[show abstract][hide abstract] ABSTRACT: In this paper, we propose a novel transceiver structure for orthogonal frequency division multiple access-based uplink multiuser multiple-input multiple-output systems. The numerical results show that the proposed frequency-domain equalization schemes significantly outperform conventional linear minimum mean square error-based equalizers in terms of bit error rate performance with moderate increase in computational complexity.
Journal on Advances in Signal Processing 08/2013; 2011(1). · 0.81 Impact Factor
[show abstract][hide abstract] ABSTRACT: Several equalization algorithms utilizing the rotationally variant nature of the received signals are presented in this paper
to combat the detrimental effect of intersymbol interference (ISI) introduced by frequency selective channels. Their adaptive
implementations and application to a time-reversal space-time block coded (TR-STBC) system are also considered. In addition,
a turbo equalization algorithm is derived for systems employing the error correction code. The proposed equalizers and turbo
equalizer are evaluated over broadband fixed wireless access channels, and are shown to yield superior performance compared
to the conventional equalization schemes.
Keywordsequalization–intersymbol interference–rotationally variant nature of the received signals–frequency selective channels
Optoelectronics Instrumentation and Data Processing 05/2012; 47(3):253-263.
[show abstract][hide abstract] ABSTRACT: We address the problem of error propagation inherent in the VBLAST detection process. To this end, two improved VBLAST schemes are proposed. The first one replaces hard decision with soft decision; whereas the other also utilizes soft symbol estimate, but in the meantime exploits the noncircular nature of the residual co-antenna interference (CAI) and noise, it involves refining the error criterion and nulling filter. Simulation results show that both schemes outperform their conventional counterpart and utilization of noncircular CAI significantly alleviates the error propagation problem and improves the performance of the VBLAST detection.
IEEE Transactions on Signal Processing 06/2011; · 2.81 Impact Factor
[show abstract][hide abstract] ABSTRACT: Different detection schemes for multiple-input, multiple-output (MIMO) systems are investigated. By enhancing the interference and noise estimation, we propose a novel MIMO receiver strategy, which is shown to achieve superior performance with moderate increase in computational complexity compared to conventional MIMO detection schemes.
IEEE Transactions on Communications 02/2011; · 1.75 Impact Factor
[show abstract][hide abstract] ABSTRACT: A novel iterative detection scheme for MIMO-OFDM systems is proposed in this work. We show that the existing detection schemes are sub-optimum and the iterative process can be optimized by utilizing the non-circular property of the residual interference after interference cancellation. Results show that the proposed iterative scheme outperforms the conventional iterative soft interference cancellation (ISIC) and V-BLAST schemes by about 1.7 and 4.0 dB, respectively, in a 4 × 4 antennas system over exponentially distributed eleven path channels.
Global Telecommunications Conference (GLOBECOM 2010), 2010 IEEE; 01/2011
[show abstract][hide abstract] ABSTRACT: This paper presents an analytical investigation on the performance of optimal beamforming scheme in multiple-input multiple-output dual-hop amplify-and-forward systems. We first derive a set of new closed-form expressions for the statistical properties of the resultant channel matrix, including the cumulative distribution function and probability density function of the maximum eigenvalue, as well as their first order asymptotic expansions. These analytical expressions are then applied to derive some important performance metrics of the system, i.e., outage probability, diversity order, array gain and ergodic capacity. Numerical simulations are carried out to validate the correctness of the analytical results.
Proceedings of the IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP 2011, May 22-27, 2011, Prague Congress Center, Prague, Czech Republic; 01/2011
[show abstract][hide abstract] ABSTRACT: Time synchronization algorithms for OFDM systems using the short and long training symbols are investigated in this paper. We only consider efficient low complexity schemes that are feasible for practical implementations. Different algorithms are compared in the context of IEEE 802.11Wireless Local Area Network (WLAN) systems. Based on the simulation results, some recommendations are made as to how the short and long training symbols can be effectively utilized for synchronization purposes.
