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     

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.     

On Trellis Coded Noncoherent Space-Time Modulation

Unitary space-time modulation (USTM) is well-tailored for noncoherent space-time modulation. Trellis coded USTM (TC-USTM) can obtain significant coding gains over uncoded USTM for the noncoherent block fading channel. Conventional TC-USTM schemes expand the signal set of uncoded USTM by a factor of two. In this letter, we propose a new TC-USTM scheme in which the size of USTM set is not limited to be just double for uncoded USTM. However, in TC-USTM schemes, because signals of the same trellis branch are transmitted over the same fading coefficients, one trellis branch can only obtain one temporal diversity. In this letter, we also propose a new trellis coded noncoherent space-time modulation scheme by interleaving space-time signals. The proposed scheme can enlarge temporal diversity at the price of increased complexity and delay. Simulation results demonstrate the excellent error performances of codes found by computer searches for both schemes.     

Space-time code design for CPFSK modulation over frequency-nonselective fading channels

We derive a novel space-time code (STC) design criterion for continuous-phase frequency-shift keying (CPFSK) over frequency-nonselective fading channels. Our derivation is based on a specific matrix that is related to the input symbols of the CPFSK modulators. With this code-design criterion, we propose a simple interleaved space-time encoding scheme for CPFSK modulation over frequency-nonselective correlated fading channels to exploit potential temporal and spatial diversity advantages. Such an encoding scheme consists of a ring convolutional encoder and a spatial encoder, between which a convolutional interleaver is placed. A decoding algorithm that generates symbol metrics for the Viterbi decoder of convolutional codes from the spatial modulation trellis is examined. Simulation results confirm that the advantages of the combination of the interleaved convolutional encoding (for temporal diversity) and the spatial encoding (for spatial diversity) are promising for various system parameters.     

The performance of type-I trellis coded hybrid-ARQ protocols overAWGN and slowly fading channels

A method is described for modifying trellis coded modulation systems for use in type-1 hybrid-ARQ protocols. The difference between the partial path metric of the survivor and that of the best nonsurvivor at each node in the trellis is used to determine the desirability of a retransmission request for a given received packet. Bounds on the reliability and throughput performance of the resulting error control scheme are derived for AWGN channels and slowly fading Rician channels. Examples are included to illustrate the achievable gain of the proposed system relative to ordinary forward-error-correcting trellis coded systems. Hybrid-ARQ protocols based on ordinary trellis coded modulation and multiple trellis coded modulation are also compared over slowly fading Rician channels. The dependence of performance on packet length is examined and illustrated by examples. All analytical results are supported by data from a series of simulations     

Cooperative Multiple Trellis Coded Modulation

In this paper, we consider the general design criteria, properties and explicit code design procedures for cooperative multiple trellis coded modulation (CMTCM) schemes over Rayleigh fading channels. The cooperative system of interest utilizes the decode and forward protocol based on orthogonal transmissions from the cooperating terminals to the destination. We design full diversity cooperative multiple trellis codes using asymmetric constellations that at a frame error probability of 10^?3 provide around 10-12 dB gains over non-cooperative coded modulation without sacrificing the data rate and/or bandwidth efficiency. This is achieved by expanding the baseline constellation used in the non-cooperative transmission, designing the signal constellation to be asymmetric, and adopting multiple mappings among users. The consistent performance gains due to coding, asymmetry, and mappings of symbols onto the constellation are evaluated in terms of the frame error probability. We present simulation results that support the theoretical designs and illustrate the viability of the proposed cooperative MTCM technique.     

The effects of phase noise on trellis coded modulation overGaussian and fading channels

In this paper, error performance bounds are derived for 8-PSK trellis coded modulation (TCM) over Gaussian and fading channels in the presence of phase noise. Coherent demodulation combined with both phase-locked loop (PLL) and transparent tone in band technique (TTIB) for phase recovery is assumed. The analysis is then applied to a number of Ungerboeck 8-PSK trellis codes and the results for the bit error rate (BER) performance, obtained both analytically and by Monte Carlo simulation, are presented. The derived bounds can be directly extended to any M-PSK trellis code     

Concatenated Trellis Coded Modulation for Quasi-Static Fading Channels

In this paper, we present a novel concatenated trellis coded modulation (CTCM) scheme for limited diversity order fading channels. Examples for such channels include those encountered in indoor wireless networks like IEEE 802.11. It is first shown that when the diversity order afforded by the channel is fixed, bit interleaved coded modulation (BICM) is no longer the best way to encode. We then develop CTCM, which is superior to both BICM and conventional TCM of similar complexities. Unlike conventional TCM where convolutional codes are designed over modulated signal sets, CTCM has TCM concatenated to short length inner codes. Each trellis branch in the TCM now corresponds to a short block-code. We discuss design of good inner codes that allow for simple decoders. CTCM design incorporates useful features of both BICM and conventional TCM. Code design is explained with examples. Simulation results and information theoretic supporting the arguments are shown.     

