Overcoming Interference Challenges when migrating from WiMAX to LTE

… and anything is possible-1-Imagine Confidential

Overcoming Interference Challenges when

migrating from WiMAX to LTE

24th June, 2015

Mike Stacey, CTO, Imagine Wireless


Overcoming Interference Challenges when migrating from WiMAX to LTE

! Imagine Background

! Mitigating interference between WiMAX and LTE

! Reducing customer churn whilst migrating

! Exploiting existing WiMAX infrastructure to migrate to LTE


Imagine Background

! Irish Broadband formed in 2003 to take advantage of the slow development of DSL services

� Initial Fixed Wireless deployment using unlicensed technology 2.4GHz, 5.4/5.8GHz,

� Followed by fixed WiMAX and pre WiMAX nomadic networks in 2005

� > 50,000 Wireless customers, 6,500 corporate (12%) 46,500 residential (88%)

! Network

� 200 sites, >1000 Base Station sectors

� Extensive National Fibre & Wireless transmission network (Population covered: ~1.8m)

! In 2008 acquired by Imagine Communications Group:

� Full Service Telecoms Group

� > 100,000 customers, Fixed Voice, Broadband, Data and ISP services to Business and Residential

� International Call Termination, Call Origination & Premium Services across Europe

� Full capability ADSL / Wireless, VOIP, ISP, WiMAX, Mobile, Triple Play

! Imagine Group is a privately owned company with turnover in excess of €100m.


Wireless Network Deployment

! Deployment of Fixed Wireless Access technology since 2003

! Over 200 High Sites Locations and >1000 Base Stations deployed

� WiMAX rollout completed in 2011 with 135 sites and over 500 base stations

! Wide range of products from entry level broadband and voice to Gbps corporate WAN

! All IP RAN, Backhaul and Core network

! Architecture NGN based and designed to easily scale, evolve and integrate with back end systems


3.5GHz Spectrum & WiMAX Coverage

• >200 MHz of 3.5GHz Spectrum in key areas

• Minimum of 100MHz Spectrum available for LTE

Rollout


Imagine Network Evolution & Spectrum

2003

2004

2005

2006

2007

2008

2009

2010

MOBILE

FIXED

CO

RP

OR

AT

E

SO

HO

& S

ME

RE

SID

EN

TIA

L

NOMADIC

2011

2012

2013

Migrated to

WiMAX

Migrate to

LTE


Summary of Radio Network Deployment

Technology No of Sites No of Sectors Frequency Band

Motorola WiMAX 16e 134 507 3.5GHz

Alvarion Breezemax

WiMAX 16d

21 51 3.5GHz

Alvarion Breeze VL 110 315 5.4-5.8GHz

Alvarion Walkair 26 40 10.5GHz & 26GHz

Microwave Pt-Pt 275+ n/a Multiple licenced

Pt-Pt bands

Navini Pre WiMAX 100+ 250 3.5GHz

NextNet Expedience 140+ 400+ 3.5GHz

Migrated to

WiMAX


Radio Network Evolution

Technology No of Sites No of Sectors Frequency Band

TD-LTE 900+ 2,700 3.5GHz-3.6GHz

(Band 42,43)

Motorola WiMAX 16e 134 507 3.5GHz

Alvarion Breezemax

WiMAX 16d

21 51 3.5GHz

Alvarion Breeze VL 110 315 5.4-5.8GHz

Alvarion Walkair 26 40 10.5GHz & 26GHz

Microwave Pt-Pt 275+ n/a Multiple licenced

Pt-Pt bands

Navini Pre WiMAX 100+ 250 3.5GHz

NextNet Expedience 140+ 400+ 3.5GHz

Migrate to

LTE


Business Objective

! Get to commercial 20MHz, 2x20MHz LTE asap, - when available, with outdoor CPE

! Issue:-

�What is cost/benefit of

− upgrading existing WiMAX pre LTE �

− deploying LTE with only indoor CPE �

− deploying new “LTE ready” WiMAX to new sites prior to full LTE �

� How to minimise risks/costs associated with deployment of new LTE technology �

− Risk minimised by keeping WiMAX network stable, grow/maintain customer base until

