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Patent Embodiments in accordance with the invention provide a state-based channel section method to improve the rate of successful transmissions for multi-channel wireless network. Channels are monitored for performance, and, based upon performance, are placed in channel state vectors having increasing levels of desirability. The higher the state vector in which a channel is placed, the more desirable the channel is considered for selection. The channel in the highest state vector is considered for selection first. A channel not in the highest desirable state vector is eligible for selection when a channel is unavailable from higher desirable state vectors. Channels not in the highest desirable state vector, are monitored for improvement to move into higher desirable state vectors as they improve.

The conversion from homogeneous global system for mobile communications (GSM) networks to heterogeneous GSM/universal mobile telecommunications system (UMTS) networks is rapidly expanding. Previous research identified vulnerabilities in the GSM network that were fixed in the UMTS standard; however, the mobile device must successfully access the UMTS network to take advantage of security improvements. Therefore, a possible vulnerability not addressed in either the GSM or UMTS standards is the potential for a malicious entity to prevent a mobile device from handing over from a GSM to UMTS network, because the GSM network maintains the stand-alone dedicated control channel (SDCCH) uplink time slots. The process of testing this vulnerability requires the development of a device that monitors a GSM base transceiver station, identifies when a handover to UMTS message is sent, tracks the time slots of the SDCCH uplink, and transmits a GSM handover-failure message. In this thesis, we present an open-source coding scheme that utilizes parts of the OpenBTS source code to transmit a GSM handover-failure message using the universal software radio peripheral. The method is validated through the collection of the GSM transmitter messages by Airprobes GSM-receiver software. http://archive.org/details/softwaredefinedr1094538978 Lieutenant, United States Navy Approved for public release; distribution is unlimited.

Covert channels in modern communication networks are a source of security concerns. Such channels can be used to facilitate command and control of botnets or inject malicious contents into unsuspected end-user devices or network nodes. The vast majority of the documented covert channels make use of the upper layers of the Open Systems Interconnection (OSI) model. In this thesis, we present a new covert channel in IEEE 802.11 networks, making use of the Protocol Version field in the Medium Access Control (MAC) header. This is achieved by forging modified Clear To Send (CTS) and Acknowledgment (ACK) frames. Forward error correction mechanisms and interleaving were implemented to increase the proposed channel's robustness to error. A laboratory implementation of the proposed channel is presented by developing the necessary code in Python, operating in a Linux environment. We present the results of tests conducted on the proposed channel, including measurements of channel errors, available data rate for transmission, and level of covertness. http://archive.org/details/amaclayercovertc1094548138 Lieutenant, Portuguese Navy Approved for public release; distribution is unlimited.

This thesis studies the performance of Multiple-Input, Multiple Output (MIMO) systems that use Space-Time Block Coding (STBC). Such systems can be employed to improve the bit error rate (BER) performance of wireless communication systems and counter the detrimental effects of channel fading and other distortion phenomena. We propose a systematic method for designing a space-time orthogonal MIMO scheme that employs an arbitrary number of transmitting and receiving antennas, and we evaluate (through simulation) the performance improvements that can be attained by employing our design approach. We present a general formula for determining the rate (i.e., the ratio of the number of symbols transmitted to the number of symbol intervals required) of systems that employ our design. Additionally, this thesis analyzes the relationship between channel correlation and antenna spacing for the case of MIMO systems that use a linear antenna configuration, and, through simulation studies, we show how such systems can take the advantage of the multipath phenomenon to reduce the detrimental effects of channel correlation. http://archive.org/details/asystematicpproa109452812 Approved for public release; distribution is unlimited.

Orthogonal frequency division multiplexing (OFDM) is an efficient multi-carrier modulation technique which can be combined with transmitter and receiver diversity communication systems. Maximal ratio combining (MRC) and space-time block coding (STBC) can be used in conjunction with receiver and transmitter diversity in order to increase the communication system's performance. For these systems, channel estimation and tracking must be performed since the receiver requires channel state information for decoding. In this thesis, block-type and comb-type channel estimation algorithms for OFDM systems over multipath fading channels are studied and simulated. Performance results using simulated frequency-selective channels are presented. http://archive.org/details/channelestimatio109452091 Approved for public release; distribution is unlimited.

This thesis investigates the simulation performance of multiple-input multiple-output (MIMO) systems utilizing Alamoutibased space-time block coding (STBC) technique. The MIMO communication systems using STBC technique employing both single- carrier modulation and orthogonal frequency division multiplexing (OFDM) are simulated in Matlab. The physical layer part of the IEEE 802.16a standard is used in constructing the simulated OFDM schemes. Stanford University Interim (SUI) channel models are selected for the wireless channel in the simulation process. The performance results of the simulated MIMO systems are compared to those of conventional single antenna systems. http://archive.org/details/simulationperfor109451311 Lieutenant Junior Grade, Turkish Navy Approved for public release; distribution is unlimited.

The radio channel places fundamental limitations on the performance of mobile ad hoc wireless networks. In the mobile radio environment, fading due to multipath delay spread impairs received signals. The purpose of this thesis is to develop a radio channel model and examine the effect of various parameters on channel behavior that is representative of environments in which mobile ad hoc wireless networks operate. The various physical phenomena considered are outdoor environments, fading and multipath propagation, type of terrains, and mobility (Doppler shift). A channel model based on a Tapped Delay Line (TDL) structure was developed and implemented in the MATLAB programming language, and the performance of the time-varying channel was studied by plotting the signal constellations. The simulation results indicate that the number of taps required in the TDL is 8 or less and the carrier frequency did not influence the performance significantly. The Jakes Doppler spectrum should be used in urban environments with high mobility; the Gaussian Doppler spectrum is the choice for low mobility urban environments and for the hilly terrain under both low and high mobility. http://archive.org/details/radiochannelmode109451510 Civilian, Singapore Ministry of Defense Approved for public release; distribution is unlimited.

