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Frequency Hopping Spread Spectrum (FHSS) is a technique that wireless devices communicate such that the transmission frequencies are alternated in a pre-determined ordered hopping pattern. In tradition, the hopping sequence is controlled by using a pseudo-random code sequence (PN code) known only to both transmitter and receiver. In this paper, the carrier frequency of a frequency shift keying FSK system is interfered by the surrounding environment. Thus, FHSS will be used instead to switch between multiple carriers within the available bandwidth to minimize the interference. Such a system requires that the generated PN code ensures that all carrier frequencies within the hopping pattern should be semiequallyused during transmission. Several simulation scenarios were carried out to compare between a single long PN code and an accumulated short one. Finally, the developed FH system is implemented using an AD9910 Direct Digital Synthesizer (DDS) and an ALTERA Cyclone-III FPGA chip. Results proved that, according to the system requirements, an accumulated short PN code offers noticeable residual correlations and provides a higher level of autocorrelation compared to a single long PN code. Results, also, verified that the developed FH system provides lower Bit Error Rate (BER) than the FSK one.

OPTIMAL SELECTION OF PN CODE SEQUENCE FOR A DDS FREQUENCY HOPPING TRANSMITTER