Reverse Link
Definition: The reverse link in an IS-95 system is any link from a mobile subscriber to a base station.
Note: In IS-95 cellular systems operating in the 800 MHz band, the physical channel of the reverse link is the approximately 1.25 MHz of bandwidth centered at a frequency 45 MHz below the physical channel of the forward link. In PCS systems operating in the 1900 MHz band, the physical channel of the reverse link is 80 MHz below the physical channel of the forward link.
Reverse Link
Application: Two different types of signals or channels may be transmitted on the reverse link in IS-95 systems. These signal types are the Access Channels and the traffic channels. There can be as many as 32 Access Channels per paging channel associated with any one pilot. The number of reverse-link traffic channels is generally determined by the system self-interference. The total number of reverse-link channels supporting calls in progress equals the total number of forward-link traffic channels also supporting the same number of calls. Therefore, the number of traffic channels cannot exceed 63, the maximum number of Walsh words available to traffic, even though there are many more than this number of long code offsets which uniquely identify the individual Access Channels and mobile users.
Reverse Link
Example: The access and traffic messages on IS-95 reverse links use rate 1/3 convolutional coding, interleaving, and a binary symbol rate of 28.8 ksym/sec. The symbols are partitioned into blocks of 6 and used to select one of 64 Walsh words which are the orthogonal waveforms in the 64-ary orthogonal modulation scheme used on the reverse link. Redundant symbols potentially created by symbol repetition are removed by the data burst randomizer. The 64-chip Walsh words are spread by the output of the long code generator and the Offset QPSK PN spreader before being transmitted. The output of the data burst randomizer causes the reverse-link signal from each mobile to have a variable duty cycle on a frame-to-frame basis. For full-rate Vocoder frames the duty cycle is unity. For half, quarter, and eighth-rate, frames the duty cycle equals the frame rate.
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