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8/7/2019 Ac RE56 33 GSM TDMA Engineering
1/20
8/7/2019 Ac RE56 33 GSM TDMA Engineering
2/20
Alexandre CAMINADA, UTBM
3 -2006
Contents
1.Spectrum use2. Frequency assignment
3. Frequency hopping
Alexandre CAMINADA, UTBM
4 -2006
Communication 1
Communication 2
Communication 3
Time
Spec
trum
Frequency Division Multiple Access (FDMA)
1G analogue systems
Plus: easy to do
Minus: interference, fading
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
8/7/2019 Ac RE56 33 GSM TDMA Engineering
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Alexandre CAMINADA, UTBM
5 -2006
Time
Spect
rum
Frequency-Time DMA (F-TDMA)
Communication 1
Communication 2
Communication 3
2G numerical systems: GSM, DECT, D-AMPS
Plus: gain in capacity
Minus: synchronisation, fading
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
6 -2006
Time
Spec
trum
Slow Frequency Hopping F-TDMA
GSM
Plus: gain in interference, gain in fading
Minus: complex to evaluateCommunication 1
Communication 2
Communication 3
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
8/7/2019 Ac RE56 33 GSM TDMA Engineering
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Alexandre CAMINADA, UTBM
7 -2006
Spectrum reuse in mobile networks1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
8 -2006
Interference brings by spectrum reuse
Reuse is depending on system ability for interference management
It is not possible to use the same frequency in adjacent cells: co-channel
interference between 2 mobiles
Interference is C/(I+N), where
C, power of expected signal
I, set of interference, often limited to co-channel
N, white noise, whereN
8/7/2019 Ac RE56 33 GSM TDMA Engineering
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Alexandre CAMINADA, UTBM
9 -2006
Downlink interference formulation
Let Pei,j the emitted power from BSj to MS i, andLi,j the global loss from BSj to MS i
Then
With TDMA, cells circuits are rightly orthogonal (=0) then there is no intra-cellinterference
0
i
0
, , ,
', , , ' , 'intra inter' , ' ' , '
, ,
, tot', , , ' , '
' , ' ' , '
orthogonality factoret ,
/
i j i j i j
i j i j i j i ji ii i i C j j j BS
i j i j
i ji j i j i j i j
i i i C j j j BS
C Pe L
Pe L Ptot L
Pe L
Pe L Ptot L
I I
C I
BS0
BS1BSk
BSk+1
Li,0
Li,1Li,k
Li,k+1
Iintra
Iinter
Iinter
Iinter
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
10 - 2006
Distance of reuse between cells
Lower required C/I means shorter reuse distance and higher capacity
Analogue system: C/I 18 dB
GSM: C/I 9dB
Reuse separation distance ranges from 4 to 6 times the cell radius (W.C.Y. LEE)
D
f1
R
f1
R
D R SeuilR: cell radiusD: frequency reuse distance
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
8/7/2019 Ac RE56 33 GSM TDMA Engineering
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Alexandre CAMINADA, UTBM
11 - 2006
Frequency reuse pattern (k=3, 7, 12)
Hypothesis
Regular network (grid)
Regular traffic demand
Regular propagation
Graph-coloring problem
Advantages
Easy to do
No propagation model
Inherent problem
High traffic demand requires small patterns
Small patterns produce interference
1
3
3
2
1
4
2
7
K=3
1
1
1
2
2
2
3
3
3
44
4
4
5
5
5
6
6
6
77
7
7
K=7
Frequency reuse pattern between cells1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
12 - 2006
The big problem of real cell coverage
Nominal cell boundaries
The cell
Radio link
Transmitter
T-antenna
Propagation &
Environmental effects
R-antenna
Receiver
Coverage:Blue: field strength > -100Yellow: field strength > -90
FrequencyDistanceWeatherObstacledependent
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
8/7/2019 Ac RE56 33 GSM TDMA Engineering
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Alexandre CAMINADA, UTBM
13 - 2006
The big problem of real cell coverage
Theory Reality
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
14 - 2006
The model is built on ideal scenario
Regular plane surface: uniform propagation (no obstacles)
Each station located at a node on a regular grid
No vacancy on node
All stations parameters settings identical (omni directionaldiagram)
Each station has a regular traffic
Co-channel interference is only considered (no adjacentinterference)
The real networks are far from theory1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
8/7/2019 Ac RE56 33 GSM TDMA Engineering
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Alexandre CAMINADA, UTBM
15 - 2006
Contents
1. Spectrum use
2.Frequency assignment3. Frequency hopping
Alexandre CAMINADA, UTBM
16 - 2006
Definition: frequency reuse consists inusing the same frequency channel onareas that are separated enough toavoid co-channel interferenceproblems
It is a graph colouring problem: thefrequency are assigned to cells asthe colours are assigned to areas
This concept is fundamental to get thegap between low bandwidth and highcapacity one need to catch a lot ofcustomers
The theoretical basis of frequency assignment1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
8/7/2019 Ac RE56 33 GSM TDMA Engineering
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Alexandre CAMINADA, UTBM
17 - 2006
Cells are overlapping each others
Cell overlap is measured from
Propagation simulation
Field and neighbor measurement reports
On one pixel, currently are 40 to 70 significant signals
6 or 7 good signals are needed (HO)
Others are multiple radio interference:I = I1+I2++In
Best server Interference
Good signals
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
18 - 2006
CIM [i,j] = surface with single radio interference between stations i (carrier) andj
(interference) at all C/I level
Computed from cell overlap
Pixels restricted to single radio interference
Cover from A
Interference from B
C/I
PixelCIM [A,B]
Carrier-to-Interference matrix computation1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
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Alexandre CAMINADA, UTBM
19 - 2006
OM [i,j] = surface with single radio interference between stations i (carrier) andj
(interference) for a given C/I compatibility threshold for co-channel and adjacent
channel
Computed from C/I matrix
Threshold per cell, per channel, per network layer.
