Global Systems for Mobile Communication (GSM)

Global Systems for Mobile Communication (GSM)

ABSTRACT:

GSM (Global System for Mobile Communication) is globally accepted standard for digital cellular communication.

Before GSM network there were public radio networks. They use analog technologies varying from country to country. These analog network did not comply with any uniform standard. Therefore GSM system which is based on digital communication are preferred.

GSM system architecture includes main blocks are MS. BTS, BSC, OMC, MSC, HLR, VLR, EIR, AUC having particular functions.

The GSM network is made up of geographic areas, including cells, location areas, Msc/VLR service areas and public land mobile network areas.

Frequency range of GSM is 1850 to 1990 MHz. Duplex distance is 80MHz, 200KHz channel separation.

Transmission rate of GSM is 270 Kbps. GSM utilizes the time division multiple access (TDMA). IT uses linear predictive coding.

GSM provides two basic subscriber services such as teleservices and data telephony services. With this it also supports some supplementary services that can complement and support both telephony and data services.

A GSM mobile can seamlessly roam nationally and internationally requiring standardized call routine and location updating functions. Within a GSM network different protocol are used. These are basically divided into three layers.

1. Physical layer
2. Data Link layer
3. Network layer.

GSM system have some features which are:

1. Roaming
2. Handover
3. Multiple equalization
4. Discontinuous transmission
5. Discontinuous reception
6. Short Message service
Security is major concern of any mobile system. GSM also supports the moderate level of security.

WIRELESS

            Wireless is an old fashioned term for a radio receiver, referring to its use as a wireless telegraph; now the term is used to describe modern wireless connections such as in cellular network and wireless broadband internet.

            In modern usage wireless is a method of communication that uses low powered radio waves to transmit data between devices. The term refers to communication without cables or cords, chiefly using radio frequency and infrared waves.

            Software and hardware developers are creating smaller computer networks ad-hoc wireless network with protocols such as WiFi and ZigBee.

            In cellular system there are two main competing network technologies, global system of Mobile Communication (GSM) and CDMA. One of the key feature of GSM is the subscriber Identity Module (SIM) commonly known as SIM card.

DEFINITION

            Global system for mobile communication (GSM) is a globally acceptable standard for digital cellular communication. GSM is the name of a standardization group established in 1982 to create a common European mobile system standard that would formulate specifications for a pan European mobile cellular radio system operating at 900 MHz. It is estimated that many countries outside of Europe will join the GSM partnership.

Topics :

1. Introduction: The evolution of mobile telephone
2. GGSM System?
3. The GSM Architecture
4. GSM network areas
5. GSM specifications
6. GSM subscriber services
7. GSM protocols/Interfacing
8. features.
9. Security.

1) Introduction : The evolution of mobile telephone system.        

            Cellular is one to the fastest growing and most demanding telecommunication application. Today it represents a continuously increasing percentage of all new telephone subscriptions around the world. Currently there are more tan 45 millions cellular subscribes worldwide.

            The concept of cellular service is the use of low power transmitters where frequencies can be reused within a geographic area. The idea of cell based mobile radio service was formulated in the United States at Bell labs in the early 1970. However the Nordic countries were the 1^st to introduce cellular services for commercial use with the introduction of the Nordic Mobile telephone (NMT) in 1981.

            Cellular Systems began in the United States with the release of the advanced mobile phone service (AMPS) system in 1983. The AMPS standard was adopted by Asia, Latin America and Oceanic countries, creating the largest potential market in the world for cellular.

            In the early 1980s most mobile telephone systems were analog rather than digital, like today’s newer systems. One challenge facing analog systems was the inability to handle the growing capacity needs in a cost efficient manner. As a result, digital technology was welcomed. The advantages of digital systems over analog systems include ease of signaling, lower switching, and increased ability to meet capacity.

2) GSM :

Throughout the evolution of cellular telecommunications various systems have been developed without the benefit of standardized specifications. This presented many problems directly related to compatibility, especially with the development of digital radio technology. The GSM standard is intended to address these problems.

