Hi,
aaron_do wrote on Nov 17^th, 2008, 12:30am:

The answer to this question it's specific to each system, in general the information that the terminal it's receiving it's useless for it's own transmission since the channel could have changed before he is able to access to the medium(except maybe for ACK-acknowledgment- packets, and some standards define the data rate and power of the ACK packet for reliable transmission).
Channel estimators typically use one of the following(depends on the System Level Architecture-by System I mean protocol,standard):

-Training sequences: if there is a preamble in the received packet this is known so it can be calculated the EVM or use of a MMSE algorithm for channel estimation.

-Some standards(GSM and UMTS if I remember well) sent continuous or periodic carrier pilots of a known power, so the terminal can estimate the power needed for transmission.Here you can use an analog RSSI to estimate the power needed for transmission(if the pilot it's continuous you have real time information on the channel).

-In a OFDM system exists the possibility to configurate the subcarriers for channel estimation:some subcarriers are not data modulated and some other carriers are nullified so it can be done a SNR estimation.

This information typically it's feedback to the terminal that it's transmitting so it can adjust the output power level and/or the modulation, so for maximum efficiency it's necessary a full-duplex system and the method should be chosed carefully taking into account the coherence time of the channel since information could be old when it's sent.

-One simple way to adjust dynamically the data rate it's to count the ACK's, if after N packets all the ACK's are received increase the data rate if some are lossed decrease the data rate(I think that method was one of the first used in WLAN).

As you can see most of this techniques are into the DSP domain(except RSSI), you can look to your particular system and see what they do.

It's difficult to give references since its a topic that falls between radio engineering,digital signal processing and network engineering...

Hope it helps,