Cooperative and relay wireless communication networks use one or more distinct wire- less nodes as relays to combat performance impairments, which include signal atten- uation due to power loss over long distances and the signal power fluctuation due to multi-path fading. The second one is the primary focus of this thesis. Diversity is an effective weapon to combat the fading effects and using multiple antennas at both the transmitter and receiver is a way of achieving it. However, using multiple antennas may not be practical for some mobile terminals due to the limited physical size, battery power and computational capability of these mobile terminals. Therefore, cooperative schemes have been proposed in which several wireless nodes cooperate with each other to achieve diversity even though each node has only one an- tenna. Many cooperative schemes have been proposed including Amplify-and-Forward (AF) and Decode-and-Forward (DF) [1] to achieve this diversity. This thesis primarily proposes and studies a DF scheme. For the DF schemes, imperfect decoding at the relay is one of the major limitations to the achievable performance. To address this problem and yet remain simple to implement, a novel DF based cooperative scheme is proposed in this thesis. This proposed scheme uses a distributed Turbo coding (DTC) scheme and is resilient to relay errors. It is analyzed by using the approximate Gaussian density evolution method. The analysis shows how the iterative Turbo decoding performs with different bit error rates (BERs) at the relay. Based on the results, a novel scheme, which adaptively changes the code used at the relay, is then proposed to further improve performance. The diversity offered by the proposed scheme is achieved at the cost of decreased spectral efficiency compared to a non-cooperative network. To recover some of the spectral efficiency loss due to cooperation, the proposed single source node cooperative scheme is extended to a two source nodes (users) scheme. The relay node forwards a combined packet which is formed by combining multiple users' information packets into a single packet. The results show that combining multiple users' information packets using superposition modulation can achieve better performance than that of using "XOR" operation (network coding) when two users have different channel qualities, which is very common in a wireless communication environment.

In our thesis, we investigate the detection of malicious behavior in cooperative networks. Our model contain one source, one destination and two relays where relays adopt Orthogonal Space Time Block Code (OSTBC) to achieve spatial diversity. Cooperative communication takes two phases to forward signal to the destination. During first phase, source broadcasts data symbols to relay and destination, and a few tracing symbols are inserted randomly in data symbols. The values and positions of tracing symbols are known at source and destination. The random placement of tracing symbols is to prevent relays evade the detection of malicious behavior. In second phase, relays adopt orthogonal space time block code to forward the received signals after decoding source message successfully. We consider two scenarios based on the decoding capability at relays. The first scenario assumes perfect source¡Vrelay links. So, relays can always decode symbols correctly. Second scenario considers decoding failures at relays. In both scenarios, relays have a certain probability to perform maliciously. After receiving symbols at destination, the destination extracts and detect the tracing symbols. The malicious behavior of relay is detected depending on the value of the correlation between detected and exact tracing symbols. Moreover, depending on the average received energy, we can distinguish whether relays behaves as in outage. Through computer simulation, we can verify that our proposed tracing algorithm and decoding strategy reduce bit error rate.

The High Frequency (HF) band lies within 2-30 MHz of the electromagnetic spectrum. In this part of the spectrum, propagation via direct wave, surface wave, and ionospheric refraction mechanisms provides means of communications from line-of-sight to beyond-line-of-sight ranges. The characteristics of ionospheric channel impose fundamental limitations on the performance of HF communication systems. The major impairment is fading which results in random fluctuations in the received signal level and affects the instantaneous signal-to-noise ratio. This requires the deployment of powerful diversity techniques to mitigate the degrading effects of fading on the performance. The range of wavelengths in HF band unfortunately restricts the use of spatial diversity (i.e., deployment of multiple antennas) for most practical purposes. This thesis focuses on an alternative method to exploit the spatial dimension of the HF channel. Specifically, we aim to extract distributed spatial diversity through relay-assisted transmission. Towards this main goal, we consider multi-carrier HF communication and investigate the performance of cooperative OFDM over HF channels.

