1. Field
The present disclosure relates generally to telecommunications, and more specifically, to noise variance estimation techniques in wireless communications.
2. Background
In a typical telecommunications system, the data to be transmitted is encoded with a turbo code, which generates a sequence of symbols, referred to as “code symbols.” Several code symbols may be blocked together and mapped to a point on a signal constellation, thereby generating a sequence of complex “modulation symbols.” This sequence may be applied to a modulator, which generates a continuous time signal, which is transmitted over a wireless channel.
At the receiver, the modulation symbols may not correspond to the exact location of a point in the original signal constellation due to noise and other disturbances in the channel. A demodulator may be used to make soft decisions as to which modulation symbols were most likely transmitted based on the received points in the signal constellation. The soft decisions may be used to extract the Log-Likelihood Ratio (LLR) of the code symbols. The turbo decoder uses the sequence of code symbol LLRs to decode the data originally transmitted.
In a receiver employing multiple antennas, a Pilot Weighted Combining (PWC) technique is often used to combine the soft decisions for each antenna. The combined soft decisions may then be used to compute the LLRs for the code symbols. One problem with this approach is the potential difference in thermal noise for each antenna. As a result, the PWC procedure for combining soft decisions may not optimize the Signal-to-Noise Ratio (SNR). Accordingly, there is a need in the art for an improved demodulation process that considers the thermal noise for one or more antennas mounted on a receiver.