Channels with state model communication settings where the channel statistics are not fully known or vary over transmissions. It is important for a communication system to obtain the channel state information in terms of increasing channel capacity. This thesis addresses the effect of the quality of state information on channel capacity. Extreme scenarios are studied to reveal the limit in increasing channel capacity with the knowledge of state information. We consider the channel with the perfect state information at the decoder, while the encoder is only available to a noisy state observation. The effect of the noisy state at the encoder to the channel capacity is studied. We show that for any binary-input channel if the mutual information between the noisy state observation at the encoder and the true channel state is below a positive threshold determined solely by the state distribution, then the capacity is the same as that with no encoder side information. A complementary phenomenon is also revealed for the generalized probing capacity. Extensions beyond binary-input channels are developed. We further investigate the channel capacity, when the causal channel state information (available at the encoder or the decoder or both) makes it deterministic. Every such a capacity is called an intrinsic capacity of the channel. Among them, the smallest and the largest called the lower and the upper intrinsic capacities, are particularly studied. Their exact values are determined in most cases when the input or the output is binary. General lower and upper bounds are also provided for the lower and the upper intrinsic capacities with causal state information available at both sides. Byproducts of this work are a generalization of the Birkhoff-von Neumann theorem and a result on the uselessness of causal state information at the encoder. / Thesis / Doctor of Philosophy (PhD) / It is well known that with the knowledge of channel state, it is possible to increase the channel capacity. In this sense, knowing channel state never hurts. However, whether it is always bene cial to actively acquire channel state is another story. If we take into account the cost of measuring the channel state against the potential gain on the capacity, sometimes it may not appear very economic to do so. This thesis studies the effect of the quality of observed channel states on the channel capacity. It has been found out in some circumstances the channel capacity is very sensitive to the noise on the state information. On the other hand, it appears that the maximum capacity can be achieved with the knowledge of a small portion of the total channel state information under a slightly different setting. This thesis proves the generality of such phenomena in binary-input channels and provides the necessary and sufficient conditions for the occurrence of such phenomena for an arbitrary channel. This paper also introduces the idea of intrinsic capacity which can be used to measure the ultimate capacity potential of a channel by exploring the channel state. By viewing an arbitrary channel as a deterministic channel with state, the greatest possible and smallest possible capacities have been either derived or bounded in the thesis.

In a CR network, the maximum SUs throughput is desired generally. In this thesis, We investigate and formulate the problem of the secondary users¡¦ throughput maximization in cognitive radio systems under channel capacity constrain. By using KKT theorem, an objec- tive function is developed to obtain an optimal solution for the SU throughput maximization problem. An numerical example is also presented for illustration. The most important results revealed in the example show that the maximum SU throughput is achieved by cooperating an optimal number of SU pairs instead of cooperating all the SU pairs.

With the rapid adoption and development of new standards, Multiple-Input Multiple-Output (MIMO) technology is becoming a necessity in current wireless systems. One problem posed by using multiple antennas at a transmitter or receiver is the undesirable effect of signal correlation between closely-spaced radiating elements. This thesis presents the concept, design, and evaluation of a hemispherical lens antenna for use in MIMO systems. A high-permittivity dielectric material allows radiating elements to be placed in close proximity with reduced spatial correlation effects. An intermediate matching layer and a hemispherical lens design facilitate the preservation of the pattern characteristics in the transition between the dielectric and free-space. The antenna was simulated against benchmark antenna arrays in free-space and showed a 35%-70% improvement in channel capacity in multipath-rich environments, showing strength as a candidate for further development in MIMO applications.

With the rapid adoption and development of new standards, Multiple-Input Multiple-Output (MIMO) technology is becoming a necessity in current wireless systems. One problem posed by using multiple antennas at a transmitter or receiver is the undesirable effect of signal correlation between closely-spaced radiating elements. This thesis presents the concept, design, and evaluation of a hemispherical lens antenna for use in MIMO systems. A high-permittivity dielectric material allows radiating elements to be placed in close proximity with reduced spatial correlation effects. An intermediate matching layer and a hemispherical lens design facilitate the preservation of the pattern characteristics in the transition between the dielectric and free-space. The antenna was simulated against benchmark antenna arrays in free-space and showed a 35%-70% improvement in channel capacity in multipath-rich environments, showing strength as a candidate for further development in MIMO applications.

In this thesis, the 2×2 MIMO performance of several low mutual coupling antennas has been investigated in indoor and hallway scenarios. Three compact antennas intended for mobile applications with low mutual coupling between the input ports are presented in this thesis. To gauge the performances of the three designed antennas, two reference antennas are also used. Channel capacity measurements were conducted in Bahen Center Antenna Lab room 8175 and the Bahen Center 8th floor hallway by using the five antennas as receivers. The antenna spatial location, orientation, line-of-sight and non-line-of-sight situation and richness of multipath effect were considered in the measurements. By averaging the results, it is found that in an indoor environment, low mutual coupling antennas can outperform the reference high mutual coupling antennas especially in higher SNR scenarios. In the hallway environment, low mutual coupling antennas always outperform the reference high mutual coupling antennas due to pattern diversity.

