WCDMA Coverage

Dr. -Ing. Alexander Seeger
W-CDMA Coverage
• Link budget
– thermal noise density
– interference margin (noise rise)
– fast fading margin (power control headroom)
– log normal fading margin
– soft handover gain
– antenna gain
– penetration loss, body loss, feeder loss ...
• Propagation model & resulting coverage area
• Coverage increasing measures
– tower mounted amplifier
– receive diversity
– higher sectorisation
Dr. -Ing. Alexander Seeger
Example Link Budget: Uplink Voice
Transmitter (mobile)
Maximum mobile transmission power in W 0,1
Maximum mobile transmission power in dBm 21,0 a
Mobile antenna gain in dBi 0,0 b
Body loss in dB 3,0 c
Euivalent isotropic radiated power (EIRP) in dBm 18,0 d = a + b - c
Receiver (base station)
Thermal noise density in dBm/Hz -174,0 e
Base station receiver noise figure in dB 5,0 f
Receiver noise density in dBm/Hz -169,0 g = e+f
Receiver noise power in dBm -103,2 h = g + 10*log(38400000)
Interference margin in dB 3,0 i
Total effective noise + interference in dBm -100,2 j = h + i
Processing gain in dB 25,0 k = 10*log(3840/12.2)
Required Eb/N0 in dB 6,1 l
Receiver sensitivity in dBm -119,0 m =l - k + j
Base station antenna gain in dBi (3 sectors) 18,0 n
Cable loss in the base station in dB 2,0 o
Fast fading margin in dB 0,0 p
Maximum path loss in dB 153,0 q = d - m + n - o - p
Log normal fading margin in dB 8,6 r
Soft handover gain in dB 5 s
In-Car loss in dB 8 t
Allowed propagation loss for cell range in dB 141,4 u = q - r + s - t
Dr. -Ing. Alexander Seeger
Example Link Budget: Downlink Voice
Transmitter (base station)
Total transmission power (per sector) in W 20
Total transmission power for dedicated channels in W 18
number of users 60
Transmission power per user in W 0,30
Transmission power per user in dBm 24,8 a
Base station antenna gain in dBi (3 sectors) 18,0 b
Cable loss at base station in dB 2,0 c
Euivalent isotropic radiated power (EIRP) in dBm 40,8 d = a + b - c
Receiver (mobile station)
Thermal noise density in dBm/Hz -174,0 e
Mobile station receiver noise figure in dB 7,0 f
Receiver noise density in dBm/Hz -167,0 g = e + f
Receiver noise power in dBm -101,2 h = g + 10*log(38400000)
Processing gain in dB 25,0 k = 10*log(3840/12.2)
Required Eb/N0 in dB 7,9 l
Receiver sensitivity in dBm -118,2 m = l - k + h
Body loss 3,0 n
Fast fading margin in dB 0,0 p
Maximum path loss in dB 156,0 q = d - m - n - p
Log normal fading margin in dB 8,6 r
Soft handover gain in dB 2 s
In-Car loss in dB 8 t
Allowed propagation loss for cell range in dB 141,4 u = q - r + s - t
Dr. -Ing. Alexander Seeger
Coverage versus Capacity
number of users number of users
range range
Pole capacity Pole capacity
(from system level simulations) (from system level simulations)
downlink downlink
uplink uplink
Dr. -Ing. Alexander Seeger
Contributions to Link Budget
• Thermal noise density:
-174 dBm/Hz = 10*log(k*T)
• k = 1,381 * 10
-23
J/K (Boltzmann constant)
• T = 290 K (temperature)
• Interference margin (noise rise)
– with increasing load in the cell interference dominates over
thermal noise as source of distortion
– noise rise = I
total
/P
N
– typ. values: 1.0 - 3.0 dB for a load of 20 - 50 %
Dr. -Ing. Alexander Seeger
Contributions to Link Budget - Interference Margin
j
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load per connection load per connection
R R
j j
: user rate for connection : user rate for connection j j
P P
j j
: power for connection : power for connection j j
I I
total total
: total interference at : total interference at NodeB NodeB
N N
0 0
: thermal noise power spectral density : thermal noise power spectral density
W: W: chip rate chip rate
Dr. -Ing. Alexander Seeger
Contributions to Link Budget - Interference Margin (cont.)
