Multiple differential detection with adaptive sequence estimation (MDD-ASE)–-mobile radio transmission performance in frequency selective fading environment

Recently, the differential detection scheme has attracted considerable attention as a demodulated scheme for digital mobile communications because of its robustness in the frequency nonselective fading channel. A problem of the differential detection scheme is that its bit error rate (BER) performance in the additive white Gaussian noise (AWGN) channel is inferior to that of the coherent detection scheme. To solve this problem, many methods to improve BER performance of the differential detection in the AWGN channel have been proposed. However, those methods require complex signal processings.This paper proposes a novel differential detection scheme as a simpler improvement method which estimates the differential phase of the transmitted signal by a sequence estimation scheme using the Viterbi algorithm. The proposed scheme is simplified in a manner such that its signal processing is composed of only additions and subtractions on the phase information of the received signal. Results of computer simulation show that BER performance of the proposed scheme is close to that of the ideal coherent detection in the AWGN channel. In addition, the trellis diagram of the Viterbi algorithm can be reduced without performance degradation introducing the signal processing similar to the Scarece State Transition (SST) type Viterbi decoding. The proposed scheme also is useful in the case of the fast Rician fading channel and the slow Rayleigh fading channel.

Analogous to multiple symbol differential detection of quadrature phase-shift-keying (QPSK), a multiple bit differential detection scheme is described for offset QPSK that also exhibits continuous improvement in performance with increasing observation interval. Being derived from maximum-likelihood (ML) considerations, the proposed scheme is purported to be the most power efficient scheme for such a modulation and detection method. Extension of the result to shaped offset QPSK is also possible.

In this paper we propose a reconfigurable multiple bit differential detection (MBDD) algorithm with diversity reception in the form of postdetection equal-gain combining (EGC) that can be used for the differential phase shift keying (DPSK) signal reception in the presence of significant frequency offsets. The proposed algorithm is based on the MBDD algorithm with the introduction of a mechanism for the estimation of the frequency offset. The algorithm is checking N c frequency offsets around zero offset and chooses the one that is the most likely. The analysis shows that the receiver with the proposed algorithm provides signal reception with almost equal quality in a wide range of carrier frequency offsets around zero frequency offset.

In this article, a computationally-efficient approach is presented for Bit Error Rate (BER) calculations in multi-user Multiple Input Multiple Output (MIMO) frequency selective fading environments, operating in spatial multiplexing transmission mode. To this end, theoretical expressions for the equivalent Signal to Interference plus Noise Ratio (SINR) per active user and transmission mode, as well as mean BER, are derived. The key idea is that all parameters related to BER calculations can be expressed as sums of identically distributed random variables (RVs). Hence, computational burden can be reduced, since summation formulas take into account the parameters of a standalone RV along with the correlation of an arbitrary pair of RVs. As results indicate, the proposed approach can accurately estimate mean BER in multiuser MIMO orientations with increased reception diversity order, for arbitrary number of transmit/receive antennas, a modulation scheme, and a number of resolvable multi-path components.

A differential recursive detection (DRD) technique for multiple phase shift keying (MPSK) is proposed, and its performance is analyzed and computer simulated. By combining the multiple-symbol differential detection algorithm with conventional (one-symbol) differential detection, based on maximum-likelihood estimation for a multisymbol observation interval, it is possible to construct a recursive algorithm with a much simpler structure and comparable performance in error rate. Results from computer simulation show 1.25 dB, 2 dB, and 2.55 dB gain over conventional differential detection for the input symbol sequence length of N=3, 5, and 10, respectively, at a bit error rate of 10/sup -5/ in additive white Gaussian noise. For N of more than 10, the performance of DRD is close to that of ideal coherent detection for the differentially encoded signal.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This paper analyzes the performance of well known Least-mean-square (LMS) and Recursive-least-squares (RLS) adaptive algorithms in terms of bit error rate (BER) verses signal to noise ratio (SNR) performances on the space-time coded multicarrier CDMA (STC-MC-CDMA) systems in frequency selective environments. For system we consider Alamouti's space-time coding scheme that involves two transmit antennas and provide transmit diversity at transmitting end. We compare the performance of RLS and LMS detector with help of computer simulation. It is found that BER performance of RLS detector is always considerably better than that of LMS detector. Thus, RLS detector outperforms the LMS detector. In this paper, we propose an application of the RLS algorithm for the detection of space-time coded MC-CDMA system. Simulation results presented in this paper confirms the performance analysis.

