beyond ofdm a systems approach to non-line-of-sight fixed wireless rajeev krishnamoorthy broadband...

BEYOND OFDMA Systems Approach to

Non-Line-of-Sight Fixed Wireless

Rajeev Krishnamoorthy

Broadband World Wireless Forum, San Francisco, CAFebruary 19, 2001

BEYOND OFDM - A Systems Approach to NLOS Fixed WirelessRajeev Krishnamoorthy, Senior Engineering Director, Iospan Wireless / Slide 2 Broadband World Wireless Forum - San Francisco, CA - February 19, 2001

Broadband Market RequirementsBroadband Market Requirements

A Mass-Deployable system with a price point that will compete favorably to DSL and Cable: Low Capital Costs for Installed CPE & Infrastructure DSL/Cable-like QoS/Availability Easy Management/Provisioning

These features require:

True Non-Line-of-Sight Coverage Multi-cell with largest possible radius (6-miles or greater)

and superior frequency reuse (scalable) Consumer installable CPE Can re-use existing cellular sites Minimum of 90% service coverage (homes passed)


FadingFrequency Selective -- OFDM

Space Selective -- MIMO + MAC

Time Selective -- Link Adaptation + RLP

Channel Impairments in Multi-CellChannel Impairments in Multi-Cell

Co-channel Interference

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Physical Layer CharacteristicsPhysical Layer Characteristics

Multicarrier (OFDM) Modulation Important Foundation, but OFDM ALONE IS NOT ENOUGH TO ACHIEVE NLOS!

MIMO (Multiple Input, Multiple Output) – Dynamic Per-user Spatial Processing Techniques

Antenna Diversity Techniques to Increase Cell Size and Provide Complete Service Coverage

Spatial Multiplexing: Increased Bit Rate to Users Aggressive Spectrum Reuse due to Interference Cancellation

Dynamic Per-user Adaptive Modulation and Coding (Link Adaptation)

Delivers Optimal System Capacity by: Exploiting good conditions to increase user data rates Accommodating poor air-link conditions

Done in conjunction with QoS Requirement & MAC Scheduling


MAC CharacteristicsMAC Characteristics

Differentiated Grades of Service & Quality of Service Reservation Schemes for Low Delay Jitter Services Dynamic Bandwidth Allocation & Scheduling for Bursty Data

Fragmentation & Reassembly and Link-Layer Retransmission Increases Link Integrity and Improves TCP Performance Better Frequency Reuse

Support for Unique PHY Modes of Operation Spatial Multiplexing and Transmit Diversity Adaptive Modulation and Coding Power Control

Uplink & Downlink Transmission Scheduling Support for multiple Service Flows (distinct QoS) on each link Service Flow Attributes - Class of Service, Bandwidth, Loss, Latency

Other Important Functions Admission Control, Link Initialization & Maintenance, Authentication & Security, etc.


Fundamental System Design RequirementsFundamental System Design Requirements

Low-cost RF enabled by digital pre-distortion, increased phase noise tolerance, carrier tracking loops, dynamic link adaptation, etc.

Low-cost mechanical design of CPE by monitoring heat dissipation, antenna design, etc.

QoS jointly guaranteed by the MAC and dynamic link adaptation High throughput by adaptive techniques, and by ensuring TCP behavior is

matched to MAC and Radio Link Protocol Link optimization by matching QoS (error rate and latency) with the

scheduling, ARQ, adaptive modulation, coding, and diversity Low required SINR (modem set-point) results in greater coverage,

higher capacity, lower PA cost, and aggressive frequency reuse

A high-performance and low-cost system requires an integrated design encompassing Antennas, RF, PHY,

MAC, mechanicals, the network layer, and applications

Supporting Slides


Diversity using antennas

Demonstrating PerformanceDemonstrating Performance

SISO 11 SIMO 12 MIMO 23

Tx Rx Tx RxTx Rx

Trials EarlyDeployment

MassDeployment


Features & Benefits of Iospan ApproachFeatures & Benefits of Iospan Approach

FEATURES Attribute BENEFITS

Modulation OFDMMore robust solution (vs. single carrier) for overcomingfrequency-selective fading / intersymbol interference (ISI)

Spatial Multiplexing 2 TxUnique patented solution - enabled by two Tx antennas -doubles throughput achievable over an air interface link

DynamicLink Adaptation

YesMaximizes spectral efficiency by ensuring each subscribersees the highest possible data rate possible for the givenchannel conditions

CPE Beamwidth 90 Simplifies CPE installation and minimizes repointing

Antenna Diversity 23(6th order)

Radio Link Protocol(RLP)

Yes

InterferenceCancellation

Yes

Hyper-Diversity, RLP and Interference cancellationmaximize

Coverage

Reliability, and

Capacity (tighter cellular frequency reuse)


The Iospan AdvantageThe Iospan Advantage

CellRadius

Coverage Capacity

Iospan Advantage Over Trial Systemwith… NO Antenna Diversity NO Spatial Multiplexing DOCSIS-Based MAC

NO Adaptive Modulation & Coding NO Fragmentation & Retransmission

5xIncreasewith IWISolution



Iospan Advantage Over EarlyDeployment System with… Limited Antenna Diversity (1x2) NO Spatial Multiplexing DOCSIS-Based MAC

NO Adaptive Modulation & Coding NO Fragmentation & Retransmission

2.5xIncreasewith IWISolution

6.25xIncreasewith IWISolution


beyond ofdm a systems approach to non-line-of-sight fixed wireless rajeev krishnamoorthy broadband...

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