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GMSK Demodulation Methods and Comparisons

Bishop, Daniel W.
http://rave.ohiolink.edu/etdc/view?acc_num=akron1216081075

Abstract Details

2008, Master of Science, University of Akron, Electrical Engineering.
Modern phase modulated communication systems, such as GSM cellular phones,require the transmitters to meet a number of performance parameters so that robust links can be achieved. A few of these parameters include: well tuned carrier frequency, low peak phase offset, and low RMS phase error. These parameters must be tested on all new cellular phones coming off the manufacturing line. The mass quantities of cellular phones being produced require that the tests be done quickly and accurately. The method for determining the frequency and phase performance of a GMSK transmitter requires a receiver to generate an ideal reference signal that contains the same symbols as the measured signal. The measured signal is subtracted from the ideal signal so that the errors generated from the transmitter can be easily determined. This work has two goals. First, it surveys methods of building robust GMSK receivers for testing the transmitter. Second, it proposes a new algorithm to improve performance. Building a GMSK receiver to test the transmitter requires three major components. These components are: the timing recovery mechanism, the carrier recovery mechanism, and the demodulator. The purpose of the timing recovery is to align the sampled data to symbols. This work surveys some previously derived methods such as cross correlation and autocorrelation methods. It then presents a new method that is an extension of the cross correlation method by adding a multiple linear regression technique. The purpose of the carrier recovery is to determine the carrier offset from the nominal frequency. Among previously derived methods we survey methods such as squaring the IQ data and using data aided carrier recovery. A new method derived from the multiple linear regression method is then presented. A maximum likelihood demodulator is essential for a robust receiver and this work discusses two methods. The integrate and dump method is by itself not a maximum likelihood detector, but with the proposed extension of the mini trellis it then becomes a pseudo-maximum likelihood detector. The Viterbi demodulator is a maximum likelihood detector and this work presents some optimizations for state reduction to decrease the number of computations and the amount of memory needed. We then compare the performance and accuracy of each of the component methods with simulations.
Nathan Ida, PhD (Advisor)
62 p.
Frequency Offset; GSM; Training Sequences; phase error; offset; bits; Viterbi

Recommended Citations

Citations

  • Bishop, D. W. (2008). GMSK Demodulation Methods and Comparisons [Master's thesis, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1216081075

    APA Style (7th edition)

  • Bishop, Daniel. GMSK Demodulation Methods and Comparisons. 2008. University of Akron, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1216081075.

    MLA Style (8th edition)

  • Bishop, Daniel. "GMSK Demodulation Methods and Comparisons." Master's thesis, University of Akron, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1216081075

    Chicago Manual of Style (17th edition)

akron1216081075
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© 2008, all rights reserved.
This open access ETD is published by University of Akron and OhioLINK.