Turbo Trellis Coded Modulation Schemes Research Articles

Turbo Trellis-Coded Differential Chaotic Modulation

In this brief, a novel turbo trellis-coded differential chaotic modulation (TTC-DCM) system is proposed, where parallel concatenated trellis codes are combined with the M-ary differential chaotic shift keying (M-ary DCSK) scheme. An extrinsic information transfer chart is employed to analyze the convergence over additive white Gaussian noise channel and multipath Rayleigh channels. Simulation results show that the new scheme can obtain considerable coding gains without impairing the bandwidth efficiency in comparison with the M-ary DCSK scheme and the trellis-coded differential chaotic modulation scheme. Moreover, compared to the direct-sequence spread-spectrum turbo trellis-coded modulation scheme, TTCDCM has lower complexity and better robustness in the absence of channel state information over multipath Rayleigh channels. Overall, because of the merits of promising performance, high bandwidth efficiency, robustness to poor channel conditions, and an easy-to-implement property, the TTC-DCM scheme is suitable for bandlimited communication applications under poor channel conditions.

Capacity-Approaching Non-Binary Turbo Codes: A Hybrid Design Based on EXIT Charts and Union Bounds

In this paper, we introduce a novel design approach for capacity-approaching non-binary turbo codes. There are two important factors that impact the performance of turbo codes in general: 1) the convergence behavior of iterative decoding in the low signal-to-noise ratio (SNR) and 2) the error-floor effect in the high SNR. We thus design the non-binary turbo codes by means of the EXIT charts and truncated union bounds. We first reduce the search space of component recursive convolutional codes by the analysis based on the truncated union bounds in conjunction with the uniform interleaver, followed by its optimization through the EXIT chart analysis. The construction of the EXIT chart for non-binary turbo codes with fixed code coefficients is a non-trivial task by the fact that these messages have multiple parameters to identify. Therefore, we develop a new EXIT chart analysis for non-binary messages which does not rely on any specific message model. It is demonstrated through computer simulations that the well-designed non-binary turbo codes achieve a better performance than their binary counterparts as well as the conventional non-binary LDPC codes of the same field size. Furthermore, the code design is extended to high-order modulation, and our turbo codes designed for quadrature amplitude modulation are shown to outperform the conventional turbo trellis coded modulation schemes.

User Pairing for Downlink Non-Orthogonal Multiple Access Networks Using Matching Algorithm

In this paper, we study the user pairing in a downlink non-orthogonal multiple access (NOMA) network, where the base station allocates the power to the pairwise users within the cluster. In the considered NOMA network, a user with poor channel condition is paired with a user with good channel condition, when both their rate requirements are satisfied. Specifically, the quality of service for weak users can be guaranteed, since the transmit power allocated to strong users is constrained following the concept of cognitive radio. A distributed matching algorithm is proposed in the downlink NOMA network, aiming to optimize the user pairing and power allocation between weak users and strong users, subject to the users’ targeted rate requirements. Our results show that the proposed algorithm outperforms the conventional orthogonal multiple access scheme and approaches the performance of the centralized algorithm, despite its low complexity. In order to improve the system’s throughput, we design a practical adaptive turbo trellis coded modulation scheme for the considered network, which adaptively adjusts the code rate and the modulation mode based on the instantaneous channel conditions. The joint design work leads to significant mutual benefits for all the users as well as the improved system throughput.

Reduced complexity Log-MAP algorithm with Jensen inequality based non-recursive max∗ operator for turbo TCM decoding

In this paper, a reduced complexity Log-MAP algorithm based on a non-recursive approximation of the max∗ operator is presented and studied for turbo trellis-coded modulation (TTCM) systems. In the algorithm, denoted as AvN Log-MAP, the max∗ operation is generalized and performed on n≥2 arguments. The approximation is derived from the Jensen inequality. The non-recursive form of the max∗ calculations allows to achieve significant reduction in the decoding effort in comparison to the conventional Log-MAP algorithm. Bit-error rate performance simulation results for serial and parallel TTCM schemes in the additive white Gaussian noise and uncorrelated Rayleigh fading channels show that the AvN Log-MAP algorithm performs close to the Log-MAP. Performance and complexity comparisons of the AvN Log-MAP algorithm against the Log-MAP and several relevant reduced complexity turbo decoding algorithms proposed in the literature reveal, that it offers favorable low computational effort for the price of small performance degradation.

Evaluation of the Effects of Co-Channel Interference on the Bit Error Rate of Wireless Networks with Error Correcting Codes in Fading Channels

This paper presents a performance analysis of wireless networks using error correcting codes on channels with Rayleigh fading in the presence of co-channel interference. The performance is evaluated in terms of the average bit error rate (BER) using TCM (Trellis-Coded Modulation) and TTCM (Turbo Trellis-Coded Modulation) schemes for QAM modulations. The effects of co-channel interference are evaluated through Monte Carlo simulation in scenarios where the system is affected by a dominant interfering synchronous and similar to the target user. For each coded-modulation schemes, the results show that there are BER floors, which vary according to the signal-interference (S/I).

Improved MIMO Turbo-Trellis Coded Modulation Under Channel Estimation Errors

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.

