Burst-by-burst adaptive joint-detection CDMA/H.26L based wireless video telephony using TTCM and LDPC codes

Bandwidth efficient parallel-concatenated turbo trellis coded modulation (TTCM) schemes were designed for communicating over uncorrelated Rayleigh fading channels. A symbol-based union bound was derived for analysing the error floor of the proposed TTCM schemes. A pair of in-phase (I) and quadrature-phase (Q) interleavers were employed for interleaving the I and Q components of the TTCM coded symbols, in order to attain an increased diversity gain. The decoding convergence of the IQ-TTCM schemes was analysed using symbol-based extrinsic information transfer (EXIT) charts. The best TTCM component codes were selected with the aid of both the symbol-based union bound and non-binary EXIT charts for the sake of designing capacity-approaching IQ-TTCM schemes in the context of 8 PSK, 16 QAM and 32 QAM signal sets. It will be shown that our TTCM design is capable of approaching the channel capacity within 0.5 dB at a throughput of 4 bit/s/Hz, when communicating over uncorrelated Rayleigh fading channels using 32 QAM.

A novel low-complexity scheme of Turbo Trellis-coded modulation (TCM) iterative equalisation and decoding is presented, which serially concatenates a soft-input-soft-output equaliser and symbol-by-symbol Turbo TCM (TTCM) decoder through an iterative process in order to realise iterative equalisation and decoding process. This scheme can not only improve the bandwidth efficiency, but also reduce the intersymbol interference. The equaliser with maximum a posteriori is replaced with linear one based on minimum mean-square error at the receiver so that the complexity of the system can be reduced greatly. Computer simulation results show that the novel low-complexity receiver on fading channels can achieve comparable performance with TTCM on Gaussian channels.

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.

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.

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.

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.

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.

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.

The classical turbo decoding algorithm is based on the use of binary waveform disturbed by a Gaussian distributed noise. Although a significant amount of coding gain can be achieved, binary turbo codes do not have good bandwidth efficiency unless they are heavily punctured. Turbo trellis coded modulation (TTCM) can provide good turbo code performance without bandwidth expansion. However, it requires unique code design. The simplest way to attain both power and bandwidth efficiency is to adopt high-order modulation schemes with a commonly studied binary turbo code. This approach requires a conversion of the demodulator output associated with the nonbinary channel symbol into bit metrics to input to the binary turbo decoder. This paper investigates various conversion functions for M-ary PSK and M-ary QAM constellations. The turbocoded bit-error-rate performances are compared using these metrics. It is shown that the likelihood metric, which is the optimum for the uncoded case, does not provide the optimum performance in the coded case. This paper also indicates that this turbo-coded waveform can perform as well as TTCM

A new family of parallel and serial concatenated concatenated codes is presented. Turbo trellis-coded modulation (T-TCM) is considered for combining turbo codes with multilevel modulation schemes to save the bandwidth of the transmission channel and to obtain a good performance for various distortions. The scheme has been investigated for a combined BFSK/QPSK modulation scheme on a mobile satellite channel with varying the length of the interleaver which links the two recursive systematic codes. The proposed technique is compared with the conventional trellis coded modulation scheme, and it is demonstrated that T-TCM performs much better than other known coded modulation schemes for the particular type of channel.

We present an improved channel equalizing scheme to be used in Coded OFDM systems over an ISI channel. The scheme uses Turbo Trellis Coded Modulation (TTCM) which retains a powerful error correction capability while elegantly incorporating turbo coding into the Trellis Coded Modulation (TCM). In OFDM over wireless communications, M-ary Quadrature Amplitude Modulation (M-QAM) schemes have been widely used to achieve high bandwidth efficiency. However, M-QAM signals require linear amplification to avoid spectral regrowth and severe performance degradation due to their large envelope fluctuations. Moreover, the OFDM transmitter shapes the signal with a linear pulse shaping filter. The combination of a linear filter with a High Power Amplifier (HPA) forms a nonlinear system with memory, which severely degrades performance. We propose an efficient one-tap-equalizer using a modified LMS algorithm and a novel adaptive predistortion technique to compensate for the nonlinear distortion caused by the high power amplifier cascaded with a linear filter in TTCM-OFDM systems. The performance of this method is compared with methods that have been used previously with OFDM. A computer simulation confirms that the proposed approach is superior to the conventional methods.

