The prime wireless spectrum is inherently a critical yet scarce resource. As the demand of wireless bandwidth grows exponentially, it becomes a crucial issue to improve the spectrum utilization for the development and deployment of any new wireless technologies. In this thesis, we seek to address this problem through cooperative diversity and dynamic spectrum trading, in the context of the envisioned primary-secondary dynamic spectrum sharing paradigm. For an OFDMA-based cellular primary network which owns an exclusive right to access a certain spectrum band, we propose XOR-assisted cooperative diversity to improve the spectral efficiency of the allocated band, as well as an optimization framework to address the resource allocation problem. For the secondary network that utilizes cognitive radios to opportunistically exploit the spectrum white spaces, we establish a spectrum secondary market, design the market institution based on double auctions, and solve the decision making problem using reinforcement learning, to improve spectrum utilization via trading among secondary users.

The prime wireless spectrum is inherently a critical yet scarce resource. As the demand of wireless bandwidth grows exponentially, it becomes a crucial issue to improve the spectrum utilization for the development and deployment of any new wireless technologies. In this thesis, we seek to address this problem through cooperative diversity and dynamic spectrum trading, in the context of the envisioned primary-secondary dynamic spectrum sharing paradigm. For an OFDMA-based cellular primary network which owns an exclusive right to access a certain spectrum band, we propose XOR-assisted cooperative diversity to improve the spectral efficiency of the allocated band, as well as an optimization framework to address the resource allocation problem. For the secondary network that utilizes cognitive radios to opportunistically exploit the spectrum white spaces, we establish a spectrum secondary market, design the market institution based on double auctions, and solve the decision making problem using reinforcement learning, to improve spectrum utilization via trading among secondary users.

Next generation wireless communication systems are expected to provide a variety of services including voice, data and video. The rapidly growing demand for these services needs high data rate wireless communication systems with reliability and high user capacity. Recently, it has been shown that reliability and achievable data rate of wireless communication systems increases dramatically by employing multiple transmit and receive antennas. Transmit diversity is a powerful technique for combating multipath fading in wireless communications. However, employing multiple antennas in a mobile terminal to achieve the transmit diversity in the uplink is not feasible due to the limited size of the mobile unit. In order to overcome this problem, a new mode of transmit diversity called cooperative diversity (CD) based on user cooperation, was proposed very recently. By user cooperation, it is meant that the sender transmits to the destination and copies to other users, called partners, for relaying to the destination. The antennas of the sender and the partners together form a multiple antenna situation. CD systems are immuned not only against small scale channel fading but also against large scale channel fading. On the other hand, CD systems are more sensitive to interuser (between sender and partner) transmission errors and user mobility. In this dissertation, we propose a bandwidth and power efficient CD system which could be accommodated with minimal modifications in the currently available direct or point-to-point communication systems. The proposed CD system is based on quadrature signaling (QS). With quadrature signaling, both sender’s and partners’ information symbols are transmitted simultaneously in his/her multiple access channels. It also reduces the synchronization as well as the interference problems that occur in the schemes reported in the literature. The performance of the proposed QS-CD system is analyzed at different layers. First, we study the bit error probability (BEP) of the QS-CD system for both fixed and adaptive relaying at the partner. It is shown from the BEP performance that the QS-CD system can achieve diversity order of two. Then, a cross-layer communication system is developed by combing the proposed QS-CD system at the physical layer and the truncated stop-and- wait automatic repeat request (ARQ) at the data link layer. The performance of the cross-layer system is analyzed and compared with existing schemes in the literature for performance metrics at the data link layer and upper layers, i.e., frame error rate, packet loss rate, average packet delay, throughput, etc. In addition, the studies show that the proposed QS-CD-ARQ system outperforms existing schemes when it has a good partner. In this respect, the proposed system is fully utilizing the communication channel and less complex in terms of implementation when compared with the existing systems. Since the partner selection gives significant impact on the performance of the CD systems, partner selection algorithms (PSAs) are extensively analyzed for both static and mobile user network. In this case, each individual user would like to take advantage of cooperation by choosing a suitable partner. The objective of an individual user may conflict with the objective of the network. In this regard, we would like to introduce a PSA which tries to balance both users and network objectives by taking user mobility into consideration. The proposed PSA referred to as worst link first (WLF), to choose the best partner in cooperative communication systems. The WLF algorithm gives priority to the worst link user to choose its partner and to maximize the energy gain of the radio cell. It is easy to implement not only in centralized networks but also in distributed networks with or without the global knowledge of users in the network. The proposed WLF matching algorithm, being less complex than the optimal maximum weighted (MW) matching and the heuristic based Greedy matching algorithms, yields performance characteristics close to those of MW matching algorithm and better than the Greedy matching algorithm in both static and mobile user networks. Furthermore, the proposed matching algorithm provides around 10dB energy gain with optimal power allocation over a non-cooperative system which is equivalent to prolonging the cell phone battery recharge time by about ten times.

