This document discusses Cellcom Israel's network and strategies for managing interference in heterogeneous networks. It describes two cases where small cells caused interference issues: a single femtocell paralyzed a neighborhood due to spillage, and duplicate small cells with the same service code impacted the macro network. The document recommends installation rules to avoid interference and using self-organizing networks to optimize neighbor relations. It also summarizes a centralized radio access network trial in a stadium that showed 30% average spectral efficiency gains compared to coordinated multipoint.

1. Managing interference
and overlay in complex
network scenarios
5G World 2016, London
Amir Shalev , Cellcom Israel
Ver 3

2. Agenda
 Israel and Cellcom Israel(*) overview
 HETNET @ Cellcom’s Network
 Interference mitigation
– Dilemmas and challenges
– Lessons learned
 C-RAN in a stadium
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(*) Cellcom Israel - hereinafter Cellcom

3. Israel overview
 Area: 22,770 km^2
 Population 8.5M
 Population density: 387.63/km^2
The Israeli Cellular market
 6 MNOs (*) & 3 MVNOs
 Aggressive competition
 Regulation
The Israeli customer
 Cheapest Price
 Low loyalty to the operator
 Embraces new technology (Early adopter)
 Still some GSM only customers (M2M , “Kosher” phones )
3 (*) Out of which: One MNO performs National Roaming ,One MNO with a network sharing agreement and One only holds spectrum

4. Cellcom Israel Group
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5. Cellcom Israel
The leading operator in Israel
 2.8M customers (Largest
market share of ~27%)
 Total 3.7M customers served
by the cellular network
– Network serves Golan’s customers
as well (0.95M) – National Roaming
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Source: Globes 19.6.16

6. HETNET @ Cellcom’s Network
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Capacity
Small cells
Femto
cells
Macro Cell
Macro Cell

7. Cellcom’s Small Cells
 Small Cell and Macro shared vendor (LTE, UMTS)
– Indoor
– Outdoor
 Femto Cell by 3rd party with Femto GW (UMTS)
 Centralized RAN (CRAN) (LTE)
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8. Some LTE features for HETNET
 Reference signal power de-boosting
 Reference signal power boosting to small cell
 DL CoMP- Downlink Interference Shaping
 eICIC
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User traffic ABS

9. Agenda
 Israel and Cellcom Israel(*) overview
 HETNET @ Cellcom’s Network
 Interference mitigation
– Case 1 – Single Femto paralyses an area
– Case 2 – Duplicate Femto SC Impacts Macro
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10. Case 1 – Single Femto paralyses an area
Customer complained :
Availability problems at his flat
 Turned out that he was served by his
neighbor’s Femtocell
 Further enquiry showed that the
Femto served many users and was
totally blocked…..
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11. Case 1 - Continued
We went to check on site.
 Macro 2100MHz coverage level
in the street is low
 Femto has spillage to the street
– including the café across the
street
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F
Cafe

12. Case 1 - Continued
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• UEs suffer from Ping-Pong
between the Femto and Macro
which cause low availability
• UEs in the café block the Femto
• UEs in passing cars perform HO
to the Femto and try to perform
HO from the Femto to the Macro.
• Many of them end with a dropped
call.
HO to
Femto
Drop
Probes

13. Case 2 – Duplicate Femto SC Impacts Macro
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MACRO DCR
Femto Hand in attempts

14. Case 2 – Continued
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SON
Fail
HO to
Femto
Macro
Drops
UE
different
Femtos
same
SC
Probes
wrong
FEMTO
HO to
Femto

15. Case 2 – Continued
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Analysis:
• Calls try to HO from
Macro to wrong Femto
and fail.
• Failure due to Femto
SC confusion.
• Fixing SC confusion –
Problem solved
MACRO DCR
Femto Hand in attempts

16. Summary of findings
 Femtocell energy spillage causes interference 
 Intra-frequency blockage
 Ping-pongs cause low availability
 If Femto is the server in a road near by – passing cars
might try to HO to Femto with low success rate (Corner
effect). (*)
 Femto SC confusion
(*) Slow process (3G: Hard HO {4G: S1 HO} with core assistance)
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Most problems arise when Hand in connected mode is defined

17. Conclusions and Recommendations
 Typically most of the problems shown -> When Femto
GW is used
 Faster / Slower HO process
 Follow installation rules (next page).
 Where possible use different spectrum for Femto
(not applicable in Cellcom’s network)
 Use SON wisely
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18. Femto cell Installation rules
 Femto cell Best Installation locations:
– Apartments in a high floor
– In a basement
 install as far from windows / balconies as possible
(especially If installed in a low floor)
 In extreme cases use an external directional antenna
 Where needed lock Femto SC not to be changed
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19. SON for HETNET
 Add Centralized SON for neighbors not sniffed directly
by Femto (e.g. when installed in a basement)
 Use smart SON for Femto neighbor addition/deletion
in the Macro network
 SON – IMSI test – If serves outside – reduce Femto
power and create an alarm
 Best SC / PCI allocation by SON – look for repeated
additions/deletions
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20. C-RAN Trial
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• Pilot was excuted on
Haifa Stadium
• More than 30,000 seats
• 3 sites, 9 Sectors
• 15MHz LTE @1800MHz

21. C-RAN Preliminary walk tests
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0
20
40
60
80
100
120
140
160
180
200
Samples
MCS UL
MCS CRAN off
0
20
40
60
80
100
120
140
160
180
200
Samples
MCS UL
MCS CRAN on
0
50
100
150
200
250
300
350
Samples
TPut UL (kbps)
TPut CRAN off
0
50
100
150
200
250
300
350
Samples
Tput UL (kbps)
TPut CRAN on

22. CRAN usage – Mass Event
(Soccer Match )
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12% avg
38% avg
50% avg
88% avg
2RX
Usage
4RX
Usage
8RX
Usage

23. CRAN efficiency gain (compared to CoMP)
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1.0 bit/s/Hz
CRAN off
MCS 11.4 translates in a
spectral efficiency of
30%
CRAN Efficiency gain
Averaged over the whole stadium, i.e. also non
cell overlapping areas
1.3 bit/s/Hz
CRAN on
MCS 13.2 translates in a
spectral efficiency of
This 30% average gain over
the stadium is quite
remarkable due to the fact
that the stadium itself is very
well setup in terms of
cell/network planning as well
as network parameters.
• Two Soccer matches were compared (CRAN off vs. CRAN on)

24. Summary
 Small cells to Macro Impact cases
– Power spillage – several effects
– SC confusion
 Conclusions and Recommendations
 Centralized RAN gain for mass events
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25. Thank you
amirsl@cellcom.co.il
Amir Shalev