UMTS Applied Radio Planning P025 Course Objectives ▪ Understand the key planning parameters of the UTRAN ▪ Produce UMTS Link Budgets for various services ▪ Understand UMTS Coverage and its KPI’s ▪ Understand Capacity dimensioning in UMTS ▪ Appreciate the Coverage/Capacity relationship in UMTS ▪ Evaluate GSM-UMTS Co-location issues
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
UMTS Applied Radio PlanningP025
Course Objectives
▪ Understand the key planning parameters of the UTRAN
▪ Produce UMTS Link Budgets for various services
▪ Understand UMTS Coverage and its KPI’s
▪ Understand Capacity dimensioning in UMTS
▪ Appreciate the Coverage/Capacity relationship in UMTS
▪ Evaluate GSM-UMTS Co-location issues
1- The UMTS Air Interface
UMTS▪ Universal Mobile Telecommunication System
▪ Also called “3G”, along with other IMT-2000 technologies
▪ The evolution from GSM-GPRS-EDGE
▪ WCDMA technology, part of the CDMA family
The UMTS Air Interface
1.1- WCDMA, Processing Gain and Codes
The UMTS Air Interface
CDMA - Direct Sequence Spread Spectrum
The UMTS Air Interface
Frame Period (we may still need frames/timeslots for signaling)
CDMA Spreading•Essentially Spreading involves changing the symbol rate on the air interface
Identical codes
Tx Bit Stream
P
f
Code Chip Stream
Spreading
P
f
Channel
Air Interface Chip Stream
P
f
Code Chip Stream
Despreading
P
f
Rx Bit Stream
P
f
The UMTS Air Interface
Spreading and Despreading
Rx Bit Stream
Air Interface Chip Stream
Tx Bit Stream1
-1
Code Chip Stream
XSpreading
Code Chip StreamXDespreading
The UMTS Air Interface
Spreading and Despreading with code Y
Air Interface Chip Stream
Tx Bit Stream1
-1
Code Chip Stream
XSpreading
Code Chip Stream YXDespreading
Rx Bit Stream
The UMTS Air Interface
Interference mitigation
▪ The gain due to Despreading of the signal over wideband noise is the Processing Gain
Rx Signal (= Tx Signal + Noise)
fP
Channel
Wideband Noise/Interference
P
f
Signal
P
f
Spreading Code
Tx SignalP
f
Spreading Code Signal
P
f
The UMTS Air Interface
Processing Gain
▪ If the Bit Rate is Rb, the Chip Rate is Rc, the energy per bit Eb and the energy per chip Ec then
▪ We say the Processing Gain Gp is equal to:
▪ Commonly the processing gain is referred to as the Spreading Factor
b
ccb R
REE ×=
b
cp R
RG =
The UMTS Air Interface
Visualising the Processing Gain
W/Hz W/Hz W/Hz
W/Hz W/Hz dBW/HzEb
No
Ec
Io
Eb
No
Eb/No
Eb
No
Eb/NoEb
No
W/Hz dBW/HzSignal
Intra-cell Noise
Inter-cell Noise
Before Spreading
After Spreading With Noise
After Despreading/Correlation
Post FilteringOrthog = 0
Post FilteringOrthog > 0
f f f
f f f
f f
The UMTS Air Interface
Types of Codes▪ Channelisation Codes
▪Are used to separate channels from a single cell or terminal
▪ Scrambling Codes▪Are used to separate cells and terminals from each other rather than purely channels
▪ Different base stations will use the same spreading codes with separation being provided by the use of different scrambling codes.