GSM Overview

Before GSM networks there were public mobile radio networks (cellular). They normally used analog technologies, which varied from country to country and from manufacturer to another. These networks did not comply with any uniform standard. There was no way to use a single mobile phone form one country to another. The speech quality in most networks was not satisfactory.

GSM became popular very quickly because it provided improved speech quality and, through a uniform international standard, made it possible to use a single telephone number and mobile unit around the world. The European Telecommunications Standardization Institute (ETSI) adopted the GSM standard in 1991, and GSM is now used in 135 countries.

The benefits of GSM include :

·         Support for international roaming

·         Distinction between user and device identification

·         Excellent speech quality

·         Wide range of services

·         Interlocking (e.g. with ISDN, DECT)

·         Extensive security features

GSM also stands out form other technologies with its wide range of services :

·         Telephony

·         Asynchronous and synchronous data services ( 2.1/4.8/9.6 dkit/s)

·         Access to packet data network (S.25)

·         Telematic services (SMS, fax, videotext, etc.)

·         Many value-added features (call forwarding, caller ID, voice mailbox)

·         E-mail and Internet connections.

GSM System Architecture

The best way to create a manageable communications system is to divide it into various subgroups that are interconnected using standardized interfaces. A GSM network can be divided into three groups The mobile station (MS), the base station subsystem (BSS) and the network subsystem.

They are characterized as follows :

The Mobile Station (MS) :

            A mobile station may be referred to as a “handset ”,  a ‘mobile”, a “portable terminal” or “mobile equipment” (ME). It also includes a subscriber identity module (SIM) that is normally removable and comes in two sizes. Each SIM card has unique identification number called IMSI (international mobile subscriber identity) In addition, each MS is assigned a unique hardware identification called IMEI (International mobile equipment identity)

            In some of the newer application (data communication in particular) an MS can also be a terminal that acts as a GSM interface, e.g. for a laptop computer. In this new application the MS does not look like normal GSM telephone.

The seemingly low price of a mobile phone can five the (false) impression that the product is not of high quality. Besides providing a transceiver (TRS) for transmission and reception of voice and data, the mobile also performs a number of very demanding tasks such as authentication, handover, encoding and channel encoding.

The base station subsystem (BSS) :

            The base station subsystem (BSS) is made up of the base station controller (BSC) and the base transceiver station (BTS.)

The base transceiver station (BTS) :

GSM uses a series of radio transmitters called BTSs to connect the mobiles to cellular network. Their tasks include channel coding/decoding and encryption/decryption. A BTS is comprised of radio transmitters and receivers, antennas, the interface to the PCM facility, etc. The BTS may contain one or more transceivers to provide the require call handling capacity. A cell site may be omni directional or split into typically three directional cells.

The base station controller  (BSC) :

A group of BTSs are connected to a particular BSC which manages the radio resources for them. Today’s new and intelligent BTSs have taken over many tasks that were previously handled by the BSCs.

The primary function of the BSC is call maintenance. The mobile stations normally send a report of their received signal strength to the BSC every 480 ms. With this information the BSC decides to initiate handovers to other cells, change the BTS transmitter power, etc.

The mobile switching center (MSC) :

Acts like a standard exchange in a fixed network and additionally provides all the functionality needed to handle a mobile subscriber. The signaling between functional entities (registers) in the network subsystem uses signaling system 7 (SS7). If the MSC also has a gateway function for communicating with other networks, it is called Gateway (GMSC).

The home location register (HLR) :

A database used for management of mobile subscribers. It stores the international mobile subscriber identity (IMSI), mobiles station ISDN number (MSISDN) and current visitor location register (VLR) address. The main information stored there concerns the location of each mobile station in order to be able to route calls to the mobile subscribers managed by each HLR. The HLR also maintains the services associated with each MS. One HLR can serve several MSCs.

