EXIT Chart Analysis of Turbo DeCodulation

For space-time bit-interleaved coded modulation (ST-BICM) systems with iterative decoding, the overall perfor- mance is affected by the chosen mapping. In bit error rate (BER) curves, one mapping reaches an error floor at a low signal- to-noise ratio (SNR), while other mappings result in a lower error floor at a higher SNR. The constellation mappings are divided into groups where each group exhibits a distinctive BER curve. We show that the convergence abscissa of the system depends on the average total bit errors and the harmonic mean of the minimum squared Euclidean distance. In this paper, we characterize all mapping groups for ST-BICM with 8PSK and present the optimal selection for each mapping group over independent fading channels. I. INTRODUCTION Space-time coding techniques significantly improve trans- mission efficiency in radio channels by using multiple transmit and/or receive antennas and coordination of the signaling over these antennas. Bit-interleaved coded modulation with iterative decoding (BICM-ID) gives good diversity gains and Euclidean distance property with higher order modulation schemes using well known binary convolutional codes (1). Tonello (2) combined these two schemes as space-time BICM (ST-BICM) with Gray mapping. In this paper, we will first show that the asymptotic BER performance of ST-BICM system is equivalent to the single antenna BICM-ID case even when the throughput of ST-BICM is higher. This indicates that the total data rate of ST-BICM can be increased linearly with the number of transmit antennas while maintaining the same error probability as BICM-ID. This demonstrates the superior performance of ST-BICM. Motivated by the fact that the ST-BICM performance can be characterized by BICM-ID with the same code and mapping, we optimize the ST-BICM mappings based on the BICM-ID parameters. While the error floor (EF) bound (1) offers a good match for an error floor region, a heuristic analysis is still needed to study BER curve behaviors of BICM-ID for the water fall region. Thus, we derive design considerations based on both

In this paper, we extend the iterative demapping technique to observation separation (OS), which is an iterative channel estimation and symbol detection procedure. We consider a bit interleaved coded modulation with iterative decoding (BICM-ID) on a multipath channel with coded packet oriented transmission system with 16QAM. The channels considered are the time-invariant multipath and the channel estimation corresponds to the pseudo-inverse type. We propose here to study the influence of mapping over the performance of turbo equalization. Turbo equalization is a receiving process performing iteratively equalization and channel decoding; soft information generated by each receiving function is improved through the iterations until the optimum behavior of the system reached. In the studied system the turbo equalization and the channel estimation part is based on our previous work. In the context of bit interleaved coded modulation (BICM), the iterative demapping is an iterative process between the soft demapping device and the channel decoding. We analyze here the improvement of mapping optimization for turbo equalization and we proposed an optimized binary mapping of 16-QAM constellation in order to increase coding gain, which can be used for some practically important cases. It is demonstrated that owning to a carefully designed mapping, different to the classical Gray mapping, bit error rate performance is improved.

This paper studies the technique of bit-interleaved coded modulation with iterative decoding (BICM-ID) in a two-way relaying communication system. Iterative decoding based on the quaternary code representation is adopted at the relay for the multiple access (MA) phase. An upper-bound of the bit error probability (BEP) under the error-free (EF) feedback assumption for BICM-ID in the MA phase is obtained. Based on the obtained EF bound of the BEP, it is found that the multiple-access interference (MAI) is successfully eliminated by performing the iterative decoding and XOR based network coding at the relay. Simulation results are provided to corroborate the analysis and demonstrate the performance superiority of the proposed framework.

Bit-interleaved coded modulation with iterative decoding (BICM-ID) is investigated for bandwidth efficient transmissions, where the error performance can be improved by employing a suitable symbol mapping. This paper first introduces a low-complexity regular mapping optimization for BICM-ID and 8PSK, for the purpose of finding the optimal mapping. Furthermore, the irregular mapping optimization is proposed for a closer approach to the channel capacity. The extrinsic information transfer (EXIT) chart analysis is aided for the proposed optimization algorithms to provide design guidelines of mappings. The bit error rate (BER) results demonstrate that the BICM-ID system with the proposed optimal irregular mapping outperforms the other mappings used for comparison, and yields about 0.5dB away from the channel capacity over the additive white Gaussian noise (AWGN) channel.

