RF design strategies for cellular technologies

RF Design Strategy
 Use optimized design.
 Influence the anchor network.
 Enforce design rules.
 Check against performance commitments in attachment
H.
 Cooperate with the RF Designer and Cingular
proactively.

Design Considerations
 In UMTS networks coverage and capacity are
interchange-able.
 The network is designed for both coverage and capacity.
 Some difference as compared to GSM.
GSM
UMTS
TDMA
AMPS
GSM
TDMA
AMPS

Guaranteeing CPICH RSCP is not enough
 UE needs to decode the CPICH to get service.
 Good CPICH RSCP (Ec) does not mean that the CPICH
can be camped on.
 Good CPICH Ec/Io is needed to camp on the system.
 Networks should be designed for good CPICH Ec/Io.
A B
E
F
C
A B
E
F
C
Sufficient RSCP
Bad Ec/Io

Design for Specified Load
 Interference increases with loading.
 Coverage decreases with loading.
 Networks should be designed for specified load,
otherwise severe coverage issues will be encountered.

Design for Service
 To get service, both uplink and downlink Eb/No targets
for the service should be met.
 If the UE can camp on a cell, that does not necessarily
imply that it can get service.
 Power is a shared resource.
3/ 038 13 - EN/LZU 108 5418 PA1 WCDMA Radio Wor kshop
3
Downlink Physical Channels
Σ
CCPICH,256,0
Sdl,n
+
S
/
P
CPICH
All 0s
GCPICH
CPICH,256,m
Sdl,n
+
S
/
P
PICH
Paging
indication GPICH
CAICH,256,m +
S
/
P
AICH
Acquisition
indication
GAICH
Sdl,n

GP-SCH
P-SCH
GS-SCH
S-SCH
Cos (ωt)
- Sin (ωt)
+
Sy stem
inf ormation
CP_CCPCH,256,1
Sdl,n
+
S
/
P
P_CCPCH
GP_CCP CH
Error Protection
GS_CCP CH
CS_CCPCH,SF, m
Sdl,n
+
S
/
P
S_CCPCH
Paging &
signaling
CDPCH,SF, m
Sdl,n
+
S
/
P
DPDCH
Data
GDPCH
M
U
X
DPCCH
Pilot,TPC
& TFCI

Feeder Changes
 UMTS 1900 forward link becomes
the limiting link for narrower feeders.
 Plans will be prepared to perform
feeder changes on sites where the
UMTS 1900 feeder loss is greater
than 3 dB.
 Comscope 1 5/8” Feeder will be used
as per Cingular Headquarter
direction.

Tower Mounted Amplifiers
 TMAs help improve coverage/indoor coverage in 1900
systems.
 Sites that do not have TMAs will get 1900 only TMAs.
 Sites that have 850 TMAs will get dual band TMAs.

Remote Electrical Tilts
 Remote Electrical Tilt (RET) units can be
used to change the antenna downtilt
remotely without climbing the tower.
 Availability of RETs speeds up initial
tuning.
 UMTS networks need to be re-configured
as traffic grows.
 RETs can reduce the cost of regular O&M
activities.

Antenna Selection
 Dual band antennas with independent electrical downtilts
will be used for UMTS 1900 overlay on GSM 850.
 All other antenna parameters will be preserved.
 Narrow horizontal beam antennas will be selected if the
following conditions can be met.
 Additional capacity commitments can be met.
 UMTS performance is improved.
 GSM composite coverage is not affected.
 UMTS CPICH coverage is not reduced.
 UMTS CPICH Ec/Io is not degraded.
 UMTS system capacity is not reduced.

Antenna Sharing UMTS1900 on GSM850
 Dual band antenna should have independent electrical
downtilts for both bands.
 All 850 antennas with horizontal beam-width greater than
90 degrees will have to be replaced with 90 degrees
antennas.
 Dual band antennas are generally heavier than single
band antennas.
 Quad-pole and Tri-pole dual band antennas are not
available.
UMTS GSM
X
X

Antenna Sharing UMTS1900 on GSM1900
 100% antenna sharing.
 RF equipment for sharing antennas is needed. This
equipment results in additional loss.
 UMTS tilts are constrained by GSM tilts.
 In a 1/1 FLP network, cell plan changes that help UMTS
should also help GSM.
X
X
UMTS GSM
DDU

Link Budgets
 Separate link budgets are needed for CPICH and for
each RAB.
 Link budgets for the RABs consider coverage as well as
capacity.
 Generally, higher rate RABs have tighter budgets and
lesser coverage/capacity.