Wireless Mobile and Computing (CCWMC 2009), IET International Communication Conference on; 01/2010
[show abstract][hide abstract] ABSTRACT: Recently, few stochastic gradient algorithms have been proposed and they are based on cost functions that have exponential dependence on the chosen error. However, we have experienced that the proposed cost function based on exponential of the squared error does not converge always. In this paper we modify this cost function in order to assure the convergence and a new IE (Improved Exponentiated) stochastic gradient algorithm has been obtained. The resulting method has attractive properties in both stationary and abrupt-change situations.
International Symposium on Circuits and Systems (ISCAS 2010), May 30 - June 2, 2010, Paris, France; 01/2010
[show abstract][hide abstract] ABSTRACT: In this paper, we consider a cognitive relay assisted single-input multiple-output (SIMO) communication scenario through Rayleigh fading channel where multiple primary and secondary users wish to communicate with two different receivers in the presence of a cognitive relay. We assume that secondary users transmit simultaneously with the primary users over the same channel instead of waiting for an idle channel which is traditional for a cognitive radio. We consider both the cases when cognitive relay is present or not and derive the expressions for the mutual information received at the primary and secondary receivers. We also present the closed form expressions for the outage probabilities and complementary cumulative distribution functions (CCDFs) of mutual information received at the primary and secondary receivers in the absence of cognitive relay.
[show abstract][hide abstract] ABSTRACT: We analyze the effect of different pulse shaping filters on the orthogonal frequency division multiplexing (OFDM) based wireless local area network (LAN) systems in this paper. In particular, the performances of the square root raised cosine (RRC) pulses with different rolloff factors are evaluated and compared. This work provides some guidances on how to choose RRC pulses in practical WLAN systems, e.g., the selection of rolloff factor, truncation length, oversampling rate, quantization levels, etc.
[show abstract][hide abstract] ABSTRACT: This paper presents a novel spatial frequency domain packet scheduling and frequency domain equalization (FDE) algorithm for uplink Single Carrier (SC) Frequency Division Multiple Access (FDMA) multiuser MIMO systems. Our analysis model is confined to 3GPP uplink SC-FDMA transmission with Multi-user (MU) Spatial Division Multiplexing (SDM). The results show that the proposed MU-MIMO scheduler in conjunction with the new FDE singificantly increases the maximum achievable rate and improves the bit error rate (BER) performance for the system under consideration.
Proceedings of IEEE International Conference on Communications, ICC 2010, Cape Town, South Africa, 23-27 May 2010; 01/2010
[show abstract][hide abstract] ABSTRACT: This paper presents a method to significantly reduce the preprocessing complexity of the sphere decoder (SD) in frequency-selective channels. The method consists of calculating an approximate QR decomposition (AQRD) of the channel matrix, making use of its special Toeptliz and block-Topelitz structure in single and multiple-antenna frequency-selective channels, respectively. The AQRD obtains the QR decomposition of a small submatrix of the channel matrix and extends that result to the rest of the matrix, resulting in a considerable complexity reduction compared to the original full QR decomposition (FQRD). Simulation results show that, despite the lower complexity of the AQRD, it causes only a small bit error rate (BER) performance degradation in the SD.
Proceedings of IEEE International Conference on Communications, ICC 2010, Cape Town, South Africa, 23-27 May 2010; 01/2010
[show abstract][hide abstract] ABSTRACT: For some time there is a large interest in variable step-size methods for adaptive filtering. Recently, a few stochastic gradient algorithms have been proposed, which are based on cost functions that have exponential dependence on the chosen error. However, we have experienced that the cost function based on exponential of the squared error does not always satisfactorily converge. In this paper we modify this cost function in order to improve the convergence of exponentiated cost function and the novel ECVSS (exponentiated convex variable step-size) stochastic gradient algorithm is obtained. The proposed technique has attractive properties in both stationary and abrupt-change situations.
