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We propose and analyze new finger assignment/management techniques that are applicable for RAKE receivers when they operate in the soft handover region. Two main criteria are considered: minimum use of additional network resources and minimum call drops. For the schemes minimizing the use of network resources, basic principles are to use the network resources only if necessary while minimum call drop schemes rely on balancing or distributing the signal strength/paths among as many base stations as possible. The analyses of these schemes require us to consider joint microscopic/macroscopic diversity techniques which have seldom been considered before and as such, we tackle the statistics of several correlated generalized selection combining output signal-to-noise ratios in order to obtain closed-form expressions for the statistics of interest. To provide a general comprehensive framework for the assessment of the proposed schemes, we investigate not only the complexity in terms of the average number of required path estimations/comparisons, the average number of combined paths, and the soft handover overhead but also the error performance of the proposed schemes over independent and identically distributed fading channels. We also examine via computer simulations the effect of path unbalance/correlation as well as outdated/imperfect channel estimations. We show through numerical exam ples that the proposed schemes which are designed for the minimum use of network resources can save a certain amount of complexity load and soft handover overhead with a very slight performance loss compared to the conventional generalized selection combining-based diversity systems. For the minimum call drop schemes, by accurately quantifying the average error rate, we show that in comparison to the conventional schemes, the proposed distributed schemes offer the better error performance when there is a considerable chance of loosing the signals from one of the active base stations.

The introduction of new schemes that are based on the communication among nodes has motivated the use of composite fading models due to the fact that the nodes experience different multipath fading and shadowing statistics, which subsequently determines the required statistics for the performance analysis of different transceivers. The end-to-end signal-to-noise-ratio (SNR) statistics plays an essential role in the determination of the performance of cascaded digital communication systems. In this thesis, a closed-form expression for the probability density function (PDF) of the end-end SNR for independent but not necessarily identically distributed (i.n.i.d.) cascaded generalized-K (GK) composite fading channels is derived. The developed PDF expression in terms of the Meijer-G function allows the derivation of subsequent performance metrics, applicable to different modulation schemes, including outage probability, bit error rate for coherent as well as non-coherent systems, and average channel capacity that provides insights into the performance of a digital communication system operating in N cascaded GK composite fading environment. Another line of research that was motivated by the introduction of composite fading channels is the error performance. Error performance is one of the main performance measures and derivation of its closed-form expression has proved to be quite involved for certain systems. Hence, in this thesis, a unified closed-form expression, applicable to different binary modulation schemes, for the bit error rate of dual-branch selection diversity based systems undergoing i.n.i.d. GK fading is derived in terms of the extended generalized bivariate Meijer G-function.

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ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California / This paper investigates the performance of a multiple-input multiple-output (MIMO) digital communication system, when the transmitter is located on a spinning vehicle. In particular, a 2x2 MIMO system is used, with Alamouti coding at the transmitter. Both Rayleigh and Rayleigh plus line-of-sight, or Rician, models combined with a deterministic model to simulate the channel. The spinning of the transmitting vehicle, relative to the stationary receive antennas, modulates the signal, and complicates the decoding and channel parameter estimation processes. The simulated system bit error rate is the primary performance metric used. The Alamouti channel code is shown to perform better than the maximal ratio receiver combining (MRRC) and single receiver (2x1) system in some circumstances and performs similarly to the MRRC in the broadside case.

In wireless communication systems, transmitted signals are corrupted by fading as well as noise. The receiver can benefit from the estimates of fading channels to detect the transmitted symbols. However, in practical wireless systems channel information cannot be estimated perfectly at the receiver. Therefore, it is crucial to examine the effect of channel estimation error on the structure and performance of the receivers. In the first part of the thesis, we study single-user systems with single-antenna reception over fading channels in the presence of Gaussian-distributed channel estimation error. By using the statistical information of the channel estimation error, we will derive the structure of maximum-likelihood receivers for a number of different modulation formats and then analyze their performance over fading channels. In the second part of the thesis, we consider the uplink of multi-user wireless systems with multi-antenna reception. For conventional diversity combining techniques such as maximal ratio combining and optimum combining we analyze the performance degradation due to imperfect channel estimates in the presence of multiple interfering users for several fading channels. By investigating the probability density function of the output signal-to-interference ratio, we will derive analytical expressions for several performance measures such as the average signal-to-interference ratio, outage probability and average bit-error probability. These expressions quantify performance degradation due to channel estimation error.

