Search

This paper proposes two detection schemes for cooperative networks comprising a source, a relay and a destination. The relay is assumed to operate in a half-duplex mode and it employs decode-and-forward (DF) relaying. The proposed schemes involve combining threshold-based relaying and maximum likelihood (ML) detection at the destination. We consider both signal-to-noise ratio (SNR)-based and log-likelihood (LLR)-based thresholding. Assuming binary phase shift keying (BPSK), we first derive the ML detector as a function of the threshold used at the relay node. Then, we obtain the optimal thresholds by minimizing the end-to-end bit error rate performance. In deriving the ML performance, we follow an approach that is different from existing approaches and is more straightforward. We compare the performance of the proposed schemes and show that they significantly outperform all existing counterpart detection methods. Qatar Foundation; Qatar National Research Fund Scopus

In this paper, we propose a joint carrier frequency offset (CFO) and channel estimation method for the uplink channel of orthogonal frequency division multiple access (OFDMA) systems. The proposed method includes two steps. In the first step, the variable projection (VP) method based on the least squares (LS) criterion is used for CFO estimation. In each iteration of the VP method, the CFOs and channel coefficients are updated separately, which distinguishes the VP method from an existing non-separated minimum mean square error (MMSE) method in which the CFOs and channel coefficients are treated together as a whole. In the second step, the channel is estimated by employing the robust MMSE method. The simulation results show that, compared with the non-separated MMSE method, the proposed method has faster convergence rate in terms of CFO estimation and achieves better channel estimation performance in most of the cases. The computational complexity of the proposed scheme is also lower than that of the non-separated MMSE method for large number of users at high signal-to-noise ratios.

This paper proposes two blind carrier frequency offset (CFO) estimation schemes for differentially modulated orthogonal frequency division multiplexing (OFDM) systems. The proposed schemes estimate the fractional part of the CFO with only two consecutive OFDM blocks, and they exploit two implicit properties associated with differentially modulated OFDM (DOFDM) systems, i.e., the channel keeps constant over two consecutive OFDM blocks, and the DOFDM systems employ an M-ary phase-shift keying constellation. One of the schemes is based on the finite alphabet (FA) constraint and the other one is based on the constant modulus (CM) constraint. They provide a trade-off between the performance and computational complexity. Furthermore, the FA based scheme can achieve better performance at high signal-to-noise ratios at the expense of some additional computational complexity as compared to the existing CM based subspace scheme. The constrained Cramer-Rao lower bound is also derived. Several numerical examples are presented to validate the efficacy of the proposed schemes.

This paper presents a new blind carrier frequency offset (CFO) estimation scheme for orthogonal frequency division multiplexing (OFDM) systems with constant modulus (CM) signaling. Both single-input single-output (SISO) systems and multiple-input multiple-output (MIMO) systems with orthogonal space-time block coding are considered. The proposed scheme is based on the reasonable assumption that the channel frequency response changes slowly in the frequency domain, which implies that the channel frequency response on two consecutive sub- carriers is approximately the same. Based on this assumption, cost functions are derived in closed-form, which minimize the difference between the signal power of two neighboring subcarriers. The identifiability of the proposed scheme is mathematically proved, which implies that minimizing the derived cost function gives an approximate estimate of the CFO. We demonstrate that the proposed scheme provides an excellent trade-off between complexity and performance as compared to prominent existing estimation schemes.

In this paper, we develop the theory for constructing linear and additive cyclic codes of odd length over GF(4) that are suitable for DNA computing. We call this class of codes reversible complement cyclic codes. We use this theory to study all such codes of lengths 7, 9, 11 and 13. We list the codes that have the largest number of codewords for a given minimum Hamming distance. We show that some of these codes have more codewords than previously known codes with the same minimum Hamming distance.

