Bit-interleaved Coded Modulation Iterative Decoding Research Articles

Demonstration of a highly bandwidth-efficient optical interconnection with symbol division multiplexing pulse amplitude modulation.

A novel symbol division multiplexing (SDM) technology is proposed in an intensity modulation and direct detection (IM/DD) pulse amplitude modulation (PAM) optical interconnection. The SDM-PAM4 symbol is the multiplexing of two standard 3-bit PAM8 symbols based on many-to-one (MTO) mapping, increasing by an extra 50% the line rate compared with a typical PAM4 under the same symbol rate and channel bandwidth. The forward error correction (FEC) based on low-density parity-check coding establishes a mechanism between the codewords of both intra- and inter-SDM-PAM4 symbols, to theoretically support the iterative decoding of symbol de-multiplexing employing an optimized bit-interleaved coded modulation iterative decoding (BICM-ID) system. Furthermore, since SDM evidently reduces the mapping order of the PAM signal, the transmission reliability can be effectively improved by alleviating the impairments mainly caused by fiber chromatic dispersion and Kerr nonlinearity. The experimental results indicate that the SDM-PAM4 can achieve more than 5 dB superior systematic receiver power sensitivity over 10-km single mode fiber transmission, and thus represent an important development in coding and modulation multiplexing techniques for optical interconnection systems.

Turbo Modulation Identification Algorithm for OFDM Software-Defined Radios

The problem of automatic modulation identification (AMI) is one of the main challenges that faces orthogonal frequency division multiplexing (OFDM) software-defined radio (SDR) systems. The previously reported studies of this aspect have limited to uncoded transmission; however, practical systems typically employ error-correcting codes. In this work, we exploit the properties of bit-interleaved coded modulation iterative decoding (BICM-ID) schemes, which are widely used in wireless communications systems, to develop a novel AMI algorithm for OFDM-SDR systems. Since the exact maximum-likelihood (ML) solution is intractable in practice, we resort to an expectation-maximization (EM) procedure as a statistical analysis tool. The proposed identification algorithm works in an iterative fashion, in which the soft information provided by the channel decoder of BICM-ID scheme is utilized as a priori information to the proposed identifier. The results indicate that the identification performance of the proposed algorithm achieves a significant improvement with iterations and outperforms that of the conventional uncoded algorithms. These favorable results are achieved with reduced processing time and acceptable sensitivity to transmission impairments, such as clock timing offset, frequency offset, Doppler shift, and phase noise.

LDPC-coded Probabilistic Shaping PAM4 Based on Many-to-One Mapping in WDM-PON

In this article, a 5 × 25-GBaud wavelength division multiplexing passive optical network (WDM-PON) is reported and experimentally demonstrated with each channel carrying a low-density parity check- (LDPC-) coded probabilistic shaping 4-ary pulse amplitude modulated signal (PS-PAM4). In such a splitter-based WDM-PON system, 8-point 3-bits/symbol PAM8 is mapped into 4-point PAM4 by adoption of a many-to-one mapping scheme, which enables improved receiver power sensitivity and increased spectral efficiency, compared with the uniformly-distributed PAM4. Different from the typical constant composition distribution matching method for PS, no shaping codes or PS overheads are needed in our PS-PAM4 signal which is to be encoded and decoded in a LDPC-based bit-interleaved coded modulation iterative decoding (BICM-ID) system for the compatibility with the forward error correction (FEC) applied in most of the optical transponders currently. In the BICM-ID system, the extrinsic messages are delivered circularly between the PS de-mapper and the LDPC decoder to deal with PS many-to-one mapping ambiguity. The experimental results strive to make the WDM-PON system better spectrum efficiency, as well as superior receiver power sensitivity and fiber nonlinear effect tolerance, thus maximizing the input power at the optical line terminal and economic efficiency of the system due to ampler loss budget provided for the legacy optical distribution networks.

