A high performance digital channel simulator for satellite transmissions

The paper describes a channel simulator especially suited for simulating transmissions over satellites. The increasingly large instantaneous bandwidths of satellite transmission systems make it challenging to perform a digital channel simulation in the lab using standard equipment, as dynamic range and bandwidth are linked and the available data converter technology and feasible clock rates for digital processing impose a certain limit, which is typically lower than the feasible bandwidth of an analogue transponder on a high operating frequency. The paper describes the architecture of a digital channel simulator, which allows combining of multiple signal processor cards for parallel processing to a signal bandwidth which exceeds the bandwidth of a single card. By cascading up to seven processor boards the channel simulator can simulate a bandwidth of up to 700 MHz. In case the transponder bandwidth to be simulated is less than the full bandwidth of the simulator, the total bandwidth can be divided up into up to three sub-bands which operate independently The propagation effects and effects of the satellite transponder itself are simulated for each sub-band. To test the behaviour of the system under interference conditions, Arbitrary Waveform Generators allow insertion of multiple interference signals with configurable bandwidths and sampling rates. A shaped noise source allows the user to simulate the presence of in-band and out-of-band interferers in each sub-band. Phase noise is implemented by a multiplication with e^jphi(t) for each sub-band. Both a memoryless non-linearity is simulated and an output filter can be configured for each sub-band. Additive white Gaussian noise may be added with variable noise density. Large scale and small scale fading can be simulated by either streaming complex fading multiplication factors from hard disk or using integrated channel models. For automated setups, the channel simulator can be fully remote controlled.