An implementation of an AMPS digital base station with adaptive Automatic Gain Control
We consider the problem of designing a wide-band digital receiver for an Advanced Mobile Phone Service (AMPS) cellular system, and the associated problem of choosing an appropriate Analog-to-Digital (ADC) converter. The probability density function of the voltage across a cellular receiving antenna is shown to be dependent on various cellular parameters. These parameters include mobile transmit power, mobile distance from the base station, mobile transmit frequency, and transmitting and receiving antenna characteristics. Given a high-resolution, wideband, uniform and symmetric quantizer, optimal gain factors are computed for uniformly-, sinusoidally- and normally-distributed input signals. These gain factors maximize the quantizer's Signal-to-Quantization Noise Ratio (SQNR) in a mean-square sense. Together, these techniques can be used to implement an adaptive Automatic Gain Control for cellular communications. Results from a comprehensive AMPS base station simulation will also be discussed in detail. These results illustrate several design tradeoff's including Signal-to-Noise Ratio (SNR), Carrier-to-Noise Ratio (CNR), system loading and quantizer resolution.