Page 38 - DCAP311_DCAP607_WIRELESS_NETWORKS

Wireless Networks

Notes
Figure 2.9: Two-way Radio Systems

Source: http://en.wikipedia.org/wiki/Base_station
The diagram shows a band-pass filter used to reduce the base station receiver’s exposure to
unwanted signals. It also reduces the transmission of undesired signals. The isolator is a one-way
device which reduces the ease of signals from nearby transmitters going up the antenna line and
into the base station transmitter. This prevents the unwanted mixing of signals inside the base
station transmitter which can generate interference.
Interference could be defined as receiving any signal other than from a radio in your own system.
To avoid interference from users on the same channel, or interference from nearby strong signals
on another channel, professional base stations use a combination of:
z z minimum receiver specifications and filtering.

z z analysis of other frequencies in use nearby.
z z in the US, coordination of shared frequencies by coordinating agencies.
z z locating equipment so that terrain blocks interfering signals.
z z use of directional antennas to reduce unwanted signals.
Base stations are sometimes called control or fixed stations in US Federal Communications
Commission licensing. These terms are defined in regulations inside Part 90 of the commissions
regulations. In US licensing jargon, types of base stations include:

z z A fixed station is a base station used in a system intended only to communicate with other
base stations. A fixed station can also be radio link used to operate a distant base station by
remote control. (No mobile or hand-held radios are involved in the system.)

z z A control station is a base station used in a system with a repeater where the base station is
used to communicate through the repeater.

z z A temporary base is a base station used in one location for less than a year.
z z A repeater is a type of base station that extends the range of hand-held and mobile radios.
z z Point-to-point communication systems
In telecommunications, a point-to-point connection refers to a communications connection
between two nodes or endpoints. An example is a telephone call, in which one telephone is
connected with one other, and what is said by one caller can only be heard by the other. This
is contrasted with a point-to-multipoint or broadcast communication topology, in which many
nodes can receive information transmitted by one node. Other examples of point-to-point
communications links are leased lines, microwave relay links, and two way radio.

32 LOVELY PROFESSIONAL UNIVERSITY