Cooperative Diversity in CDMA over Nakagami−m Fading Channels

Spatial diversity can be employed by sending copies of the transmitted signal using multiple antennas at the transmitter/receiver, as implemented in multiple-input multipleoutput (MIMO) systems. Spatial receive diversity has already been used in many applications with centralized systems where base station receivers are equipped with multiple antennas. However, due to the power constraints and the small size of the mobile terminal, it may not be feasible to deploy multiple transmit antennas. User cooperation diversity, a new form of space diversity, has been developed to address these limitations. Recently, user cooperative diversity has gained more attention as a less complex alternative to centralized MIMO wireless systems. It revealed the ability to improve wireless communications through reliable reception. One common network of the user cooperation diversity is the direct sequence code division multiple access (DS-CDMA) in which the Rayleigh fading channels are adopted and the orthogonality between users is assumed. The Rayleigh fading channels are unrealistic since they cannot represent the statistical characteristics of the complex indoor environments. On the other hand, Nakagami-m fading model is well known as a generalized distribution, where many fading environments can be modeled. It can be used to model fading conditions ranging from severe, light to no fading, by changing its fading parameter m. The bit-error-rate (BER) and outage probability of uplink cooperative DS-CDMA over Nakagami-m has not been addressed in the literature. Thus, in this thesis, the performance of both decode-and-forward (DF) and amplify-and-forward (AF) cooperative asynchronous DS-CDMA system over Nakagami-m fading channels is investigated. The Rake receiver is used to exploit the advantages of multipath propagation. Besides, multiuser detection (MUD) is used to mitigate the effect of multiple-access interference (MAI). We show that our proposed multi-user system achieves the full system diversity gain. The first part of the thesis introduces a new closed-form expression for the outage probability and the error probability of the DF cooperative DS-CDMA over asynchronous transmission over independent non-identical Nakagami-m fading channels. The underlying system employs MUD such as minimum mean square error (MMSE) and decorrelator detector (DD) to achieve the full diversity. The aforementioned closed-form expression is obtained through the moment generating function (MGF) for the total signal-to-noise ratio (SNR) at the base station where the cumulative density function (CDF) is obtained. Furthermore, we investigate the asymptotic behavior of the system at high SNR to calculate the achievable diversity gain. The results demonstrate that the system diversity gain is fulfilled when MUD is used to mitigate the effect of MAI. In the second part of the thesis, we study the performance of cooperative CDMA system using AF relaying over independent non-identical distribution (i.n.i) Nakagami-m fading channels. Using the MGF of the total SNR at the base station, we derive the outage probability of the system. This enables us to derive the asymptotic outage probability for any arbitrary value of the fading parameter m. The last part of the thesis investigates the optimum power allocation and optimum relay location in AF cooperative CDMA systems over i.n.i Nakagami-m fading channels. Moreover, we introduce the joint optimization of both power allocation and relay location under the transmit power constraint to minimize the outage probability of the system. The joint optimization of both power allocation and relay location is used to minimize the outage performance of the system, thereby achieving full diversity gain

Efficiency of two decoders based on hash techniques and syndrome calculation over a Rayleigh channel

The explosive growth of connected devices demands high quality and reliability in data transmission and storage. Error correction codes (ECCs) contribute to this in ways that are not very apparent to the end user, yet indispensable and effective at the most basic level of transmission. This paper presents an investigation of the performance and analysis of two decoders that are based on hash techniques and syndrome calculation over a Rayleigh channel. These decoders under study consist of two main features: a reduced complexity compared to other competitors and good error correction performance over an additive white gaussian noise (AWGN) channel. When applied to decode some linear block codes such as Bose, Ray-Chaudhuri, and Hocquenghem (BCH) and quadratic residue (QR) codes over a Rayleigh channel, the experiment and comparison results of these decoders have shown their efficiency in terms of guaranteed performance measured in bit error rate (BER). For example, the coding gain obtained by syndrome decoding and hash techniques (SDHT) when it is applied to decode BCH (31, 11, 11) equals 34.5 dB, i.e., a reduction rate of 75% compared to the case where the exchange is carried out without coding and decoding process

