INTRODUCTION TO CELLULAR CONCEPT
Trunking and Grade of Service(GoS)
Introduction To Wireless Communication
ATM(Asynchronous Transfer Mode)
INTRODUCTION TO CELLULAR CONCEPT:
Cellular concept was a major breakthrough in solving the problem of spectral congestion and
user capacity. It offered very high capacity in a limited spectrum allocation without any major
technological changes. It is a system level idea which calls for replacing a single, high power
transmitter into many low power transmitter. Each neighboring base station is assigned with
different frequency of channel so that interference will not occur.
It is a major limiting factor in the performance of cellular radio systems.(In comparison with
wired comm. Systems, the amount and sources of interferences in Wireless Systems are greater.
Sources of interference are:
1. Mobile Stations 2.Neighboring Cells
3. The same frequency cells 4.Non-cellular signals in the same spectrum
Interference in Voice Channels: Cross-Talk & Interference in Control Channels: missed/blocked
calls. Urban areas usually have more interference, because of: Greater RF Noise Floor & More
Number of Mobiles.
TYPES OF INTERFERENCE
1. Co-Channel Interference (CCI)
2. Adjacent Channel Interference (ACI)
Co-Channel Interference CCI:
The cells that use the same set of frequencies are called co-channel cells. The interference between
signals from these cells is called Co-Channel Interference (CCI). It cannot be controlled by increasing
RF power. Rather, this will increase CCI. It depends on minimum distance between co-channels.
The yellow cells use the same set of frequency channels, and hence, interfere with each other. In
the cellular system there are 6 first- layer co-channels
In constant cell size and RF power, CCI is a function of Distance between the co-channel cells (D), and
the size of each cell (R). Increasing ratio D/R, CCI also decreases.
Define Channel Reuse Ratio = Q = D/R=√3𝑁
For hexagonal geometry, D/R can be calculated:
Smaller Q provides larger capacity, since that would mean smaller N. (Capacity ∝ 1/N).
Larger Q improves quality, owing to less CCI.