Trellis Coded Hybrid Selective Repeat ARQ Schemes for Point-to-Multipoint Communication over Rayleigh Fading Channels

In this paper, the hybrid selective repeat (SR) automatic repeat request (ARQ) scheme using trellis coded modulation (TCM) proposed by Tellambura and Bhargava [21] is generalized to point-to-multipoint communications for Rayleigh fading channel. Analytical expressions are derived for the throughputs of the point-to-multipoint communication schemes with and without code combining technique. Numerical results show that the protocol using code combining technique yields better throughput than the protocol without code combining and the throughputs decrease when the number of receivers and the value of erasure threshold increase. When the number of receivers equals 1, the scheme without code combining becomes the point-to-point communication scheme proposed in [21].     

无线信道中网格编码调制技术研究

网格编码调制技术（TCM）是一种将编码与调制有机结合起来的技术,可使系统的频带利用率和功率资源同时得到有效利用。在对TCM原理和结构分析的基础上,研究了网格编码调制技术中的几个关键技术,主要包括集分割原理和无线信道下TCM误码率的分析,最后对无编码的QPSK与8PSK—TCM进行了仿真比较。仿真结果表明,在无线信道相同的误码率下,采用网格编码调制技术比未编码QPSK获得2dB的编码增益。     

Novel full diversity space time codes

A novel full diversity space-time trellis code, referred to as an assembled space-time trellis code (ASTTC), is presented in this letter. For this scheme, space-time trellis coded signals are first linearly transformed, and then the transformed signals are coded by using the Alamouti space-time block code. A new design criterion is proposed. It is shown that the ASTTCs can achieve not only the full diversity order but also a significant coding gain determined by the minimum weighted code distance (MWCD). Based on this design criterion, a new 4-state code is derived by a systematic code search. Simulation results show that the new ASTTC is superior by about 1.7 dB to the TSC (TarokhSeshadri-Calderbank) code at the frame error rate (FER) of 1.0e-2 over quasi-static fading channels.     

Space–Time Code Design for CPFSK Modulation Over Frequency-Nonselective Fading Channels

We derive a novel space–time code-design criterion for continuous-phase frequency-shift keying (CPFSK) over frequency-nonselective fading channels. Our derivation is based on a specific matrix that is related to the input symbols of the CPFSK modulators. With this code-design criterion, we propose a simple interleaved space–time encoding scheme for CPFSK modulation over frequency-nonselective correlated fading channels to exploit potential temporal and spatial diversity advantages. Such an encoding scheme consists of a ring convolutional encoder and a spatial encoder, between which a convolutional interleaver is placed. A decoding algorithm that generates symbol metrics for the Viterbi decoder of convolutional codes from the spatial modulation trellis is examined. Simulation results confirm that the advantages of combination of the interleaved convolutional encoding (for temporal diversity) and the spatial encoding (for spatial diversity) are promising for various system parameters.     

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.     

Application of Coded Modulation to 1.544-Mbit/s Data-in-Voice Modems for FDM FM and SSB Analog Radio Systems

The technical issues relevant to providing high-quality digital service over analog radio using 1.544-Mbit/s DS-1 data-invoice modems operating through analog supergroup channels with 256-QAM modulation are reviewed. By means of a typical example, the desirability of increasing the fading margin when operating over FM radio systems is demonstrated. This motivates the consideration of coded modulation as a means of extending the threshold of the modem System, so that operation of the modem can be achieved in supergroup channels located higher in the radio baseband. It is found that trellis coded modulation provides better improvement of threshold performance than lattice coded modulation when the actual coding gain realized near the R0channel bound is used rather than the high signalto-noise-ratio (SNR)asymptotic coding gains. Using Ungerboeck's eight-state trellis code [3], a coding gain of approximately 2 dB is found for operation at 28 dB SNR (1 dB from the R0bound). Furthermore, it is found that even at this low operating SNR (where error events at the coded modulation receiver ouput can be long), high-rate, interleaved Reed-Solomon codes, used for burst noise protection at high SNR, still provide over 2 dB of additional coding gain.     

Space‐time ring‐TCM codes with CPM based on the decomposed model for transmission over Rayleigh fading channels

Space–time (ST) coding is a proved technique for achieving high data rates in 3G mobile systems that combines coding, modulation and multiple transmitters and receivers. A novel algorithm is proposed for ST ring trellis‐coded modulation (ST‐RTCM) systems with continuous‐phase modulation (CPM) when the channel coefficients are known to the receiver. This algorithm is based on the CPM decomposed model, which exploits the memory properties of this modulation method, resulting in a straightforward implementation of joint ST coding and CPM, which is particularly suitable for ring codes. This new scheme is used to investigate the performance of the delay diversity code with CPM over slow Rayleigh fading channels, in particular with MSK which is one of the most widely used modulation methods of continuous phase. Furthermore, a feedback version of delay diversity allowed by the decomposition is tested in 1REC and 1RC systems. This feedback configuration is seen to provide good results for low signal‐to‐noise ratios. Simulations results are also provided for multilevel ST‐RTCM codes that achieve a higher throughput than MSK‐coded systems. Additionally the serial concatenation of an outer Reed–Solomon code with an ST‐RTCM code is shown, this combination further reduces the error probability and achieves even more reliable communications. Copyright © 2005 John Wiley & Sons, Ltd.     

