Article
Design of lowdensity paritycheck codes for modulation and detection
Bell Labs., Crawford, NJ, USA
IEEE Transactions on Communications (Impact Factor: 1.75). 05/2004; DOI: 10.1109/TCOMM.2004.826370 Source: DBLP

Article: Mary Detection and qary Decoding in LargeScale MIMO: A NonBinary Belief Propagation Approach
[Show abstract] [Hide abstract]
ABSTRACT: In this paper, we propose a nonbinary belief propagation approach (NBBP) for detection of $M$ary modulation symbols and decoding of $q$ary LDPC codes in largescale multiuser MIMO systems. We first propose a message passing based symbol detection algorithm which computes vector messages using a scalar Gaussian approximation of interference, which results in a total complexity of just $O(KN\sqrt{M})$, where $K$ is the number of uplink users and $N$ is the number of base station (BS) antennas. The proposed NBBP detector does not need to do a matrix inversion, which gives a complexity advantage over MMSE detection. We then design optimized $q$ary LDPC codes by matching the EXIT charts of the proposed detector and the LDPC decoder. Simulation results show that the proposed NBBP detectiondecoding approach using the optimized LDPC codes achieve significantly better performance (by about 1 dB to 7 dB at $10^{5}$ coded BER for various system loading factors with number of users ranging from 16 to 128 and number of BS antennas fixed at 128) compared to using linear detectors (e.g., MMSE detector) and offtheshelf $q$ary irregular LDPC codes. Also, even with estimated channel knowledge (e.g., with MMSE channel estimate), the performance of the proposed NBBP detector is better than that of the MMSE detector.10/2013;  [Show abstract] [Hide abstract]
ABSTRACT: In this paper, we propose a physicallayer rateless code for wireless channels. A novel rateless encoding scheme is developed to overcome the high error floor problem caused by the lowdensity generator matrix (LDGM)like encoding scheme in conventional rateless codes. This is achieved by providing each symbol with approximately equal protection in the encoding process. An extrinsic information transfer (EXIT) chart based optimization approach is proposed to obtain a robust check node degree distribution, which can achieve nearcapacity performances for a wide range of signal to noise ratios (SNR). Simulation results show that, under the same channel conditions and transmission overheads, the biterrorrate (BER) performance of the proposed scheme considerably outperforms the existing rateless codes in additive white Gaussian noise (AWGN) channels, particularly at low BER regions.IEEE Transactions on Communications 06/2013; 61(6). · 1.75 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In this paper, we propose a MIMO receiver algorithm that exploits {\em channel hardening} that occurs in large MIMO channels. Channel hardening refers to the phenomenon where the offdiagonal terms of the ${\bf H}^H{\bf H}$ matrix become increasingly weaker compared to the diagonal terms as the size of the channel gain matrix ${\bf H}$ increases. Specifically, we propose a message passing detection (MPD) algorithm which works with the realvalued matched filtered received vector (whose signal term becomes ${\bf H}^T{\bf H}{\bf x}$, where ${\bf x}$ is the transmitted vector), and uses a Gaussian approximation on the offdiagonal terms of the ${\bf H}^T{\bf H}$ matrix. We also propose a simple estimation scheme which directly obtains an estimate of ${\bf H}^T{\bf H}$ (instead of an estimate of ${\bf H}$), which is used as an effective channel estimate in the MPD algorithm. We refer to this receiver as the {\em channel hardeningexploiting message passing (CHEMP)} receiver. The proposed CHEMP receiver achieves very good performance in largescale MIMO systems (e.g., in systems with 16 to 128 uplink users and 128 base station antennas). For the considered large MIMO settings, the complexity of the proposed MPD algorithm is almost the same as or less than that of the minimum mean square error (MMSE) detection. This is because the MPD algorithm does not need a matrix inversion. It also achieves a significantly better performance compared to MMSE and other message passing detection algorithms using MMSE estimate of ${\bf H}$. We also present a convergence analysis of the proposed MPD algorithm. Further, we design optimized irregular low density parity check (LDPC) codes specific to the considered large MIMO channel and the CHEMP receiver through EXIT chart matching. The LDPC codes thus obtained achieve improved coded bit error rate performance compared to offtheshelf irregular LDPC codes.10/2013;
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.