Opportunistic relaying

When traditional half-duplex (HD) radios are employed in indoor wireless mesh networks, such as home networks, interference among mesh nodes is a major impairment, as the endto-end throughput is to be shared between all transmitting nodes. Full-duplex (FD) relaying can improve the end-to-end throughput, as simultaneous transmissions and receptions, hence simultaneous links are enabled, but FD nodes are subject to self-interference(SI) in addition to inter-node interference, resulting in a more complicated, full interference scenario. In this work, a power allocation solution is proposed along with routing for enabling FD in such multi hop wireless networks subject to full interference. First, an optimization problem is formulated for maximizing the end-to-end throughput of FD relaying on a given, known path, considering the full interference model. A linear programming based solution is devised to obtain the optimal transmit power levels for FD relaying nodes on the path. Then, for joint power allocation and routing in an FD mesh network, Dijkstra's algorithm is modified by applying the proposed power allocation in the calculation of the path metrics. Via detailed numerical experiments considering different system parameters, such as network size, SI cancellation capability, maximum power level per node, it is shown that the proposed FD relaying with power control based on full interference model outperforms not only HD relaying, but also an existing FD relaying solution based on a single hop interference model. The amount of improvement by FD relaying depends on the system settings. For instance, for low power budget systems, HD throughput can be tripled, while for systems with high power budget, FD relaying achieves 80 percent higher throughput over HD relaying. When power control is combined with routing, the end-to-end throughput performance of the proposed FD routing solution again outperforms the existing solutions. Depending on the power budget, up to two times higher throughput is achieved over FD routing based on single hop interference, and HD routing can be improved by up to five times even for moderate SI cancellation levels. Our results suggest that employing proposed joint power allocation and routing scheme, migration to FD can be beneficial for home wireless mesh networks under full interference, especially for bandwidth-hungry applications, such as video streaming, gaming.

This letter analyzes the outage probability of opportunistic amplify-and-forward relaying over asymmetric and independent but non-identically distributed (i.n.d) fading environments. The work investigates the scenarios where cooperative nodes are located at different geographical locations. As a result, the different signals are affected by different i.n.d fading channels, one may undergo Rician fading distribution and others may undergo Rayleigh fading distribution. In this letter, a lower bound of the outage probability for various asymmetric fading environments is derived at high SNR by applying the initial value theorem. The analytical model is validated through Monte-Carlo simulation results.

In this thesis, performance of cooperative relaying with multi-antenna system in Rayleigh/Nakagami-m fading channels has been investigated. The relay is assumed to operate in adaptive decode and forward mode and perform threshold based decoding. Installation of multiple receiving antennas on infrastructure based fixed relay is feasible thereby increasing the probability of relay participation and hence diversity order may be increased for systems which contain such relays. Such systems in different configurations have been analyzed in various path-loss conditions, severity of fading, relay placement at different locations and antennas installed on it. It has been found that for some locations of relay placement, performance of system depends only marginally on the number of antennas installed on relay and combining schemes at relay and destination. System performance can be improved significantly by appropriately positioning the relay. For such positioning, system performance depend...

In this article, we consider the diversity-multiplexing tradeoff (DMT) of relay-assisted communication through correlated frequency selective fading channels. Recent results for relays in flat fading channels demonstrate a performance and implementation advantage in using relay selection as opposed to more complicated distributed space-time coding schemes. Motivated by these results, we explore the use of relay selection for the case when all channels have intersymbol interference. In particular, we focus on the performance of relaying strategies when multiple decode-and-forward relays share a single channel orthogonal to the source. We derive the DMT for several relaying strategies: best relay selection, random relay selection, and the case when all decoding relays participate. The best relay selection method selects the relay in the decoding set with the largest sum-squared relay-to-destination channel coefficients. This scheme can achieve the optimal DMT of the system under consideration and generally dominates the other two relaying strategies which do not always exploit the spatial diversity offered by the relays. Different from flat fading, we found special cases when the three relaying strategies have the same DMT. We further present a transceiver design which is proven to asymptotically achieve the optimal DMT. Monte Carlo simulations are presented to corroborate the theoretical analysis and to provide a detailed performance comparison of the three relaying strategies in channels encountered in practice.

In this article, we consider the diversity-multiplexing tradeoff (DMT) of relay-assisted communication through correlated frequency selective fading channels. Recent results for relays in flat fading channels demonstrate a performance and implementation advantage in using relay selection as opposed to more complicated distributed space-time coding schemes. Motivated by these results, we explore the use of relay selection for the case when all channels have intersymbol interference. In particular, we focus on the performance of relaying strategies when multiple decode-and-forward relays share a single channel orthogonal to the source. We derive the DMT for several relaying strategies: best relay selection, random relay selection, and the case when all decoding relays participate. The best relay selection method selects the relay in the decoding set with the largest sum-squared relay-to-destination channel coefficients. This scheme can achieve the optimal DMT of the system under consideration and generally dominates the other two relaying strategies which do not always exploit the spatial diversity offered by the relays. Different from flat fading, we found special cases when the three relaying strategies have the same DMT. We further present a transceiver design which is proven to asymptotically achieve the optimal DMT. Monte Carlo simulations are presented to corroborate the theoretical analysis and to provide a detailed performance comparison of the three relaying strategies in channels encountered in practice.

