Master of Philosophy / Wireless technology is experiencing spectacular developments, due to the emergence of interactive and digital multimedia applications as well as rapid advances in the highly integrated systems. For the next-generation mobile communication systems, one can expect wireless connectivity between any devices at any time and anywhere with a range of multimedia contents. A key requirement in such systems is the availability of high-speed and robust communication links. Unfortunately, communications over wireless channels inherently suffer from a number of fundamental physical limitations, such as multipath fading, scarce radio spectrum, and limited battery power supply for mobile devices. Cooperative diversity (CD) technology is a promising solution for future wireless communication systems to achieve broader coverage and to mitigate wireless channels’ impairments without the need to use high power at the transmitter. In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version message to an intended destination node. The destination node combines the signal received from the relays, and takes into account the source’s original signal to decode the message. The CD communication systems exploit two fundamental features of the wireless medium: its broadcast nature and its ability to achieve diversity through independent channels. A variety of relaying protocols have been considered and utilized in cooperative wireless networks. Amplify and forward (AAF) and decode and forward (DAF) are two popular protocols, frequently used in the cooperative systems. In the AAF mode, the relay amplifies the received signal prior to retransmission. In the DAF mode, the relay fully decodes the received signal, re-encodes and forwards it to the destination. Due to the retransmission without decoding, AAF has the shortcoming that noise accumulated in the received signal is amplified at the transmission. DAF suffers from decoding errors that can lead to severe error propagation. To further enhance the quality of service (QoS) of CD communication systems, hybrid Automatic Repeat-reQuest (HARQ) protocols have been proposed. Thus, if the destination requires an ARQ retransmission, it could come from one of relays rather than the source node. This thesis proposes an improved HARQ scheme with an adaptive relaying protocol (ARP). Focusing on the HARQ as a central theme, we start by introducing the concept of ARP. Then we use it as the basis for designing three types of HARQ schemes, denoted by HARQ I-ARP, HARQ II-ARP and HARQ III-ARP. We describe the relaying protocols, (both AAF and DAF), and their operations, including channel access between the source and relay, the feedback scheme, and the combining methods at the receivers. To investigate the benefits of the proposed HARQ scheme, we analyze its frame error rate (FER) and throughput performance over a quasi-static fading channel. We can compare these with the reference methods, HARQ with AAF (HARQ-AAF) and HARQ with perfect distributed turbo codes (DTC), for which correct decoding is always assumed at the relay (HARQ-perfect DTC). It is shown that the proposed HARQ-ARP scheme can always performs better than the HARQ-AAF scheme. As the signal-to-noise ratio (SNR) of the channel between the source and relay increases, the performance of the proposed HARQ-ARP scheme approaches that of the HARQ-perfect DTC scheme.

Master of Philosophy / Wireless technology is experiencing spectacular developments, due to the emergence of interactive and digital multimedia applications as well as rapid advances in the highly integrated systems. For the next-generation mobile communication systems, one can expect wireless connectivity between any devices at any time and anywhere with a range of multimedia contents. A key requirement in such systems is the availability of high-speed and robust communication links. Unfortunately, communications over wireless channels inherently suffer from a number of fundamental physical limitations, such as multipath fading, scarce radio spectrum, and limited battery power supply for mobile devices. Cooperative diversity (CD) technology is a promising solution for future wireless communication systems to achieve broader coverage and to mitigate wireless channels’ impairments without the need to use high power at the transmitter. In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version message to an intended destination node. The destination node combines the signal received from the relays, and takes into account the source’s original signal to decode the message. The CD communication systems exploit two fundamental features of the wireless medium: its broadcast nature and its ability to achieve diversity through independent channels. A variety of relaying protocols have been considered and utilized in cooperative wireless networks. Amplify and forward (AAF) and decode and forward (DAF) are two popular protocols, frequently used in the cooperative systems. In the AAF mode, the relay amplifies the received signal prior to retransmission. In the DAF mode, the relay fully decodes the received signal, re-encodes and forwards it to the destination. Due to the retransmission without decoding, AAF has the shortcoming that noise accumulated in the received signal is amplified at the transmission. DAF suffers from decoding errors that can lead to severe error propagation. To further enhance the quality of service (QoS) of CD communication systems, hybrid Automatic Repeat-reQuest (HARQ) protocols have been proposed. Thus, if the destination requires an ARQ retransmission, it could come from one of relays rather than the source node. This thesis proposes an improved HARQ scheme with an adaptive relaying protocol (ARP). Focusing on the HARQ as a central theme, we start by introducing the concept of ARP. Then we use it as the basis for designing three types of HARQ schemes, denoted by HARQ I-ARP, HARQ II-ARP and HARQ III-ARP. We describe the relaying protocols, (both AAF and DAF), and their operations, including channel access between the source and relay, the feedback scheme, and the combining methods at the receivers. To investigate the benefits of the proposed HARQ scheme, we analyze its frame error rate (FER) and throughput performance over a quasi-static fading channel. We can compare these with the reference methods, HARQ with AAF (HARQ-AAF) and HARQ with perfect distributed turbo codes (DTC), for which correct decoding is always assumed at the relay (HARQ-perfect DTC). It is shown that the proposed HARQ-ARP scheme can always performs better than the HARQ-AAF scheme. As the signal-to-noise ratio (SNR) of the channel between the source and relay increases, the performance of the proposed HARQ-ARP scheme approaches that of the HARQ-perfect DTC scheme.

