M-ary Coded Mouldation Assisted Genetic Algorithm Based Multiuser Detection for CDMA Systems

In this contribution we propose a novel M-ary Coded Modulation assisted Genetic Algorithm based Multiuser Detection (CM-GA-MUD) scheme for synchronous CDMA systems. The performance of the proposed scheme was investigated using Quadrature-Phase-Shift-Keying (QPSK), 8-level PSK (8PSK) and 16-level Quadrature Amplitude Modulation (16QAM) when communicating over AWGN and narrowband Rayleigh fading channels. When compared with the optimum MUD scheme, the GAMUD subsystem is capable of reducing the computational complexity significantly. On the other hand, the CM subsystem is capable of obtaining considerable coding gains despite being fed with sub-optimal information provided by the GA-MUD output

Approximate Message Passing under Finite Alphabet Constraints

In this paper we consider Basis Pursuit De-Noising (BPDN) problems in which the sparse original signal is drawn from a finite alphabet. To solve this problem we propose an iterative message passing algorithm, which capitalises not only on the sparsity but by means of a prior distribution also on the discrete nature of the original signal. In our numerical experiments we test this algorithm in combination with a Rademacher measurement matrix and a measurement matrix derived from the random demodulator, which enables compressive sampling of analogue signals. Our results show in both cases significant performance gains over a linear programming based approach to the considered BPDN problem. We also compare the proposed algorithm to a similar message passing based algorithm without prior knowledge and observe an even larger performance improvement.Comment: 4 pages, 2 figures, to appear in IEEE International Conference on Acoustics, Speech, and Signal Processing ICASSP 201

Trellis-Based Equalization for Sparse ISI Channels Revisited

Sparse intersymbol-interference (ISI) channels are encountered in a variety of high-data-rate communication systems. Such channels have a large channel memory length, but only a small number of significant channel coefficients. In this paper, trellis-based equalization of sparse ISI channels is revisited. Due to the large channel memory length, the complexity of maximum-likelihood detection, e.g., by means of the Viterbi algorithm (VA), is normally prohibitive. In the first part of the paper, a unified framework based on factor graphs is presented for complexity reduction without loss of optimality. In this new context, two known reduced-complexity algorithms for sparse ISI channels are recapitulated: The multi-trellis VA (M-VA) and the parallel-trellis VA (P-VA). It is shown that the M-VA, although claimed, does not lead to a reduced computational complexity. The P-VA, on the other hand, leads to a significant complexity reduction, but can only be applied for a certain class of sparse channels. In the second part of the paper, a unified approach is investigated to tackle general sparse channels: It is shown that the use of a linear filter at the receiver renders the application of standard reduced-state trellis-based equalizer algorithms feasible, without significant loss of optimality. Numerical results verify the efficiency of the proposed receiver structure.Comment: To be presented at the 2005 IEEE Int. Symp. Inform. Theory (ISIT 2005), September 4-9, 2005, Adelaide, Australi

Blind multi-user combining at the base station for asynchronous CDMA systems

This paper studies the potential benefits of antenna arrays in cellular CDMA communications and proposes a powerful scheme to undertake the array processing at the base station in CDMA mobile systems. The proposed technique exploits the temporal structure of CDMA signals. The necessary information is extracted directly from the received signals, thus no training signal orPeer ReviewedPostprint (published version

Recursive receivers for diversity channels with correlated flat fading

Copyright © 2003 IEEEThis paper addresses the design and performance of time-recursive receivers for diversity based communication systems with flat Rayleigh or Ricean fading. The paper introduces a general state-space model for such systems, where there is temporal correlation in the channel gain. Such an approach encompasses a wide range of diversity systems such as spatial diversity, frequency diversity, and code diversity systems which are used in practice. The paper describes a number of noncoherent receiver structures derived from both sequence and a posteriori probability-based cost functions and compares their performance using an orthogonal frequency-division multiplex example. In this example, the paper shows how a standard physical delay-Doppler scattering channel model can be approximated by the proposed state-space model. The simulations show that significant performance gains can be made by exploiting temporal, as well as diversity channel correlations. The paper argues that such time-recursive receivers offer some advantages over block processing schemes such as computational and memory requirement reductions and the easier incorporation of adaptivity in the receiver structures.Nguyen, V.K.; White, L.B.; Jaffrot, E.; Soamiadana, M.; Fijalkow, I

