written 7.5 years ago by
modified 4.4 years ago
There are two channel assignment strategies in cellular system.
A. Fixed channel assignment:
- In fixed channel assignment each cell is permanently allocated predetermined group of channels. Any call attempt within cell can only be served by unused channels in that particular cell.
- If all channels are occupied, the call is blocked and subscriber does not receive service.
- Borrowing technique where a cell is allowed to borrow channels from a neighbouring cell if all channels are already occupied is always used with this type of strategy. Mobile Base station (MSC) monitors the function of base station including borrowing ensuring that borrowing does not interfere with any call in progress in donor cell.
B. Dynamic channel assignment:
- In dynamic channel assignment strategy, voice channels are not allocated permanently.
- Entire pool of frequency channels lies with MSC and each time a call request is made, the serving base station requests a channel from the MSC. Switch then allocates a channel to the requested cell following a algorithm.
- MSC allocates frequency channels on dynamic basis if that frequency channel is not presently in use in the cell or any other cell which falls within the minimum restricted distance of frequency reuse to avoid co-channel interference.
- It reduces chances of blocking which increases trunking capacity of system as all available channels are accessible to all cells.
- In this MSC has to collect real time data on channel occupancy, traffic distribution, radio signal strength indication of all channels on continuous basis, thus increasing the computational load on MSC.