This paper proposes a novel adaptive differential detection scheme (adaptive DD), which can significantly reduce the irreducible bit-error rate (BER) of M-ary DPSK due to Doppler spread by the adaptive linear prediction of the reference signal. The predictor coefficient is adapted to changing channel conditions by using the recursive least-square (RLS) algorithm. A phase sequence estimation based on the M-state Viterbi algorithm (VA) and another based on the decision feedback algorithm (DFA) are presented. A theoretical BER analysis is presented for adaptive DD-DFA. BER performances of 2 and 4DPSK in Rayleigh fading channels are evaluated by computer simulations. When the RLS forgetting factor of /spl beta/=1 is used, simulation results show that the irreducible BER of 4DPSK can be reduced to 7.2/spl times/10/sup -5/ (3.9/spl times/10/sup -4/) for VA (DFA) while conventional DD offers 3.9/spl times/10/sup -3/ when f/sub D/T/sub b/ (maximum Doppler frequency times bit duration)=0.01 and average E/sub b//N/sub 0/ (signal energy per bit-to-additive white Gaussian noise (AWGN) power spectrum density ratio)=60 dB, where most errors are produced by Doppler spread. Adaptive DD is also effective in AWGN channels-simulations show that for the case of 4DPSK, a performance gain of 1.2 (0.7) dB is achieved over conventional DD for VA (DFA) at BER=10/sup -3/.

This paper describes the bit error rate (BER) performance of the Enhanced Packet Mode (EPM) of the Eureka 147 Digital Audio Broadcast (DAB) system in a mobile environment. The BER performance of DAB-EPM is characterized by computer simulations in frequency selective (typical case) and flat faded (worst case) mobile channels. For each of these channels, simulations are performed at vehicle speeds ranging from very slow (walking speed) to very fast (high speed trains). Simulation results show that, in typical frequency selective mobile environments, the target BER of 10 8 required to deliver adequate packet data service via the EPM is achieved at Carrier to Noise Ratio (C/N) values smaller than the target value of 14 dB used in coverage and frequency planning at most of the vehicle speeds tested. Moreover, the coverage area of packet data services is equivalent to the coverage of audio services delivered with the MPEG Layer 2 audio codec and the Unequal Error Protection Level 3 of DAB.

In this paper we present decision-feedback differential detection (DF-DD) schemes for autocorrelation-based detection in impulse-radio ultra-wideband (IR-UWB) systems, a signaling scheme regarded as a promising candidate in particular for low-complexity wireless sensor networks. To this end, we first discuss ideal noncoherent sequence estimation and approximations thereof based on block-wise multiple-symbol differential detection (MSDD) and the Viterbi algorithm (VA) from the perspective of tree-search/trellis decoding. Exploiting relations well-known from tree-search decoding, we are able to derive the novel decision-feedback differential detection (DF-DD) schemes. A comprehensive comparison with respect to performance and complexity of the presented schemes in a typical IR-UWB scenario reveals-along with novel insights in techniques for complexity reduction of the sphere decoder applied for MSDD- that sorted DF-DD achieves close-to-optimum performance at very low, and in particular constant receiver complexity.

Bit error rate (BER) is analyzed theoretically for diversity reception in the quasi-static Rayleigh fading environment with noise and co-channel interference conditions. The analysis is based upon the canonic receiver model with postdetection combining. This model presents exact BER formulas with respect to carrier-to-noise ratio (CNR) and carrier-to-interference ratio (CIR) for both coherent and differential detections (CD and DD) of binary angle modulations. In the case of CD, an exact and explicit BER formula for the maximal-ratio combining diversity (MRC) is obtained. On the other hand, in the case of DD, an explicit BER formula for the equal-gain combining diversity (EGC) is obtained. These results are applied to derive an approximate BER formula of M-ary (M = 4, 8, 16) angle modulations. Phase-shift keying (PSK) and continuous-phase frequency-shift keying (CP-FSK) are demonstrated as examples of angle modulations.

