Double conversion dual-carrier radio frequency receiver

摘要

In a dual-carrier, double-conversion Orthogonal Frequency Division Multiplexing (OFDM) receiver a frequency synthesizer generates a first local oscillator signal for the first down-conversions stage of the receiver. A frequency divider is used to derive a second local oscillator signal from the first local oscillator signal, thus eliminating the need for a separate frequency synthesizer for the second down-conversion stage. A controller determines the frequency of the first local oscillator signal and a divisor M to align subcarrier grids for said first and second baseband signals with DC.

主权项

1. A dual-carrier receiver for an Orthogonal Frequency Division Multiplexing (OFDM) system comprising:
a first down-converter configured to down-convert a received dual-carrier signal having first and second OFDM carriers to generate an intermediate frequency dual-carrier signal; a frequency synthesizer configured to generate a first local oscillator frequency for the first down-converter, said first local oscillator frequency being between the first and second carriers; a second down-converter configured to separate and down-convert said first and second carriers from the intermediate frequency dual-carrier signal to generate first and second baseband signals; a frequency divider coupled to said frequency synthesizer and configured to divide the first local oscillator frequency by a divisor M to generate a second local oscillator frequency for said second down-converter; and a controller configured to select the first local oscillator frequency and the divisor M to align subcarrier grids for said first and second baseband signals with direct current (DC); wherein the controller is configured to select the first local oscillator frequency by: determining an initial local oscillator frequency between the first and second carriers; and determining a frequency adjustment that when added to said initial local oscillator frequency aligns the subcarrier grids for said first and second baseband signals with DC; wherein the controller is configured to determine the frequency adjustment by: computing, as a function of a first parameter and a subcarrier spacing of the subcarrier grids, a first frequency translation to align the subcarrier grid for the first baseband signal to DC; computing, as a function of a second parameter and the subcarrier spacing, a second frequency translation to align the subcarrier grid for the second baseband signal to DC; selecting the first and second parameters to minimize a difference between actual and desired frequency translations for the first and second carriers; andcomputing the frequency adjustment as a function of one or both of the first and second parameters;
wherein the first and second parameters comprise integer values.