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ABSTRACT: Multi-carrier code division multiple access (MC-CDMA) allows multiuser communication with frequency diversity. To increase the system data rates, spatial multiplexing for multiple-input multiple-output (MIMO) MC-CDMA has been investigated. This study proposes a chip level layered space-time (LST) receiver architecture for coded downlink MIMO MC-CDMA systems. As the conventional chip level ordered successive interference cancellation (OSIC) receiver is unable to overcome multiple access interference and performs poorly in multiuser scenarios, the proposed receiver cancels both spatial and multiuser interference in an ordered LST detection process by requiring only the knowledge of the desired user-s spreading sequence. Simulation results show that the proposed receiver not only performs better than the existing linear detectors but also outperforms both the chip and symbol level OSIC receivers. In this study the authors also compare the error rate performance between the proposed system and MIMO orthogonal frequency division multiple access (MIMO OFDMA) system and they justify the comparisons by deriving and analysing the pairwise error probability (PEP) for both systems. MIMO MC-CDMA demonstrates a better performance over MIMO OFDMA under low system load. If all users- spreading sequences are known, multiuser interference can be reduced and MIMO MC-CDMA performs better than MIMO OFDMA at all system loads.
IET Communications 10/2011; · 0.83 Impact Factor
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ABSTRACT: Nodes in most cooperative networks are powered by batteries and some of which are even non-rechargeable. Therefore, power allocation schemes must be developed to save the transmit power and improve the life-time of the system. In this context, we present a novel power allocation scheme for multiple relay nodes that results in efficient cooperative communication. Considering channel path loss, the total transmission energy is distributed between the source and the relay nodes. The energy distribution ratio between the relay and direct link is optimized such that the quality of received signal is maintained with minimum total transmission energy consumption. We calculate the energy distribution ratio analytically and verified it through computer simulation. With the new power allocation scheme, the system also obtains an increased channel capacity as compared to cooperative scheme with conventional equal power allocation. Optimal relay positioning with proposed energy allocation scheme is also explored to maximize the capacity.
Communications (ICC), 2011 IEEE International Conference on; 07/2011
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ABSTRACT: Cooperative communication exploits the broadcast nature of wireless channel and uses relay nodes to provide better reliability and higher data rates without increasing power and bandwidth. In this paper, the energy analysis of the asynchronous polarized cooperative (APC) scheme is performed. APC employs multiple antennas at the relay and destination nodes to achieve full duplex amplify-and-forward (ANF) communication. Hence the transmission duration is reduced which results into an increased spectral efficiency. Considering channel path loss, the APC scheme consumes less total transmission energy as compared to ANF and non-cooperative scheme over more practical distance between the nodes. Thus the APC scheme is both spectral and energy efficient, and is suitable for the cooperative communication systems.
Personal Indoor and Mobile Radio Communications (PIMRC), 2010 IEEE 21st International Symposium on; 10/2010
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ABSTRACT: Cooperative communication achieves diversity through spatially separated cooperating nodes, which are battery powered in most applications. Therefore the energy consumption must be minimized without compromising the transmission quality (bit error rate). In this context, we present a novel power allocation scheme that results in efficient cooperative multiple-input multiple-output (MIMO) communication. Considering channel path loss, the total transmission energy is distributed between the source and the relay nodes. The energy distribution ratio between the relay and direct link is optimized such that the quality of received signal is maintained with minimum total transmission energy consumption. We calculate the energy distribution ratio analytically and verified it through computer simulation. With the new power allocation scheme, the system also obtains an increased channel capacity as compared to cooperative scheme with conventional equal power allocation and non-cooperative scheme. Optimal relay positioning with proposed energy allocation scheme is explored to maximize the capacity.
Personal, Indoor and Mobile Radio Communications, 2009 IEEE 20th International Symposium on; 10/2009
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ABSTRACT: In cooperative wireless network, the users exploit spatial diversity by cooperating with each other. This alleviates the detrimental effects of fading and offers reliable data transfer. In this paper, we present a novel asynchronous cooperative multi-input multi-output (MIMO) communication scheme in the presence of polarization diversity which does not require synchronization at the relay node. Utilizing dual-polarized antennas, the relay node achieves full duplex amplify-and-forward (ANF) communication. Hence the transmission duration is significantly reduced which in turn results into an increased throughput rate. Capacity analysis of the proposed system ascertains the high data rate as compared to the conventional ANF protocol. Bit error rate simulation also shows that the proposed scheme significantly outperforms both the non-cooperative single-input single-output and the conventional ANF schemes.