LTE fully ready

− Rollout LTE in areas where WiMAX was not rolled out

− focus on areas where broadband demand not met by current infrastructure

− Migrate WiMAX areas to LTE eventually if there is sufficient demand to justify


Mitigating interference between WiMAX and LTE

Physical

Isolation

Spectrum and

Geographic

Separation

Synchronisation

and Frame

Alignment


Spectrum and Geographic Separation

! Spectrum:

�With sufficient spectrum it is possible to avoid re-use of frequencies on WiMAX and LTE

� Interference issues at co-located sites still requires attention

! Geographic:

� Prioritisation of LTE rollout into areas where WiMAX was not rolled out

� Commercially driven decision to focus on areas where broadband demand not met by

current infrastructure

�Where LTE and WIMAX areas are adjacent careful use of frequencies minimises

interference


WiMAX -LTE Interference Scenarios

Majority of the interference

occurs between un-

synchronized

Base Stations


WiMAX –LTE Interference Scenario

BS receives BS receives

TD

D(U

nsy

nch

ron

ised

)T

DD

(Syn

chro

nis

ed)

BS transmits BS transmits

Net

wor

k B

Time

Net

wor

k A

Net

wor

k B

Time

Net

wor

k A

BS transmits BS receives BS transmits BS receives

BS transmits BS receives BS transmits

BS transmits BS receives BS transmits BS receives

BS receiv

Downlink (DL) Uplink (UL) BS-to-BS Interference

Interference occurs when one system transmits at the same time as the other receives


WiMAX & LTE Frame Structure

LTE Frame Structure

WiMAX Frame Structure

Downlink Uplink

LTE Subframes may be

Downlink, Uplink or Special Interference


TDD-LTE Frame Structure

! TDD-LTE frame structure: 10ms.

! It consists of “2 half frame” X “5 sub-frames” (1ms)

! Each sub-frame can be used for DL (D), UL (U), S (Special)

Uplink-downlink

configuration

Downlink-to-Uplink

Switch-point

periodicity

Subframe number

0 1 2 3 4 5 6 7 8 9

0 5 ms D S U U U D S U U U

1 5 ms D S U U D D S U U D

2 5 ms D S U D D D S U D D

3 10 ms D S U U U D D D D D

4 10 ms D S U U D D D D D D

5 10 ms D S U D D D D D D D

6 5 ms D S U U U D S U U D

Configuration #2 allows 3:1

DL:UL ratio and alignment

with existing WiMAX Frame


TDD LTE Special Frame Introduction

　　　　Index DwPTS GP UpPTS0 3 10

1 9 4

2 10 3

3 11 2

4 12 1

5 3 9

6 9 3

7 10 2

2

Number of symbols occupied by DwPTS, GP and UpPTS

1

Special Sub Frame 9:3:2 gives optimal alignment to WiMAX Frame


WiMAX & LTE Frame Structure

LTE Frame Structure

WiMAX Frame Structure

D S U DDD S U DD

5 7


Feasible Co-existence Configurations

WiMAX DL/UL configuration

TDD-LTE DL/UL configuration

WiMAX Performance TDD-LTE Performance

35:12 3:1 No impact to WiMAX network

No impact to WiMAX network;LTE DwPTS length is changed to 9os, about 2% capacity loss (compare with special frame configuration 7)

35:12 2:2

WiMAX will impact UpPTS which transmits RACH in LTE, subscribers of LTE can not access Network; WiMAX lose 8 Symbols for synchronization, system DL capacity lose 26%

No impact to LTE;

29:18 3:1WiMAX UL symbol which used by common channel will be impacted, WiMAX subscriber can not access the network

29:18 2:2The last two symbols of WIMAX downlink need to be punctured, about 6% capacity loss

No impact to LTE;

Special Sub Frame 9:3:2 gives optimal alignment to WiMAX Frame without altering DL:UL Ratio


Test Results

Results vary – on one instance 9:3:2 resulted in 15% loss of performance, in another there was

negligible decrease in LTE throughput. There was no interference on the existing WiMAX

network.

