to specifications. For some transmitters, a frequency offset associated with output signals may not be constant. In other words, alteration of phase is not linear with time. Accordingly, it is desirable to compensate the phase ramp to enable averaging of channel estimations of each symbol within a super frame (thus enabling transmitter performance parameters, such as MER, to be discerned). Mathematically, the received signal with a frequency offset can be written as:
where Rn is the complex amplitude of the nth sub carrier, ω0 is the frequency of a zeroth sub carrier (at an intermediate frequency (IF) upon which the zeroth sub carrier is processed), ωs is the sub carrier spacing, Δω is the frequency offset, and t is time.
From reviewing the above algorithm, it can be ascertained that a constant frequency offset results in a phase change that is linear with time, while a frequency offset that is linear with time results in a phase change that is parabolic with respect to time. As stated above, correction of phase change is desirable prior to averaging channel estimations associated with OFDM symbols within a super frame, for example. Theoretically, if a channel is perfect, phase change due to constant frequency offset can be cancelled by way of calculating slope of such phase change and utilizing a first order least-square phase correction algorithm based upon the calculated slope. Such an algorithm is provided below:
φest=a·t+b,
where parameters a, b are determined by least-square estimation algorithm. Additionally or alternatively, a first order phase correction algorithm can be of the form
where Δφk+1=φk+1−φk is the phase change of a channel estimation of two adjacent OFDM symbols, and TOFDM is a time period. If, on the other hand, it is assumed that the frequency offset is linear over time, then a second order least-squared algorithm can be utilized to discern parameters a, b, and c. The estimated phase can be written as:
φest=a·t2+b·t+c.
Typically, however, assumptions of constancy and linearity with respect to frequency offset over an entirety of a super frame are inaccurate, such that correcting phase alteration through use of first or second order algorithms does not enable sufficiently accurate averaging of channel estimates. To increase accuracy of estimates of phase alterations, a segmentor 104 can be employed to partition a super frame according to time. In other words, a super frame can be associated with a time T, and such time segment can be partitioned into N time segments (e.g., time segments that accord to 300 OFDM symbols), where N can be any suitable number. Assumptions relating to constancy and linearity with respect to a frequency offset over the plurality of time segments individually enable a much more accurate estimation of phase alteration of the received signal.
To calculate MER, however, it may not be desirable to increase N to an extremely large number, such as equating N to a number of OFDM symbols within a super frame. In more detail, if N is selected as being very large, then additive noise (which is desirably retained for analysis) will be cancelled together with nonlinear noise. With more specificity, a noise term with respect to a channel for each OFDM symbol derived from the received signal can be decomposed into two orthogonal dimensions: {right arrow over (a)} (amplitude direction) and {right arrow over (p)} (phase direction). A noise term in the {right arrow over (a)} dimension can be considered additive white Gaussian noise n{right arrow over (a)} (k, n), where k is a sub carrier index and n is an OFDM symbol index. A noise term in the {right arrow over (p)} dimension can be considered as a summation of additive white Gaussian noise n{right arrow over (p)} (k, n), with distortion d{right arrow over (p)} (k, n) associated with the frequency offset Δω. With respect to calculating MER, it is desirable to reduce or eliminate d{right arrow over (p)} (k, n) while not eliminating n{right arrow over (p)} (k, n).
In one example, if the variance of n{right arrow over (a)} (k, n) is substantially similar to that of {right arrow over (p)} (k, n), N can be set to a number of symbols being processed (e.g., a number of symbols within a super frame). Thus, both n{right arrow over (p)} (k, n) and d{right arrow over (p)} (k, n) are eliminated. In such an instance, a true MER will be equal to a processing MER minus a constant (e.g., 3.01 dB). In another example, segmentor 104 can perform segmentation with respect to time, where time is associated with a number of symbols being processed, such that the nonlinear noise (d{right arrow over (p)} (k, n)) is substantially cancelled while the additive (quantization) noise n{right arrow over (p)} (k, n) is left substantially unchanged. A number of segments can be determined empirically, for instance. In yet another example, a super frame can be segmented into four segments (N=4).
