Multiple antennas help in combating the destructive effects of fading as well as improve the spectral efficiency of a communication system. Receive diversity techniques like maximal ratio receive combining have been popular means of introducing multiple antennas into communication systems. Space-time block codes present a way of introducing transmit diversity into the communication system with similar complexity and performance as maximal ratio receive combining. In this thesis we study the performance of space-time block codes in Rayleigh fading channel. In particular, the quasi-static assumption on the fading channel is removed to study how the space-time block coded system behaves in fast fading. In this context, the complexity versus performance trade-off for a space-time block coded receiver is studied. As a means to improve the performance of space-time block coded systems concatenation by convolutional codes is introduced. The improvement in the diversity order by the introduction of convolutional codes into the space-time block coded system is discussed. A general analytic expression for the error performance of a space-time block coded system is derived. This expression is utilized to obtain general expressions for the error performance of convolutionally concatenated space-time block coded systems utilizing both hard and soft decision decoding. Simulation results are presented and are compared with the analytical results. / Master of Science

No description available.

No description available.

No description available.

Wireless Sensor Networks (WSNs) that use tiny wireless devices capable of communicating, processing, and sensing promise to have applications in virtually all fields. Smart homes and smart cities are just few of the examples that WSNs can enable. Despite their potential, WSNs suffer from reliability and energy limitations. In this study, we address the problem of designing Distributed Data Storage Systems (DDSSs) for WSNs using decentralized erasure codes. A unique aspect of WSNs is that their data is inherently decentralized. This calls for a decentralized mechanism for encoding and decoding. We propose a distributed data storage framework to increase data survivability in WSNs. The framework utilizes Decentralized Erasure Codes for Data Survivability (DEC-DS) which allow for determining the amount of redundancy required in both hardware and data to allow sensed data to survive failures in the network. To address the energy limitations, we show two approaches to implement the proposed solution in an energy efficient manner. The two approaches employ Random Linear Network Coding (RLNC) to exploit coding opportunities in order to save energy and in turn prolong network life. A routing based scheme, called DEC Encode-and-Forward (DEC-EaF), applies to networks with routing capability, while the second, DEC Encode-and-Disseminate (DEC-EaD), uses a variation of random walk to build the target code in a decentralized fashion. We also introduce a new decentralized approach to implement Luby Transform (LT)-Codes based DDSSs. The scheme is called Decentralized Robust Soliton Storage (DRSS) and it operates in a decentralized fashion and requires no coordination between sensor nodes. The schemes are tested through extensive simulations to evaluate their performance. We also compare the proposed schemes to similar schemes in the literature. The comparison considers energy efficiency as well as coding related aspects. Using the proposed schemes can greatly improve the reliability of WSNs especially under harsh working conditions. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2013-09-30 22:43:04.509

The performance of turbo codes can often be improved by improving the weight spectra of such codes. Methods of producing the weight spectra of turbo codes have been investigated and many improvements were made to refine the techniques. A much faster method of weight spectrum evaluation has been developed that allows calculation of weight spectra within a few minutes on a typical desktop PC. Simulation results show that new high performance turbo codes are produced by the optimisation methods presented. The two further important areas of concern are the code itself and the decoding. Improvements of the code are accomplished through optimisation of the interleaver and choice of constituent coders. Optimisation of interleaves can also be accomplished automatically using the algorithms described in this work. The addition of a CRC as an outer code proved to offer a vast improvement on the overall code performance. This was achieved without any code rate loss as the turbo code is punctured to make way for the CRC remainder. The results show a gain of 0.4dB compared to the non-CRC (1014,676) turbo code. Another improvement to the decoding performance was achieved through a combination of MAP decoding and Ordered Reliability decoding. The simulations show a performance of just 0.2dB from the Shannon limit. The same code without ordered reliability decoding has a performance curve which is 0.6dB from the Shannon limit. In situations where the MAP decoder fails to converge ordered reliability decoding succeeds in producing a codeword much closer to the received vector, often the correct codeword. The ordered reliability decoding adds to the computational complexity but lends itself to FPGA implementation.

M.Ing. (Electrical and Electronic Engineering) / In this thesis, spectral shaping techniques are applied to the insertion/deletion error correcting codes. Spectral shaping techniques are introduced and applied to insertion/deletion error correcting codes. The attainable rates for subcodes with spectral properties are computed and presented. The theory of comma-free codes is briefly reviewed and a new construction method is given : for comma-free insertion/deletion correcting codes. This method serves as a lower bound on the cardinality of comma-free insertion/deletion codes. The idea of a marker is introduced as an alternative method of finding word boundaries. Rules are given for governing the construction of marker code books that can differentiate between additive and insertion/deletion errors. The marker code books are then used in such: a way as not to violate the spectral properties of the abovementioned insertion/deletion correcting codes. A new class of codes is presented that has higher order spectral zeros at both DC and the Nyquist frequency. It is shown that these codes are insertion/deletion and additive error correcting. Besides this, it is shown that the abovementioned class of codes can correct two adjacent additive errors.

In some practical systems, most of the errors are of 1 → 0 type and 0 → 1 errors occur very rarely. In this thesis, first, the capacity of the asymmetric channel is derived. The capacity of the binary symmetric channel (BSC) and the Z-channel can be derived from this expression as special cases. Second, the error detecting capability of Bose-Lin codes beyond the maximum designed error detection capability are described. Third, a new class of a systematic t-unidirectional error detecting codes over Z [subscript m], m≥2 is designed. These codes can detect 2 errors using r=2 check bits and up to m[superscript (r-2)] + r-2 errors using r>2 check bits. Some upper bound on the maximum number of detectable errors when using r check bits are given. Finally, some analysis on the data throughput when using the following protocols over the m-ary Z-Channel, m≥2 are derived: (1) ARQ protocols using t-Asymmetric Error Detecting (t-AED) codes. (2) ARQ protocols using All Asymmetric Error Detecting (AAED) codes. (3) Type-I Hybrid ARQ protocols using t-Asymmetric Error Correcting and All Asymmetric Error Detecting (t-EC/AAED) codes. (4) ARQ Protocols with diversity combining using t-Asymmetric Error Correcting and All Asymmetric Error Detecting (t-EC/AAED) codes. Finally, some open research problems are described. / Graduation date: 2005

Stabilizer codes form a special class of quantum error correcting codes. Nonbinary quantum stabilizer codes are studied in this thesis. A lot of work on binary quantum stabilizer codes has been done. Nonbinary stabilizer codes have received much less attention. Various results on binary stabilizer codes such as various code families and general code constructions are generalized to the nonbinary case in this thesis. The lower bound on the minimum distance of a code is nothing but the minimum distance of the currently best known code. The focus of this research is to improve the lower bounds on this minimum distance. To achieve this goal, various existing quantum codes are studied that have good minimum distance. Some new families of nonbinary stabilizer codes such as quantum BCH codes are constructed. Different ways of constructing new codes from the existing ones are also found. All these constructions together help improve the lower bounds.

No description available.