Table
of Contents
Introduction
This paper is a general overview of the IEEE 802.11 standard
and the working group. The IEEE 802.11 defines physical layer options
for wireless transmission and MAC layer protocol.
WLANA
Commentary
The IEEE 802.11 represents the first standard for WLAN products
from an internationally recognized, independent organization. The IEEE
manages most of the standards for wired LANs. It represents an important
milestone in WLAN systems since customers can now have multiple sources
for the components of their WLAN systems. There are still applications
where the existing proprietary data communications are a good fit because
they may optimize some aspect of the network performance. However, 802.11
compliant products expand the users' options.
The Economics
for Standards Based Solutions The majority of the WLAN products available
in the marketplace today are proprietary spread spectrum solutions targeting
vertical applications operating in the 900MHz and 2.4GHz ISM frequency
bands. These products include wireless adapters and access points in
PCMCIA, ISA and custom PC board platforms. Proprietary solutions for
some applications are beneficial, especially for those requiring market
differentiation or customization of a wireless LAN network. Proprietary
solutions are typically customized and constrain the end users into
purchasing products from a single equipment supplier. However, as products
are introduced compliant to the standard, users can choose from a number
of vendors that provide compatible products. This increases competition
and provides the potential for lower cost products. Interoperability,
low cost and stimulation of market demand are some of the advantages
that standards based solutions offers.
How
it will be used in End Applications
The
IEEE 802.11 standard defines the protocol for two types of networks;
Ad-hoc and client/server networks. An Ad-hoc network is a simple network
where communications are established between multiple stations in a
given coverage area without the use of an access point or server. The
standard specifies the etiquette that each station must observe so that
they all have fair access to the wireless media. It provides methods
for arbitrating requests to use the media to ensure that throughput
is maximized for all of the users in the base service set. The client/server
network uses an access point that controls the allocation of transmit
time for all stations and allows mobile stations to roam from cell to
cell as illustrated in the figure below. The access point is used to
handle traffic from the mobile radio to the wired or wireless backbone
of the client/server network. This arrangement allows for point coordination
of all of the stations in the basic service area and ensures proper
handling of the data traffic. The access point routes data between the
stations and other wireless stations or to and from the network server.
Typically WLANs controlled by a central access point will provide better
throughput performance.
The
Standards Committee
The
IEEE 802 standards committee formed the 802.11 Wireless Local Area Networks
Standards Working Group in 1990. The 802.11 working group took on the
task of developing a global standard for radio equipment and networks
operating in the 2.4GHz unlicensed frequency band for data rates of
1 and 2Mbps. The 802.11 working group has recently completed the standard.
The standard does not specify technology or implementation but simply
specifications for the physical layer and Media Access Control (MAC)
layer. The standard allows for manufacturers of wireless LAN radio equipment
to build interoperable network equipment.
The membership
of the committee consists of individuals from a number of companies
and universities, who research, manufacturer, install and use products
in wireless LAN network applications. Manufacturers of semiconductors,
computers, radio equipment, WLAN systems solution providers, University
research labs and end-users make up the core group. The working group
is globally represented by companies from the United States, Canada,
Europe, Israel and the Pacific Rim.
Physical
Layer Implementation Choices
The
Physical Layer in any network defines the modulation and signaling characteristics
for the transmission of data. At the physical layer, two RF transmission
methods and one infrared are defined. Operation of the WLAN in unlicensed
RF bands requires the of spread spectrum modulation to meet the requirements
for operation in most countries. The RF transmission standards in the
standard are Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence
Spread Spectrum (DSSS). Both architectures are defined for operation
in the 2.4GHz frequency band typically occupying the 83 MHz of bandwidth
from 2.400 GHz to 2.483 GHz. Differential BPSK (DBPSK) and DQPSK is
the modulation for the direct sequence. Frequency hopping uses 2-4 level
Gaussian FSK as the modulation signaling method. The radiated RF power
at the antenna is set by the rules governed by FCC part 15 for operation
in the United States. Antenna gain is also limited to 6 dBi maximum.
The radiated power is limited to 1W for the United States, 10mW per
1Mhz in Europe and 10mW for Japan. There are different frequencies approved
for use in Japan, United States and Europe and any WLAN product must
meet the requirements for the country where it is sold. See the appendix
for details of the different frequency allocations for unlicensed operation
in US, Europe and Japan. The physical layer data rate for FHSS system
is 1 Mbps. For DSSS both 1 Mbps and 2 Mbps data rates are supported.
The choice between FHSS and DSSS will depend on a number of factors
related to the users application and the environment that the system
will be operating.
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