Radius (km)	Area (sq km)	Subscribers	RF Channels
1	3.14	100	8
3	28.03	900	38
10	314	10,000	360

For 10,000 subscribers, to allocate 360 radio channels, we would need a bandwidth of 360 x 50 KHz = 18 MHz. Having this much bandwidth is not possible. Therefore to avoid needing extremely large bandwidths, subscribers have to share channels instead of dedicated channels for each. The cellular concept allows the efficient use and reuse of the channels to provide the service with the limited bandwidth.

Cellular Approach

With limited radio frequency resources, the cellular principle can serve many subscribers at an affordable cost. In a cellular network, the total area is divided into smaller areas called “cells”. Each of the cell can cover the limited number of mobile subscribers within its boundaries. Each cell can have the base station with the number of radio channels.

Frequencies used in one cell area will be reused at the same time in a different cell that is far away. For example The typical seven cell pattern can be used.

The total available frequency resources are divided into seven parts, with each part having a number of radio channels. One part is allocated to the each cell site. In the group of 7 cells the available frequency spectrum is fully used. The same seven sets of the frequency can be reused after the certain distance. The group of cells where the available frequency spectrum is totally used up is called a cluster of cells.

Two cells with the same number in adjacent clusters use the same set of radio channels. These are called “co-channel cells“. The distance between the cells using the same frequency should be enough to keep the interference between them at an acceptable level. Cellular systems are limited by this co-channel interference.

The cellular principle enables the following :

1. More efficient use of limited radio frequency resources.
2. Manufacturing of all subscriber devices in a region with the same set of channels, so any mobile can be used anywhere within that region.

Adjacent Channel Interference

A given data center zone/rack uses a number of server ports. Because the network switches are not perfect, they allow nearby traffic to leak into the designated bandwidth. This causes adjacent port interference. This interference can be reduced by keeping the port number separations between each server in a given rack as large as possible. When the utilization factor is high, this separation may not be enough.

A port separation, by selecting server ports that are more than 6 numbers apart, is sufficient to keep adjacent port interference within acceptable limits.

For example, the data center which follows the 4/12 pattern N = 4

Racks = 3 per zone

1. Rack A will use server ports 1, 13, 25, and so on.
2. Rack B will use server ports 5, 17, 29, and so on.
3. Rack C will use server ports 9, 21, 33, and so on.

Trunking

Cellular radios rely on trunking to serve a large number of users with limited radio spectrum. Each user is given a channel when needed for a call. When the call ends, the channel is returned to the common pool of radio channels. By sharing channels from a pool in this way, instead of dedicating channels to each user, trunking allows many users to be accommodated with fewer channels overall. This makes efficient use of the limited radio spectrum available.

Grade of Service (GOS)

Because of trunking, there is a chance that a call may be blocked if all the radio channels are being used. This is called ‘Grade of Service’ or ‘GOS’. Cellular designers estimate the maximum number of users and allocate the proper number of radio channels, in order to meet the desired GOS. For these calculations, an ‘Erlang B’ table is used.

The Erlang B table helps determine how many channels are needed to provide a certain level of service, based on the expected traffic load. By referring to this table, designers can plan the right number of channels to achieve the target GOS, which is the probability of a call being blocked.

Cell Splitting

When the number of employees reaches a maximum in a starter office floor (initial layout) and no more workstations are available, then the starter floor is divided, usually into four smaller sections. After dividing, the workforce capacity increases by four times, and more employees can be accommodated.

After ‘n’ divisions the workforce capacity will be:

W2 = W0 × 4n
(W2 is the new workforce capacity and W0 is the original workforce capacity)

The ambient noise level will be reduced:

N2 = N0 – n × 6 dB
(N2 is the new noise level and N0 is the original noise level)

Office space division improves the capacity to accommodate more employees and also lowers the ambient noise level in each section.

Conclusion

The cellular concept allows efficient use of limited radio spectrum by dividing the coverage area into small cells. Each cell has its own base station and set of channels that can be reused in other cells far away. This enables serving many mobile subscribers with better quality service using the same frequencies multiple times across the network.

Key aspects like frequency reuse, channel sharing through trunking, controlling interference, and cell splitting help maximize capacity while minimizing required bandwidth. The cellular approach is essential for providing widespread mobile communication affordably.

Frequently Asked Questions on Cellular – FAQ’s

Why can’t we just have one powerful transmitter to cover an entire city for mobile communication?

This would require an extremely large amount of bandwidth which is impractical and wasteful. The cellular concept allows reusing the same frequencies across multiple smaller cells.

How my mobile phone stay connected when I am moving between different cell areas?

As you move from the one cell to the another your phone automatically switches to the new cell’s base station through the seamless “handoff” process without you noticing it.

My neighborhood has many mobile users. How does the network ensure everyone can make calls without issues?

The cellular approach uses techniques like channel sharing (trunking), interference management through frequency allocation, and cell splitting to increase capacity as user density grows in an area.