Industrial radio control systems require a high degree of safety and reliability even in operating environments where harsh interference conditions exist. In order to implement Spread Spectrum (SS) modulation techniques in industrial radio control systems, a hybrid Direct Sequence/Frequency Hopping (DS/FH) system with high speed synchronization capability was designed, implemented and evaluated. In this system, a digital matched filter was utilized for despreading the DS signal. By manipulating the despread signal and sensing the correlation peak, the frequency hopping circuit can operate without a special synchronizing circuit. The focus of this report is on an engineering sample created for the 900MHz band available as an ISM band in the U.S. In this sample, error correction code was integrated with the hybrid DS/FH which gives the system excellent narrow-band interference rejection properties and Code Division Multiple Access (CDMA) capabilities.

PSK coherent demodulation has difficulty in achieving high speed carrier extraction and symbol synchronization when implementing to slow FH-SS radio system. On the other hand, implementation to FPGA has the requirement of a small gate size to design because of FPGA cost issue. We developed a QPSK coherent demodulation digital modem for FH-SS radio systems using FPGA by solving problems. The designed modem performs symbol synchronization with no carrier extractions, under the limitation of the small gate size requirement. The modem employs shift arithmetic operation and a comb digital BPF to achieve very good synchronization lock-up performance with small gate size. In this paper, the symbol synchronization and the carrier tracking scheme are mainly discussed. Analysis of its performance and stability are also explained. The achievement of its very good performance is presented by experimental measurement.