A Study into the Application of Interference Cancellation ... Study into the Application of Interference Cancellation Techniques – Presentation to Industry © Roke Manor Research

A Study into the Application of Interference Cancellation Techniques – Presentation to Industry

© Roke Manor Research Ltd a Siemens Company

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Presentation Order

Introduction● Ken Richardson (Roke)

Fixed Links Case Study● Bachir Belloul (Red-M)

BFWA Case Study● Chris Williams (University of Bristol)

Conclusions● Steve Wales (Roke)

Question & Answer Session


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Introduction

Ken Richardson (Roke)


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Introduction

Purpose of Study

● To investigate the Application of Interference Cancellation Techniques to wireless systems as a means of improving Spectrum Efficiency

Approach

● Literature Review● Techniques● Applications

● Case Studies● BFWA● Fixed Links

● Each Case Study Examined:● Link Level Performance● System Level Performance● Cost Analysis● Regulatory Aspects

● General Conclusions


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IC Techniques

All IC Techniques exploit some difference between the wanted andinterfering signals: for example,● Bandwidth● Angle of Arrival● Spreading Code● Channel Impulse Response● Modulation Type

Some Specific Techniques Examined:● Transform Space Techniques with Excision● Frequency Shift Filtering● Joint Detection/Multi-User Detection● Diversity and Beamforming● Higher order Statistics


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IC Applications

The following Key Applications were considered:

3G overlay on GSM● Ease transition from GSM to 3G. Cancellation of GSM signals in 3G receiver.

GSM to GSM● Ease transition from GSM to 3G. IC option in GSM.

BFWA● IC thought to be required by operators.

Fixed Link to Fixed Link● Potential to reduce large wanted to unwanted ratios.

Radar● Potential for facilitating band sharing.

WLAN● Limited to overcoming ‘hidden terminal problem’.

Broadcast● Improve co-channel re-use in DVB-T/DVB-H.


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Fixed Links Case Study

Bachir Belloul (Red-M)


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Introduction

Considered Dual and Single Antenna IC

64-QAM Modulation

Receiver is extension of Decision Feedback Equaliser that:● Handles multiple signals (Joint Detection)● Handles multiple antennas

System Level evaluation based on● Assignment database for 7.5GHz band● Link Level results used to develop simple IC Receiver Model


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DFE Block Diagram

2-Antenna, 2-Signal DFE

+

+

-

-

2x2 Matrix Forward Filter 2x2 Matrix Feedback Filter

Decision Devices

Rx 1

Rx 2


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Link Level Simulation Example

● Two Receive Antennas

● Dominant Interferer plus another Interferer

● Vary Signal to Dominant Interferer Ratio (S/I) and Dominant to Remainder (D/R)

0.00001

0.0001

0.001

0.01

0.1

1

0 5 10 15 20 25 30 35 40

SIR (dB)

BER

No IC

IC 2 D/R=20dB

IC D/R=10dB

IC D/R=5dB

64-QAMRRC 0.3

DFE (16,11,15)30dB Fade Depth

0.25xfsymb Notch Freq-10dB Cross-Coupling 1,2-20dB Cross-Coupling 1,3

Es/No=25dB


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Link Level Summary

Insufficient Performance Benefit from Single Receive Antenna● ~1-2dB reduction in W/U, High baseband complexity

Good Performance Improvements obtained with Dual Receive Antennas allowing for presence of more than one interferer

● 12dB reduction in W/U for D/R>20dB

Performance Improvements Obtained Despite Interferer on boresight● Joint detection rather than reliance on antenna discrimination

Some manufacturer’s existing Cross-Polar Interference Cancellation (XPIC) Equipment could be used for more general Co-Channel interference cancellation


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System Level Simulation

Actual positions of TX & RX from database

Define two regions:

● 200km radius from Charing Cross – links re-assigned

● 400km radius from Charing Cross –interference buffer

Consider only STM-1 (155 Mbps) links within regions, 8 x 2 channels

Use ‘Lowest Channel First’assignment algorithm


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System Level Simulation Results

● Results show ratio of channel re-use with and without IC

● Reassignment of Existing Links

● Slope is a characteristic of assignment algorithm


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● Results show ratio of channel re-use with and without IC

● Created additional links between existing sites

● Band is fully allocated both with and without IC

● With IC can make 50% more assignments


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Cost Analysis

Additional equipment cost for IC

● ~£2000 per link (excluding antennas)

Cost Elements:● Equipment Cost● Deployment Cost● Installation Cost● Development Cost● Running Cost

Cost Models developed● Three Cost Scenarios (Low, Typical, High)● Three Deployment Scenarios (Conservative, Moderate, Aggressive)

Deployment/Cost Matrix

Fixed-links Conservative Moderate Aggressive

Low cost 40% 20% 10%

Typical 60% 70% 50%

High cost 0% 10% 40%


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Cost Analysis

• Additional cost of IC

Deployment Scenario

100% of Links in Network

Single Link

Conservative 30% 11%

Moderate 37% 40%

Aggressive 45% 48%


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Regulatory Issues

Market Led

● Congested band or operator preferred sub-band

Interventionist

● Relaxation of Link Length Policy

● Technology Factor in Pricing Formula

● Congestion charging

● Reducing W/U Ratios

TX FH RX FL

TX FH RX FL

TX FL RX FH

TX FL RX FH


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BFWA Case Study

Chris Williams (University of Bristol)


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Introduction

IEEE 802.16 OFDM Variant for frequencies <11GHz● 256 Carrier OFDM, 5MHz bandwidth, 3.5 GHz Band● BPSK, QPSK, 16-QAM, 64 QAM modulations● Concatenated Reed-Solomon & Convolutional Code● Throughputs 1.73-15.57Mb/s

