This document discusses frequency hopping in wireless communication systems. It begins by explaining that in frequency hopping systems, each call hops between a defined set of frequencies to reduce the impact of poor signal quality on any single frequency. This provides frequency diversity and averages out interference. The document then discusses various types of frequency hopping including baseband and synthesizer hopping. It also covers topics like why frequency hopping is used, factors like multipath fading and interference, and specifications of frequency hopping systems including hopping sequences, mobile allocation lists, and fractional loading.

1. General conceptGeneral concept
ofof
Frequency hoppingFrequency hopping
By:
Rohit Kumar Singh
EGIL-Ranchi

2. The Flow……
1) What is FH?
2) Why FH?
1) Multipath fading
2) Interference
3) Different types of FH
1) Baseband FH
2) Synthesizer FH
4) FH Specifications
5) Fractional Loading

3. FREQUENCY HOPPINGFREQUENCY HOPPING
**In frequency hopping systems, each call hops between aIn frequency hopping systems, each call hops between a
defined set of frequencies. So poor signal quality on anydefined set of frequencies. So poor signal quality on any
specific frequency affects only a small portion of thespecific frequency affects only a small portion of the
transmission.transmission.
* This makes it much easier to recreate any lost bits and so* This makes it much easier to recreate any lost bits and so
preserve overall call quality.preserve overall call quality.
*GSM networks use “slow” frequency hopping;*GSM networks use “slow” frequency hopping;
*A hop occurs before each time slot is transmitted*A hop occurs before each time slot is transmitted
(every 4.615 millisecond, or 217 hops per second).(every 4.615 millisecond, or 217 hops per second).

4. Frequency
Time
* This shows the FH in time frequency domain
* Each block of TDMA frame is transmitted in
different frequencies

5. WHY FH?WHY FH?
During a call, a number of physical effects influence the
perceived radio environment between a mobile station and a
base station. One such effect is multipath fading, which
means that transmitted signals reach the receiver via multiple
paths. Depending on the difference in path length.
Another effect is various types of interference. The
dominating type is normally co-channel interference, but
other types, such as adjacent channel interference,
intermodulation products, military sources etc. must be
considered as well.

6. Multipath fadingMultipath fading
The destructive interference produced by multipath
fading is called “fading-dips”. Fading dips may cause speech
quality degradation.
 For a given position the fading depends on the
transmission frequency.
This multipath fading particularly impacts slow moving
mobiles, as they may stay in one position and hence a fade
long enough to suffer information loss.

7. Rayleigh FadingRayleigh Fading
• This phenomenon is due to multipath propagation of the signal.
• The Rayleigh fading is applicable to obstructed propagation paths.
• All the signals are Non-LOS signals and there is no dominant direct path.
• Signals from all paths have comparable signal strengths.
• The instantaneous received power seen by a moving antenna becomes a
random variable depending on the location of the antenna.

8. Ricean FadingRicean Fading
• This phenomenon is due to multipath propagation of the signal.
• In this case there is a partially scattered field.
• One dominant signal.
• Others are weaker.

9. Co-channel interferenceCo-channel interference
The interference situation for a mobile is strongly dependent
on which frequency and time-slot that the mobile happens to
use.
Normally co-channel interference is caused by frequency re-
use

10. What can be achivedWhat can be achived
Frequency diversity
Interference averaging

11. Frequency diversityFrequency diversity
Frequency hopping can reduce the
influence of signal strength variations caused
by multipath fading.
Multipath fading is frequency
dependent. This implies that the fading dips
appear at different locations for different
frequencies.

12. Interference averagingInterference averaging
Frequency hopping can also break up persistent
interference into periodic occasions of single burst
interference.
Changing frequency at each burst offers a way to
improve the interference situation described above. The co-
channel interference will change at every burst.
The more frequencies that are used in the hopping, the
more rare such frequency collisions will be.

13. Short technical descriptionShort technical description
Baseband frequency hopping
Synthesizer frequency hopping

14. Baseband frequency hoppingBaseband frequency hopping
At baseband hopping each transmitter operates
on a fixed frequency.
The advantage with this mode is that narrow-band
tuneable filter combiners can be used.
The disadvantage is that it is not possible to use a
larger number of frequencies than there are
transmitters.

15. Baseband frequency hoppingBaseband frequency hopping
Controller
TRX1
Controller
TRX4
Controller
TRX3
Controller
TRX2
Transmitter
f1
Transmitter
f4
Transmitter
f3
Transmitter
f2
Bus for routing of burst
Combiner
X
X
X
X

16. Synthesizer frequencySynthesizer frequency
hoppinghopping
 The transmitter tunes to correct frequency at
transmission of each burst.
The advantage is that the number of frequencies
that can be used for hopping is not dependent on the
number of transmitters.
The advantage of Synthesizer over Base band is
that we need only as many TRX as the Capacity
 The disadvantage is that wide-band hybrid
combiners have to be used .

17. Synthesizer frequencySynthesizer frequency
hoppinghopping
Controller
TRX1
Controller
TRX4
Controller
TRX3
Controller
TRX2
Transmitter
f1,f2,…,fn
Transmitter
f1,f2,…,fn
Transmitter
f1,f2,…,fn
Transmitter
f1,f2,…,fn Hybrid
Combiner

18. AlgorithmAlgorithm
Hopping sequence
Cyclic hopping
Random hopping

19. Cyclic hoppingCyclic hopping
 In cyclic hopping the frequencies are used in a
consecutive order. For instance,the sequence of
frequencies for cyclic hopping between four
frequencies may appear as follows:
... , f 4 , f 1 , f 2 , f 3 , f 4 , f 1 , f 2 , f 3 , f 4 , f 1 , f 2 , ...
 A cyclic sequence is specified by setting the
parameter HSN (hopping sequence number) to zero.

