Automatic gain control method and apparatus for wireless communication systems
View Patent ↗A system and method are provided for automatic gain control (AGC) using an adaptive reference and a threshold. An adaptive reference allows for adjusting the target power based on variations in operating parameters and conditions, such as a change to a modulation schemes which requires a different signal to noise ratio (SNR) to maintain performance. A gain adjustment threshold allows for rapid AGC response while reducing the potential effects of hysterisis. AGC levels may be changed during symbol prefixes or suffixes, and avoided during a data portion of a signal. Embodiments allow for symbol-by symbol AGC changes in OFDM, OFDMA, and TDD systems.
1. A method of automatic gain control (AGC) for a signal, said method comprising:
determining a power level of said signal;
comparing said power level with an adaptive reference to determine a target gain change, wherein said adaptive reference increases when a modulation change of said signal requires additional signal power to maintain a performance level and said adaptive reference decreases when said modulation change of said signal requires less power to maintain said performance level; and
adjusting amplification of said signal based on said target gain change, if said target gain change exceeds a threshold.
2. The method of claim 1 wherein said threshold is a threshold for increasing gain or decreasing gain.
3. The method of claim 1 further comprising: adjusting said reference in response to a change in operating parameters or conditions.
4. The method of claim 3 wherein said change in operating parameters or conditions is a change in a modulation scheme.
5. The method of claim 1 wherein said adjusting amplification occurs outside a data portion of said signal.
6. The method of claim 1 wherein said adjusting amplification occurs on a symbol-by-symbol basis.
7. The method of claim 1 wherein said signal is selected from the list including: time division duplex, orthogonal frequency division multiplexing, and orthogonal frequency division multiple access signals.
8. An apparatus for automatic gain control (AGC) for a signal comprising:
logic for determining a power level of said signal;
logic for comparing said power level with an adaptive reference to determine a target gain change, wherein said adaptive reference increases when a modulation change requires additional signal power to maintain a performance level and said adaptive reference decreases when said modulation change requires less power to maintain said performance level;
logic for comparing said target gain change with a threshold, wherein said threshold is adjusted to avoid detrimental effects in said signal; and
logic for adjusting amplification of said signal based on said target gain change, if said target gain change exceeds said threshold.
9. The apparatus of claim 8 wherein said threshold is a threshold for increasing gain or decreasing gain.
10. The apparatus of claim 8 wherein said adaptive reference is varied in response to a change in operating condition additional to said modulation change.
11. The apparatus of claim 8 wherein said adjusting amplification occurs outside a data portion of said signal.
12. The apparatus of claim 8 wherein said adjusting amplification occurs on a symbol-by-symbol basis.
13. The apparatus of claim 8 wherein said signal is selected from the list including: time division duplex, orthogonal frequency division multiplexing, and orthogonal frequency division multiple access signals.
14. An automatic gain control (AGC) system comprising:
a variable gain amplifier;
a power determination unit coupled to an output of said amplifier;
an adaptive reference that increases when a modulation change requires additional signal power to maintain a performance level and said adaptive reference decreases when said modulation change requires less power to maintain said performance level;
a comparison unit operable to compare an output of said power determination unit with said adaptive reference and produce a comparison signal; and
a threshold trigger coupled to an output of said comparison unit, said trigger operable to prevent adjustment of said variable gain amplifier when a magnitude of said comparison signal is below a threshold.
15. The system of claim 14 wherein said adaptive reference is varied in response to a change in operating condition additional to said modulation change.
16. The system of claim 14 wherein said adjustment of variable gain amplifier occurs on a symbol-by-symbol basis.
17. The system of claim 14 wherein a signal received by said variable gain amplifier is selected from the list including: time division duplex, orthogonal frequency division multiplexing, and orthogonal frequency division multiple access signals.
18. The system of claim 17 wherein said adjustment of variable gain amplifier occurs during a prefix or a suffix of said signal.