General overview of GSM cell design and frequency reuse concept. fading and frequency hopping network design

2.  Conventional Cell and Frequency Planning
 Radio Network Features and their impact
 Real” Cell and Frequency Planning
 Site selection

3. Spectrum available
Traffic
Cost
GoS
QoS
Quality
Coverage
Speech Quality
C/I

4. Lee’s model and other empirical models
 Ploss = PR1 + g10log(d / d1) + n10 log( f / f0) - a0
 PR1 is the reference loss at d1(normally 1 mile)
 (e.g. -84dBm in a city like Tokyo and -49dBm for
 open areas)
 g depends on the type of terrain
 (value between 2 and 4)
 n is between 2 and 3

5. Info
bits
Coding
bits
Code
Rate
Max data
rate
(kbs) /TS
Required
C/I (dB)
modulation
GSM 260 196 0.5 13.3 9 GMSK
CS-1 181 275 0.45 9.05 9 GMSK
CS-2 268 188 0.65 13.4 13 GMSK
CS-3 312 144 0.75 15.6 15 GMSK
CS-4 428 28 21.4 23 GMSK
MCS-1 176 0.53 8.4 9 GMSK
MCS-2 224 0.69 11.2 13 GMSK
MCS-3 296 0.89 14.8 15 GMSK
MCS-4 352 1 16.8 23 GMSK
MCS-5 448 0.38 22.4 14.5 8PSK
MCS-6 592 0.5 29.6 17 8PSK
MCS-7 896 0.78 44.8 23.5 8PSK
MCS-8 1088 0.92 54.4 29 8PSK
MCS-9 1184 1 59.2 32 8PSK

6.  for co-channel interference C/Ic=9 Db
 for adjacent (200 kHz) interference C/Ia1=-9 dB
 for adjacent (400 kHz) interference C/Ia2=-41 dB
 for adjacent (600 kHz) interference C/Ia3=-49 dB

7. GSM cell are basically geographical area
Covered by radio frequencies of BTS antennas
The hypothetical shape of a GSM cell is a Hexagon.
Two types of GSM cell
 Omni directional
 Sector cell

8. dc
a e
f
b
R
d
Area
A=3(3)½R²/2
Distance between centers
of two adjacent cells:
d = (3)½R

9.  An omni-directional cell (or omnicell) is served by a
BTS with an antenna which transmits equally in all
directions (360 degrees).
BTS

10. A sector cell is the area of coverage from an antenna,
which transmits, in a given direction only. For example,
this may be equal to 120 degrees or 180 degrees of an
equivalent omni- directional cell. One BTS can serve one
of these sector cells with a collection of BTS’s at a site
serving more than one, leading to terms such as two-
sectored sites and more commonly, three-sectored sites.
Typically, omni-directional cells are used to gain
coverage, whereas sector cells are used to gain capacity.

11. BTS

12. • The frequency reuse concept is to use same frequency channel
with another cell within the same GSM cell cluster.
• Since cells are more or less close to each other there is not perfect
solution.
• Cells will always interfere with each other even if they are not
immediate neighbors.
• How many cells must we consider when we do our planning?
how many closest neighbors do we have?
• The frequency re-use patterns recommended for GSM are the 4/12
and the 3/9 pattern.

13. The only (almost) noise we have to consider comes from interfering
base stations.
If we want to reduce interference from neighbors we need to increase
the D/R ratio.
If D = R sqr(3k) then sqr(3k) should be big, that is increase k!
If we need a C/I ratio of 18dB then we need k > 6.
In GSM networks a frequency reuse pattern with k = 3, 7 or 12.
In the 900-band, which is 2x25MHz wide, we can have 124 carriers.
If these are divided into groups of 12 frequencies we can have 10
groups.
One cell can thus be covered by 10 carriers.
Each carrier can have 8 connections thus a
maximum of 80 calls in an area covered by a cell.

