comparing wimax 802.16d and 802.16e v1.0

Comparing WiMAX™ 802.16d with WiMAX™ 802.16e

Prepared by Doug Gray

August 2009

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About the Author

Doug Gray is a Telecommunications Consultant and is currently under contract to the WiMAX Forum®. Gray has had extensive experience in broadband wireless access systems in engineering and management positions at Hewlett-Packard, Lucent Technologies and Ensemble Communications.

Acknowledgements

The author would like to acknowledge the contributions of the many WiMAX Forum®

members who have taken the time to review and provide comments and insights regarding the contents of this paper and the conclusions drawn.



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Table of Contents

1.0 Introduction..............................................................................................................6

2.0 Technical Requirements for Broadband Mobile Services.......................................7

3.0 802.16d and 802.16e Technical Differences...........................................................7

4.0 Business Case Considerations...............................................................................10

5.0 Conclusion..............................................................................................................10

Acronyms...........................................................................................................................11

Tables

Table 1: 802.16d – 802.16e Summary.................................................................................8

Table 2: Symbol Duration with S-OFDMA......................................................................10



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Comparing WiMAX™ 802.16d with WiMAX™ 802.16e

1.0 Introduction

With a focus on frequencies below 11 GHz in licensed and license-exempt bands, the 802.16d-2004 amendment to the IEEE 802.16 Air Interface Standard introduced OFDM for improved performance in non-line-of-sight, high multipath environments. Commercial WiMAX™ systems based on the 802.16d-2004 amendment were first deployed in 2006. Networks based on this technology have been deployed worldwide in licensed bands in the 2 and 3.5 GHz range and unlicensed bands in the 5.8 GHz range. These systems quickly established themselves as an alternative to fixed access technologies in competition with DSL and cable.

Soon after completion of the 802.16d-2004 amendment, the IEEE launched an effort to address the requirements for mobility. This project, done in conjunction with ETSI, resulted in the 802.16e amendment which was ratified in December 2005. The 802.16e-2005 amendment not only provided the features and attributes necessary to support mobile services but also added other performance-enhancing features to the 802.16 Air Interface Standard. Termed as Mobile WiMAX Release-1, the first commercially available WiMAX-compliant systems based on this amendment occurred in 2008. The rapid market acceptance of Mobile WiMAX Release-1 has prompted chip and equipment vendors to focus development efforts on 802.16e-based technology while de-emphasizing further work on 802.16d-based chips and products. Taking note of these trends the WiMAX Forum has dissolved the working group that was responsible for the development of 802.16d-based profiles.

Although it was not feasible to support a backwards compatible migration path from WiMAX 802.16d systems to 802.16e systems without compromising the technical requirements for the support of mobile applications, backwards compatibility is assured going forward from Mobile WiMAX Release-1 based on 802.16e to Mobile WiMAX Release-2 based on 802.16m.

Since 2006, 114 products1 have received WiMAX Forum® certification. Over 75% of these are certified for Mobile WiMAX Release-1.

This paper will provide a brief a comparison of WiMAX systems based on 802.16d-2004 with WiMAX systems based on 802.16e-2005.

1 Data as of the end of June 2009. This data is updated regularly by the WiMAX Forum and is available on the WiMAX Forum website “Research-Dashboard”.



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2.0 Technical Requirements for Broadband Mobile Services

Whereas fixed and nomadic networks experience propagation channels that are relatively stable over time, mobile networks experience channel conditions that can change very rapidly. Mobile systems must be able to deal with rapid changes in RF signal level and Doppler shifts and must be able to support seamless handoffs from one base station to another as actively-connected subscribers move throughout the network coverage area. Fast scheduling is required to efficiently allocate resources and maintain QoS (Quality of Service) under these conditions.

The demand for mobile hand-held subscriber devices to be small and lightweight to facilitate portability creates other challenges unique to mobile networks. These requirements dictate the following:

Antennas must be omni-directional for ease of use: This results in very low antenna gain and increases the potential for interference

Limited space for multiple antennas: Limits the use of higher order MIMO techniques in the subscriber station

Battery must be small and light weight: This limits the available transmit power

Long battery life: Must support sleep and idle modes

Indoor and outdoor performance: Can add 10-20 dB of path loss for indoor locations

As a result of the above, the uplink system gain generally determines the potential range and coverage for mobile base station.

Global roaming must also be supported since mobile subscribers have the expectation for access; anytime, anywhere.

3.0 802.16d and 802.16e Technical Differences

A comparison of key attributes and features for WiMAX systems based IEEE 802.16d and WiMAX systems based on IEEE 802.16e is summarized in Table 1.

