Demodulator for symbols transmitted over a cellular channel
AssigneeHughes Aircraft Company
InventorYoungky Kim
Life of this patent
Estimating the term…
Abstract
A lower order Viterbi system for estimating symbols being transmitted over a digital cellular channel. The received signal is oversampled at a rate at least twice the frequency of the symbol duration. The energy contained in the main and interference symbol signal is thus sampled and permits a superior BER to be obtained. The branch metric for the lower order Viterbi algorithm is calculated using both signal samples. Channel status information is individually estimated for both samples, further improving system BER. The channel status is obtained for both frequency offset errors, amplitude fading and phase occurring within the channel.
Claims7
A circuit for processing a data signal transmitted as symbols in a multipath fading transmission channel comprising:
- a sampling circuit for producing a sampled data signal at a rate of substantially twice the rate of symbols being transmitted to obtain signal samples of a transmitted symbol signal and an interference symbol signal;
- a channel estimator connected to receive said sampled signal, computing a frequency offset function, an amplitude fading function and a phase function, occurring in said transmission channel on a two sample per symbol basis;
- and,
- a Viterbi equalizer for estimating the value of each received symbol from said sampled data, representing a transmitted symbol signal and an interference symbol signal, including calculating a branch metric for each possible state of said symbol based upon two samples per symbol and based upon a frequency offset, amplitude fading, and phase determined from said channel estimator, said equalizer providing from said sampled data signal an estimate of said symbol from energy contained in said symbol signal and interference symbol signal.
A method for processing a data signal transmitted as symbols in a multipath fading transmission channel comprising:
- sampling said data signal at a rate of substantially twice the rate of symbols being transmitted;
- estimating from said sampled data signal a frequency offset function, an amplitude fading function, and a phase function occurring in said transmission channel on a two sample per symbol basis;
- and,
- estimating the value of each received symbol from said sampled data using a Viterbi equalizer, including calculating a branch metric for each possible state of said symbol based upon two samples per symbol and based upon said estimated frequency offset, estimated amplitude fading, and estimated phase.
Dependencies are inferred from the claim text.