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Mobile and Wireless Communication
This paper is mainly about designing the wireless system choosing the appropriate communication system according to their requirement and specification. Along with that, the access mechanism for each system is described ensuring high performance, fairness and simplicity.
1. Considering Region as satellite communication with the earth receiver, City as GSM communication, Campus as Wi-Fi and in building can be wire or wireless communication.
2. Mobile Switching Centre (MSC) as a central manager.
3. Using TDMA as a multiple Access Techniques for Wireless Communication.
Description of each node and their access mechanism:
Node 1: Region (Satellite communication)
The node consist of the satellite (GEO,LEO, MEO ) according to the several restriction and application requirement over the earth and antenna system on or near the earth known as earth station . Assuming the system which covers the whole world and allows voice and data communication:
Type of satellite: LEO
Frequency range : 1.6138-1.6265 GHz (according to iridium system)
Data rate: 2.4 kbit /sec to the satellite and 4.8 kbit/s down
Uplink/downlink frequencies:29.1-29.3/19.4-19.6 GHz (according to iridium system)
Access medium: TDMA
Leo is satellite which has low delay for packets delivered, better frequency reuse due to smaller footprints and does not require high signal strength (Schiller, 2003) .The scheme used is TDMA and more precisely it is reservation aloha which is distributed contention- oriented protocol with implicit reservation. Here the channel bandwidth is divided into slot sizes equal to the transmission time of a single packet assuming the packet sizes are of constant length. These slots are again arranged in frames whose length span is equal to propagation delay which is a main requirement for satellite communication i.e. the duration of the frame must be greater than the satellite propagation delay. The advantage of R-ALOHA scheme is it has high efficiency and efficiently handles brusty data traffic.
Node 2: City (GSM)
Considering this node as GSM (Global System for Mobile Communication).Its has been introduced worldwide as second generation communication system .Originally it was
developed to transmit voice but is also able for the data transmission of 2.4-9.6 kbit/s data rate.
Assuming High Speed Circuit Switched Data (HSCSD) technique, which allows a single mobile subscriber to use consecutive user time slots in the GSM standard, the maximum data rate was increased to14.4 kbit/s (Rappaport,2006).
The GSM network can be accessed by using the combination of TDMA and FDMA(Stalling,2006) .FDMA divides frequency bandwidth into carrier frequencies and each carrier frequency is divided in time by the TDMA scheme which forms logical channel.
Assuming Mobile Switching Centre (MSC) as a central manager which form the fixed backbone network of the GSM system by setting up the connection between MSCs and BSCs (Schiller,2003).
Node 3: Campus (Wireless LAN)
Considering Campus as Wireless LAN. Assuming IEEE 802.11b as the WLAN technology which has the maximum data rate of 11 Mbps works in the 2.4 GHz band.
It uses Distributed Coordinate Function(DCF) that follow the principle of CSMA/CA as a media access method .In CSMA/CA , a channel is sense by the host who wants to transmit and wait for certain period of time (DIFS) and sent the packet if there is still a free medium. The receiving host will send an ACK frame if the packet is received correctly after fixed time period (SIFS).If this ACK frame does not reach the sending host, then it is considered that the collision has occurred. Therefore the sending host will send the packet again if the channel is free .
Node 4: In Building (WI-FI)
This node is a part of a campus and we can assume this as Wi- Fi (802.11b). Alternatively we can consider this as a wirelink LAN .i.e Ethernet.
As control manager is assumed to be MSC in city, the maximum data rate from city to in-building will be the max. Data rate of GSM i.e. 9.6 kbps.
The maximum data rate from in-building to campus node will be the maximum data rate of 802.11b as assumed. So maximum data rate will be 11Mbps.But this value keeps on fluctuating to 5.5 Mbps if computer is moved away from the router. The maximum data rate from region to city will be 43.2kpbs which is the downlink data rate of GSM.
The maximum data rate campus to in-building will be same as task 2.i.e. 11 Mbps .But the maximum data rate from city to region will be the uplink data rate of GSM which is 14.4 Kbps.
Suppose that the wireless link was not working that we can replace by optical fibre connection in city and wired LAN or Ethernet in the campus and in building. Optical fibre has very high data rate of gigabits per seconds and higher and can be transmitted over very long distance. Wireless LAN can be replaced by Ethernet. There are many advantages of using Ethernet. It is cost effective, has very good performance, has a high reliability, more stability in the connection. Considering the Gigabit Ethernet, the maximum data rate is 1 Gbps/1000 Mbps. Therefore the data rate in the campus and in-building will be the same.
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 Rappaport, T.S., 2006.Wireless Communications: Principles and Practice. 2nd edition. India: Prentice Hall
 Stalling, W., 2006.Wireless Communication and Networks.2nd edition. India: Pearson Prentice Hall.
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