Coherent random access channel in a spread-spectrum communication system and method

A communication unit for use in a communication system comprising:

• (a) correlator means for correlating a known synchronization sequence with a received communication signal to generate a correlation peak when a synchronization message is present in the received communication signal;
• (b) demodulator means, operatively coupled to the correlator means, for despreading the received communication signal with a spreading code to derive a stream of reference samples and a stream of data samples when the correlation peak is generated;
• (c) channel estimator means, operatively coupled to the correlator means and the demodulator means, for determining an initial channel response from the correlation peak and revising the initial channel response based on an estimated channel response derived from the stream of reference samples to form a modified channel response estimate;
• and
• (d) detector means, operatively coupled to the demodulator means and the channel estimator means, for generating an estimated data symbol from the stream of data samples by utilizing the modified channel response estimate.

A communication system comprising:

• (a) a transmitter, comprising:
• (i) a reference insertion mechanism which inserts reference symbols into a stream of access channel message data symbols to form a reference coded stream of access channel message data symbols;
• (ii) a synch insertion mechanism, operatively coupled to the reference insertion mechanism, which appends the reference coded stream of access channel message data symbols onto the end of a synchronization message to form a reference coded access channel transmission;
• (iii) a modulator, operatively coupled to the synch insertion mechanism, which prepares the synch coded access channel transmission for transmission over a communication channel by spreading the reference coded access channel transmission with a spreading code to form a spread reference coded access channel transmission prior to transmission over the communication channel;
• and
• (iv) a transmitting mechanism, operatively coupled to the modulator, for transmitting the spread reference coded access channel transmission over the communication channel;
• and
• (b) a receiver, comprising:
• (i) a receiving mechanism for receiving the spread reference coded access channel transmission over the communication channel;
• (ii) correlator, operatively coupled to the receiving mechanism, for correlating a known synchronization sequence with the received spread reference coded access channel transmission to generate a correlation peak when a synchronization message is present in the received spread reference coded access channel transmission;
• (iii) demodulator, operatively coupled to the receiving mechanism, for despreading the received spread reference coded access channel transmission with a spreading code to derive a stream of reference samples and a stream of data samples when the correlation peak is generated;
• (iv) channel estimator, operatively coupled to the correlator and the demodulator, for determining an initial channel response from the correlation peak and revising the initial channel response based on an estimated channel response derived from the stream of reference samples to form a modified channel response estimate;
• and
• (v) detector, operatively coupled to the demodulator and the channel estimator, for generating an estimated data symbol from the stream of data samples by utilizing the modified channel response estimate.

A method of communication in a communication system comprising the steps of:

• (a) inserting reference symbols into a stream of access channel message data symbols to form a reference coded stream of access channel message data symbols;
• (b) appending the reference coded stream of access channel message data symbols onto the end of a synchronization message to form a reference coded access channel transmission;
• and
• (c) preparing the reference coded access channel transmission for transmission over a communication channel by spreading the reference coded access channel transmission with a spreading code to form a spread reference coded access channel transmission prior to transmission over the communication channel.

A method of communication in a communication system comprising the steps of:

• (a) correlating a known synchronization sequence with a received communication signal to generate a correlation peak when a synchronization message is present in the received communication signal;
• (b) determining an initial channel response from the correlation peak;
• (c) despreading the received communication signal with a spreading code to derive a stream of reference samples and a stream of data samples when the correlation peak is generated;
• (d) revising the initial channel response based on an estimated channel response derived from the stream of reference samples to form a modified channel response estimate;
• and
• (e) generating an estimated data symbol from the stream of data samples by utilizing the modified channel response estimate.