Joint demodulation of cochannel signals using MLSE and MAPSD algorithms
27 Apr 1993-Vol. 4, pp 160-163
TL;DR: In this paper, sequence estimation and symbol detection algorithms for the demodulation of co-channel narrowband signals in additive noise are proposed based on the maximum likelihood (ML) and maximum a posteriori (MAP) criteria for the joint recovery of both cochannel signals.
Abstract: Sequence estimation and symbol detection algorithms for the demodulation of cochannel narrowband signals in additive noise are proposed. These algorithms are based on the maximum likelihood (ML) and maximum a posteriori (MAP) criteria for the joint recovery of both cochannel signals. The error rate performance characteristics of these nonlinear algorithms were investigated through computer simulations. The results are presented. >
Citations
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18 Jun 1995
TL;DR: A method for co-channel interference cancellation in TDMA mobile systems exploiting the characteristics of mobile channels is proposed, which enables the use of joint detection methods in receivers provided that accurate channel estimates can be obtained for all the cochannels.
Abstract: A method for co-channel interference cancellation in TDMA mobile systems exploiting the characteristics of mobile channels is proposed. The independently fading multipath channels provide a distinct waveform coding on each of the co-channel signals, which is a basis for signal separation in receivers. This enables the use of joint detection methods in receivers provided that accurate channel estimates can be obtained for all the cochannels. A joint detection and channel estimation algorithm for multiple co-channel signals are derived. The performance of the receiver is verified by simulations with the GSM system assuming that the strongest interferer is cancelled.
141Â citations
TL;DR: Novel joint estimators are proposed that employ a single-input demodulator with oversampling to compensate for timing uncertainties and a (suboptimal) two-stage joint MAP symbol detector (JMAPSD) is introduced that has a lower complexity than the single-stage estimators while accruing only a marginal loss in error-rate performance at high signal-to-interference ratios.
Abstract: Cochannel interference occurs when two or more signals overlap in frequency and are present concurrently. Unlike in spread-spectrum multiple-access systems where the different users necessarily share the same channel, cochannel interference is a severe hindrance to frequency- and time-division multiple-access communications, and is typically minimized by interference rejection/suppression techniques. Rather than using interference suppression, we are interested in the joint estimation of the information-bearing narrow-band cochannel signals. Novel joint estimators are proposed that employ a single-input demodulator with oversampling to compensate for timing uncertainties. Assuming finite impulse-response channel characteristics, maximum likelihood (ML) and maximum a posteriori (MAP) criteria are used to derive cochannel detectors of varying complexities and degrees of performance. In particular, a (suboptimal) two-stage joint MAP symbol detector (JMAPSD) is introduced that has a lower complexity than the single-stage estimators while accruing only a marginal loss in error-rate performance at high signal-to-interference ratios. Assuming only reliable estimates of the primary and secondary signal powers, a blind adaptive JMAPSD algorithm for a priori unknown channels is also derived. The performance of these nonlinear joint estimation algorithms is studied through example computer simulations for two cochannel sources.
113Â citations
Cites background or methods from "Joint demodulation of cochannel sig..."
...Since the cochannel data symbols are jointly recovered, we refer to the corresponding algorithms as joint MLSE (JMLSE) and joint MAPSD (JMAPSD) [19], [20]....
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...) For the joint detection of two cochannel signals, the objective of JMLSE [19], [20] is to determine thepair of sequences that minimize the sum of squared errors defined by the error (likelihood) sequence , as illustrated in Fig....
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...3It should be mentioned that this two-stage JMAPSD structure (also described in [20]) is slightly different from the one proposed in [19], but is exactly equivalent in function....
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...The joint VA (JVA) [19], [20], for JMLSE is implemented with a method very similar to that of the standard VA....
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TL;DR: A discrete-time multirate formulation is introduced for asynchronous CDMA systems, which can incorporate multipath effects and reveals interesting links between CDMA receivers and array processing problems.
Abstract: Code division multiple access (CDMA) schemes allow a number of asynchronous users to share a transmission medium with minimum cooperation among them. However, sophisticated signal processing algorithms are needed at the receiver to combat interference from other users and multipath effects. A discrete-time multirate formulation is introduced for asynchronous CDMA systems, which can incorporate multipath effects. This formulation reveals interesting links between CDMA receivers and array processing problems. In this framework, linear receivers are derived that can completely suppress multiuser interference (decorrelating receivers). A criterion is introduced, which guarantees the decorrelating property, while providing optimal solutions in the presence of noise. Parametric FIR designs as well as nonparametric solutions are delineated, and their performance is analyzed. The proposed receivers are resistant to near-far effects and do not require the estimation of the users' and noise powers.
