GMSK narrowband modem

Details GMSK narrowband modem GMSK narrowband modem

1989-09-11

1992-02-18

Olms, Douglas W.

Pulse or digital communications

Repeaters

Testing

375 60, 375 64, 375 90, 332100, 329300, H04L 2712, H04L 2714

Patent

active

050900269

ABSTRACT:
A GMSK modem is provided and comprises a baseband modulator section and demodulator section coupled to an FM transmitter and receiver, respectively. The Modulator section includes a digital waveform generator for generating a GMSK baseband signal from a binary digital data source. The output of the waveform generator approximates the baseband signal output of a premodulation filter with a Gaussian impulse response having a normalized noise bandwidth of between 0.25 and 0.45 in series with a gain controlled amplifer. The gain is adjusted such that the modulation index of an RF signal modulated with the baseband signal is between 0.5 and 0.7.
The demodulator section receives the analog output of a discriminator-based FM receiver with a phase equalized Butterworth IF filter. The demodulator section comprises a binary quantized loop bit timing recovery subsystem and one or the other of two data detectors. The two data detectors comprise a two-bit integrate-and-dump type filter and a two-bit multithreshold integrate-and-dump type filter. The binary quantized loop is also connected to a signal quality detector for altering the mode of operation of the loop according to the amount of noise in the baseband signal.

REFERENCES:
patent: 4500856 (1985-02-01), Childs
patent: 4648099 (1987-03-01), Kerr
W. A. Sulllivan, "High Capacity Microwave System for Digital Data Transmission," 7th International Conference on Communications, Jun. 14-16, 1971, pp. 23-4 to 23-8.
Nakajima et al., "Gaussion Filtered and Amplitude Limited MSK", The Transactions of the IECE of Japan, vol. E 64, No. 11, 11/81, pp. 716-723.
Daikoku et al., "High-Speed Digital Transmission Experiments in 920 MHZ Urban and Suburban Mobile Radio Channels", IEEE Transactions on Vehicular Technology, vol. VT-31, No. 2, May 1982, pp. 70-75.
James R. Cessna and Donald M. Levy, "Phase Noise and Transient Times for a Binary Quantized Digital Phase-Locked Loop in White Gaussian Noise", Apr. 1972.
Jack K. Holmes, "Performance of a First-Order Transition Sampling Digital Phase-Locked Loop Using Random-Walk Models", Apr. 1972.
"GMSK Modulation for Digital Mobile Radio Telephone", IEEE Transactions on Communications (Jul. 1981) by K. Murota & K. Hirade.
"Spectrum Efficiency of GMSK Land Mobile Radio," IEEE International Conference on Communications (1981), by K. Murota, K. Kinoshita & K. Hirade.
"GMSK Transmission Performance in Land Mobile Radio", IEEE (1983) by K. Hirade, K. Murota & M. Hata.
"Performance of CPM Using A Discriminator Based Data Detector", IEEE Int. Conference On Communications (1988) by El-Tanany & Mahmoud.
"Continuous Phase Modulation", IEEE Communications Magazine (Apr. 1986) by C. Sundberg.
"Continuous Phase Modulation-Part I: Full Response Signaling", IEEE Transactions on Communications (Mar. 1981) by Auline & Sandberg.
"Continuous Phase Modulation-Part II: Partial Response Signaling", IEEE Transactions on Communications (Mar. 1981) by Auline & Sundberg.
G.E. "Voice Guard System" for Delta-SX Mobile Radios, Data Wave Communications, Inc., Radio Modem Hybrid Module, Model #MM9612.
GLB Electronics Model HSM 5 High Speed Radio Modem.

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