This paper studies the performance of the concatenation of an outer channel code with an orthogonal space-time block code (STBC), where the outer code can be a convolutional code (CC) or a trellis-coded modulation (TCM) code. In particular, upper bounds on the bit error rate (BER) for this concatenation scheme with receive antenna selection are derived. In the analysis, the authors assume that 1) the receiver uses only L out of the available M receive antennas, where, typically, LlesM; 2) the selected antennas are those that maximize the instantaneous received signal-to-noise ratio (SNR); 3) the channel state information is perfectly known at the receiver; 4) the underlying channel is fully interleaved; and 5) the underlying orthogonal STBC is full rate. An explicit upper bound on the BER for the above concatenation scheme for any N, M, and L is derived, where N denotes the number of transmit antennas. It has been shown that the diversity order with antenna selection is the same as that of the full-complexity system, whereas the deterioration in SNR is upper bounded by 10log10(M/L) dB. The authors also derive a tighter upper bound on the BER for the Alamouti scheme when the receiver uses the best antenna, i.e., L=1. These upper bounds can be extended in a straightforward manner to other types of outer codes and fading channels, including fast, block, and slow fading channels. Finally, simulation results that validate the analysis are derived

In this correspondence, we present a comprehensive performance analysis of orthogonal space-time block codes (STBCs) with receive antenna selection. For a given number of receive antennas M, we assume that the receiver uses the best L of the available M antennas, where, typically, L/spl les/M. The selected antennas are those that maximize the instantaneous received signal-to-noise ratio (SNR). We derive explicit upper bounds on the bit-error rate (BER) performance of the above system for any M and L, and for any number of transmit antennas. We show that the diversity order, with antenna selection, is maintained as that of the full complexity system, whereas the deterioration in SNR is upper-bounded by 10log/sub 10/(M/L) decibels. Furthermore, we derive a tighter upper bound for the BER performance for any N and M when L=1, and derive an expression for the exact BER performance for the Alamouti scheme when L=1. We also present simulation results that validate our analysis.

In this paper, we address the problem of joint optimal threshold-based relaying and maximum likelihood (ML) detection in network-coded cooperative systems. The purpose of using threshold-based relaying is to circumvent the impact of error propagation, which could lead to degrading the system diversity. For simplicity, we consider a simple network comprising two source nodes and one relay node. The relay operates in the decode-and-forward (DF) mode and employs binary network coding. The communication between the two source nodes is bidirectional, resulting in a two-way relay channel. We assume binary phase shift keying (BPSK) signaling. For a given log-likelihood ratio (LLR)-based threshold used at the relay, we derive the ML detector at the destination assuming that the destination has full knowledge of the locations of the blocked bits at the relay. We then derive an expression for the corresponding end-to-end (E2E) bit error rate (BER) performance, which is used to find the optimal threshold. We also derive two practical discontinuous transmission detectors at the destination for the purpose of identifying whether the relay is forwarding or not. The performance of one of the detectors is similar to that when the destination knows the locations of the blocked bits, whereas the performance of the other detector suffers some performance degradation. We present several numerical examples that illustrate the efficacy of the proposed scheme as compared to existing schemes. Qatar Foundation; Qatar National Research Fund Scopus

In this paper, we study a special class of nonbinary additive cyclic codes over GF(4) which we call reversible complement cyclic codes. Such codes are suitable for constructing codewords for DNA computing. We develop the theory behind constructing the set of generator polynomials for these codes. We study, as an example, all length—7 codes over GF(4) and list those that have the largest minimum Hamming distance and largest number of codewords.

In this paper, we present a comprehensive performance analysis of combined convolutional coding and space-time block coding with receive antenna selection. In our analysis we assume that the receiver uses only L out of the available M receive antennas, where, typically, L /spl les/ M. The selected antennas are those that maximize the instantaneous received signal-to-noise ratio (SNR). We derive explicit upper bounds on the bit error rate (BER) performance of the above concatenation scheme for any N, M and L, where N denotes the number of transmit antennas. We show that the diversity order, with antenna selection, is maintained as the same as that of the full complexity system, whereas the deterioration in SNR is upper bounded by 10log/sub 10/(M/L) dB. We also derive two tighter upper bound on the BER for generalized orthogonal STBC and the Alamouti scheme when L = 1. Finally, we present simulation results that validate our analysis.

In this paper we derive upper bounds on the bit error rate (BER) performance of orthogonal space-time block codes (STBC) with receive antenna selection. In our analysis, we assume that the receiver uses only L out of the available M receive antennas, where, typically, L /spl les/ M. The selected antennas are those that maximize the instantaneous received signal-to-noise ratio (SNR). We show that the diversity order with antenna selection is maintained as that of the full complexity system, whereas the deterioration in SNR is upper bounded by 10log/sub 10/(M/L) dB. Furthermore, we derive an expression for the exact BER performance for the Alamouti (1998) scheme when L = 1. Finally, we present simulation results that validate our analysis.