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FPGA-Based Implementation of a Hybrid DS/FFH Spread-Spectrum Transceiver

In recent years there has been great interest in using hybrid spread-spectrum (HSS) techniques for commercial applications, particularly in the Smart Grid, in addition to their inherent uses in military communications. This is because HSS can accommodate high data rates with high link integrity, even in the presence of significant multipath effects and interfering signals. A highly useful form of this transmission technique for many types of command, control, and sensing applications is the specific code-related combination of standard direct-sequence modulation with "fast" frequency-hopping, denoted hybrid DS/FFH, wherein multiple frequency hops occur within a single data-bit time. In this paper, we present the efforts carried out at Oak Ridge National Laboratory toward exploring the design and implementation of a hardware prototypic hybrid DS/FFH spread-spectrum radio transceiver using a single Field Programmable Gate Array (FPGA). The high integration within a single FPGA allows the various subsystems to easily communicate with each other and thereby maintain tight synchronization. Experimental results are presented to show the receiver sensitivity and jamming-rejection capability of the implemented hybrid DS/FFH spread-spectrum system under widely varying design parameters. Keywords—Hybrid spread-spectrum; direct-sequence; frequency-hopping; jamming; Field Programmable Gate Array (FPGA); Phase-Locked Loop (PLL)