Frequency Reuse and Channel Allocation in Cellular Systems
Frequency Reuse in Cellular Systems
Frequency reuse is a key concept in cellular communications, allowing for the optimization of limited frequency resources by using the same frequencies in different geographical areas, thus enhancing call capacity.
Finding Co-Channel Cells
In a cellular system, co-channel cells are those that use the same frequency channels for communication. The number of these cells within a cluster can be represented by the parameter N. An example would be a configuration where N = 19, illustrated through the positioning of cells in the cluster to minimize interference while maximizing coverage.
Example 2.1: Channel Availability Calculation
To understand how many channels are available in each cell based on different frequency reuse (N) settings, we can analyze the example given:
Total available bandwidth: 33 MHz
Channel bandwidth: 25 kHz for one simplex channel (50 kHz for a duplex channel)
Total available channels: This can be calculated as follows:
[ Total \ channels = \frac{33,000 \ kHz}{50 \ kHz/channel} = 660 \ channels ]
Available Channels per Cell for Different Values of N
For N = 4:
[ Total \ channels \ per \ cell = \frac{660}{4} \approx 165 \ channels ]For N = 7:
[ Total \ channels \ per \ cell = \frac{660}{7} \approx 95 \ channels ]For N = 12:
[ Total \ channels \ per \ cell = \frac{660}{12} \approx 55 \ channels ]
Allocation of Control and Voice Channels
The system allocates a segment of its spectrum for control channels. Here, 1 MHz of the total bandwidth is dedicated to control channels:
Control channels available:
[ Total \ control \ channels = \frac{1,000 \ kHz}{50 \ kHz/channel} = 20 \ control \ channels ]
When distributing the total channels evenly across the cells, it's important to note that control channels are typically allocated per cell:
In practice: Only 640 of the 660 channels are allocated for voice, while each cell will have one control channel set aside.
Example Allocation for Each N
For N = 4:
Total channels per cell = 165
Control channels: 5
Voice channels: 160
For N = 7:
Total channels per cell = 95
Control channels: 1
Voice channels: 94
For N = 12:
Total channels per cell = 55
Control channels: 1
Voice channels: 54
This distribution ensures an efficient utilization of the channels in a cellular network, balancing the need for communication control with the voice communication capacity.