DFT-Spread DMT-WDM-PON Employing LDPC-Coded Probabilistic Shaping 16 QAM

A 5 × 100-Gb/s discrete-Fourier-transform spread (DFT-spread) discrete multi-tone wavelength division multiplexing passive optical network (DMT-WDM-PON) employing low-density parity-check (LDPC) coded probabilistic shaping 16-ary quadrature amplitude modulation (PS-16 QAM) is proposed and experimentally demonstrated. We first introduce PS-16 QAM mapping scheme with 16-point constellation reshaped from 32 symbols into splitter-based DMT-WDM-PON. The DMT-WDM-PON employing PS-16 QAM can achieve superior receiver power sensitivity (RPS) and enhanced spectral efficiency (SE) compared with the unshaped one. Compatible with the forward error correction (FEC) implemented in most of the optical transponders today, an optimized bit-interleaved coded modulation iterative decoding (BICM-ID) system based on LDPC coding is proposed to encode the PS-16 QAM DMT signal without any extra shaping codes or overheads. Then the labeling optimization with the assistance of extrinsic information transfer (EXIT) chart is investigated, in which the extrinsic messages are transferred between the PS demapper and the LDPC decoder for retrieving the PS-16 QAM DMT signal. Furthermore, the experimental results show that 1.5-dB RPS improvement and 2-dB fiber nonlinear effect tolerance enhancement are respectively realized over a 20-km standard single-mode fiber (SSMF) link by using joint applications of DFT-spread scheme and PS-16 QAM mapping in proposed DMT-WDM-PON system, which can thus provide abundant system loss budget for the legacy optical distribution networks (ODNs).

Iterative Receiver Design for Uplink OFDMA Cooperative Systems

Recently, alternate-relaying cooperative (ARC) systems have appeared as an efficient technique to overcome the bandwidth loss problem of traditional cooperative transmissions. However, to the best of the authors’ knowledge, the previously reported investigations for ARC systems are limited to single-carrier and single-user transmissions. In addition, they follow the assumption of having perfect knowledge about channel impulse responses (CIRs) between nodes; however, practical systems typically employ a channel estimation algorithm. In this paper, we propose the use of ARC with orthogonal frequency division multiple access (OFDMA) to improve the performance of wireless broadcasting systems. We address the problem of joint data detection and CIRs estimation for uplink OFDMA-ARC systems. The problem is investigated in the context of bit-interleaved coded modulation iterative decoding (BICM-ID) and decode-and-forward relaying scheme. The structure of ARC and BICM-ID transmission is beneficially exploited to develop an optimal detector and an optimal CIRs estimator. It is shown that the optimal detector can be implemented by a bank of maximum a posteriori algorithms and the CIRs estimation can be computed using the space alternating generalized expectation-maximization algorithm, in which the soft information provided by the detector is utilized as a priori information to refine the estimates. The performance of the proposed estimator and the detector is evaluated via Monte Carlo simulations, and the results demonstrate their effectiveness.

A Novel Decoding Algorithm for BICM-ID Embedded Turbo Codes

Bit-interleaved coded modulation iterative decoding (BICM-ID) embedded turbo code is widely used in wireless communication because of its excellent performance. This paper proposes an improved logarithmic maximum a posteriori (Log-MAP) algorithm for BICM-ID embedded turbo codes. It can yield excellent bit error rate (BER) performance with much lower complexity. The proposed algorithm exploits a linear interpolation and Least Squares approximation function to replace the logarithmic correction in the Jacobian logarithmic function, which avoids complicated logarithm look-up table operations in Log-MAP algorithm. Simulation results show that the novel algorithm can offer almost equivalent performance to the optimal algorithm with much less computation. Compared with the improved MAX-Log-MAP algorithm proposed by Talakoub, the proposed algorithm can reduce about 36% of computational complexity, meanwhile it achieves 0.1db-0.16db performance gains. In addition, it obtains 0.35-0.4db gains than MAX-Log-MAP algorithm.

