Reason For Choosing Wireless Communication Computer Science Essay

Published Date: 02 Nov 2017

Chapter III

Wireless communication techniques

Overview and comparisons:

In this project, we will use a wireless communication technique to transfer the data from the energy meter to the power station and vice versa.

The reason for choosing wireless communication because it has some advantages over wired communication. Ethernet is a common type of wired cable that is widely used but the signal in the Ethernet cables needs to be enhanced to maximum every 100 meters due to signal loss.

This is not an easy task not to mention the high cost.

On other hand, wireless technology is convenient because there will be no need to run wires in constricted places.

Wireless communication is the transfer of information without using any electrical conductors. It makes a backup communication link when the network fails and it also uses a movable link or temporary workstations to overcome situations of the cabling difficulties [5].

There are a lot of technologies that support wireless communication such as Wi-Fi, Bluetooth, Zigbee and GSM.

In this chapter we will compare between some wireless technologies to choose the best one that serves our needs in the project.

Wireless fidelity (Wi-Fi):

Wi-Fi is a wireless network that uses radio waves to provide wireless Internet and network connections with high speed. The Wi-Fi Alliance defined it as "wireless local area network (WLAN)" products that are based on IEEE (the Institute of Electrical and Electronics Engineers) 802.11 standards. It uses radio frequency (RF) technology to connect between sender and receiver with radio frequency band (2.5GHz for 802.11b, 802.11n, 802.11g, or and 5GHz for 802.11a).The data transfers in Wi-Fi with rate up to 54 Mbps. Wi-Fi has a nominal transmitted power (from 15 dBm To 20 dBm) and covers a nominal range of up to 100m.

Although Wi-Fi has all the above specifications, it doesn't fit as the method of communication in this project for the following reasons:

Wi-Fi network has a limited area (up to 100 m) to access to internet but as you go further, the signal strength will decrease and interference might happen.

(We need the data to be transmitted all the time for a long distance without any loss)

Setting up a Wi-Fi network is very easy but it needs a lot of effort to maintain its security. The access point of Wi-Fi network has no methods to organize the encryption of data on it. Hackers can access the Wi-Fi network, steal the data and reduce the performance of the network. In addition, when a lot of users are getting access to internet via the same network, then the speed of data transfer is decreased. (The transfer of data isn’t secure enough).

Wi-Fi supports many applications and devices such as PDAs and mobile phones but it costs a lot while many users can't offer to buy them. (We need to choose a technology that suits most users).

Zigbee:

Zigbee is a wireless technology based on the IEEE 802.15.4 standard. It makes the transmission of the data more secured as it uses symmetric key with 128-bit AES (Advanced Encryption Standard) algorithm. In addition, it has low data rate, it transfers the data with maximum data rate of 250 kbps. It uses 868/915 MHZ and 2.4 GHZ frequency band of RF technology and has a nominal transmitted power (from -25 dBm to 0 dBm) and covers a nominal range of up to 75m.

Advantages:-

low cost

low power consumption

high reliability

secured

Disadvantages:-

Low transmission rate

Short range

In this project, we chose GSM because it provides quick transfer of the data over large areas.

Global System for Mobile communication (GSM):

GSM is a digital mobile telephony system. It uses TDMA (time division multiple access). It use the same number of channels of the old telephone analog system but it increases the capacity up to three times.GSM converts the data to digital signal, compresses it and sends it through a channel with two other streams of data each of them in its own time slot. It uses the 900 MHz or 1800 MHz frequency channel bands. This frequency bands are widely used in Europe, Australia, Middle East, Oceania, Africa and Asia.

GSM has a lot of advantages:

GSM operators have roaming agreements with foreign operators so the users can use their mobiles while they are travelling from one country to another.

A lot of phones that operate on GSM spread worldwide so consumers have elasticity in choosing a phone that fits their requirements.

Architecture of the GSM network

PSTN and ISDN

Figure (3.1): GSM architecture [5]

The GSM network consists of three parts which are the mobile station, the base station subsystem and the network subsystem.