Recent technological advances and pervasiveness of wireless communication devices have offered novel and promising solutions to the road safety problem and on-the-go entertainment. One such solution is the Inter-Vehicular Communications (IVC) where vehicles cooperate in receiving and delivering the messages to each other, establishing a decentralized communication system. The communication between vehicles can be made more effective and reliable at the physical layer by using the concept of space-time coding (STC). STC demonstrated that the deployment of multiple antennas at the transmitter allows for simultaneous increase in throughput and reliability because of the additional degree of freedom offered by the spatial dimension of the wireless. However, the use of multiple antenna at the receiver is not feasible because of the size and power limitations. Cooperative diversity, which is also known as user cooperation is ideal to overcome these limitations by introducing a new concept of using the antenna of neighboring node. This technique exploits the broadcast nature of wireless transmissions and creates a virtual (distributed) antenna array through cooperating nodes to realize spatial diversity advantage. Although there has been a growing literature on cooperative diversity, the current literature is mainly limited to Rayleigh fading channel model which typically assumes a wireless communication scenario with a stationary base station antenna above roof-top level and a mobile station at street level. In this thesis, we investigate cooperative diversity for inter-vehicular communication based on cascaded Rayleigh fading. This channel model provides a realistic description of inter-vehicular channel where two or more independent Rayleigh fading processes are assumed to be generated by independent groups of scatters around the two mobile terminals. We investigate the performance of amplify-and-forward relaying for an inter-vehicular cooperative scheme assisted by either a road-side access point or another vehicle which acts as a relay. Our diversity analysis reveals that the cooperative scheme is able to extract the full distributed spatial diversity. We further formulate a power allocation problem for the considered scheme to optimize the power allocated to broadcasting and relaying phases. Performance gains up to 3 dB are obtained through optimum power allocation depending on the relay location.

Although there already exists a rich literature on cooperative diversity, current results are mainly restricted to the conventional assumption of additive white Gaussian noise (AWGN). AWGN model realistically represents the thermal noise at the receiver, but ignores the impulsive nature of atmospheric noise, electromagnetic interference, or man-made noise which might be dominant in many practical applications. In this thesis, we investigate the performance of cooperative communication over Rayleigh fading channels in the presence of impulsive noise modeled by Middleton Class A noise. We consider a multi-relay network with amplify-and-forward relaying and orthogonal cooperation protocol. As for the coding across the relays, we employ either space-time coding or repetition coding. For each scheme, we assume various scenarios based on relays’ location and quantify the diversity advantages through the derivation of the pairwise error probability. Based on the minimization of a union bound on the error rate performance, we further propose optimal power allocation schemes and demonstrate significant performance gains over their counterparts with equal power allocation. We finally present an extensive Monte Carlo simulation to confirm our analytical results and corroborate on our results.