In this paper, we consider the analysis of cooperative relay-based amplify-and-forward system in terms of Shannon capacity, probability of error, and outage probability over fading channels. The relay gain is optimized with the objective of maximizing the received signal-to-noiseratio (SNR) at the destination, given that the fading statistics of the links in the cooperative system are known at the relay node. The Gaussian finite mixture is utilized to mathematically formulate, in a simple and unified way, the statistics of the received SNR at optimal power gain. These statistics include the probability density function (pdf), the cumulative distribution function (CDF), the moment generating function (MGF), and the amount of fading (AoF). Using this technique, the symbol error probability (SEP) for coherent and differentially coherent modulations are derived. Analytical expressions for Shannon capacity and the outage capacity are also derived. Monte Carlo simulation results are presented to validate the derived approximate expressions.

In the paper, new and easy-to-compute closedform expressions for average symbol error probability of digital M -ary chirp communication system impaired by additive white Gaussian noise and fading are derived. Three fading environments, Rayleigh, Nakagami-m, and generalized-K, that represent most practical wireless channels are considered. The closed-form expressions derived are then used to illustrate the performances of 2-,4-, and 8-ary chirp systems as a function of average received signal-to-noise ratio (SNR), modulation and fading environment parameters. The proposed mathematical analysis can be easily used to design an efficient and reliable M -ary chirp communication system for application over fading channels.

In this paper, we analyze the performance of cooperative diversity using adaptive Decode and Forward (DF) relaying over independent but non-necessarily identical flat composite fading channels which include multipath fading and shadowing simultaneously. We have considered the transmission of M-QAM modulated signals over Generalized-K channel model which is very versatile and accurately approximates many of the commonly used channel models as Nakagami-m, Log-Normal distributions and the mixture of the two distributions for the composite fading. Using an approximation of the Generalized-K pdf by a Gamma pdf, we derive analytical expressions for the outage probability and the Average Symbol Error Probability (ASEP) of the proposed scenario and analyze their dependence on the channel parameters. We assume in our context that the relay decides independently whether or not to forward the signal to the destination based on the received signal quality. Simulations are provided for 16-QAM modulation for both the outage and the ASEP. The obtained results are discussed and proved to be in good agreement with our theoretical analysis.

In deterministic networks where relay nodes are stationary, combined relay selection is an efficient relay selection scheme, which is capable of achieving the near-optimal outage performance with much lower system complexity. However, the efficiency of combined relay selection is only validated upon fixed topological settings. To investigate the performance of combined relay selection in spatially random networks (SRNs), we employ the Poisson point process to model the dynamical nature of cooperative networks and study the outage performance of the proposed system. It is surprising that the equivalence principle of combined relay selection appearing in deterministic networks does not hold in SRNs.

The success of fifth generation (5G) mobile network and its long-term evolution (LTE) relies on enabling demanding services with massive connectivity requirements, including Internet of Things (IoT) nodes, mobile devices, or unmanned aerial vehicles (UAVs). Towards this end, non-orthogonal multiple access (NOMA) schemes allow multiple users and devices to communicate using the same temporal and spectral resources. In this context, buffer-aided (BA) relay selection can significantly enhance the quality and reliability of communication, through increased diversity. So, in this paper, we employ BA relay selection in the uplink of the NOMA networks where users and devices coexist and demand access to the wireless resources. The presented relay selection policy, namely flex − NOMA, facilitates simultaneous transmissions from multiple sources to multiple relays, exploiting channel state information at the reception, and dynamic decoding ordering by the relays performing successive interference cancellation (SIC). The theoretical analysis and performance evaluation results are provided and comparisons, in terms of outage probability, average sum-rate and average delay show that flex − NOMA offers improved performance without incurring high complexity and coordination overheads.

