An Interpolated Frequency-Hopping Spread-Spectrum Transceiver

A technique of spread-spectrum transmission, interpolated frequency-hopping (IFH), is presented. IFH employs a carrier that moves smoothly and continuously in frequency, helping to alleviate problems, such as spectral splatter and transient mismatch, which are a concern in conventional phase-locked loop (PLL)-based frequency-hopping spread-spectrum systems. In IFH, the pseudorandom hopping code is passed through a digital interpolation filter prior to controlling the synthesizer instantaneous frequency output. While such filtering is commonly used in data pulse-shaping to improve the spectral characteristics of the modulated carrier, such filtering has not been reported for IFH codes, where the frequency deviations are changing and can span several MHz. The implications of matching the transient responses of two PLL-based frequency synthesizers using this method have also not been reported. Initial simulation and laboratory measurements indicate that, for certain cases, IFH shows a 1.9 dB improvement in received IF power, has a much sharper roll-off of inband phase noise when compared to conventional hopping, and provides a phase-coherent IF after despreading. An IFH transceiver system using – frequency synthesis and a – frequency discriminator is proposed. The system would be suitable for integrated mobile radio applications in slow-fading environments.