Omni sectorization
 All omnis will be sectorized.

Worst Offenders
 Worst offenders may be lowered or downtilted
aggressively.
 If possible, worst offenders may be removed from the
UMTS plan.

Adding sites to Anchor Network
 Initial design is performed on mostly Cingular sites: like
for like antenna.
 Plots and stats are produced from the Initial design.
 Problem areas are identified and ranked.
 Sites are added if the problem area cannot be resolved
by antenna system modifications.
 Simulations are re-run to verify changes.
GSM Design UMTS Initial Design
UMTS Final Design

Problem Areas
 Loss of GSM coverage
 Insufficient CPICH RSCP.
 Insufficient CPICH Ec/Io.
 Excessive path loss.
 RAB Eb/No not met.
 Imbalanced links.
 Low service probability of indoor coverage.
 High failure rate.
 Pilot Pollution.
 Poor throughput.
 Poor BLER.

Design Priorities
 Establish sufficient CPICH RSCP.
 Establish good CPICH Ec/Io under load.
 Ensure high probability of service coverage under load
on both links.
 Which service?
 What about HSDPA?
CPICH RSCP
CPICH Ec/Io
Service Coverage
Design is built up by
covering the basics
first.

Optimized Tilts
 No uptilting beyond 0°.
 Optimi ACP will be used if available.
 For UMTS1900 over GSM850, few downtilts are
expected.

Why are downtilts more important
 Power is a shared resource in UMTS.
 As load increases in a cell, total transmitted power
increases also.
 Max transmit power cannot be used to control interference.
A B
C
D
E
A B
C
D
E
Unloaded Loaded

Coverage Overlap
 Overshooting sites should be lowered, downtilted or
removed from the UMTS plan if possible.
 For neighboring cells, some optimum coverage overlap is
needed.
Too much overlap results in
loss of capacity
Too little overlap results in
increased interference
Optimum
Overlap

Narrow-beam (65° antennas) Usage
 Cingular’s GSM networks are on 90° grids.
 Replacing 90° antenna with a 65° antenna means higher
capacity commitment.
 Use 65° antenna only if:
 GSM composite coverage is preserved.
 Site is in urban or dense urban morphology with <= 1 mile
site to site distance.
 No UMTS coverage (CPICH and all RABs) holes are
created.
 Increased capacity commitments can be fulfilled.

Design Targets
 CPICH RSCP
 CPICH Ec/Io (loaded)
Morphology
Target CPICH RSCP at
Cell Edge
Urban -80 to –85 dBm
Suburban -85 to –90 dBm
Rural -90 to –105 dBm
Morphology
Target CPICH Ec/Io at
Cell Edge
Urban -10 dB
Suburban -10 to -12 dB
Rural -12 to –15 dB

Design Targets – RAB Coverage
 RAB coverage under committed load.
 Meet the following four criteria:
1. DL Achieved Eb/No is equal to or better than the target
Eb/No everywhere in the cluster.
2. UL Eb/No failure is less than 2% everywhere in the
cluster.
3. Probability of Coverage (indoor) is 98% or higher
everywhere in the cluster.
4. Path balance is achieved everywhere in the cluster.

 IRAT will be activated for all the cells pointing out of the
UMTS Coverage Area.
 64k CS Video calls will not be tested in the cells pointing
out of the UMTS Coverage Area.
Target Design Area

Tune and verify propagation
model
Suggested Steps
Design Kick-off
Obtain design inputs – site
database, site walk downs
etc.
Sanitize databases
Prepare a list of all site that
will have tower work
Send the list to Site
Development Vendor for
approval
Populate the Planning Tool.
Prepare Initial Plots/Stats
Prepare a list of changes to
improve system
performance in agreement
with the local market. This
list includes automatic
changes to the network
Modify design from Site
Development Vendor Input
Consolidate a list of sites
where no changes will be
possible
Make changes in the
planning tool after filtering
the no-change list and run
simulations on the modified
design
Prepare a list of changes to
improve system
performance in agreement
with the local market. This
new list will not include sites
where tower work cannot be
performed
Fine tune the design
Prepare deliverables
Finalize clusters

 The RF Designer pays for any changes over the first
20% of the changes after the delivery of the initial design.
Limits on Design Changes

 UMTS Link Budgets
 ASSET 3G for RF design.
 Optimi Automatic Cell Planning (ACP).
 Volcano Ray Tracing.
Design Tools

RF design strategies for cellular technologies

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