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UL
1 q
55 . 0
ce interferen cell own
ce interferen cell other
~ = i
Extension to multi-cell scenario:
factor load :
UL
q
Dr. -Ing. Alexander Seeger
Contributions to Link Budget
• Fast fading margin = power control headroom
– especially for slow moving mobiles some headroom is needed in the
mobile station transmission power for maintaining closed-loop fast
power control, typ. values: 2.0 dB
• Log normal fading margin
– rises with increasing coverage probability requirement
– rises with increasing log normal fading variation
• Soft handover gain
– reducing required log normal fading margin because slow fading is
only partly correlated between base stations
– reduction of required Eb/N0
• uplink: due to selection diversity gain (softer handover: antenna gain +
diversity gain)
• downlink: due to diversity gain
– typ. values: 5.0 dB (uplink), 2.0 dB (downlink)
Dr. -Ing. Alexander Seeger
Propagation Model and Resulting Coverage Area
• Okumura-Hata propagation model for an urban macro cell
• path loss L = 137.4 dB + 35.2*log
10
(R)
– base station height: 30 m
– mobile antenna height: 1.5 m
– carrier frequency: 1950 MHz
– path loss exponent: 35.2 (free space: 20.0)
• Site area: approx. 2.6*R
2
Dr. -Ing. Alexander Seeger
Idealised Hexagonal Cellular Network Structure
Real inhomogeneous cell layout

Ideal homogeneous cell layout
90° antenna 90° antenna beamwidth beamwidth
Dr. -Ing. Alexander Seeger
Coverage Increasing Measures
• Tower mounted amplifier (TMA)
• Receive diversity
• Higher sectorisation
Dr. -Ing. Alexander Seeger
Tower Mounted Amplifier
• Purpose & Effects:
– Compensates the feeder loss in uplink
– Reduces the noise figure of the Node B
– Improved receiver sensitivity
– Better link quality at cell borders
Dr. -Ing. Alexander Seeger
Node B Noise Figures @ Reference Points
• Node B without TMA: NF @ reference point: typical 5 dB
• Node B with TMA: NF @ reference point: typical 3 dB,
cable losses up to 12 dB can be compensated
TMA DUAMCO TRX
Node B
Reference Point
with TMA
DUAMCO TRX
Node B
Reference Point
without TMA
DUAMCO: Duplexer, Amplifier, Coupler
TRX: Transceiver (Transmitter + Receiver)
Dr. -Ing. Alexander Seeger
Receive Diversity Considerations
• Increase antenna gain ~ 10log
10
(Nant)
• Increase degree of diversity by additional Rx antennas per
sector
– step from 1 Rx to 2 Rx yields highest gain
– gain depends on multipath diversity
• Implementation loss due to real channel estimation and
inaccurate acquisition
• For example uplink coverage can be expanded by about
2.5 dB with the step from 2 Rx to 4 Rx
• Drawback: Additional antennas, TMAs, cables, Rx filters,
low noise amplifiers, TRX units, connections to baseband
units
Dr. -Ing. Alexander Seeger
6 sectors with 2 path Rx
antennas
– 45
o
antenna width, antenna
gain 19 dBi, ǻ = 1 dB
– 25% traffic load per cell ->
interference margin UL: 1.2
dB, ǻ = 1.8 dB
3 sectors with 4 path Rx
antennas
– 65
o
antenna width, antenna
gain 18 dBi
– 50% traffic load per cell ->
interference margin UL: 3 dB
– ca. 2.5 dB gain (4 instead of
2 RX antennas) , ǻ = 2.5 dB
Uplink: Comparison 4 Path Rx Diversity versus 6 Sectors
Coverage and capacity in UL are comparable in both cases