# Presentation: 102929

## FCC Office of Engineering and Technology
7 September 2001

Marc Goldburg
CTO, Internet Products Group
ArrayComm, Inc.
http://www.arraycomm.com
marcg@arraycomm.com

- 7 September 2001
- Marc Goldburg
- CTO, Internet Products Group
- ArrayComm, Inc.
- http://www.arraycomm.com
- marcg@arraycomm.com

**Adaptive Antenna Tutorial:*****Spectral Efficiency and ******Spatial Processing*****	**

## Cellular Technology

**Cellular Technology**

- cell

- sector

**Cellular networks divide a coverage area into multiple “cells” **
**each has its own radio infrastructure and users**
**Basis for most two-way wireless services **
**cellular phones (1G, 2G, 3G, ...)**
**MMDS broadband data (Sprint, Worldcom)**
**Wireless LANs**
**LMDS broadband data (Teligent, Winstar, ...)**

- Switching/Routing

- Data Networks

- Telephony Networks

- base station

## Motivation For This Talk

**Cellular system design trades off competing requirements**
- service definition
- service quality
- capacity
- capital and operating costs
- resource requirements including spectrum
- end-user pricing/affordability
- coexistence with other radio technologies
**Adaptive antenna technology fundamentally changes the nature of this trade-off**

## Outline

**Spectral Efficiency and System Economics**
**Adaptive Antenna Fundamentals**
**Adaptive Antenna Technologies**
**Adaptive Antenna Performance Determinants**
**Adaptive Antenna Regulatory Issues**
**Summary**

## 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

**Improves operator economics**
- reduced equipment CapEx/OpEx per subscriber
- reduced numbers of sites in capacity limited areas
- reduced spectrum requirements
**Reduces barriers to new operators and new services**
**Makes better use of available spectrum **
- especially important for limited spectrum suitable for mobile applications
**Improves end-user affordability, especially for broadband services**
- cost of service delivery directly reflected in service pricing
- cost of delivering broadband services higher than cost to deliver voice
- voice is only 10 kbps of data
- data quality requirements higher for broadband than voice

## Designing For Spectral Efficiency

**Spectral/Temporal tools**
- multiple access method and data compression (source coding): TDMA, FDMA, CSMA, CDMA, Vocoding (e.g., CELP), MPEG
- both optimize efficiency based on traffic characteristics
- compression/source coding can change service definition
- modulation, channel coding, equalization: QPSK, OFDM, Trellis Coding...
- optimize efficiency based on link quality
**Spatial tools (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

## Avenues For Further Improvement

**Temporal/Spectral aspects 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

- sectors

- serving sector

- user

- interference

**Spatially uniform transmission and reception throughout sector**
**Causes interference in nearby cells**
**Increases sensitivity to interference from nearby cells**
**Cellular “reuse” mitigates this effect by separating co-channel users**
**Cost: decreased resources per sector and reduced spectral efficiency**
**Tradeoff of quality and capacity**

## 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

- sectors

- serving sector

- user

- interference

**Spatially selective transmission reduces required power for communication**
**Reduces interference to nearby cells**
**Decreases sensitivity to interference from nearby cells**
**Allows reuse distances to be decreased **
**Benefits: increased resources per sector, increased spectral efficiency**
**Improved tradeoff of capacity and quality**