S1
S2
S3
C1 C2 C3
C1 C2 C3
C1 C2 C3
The UMTS Air Interface
Channelisation Codes
▪ Channelisation codes are orthogonal and hence provide channel separation
▪ Number of codes available is dependant on length of code
▪ Channelisation codes are used to spread the signal
The UMTS Air Interface
Channelisation Code Generation
▪ Channelisation codes can be generated from a Hadamard matrix
▪ A Hadamard matrix is:
▪ Where x is a Hadamard matrix of the previous level
▪ For example 4 chip codes are:▫ 1,1,1,1
▫ 1,-1,1,-1
▫ 1,1,-1,-1
▫ 1,-1,-1,1
− xx
xx
Note : These two codes correlate if they are time shifted
The UMTS Air Interface
▪ Orthogonal Variable Spreading Factor Codes can be defined by a code tree:
SF = Spreading Factor of code (maximum 512 for UMTS)
SF = 1 SF = 2 SF = 4
Cch,1,0 = (1)
Cch,2,0 = (1,1)
Cch,2,1 = (1,-1)
Cch,4,0 =(1,1,1,1)
Cch,4,1 = (1,1,-1,-1)
Cch,4,2 = (1,-1,1,-1)
Cch,4,3 = (1,-1,-1,1)
OVSF codesThe UMTS Air Interface
SF = 1 SF = 2 SF = 4
Cch,1,0 = (1)
Cch,2,0 = (1,1)
Cch,2,1 = (1,-1)
Cch,4,0 =(1,1,1,1)
Cch,4,1 = (1,1,-1,-1)
Cch,4,2 = (1,-1,1,-1)
Cch,4,3 = (1,-1,-1,1)
IN USE
IN USESF = 1 SF = 2 SF = 4
Cch,1,0 = (1)
Cch,2,0 = (1,1)
Cch,2,1 = (1,-1)
Cch,4,0 =(1,1,1,1)
Cch,4,1 = (1,1,-1,-1)
Cch,4,2 = (1,-1,1,-1)
Cch,4,3 = (1,-1,-1,1)
IN USE
IN USE
Code Usage Efficiency▪ Any codes further down the trunk of
a branch in use cannot be used
▪ Any codes further out from the branch in use cannot be reused
▪ By filling up branches of the code tree before starting new branches a greater capacity can be achieved
▪ Multiple code trees can be used from a cell but at an increased level of interference between channels
The UMTS Air Interface
Scrambling Codes
▪ The spread data symbols are then scrambled by multiplying with a complex scrambling sequence
▪ Scrambling codes do not affect the chip rate
▪ The scrambling code is specific for a cell and thus serves to provide isolation between signals from adjacent cells
▪ There are 512 Scrambling Codes in the DL which can be allocated by Radio Planners
The UMTS Air Interface
1.2- Ec/Io, Eb/No, NR and Loading
The UMTS Air Interface
Interference and Noise DensitiesThe UMTS Air Interface
▪ From the point of view of a UE, every other UE’s power appears as Interference
▪ Io is the Interference Density
▪ No is the Interference + Noise Density
▪ In general, when you talk about chips, or “Ec”, you use Io. When you talk about bits, or “Eb”, you use No.
▪ “No” considers Thermal Noise at the NodeB
Ec/Io
▪ Ec/Io is the Chip Energy we obtain in the presence of the Interference generated by all other users
▪ Ec/Io of the Pilot Channel is used to:
▫ Estimate (“sound”) the channel (multipath characteristics)
▫ Decide which server is “best server”
▫ Make handover decisions
▫ Typical requirement -15 dB
The UMTS Air Interface
Eb/No
▪ Eb/No is the Bit Energy we obtain after despreading in the presence of the Noise generated by all other users and the Noise from NodeB equipment
▪ There’s a different Eb/No requirement for UL and DL:
▫ Typical requirement 1 to 10 dB
▫ Requirement varies by Bearer, Service, Multipath Profile, Mobile Speed, and Type of Receiver.
The UMTS Air Interface
Noise Rise▪ The effective noise floor of the receiver increases as the
number of active mobile terminals increases.
▪ This rise in the noise level appears in the link budget and limits maximum path loss and coverage range.
Three Users
Background NoiseOne User
Two Users
The UMTS Air Interface
Effect of Neighbouring Cells
Users in other cells cause interference.
