Near-Capacity Turbo Trellis Coded Modulation Design

In this paper, we have proposed a bandwidth efficient turbo trellis-coded modulation scheme for the non-coherent multiple-antenna Rayleigh fading channel, where the channel state information (CSI) is not necessary both at the transmitter and the receiver. In this scheme, we merge the unitary space-time modulation (USTM) as constellations with the turbo trellis-coded modulation, resulting in the turbo trellis-coded USTM (TTC-USTM), with the trellis-coded USTM encoder as the component encoders. We have also derived the iterative maximum a posteriori (MAP) algorithm. Through computer simulations, we demonstrated that without bandwidth expansion, TTC-USTM produces significant coding gains over its uncoded counterparts.

This paper proposes an extrinsic information transfer (EXIT) chart analysis and an asymptotic bit error rate (BER) prediction method to speed up the design of high rate RCM-LDGM hybrid codes over AWGN and fast Rayleigh channels. These codes are based on a parallel concatenation of a rate compatible modulation (RCM) code with a low-density generator matrix (LDGM) code. The decoder uses the iterative sum-product algorithm to exchange information between the variable nodes (VNs) and the two types of constituent check nodes: RCM-CN and LDGM-CN. The novelty of the proposed EXIT chart procedure lies on the fact that it mixes together the analog RCM check nodes with the digital LDGM check nodes, something not possible in previous multi-edge EXIT charts proposed in the literature.

EXtrinsic Information Transfer (EXIT) chart is a graphical tool for analysis of low density parity check (LDPC) and other codes with iterative decoding. In this paper, we propose the design of LDPC codes for coded modulation schemes by application of linear programming with conditions derived from EXIT charts. Points on the EXIT curve for bit and check node operations are first computed either using analysis or by simulation. The entire EXIT curve is then obtained by linear interpolation. Finally, the EXIT curves are optimized to obtain the maximum possible rate for the code under a given threshold condition. To demonstrate the design procedure, we consider the cases of M-PAM and 8-PSK over the additive white Gaussian noise (AWGN) channel. The optimization method presented is versatile, and can be extended to other constellations and situations easily.

Turbo-trellis coded modulation (TTCM) schemes are designed for reliable transmission over quasi-static fading channels. Assuming pilot-assisted channel estimation, practical limitations in power and the number of pilot symbols lead to imperfect channel estimates. A general method for robust multiple-input multiple-output (MIMO) receiver design under channel estimation errors was recently proposed by Sadough et al.. Here, this technique is applied to improve the performance of MIMO-TTCM receivers under channel estimation errors in quasi-static fading channels where the TTCM scheme is commonly used. We compare our proposed reception method to the conventional mismatched receiver in terms of bit error rate and extrinsic information transfer chart analysis. Our results confirm the adequacy of the proposed receiver for improving MIMO-TTCM iterative decoding in situations where only an imperfect channel estimate is available at the receiver.

Space-time block coded (STBC) in-phase quadrature-phase (IQ)-interleaved coded modulation (CM) schemes are proposed for orthogonal frequency division multiplexing (OFDM). Trellis coded modulation (TCM), turbo TCM (TTCM), bit-interleaved coded modulation (BICM) and iteratively decoded BICM (BICM-ID) schemes having a similar decoding complexity are employed in conjunction with 16-level quadrature amplitude modulation (16QAM) for yielding an effective throughput of 3 information bits per symbol. The IQ-diversity attained by the proposed schemes provides a significant additional coding gain. It was found that TTCM and BICM-ID assisted STBC-IQ-OFDM were the best schemes in terms of the achievable bit error ratio and frame error ratio, respectively.

In this letter, the concept of multiple serially-concatenated codes is invoked in the context of stochastic resonance (SR), where the achievable performance is improved by increasing noise power. More specifically, the receiver's iterative decoding process is characterized with the aid of extrinsic information transfer (EXIT) charts, such that the SR effect induced by a non-linear component is taken into account. Our simulation results demonstrate that although the SR demodulator's log-likelihood ratio (LLR) outputs are not Gaussian distributed, the corresponding EXIT trajectory matches the prediction from the associated inner- and outer-codes' EXIT curves, while reaching the perfect convergence point in terms of mutual information. Therefore, an infinitesimally low bit-error ratio (BER) is attained by appropriately designing the channel code's parameters based on EXIT charts.

In this paper, we analyze an orthogonal frequency division multiplexing (OFDM) system employing combined space- time-frequency (STF) codes and an iterative receiver with extrinsic information transfer (EXIT) charts and bit-error rate plots. As STF codes, we examine orthogonal space-time block codes (OSTBCs), cyclic delay diversity, and discontinuous Doppler diversity. We present a combined STF code for eight transmit antennas with rate one. Another contribution of this work is the EXIT chart analysis demonstrating that EXIT charts are not always a suitable tool to analyze the performance of iterative receivers for STF coded OFDM systems. Further, error floors due to the mapping can be removed even for correlated channels by differential encoding and code doping the bits before the modulator.

In this paper, a new turbo trellis coded modulation (T-TCM) scheme is proposed for 8-PSK modulation. A belief propagation algorithm is used for T-TCM decoding. Bit and symbol interleaving techniques are considered for the T-TCM scheme and it is concluded that the symbol interleaved scheme provides better error performance. It is also shown by computer simulations that the distance distribution of the output symbol sequences for the two-weight inputs is improved when primitive feedback polynomials are selected for the constituent encoders instead of nonprimitive ones. Factors that determine performance at high signal to noise ratio are stated. If constituent encoders which maximize the output distances for two- and three-weight inputs are selected, those with maximum effective free distance with minimum multiplicity among them will provide the best error performance. From this issue, a new 8-state punctured T-TCM code for 8-PSK is designed and it is shown by computer simulations that it performs better especially at high SNR ratios with half decoding complexity, compared to the corresponding codes given in the literature.

