FCC Adaptive Antenna Tutorial

Project MESA Meeting

30 October – 2 November 2006

Joanne Wilson VP, Standards

ArrayComm, LLC.

Adaptive Antenna Tutorial: Spectral Efficiency and

Spatial Processing

ArrayComm: Industry Leadership

• ArrayComm background

World leader in adaptive antenna technology (also referred to as “Adaptive –Multi-Antenna Signal processing” (A-MAS) or “smart antenna” technology)

Founded 1992

Over 300,000 base stations deployed

Extensive patent portfolio in A-MAS Technology

$250M invested in technology development & commercialization

• Technology and end-to-end systems

IntelliCell A-MAS technology for PHS, GSM, W-CDMA, 802.16

End-to-end wireless systems including HC-SDMA, WLL

Consistently reducing costs of coverage and capacity

• Business model

Software products, services

Technology development, transfer

Chipsets

The spectral efficiency bottleneck

• Today’s principal spectral inefficiency

omnidirectional radiation and reception

• Why?

tiny fraction of power used for communication

the rest: interference for co-channel users

• So:

Exploit spatial properties of RF signals

Provide gain and interference mitigation

Improve capacity/quality tradeoff

And…

New air interfaces should be built from the ground up to be optimized for spatial processing

What is spectral efficiency?

bits/seconds/Hz/cell

Measures how well a wireless network utilizes radio spectrum

Determines the total throughput each base station (cell) can support in a network in a given amount of spectrum

The Capacity/Coverage Tradeoff

Technical Interpretation

• Gain vs. noise, fading, ... expands envelope to right

• Interference mitigation (+ gain) expands it upwards

Economic Interpretation

• Coverage improvements reduce CapEx, OpEx (esp. backhaul, sites)

• Capacity improvements reduce delivery cost, spectrum requirements

range (km)

Throughput/cell

(Mbps)

2/2.5/3G

802.11b

Noise Limited

Interference Limited

A-MASBenefit

Motivation

• Wireless system design is a trade-off of competing requirements

service definition

service quality

capacity

capital and operating costs

resource requirements including spectrum

end-user pricing/affordability

coexistence with other radio technologies

• A-MAS technology fundamentally changes the nature of this trade-off and achievable system performance

LTECL/OL Diversity, MIMO

Adaptive Antennas in All New Broadband Systems

Fixed Local Area Wide Area

Use

r D

ata

Rat

e

Mobility

Dialup

Satellite

MMDS/FWA

Cable/DSL

802.16 W-LANWiFi

802.11

3G3G3GPP, 3GPP2

802.16d

802.16e

802.11n

ITU Recommendation M.1678 (2004):

“This Recommendation considers the ability of adaptive antenna systems to improve the spectral efficiency of land mobile networks and recommends their use in the deployment of new and the further enhancement of existing mobile networks. It also recommends the integration of this new technology into the development of new radio interfaces.”

MBWA

802.20ANSI/ATIS HC-SDMA (iBurst)

Outline

• Spectral Efficiency and System Economics

• Adaptive Antenna Basics

• Adaptive Antenna Technologies

• Adaptive Antenna Performance Determinants

• Summary

• Backup Slides

Spectral Efficiency Defined

• A measure of the amount of information – billable services – that carried by a wireless system 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

fundamental spectral efficiency limitation in most systems is self-generated interference

results for isolated base stations are not representative of real-world performance

Why Is Spectral Efficiency Important?

