Techniques for improving the performance of frequency-hopped multiple-access communication systems

Imperial Users onl

The Deep Space Network: A Radio Communications Instrument for Deep Space Exploration

The primary purpose of the Deep Space Network (DSN) is to serve as a communications instrument for deep space exploration, providing communications between the spacecraft and the ground facilities. The uplink communications channel provides instructions or commands to the spacecraft. The downlink communications channel provides command verification and spacecraft engineering and science instrument payload data

Variable Redundancy Coding for Adaptive Error Control

This thesis is concerned with variable redundancy(VR) error control coding. VR coding is proposed as one method of providing efficient adaptive error control for time-varying digital data transmission links. The VR technique involves using a set of short, easy to implement, block codes; rather than the one code of a fixed redundancy system which is usually inefficient, and complex to decode. With a VR system, efficient data-rate low-power codes are used when channel conditions are good, and very high-power inefficient codes are used when the channel is noisy. The decoder decides which code is required to cope with current conditions, and communicates this decision to the encoder by means of a feedback link. This thesis presents a theoretical and practical investigation of the VR technique, and aims to show that when compared with a fixed redundancy system one or more of the advantages of increased average data throughput, decreased maximum probability of erroneous decoding, and decreased complexity can be realised. This is confirmed by the practical results presented in the thesis, which were obtained from field trials of an experimental VR system operating over the HE’ radio channel, and from computer simulations. One consequence of the research has been the inception of a study of codes with disjoint code books and mutual Hamming distance (initially considered for combatting feedback errors), and this topic is introduced in the thesis

A permutation coding and OFDM-MFSK modulation scheme for power-line communication

Power-line communication offers a networking communication over existing power lines and finds important applications in smart grid, home and business automation and automatic meter reading. However, the power-line channel is one of the harshest known communication channels currently in use and it requires robust forward error correction techniques. Powerful decoding algorithms tend to be complex and increase latency while robust modulation schemes offer lower data rates and reduced spectral efficiency. The presented research is a frequency domain error-correcting scheme that extends the existing narrowband power-line communication forward error correction concatenated scheme of Reed-Solomon and Convolutional codes in the OFDM framework. It introduces a combination of M-ary phase shift keying as an OFDM subcarrier modulation scheme and a permutation sequence encoding between subcarriers to combat narrowband interference and carrier frequency offsets by introducing frequency diversity. The scheme offers improved BER performance over OFDM and OFDM-MFSK in high narrowband disturbance and impulse noise probability channels and improves the performance of OFDM in the presence of carrier frequency offsets

WIMAX 802.16 PHYSICAL LAYER IMPLEMENTATION AND WIMAX COVERAGE AND PLANNING.

Over the last decade, the impact of wireless communication on the way we live and carry out business has been surpassed only by impact of the internet. But wireless communications is still in its infancy and the next stage of its development will be supplementing or replacing network infrastructure that was traditionally wired. The advent and adoption of the computer and the myriad software packages available for it offered the ability to generate a new wave of communication combining art, pictures, music and words into a targeted multimedia presentation. These presentations are large so that is requires higher bandwidth transmission facilities. Coupling this with the need for mobility, the solution would be wireless data delivery putting in consideration the bandwidth request. WiMAX technology is based on the IEEE 802.16 standard, it was only recently when the first IEEE 802.16 based equipment broadband began to enter the market. The additional spectrum, bandwidth and throughout capabilities of 802.16 will remarkably improve wireless data delivery and should allows even more wireless data service areas to be deployed economically. In this Final Year Project, a study about the IEEE 802.16 standard and mainly concentrate on the 802.16 PHY Layer behaviors was performed. A Simulink based model for the 802.16 PHY Layer was built for simulation and performance evaluation of WiMAX. MATLA

Cooperative Transmission Techniques in Wireless Communication Networks

Cooperative communication networks have received significant interests from both academia and industry in the past decade due to its ability to provide spatial diversity without the need of implementing multiple transmit and/or receive antennas at the end-user terminals. These new communication networks have inspired novel ideas and approaches to find out what and how performance improvement can be provided with cooperative communications. The objective of this thesis is to design and analyze various cooperative transmission techniques under the two common relaying signal processing methods, namely decode-and-forward (DF) and amplify-and-forward (AF). For the DF method, the thesis focuses on providing performance improvement by mitigating detection errors at the relay(s). In particular, the relaying action is implemented adaptively to reduce the phenomenon of error propagation: whether or not a relay’s decision to retransmit depends on its decision variable and a predefined threshold. First, under the scenario that unequal error protection is employed to transmit different information classes at the source, a relaying protocol in a singlerelay network is proposed and its error performance is evaluated. It is shown that by setting the optimal signal-to-noise ratio (SNR) thresholds at the relay for different information classes, the overall error performance can be significantly improved. Second, for multiple-relay networks, a relay selection protocol, also based on SNR thresholds, is proposed and the optimal thresholds are also provided. Third, an adaptive relaying protocol and a low-complexity receiver are proposed when binary frequency-shift-keying (FSK) modulation is employed and neither the receiver nor the transmitter knows the fading coefficients. It is demonstrated that large performance improvements are possible when the optimal thresholds are implemented at the relays and destination. Finally, under the scenario that there is information feedback from the destination to the relays, a novel protocol is developed to achieve the maximum transmission throughput over a multiple-relay network while the bit-error rate satisfies a given constraint. With the AF method, the thesis examines a fixed-gain multiple-relay network in which the channels are temporally-correlated Rayleigh flat fading. Developed is a general framework for maximum-ratio-combining detection when M-FSK modulation is used and no channel state information is available at the destination. In particular, an upper-bound expression on the system’s error performance is derived and used to verify that the system achieves the maximal diversity order. Simulation results demonstrate that the proposed scheme outperforms the existing schemes for the multiple-relay network under consideration

