Adaptive Antennas (or “doing more with less”)

1. Adaptive Antennas(or “doing more with less”) Spectrum Management 2002 Marc Goldburg CTO, Internet Products Group ArrayComm, Inc. marcg@arraycomm.com

2. base station cell sector Telephony Networks Backhaul Network Switching/Routing Switching/Routing Data Networks 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 2

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 3

4. Outline • Spectral efficiency • Adaptive antenna fundamentals • Coexistence 4

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 5

6. offered load (bits/s/km2) number of cells/km2 = available spectrum (Hz) x spectral efficiency (bits/s/Hz/cell) 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 6

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 7

8. interference cells cells serving sector sectors sectors serving sector interference user user sectorized adaptive antennas Self-Interference and Capacity 8

9. Outline • Spectral efficiency • Adaptive antenna fundamentals • Coexistence issues 9

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 10

11. User 2, s2(t)ejt User 1, s1(t)ejt as1(t)+bs2(t) as1(t) as1(t)-bs2(t) as1(t) +1 -1 +1 +1 2as1(t) 2bs2(t) Adaptive Antenna Concept • Users’ signals arrive with different relative phases and amplitudes • Processing provides gain and interference mitigation 11

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 received signal s + ... + s = noise n1 + … + nM (Ms)2 s2 therefore, Uplink SNR = = M Ms2 s2 = M x single antenna SNR 12

13. (P/M s + … + P/M s)2 ( Ps)2 In-Band Downlink Gain • 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 EIRP (Adaptive Antenna) = = M EIRP (Single Antenna) 13

14. Out-of-Band Downlink Gain • 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 (MP/M s)2 In-band gain (Adaptive Antenna)  = M Out-of-band gain (Adaptive Antenna) M(P/M s)2 14

15. 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 15

16. In-Band Benefits Processing Gain Operational Significance Selective Uplink Gain Increased Range & Coverage Increased Data Rates Reduced System – Wide Uplink Noise Improved Uplink Multipath Immunity Improved Signal Quality Maintained Quality with Tightened Reuse Increased Range & Coverage Increased Data Rates Reduced System–Wide Downlink Interference Improved Co–existence Behavior Reduced Downlink Multipath Maintained Quality with Tightened Reuse Uplink Interference Mitigation Selective Downlink Gain Downlink Interference Mitigation • Actual level of benefits depends on implementation details 16

17. Outline • Spectral efficiency • Adaptive antenna fundamentals • Coexistence issues 18

18. 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 19

19. 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 20

20. 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 21