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Canada KIA 024 squarer All O(dc) sq-r DSBPSK 2fc Abstruct-The laboratory performance of four spreadspectrum (SS) detectors (full-band and partial-band radiometers, chip-rate detector (CRD) and squaring carrier detector) was measured for direct sequence (DS) and frequency hop (FH) S S signals, FHDS hybrids, and time hop (TH) DS signals. Probability of detection as a function of input SNR for a constant false-alarm rate was measured for numerous combinations of SS waveform and detector. Theories were compiled from the literature and extended as necessary to provide a unified theoretical description. The results usually agreed with theory to within one dB. A constant-false-alarm-rate method was used to reduce the drift problem of radiometers. The fact that chip-rate and squaringcarrier detectors have a much reduced drift problem was confirmed. It is concluded that the four SS detectors used are relatively simple and inexpensive devices with laboratory detection performance close to theoretical. 28.6-1 785 7803-9828-5194 $4.00 0 1994 IEEE

Frequency hopping (FH) spread spectrum is used in communications systems to provide protection against jamming.With fast FH, there are L 2 1 hops per data symbol transmitted. In the presence of severe interference, additional protection can be obtained by processing the L M values obtained from the demodulator. This processing is termed diversity combining. Many powerful and robust types of diversity combining have been developed to reduce the effects of a large jamming signal on some of the L hops. In this paper, a survey of combining methods is presented. Simulation performance results are given for severe noise and multitone jamming (SJR = 0.0 dB). It is found that bit error rates as high as 0.4 can be reduced to < 0.1 for L < 10 using any of several diversity combining methods.

The use of error correction coding and diversity has been shown to be very effective against jamming in a fast frequency hopped M-ary !?SI< (FFH/AlFSI<) system. In the system design, it is usually implied that the hop rate is variable to accommodate the optimum design parameters. Unfortunately, systems such as satellite comniuncations may have the hop rate fixed before other system parameters are decided. This paper evaluates the pcrformance of FFHIAI FSK with a fixed hop rate for both uncoded and coded systems. The performance criterion used is a throughput measure, i.e. information rate sustained by a system for a given bit error rate normalized by the hop rate. Codes with superior performance are identified.

Frequency hopping (FH) spread spectrum is a well known technique used in communications systems to provide protection against interference such as jamming. With fast FH (FFH) (one or more hops per transmitted data symbol), powerful and robust methods for diversity combining have been developed as an additional jamming countermeasure. These same techniques can be applied to reduce the effects of multiple access interference, and so can be considered for civilian CDMA applications. Although the performance of a FFH communications system can be degraded considerably by fading, few results exist which show the effects of fading on the diversity combining process. In this paper, both analytic and simulation results are presented for several diversity combining methods in a Rayleigh fading channel, which is often considered to be the worst case. The performance of these combining methods in fading is compared with that in AWGN and multitone interference to determine which methods are effective against these degradations. (1) This work was supported in part by the Natural Sciences and Engineering Research Council of Canada. V01.6, NO. 1 J a~~~a~y -F e b m~y 1995