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ABSTRACT: We consider relay broadcast channels (RBCs) with multiple antennas at all nodes. A practical linear precoding, relaying and combining scheme is proposed. Under an overall power constraint, we derive the optimal power allocation solution in a closed form. A low complexity beamforming vector optimization algorithm is proposed to maximize the effective channel gains and improve the system performance. Simulation results are presented for various channel configurations, which show that the proposed cooperative beamforming algorithm achieves performance very close to that of the exhaustive search algorithm but with a much lower complexity, and the maximum diversity gain is always attained.
IEEE Transactions on Wireless Communications 04/2011; · 2.59 Impact Factor
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ABSTRACT: We consider relay broadcast channels (RBCs) with multiple antennas at all nodes. A practical linear preceding, relaying and combining scheme is proposed. Under an overall power constraint, we derive the optimal power allocation solution in a closed form. A low complexity beamforming vector optimization algorithm is proposed to maximize the effective channel gains and improve the system performance. Simulation results are presented for various channel configurations, which show that the proposed optimized beamforming algorithm achieves performance very close to that of the exhaustive search algorithm but with a much lower complexity, and the maximum diversity gain is always attained.
Global Telecommunications Conference, 2009. GLOBECOM 2009. IEEE; 01/2010
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ABSTRACT: Interference among multiple base stations that co-exist in the same location limits the capacity of wireless networks. In this paper, we propose a method to design a spectrally efficient cooperative downlink transmission scheme employing precoding and beamforming for multi-user multiple-input-multiple-output (MIMO) systems. The algorithm eliminates the interference and achieves symbol error rate (SER) fairness among different users. To eliminate the interference, Tomlinson Harashima precoding (THP) is used to cancel part of the interference while the transmit-receive antenna weights are chosen to cancel the remaining interference. A new novel iterative method is applied to generate the transmit-receive antenna weights. To achieve SER fairness among different users and further improve the performance of multi-user MIMO systems, we develop algorithms that provide equal signal-to-interference-plus-noise-ratio (SINR) across all users. The users are also ordered so that the minimum SINR for each user is maximized. The simulation results show that the proposed scheme considerably outperforms existing cooperative transmission schemes in terms of the SER performance and complexity and approaches an interference free performance under the same configuration.
Global Telecommunications Conference, 2009. GLOBECOM 2009. IEEE; 01/2010
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ABSTRACT: Interference among multiple base stations that coexist in the same location limits the capacity of wireless networks. In this paper, we propose a method to design a spectrally efficient cooperative downlink transmission scheme employing precoding and beamforming. The algorithm eliminates interference and achieves symbol error rate (SER) fairness among different users. To eliminate the interference, Tomlinson Harashima precoding (THP) is used to cancel part of the interference while the transmit-receive antenna weights are chosen to cancel the remaining interference. A novel iterative method is applied to generate the transmit-receive antenna weights. The convergence behaviour of the iterative process is investigated. To achieve SER fairness among different users and improve the performance of the system, we develop algorithms that provide equal signal to-interference-plus-noise-ratios (SINR) across all users under both per base station (BS) and total BSs power constraints. Per BS and total BSs power constraints are constraints where the power for each BS and all BSs is limited to a particular value. The simulation results show that the proposed scheme outperforms existing cooperative transmission schemes in terms of the SER performance and complexity and closely approaches an interference free performance under the same configuration.
IEEE Transactions on Wireless Communications 01/2010; · 2.59 Impact Factor
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ABSTRACT: In this paper, we propose and analyze three new transmit antenna selection schemes with reduced feedback rate requirement compared with the conventional scheme. In scheme 1, L<sub>t</sub> available transmit antennas are divided as equally as possible into two groups with consecutive antennas. The best single antenna within each group is selected. In scheme 2, only the best one among L<sub>t</sub> antennas is made known to the transmitter, and the other one is selected at random. In Scheme 3, L<sub>t</sub> antennas are divided into multiple subsets each consisting of two adjacent antennas, and the best subset is selected. Bit error rate (BER) expressions for the proposed schemes with Alamouti code are derived for independent flat Rayleigh fading channels. It is found that all the three schemes achieve a full diversity order. The relative merit of each proposed scheme is delineated based on the trade-off between the asymptotic performance loss and feedback reduction, both relative to the conventional scheme. We conclude that Schemes 1 and 3 are more favorable for practical applications, and the appropriate application scenarios are also identified. The proposed schemes enrich the choices for antenna selection system design for various feedback channel bandwidths and different requirements for quality of service.
