Source: http://www.google.com/patents/US6885708?dq=5319712
Timestamp: 2014-08-27 13:26:02
Document Index: 207185140

Matched Legal Cases: ['art 40', 'art 40', 'art 70', 'art 40', 'art 90', 'art 70', 'art 70', 'art 70', 'art 70', 'art 40', 'art 90', 'art 90', 'art 90', 'art 90', 'art 90', 'art 90', 'art 90', 'art 130']

Patent US6885708 - Training prefix modulation method and receiver - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsA receiver for implementing a training prefix modulation method in response to a reception of a signal propagating through a channel is disclosed. The signal as received includes training blocks with each training block having a data inter-block-interference therein, and data blocks with each data block...http://www.google.com/patents/US6885708?utm_source=gb-gplus-sharePatent US6885708 - Training prefix modulation method and receiverAdvanced Patent SearchPublication numberUS6885708 B2Publication typeGrantApplication numberUS 10/198,487Publication dateApr 26, 2005Filing dateJul 18, 2002Priority dateJul 18, 2002Fee statusPaidAlso published asCN1669259A, EP1525698A1, EP1525698A4, US20040013084, WO2004010628A1Publication number10198487, 198487, US 6885708 B2, US 6885708B2, US-B2-6885708, US6885708 B2, US6885708B2InventorsTimothy A. Thomas, Vijay Nangia, Kevin L. Baum, Frederick W. VookOriginal AssigneeMotorola, Inc.Export CitationBiBTeX, EndNote, RefManPatent Citations (6), Non-Patent Citations (4), Referenced by (7), Classifications (14), Legal Events (5) External Links: USPTO, USPTO Assignment, EspacenetTraining prefix modulation method and receiverUS 6885708 B2Abstract A receiver for implementing a training prefix modulation method in response to a reception of a signal propagating through a channel is disclosed. The signal as received includes training blocks with each training block having a data inter-block-interference therein, and data blocks with each data block having a training inter-block-interference therein. The signal is selectively reconstructed to provide a circular appearance of the channel over the data blocks. Specifically, an estimate of the training inter-block-interferences is generated and subtracted from the data blocks. And, an estimate of the data inter-block interferences is generated and added to the data blocks.
generating an estimate of the first inter-block interference; subtracting the estimate of the first inter-block interference from the data block; and reconstructing the data block to include the second inter-block-interference. 17. The method of claim 16, wherein the estimate of the first inter-block interference is generated according to: t l ⁢ ibi = ∑ m = 0 M ⁢ t l + v - m � p ^ l a ⁢ ⁢ l = 0 ⁢ ⁢ � ⁢ ⁢ ( M - 1 ) . 18. A method for reconstructing a signal including a data block having a first inter-block-interference and a training block having a second inter-block-interference, said method comprising:
reconstructing the data block to exclude the first inter-block-interference; generating an estimate of the second inter-block interference; and adding the estimate of the second inter-block interference to the data block. 19. The method of claim 18, wherein the estimate of the second inter-block interference is generated according to: d l ⁢ ibi = ( 1 - α ) � ( y N + 1 - ∑ m = 0 M ⁢ t l - m � p ^ m b ) + α ⁢ ∑ m = 0 M ⁢ x ^ l + N - m � p ^ m c ⁢ ⁢ l = 0 ⁢ ⁢ � ⁢ ⁢ ( M - 1 ) . 20. A receiver, comprising:
a buffer operable to a store a signal including a data block having a first inter-block-interference and a training block having a second inter-block-interference; and one or more modules operable to generate an estimate of the first inter-block-interference, to subtract the estimate of the first inter-block-interference from the data block, and to reconstruct the data block to include the second inter-block-interference. 21. The receiver of claim 20, wherein said one or more modules generate an estimation of the first inter-block-interference according to: t l ⁢ ibi = ∑ m = 0 M ⁢ t l + v - m � p ^ l a ⁢ ⁢ l = 0 ⁢ ⁢ � ⁢ ⁢ ( M - 1 ) . 22. A receiver, comprising:
a buffer operable to store a signal including a data block having a first inter-block-interference and a training block having a second inter-block-interference; and one or more modules operable to reconstruct the data block to exclude the first inter-block-interference, to generate an estimate of the second inter-block-interference, and to add the estimate of the second inter-block-interference to the data block. 23. The receiver of claim 22, wherein said one or more modules generate an estimation of the second inter-block interference according to: d l ibi = ( 1 - α ) � ( y N + l - ∑ m = 0 M ⁢ ⁢ t l - m � p ^ m b ) + α ⁢ ∑ m = 0 M ⁢ x ^ l + N - m � p ^ m c ⁢ ⁢ l = 0 ⁢ ⁢ � ⁢ ⁢ ( M - 1 ) . 24. A method for facilitating a detection of data symbols within a received signal block, said method comprising:
This equation is presented for the case where the training prefixes 22 a and 22 b are identical, but this equation can be reformulated for the case where these training prefixes are different. The (CPR) pl is a combined response of transmit filters, the channel and receiver filters and is assumed to be of length M+1, where the training prefix length v is preferably chosen such that M≦v. The baseband received samples, yl, of baud 21 a and training prefix 22 b of FIG. 2, after propagating through the multipath channel and being corrupted by additive noise and/or interference nl, can be modeled in accordance with the following equation [2]: y l = ∑ m = 0 M ⁢ ⁢ x l - m � p m + n l ⁢ ⁢ l = - v ⁢ ... ⁢ ⁢ ( N + v - 1 ) [ 2 ] During a stage S44 of the flowchart 40, the SDD module 33 ascertains whether to execute a signal reconstruction of the data block 23 a′ based on the characteristics of the transmitted signal and the available receiver processing power. If the SDD module 33 determines that an execution of a signal reconstruction of the data block 23 a′ is not warranted, the SDD module 33 proceeds to a stage S46 of the flowchart 40 to implement a flowchart 70 representative of a first embodiment of an information detection method of the present invention. If the SDD module 33 determines that an execution of a signal reconstruction of the data block 23 a′ is warranted, the SDD module 33 proceeds to a stage S48 of the flowchart 40 to implement a flowchart 90 representative of one embodiment of a signal reconstruction method of the present invention.
During a stage S78 of the flowchart 70, the SDD module 33 conventionally removes the training prefix (i.e., a guard period) of the equalized signal. During a stage S80 of the flowchart 70, the SDD module 33 conventionally transforms the equalized signal without the training prefix into the frequency domain, preferably with a FFT of a size=N. In one embodiment, stage S80 is performed only for OFDM and any variations thereof (e.g. MC-CDMA/SOFDM), and is omitted for single carrier signals. During a stage S82 of the flowchart 70, the SDD module 33 conventionally detects the channel symbols (e.g., by outputting one or more of: soft or un-sliced symbols, hard or sliced symbols, soft bits, hard bits). The flowchart 70 is terminated upon a completion of stage S82 with the result being a detection of the channel