Once segmentor 104 performs appropriate segmentation, a phase corrector 106 can estimate and correct phase alteration through use of a linear estimation or a second order estimation. For example, once phase corrector 106 estimates phase alteration through first and/or second order estimation algorithms, phase corrector 106 can utilize the linear estimation or the second order estimation to substantially cancel nonlinear noise while retaining quantization noise (additive noise). Such estimation can be undertaken, for instance, to compensate for the phase alteration, thereby enabling an average of channel estimations with respect to each OFDM symbol to be achieved.
While shown as being comprised within receiver 102, it is understood that segmentor 104 and phase corrector 106 can be located in any suitable computing device that can be coupled to a transmitter (e.g., directly coupled to a transmitter to maintain a clean channel). Additionally, segmentor 104 and phase corrector 106 can be employed to test a transmitter that is desirably utilized in a FLO broadcasting system. A FLO wireless system can be designed to broadcast real time audio and video signals, as well as non-real time services. The respective FLO transmission is carried out utilizing tall, high power transmitters to ensure wide coverage in a given geographical area. It is common to deploy multiple transmitters in certain regions to ensure that the FLO signal reaches a significant portion of the population in a given area. Typically, FLO technology utilizes OFDM to transmit data. It is to be understood, however, that the claimed subject matter is applicable to various communications protocols (wireless or wirelined, multiple carrier or single carrier).
Referring now to
As described above, segmentor 104 segments a time frame associated with desirably processed symbols into a plurality of time segments. A number of time segments can be adjustable depending upon a number of processed symbols, can be selected through analyzing empirical data, or any other suitable manner for determining an appropriate number of segments. Phase corrector 106 can utilize a first or second order estimation algorithm in connection with estimating and correcting phase alteration, such as to significantly reduce nonlinear noise while retaining quantization noise (noise from amplifiers, filters, etc.). Additionally, a least-squared model can be employed by phase corrector 106 with respect to both first and second order phase estimation and correction. Segmenting in the above-described manner enables additive (quantization) noise to be retained for analysis while substantially canceling nonlinear noise.
Referring now to
Each of the base stations 302 and mobile devices 304 can include one or more transmitters utilized to transmit signals to other base stations and mobile devices. Transmitters can be tested prior to utilization of such transmitters within a wireless communications environment. As described above, the transmitters can be associated with test receivers to enable testing of certain parameters relating to the transmitters. For instance, a series of desirably processed symbols can be partitioned with respect to time, such that a subset of symbols is analyzed. Thereafter, first and/or second order phase correction can be undertaken with respect to each subset of symbols, thus enabling more accurate estimation and correction of phase alteration. Additionally, white Gaussian noise can be retained while distortion is substantially compensated, thereby facilitating calculation of a metric that describes performance of the transmitter.
Now turning to
Wireless communications apparatus 400 additionally includes a processor 404 that can analyze a received signal and segment such signal according to instructions within memory 402. The received signal can be a super frame that includes a plurality of symbols (e.g., OFDM symbols), and processor 404 can segment the super frame into a plurality of partitions. As can be appreciated, segmenting the super frame is done with respect to time, as symbols of the super frame are received sequentially at a receiver. Processor 404 can, upon segmenting at least a portion of the super frame, execute instructions within memory 402 relating to estimating/correcting phase alteration in the received signal. As described above, processor 404 can employ a first order estimation/correction algorithm and/or a second order estimation/correction algorithm in connection with estimating/correcting phase alteration. Additionally, processor 404 can output a metric indicating transmitter performance, such as an amount of additive noise associated with the received signal.
