CDMA FORWARD AND REVERSE CHANNELS. Forward Channels. The Forward CDMA channel is the cell-to-mobile direction of communication or the. The Forward IS95 Channel consists of several code channels: the Pilot Channel, The Pilot tone is always transmitted by the base station on each active Forward CDMA Channel. a number of Forward Traffic Channels (at , , , and bit/s). There can be up to 32 Access Channels on the IS reverse link for each Paging Channel on forward link. Reverse traffic channel (RTC): Like the Forward Traffic Channel, this reverse link IS channel is used to carry variable rate voice data, user data and signaling.
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As with other channels there are a number of stages taken to produce the final channel.
First the baseband information is error protected. After this the data is repeated if it is at a rate of 4. Following this the data is interleaved and then scrambled by the decimated long PN sequence, and finally spread by the Walsh is-95 cdma forward channel for the particular channel assignment.
In this process the long PN code is itself masked with a code which is specific to the channel being used. This IS channel is used to provide the timing reference to access the cell.
This IS channel always uses Walsh code Each base station has a is-95 cdma forward channel timing offset to reduce the interference between adjacent base-stations.
is-95 cdma forward channel The Sync channel incorporates an 80 mS superframe structure. This is divided into three This means that they align with the timing on the Pilot channel.
The data that is transmitted on this channel includes the system time, pilot PN of the base station, long code state, system ID, and the network ID.
As the name implies, the Forward Traffic Channel is used to carry voice, user data, and also signalling information. Is-95 cdma forward channel carrying voice, the coded voice data does not require a constant bit rate and IS allows the rate of the frames to change dynamically every 20 ms.
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When the rate is reduced it reduces the level of interference to other users. The original vocoder specification used a set of rates based on divisions of 9.
This is reflected in ISA. Later the vocoder was improved to give better voice quality and in ISB a vocoder was introduced with a rate set based on Is-95 cdma forward channel data is always carried at full rate.
IS Channels | cdmaOne Channels |
It is continuously transmitted by each base station on each active CDMA is-95 cdma forward channel. And, each mobile station tracks this signal continuously. Likewise, the mobile station can have the exact system time by the means of synchronizing to the short code. Forward traffic channels[ edit ] The Walsh space not dedicated to broadcast channels on the BTS sector is available for traffic channels.
Explain in detail IS forward and reverse Channels in detail
These channels carry the individual voice and data calls supported by IS Like the paging channel, traffic channels have a frame time of 20ms. Since is-95 cdma forward channel and user data are intermittent, the traffic channels support variable-rate operation.
Every 20 ms frame may be transmitted at a different rate, as determined by the service in use voice or data. For voice calls, the traffic channel carries frames of vocoder data.
A number of different vocoders are defined under IS, the earlier of which were limited to rate set 1, and were responsible for some user complaints of poor voice quality. More sophisticated vocoders, taking advantage of modern DSPs and rate set 2, remedied is-95 cdma forward channel voice quality situation and are still in wide use in