Performance requirements for analog-to-digital converters in wideband reconfigurable radios

With the current trend towards software defined radio, several candidate architectures for the analog receiver front-end have been presented. A common proposal for software defined reconfigurable radio is to develop a wideband ADC and utilise this for capturing a large segment of the spectrum. This would enable the subsequent signal processing operations of channel selection and data extraction to be carried out by a digital processor. This would allow the radio to be reconfigured by simply changing the software. In analysis of these systems, powerful neighbouring signals, or blockers, are considered but it has been conveniently assumed that suitable dynamic range will be available at the ADC. This is an acceptable assumption in narrowband systems where automatic gain control and analogue channel select filters can be used, but is not appropriate for a wideband system. In this paper we present an analysis based on bit-error-rates (BER) which shows the effect of blockers in a wideband architecture on the performance of the communication link and on the dynamic range requirements of the ADC. We consider, as a representative example of a real world situation, the use of a wideband receiver on a Rayleigh fading channel. In any analysis of wideband receivers, the behaviour of the channel must also be included as the performance of the communication link is a combination of noise sources from both the channel and the electronics. The effect of high power interferers and blockers on the quantisation noise from the ADC will be mathematically modelled and the BER rates for the communication system will be presented. Given these results, it is possible to determine the minimum required resolution and dynamic range for an ADC in a wideband system given the spectral environment at the frequencies of interest.