Spectrum Management 2002

1
Adaptive Antennas(or doing more with less)

• Spectrum Management 2002
• Marc Goldburg
• CTO, Internet Products Group
• ArrayComm, Inc.
• marcg_at_arraycomm.com

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

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

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
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

• Users signals arrive with different relative
  phases and amplitudes
• Processing provides gain and interference
  mitigation

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
• M10, 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 ... s
received signal

noise
n1 nM
(Ms)2
s2
therefore, Uplink SNR
M


Ms2
s2
M x single antenna SNR
13
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
• M10, 10 dB gain examples
• 10 elements with 1 W PAs, 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)
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-bandout-of-band gains approximately
  M
• very different from conventional systems
• M10, 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
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

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 SystemWide Downlink
Interference Improved Coexistence
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

17
Antenna Arrays

• Wide variety of geometries and element types
• arrangements of off-the-shelf single elements
• custom arrays
• Array size
• vertical extent determined by element
  gain/pattern as usual
• horizontal extent, typically 3-5 lambda
• 2 GHz, eight 10 dBi element array is 0.5 x 0.75 m
• small!
• conformal arrays for aesthetics

18
Outline

• Spectral efficiency
• Adaptive antenna fundamentals
• Coexistence issues

19
Co-Channel Coexistence

• Adaptive antennas (AAs) 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
• AAs 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
• AAs 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