The mobile station

The mobile station is carried by the subscriber. It is composed of the mobile equipment and the subscriber identity module (SIM card). The mobile equipment is defined as international mobile equipment identity (IMEI). The GSM provides the user with freedom of movement so that the user is able to access to a subscribed services nevertheless of a specific terminal. When we insert the SIM card into another GSM terminal, the user can receive and make calls at that terminal and it also can receive other subscribed services. The SIM card contains the International Mobile Subscriber Identity (IMSI), ciphering key (Kc), a secret key for authentication and other information. The SIM card is protected against unauthorized use by personal identity number or a password [5].

The base station subsystem:

The base station subsystem consists of two parts, the base transceiver station (BTS) and the base station controller (BSC). They communicate with each other through Abis interface.

The base transceiver station switches the radio-link protocols (Um interface) with the mobile station and dynasties the radio transceivers that define a cell.

The base station controller connects between the mobile station and the mobile service switching center (MSC). It makes a lot of functions such as managing the radio resources for one or more BTSs, handling radio-channel setup, handovers and frequency hopping.

Network Subsystem

The MSC is the main component of the network subsystem. It provides all the needed functions to handle a mobile subscriber, such as authentication, registration, handovers, location updating, and call routing to a roaming subscriber.

The routing of calls and the capability of GSM for roaming capabilities provided by the Home Location Register (HLR) and Visitor Location Register (VLR), together with the MSC. The HLR contains all the organizational information of each subscriber and the up-to-date location of the mobile. GSM can be executed as a distributed database, although each GSM network has one HLR.

The Visitor Location Register (VLR) contains the administrative information that is selected from the HLR. The recent location of the mobile is in the form of a signaling address of the VLR. The location registers contain information about mobile stations [5].

The EIR and the AUC registers are used for GSM security and authentication. The Equipment Identity Register (EIR) is like a database that contains a list of all usable mobile equipment on the network. Each mobile station is identified by its International Mobile Equipment Identity (IMEI).The Authentication Center (AUC) stores a copy of the secret key stored in each subscriber's SIM card that is used for authentication and encryption over the radio channel [5].

Encryption of the data in GSM:

Ciphering mode request

Mobile station

Base station

A5 Algorithm

A5 Algorithm Kc Kc

dataData

Figure (3.2): GSM encryption

GSM uses ciphering key to protect both user signal and data on the air interface. First, a ciphering mode request command from the GSM Network initiate the Encrypted communication. Upon receiving of this command, the mobile station begins to encrypt and decrypt the data. The A5 algorithm used to encrypt the data in each frame in the air traffic and the KC, thus generating a different key stream for every frame. The same KC is used when the MS isn’t authenticated by the MSC again so in this case a new KC is generated. In practice, the same KC is used for days. When it is switched off, the mobile station stores the TMSI (Temporary Mobile Subscriber Identity) on the SIM card so that it will be available when it is switched on again. The A5 algorithm is implemented in the hardware of the mobile phone, as it has to encrypt and decrypt data on the fly [7].

GSM frequency bands:

System

Band

Reverse channel BW

Uplink(MHz)

Forward channel BW

Downlink (MHz)

Channel number

GSM-450

450

450.4–457.6

460.4–467.6

259–293

GSM-850

850

824 - 849

869 - 894

128–251

GSM-900

900

890–915

935–960

1-124

E-GSM -900

900

880 - 915

925 - 960

975 – 1023

R- GSM-900

900

876 - 915

921 - 960

955 – 1023

GSM-1800

1800

1710 - 1785

1805 - 1880

512–885

GSM-1900

1900

1850 - 1910

1930 - 1990

512–810

Table (3.1): GSM frequency bands

Specification of GSM-900:[7]

(It is widely used in Egypt)

GSM-900 uses 935–960 MHz (downlink) to send information from the base station transceiver to the mobile station and 890–915 MHz (uplink) for the other direction, providing 124 RF channels spread out at 200 kHz. Its channel numbers are from 1to 124. Duplex spacing is 45 MHz.