Cable WiFi Cable WiFi Cable WiFi Cable WiFiIndoor Gemtek (Cat 4) 95.5 84.7 96.2 101.5 Indoor Gemtek (Cat 4) 92 85Indoor BM593 (Cat3) 75.0 42.2 75.2 69.1Mifi E5776 (Cat 4) 104.3 66.5 108.9 70.2Outdoor B222s (Cat 3) 77.5*

Cable WiFi Cable WiFi Cable WiFi Cable WiFiIndoor Gemtek (Cat 4) 9.6 9.5 9.6 10.3 Indoor Gemtek (Cat 4) 10Indoor BM593 (Cat3) 9.3 9.5 10.3 10.3Mifi E5776 (Cat 4) 9.3 9.2 10.3 10.3Outdoor B222s (Cat 3) 9.6*

Indoor BM593 (Cat 3) x3 Indoor Gemtek (Cat 4) x9

Indoor BM593 (Cat 3) x3 Indoor Gemtek (Cat 4) x9

Mifi E5776 (Cat 4) x2

* Not peak, tested outdoor UE installed on office and connecting to Belmont ** Not peak, highest coding rate could not be achieved on all UE

Notes1) Frame structure 10:2:2 in theory provides higher DL throughputs than frame structure 9:3:22) Frame structure 9:3:2 is required for synchronisation with WiMAX base stations to avoid co-channel interference

Frame 10:2:2 Frame 9:3:2PEAK MULTI USER DOWNLOAD (Mb/s) 20MHz

107.5 104.3

PEAK MULTI USER UPLOAD (Mb/s) 20MHz Frame 10:2:2 Frame 9:3:2

Frame 9:3:2

PEAK SINGLE USER DOWNLOAD (Mb/s) 20MHz

PEAK SINGLE USER UPLOAD (Mb/s) 20MHz Frame 10:2:2 Frame 9:3:2

Frame 10:2:2 Frame 9:3:2

Vendor A Vendor BPEAK SINGLE USER DOWNLOAD (Mb/s) 20MHz

Frame 10:2:2 Frame 9:3:2

203.4

9.8 10.18

PEAK MULTI USER DOWNLOAD (Mb/s) 2x20MHz

Frame 10:2:2 Frame 9:3:272** 57**

PEAK SINGLE USER UPLOAD (Mb/s) 20MHz Frame 10:2:2 Frame 9:3:2

PEAK MULTI USER DOWNLOAD (Mb/s) 20MHz

PEAK MULTI USER UPLOAD (Mb/s) 20MHz Frame 10:2:2 Frame 9:3:2

9


Physical Isolation

ScenarioScenarioScenarioScenarioSensitivity Sensitivity Sensitivity Sensitivity

worse than 1dBworse than 1dBworse than 1dBworse than 1dB

Sensitivity Sensitivity Sensitivity Sensitivity

worse than 3dBworse than 3dBworse than 3dBworse than 3dB

Isolation for co-site 76.87dB 71.02dB

Isolation for different

site85.27dB 79.42dB

Assumption

1. Capacity/Coverage loss <5%，which equals to sensitivity worse than 1dB

2. Capacity loss <7%，coverage loss <17.7% ，which equals to sensitivity worse than 3dB

3. Consider the worst situation for different scenario

• Two antenna radiate each other

• Antenna down tilt is 6 deg

• Antenna height is same


Space Distance Analysis

Different-site：

Co-site：

IsolationHorizontal

distance

1dB 85.27dB 176m

3dB 79.42dB 90m

IsolationHorizontal

distance only

Vertical

distance only

Simultaneous

Horizontal Vertical

1dB 76.87dB 37m 6.2m27m 1m

0.7m 2m

3dB 71.02dB 18.9m 3.2m

0.2m 1m

0m 2m

27m 1m

! Required isolation using combination of vertical and horizontal separation feasible on most sites

! In other cases isolation can be achieved by careful selection of antenna location


