Automatic gain control in a communications system
An automatic gain control technique generates one or more gain control signals based on a known sequence of samples received in a preamble of a packet received over a particular communications link and generates one or more adjusted gain control signals based on a previously unknown sequence of samples received in a payload of a packet. In at least one embodiment of the gain control technique, time domain samples of the preamble of a symbol are used to generate the one or more gain control signals. In at least one embodiment of the gain control technique, frequency domain samples are used to generate the one or more adjusted gain control signals. The one or more gain control signals include digital and/or analog gain control signals that are provided to digital signal processing modules and/or analog circuits in an interface circuit, respectively, to adjust the gain applied to a received signal.
1. A method comprising:
receiving a payload portion of a received packet based on a gain control signal having a first value; and
selectively adjusting the gain control signal to have a second value, the second value being based on the payload portion of the received packet, the selectively adjusting comprising:
generating an update indicator in response to a payload detection indicator based on the received packet and an error detection indicator based on decode of the payload portion of the received packet;
generating the second value based on frequency domain samples of the payload portion of the received packet, the first value being based on time domain samples of a preamble portion of a second received packet; and
adjusting the gain control signal to have the second value in response to the update indicator.
2. The method, as required by claim 1 , further comprising:
generating the first value based on the preamble portion of the second received packet.
3. The method, as required by claim 2 , wherein generating the first value comprises:
determining the first value based on the time domain samples of the preamble portion of the second received packet.
4. The method, as required by claim 2 , wherein the received packet and the second received packet are the same packet.
5. The method, as required by claim 2 , wherein the payload portion of the received packet includes previously unknown data and the preamble portion of the second received packet includes previously known data.
6. The method, as required by claim 1 , further comprising:
determining the second value based on at least one frequency domain symbol of the payload portion of the received packet.
7. The method, as required by claim 1 , wherein the adjusting the gain control signal to have the second value is in response to the error indicator indicating an absence of an error condition.
8. The method, as required by claim 1 , wherein the selectively adjusting comprises:
maintaining the gain control signal at the first value in response to the error detection indicator indicating an error in the decode of the payload portion.
9. The method, as required by claim 1 , wherein the detection indicator is based on a number of received symbols of the payload portion equaling a number of expected symbols.
10. The method, as required by claim 1 , wherein the error detection indicator indicates an absence of an error condition in response to timing acquisition completing for the received packet and a cyclic redundancy check associated with the payload portion failing.
11. The method, as required by claim 1 , wherein the error detection indicator is based on an indicator of a timeout condition.
12. The method, as required by claim 1 , wherein the gain control signal comprises an analog gain control signal and a digital gain control signal, wherein the method further comprises:
providing the analog gain control signal to a receiver interface circuit; and
providing the digital gain control signal to a digital signal processing circuit.
13. The method, as required by claim 1 , wherein the second value is based on a demodulated symbol of the payload portion of the received packet.
14. The method, as recited in claim 1 , wherein selectively adjusting comprises
generating the error detection indicator based on the payload portion of the received packet; and
generating the payload detection indicator based on the received packet.
15. A receiver comprising:
a receiver interface circuit;
a gain generation circuit configured to generate a gain signal having a first value based on time domain samples of a preamble portion of a packet received using the receiver interface circuit and configured to generate the gain signal having a second value based on frequency domain samples of a payload portion of a second packet received using the receiver interface circuit;
a control circuit configured to generate an update indicator based on detection of the payload portion of the second packet and an error indicator based on the payload portion of the second packet; and
a selection circuit configured to provide the second gain value as an update to the gain signal having the first value in response to the update indicator.
16. The receiver, as recited in claim 15 , further comprising:
a demodulator configured to generate a frequency domain symbol based on the payload portion of the second packet, wherein the second value is based on the frequency domain symbol.
17. The receiver, as required by claim 15 , wherein the packet and the second packet are the same packet.
18. The receiver, as recited in claim 15 , wherein the selection circuit provides the second gain value in response to the timing acquisition completing and a fail of a cyclic redundancy check of a payload portion of the second packet.
19. The receiver, as recited in claim 15 , wherein the gain signal includes the analog gain signal and the digital gain value and the receiver interface circuit comprises:
an analog portion configured to generate an analog baseband signal in response to a radio frequency analog signal and an analog gain signal;
an analog-to-digital converter circuit configured to convert the analog baseband signal into a digital baseband signal, and
a digital portion configured to recover data from packets of the digital baseband signal based on a digital gain signal.
20. An apparatus comprising:
means for receiving packets; and
means for selectively adjusting a gain of the means for receiving to have one of a first value and a second value, the first value being based on time domain samples of a preamble portion of a packet received by the receiving means and the second value being based on frequency domain samples of a payload portion of a second packet received by the receiving means,
wherein the means for selectively adjusting provides the second value to the means for receiving as an update to the gain having a first value in response to detection of the payload portion of the second packet and an absence of an error in decode of the payload portion of the second packet.