IEEE Transactions on Wireless Communications 03/2009; · 2.59 Impact Factor
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IEEE Transactions on Wireless Communications. 01/2009; 8:1006-1016.
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IEEE Transactions on Wireless Communications. 01/2009; 8:5871-5882.
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ABSTRACT: We consider multiuser Gaussian broadcast channels with multiple antennas at both transmitter and receivers. An iterative multiple beamforming algorithm is proposed, which is flexible in the antenna configuration and performs well in low to moderate data rates. Its capacity and bit error rate performance are compared with the ones achieved by the traditional zeroforcing method.
IEEE Communications Letters 11/2008; · 0.98 Impact Factor
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ABSTRACT: We consider relay broadcast channels (RBCs) with multiple antennas at all nodes. A practical precoding, relaying and combining scheme is proposed. Under an overall power constraint, we derive the optimal power allocation solution in a closed form. The conditions for an effective RBC scheme are identified with a qualitative analysis to the relationship between the relay gain and the relative strengths of the direct and relay links. Simulation results are shown for various channel configurations, which verify the analysis and conclude that the first hop in the relay chain is a determining factor to the overall performance of the RBC.
Personal, Indoor and Mobile Radio Communications, 2008. PIMRC 2008. IEEE 19th International Symposium on; 10/2008
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ABSTRACT: In this paper, we propose three different transmit antenna selection schemes with reduced feedback requirement compared with the conventional scheme. In Scheme 1, all the Lt available transmit antennas are divided as equally as possible into two groups. The best single antenna within each group is selected. In Scheme 2, only the best one among Lt antennas is made known to the transmitter, and the other one is selected at random. Scheme 3 is for even Lt, and Lt antennas are divided into multiple subsets each consisting of two adjacent antennas, among which the best subset is selected. Analytical performances of these three schemes with the Alamouti space-time block code (STBC) are derived for flat Rayleigh fading channels. The asymptotic signal-to-noise ratio (SNR) loss of each proposed scheme relative to the conventional transmit antenna selection scheme is quantified. Together with the reduction in feedback requirement, the relative merit of each proposed scheme is delineated. In general, all of the three schemes provide a good trade-off between error performance and feedback requirement. And the application scenario for each scheme is also identified. The results in this paper provide guidance for the design of transmit antenna selection systems with various feedback channel bandwidths, different requirements for quality of service, and specific antenna configuration.
Personal, Indoor and Mobile Radio Communications, 2007. PIMRC 2007. IEEE 18th International Symposium on; 10/2007
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ABSTRACT: One of the advantages of multiple-input multiple-output (MIMO) systems is the multiplexing gain over single-input single-output (SISO) systems. We consider adaptive modulation and coding (AMC) as a practical technique in achieving the full multiplexing gain of MIMO systems. The multiplexing gain of AMC MIMO systems is analyzed quantitatively, and a practical way of predicting the multiplexing gain of a generic AMC MIMO system is presented.
Wireless Broadband and Ultra Wideband Communications, 2007. AusWireless 2007. The 2nd International Conference on; 09/2007
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ABSTRACT: In this paper, we consider a 2-hop wireless diversity relay network. We explore transmit power allocation among the source and relays to maximize the received signal to noise ratio (SNR) at the destination. We consider two relay protocols, "amplify and forward" (AAF) and "decode and forward" (DAF) and design the respective power allocations for both uneeded and coded systems. For a 2-hop relay system with one relay node, we derive a closed-form power allocation solution and, based on it, we propose a relay activation condition. If and only if the fading channel coefficients satisfy this condition, the relay transmits the signals to the destination; otherwise, the relay will stay in the idle state. For a system with more than one relay node, general closed-form power allocation solutions based on an exact SNR expression are difficult to derive; we hence, calculate a SNR upper bound and derive a sub-optimum power allocation solution based on this bound. The simulation results show that for a 2-hop diversity relay channel with one relay node the proposed adaptive power allocation (APA) scheme yields about 1- 2 dB SNR gains compared to the equal power allocation. This SNR gain increases monotonically as the number of relays increases
IEEE Transactions on Wireless Communications 04/2007; · 2.59 Impact Factor
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Proceedings of IEEE International Conference on Communications, ICC 2007, Glasgow, Scotland, 24-28 June 2007; 01/2007
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IEEE Transactions on Wireless Communications. 01/2007; 6:948-958.