• Spectral efficiency directly affects an operator’s cost structure

• For a given service and grade of service, it 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

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

Increased Spectral Efficiency

• Increased spectral efficiency leads to

improved operator costs

• reduced equipment CapEx/OpEx per subscriber

• reduced numbers of sites in capacity limited areas

reduced barriers to new operators

better use of available spectrum

• especially important for limited mobility spectrum

improved end-user affordability, especially for broadband services

• Spectral efficiency will become even more important

as subscriber penetration increases

as per-user data rates increase

as quality of service (esp. data) requirements increase

Spectral Efficiency Design Elements

• Spectral/Temporal elements

multiple access method: TDMA, FDMA, OFDMA…

• optimize efficiency based on traffic types

modulation, channel coding, equalization: QPSK, QAM, OFDM, …

• optimize efficiency based on link quality

• Spatial elements (all to minimize interference)

cellularization

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

sectorization

• mitigate co-channel interference by more selective downlink patterns and increased uplink sensitivity

power control

• use minimum power necessary for successful communications

Increasing Spectral Efficiency

• Temporal/Spectral issues are mature, well understood, well exploited

no significant future improvements in spectral efficiency here

proper application is important

• Least spectrally efficient aspect of most systems

omnidirectional/sectorized distribution and collection of radio energy

Why?

• Most of the energy is wasted.

• Worse, it creates interference in the system and limits reuse.

Sectorized Transmission/Reception

cells

sectorsserving sector

user

interference Sectorized, spatially non-

selective, transmission causes interference in adjacent cells

Similarly, increases sensitivity to interference from adjacent cells

Cellular “reuse” mitigates this effect by separating co-channel users

Cost: decreased resources per sector and reduced spectral efficiency

How Do Adaptive Antennas Help?

• Adaptive antennas are spatial processing systems

• Combination of

antenna arrays

sophisticated signal processing

• Adapt the effective pattern to the radio environment

users

interferers

scattering/multipath

• Provide spatially selective transmit and receive patterns

Adaptive Transmission/Reception

cells

sectorsserving sector

user

interference

Spatially selective transmission reduces required power for communication

Decreases sensitivity to interference from adjacent cells

Allows reuse distances to be decreased

possible to reuse resources within a cell in some cases

Benefits: increased resources per sector, increased spectral efficiency

Outline





• Summary

• Backup Slides

Adaptive Antennas Defined

• Systems comprising

multiple antenna elements (antenna arrays)

coherent processing

signal processing strategies (algorithms) that vary the way in which those elements are used as a function of operational scenario

• Providing

gain and interference mitigation

leading to improved signal quality and spectral efficiency

Adaptive Antenna Fundamentals

• Solution elements

multiple antenna elements and transceiver chains

scenario-dependent signal processing

air interface support for highest performance, e.g., training

• Link-level performance benefits

diversity

gain

interference mitigation

SISO, MISO, SIMO, MIMO, …

SISO

Single Input, Single Output

MISO

Multiple Input, Single Output

SIMO

Single Input, Multiple Output

MIMO

Multiple Input, Multiple Output

SDMA

Adaptive Antenna Gains (transmit or receive)

Diversity• differently fading paths• fading margin reduction• no gain when noise-limited

Coherent Gain• energy focusing• improved link budget• reduced radiation

Interference Mitigation• energy reduction• enhanced capacity• improved link budget

Enhanced Rate/Throughput• co-channel streams• increased capacity• increased data rate

Diversity

• Slope of error curve proportional to diversity order (# antennas)

• Transmit/receive channel knowledge not required

• Reduces required fading margin

1 antenna

8 antennas

2x: 7 dB reduction

8x: 12 dB reduction

•Selection diversity

•Single Tx antenna

•Independent fading

Going Further: Gain, Capacity, QoS, Data Rate

• (Multi)Channel state information (CSI) required to go further

coherent gain, interference mitigation, capacity/rate increases

• Theoretical SNR gain with M antennas: M or 10log10M dB

achievable in practice with good design, esp. for receive processing

Rx and Tx

• Theoretical interference rejection is infinite

limited in practice by scenario, protocol, equipment.

