Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1998-06-19
2001-01-23
Pham, Chi H. (Department: 2731)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C714S796000
Reexamination Certificate
active
06178209
ABSTRACT:
BACKGROUND OF THE INVENTION
Equalizers are typically used in coded digital communications systems to compensate for multipath/linear filtering effects caused by the transmission channel. These effects are commonly referred to as channel impairments and include signal distortion which may occur in the transmitter, in the receiver or in the channel through which the signal is transmitted. The equalizer is an adaptive filter, often implemented as a finite impulse response (FIR) filter, an infinite impulse response (IIR) filter or a combination of FIR and IIR filters. Each filter has a plurality of coefficients which are adapted to minimize an error criterion. This error criterion may be, for example, the mean-square error between a transmitted training signal and the received training signal. A typical equalizer maintains a copy of the transmitted training signal to compare with the received training signal. It is generally believed that a decision-feedback equalizer (DFE) has better asymptotic performance than a linear equalizer as described in a text book by J. G. Proakis, entitled
Digital Communications.
A typical DFE is shown in FIG.
1
. The received signal is applied to an FIR filter and the output signal produced by the FIR filter is applied to an IIR filter. The IIR filter includes a subtracter
111
, a slicer
112
and an IIR filter section
114
. The subtracter
111
subtracts the filtered signal provided by the IIR filter section
114
from the output signal of the FIR filter
110
. The slicer
112
quantizes the signal provided by the subtracter
111
to produce an approximation of the signal that was transmitted. The IIR filter section, which may, for example, be an FIR filter in a feedback loop, processes the quantized signal to produce the signal which is subtracted by the subtracter
111
. For an uncoded modulation scheme, the DFE uses the slicer to get decisions for the feedback portion. The output signal of the slicer is compared to the training signal to determine in what way the coefficients of the FIR and IIR filter sections should be updated to minimize any differences.
For a coded modulation scheme, it may be desirable to replace the slicer with a decoder, which may include, for example, a trellis decoder, a deinterleaver, and a Reed Solomon (RS) decoder. Such a decoder, however, results in many symbol delays before a decision can be made on the symbol that was transmitted. These delays can be prohibitive for the DFE, since it relies on canceling the inter-symbol-interference of the previous symbols on the current symbol by using previously available decisions. Hence, the state of the art has typically not used a complete decoder, but a range of simplified decoders including the simple slicer
112
, which does not perform any decoding. A typical problem with using only a slicer in a DFE is a loss in performance due to incorrect decisions. Because an incorrect decision used in the DFE to remove inter-symbol interference (ISI) can cause further errors, this performance loss is known as ‘error propagation’.
More complex decoding techniques may also be used, for example, Reduced-State Sequence Estimation (RSSE) and parallel decision feedback decoding (PDFD). These techniques are described in an article by V. Eyuboglu and S. Qureshi, entitled “Reduced-State Sequence Estimation for Coded Modulation on Intersymbol Interference Channels”
IEEE Journal on Selected Areas of Communications
, August 1989. Furthermore, U.S. Pat. No. 5,056,117 entitled DECISION-FEEDBACK EQUALIZATION WITH TRELLIS CODING to R. Gitlin, describes a method by which multiple possible decisions are fed back and the best among them is chosen using a given criteria. Other techniques are described in an article by A. Duel-Hallen and C. Heegard, entitled “Delayed Decision-Feedback Equalization”,
IEEE Transactions on Communications
May 1989. All of the above cited references are incorporated herein by reference for their teachings on equalization and decoding techniques.
Generally the common idea among these decoders is to use multiple possible decisions or to use more complicated trellis decoders which include a channel state estimate. The implementation complexity of these approaches, however, is significant and may undesirably add to the cost of the decoder.
SUMMARY OF THE INVENTION
The present invention is embodied in a quantizer which may be used to recover N-bit symbols from successive channel impaired input samples representing a trellis encoded signal. The quantizer includes a partial trellis decoder which generates an estimate of a subset of the N bits of each symbol and, based on the estimate, selects a decision device for a reduced constellation to generate an estimate of the N bits.
According to one aspect of the invention, the trellis encoder which generated the input samples is based on a set-partitioned code and the partial trellis decoder computes path metrics for the current symbol based on path metrics of the previous symbol. The best path metric of the current symbol is used to select the reduced-constellation decision device.
According to another aspect of the invention, the trellis encoder which generated the input samples is based on a set-partitioned code with feedback convolutional encoding and the partial trellis decoder computes path metrics for the current symbol based on path metrics of the previous symbol. The best path metric of the previous symbol is used to select the reduced-constellation decision device.
According to yet another aspect of the invention, the trellis encoder which generated the input samples is based on a set-partitioned code and the partial trellis decoder computes path metrics for the current symbol based on path metrics of the previous symbol. The best path metric from among the path metrics of the current symbol, corresponding to a subset of states for the previous symbol, is used to select the reduced-constellation decision device.
REFERENCES:
patent: 5056117 (1991-10-01), Gitlin et al.
patent: 5548648 (1996-08-01), Wang et al.
patent: 5588025 (1996-12-01), Strolle et al.
patent: 5757855 (1998-05-01), Strolle et al.
patent: 5907586 (1999-05-01), Katsuragawa et al.
patent: 5923711 (1999-01-01), Willming
patent: 5946361 (1999-08-01), Araki et al.
J.G. Proakis,Digital Communication.
V. Eyuboglu and S. Qureshi, “Reduced-State Sequence Estimation for Coded Modulation on Intersymbol Interference Channels”IEEE Journal on Selected Areas of Communications, Aug. 1989.
A. Duel-Hallen and C. Heegard, Delayed Decision-Feedback Equalization,IEEE Transactions on Communications, May 1989.
G. Ungerboeck, “Trellis Coded Modulation with redundant Signal Sets Part I and II”,IEEE Communications, Feb. 1987.
G. Ungerboeck, “Channel Coding With Multilevel/Phase Signals”,IEEE Transactions of Information Theory, Jan. 1982.
A. Viterbi et al.,Principles of Digital Communications and Coding,.
Advanced Television Systems Committee, “ATSC Digital Television Standard” Doc. A/53, Apr. 12, 1995.
Advanced Television Systems Committee,—Guide To The Use Of The ATSC Digital.Television Doc A/54, Apr. 12, 1995.
Endres Thomas J.
Hulyalkar Samir N.
Schaffer Troy A.
Strolle Christopher H.
Corrielus Jean
Pham Chi H.
Ratner & Presia
Sarnoff Digital Communications
LandOfFree
Method of estimating trellis encoded symbols utilizing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of estimating trellis encoded symbols utilizing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of estimating trellis encoded symbols utilizing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2477909