International Symposium on Wireless and Pervasive Computing, 2011
In a distributed MIMO system (D-MIMO), multiple base stations work in cooperation manner to enhan... more In a distributed MIMO system (D-MIMO), multiple base stations work in cooperation manner to enhance system throughput by suppressing inter-cell and inter-user interference. In this paper, we propose two practical distributed algorithms that are based on block diagonalization technique. The proposed schemes eliminate the need of iterative computations, and hence can be implemented without information exchange between multiple base stations. We also construct a suboptimal solution that requires only partial channel state information to be available at each base station. The sensitivity of system throughput versus number of users for various algorithms was demonstrated.
2010 IEEE International Conference on Communication Systems, 2010
ABSTRACT In this paper, a beacon structure is proposed for the protection of incumbent wireless m... more ABSTRACT In this paper, a beacon structure is proposed for the protection of incumbent wireless microphones in a cognitive radio system. The proposed beacon structure consists of two consecutive parts: synchronization bursts followed by payload bursts. Each part is transmitted on two orthogonal channels in parallel to shorten the required sensing windows for fast detection of the beacon. Compared to the current beacon design, the required two (long and short) sensing windows can be shortened significantly and it brings in substantial overhead reduction for the cognitive radio system. A flexible window scheduling method is proposed as well to guarantee the capture of the synchronization bursts.
... Zhongding Lei, Yan Wu, Chin Keong Ho, Sumei Sun, Ping He, and Yuan Li Institute for lnfocomm ... more ... Zhongding Lei, Yan Wu, Chin Keong Ho, Sumei Sun, Ping He, and Yuan Li Institute for lnfocomm Research 20 Science Park Road, #02-34/37 TeleTech Park, Singapore 117674 Tel: +65 68729030, Fax: +65 67795441, Email: leizd{wuyan,hock,sunsm,liyuan} @iZr.a-star.edu.sg ...
2004 IEEE 15th International Symposium on Personal, Indoor and Mobile Radio Communications (IEEE Cat. No.04TH8754), 2004
... case, even for the case when i = 0. However, since the instantaneous SNK is lower (upper) bou... more ... case, even for the case when i = 0. However, since the instantaneous SNK is lower (upper) bounded by ylow,i (yUp,,) given in (51, the instantaneous BEK can be upper ... In fact, a closed form solution can he found as shown next for L = 1 and 2 for QPSK modulated symbols. ...
21st Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, 2010
ABSTRACT In this paper, a class of quasi-orthogonal space-time block codes (Q-STBC) is proposed f... more ABSTRACT In this paper, a class of quasi-orthogonal space-time block codes (Q-STBC) is proposed for systems with 2 antennas and 3 time slots, where the orthogonal Alamouti code can not be applied due to the “odd symbol” problem inherited in the 3GPP frame structure. The proposed codes can achieve rate one and full diversity with lower complexity maximum likelihood detection. The design takes into consideration the signal power fluctuation and minimizes the potential peak-to-average ratio (PAPR) in the transmitted signals. The application to Single Carrier Frequency Division Multiple Access (SC-FDMA) has been investigated further. A transmission scheme is proposed to preserve the good PAPR property of SC-FDMA. In addition, linear and iterative decoding algorithms are proposed to simplify the receiver complexity. Simulations have been conducted to demonstrate the superior performance.
2005 IEEE 16th International Symposium on Personal, Indoor and Mobile Radio Communications, 2005
In this paper, we present a pre-transformed (PT) multiple input multiple output (MIMO) orthogonal... more In this paper, we present a pre-transformed (PT) multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) system, in short PT-MIMO-OFDM system. We propose two receiver structures that combine the iterative subcarrier reconstruction and iterative interference cancellation to fully exploit both the spatial and the frequency diversity of MIMO-OFDM systems. Significant performance gain can be achieved. Based on the
2005 IEEE 16th International Symposium on Personal, Indoor and Mobile Radio Communications, 2005
... hypersphere. In this paper, we present a comparative study of QRD-M and SD algorithms for MIM... more ... hypersphere. In this paper, we present a comparative study of QRD-M and SD algorithms for MIMO orthogonal frequency division multiplexing (OFDM) systems. ... SD. We will then compare the average and the worst-case implementation ...
2003 IEEE Wireless Communications and Networking, 2003. WCNC 2003., 2003
A scheme for selecting two beams in a switched beam antenna system for providing downlink transmi... more A scheme for selecting two beams in a switched beam antenna system for providing downlink transmit diversity based on space-time block coding (STBC) technique is proposed. The scheme involves selecting a pair of beams based on the uplink reception of the switched beam antenna system, and determining from the pair of beams a corresponding pair of orthogonal beams. The scheme also involves providing the pair of orthogonal beams as pair of transmit beams, the switched beam antenna system achieves nearly the same system performance, in terms of bit error rate (BER), as much complex adaptive antenna system with STBC. Simulation results demonstrate the promising scheme.
