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/

)

GSM

GSM is developed in 1982 by Groupe Speciale Mobile. Global Service Mobile (GSM) communication is one of the most popular second generation mobile communication standard which basically uses cellular network.
GSM operates in frequency ranges such as 900MHz, 1800 MHz and 1900 MHz. Easy international roaming in GSM network is enabled by triband phones operating in GSM 900/1800/1900.GSM gives integrated services for data as well as voice.
Basically Services provided by GSM are divided into three different types such as teleservices, supplementary services and bearer service which are as shown in following figure.




Teleservices are the services provided to user by mobile service network. It is a point-to-point service which means a service is from one terminal provided to another terminal. Teleservices provides many services some of them are SMS, MMS, Fax, Voice communication at full data rate 13.4 kbps, emergency numbers for emergency calls etc.
Whereas GSM also provides some additional services that are available by subscription only called as supplementary services. Caller line forwarding, caller line identification at connected terminal, closed group formation, multiparty groupings, call holding, l waiting and barring calls from specified numbers or groups etc are some of the examples of supplementary services.
Bearer services are the services which are responsible for transmission of voice and data in terms of digital format over the network. Bearer services are transparent which uses only physical layer protocol for transmission or non-transparent which uses physical layer, data link layer and flow control layer protocol for transmission. Bearer services are also categorized depending on synchronous data transfer, asynchronous data transfer or synchronous data packet transfer.

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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/

)

Mobile Communication

Mobile Computing is the process in which the set of distributed computing system participate, connect, and synchronize through mobile communication protocols. Mobile computing is also referred as pervasive computing when a set of computing devices, systems, or networks have the characteristics such as transparency, application aware adaptation and environment sensing ability.

Pervasive computing is nothing but the next generation of computing in which information and communication technology is used. Pervasive computing devices are very tiny or even invisible devices such as mobile phones. Mobile computing systems have large number of applications; for example, mobile computing has recently made Mobile TV which to make TV viewing on tiny cell phones easier and cheaper. A Smartphone is a mobile phone with additional computing functions such as SMS, MMS, E-Mail, Address Book, Web Browsing, Calendar, Bluetooth, Speaker Phone etc. BlackBerry 7130e is the example of Smartphone. Another application of mobile computing is enterprise solutions which provide business solutions for corporations and enterprises.

An innovative application of mobile computing is the iPod-Nano from Apple. The Apple iPods made it possible to listen to one’s favorite tunes anytime and anywhere. It can be also used for viewing photo albums, slide shows, and video clips etc. An additional example is the Sony Network Walkman. It can store and play 33 hours of music without charging the battery and stores music equivalent to 11 CDs.

A further important application is Mobile-Cheque. A mCheque is mobile –based payment system. This service is activated through text-message exchanges between a customer, a retailer and mobile service provider. It basically transfers money from customer account to retailer account. Mobile Commerce is one more application with much wider scope in which mobile devices are used to obtain stock quotes, for booking cinema, train, flight and bus tickets etc.

Mobile computing is also widely used today in the Supply Chain Management. Though mobile computing is useful in many areas, it has some limitations. Battery recharging requirements is biggest constraints of mobile computing. Interference in wireless signals affects the quality of service. There may be the problem related to connection such as link delays or connection losses while communication is going on. The problem may arise related to connection stability and data security also.

for more detail on mobile computing refer following mobile computing ppt :

mobile computing ppt : Mobile Computing.pptx

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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/

)