Cooperative communications have the ability to induce spatial diversity, increase channel capacity, and attain broader cell coverage with single-antenna terminals. This thesis focuses on the performance study of both unidirectional and bidirectional cooperative diversity networks employing the decode-and-forward (DF) protocol. For the unidirectional cooperative diversity network, we study the average bit-error rate (BER) performance of a DF protocol with maximum-likelihood (ML) detection. Closed-form approximate average BER expressions involving only elementary functions are presented for a cooperative diversity network with one or two relays. The proposed BER expressions are valid for both coherent and non-coherent binary signallings. With Monte-Carlo simulations, it is verified that the proposed BER expressions are extremely accurate for the whole signal-to-noise ratio (SNR) range. For the bidirectional cooperative diversity network, we study and compare the performance of three very typical bidirectional communication protocols based on the decode-and-forward relaying: time division broadcast (TDBC), physical-layer network coding (PNC), and opportunistic source selection (OSS). Specifically, we derive an exact outage probability in a one-integral form for the TDBC protocol, and exact closed-form outage probabilities for the PNC and OSS protocols. For the TDBC protocol, we also derive extremely tight upper and lower bounds on the outage probability in closed-form. Moreover, asymptotic outage probability performance of each protocol is studied. Finally, we study the diversity-multiplexing tradeoff (DMT) performance of each protocol both in the finite and infinite SNR regimes. The performance analysis presented in this thesis can be used as a useful tool to guide practical system designs for both unidirectional and bidirectional cooperative diversity networks. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2009-09-12 14:36:05.05

Master of Philosophy / Wireless technology is experiencing spectacular developments, due to the emergence of interactive and digital multimedia applications as well as rapid advances in the highly integrated systems. For the next-generation mobile communication systems, one can expect wireless connectivity between any devices at any time and anywhere with a range of multimedia contents. A key requirement in such systems is the availability of high-speed and robust communication links. Unfortunately, communications over wireless channels inherently suffer from a number of fundamental physical limitations, such as multipath fading, scarce radio spectrum, and limited battery power supply for mobile devices. Cooperative diversity (CD) technology is a promising solution for future wireless communication systems to achieve broader coverage and to mitigate wireless channels’ impairments without the need to use high power at the transmitter. In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version message to an intended destination node. The destination node combines the signal received from the relays, and takes into account the source’s original signal to decode the message. The CD communication systems exploit two fundamental features of the wireless medium: its broadcast nature and its ability to achieve diversity through independent channels. A variety of relaying protocols have been considered and utilized in cooperative wireless networks. Amplify and forward (AAF) and decode and forward (DAF) are two popular protocols, frequently used in the cooperative systems. In the AAF mode, the relay amplifies the received signal prior to retransmission. In the DAF mode, the relay fully decodes the received signal, re-encodes and forwards it to the destination. Due to the retransmission without decoding, AAF has the shortcoming that noise accumulated in the received signal is amplified at the transmission. DAF suffers from decoding errors that can lead to severe error propagation. To further enhance the quality of service (QoS) of CD communication systems, hybrid Automatic Repeat-reQuest (HARQ) protocols have been proposed. Thus, if the destination requires an ARQ retransmission, it could come from one of relays rather than the source node. This thesis proposes an improved HARQ scheme with an adaptive relaying protocol (ARP). Focusing on the HARQ as a central theme, we start by introducing the concept of ARP. Then we use it as the basis for designing three types of HARQ schemes, denoted by HARQ I-ARP, HARQ II-ARP and HARQ III-ARP. We describe the relaying protocols, (both AAF and DAF), and their operations, including channel access between the source and relay, the feedback scheme, and the combining methods at the receivers. To investigate the benefits of the proposed HARQ scheme, we analyze its frame error rate (FER) and throughput performance over a quasi-static fading channel. We can compare these with the reference methods, HARQ with AAF (HARQ-AAF) and HARQ with perfect distributed turbo codes (DTC), for which correct decoding is always assumed at the relay (HARQ-perfect DTC). It is shown that the proposed HARQ-ARP scheme can always performs better than the HARQ-AAF scheme. As the signal-to-noise ratio (SNR) of the channel between the source and relay increases, the performance of the proposed HARQ-ARP scheme approaches that of the HARQ-perfect DTC scheme.

