UMTS/3G RAN Capacity Management Guideline Part-02 (Sectorization))

UMTS RAN Capacity Management
Guideline-Sectorization
MD MUSTAFIZUR RAHMAN
Principal Engineer
Radio Network Planning & Optimization
Grameenphone Ltd.

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Md MustafizurRahman| RNPOEngineer| Grameenphone Ltd.
choton.05@gmail.com | LinkedIN
Contents
1. Objectives.................................................................................................................................2
2. UMTS Hard Capacity Expansion..............................................................................................2
2.1 MBB Capacity Solution .....................................................................................................2
2.2 3G Expansion Triggering Parameter ................................................................................2
2.3 Cell Split Triggering Threshold..........................................................................................4
2.4 Cost vs Capacity of Sectorization.....................................................................................7
2.5 Cell Split Capacity Gain & Prioritization............................................................................8
3. Sector Split Planning Guideline..............................................................................................11
3.1 Split Cell Optimization.....................................................................................................11
3.1.1 Load Imbalance........................................................................................................11
3.1.2 Load Imbalance Optimization ..................................................................................12
3.1.3 Optimum Utilization of Split Cell RRU Power ..........................................................15
3.1.4 LowUtilized Split Cell Swap ....................................................................................16
4. Conclusion..............................................................................................................................17

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1. Objectives
UMTS RAN capacity management is one of the Key activities to maintain the good QoS &
stability of the 3G system. A relatively high load can affect the accessibility, coverage and
QoS of established services. The capacity, coverage and QoS of the WCDMA system are
mutually affected. Hence, for a stable & good quality 3G network, UMTS capacity need to be
monitored, expanded & manage regularly.
In the first part of document (Part-1) UMTS soft capacity management along with the
correlation between capacity vs accessibility, UMTS expansion threshold, counters & effective
mechanism of UMTS Soft capacity management have been depicted. This part of the
Document is focused on UMTS Hard Expansion Methodology. 3G Capacity management by
Sectorization has been explained thoroughly.
After completing this, you will be able to gain knowledge on 3G Expansion Parameters, 3G
Expansion Threshold, Capacity Gain, Cost vs Capacity Gain by Sectorization. Moreover, you
will be familiar with Planning, Optimization & Post Performance activities of Sectorization.
2. UMTS Hard Capacity Expansion
2.1 MBB Capacity Solution
3G traffic load can be offloaded by LTE/5G Deployment, Additional Carrier Deployment,
Sectorization & Standalone sites deployment. Traffic steering to upper technology (LTE/5G)
is the best option to enhance network efficiently. In many networks, this might not be possible
due to poor 4G/5G HS penetration. In these cases, sectorization is the most feasible cost-
effective solution. However, sectorization must be done wisely by assessing soft & hard
optimization scope. Moreover, prioritization and post tuning need to be done carefully to
maximize the sectorization gain.
2.2 3G Expansion Triggering Parameter
Usually, data utilization is measured by spectrum efficiency, meaning measuring the ratio
between Busy Hour Traffic (Mbps) to Theoretical Maximum Capability of the Technology
(max. spectrum efficiency). Data volume forecast based on APPMB, APPU & company
revenue target is relatively easy compared to simultaneous active user projection. Thus,
Cell Split/9-
Sector
Additional
Carrier
Standalone
Site
LTE/5G
Deployment

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volume is used for data capacity measurement & it is best parameter for Transmission& Core
Network dimensioning. However, in RAN domain, maximum generating data volume is not
main driving factor for expansion. Simultaneous active user has a strong impact on user
throughput & cell capacity.
During low load periods, few users can generate maximum amount of value for better network
quality. On the other hand, during the peak user BH volume can be lower than non-BH period
due to degraded QoS, capacity chocking & for higher Signaling/Payload ratio. This type of
phenomenon easily misleads to expand in wrong cells. Especially in 3G network (self-
interference technology) is highly vulnerable to high load condition. Signaling overhead soars
exponentially during busy hours resulting system capacity dropping. As a result, during the
high load period cell might be chocked to deliver maximum cable volume compared to no
loading period.
Fig: Cell BH Distribution based on Volume & HSDPAUser
Above chart suggests, most of the Volume based Cell BH triggers during the mid-night, i.e.
during low load period for low interference. On the contrary, user-based cell triggers during
the network’s actual BHs, during the peak user concentration time.
Active User & Data Volume impacts on User Throughput has been analyzed in different
network and in all cased similiter result is being observed. Below charts, suggest that there is
no strong relation between Data Volume vs User throughput. However, there is strong
correlation visible between Active User vs User Throughput. User OoS decreases with the
increase of active user. On the other hand, no relation is found between Data Volume vs User
throughput. Hence, Simultaneous Active User (HSDPA User) is key factor of Capacity
Expansion for a desirable QoS (Throughput)
Hour