In wireless communication systems, transmitted signals are corrupted by fading as well as noise. The receiver can benefit from the estimates of fading channels to detect the transmitted symbols. However, in practical wireless systems channel information cannot be estimated perfectly at the receiver. Therefore, it is crucial to examine the effect of channel estimation error on the structure and performance of the receivers. In the first part of the thesis, we study single-user systems with single-antenna reception over fading channels in the presence of Gaussian-distributed channel estimation error. By using the statistical information of the channel estimation error, we will derive the structure of maximum-likelihood receivers for a number of different modulation formats and then analyze their performance over fading channels. In the second part of the thesis, we consider the uplink of multi-user wireless systems with multi-antenna reception. For conventional diversity combining techniques such as maximal ratio combining and optimum combining we analyze the performance degradation due to imperfect channel estimates in the presence of multiple interfering users for several fading channels. By investigating the probability density function of the output signal-to-interference ratio, we will derive analytical expressions for several performance measures such as the average signal-to-interference ratio, outage probability and average bit-error probability. These expressions quantify performance degradation due to channel estimation error.

Cooperative communication is a new class of wireless communication techniques in which wireless nodes help each other relay information and realize spatial diversity advantages in a distributed manner. This new transmission technique promises significant performance gains in terms of link reliability, spectral efficiency, system capacity, and transmission range. Analysis and design of cooperative communication wireless systems have been extensively studied over the last few years. The introduction and integration of cooperative communication in next generation wireless standards will lead to the design of an efficient and reliable fully-distributed wireless network. However, there are various technical challenges and open issues to be resolved before this promising concept becomes an integral part of the modern wireless communication devices. A common assumption in the literature on cooperative communications is the equal distribution of power among the cooperating nodes. Optimum power allocation is a key technique to realize the full potentials of relay-assisted transmission promised by the recent information-theoretic results. In this dissertation, we present a comprehensive framework for power allocation problem. We investigate the error rate performance of cooperative communication systems and further devise open-loop optimum power allocation schemes to optimize the performance. By exploiting the information about the location of cooperating nodes, we are able to demonstrate significant improvements in the system performance. In the first part of this dissertation, we consider single-relay systems with amplify-and-forward relaying. We derive upper bounds for bit error rate performance assuming various cooperation protocols and minimize them under total power constraint. In the second part, we consider a multi-relay network with decode-and-forward relaying. We propose a simple relay selection scheme for this multi-relay system to improve the throughput of the system, further optimize its performance through power allocation. Finally, we consider a multi-source multi-relay broadband cooperative network. We derive and optimize approximate symbol error rate of this OFDMA (orthogonal frequency division multiple access) system.

Cooperative communication is a new class of wireless communication techniques in which wireless nodes help each other relay information and realize spatial diversity advantages in a distributed manner. This new transmission technique promises significant performance gains in terms of link reliability, spectral efficiency, system capacity, and transmission range. Analysis and design of cooperative communication wireless systems have been extensively studied over the last few years. The introduction and integration of cooperative communication in next generation wireless standards will lead to the design of an efficient and reliable fully-distributed wireless network. However, there are various technical challenges and open issues to be resolved before this promising concept becomes an integral part of the modern wireless communication devices. A common assumption in the literature on cooperative communications is the equal distribution of power among the cooperating nodes. Optimum power allocation is a key technique to realize the full potentials of relay-assisted transmission promised by the recent information-theoretic results. In this dissertation, we present a comprehensive framework for power allocation problem. We investigate the error rate performance of cooperative communication systems and further devise open-loop optimum power allocation schemes to optimize the performance. By exploiting the information about the location of cooperating nodes, we are able to demonstrate significant improvements in the system performance. In the first part of this dissertation, we consider single-relay systems with amplify-and-forward relaying. We derive upper bounds for bit error rate performance assuming various cooperation protocols and minimize them under total power constraint. In the second part, we consider a multi-relay network with decode-and-forward relaying. We propose a simple relay selection scheme for this multi-relay system to improve the throughput of the system, further optimize its performance through power allocation. Finally, we consider a multi-source multi-relay broadband cooperative network. We derive and optimize approximate symbol error rate of this OFDMA (orthogonal frequency division multiple access) system.

In this thesis, a blind symbol timing synchronization algorithm based on cyclic prefix for OFDM systems in multipath fading channels is proposed. It finds the starting point of symbol timing for using appropriate weights which are designed from channel delay spread characteristics. In multipath fading channels, the conventional ML (maximum likelihood) algorithm estimate is biased and has a large variance due to the effect of channel delay spread. The proposed exponential weighting methods not only solve the above problems but also improve the accuracy of symbol timing. Particularly, the proposed method does not require the information of SNR and channel length. From computer simulation results, the proposed method outperforms the other conventional algorithms and is also robust against the effect of multipath fading channels.