Reducing customer churn whilst migrating

Technology Solutions

! Single RAN solutions:- Base station supports WiMAX and LTE Simultaneously

Source: WiMAX Forum/Heavy Reading “WiMAX Advanced to Harmonize with TD-LTE in the 2.3, 2.5 & 3.5GHz Bands: Opportunities & Challenges for WiMAX 2”

! Introduce LTE Carriers in

parallel with WiMAX

! Deploy dual mode CPE

during migration phase

! May impact coverage from

some sites requiring infill

! When customers migrated

change WiMAX carriers to

LTE


Dual Mode WiMAX – TD LTE CPE

! 3.5GHz TD-LTE Indoor & Outdoor Units

! WiMAX Capability can be incorporated for relatively small cost



Technology Solutions

! Potential Drawbacks of Single RAN solution

! Capacity of WiMAX & LTE not optimised during migration

! Possible coverage gaps

! Dependant on Core network ability to support new base stations

! Works well if existing WiMAX base stations can be upgraded but…

! E.g. Current Imagine WiMAX base stations not able to support upgrade

! Case for new “LTE Ready” WiMAX deployment not as good as deploying LTE in

new areas

! If existing WiMAX base stations require swap out then why not migrate directly to

LTE



Managing Technology/Base Station swap

! Used successfully to migrate pre-WiMAX technologies to WiMAX

! Hard Cut-over on Network from non WiMAX to WiMAX:

! Customers informed and signed up well in advance

! CPE shipped to customer in advance

! LTE has option for dual mode device to be installed in advance of

cutover

! Significantly Improved service offering to customers – minimises churn

! New Base Stations built, commissioned and integrated quickly 24-48Hrs

maximum


! The existing WiMAX Network has been deployed with the following capabilities:

� High Capacity Base Stations

� Beamforming and MIMO technology to give superior coverage and capacity

� 10MHz Channel bandwidth to give over 15Mbps throughput per sector

� Architecture designed to facilitate simple upgrades to increase capacity via additional

cards/ports

� High Capacity all IP Backhaul via microwave and managed bandwidth

� Minimum bandwidth 100Mbps from High Sites

� High sites designed and built with capability to readily upgrade to LTE

Exploiting existing WiMAX infrastructure to migrate to LTE


! The existing WiMAX Network has been deployed with the following capabilities:

� High Capacity WiMAX Base Stations

� Beamforming and MIMO technology to give superior coverage and capacity

� 10MHz Channel bandwidth to give over 15Mbps throughput per sector

� Architecture designed to facilitate simple upgrades to increase capacity via additional

cards/ports

� High Capacity all IP Backhaul via microwave and managed bandwidth � capacity

expansion required

� Minimum bandwidth 100Mbps from High Sites � Requires upgrade to 300-400Mbps

per site

� High sites designed and built with capability to readily upgrade to LTE � basic site

infrastructure re-used

Exploiting existing WiMAX infrastructure to migrate to LTE


Exploiting existing WiMAX infrastructure to migrate to LTE: Core Network

! WiMAX

� Proprietary platforms

� WiMAX Specific elements:

• ASN G/W

• NMS, EMS

! LTE

� Generic Computing Platforms with LTE

specific S/W e.g:

• MME, HSS, PCRF etc.

With the exception of some generic elements e.g AAA, and Switch/Router elements majority of WiMAX core cannot be reused, however

More recent LTE solutions are capable of supporting WiMAX with additional cards/software


Conclusions

! In the short term migration may not be best business case

� Greater revenue opportunity from deploying LTE in non WiMAX areas

� in the short term avoids migration issues

! Solutions do however exist to support migration

� Single RAN, Core, CPE support for dual LTE/WiMAX in later generations of equipment

� Interference can be mitigated with synchronisation and physical isolation

! Churn can be minimised by timely and clear communication with customers and attraction of

greatly improved service

! Some elements of the WiMAX network can be re-used – mostly more generic elements, re-use

better on later generations of WiMAX equipment

! Biggest challenge in migration is getting LTE industry into a fixed broadband mindset when

planning the LTE network