Channel Assignment Strategies
Introduction:
Channel assignment affects the performance of the system, especially when it comes to handoffs. There are several channel assignment strategies
Two basic types Channel Assignment Strategies
Fixed Channel Assignment
In this channel assignment, channels are preâ€allocated to different cells meaning that each cell is assigned a specific number of channels and the frequencies of these channels are set.
Such a channel assignment has the following aspects:
· Any call attempts in a cell after all channels of that cell become occupied gets BLOCKED
· Very simple and requires least amount of processing
· A variation of this method is the Borrowing Strategy:
· Cells in this strategy are allowed to borrow channels from adjacent cells if their channels are fully occupiedwhile adjacent cells have free channels
· MSC (Mobile Switching Center) monitors the process and gives permission to borrowingcell to borrow channels putting in mind
· donating cell is not affected by the borrowingprocess,
· No interference will occur by moving the channel from one cell to another.
Dynamic Channel Assignment
In this channel assignment, channels are NOT preâ€allocated to any cells meaning that any channel can be allocated to any desired cell during the operation of the system.
Such a channel assignment has the following aspects:
· MSC (Mobile Switching Center)monitors all cells and all channels,
· Each time a call request is made, serving BS requests a channel from the MSC,
· MSC runs an algorithm that takes into account:
1. Possibility of future blocking in cells
2. Frequency being used for channel
3. The reuse distance of the channel
· MSC assigns a channel only if it is not used and if it will not cause coâ€channel interference with
· any cell in range,
· This algorithm provides higher capacity (less blocking),
· It requires huge computational power,
· MSC collects realâ€time data of channel occupancy, traffic distribution, and radio signal strengths
· Indicators (RSSI).