C/I
Pixel Pixel
Threshold
OM [A,B]
Carrier-to-Interference matrix computation1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
20 - 2006
Co-channel and adjacent channel interference rating for cell pairs are specified in terms of
affected areas
Specification are cell planned ; it supposes that TRX in a cell use the same technology and
the same transmission power, and emit from the same antenna ; or several cells have to be
defined
0,15
0
0,18
0,12
D
0,34
0,08
C
0,12
0
B
0,25
0,15
0,30
0,12
A
DCBAStations
Carrier-to-Interference matrix computation1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
8/7/2019 Ac RE56 33 GSM TDMA Engineering
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Alexandre CAMINADA, UTBM
21 - 2006
Matrix of channel separations between cells
Additional separations required for engineering constraints
Co-station separation: 3 channels (>= 3)
Co-site separation: 2 channels (>= 2) ; A and C are co-located
SM [i,j] = channel separation requirement between frequency assigned to stations i
and j to avoid any interference from j on i
Computed from overlapping matrix for (i,j) where i j
3102D
2302C
0031B
2223A
DCBAStations
Etc.
0,12
0
B
0,25
0,15
0,30
0,12
A
DCBAStations
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
22 - 2006
Major FAP problems for operators
Assigning frequency to cell is computing afrequency plan followingone of the problems below
Problem 1: Minimize Spectrum FAPA number of frequencies is available for the network
Objective is to minimize the number of frequencies used while satisfying allcompatibility constraints and demand constraints
Problem 2: Minimum Span FAPSpan of an assignment is the difference between the largest channel used and thesmallest channel used
Objective is to minimize the span needed to satisfy all EMC and demandconstraints
Problem 3: Minimize Interference FAPFinite, fixed number of frequencies available for the network
Objective is to satisfy all demands constraints (its increases the reuse factor!) andto minimize some measure of interference (e.g. EMC constraints violation) with thegiven frequencies
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
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Alexandre CAMINADA, UTBM
23 - 2006
Evaluating the quality of frequency plan
Networks
stations
InterferenceComputation
Frequency
plan
Cell
coverage
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
24 - 2006
Evaluating the quality of frequency plan
Radio interference C/I+N ; N
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Alexandre CAMINADA, UTBM
25 - 2006
Communications quality thresholds
C/I thresholds depend on the engineering on frequency planning
Most of the time radio interference are considered around 14 dB on non hoppingnetwork
Several FP evaluation are available on one pixel
C/I worst case on the pixel; non hopping
C/I mean value on the pixel; average of all frequencies; band base hopping
C/I worst case among the best frequency per cell; BCCH
C/I minimum threshold depends on channel separation between communications
C/I = - 49 dB3rd adjacentC/I = -9 dB1st adjacent
C/I = - 41dB2nd adjacentC/I = 9 dBCo-channel
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
26 - 2006
Contents
1. Spectrum use
2. Frequency assignment
3.Frequency hopping
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Alexandre CAMINADA, UTBM
27 - 2006
Why Frequency Hopping?