For ADSL applications, very large constellation sizes are used, which can be as large as 32768QAM. It is a big challenge to design turbo TCM for such a large constellation size while still maintaining low decoding complexity. We propose a new turbo coded QAM scheme with a unique concatenated Gray for an ADSL system. This new mapping can not only provide good performance for turbo coded bits but can also efficiently maximize the minimum Euclidean distance of uncoded bits. This new turbo coded QAM scheme not only has as good error correcting performance as the conventional bit-interleaved turbo coded QAM and symbol-interleaved turbo TCM schemes, but also has very low decoding complexity which is only about 17% of the conventional bit-interleaved turbo coded QAM.

In this paper, low-density parity-check (LDPC) codes are applied in spectrally efficient frequency-division multiplexing (SEFDM) with iterative decoder to eliminate the influence from inter-carrier interference (ICI). SEFDM has higher spectral efficiency than orthogonal frequency-division multiplexing (OFDM) by compressing the subcarrier spacing. This self-induced ICI is eliminated by LDPC codes and iterative decoder. The SEFDM scheme analyzed in this paper is not limited by subcarrier number and modulation order because the ICI cancellation scheme has relatively low computational complexity. With LDPC codes, the iterative-SEFDM scheme supports QPSK, 16QAM, 64QAM and 256QAM modulation formats. To the best of our knowledge, the SEFDM scheme with high-order 256QAM modulation is first demonstrated. With bandwidth compression and effective ICI cancellation, LDPC-coded iterative-SEFDM can achieve better bit error rate performance than its counterpart LDPC-coded OFDM at the same spectral efficiency.

Space Division Multiple Access (SDMA) aided Orthogonal Frequency Division Multiplexing (OFDM) systems assisted by efficient Multi-User Detection (MUD) techniques have recently attracted intensive research interests. As expected, Maximum Likelihood (ML) detection was found to attain the best performance, although this was achieved at the cost of a high computational complexity. Forward Error Correction (FEC) schemes such as Turbo Trellis Coded Modulation (TTCM) can be efficiently amalgamated with SDMA-OFDM systems for the sake of improving the achievable performance without bandwidth expansion. In this contribution, a MMSE-aided Iterative GA (IGA) MUD is proposed for employment in a TTCM-assisted SDMA-OFDM system, which is capable of achieving a similar performance to that attained by its optimum ML-aided counterpart at a significantly lower complexity, especially at high user loads. Moreover, when the proposed novel Biased Q-function Based Mutation (BQM) scheme is employed, the IGA-aided system’s performance can be further improved by achieving an Eb/N0 gain of about 6dB in comparison to the TTCM-aided MMSE-SDMA-OFDM benchmarker system both in low- and high-throughput modem scenarios, respectively, while still maintaining a modest complexity.

In this paper, we construct binary spatially coupled (SC) low-density parity-check (LDPC) codes based on Euclidean geometry (EG) LDPC codes for storage applications, where high error correction capability, extremely low uncorrectable bit error rate (UBER), and low decoding complexity are required. We propose a systematic way to construct the families of SC LDPC codes from $(m,2^{s})$ EG LDPC codes, which are termed EG-SC LDPC codes. In the construction method, we propose a 2-D edge-spreading process to construct the base matrix of EG-SC LDPC codes, which consists of matrix unwrapping and periodically time-varying of a protograph. A lower bound on the rank of the parity-check matrix of an EG-SC LDPC code is derived. We evaluate the error rate performance of the constructed EG-SC LDPC codes by using a weighted bit-flipping decoding algorithm for its low decoding complexity. Numerical results show that the UBER performance of the constructed EG-SC LDPC codes is superior to that of their EG LDPC code counterparts, and show no error floor compared with the constructed protograph SC LDPC codes and regular LDPC codes.