The visitor location register (VLR) :

Contains the current location of the MS and selected administrative information form the HLR, necessary for call control and provision of the subscribed services, for each mobile currently located in the geographical area controlled by the VLR. AVLR is connected to one MSC and is normally integrated into the MSC’s hardware.

The authentication center (AuC) :

A protected database that holds a copy of the secret key stored in each subscriber’s SIM card, which is used fro authentication and encryption over the radio channel. The AuC provides additional security against fraud. It is normally located close to each HLR within a GSM network.

The equipment identity register (EIR) :

The EIR is a database that contains a list of all valid mobile station equipment within the network, where each mobile station is identified by its international mobile equipment identity (IMEI). The EIR has three databases :

White list : for all known, good IMEIs

Black list : for bad or stolen handsets

Grey list : for handsets/IMEIs that are uncertain

Operation and Maintenance Center (OMC)

            The OMC is a management system that oversees the GSM functional blocks. The OMC assists the network operator in maintaining satisfactory operation of the GSM network. Hardware redundancy and intelligent error detection mechanisms help prevent network down-time. The OMC is responsible for controlling and maintaining the MSC. BSC and BTS. It can be in charge of an entire public land mobile network (PLMN) or just some parts of the PLMN.

GSM Network Areas

The GSM network is made up of geographic areas. As shown in figure. These areas include cells, location areas (Las), MSC/VLR service areas, and public land mobile network (PLMN) areas.

The cell is the area given radio coverage by one base transceiver station. The GSM network identifies each cell via the cell global identity (CGI) number assigned to each cell. The location are is a group of cells. It is the area in which the subscriber is paged. Each LA is served by one or more base station controllers yet only by a single MSC (See figure) Each LA is assigned a location area identity (LAI) number.

An MSC/VLR service area represents the part of the GSM network that is covered by one MSC and which is reachable, as it is registered in the VLR of the MSC (See figure)

The PLMN service area is an area served by one network operator (see figure)

GSM Specifications :

Before looking at the GSM specifications, it is important to understand the following basic terms :

Bandwidth : the range of channel’s limits; the broader the bandwidth, the faster data can

be sent.

Bits per second (bps) : a single on-off pulse of data; eight bits are equivalent to one byte.

Frequency : the number of cycles per units of time; frequency is measured in hertz (Hz)

Kilo (k) : kilo is the designation for 10002; the abbreviation kbps represents 1000 bits per

                 second.

Megahertz (MHz): 1000000 hertz (cycle per second)

Milliseconds (ms) : one thousand of a second

Watt (W) : a measure of power of a transmitter.

Specific for different personal communication services (PCS) systems vary among the different PCS networks. Listed below is a description of the specification and characteristics for GSM.

Frequency band :

The frequency range specified for GSM is 1,850 to 1,990 MHz (mobile station to base station)

Duplex distance :

The duplex distance is 80 Mhz. Duplex distance is the distance between the uplink and downwind frequencies. A channel has two frequencies, 80 MHz apart.

Channel separation :

The separation between adjacent carrier frequencies. In GSM, this is 200 KHz.

Modulation :

Modulation is the process of sending a signal by changing the characteristics of a carrier frequency. This is done in GXM via Gaussian minimum shift keying (GMSK)

Transmission rate : GSM is a digital system with an over the air bit rate of 270 kbps.

Access method :

GSM utilizes the time division multiple access (TDMA)  concept. TDMA is a technique in which several different calls may share the same carrier. Each call is assigned a particular time slot.

Speech coder :

GSM uses linear predictive coding (LPC). The purpose of LPC is to reduce the bit rate. The LPC provides parameters for a filter that mimics the vocal tract. The signal passes through this filter leaving behind a residual signal. Speech is encoded at 13 kbps.

GSM Subscriber Services

There are two basic types of services offered through GSM :

telephony also referred to as teleservices) and data (also referred to as bearer services)

Telephony services are mainly voice services that provide subscribers with the complete capability (including necessary terminal equipment) to communicate with other subscribers. Data services provide the capacity necessary to transmit appropriate data signals between two access points creating an interface to the network. In addition to normal telephony and emergency calling, the following subscriber services are supported by GSM:

Dual-tone multifriquency (DTMF) : DTMF is a tone signaling scheme often used for various control purposes via the telephone network, such as remote control of an answering machine. GSM supports full originating DTMF.