20 dB for significant interferers readily achievable

• New protocols include training/feedback for spatial processing

analogous to training for equalizers

Adaptive Antenna Concept

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

+1

+1 +1-1

User 1,s1(t)ejt

2as1(t) 2bs2(t)

User 2,s2(t)ejt

• Users’ signals arrive with different relative phases and amplitudes at array

• Processing provides gain and interference mitigation

Protocol Independence

• Fundamental concepts applicable to all access methods and modulation methods

Transceiver

Channelizer

(TDMA, FDMA, CDMA)

Transceiver

Channelizer

(TDMA, FDMA, CDMA)…

…

…

Spatial and Temporal Processing

baseband signals/user data

antenna antenna

Interference Mitigation

• Gain and interference mitigation performance are actually statistical quantities

• Theoretical gain performance closely approached (within 1 dB) in practice

• Theoretical interference mitigation, , harder to achieve

limited by calibration, environment, number of interferers

• Practically, active mitigation in excess of 20 dB can be achieved for significant interferers

• Active interference mitigation independent of and in addition to gain

• Directive gain term generally results in some passive interference mitigation

Comments

• Fundamental concept is coherent processing

• Generally applicable to all air interfaces

• Processing is done in parallel on all traffic resources

• Line-of-sight is not required

• Many important issues that can’t be addressed here

estimation of radio environment (algorithms)

processing requirements (easily > 1Gbps of data from the array)

performance validation

equipment calibration

effects of air interface specifics (will comment on this later)

reliability benefits of redundant radio chains

intrinsic diversity of an array

Antenna Arrays

• Wide variety of geometries and element types possible

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

• Array of eight 10 dBi elements at 2 GHz is about 0.5 x 0.75 m

small!

conformal arrays for aesthetics

Processing At The User Terminal

• This presentation focuses on adaptive antennas at the base station

• Adaptive antennas can also be incorporated at the user terminal

base station and user terminal can perform independent adaptive antenna processing

base station and user terminal can perform joint adaptive antenna processing, so called “MIMO” systems, with additional benefits

• Fundamental issue is an economic one

incremental costs at base station are amortized over many subscribers

incremental costs at user terminal are amortized over one user, solutions must be inexpensive for consumer electronics applications

Outline





• Summary

• Backup Slides

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

Adaptive Antenna Potential

Adaptive Antenna Technologies (1)

• Actual level of benefits depends on details of the implementation, little variation in general hardware architecture across implementations

• Basis for comparison

predictability and consistency of performance

balance of uplink and downlink performance (key for capacity improvements)

• downlink is generally most challenging aspect of adaptive antennas

• base station directly samples environment on uplink; must infer the environment on the downlink

robustness of performance across variations in propagation and interference scenarios


• Switched Beam

selects from one of several patterns based on power

can be thought of as micro-sectorization

predictable gain and scenario-dependent interference mitigation in positive C/I environments

peak gain typically traded off for in-sector gain uniformity

variant: cell sculpting, select from several patterns for load balancing

• Adaptive Energy Extraction

attempts to extract maximum energy from radio channel

maximal ratio and combined diversity are examples

scenario-dependent gain and interference mitigation in positive C/I environments

gain near theoretical maximum in high SINR environments


• Model-Based or fully adaptive

continuous adaptation based on model including users and interferers

simultaneous gain and active interference rejection possible, even at low SINR’s

manageable increase in computation as compared to other methods

availability of channel assignments and other high-level protocol information improve performance

Outline





• Summary

• Backup Slides

Adaptive Antenna Performance

• Primary determinants

environmental complexity

degree of mobility

duplexing: frequency-division or time-division (FDD vs. TDD)

• issue is correlation of uplink and downlink propagation environments

• Capacity increases in operational systems

Application Capacity Increase

Deployments

FWA, TDD 20x 1996-present

Low Mobility PHS, TDD 5x 1996-present

High Mobility AMPS & GSM (900, 1800, 1900), FDD

>2x 1993-present

Comparing TDD and FDD

• Advantages and disadvantages to both

Advantages Disadvantages

FDD No need for synchronized network Suited to extended range, 10’s of km Good adaptive antenna performance

Requires paired allocations Relatively hard to support asymmetry Expensive for small duplex distances

TDD Operates in unpaired allocations Best adaptive antenna performance Cost-reduced user terminals Simple to support asymmetry

