S. Y. Kruglikov, Rybinsk State Academy of Aviation Technology, Rybinsk, Russia
SYNCHROINFO JOURNAL. Volume 5, Number 2 (2019). P. 14-16.
The Japanese personal digital cellular (PDC) and North American TDMA cellular systems employ receivers that use either differential detection or coherent detection along with a sequence estimator or decision feedback equalizer (DFE). Time-division multiple-access (TDMA) receivers must have the ability to synchronize accurately on each received burst. Synchronization is difficult to achieve in the presence of signal impairments such as carrier frequency offset, Doppler spread, cochannel interference, multipath fading, thermal noise, and nonlinear disunion . Of these impairments, carrier frequency offset is one of the main causes for the failure of a maximum likelihood sequence estimation (MLSE) receiver. Frequency offset rotates the overall discrete-time channel impulse response so that the adaptive channel estimator in the MLSE receiver cannot track the channel variations . Frequency offset also degrades the performance of differential detectors operating under conditions of high Doрpler shift and/or low signal-to-noise ratio (SNR). In this case, the received signal points are likely to cross decision boundaries because the phase of the received signal point is shifted in an amount proportional to the Doppler shift. For these reasons, it is important to correct frequency offset before any further processing on the received signal . Synchronization is difficult to achieve in the presence of high-level noise in satellite communication systems too. Thus, it is necessary to develop a robust frequency offset estimators that provides satisfactory performance over a wide range of channel char-acteristics. In this connection, a novel frequency offset estimation algorithm is proposed for π/4-DQPSK on multipath channels of cellular communications and on AWGN channel of satellite communication.
Keywords: Japanese personal digital cellular, North American TDMA cellular systems, maximum likelihood sequence estimation.
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