Referring now to
Turning now to
Now referring to
Referring to
Referring specifically to
At 806, phase alteration is estimated/corrected with respect to each of the plurality of segments. For instance, phase can be estimated/corrected through utilization of a first order correction algorithm, which can be least squared-based. The first order algorithm, however, need not be least-squared based, but can be any suitable first order algorithm. Additionally or alternatively, phase of at least one segment can be estimated/corrected by way of employment of a least-square based second order phase estimation/correction algorithm. Such an algorithm was described in detail above with respect to
Referring now to
Here Rn is the complex amplitude of the nth sub carrier and N is the total number of sub carriers. The frequency of the initial sub carrier is represented by ω0, ωs represents the sub carrier spacing and Δω is the frequency offset. A constant frequency offset will result in a linear phase change with time. A frequency offset that varies linearly with time will result in a parabolic phase change over time. Either a constant or linearly changing frequency offset results in a predictable phase change which can be corrected prior to averaging, as shown in
A linear phase change can be corrected using a first order phase correction algorithm by calculating the slope of phase change. For example, the phase change can be calculated as follows:
Here, Δφk+1=φk+1−φk is the phase change of the channel estimation between two adjacent OFDM symbols, φ0 is the phase of the initial channel estimation, L is the number of OFDM symbols and TOFDM is a period.
A parabolic phase change can be corrected using a second order phase correction with a least square algorithm to determine the parameters, a, b and c, of the parabolic function. The estimated phase can be written as follows:
φest=a·t2+b−t+c
Here, t is time. The estimated phase can be used to correct the estimated channels prior to averaging.
A parabolic phase change can be corrected using a second order phase correction with a least square algorithm to determine the parameters, a, b and c, of the parabolic function. The estimated phase can be written as follows:
φest=a·t2+b·t+c
Here, t is time. The estimated phase can be used to correct the estimated channels prior to averaging.
However, the frequency offset is not necessarily constant or linearly varying. Consequently, the phase change is not necessarily linear or parabolic and predictable. One possible solution for correcting for a variable frequency offset includes separating the time duration into segments and then estimating the phase change for each segment. As a result, the estimated noise variance Bk described below in
where, Bk is noise variance with respect to a sub carrier k, L is a number of OFDM symbols in a super frame, N is the number of segments, l identifies an OFDM symbol, and Wis noise. Such noise variance can be employed in connection with determining MER.
The noise term for each channel of each OFDM symbol derived from the received signal can be decomposed into two orthogonal dimensions: amplitude dimension and phase dimension. The noise term in the amplitude dimension can be considered additive white Gaussian noise. The noise term in the phase direction can be considered the sum of the additive white Gaussian noise (AWGN) and the distortion that comes from the frequency offset. The distortion caused by the frequency offset should be substantially eliminated. However, the component of AWGN in the phase dimension should be substantially maintained.
The methodology 900 starts at 902, and at 904 the number of segments into which the time will be divided is determined. At 906 the phase change due to frequency offset is estimated for a segment. The segment is corrected using either a first or second order correction algorithm at 908. At 910 a determination is made as to whether there are additional segments to correct. If yes, the process returns to 906 to determine the phase correction for the next segment. If no, the process terminates at 912.
In one extreme case, if the variance of the noise in the amplitude dimension is equal to that of the variance of the noise in the phase dimension, maximum number of segments is equal to the number of OFDM symbols being processed. Consequently, the noise in the phase dimension will be eliminated as well as the distortion due to frequency offset. As a result, the true value of MER, which includes the noise in the phase dimension, will be equal to the value of the generated MER minus a constant (e.g., 3.01 dB).
Now referring to
Referring now to
Processor 1106 can provide various types of user interfaces for display component 1112. For example, processor 1106 can provide a graphical user interface (GUI), a command line interface and the like. For example, a GUI can be rendered that provides a user with a region to view transmitter information. These regions can comprise known text and/or graphic regions comprising dialogue boxes, static controls, drop-down-menus, list boxes, pop-up menus, as edit controls, combo boxes, radio buttons, check boxes, push buttons, and graphic boxes. In addition, utilities to facilitate the presentation such as vertical and/or horizontal scroll bars for navigation and toolbar buttons to determine whether a region will be viewable can be employed.
