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 0,1Maximum mobile transmission power in dBm 21,0 aMobile antenna gain in dBi 0,0 bBody loss in dB 3,0 cEuivalent isotropic radiated power (EIRP) in dBm 18,0 d = a + b - c
Receiver (base station)Thermal noise density in dBm/Hz -174,0 eBase station receiver noise figure in dB 5,0 fReceiver noise density in dBm/Hz -169,0 g = e+fReceiver noise power in dBm -103,2 h = g + 10*log(38400000)Interference margin in dB 3,0 iTotal effective noise + interference in dBm -100,2 j = h + iProcessing gain in dB 25,0 k = 10*log(3840/12.2)Required Eb/N0 in dB 6,1 lReceiver sensitivity in dBm -119,0 m =l - k + j
Base station antenna gain in dBi (3 sectors) 18,0 nCable loss in the base station in dB 2,0 oFast fading margin in dB 0,0 pMaximum path loss in dB 153,0 q = d - m + n - o - p
Log normal fading margin in dB 8,6 rSoft handover gain in dB 5 sIn-Car loss in dB 8 tAllowed 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 20Total transmission power for dedicated channels in W 18number of users 60Transmission power per user in W 0,30Transmission power per user in dBm 24,8 aBase station antenna gain in dBi (3 sectors) 18,0 bCable loss at base station in dB 2,0 cEuivalent isotropic radiated power (EIRP) in dBm 40,8 d = a + b - c
Receiver (mobile station)Thermal noise density in dBm/Hz -174,0 eMobile station receiver noise figure in dB 7,0 fReceiver noise density in dBm/Hz -167,0 g = e + fReceiver 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 lReceiver sensitivity in dBm -118,2 m = l - k + h
Body loss 3,0 nFast fading margin in dB 0,0 pMaximum path loss in dB 156,0 q = d - m - n - p
Log normal fading margin in dB 8,6 rSoft handover gain in dB 2 sIn-Car loss in dB 8 tAllowed propagation loss for cell range in dB 141,4 u = q - r + s - t
Dr. -Ing. Alexander Seeger
Coverage versus Capacity
number of usersnumber of users
rangerange
Pole capacity Pole capacity (from system level simulations)(from system level simulations)
downlinkdownlink
uplinkuplink
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 = Itotal/PN�– typ. values: 1.0 - 3.0 dB for a load of 20 - 50 %
Dr. -Ing. Alexander Seeger
Contributions to Link Budget - Interference Margin
j
j
jj
b
PIP
RW
NE
total0
total
0
/1
1 I
NE
RWP
j
b
jj
j
b
jj
NE
RWL
0
/1
1
load per connectionload per connection
RRjj: user rate for connection : user rate for connection jjPPjj: power for connection : power for connection jjIItotaltotal: total interference at: total interference at NodeB NodeB NN00: thermal noise power spectral density: thermal noise power spectral densityW:W: chip ratechip rate
Dr. -Ing. Alexander Seeger
Contributions to Link Budget - Interference Margin (cont.)
N
jNj PILI
1totaltotal N
N
jj PLI
1total 1
UL
1
total
11
1
1N
jj
N LPI
N
jjLi
1UL 1 55.0
ceinterferen cellown ceinterferen cellother i
Extension to multi-cell scenario:
factor load :UL
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*log10(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*R2
Dr. -Ing. Alexander Seeger
Idealised Hexagonal Cellular Network Structure
Real inhomogeneous cell layout
Ideal homogeneous cell layout
90° antenna90° antenna beamwidthbeamwidth
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 TRXNode B
Reference Pointwith TMA
DUAMCO TRXNode B
Reference Pointwithout TMA
DUAMCO: Duplexer, Amplifier, CouplerTRX: Transceiver (Transmitter + Receiver)
Dr. -Ing. Alexander Seeger
Receive Diversity Considerations
�• Increase antenna gain ~ 10log10(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 basebandunits
Dr. -Ing. Alexander Seeger
6 sectors with 2 path Rx antennas�– 45o antenna width, antenna
gain 19 dBi, = 1 dB�– 25% traffic load per cell ->
interference margin UL: 1.2 dB, = 1.8 dB
3 sectors with 4 path Rx antennas�– 65o 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) , = 2.5 dB
Uplink: Comparison 4 Path Rx Diversity versus 6 Sectors
Coverage and capacity in UL are comparable in both cases