Vehicular Technology Conference, 2009. VTC Spring 2009. IEEE 69th; 05/2009
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ABSTRACT: In this paper, we analyze and compare the error rate performance of downlink coded multiple-input multiple-output multi-carrier code division multiple access (MIMO MC-CDMA) and coded MIMO orthogonal frequency division multiple access (MIMO OFDMA) systems under frequency selective fading channel conditions. In particular, the pairwise error probabilities (PEP) for both systems are derived. Simulation results illustrate that when the number of users, hence the system load is low, MIMO MC-CDMA outperforms MIMO OFDMA. However when the system load increases, the performance of MIMO MC-CDMA deteriorates and becomes worse than MIMO OFDMA. This can be explained by the PEP analysis of MIMO MC- CDMA which shows that when the number of users is small, the multiuser interference is also small and frequency diversity is better exploited. Conversely at high system load, MIMO OFDMA outperforms MIMO MC-CDMA as it is insensitive to multiuser interference. Nevertheless if the other users' spreading sequences are available at the receiver of the desired user, the impact of multiuser interference can be minimised and MIMO MC-CDMA outperforms MIMO OFDMA at all system loads.
Vehicular Technology Conference, 2009. VTC Spring 2009. IEEE 69th; 05/2009
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ABSTRACT: Multiple antennas wireless systems can achieve large capacity at the expense of high hardware cost associated with the radio frequency chains. Antenna selection schemes make use of more antennas than RF chains and select a subset of antennas to effectively reduce the hardware cost and power consumption without much capacity loss. In this paper, the problem of receive antenna selection in V-BLAST systems is investigated. Two performance based selection criteria are proposed, namely the min-max MSE and min-first stage MSE criteria. The min-max criterion achieves the best performance at the expense of high computational complexity. Complexity reduced algorithms for this selection scheme are discussed. Analytical proof is provided to show the suboptimality of the capacity based selection to the performance based selection. The hybrid scheme, which combines the performance and capacity based selection approaches is proposed, it provides a good trade-off between performance and complexity. Computer simulations demonstrate that the complexity reduction algorithms and the hybrid scheme perform better and also with a lower complexity than the capacity based selection algorithm under most system configurations. Finally, robustness of the min-max MSE criterion under channel estimation errors is evaluated via computer simulations.
IEEE Transactions on Wireless Communications 02/2009; · 2.59 Impact Factor
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ABSTRACT: Multiple-input multiple-output (MIMO) antenna systems are capable of providing very high spectral efficiency due to the use of multiple antennas at transceivers. The problem of the expensive hardware cost associated with MIMO systems can be effectively mitigated by performing antenna selection at either or both ends. However, most works on antenna selection consider uncoupled antennas only, which might not be practical when implemented in a small-sized mobile unit. In this paper, effects of mutual coupling between antenna elements are included in the system model. We evaluate the system error performance of different antenna selection schemes in correlated channels when mutual coupling effects exist. Simulation results show that when the separation between two adjacent antennas is small, antenna selection schemes can significantly improve the performance degradation caused by the highly correlated and coupled receive signals. It could even outperform the full system, which is not possible under ideal channel conditions. In particular, the performance based selection scheme has the best performance in this scenario over capacity based selection and RF pre-processing.
Personal, Indoor and Mobile Radio Communications, 2008. PIMRC 2008. IEEE 19th International Symposium on; 10/2008
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ABSTRACT: Layered space time processing in spatial multiplexing systems has a stringent requirement that the number of receive antennas must be equal to or larger than the number of transmit antennas. A novel concept of virtual receive antennas (VRA) proposed in our previous work can loosen this requirement. In this paper, we present a low complexity frequency domain equalizer (FDE) and show the potentials of VRA by analysing the system capacity. In addition, we consider a more practical pulse shaping filter for the VRA system. Results show that the VRA system can achieve higher ergodic capacity and outage rate than the conventional overloaded MIMO system. With the proposed low complexity FDE receiver, VRA allows layered processing for spatial multiplexing system with less number of physical antenna.