Single User (SU) and Multi-User (MU) IC Algorithms Studied● Reference Based MMSE Algorithm

Results obtained for 1, 2 & 4 antennas● Omni and Directional Elements


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Link Level Simulation Results

● Stanford University (SUI) Channel Models

-5 0 5 10 15 20 25 30 35 400

2

4

6

8

10

12

14

16

C/I (dB)

Thro

ughp

ut (M

bps)

SUI4 channel, om nidirectional e lements

m ode 1, no ICMU, 2 Rx antennasMU, 4 Rx antennasm ode 6, no ICMU, 2 Rx antennasMU, 4 Rx antennas

-5 0 5 10 15 20 25 30 35 400

2

4

6

8

10

12

14

16

C/I (dB)

Thro

ughp

ut (M

bps)

SUI4 channel, directional elements

m ode 1, no ICMU, 2 Rx antennasMU, 4 Rx antennasm ode 6, no ICMU, 2 Rx antennasMU, 4 Rx antennas


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Link Level Simulation Results Summary

● Multi-User Algorithm superior to Single User Algorithm

● Performance benefits greater with Omnidirectional Antennas

● IC performs better in NLOS channels (both wanted and interferer)


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System Level Simulations

Area in central Bristol used

● FDD/TDMA, 3 sectors

● Ray tracing model generates channel impulse responses

● Link level simulation ran for each CPE position using channel impulse responses

● Computationally intensive – but avoids difficulties of abstracting link level results in system level simulation


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● Throughput-Coverage Maps ● 0 Mbps (dark)● 16Mbps (light)

● Downlink● Directional

0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.20

0.3

0.6

0.9

1.2

1.5

1.8

0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.20

0.3

0.6

0.9

1.2

1.5

1.8

No IC MU 1x2


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System Level Simulations Summary

● Directional elements alone will not give full coverage of higherthroughputs

● IC provides greater coverage to higher throughputs

● MU algorithm better than SU algorithm

● Transmit diversity more effective on uplink than downlink

● Uplink/downlink asymmetry can be equalised with MU algorithm

Summary of relative throughput gains:

Downlink Uplink

Omni 2.5-8.6 1.7-11.1

Directional 1.3-1.9 1.3-3.5


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Cost Analysis

Methodology as for Fixed Links Case

Cost Elements● Equipment Cost● Deployment Cost● Installation Cost● Development Cost● Running Cost

Three Cost Scenarios

Three Deployment Scenarios

Deployment/Cost Matrix

BFWA Conservative Moderate Aggressive

Low cost 80% 40% 10%

Typical 20% 50% 50%

High cost 0% 10% 40%


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Cost Analysis

Higher capacity with fewer base stations

Cost of IC in CPE offset through reduced number of Base Stations

Scenario assumes BFWA with IC doubles capacity● IC: 1 BS and 50 CPE’s● No IC: 2 BS and 50 CPE’s

Scenario Saving

Conservative 40%

Moderate 33%

Aggressive 27%


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Regulatory Issues

Market Led

● Reduced roll-out cost and higher capacity would encourage use of IC

Interventionist

● Little scope given current licensing regime for BFWA systems

● Only adopting a lighter licensing approach than current practice● Registering only Base Stations● Review co-ordination mechanisms

● In auctions less spectrum is released forcing operators to adoptIC in their business plan


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Conclusions

Steve Wales (Roke)


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Fixed Links Conclusions

● Single Antenna IC gives insufficient performance gain

● Dual Antenna IC gives significant performance gain using techniques similar to XPIC in receiver

● XPIC baseband devices handling asynchronous horizontal and vertical transmissions could be used for IC

● Presence of other interferers limits the performance gain of dual antenna IC

● Majority of interference close to link axis

● Achieve factor of 1.7 improvement in spectral efficiency (based on Ofcom7.5GHz assignment database)

● Increased cost of adding IC is between 30-45% if all links equipped

● IC permits assignments to be made in congested band, or in an operator preferred sub-band


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BFWA Conclusions

● Use of directional elements alone cannot provide full sector coverage at high throughput in urban areas

● Largest relative throughput gain found was with the multi-user algorithm and omni-directional antennas

● Throughput gains with IC are reduced with directional antennas● Combination of IC and directional antennas gives best coverage of high

throughputs

● Transmit diversity offers little benefit on downlink, greater benefit on uplink

● For a given installed capacity IC can reduce infrastructure costs by between 27-40%.


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System Specific Conclusions

Cellular

● Already demonstrated in GSM● Would be most effective in new bands

BFWA

● Cost savings to be had in early roll-out of BFWA in urban areas

Fixed Links

● Allows new assignments to continue in congested bands. Legacy issues will prevent full benefit of IC being realised

Radar

● Potential for IC to improve band sharing. Legacy issues will hinder short-term spectral efficiency gains

Broadcast

● Potential to improve co-channel re-use in DVB-T, DVB-H. Retro-fitting necessary for existing DVB-T systems, but likely to be confined to fringes of coverage.

WLAN

● Protocols used in WLAN applications limit benefits. In WLAN systems with cellular-like infrastructure IC helps to overcome hidden terminal problem


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General Conclusions

Spectral Efficiency benefits of IC:● Proportional to number of receivers equipped

Maximum benefit from IC:● By applying an existing technology in a new band and mandating IC

New technologies should consider IC to be introduced at some stage in the system lifetime● Ideally defined from the beginning

Market forces could lead to IC adoption in new deployments● Regulatory involvement necessary for existing deployments.


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Questions and Answers

Contact: Ken RichardsonTel: 01794 833491E-mail: [email protected]


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Documents

A Study into the Application of Interference Cancellation ... Study into the Application of Interference Cancellation Techniques – Presentation to Industry © Roke Manor Research