Forward Decoding Kernel Machines (FDKM) combine largemargin classifiers with Hidden Markov Models (HMM) for Maximum a Posteriori (MAP) adaptive sequence estimation. State transitions in the sequence are conditioned on observed data using a kernel-based probability model, and forward decoding of the state transition probabilities with the sum-product algorithm directly produces the MAP sequence. The parameters in the probabilistic model are trained using a recursive scheme that maximizes a lower bound on the regularized cross-entropy. The recursion performs an expectation step on the outgoing state of the transition probability model, using the posterior probabilities produced by the previous maximization step. Similar to Expectation-Maximization (EM), the FDKM recursion deals effectively with noisy and partially labeled data.We also introduce a multi-class support vector machine for sparse conditional probability regression, GiniSVM based on a quadratic formulation of entropy. Experiments with benchmark classification data show that GiniSVM generalizes better than other multi-class SVM techniques. In conjunction with FDKM, GiniSVM produces a sparse kernel expansion of state transition probabilities, with drastically fewer non-zero coefficients than kernel logistic regression. Preliminary evaluation of FDKM with GiniSVM on a subset of the TIMIT speech database reveals significant improvements in phoneme recognition accuracy over other SVM and HMM techniques.

We investigate the effects of correlation on the performance of diversity systems in wideband wireless radio environments. Specifically, the average bit error rate (BER) performance of M-ary differential phase shift keying (MDPSK) on correlated frequency-selective slow Rayleigh fading channels is analyzed. A two-branch diversity receiver with postdetection equal gain combining is considered. Nyquist pulse shaping is used and differential detection is employed at the receiver. The effects of cochannel interference on the system performance are assessed using a Gaussian interference model. To further enhance the system performance, the effects of combined diversity and forward error correction (FEC) coding on the average BER are investigated. Results using short cyclic block codes with perfect bit interleaving are obtained. The effects of the root mean square (RMS) delay spread, the amount of correlation, and the level of modulation, M, on the average BER are investigated in detail for both coded and uncoded systems. The results show that dual branch diversity combining with a correlation coefficient of 0.5 outperforms (in terms of BER) short block codes with perfect bit interleaving, and that combined diversity and coding strategies are effective in combatting the effects of frequency-selective fading.

A novel algorithm for decoding a general rate K/N convolutional code based on recurrent neural network (RNN) is described and analysed. The algorithm is introduced by outlining the mathematical models of the encoder and decoder. A number of strategies for optimising the iterative decoding process are proposed, and a simulator was also designed in order to compare the Bit Error Rate (BER) performance of the RNN decoder with the conventional decoder that is based on Viterbi Algorithm (VA). The simulation results show that this novel algorithm can achieve the same bit error rate and has a lower decoding complexity. Most importantly this algorithm allows parallel signal processing, which increases the decoding speed and accommodates higher data rate transmission. These characteristics are inherited from a neural network structure of the decoder and the iterative nature of the algorithm, that outperform the conventional VA algorithm.

In this paper, we develop a detection algorithm at the receiver, for a wireless system employing multiple antennas at both the transmitter and receiver, where the knowledge of channel is not available at the transmitter (a.k.a open-loop system). The proposed algorithm offers a very good trade-off between implementation complexity and bit-error-rate (BER) performance. In the literature, the fixed complexity sphere decoding (FSD) is known to be state-of-the art decoding algorithm for open-loop multiple input and multiple output (MIMO) systems. The reduced state maximum aposteriori (RS-MAP) algorithm is an extension of FSD where reduced state (RS) receiver delivers bit level soft decisions using maximum aposteriori (MAP) Bahl, Cocke, Jelinek and Raviv (BCJR) recursions that are implemented on the reduced state tree. While RS-MAP employs state dependent hard decision feedback, the proposed algorithm uses a) a state dependent soft/hard symbol feedback b) a scaling of the branch metric with the assumption that soft decision feedback is employed, to obtain a performance improvement over standard RS-MAP algorithm. The proposed modifications to the branch metric are general and can be applied to a number of other sequence estimators such as maximum likelihood soft output viterbi algorithm (ML-SOVA), FSD-SOVA, RS-MAP with forward only recursion etc.

Recently we proposed a novel differential encoder by a look-up table. In this paper, we present further research results on this subject. We first propose a bit-assigning algorithm and construct some new tables for various constellations that maximize the minimum noncoherent distance. Then differential encoding for multiple-symbol differential detection is proposed. After that, we indicate that differential encoding by a table is equivalent to differential encoding by a trellis, so we propose a novel differential detector which uses the Viterbi algorithm on the trellis. A theorem about the sufficient number of states for various modulations is proposed. In addition, we further enhance the error performance of the proposed differential encoder by concatenating it with trellis coding. For this noncoherent trellis coding scheme, we propose augmented-state Viterbi decoding. Finally, we extend the proposed differential encoding and detection to differential space-time modulation (DSTM). We propose a new definition of DSTM by which the set of transmitted blocks is determined first. The differential encoding is implemented by a look-up table which can be optimized. The proposed DSTM has satisfactory error performance without constellation expansion.