System and method for performing accurate demodulation of turbo-encoded signals via pilot assisted coherent demodulation

DETAILED DESCRIPTION The need in the art is addressed by the efficient telecommunications receiver system for accurately decoding a received composite signal having data signal and pilot signal components of the present invention.
In the illustrative embodiment, the inventive receiver system is adapted for use with a wireless code division multiple access (CDMA) communications system and includes a first circuit for receiving the composite signal and extracting a pilot signal and a data signal from received composite signal.
A second circuit calculates a preliminary log-likelihood ratio as a function of a channel estimate based on the pilot signal and/or the data signal.
A third circuit scales the preliminary log-likelihood ratio by a predetermined log-likelihood ratio scaling factor and provides an accurate log-likelihood value in response thereto.
A fourth circuit decodes the received composite signal based on the accurate log-likelihood value and the data signal.
In a specific embodiment, the pilot signal and the data signal comprise pilot samples and data samples, respectively.
The third circuit includes a carrier signal-to-interference ratio circuit for computing a first signal-to-interference ratio and a second signal-to-interference ratio based partly on the data and pilot signals.
The first signal-to-interference ratio is based on the data samples, and the second signal-to-interference ratio is based on the pilot samples.
The first signal-to-noise ratio and the second signal-to-noise ratio provide input to a scaling factor computation circuit included in the third circuit.
In a more specific embodiment, the first circuit includes a despreader for despreading the received composite signal in accordance with a predetermined spreading function and providing a despread signal in response thereto.
The spreading function is a pseudo noise sequence or a Walsh function.
The first circuit further includes a decovering circuit that extracts the pilot signal and the data signal from the despread signal