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Posted on May 17th, 2012, by

Infrared light based vs radio based WLAN

WLAN is a wireless local area network. WLAN technology is very popular nowadays because of its moderateness and availability. The principle of operation of WLAN is that there are wireless access points situated in a certain area, which are cable connected to the server, and people can access the LAN while on this area through wireless devices built in their notebooks, cellular phones, PDAs (Personal Digital Assistants) etc. The most commonly used wireless devices communicate through infrared light or radio waves and this paper is targeted to compare these two approaches and emphasize their advantages and disadvantages.

 

Infrared-based WLANs

Infrared WLANs uses IEEE (Institute of Electrical and Electronics Engineers) 802.11 standard, which includes Infrared physical layer called 802.11IR. It provides access from 1Mbps up to 2Mbps. Infrared light repulses from walls and other surfaces and thus devices can communicate with each other. The important fact is that infrared light can not pass through the walls and conformably infrared-based WLANs can communicate within a room only. It can be considered as a disadvantage but from the other side it makes WLAN more secure.

Infrared light can not be seen by human eye (but some animals can see it), it uses enormously high frequency it is measured in terahertz. Such feature prevents an interference of infrared devices with other radio-based devices such as cellular phones, cordless phones or even microwave ovens.

One more feature that infrared devices are tightly attached to its manufacturer problems often occur when infrared devices, produced by different manufacturers, can not communicate with each other. So in order to establish indeed a full-service wireless network based on the infrared light it is necessary to use the devices of the same manufacturer.

All the above makes infrared-based WLANs inappropriate for application in public places such as airports. But such WLANs are completely appropriate for little companies which require increased security measures.

 

 

Radio-based WLANs

Radio-based WLAN technology uses IEEE standards too, but there are four different standards (not only one as for infrared WLANs): 802.11a, 802.11b, 802.11g and 802.11n. They differ from each other in the data rate (11Mbps, 54Mbps and 100Mbps) and frequency (2,4Hz and 5Hz). Obviously radio-based WLANs can interfere with other radio devices cordless phones, microwave ovens, cellular phones, radio stations, Bluetooth devices etc because they often use the same frequency. Thus devices can be disabled or provide lower performance.

From the other side such WLANs can cover significant areas (up to 500 feet outdoors) and radio waves can move through the walls, doors and ceilings.  Thus they are not limited by the room space or even building.

Most radio devices support roaming it implies that user can receive data from different wireless access points (as a rule it is the closest one). But here comes a disadvantage sometimes WLAN user can receive data from two wireless access points simultaneously and this in turn lowers the performance.

Radio-based WLANs are not as secure as infrared because they can be accessed by outside users, but there are plenty methods and software products which minimize security problems.

Radio-based WLANs can use different methods of data transmission: DSSS (Direct Sequence Spread Spectrum) and FHSSS (Frequency-Hoping Sequence Spread Spectrum).

DSSS transmits redundant data flow in order to minimize the data losses and thus it is more reliable. Even if the data loss occurs the recipient can restore it using extrapolation methods. Transmitted signals are interpreted as a noise by the outside receivers.

FHSSS transmits data flow on different frequencies depending on the patterns, known to the receiver and the transmitter. This data flow can be received and interpreted only by devices which know the corresponding pattern; those which do not know the pattern interpret the signal as a noise.

Of course the data rate of DSSS and FHSSS is different (DSSS can transmit 11Mbps) but FHSSS consumes less energy. These two methods are incompatible with each other.

 

Summary

WLAN can not completely replace cable LAN, it can only expand it to the areas where cabling is not available, inappropriate or too expensive. Radio-based WLANs are the most popular nowadays but it does not make infrared-based WLANs noncompetitive. Both types of WLANs have their advantages and disadvantages, which determine the scope of each.

Main advantages of infrared-based WLAN there are:

–         security (outside users can not access the network because it is limited by the room space);

–         no interference with radio devices;

Among the main disadvantages of infrared-based WLANs there are:

–         limited range;

–         low device compatibility;

–         lower data rate;

 

Main advantages of radio-based WLAN are:

–         wide range;

–         high data rate (indoors and outdoors);

–         roaming support;

–         absolute device compatibility;

Among the main disadvantages of radio-based WLANs there are:

–         interference with other radio devices;

–         accessibility to outsiders;

 

The main differences between infrared and radio-based WLANs are that they use different frequency bands; infrared light do not pass through walls while radio waves do pass; infrared light does not allow to cover large areas and its range is limited by the room while radio waves cover large areas and do not limit their range by the room or building; infrared light does not support high data rate as radio waves do; radio-based WLANs support roaming while infrared-based do not.

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