Facsimile group II :

GSM supports CCITT Group 3 facsimile. As standard fax machines are designed to be connected to a telephone using analog signals, a special fax converter connected to the exchange is used in the GSM system. This enables a GSM : connected fax to communicate with any analog fax in the network.

Short message services :

A convenient facility of the GSM network is the short message service. A message consisting of a maximum of 160 alphanumeric characters can be sent to or from a mobile station. This service can be viewed as an advanced form of alphanumeric paging with a number of advantages. If the subscriber’s mobile unit is offered back to the subscriber when the mobile is powered on or has tendered the coverage area of the network. This function ensures that the message will be received.

Cell broadcast :

A variation of the short message service is the cell broadcast facility. A message of a maximum of 93 characters can be broadcast to all mobile subscribers in a certain geographic area. Typical applications include traffic congestion warnings and reports on accidents.

Voice mail :

This service is actually an answering machine within the network, which is controlled by the subscriber. Calls can be forwarded to the subscriber’s voice-mail box and the subscriber checks for messages via a personal security code.

Fax mail :

With this service, the subscriber can receive fax messages at any fax machine. The messages are stored in a service center form which they can be retrieved by the subscriber via a personal security code to the desired fax number.

Supplementary Services

GSM supports a comprehensive set of supplementary services that can complement and support both telephony and data services. Supplementary services are defined by GSM and are characterized as revenue-generating features. A partial listing of

Supplementary services follows :

Call forwarding : This service gives the subscriber the ability to forward incoming calls to another number if the called mobile unit is not reachable, if it is busy, if there is no reply, or if call forwarding is allowed unconditionally.

Barring of outgoing calls : This service makes it possible for a mobile subscriber to prevent all outgoing.

Barring of incoming calls : This function allows the subscriber to prevent incoming calls. The following two conditions for incoming call barring exits : baring of all incoming calls and barring of incoming calls when roaming outside the home PLMN.

Advice of charge (AoC) : The AoC service provides the mobile subscriber with an estimate of the call charges. There are two types of AoC information : One that provides the subscriber with an estimate of the bill and one that can be used for immediate charging purposes. AoC for data calls is provided on the basis of time measurements,

Call hold : This service enables the subscriber to interrupt an ongoing call and then subsequently reestablish the call. The call hold service is only applicable to normal telephony.

Call waiting : This service enables the mobile subscriber to be notified of an incoming call during a conversation. The subscriber can answer, reject, or ignore the incoming call. Call waiting is applicable to all GSM telecommunication services using a circuit switched connection.

Multiparty service : The multiparty service enables a mobile subscriber to establish a multiparty conversation-that is, a simultaneous conversation between three and six subscribers. This service is only applicable to normal telephony.

Calling line identification presentation/restriction : These services supply the called party with the integrated services digital network (ISDN) number of the calling party. The restriction service enables the calling party to restrict the presentation. The restriction overrides the presentation.

Closed user groups (CUGs) : CUGs are generally comparable to a PBS. They are a group of subscribers who are capable of only calling themselves and certain numbers.

Providing voice or data transmission quality over the radio link is only part of the function of cellular mobile network. A GSM mobile can seamlessly roam nationally and internationally, requiring standardized call routing and location updating functions in GSM networks. A public communications system also needs solid security mechanisms to prevent misuse by third parties. Security functions such as authentication, encryption and the use of Temporary Mobile Subscriber Identities (TMSIs) are an absolute must.

            Within a GSM network, different protocols are needed to enable the flow of data and signaling between different GSM subsystems. Figure shows the intervals that link the different GSM subsystems and the protocols used to communicate on each interface.

GSM protocols are basically divided into three layers :

Layer 1 : Physical layer

Enables physical transmission (TDMA, FDMA, etc.)

