A 2-Day Short Course
The primary standard for commercial wireless local area networking is IEEE 802.11. The IEEE 802.11a/g amendments added OFDM transmission with data rates up to 54 Mbps, while 802.11e improved MAC efficiency, among other things, through data bursting and the addition of the block acknowledgement protocol. IEEE 802.11n builds upon these prior amendments and enhances the physical layer through MIMO, spatial division multiplexing, and 40 MHz channels that, together with a few other minor changes, enable data rates of up to 600 Mbps. It also enhances the MAC layer, primarily through the addition of aggregation techniques and enhancements to the block acknowledgement protocol. The throughput enhancements delivered by 802.11n will support more effective home and enterprise networking (increased throughput and range) and enable new classes of applications, such as the near real-time streaming of high-definition video in the home. Due to the large installed base of legacy IEEE 802.11 devices, the coexistence interoperability mechanisms provided by the standard are critical to its success.
The 802.11n standard provides enormous scope for product innovation. The first generation of 802.11n products based on Draft 2.0 have appeared well before the release of the standard (expected in December 2009) and achieve raw data rates of 300Mbps using core features of the standard. Later generations of products will add advanced features, such as fast link adaptation, transmit beamforming, higher-order spatial multiplexing, and improved MAC efficiency and range over which the high data rates can be achieved.
This course is intended for communications system designers of wireless systems. Due to the increased interest in dual mode Wi-fi/cellular handsets, designers of cellular systems should gain valuable insight into the features of 802.11n. It also is intended for design and test engineers of IEEE 802.11a/g systems transitioning to 802.11n products, as well as network managers of WLAN systems wishing to understand how 802.11n techniques will affect network performance.
The course provides background, design trade-offs, and explanations for the new features of 802.11n that offer a much deeper understanding of the technology than can be gained from reading the standard directly. The primary focus is on physical layer enhancements, but instruction also gives an overview of the MAC enhancements. Examples are presented to demonstrate the applications and benefits of the new features.
The course begins with a summary of the applications, environments, channel models, use cases, and usage models developed by the study group and task group that provided the framework for proposal development. This is followed by a history of the various coalitions that ultimately led to the final joint proposal adopted as the draft standard. The basics of OFDM and 802.11a/g are covered to give participants the background for 802.11n.
The technical description of the new features starts with a detailed discussion of the key throughput enhancing feature in the PHY: multiple-input, multiple-output (MIMO)/space-division multiplexing (SDM). The three main PHY design criteria of interoperability with 11a/g legacy OFDM devices, high throughput, and robust performance are addressed. PHY interoperability techniques, such as the mixed format preamble, legacy spoofing, and auto-preamble detection, are then presented. Throughput enhancements beyond MIMO/SDM in the PHY include 40 MHz channelization, reduced guard interval, sub-carrier filling, high rate coding, and efficient (Greenfield) preambles. The introduction of 40MHz channelization to 802.11n creates numerous interoperability and coexistence issues with legacy 20MHz devices and neighboring networks. These issues are discussed and solutions enabled by the standard are described, as well as the PHY techniques that improve robustness, including spatial spreading, receive diversity, transmit beamforming, space-time block code (STBC), and low-density parity-check (LDPC) codes. Lastly, transmitter and receiver block diagram and state machine are presented to illustrate how a typical 802.11n transceiver is designed.
The overview of the MAC enhancements begins with a discussion of MAC efficiency and the limitations of the current MAC at high PHY data rates. The techniques for improving MAC efficiency are then introduced. These include packet aggregation where both MSDU and MPDU aggregation techniques are described. Further efficiency improvement is gained from enhancements to the block acknowledgement (BA) protocol. With many new features in 802.11n, an important aspect of system design is protecting legacy systems. Most features in 802.11n also are optional, requiring protection between 802.11n devices supporting different feature sets. An overview of protection mechanisms that address this issue is provided.