14. reuse distance
D
k = 6
number of
cells in
pattern
U
V
j
i
30º

15. D = (i2 + ij + j2)½2Rcos 30°
D = (i2 + ij + j2)½ (3) ½ R
Number of cells in the
re-use pattern
N = i2 + ij + j2
i in (1,2,3,4 …..)
j in (0,1,2,3,4 …..)
D/R = (3N)½

16.  Umbrella Cell:
 Macro Cell: Antenna above average rooftop height
 Micro Cell: Antenna below average rooftop height
 Pico Cell: Indoors

17. Average Voice activity is around 50%
DTX is a feature that allows to be transmitted only when
there is something to be transmitted
Uses VAD (Voice Activity Detector)
It safes on battery power
Improves the overall network quality by reducing
unnecessary interference

18. This enable the BTS and the Mobile to transmit
only the power necessary for effective communications
Power Control Commands are via the SACCH
This improves the battery live of Mobile Phones
And it improve the overall network quality by reducing
unnecessary interference

19.  Number of frequencies equal to number of transceiivers
Controller
Call 1
Controller
Call 2
Controller
Call 3
Controller
Call 4
Tx and Rx on
f0
Tx and Rx on
f1
Tx and Rx on
f2
Tx and Rx on
f3
C
O
M
B
I
N
E
R
f2 f3 f0 f1
f3 f0 f1 f2
f1 f2 f3 f0
f0 f1 f2 f3

20.  Number of frequencies more or equal to number of transceiivers
Controller
Call 1
Controller
Call 2
Controller
Call 3
Controller
Call 4
Tx and Rx
hopping
Tx and Rx
hopping
Tx and Rx
hopping
Tx and Rx
hopping
f2 f3 f0 f1
f3 f0 f1 f2
f1 f2 f3 f0
f0 f1 f2 f3

21.  Raleigh fading is frequency dependent
 Diversity: combining two or more uncorrelated versions of the
same signal
 For “conventional” frequency diversity the info is sent on two
different frequencies at the same time.
 To be uncorrelated the two frequencies should be more than
1/(multi-path spread), where the multi-path spread is dependent on
the environment.
 For urban areas the frequencies should be more than 600kHz apart

22. Review interleaving
 If one timeslot gets completely lost during transmission
1/8 of two speech frames are lost.
 At the receiver the speech frames are de-interleaved
 The channel coding can recover from the 12.5% BER.
 Interleaving and Channel Coding is part and parcel of
the GSM standard - it works even without hopping.

23.  Extent of Interference diversity depends on:
Interference load (DTX and Power Control)
Frequency reuse: low re-use -> low gain;
dependent on area type.
Number of Frequencies (less -> less gain)
Cyclic or Random
 Interference diversity gain reached with 25%
load, 12 frequencies in Urban area with
random hopping is 2.5dB - mostly it is less.

24.  Use separate frequency blocks for TCH and BCCH
 BCCH frequency channel must be Always On No
hopping over BCCH.
 Plan TCH layer:
 MAL : Mobile radio frequency channel Allocation List
 HSN: Hopping sequence number
 MAIO: Mobile Allocation Index Offset
 MAI: Mobile Allocation Index

25.  Why a BCCH block?
Identifying the source of interference
Re-evaluation of the neighbor list
For collecting data for a measurement based plan
 Optimum size?
 Where a change in a BCCH carrier will on average
make the same difference as a change in a TCH carrier
in the optimized plan

26. Block Size BCCH =
Total Number of Carriers Available/(Average Traffic on TCH layer per
cell/8)*Scaling (DTX.PC) + 1

27. MAIO MA
MAI 0 2 1A 2A 3A 1B 2B 3B 1C 2C 3C
1 1 3 1 2 3 4 5 6 7 8 9
2 2 4 10 11 12 13 14 15 16 17 18
3 3 1 19 20 21 22 23 24 25 26 27
4 4 2 28 29 30 31 32 33 34 35 36
HSN = X 4 1 2 3 2 4 3 1
TRX1 ON 1A has MAIO = 0 28 1 10 19 10 28 19 1
TRX1 ON 1A has MAIO = 2 10 19 28 1 28 10 1 19

28. SHASHANK ASTHANA