Abstract The paper proposes a downlink transmission scheme achieving both transmit diversity gain... more Abstract The paper proposes a downlink transmission scheme achieving both transmit diversity gain and beamforming gain via combining space-time block coding (STBC) with adaptive beamforming techniques. The beamforming weights of the combined system are ...
2005 IEEE 16th International Symposium on Personal, Indoor and Mobile Radio Communications, 2005
ABSTRACT A list MIMO detection scheme is proposed to achieve near optimal maximum likelihood dete... more ABSTRACT A list MIMO detection scheme is proposed to achieve near optimal maximum likelihood detection performance. The scheme is especially efficient in high data rate packet transmission systems, such as wireless LAN based hotspots, fixed broadband wireless access systems, 4G cellular based hotspots etc. The complexity of the optimal performance achieving scheme is significantly lower than that of the ML detection and the state of art technologies
Abstract---We propose a pseudo-inverse minimum mean squared error (MMSE) based QR decomposition (... more Abstract---We propose a pseudo-inverse minimum mean squared error (MMSE) based QR decomposition (QRD) M-algorithm (QRD-M) for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. The proposed algorithm can effectively mitigate ...
IEEE Journal on Selected Areas in Communications, 2015
We consider a heterogeneous cellular network with densely underlaid small cell access points (SAP... more We consider a heterogeneous cellular network with densely underlaid small cell access points (SAPs). Wireless backhaul provides the data connection from the core network to SAPs. To serve as many SAPs and their corresponding users as possible with guaranteed data rates, admission control of SAPs needs to be performed in wireless backhaul. Such a problem involves joint design of transmit beamformers, power control, and selection of SAPs. In order to tackle such a difficult problem, we apply 1 -relaxation and propose an iterative algorithm for the 1 -relaxed problem. The selection of SAPs is made based on the outputs of the iterative algorithm, and we prove such an algorithm converges locally. Furthermore, this algorithm is fast and enjoys low complexity for small-to-medium sized systems. However, its solution depends on the actual channel state information, and resuming the algorithm for each new channel realization may be unrealistic for large systems. Therefore, we make use of the random matrix theory and also propose an iterative algorithm for large systems. Such a large-system iterative algorithm can produce the asymptotically optimum solution for the 1 -relaxed problem, which only requires large-scale channel coefficients irrespective of the actual channel realization. Near optimum results are achieved by our proposed algorithms in simulations.
ABSTRACT We study the performance of a Walsh-Hadamard transformed (WHT) space-time block coded (S... more ABSTRACT We study the performance of a Walsh-Hadamard transformed (WHT) space-time block coded (STBC) OFDM system, which we refer as the WHT-STBC-OFDM system. We show that, with the WHT transform, the error performance of the STBC coded OFDM system can be improved in terms of both bit error rate (BER) and packet error rate (PER) through simple linear detection. In (L. Zhongding et al., IEEE Vehic. Tech. Conf. vol.1, p.637-640, 2003), an iterative detection scheme is proposed for a WHT-OFDM system, where significant improvement can be achieved through only linear processing. We extent the algorithm to WHT-STBC-OFDM systems and show that the BER and PER can be further reduced through iterations.
2010 IEEE Symposium on New Frontiers in Dynamic Spectrum (DySPAN), 2010
Cognitive radio is widely expected to be the next Big Bang in wireless communications. Government... more Cognitive radio is widely expected to be the next Big Bang in wireless communications. Government spectrum regulatory committees in many countries have been taking steps to open the door to dynamic spectrum access using this technology and also laying down the rules for its implementation. International organizations have also been striving for standardizing this technology for various applications. This paper overviews the state of art in the regulatory and standardization activities on cognitive radio all over the world, which are deemed to have fundamental impact on the future of wireless communications.
GLOBECOM 2009 - 2009 IEEE Global Telecommunications Conference, 2009
ABSTRACT Zero-IF architecture is a competitive alternative to the conventional super-heterodyne a... more ABSTRACT Zero-IF architecture is a competitive alternative to the conventional super-heterodyne architecture for RF-to-baseband conversion in OFDM systems. Despite its advantages of low cost and high integratability, it suffers from the I/Q imbalance that contributes amplitude and phase mismatches between in-phase and quadrature branches, resulting in signal distortion and performance degradation. In this paper, we revisit the problem in a theoretical viewpoint through a minimum distance analysis. In particular, we aim at proving that when the subcarriers are paired symmetrically to a center frequency and the maximum likelihood decoding is employed, the transmitter I/Q imbalance can provide an additional degree of diversity in frequency selective fading channels.