A salient feature of millimeter-wave (mmW) wireless systems is their large bandwidths. A direct consequence is that radio frequency (RF) non-idealities, such as phase noise, I-Q imbalance, and non-ideal frequency response of bandpass filters, become more pronounced compared to existing systems operating below 6 GHz. However, investigations of the impact of such nonidealities and techniques for their compensation are limited. In this paper, the problem of I-Q mismatch is investigated, motivated by the authors' recent work on mmW prototype design and development. First, a model for the non-ideal system is developed by modeling the in-phase (I) and quadrature (Q) passband channels separately, rather than the common complex baseband representation. The resulting channel matrix reveals the structure of interference introduced across I-Q channels and frequencies. Second, a new approach is developed for estimating the non-ideal channel using the new model. Third, a linear receiver architecture is developed to compensate for the interference caused by the I-Q mismatch. Finally, the performance of the new proposed system is compared to a baseline conventional system which ignores I-Q mismatch. The results indicate significant loss in performance even for modest values of I-Q mismatch parameters. In particular, the baseline system exhibits a saturation of output signal-to-interference-and-noise ratio (SINR) regardless of the input SNR. The new proposed system does not suffer from such saturation and its SINR can be increased indefinitely by increasing the input SNR. The analytical results are validated with experimental evaluation on a 28 GHz mmW wireless testbed.

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In this paper, an incremental selective decode-andforward (ISDF) relay strategy is proposed for power line communication (PLC) systems to improve the spectral efficiency. Traditional decode-and-forward (DF) relaying employs two time slots by using half-duplex relays which significantly reduces the spectral efficiency. The ISDF strategy utilizes the relay only if the direct link quality fails to attain a certain information rate, thereby improving the spectral efficiency. The path gain is assumed to be log-normally distributed with very high distance dependent signal attenuation. Furthermore, the additive noise is modeled as a Bernoulli-Gaussian process to incorporate the effects of impulsive noise contents. Closed-form expressions for the outage probability and the fraction of times the relay is in use, and an approximate closed-form expression for the average bit error rate (BER) are derived for the binary phase-shift keying signaling scheme. We observe that the fraction of times the relay is in use can be significantly reduced compared to the traditional DF strategy. It is also observed that at high transmit power, the spectral efficiency increases while the average BER decreases with increase in the required rate.

This paper derives an optimum relay position of amplify-and-forward (AF) cooperative communications with the differential transmission. As a performance benchmark, we utilize the probability of outage, which is defined as a probability that the instantaneous signal-tonoise power ratio (SNR) becomes lower than a certain threshold. The optimum relay position is found based on the theoretical expression of the outage probability, Computer simulations are also conducted to verify the validity of the theoretical analysis.

A salient feature of millimeter-wave (mmW) wireless systems is their large bandwidths. A direct consequence is that radio frequency (RF) non-idealities, such as phase noise, I-Q imbalance, and non-ideal frequency response of bandpass filters, become more pronounced compared to existing systems operating below 6 GHz. However, investigations of the impact of such nonidealities and techniques for their compensation are limited. In this paper, the problem of I-Q mismatch is investigated, motivated by the authors' recent work on mmW prototype design and development. First, a model for the non-ideal system is developed by modeling the in-phase (I) and quadrature (Q) passband channels separately, rather than the common complex baseband representation. The resulting channel matrix reveals the structure of interference introduced across I-Q channels and frequencies. Second, a new approach is developed for estimating the non-ideal channel using the new model. Third, a linear receiver architecture is developed to compensate for the interference caused by the I-Q mismatch. Finally, the performance of the new proposed system is compared to a baseline conventional system which ignores I-Q mismatch. The results indicate significant loss in performance even for modest values of I-Q mismatch parameters. In particular, the baseline system exhibits a saturation of output signal-to-interference-and-noise ratio (SINR) regardless of the input SNR. The new proposed system does not suffer from such saturation and its SINR can be increased indefinitely by increasing the input SNR. The analytical results are validated with experimental evaluation on a 28 GHz mmW wireless testbed.

In this paper, an incremental selective decode-andforward (ISDF) relay strategy is proposed for power line communication (PLC) systems to improve the spectral efficiency. Traditional decode-and-forward (DF) relaying employs two time slots by using half-duplex relays which significantly reduces the spectral efficiency. The ISDF strategy utilizes the relay only if the direct link quality fails to attain a certain information rate, thereby improving the spectral efficiency. The path gain is assumed to be log-normally distributed with very high distance dependent signal attenuation. Furthermore, the additive noise is modeled as a Bernoulli-Gaussian process to incorporate the effects of impulsive noise contents. Closed-form expressions for the outage probability and the fraction of times the relay is in use, and an approximate closed-form expression for the average bit error rate (BER) are derived for the binary phase-shift keying signaling scheme. We observe that the fraction of times the relay is in use can be significantly reduced compared to the traditional DF strategy. It is also observed that at high transmit power, the spectral efficiency increases while the average BER decreases with increase in the required rate.

