Capacity and Load Sharing in Dual-Mode Mobile Networks

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Capacity and Load Sharing in Dual-Mode Mobile
Networks
Author Juha Peura Supervisor Prof. Patric
Östergård Instructor M.Sc. Jarkko Laari, DNA
Finland Oy
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Agenda

• Background
• Objectives of the thesis
• Capacity
• Load sharing
• Conclusions

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Background

• The amount packet data in mobile networks
• have increased dramatically
• Operators have to guarantee quality of service
• New solutions needed for traffic handling

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Objectives of the thesis

• What are the main performance bottlenecks in
• todays mobile networks?
• Is it possible to ease the situation with load
  sharing
• algorithms?

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Capacity channel elements

• Channel element is a measure of node B hardware
  resources
• Separate CE pools for UL/DL, common to all
  sectors
• One 12.2 kbps speech service uses one channel
  element
• HSUPA takes up to 32 CEs, non-serving cells
• reserves also CEs
• CEs are a capacity bottleneck in uplink
  direction
• Many RAX-boards have 64 CEs
• Suggested minimum is 128 CEs

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Capacity Iub transmission

• Symmetric bit pipe between base station and RNC
• 3GPP have specified two transport methods ATM
  and IP
• Implemented using so called E1s
• Maximum throughput of one E1 is 2 Mbps
• For speech traffic one E1 has been sufficient
• Fast packet connections need multiple E1s
• Transmission is a capacity bottleneck in
  downlink
• Base station buffers data from Iub
• Future choice Ethernet/IP transmission

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Capacity HSDPA

• HSDPA uses the power margin left over from R99
  services
• HSDPA throughput depends on achievable
  Signal-to-
• interference and noise ratio (SINR)
• Power allocated for HSDPA effects the throughput
  largely

ThroughputMbps 0.0039 x SINR2 0.0476 x
SINR 0.1421
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Load sharing

• Enhances performance by pooling together
  resources
• Inter Frequency Load Sharing
• - Traffic sharing between WCDMA carriers
• Directed Retry to GSM
• - Speech traffic diverted from WCDMA to GSM

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Directed Retry to GSM

• Why?
• 3G most beneficial for PS data users
• 3G UEs are becoming more common and
• coverage improves constantly
• -gt free capacity to GSM
• More resources for data users
• Balances load between networks
• No additional investments

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Directed Retry to GSM - limitations

• Only applicable to speech traffic
• Coverage of UMTS and GSM cells should be same
• Overloading of GSM network possible
• Should not be used if GSM -gt UMTS
• handovers are in use (ping-pong effect)
• GSM target cell quality not guaranteed (blind
  ISHO)
• -gt call drops
• Increased signaling, mobiles not reachable
  during
• LA updates
• Configuration to entire network can be laborious
• 3G users may wonder why they are in GSM

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Directed Retry to GSM - principles

• Redirection decission based on cell load
• (used downlink carrier power)
• After cell load exeeds specified sharing
  threshold, speech calls
• are diverted to GSM network
• Sharing fraction parameter specifies the
  percentage of directed calls
• while the cell load is above the sharing
  threshold
• Released power can be allocated for PS users
• Sharing parameters can be assigned independently
  to each cell

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Load sharing - traffic profiles
speech
packet
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Load sharing - measurements

• Functionality and different parameters were
  first
• tested in a single cell
• Larger scale test in live network for a three
  week period
• 20 most loaded cells were chosen for the
  measurement
• Feature was tested with radical parameters to
  really find
• out how load sharing performed
• A set of key performance indicators (KPI) was
  defined to
• assess the effects of the feature
• DR-success ratio, Speech setup success rate,
  dropped calls,
• admission number, lack of CEs, speech traffic
  (Erl), PS traffic .
• Network counters were used to gather information
• about the functionality
• Raw data was filtered and manipulated for final
  results

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Load sharing - results

• Directed Retry to GSM worked well in overall
• Total of 93117 speech call redirection attempts,
  86033
• were succesful
• DR-success rate was 92 , with carefull cell
  selection
• gt 95 success rate possible

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Load sharing results UMTS
KPI DR - FALSE DR - TRUE Difference

Speech setup success rate 99,63 29,29 -71
Dropped calls percentage 0,36 0,53 48
Speech traffic (Erl) 1,12 0,39 -65
PS R99 traffic (Erl) 1,86 2,06 11
PS R99 setup success rate 94,41 98,96 5
PS R99 retainability 94,14 97,97 4
HS traffic (Erl) 0,72 0,79 10
HS User Thu DL (kbps) 139,24 158,21 14
HS User Thu UL (kbps) 33,38 42,58 28
HS setup success rate 97,32 97,65 0
HS completion success rate 79,35 76,36 -4
CS speech payload (kbits) 240 706 657 99 813 954 -59
HSDPA RAB attempts 153 603 164 147 7
HS drop 17,13 20,06 17
Admission number 2 949 1 504 -49
Failed after admission 3 013 2 789 -7
NG user down-switches 15 733 8 057 -49
UL hardware lack 2 351 817 -65

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Load sharing results GSM
KPI DR - FALSE DR - TRUE Difference

TCH attempts 623 921 820 990 32
TCH H_Block 0,06 0,02 -62
TCH T_Block 0,73 1,66 129
TCH RF_Loss 0,14 0,23 60
TCH traffic (Erl) 2,67 3,26 22
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Conclusions

• Transmission, CEs and HSDPA power allocation
• can form a capacity bottleneck
• Load sharing between UMTS and GSM works
  reliably,
• if configured well
• Performance of PS users can be enhanced with
• Directed Retry to GSM, at least a little
• 3G traffic still relatively low, it is
  questionable if
• load sharing is needed at this point.

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Future research

• Load sharing between UMTS carriers
• more sophisticated feature than Directed Retry
  to GSM
• between UMTS2100 and UMTS900
• two way directions taking into account cell load
• applicable to all services
• Service based handover

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THANK YOU !