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far outweigh the speed advantage and prevent this method from becoming the

standard. The major drawback is that communication is restricted to line of

sight. Also, very thick fog or blizzard conditions will diffuse the laser beam

and causing interference and reducing data integrity. d. Infrared: This method

is similar to Laser. High-speed communications are easy to achieve using this

method. However, it suffers from the same problems that plague laser

communications. It requires line of sight transmission and can be disrupted by

strong ambient light. Infrared wireless computing exists more commonly in the

form of peripheral connections in a small area. e. Cellular connections although

expensive to use now is the area of much development by private companies.

Cellular computing can be likened to the current wire-based Internet network.

Data is packaged in to units, size of the unit is dependent on the actual

hardware, and is sent to the nearest participating cell. That cell then forwards

the packet to the next cell and so forth until the packet reaches its

destination. f. Microwave: This method of communication has been utilized for

quite some time now. However this method has makes little provision for data

aware transmission. It used extensively in Europe where wired transmission of

any type including voice is poor. For data transmission, a lot of technology is

utilized in packaging the data into a form that is compatible to voice

communication. On the receiving end, the process is reversed. The advantage of

this method however is that communication can be accomplished using existing

satellite connections making worldwide connectivity possible. 3 Standards The

IEEE 802.11 committee has voted to create a minimum requirement for wireless

computing connections. In their consideration: (1) Use the frequencies 2.4 to

2.5 GHz. This is in the low end of the high frequency spectrum and is currently

not licensed by the FCC. (2) Use spread spectrum technology. Compared to the

current bandwidth 26 MHz, 902 MHz to 928 MHz, the range 2.4 to 2.5 GHz yields a

bandwidth of 100 MHZ. Spread spectrum transmission now gives 385% percent

increase in data reliability. (3) Many more sub-channels can be formed in a

bandwidth of 100 MHZ. This increases the capability of frequency hopping which

in turn yields greater data security. (4) Utilize Gaussian Frequency

Shift-Keying. Frequency shift-keying is a form of frequency modulation in which

binary signaling is accomplished by using two frequencies separated by some Df

Hz. The frequency duration is small compared with the carrier frequency, fc. A

signal received at frequency fc, would represent a digital low and signals

received at frequency fc + Df, would represent a digital high. Note that this

does not interfere with spread spectrum or frequency hopping capabilities since

those function on frequencies separated by 1 MHz or more. As part of setting a

wireless standard some modifications of the standard set by the IEEE 802.3

committee have been adopted. The most significant of these is the modification

to the carrier sense multiple access / collision detection, or CSMA/CD, protocol

used in wired networks today. This is a method whereby any machine at any time,

wishing to send a message on the net, will first send a token out to ensure that

a carrier exists (network ready). After establishing this, the message will be

sent. Because any machine may send at any time, collisions of information will

occur. If any machine detects a collision, it will send out a jamming signal to

all the others. All machines will then wait on a random interval timer after

which they will try to send again. For wireless networks however, since a

machine is not in constant communication with the rest of the LAN, detecting a

collision and notifying all other machines on the net is impossible. A

modification in the way of the collision handling had to be made. A method known

as collision avoidance is employed to create the CSMA/CA standard. In a

collision avoidance strategy, the net estimates the average time of collisions

and sends a jamming signal at that time. A wireless transceiver will not only

sense a carrier but will also listen for the jamming signal. When all is clear

it then send its message. This collision avoidance method has two drawbacks: 1)

It cannot completely filter all collisions since it operates on estimated times

of collisions; 2) -If it did, it slows the network significantly by sending

jamming signals whether or not a collision actually occurs. IV. Physical Layer

Much of the focus of wireless computing development is centered on the physical

and media access control layers of a system. It is on this level of the LAN

protocol of which wireless products like modems and transceivers. On the

physical layer issue, the 802.11 is focusing on the one proposed by Apple

Computer Corporation. The Apple physical-layer protocol appears the most robust

of any considered to date in 802.11. Apple?s system is a full-duplex, slow

frequency-hopping protocol. By using a frequency-hop spread-spectrum radio, the

system fits with the spread-spectrum methods of virtually all 802.11

specifications. Apple splits the data-transport protocol into two layers: ?The

RF Adoption Layer is similar in some respects to cell-based

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