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ABSTRACT: In this paper, the performance of a computationally efficient adaptive MMSE receiver is investigated for asynchronous MC-CDMA systems over multipath fading channels. According to Wiener filter and LMS algorithm theories, we prove that the proposed computationally efficient MMSE receiver has the same BER and convergence performance as that of the conventional MMSE receiver, assuming the sampling rate per symbol is equal to the number of subcarriers. When the sampling rate per symbol is increased, the proposed receiver can outperform the conventional MMSE receiver without sacrificing the convergence speed. The theoretical analysis is verified by the results through Monte-Carlo simulation
Acoustics, Speech and Signal Processing, 2006. ICASSP 2006 Proceedings. 2006 IEEE International Conference on; 06/2006 · 4.63 Impact Factor
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ABSTRACT: A transmitter-based linear precoding technique is considered for downlink multicarrier code division multiple access systems. The key idea is to shift the required signal processing to the base station, where power and computational resources are plentiful, thus simplifying the receiver complexity and extending the battery life of mobile terminals. The multiple access interference (MAI) resulting from the frequency-selective channel inevitably limits the system performance. The minimum mean square error criterion is employed to optimise the linear transformation at the transmitter subject minimising the total transmitted energy in order to presuppress the MAI before the transmission. Two types of transmitter precoders are investigated in uncorrelated and correlated frequency-selective Rayleigh fading channels; one is combined with equal gain combining (PRE-EGC) and the other with maximum ratio combining (PRE-MRC) at the receiver. Numerical results show that the PRE-EGC can provide the same performance to all users and outperform the PRE-MRC. More importantly, the performance of the former is comparable to, or superior to, receiver-based techniques, such as the decorrelating detector using EGC (DEC-EGC) and MRC (DEC-MRC), provided the channel state information of all users is slowly time-varying and known to the transmitter.
IEE Proceedings - Communications 01/2006; · 0.32 Impact Factor
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ABSTRACT: A linear transmitter precoding technique based on partial equalization receiver (TP-PER) is proposed for time-duplex division (TDD) downlink multi-carrier code-division multiple-access (MC-CDMA) systems to pre-suppress multiple access interference (MAI) in frequency selective Rayleigh fading channels. Given that the channel state information (CSI) is known to the transmitter and the channel is slowly varying, the proposed transmitter precoding algorithm can outperform conventional precoding schemes, such as transmitter precoding with equal gain combining (TP-EGC), transmitter precoding with maximum ratio combining (TP-MRC), and the linear equalization receiver. Numerical results show that the proposed algorithm achieves optimal performance by using an appropriate partial equalization factor that depends on the system specification
Personal, Indoor and Mobile Radio Communications, 2005. PIMRC 2005. IEEE 16th International Symposium on; 10/2005
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ABSTRACT: An adaptive receiver is proposed for multicarrier code-division multiple-access (MC-CDMA) systems to suppress both intersymbol interference and multiple access interference. The proposed minimum mean squared error (MMSE)-based receiver eliminates the need of the discrete or fast Fourier transform operation without any performance loss in the communications channels considered.
Electronics Letters 11/2003; · 0.96 Impact Factor
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ABSTRACT: An Adaptive minimum bit error rate (MBER) based linear multiuser detection scheme is proposed for an asynchronous multicarrier code-division multiple-access (MC-CDMA) system in frequency selective Rayleigh fading channels. In general, a MC-CDMA system employs the minimum mean square error (MMSE) receiver due to its good performance and amenability to adaptive implementation. However, the MSE cost function is nut optimal in terms of the bit error probability performance of the system. The proposed multiuser detector (MUD) that directly minimizes the BER can significantly improve the performance by employing an adaptive stochastic gradient algorithm based on the estimation of kernel density function in order to adjust the weights in the receiver. Simulation results demonstrate a clear performance improvement by using the proposed multiuser detection scheme.
Personal, Indoor and Mobile Radio Communications, 2003. PIMRC 2003. 14th IEEE Proceedings on; 10/2003
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ABSTRACT: An asynchronous multicarrier code division multiple access (MC-CDMA) scheme over frequency selective multipath Rayleigh fading channels for the reverse link of a mobile communication system is investigated when the delay spread is in excess of a symbol interval. An architecture of a centralized decision feedback equalizer (CDFE) based on the minimum mean-square-error (MMSE) criterion is suggested to reduce both inter-symbol-interference (ISI) and multiple access interference (MAI) due to the multi-path propagation, and the MAI due to the effect of the reverse asynchronous reception mode at the base station. The receiver architecture is for multi-user detection (MUD) consisting of a multiple-layer feed-forward filter (ML-FFF) and a centralized feed back filter (CFBF). Results indicate that an enhancement in capacity and good interference resistance are obtained by the proposed multi-user detection scheme over the structure without CFBF (NCDFE), which only uses ML-FFF and FBF. Additionally, it is demonstrated that the structure performs multi-path energy Rake combining.
Personal, Indoor and Mobile Radio Communications, 2003. PIMRC 2003. 14th IEEE Proceedings on; 10/2003
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ABSTRACT: The multi-carrier code-division multiple access (MC-CDMA) system is characterized by implementing the spectral spreading operation in the frequency domain, however, it can be also viewed as a special form of DS-CDMA in the time domain. In this paper, a time-domain adaptive centralized decision-feedback multiuser detector (MUD) is proposed for a synchronous MC-CDMA system in a frequency-selective multipath-fading channel. The suggested receiver employs a nonlinear centralized decision-feedback equalizer to suppress both intersymbol interference (ISI) and multi-access interference (MAI). The recursive least-squares (RLS) algorithm is employed to optimize the receiver parameters by minimizing the time-average weighted squared error. The performance of the proposed receiver architecture is evaluated in a multipath-fading channel exhibiting four propagation paths. Uniform and exponential multipath intensity profiles (MIP) are investigated. Computer simulation results demonstrate that the overall performance of the considered system which uses the proposed MUD outperforms both the conventional equal gain and maximum ratio combiner (EGC, MRC), as well as the single-user detector (SUD).
3G Mobile Communication Technologies, 2003. 3G 2003. 4th International Conference on (Conf. Publ. No. 494); 07/2003
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ABSTRACT: Data transmission over HF channels is subject to phenomena of dispersion, absorption and multiple paths. Performance may be improved by using orthogonal frequency division multiplexing spread spectrum (OFDM-SS) systems. In OFDM-SS systems, transmitting data over slowly varying multi-path channels, both intersymbol interference (ISI) and multiple-access interference (MAI) arise and should therefore be mitigated. Two adaptive nonlinear equalization architectures based on the minimum mean-square error (MMSE) criterion are proposed and examined over such channels. The first receiver architecture is for single-user detection (SUD) consisting of a multiple-layer feed-forward filter (ML-FFF) and a feedback filter (FBF). The ML-FFF acts as a multipath diversity combiner as well as canceller of precursor ISI and main-cursor MAI while the FBF acts as a canceller of post-cursor ISI. The second receiver architecture is for multiuser detection (MUD) where in addition to the first structure, it employs a centralized FBF (CFBF) for cancelling the MAI of previous symbols. Results indicate that an enhancement in capacity is obtained by the multi-user structure over the single-user structure. Additionally, it is demonstrated that both structures perform multipath energy combining (RAKE-like) when the delay spread is in excess of a symbol interval.
HF Radio Systems and Techniques, 2003. Ninth International Conference on (Conf. Publ. No. 493); 07/2003