Master of Philosophy / Wireless technology is experiencing spectacular developments, due to the emergence of interactive and digital multimedia applications as well as rapid advances in the highly integrated systems. For the next-generation mobile communication systems, one can expect wireless connectivity between any devices at any time and anywhere with a range of multimedia contents. A key requirement in such systems is the availability of high-speed and robust communication links. Unfortunately, communications over wireless channels inherently suffer from a number of fundamental physical limitations, such as multipath fading, scarce radio spectrum, and limited battery power supply for mobile devices. Cooperative diversity (CD) technology is a promising solution for future wireless communication systems to achieve broader coverage and to mitigate wireless channels’ impairments without the need to use high power at the transmitter. In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version message to an intended destination node. The destination node combines the signal received from the relays, and takes into account the source’s original signal to decode the message. The CD communication systems exploit two fundamental features of the wireless medium: its broadcast nature and its ability to achieve diversity through independent channels. A variety of relaying protocols have been considered and utilized in cooperative wireless networks. Amplify and forward (AAF) and decode and forward (DAF) are two popular protocols, frequently used in the cooperative systems. In the AAF mode, the relay amplifies the received signal prior to retransmission. In the DAF mode, the relay fully decodes the received signal, re-encodes and forwards it to the destination. Due to the retransmission without decoding, AAF has the shortcoming that noise accumulated in the received signal is amplified at the transmission. DAF suffers from decoding errors that can lead to severe error propagation. To further enhance the quality of service (QoS) of CD communication systems, hybrid Automatic Repeat-reQuest (HARQ) protocols have been proposed. Thus, if the destination requires an ARQ retransmission, it could come from one of relays rather than the source node. This thesis proposes an improved HARQ scheme with an adaptive relaying protocol (ARP). Focusing on the HARQ as a central theme, we start by introducing the concept of ARP. Then we use it as the basis for designing three types of HARQ schemes, denoted by HARQ I-ARP, HARQ II-ARP and HARQ III-ARP. We describe the relaying protocols, (both AAF and DAF), and their operations, including channel access between the source and relay, the feedback scheme, and the combining methods at the receivers. To investigate the benefits of the proposed HARQ scheme, we analyze its frame error rate (FER) and throughput performance over a quasi-static fading channel. We can compare these with the reference methods, HARQ with AAF (HARQ-AAF) and HARQ with perfect distributed turbo codes (DTC), for which correct decoding is always assumed at the relay (HARQ-perfect DTC). It is shown that the proposed HARQ-ARP scheme can always performs better than the HARQ-AAF scheme. As the signal-to-noise ratio (SNR) of the channel between the source and relay increases, the performance of the proposed HARQ-ARP scheme approaches that of the HARQ-perfect DTC scheme.

The imperfections of the propagation channel due to channel fading and the self-generated noise from the RF front-end of the receiver cause errors in the received signal in electronic communication systems. When network coding is applied, more errors occur because of error propagation due to the inexact decoding process. In this dissertation we present a system called Partial Network Coding with Cooperation (PNC-COOP) for wireless ad hoc networks. It is a system which combines opportunistic network coding with decode-and-forward cooperative diversity, in order to reduce this error propagation by trading off some transmission degrees of freedom. PNC-COOP is a decentralized, energy efficient strategy which provides a substantial benefit over opportunistic network coding when transmission power is a concern. The proposed scheme is compared with both opportunistic network coding and conventional multi-hop transmission analytically and through simulation. Using a 3-hop communication scenario, in a 16-node wireless ad hoc network, it is shown that PNC-COOP improves the BER performance by 5 dB compared to opportunistic network coding. On average, it reduces the energy used by each sender node around 10% and reduces the overall transmitted energy of the network by 3.5%. When retransmission is applied, it is shown analytically that PNC-COOP performs well at relatively low to medium SNR while the throughput is comparable to that of opportunistic network coding. The effectiveness of both opportunistic network coding and PNC-COOP depends not only on the amount of network coding but also on other factors that are analyzed and discussed in this dissertation. / Graduation date: 2011 / Access restricted to the OSU Community at author's request from May 12, 2011 - May 12, 2012

