Decision-feedback Differential Detection Research Articles

Decision feedback differential detection for differential orthogonal space-time modulation with APSK signals over flat-fading channels

Differential orthogonal space-time modulation (DOSTM) with amplitude/phase shift keying (APSK) signals has been recently proposed to improve the data throughput of the DOSTM with PSK signals over quasi-static channels. In this letter, decision feedback differential detection (DF-DD) based on linear prediction is presented for the DOSTM with APSK Signals (DOSTM-APSK) over flat-fading channels. The proposed DF-DD offers better performance than the differential detection when the channel experiences fast fading. The coefficients of the linear prediction based DF-DD can be obtained by an adaptive recursive least-squares algorithm, where the channel statistics are not needed. The proposed DF-DD is also applicable to the general unitary differential space-time modulation.

Noncoherent Receivers for Multichip Differentially Encoded DS-CDMA

We design and analyze novel noncoherent receivers for direct-sequence code-division multiple access (DS-CDMA) with multi-chip (MC) differential encoding (DE). The proposed receivers for MC-DE are based on multiple-symbol detection and decision-feedback differential detection, which have been previously applied for symbol-level DE. While the complexity of the proposed receivers is moderate, it is shown that they enable large performance gains over conventional differential detection for various channel environments, such as additive white Gaussian noise (AGWN) channels, Rayleigh and Ricean fading channels, and channels with frequency offset and phase noise. Furthermore, we show that in most cases MC-DE outperforms single-chip differential encoding and, in addition, decreases receiver complexity. Another result of this paper is that quaternary differential phase-shift keying (QDPSK) is more suitable for chip-level DE than binary DPSK.

On the Robustness of Decision-Feedback Detection of DPSK and Differential Unitary Space-Time Modulation in Rayleigh-Fading Channels

Decision-feedback differential detection (DFDD) of differential phase-shift keying (DPSK) and differential unitary space-time modulation (DUST) in Rayleigh-fading channels exhibits significant performance improvement over standard single-symbol maximum-likelihood detection. However, knowledge of channel fading correlation and signal-to-noise ratio (SNR) is required at the receiver to compute the feedback coefficients used in DFDD. In this letter, we investigate the robustness of the DFDD to imperfect knowledge of the feedback coefficients by modeling the mismatch between estimated feedback coefficients and ideal coefficients in terms of mismatch between the estimated values of fading correlation and SNR and the true values. Under the assumption of a block-fading channel when nondiagonal DUST constellations are used and a continuous fading channel otherwise, we derive exact and Chernoff bound expressions for pair-wise word-error probability and then use them to approximate the bit-error rate (BER), finding close agreement with simulation results. The relationships between BER performance and various system parameters, e.g., DFDD length and Doppler mismatch, are also explored. Furthermore, the existence of an error floor in the BER-vs-SNR curve is investigated for the infinite-length DFDD. For the special case of Jakes' fading model, it is shown that the error floor can be removed completely even when the Doppler spread is over-estimated.

DF-DD for channels with phase noise

In this letter, we design decision-feedback differential detection (DF-DD) schemes for channels with phase noise. If the DF-DD feedback filter is properly optimized, a performance similar to that of a more complex scheme, recently reported by Chiavaccini and Vitetta, based on expectation maximization, can be achieved. However, it is also shown that an error floor is unavoidable for channels with phase noise. If a constraint is introduced, the DF-DD receiver can be made robust against unknown frequency offsets.

On the error probability of decision-feedback differential detection

We give a tight approximation for the bit-error rate (BER) of decision-feedback differential detection (DF-DD). The influence of error propagation is modeled by a Markov chain. A simple state reduction method is proposed to limit computational complexity. Our results show that error propagation strongly depends on the chosen feedback filter. In particular, the popular assumption that error propagation increases BER by a factor of two is not always justified.