symbols within data block 23 a′. Referring again to FIG. 6, upon completion of stage S46, the receiver 30 proceeds to stage S54 of the flowchart 40 to ascertain whether to improve upon the performance of the receiver 30 by using iteration. FIG. 8 illustrates the flowchart 90. During a stage S92 of the flowchart 90, the SDD module 33 generates or receives an estimate of the training IBI 24 a. In one embodiment, the SDD module 33 generates the estimate of the training IBI 24 a as a weighted sum of training prefix samples 22 a where the weights are proportional to an estimate of the channel pulse response, {circumflex over (p)}l a (where {circumflex over (p)}l a is the current (or previous) iteration estimate of the CPR), in accordance with the following equation [3]: t l ⁢ ibi = ∑ m = 0 M ⁢ t l + v - m � p ^ l a ⁢ ⁢ l = 0 ⁢ ⁢ � ⁢ ⁢ ( M - 1 ) [ 3 ] Upon completion of the stage S92, the SDD module 33 proceeds to a stage S94 of the flowchart 90 to subtract the estimate of the training IBI 24 a from the data block 23 a′ to yield the data block 23 a′ of signal 20 c (FIG. 3), which is illustrated over multiple bauds for the purpose of illustration, in accordance with the following equation [4]: z l = y l - t l ⁢ ibi ⁢ ⁢ l = 0 ⁢ ⁢ � ⁢ ⁢ ( M - 1 ) [ 4 ] Upon completion of the stage S94, the SDD module 33 proceeds to a stage S96 of the flowchart 90 to generate an estimate of the data IBI 25 a. In one embodiment, the SDD module 33 generates an estimate of the data IBI 25 a based on the received signal samples, training prefix samples, estimates of the CPR {circumflex over (p)}l b {circumflex over (p)}l c and a remodulated signal {circumflex over (x)}l in accordance with the following equation [4]: d l ⁢ ibi = ( 1 - a ) � ( y N + 1 - ∑ m = 0 M ⁢ t l - m � p ^ m b ) + a ⁢ ∑ m = 0 M ⁢ x ^ l + N - m � p ^ m c ⁢ ⁢ l = 0 ⁢ ⁢ � ⁢ ⁢ ( M - 1 ) [ 5 ] In this equation, the remodulated signal {circumflex over (x)}l (as elaborated later) is an estimate of the data transmitted within data block 23 a. The estimates of the CPR, {circumflex over (p)}l a, {circumflex over (p)}l b, {circumflex over (p)}l c can be the current iteration CPR estimate, or any one of the previous iteration CPR estimates. The feedback gain factor, α, on the remodulated signal (0<α<=1) determines the percentage of data portion IBI being updated in the current iteration relative to first iteration estimate, previous iteration estimates, or a combination thereof. In one embodiment, the feedback gain α is set to 0 on the first iteration. When α=0, the data IBI estimate is affected by channel noise. As a result, when the data IBI estimate is added to the data block, the total noise power is increased. In order to counter the increased noise power, an iterative, decision aided IBI estimation method may be used. During the initial iterations, small values of alpha can be used thereby introducing less error due to incorrect symbol/bit decisions, while improving the receiver performance as the estimator noise is reduced. On subsequent iterations, as the confidence in the decoded/detected symbol/bit decisions improve, the value of alpha can be increased (preferred) making it closer to one, further reducing the estimator noise and improving receiver performance. In an alternate embodiment, an initial signal detection based on conventional methods can be performed to estimate the remodulated signal {circumflex over (x)}l prior to the first iteration, thus enabling the option of setting α>0 for the first iteration. This alternate embodiment is anticipated to be useful when the channel pulse response is much smaller than the cyclic prefix length.
