Digital automatic gain control design with large dynamic range in wireless communication receivers

Automatic gain control technology is usually adopted to solve the problem of large dynamic range of input signals. Aiming at the challenges existing in digital automatic gain control (DAGC) algorithm, this paper proposes an approximate method based on logarithmic space, and solves the problem of circuit complexity and low dynamic range in traditional DAGC algorithm with the employment of a lookup table. The novel algorithm can change gains of multiple modules on the receiving path at one time, and realize a large dynamic gain control range of 76dB without sacrificing the convergence speed and accuracy. The simulation results show that this new type of DAGC can adjust the overall gain of the receiver rapidly and efficiently according to different input signal amplitudes, and has good engineering practicability with the advantage of simplified circuit.

I. Introduction

In a wireless communication system, influenced by the difference of the environment in the process of signal transmission, the effect of multipath fading and the interference from other frequency signals, the intensity of signals received by a receiver fluctuates in a wide range which is often greater than 60 dB in most cases. For example, a receiver working under GSM communication protocol has an input power range from −102dBm to −15dBm, while the signals fed into a radar receiver may float from −110dbm to 20dBm. On the other hand, the signal strength that the receiver needs to transmit to the baseband processor must be within the range in which the latter can operate normally, otherwise the loss of effective signals or system performance errors may occur. For the purpose of maintaining a relatively constant output signal, there are three methods that can be adopted [1]: reducing the noise figure of the front-end amplifier, choosing analog to digital converter (ADC) with a big dynamic range, and using the Automatic Gain Control (AGC) technology. Constrained by hardware conditions, the structure of RF front-end amplifier and ADC can be improved in relatively small space. Therefore, designing a suitable AGC structure has rising to be a hotspot issue for wireless receiver design in recent years.