Noncoherent receivers for differential space-time modulation

In this paper, noncoherent receivers for differential space-time modulation (DSTM) are investigated. It is shown that the performance of the previously proposed conventional differential detection (DD) receiver is satisfactory only for very slow flat fading channels. However, conventional DD suffers from a considerable loss in performance even for moderately fast fading, especially if more than one transmit antenna is used. In order to overcome this problem, two improved noncoherent receivers are considered. The first one is the multiple-symbol detection (MSD) receiver. Because of the high computational complexity of MSD, also a low-complexity decision-feedback differential detection (DF-DD) receiver is derived. Analytical and simulation results confirm that both receivers perform equally well and can take full advantage of the enhanced diversity provided by multiple transmit antennas even for fast fading.

A VLSI Architecture for Novel Decision Feedback Differential Phase Detection with an Accumulator

This paper proposes a novel decision feedback differential phase detection (DF-DPD) for M-ary DPSK. A conventional differential phase detection method for M-ary Differential Phase Shift Keying (DPSK) can simplify the receiver architecture. However, it possesses a poorer bit error rate (BER) performance than coherent detection because of the prior noisy phase sample. Multiple-symbol differential detection methods, such as maximum likelihood differential phase detection, Viterbi-DPD, and DF-DPD using L-1 previous detected symbols, have attempted to improve BER performance. As the detection length, L, increases, the BER performance of the DF-DPD improves but the complexity of the architecture increases dramatically. This paper proposes a simplified DF-DPD architecture replacing the conventional delay and additional architecture with an accumulator. The proposed architecture also improves BER performance by minimizing the current differential phase noise through the accumulation of previous differential phase noise samples. The simulation results show that the BER performance of the proposed architecture approaches that of a coherent detection with differential decoding.

Decision feedback differential detection for 16DAPSK using knowledge of signal power

A decision feedback differential detection (DFDD) scheme for differentially encoded 16-APSK signals is modified using knowledge of the signal power. Using such information can improve the error performance. It is shown that this DFDD scheme is almost identical to a previously proposed DFDD scheme in terms of the error performance.

Decision-feedback differential detection based on linear prediction for 16DAPSK signals transmitted over flat Ricean fading channels

In this article, prediction-based decision-feedback differential detection (DF-DD) for 16-level differentially encoded amplitude/phase-shift keying is proposed. Unlike previously reported DF-DD schemes, this scheme provides a performance gain over conventional differential detection under general Ricean fading conditions. A further important advantage of the novel scheme is that it is able to compensate a small carrier frequency offset. The linear predictor coefficients may be updated using the recursive least-squares algorithm, which can start blind, i.e., without a priori knowledge about the channel statistics and without a training sequence. This makes the scheme attractive for application in mobile communications since the statistics of a nonstationary mobile channel can be tracked.

Decision-feedback differential detection based on linear prediction for MDPSK signals transmitted over Ricean fading channels

In this paper, linear prediction-based decision-feedback differential detection (DF-DD) for M-ary differential phase-shift keying (MDPSK) signals transmitted over Ricean fading channels is proposed. This scheme can improve conventional DD significantly for a multitude of frequency-nonselective channels, as shown analytically and by computer simulations. Prediction-based DF-DD is particularly well suited for application in mobile communications since the predictor coefficients may be updated regularly using the recursive least squares (RLS) algorithm. Here, adaptation can start blind, i.e., no training sequence and no a prior knowledge about the channel statistics are required. A further important characteristic of the proposed detection scheme is that no degradation occurs under frequency offset. The bit error rate (BER) performance of QDPSK with genie-aided prediction-based DF-DD is analyzed, and it is shown under which conditions the irreducible error floor of conventional DD can be removed entirely. In addition, the influence of Doppler shift is discussed. Last, the proposed scheme is compared with a second DF-DD scheme, which is based on multiple-symbol detection.

Decision-feedback differential detection of MDPSK for flat Rayleigh fading channels

In this paper, decision-feedback differential detection (DF-DD) of M-ary differential phase-shift keying (MDPSK) signals, which has been introduced previously for the additive white Gaussian noise (AWGN) channel by Leib et al. (1988) and Edbauer (1992), is extended to flat Rayleigh fading channels. The corresponding DF-DD metric is derived from the multiple-symbol detection (MSD) metric and for genie-aided DF-DD, an exact expression for the bit-error rate (BER) of QDPSK (M=4) is calculated. Furthermore, the dependence of BER on the power spectrum of the fading process is investigated for feedback filters of infinite order. It is shown that in this case, for ideally bandlimited fading processes, the error floor of conventional differential detection (DD) can be removed entirely. Simulation results confirm that both MSD and DF-DD with feedback filters of finite order can reduce the error floor of conventional DD significantly. DF-DD thereby causes considerably less computational load.