International Symposium on Wireless and Pervasive Computing, 2011
In a distributed MIMO system (D-MIMO), multiple base stations work in cooperation manner to enhan... more In a distributed MIMO system (D-MIMO), multiple base stations work in cooperation manner to enhance system throughput by suppressing inter-cell and inter-user interference. In this paper, we propose two practical distributed algorithms that are based on block diagonalization technique. The proposed schemes eliminate the need of iterative computations, and hence can be implemented without information exchange between multiple base stations. We also construct a suboptimal solution that requires only partial channel state information to be available at each base station. The sensitivity of system throughput versus number of users for various algorithms was demonstrated.
2010 IEEE International Conference on Communication Systems, 2010
ABSTRACT In this paper, a beacon structure is proposed for the protection of incumbent wireless m... more ABSTRACT In this paper, a beacon structure is proposed for the protection of incumbent wireless microphones in a cognitive radio system. The proposed beacon structure consists of two consecutive parts: synchronization bursts followed by payload bursts. Each part is transmitted on two orthogonal channels in parallel to shorten the required sensing windows for fast detection of the beacon. Compared to the current beacon design, the required two (long and short) sensing windows can be shortened significantly and it brings in substantial overhead reduction for the cognitive radio system. A flexible window scheduling method is proposed as well to guarantee the capture of the synchronization bursts.
... Zhongding Lei, Yan Wu, Chin Keong Ho, Sumei Sun, Ping He, and Yuan Li Institute for lnfocomm ... more ... Zhongding Lei, Yan Wu, Chin Keong Ho, Sumei Sun, Ping He, and Yuan Li Institute for lnfocomm Research 20 Science Park Road, #02-34/37 TeleTech Park, Singapore 117674 Tel: +65 68729030, Fax: +65 67795441, Email: leizd{wuyan,hock,sunsm,liyuan} @iZr.a-star.edu.sg ...
2004 IEEE 15th International Symposium on Personal, Indoor and Mobile Radio Communications (IEEE Cat. No.04TH8754), 2004
... case, even for the case when i = 0. However, since the instantaneous SNK is lower (upper) bou... more ... case, even for the case when i = 0. However, since the instantaneous SNK is lower (upper) bounded by ylow,i (yUp,,) given in (51, the instantaneous BEK can be upper ... In fact, a closed form solution can he found as shown next for L = 1 and 2 for QPSK modulated symbols. ...
21st Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, 2010
ABSTRACT In this paper, a class of quasi-orthogonal space-time block codes (Q-STBC) is proposed f... more ABSTRACT In this paper, a class of quasi-orthogonal space-time block codes (Q-STBC) is proposed for systems with 2 antennas and 3 time slots, where the orthogonal Alamouti code can not be applied due to the “odd symbol” problem inherited in the 3GPP frame structure. The proposed codes can achieve rate one and full diversity with lower complexity maximum likelihood detection. The design takes into consideration the signal power fluctuation and minimizes the potential peak-to-average ratio (PAPR) in the transmitted signals. The application to Single Carrier Frequency Division Multiple Access (SC-FDMA) has been investigated further. A transmission scheme is proposed to preserve the good PAPR property of SC-FDMA. In addition, linear and iterative decoding algorithms are proposed to simplify the receiver complexity. Simulations have been conducted to demonstrate the superior performance.
2005 IEEE 16th International Symposium on Personal, Indoor and Mobile Radio Communications, 2005
In this paper, we present a pre-transformed (PT) multiple input multiple output (MIMO) orthogonal... more In this paper, we present a pre-transformed (PT) multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) system, in short PT-MIMO-OFDM system. We propose two receiver structures that combine the iterative subcarrier reconstruction and iterative interference cancellation to fully exploit both the spatial and the frequency diversity of MIMO-OFDM systems. Significant performance gain can be achieved. Based on the
2005 IEEE 16th International Symposium on Personal, Indoor and Mobile Radio Communications, 2005
... hypersphere. In this paper, we present a comparative study of QRD-M and SD algorithms for MIM... more ... hypersphere. In this paper, we present a comparative study of QRD-M and SD algorithms for MIMO orthogonal frequency division multiplexing (OFDM) systems. ... SD. We will then compare the average and the worst-case implementation ...
2003 IEEE Wireless Communications and Networking, 2003. WCNC 2003., 2003
A scheme for selecting two beams in a switched beam antenna system for providing downlink transmi... more A scheme for selecting two beams in a switched beam antenna system for providing downlink transmit diversity based on space-time block coding (STBC) technique is proposed. The scheme involves selecting a pair of beams based on the uplink reception of the switched beam antenna system, and determining from the pair of beams a corresponding pair of orthogonal beams. The scheme also involves providing the pair of orthogonal beams as pair of transmit beams, the switched beam antenna system achieves nearly the same system performance, in terms of bit error rate (BER), as much complex adaptive antenna system with STBC. Simulation results demonstrate the promising scheme.