In an example, a command line interface can be employed. For example, the command line interface can prompt (e.g., by a text message on a display and an audio tone) the user for information by providing a text message or alert the user that the transmitter performance is outside of predetermined bounds. It is to be appreciated that the command line interface can be employed in connection with a GUI and/or application program interface (API). In addition, the command line interface can be employed in connection with hardware (e.g., video cards) and/or displays (e.g., black and white, and EGA) with limited graphic support, and/or low bandwidth communication channels.
In addition, the evaluation system can generate an alert to notify users if the transmitter performance is outside of an acceptable range. The alert can be audio, visual or any other form intended to attract the attention of a user. The evaluation system can include a predetermined set of values indicating the boundaries of the acceptable range. Alternatively, users may dynamically determine the boundaries. In addition, the evaluation system can generate an alert based upon a change in transmitter performance.
To evaluate transmitter performance, the RF signal data produced by exciter 1212 can be monitored. Possible sources of transmitter error or noise include up-sampling, digital to analog conversion and RF conversion. The signal data can be sampled at the output of the exciter and at the output of the channel filter, such that the RF signal can be sampled either before or after power amplification and filtering. If the signal is sampled after amplification, the signal should be corrected for power amplification nonlinearity.
Referring now to
Referring now to
The transmitter evaluation system can generate one or more metrics to evaluate the performance of the transmitter. Metrics generated by processor include, but are not limited to, modulation error ratio (MER), group delay or channel frequency response. In particular, MER measures the cumulative impact of flaws within the transmitter. MER for a sub carrier is equivalent to signal to noise ratio (SNR) for a sub carrier. MER can be generated using the following equation:
Here, I is the in phase value of the measured constellation point, Q is the quadrature value of the measured constellation point and N is the number of sub carriers. ΔI is the difference between the in phase values of the transmitted and measured signals and ΔQ is the difference between the quadrature values of the transmitted and measured signals.
Referring now to
The methodology 1500 starts at 1502, and at 1504, the signal is received or sampled from the transmitter. The received signal can be written as follows:
Yk=Hk·Pk+Nk
Here, Hk is the channel of a sub carrier, k. A known modulation symbol, Pk, can be transmitted on the sub carrier k. Complex additive white Gaussian noise (AWGN) with a zero mean and a variance of σ2 can be represented by Nk.
The possible modulation types for the sub carriers can include, but are not limited to, quadrature phase-shift keying (QPSK), layered QPSK with an energy ratio of 6.25 (ER6.25), 16 QAM (quadrature amplitude modulation) and layered QPSK with energy ratio of 4.0 (ER4). When analyzed based upon the constellation point of view, the layered QPSK with energy ratio 4.0 is identical to that of 16 QAM. Constellation point of view, as used herein, refers to utilization of constellation diagrams to represent digital modulation schemes in the complex plane. Modulation symbols can be represented as constellation points on a constellation diagram.
An initial frequency domain channel estimate for a sub carrier can be determined at 1506. An initial channel estimate for each sub carrier can be obtained by dividing the received signal Yk by a known symbol, Pk. Selected symbols can be transmitted, such that the symbols are known for the purpose of performance evaluation. The initial frequency domain channel estimate for each sub carrier, k, of every OFDM symbol, l, within a super frame, can be represented as follows:
Here, Zk,l is an initial channel estimate for sub carrier k and OFDM symbol l.
An Average channel estimate is determined at 1508. The channel estimate Zk,l of sub carrier can be refined by averaging over the entire super frame, such that:
Here, k is the OFDM symbol index and L is the number of the OFDM symbols in the super frame (e.g., 1188 symbols). Since the variance of the average channel estimate is smaller than the variance of the initial channel estimate, the variance of the average channel estimate can be used to approximate the channel gain of the sub carrier during metric generation.
At 1510, a metric for evaluating the transmitter performance is generated. For example, the MER for a sub carrier k can be generated. Assuming that the transmitted symbols are known, noise variance can be estimated as follows:
Here, the Xk,m represents the transmitted symbol for sub carrier k. It can be shown that the in-phase and quadrature components of the noise, Wk, is approximately:
if, random variable Bk is the estimated noise variance, such that:
The MER can be determined based upon the average channel estimate for the sub carrier, the symbol transmitted on the sub carrier and the signal received for the sub carrier. A MER can be calculated based upon the following example equation:
Here, Ĥk is the average channel estimate for sub carrier k, Pk is the symbol transmitted on the sub carrier, Yk is the received signal and Nk is the AWGN. In addition, MER can be calculated by averaging over all of the sub carriers.
