Orthogonal frequency division multiplexing receiver system and its automatic gain control method

Abstract

The invention provides an orthogonal frequency division multiplexing receiving system and an automatic gain control method. The antenna of the system is connected with a band-pass filter, a radio frequency gain amplifier, an orthogonal demodulator, a baseband gain amplifier, a first digital-to-analog converter, a decoder, a frame alignement judging device, an automatic gain controller, a signal power processor, a second digital-to-analog converter, a ogarithmic detector, a band-pass filter in turn, wherein the automatic gain controller is respectively connected with the baseband gain amplifier, the radio frequency gain amplifier, while the first digital-to-analog converter is connected with the frame alignement judging device. The gain control method is that the receiver carries the logarithm demodulation on the received signals, to control the system gain according to the power detecting result and the state of the two modules of frame synchronization and the decoder, to reach the aim of correctly adjusting the system gain. The invention has high detecting precision, small computation complexity, short response time, which is suitable to orthogonal frequency division multiplexing receiving system and can effectively increase the significant figure of the analog-to-digital converter.

Description

technical field [0001] The invention relates to the technical field of wireless digital communication, in particular to an orthogonal frequency division multiplexing receiver system and an automatic gain control method thereof. Background technique [0002] OFDM (Orthogonal Frequency Division Multiplexing) technology is actually a type of MCM (Multi-Carrier Modulation, multi-carrier modulation). The main idea is to divide the channel into several orthogonal sub-channels, convert high-speed data signals into parallel low-speed sub-data streams, and modulate them for transmission on each sub-channel. Orthogonal signals can be separated by using correlation techniques at the receiver, which can reduce the mutual interference (ICI) between sub-channels. The signal bandwidth on each sub-channel is smaller than the correlation bandwidth of the channel, so each sub-channel can be regarded as flat fading, so that inter-symbol interference can be eliminated. And since the bandwidth...

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Problems solved by technology

[0004] The traditional automatic gain control is an isolated module, which estimates the signal power and controls the system receiving gain according to the current measurement value, but the gain controller has a settling time (Settling Time), that is, from setting a new gain to the signal reaching the new gain During this time, the signal is in an unpredictable oscillating state. According to the OFDM signal bandwidth and the stabilization time of different gain controllers, the stabilization period affects 0.5 to 5 time-domain signal samples, and the gain is changed during effective signal transmission. It will affect all subcarriers contained in the OFDM symbol (symbol), which increases the bit error rate; the traditional method tracks the change of signal power at any time, and because the peak-to-average ratio of OFDM is large, it must balance the response time and power estimation, and Due to the inevitable control delay of the digital control loop, it will cause the power estimation to be too small in a certain period of time, so that the gain setting is too large, resulting in too large baseband output level. Since there are many peaks in the time domain of the OFDM signal, such too large The peak output will cause the analog circuit to slow down for a period of time, causing the analog-to-digital converter to output a meaningless full-level signal for a period of time, causing the effective signal to be blocked by the slow down after the peak; traditional power measurement mostly uses the digital signal of the baseband signal. Sampling, limited by the number of bits of the analog-to-digital converter, when the signal power changes greatly, it takes a long time to get an accurate estimate.

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