Assessment of channel quality

Except on the air interface (GSM Rec.04.04) PCM 30 or ISDN links are used (GSM Rec.08.54 on A interface and 08.04 on A to F interface)

Layer 2 : Data link layer

Multiplexing of one or more layer 2 connections on control/signaling channels

Error detection (based on HDLC)

Flow control

Transmission quality assurance

Routing

Layer 3 : Network layer

Connection management (air interface)

Management of location data

Subscriber identification

Management of added services (SMS,  call forwarding, conference calls , etc.)

System Features

The section provides a brief description of the GSM network features :

Roaming  : The roaming feature allows a user to make and receive calls in any GSM network and to use the same user specific services worldwide. This requires a roaming agreement between the individual operators. With worldwide roaming the MS is accessible under the same phone number everywhere.

Handover : In a cellular network, the radio and fixed voice connections are not permanently allocated for the duration of a call. Hanover, or handoff as it is called in North America, means switching and ongoing call to a different channel or cell. The execution and measurements require for handover are a basic function of the RR protocol layer.

Multipath equalization : At the 900 MHz range, radio waves bounce off everything- buildings, hills, cars, airoplanes, etc. Many reflected signals, each with a different phase, can reach an antenna (also known as “multipath propagation”) Equalization is used to extract the desired signal from the unwanted reflections. It works by finding out how a known transmitted signal is modified by multipath fading, and constructing an inverse filter to extract the rest of the desired signal. This known signal is the 26-bit training sequence transmitted in the middle of every time-slot burst. The actual implementation of the equalizer is not specified in the GS< specifications.

Discontinuous Transmission (DTX) : To reduce the MS’s power consumption and minimize interference on the air interface, user signal transmission is interrupted during pauses in speech. “Comfort noise” is artificially generated by the MS to avoid disruption due to an abrupt interruption in speech.

Discontinuous Reception (DRS) : Another method used to conserve power at the mobile station is discontinuous reception. The paging channel, used by the base station to signal an incoming call, is structured into sub-channels. Each mobile station needs to listen only to its own sub-channel. In the time between successive paging sub-channels, the mobile can go into sleep mode, when almost no power is used.

Short Message Service(SMS) : SMS offers message delivery (similar to “two-way-paging”) that is guaranteed to reach the MS. If the GSM telephone is not turned on, the message is held for later delivery. Each time a message is delivered to an MS, the network expects to receive an acknowledgement from this MS that the message was correctly received. Without a positive acknowledgement the network will re-send the message or store it for later delivery. SMS supports messages up to 160 characters in length that can be delivered by any GSM network around the world wherever the MS is able to roam.

Call Waiting(CW) : CW is a network-based feature that must also be supported by the GSM telephone(MS). With CW, GSM users with a call in progress will receive an audible beep to alert them that there is an incoming call for the MS. The incoming call can be accepted, sent to voice mail or rejected. If the incoming call is rejected, the dealer will receive a busy signal. Once the call is accepted, the original call is put on hold to allow a connection to the new incoming call.

Call Hold (CH) : CH must be supported by the MS and the network. It allows the MS to “park” and “in progress call”, to make additional calls or to receive incoming calls.

Call Forwarding(CF) : This is a network-based feature that can be activated by the MS. CF allows calls to be sent to other numbers under conditions defined by the user. Theses conditions can be either unconditional or dependent on certain criteria. (no answer, busy, not reachable)

Calling Line ID : Calling Line ID must be supported by the GSM network and the telephone. The GSM telephone displays the originating telephone number of incoming calls. This feature requires the caller’s network to deliver the calling line ID (telephone no.) to the GSM network.

GSM Security

            GSM was designed with a moderate level of  security. The system was designed to authenticate the subscriber using shared secret cryptography communication between the subscriber and the base station can be encrypted. The development of UMTs introduces an optional USIM, that uses a longer authentication key to five greater security, as well as mutually authenticating the network and the user whereas GSM only authenticated the user to network (can not vise versa). The security model therefore offers confidentiality and authentication but limited authorization capabilities and no reproduction.