In this thesis, we argue for node selection in cooperative decode-and-forward networks. In a single-hop network with multiple relays, we show that selecting a single node to aid in the transmission between a source and a destination outperforms both traditional orthogonal transmissions and distributed space-time codes. In networks where sources transmit information over multiple hops and relays can communicate with each other, we study the relationship between cooperation and channel-adaptive routing. We show that cooperation is only beneficial if designed jointly with a routing scheme. This motivates a search for optimal algorithms in generalized relay networks. In networks without restrictions on the relays in terms of whom they can communicate with, we study the problem of optimal resource allocation in terms of transmission time. The resource allocation selects the relays to participate in the transmission and optimally allocates time resource between the selected relays. To implement this resource allocation algorithm, we propose a recursive solution which reduces the computational complexity of the algorithm. For large networks, the resulting computational complexity of implementing the algorithm is exponential in the size of the network and is likely to preclude its implementation. We thus propose that the resource allocation be implemented sub-optimally through node selection: a subset of the nodes in the network should be selected and used as input to the optimal resource allocation algorithm. We provide guidelines for selecting the nodes and propose four heuristics which offer various complexity-performance trade-offs. Compared to the optimal resource algorithm, all four heuristics significantly decrease the required computation complexity of the optimal algorithm.

In this thesis, we argue for node selection in cooperative decode-and-forward networks. In a single-hop network with multiple relays, we show that selecting a single node to aid in the transmission between a source and a destination outperforms both traditional orthogonal transmissions and distributed space-time codes. In networks where sources transmit information over multiple hops and relays can communicate with each other, we study the relationship between cooperation and channel-adaptive routing. We show that cooperation is only beneficial if designed jointly with a routing scheme. This motivates a search for optimal algorithms in generalized relay networks. In networks without restrictions on the relays in terms of whom they can communicate with, we study the problem of optimal resource allocation in terms of transmission time. The resource allocation selects the relays to participate in the transmission and optimally allocates time resource between the selected relays. To implement this resource allocation algorithm, we propose a recursive solution which reduces the computational complexity of the algorithm. For large networks, the resulting computational complexity of implementing the algorithm is exponential in the size of the network and is likely to preclude its implementation. We thus propose that the resource allocation be implemented sub-optimally through node selection: a subset of the nodes in the network should be selected and used as input to the optimal resource allocation algorithm. We provide guidelines for selecting the nodes and propose four heuristics which offer various complexity-performance trade-offs. Compared to the optimal resource algorithm, all four heuristics significantly decrease the required computation complexity of the optimal algorithm.

A multi-hop, amplify-and-forward (AF), cooperative diversity system with K relays is studied. An accurate approximate expression for the symbol-error-rate (SER) is derived for the multi-hop system. Also, a lower bound for the outage probability of the system, that is tight throughout nearly the entire signal-to-noise ratio (SNR) range, is presented. Neither an SER expression nor an outage probability expression had previously been reported in the literature for the multi-hop system. To assist in the derivation of the SER expression, the cumulative density function (CDF), probability density function (PDF), and moment generating function (MGF) are found for the random variable (RV), Z = X Y / (X + Y + c), where X and Y are RVs which have PDFs that are sums of terms of the form x^n exp(-b x). It is shown that with the CDF, PDF, and MGF of this type of RV, it is possible to derive an expression for the SER of the multi-hop system for several important scenarios with respect to what type of fading is present in the channels of the system. To assist in the derivation of the lower bound of the outage probability, the CDF is found for an interesting new RV, presented in a recursive formula, that is used to represent the upper bound of the instantaneous end-to-end SNR of the multi-hop system. These mathematical results are useful beyond the scope of the multi-hop system researched in this thesis. Also, many of the results found in this thesis for the previously-scarcely-studied multi- hop sytem are shown to be generalizations of results that had been found for the previously-often-studied two-hop, AF, cooperative diversity system with K relays. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2009-08-04 12:02:41.495

Cooperative wireless communication uses relays to enhance the capacity and reliability of data transmission. Adaptive transmission is typically used in conventional non-cooperative communications to exploit the time-varying nature of the wireless channel. In this thesis, we combine these two techniques. We consider decode-and-forward (DF) and amplify-and-forward (AF) relays. The wireless environment is modeled by using the Nakagami-m distribution. The achievable channel capacity with rate adaptive transmission is analytically derived for DF and AF cooperative networks. The performance of a DF cooperative network is analyzed with a constant power rate adaptive scheme consisting of a discrete set of transmission modes. The effect of decoding errors on DF cooperative networks is also analyzed. To this end, a new heuristic approximation of the total received signal-to-noise ratio at the destination is developed. This approximation enables simple yet accurate performance analysis. / Communications