Upon completion of the stage S96, the SDD module 33 proceeds to a stage S98 of the flowchart 90 ascertain whether to implement a null prefix reconstruction. When the SDD module 33 determines a null prefix reconstruction is not warranted, the SDD module 33 proceeds to a stage S100 of the flowchart 90 to add the estimate of the data IBI 25 a to the data block 23 a″ to thereby yield data block 23 a′″ of the signal 20 d (FIG. 3), which is illustrated over multiple bauds for the purpose of illustration, in accordance with the following equation [6]: y l ⁢ cir = { z l + d l ⁢ ibi l = 0 ⁢ ⁢ � ⁢ ⁢ ( M - 1 ) y l l = M ⁢ ⁢ � ⁢ ⁢ ( N - 1 ) [ 6 ] Upon completion of the stage S100, the N samples of the data block 23 a′″ of signal 20 replace the training prefix 22 b with a null prefix 26 b, to thereby yield a corresponding portion of the signal 20 e (FIG. 4). Thereafter, the SDD module 33 proceeds to a stage S104 of the flowchart 90 to add the estimate of the data IBI 25 a to the null prefix 26 b, to thereby yield a corresponding portion of the signal 20 f (FIG. 4). Upon completion of the stage S102 and S104, the N+v samples corresponding to the combined data block 23 a′″ and prefix block 26 b′ of signal 20 f channel appear to have been received over a circular channel and are in accordance with the following equation [7]: y l ⁢ null = { z l l = 0 ⁢ ⁢ � ⁢ ⁢ ( M - 1 ) ⁢ y l l = M ⁢ ⁢ � ⁢ ⁢ ( N - 1 ) ⁢ d l - N ⁢ ibi ⁢ l = N ⁢ ⁢ � ⁢ ⁢ ( N + M - 1 ) ⁢ 0 l = ( N + M ) ⁢ ⁢ � ⁢ ⁢ ( N + v - 1 ) [ 7 ] In another embodiment of the invention, the null prefix 26 b′ with the data IBI 25 a is obtained by subtracting out an estimate of the training prefix block 22 b′. Referring again to FIG. 6, upon completion of stage S48, the receiver 30 proceeds to a stage S50 to ascertain whether a null prefix reconstruction was implemented during stage S48. When a null prefix reconstruction was implemented during stage S48, the receiver 30 proceeds to stage S46 to detect information within data block 23 a′″ of signal 20 f (FIG. 4) in a manner analogous to the detection of information within data block 23 a′ of signal 20 b as described in connection with FIG. 7. Thereafter, the receiver 30 proceeds to stage S54 to ascertain whether to improve upon the performance of the receiver 30 by using iteration.
The flowchart 130 is terminated upon completion of stage S138. Upon completion of the stage S58, the stages S44-S54 are selectively executed as previously described herein in connection with FIGS. 5-9. These subsequent iterations of the stages S44-S54 facilitate a circular appearance of the channel in accordance with either the following equations [10] or [11]: y l ⁢ cir = { z l + d l ⁢ ibi l = 0 ⁢ ⁢ � ⁢ ⁢ ( M - 1 ) y l l = M ⁢ ⁢ � ⁢ ⁢ ( N - 1 ) [ 10 ] y l ⁢ null = { z l l = 0 ⁢ ⁢ � ⁢ ⁢ ( M - 1 ) ⁢ y l l = M ⁢ ⁢ � ⁢ ⁢ ( N - 1 ) ⁢ d l - N ⁢ ibi ⁢ l = N ⁢ ⁢ � ⁢ ⁢ ( N + M - 1 ) ⁢ 0 l = ( N + M ) ⁢ ⁢ � ⁢ ⁢ ( N + v - 1 ) [ 11 ] For the present invention, the choice of waveforms for the training prefix can be any signal such as a reduced symbol duration OFDM training symbol (short OFDM symbol) or a single carrier training sequence. A signal with a close to flat amplitude spectrum and low peak-to-average power ratio is desirable as it enables the channel estimate errors to be frequency independent and may allow the training prefix to be transmitted at a higher power level than the data block while maintaining the same power amplifier backoff requirement. The present invention also enables the training prefix waveform to be different for different data blocks, except for the case of OFDM-type signals where signal reconstruction is not used (i.e., �no� is selected in S44 of FIG. 6). For this latter case, it is preferred that the training prefixes be identical for adjacent data blocks, so that the equalizer performance will be improved. Since the present invention can enable the use of different training prefixes for different data blocks, it can be applied to CDMA systems where the training prefix is a pilot block multiplied by a long code or scrambling code or PN sequence. In this case, the long code/scrambling code/PN sequence causes the transmitted training prefixes to be different even if they were the same prior to applying the long code/scrambling code/PN sequence. The proposed methods can also be used when a data slot is preceded and/or followed by an idle slot. In this case, the idle slot is treated as a training prefix/postfix containing zeros (null prefix or postfix), as appropriate.
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