Advanced index modulation techniques for future wireless networks

In the research study proposed in this Ph.D Thesis, we consider Index Modulation as a novel tool to enhance energy and spectral efficiencies for upcoming 5G networks, including wireless sensor networks and internet of things. In this vein, spatial modulation was proposed to enhance the capacity of wireless systems to partially achieve the capacity of MIMO systems but at lower cost, making it a technique that has attracted significant attention over the past few years. As such, SM schemes have been regarded as possible candidates for spectrum- and energy-efficient next generation MIMO systems. However, the implementation of the SM is also challenging because of its heavy dependence on channel characteristics, channel correlation, corrupted CSI and the need to have adequate spacing between antennas. Moreover, the SM requires multiple antennas at the transmitter which adds cost to the hardware implementation. In addition, the number of mapped bits in SM is limited by the physical size of the wireless device where only small number of antennas can be used. The switching time wasted by RF antenna switches adds to the complexity of the issue. In this Thesis, we study the drawbacks of SM in the articles indicated, namely Performance Comparison of Spatial Modulation Detectors Under Channel Impairments that is placed in the Appendix at the end of Thesis as it is a conference paper, and The Impact of Antenna Switching Time on Spatial Modulation that is put in Chapter 1. In the first article, we have shown that channel impairments have serious impacts on the BER performance and on the capacity of the SM system and that the SM is too sensitive to both imperfect and correlated channels. In the second article, we have demonstrated that the switching time defined as the time needed by the system to turn off an antenna and turn on another one, which is an inherent property of RF industrial switches used in SM systems, is in the order of nanoseconds and naturally influences the transmission rate of SM systems because of introducing systematic transmission gaps or pauses. Given the speed limitation of practical RF switches in performing transitions, antenna transition-based technologies like SM schemes are capped in terms of data rate performance. In fact, the effective data rate of SM will remain hostage to developments in industrial RF switches. This brings restrictions to the implementation and operation issues when extremely high data rates become a necessity. It is shown by the assemblage of our results that the switching time Tsw which is a requirement for transitions between antennas to happen, dictates restrictions on data rate, capacity and spectral efficiency of SM systems. Furthermore, we propose baseband non-hardware-based indexing modulation schemes based on frequency-index modulation, coherent chaotic modulation and non-coherent differential chaotic modulation schemes as potential alternatives to SM, that would also fit wireless sensor networks and internet of things applications. In this regard, we have proposed three articles. The first article which represents frequency index modulation is called Frequency Index Modulation for Low Complexity Low Energy Communication Networks and is placed in Chapter 2 of this Thesis. In this article, we explore a low complexity multi-user communication system based on frequency index modulation that suits Internet of Things (IoT) applications and we show that such a system would constitute an excellent candidate for wireless sensor applications, where it represents a simpler substitution for frequency-hopping (FH) based architectures, in which the hops carry extra bits. The third article which concerns coherent chaotic modulation is called Design of an Initial-Condition Index Chaos Shift Keying Modulation and is located in Chapter 3. In this article, an initial condition index chaos shift keying modulation is proposed. This design aims to increase the spectral and energy efficiencies to unprecedented levels. The proposed scheme exploits the initial conditions to generate different chaotic sequences to convey extra bits per transmission. In comparison to rival modulation schemes, the results obtained in the proposed work show a promising data rate boost and a competitive performance. The last article employs a non-coherent differential chaotic shift-key system named Permutation Index DCSK Modulation Technique for Secure Multi-User High-Data-Rate Communication Systems that is found in the Appendix. In this original design, where each data frame is divided into two time slots in which the reference chaotic signal is sent in the first time slot and a permuted replica of the reference signal multiplied by the modulating bit is sent in the second time slot, we target enhancing data security, energy and spectral efficiencies. Overall, in light of the high demands for bandwidth and energy efficiencies of futuristic systems, the suggested soft indexing mechanisms are successful candidates with promising results

Wireless networks physical layer security : modeling and performance characterization

