Salam A. Zummo

Error probability of bit-interleaved coded modulation in wireless environments

The bit-interleaved coded modulation (BICM) method is efficient in mitigating multipath fading by providing time diversity. In this paper, union bounds on the bit and packet error probabilities of the BICM are derived. In the derivation, the authors assume the uniform interleaving of coded bits prior to mapping them onto the signal constellation. This results in a random distribution of the error bits in a codeword over the transmitted symbols. This distribution is evaluated, and the corresponding pairwise error probability is derived. Union bounds are functions of the distance spectrum of the channel code and the signal constellation used in the BICM system. The authors consider BICM systems operating over additive white Gaussian noise (AWGN), Rayleigh, Rician, and Nakagami fading channels. Results show that the new bounds are tight to simulation curves for different channel models. The proposed bounds are general for any coding scheme with a known distance spectrum.

A variable step-size strategy for distributed estimation over adaptive networks

A lot of work has been done recently to develop algorithms that utilize the distributed structure of an ad hoc wireless sensor network to estimate a certain parameter of interest. One such algorithm is called diffusion least-mean squares (DLMS). This algorithm estimates the parameter of interest using the cooperation between neighboring sensors within the network. The present work proposes an improvement on the DLMS algorithm by using a variable step-size LMS (VSSLMS) algorithm. In this work, first, the well-known variants of VSSLMS algorithms are compared with each other in order to select the most suitable algorithm which provides the best trade-off between performance and complexity. Second, the detailed convergence and steady-state analyses of the selected VSSLMS algorithm are performed. Finally, extensive simulations are carried out to test the robustness of the proposed algorithm under different scenarios. Moreover, the simulation results are found to corroborate the theoretical findings very well.

Outage Analysis of N^{th}-Best DF Relay Systems in the Presence of CCI over Rayleigh Fading Channels

This letter investigates the outage behavior of a dual-hop N^{th}-best decode-and-forward (DF) relay system in which the relay and the destination undergo independent sources of co-channel interference (CCI). The fading envelopes associated with the desired and interfering users are assumed to follow independent but non-identically distributed (i.n.d.) Rayleigh fading models. Through the analysis, exact and approximate outage probability are derived based on which the diversity order and coding gain are obtained. Our findings suggest that the diversity order linearly increases with the number of relays and decreases with the order of the relay. Furthermore, results reveal that the system is still able to achieve full diversity gain in the presence of finite number of interferers with finite powers. The analytical results are supported and validated by Monte-Carlo simulations.

Space-time coded QPSK for rapid fading channels

This paper presents the design of space-time codes suitable for rapid fading channels. The codes are designed using the QPSK signal constellation. The design of the proposed codes utilizes two different encoding methods. The first method uses a large time diversity trellis encoder, and the second one uses the I-Q encoding technique. Both methods are expected to produce space-time codes that perform better than the codes presented in the literature. The proposed codes were simulated over different Rayleigh fading channels. Coding gains up to 3 dB have been observed over similar codes in the literature.

A union bound on the error probability of binary codes over block-fading channels

Block-fading is a popular channel model that approximates the behavior of different wireless communication systems. In this paper, a union bound on the error probability of binary-coded systems over block-fading channels is proposed. The bound is based on uniform interleaving of the coded sequence prior to transmission over the channel. The distribution of error bits over the fading blocks is computed. For a specific distribution pattern, the pairwise error probability is derived. Block-fading channels modeled as Rician and Nakagami distributions are studied. We consider coherent receivers with perfect and imperfect channel side information (SI) as well as noncoherent receivers employing square-law combining. Throughout the paper, imperfect SI is obtained using pilot-aided estimation. A lower bound on the performance of iterative receivers that perform joint decoding and channel estimation is obtained assuming the receiver knows the correct data and uses them as pilots. From this, the tradeoff between channel diversity and channel estimation is investigated and the optimal channel memory is approximated analytically. Furthermore, the optimal energy allocation for pilot signals is found for different channel memory lengths.

Variable step-size least mean square algorithms over adaptive networks

This paper presents two new variations for algorithms over adaptive networks using a variable step-size strategy in order to enhance the overall performance. Variable step-size least mean square (VSSLMS) algorithms for incremental as well as diffusion strategies are studied and the results are compared with existing results. A comparison is done with the recently proposed Diffusion LMS algorithm with adaptive combiners and it is shown that VSSLMS provides a simplified solution than that of the Diffusion LMS algorithm with adaptive combiners. Also, a great improvement in performance is obtained when compared with the fixed step-size Incremental and Diffusion LMS techniques.