IEEE 802.11 continues to progress beyond 802.11n. IEEE 802.11ac and 802.11ad (Very High Throughput) will further advance wireless networking throughput to beyond gigabit rates. 802.11ac will explore using multi-user access techniques and wider channels in the 5 GHz band for applications such as multiple simultaneous video streams throughout the home. 802.11ad will take advantage of the large swath of available spectrum in the 60 GHz band to develop a protocol to enable throughput intensive applications, such as wireless I/O or uncompressed video.
The text, Next Generation Wireless LANs: Throughput, Robustness, and Reliability in 802.11n, Eldad Perahia and Robert Stacey (Cambridge University Press, 2008), and lecture notes are distributed on the first day of the course. The notes are for participants only and are not for sale.
Coordinator and Lecturer
Eldad Perahia, PhD, Principal Engineer, Wireless Standards and Technology Group, Intel Corporation, Hillsboro, Oregon. At Intel, Dr. Perahia led a team developing a fully compliant IEEE 802.11n PHY simulation platform, as well as an interdisciplinary team investigating voice and handheld system design based on the IEEE 802.11 protocol. He has been involved in the IEEE 802.11n task group since its inception and is chair of the Coexistence Ad Hoc Committee. He is actively investigating next-generation 802.11 technology and is the chair of the IEEE 802.11 Very-High Throughput Study Group. His interests also lie in coexistence between wireless systems.
A senior member of IEEE, Dr. Perahia is the IEEE 802.11 liaison to IEEE 802.19 (Coexistence Technical Advisory Group) and the author of the Coexistence Assurance documents for both 802.11n and 802.11y. He contributed to the “Coexistence of IEEE 802.11n and Bluetooth” chapter in the book, Emerging Technologies in Wireless LANs: Theory, Design, and Deployment, Benny Bing (Editor), Cambridge University Press, 2007. He has presented several tutorials on 802.11n, including Globecom 2006. Due to interest in his latest tutorial, it was made available online by the IEEE Communication Society and is the subject of the course text, Next Generation Wireless LANs: Throughput, Robustness, and Reliability in 802.11n.
Prior to joining Intel, Dr. Perahia was the 802.11n lead for Cisco Systems, including algorithm design for MIMO/OFDM systems. He also was an active participant in the FCC rule-making for 70/80/90 GHz and was an invited speaker at the 6th Topical Symposium on Millimeter Waves, Yokosuka, Japan, 2004.
Dr. Perahia has 18 patents and numerous papers and patent filings in various areas of wireless, including satellite communications, cellular, WLAN, millimeter-wave technology, and radar.
- History of IEEE 802.11
- History of High Throughput and 802.11n
- Environments and Applications for 802.11n
- Major Features of 802.11n
Orthogonal Frequency Division Multiplexing
- Comparison to Single Carrier Modulation
- SISO (802.11a/g) Background
- MIMO Basics
- SDM Basics
- 802.11n Propagation Model
- Linear Receiver Design
- Maximum Likelihood Estimation
PHY Interoperability with 11a/g Legacy OFDM Devices
- 11a Packet Structure Review
— Training Fields
— Receive Procedure
- Mixed Format, High-Throughput Preamble
— Non-HT Part of the MF Preamble
— HT Portion of the MF Preamble
— HT MF Receive Procedure
- 40 MHz Channel
- 20 MHz Enhancements
- Greenfield (GF) Preamble
- Short Guard Interval
- Receive Diversity
- Spatial Expansion
- Space-Time Block Coding
- Low-Density Parity-Check Codes
- Singular Value Decomposition
- Eigenvalue Analysis
- Receiver Design
- Channel Sounding
- Channel State Information Feedback
— Implicit Feedback
— Explicit Feedback
- Efficiency Enhancements
— Enhanced Block Ack
— RIFS Bursting
- 40 MHz Coexistence
- Protection Mechanisms
- Task Group AC (VHT in 5 GHz)
- Task Group AD (VHT in 60 GHz)
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