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System and method for estimating a set of parameters for a transmission channel in a communication system
| Details |
Inventors: Rahmatullah, Muhammad M.; Yip, Philip; Asghar, Saf;
Assignee: Advanced Micro Devices, Inc. (Sunnyvale, CA)
Primary Examiner: Chan; Jason
Assistant Examiner: Corrielus; Jean B
Attorney, Agent or Firm: Conley, Rose & Tayon, Hood; Jeffrey C.
The present invention comprises a system and method for a GSM receiver to perform channel estimation under the assumption that the analog-to-digital (A/D) converter is free-running. A search process is employed, whereby the known GSM training signal is sampled with a plurality of phases which vary incrementally from zero to a full symbol period. For each phase a sample set (of the training signal) is generated. Furthermore, each sample set is used, together with the received samples, in a cross-correlation procedure to obtain a candidate impulse response vector for the transmission channel. Thus a plurality of candidate impulse response vectors are produced, one of which will be selected to be the optimal representative for the transmission channel. The optimal impulse response vector is selected as follows. Each impulse response vector is convolved with the corresponding sample set, thus producing an estimated output vector. The estimated output vectors are compared with the vector of received samples (from the free-running A/D converter), and the estimated output vector which is closest in the Euclidean (square-norm) sense designates the impulse response vector which is optimal. |
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DETAILED DESCRIPTION The present invention comprises a system and method for performing channel estimation in a GSM receiver.
The channel estimation operates under the assumption that the analog-to-digital (A/D) converter is free-running.
Thus, samples of the received baseband signal are obtained with unknown (but constant) phase.
The received baseband signal is a distorted version of a transmitted baseband signal, due to the effects of the transmission channel.
During the training phase of every GSM signal burst, the transmitted baseband signal is completely known to the receiver: this known signal is called the training signal.
Since the phase used to obtain the received samples is not controlled, it is not known apriori which samples of the training signal would best correspond with the received samples.
In other words, since the phase offset of the received samples is not known, it is not known which samples of the transmitted training signal should be used in correlation with the received samples.
In the system and method of the present invention a search process is employed.
First, the training signal is sampled with a plurality of phases which vary incrementally from zero to a full symbol period.
For each phase a sample set of the training signal is generated.
Furthermore, each sample set is used, together with the received samples, in a cross-correlation procedure to obtain a candidate impulse response vector for the transmission channel.
Thus, a plurality of candidate impulse response vectors are produced, one for each of the phase offsets.
Finally, one of the impulse response vectors is selected to be the optimal representative for the transmission channel.
The cross-correlation procedure operates on a sample set and the received samples to produce a candidate impulse response vector; one candidate impulse response vector is produced for each sample set.
In the preferred embodiment, the cross-correlation procedure involves performing two cross-correlations: a cross-correlation between the received samples and the known binary data (embedded in the training signal), and a cross-correlation between the sample set and the same binary data
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