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ABSTRACT: In this paper, following an analysis on the effect of channel state information (CSI) feedback delay over the eigenmode transmission MIMO system, we incorporated a bit-interleaved coded modulation (BICM) technique into the previously proposed adaptive modulation multiple-input multiple-output (MIMO) system to combat the CSI imperfection. Under a perfect CSI assumption, the optimum adaptation policy for the adaptive BICM MIMO system was obtained and both analytical and simulation results were presented showing the robustness of this system to the CSI feedback delay. Based on that, a modified adaptation algorithm was proposed, which further improved the BER performance by trading off the achieved spectral efficiency in an adaptive way.
Communications, 2006. ICC '06. IEEE International Conference on; 07/2006
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IEEE Transactions on Wireless Communications. 01/2006; 5:296-300.
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ABSTRACT: In this paper, we first address the effects of the feedback delay on a variable-rate variable-power adaptive modulation MIMO system that is designed under a perfect channel state information (CSI) assumption. Closed-form expressions for the average bit error rate (BER) and average spectral efficiency (ASE) are derived. Based on that, simple but effective adaptive modulation designs using the outdated instantaneous CSI and time correlation coefficient are proposed based on the signal-to-interference and noise ratio (SINK) and BER analysis. Analytical and simulation results show that these designs provide good trade-offs between the ASE and BER in an adaptive way, and make the adaptive MIMO system much more robust to the CSI imperfection
Personal, Indoor and Mobile Radio Communications, 2005. PIMRC 2005. IEEE 16th International Symposium on; 10/2005
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ABSTRACT: In this paper, we propose a novel distributed turbo coding (DTC) scheme which can be used in a system where imperfect decoding occurs at a relay. For the proposed scheme, rather than making a decision on the transmitted information symbols at the relay as in the conventional DTC, we calculate and forward the corresponding soft information at the relay. For the proposed scheme, we derive the parity symbols soft estimates for the interleaved source information when only the a posteriori probabilities (APP) of the information symbols are known. Analytical results show that the performance of the proposed scheme, at high SNR, is limited by the ratio of the received SNR at the relay and that at the destination. In order to make the performance loss of the proposed scheme, compared to the perfect DTC as small as possible, the relay should be placed closer to the source than to the destination and/or make the transmit power from the source larger than that from the relay
Personal, Indoor and Mobile Radio Communications, 2005. PIMRC 2005. IEEE 16th International Symposium on; 10/2005
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ABSTRACT: Adaptive modulation (AM) schemes in multiple input multiple output (MIMO) systems with a perfect or imperfect channel state information (CSI) at both the transmitter and receiver were investigated. Under an average transmit power and instantaneous bit error rate (BER) constraint, the transmit parameters including the subchannel transmit power and/or spectral efficiency are optimally adapted in the spatial and/or temporal domain to maximize the average spectral efficiency (ASE). Two categories, the continuous rate and discrete rate, of adaptive systems were considered, where the derived asymptotic closed form expressions for the former provided much insight into the latter. Analytical and numerical results showed that a full multiplexing gain was achieved in variable rate variable power (VRVP) systems and variable rate (VR) systems. Variable power (VP) systems with unequal numbers of transmit and receive antennas also achieved the full multiplexing gain, unlike VP systems with equal number of transmit and receive antennas. The effect of CSI imperfection on the ASE and BER was evaluated for VR systems and closed form expressions for the ASE and BER were obtained. They prove to be a useful tool to assess the system performance without taking time consuming AM MIMO system simulations.
IEEE Transactions on Vehicular Technology 10/2005; · 1.92 Impact Factor
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ABSTRACT: We investigate the error performance of the Alamouti scheme with transmit antenna selection. The exact bit error rate (BER) is derived for binary phase-shift keying (BPSK) in flat Rayleigh fading channels. The analysis reveals that this scheme achieves a full diversity order at high SNRs, as if all the transmit antennas were used. Simulation results are provided to substantiate the analysis. It is shown that compared with conventional space-time block codes (STBCs), this scheme incurs much less SNR loss inherent to the transmit-diversity system. Therefore, the Alamouti scheme with transmit antenna selection provides a new general approach to the design of MIMO systems for high-data-rate downlink transmission with a high diversity order.
Personal, Indoor and Mobile Radio Communications, 2004. PIMRC 2004. 15th IEEE International Symposium on; 10/2004