Near-capacity turbo trellis coded modulation design based on EXIT charts and union bounds - [transactions papers

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 symbolbased union bound and non-binary EXIT charts, for designing capacity-approaching IQ-TTCM schemes in the context of 8 PSK, 16 QAM, 32 QAM and 64 QAM modulation schemes.

Burst-by-burst adaptive decision feedback equalized TCM, TTCM, and BICM for H.263-assisted wireless video telephony

Decision feedback equalizer-aided wide-band burst-by-burst adaptive trellis-coded modulation, turbo trellis-coded modulation (TTCM), and bit-interleaved-coded modulation-assisted H.263-based video transceivers are proposed and characterized in performance terms when communicating over the COST 207 typical urban wide-band fading channel. Specifically, four different modulation modes, namely 4QAM, 8PSK, 16QAM, and 64QAM are invoked and protected by the above-mentioned coded modulation schemes. The TTCM assisted scheme was found to provide the best video performance, although at the cost of the highest complexity. A range of lower-complexity arrangements will also be characterized. Finally, in order to confirm these findings in an important practical environment, we have also investigated the adaptive TTCM scheme in the CDMA-based universal mobile telecommunications systems terrestrial radio access (UTRA) scenario and the good performance of adaptive TTCM scheme recorded when communicating over the COST 207 channels was retained in the UTRA environment.

Turbo Trellis Coded Modulation with Enhanced Transition Metric over Rayleigh Fading Channels

This paper investigates the performance of a new Turbo Trellis Coded Modulation scheme over correlated flat fading channels with channel interleaving. The novelty of the scheme is based on the application of a new modified transition metric incorporated in the symbol-by-symbol MAP algorithm. We consider frequency non-selective, slow Rayleigh fading channels. Extensive simulation results together with EXIT chart analysis show that the proposed scheme achieves better performance compared to the conventional transition metric when channel state information is not available at the decoder.

Phase-Noise Effects on Turbo Trellis-Coded Modulation Over<tex>$M$</tex>-ary Coherent Channels

The effect of the phase noise on the performance of bandwidth-efficient coded modulation is studied. To this end, the average mutual information (AMI) for specific constellations such as 8-phase-shift keying and 16-quadrature amplitude modulation is calculated in the presence of carrier phase error caused by imperfect carrier tracking over an additive white Gaussian noise channel. The AMI not only quantifies the effect of the phase noise from an information-theoretic viewpoint, but also serves as an estimate for a permissible amount of the phase noise for a given signal-to-noise ratio. The bit-error rate (BER) performance of a near-optimal turbo trellis-coded modulation scheme is then investigated over such a channel. For this purpose, an optimal branch metric which best fits the channel characteristics is derived. Furthermore, simple branch metrics (referred to as suboptimal, simplified, and Gaussian metrics) are derived, which may offer the tradeoff between BER performance and computational complexity. Numerical analysis shows that a near-optimal coded-modulation scheme renders a transmission system more robust against phase noise than is the case with a conventional trellis-coded modulation scheme.

TTCM schemes based on time-varying trellis approach

An efficient time-varying trellis approach is proposed for turbo trellis coded modulation (TTCM). Using a time-varying trellis, the efficient free Euclidean distance is increased, thus improving the performance of TTCM. Experimental results show that the bit error rate (BER) of the proposed time-varying TTCM is better than that of the conventional TTCM scheme. Also, compared with an eight-state time-invariant TTCM scheme, a two-state time-varying TTCM scheme can achieve nearly the same BER performance.

Space-time IQ-interleaved TCM and TTCM for AWGN and Rayleigh fading channels

Space-time block coded inphase-quadrature phase (IQ)-interleaved trellis coded modulation (TCM) and turbo TCM (TTCM) schemes are proposed, which are capable of quadrupling the diversity order of conventional symbol-interleaved TCM and TTCM schemes. The increased diversity order of the proposed schemes provides significant coding gains, when communicating over non-dispersive Rayleigh fading channels without compromising the coding gain achievable over Gaussian channels.

DMT scheme with multidimensional turbo trellis code

Turbo codes can be naturally extended to bandwidth-efficient applications. A turbo code with powerful bandwidth-efficient component codes is investigated and its application in the discrete multitone environment is considered. Simulation results show that the multidimensional turbo trellis-coded modulation scheme can achieve outstanding performance even at relatively low signal-to-noise ratio.

Performance of turbo trellis-coded modulation (T-TCM) on frequency-selective Rayleigh fading channels

Turbo trellis-coded modulation (T-TCM) is one of several techniques for combining turbo codes with multilevel modulation schemes to save the bandwidths of the transmission systems. T-TCM has been shown to perform very well on AWGN channels, but its performance on frequency-selective fading channels is still unknown. A system model to investigate the performance of various T-TCM schemes on frequency-selective fading channels is proposed and simulation results show that when an appropriate receiver is available, T-TCM performs much better than any other known coded-modulation scheme for this type of channel.

Turbo TCM schemes for WCDMA systems

Three novel turbo TCM schemes, l/n TTCM, TTC-SPM and NP-TTC-SPM, are proposed. They are derived from the TTCM scheme but have better performance for use in WCDMA systems over fading channels. Simulation results are presented.