Trellis-coded differential unitary space-time modulation over flat fading channels

Coding and modulation for multiple-antenna systems have gained much attention in wireless communications. This paper investigates a noncoherent trellis-coded scheme based on differential unitary space-time modulation when neither the transmitter nor the receiver know the channel. In a time-varying flat Rayleigh fading environment, we derive differentially noncoherent decision metrics and obtain performance measures for systems with either an ideal interleaver or no interleaver. We demonstrate that with an ideal interleaver, the system performance is dominated by the minimum Hamming distance of the trellis code, while without an interleaver, the performance is dominated by the minimum free squared determinant distance (a novel generalization of the Euclidean distance) of the code. For both cases, code construction is described for Ungerboeck-type codes. Several examples that are based on diagonal cyclic group constellations and offer a good tradeoff between the coding advantage and trellis complexity are provided. Simulation results show that, by applying the soft-decision Viterbi decoder, the proposed scheme can achieve very good performance even with few receive antennas. Extensions to trellis-coded differential space-time block codes are also discussed.     

Unitary space-time modulation for multiple-antenna communicationsin Rayleigh flat fading

Motivated by information-theoretic considerations, we propose a signaling scheme, unitary space-time modulation, for multiple-antenna communication links. This modulation is ideally suited for Rayleigh fast-fading environments, since it does not require the receiver to know or learn the propagation coefficients. Unitary space-time modulation uses constellations of T×M space-time signals (Φ_i, l=1, ..., L), where T represents the coherence interval during which the fading is approximately constant, and Mi are orthonormal. When the receiver does not know the propagation coefficients, which between pairs of transmitter and receiver antennas are modeled as statistically independent, this modulation performs very well either when the signal-to-noise ratio (SNR) is high or when T≫M. We design some multiple-antenna signal constellations and simulate their effectiveness as measured by bit-error probability with maximum-likelihood decoding. We demonstrate that two antennas have a 6-dB diversity gain over one antenna at 15-dB SNR     

相关时变衰落信道中DSTM非相干接收机的结构与性能

针对空间相关时变衰落信道中的差分空时调制系统,推导得出了一种新的基于信道相关矩阵和时变衰落参数的最优非相干接收机结构,并针对几种特殊信道条件对该接收机进行了简化.实际应用该最优接收机时,基于判决反馈得到的数据,提出了一种次优的非相干接收机结构DF-NCR.理论分析和仿真结果表明,在相关时变衰落信道条件下,采用DF-NCR的差分空时调制系统的误码性能优于传统的差分传输模式.     

Differential space-time modulation with eigen-beamforming for correlated MIMO fading channels

In this paper, joint differential space-time modulation (DSTM) and eigen-beamforming for correlated multiple-input multiple-output (MIMO) fading channels. While DSTM does not require knowledge of each channel realization, the channel's spatial correlation can be easily estimated without training at the receiver and exploited by the transmitter to enhance the error probability performance. A transmission scheme is developed here that combines beamforming with differential multiantenna modulation based on orthogonal space-time block coding. Error probability is analyzed for both spatially correlated and independent Rayleigh fading channels. Based on the error probability analysis, power loading coefficients are derived to improve performance. The analytical and simulation results presented here corroborate that the proposed scheme can achieve considerable performance gain in correlated channels relative to DSTM without beamforming.     

用于快时变MIMO衰落信道的一种差分空时调制技术

针对快时变多输入多输出(MIMO)平坦衰落信道,利用时变信道的基扩展模型(BEM),提出了一种差分空时调制方案。差分编码按块进行,发射信号矩阵为对角酉矩阵。通过设计发射端的交织及接收端的解交织,判决反馈差分检测不需要信道状态信息。理论分析和仿真表明,该方案能同时实现最大的天线分集和信道时变性所提供的Doppler分集。     

WATER—FILLING SPACE—TIME GODE IN CORRELATED FLAT RAYLEIGH FADING MISO CHANNELS

In this paper,STC with water-filling transmit power distribution in MISO system is proposed when the partial channel information feedback is possible,for example,at slow fading scenarion.The performances of the water-filling STC including water-filling STTC and waterfilling STBC are analyzed.Performance comparison of the Ungerboeck‘s2/3 trellis coded 8PSK modulated 2-STBC and 2-STTCs with QPSK is given out different channel correlation.     

