Spectrum Management 2002

Marc GoldburgCTO, Internet Products Group

ArrayComm, Inc.marcg@arraycomm.com

Adaptive Antennas

(or “doing more with less”)

2

Cellular Technology

Coverage area divided into cells

Each with infrastructure and users

Typical of two-way wireless

“cellular” (1G, 2G, 3G, …)

MMDS

Wireless LANs

LMDS

Switching/Routing

cell

sector

Switching/Routing

Data Networks

Telephony Networks

Backhaul Network

base station

3

Spectrum Management Challenges

Inter-System management co-channel at service boundaries adjacent channel within coverage area

Intra-system management balancing service quality and capacity self-interference reduces capacity

Preview of adaptive antennas reduce adjacent band emissions reduce sensitivity to in-band emissions mitigate in-band interference, increasing capacity provide gain, increasing range and quality

4

Outline

Spectral efficiency

Adaptive antenna fundamentals

Coexistence

5

Spectral Efficiency Defined

Information delivered per unit of spectrum

Measured in bits/second/Hertz/cell, includes effects of multiple access method modulation methods channel organization resource reuse (code, timeslot, carrier, …)

“Per-Cell” is critical primary spectral efficiency limitation generally self-interference isolated base station results not representative of real-world

Spectral Efficiency Interference Management

6

Why Is Spectral Efficiency Important?

For given service and grade of service, determines required amount of spectrum (CapEx) required number of base stations (CapEx, OpEx) required number of sites and associated site maintenance (OpEx) and, ultimately, consumer pricing and affordability

Quick calculation (capacity limited system)

Affects radiated power per km2, too

number of cells/km2 = offered load (bits/s/km2)available spectrum (Hz) x spectral efficiency (bits/s/Hz/cell)

7

Designing For Spectral Efficiency

Spectral/Temporal tools multiple access method and data compression

• optimize efficiency based on traffic characteristics modulation, channel coding, equalization

• optimize efficiency based on link quality

Spatial tools, interference management cellularization

• mitigate co-channel interference by separating co-channel users sectorization

• mitigate co-channel interference through static directivity power control

• use minimum power necessary for successful communications

8

Self-Interference and Capacity

cells

sectorsserving sector

user

interference

sectorized

cells

sectorsserving sector

user

interference

adaptive antennas

9

Outline

Spectral efficiency

Adaptive antenna fundamentals

Coexistence issues

10

Adaptive Antennas Defined

Systems comprising multiple antenna elements (antenna arrays) coherent processing processing strategies that adapt to environment

Providing gain and interference mitigation improved signal quality and spectral efficiency improved coexistence behavior

11

Adaptive Antenna Concept

+1-1

2bs2(t)

+1

+1

2as1(t)

as1(t)+bs2(t) as1(t)-bs2(t)

User 2,s2(t)ejt

Users’ signals arrive with different relative phases and amplitudes

Processing provides gain and interference mitigation

User 1,s1(t)ejt

as1(t) as1(t)

12

In-Band Uplink Gain

Signal s, M antennas, M receivers with i.i.d. noises ni

Adaptive antennas improve uplink SNR by factor of M

M=10, 10x SNR improvement, examples double data rate if single antenna SNR is 10 dB reduce required subscriber transmit power by 10 dB increase range by 93% with R3.5 loss

s + ... + sreceived signalnoise n1 + … + nM

=

therefore, Uplink SNR (Ms)2

M2

s2

2M= =

= M x single antenna SNR

13

Similar to uplink calculation, except dominant noise is due to (single) receiver at user terminal

With same total radiated power P in both cases

Adaptive antennas improve downlink EIRP by factor of M

M=10, 10 dB gain examples 10 elements with 1 W PA’s, same EIRP as single element with 100 W PA 90% reduction in total radiated power for same EIRP

In-Band Downlink Gain

EIRP (Adaptive Antenna) EIRP (Single Antenna)

=(P/M s + … + P/M s)2

( Ps)2 = M

14

Out-of-band gain different from in-band gain non-linearities that create out-of-bands destroy coherency

With same total in-band radiated power P in both cases

Ratio of in-band:out-of-band gains approximately M very different from conventional systems

M=10, 10 dB gain examples out-of-band gain up to 90% less than in-band gain

Out-of-Band Downlink Gain

In-band gain (Adaptive Antenna) Out-of-band gain (Adaptive Antenna)

M(P/M s)2

= M(MP/M s)2

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In-Band Interference Mitigation

Directive gain results in passive interference mitigation

Active interference mitigation additive (in dB) to gain

Gain and interference mitigation statistical quantities Theoretical gain closely approached (within 1 dB) in practice Theoretical interference mitigation, , harder to achieve

• limited by calibration, environment, scenario

• active mitigation in excess of 20 dB can be reliably achieved

16

Processing Gain Operational SignificanceSelective Uplink Gain Increased Range & Coverage

Increased Data RatesReduced System – Wide Uplink NoiseImproved Uplink Multipath Immunity

Improved Signal QualityMaintained Quality with Tightened Reuse

Increased Range & CoverageIncreased Data RatesReduced System–Wide Downlink InterferenceImproved Co–existence BehaviorReduced Downlink Multipath

Maintained Quality with Tightened Reuse

Uplink Interference Mitigation

Selective Downlink Gain

Downlink Interference Mitigation

In-Band Benefits

Actual level of benefits depends on implementation details

18

Outline

Spectral efficiency

Adaptive antenna fundamentals

Coexistence issues

19

Co-Channel Coexistence

Adaptive antennas (AA’s) reduce in-band emissions factor of M less total radiated power for same EIRP peak interference remains the same average interference significantly improved RF safety/exposure benefits

AA’s less sensitive to in-band interference active interference mitigation can “null” interferers reduced planning (frequency, separation) requirements

20

Adjacent Channel Coexistence

AA out-of-bands have reduced directionality generating non-linearities destroy element-to-element coherence lack of coherence reduces directionality out-of-band gain roughly a factor of M less than in-band gain peak out-of-band gain closer to average out-of-band gain

AA’s less sensitive to out-of-band interference active interference mitigation can “null” interferers reduced planning (frequency, separation) requirements

21

Summary

Adaptive antennas lead to increased spectral efficiency, better use of spectrum affordable, diverse services improved coexistence behavior

Adaptive antennas are becoming pervasive more than 100,000 deployments worldwide as a backwards compatible upgrade to existing networks as a fundamental element of new broadband networks