            GSM uses several cryptographic algorithms for security The AS/1 stream ciphers are used for ensuring over air voice privacy. A large security advantage of GSM is that the kit, the crypto variable stored on SIM card that is the key to any GSM ciphering algorithms is never send over the air interface.

 CONCLUSION

             In the modern world where faster common is needed the wireless communication systems are best to use. For mobile communication various systems are used in which GSM is most reliable and accepted digital system.

MIMO technology: Future of wireless communication

ABSTRACT:

            Last few years have seen rapid changes in the wireless technologies. The stage is set for third generation (3G) technology and R&D is aiming at fourth generation (4G) technology.

            The future communication aims at becoming all wireless and mobile supporting any communication, any where, any time and for anybody with a single unique identification number of a person world over for all communication.

            It’s defined as personal communication services (PCS) and may be supported by personal communication network- a global wireless and mobile networks.

This paper briefs out the consequences of multipath fading, the reason of poor quality of services. This paper also put light on the concept of MIMO technology and gives reason why it’s preferable over present day technology.

INTRODUCTION:

            Comprehensive broadband, integrated mobile communication will step into all mobile 4G service and communication. The 4G will be the migration from the other generation of mobile services to overcome the limitation of boundary and achieve the integration. The 4G of mobile services aims to total wireless.

            The 4G will be developed to provide high speed transmission, next generation internet support, seamless integrated services and coverage, utilization of higher frequency, lower system cost, seamless personal mobility, mobile multimedia, sufficient spectrum use, quality of service (QoS), reconfigurable network and end-to-end IP systems.

            In conventional wireless communication a single antenna is used at the source and another antenna is used at destination. In many cases it gives rise to problem with multipath fading, making difficult to meet promises aim by the 4G.

            The solution to multipath fading can be solved using MIMO technology. The following paper will outline the concept of MIMO technology and why it’s superior to present the present day technology.

Multipath fading:

            Wireless technologies are not free from the limitations of the available frequency spectrum, fading and multipath fading.

            Multipath fading results when the transmitted signal bounces off object like buildings, office cabinets and hills creating multiple paths for signal to reach the receiver. The same transmitted signal that follows the different path reaches the receiver at different time with different phases. Added together, the several incidences of same signal with different phases and amplitudes may cancel each other, causing signal loss or drop of signal power.

            The expectation from the future wireless mobile networks are high data rate, higher network capacity, better quality of service and lower probability of call drop. With increase data rates, the problem of multipath fading becomes severe.

            The consequences of multipath fading may be delay spread, short time fading, long time fading and Doppler Effect.

            In mobile environments as channel condition changes with the motion of receiver, fading causes short term effect, resulting fluctuation in the received power over time. The receiver may not adapt to the changes .This may degrades quality of service. Short term fading occurs over short time duration.

            The long term fading results in the decreased received power over long time/distance as time increases, the moving receiver usually goes farther away.

            The Doppler Effect occurs in the moving mobiles. It results in the shift of the frequency randomly. Multipath fading, in effect, either causes low received signal power or degraded quality of services, both of which are highly unexpected in future all wireless and mobile communication. The low received power increases the bit-error rate, which in turn limits the data rate.

             

Concept of MIMO technology:

            Wireless channels input and output modulated signals. For the purpose of modulation, the two basic things are considered are frequency and time. The frequency plan and time plan use ‘bits per hertz’ and ‘bits per second’ as measures for data rate transportation.

            A new dimension to upgrade the data transportation rate is spatial dimension. This is the concept behind multiple input multiple output (MIMO) technology.

            MIMO technology may be seen as an upgrade of single input multiple output

And multiple input single output (MISO). All three technologies namely SIMO, MISO and MIMO uses multipaths for increasing data rate, throughput and reliability. Multiple paths are used by multiple transmit antenna and multiple receiver antenna.