Next generation wireless communication systems are expected to provide a variety of services including voice, data and video. The rapidly growing demand for these services needs high data rate wireless communication systems with reliability and high user capacity. Recently, it has been shown that reliability and achievable data rate of wireless communication systems increases dramatically by employing multiple transmit and receive antennas. Transmit diversity is a powerful technique for combating multipath fading in wireless communications. However, employing multiple antennas in a mobile terminal to achieve the transmit diversity in the uplink is not feasible due to the limited size of the mobile unit. In order to overcome this problem, a new mode of transmit diversity called cooperative diversity (CD) based on user cooperation, was proposed very recently. By user cooperation, it is meant that the sender transmits to the destination and copies to other users, called partners, for relaying to the destination. The antennas of the sender and the partners together form a multiple antenna situation. CD systems are immuned not only against small scale channel fading but also against large scale channel fading. On the other hand, CD systems are more sensitive to interuser (between sender and partner) transmission errors and user mobility. In this dissertation, we propose a bandwidth and power efficient CD system which could be accommodated with minimal modifications in the currently available direct or point-to-point communication systems. The proposed CD system is based on quadrature signaling (QS). With quadrature signaling, both sender’s and partners’ information symbols are transmitted simultaneously in his/her multiple access channels. It also reduces the synchronization as well as the interference problems that occur in the schemes reported in the literature. The performance of the proposed QS-CD system is analyzed at different layers. First, we study the bit error probability (BEP) of the QS-CD system for both fixed and adaptive relaying at the partner. It is shown from the BEP performance that the QS-CD system can achieve diversity order of two. Then, a cross-layer communication system is developed by combing the proposed QS-CD system at the physical layer and the truncated stop-and- wait automatic repeat request (ARQ) at the data link layer. The performance of the cross-layer system is analyzed and compared with existing schemes in the literature for performance metrics at the data link layer and upper layers, i.e., frame error rate, packet loss rate, average packet delay, throughput, etc. In addition, the studies show that the proposed QS-CD-ARQ system outperforms existing schemes when it has a good partner. In this respect, the proposed system is fully utilizing the communication channel and less complex in terms of implementation when compared with the existing systems. Since the partner selection gives significant impact on the performance of the CD systems, partner selection algorithms (PSAs) are extensively analyzed for both static and mobile user network. In this case, each individual user would like to take advantage of cooperation by choosing a suitable partner. The objective of an individual user may conflict with the objective of the network. In this regard, we would like to introduce a PSA which tries to balance both users and network objectives by taking user mobility into consideration. The proposed PSA referred to as worst link first (WLF), to choose the best partner in cooperative communication systems. The WLF algorithm gives priority to the worst link user to choose its partner and to maximize the energy gain of the radio cell. It is easy to implement not only in centralized networks but also in distributed networks with or without the global knowledge of users in the network. The proposed WLF matching algorithm, being less complex than the optimal maximum weighted (MW) matching and the heuristic based Greedy matching algorithms, yields performance characteristics close to those of MW matching algorithm and better than the Greedy matching algorithm in both static and mobile user networks. Furthermore, the proposed matching algorithm provides around 10dB energy gain with optimal power allocation over a non-cooperative system which is equivalent to prolonging the cell phone battery recharge time by about ten times.

Recent technological advances and pervasiveness of wireless communication devices have offered novel and promising solutions to the road safety problem and on-the-go entertainment. One such solution is the Inter-Vehicular Communications (IVC) where vehicles cooperate in receiving and delivering the messages to each other, establishing a decentralized communication system. The communication between vehicles can be made more effective and reliable at the physical layer by using the concept of space-time coding (STC). STC demonstrated that the deployment of multiple antennas at the transmitter allows for simultaneous increase in throughput and reliability because of the additional degree of freedom offered by the spatial dimension of the wireless. However, the use of multiple antenna at the receiver is not feasible because of the size and power limitations. Cooperative diversity, which is also known as user cooperation is ideal to overcome these limitations by introducing a new concept of using the antenna of neighboring node. This technique exploits the broadcast nature of wireless transmissions and creates a virtual (distributed) antenna array through cooperating nodes to realize spatial diversity advantage. Although there has been a growing literature on cooperative diversity, the current literature is mainly limited to Rayleigh fading channel model which typically assumes a wireless communication scenario with a stationary base station antenna above roof-top level and a mobile station at street level. In this thesis, we investigate cooperative diversity for inter-vehicular communication based on cascaded Rayleigh fading. This channel model provides a realistic description of inter-vehicular channel where two or more independent Rayleigh fading processes are assumed to be generated by independent groups of scatters around the two mobile terminals. We investigate the performance of amplify-and-forward relaying for an inter-vehicular cooperative scheme assisted by either a road-side access point or another vehicle which acts as a relay. Our diversity analysis reveals that the cooperative scheme is able to extract the full distributed spatial diversity. We further formulate a power allocation problem for the considered scheme to optimize the power allocated to broadcasting and relaying phases. Performance gains up to 3 dB are obtained through optimum power allocation depending on the relay location.

