Cellular Radio
Cellular phone networks use cellular frequency reuse.
In the cellular reuse concept, frequencies allocated to the service are reused in a regular pattern of areas, called "cells", each covered by one base station. In mobile-telephone nets these cells are usually hexagonal.
To ensure that the mutual interference between users remains below a harmful level, adjacent cells use different frequencies. However in cells that are
separated further away, frequencies can be
reused.
Typical frequency reuse plan for 7 different radio frequencies, based on
hexagonal cells. Radio channels are indicated by color. In fact some problems in cellular frequency assignment are solved using map coloring theory.
Particularly in the United States, the term "cell phone" is often used by the public when a
wireless phone is meant. The cellular approach was proposed and
developed predominantly by the Bell System, in the U.S. in the early 70's,
after the regulatory agency FCC has asked for an upgrade of the existing radio telephone
service. The FCC had the foresight to require:
- a large subscriber capacity
- efficient use of spectrum resources
- nationwide coverage
- adaptability to traffic density
- telephone service to both vehicle and portable user terminals
- telephony but also other services including closed user groups with voice dispatch
operations
- toll quality
- affordability, which could eventually make it a mass-market service
Start page of video from Short Course
by
BMRC
Video from Wireless Communications Networks Short Course
"In wireless communication, we attempt to accommodate as many users as possible, and the way we do this is by very dense
frequency reuse. We split the area that we want to cover into many small "cells" and in each of these cells we use a different frequency. If we use a frequency in one geographical area, we want
to reuse it in another area. Relative to the size of the cell, we want to make the distance
between the cells that use the same frequency as small as possible. The price that we pay is that we get interference from one cell to other cells. So we have to build a system in which the receivers are relatively immune to interfering signals. .....
Examples of systems using cellular frequency reuse are
GSM and
AMPS.
Coverage of cellular telephone systems by the year 2000.
There was an estimated 13,000,000 users of cellular phones in the
U.S. alone in 1995, and marketeers expected that the cellular market
growed by more than 25% per year for the next five years.
Worldwide sales of mobile phones was around 500 Million in 2003 and
is expected to reach 1 Billion around 2012.
More on Cellular Telephone Networks
- Frequency reuse, cell sizes
- Multiple access: FDMA, TDMA, CDMA
- Network aspects,
- Cell sectorization, reuse partitioning, dynamic channel allocation
- Practical aspects of cell planning
- Cumulation of interference, Nakagami fading, model by Schwartz & Yeh
- Spectrum efficiency versus performance
- Outage probability, Computer methods.
- Call blocking, speech clipping, subjective speech
quality, Erlang B and C formulas
- Digital Speech Interpolation (DSI)
- Man-made noise and link-budget
- Radio Technologies and Standards:
- Business aspects: costs, tariffs, ...
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