Vehicular Technology Conference, 2008. VTC Spring 2008. IEEE; 06/2008
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ABSTRACT: In this paper, a chip level ordered successive spatial and multiuser interference cancellation (OSSMIC) receiver architecture is presented for downlink multiple-input multiple- output multi-carrier code division multiple access (MIMO MC-CDMA) systems. The proposed receiver performs ordered layer space-time detection. Unlike the existing ordered successive interference cancellation (OSIC) receiver, the proposed receiver cancels both spatial & multiuser interference in the SIC process. This allows detection in multiuser scenario, which is not possible in conventional chip level OSIC receiver. Simulation results show that the proposed receiver significantly outperforms both the existing chip level OSIC detector and the chip level linear receiver. As the proposed receiver only requires the knowledge of the desired user's spreading sequence, it is a viable solution for downlink MIMO MC-CDMA communications.
Vehicular Technology Conference, 2008. VTC Spring 2008. IEEE; 06/2008
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ABSTRACT: Spatial multiplexing with layered space-time receiver is one of the multiple input multiple output (MIMO) schemes that can achieve the linearly increasing capacity. However, layered space-time processing requires the number of receive antennas to be the same or larger than the number of transmit antennas. It is difficult to design a small sized mobile unit with such number of antennas, and hinders the broad dissemination of this promising technology. The authors investigate this problem and present the novel concept of virtual receive antennas for spatial multiplexing system. Each substream is transmitted with a specific timing offset, and the received matched filter output signal is oversampled. The oversampled signals have certain properties such that they can be considered as signals from correlated antennas. Hence, virtual receive antennas are created and the number of physical receive antennas can be reduced. Simulation results are presented to demonstrate the system performance.
Wireless Communications and Networking Conference, 2007.WCNC 2007. IEEE; 04/2007
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ABSTRACT: Vertical Bell laboratory layered space-time (V-BLAST) is one of the promising multiple input multiple output (MIMO) architectures. Layered space time processing in V-BLAST requires the number of receive antennas to be equal to or larger than the number of transmit antennas. However, it is impractical for small-sized mobile units to accommodate all the required antennas. Focusing on this problem, we have presented a novel concept of virtual receive antennas (VRA) for spatial multiplexing system in flat fading channels. In that work, time domain equalization is utilized to eliminate inter-symbol interference, which is generated in the VRA. However, the employed time domain equalizer has a high computational complexity. In this paper, the VRA system with low complexity frequency domain equalizer (FDE) is investigated. Moreover, as the noise in the VRA system is correlated due to oversampling, we also present the noise decorrelating filter design. Through complexity and performance evaluation, FDE is demonstrated to be more suitable for the VRA system.
Wireless Communications and Networking Conference, 2007.WCNC 2007. IEEE; 04/2007
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ABSTRACT: Multiple antennas wireless systems can achieve large capacity at the expense of high hardware cost associated with the radio frequency (RF) chains. Antenna selection schemes make use of more antennas than RF chains and select a subset of antennas. It is an effective approach to reduce the hardware cost without much capacity loss. Antenna selection schemes in layered space-time system are mostly investigated in terms of capacity, and for zero-forcing (ZF) linear receivers. In this paper we analyse and compare the performance of antenna selection for zero-forcing and minimum mean square error (MMSE) based V-BLAST receivers, and derived a new performance bound for MMSE receivers. A novel performance based selection criterion for MMSE V-BLAST system is proposed, and named the minmax MSE criterion. Computer simulation shows that this new criterion can obtain the diversity of a full system and outperforms other previously proposed schemes with a near-optimal performance
Personal, Indoor and Mobile Radio Communications, 2006 IEEE 17th International Symposium on; 10/2006
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ABSTRACT: Antenna selection is an effective approach to reduce RF (radio frequency) hardware cost and implementation complexity of multiple-input multiple-output systems. A subset of antennas is selected out of all available ones based on a certain criterion. Many researches on antenna selection for spatial multiplexing system focused on capacity based selection criterion, which do not necessarily optimise the system performance. In this paper, two novel error rate performance based criteria for receive antenna selection in layered space-time system are proposed. These criteria are namely the max-min and max-first layer criteria. A reduced complexity algorithm is also proposed for the max-min selection criterion. Computer simulations demonstrate that our proposed algorithms can obtain the diversity of a full system. In particular, the proposed max-min algorithm outperforms capacity based selection algorithms, while the max-first layer algorithm provides a low complexity solution to the problem
Vehicular Technology Conference, 2006. VTC 2006-Spring. IEEE 63rd; 06/2006