An Improved Simplified-CE Stopping Criterion for BICM-ID System

Bit-interleaved coded modulation iterative decoding (BICM-ID) is an excellent bandwidth efficient transmission scheme,which owns remarkable bit-error-rate (BER) performance both in additive Gaussian noise (AWGN) channel and Rayleigh fading channel.But it leads to the increase of computational complexity and decoding delay at the receiver at the same time. In order to decrease the unnecessary iterations ,a variety of the stopping criteria are put forward . This paper presents an improved simplified cross-entropy (CE) stopping criterion based on Simplified-CE criterion, which calculates the value of CE just one time when Signal to Noise Ratio (SNR) is under 2dB to simplified the iterative process. Simulation results show that the improved Simplified-CE criterion can own the least iterative number when the SNR is under 2dB.And when the SNR is from 2.5dB to 4dB, it is about 12% less than CE criterion in the average iterative numbers.

An Improved Log-MAP Algorithm For BICM-ID Embedded Turbo Codes

This paper presents a novel decoding algorithm for bit-interleaved coded modulation iterative decoding (BICM-ID) embedded turbo codes. It can yield good bit error rate (BER) performance with much lower complexity. The improved algorithm exploits a linear interpolation and optimal mean square approximation function to replace the logarithmic correction in the Jacobian logarithmic function based on the MacLaurin Series, which avoids complicated logarithm look-up table operations in Log-MAP. Simulation results show that the novel algorithm obtains can offer almost equivalent performance to the optimal algorithm. Compared with the improved MAX-Log-MAP algorithm, the proposed algorithm can reduce about 34% of computational complexity, meanwhile it achieves 0.1db-0.16db performance gains.

A Simplified CE Stopping Criterion for BICM-ID System

The iterative process of bit-interleaved coded modulation iterative decoding (BICM-ID) leads to the increase of computational complexity and decoding delay at the receiver, although it owns remarkable bit-error-rate (BER) performance both in additive Gaussian noise (AWGN) channel and Rayleigh fading channel. A variety of the stopping criteria are put forward to reduce the unnecessary iterations in the process. This paper presents a simplified cross-entropy (CE) stopping criterion based on CE criterion, which sets self-adaptive thresholds for different SNRs to decide whether to calculate the CE in the receiver. Simulation results show that the simplified CE criterion can obtain a better performance and lower computational complexity. The iterative number of the simplified CE criterion is about 12.2% less than the conventional CE criterion.

Cooperative Networks: Bit-Interleaved Coded Modulation with Iterative Decoding

In this paper the performance of bit-interleaved coded modulation-iterative decoding (BICM-ID) based cooperative network is analyzed over Rayleigh, Nakagami-m and Rician fading channels. In this system coding diversity is obtained through BICM and spatial diversity through cooperative relaying network. The analysis is performed for the relays operating in both amplify-and-forward (AF) and decode-and-forward (DF) modes. The bit error rate (BER) bound of multiple-relay cooperative system with the serial concatenated BICM-ID using the set partitioning (SP) and Gray mapped (GM) labeling for M-ary Phase Shift Keying (M-PSK) modulations over Nakagami-m fading channels is obtained. For the numerical results of union bound on BER, moment generating function (MGF) based approach is used. The expression of MGF derived for Nakagami distribution is then extended to Rayleigh and Rician fading channels. The comparisons of BER theoretical and simulation results are also shown. The performance of bit-interleaved low-density parity-check coded modulation with iterative decoding (BILDPCM-ID) based cooperative system, using low-density parity-check (LDPC) code instead of convolutional code, is also analyzed in term of bit-error rate (BER). The performance comparisons of BICM-ID and BILDPCM-ID based systems are shown using the set partitioning (SP) labeling for 8-PSK modulation scheme by performing Monte Carlo simulation.