## Comparative Spectral Efficiencies

**Air Interface****	****Carrier BW ****	****Peak User Data  ****	****Average Carrier****	****Efficiency ****	****Comments **
**	****	****Rate (kbps)****	****	****Throughput (kbps)****	****b/s/Hz/cell**
_**Without Adaptive Antennas**_
**IS95A****	****1.25 MHz****	****14.4****	****	****100****	****	****0.08****	****Source: Viterbi**
**IS95C****	****1.25 MHz****	****144****	****	****200****	****	****0.16****	****Source: Viterbi**
**cdma2000     ****	****5      MHz****	****384****	****	****800-1000****	****	****0.16-0.20****	****Source: Viterbi**
**GSM****	**** 200 kHz****	****13.3****	****	****15.2 (13.3*8/7)****	****	****0.08****	****effective reuse = 7**
**PHS****	**** 300 kHz****	****32****	****	****12.8 (32*8/20)****	****	****0.04****	****effective reuse = 20**
_**With Adaptive Antennas**_
**PHS****	****300 kHz****	****32****	****	****64   (32*8/4)****	****	****0.21****	****effective reuse = 4, DDI Pocket**
**GSM****	****200 kHz****	****13.3****	****	****53.2 (13.3*8/2)****	****	****0.27****	****effective reuse = 2, AC/OEM ****	****	****	****	****	****	****	****	****Trials**
**IntelliWave FWA  300 kHz****	****128****	****	****640  (128*2*2.5)****	****2.1****	****effective reuse = 1/2.5, Various ****	****	****	****	****	****	****	****	****Operators**
** **

**Adaptive antenna gains are significant**
**Adaptive antenna benefits vary with air interface and adaptive antenna type (more on this later)**

## A Word About Reuse

**When talking about spectral efficiency, “reuse” means feasible reuse of traffic resources**
**Traffic resource examples**
- AMPS (FDMA): 30 kHz carrier
- DAMPS/IS-136 (TDMA/FDMA): 30 kHz carrier + time slot
- GSM (TDMA/FDMA): 200 kHz carrier + time slot
- IS-95 (CDMA): 1.25 MHz carrier + code
**From previous slide, spectral efficiency of GSM and IS-95 comparable even though IS-95 might use the same carrier in each sector**

## Outline

**Spectral Efficiency and System Economics**
**Adaptive Antenna Fundamentals**
**Adaptive Antenna Technologies**
**Adaptive Antenna Performance Determinants**
**Adaptive Antenna Regulatory Issues**
**Summary**

## 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 Concept

- as1(t)+bs2(t)

- as1(t)-bs2(t)

- +1

- +1

- +1

- -1

- User 1,
- s1(t)ejt

- 2as1(t)

- 2bs2(t)

- User 2,
- s2(t)ejt

**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 and modulation methods**

- Transceiver

- Channelizer
- (TDMA, FDMA, CDMA)

- Transceiver

- Channelizer
- (TDMA, FDMA, CDMA)

- ...

- ...

- ...

- Spatial and Temporal Processing

- baseband signals/user data

- antenna

- antenna

## Basic Uplink Gain Calculation

**Signal s, M antennas, M receivers with i.i.d. noises n****i**
**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 + ... + s

- received signal

- noise

- n1 + ... + nM

- =

- therefore, Uplink SNR

- (Ms)2

- M2

- s2

- 2

- M

- =

- =

- =     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 10log****10****M 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 (Adaptive Antenna)

-  Received Power (Single Antenna)

- =

- = M

## Interference Mitigation

**Directive gain term generally results in some passive interference mitigation **
**Active interference mitigation independent of and in addition (dB) to gain**
**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
- active mitigation in excess of 20 dB can be reliably achieved for significant interferers

## Base Station Architecture

## 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

## Comments

**Fundamental concept is coherent processing**
**Generally applicable to all air interfaces**
**Parallel, independent processing on all traffic resources**
**Many important issues that are not addressed here**
- estimation/prediction of radio environment (will comment later)
- processing requirements & architectures (easily > 1Gbps array data rate)
- performance validation
- equipment calibration
- effects of air interface specifics (will comment later)
- broadcast channel support
- reliability benefits of redundant radio chains
- intrinsic diversity of an array (fading immunity)
- multipath processing

## 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

**Spectral Efficiency and System Economics**
**Adaptive Antenna Fundamentals**
**Adaptive Antenna Technologies**
**Adaptive Antenna Performance Determinants**
**Adaptive Antenna Regulatory Issues**
**Summary**