The High Frequency (HF) band lies within 2-30 MHz of the electromagnetic spectrum. In this part of the spectrum, propagation via direct wave, surface wave, and ionospheric refraction mechanisms provides means of communications from line-of-sight to beyond-line-of-sight ranges. The characteristics of ionospheric channel impose fundamental limitations on the performance of HF communication systems. The major impairment is fading which results in random fluctuations in the received signal level and affects the instantaneous signal-to-noise ratio. This requires the deployment of powerful diversity techniques to mitigate the degrading effects of fading on the performance. The range of wavelengths in HF band unfortunately restricts the use of spatial diversity (i.e., deployment of multiple antennas) for most practical purposes. This thesis focuses on an alternative method to exploit the spatial dimension of the HF channel. Specifically, we aim to extract distributed spatial diversity through relay-assisted transmission. Towards this main goal, we consider multi-carrier HF communication and investigate the performance of cooperative OFDM over HF channels.

This thesis proposes an alternative cooperating strategy for cooperative communications through the use of parley algorithm in cooperative communications. When employing parley algorithm in cooperative communications, the relay nodes and the destination node need to disseminate and agree on a common decision throughout the cooperation network via a consensus flooding procedure. In this thesis, a heuristic approach for improving the performance of the parley algorithm is proposed. This heuristic approach is to design power allocation method during each iteration of consensus flooding protocol. Specifically, when distributing the power to each node within the cooperative network, this thesis adopts the criterion of maximum capacity of the broadcast channel used for consensus flooding procedures. The simulation result obtained from the investigation of this thesis shows that the proposed power allocation approach can improve the performance in terms of bit error rate as compared with the parley algorithm with uniform power allocation, and, hence, confirms the proposed idea is useful.

In wireless communication, multipath fading distorts the phase and the amplitude of received signals and increases error rate, which degrades causes communication quality. Multiple-input-multiple-output (MIMO) techniques can be adopted to achieve diversity gain and reduce error rate. However, MIMO is hard to be implemented in mobile devices due to size limitation. With this regard, cooperative communications are proposed to allow users to cooperate each other¡¦s and then achieve diversity without equipping multiple antennas. On the other hand, if source and relays adopt fixed-rate transmission under time-varying wireless channels, it requires timely feedback about channel-information for transmitters to adjust the rate of channel encoder. To reduce overhead required for aforementioned scheme, we adopt rateless fountain codes in cooperative networks. In recent year, most related studies focus on information-theoretical aspect, but it lacks discussion of practical coding. In our work, we use fountain codes in dual-hop cooperative communication and analyse transmission rate in terms of transmitting time. Fountain code was first proposed as Luby transform codes(LTC) for erasure channels. We combine low-density parity-check code( LDPC code) and LTC in cooperative communication networks, and analyze required transmission time under different cooperative protocols.

Cognitive radio (CR) is a promising technique to improve spectrum efficiency for wireless communications. This thesis focuses on the resource allocation in two kinds of CR networks (CRNs), traditional CRNs (TCRNs) and cooperative CRNs (CCRNs). In TCRNs, CR sources and destinations communicate directly. By exploring the heterogeneity among CRs, a prioritized CSMA/CA is proposed for demand-matching spectrum allocation. A distributed game is formulated and no-regret learning is adopted to solve the game. Simulation results indicate increase on the number of satisfied CRs. In CCRNs, some nodes are selected as relays to assist the communication. A two-layer auction game is proposed with the first layer performing spectrum allocation and relay formation, and the second layer performing relay allocation. These two layers interact and jointly solve the resource allocation problem. Simulation results show that, compared to counterparts, both the network throughput and convergence time can be improved.