Typical ratio of power from other cells to power from
own cell, i, is 0.6 (Urban Macrocells)
The UMTS Air Interface
The Noise Rise Equation
jb
jUL
Mj
jj
N
total
R
W
E
NL
LP
I
+=
−=
−=
∑=
=
0
11
1
11
1
1η
If we have M identical users:
jb
Mj
jj
R
W
E
N
ML
+=∑
=
= 01 1
jb
N
total
R
W
E
N
MP
I
+−
==
01
1
1 Rise Noise
The UMTS Air Interface
Noise Rise and Loading Factor
▪ Capacity is linked to Eb/No value
▪ Maximum Path Loss tolerated is linked to maximum NR
Noise Rise Loading Factor
1 dB 20%3 dB 50%6 dB 75%10 dB 90%
( )ULη−−= 1log10Rise Noise 10
The UMTS Air Interface
Loading Factor
( )
( )
RW
viMNE
iNE
WMvR
RM
b
b
+
=
+
=
=
1
1
Factor Loading
: rate data with users identical For
Capacity Pole
Throughput Actual Factor Loading
0
0
The UMTS Air Interface
UL Pole Capacity
( )iNE
W
b +
≈
1
Capacity Pole
users ofnumber largeFor
0
( )( ) kbps 8535.013
3840000 Capacity Pole
0.5 3 Eb/No 3840000W
=+
≈
=== i
• 50% of this would give a Noise Rise of 3 dB.
•50% of 853 kbps = 426 kbps
The UMTS Air Interface
DL Pole Capacity
The Downlink benefits from orthogonality between channelisation codes.
α is orthogonality factor and has a value between zero and 1.
The UMTS Air Interface
( )iNE
W
b +−
≈
α1
CapacityPole
0
1.3- Power Control and Handovers
The UMTS Air Interface
Power Control and Near/Far EffectThe UMTS Air Interface
▪ When a UE is near the NodeB it doesn’t need much power to reach it
▪ In the same manner, if a UE is far away it needs greater power to communicate with the NodeB
▪ Power Control is needed in the UL because a single over-powered mobile could block a Cell
▪ Power Control is also needed in the DL to provide far away userswith enough power and to keep power low for near-by UEs
Soft and Softer HandoverThe UMTS Air Interface
▪ In UMTS it is possible to have a UE connected to more than 1 NodeB. This is called Soft Handover
▪ When in Soft Handover, the RNC can combine the best signals from the NodeB’s, hence providing a Soft Handover Gain
▪ Softer Handover applies when the mobile is being served by two cells on the same site. A Softer Handover gain also occurs.
▪ However, too many mobiles in Soft or Softer Handover could impose a significant Overhead on the system
Active Set and Pilot PollutionThe UMTS Air Interface
▪ The Cells with which the UE is communicating form the UE’sActive Set
▪ This Active Set is made typically of 3 cells/pilot signals
▪ Any Pilot which is not a member of a UE’s Active Set and exceeds a certain threshold (typ. Ec/Io>-15dB) is considered a Polluter
▪ Pilot Pollution is a common WCDMA issue that needs to be sorted immediately
Summary of Key ConceptsThe UMTS Air Interface
▪ Processing Gain
▪ Channelisation and Scrambling Codes
▪ Ec/Io
▪ Eb/No
▪ Noise Rise
▪ Cell Loading
▪ Pole Capacity
▪ Near/Far Effect
▪ Soft and Softer Handover Gain
Summary of Key Formulas▪ Eb/No
( )iN
E
W
b +
≈
1
Capacity Pole UL
0
The UMTS Air Interface
( ) pcb G
I
EdB
N
E+=
00
▪ Pole Capacity
( )iN
E
W
b +−
≈
α1
Capacity Pole DL
0
2- The UMTS Link Budget
UMTS Link Budget vs. GSM’s
▪ Interference Margin for Noise Rise
▪ Target Eb/no
▪ Processing Gain (dBs) in UMTS
= 10 log (3840000/User Rate (bps))
▪ Power Control margin
▪ Handover Gains
The UMTS Link Budget
Interference Margin
▪ An admission control parameter. Same as “Noise Rise Limit”
▪ Puts a limit to how many users can be taken in the UL
▪ Has an associated Loading Factor:
▫ NR= 3dB, Load Factor=50%
▫ NR=6dB, Load Factor=75%
The UMTS Link Budget
Target Eb/No
▪ UMTS Link Budgets are made for Bearers
▪ A UMTS service may use one or more Bearers, with each
Bearer having a QoS Eb/No requirement
▪ A typical Voice Bearer requires an Eb/No of 5dB
▪ A typical 128 kbps Bearer requires and Eb/No of about 2dB
The UMTS Link Budget
Processing Gain
▪ Depends on the bitrate of the Bearer
▪ Helps with the required Ec/Io at the receiver
▪ For a 12.2 kbps voice Bearer, Gp = 25dB
▪ For a 128 kbps data Bearer, Gp= 15dB
The UMTS Link Budget
Power Control (Fast Fading) Margin
▪ It’s entered to allow for adequate Power Control to compensate
for Fast Fading
▪ It’s dependent on the Speed Profile of the Mobile
▪ At higher speeds, its smaller as the network cannot effectively
compensate for Fast Fading
The UMTS Link Budget
Handover Gains
▪ If a UE is in Soft or Softer Handover, this will provide Diversity
Gains
▪ These gains can help the Link Budget by helping in achieving
the Target Eb/No with less power
▪ This gain is dependent on the Delta on the Ec/Io of the involved
paths
The UMTS Link Budget
UL Link Budget
▪ Because UL power is lower than DL power coverage is
“UL limited”.