20. Random hoppingRandom hopping
 A random hopping sequence is actually implemented as a
pseudo-random sequence.
 63 independent sequences are defined.
 When random hopping is used, the frequencies will be
used (pseudo-) randomly, and a hopping sequence for four
frequencies may appear as follows:
... , f 1 , f 4 , f 4 , f 3 , f 1 , f 2 , f 4 , f 1 , f 3 , f 3 , f 2 , ...
 The period for a random sequence is 6 minutes.

21. Implementation with SFHImplementation with SFH
Constrain
Separate frequency band for BCCH
Re-use pattern
MA List
HSN
MAIO
Fraction load

22. ConstrainConstrain
Coverage overlapping constrain
Frequency constrain

23. Coverage overlappingCoverage overlapping
constrainconstrain
Due to SFH with 1x1 or 1x3 are tight re-use
patterns then coverage control is major
constrain.
Homogeneous network is recommended.

24. Frequency constrainFrequency constrain
Performance of SFH depends on one factor
which called “Fractional load”
Maximum fractional load is 50% means
number of frequency required is at least 2
time number of TCH Trxs used.

25. Separate frequency band forSeparate frequency band for
BCCHBCCH
BCCH cannot handle with high interference as
TCH due to :
 BCCH is not hop with SFH.
 Power control and DTX are not support on BCCH.

26. Re-use pattern for SFHRe-use pattern for SFH
 Standard re-use pattern
1. Re-use 1x1
2. Re-use 1x3
3. Multi re-use pattern for SFH (Adhoc AFP
Plan)

27. Re-use 1x1Re-use 1x1
 Define every frequencies to every BTS.
 Avoid co-channel by MAIO and HSN
 Consider all frequencies assigned as frequency group A re-
use pattern will be as follow:
GroupA
GroupAGroupA
GroupA
GroupAGroupA
GroupA
GroupAGroupA

28. Re-use 1x3Re-use 1x3
 Separate all frequencies into 3 groups.
 Define 3 frequency groups to every sites.
 Avoid co-channel by MAIO and HSN
 Consider all frequencies assigned as frequency group A,B and C re-
use pattern will be as follow:
GroupA
GroupCGroupB
GroupA
GroupCGroupB
GroupA
GroupCGroupB

29. Multi re-use patternMulti re-use pattern
 Separate all frequencies into different groups.
 Define these groups to different sites.
 Avoid co-channel by MAIO and HSN
 Consider all frequencies assigned as frequency group G1,G2, G3 and
so on re-use pattern will be as follow:
G1
G2G3
G7
G8G9
G4
G5G6

30. Mobile Allocation MA ListMA List
Set of frequencies the mobile is allowed to
hop over. Maximum of 63 frequencies can
be defined in the MA list
MAL1= f1,f3,f5,f7,f9
MAL2=f2,f4,f6,f8……
MAL3=f1,f4,f7,f11…..

31. Hopping Sequence Number (HSN)
Determines the hopping order used in the
cell. It is possible to assign 64 different
HSNs.
Range: 0 to 63
Setting HSN = 0 provides cyclic hopping
sequence and HSN = 1 to 63 provide
various pseudo-random hopping
sequences.

32. Mobile allocation index offsetMobile allocation index offset
 Define the first frequency of group for the first
burst.
Index 0 1 2 3 4 … N-1
Frequency group f1 f2 f3 f4 f5 .. fn

33. Example of MAIO settingExample of MAIO setting
 The random sequence of synthesizer hopping will appear
as follows for eight frequencies: (HSN = 0)
Controller
TRX1
Controller
TRX4
Controller
TRX3
Controller
TRX2
Transmitter
f1, f2, .., f8
Transmitter
f1, f2, .., f8
Transmitter
f1, f2, .., f8
Transmitter
f1, f2, .., f8
Combiner
f1, f2, f3, f4, f5, f6, f7, f8 (MAIO = 2)
f1, f2, f3, f4, f5, f6, f7, f8 (MAIO = 0)
f1, f2, f3, f4, f5, f6, f7, f8 (MAIO = 4)
f1, f2, f3, f4, f5, f6, f7, f8 (MAIO = 6)
Index : 0, 1, 2, 3, 4, 5, 6, 7
fn : frequency of the first burst
fn : frequency of the second burst

34. Fraction loadFraction load
 Ratio to determine how tight of frequency re-use
for SFH.
 Define by :
Number of frequencies used at a time (per re-use cluster) * 100
Number of frequencies per group
 GSM recommends maximum fraction load = 50%

35. Example of fraction loadExample of fraction load
calculationcalculation
 1x3
Number of frequencies : 46
Number of frequencies for BCCH : 16
Number of TCH frequencies per group : 10
Site configuration : 6+6+6 (Tch : 5+5+5)
Fractional load = 5/10 = 50%

36. Example of fraction loadExample of fraction load
calculationcalculation
 1x1
Number of frequencies : 46
Number of frequencies for BCCH : 16
Number of TCH frequencies per group : 30
Site configuration : 6+6+6 (Tch : 5+5+5)
Fractional load = 15/30 = 50%

37. Thank YouThank You