We propose a novel class of short block codes (SBCs) designed for guaranteed convergence to an infinitesimally low bit error ratio (BER), which relies on the joint optimisation of soft-bit assisted iterative source and channel decoding. An iterative detection aided combination of SBC assisted soft-bit source decoding (SBSD) and a rate-1 precoder was used to evaluate the attainable performance of the proposed scheme for transmission of data-partitioned (DP) H.264 source coded video over correlated narrowband Rayleigh fading channels. Additionally, we demonstrated the effects of different SBCs having diverse minimum Hamming distances [d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H,min</sub> ] but identical coding rates on both the overall BER performance as well as on the objective video quality expressed in terms of the Peak Signal-to-Noise Ratio (PSNR). The convergence behaviour of the iterative decoding scheme using SBCs as a function of d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H,min</sub> is analysed by utilising extrinsic information transfer (EXIT) charts. Explicitly, our experimental results show that the proposed error protection scheme using SBCs associated with d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H,min</sub> = 6 outperforms the identical-code-rate SBCs having d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H,min</sub> = 3 by about 3 dB at the PSNR degradation point of 1 dB. Additionally, an E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> gain of 27 dB is attained using iterative soft-bit source and channel decoding with the aid of rate-1/3 SBCs relative to the identical-rate benchmarker.

Exploiting signal space diversity (SSD) to improve the error performance of communications systems over fading channels has been shown to be a very effective technique. The application of SSD in bit-interleaved coded modulation with iterative decoding (BICM-ID) is considered for cascaded Rayleigh fading channels, which are suitable for mobile-to-mobile communications. A tight bound on the asymptotic error performance is first derived. The bound is then used to find the optimal rotation matrix. It is shown that employing SSD in a sufficiently large constellation can close the performance gap between a conventional Rayleigh fading channel and a cascaded Rayleigh fading channel. In fact, similar to the case of conventional Rayleigh fading, it is demonstrated that the error performance of BICM-ID with SSD over a cascaded Rayleigh fading channel can also closely approach the performance of BICM-ID over an AWGN channel. Various analytical and simulation results are provided to confirm the analysis.

The demands for high data rates and spectrally efficient modulation techniques are increasing due to the evolution of multimedia service in wireless communication systems. Bit-interleaved coded modulation with iterative decoding (BICM-ID) is a bandwidth efficient transmission scheme and is well suitable for the next-generation mobile communications. But the performance of BICM-ID is poor in slow fading channels. As we know that diversity is an effective method to cope with fading and channel interleaving with error correction coding brings time diversity, an effective scheme is proposed in the paper in which a block interleaver is introduced to the BICM-ID encoder at the transmitter. This block interleaver serves as a channel interleaver which makes the burst errors induced by slow fading to be changed into random errors. Simulation results show that channel interleaving greatly improves the performance of BICM-ID in slow fading channels.

Employing multi-dimensional constellation and mapping to improve the error performance of the bit-interleaved coded modulation with iterative decoding (BICM-ID) has recently received a lot of attention, both in single-antenna and multiple-antenna systems. To date, except for the cases of BPSK and QPSK constellations, good multi-dimensional mappings have only been found by computer searching techniques. This paper introduces an explicit algorithm to construct a good multidimensional mapping of 8-PSK for improving the asymptotic performance of BICM-ID systems. By comparing the performance of the proposed mapping with an unachievable lower bound, it is conjectured that the proposed mapping is the global optimal mapping. The superiority of the proposed mapping over the best conventional (two-dimensional) mapping and the multidimensional mapping found previously by computer search is also thoroughly demonstrated

We study the impact of imperfect channel state information (CSI) on the bit-error rate (BER) of QAM bit-interleaved coded modulation with iterative decoding (BICM-ID), in flat Rayleigh fading. The key parameter characterizing this effect is the power correlation coefficient /spl rho/ between the fading gain and its estimate. An accurate and efficient bound is developed to predict the asymptotic BER. We also show simulation results for QAM BICM-ID with 8-state and 16-state convolutional codes to provide the performance evaluation. For the 16-state code with modified set partitioning labeling and power correlation /spl rho/=0.95, a BER of 10/sup -6/ can be achieved at E/sub b//N/sub 0/=11 dB, with 4 passes of soft feedback. This corresponds to about 3.5 dB increase in the required E/sub b//N/sub 0/ compared to that of perfect CSI.

