Characteristics of the OFDM PHY

Parameters specific to the OFDM PHY are listed in Table 13-5. Like the physical layers presented in Chapters 11 and 12, the OFDM PHY also incorporates a number of parameters to adjust for the delay in various processing stages in the electronics. As a final note, the extra radio bandwidth provided offers a great deal of throughput. In the United States, there are currently 12 channels, with the additional space for eight channels recently cleared. 20 co-located channels operating with 50% of the transmission time devoted to user traffic can move over 500 Mbps. This number is far greater than any other physical layer yet standardized.

Table 13-5. OFDM PHY parameters




Maximum MAC frame length

4,095 bytes


Slot time

9 ms


SIFS time

16 ms

The SIFS is used to derive the value of the other interframe spaces (DIFS, PIFS, and EIFS).

Contention window size

15 to 1,023 slots


Preamble duration

20 ms


PLCP header duration

4 ms


Receiver sensitivity

-65 to -82 dBm

Depends on speed of data transmission.

Like the other physical layers, the OFDM PHY has a number of attributes that can be adjusted by a vendor to balance delays in various parts of the system. It includes variables for the latency through the MAC, the PLCP, and the transceiver, as well as variables to account for variations in the transceiver electronics.

Introduction to Wireless Networking

Overview of 802.11 Networks

11 MAC Fundamentals

11 Framing in Detail

Wired Equivalent Privacy (WEP)

User Authentication with 802.1X

11i: Robust Security Networks, TKIP, and CCMP

Management Operations

Contention-Free Service with the PCF

Physical Layer Overview

The Frequency-Hopping (FH) PHY

The Direct Sequence PHYs: DSSS and HR/DSSS (802.11b)

11a and 802.11j: 5-GHz OFDM PHY

11g: The Extended-Rate PHY (ERP)

A Peek Ahead at 802.11n: MIMO-OFDM

11 Hardware

Using 802.11 on Windows

11 on the Macintosh

Using 802.11 on Linux

Using 802.11 Access Points

Logical Wireless Network Architecture

Security Architecture

Site Planning and Project Management

11 Network Analysis

11 Performance Tuning

Conclusions and Predictions

802.11 Wireless Networks The Definitive Guide
802.11 Wireless Networks: The Definitive Guide, Second Edition
ISBN: 0596100523
EAN: 2147483647
Year: 2003
Pages: 179
Authors: Matthew Gast © 2008-2020.
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