A solution for the precise and cost-effective generation of frequency-hopping spread-spectrum waveforms using digital frequency synthesis based on read-only-memories (ROM, PROM, EPROM) is studied. For matched filter reception of frequency-hopping spread-spectrum waveforms a new approach based on lock-in amplifiers combined with synchronous voltage controlled oscillators (SVCO) brought remarkable results in practical field tests. An application-specific digital signal processor for receiver operation in form of a CMOS gate array was also designed. Prototypes according to two different system concepts were built, and measurements of bit error probability were carried out on indoor and outdoor power-line networks. Computer simulations based on channel analysis to predict bit error probability are proposed and compared with measured results. Indoor prototypes are designed for a data rate of 300 b/s and a frequency-hop rate of 900 s/sup -1/ with a transmission voltage approximately=0.35 V/sub rms/ in a spectral range from 30 to 146 kHz. Outdoor prototypes are intended for remote meter reading featuring a data rate of 60 b/s and a frequency-hop rate of 300 s/sup -1/. Transmission voltage is variable from 0.35 to 1 V/sub rms/ in a spectral range from 30 to 146 kHz.>

In spread-spectrum communication systems, a basic task which has to be performed is the synchronization of the receiver pseudonoise (PN) signal with the pseudonoise signal contained in the input. In this paper, a synchronization system employing a surface acoustic wave tapped delay line (SAW TDL) matched filter for both initial synchronization (acquisition) and tracking is presented. The periodic correlation peaks at the SAW TDL output repeatedly correct the epoch of the local PN signal clock phase and the code generator initial condition to their correct values. As the correlation impulses are distorted and attenuated due to the effects of message modulation, Doppler frequency shifts and unavoidable interferences, a modulation canceller and a differentiating device are employed to improve synchronization performance. Formulas for estimating the performance of a system incorporating these ideas are given. A hardware implementation of the suggested system has been built and tested. Experimental results obtained with the system are presented.

The large time-bandwidth products realizable with the aid of surface acoustic wave (SAW) tapped delay lines facilitate the construction of accurate timing circuits which can be employed e.g. in the p-n signal synchronizing circuit of a spread spectrum system. The performance of such a timing circuit, which employs a 255 chip SAW tapped delay line and a circuit for detecting the maximum of the correlation peak, is investigated theoretically and the theoretical results are checked by experiment. It is found that the input signal level required for the timing circuit with differentiation to achieve a specified timing variance is less than that of a timing circuit without differentiation by about 3 dB. Furthermore, differentiation makes the timing circuit practically immune to changes of the threshold level.