In this paper, we analytically derive the bit error rate (BER) for bit-interleaved coded modulation (BICM) under the assumption of a temporally correlated flat Rayleigh fading channel. We assume the channel state information (CSI) to be unknown at receiver side and consider a linear minimum mean-squared error (LMMSE) channel estimator that relies on periodically inserted pilot symbols. We give asymptotic results for both non-iterative BICM and BICM with iterative decoding (BICM-ID). Furthermore, we show that the interpretation of the channel estimation error as an SNR degradation holds true in these cases.

Chapter 5 - The interplay between modulation and channel coding

Physical layer network coding (PNC) is a novel technique that allows two users to exchange messages in a wireless network. PNC takes place at a relay node and exploits the interference caused by incoming signals from the two users to increase throughput. In this paper, the performance of a two-way relay network employing PNC is evaluated with three types of error-correcting codes used at the source and destination nodes, namely low-density parity-check codes, turbo codes and bit-interleaved coded modulation with iterative decoding (BICM-ID). All three coding schemes perform similarly in a single user system on the AWGN channel with no relay, but results obtained when employing PNC show that although there is an overall degradation in their performance of all three codes, the LDPC code performance is more seriously affected due to the Sum-Product decoding algorithm being less robust to unreliable symbols broadcast from the relay.

This paper presents a performance analysis of bit-interleaved coded-modulation with iterative decoding (BICM-ID) and complex N-dimensional signal space diversity in fading channels to investigate its performance limitation, the choice of the rotation matrix and the design of a low-complexity receiver. The tight error bound is first analytically derived. Based on the design criterion obtained from the error bound, the optimality of the rotation matrix is then established. It is shown that using the class of the optimal rotation matrices, the performance of BICM-ID systems over a Rayleigh fading channel approaches that of the BICM-ID systems over an AWGN channel when the dimension of the signal constellation increases. Furthermore, by exploiting the sigma mapping for any M-ary QAM constellation, a very simple sub-optimal, but yet effective iterative receiver structure suitable for signal constellations with large dimensions is proposed. Simulation results in various cases and conditions indicate that the proposed receiver can achieve the analytical performance bounds with low complexity

We investigate the impact of imperfect channel state information (CSI) on the bit error rate (BER) performance of uncoded and coded modulation schemes over Nakagami fading channels using the model proposed in C. Polprasert and JA Ritcey (2005). The analytical and asymptotic BER performance of uncoded M-PSK modulation is evaluated and verified by the simulation. For coded modulation, the error free feedback bound (EF bound) of the bit-interleaved coded modulation with iterative decoding (BICM-ID) for both perfect and imperfect CSI is developed. We show that asymptotically, the error floor generated due to imperfect CSI depends on the fading parameter and the power correlation coefficient between the fading coefficient and its estimate.

Double differential phase shift keying(DDPSK) modulation is an efficient method to compensate the Doppler shifts, whereas the phase noise will be amplified which results in the signal-to-noise ratio (SNR) loss. In this paper, we propose a novel receiver architecture for underwater acoustic DSSS communications with Doppler shifts. The proposed method adopts not only the DDPSK modulation to compensate the Doppler shifts, but also the improved bit-interleaved coded modulation with iterative decoding (BICM-ID) algorithm for DDPSK to recover the SNR loss. The improved DDPSK demodulator adopts the multi-symbol estimation to track the channel variation, and an extended trellis diagram is constructed for DDPSK demodulator. Theoretical simulation shows that our system can obtain around 10.2 dB gain over the uncoded performance, and 7.4 dB gain over the hard-decision decoding performance. Besides, the experiment conducted in the Songhua Lake also shows that the proposed receiver can achieve lower BER performance when Doppler shifts exists.