Analisa Kinerja Kode Konvolusi pada Sistem Successive Interference Cancellation Multiuser Detection CDMA dengan Modulasi QAM Berbasis Perangkat Lunak

Pada Proyek Akhir ini dilakukan Analisa Kinerja Kode Konvolusi pada Sistem Successive Interference Cancellation Multiuser Detection CDMA dengan Modulasi Quadrature Amplitude Modulation Berbasis Perangkat Lunak. Encoder kode konvolusi digunakan di sisi transmitter dengan rate 1/2 dan decoder di sisi receiver menggunakan algoritma viterbi. Hasil berupa kurva nilai BER terhadap fungsi SNR. Dari hasil simulasi didapatkan hasil bahwa pada sistem tanpa menggunakan kode konvolusi memiliki kinerja yang lebih baik karena sudah mencapai BER 10-3 ketika SNR 15.5 dB sedangkan sistem tanpa menggunakan kode konvolusi belum dapat mencapai nilai BER 10-3. Pada system perbandingan stage pada SIC menunjukkan bahwa penggunaan SIC 3 stage memiliki kinerja yang lebih baik 1.5 dB dibandingkan dengan jika menggunakan 1 atau 2 stage saja. Sedangkan untuk sistem dengan menggunakan 6 user memiliki kinerja yang lebih baik 9.5 dB jika dibandingkan dengan sistem yang menggunakan 10 user. Kata Kunci : BER, Convolution Code, CDMA, Quadrature Amplitude Modulation, Successive Interference Cancellation, multipath fadin

Menekan Tingkat Ber Pada Sistem Komunikasi Direct-Sequence CDMA(DS-CDMA) Menggunakan Jaringan Syaraf Tiruan Transient Chaos

Sistem penerima konvensional pada sistem komunikasi DS-CDMA, terjadi degradasi kinerja akibat perbedaan daya dengan sinyal penginterferensi yang tinggi (Nearto- Far) dan nilai korelasi silang kode user yang berbeda tidak nol, yang mengakibatkan Multiple Access Interference (MAI). Jaringan Saraf Tiruan Transient Chaos (TCNN), sangat potensial untuk mengatasi permasalahan MAI dan Near-to-Far pada penerima konvensional DS-CDMA. Sistem penerima Jaringan Saraf Tiruan Transient Chaos (TCNN) dapat diturunkan dengan memanfaatkan fungsi Likelihood. Dengan fungsi Likelihood tersebut akan diperoleh fungsi energi atau fungsi cost dari sistem penerima multiuser DS-CDMA. Fungsi energi sistem penerima multiuser DS-CDMA diselesaikan dengan algoritma TCNN. Pengujian dilakukan dengan simulasi komputer untuk membandingkan kinerja penerima TCNN dengan konvensional. Hasil simulasi, dapat dilihat bahwa sistem penerima Jaringan Saraf Tiruan Transient Chaos dapat memberikan perbaikan kinerja dibandingkan sistem penerima konvensional (Mathced Filter). Perbaikan kinerja penerima TCNN sebesar 85.092 % pada kondisi E N dB o 6 1 / = , Near-to-Far E E 6dB 2 1 / = , tetapi memerlukan tambahan waktu 0.4845 sekon-per-iterasi algoritma TCNN

A Method to Partially Suppress IS1 and MA1 for DS SS CDMA Wireless Networks

We propose a method to partially suppress ISI and MAI for US SS CDMA schemes in wireless LANs. The method can be regarded as an alternative approach to combat ISI and in particular MAI by the use of advanced multiuser detection. Instead of using very sophisticated detectors, we propose introduction of a simple modification to the carrier waveform which results in very substaiitial reduction in cross-correlation belween users and an off-peak auto-correlation. The method can be applied to any DS SS CDMA scheme, but should be particularly useful in the case of short spreading signatures, as is the case of WLAN

Turbo receivers for interleave-division multiple-access systems

In this paper several turbo receivers for Interleave-Division Multiple-Access (IDMA) systems will be discussed. The multiple access system model is presented first. The optimal, Maximum A Posteriori (MAP) algorithm, is then presented. It will be shown that the use of a precoding technique at the emitter side is applicable to IDMA systems. Several low complexity Multi-User Detector (MUD), based on the Gaussian approximation, will be next discussed. It will be shown that the MUD with Probabilistic Data Association (PDA) algorithm provides faster convergence of the turbo receiver. The discussed turbo receivers will be evaluated by means of Bit Error Rate (BER) simulations and EXtrinsic Information Transfer (EXIT) charts