Improved space-time trellis coded modulation scheme on slowRayleigh fading channels

It has been established that the appropriate criteria for space-time trellis coded modulation (STTCM) design on slow Rayleigh fading channels are maximisation of the minimum rank and the minimum determinant of the distance matrices. It is demonstrated that when STTCM is used in systems with a large product (>3) of the numbers of transmit and receive antennas, the design of codes with maximum coding gain is governed by the minimum trace of the distance matrices. A number of new codes based on the proposed design criterion have been constructed and shown to be superior to other known codes     

On decision-feedback detection of differential space-time modulation in continuous fading

We show that linear prediction (LP)-based decision-feedback detection (DFD) for nondiagonal differential space-time modulation (DSTM) may suffer from a severe performance degradation in continuously fading channels. DSTM constellations that incur no degradation in LP-DFD are identified as those with a diagonal generator. To cater to other constellations, we propose a low-complexity DFD scheme by inserting decision-feedback symbols into the metric of multiple-symbol differential detection.     

连续衰落信道下适用于酉空时调制的多符号差分球形译码算法

基于连续衰落信道假设,将一种具有递推形式的近似最大似然(ML)度量嵌入自动球形译码算法中,提出了多符号差分近似自动球形译码(MSDAASD)。该算法适用于一般酉空时星座,克服了准静态信道假设下多符号差分球形译码(MSDSD)的错误平层现象,具有接近ML检测的性能,其平均复杂度在大多数情况下低于相同假设下的判决反馈检测算法。     

Concatenated space-time block coding with trellis coded modulation in fading channels

Trellis coded modulation (TCM) is a bandwidth efficient transmission scheme that can achieve high coding gain by integrating coding and modulation. This paper presents an analytical expression for the error event probability of concatenated space-time block coding with TCM which reveals some dominant factors affecting the system performance over slow fading channels when perfect interleavers are used. This leads to establishing the design criteria for constructing the optimal trellis codes of such a concatenated system over slow flat fading channels. Through simulation, significant performance improvement is shown to be obtained by concatenating the interleaved streams of these codes with space-time block codes over fading channels. Simulation results also demonstrate that these trellis codes have better error performance than traditional codes designed for single-antenna Gaussian or fading channels. Performance results over quasi-static fading channels without interleaving are also compared in this paper. Furthermore, it is shown that concatenated space-time block coding with TCM (with/without interleaving) outperforms space-time trellis codes under the same spectral efficiency, trellis complexity, and signal constellation.     

Diagonal block space-time code design for diversity and coding advantage over flat fading channels

The potential promised by multiple transmit antennas has raised considerable interest in space-time coding for wireless communications. In this paper, we propose a systematic approach for designing space-time trellis codes over flat fading channels with full antenna diversity and good coding advantage. It is suitable for an arbitrary number of transmit antennas with arbitrary signal constellations. The key to this approach is to separate the traditional space-time trellis code design into two parts. It first encodes the information symbols using a one-dimensional (M,1) nonbinary block code, with M being the number of transmit antennas, and then transmits the coded symbols diagonally across the space-time grid. We show that regardless of channel time-selectivity, this new class of space-time codes always achieves a transmit diversity of order M with a minimum number of trellis states and a coding advantage equal to the minimum product distance of the employed block code. Traditional delay diversity codes can be viewed as a special case of this coding scheme in which the repetition block code is employed. To maximize the coding advantage, we introduce an optimal construction of the nonbinary block code for a given modulation scheme. In particular, an efficient suboptimal solution for multilevel phase-shift-keying (PSK) modulation is proposed. Some code examples with 2-6 bits/s/Hz and two to six transmit antennas are provided, and they demonstrate excellent performance via computer simulations. Although it is proposed for flat fading channels, this coding scheme can be easily extended to frequency-selective fading channels.     

Iterative decision-feedback differential demodulation ofbit-interleaved coded MDPSK for flat Rayleigh fading channels

A simple receiver structure previously proposed by the authors for convolutional coded M-ary differential phase-shift keying transmission over flat Rayleigh fading channels without channel state information is analyzed in detail. We present a thorough discussion of the iterative decoding procedure, which is referred to as iterative decision-feedback differential demodulation (iterative DF-DM). The convergence behavior of iterative DF-DM is theoretically examined. The analysis supports the observation that the iterative decoding scheme works well for target bit-error rates which are usually of interest. Furthermore, the associated cut-off rate for error-free decision feedback is studied. Judging from this performance parameter, remarkable gains in power efficiency compared to conventional differential demodulation are indicated, while the computational complexity of the decoding remains low. The results from information theory are in good agreement with the given simulation results     