▪ Initially, most attention is paid to the UL budget.
The UMTS Link Budget
-120 dBm Receiver Sensitivity
▪ Typical noise floor of cell receiver is -104 dBm.
▪ Considering full rate voice (12.2 kbps) processing gain is 25 dB.
▪ If target Eb/No is 5 dB and allowed Noise Rise is 4 dB then:
▫ UE must be capable of delivering (-104-25+5+4)= -120 dBm for
a successful connection.
▫ -120 dBm is effectively the receiver sensitivity for 12.2k voice.
▫ For a 128kbps service, the Rec. Sensitivity is around -110dBm
The UMTS Link Budget
UL Link Budget - voice
▪ If the UE can transmit at powers up to +21 dBm, the maximum
link loss is: 21 - (-120) = 141 dB.
▪ The maximum air interface path loss can be calculated by
considering antenna gains and miscellaneous losses (e.g.
feeder loss, body loss)
▪ If antenna gain = 17 dBi and losses = 4 dB, then maximum path
loss = 141 + 17 - 4 = 154 dB
▪ Note: margins not considered (e.g. shadow fading, building
penetration loss). These could total 24 dB.
The UMTS Link Budget
Link Budget - voice
Noise Floor -104 dBm Noise Rise Limit 4 dB Processing Gain 25 dB Target Eb/No 5 dB Receiver Sensitivity -120 dBm UE Tx Power +21 dBm Maximum Link Loss 141 dB Antenna Gain 17 dBi Feeder loss 3 dB Body loss 1 dB Maximum path loss 154 dB Margins 24 dB Target path loss 130 dB
The UMTS Link Budget
UL Link Budget - VT
▪ UMTS is introduced to offer higher level services such as video
telephony (VT).
▪ VT will typically operate at 64 kbit/s.
▫ Processing gain = 17.8 dB
▪ If all other parameters remain the same, then the maximum
▪ This allows maximum path loss to each cell to be determined and UL coverage to be calculated directly.
•VT coverage achieved
•Voice coverage achieved
Assessing Interference with a Static Analyser - Ec/Io
Coverage Planning
▪ Pilot Ec/Io indicates pilot power as a ratio of total wideband power (including the pilot itself).
▪ Not terribly “scientific” but it corresponds directly to measurement reported by the UE in drive tests.
Assessing Interference with a Static Analyser - Pilot SIR
Coverage Planning
▪ Pilot SIR gives the quality of the pilot.
▫ Effect of orthogonality on own-cell interference is considered.
▫ Pilot power not considered as interference.
▪ Pilot SIR is always better than Ec/Io.
3.3 Overcoming Coverage Problems
Coverage Planning
Limiting mutual interference
• Downtilt antennas.• Consider mounting antennas on the side of buildings.
Coverage Planning
Limiting mutual interference
Controlling the backlobe can produce a small but significant improvement in capacity.
0º
0ºElec 6ºMech
0º0º
6º
6º
6º
6ºElec 0ºMech
0º
6º6º0º
6ºElec -6ºMech
0º
-6º
12º
0º
Coverage Planning
Limiting mutual interference
• Key parameter: Frequency Re-use Efficiency (FRE).