This thesis examines the compression performance of the JPEG2000 standard for image transmission over noisy channels. Other features of the standard, such as error resilience and region of interest, have been studied and their effectiveness tested on several images. The JPEG2000 still image compression standard has provided higher compressions performance with lower distortion and better image quality than JPEG. JPEG2000 has the capability to define regions of interest of any shape and size and code the selected regions with a higher fidelity than the rest of the image. Compressed image data is transmitted over a noisy wireless channel based on Gilbert-Eliot model, which simulates both isolated and burst errors. JPEG2000 error resilient tools are used to allow the decoder to detect and conceal errors introduced in the channel. The results indicate up to 10 dB improvement in the peak signal to noise ratio when these tools are used. http://archive.org/details/jpegimagecompres109455974 Lieutenant, Hellenic Navy Approved for public release; distribution is unlimited.

The objective of this thesis is to study the performance of the MPEG-4 video coding standard in the presence of highly erroneous media, such as a wireless channel. MPEG-4 treats video sequences as a collection of objects rather than a collection of frames. A Matlab encoder that conforms to this approach is built for compressing raw video signals at various compression rates. A two-state Markov channel was used to simulate a wireless channel that introduces errors in the video bitstream and a decoder that utilizes error concealment techniques to hide these errors from the user was used to reconstruct the video sequence. The error resilient tools that the MPEG-4 standard provides to enhance the robustness in the presence of errors were simulated and proven to be advantageous compared to methods used in previous standards (MPEG-2, H.263, etc.). At the decoder, the use of error concealment techniques significantly enhanced the quality of the reconstructed video in high bit error rate environments. http://archive.org/details/transmissionoflo109456099 Hellenic Navy author.

The performance of a Direct Sequence Spread Spectrum system utilizing Differential Phase Shift-Keying modulation over a fading channel in the presence of pulse noise interference and additive white Gaussian noise is considered. Time and spatial diversity receivers utilizing various normalization schemes and post-detection selection combining are employed to overcome performance limitations inherent in the adverse environments. Numerical results are presented over a range of environmental conditions demonstrating the efficacy of such receivers. The performance analysis is extended through the utilization of convolutional coding and soft decision Viterbi decoding. Here the performance of the maximum likelihood decoding operation is expressed in terms of an equivalent uncoded system for both the Rayleigh and Rician fading channel with interference effects. Numerical results are then presented demonstrating the efficacy of such a receiver. http://archive.org/details/softdecisiondive1094513650 Lieutenant Commander, United States Navy Approved for public release; distribution is unlimited.

With the growth of information dissemination over digital communication networks, much research has been devoted to compressing digital image information for efficient transmission. The ability to adjust the desired resolution of an image as the available bandwidth on the network changes allows the user to control the flow of data according to the resources available. In this thesis we integrate multiresolution image compression methods with image recognition techniques to assist in automatic image recognition at several levels of resolution. Features of grayscale and binary images of text characters and aircraft line drawings are described using wavelet transform coefficients, wavelet transform subband energy, and Fourier transform coefficients. Transmission of these features over a digital communication link is simulated, and multiresolution recognition performance in the presence of channel noise is presented. http://archive.org/details/multiresolutioni1094532113 NA U.S. Navy (U.S.N.) author Approved for public release; distribution is unlimited.

In this thesis, a hybrid lossless compression model is tested which employs a combination of both a lossy compression method and one or more lossless image compression methods to produce an overall lossless image compression. The hybrid model decomposes the original image into a browse and a residual image. The hybrid model is tested and evaluated using various combinations of lossy and lossless image compression methods. The lossy compression method used in the model is JPEG (Joint Photographic Experts (Group) . The lossless compression methods used are Huffman, Arithmetic, LZW, lossless JPEG. and Diagonal coding. The compression results achieved using the hybrid compression model are compared to the compression achieved using the corresponding direct lossless compression. Additionally, the hybrid model is evaluated as to the advantages that the decomposition of the image into browse and residual images provide to the user. http://archive.org/details/asimplelowoverhe1094527264 Lieutenant, United States Navy

A multiple-input, multiple-output (MIMO) recursive least squares (RLS) algorithm is developed to shape and control the Loran-C RF pulse of the AN/FPN-44A tube type transmitter. The control algorithm is incorporated into a transmitter simulation program, where it seeks to produce an optimal transmitter drive waveform (TDW). An optimal TDW produces a near ideal RF pulse. The control algorithm uses a MIMO reference model of the transmitter; parameters of the model are obtained using recursive least squares multichannel time series techniques. The MIMO reference model has the ability to adapt to the non-LTI characteristics of the simulated transmitter. The MMO RLS control algorithm is implemented in both an ideal and a realistic noisy environment. In the ideal environment, when representing the RF pulse with parameters of its half-cycle peak amplitudes and zero-crossings, the MIMO RLS controller is able to shape the RF pulse and control its zero-crossings. Quantization and system noise in the non-ideal environment results in performance deterioration of the control algorithm. The performance of the MIMO RLS algorithm is compared against another method of control, the steepest descent algorithm. http://archive.org/details/mimorecursivelea1094540014 Lieutenant, United States Coast Guard Approved for public release; distribution is unlimited.