a)
Path Loss
Increase
Power
Path loss if fading the transmitting or receiving
signals with the distance increases. Increasing the transmit power is a
solution for this problem. But there are limitations in transmit power.
Idle mode
cell changing
To avoid receiving strength failures, MS always
measure the receiving signal strength from connected cells and its neighboring
cells. If a neighboring cell’s signal strength is higher and MS is in idle mode
then MS listen to its BCCH and make connection to that cell’s BTS.
Handover
However when MS is in active mode (In a call) then
this procedure is bit of tricky since traffic channels should be changed. Handovers
are controlled by the BSC according to the hand over definitions in the site.
b)
Shadowing
Shadowing is path failures due to obstacles in the air
interface. This is unavoidable but it can be minimized by proper planning.
c)
Multipath Fading
Multipath fading occurs due to existence of more than
one receiving paths of signal.
Rayleigh
fading
These signals might be a reflection from a space and
it is identical to the original signal and only a phase changes are there. This
is also called ghost signals. There are some ghost cancellation technologies to
avoid the problem.
Time
Dispersion
Time Dispersion is also a multipath fading but due to
reflecting from distance bodies there may be time differences in signals.
d)
Time
Alignment
A large distance between the MS and the BTS causes
time alignment. Effectively, the signal cannot travel over the large distance
within the given time. So the part of a particular timeslot’s signal may come
in next timeslot’s time. To avoid this problem a special time adjustment is
used in air interface. This is called the Timing Advance (TA). It instructs MS
to transmit certain time before the actual time it transmits. BSC calculate and
transmits the TA to the MS.
e) Capacity and Frequency
Limitations
Allocating same set of frequencies in neighboring
cells is not applicable with conventional GSM. But with the growth of the
network need of more capacity raised as a big problem. Frequency hopping
techniques were introduced to overcome this problem.