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Fig: User Throughput relation with Simultaneous Active User & Data Volume
2.3 Cell Split Triggering Threshold
As mentioned above, there is strong correction between User Throughput vs HSDPA
Simultaneous user and cell capacity. Same result found in different operators. From the below
charts it can be concluded that in all operators, Volume generation loses linearity after 10
user, somewhat OK upto 15, after which throughput degradation limits volume generation
severely and completely flattens out beyond 20!. And when simultaneous user reaches to 22,
user throughput goes down to 700Kbps.
No clear relationship observed between
MB/MHz/Cell & HSDPA User Throughput
Throughput of all operators are getting
decreased with the increase in UE per Cell
X
Z
Y
W
Y Z W Z

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Fig: User vs User Throughput and Cell Capacity
Above correlation strongly indicates, cell capacity becomes stagnate after 20 user. This is due
to high signaling load & low user QoS. Being a self-interference generating system, UMTS is
highly vulnerable to connected user. With >20 HSDPA users, system capacity drastically
reduced, overhead become prominent.
Fig: Illustration of System Stability
Operator-W Operator-X
Operator-Y Operator-Z

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Fig: User vs Cell Capacity
In fact, UMTS Uplink more vulnerable than Downlink. RTWP exponentially raises after 19
HSUPA user. Consequently, most of the vendor limit the UP-Link user (HSUPA User)
Threshold to 20. HSDPA user threshold usually defined 64.
Fig: HSUPA User vs RTWP
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0-1
1-2
2-3
3-4
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25-26
26-27
27-28
28-29
29-30
>30
Volume(GB)/Cell
HSDPA User
User vs Busy Hour Volume
Slop m3: 0.0
Good Experience
Region
Moderate Experience Region Experience Bottleneck Region

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Even though, data suggests 20 users should be the expansion threshold for cell split, yet 10%
hysteresis should be considered for optimization scope (soft & physical). Therefore, 22 is the
triggering threshold for cell spilt, accepting average user throughput approx. 600~700Kbps.
Theoretically, cell split capacity is 1.7 times compared to normal cell. Hence, 9-sector triggering
threshold is (22*1.7*1.1) = 41 Users & for standalone new sites threshold is (22*2.2*1.1) around
51 users. Here 9-sectors theoretical capacity is 2.2.
Fig: Triggering threshold for UMTS Expansion
2.4 Cost vs Capacity of Sectorization
Traffic steering to upper technology or Additional spectrum is the best solution for 3G expansion.
However, this involves availability of spectrum, regularity & other issues. In this no additional
spectrum/high 3G HS pone scenario, only sectorization is the feasible hard expansion solution.
During the solution design, cost vs capacity comparison needs to take consideration. Cost of 9-
sector & 18-sector solutions is Significantly Higher Cost/Capacity Gain Compared to traditional
Cell Split (6 sector) solutions. Additionally, load imbalance & complex network architecture are
700 Kbps user
Throughput
HSDPA USER

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also big problem of 9-Sector and 18-Sector Solution. Hereafter, 9-sector & 18-sectors are not
recommended for mass level deployment.
Even, mass level of 6-Sector is not also a recommended solution for 3G capacity management.
Massive level of 6-Secor deployment will make network architecture complex for future
upgradation & regular performance management. Ontop this, massivesectorizationwill increase
overall noise floor. Consequently, cost benefit result will be negative in massive level 6-
Sectorization deployment.
Fig: Cost vs Capacity Comparison
2.5 Cell Split Capacity Gain & Prioritization
As per OEM feedback 6-Sector (Cell Split) can boost up 70% capacity on sectorized cells.
From the statistical analysis similar result observed during the Busy Hours. Daily volume gain
might be lower, since cell can still providing better quality during non-Busy Hour. However,
Busy Hour capacity gain should be considered as split cell gain.

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Fig: Cell Split’s Busy Hour Capacity Gain
Cell split capacity gain certainly depends on the congestion level. Severely congested cells have
the better gain compared low congested cells.Therefore, during the cell split candidate selection,
high user & low throughput cells should be prioritized first. Service mix might be another
dimension to select high revenue cells. For the same QoS & same User number, cells having
high video demand should be prioritized.
Split Sector
Result
Non-Split
Sector Result