Intrigued by the rapid growth and expand of wireless devices, data security is increasingly playing a significant role in our daily transactions and interactions with different entities. Possible examples, including e-healthcare information and online shopping, are becoming vulnerable due to the intrinsic nature of wireless transmission medium and the widespread open access of wireless links. Traditionally, the communication security is mainly regarded as the tasks at the upper layers of layered protocol stack, security techniques, including personal access control, password protection, and end-to-end encryption, have been widely studied in the open literature. More recently, plenty of research interests have been drawn to the physical layer forms of secrecy. As a new but appealing paradigm at physical layer, physical layer security is based on two pioneering works: (i) Shannon’s information-theoretic formulation and (ii) Wyner’s wiretap formulation. On account of the fundamental of physical layer security and the different nature of various wireless network, this dissertation is supposed to further fill the lacking of the existing research outcomes. To be specific, the contributions of this dissertation can be summarized as three-fold:(i) exploration of secrecy metrics to more general fading channels; (ii) characterization a new fading channel model and its reliability and security analysis in digital communication systems; and (iii) investigation of physical layer security over the random multiple-input multiple-output (MIMO) α −μ fading channels. Taking into account the classic Alice-Bob-Eve wiretap model, the first contribution can be divided into four aspects: (i) we have investigated the secrecy performance over single-input single-output (SISO) α −μ fading channels. The probability of non-zero (PNZ) secrecy capacity and the lower bound of secrecy outage probability (SOP) are derived for the special case when the main channel and wiretap channel undergo the same non-linearity fading parameter, i.e., α. Later on, for the purpose of filling the gap of lacking closed-form expression of SOP in the open literature and extending the obtained results in chapter 2 to the single-input multiple-output (SIMO) α − μ wiretap fading channels, utilizing the fact that the received signal-tonoise ratios (SNRs) at the legitimate receiver and eavesdropper can be approximated as new α −μ distributed random variables (RVs), the SOP metric is therefore derived, and given in terms of the bivariate Fox’s H-function; (ii) the secrecy performance over the Fisher-Snedecor F wiretap fading channels is initially considered. The SOP, PNZ, and ASC are finalized in terms of Meijer’s G-function; (iii) in order to generalize the obtained results over α −μ and Fisher-Snedecor F wiretap fading channels, a more flexible and general fading channel, i.e., Fox’s H-function fading model, are taken into consideration. Both the exact and asymptotic analysis of SOP, PNZ, and average secrecy capacity (ASC), are developed with closed-form expressions; and (iv) finally, motivated by the fact that the mixture gamma (MG) distribution is an appealing tool, which can be used to model the received instantaneous SNRs over wireless fading channels, the secrecy metrics over wiretap fading channels are derived based on the MG approach. Due to the limited transmission power and communication range, cooperative relays or multi-hop wireless networks are usually regarded as two promising means to address these concerns. Inspired by the obtained results in Chapters 2 and 3, the second main contribution is to propose a novel but simple fading channel model, namely, the cascaded α −μ. This new distribution is advantageous since it encompasses the existing cascaded Rayleigh, cascaded Nakagami-m, and cascaded Weibull with ease. Based on this, both the reliability and secrecy performance of a digital system over cascaded α −μ fading channels are further evaluated. Closed-form expressions of reliability metrics (including amount of fading (AF), outage probability, average channel capacity, and average symbol error probability (ABEP).) and secrecy metrics (including SOP, PNZ, and ASC) are respectively provided. Besides, their asymptotic behaviors are also performed and compared with the exact results. Considering the impacts of users’ densities, spatial distribution, and the path-loss exponent on secrecy issue, the third aspect of this thesis is detailed in Chapter 8 as the secrecy investigation of stochastic MIMO system over α −μ wiretap fading channels. Both the stochastic geometry and conventional space-time transmission (STT) scheme are used in the system configuration. The secrecy issue is mathematically evaluated by three metrics, i.e., connection outage, the probability of non-zero secrecy capacity and the ergodic secrecy capacity. Those three metrics are later on derived regarding two ordering scheme, and further compared with Monte-Carlo simulations

Journal of Telecommunications and Information Technology

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