Characteristics of the FH PHY

Table 11-4 shows the values of a number of parameters in the FH PHY. In addition to the parameters in the table, which are standardized, the FH PHY has a number of parameters that can be adjusted to balance delays through various parts of an 802.11 frequency-hopping 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. One other item of note is that the total aggregate throughput of all frequency-hopping networks in an area can be quite high. The total aggregate throughput is a function of the hop set size. All sequences in a hop set are orthogonal and noninterfering. In North America and most of Europe, 26 frequency-hopping networks can be deployed in an area at once. If each network is run at the optional 2 Mbps rate and half the airtime is able to carry user payload data, the area can have a total of 26 Mbps throughput provided that the ISM band is relatively free of interference.

Table 11-4. FH PHY parameters




Slot time



SIFS time


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

Contention window size

15-1,023 slots


Preamble duration


Preamble symbols are transmitted at 1 MHz, so a symbol takes 1 ms to transmit; 96 bits require 96 symbol times.

PLCP header duration


The PLCP header is 32 bits, so it requires 32 symbol times.

Maximum MAC frame

4,095 bytes

802.11 recommends a maximum of 400 symbols (400 bytes at 1 Mbps, 800 bytes at 2 Mbps) to retain performance across different types of environments.

Minimum sensitivity

-80 dBm


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

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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
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