98Â citations
Patent•
05 Oct 1995TL;DR: In this article, an improved signal detection method in a TDMA mobile system with co-channel interference is proposed. But the method is not suitable for the case of multiple co-channels.
Abstract: The present invention relates to an improved signal detection method in a TDMA mobile system with co-channel interference. In the method, a primary signal (r1) and at least one interfering co-channel signal (r2-rN) are received on the same TDMA channel (F1, TS3). The co-channel signals propagate through multipath channels (hL,1...hL,N) independent of one another, which provide them with a unique wave form coding. In addition, the co-channel signals have different but known training sequences. In the invention, the multipath channel estimates of the primary signal (r1) and said at least one interfering co-channel signal (r2-rN) are determined by means of the received training sequences. After this, the primary signal is detected by utilizing the transmission channel estimates of both the primary signal and said at least one interfering co-channel signal. The invention also relates to receivers for implementing the method of the invention.
72Â citations
TL;DR: It is shown through simulation results for a severe amplitude distorted co-channel system that the decision feedback functional-linkequalizer (DFFLE) provides significantly superior bit-error rate (BER) performance characteristics compared to the conventional DFE, the linear transversal equalizer (LTE), the nonlinear radial basis function (RBF) neural-network-based structures and the feed-forward functional- link equalizer(FFLE)-based structures.
Abstract: A new approach for the decision feedback equalizer (DFE) based on the functional-link neural network is described. The structure is applied to the problem of adaptive equalization in the presence of intersymbol interference (ISI), additive white Gaussian noise, and co-channel interference (CCI). It is shown through simulation results for a severe amplitude distorted co-channel system that the decision feedback functional-link equalizer (DFFLE) provides significantly superior bit-error rate (BER) performance characteristics compared to the conventional DFE, the linear transversal equalizer (LTE), the nonlinear radial basis function (RBF) neural-network-based structures and the feed-forward functional-link equalizer (FFLE)-based structures. The DFFLE is also shown to have a significantly simpler computational requirement relative to the RBF and the FFLE.
54Â citations
References
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TL;DR: A simple technique for quadrature partial-response signaling (QPRS) is described that eliminates the quasicatastrophic nature of the ML trellis and shows that a good performance/complexity tradeoff can be obtained.
Abstract: A reduced-state sequence estimator for linear intersymbol interference channels is described. The estimator uses a conventional Viterbi algorithm with decision feedback to search a reduced-state subset trellis that is constructed using set-partitioning principles. The complexity of maximum-likelihood sequence estimation (MLSE) due to the length of the channel memory and the size of the signal set is systematically reduced. An error probability analysis shows that a good performance/complexity tradeoff can be obtained. In particular, the results indicate that the required complexity to achieve the performance of MLSE is independent of the size of the signal set for large enough signal sets. Simulation results are provided for two partial-response systems. A simple technique for quadrature partial-response signaling (QPRS) is described that eliminates the quasicatastrophic nature of the ML trellis. >
780Â citations
01 May 1970
TL;DR: Simulation results show the optimum detector under a fixed delay constraint D to outperform a transversal equalizer even for relatively small values of D.
Abstract: The optimum detector under a fixed delay constraint D is derived for channels having memory and additive noise. The resulting receiver is recursive and does not grow with the message length. Its structure is presented for linear channels (AM and PSK) with known (or estimated) impulse response and noise statistics. The intersymbol interference is assumed to extend for L sampling periods and the receiver is allowed a "look-ahead" at D future received samples. Simulation results using actual channel characteristics show the detector to outperform a transversal equalizer even for relatively small values of D.
304Â citations
01 Jan 1989
129Â citations
TL;DR: A new blind equalization algorithm is presented that incorporates a Bayesian channel estimator and a decision-feedback (DF) adaptive filter that is more robust to catastrophic error propagation and only a modest increase in the computational complexity.
Abstract: A new blind equalization algorithm is presented that incorporates a Bayesian channel estimator and a decision-feedback (DF) adaptive filter. The Bayesian algorithm operates as a preprocessor on the received signal to provide an initial estimate of the channel coefficients. It is an approximate maximum a posteriori (MAP) sequence estimator that generates reliable estimates of the transmitted symbols. These decisions are then filtered by an adaptive decision-feedback algorithm to further reduce the intersymbol interference. The new algorithm is more robustto catastrophic error propagation thanthe standard decision-feedback equalizer (DFE), with only a modest increase in the computational complexity.
32Â citations