            Multiple antennas at one end either at transmitter or at the receiver were in use long ago. The then use of multiple antennas aimed at beam forming and spatial diversity, which are mainly used to increase the signal to noise ratio. The improved signal to noise ratio decreases the bit-error rate.

            The use of multiple antennas adds the new dimension to digital communication technology which forms the basis of 3G and 4G. The natural dimension of digital technology is time. Added with that, MIMO offers a new space time axis to digital technology. MIMO is therefore termed as ‘space time wirelesses or ‘smart antenna’.

            Digital MIMO is called volume to volume wireless links as it offers parallel bit pipes between transmitter and the receiver.  

Why MIMO?:

            MIMO technology promises higher data rate, higher quality of service and better reliability by exploiting antenna array at both the transmitter and the receiver. Signals at both sides (transmitter and receiver) are mixed such that they either generate multiple parallel, spatial bit pipes and /or add diversity to decrease the bit-error rate.

            Diversity helps in selecting the clearest signal out of many signals, resulting in lower bit-error rate. Multiple bit pipes effectively increases the data rate (quantitative improvement), whereas the reduced bit-error rate improve the quality of service, throughput and reliability (qualitative improvement).

            The fundamental gain in MIMO is increased data rate. Why not use more bandwidth or complex modulation scheme to increase the data rate? The use of more bandwidth depends upon the availability of spectrum and again the use may be difficult to meet the spectral efficiency. All wireless devices use a particular part of radio spectrum. Air traffic radar, for example, operates between 960 and 1215 megahertz and cellphone between 824 to 849 megahertz. As growing number of wireless devices enter the consumer market, the spectrum becomes congested every year. MIMO has potential to expand radio capacity and relieve the burden on existing bandwidth.

            By spreading the transmitted signal over the multiple paths, the MIMO technology increases the chances of signal reception at receiver. It also increases the range of operation.

            Multipath fading causes the distortion by scrambling the copy of the signals reaching the receiver via multiple paths on bouncing of the objects. Then how does the multipath signals work in MIMO? Proper algorithms are used at both the transmitter and receiver to analyses the signal received from different path and different antenna of array.

            Proper spacing of antenna and signal analysis via a matrix manipulation technology that cross-correlate the signals are the requirement of MIMO technology.

Conclusion:

            MIMO technology will prove basic building block of total wireless communication. The problems of multipath fading will fade away and uninterrupted service will be available to one and all.

            Future wireless technologies will provide unique and single identification globally. In future this number will be unique like our names.

            With on going R&D in MIMO technology is exploring way towards our fantasies.

If MIMO technology stands on it promises that day is not far when the James Bond style video conversation will be reality?

Reference:

1. my oh MIMO, http:\\www.networkworld.com.
2. www.ece.utexas.edu.
3. www.engineer.ucla.edu.
4. MIMO technology: future wireless, EFY,vol: 38 No.1, January 2006.

BLUETOOTH A wireless system

ABSTRACT                                         

             

 The Bluetooth wireless technology was created to solve a simple problem: replace the cables used on mobile devices with radio frequency waves. The technology encompasses a simple low-cost, low-power, global radio system for integration into mobile devices. Such devices can form a quick ad-hoc secure "piconet" and communicate among the connected devices. This technology creates many useful mobile usage models because the connections can occur while mobile devices are being carried in pockets and briefcases                                            

         Bluetooth uses radio waves in 2.4GHz band. The main disadvantage of infrared communication i.e. requirement of ‘line of sight’, gets eliminated as radio waves are used for communication in Bluetooth. Bluetooth only operates at weak wattage levels. Bluetooth works in small confined area of 10 to 15 meters and it can also be increased upto 100 meters by increasing power. Bluetooth use a technology called spread spectrum frequency hopping. It gives security to the system in terms of interference problem. Bluetooth supports not only point-to-point connections but also multipoint connections. The multipoint connection of devices is called as piconet and network of many piconets form scatternet.  Piconet is also called as PAN i.e. ‘Personal Area Network’.In this paper ww will discuss brief about working                                                                        

         Chipsets are very small in size and further smaller chips are in development, hence now a days Bluetooth technology has moved fast in terms of adoptation. So the ‘Special Interest Group’ of Bluetooth (SIG) introduced by Ericsson in 1994, has now tripled in size and has over 2000 companies on board. 

v  HISTORY

The name Bluetooth refers to the Danish king Harald Blåtand (Bluetooth) who unified Denmark and Norway in the 10^th Century.In the beginning of the Bluetooth wireless technology era, Bluetooth was aimed at unifying the telecom and computing industries.