Decision-feedback differential detection schemefor 16-DAPSK

A novel decision-feedback differential detection (DF-DD) scheme for 16-level differentially encoded amplitude phase shift keying signals is proposed. It is shown that, by using the new technique based on multiple-symbol detection, a significant performance gain may be obtained compared to a previously proposed DF-DD scheme. This gain increases with decreasing number of feedback symbols, which makes the novel scheme attractive for implementation.

Modified decision feedback differential detectionfordifferentially encoded 16 APSK signals

In 1996, a version of decision feedback differential detection (DFDD) was proposed for detecting differentially encoded 16-level amplitude/phase shift keying (16 DAPSK) signals. The authors propose two modified DFDD methods, each of which uses an amplitude-state indicator. Both DFDD methods provide an improved error performance compared with the original DFDD.

Differential phase detection using recursively generated phase references

We show that decision-feedback differential phase detection (DFDPD) is equivalent to a technique which generates a phase reference by averaging several primitive phase references. We then modify the DFDPD into a differential phase detection (DPD) technique which generates the phase reference using a simple recursive form. The proposed technique can be easily implemented and has satisfactory error performance.

Decision feedback differential detection of differentially encoded 16APSK signals

Multiple-symbol differential detection (DD) with reference signal estimation based on the feedback of past detected symbols is presented for differentially encoded 16-level amplitude/phase shift keying (16DAPSK). A suboptimal decision is derived. The approximate analysis of the bit-error rate (BER) performance taking into account the decision error propagation effect is presented in an additive white Gaussian noise (AWGN) channel and the BER performance is compared with those of 16DPSK and 16 quadrature amplitude modulation (16QAM).

Decision feedback differential phase detection of M-ary DPSK signals

Multiple-symbol differential phase detection (DFDPD) based on decision feedback of past detected symbols is presented for M-ary DPSK modulation. Adopting a Gaussian phase noise assumption, we obtain the a posteriori joint probability density function (PDF) of the outputs of L DPD defectors of orders of 1 to L symbols and derive a DF-DPD algorithm which is based on feeding back the L-1 past detected symbols and minimizing the sum of phase errors of L DPD detectors. A practical implementation of the DF-DPD receiver is presented that uses a single conventional (one-symbol) DPD detector. The bit error rate (BER) performance in an additive white Gaussian noise (AWGN) channel is analyzed taking into account decision error propagation. Performance improvements are evaluated by computer simulations in AWGN and Rayleigh fading channels.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Differentially detected GMSK signals in CCI channels for mobile cellular telecommunication systems

The performance of conventional and decision feedback differential detection receivers for Gaussian minimum-shift keying (GMSK) signals transmitted in the presence of cochannel interference (CCI) and additive white Gaussian noise (AWGN) is evaluated. For the interference, the authors adopt a model which includes N statistically independent static as well as faded CCI. Various bit-error-rate (BER) performance evaluation results have indicated that the receiver under investigation performs better as compared to other more conventional receiver structures. Especially significant BER improvements are obtained for the static CCI channel. For example, it is shown that with a carrier-to-interference ratio of 14 dB, the performance of a 2-b decision feedback differential receiver outperforms a conventional 2-b differential detector by more than 14 dB (at a BER 10/sup -3/). For the faded CCI, the improvement is less: mainly they result in error-floor reductions of about half an order of magnitude. By comparing the performance of static and faded CCI, it was also found that for a given C/I, the performance of the former would depend on the number of interferers, whereas this is not the case for the latter. >

Decision feedback differential detection of 16-DAPSK signals

An improved differential detection scheme called DF-DD, based on decision feedback, is proposed for 16-level differentially encoded amplitude/phase shift keying (16-DAPSK). Computer simulation of BER performance in additive white Gaussian noise (AWGN) channels is presented and compared with that of 16DPSK.