Wireless Medium Access

Here we talk about the access to transmission media in wireless networks through various modulation methods and controlling the access by multiplexing the modulated signals.
When no of signals from different sources attempt to access a wireless medium simultaneously, it creates a problem of receiving the signals from each radio carrier distinctly. To overcome these problem, communication system receives the different signals from various terminals in the presence of signals divided into different cells, time slot , frequencies and codes called as SDMA, TDMA, FDMA, and CDMA signals respectively . The big challenge is to control the collision between the signals from one wireless station and other wireless station.
Whenever different wireless stations from different cells transmits signals then it uses SDMA i.e Space division multiple access which is as shown in following figure. It avoids the problem of collision but there is a limit to the number of cells which can be formed among the wireless stations using direct antennae. Hence SDMA does not resolve the interference issue completely.



When wireless stations are located in same cell transmitting the signals access access the medium using m different time slots is referred as TDMA i.e time division multiple access when there are m slots in TDMA communication system which is as depicted in following figure.

When the wireless stations in same cell access the transmission medium uses different ratio carrier frequencies then is called as FDMA i.e frequency division multiple access as shown in figure.

Suppose wireless stations in same cell uses same time-slot and frequency then the only choice is CDMA i.e code division multiple access. It access the transmission medium using distinct codes.
GSM communication standards uses TDMA and FDMA where as some CDMA-based standards are also available such as IS-95, WCDMA, CDMA2000 etc.

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This article is the topic of unit " Communication Technologies-II " from RTMNU MBA 3 rd sem IT syllabus notes.Further topics will be covered in upcoming blogs For more notes you can also refer to other links as given below:

1. http://rtmnupervasivecomp.blogspot.com/

2. http://rtmnuittrends.blogspot.com/

3. http://www.rtmnunetworkingtechnology.blogspot.com/

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