8-PSK trellis codes for a Rayleigh channel

A suboptimal trellis coding approach based on the concept of combining a good convolutional code and bit interleavers is presented. The aim is to improve the reliability of digital radio communication over a fading channel. It is shown that over a Rayleigh channel and for a fixed code complexity the proposed system is superior to the baseline system. Its performance is analyzed using the generalized R_o and the upper bound on the bit error rate. The results suggest that on a Rayleigh channel, the standard trellis codes may not be the correct approach for improving the reliability of the communication channel. The discussion is restricted to a rate 2/3 coded system with 8-PSK modulation     

Golden Space–Time Trellis Coded Modulation

In this paper, we present a multidimensional trellis coded modulation scheme for a high rate 2times2 multiple-input multiple-output (MIMO) system over slow fading channels. Set partitioning of the Golden code is designed specifically to increase the minimum determinant. The branches of the outer trellis code are labeled with these partitions and Viterbi algorithm is applied for trellis decoding. In order to compute the branch metrics, a sphere decoder is used. The general framework for code design and optimization is given. Performance of the proposed scheme is evaluated by simulation and it is shown that it achieves significant performance gains over the uncoded Golden code     

A Parallel Concatenated Convolutional-Based Distributed Coded Cooperation Scheme for Relay Channels

In this paper, we investigate a coded cooperation diversity scheme suitable for L-relay channels operating in the soft-decode-and-forward (soft-DF) mode. The proposed scheme is based on parallel concatenated convolutional codes (PCCC). To improve the overall performance through diversity, the coded cooperation operates by sending the systematic and the first parity outputs via L?+?1 independent fading paths. Instead of using only a centralized turbo code system at the source node, we have proposed a DCC scheme, where the first recursive systematic coding is done at both source and relay nodes. At the destination, the received replicas are combined using the maximal ratio combining (MRC). The entire codeword, comprising the MRC sequence and the second parity part, is decoded via the maximum a-posteriori (MAP) algorithm and turbo decoding principle. We analyze the proposed scheme in terms of bit error rate (BER). In fact, we define the explicit upper bounds for error rate assuming Binary phase shift keying (BPSK) transmission for fully interleaved channels with channel state information (CSI). We use the Rayleigh fading channels with independent fading. Our study shows that the full diversity order is achieved when the source-relay link is more reliable than the other links. Otherwise, the diversity decreases. However, in both cases, it is shown that significant performance improvements are possible to achieve over non-cooperative coded systems. Theorical and simulation results are presented to demonstrate the efficacy of the proposed scheme.     

Bounds on the error performance of coding for nonindependentRician-fading channels

New upper bounds on the error performance of coded systems for Rician channels are presented. The fading channels need not be fully interleaved to obtain meaningful performance results. These bounds hold for coherent, differentially coherent and noncoherent demodulation of binary signals. They provide a useful analytical approach to the evaluation of the error performance of convolutional or block coding and they may be generalized to M-ary signals and trellis modulation. The approach allows for complex bounds using the fine structure of the code, for simpler bounds similar to those on memoryless channels and finally for a random coding bound using the cutoff rate of the channel. The analysis thus permits a step by step evaluation of coded error performances for Rician-fading channels     

Trellis Coded Modulation for 4800-9600 bits/s Transmission Over a Fading Mobile Satellite Channel

The combination of trellis coding and MPSK signaling with the addition of asymmetry to the signal set is discussed with regard to its suitabllity as a modulation/coding scheme for the fading mobile satellite channel. For MPSK, introducing nonuniformity (asymmetry) into the spacing between signal points in the constellation buys a further improvement in performance over that achievable with trellis coded symmetric MPSK, all this without increasing the average or peak power, or changing the bandwidth constraints imposed on the system. Whereas previous contributions have considered the performance of trellis coded modulation transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in this paper is on the performance of trellis coded MPSK in the fading environment. The results will be obtained by using a combination of analysis and simulation. It will be assumed that the effect of the fading on the phase of the received signal is fully compensated for either by tracking it with some form of phase-locked loop or with pilot tone calibration techniques. Thus, our results will only reflect the degradation due to the effect of the fading on the amplitude of the received signal. Also, we shall consider only the case where interleaving/deinterleaving is employed to further combat the fading. This allows for considerable simplification of the analysis and is of great practical interest. Finally, the impact of the availability of channel state information on average bit error probability performance is assessed.