Additional metrics can be generated to evaluate transmitter performance. For example, metrics can include frequency response and group delay. Group delay of sub carrier k can be calculated as follows:
Here, k=1, . . . , 4000; Δφk,k−1 is the phase difference between sub carriers k and k−1; and Δfk,k−1 is the frequency difference between sub carriers k and k−1. The methodology 1500 then completes at 1512.
Referring now to
At 1612, the channel estimates are averaged over the super frame to increase accuracy. The average channel estimate can be determined using the coarse modulation type for a. subset of the sub carriers having a consistent modulation type. A half-interlace is used herein as an example of a subset of sub carriers having a consistent modulation type. However, in the systems and methods discussed herein, the subset of sub carriers having a consistent modulation type is not limited to a half-interlace. Errors in modulation symbol selection can be avoided by checking the modulation symbol for a sub carrier against the modulation type for the subset of sub carriers. The modulation type for the subset of sub carriers can be determined at 1808. At 1810, it is determined whether the modulation symbol is consistent with the modulation type. If yes, the process terminates. If no, the modulation symbol is reevaluated and a modulation symbol consistent with the modulation type is selected at 1812.
Typically, the modulation type remains consistent during a half interlace. In general, the modulation type does not change within an interlace due to constraints in the FLO protocol. An interlace, as used herein is a set of sub carriers (e.g., 500 sub carriers). Consequently, a half-interlace is one half of an interlace (e.g., 250 sub carriers). However, for rate-⅔ layered modulation, the modulation type can be switched to QPSK within an interlace when operating in base-layer only mode. Even under these conditions the modulation type within each half-interlace remains constant. Therefore, the modulation type for each half-interlace can be determined using majority voting. To determine the modulation type for a half-interlace or any other subset of sub carriers having a consistent modulation type, the modulation symbol, and consequently the modulation type, can be determined for each sub carrier within the subset. A majority vote based on the modulation type corresponding to each sub carrier can be used to determine the modulation type for the subset. For example, for a half-interlace including 250 sub carriers, the modulation type for 198 of the sub carriers could be consistent with the QPSK modulation type and the modulation symbols for the remaining 52 sub carriers could be consistent with the 16 QAM modulation type. Since the majority of the sub carriers are detected as QPSK, QPSK would be selected as the modulation type for the half-interlace. The 52 sub carriers that were associated with the 16 QAM modulation type can be reevaluated and reassigned to QPSK modulation symbols based upon their location in the constellation diagram. Comparing the modulation symbol to the modulation type for the half-interlace and reevaluating modulation symbols as needed increases the accuracy of modulation symbol selection. The methodology 1800 completes at 1814.
Referring now to
The transmitter evaluation systems and methods described herein should also include phase correction, intended to reduce or eliminate error or distortions caused by time frequency offsets. If phase correction is not performed, the channel estimate average can be inaccurate and consequently, the evaluation metrics may be incorrect. Typically, phase correction can be performed prior to the averaging of the channel estimates to correct for phase ramp due to frequency offsets. The methodology 1900 completes at 1914.
Referring now to
Referring now to
Base station 2302 can also include a transmitter monitor 2324. Transmitter monitor 2324 can sample transmitter output and/or transmitter antenna output and evaluate the performance of transmitter 2320. Transmitter monitor 2324 can be coupled to processor 2314. Alternatively, transmitter monitor 2324 can include a separate processor for processing transmitter output. In addition, transmitter monitor 2324 may be independent of base station 2302.
