Motorola E685, Руководство по обслуживанию, Страница: 11 / 97

11
Operation
In Figure1: “Hypothetical Cell System”the area bounded by bold lines represents
the total coverage area of a cellular system.
This area is divided into several cells, each containing a cell site base station
which interfaces radiotelephone subscribers to the switching system.
Since there are no channels in CDMA, a user has a better chance of completing a
call.
Also, now there is no hard handoff between cell sites since all sites operate on the
same frequency. This is called soft handoffs, In this system, subscribers in cell A
& D simultaneously operate in the same frequency.
As a user moves from cell site to cell site, the base station monitors the signal
strength of the user. Based on this signal strength, the base station decides which
cell shall carry the call.
When a radiotelephone is in use well within a cell, the signal strength received at
the cell site base station will be high. As the phone is moved towards the edge of
the cell, its received signal strength decreases.
Signal strength information therefore provides an indication of the subscriber’s
distance from a cell’s base station. This change is handled automatically, and I
completely transparent to the user.
For example, assume that a cellular telephone initiates a call in cell A and the
moves across the system area through cells B and C to cell D. As the phone
moves into cell B, it is instructed to change to a different frequency that operates
through the B cell on that frequency.
A similar change is performed when the phone moves from cell B to cell C and
again when the phone moves from cell C to cell D.
In this example, the radiotelephone had operated in four cell sites, through four
cell sites, and on the same spread spectrum without interruptions in voice
communications, As the radiotelephone leaves a cell, the frequency on which the
phone and base station were operation is made available to another subscriber in