Abstract The paper proposes a downlink transmission scheme achieving both transmit diversity gain... more Abstract The paper proposes a downlink transmission scheme achieving both transmit diversity gain and beamforming gain via combining space-time block coding (STBC) with adaptive beamforming techniques. The beamforming weights of the combined system are ...
2005 IEEE 16th International Symposium on Personal, Indoor and Mobile Radio Communications, 2005
ABSTRACT A list MIMO detection scheme is proposed to achieve near optimal maximum likelihood dete... more ABSTRACT A list MIMO detection scheme is proposed to achieve near optimal maximum likelihood detection performance. The scheme is especially efficient in high data rate packet transmission systems, such as wireless LAN based hotspots, fixed broadband wireless access systems, 4G cellular based hotspots etc. The complexity of the optimal performance achieving scheme is significantly lower than that of the ML detection and the state of art technologies
Abstract---We propose a pseudo-inverse minimum mean squared error (MMSE) based QR decomposition (... more Abstract---We propose a pseudo-inverse minimum mean squared error (MMSE) based QR decomposition (QRD) M-algorithm (QRD-M) for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. The proposed algorithm can effectively mitigate ...
IEEE Journal on Selected Areas in Communications, 2015
We consider a heterogeneous cellular network with densely underlaid small cell access points (SAP... more We consider a heterogeneous cellular network with densely underlaid small cell access points (SAPs). Wireless backhaul provides the data connection from the core network to SAPs. To serve as many SAPs and their corresponding users as possible with guaranteed data rates, admission control of SAPs needs to be performed in wireless backhaul. Such a problem involves joint design of transmit beamformers, power control, and selection of SAPs. In order to tackle such a difficult problem, we apply 1 -relaxation and propose an iterative algorithm for the 1 -relaxed problem. The selection of SAPs is made based on the outputs of the iterative algorithm, and we prove such an algorithm converges locally. Furthermore, this algorithm is fast and enjoys low complexity for small-to-medium sized systems. However, its solution depends on the actual channel state information, and resuming the algorithm for each new channel realization may be unrealistic for large systems. Therefore, we make use of the random matrix theory and also propose an iterative algorithm for large systems. Such a large-system iterative algorithm can produce the asymptotically optimum solution for the 1 -relaxed problem, which only requires large-scale channel coefficients irrespective of the actual channel realization. Near optimum results are achieved by our proposed algorithms in simulations.
ABSTRACT We study the performance of a Walsh-Hadamard transformed (WHT) space-time block coded (S... more ABSTRACT We study the performance of a Walsh-Hadamard transformed (WHT) space-time block coded (STBC) OFDM system, which we refer as the WHT-STBC-OFDM system. We show that, with the WHT transform, the error performance of the STBC coded OFDM system can be improved in terms of both bit error rate (BER) and packet error rate (PER) through simple linear detection. In (L. Zhongding et al., IEEE Vehic. Tech. Conf. vol.1, p.637-640, 2003), an iterative detection scheme is proposed for a WHT-OFDM system, where significant improvement can be achieved through only linear processing. We extent the algorithm to WHT-STBC-OFDM systems and show that the BER and PER can be further reduced through iterations.
2010 IEEE Symposium on New Frontiers in Dynamic Spectrum (DySPAN), 2010
Cognitive radio is widely expected to be the next Big Bang in wireless communications. Government... more Cognitive radio is widely expected to be the next Big Bang in wireless communications. Government spectrum regulatory committees in many countries have been taking steps to open the door to dynamic spectrum access using this technology and also laying down the rules for its implementation. International organizations have also been striving for standardizing this technology for various applications. This paper overviews the state of art in the regulatory and standardization activities on cognitive radio all over the world, which are deemed to have fundamental impact on the future of wireless communications.
GLOBECOM 2009 - 2009 IEEE Global Telecommunications Conference, 2009
ABSTRACT Zero-IF architecture is a competitive alternative to the conventional super-heterodyne a... more ABSTRACT Zero-IF architecture is a competitive alternative to the conventional super-heterodyne architecture for RF-to-baseband conversion in OFDM systems. Despite its advantages of low cost and high integratability, it suffers from the I/Q imbalance that contributes amplitude and phase mismatches between in-phase and quadrature branches, resulting in signal distortion and performance degradation. In this paper, we revisit the problem in a theoretical viewpoint through a minimum distance analysis. In particular, we aim at proving that when the subcarriers are paired symmetrically to a center frequency and the maximum likelihood decoding is employed, the transmitter I/Q imbalance can provide an additional degree of diversity in frequency selective fading channels.
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