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Fig: User, Throughput & Payload 3D Chart
It is clearly visible that, both user and User QoS are the function of Payload. User throughput
falls w.r.t user number increment & for a similar user number QoS might be varied due to traffic
pattern and user location. With a same number of user rural clusters’ user throughput will lower
that City cluster due to high distance traffic.
This figures also suggests, payload can be improved by increasing the user throughput. In fact,
due to poor QoS desired payload cannot be generated even with low user load. Therefore, high
congested cells with low user throughput split cells will give more benefit compared to better QoS
cells. That’s why during the cell split candidate selection both HSDPA User >=22 & User
throughput <700Kbps should be considered for candidate selection.
200-400-600-800-1000
3

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3. Sector SplitPlanning Guideline
Before sector split, current traffic pattern & clutter need to be analyzed carefully. Use of both
Geolocation & Planning tool must be incorporated during traffic & clutter analysis. This is
needed to make proper load balancing among sectorized cells. After cell split, post-
performance along with load balancing is must. For load balancing, fine tuning might be
required in many causes, load distribution among sectors should be at least 40:60 or 60:40
ratio for maximum capacity gain.
Fig: Cell Split Basic Modality
3.1 Split Cell Optimization
3.1.1 Load Imbalance
Load imbalance is one of the critical drawbacks of spit cells. It is very difficult to balance the
traffic among cells due to diversified traffic distribution & maintaining proper grid among
neighbors. Due to load imbalance capacity gain cannot be fully capitalized which will trigger
another capacity solution. Moreover, imbalance load impacts the subscriber’s experiences. High
loaded cell cannot provide expected throughput. Hence, load should be the integral part of cell
split activity. Load balance should be at least 60:40 & 40:60 between Split Cell & Mother Cell.

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Fig: Imbalance Cell Example
3.1.2 Load Imbalance Optimization
Improper UMTS cell design is the main case of Imbalance that can be solved by Antennal
Optimization. Nevertheless, some cases Hardware fault & Configuration mismatch can
lead to imbalance in split cell.

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Fig: Imbalance Example
Common Root Cause & Solution of Imbalance Slit Cell
Root cause CPICH Power Mismatch betweensectors
Inter Cell Neighbor Mismatch
Hardware Fault
Configuration &PlanMismatch
Improper antenna design
Solution
Same CPICH PowerConfigured forallCells
Missing Neighbor CellsAddition
Hardware Checking &Rectification
Configuration Checking& Same tiltingfor allsectors
ProperAntenna Design&Post Imbalance OptimizationbyNASTAR and Google Earth Traffic
Analysis

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Example of Neighbor Mismatch Rectification
CME

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Fig: Imbalance Cell Optimization Outcome-Capacity triggered cell Reduced by 25%
3.1.3 Optimum Utilization of Split Cell RRU Power
Since, all new RUs are higher power capable compared to old one, performance of the
imbalanced split cell can be improved by proper RU installation. For better performance &
proper HW utilization of Split Cell, following steps need to be followed.
 During the Cell Split Planning, high power RRU need to be installed in projected
high loaded cell
 Increasing service power if high power RRU is already installed in high loaded cell
 Swapping high power RRU with low power one if it is reversely installed (low load
high power RU)

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Fig: Optimum Utilization of High Power RRU
Result of High Power Utilization: Performance Gain from 30W to 4OW (KSMOT1B &
KSMOT1S): 33% Throughput Gain
Fig: Throughput Gain from High Power RRU Utilization
3.1.4 Low Utilized Split Cell Swap
Another important Split Cell Optimization is to monitor the cell performance at least
monthly or quarterly to identify the low utilized split cells. Utilization of the split cell might
be reduced due to Neighbors’ 3G site on-air/configuration issue/antenna optimization/
UMTS coverage enhancement initiatives. These low utilized cells can be swapped in the
high loaded areas where cells split demands. During the swap possibility checking cell by
cell analysis is needed. Strategic, Sudden Traffic Surge or any other event supported cell
should be excluded from the swap list.
Performance will be degraded after Cell Split Dismantle. To compensate the certain
portion of degraded throughput, high power RRU should be kept in dismantled split cell.
In some cases, high power RRUswap might be required.

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Fig: Low Utilized Cell Identification Methodology
4. Conclusion
It is evident that mostly practiced Data Volume is not the key parameter for 3G RAN Capacity
expansion rather Simultaneous Active User (HSDPA User) has a strong impact on 3G RAN
capacity. This is also true for the 4G or any other MBB Capacity management as well. With
no spectrum scenario, Sectorization is the only feasible hard solution for 3G capacity
management. By proper planning & prioritization, sectorization can boost up 70% capacity.
However, massive deployment of sectorization is not recommended due to complex network
architecture & efficiency reduction in mass level deployment. Regular performance monitoring
& load balancing are two major activities need to done after sectorization to capitalize
maximum gain of Sectorization.

UMTS/3G RAN Capacity Management Guideline Part-02 (Sectorization))

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