Frequency Hopping stands for the dynamic changing of frequency during communications
On each hop, only a burst of information is transmitted on one frequency
The transmitter and the receiver must have the foreknowledge of the correct sequence offrequency changes
Advantages on jamming
The jamming frequency is not always the same, sometime jamming sometime not
Spread Spectrum ability (FH-SS): the total transmission, viewed over a long period such 1 sec,appears to occupy the entire bandwidth (spreading of spectrum)
We are not trying to eliminate interference with channelization, interference levels will risegradually with the number of mobiles
Advantage on multi-path fading
Deep fades tend to be frequency selective
If the hops are separated by a given distance (coherence bandwidth = 600 KHz at 900 MHz), twosuccessive hops are not faded
The average fade on the whole frequency range is much less: equivalent of about 2-3 dB insteadof 20 dB
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
28 - 2006
Family of Frequency Hopping
Slow Frequency Hopping (SFH): GSM Speed: 1733 times per second (at every burst)
Base band hopping: few frequency are used
Synthesized hopping: all spectrum can be used
Fast Frequency Hopping (FFH): military system A burst is a very few bits: frequency hopping each n electric symbols
(eventually n=1) where 1 electric symbol = 1, 2 or 4 bits
The length of the burst must be lower than the propagation time from thetransmitter to the receiver (typically 10-100 microseconds)
The time the jammer detects the signal, the transmitter has already shifted to anew frequency
The sequences are randomized
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
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Alexandre CAMINADA, UTBM
29 - 2006
SFH Base band hopping
time
Base band hopping
21 3 4 5 6 7
TDMA frame
4.62 ms
TRX0
(f0)
TRX1
(f1)
0
f0 f0 f0f0
f1f1 f1 f1f1
f0
0.577ms
TRX2
(f2) f2f2 f2 f2 f2
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
30 - 2006
SFH Synthesized hopping
Synthesized hopping
f0 f0 f0f0 f0 f0
f1 f2 f1f1 f2 f1
time21 3 4 5 6 7
TDMA frame
4.62 ms
TRX0
(f0)
TR
X1
(f1
,f2)
0
0.577ms
TRX2
(f1,f
2)
f2 f1 f2
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
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Alexandre CAMINADA, UTBM
31 - 2006
Power
Time
Freque
ncy
Interferencethreshold
Carrier
Interferer 1, low power
Interferer 2, high power
SFH Synthesized hopping1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
32 - 2006
SFH Synthesized hopping parameters
Implementing synthesized frequency hopping allows the planner to assign much
more frequency than TRX
Gain in frequency diversity (quality of radio path is frequency dependent)
Gain in interference diversity (successive bursts suffer from varying sources ofinterference)
In TU50, diversity gains are low
New parameters: MAL, HSN and MAIO
Size ofMobile Allocation Lists (number of frequency channels) per station
Frequency to assign toMobile Allocation Lists per station
Hopping Sequence Numberto assign to stations or sites (station versus site driven)
Mobile Allocation Index Offset to assign to TRX
New evaluation criteria: FER
Frame Erasure Rate: number of erased vocal frame, that is after FEC application
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
8/7/2019 Ac RE56 33 GSM TDMA Engineering
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Alexandre CAMINADA, UTBM
33 - 2006
SFH Frequency diversity gains
Gain at 2% FER from random hopping in test conditions
(Ref: GSM, GPRS and EDGE performance, WILEY, 2002)
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
34 - 2006
Synthesized hopping Parameters setting
SITE DRIVEN
3 BCCH = 3 channels
MAL TCH = 1 for all stations
Size of MAL: greater than the number
of TRX TCH on the site
STATION DRIVEN
3 BCCH = 3 channels
MAL TCH = 1 per station
Size of MAL: greater than the numberof TRX TCH on the station
BCCH 1
BCCH 2
BCCH 3
1 MAL TCH
BCCH 1
BCCH 2
BCCH 3
3 MAL TCH
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
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Alexandre CAMINADA, UTBM
35 - 2006
Synthesized hopping Parameters setting
Let MAL = N frequencies (
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Alexandre CAMINADA, UTBM
37 - 2006
Synthesized hopping Interfering cells
Non hopping Cell are interfering continuously
But interfering powers: low
Synthesized hopping Cell are interfering with intermittence
But interfering powers: high (HO areas)
NB: further interfering cells (second circleof neighbours) are still present but alsointermittently and with a higher loss =>not a problem
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
Alexandre CAMINADA, UTBM
38 - 2006
SFH Quality thresholds in FER
FER evaluation with synthesized hopping: thresholds to 4% and 7%
C/I mean: 12 dB on base band hopping network
C/I mean: 8 dB on synthesized hopping network on theoretical conditions
SFH quality measurement is complex
Traffic load is needed
Go from C/I to FER needs to estimate error corrections process between BER and FER
NB: BER is calculated before the decoding with no gain from FH, so the BER is the same for allhopping configuration
Simulated quality tables are required
SFH gain is strong for TU3 and week for TU50 because of the natural diversity of the
channel (fast variations)
3%6%TU50
3%21%TU3
FER with SFHFER without SFHAt C/I = 9 dB
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping
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Alexandre CAMINADA, UTBM
39 - 2006
SFH FER(C/I) estimation
TU3 full hopping link with 6 interferers for different loads in the case of power control
(Ref: GSM, GPRS and EDGE performance, WILEY, 2002)
1/ Spectrum use
2/ Frequency assignment
3/ Frequency hopping