Although there already exists a rich literature on cooperative diversity, current results are mainly restricted to the conventional assumption of additive white Gaussian noise (AWGN). AWGN model realistically represents the thermal noise at the receiver, but ignores the impulsive nature of atmospheric noise, electromagnetic interference, or man-made noise which might be dominant in many practical applications. In this thesis, we investigate the performance of cooperative communication over Rayleigh fading channels in the presence of impulsive noise modeled by Middleton Class A noise. We consider a multi-relay network with amplify-and-forward relaying and orthogonal cooperation protocol. As for the coding across the relays, we employ either space-time coding or repetition coding. For each scheme, we assume various scenarios based on relays’ location and quantify the diversity advantages through the derivation of the pairwise error probability. Based on the minimization of a union bound on the error rate performance, we further propose optimal power allocation schemes and demonstrate significant performance gains over their counterparts with equal power allocation. We finally present an extensive Monte Carlo simulation to confirm our analytical results and corroborate on our results.

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The high frequency (HF) band lies within 2-30 MHz of the electromagnetic spectrum. For decades, the HF band has been recognized as the primary means of long-range wireless communications. When satellite communication first emerged in 1960s, HF technology was considered to be obsolete. However, with its enduring qualities, HF communication survived through this competition and positioned itself as a powerful complementary and/or alternative technology to satellite communications. HF systems have been traditionally associated with low-rate data transmission. With the shift from analog to digital in voice communication, and increasing demands for high-rate data transmission (e.g., e-mail, Internet, FTP), HF communication has been going through a renaissance. Innovative techniques are required to push the capacity limits of the HF band. In this dissertation, we consider cooperative communication as an enabling technology to meet the challenging expectations of future generation HF communication systems. Cooperative communication exploits the broadcast nature of wireless transmission and relies on the cooperation of users relaying the information to one another. We address the design, analysis, and optimization of cooperative HF communication systems considering both multi-carrier and single-carrier architectures. As the multi-carrier HF system, we consider the combination of the orthogonal frequency division multiplexing (OFDM) with the bit interleaved coded modulation (BICM) as the underlying physical layer platform. It is assumed that cooperating nodes may use different HF propagation mechanisms, such as near-vertical-incidence sky wave (NVIS) and surface wave, to relay their received signals to the destination in different environmental scenarios. Diversity gain analysis, optimum relay selection strategy and power allocation between the source and relays are investigated for the proposed cooperative HF system. For single-carrier HF systems, we first derive a matched-filer-bound (MFB) on the error rate performance of the non-regenerative cooperative systems. The results from the MFB analysis are also used for relay selection and power allocation in the multi-relay cooperative systems. To overcome the intersymbol interference impairment induced by frequency-selectivity of the HF channel, equalization is inevitable at the destination in a single-carrier system. In this work, we investigate the minimum-mean-square-error (MMSE) based linear/decision-feedback frequency domain equalizers (FDEs). Both symbol-spaced and fractionally-spaced implementations of the proposed FDEs are considered and their performance is compared under different channel conditions and sampling phase errors at the relay and destination nodes.