Abstract: The disclosed invention provides a method, a system and a computer program product for the maximum likelihood sequence estimation of transmitted MSK symbols. The disclosed invention provides a set of optimizations of the Viterbi algorithm for equalizing MSK symbols. The transmitted MSK symbols are alternately real and imaginary. Therefore, based on whether the transmitted MSK symbol is real or imaginary, the disclosed invention divides the set of Viterbi states into two sets of states. The disclosed invention obtains the surviving path only for the first set of states at stages corresponding to real transmitted symbols. A real hypothesis is used to obtain the surviving paths for the first set of states. The disclosed invention also obtains the surviving path only for the second set of states at stages corresponding to imaginary transmitted symbols. An imaginary hypothesis is used to obtain the surviving paths of the second set of states.

Abstract: The disclosed invention provides a system, a method and a computer program product for timing offset estimation for frequency selective fading channels in wireless communication systems. The disclosed invention first obtains a corrected received signal using the received signal and a pre-estimated timing offset. The pre-estimated timing offset is further tracked in two steps. In the first step a plurality of probable deviations in the pre-estimated timing offset are considered. Then a training sequence is used to determine an expected signal corresponding to each of the probable deviations. The corrected received signal is then shifted through the probable deviations. Thereafter error factor between the expected signals and corresponding shifted received signals is obtained. The probable deviation yielding optimum error factor is then identified as the first estimate of the deviation in timing offset.

Abstract: A computationally efficient method and system for decoding shortened cyclic codes is presented. The increase in computational efficiency is achieved by improvement of the syndrome calculation step. Two embodiments of the present invention are described; the first embodiment is optimized for a hardware implementation and the second embodiment is optimized for a Digital Signal Processor (DSP) implementation. The present invention is applicable to decoding of all the binary shortened cyclic codes, including Fire codes used for Coding Scheme-1 (CS-1) for GSM.

Abstract: A method, system and computer program product for obtaining the reliability values for the hard decisions obtained by a Viterbi equalizer in a wireless communication system. A difference parameter is obtained for each Viterbi state at a stage while advancing the Viterbi trellis by the stage. The difference parameter for a Viterbi state at a stage is obtained by subtracting the path metric of the non-surviving path from the path metric of the surviving path for the Viterbi state at the stage. The difference parameter corresponding to the Viterbi state on the ML path at a stage is used as the reliability value for the hard decision obtained at L stages behind the stage, where L is the memory of the Viterbi trellis. A method for obtaining the accurate reliability values for the hard decisions corresponding to the last L stages of a truncated Viterbi trellis is also provided.

Abstract: The disclosed invention provides a method, a system and a computer program product for the maximum likelihood sequence estimation of transmitted MSK symbols. The disclosed invention provides a set of optimizations of the Viterbi algorithm for equalizing MSK symbols. The transmitted MSK symbols are alternately real and imaginary. Therefore, based on whether the transmitted MSK symbol is real or imaginary, the disclosed invention divides the set of Viterbi states into two sets of states. The disclosed invention obtains the surviving path only for the first set of states at stages corresponding to real transmitted symbols. A real hypothesis is used to obtain the surviving paths for the first set of states. The disclosed invention also obtains the surviving path only for the second set of states at stages corresponding to imaginary transmitted symbols. An imaginary hypothesis is used to obtain the surviving paths of the second set of states.

Abstract: A system, method and computer program product for detecting a frequency burst in a received signal at a wireless receiver is disclosed. The invention predicts the current sample of the received signal by filtering the past samples of the received signal through an adaptive filter. A prediction error is further obtained by subtracting the actual current sample and the predicted current sample. The prediction error is then used to adapt the adaptive filter. Since the frequency burst is a substantially predictable signal, the adaptive filter adapts to accurately predict the samples of the frequency burst. Therefore, the prediction error decreases when the frequency burst is received at the receiver. The end of the frequency burst is identified using the prediction error at each discrete time instant.

Abstract: A method and an apparatus for improving the equalization performance of a wireless receiver in the presence of co-channel interference by selectively filtering a received signal are disclosed. In the presence of co-channel interference, the noise in the received signal comprises a white noise component and a non-white noise component. Improvement in equalization is achieved by whitening the non-white noise component by selectively filtering the received signal. The selective filtering is governed by the dominant component of the noise in the received signal. The disclosed invention is suitable for use in Global System for Mobile Communications (GSM) wireless receivers using Gaussian Minimum Shift Keying (GMSK) signaling. The non-white noise component in the received signal, caused predominantly by co-channel interference, is whitened before feeding the received signal to Maximum Likelihood Sequence Estimator (MLSE), thereby improving the performance of MLSE.