Base station 2302 can additionally comprise memory 2316 that is operatively coupled to processor 2314 and that can store information related to constellation regions and/or any other suitable information related to performing the various actions and functions set forth herein. It will be appreciated that the data store (e.g., memories) components described herein can be either volatile memory or nonvolatile memory, or can include both volatile and nonvolatile memory. By way of illustration, and not limitation, nonvolatile memory can include read only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM), which acts as external cache memory. By way of illustration and not limitation, RAM is available in many forms such as synchronous RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), Synchlink DRAM (SLDRAM), and direct Rambus RAM (DRRAM). The memory 1516 of the subject systems and methods is intended to comprise, without being limited to, these and any other suitable types of memory.
Referring now to
TMTR 2420 receives and converts the stream of symbols into one or more analog signals and further conditions (e.g., amplifies, filters, and frequency upconverts) the analog signals to generate a downlink signal suitable for transmission over the wireless channel. The downlink signal is then transmitted through an antenna 2425 to the user devices. At user device 2430, an antenna 2435 receives the downlink signal and provides a received signal to a receiver unit (RCVR) 2440. Receiver unit 2440 conditions (e.g., filters, amplifies, and frequency downconverts) the received signal and digitizes the conditioned signal to obtain samples. A symbol demodulator 2445 demodulates and provides received pilot symbols to a processor 2450 for channel estimation. Symbol demodulator 2445 further receives a frequency response estimate for the downlink from processor 2450, performs data demodulation on the received data symbols to obtain data symbol estimates (which are estimates of the transmitted data symbols), and provides the data symbol estimates to an RX data processor 2455, which demodulates (e.g., symbol demaps), deinterleaves, and decodes the data symbol estimates to recover the transmitted traffic data. The processing by symbol demodulator 2445 and RX data processor 2455 is complementary to the processing by symbol modulator 2415 and TX data processor 2410, respectively, at access point 2405.
On the uplink, a TX data processor 2460 processes traffic data and provides data symbols. A symbol modulator 2465 receives and multiplexes the data symbols with pilot symbols, performs modulation, and provides a stream of symbols. A transmitter unit 2470 then receives and processes the stream of symbols to generate an uplink signal, which is transmitted by the antenna 2435 to the access point 2405.
At access point 2405, the uplink signal from user device 2430 is received by the antenna 2425 and processed by a receiver unit 2475 to obtain samples. A symbol demodulator 2480 then processes the samples and provides received pilot symbols and data symbol estimates for the uplink. An RX data processor 2485 processes the data symbol estimates to recover the traffic data transmitted by user device 2430. A processor 2490 performs channel estimation for each active user device transmitting on the uplink. Multiple user devices may transmit pilot concurrently on the uplink on their respective assigned sets of pilot subcarriers, where the pilot subcarrier sets may be interlaced.
Processors 2490 and 2450 direct (e.g., control, coordinate, manage, etc.) operation at access point 2405 and user device 2430, respectively. Respective processors 2490 and 2450 can be associated with memory units (not shown) that store program codes and data. Processors 2490 and 2450 can utilize any of the methodologies described herein. Respective Processors 2490 and 2450 can also perform computations to derive frequency and impulse response estimates for the uplink and downlink, respectively.
For a software implementation, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in memory units and executed by processors. The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.
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 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.
This application is a continuation in part of U.S. patent application Ser. Nos. 11/361,085 and 11/361,088, entitled EVALUATION OF TRANSMITTAL PERFORMANCE and MODULATION TYPE DETERMINATION FOR EVALUATION OF TRANSMITTAL PERFORMANCE, respectively, both filed on Feb. 22, 2006. This application also claims the benefit of U.S. Provisional Patent application Ser. No. 60/739,481, entitled “METHODS AND APPARATUS FOR COLLECTING INFORMATION FROM A WIRELESS DEVICE,” which was filed Nov. 23, 2005. The entirety of the aforementioned applications are incorporated herein by reference.
Number | Date | Country | |
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60739481 | Nov 2005 | US | |
60739491 | Nov 2005 | US |
Number | Date | Country | |
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Parent | 11361085 | Feb 2006 | US |
Child | 11417400 | May 2006 | US |
Parent | 11361088 | Feb 2006 | US |
Child | 11417400 | May 2006 | US |