1,720,973 research outputs found
Sample-Spaced and Fractionally-Spaced CIR Estimation Aided Decision Directed Channel Estimation for OFDM and MC-CDMA
No full textThe achievable performance of decision-directed channel estimation (DDCE) is analysed in the context of both OFDM and MC CDMA systems. Two different estimation methods suitable for both OFDM and MC-CDMA systems are considered, which employ sample-spaced (SS) as well as fractionally-spaced (FS) a posteriori channel impulse response (CIR) estimators. The performance of both estimation methods is compared and it is shown that the DDCE scheme employing the FS-CIR estimator outperforms its SS-CIR estimator-based counterpart. Furthermore, the FS-CIR estimator-based method exhibits higher robustness to various channel parameters such as the channel’s root mean square delay spread. Finally, it is shown that the MC-CDMA system employing the channel estimation scheme advocated outperform its OFDM counterpart
Generic Reduced-Complexity MMSE Channel Estimation for OFDM and MC-CDMA
No full textThe performance of a decision-directed channel estimation scheme is analyzed in the context of both OFDM and MC-CDMA systems. A difficulty associated with the employment of the Least Squares (LS) approach to the problem of a posteriori channel estimation in the context of a MC-CDMA system is described and a suitable MMSE-based estimator is proposed instead. It is demonstrated that the computational complexity associated with the MMSE estimation method proposed is relatively high in comparison to that of the conventional LS technique. Thus a low-complexity version of the MMSE estimator is proposed. The MC-CDMA system using a low-complexity MMSE estimator proposed is shown to outperform the corresponding OFDM-based scheme
Low Complexity Approximate Log-MAP Detection for MIMO Systems
Full text linkIn this paper we propose a novel low-complexity Log-MAP space-time detection method, which can be regarded as an advanced extension of the Complex Sphere Decoder (CSD). We demonstrate that as opposed to the previously published variants of the soft-output CSD, the proposed technique may be employed in the so-called “over-loaded” scenario, where the number of transmit antennas exceeds that of the receive antennas. The proposed method closely approaches the optimum performance of the Log-MAP detector even in heavily over-loaded scenarios, while the associated computational complexity is only moderately increased
Decision Directed Channel Estimation Employing Projection Approximation Subspace Tracking
No full textThe attainable capacity and integrity of a state-of-the-art broadband multi-carrier communication system is highly sensitive to the accuracy of the information available concerning the channel conditions encountered. The majority of existing advanced channel estimation schemes assume knowledge of the channel’s Power Delay Profile (PDP) in order to estimate the corresponding instantaneous Channel Impulse Response (CIR). It is evident however that in realistic mobile channels, where at least one of the communicating terminals is in motion, the power delay profile will also be time-variant and thus may not be known a priori at the receiver. In this paper we propose a decision directed channel estimation scheme employing the so-called Projection Approximation Subspace Tracking (PAST) algorithm. The PAST algorithm is utilised for the sake of achieving low-complexity recursive tracking of the channel’s PDP. The achievable performance of the proposed method is documented in the context of an OFDM system communicating in realistic channel conditions characterized by a time-variant fractionally-spaced PDP
Iterative Joint Channel Estimation and Multi-User Detection for Multiple-Antenna Aided OFDM Systems
No full textMultiple-Input-Multiple-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) systems have recently attracted substantial research interest. However, compared to Single-Input-Single-Output (SISO) systems, channel estimation in the MIMO scenario becomes more challenging, owing to the increased number of independent transmitter-receiver links to be estimated. In the context of the Bell LAyered Space-Time architecture (BLAST) or Space Division Multiple Access (SDMA) multi-user MIMO OFDM systems, none of the known channel estimation techniques allows the number of users to be higher than the number of receiver antennas, which is often referred to as a “rank-deficient” scenario, owing to the constraint imposed by the rank of the MIMO channel matrix. Against this background, in this paper we propose a new Genetic Algorithm (GA) assisted iterative Joint Channel Estimation and Multi-User Detection (GA-JCEMUD) approach for multi-user MIMO SDMA-OFDM systems, which provides an effective solution to the multi-user MIMO channel estimation problem in the above-mentioned rank-deficient scenario. Furthermore, the GAs invoked in the data detection literature can only provide a hard-decision output for the Forward Error Correction (FEC) or channel decoder, which inevitably limits the system’s achievable performance. By contrast, our proposed GA is capable of providing “soft” outputs and hence it becomes capable of achieving an improved performance with the aid of FEC decoders. A range of simulation results are provided to demonstrate the superiority of the proposed scheme. Index Terms—Channel estimation, genetic algorithm, multiple-input-multiple-output, multi-user detection, orthogonal frequency division multiplexing, space division multiple access