Improved design criteria and new trellis codes for space-time codedmodulation in slow flat fading channels

The design criteria for space-time codes under slow flat Rayleigh fading environments are well known to be the rank criterion and the determinant criterion. However, the derivation of these two criteria is based on the assumption that the signal-to-noise ratio (SNR) is sufficiently high. Hence these criteria are loose when the SNR does not satisfy this assumption. In this letter, we consider this practical issue and derive tighter design criteria for moderate and low SNRs. Some new space-time trellis codes are found based on the new criteria through computer search. Simulation results show that these codes outperform existing codes under their designed SNR conditions     

Robust space-time codes for correlated Rayleigh fading channels

Space-time (ST) coding has emerged as an effective strategy to enhance performance of wireless communications in fading environments. Many different ST coding schemes have been proposed to achieve reliable communications in independent fading channels. However, a design of robust ST codes for correlated fading channels has not been addressed. We propose a simple robust ST coding scheme that achieves robust performance over a wide range of fading conditions. The key to achieve robust performance is to formulate code design criteria that are not dependent on the channel correlation statistics. A provably robust scheme can be formulated by concatenating a full-rank ST block code with an outer encoder. We derive several robust code examples via the concatenated orthogonal ST block code and TCM construction. The simulation results show that some traditional ST codes perform poorly, whereas the proposed codes achieve robust performance over a broad range of fading conditions.     

Signal constellations design for differential unitary space-time in MIMO-OFDM system over frequency-selective fading channels

In this paper, the design of signal constellations parameters is studied for Differential Unitary Space-Time Modulation （DUSTM） based on the design criterion of maximizing the diversity product. Further, noninteger searching method for the signal constellation parameters design is proposed in order to get better codes. Experimental results show that under the different Doppler spread and data transmission rate, the proposed design performs better than the previous design using integer parameters in Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing （MIMO-OFDM） system over frequency-selective fading channels.     

Performance of coded modulation employing differential encodingover Rayleigh fading channels

Multilevel coding and bit-interleaved coded modulation employing differential encoding and non-coherent reception over flat fading channels are assessed. To achieve high bandwidth efficiencies mixed amplitude/phase modulation is performed. It is shown that multiple symbol detection only provides gains for multilevel coding as Gray labelling of the differential symbols is not possible     

Adaptive coded modulation for fading channels

We apply coset codes to adaptive modulation in fading channels. Adaptive modulation is a powerful technique to improve the energy efficiency and increase the data rate over a fading channel. Coset codes are a natural choice to use with adaptive modulation since the channel coding and modulation designs are separable. Therefore, trellis and lattice codes designed for additive white Gaussian noise (AWGN) channels can be superimposed on adaptive modulation for fading channels, with the same approximate coding gains. We first describe the methodology for combining coset codes with a general class of adaptive modulation techniques. We then apply this methodology to a spectrally efficient adaptive M-ary quadrature amplitude modulation (MQAM) to obtain trellis-coded adaptive MQAM. We present analytical and simulation results for this design which show an effective coding gain of 3 dB relative to uncoded adaptive MQAM for a simple four-state trellis code, and an effective 3.6-dB coding gain for an eight-state trellis code. More complex trellis codes are shown to achieve higher gains. We also compare the performance of trellis-coded adaptive MQAM to that of coded modulation with built-in time diversity and fixed-rate modulation. The adaptive method exhibits a power savings of up to 20 dB     

Coded M-DPSK with built-in time diversity for fading channels

Good coded modulation for fading channels requires built-in time diversity. Under a constraint on the interleaving delay, the authors construct and compare three categories of coded M-DPSK (M-ary differential phase-shift keying) schemes with 4⩽M⩽16 for fading channels: two-dimensional trellis-coded, multidimensional trellis-coded, and block-coded. General rules for designing these schemes and their matched bit or symbol interleavers are given. A universal two-state interleaver is shown. These schemes have been extensively evaluated, using computer simulations, for a narrow-band cellular radio channel at different vehicle speeds, with and without twofold antenna diversity     

Adaptive differentially coherent orthogonally multiplexed orthogonal phase modulation over flat fading channels

A constant-power adaptive transmission technique adopting differentially coherent orthogonally multiplexed orthogonal phase modulation (DOMOPM) signals is studied for flat fading channels. Numerical results show that the constant-power adaptive DOMOPM system significantly outperforms the constant-power adaptive noncoherent frequency shift keying system in average spectral efficiency.     

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.