Bandwidth efficient turbo trellis-coded unitary space-time modulation for non-coherent multiple-antenna Rayleigh fading channel

Unitary (USTM) has got more attention for its potential in implementing high data rate transmission in a noncoherent multiple-antenna Rayleigh flat fading channel. In this paper, we have given out 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 proposal, we combine 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 applied the iterative maximum a posteriori (MAP) algorithm. According to PC simulations, we demonstrated that without bandwidth expansion, TTC-USTM produces obvious coding gains over its uncoded counterparts.

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.

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.

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].

In designing of any digital communication system, coding and modulation are generally treated as two independent functions. The role of modulator and demodulator is restricted primarily to convert an analog waveform channel to a discrete channel and the role of encoder and decoder is to correct the errors those occurred in this discrete channel. To achieve the higher performance, code rate is lowered and the redundancy in the code increased at the cost of bandwidth expansion. This code can be integrated with the expanded bandwidth efficient signal set so as to utilize the redundancy resulted from such an expansion in order to avoid bandwidth expansion. The convolutional code when integrated with a bandwidth efficient modulation scheme is termed as Trellis Coded Modulation (TCM). TCM is a bandwidth efficient transmission scheme that can achieve high coding gain by integrating coding and modulation. It was discovered in the late 1970s and is presently used in many systems for modern information transmission. In this paper, a new scheme has been proposed for designing 8 State Rate 2/3 TCM code for fading Channel.

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.

Space-time modulation exploiting diversity or/and coding gains has been a major focus in high-speed wireless communications systems against channel fading. We employ noncoherent space-time modulation in cyclic-prefix (CP) based single-carrier (SC) block systems over frequency selective Rayleigh block fading channels, where channel order, upper-bounded by the CP length, is assumed known. Capitalizing on multi-channel input-output relation for time-domain processing, we reveal that employing complex orthogonal m-sequences can enable a simplified maximum-likelihood (ML) detector. Further, code construction is addressed so as to adaptation of a variety of transmission rates and trellis-coded unitary space-time modulation is also investigated. Numerical results suggest that this noncoherent space-time modulation for SC block system, coupled with time-domain ML detection, can realize multipath diversity under certain circumstances.

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

Turbo trellis-coded modulation (TCM) with code matched interleaver (CMI) is applied to develop a trellis coded quantization (TCQ). It can been shown that TCQ of memoryless Gaussian sources results in substantial improvement of performance with iterative decoding of turbo TCM and iterative optimization of minimum overall distortion between the source input and decoding output. Numerical results indicate substantial improvement of performance because optimal TCQ based on turbo TCM can be achieved at moderate to high signal-to-noise ratio (SNR) on an additive white Gaussian noise (AWGN) channel for a memoryless Gaussian source and a memoryless uniform source.

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.

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.

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, the formulae for the pairwise error-event probability (PEP) and the bit error probability (BEP) of the trellis coded unitary space-time modulation (TC-USTM) in a piecewise constant Rayleigh fading channel are derived. These analyses demonstrate that a multi-input multi-output (MIMO) system with M transmit and N receive antennas, apart from a diversity gain of MN for the space-time signal design, a coding gain of l/sub min/ can also be obtained for the TC-USTM, where l/sub min/ is the length of the shortest error event. Additional coding gain comes from the product of the dissimilarities along the path of the shortest error event. These analyses suggest the design criteria of the TC-USTM encoder to obtain an optimal BEP performance. Propositions are also presented to satisfy these criteria. We demonstrate through simulations that these analyses are accurate, especially at sufficiently high signal to noise ratio (SNR).

In this paper, the performance of Space Time-Turbo Trellis Coded Modulation (ST-TTCM) is evaluated over Rician and Rayleigh fading channels with imperfect phase. We use Baum-Welch (BW) algorithm to estimate the fading and phase jitter parameters. Thus we assume that the channel parameters change slower than carrier frequency. We know that at high data rate transmissions over wireless fading channels, Space-Time Block Codes provide the maximal possible diversity advantage. Here, the combined effects of the amplitude and the phase of the received signal are considered, each one modeled by Rician and Tikhonov distributions respectively. We investigate Space Time-Turbo Trellis Coded Modulation (ST-TTCM) for 8-PSK for several Rician factor K and phase distortion factor /spl eta/. Thus, our results reflect the degradations both due to the effects of the fading on the amplitude and phase noise of the received signal while the channel parameters are estimated by BW algorithm.

Spread adaptive quadrature amplitude modulated (AQAM) code-division multiple access (CDMA) is proposed as a powerful means of exploiting the time-variant channel capacity fluctuations of wireless channels. It is studied in comparison to variable spreading factor (VSF)-based techniques. These adaptive-rate transmission methods are compared in the context of joint detection and interference cancellation assisted adaptive CDMA (ACDMA) systems. More explicitly, we exploit the time-variant channel quality of mobile channels by switching either the modulation mode (AQAM) or the spreading factor (VSF) on a burst-by-burst basis. The most appropriate modulation mode or spreading factor is chosen based on the instantaneous channel quality estimated. The chosen modem mode or spreading factor is communicated to the remote communicator either through explicit signalling or extracted at the receiver using blind detection techniques. The multiuser joint detector (JD) and the successive interference cancellation (SIC) receiver are compared in the context of these adaptive schemes, with the conclusion that the JD outperformed the SIC receiver in the ACDMA schemes at the cost of increased complexity. Finally, the performance of the uncoded AQAM JD-CDMA scheme is also compared to that of adaptive trellis coded modulation (TCM) assisted AQAM JD-CDMA, which allows us to incorporate adaptive channel coding without any bandwidth expansion. We also show that in the particular scenario studied, adaptive TCM outperformed adaptive turbo TCM since the system was designed for maintaining a low turbo-interleaver delay.