1. Antenna Hopping

2. INTRODUCTION
› Sometimes it so happens that while in a dedicated mode a MS falls in the fading
dip of the received signal.Then there is a high probability of the call getting
disconnected.So in order to overcome this problem you have to transmit the signal
over different paths.This means introducing diversity in the transmit path.This can
be done using ANTENNA HOPPING. With antenna hopping, transmit diversity is
introduced by altering transmit antenna between bursts.

3. AREA OF IMPLEMENTATION……
› In the channels which doesnot have frequency hopping
(e.g. BCCH).
› It is used for traffic channels with frequency hopping over
a relatively low number of frequencies (less than 8).
› This feature brings about a considerable amount of
signal strength improvement in slow/non-moving mobiles
than the fast moving mobiles.

4. Advantages of Antenna Hopping
› It can be used without increasing the number of TRXs in
a base station.
› More robust radio environment.
› Improved signaling performance.
› Possibility to give subscribers a more uniform speech
quality.
› It can also be used along with Frequency Hopping.

5. WORKING PRINCIPLE OF ANTENNA
HOPPING
The combinations of the same signal from two different transmit paths
results in averaging out their fading dips at any particular distance and thus
helps us to get a fairly uniform signal strength at any point.

6. ANTENNA vs FREQUENCY
HOPPING
ANTENNA
HOPPING
With antenna
hopping and no
frequency hopping,
the same interference
is present in all
bursts.This means
that only the fast
fading changes
between the bursts
resulting in only
averaging out the
fading dips of that
signal at any point.
FREQUENCY
HOPPING
In it a mobile is
interfered by different
base stations in
different bursts, i.e.
“interference
diversity”.Thus results
in averaging out the
interference of that
channel from other
channels.

7. EFFECTS ON CODECS
› GAINERS
EFR, AMR, GPRS CS1 and CS2 as well as EGPRS
MCS-1, MCS-2, MCS-5 and MCS-6.
› SUFFERERS
EGPRS MCS-4 and MCS–9.
› NO EFFECT
MCS-3, MCS-7 and MCS-8.

8. ANTENNA HOPPING--
A SPECIAL CASE
› PROBLEM
This technique of altering antenna on every burst is not
going to work in case of HR channels as this would result
in no transmit diversity in a two antenna configuration.
› SOLUTION
By transmission of the first two bursts via the first
antenna and the next two bursts via the second antenna
and so on, the antenna hopping gain will be achieved for
half rate channels as well.

9. REQUISITES OF ANTENNA HOPPING
› An antenna hopping enabled configuration needs two
transmit antennas or a dual-polarized antenna in at least
one antenna system.
› Antenna Hopping can be enabled in a TG and not
sectorwise.
› It is of importance that all antennas in a cell are pointing
in the same direction otherwise the measured average
signal strength will decrease which may cause change of
cell borders as shown in the next slide.

11. ALGORITHM USED IN
ANTENNA HOPPING
› Antenna hopping is started on each Antenna Hopping
Set(AHS) when the AHSs has been created.The hopping
is performed such that the following pattern is achieved:
• Target antenna = (FN + (FN DIV 2)) MOD 2, if the number of
antennas is two.
Note: This pattern is selected to achieve transmit diversity gain
even for half rate channels, where the channel is sent every second
burst
• Target antenna = FN MOD Nant, if the number of antennas
is three or more.
where FN = Frame Number and Nant = number of antennas.

12. ANTENNA HOPPING GAIN
› The gain from Antenna Hopping depends on
1. Propagation Environment,
2. Signal Strength,
3. Number of antenna to hop on,
4. Number of hopping frequencies,&
5. Interference Characteristics.

13. ANTENNA HOPPING GAIN contd….
› The following table can be used as an approximation for
the expected gain from antenna hopping in a typical
urban (TU) environment. The expected gain in other
environments may be smaller.

14. A CASE STUDY ON EFFECTS OF
ANTENNA HOPPING

15. CONCLUSION
› Thus Antenna Hopping is a great feature to work with
which will help us improve the signal strength at any
point by averaging out the fading dips at that point.This
feature makes use of the transmit diversity.
› There is a cellwise parameter AHOP which turns this
feature ON or OFF.The settings of this parameter is as
below.