Our main objective in this thesis is to study the effect of narrow band interference on OFDM systems operating in the 2.4 Ghz ISM band and identify ways to improve upon existing techniques to deal with them. We first consider how narrow band signals interfere with OFDM systems. Various noise variance estimation and signal to noise ratio estimation techniques for OFDM systems are then discussed....

A new insertion/deletion correction scheme is presented for standard convolutional codes that makes use of multiple parallel-interconnected Viterbi decoders. Whenever an insertion or deletion error occurs, the connections between different Viterbi decoders ensure that decoding will proceed from the decoder that is in synchronization. In this way, a larger Viterbi decoder is created that can cor...

DBNs (Dynamic Bayesian Networks) [1] are powerful tool in modeling time-series data, and have been used in speech recognition recently [2,3,4]. The “decoding” task in speech recognition means to find the viterbi path [5](in graphical model community, “viterbi path” has the same meaning as MPE “Most Probable Explanation”) for a given acoustic observations. In this paper we describe a new algorit...

In this paper we extend an estimation technique based on Viterbi algorithm for discrete-time chaotic signals immersed in noise. The proposed modification allows for orbits generated by maps with nonuniform invariant density to be estimated. This modified Viterbi algorithm is used in two digital modulation schemes: the Modified Maximum Likelihood Chaos Shift Keying using one and two maps. Both h...

We present an algorithm for the incremental generation of word graphs. Incremental means that the speech signal is processed left-to-right by a time synchronous Viterbi algorithm and word hypotheses are generated with some delay to Viterbi decoding. The incrementally generated word hypotheses can be used for early interaction between linguistic analysis and acoustic recognition. Therefore, it i...

Sequence detection is studied for communication channels with intersymbol interference and non-Gaussian noise using a novel adaptive receiver structure. The receiver adapts itself to the noise environment using an algorithm which employs a Gaussian mixture distribution model and the expectation maximization algorithm. Two alternate procedures are studied for sequence detection. These are a proc...

In this paper, a multiple-symbol combined differential Viterbi decoding algorithm which is insensitive to frequency offset is proposed. According to the theories of multiple-symbol differential detection and maximum-likelihood detection, we combine the multiple-order differential information with the Viterbi algorithm. The phase shift caused by the frequency offset is estimated and compensated ...

Communication over wireless media is vulnerable to distortion by noise. Therefore, the application of error control mechanism is necessary to minimize the Bit Error Rate (BER). It is proposed to use locked binary convolutional code with Non-Transmittable codewords to enhance Viterbi Algorithm decoders; as one of the forward error correction mechanisms. The proposed enhancement empowers Viterbi ...