Published:2011/8/18 1:57:00 Author:Amy From:SeekIC
Stefan Tauschek
Wireless data communication is the latest rage. From wireless mice to Formula-] telemetry systems, digital radio systems are used in many applications, and they are penetrating into many new areas. In this article, we examine the current state of affairs in the ’airwave jungle’.
The enormous popularity of wireless communication is a direct consequence or international agreements to designate certain regions of the radio spectrum as ’ISM bands’, since widespread use of wireless connectivity would otherwise never have been possible. The demand for unrestricted mobile communication is the driving force behind the rapid development of technologies such as Bluetooth, WLAN. HomreRF, and other new technologies with resplendent names. When we talk about WIAN or Bluetooth, we’re talking about applications employing ISM ’ISM’ stands for ’Industrial, Scientific & Medical’, which means radio services in these fields. The ISM bands can be used without a license, and they are subject to relatively little regulation. The only restrictions relate to the maximum transmitted power and (naturally) the bandwidth, which must be kept within certain limits. Besides the traditional 27-MHz ISM band (used for CB radio], there ore now ISM bonds in (lie 433 MHz, 868 MHz, 2.4 GHz and 5.8 GHz regions. The currently used bands and their individual characteristics are summarized in Table 1.
Naturally, the fact that the ISM bands are subject lo minimal regulation is both a blessing and a curse. As there are no restrictions on the number of transmitters and no defined protocols, reliable data transmission cannot be guaranteed if simple data transmission techniques are used. The fact that the ISM bonds must share the airwaves with other users, as well as the existence of other potential sources of interference, can be readily seen from the poster-sized international frequency allocation chart. Figure 1 shows the allocations for the 2.4-GHz and 5.8-GHz ISM bands, which ore the most important bands for wireless networking. The complete chart can be obtained free of charge from http://www.ntia.doc.qov/osmhome/osmhome.hlml.
As you can see, 0 large number of other radio sources are also active in these bonds, with amateur radio transmitters being the most prominent. Microwave ovens and radar signals can also do a good job of polluting the airwaves in these bonds and making reliable data transmission more difficult. This means that techniques for avoiding and overcoming mutual interference are necessary if these bands are to be widely used for data traffic.
Reprinted Url Of This Article: http://www.seekic.com/blog/project_solutions/2011/08/18/Wireless_Connectivity__ISM_WLAN_WMAN_Bluetooth_et_al_1.html
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