In previous works, density evolution schemes have been used to design an irregular low-density parity-check (LDPC) code for the multi-input multi-output (MIMO) systems. However the code design based on the density evolution can be used only for simple code structure like LDPC codes and repeat-accumulate (RA) codes. Recently simple and accurate irregular LDPC code design method based on the extrinsic information transfer (EXIT) chart was introduced for an AWGN channel. This code design scheme is much flexible, therefore it can be used for any kind of code structure like turbo codes. In this paper we design an irregular LDPC code for a MIMO system using the EXIT chart based scheme. The EXIT charts are used to obtain the optimal edge degree distribution of the irregular LDPC code combined with the MMSE-SIC MIMO detector. This scheme can be generalized for designing the optimal iterative MIMO detector combined with any kind of channel codes including turbo codes.

The joint Viterbi detector/decoder (JVDD) has been proposed as an alternative to the powerful and ubiquitous low-density parity check (LDPC) coding schemes, that are used in the majority of channel coding applications today. At shorter block lengths, the JVDD is able to outperform the state-of-the-art LDPC decoder that can be found in many of today’s systems, from deep-space communications to the digital video broadcasting standard, to the advanced television standard committee 3.0. Researchers have developed the tools to analyze the performance of the LDPC decoder, which is known as the sum-product algorithm or message passing algorithm. These tools include density evolution (DE) and extrinsic information transfer (EXIT) charts. To date, no similar such analysis exists for the JVDD. In the current paper we perform a similar preliminary analysis on the JVDD algorithm akin to what DE and EXIT charts are for the LDPC decoder. The current new analysis of the JVDD allows prediction of its probability of error based on the probability distribution functions of the metrics used within the algorithm. Our analysis plays a similar role to the abovementioned tools developed for the LDPC decoder: it allows us to predict the performance of the JVDD under various conditions (such as varying SNR’s, thresholds, and block lengths), it improves our understanding of the JVDD algorithm and the match against Monte-Carlo simulations verifies our assumptions on the main error-causing mechanisms within the JVDD.

An optimal MAP equivalent SOVA decoding algorithm and its simplified suboptimal algorithm for non-binary codes are proposed. The implementation of its suboptimal algorithm is simpler, while its performance is very close to the optimal log-MAP algorithm. The proposed SOVA can be used as a decoder for turbo trellis coded modulation (TTCM). Simulation results for both the proposed SOVA and the log-MAP algorithms for TTCM and binary turbo codes are presented. It is concluded that the proposed SOVA performs very close to the log-MAP algorithm for both the TTCM and binary turbo codes, and its performance is better than the conventional SOVA.

Turbo trellis coded modulation (TTCM) invented by Patrick Robertson adapted the bandwidth efficiency of TCM and iterative decoding of turbo codes and presented better performance without bandwidth expansion [P. Robertson et al., 1996]. But TTCM has a difficulty of implementing a hardware owing to decoder complexity. So, we need efficient scheduling and date storage management. In order to solve this essential problem, we propose a novel TTCM decoder using sliding window technique by using trace back technique, which is popular for realizing long path memories for Virterbi decoders [A.J. Viterbi, Feb. 1998].

A low bit-rate video coding techniques using the H.26L standard codec for robust transmission in mobile multimedia environments are presented. For the sake of achieving error resilience, the source codec has to make provisions for error detection, resynchronization and error concealment. Thus a packetization technique invoking adaptive bit-rate control was used in conjunction with the various modulation scheme employed. In this contribution, we propose a burst-by-burst adaptive coded modulation-aided joint detection-based CDMA (ACM-JD-CDMA) scheme for wireless video telephony and characterise its performance when communicating over the UTRA wideband vehicular fading channels. The coded modulation schemes invoked in our fixed modulation mode based systems are low density parity check code based block coded modulation (LDPC-BCM) and turbo trellis coded modulation (TTCM). The performance of LDPC-BCM was evaluated and compared to that of TTCM in the context of the ACM-JD-CDMA system using a practical modem mode switching regime. Both schemes exhibited a similar transmission integrity, although the LDPC arrangement is capable of achieving this at a lower complexity.

Turbo-trellis coded modulation (TTCM) schemes are designed for reliable transmission over quasi-static fading channels. Assuming pilot-assisted channel estimation, practical limitations in power and the number of pilots lead to imperfect channel estimates. A general method for robust receiver design under channel estimation errors was recently proposed by Sadough and Duhamel. In this paper, this technique is applied to improve the TTCM reception performance under channel estimation errors. We compare our proposed reception method to conventional receivers (also called mismatched receivers) in terms of bit error rate and EXIT chart analysis. Our results confirm the adequacy of the proposed receiver for improving TTCM iterative decoding performance under channel estimation errors.

We investigate trellis coded modulation (TCM) and turbo trellis coded modulation (TTCM) assisted iterative parallel interference cancellation aided CDMA schemes. The symbol-based maximum a posteriori (MAP) algorithm is invoked in both the TTCM and TCM decoder. In the context of the 8PSK TCM/TTCM CDMA schemes, typically two iterations are necessary for approaching the best possible performance attained with the aid of an infinite number of iterations. By contrast, the number of iterations has to be increased to three or four in conjunction with 16QAM when the effective information throughput is increased from 2 to 3 bits per symbol.