GSM-900 band has been extended in some countries to cover a larger frequency range. E-GSM (extended GSM) uses frequency range 925 - 960 MHz (downlink) and 880 - 915 MHz (uplink). Its channel numbers are from 975 to 1023 and 0. This GSM added 50 channels to the original GSM.

R- GSM (railways GSM) uses frequency range 921 - 960 MHz (downlink) and 876 - 915 MHz (uplink) .Channel numbers 955 to 1023. R- GSM is a specialized service for use by railway personnel.

Specification of GSM-1800:[7]

GSM-1800 uses 1805 - 1880 MHz to send information from the Base Transceiver Station to Mobile Station (downlink) and 1710 - 1785 MHz for the other direction (uplink). It provides 374 channels. Its channel numbers are from 512 to 885. Duplex spacing of 95 MHz is used.

Specification GSM-850 and GSM-1900:[8]

GSM-1900 and GSM-850 are used in the United States, Canada, and many other countries in the Americas.

GSM-850

GSM-850 uses frequency range (869 - 894 MHz) to send information from the Base Transceiver Station to the Mobile Station (downlink) and frequency range (824 - 849 MHz) for the opposite direction (uplink). It has Channel numbers from 128 to 251.

GSM-1900

GSM-1900 uses frequency range (1930 - 1990 MHz) to send information from the base transceiver station to the mobile station (downlink) and frequency range (1850 - 1910 MHz) for the opposite direction (uplink). It has channel numbers from 512 to 810.

GSM-450

GSM-450 is a less common GSM version. It uses 450.4 - 457.6 MHz (uplink) to send information from the mobile station to the base station transceiver and 460.4 - 467.6 MHz (downlink) for the other direction. It has channel numbers from 259 to 293.

Multi-band and multi-mode phones:[8]

Nowadays a lot of countries use multi band phones. The Dual- band phones can use both the frequency band 900 and 1800 MHZ of GSM Network together (Europe, Asia, Australia and Brazil) or the frequency band 850 and 1900 MHZ (North America). The tri- band phones use the frequency bands 900, 1800 and 1900 so it gives an excellent coverage in Europe, also the quad –band use the four major GSM bands (850, 900, 1800 and 1900).

There are also Multimode-phones which operate similarly in both mobile-phone systems and GSM systems. For example, one version of Nokia 6340i GIAT phone operates on GSM-850, GSM 900. This makes it both multi- band and multi-mode.

Arduino GSM/GPRS shield:

Figure (3.3): Arduino GSM shield

GSM/GPRS shield for Arduino based on the SIM900 Quad-band GSM/GPRS module. It is controlled via AT commands and fully compatible with Arduino. In this project we interface the shield with Arduino in the meter.

The shield has an antenna and extension interface cable that comes with it. It can be powered on and off via software control.[9]

Arduino interface

Figure (3.4): GSM shield schematic

Features:

Quad-Band 850/900/1800/1900MHz

GPRS mobile station class B

GPRS multi-slot class 10/8

Class 4 (2W) at (850/900MHz)

Class 1 (1W )at (1800/1900MHz)

Low power consumption: 1.5mA(sleep mode)

Supply voltage range : 3.2 ... 4.8V

Control via AT Commands.

Short message service (SMS).

Free serial port selection.

RTC (real time clock) .

Operation temperature: -40℃ ~ +85℃

GSM GPRS wireless module SIM900D

Figure (3.5): GSM wireless module sim900D

SIM900D is a compressed wireless module. It is a Quad-band (850/900/1800/1900MHz) GSM/GPRS module.

The SIM900D provides the GSM/GPRS module performance for SMS, voice, Fax and Data although it has small size (33mm x 33mm x 3 mm) configuration and low power consumption. [10].

AT Commands :

AT commands are used to configure the GSM/ GPRS Arduino shield. They allow the simple transmission and reception of serial data. They are named AT commands as all commands start with AT.