In this thesis, the 2×2 MIMO performance of several low mutual coupling antennas has been investigated in indoor and hallway scenarios. Three compact antennas intended for mobile applications with low mutual coupling between the input ports are presented in this thesis. To gauge the performances of the three designed antennas, two reference antennas are also used. Channel capacity measurements were conducted in Bahen Center Antenna Lab room 8175 and the Bahen Center 8th floor hallway by using the five antennas as receivers. The antenna spatial location, orientation, line-of-sight and non-line-of-sight situation and richness of multipath effect were considered in the measurements. By averaging the results, it is found that in an indoor environment, low mutual coupling antennas can outperform the reference high mutual coupling antennas especially in higher SNR scenarios. In the hallway environment, low mutual coupling antennas always outperform the reference high mutual coupling antennas due to pattern diversity.

The purpose of this dissertation is to find the channel capacity in optical fiber communication systems when incoherent detection is used with single (polarization filtering) and two-polarizations (no polarization filtering). Optical fiber systems employ photodetectors that convert optical intensity to electrical current. Bandpass vector fields may be represented by four orthogonal baseband components corresponding to two quadrature phases and two orthogonal polarizations. Intensity is proportional to the sum of the squares of these four components. In the case of a coherent receiver, a strong optical local oscillator (in phase and with same polarization as the signal) is added to the signal prior to the photodetector. This results in the removal of the quadrature phase and polarization components, and reduces to the one degree of freedom (DOF) case of signal plus local oscillator shot noise for which the Shannon channel capacity formula applies. Electrical noise following the photodetector may also be neglected if there is an optical amplifier before the photodetector in the receiver. The amplifier introduces amplified spontaneous emission noise containing both quadrature phase components and both polarizations (4 DOFs), but the 2 DOF case would result if a polarization filter were used. Although the 1 and 2 DOF cases are of less practical interest than the 4 DOF case, they provide useful benchmarks for comparing performance limits. We evaluate both spectral efficiency limits (bps/Hz) in the limit of high and low SNR for the 1,2 and 4 DOF cases and also find the power efficiency (minimum number of photons per bit) for each of these cases. It is shown that for high SNR the spectral efficiency is the same independent of the number of DOFs and that the half-Gaussian distribution is the optimum distribution. We are able to thus obtain a compact equation for spectral efficiency which behaves in a similar way to the Shannon capacity formula but with the SNR scaled by a constant. We also show that for low SNR the half-Gaussian distribution is not the optimum distribution as the slope of the mutual information changes with the square of SNR which would lead to the number of photons per bit becoming infinite in the limit of SNR going to zero. We use a modified half-Gaussian distribution which has a discrete component (an impulse function at the origin) and provide a simple proof that this distribution results in a mutual information that goes to zero linearly with SNR resulting in a minimum number of photons per bit. Furthermore, by increasing the magnitude of the discrete component at the origin, it is shown that the minimum number of photons per bit for the incoherent channel approaches that of the coherent channel. / Ph. D.

<p> Wireless optical communication systems have the potential of establishing secure high data rate communication links. In order to realize the ultimate promise of these links, channel modeling and communication algorithms must be developed. This thesis addresses free-space optical (FSO) system design and provides novel contributions in four major areas: 1) channel modeling, 2) channel capacity and optimal signal design, 3) signaling algorithms, and 4) formal methods to jointly design code rate and beamwidth for FSO systems.</p> <p> A novel statistical channel model taking into account atmospheric and misalignment fading is developed that generalizes the existing models and accounts for transmitter beamwidth. The channel capacity is analyzed under average and peak optical power constraints and a new class of non-uniform discrete input distributions are developed with mutual information that closely approaches the channel capacity. Algorithms to realize the proposed non-uniform signaling and achieve the promising rates are also presented. Numerical simulations are conducted with finite length low density parity check codes showing significant improvement in system performance. Finally, the developed signaling is applied to FSO channels considering the above impairments. Beamwidth optimization is considered to maximize the channel capacity subject to outage. It is shown that a rate gain of 80% can be achieved with beamwidth optimization.</p> / Thesis / Doctor of Philosophy (PhD)

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / Multiple-input multiple-output (MIMO) communication systems are attracting attention because their channel capacity can exceed single-input single-output systems, with no increase in bandwidth. While MIMO systems offer substantial capacity improvements, it can be challenging to characterize and verify their channel models. This paper describes a software MIMO channel simulator with a graphical user interface that allows the user to easily investigate a number of MIMO channel characteristics for a channel recently proposed by the 3rd Generation Partnership Project (3GPP).

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / Wireless communication systems may use training signals for the receiver to learn the fading coefficients of the channel. Obtaining channel state information (CSI) at the receiver is often times necessary for the receiver to correctly detect and demodulate transmitted symbols. The type of training signal, the length of time to spend training, and the frequency of training are all important parameters in these types of systems. In this work, we derive an analytic expression for calculating the optimal training parameters for continuously fading channels. We also provide simulation results showing why this training scheme is considered optimal.