Performance Analysis of Coded Cooperation Diversity in Wireless Networks

Diversity is an effective technique in enhancing the link quality and increasing network capacity. When multiple antennas can not be used in mobile units, user cooperation can be employed to provide transmit diversity. In this paper we analyze the error performance of coded cooperation diversity with multiple cooperating users. We derive the end-to-end bit error probability of coded cooperation (averaged over all cooperation scenarios). We consider different fading distributions for the interuser channels. Furthermore, we consider the case of two cooperating users with correlated uplink channels. Results show that more cooperating users should be allowed under good interuser channel conditions, while it suffices to have two cooperating users in adverse interuser conditions. Furthermore, under bad interuser conditions, more cooperating users can be accommodated as the fading distribution becomes more random.

Spectral efficiency of maximum ratio combining (MRC) over slow fading with estimation errors

In this paper, we derive closed-form expressions for capacity statistics of the maximal ratio combining (MRC) system, taking into account the effect of imperfect channel estimation at the receiver. The channel considered is a slowly varying flat Rayleigh fading that is also spatially independent. The combiner weights are assumed to be affected by Gaussian errors at the receiver. In particular, we derive the moment generating function (MGF), complementary cumulative distribution function (CDF) and the probability density function (PDF) of the capacity. Furthermore, we derive closed-form expressions for the system capacity when employing different adaptive transmission schemes such as (1) optimal power and rate adaptation (opra); (2) constant power with optimal rate adaptation (ora); and (3) channel inversion with fixed rate (cifr). Analytical results show accurately the impact of the channel estimation error on the achievable spectral efficiency.

Performance Analysis of Wireless Networks With Directional Antennas

In this paper, we consider wireless networks with directional antennas using slotted ALOHA medium access control. The channel model incorporates the effects of propagation loss and shadowing with Rayleigh fading. By deriving the cumulative distribution function of the signal-to-interference-and-noise ratio (SINR) of a certain link in the network, the outage probability of the link is analyzed. In particular, the analysis works for the arbitrary beam patterns of the directional antennas used in the networks. Moreover, we propose a new parameter, i.e., the array interference factor, which can characterize the average performance of an arbitrary beam pattern in random wireless networks. This provides an efficient way for designers to evaluate the system performance under different beam patterns. The network throughput and the transport capacity of a random wireless network with directional antennas are also analyzed. It is shown that the network transport capacity is of the same order as the square root of the node density, which conforms with the well-known capacity of wireless networks. The analysis is useful for designers to optimize the system performance of wireless networks with directional antennas.

A low-complexity relay selection scheme based on switch-and-examine diversity combining for AF relay systems

In this study, the authours present a low-complexity relay selection scheme for channel-state information (CSI)-assisted dual-hop amplify-and-forward cooperative systems. The scheme is mainly based on the switch-and-examine diversity combining (SEC) and SEC post-selection (SECps) techniques in which a relay out of multiple relays is selected to forward the source signal to destination. The selection process is performed such that the selected relay signal-to-noise ratio (SNR) satisfies a predetermined switching threshold instead of best relay. Such a relay that satisfies this threshold will be chosen instead of the best relay. In this study, the authorsuse an upper bound on the end-to-end (e2e) SNR of the selection scheme and derive the probability density function and the cumulative distribution function of this SNR assuming the Rayleigh fading channels. These statistics are then used to derive accurate approximations for both the e2e outage probability and bit error probability, where the direct link in considered. The authours assume that maximal-ratio combining is used at the destination to combine the signals through the relay and the direct link. To obtain more about system insights, the outage performance is studied at high SNR regime, where approximate expressions for the outage probability as well as the diversity order and coding gain are derived and analysed. The Monte-Carlo simulations are provided to illustrate the validity of the analytical results and to show the tightness of the used SNR bound. Results illustrate the effectiveness of the proposed relaying schemes in reducing the required number of channel estimations and hence, reducing the system complexity compared with the opportunistic relaying. Furthermore, results show the gain achieved in the system performance; especially, at low-to-medium SNR values when the SECps selection scheme is used compared with the conventional SEC relaying. Finally, findings show that the system with the SEC and the SECps relaying schemes has the same diversity order of two and the same coding gain.