Requires synchronized network 50% duty cycle for radio electronics

Outline





• Summary

• Backup Slides

Summary

• Increased spectral efficiency leads to

better spectrum conservation

diversity of services

affordability of services

• A-MAS is the single best technology for increasing spectral efficiency

• Wide range of A-MAS technologies

same basic principles

wide variations in goals and performances

intracell reuse (reuse < 1) possible for certain applications

• Proven technology

more than 300,000 deployments worldwide

Outline





• Summary

• Backup Slides

End-User Affordability

• Example

A wireless operator charges $60/mo. for 450 minutes of 10 kbps speech over system A, about $0.22/Mbit

Another wireless operator charges about $500/mo. for 1 Gbyte/yr over system B, about $0.75/Mbit

similar spectral efficiency for systems A and B, similar operating costs, similar price/bit

advanced, high-speed, services are not affordable for most end-users at this spectral efficiency

• Important point, although oversimplified example

data and voice network and service costs differ

new equipment cost must be recaptured

1 Gbyte/yr is casual primary internet access, operators may be trying to discourage this use of their network

Basic Uplink Gain Calculation

• Signal s, M antennas, M receivers with i.i.d. noise ni

• Adaptive antennas provide uplink gain of M or 10log10M dB

• 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

Basic Downlink Gain Calculation

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

• With same total radiated power P in both cases

• Again, factor of M or 10log10M dB

• M=10, 10 dB gain examples

10 element array with 1 W PA’s, has same EIRP as single element with 100 W PA

For given EIRP can reduce total radiated power by 10 dB, 90% interference reduction

Received Power (AA) Received Power (SA)

=(P/M s + … + P/M s)2

( Ps)2 = M

Spatial processing creates unique advantage

Mobile Wireless System Capacity in Mature Networks,Mbps aggregate BTS capacity per MHz available

Sources: Vendor claims for maximum BTS throughput, ArrayComm field experience in Korea and Australia, various analysts.

System Capacity

*Standard protocol with base station enhanced by A-MAS technology

System Range

With A-MAS (i.e smart antennas)

Without

4.0HC-SDMA

1.7802.16+A-MAS*

0.4EV-DO or HSDPA

0.3802.16

0.2TD-CDMA

0.2WCDMA

1.2MC-SCDMA(proprietary variant)

0.4WCDMA+A-MAS*

0.4Flash-OFDM

0.6GSM+A-MAS*

0.7PHS+A-MAS*

0.1GSM

0.04PHS

System Spectral Efficiency

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

IS-9

5 A

IS-9

5B

IS-9

5C

Cdm

a200

0

IS-9

5 H

DR

GS

M

GS

MH

SC

SD

PH

S

Inte

lliC

ell®

WLL

HC

-SD

MA

Sp

ectr

al E

ffic

ien

cy in

bit

s/se

c/H

z/ce

llSome Comparisons

250

19 18 12 1

GPRS CDMA2000WCDMA 1xEV-DO HC-SDMA

Network CapacityNumber of cells to deliver the

same information density, Mbps per KM2

0.16 2.1 2.2 3.4

40

GPRS CDMA2000 WCDMA 1xEV-DO HC-SDMA

Cell CapacityThroughput in 10 MHz (Mbps)

Adaptive Antenna Performance

Performance Determinant

Import GSM/

GPRS

CDMA2000/

WCDMA

WLAN HC-SDMA

DuplexingMethod

Downlink environment generally estimated from uplink

Up/down highly correlated with TDD

Up/down less correlated with FDD

FDD FDD TDD TDD

Protocol Choices affect AA performance

Spatial broadcast channels limit reuse

Downlink performance highest with recent uplink training data

•Broadcast

•Limited training

•Broadcast

•Limited training

•Broadcast (all channels)

