Adaptive Antennas or doing more with less Spectrum

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

Cellular Technology base station cell sector n Coverage area divided into cells n Each with infrastructure and users n Typical of two-way wireless n “cellular” (1 G, 2 G, 3 G, …) n MMDS n Wireless LANs n LMDS Telephony Networks Backhaul Network Switching/ Routing 2 Data Networks

Spectrum Management Challenges n Inter-System management u u n Intra-system management u u n co-channel at service boundaries adjacent channel within coverage area balancing service quality and capacity self-interference reduces capacity Preview of adaptive antennas u u reduce adjacent band emissions reduce sensitivity to in-band emissions mitigate in-band interference, increasing capacity provide gain, increasing range and quality 3

Outline n Spectral efficiency n Adaptive antenna fundamentals n Coexistence 4

Spectral Efficiency Defined n Information delivered per unit of spectrum n Measured in bits/second/Hertz/cell, includes effects of u u n “Per-Cell” is critical u u n multiple access method modulation methods channel organization resource reuse (code, timeslot, carrier, …) primary spectral efficiency limitation generally self-interference isolated base station results not representative of real-world Spectral Efficiency Interference Management 5

Why Is Spectral Efficiency Important? n For given service and grade of service, determines u u n required amount of spectrum (Cap. Ex) required number of base stations (Cap. Ex, Op. Ex) required number of sites and associated site maintenance (Op. Ex) and, ultimately, consumer pricing and affordability Quick calculation (capacity limited system) number of n cells/km 2 = offered load (bits/s/km 2) available spectrum (Hz) x spectral efficiency (bits/s/Hz/cell) Affects radiated power per km 2, too 6

Designing For Spectral Efficiency n Spectral/Temporal tools u multiple access method and data compression • optimize efficiency based on traffic characteristics u modulation, channel coding, equalization • optimize efficiency based on link quality n Spatial tools, interference management u cellularization • mitigate co-channel interference by separating co-channel users u sectorization • mitigate co-channel interference through static directivity u power control • use minimum power necessary for successful communications 7

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

Outline n Spectral efficiency n Adaptive antenna fundamentals n Coexistence issues 9

Adaptive Antennas Defined n Systems comprising u u u n multiple antenna elements (antenna arrays) coherent processing strategies that adapt to environment Providing u u u gain and interference mitigation improved signal quality and spectral efficiency improved coexistence behavior 10

Adaptive Antenna Concept User 2, s 2(t)ej t User 1, s 1(t)ej t (t)+bs 2(t) as 1(t) (t)-bs 2(t) +1 -1 +1 +1 2 as 1(t) 2 bs 2(t) n Users’ signals arrive with different relative phases and amplitudes n Processing provides gain and interference mitigation 11

In-Band Uplink Gain n Signal s, M antennas, M receivers with i. i. d. noises n i received signal noise = therefore, Uplink SNR = = s +. . . + s n 1 + … + n M (Ms)2 Ms 2 = M s 2 M x single antenna SNR n Adaptive antennas improve uplink SNR by factor of M n M=10, 10 x SNR improvement, examples u u u double data rate if single antenna SNR is 10 d. B reduce required subscriber transmit power by 10 d. B increase range by 93% with R 3. 5 loss 12

In-Band Downlink Gain n Similar to uplink calculation, u n except dominant noise is due to (single) receiver at user terminal With same total radiated power P in both cases EIRP (Adaptive Antenna) EIRP (Single Antenna) = ( P/M s + … + P/M s)2 ( Ps)2 =M n Adaptive antennas improve downlink EIRP by factor of M n M=10, 10 d. B gain examples u u 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 13

Out-of-Band Downlink Gain n Out-of-band gain different from in-band gain u n non-linearities that create out-of-bands destroy coherency With same total in-band radiated power P in both cases In-band gain (Adaptive Antenna) Out-of-band gain (Adaptive Antenna) n M( P/M s)2 =M Ratio of in-band: out-of-band gains approximately M u n (M P/M s)2 very different from conventional systems M=10, 10 d. B gain examples u out-of-band gain up to 90% less than in-band gain 14

In-Band Interference Mitigation n Directive gain results in passive interference mitigation n Active interference mitigation additive (in d. B) to gain n Gain and interference mitigation statistical quantities u u Theoretical gain closely approached (within 1 d. B) in practice Theoretical interference mitigation, , harder to achieve • limited by calibration, environment, scenario • active mitigation in excess of 20 d. B can be reliably achieved 15

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 Uplink Interference Mitigation Improved Signal Quality Maintained Quality with Tightened Reuse Selective Downlink Gain Downlink Interference Mitigation n Increased Range & Coverage Increased Data Rates Reduced System–Wide Downlink Interference Improved Co–existence Behavior Reduced Downlink Multipath Maintained Quality with Tightened Reuse Actual level of benefits depends on implementation details 16

Outline n Spectral efficiency n Adaptive antenna fundamentals n Coexistence issues 18

Co-Channel Coexistence n Adaptive antennas (AA’s) reduce in-band emissions u u n 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 u u active interference mitigation can “null” interferers reduced planning (frequency, separation) requirements 19

Adjacent Channel Coexistence n AA out-of-bands have reduced directionality u u n 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 u u active interference mitigation can “null” interferers reduced planning (frequency, separation) requirements 20

Summary n Adaptive antennas lead to u u u n increased spectral efficiency, better use of spectrum affordable, diverse services improved coexistence behavior Adaptive antennas are becoming pervasive u u u more than 100, 000 deployments worldwide as a backwards compatible upgrade to existing networks as a fundamental element of new broadband networks 21