## Adaptive Antenna Potential

**Adaptive Antenna Potential**

** ****Actual level of benefits depends on implementation details **

## Comparing Adaptive Antennas

**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; generally must infer the environment on the downlink
**Robustness of performance across propagation and interference scenarios **
**Performance in non line-of-sight environments**
- “beams” useful for visualization, but not what happen in practice

## Cell Sculpting and Switched Beam 

**Cell Sculpting and Switched Beam **

**Cell Sculpting**
- load balancing technique
- sector sizes slowly (e.g., monthly) updated to match offered traffic
- different from other adaptive antenna techniques mentioned here, doesn’t affect reuse

**Switched Beam**
- selects from one of several fixed patterns to maximize received power
- selection problems for low SINR
- moderate gain uniformity/predictability
- less predictable active interference mitigation

- high traffic sector

- medium traffic sector

- low traffic sector

## Energy Extraction and Fully Adaptive 

**Energy Extraction**
- extracts maximum energy from environment (“greedy”)
- infinite variety of patterns
- good performance/predictability in high SINR scenarios, poor in low SINR
- no clear downlink strategy
- Examples: maximal ratio, combined diversity

**Fully Adaptive**
- incorporates full model including propagation, users, interferers, air interface
- infinite variety of patterns
- consistent gain/interference performance in wide range of SINR scenarios
- benefits at cost of manageable increase in processing

- interferer

- user

- interferer

## Outline

**Spectral Efficiency and System Economics**
**Adaptive Antenna Fundamentals**
**Adaptive Antenna Technologies**
**Adaptive Antenna Performance Determinants**
**Adaptive Antenna Regulatory Issues**
**Summary**

## Adaptive Antenna Performance

**Primary determinants **
- environmental complexity, including mobility
- air interface support for adaptive antennas (“hooks”)
- duplexing: frequency-division or time-division (FDD vs. TDD)
- issue is correlation of uplink and downlink propagation environments
**Capacity increases in operational systems**

## Comparing TDD and FDD

**Two-way communications schemes need separate channels for each direction of communication**
- Frequency Division Duplex (FDD): directions separated in frequency
- Time Division Duplex (TDD): directions separated in time
**TDD**
- requires single block of spectrum
- especially efficient where communications may be asymmetric (e.g., data)
- leverages maximum benefits from adaptive antennas
**FDD**
- requires paired spectrum
- less efficient with unknown or varying data asymmetry
- benefits for extreme long-range operation (10’s of km)
- adaptive antennas provide significant benefits

## Outline

**Spectral Efficiency and System Economics**
**Adaptive Antenna Fundamentals**
**Adaptive Antenna Technologies**
**Adaptive Antenna Performance Determinants**
**Adaptive Antenna Regulatory Issues**
**Summary**

## Co-Channel 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 TRP plus gain of individual array elements **
- EIRP is still worst case directive power
**Regulatory relevance **
- safety/RF exposure considerations
- coordination of co-channel systems in different markets

## Adjacent Channel/Out-Of-Band 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
**Regulatory relevance**
- A per-PA “43+10logP-10logM rule” would result in comparable operational out-of-bands to single antenna 43+10logP rule
- significant positive effect on adaptive antenna power amplifier economics
- may help to foster adoption

## Outline

**Spectral Efficiency and System Economics**
**Adaptive Antenna Fundamentals**
**Adaptive Antenna Technologies**
**Adaptive Antenna Performance Determinants**
**Adaptive Antenna Regulatory Issues**
**Summary**

## Summary

**Increased spectral efficiency leads to**
- better spectrum conservation
- diversity of services
- affordability of services
**Adaptive antennas is the single best technology for increasing spectral efficiency**
**Wide range of adaptive antenna technologies**
- same basic principles
- wide variations in goals and performances
- intracell reuse (reuse < 1) possible for certain applications
**Proven technology**
- more than 80,000 deployments worldwide