•Limited training

AA optimized protocol

Service Definition

Degree of mobility limits capacity

Nulling performance degrades with high mobility

High mobilitylower capacity

High mobility High mobility Portable Mobile

Adaptive antennas benefit all systems, but

HC-SDMA extracts maximum benefits by design

Co-Channel Regulatory Issues

• Recall adaptive antennas’ high ratio of EIRP to total radiated power (TRP)

factor of M higher than comparable conventional system

result of directivity of adaptive antennas

• Average power radiated in any direction is then TRP plus gain of individual array elements (worst case directive power remains EIRP)

• Relevant in setting EIRP limits for coordination of co-channel systems in different markets

• Very relevant in RF exposure considerations

Adjacent Channel/Out-Of-Band Regulatory Issues

• Recall that adaptive antenna gains result from coherent processing

• Out-of-band radiation due to intermodulation, phase noise, spurs

nonlinear processes

reduce/eliminate coherency of signals among PAs’ out-of-bands

• Result

ratio of in-band EIRP to out-of-band radiated power is up to a factor of M less than for comparable conventional system

• Rules may want to anticipate adaptive antennas

A per-PA “43+10logP-10logM rule” would result in comparable operational out-of-bands as single antenna 43+10logP rule

significant positive effect on adaptive antenna power amplifier economics

may help to foster adoption

iBurst (HC-SDMA) Highlights

• Time division duplex (TDD)

• Packet switched TDMA/SDMA multiple access scheme

• Adaptive modulation & coding

• Fast ARQ for reliability, low latency

• Peak per-user rate 16 Mbps (initial products support 1 Mbps peak)

• 40 Mbps throughput in 10 MHz (DSLAM equivalent)

• Centralized resource allocation for efficiency, QoS

• Inter-cell and inter-system (e.g., 802.11) handover

• Standardized by American National Standards Institute (ANSI)

ANSI ATIS 0700004-2005, High Capacity-Spatial Division Multiple Access (HC-SDMA)

• Soon to be officially recommended by the ITU-R

Included in Draft New Recommendation ITU-R M.[8A-BWA]

iBurst Frame and Traffic Bursts

• iBurst uplink/downlink traffic slots paired

• spatial+temporal training

Cross Layer Design: Spatial Processing MAC

Multiple logical channels per physical resource

paging and/or traffic and/or access

• Spatial collision resolution

enables low latency/low jitter designs

BS BS

Traffic

Traffic

Page

Access

TrafficUT

UT

UT

UT

UT

• Major city trial to assess reuse < 1 performance

• Most challenging case: colocated terminals, LOS

• Reuse of ½ at peak data rate

Spectral Efficiency Evaluation

600

700

800

900

1000

1100

0 10 20 30 40 50 60

Elasped Time [sec]

Th

rou

gh

pu

t [k

bp

s]

Downlink

Uplink

220

240

260

280

300

320

340

0 10 20 30 40 50 60Elasped Time [sec]

Thr

ough

put

[kbp

s]

2,629 7,966 Total

3281,025 UT#6

3281,027 UT#8

328982 UT#7

3321,026 UT#5

331892 UT#4

3251,027 UT#3

329964 UT#2

3281,023 UT#1

UplinkDownlink　

Average Data Rate [kbps]

Base Case: 8 Terminals, 8 Carriers

600

700

800

900

1000

1100

0 10 20 30 40 50 60

Elasped Time [sec]

Thr

ough

put

[kbp

s]

220

240

260

280

300

320

340

0 10 20 30 40 50 60

Elasped Time [sec]

Th

rou

gh

pu

t [k

bp

s]

2,649 7,909 Total

329 981 UT#8

332 1,025 UT#7

331 1,017 UT#6

333 979 UT#5

332 936 UT#4

332 1,020 UT#3

329 976 UT#2

331 975 UT#1

UplinkDownlink　

Average Data Rate [kbps]Downlink

Uplink

Reuse 1/2: 8 Terminals, 4 CarriersReuse 1/2: 8 Terminals, 4 Carriers

10,558 kbps/2.5 MHz

or 4.2 b/s/Hz/sector

• Data rates unchanged

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