(W) ceinterferen cell-inter theis
(W) ceinterferen cell-intra theis
FRE
Inter
Intra
InterIntra
Intra
N
N
NN
N
+=
Coverage Planning
▪ Used to lower the Noise Figure of the receiver
▪ Can “offset” feeder losses
▪ MHA used to increase coverage range
▪ Typ. 1.6 dB Noise Figure (NF)
▪ Typ. Gain of 12dB (adjustable)
▪ Increase uplink capacity
▪ Adds Insertion loss on DL (~ 1.3 dB)
AntAntBiasBias--TT
DCDC
TMATMAby passby pass
Mast Head Amplifiers (TMA’s)Coverage Planning
Uplink Receive Space Diversity
▪ Common to have two receive antennas per sector at the base station.
▪ Even if highly correlated, coherent combination should yield ~3 dB
improvement.
▪ In practice a gain of 4 dB or more is expected from antennas spaced 2-3
m apart.
Receive antenna 1
Receive antenna 2
Coverage Planning
Uplink Receive Space Diversity
▪ This is not “conventional” space diversity.
▪ Each antenna is connected to a separate finger of the Rake receiver.
▪ This is possible due to the synchronisation and channel estimation derived from the Pilot channel.
▪ Thus Eb/No is improved, rather than simply an effective power gain.
▪ Very low individual Eb/No will probably mean a very low pilot level which will lead to poor coherence and little gain - process becomes “self-defeating”.
Coverage Planning
3.4 Coverage in the Real World
Coverage Planning
Typical vendor values▪ Pilot Power = 5-10% of Total Power (30-35 dBm)
▪ Control Channel Powers = 3-5 dB below Pilot (27-33 dBm)▫ CCPCH’s
▪ Other signalling Channels = 3-5 dB below Pilot (27-33 dBm)▫ PICH, AICH, SCH’s
▪ Summary: Total Non-Traffic Channels = 20-25% of total power
Coverage Planning
Some additional constraints▪ GSM existing coverage
▪ GSM legacy sites
▪ Antenna limitations: height, azimuths, etc.
Coverage Planning
4- Capacity Planning
Capacity Objectives▪ Manage effectively predicted Load on Service Area
▪ Capacity dependant on:▫ Number of users
▫ Position of users relative to the cell
▫ Services demanded
▫ UE Power Control
▪ KPI’s▫ Cell UL Load Factor
▫ Cell DL Power
Capacity Planning
Factors affecting CapacityCapacity Planning
▪ Number of Users: The more users the more noise
▪ Position of Users: The farther away, the more noise
▪ Services demanded: The more high-bitrate users on the cell, the less overall number of users possible
▪ UE Power Control: Imperfect power control will account for more noise in the network
Soft and Hard CapacityCapacity Planning
▪ Hard Capacity: Hard limit imposed by actual channel elements
▪ Typ. 16 Kbps Channel elements. Also called “Resources” or “Cards”
▪ Soft Capacity: Variable, depending on Network loading
UL Pole Capacity
▪ Capacity is typically limited on the UL
▪ This is because, in the UL we don’t have Orthogonality to help us
Capacity Planning
( )iN
E
W
b +
≈
1
Capacity Pole UL
0
UL Pole Capacity Exercise- VoiceCapacity Planning
▪ If we assume a service with Eb/No = 6dB and i = 0.8
▪ Eb/No= 4 (linear) UL Pole Capacity= 533 kbps
▪ If you consider 12.2 kbps Voice bearers: ▫ 533/12.2 = 43.7 Voice Trunks
▪ Adding a typ. Voice activity factor (+overhead) of 58%
▪ New number of voice trunks is 533/(12.2x0.58) = 75.3
UL Pole Capacity Exercise- VoiceCapacity Planning
▪ A typical UMTS Cell can handle about 40E of Voice services
▪ With 75.3E being 100% capacity, 40E = 53% Loading
▪ Noise Rise= -10log (1-0.53) = 3.2dB
▪ Typically, 25% of this capacity will be allocated to Soft Handover
UL Pole Capacity Exercise- VTCapacity Planning
▪ If we assume a service with Eb/No = 3dB and i = 0.8
▪ Eb/No= 2 (linear) UL Pole Capacity= 1066 kbps
▪ If you consider 64 kbps VT bearers with 100% activity factors: ▫ 1066/64 = 16.6 Voice Trunks
▪ It is important to realise that the weightings are in terms of terminal densities.
▪ Sometimes the clutter category with the highest weighting occupies a small percentage of the area.
▪ Notice that the actual traffic volume per category differs from the traffic density. Traffic density is the parameter entered in the simulation tool.