The brief bit error rate (BER) analysis of dual-hop amplify-and-forward relaying systems in the extended generalized K fading environment is presented in this paper. Assuming N nonidentical dual hops together with direct link between transmitter and receiver and maximal-ratio combining at the destination, the novel lower bound BER analytical expression is derived. The presented results illustrate that the BER lower bound is relatively tight to the obtained numerical integration and Monte Carlo simulation results. In some special cases, new derived expression is simplified to the ones previously reported in literature. This expression is utilized for determining the effects of fading and shadowing phenomena, as well as the number of relays on BER performance and can be used in designing contemporary mobile systems.

Spectrum scarcity is a critical problem that may reduce the effectiveness of wireless technologies and services. To address this problem, different spectrum management techniques have been proposed in the literature such as overlay cognitive radio (CR) where the unlicensed users can share the same spectrum with the licensed users. The main challenges in overlay CR networks are the identification and detection of the Primary User (PU) signals in a multi-source narrow-band interference (NBI) scenario. Therefore, in this paper, we investigate the performance of an orthogonal frequency division multiplexing (OFDM) overlay CR network with Secondary Users (SUs) and subcarriers selection schemes. Three approaches for SUs and subcarriers Selection named Direct, Distributed and Incremental selection techniques are proposed in this paper to increase the expected signal to interference and noise ratio based on full or partial knowledge of the channel state information (CSI). We also show that Distributed selection techniques provide all the SUs equal chances to be selected without affecting the selection diversity gain. General as well as simplified outage probability expressions are derived and extensive simulations are conducted to evaluate the performance of the proposed techniques and support the theoretical derivations. To accommodate more SUs, a new approach for asynchronous NBI estimation and mitigation in CR networks is investigated. Without any prior knowledge of the NBI characteristics and based on sparse signal recovery theory, the proposed approach allows the PU to exploit the sparsity of the SUs interference to recover it and approach the interference-free limit over practical ranges of NBI power levels.

To date the majority of research in the area of cooperative communications focuses on maximizing throughput and reliability while assuming perfect channel state information (CSI) and synchronization. This thesis, seeks to address performance enhancement and system parameter estimation in cooperative networks while relaxing these idealized assumptions. In Chapter 3 the thesis mainly focuses on training-based channel estimation in multi-relay cooperative networks. Channel estimators that are capable of determining the overall channel gains from source to destination antennas are derived. Next, a new low feedback and low complexity scheme is proposed that allows for the coherent combining of signals from multiple relays. Numerical and simulation results show that the combination of the proposed channel estimators and optimization algorithm result in significant performance gains. As communication systems are greatly affected by synchronization parameters, in Chapter 4 the thesis quantitatively analyzes the effects of timing and frequency offset on the performance of communications systems. The modified Cramer-Rao lower bound (MCRLB) undergoing functional transformation, is derived and applied to determine lower bounds on the estimation of signal pulse amplitude and signal-to-noise ratio (SNR) due to timing offset and frequency offset, respectively. i I have had the honor and pleasure of working with Dr. Steven D. Blostein throughout my Masters and Ph.D. years at Queen's University. Through Dr. Blostein's help and guidance, we have been able to address many challenging topics in the area of wireless communications and advance the research in this discipline. I would like to thank Dr. Blostein for not just being a supervisor but also for being a great mentor and friend through the ups and downs of this challenging but rewarding program. I look forward to continuing my collaboration with him after the completion of my Ph.D. degree. I would also like thank my beloved fiance, Sonia Perizzolo for being by my side throughout the years. My parents, Fatemeh and GolAli for supportingly me unequivocally. Without their help and support I would have never made it this far. My Sister, Hoda for always cheering me up with her beautiful smile from a very young age. I want to thank you all from the bottom of my heart. To all my friends here in Kingston and British Colombia (BC), who have made the past five years a blast. I would like to specially thank Chris Mitchell, and my

The exact closed-form expression for the outage probability (OP) of cognitive radio dual-hop amplify-and-forward (AF) relay networks is derived. The tractable expression of the OP, given in the form of elementary functions, readily enables evaluating the effect of primary users on the secondary system performance. It has been shown that the use of AF relaying significantly improves the performance of cognitive radio networks compared to its direct transmission counterpart.

We perform error probability analysis of the uncoded OFDM fixed gain Amplify-and-Forward (AF) relaying system with subcarrier permutation (SCP). Two SCP schemes, named: the best-to-best SCP (BTB SCP) and the best-to-worst SCP (BTW SCP) are considered. Closedform expressions for the bit error rate (BER) of the above SCP methods are derived. Numerical results manifest that these SCP schemes may outperform one another, depending on the average channel conditions of the links involved. That is, BTB SCP is better at low signal-to-noise ratio (SNR) values, while BTW SCP prevails in the medium and high SNR regime. Thus, it could be concluded that OFDM AF relaying systems may switch from the BTB SCP to BTW SCP in order to achieve optimum BER performance. Moreover, using the derived end-to-end SNR probability density functions (PDF), tight upper bounds for the ergodic capacities of both SCP schemes are obtained.