[show abstract][hide abstract] ABSTRACT: The average channel capacity for 3GPP LTE downlink multiuser Multiple Input Multiple Output (MIMO) systems is analyzed in this paper. A packet scheduler is used to exploit the available multiuser diversity in all the three physical domains (i.e., space, time and frequency). A mathematical model is established to derive the channel capacity of multiuser MIMO systems with the frequency domain packet scheduler (FDPS). This work provides a theoretical reference for the future version of the LTE standard and a useful source of information for the practical implementation of the LTE systems.
Proceedings of the 72nd IEEE Vehicular Technology Conference, VTC Fall 2010, 6-9 September 2010, Ottawa, Canada; 01/2010
[show abstract][hide abstract] ABSTRACT: In this paper, we address the problem of interference mitigation with data pre-processing in the 4G uplink systems, and propose to use the Grubbs/Wright algorithm to detect and remove the interference contaminated data. The Markov algorithm is also applied to correct the system errors. The pre-processed data are used for channel estimation and data detection in base stations.
[show abstract][hide abstract] ABSTRACT: In this paper, we consider a 2-hop downlink point-to-multipoint fixed relay systems and propose a novel linear processing strategy at the base station and relay station to improve the reliability of the source-relay and relay-to-destination links. When coupled with a soft-decode-and-forward protocol, the proposed scheme leads to significant performance gain compared to the conventionl solutions for fixed relay networks.
[show abstract][hide abstract] ABSTRACT: This study investigates the superposition-based cooperative transmission system. In this system, a key point is for the relay node to detect data transmitted from the source node. This issued was less considered in the existing literature as the channel is usually assumed to be flat fading and a priori known. In practice, however, the channel is not only a priori unknown but subject to frequency selective fading. Channel estimation is thus necessary. Of particular interest is the channel estimation at the relay node which imposes extra requirement for the system resources. The authors propose a novel turbo least-square channel estimator by exploring the superposition structure of the transmission data. The proposed channel estimator not only requires no pilot symbols but also has significantly better performance than the classic approach. The soft-in-soft-out minimum mean square error (MMSE) equaliser is also re-derived to match the superimposed data structure. Finally computer simulation results are shown to verify the proposed algorithm.
[show abstract][hide abstract] ABSTRACT: A spectrally efficient cooperative protocol for uplink wireless transmission in a centralised communication system is proposed, where each of the N users play the relaying and source roles simultaneously by using superposition (SP) modulation. The probability density function of the mutual information between SP-modulated transmitted and received signals of the cooperative uplink channels is derived. Using the high-signal-to-noise ratio (SNR) approximation of this density function, the outage probability formula of the system as well as its easily computable tight upper and lower bounds are obtained and these formulas are evaluated numerically. Numerical results show that the proposed strategy can achieve around 3 dB performance gain over comparable schemes. Furthermore, the multiplexing and diversity trade-off formula is derived to illustrate the optimal performance of the proposed protocol, which also confirms that the SP relaying transmission does not cause any loss of data rate. Moreover, performance characterisation in terms of ergodic and outage capacities are studied and numerical results show that the proposed scheme can achieve significantly larger outage capacity than direct transmission, which is similar to other cooperative schemes. The superiority of the proposed strategy is demonstrated by the fact that it can maintain almost the same ergodic capacity as the direct transmission, whereas the ergodic capacity of other cooperative schemes would be much worse.
IET Signal Processing 10/2009; · 0.71 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper presents the field-programmable gate array (FPGA) implementation of a variant of the Lenstra-Lenstra-Lovasz (LLL) lattice reduction (LR) algorithm, known as the Clarkson's Algorithm (CA), and its application to uncoded multiple input-multiple output (MIMO) detection. The CA provides practically the same performance as the LLL algorithm while having a considerably lower complexity, especially for MIMO systems with a large number of transmit and receive antennas. The algorithm has been implemented in real-time using a rapid prototyping methodology, greatly reducing its development time. Implementation results indicate that the variable complexity and the sequential nature of LR algorithms, like the CA, remain their main drawbacks from an implementation point of view.
Communications, 2009. ICC '09. IEEE International Conference on; 07/2009