Next generation wireless communication networks are expected to provide ubiquitous high data rate coverage and support heterogeneous wireless services with diverse quality-of-service (QoS) requirements. This translates into a heavy demand for the spectral resources. In order to meet these requirements, Orthogonal Frequency Division Multiple Access (OFDMA) has been regarded as a promising air-interface for the emerging fourth generation (4G) networks due to its capability to combat the channel impairments and support high data rate. In addition, OFDMA offers flexibility in radio resource allocation and provides multiuser diversity by allowing subcarriers to be shared among multiple users. One of the main challenges for the 4G networks is to achieve high throughput throughout the entire cell. Cooperative relaying is a very promising solution to tackle this problem as it provides throughput gains as well as coverage extension. The combination of OFDMA and cooperative relaying assures high throughput requirements, particularly for users at the cell edge. However, to fully exploit the benefits of relaying, efficient relay selection as well as resource allocation are critical in such kind of network when multiple users and multiple relays are considered. Moreover, the consideration of heterogeneous QoS requirements further complicate the optimal allocation of resources in a relay enhanced OFDMA network. Furthermore, the computational complexity and signalling overhead are also needed to be considered in the design of practical resource allocation schemes. In this dissertation, we conduct a comprehensive research study on the topic of radio resource management for relay-based cooperative OFDMA networks supporting heterogeneous QoS requirements. Specifically, this dissertation investigates how to effectively and efficiently allocate resources to satisfy QoS requirements of 4G users, improve spectrum utilization and reduce computational complexity at the base station. The problems and our research achievements are briefly outlined as follows. Firstly, a QoS aware optimal joint relay selection, power allocation and subcarrier assignment scheme for uplink OFDMA system considering heterogeneous services under a total power constraint is proposed. The relay selection, power allocation and subcarrier assignment problem is formulated as a joint optimization problem with the objective of maximizing the system throughput, which is solved by means of a two level dual decomposition and subgradient method. The computational complexity is finally reduced via the introduction of two suboptimal schemes. The performance of the proposed schemes is demonstrated through computer simulations based on OFDMA network. Numerical results show that our schemes support heterogeneous services while guaranteeing each user's QoS requirements with slight total system throughput degradation. Secondly, we investigate the resource allocation problem subject to the satisfaction of user QoS requirements and individual total power constraints of the users and relays. The throughput of each end-to-end link is modeled considering both the direct and relay links. Due to non-convex nature of the original resource allocation problem, the optimal solution is obtained by solving a relaxed problem via two level dual decomposition. Numerical results reveal that the proposed scheme is effective in provisioning QoS of each user's over the conventional resource allocation counterpart under individual total power constraints of the users and relays . Lastly, decentralized resource allocation schemes are proposed to reduce the computational complexity and CSI feedback overhead at the BS. A user centric distributed (UCD) scheme and a relay centric distributed (RCD) scheme are proposed, where the computation of the centralized scheme is distributed among the users and relays, respectively. We also proposed suboptimal schemes based on simplified relay selection. The suboptimal schemes can be combined with the distributed schemes to further reduce of signalling overhead and computational complexity. Numerical results show that our schemes guarantee user's satisfaction with low computational complexity and signalling overhead, leading to preferred candidates for practical implementation. The research results obtained in this dissertation can improve the resource utilization and QoS assurance of the emerging OFDMA networks.

Cognitive radio (CR) is a promising technique to improve spectrum efficiency for wireless communications. This thesis focuses on the resource allocation in two kinds of CR networks (CRNs), traditional CRNs (TCRNs) and cooperative CRNs (CCRNs). In TCRNs, CR sources and destinations communicate directly. By exploring the heterogeneity among CRs, a prioritized CSMA/CA is proposed for demand-matching spectrum allocation. A distributed game is formulated and no-regret learning is adopted to solve the game. Simulation results indicate increase on the number of satisfied CRs. In CCRNs, some nodes are selected as relays to assist the communication. A two-layer auction game is proposed with the first layer performing spectrum allocation and relay formation, and the second layer performing relay allocation. These two layers interact and jointly solve the resource allocation problem. Simulation results show that, compared to counterparts, both the network throughput and convergence time can be improved.

Wireless networks have received considerable attention recently due to the high user demand for wireless services and the emergence of new applications. This thesis focuses on the problem of information dissemination in a class of wireless networks known as the multi-way relay channel. Physical layer network coding is considered to increase the throughput in these networks. First, an algorithm is proposed that increases the full data exchange throughput by 33% compared to traditional routing. This gain arises from providing common knowledge to users and exploiting this knowledge to restrain some users from transmitting. Second, for complex field network coding, a transmission scheme is designed that ensures the receipt of a QAM constellation at the relay. This requires precoding the user symbols to make all possible combinations distinguishable at the relay. Using this approach, the throughput of data exchange is 1/2 symbol per user per channel use. The error performance of both schemes is derived analytically for AWGN channels. / Graduate