PERFORMANCE COMPARISON OF NON-INTERLEAVED BCH CODES AND INTERLEAVED BCH CODES

This project covers the research about the BCH error correcting codes and the performance of interleaved and non-interleaved BCH codes. Both long and short BCH codes for multimedia communication are examined in an A WGN channel. Algorithm for simulating the BCH codes was also being investigated, which includes generating the parity check matrix, generating the message code in Galois array matrix, encoding the message blocks, modulation and decoding the message blocks. Algorithm for interleaving that includes interleaving message, including burst errors and deinterleaving message is combined with the BCH codes algorithm for simulating the interleaved BCH codes. The performance and feasibility of the coding structure are tested. The performance comparison between interleaved and noninterleaved BCH codes is studied in terms of error performance, channel performance and effect of data rates on the bit error rate (BER). The Berlekamp-Massey Algorithm decoding scheme was implemented. Random integers are generated and encoded with BCH encoder. Burst errors are added before the message is interleaved, then enter modulation and channel simulation. Interleaved message is then compared with noninterleaved message and the error statistics are compared. Initially, certain amount of burst errors is used. "ft is found that the graph does not agree with the theoretical bit error rate (BER) versus signal-to-noise ratio (SNR). When compared between each BCH codeword (i.e. n = 31, n = 63 and n = 127), n = 31 shows the highest BER while n = 127 shows the lowest BER. This happened because of the occurrence of error bursts and also due to error frequency. A reduced size or errors from previous is used in the algorithm. A graph similar to the theoretical BER vs SNR is obtained for both interleaved and non-interleaved BCH codes. It is found that BER of non-interleaved is higher than interleaved BCH codes as SNR increases. These observations show that size of errors influence the effect of interleaving. Simulation time is also studied in terms of block length. It is found that interleaved BCH codes consume longer simulation time compared to non-interleaved BCH codes due to additional algorithm for the interleaved BCH codes

Analysis of hybrid-ARQ based relaying protocols under modulation constraints

In a seminal paper published in 2001, Caire and Tuninetti derived an information theoretic bound on the throughput of hybrid-ARQ in the presence of block fading. However, the results placed no constraints on the modulation used, and therefore the input to the channel was Gaussian. The purpose of this thesis is to investigate the impact of modulation constraints on the throughput of hybrid-ARQ in a block fading environment. First, we consider the impact of modulation constraints on information outage probability for a block fading channel with a fixed length codeword. Then, we consider the effect of modulation constraints upon the throughput of hybrid-ARQ, where the rate of the codeword varies depending on the instantaneous channel conditions. These theoretical bounds are compared against the simulated performance of HSDPA, a newly standardized hybrid-ARQ protocol that uses QPSK and 16-QAM bit interleaved turbo-coded modulation. The results indicate how much of the difference between HSDPA and the previous unconstrained modulation bound is due to the use of the turbo-code and how much is due to the modulation constraints. (Abstract shortened by UMI.)

Fifty Years of Noise Modeling and Mitigation in Power-Line Communications.

Building on the ubiquity of electric power infrastructure, power line communications (PLC) has been successfully used in diverse application scenarios, including the smart grid and in-home broadband communications systems as well as industrial and home automation. However, the power line channel exhibits deleterious properties, one of which is its hostile noise environment. This article aims for providing a review of noise modeling and mitigation techniques in PLC. Specifically, a comprehensive review of representative noise models developed over the past fifty years is presented, including both the empirical models based on measurement campaigns and simplified mathematical models. Following this, we provide an extensive survey of the suite of noise mitigation schemes, categorizing them into mitigation at the transmitter as well as parametric and non-parametric techniques employed at the receiver. Furthermore, since the accuracy of channel estimation in PLC is affected by noise, we review the literature of joint noise mitigation and channel estimation solutions. Finally, a number of directions are outlined for future research on both noise modeling and mitigation in PLC