Table 1: 802.16d – 802.16e Summary. Copyright 2009 WiMAX Forum


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Attribute or Feature WiMAX Based on 802.16d-2004

WiMAX Based on 802.16e-2005

802.16e Benefit

Spectrum Licensed: 3.5 GHz & License-Exempt:

5.8 GHz

Licensed Bands:2.3, 2.5, 3.5, 3.8

GHz, (700 MHz)*

Profiles for WW spectrum allocations

Duplex TDD/FDD/HD-FDD

TDD, (FDD/HD-FDD)*

Access OFDM S-OFDMA Scalable channel BW, immunity to interference and

fading

Channel BW 3.5, 7, 10 MHz 5, 7, 8.75, 10, 20* MHz

FFT Size 256 512, 1024, 2048* Longer symbol time tolerates larger delay spread

Advanced Antenna Technology

STC STC, SM, Adaptive MIMO switching, UL Collaborative

SM, & Beamforming

Improved peak and average channel

throughput in both DL and UL

Fast CQI No Yes Mobility support up to 120 km/hrH-ARQ No Yes

Hand-off Support No Yes

Sleep and Idle Mode No Yes

Multi-Cast/Broadcast Support

No Yes

Fractional Frequency Reuse

No Yes More aggressive frequency reuse

improves spectral efficiency



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Attribute or Feature WiMAX Based on 802.16d-2004

WiMAX Based on 802.16e-2005

802.16e Benefit

Extended Real Time Polling Service

No Yes Latency and Jitter control for VoIP

IMT-2000 Technology

No Yes UMTS spectrum availability

Backwards Compatible Migration Path

No Yes Path to meet or exceed IMT-

Advanced requirements

* Denotes features or attributes not currently available but approved for certification by the WiMAX Forum

A very important benefit of 802.16e-2005 based WiMAX systems over 802.16d is the forward looking migration path for operators. Work on the 802.16m amendment to the IEEE standard is scheduled to be completed by the end of this year. This amendment, which is backwards compatible with 802.16e, is designed to meet or exceed the performance requirements established by IMT-Advanced. In close cooperation with the IEEE, the WiMAX Forum is well on its way to defining Mobile WiMAX Release-2 profiles based on the IEEE 802.16m-2009 amendment. There is no migration path for WiMAX based on 802.16d.

Table 2 provides a summary of the symbol duration for Scalable-OFDMA as a function of the channel BW with 802.16e. The longer symbol duration with 802.16e provides an increased tolerance to delay spread resulting in better multipath immunity. With Scalable-OFDMA operators gain greater flexibility in establishing a channel BW to best fit deployment requirements which, in many cases, may vary over time. 802.16d with a fixed FFT size of 256 has a symbol duration which is shorter and therefore less tolerant to delay spread and multipath.

Table 2: Symbol Duration with S-OFDMA

Mobile WiMAX Release-1 based on 802.16e-2005

Channel BW 5 MHz 10 MHz 20 MHz 7 MHz 8.75 MHz



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FFT Size 512 1024 2048 1024

Sub-Carrier Spacing

10.94 kHz 7.81 kHz 9.77 kHz

Symbol Duration

102.9 microsec 144.0 microsec

115.2 microsec

4.0 Business Case Considerations

The performance features and attributes available with Mobile WiMAX Release-1 based on the 802.16e-2005 amendment leads to a more cost-effective deployment with fewer base stations to meet desired capacity and coverage requirements. This will assure rapid growth in production volumes and continued cost reductions.

The WiMAX Forum has no plans to develop any new profiles for 802.16d nor is there a migration path for performance enhancements for existing profiles. Efforts throughout the WiMAX Forum ecosystem are now focused on profiles based on 802.16e and 802.16m. Mobile WiMAX Release-1 provides operators an access solution with the best performance with a clear backwards compatible migration path for future performance enhancements. With the ability to address varied usage models, Mobile WiMAX Release-1 gives operators multiple business plan options.

5.0 Conclusion

Fixed WiMAX deployments based on 802.16d-2004, with performance comparable to DSL and broadband cable services, quickly established WiMAX as a viable technology for broadband wireless access. The 802.16e-2005 amendment, with the adoption of Scalable-OFDMA, added mobility and other major performance enhancements to the standard. Adopting these and other features supported by the IEEE 802.16 air interface standard enabled the WiMAX Forum to develop Mobile WiMAX Release-1. With improved throughput, multipath tolerance, and lower costs, even operators only intending to offer fixed services will experience a stronger business case by adopting Mobile WiMAX Release-1 based on the 802.16e amendment.



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Acronyms

BW Bandwidth

CQI Channel Quality Indicator

FDD Frequency Division Duplex

FFT Fast Fourier Transform

H-ARQ Hybrid Automatic Repeat Request

HD-FDD Half Duplex Frequency Division Duplex

SM Spatial Multiplexing

S-OFDMA Scalable Orthogonal Frequency Division Multiple Access

STC Space Time Coding

TDD Time Division Duplex

WiMAX Worldwide Interoperability for Microwave Access



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comparing wimax 802.16d and 802.16e v1.0

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