Measurement of radio channels using an elastic convolver and spread spectrum modulation. I. Implementation

Using spread spectrum signals a measurement system has been built in order to measure the radio channel in steel works. It transmits a 511-chip long maximum length sequence with a chip rate of 44 MHz: binary phase shift keying modulated onto a 1.75 GHz carrier. A surface acoustic wave convolver yields the channel´s impulse response with a time resolution of about 20 ns. The periodic autocorrelation performed within a measurement window removes aperiodic correlation sidelobes which limit the dynamic range of a matched-filter implementation. Additionally, absolute time delay measurements of all echoes were obtained using a synchronization cable connecting receiver and transmitter. Compared to other spread spectrum correlation techniques, the convolver makes possible a much simpler real-time measurement setup