Advanced Channel Estimation for MIMO-OFDM in Realistic Channel Conditions
No full textAn advanced decision-directed channel estimation scheme is proposed, which is suitable for employment in a wide range of multi-antenna multi-carrier systems as well as for communications over the entire range of practical channel conditions. In particular, we consider a MIMO-OFDM system operating in a mobile wireless multipath channel, which exhibits frequency-selective Rayleigh fading and is characterized by a time-variant power delay profile. Both the mean square error as well as the bit error rate performances achieved by the proposed system are documented. Specifically, we report a virtually errorfree performance of a rate 1/2 turbo-coded 8x8-QPSK-OFDM system, exhibiting an effective throughput of 8·2·1/2=8bits/sec/Hz, while having a pilot overhead of only 10%, at an SNR of 10dB and an OFDM-symbol-normalized Doppler frequency of 0.003, which corresponds to the mobile terminal speed of about 65 km/h
Peak-to-average power ratio reduction for OFDM modems
No full textA novel technique of reducing the Peak-to-Average Power Ratio (PAPR) of Multi-Carrier (MC) modulated signals is proposed. The method advocated is spectrally efficient, has a low implementational complexity and hence it is also suitable for low-power, portable implementation. Moreover, it was designed to be compatible with existing standard-based Orthogonal Frequency Division Multiplex (OFDM) systems. As an example of the performance of the proposed scheme, the amplifier back-off requirement in a Terrestrial Digital Video Broadcast (DVB-T) system can be reduced from 12 to 6 dB, while satisfying the out-of-band emission specifications imposed by the Federal Communications Commission (FCC) spectral mask
Iterative Receiver Architectures for MIMO-OFDM
Full text linkIn this paper we propose a turbo-detected multiantenna-multi-carrier receiver scheme. Following the philosophy of the turbo processing, our turbo MIMO-OFDM receiver comprises a succession of detection modules, namely the channel estimator, the space-time detector and the decoder, which iteratively exchange soft bit-related information and thus facilitate a substantial improvement of the overall system performance. In this paper we analyse the achievable performance of the iterative system proposed with the aim of documenting the various design trade-offs, such as the achievable error-rate performance, the attainable data-rate as well as the associated computational complexity. Specifically, we report a virtually error-free performance for a rate-12 turbo-coded 8x8-QPSK-OFDM system, exhibiting an effective throughput of 8·2·1 2=8 bits/sec/Hz and having a pilot overhead of only 10%, at SNR of 7.5dB and normalized Doppler frequency of 0.003, which corresponds to a mobile terminal speed of about 65 km/h
Iterative Joint Channel Estimation and Symbol Detection for Multi-User MIMO OFDM
No full textMultiple-Input-Multiple-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) systems have recently attracted substantial research interest. However, compared to Single-Input-Single-Output (SISO) systems, channel estimation in the MIMO scenario becomes more challenging, owing to the increased number of independent transmitter-receiver links to be estimated. In the context of the Bell LAyered Space-Time architecture (BLAST) or Space Division Multiple Access (SDMA) multi-user MIMO OFDM literature, no channel estimation technique allows the number of users to be higher than the number of receiver antennas, which is often referred to as an “overloaded” scenario. In this contribution we propose a new Genetic Algorithm (GA) assisted iterative joint channel estimation and multiuser detection approach for MIMO SDMA-OFDM systems, which exhibits a robust performance in the above-mentioned overloaded scenario. Furthermore, GA-aided Multi-User Detection (MUD) techniques found in the literature can only provide a hard-decision output, while the proposed GA is capable of providing “soft” outputs, hence achieving an improved performance with the aid of channel decoders. Finally, a range of simulation results are provided to demonstrate the superiority of the proposed scheme
Reduced-Complexity Maximum-Likelihood Detection in Downlink SDMA Systems
Full text linkThe literature of up-link SDMA systems is rich, but at the time of writing there is a paucity of information on the employment of SDMA techniques in the down-link. Hence, in this paper a Space Division Multiple Access (SDMA) down-link (DL) multi-user communication system invoking a novel low-complexity Maximum Likelihood (ML) space-time detection technique is proposed, which can be regarded as an advanced extension of the Complex Sphere Decoder (CSD). We demonstrate that as opposed to the previously published variants of the CSD, the proposed technique may be employed for obtaining a high effective throughput in the so-called “over-loaded” scenario, where the number of transmit antennas exceeds that of the receive antennas. The proposed method achieves the optimum performance of the ML detector even in heavily over-loaded scenarios, while the associated computational complexity is only moderately increased. As an illustrative example, the required Eb/N0 increased from 2 dB to 9 dB, when increasing the normalized system load from unity, representing the fully loaded system, to a normalized load of 1.556
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