                                                                 

The logo for Bluetooth is based on Runes surrounding the  legend of Harald Bluetooth Bluetooth the technology is based on communications central to man’s own personal space. Fundamentally Bluetooth operates within the Industrial, Scientific and Medical (ISM) band at 2.4 GHz. It

is a short-range wireless communication standard defined as cable replacement for a   Personal Area Network (PAN).

v  Introduction

ð  what is bluetooth?

                "Think of a connected world of electronic devices and appliances around you!  You click on an icon for a device and you are linked to it, automatically and transparently"  .

     A cable replacement standard has been defined because cables limit mobility of the consumer; they are cumbersome to carry around, are easily lost or broken. Often connectors are prone to difficult to diagnose failures; or are proprietary. To counteract these limitations Bluetooth is designed to be light and portable. It can be embedded to take the riggers of physical knocks and shocks. It includes standards and protocols to make it mobile, robust, reliable and not limited to one manufacturer.

                  The operating band also fits the goals of Bluetooth, imposing requirements as a cable replacement. The cost needs to be comparable with cable. Reductions can be achieved by operating in the licence free 2.4 GHz ISM band, keeping backward compatibility wherever possible lowers the cost of ownership by avoiding upgrades and having a relaxed radio specification enables single chip integrated circuit solutions. It also needs to be as reliable and resilient as cable and cope with errors and degradation caused by interference. For mobile devices it must be compact, lightweight, low power and easy to use.

Briefly, Bluetooth technology

Ø  Evolved from basic cellular digital radio designs implemented in mobile phones since the early 1980s.

ü  Based on 802.11 in ad-hoc mode

Ø  Short range (up to 10m) radio communications standard

Ø  Runs at 2.4 GHz, near microwave frequency                                                               Unlicensed part of spectrum

Ø  No line of sight is required

Ø  Performs fast frequency hopping (1600 hops/sec) between 79 points to avoid interference

Ø  Is full duplex

Ø  Low power, 30-100mA during sustained data transmissions

Ø  Devices automatically switch to power saving mode

Ø  Bandwidth is wide enough to carry voice & data

ü  an asynchronous data channel, or

ü  up to 3 simultaneous synchronous voice channels, or

ü  a channel which simultaneously supports asynchronous data and synchronous voice.

Ø  Transfers data at 721 Kbps

Ø  three to eight times the average speed of parallel and serial ports, respectively.

Ø  Up to 7 simultaneous connections can be established and maintained

q   

v  Frequency Hopping technique

We have addressed the reasons for the Bluetooth without delving into the ‘nuts and bolts’ of the technology to discover how it operates. For the majority of countries the ISM band used by Bluetooth is available from 2.40-2.4835 GHz, although some countries impose restrictions. In this band Bluetooth uses Frequency Hopping Spread Spectrum (FHSS) techniques in order to improve its immunity from interference.

In unrestricted countries the radios hop in pseudo random sequences around all available channels, this equates to 79 RF channels with a channel spacing of 1 MHz. Starting at a base frequency of 2402 MHz then the frequency of the channels, f, can be expressed as:

f =2402 + n MHz

where, n, is the channel number with an integer value in the range of 0 to 78. In restricted countries a limited frequency hopping schemes with just 23 channels is used and is catered for in the Bluetooth specification. Both hopping schemes have a 1 MHz channel spacing making it possible to design a simple radio interface whereby the baseband only has to specify a channel number and the radio multiplies this up to the appropriate frequency offset.

In this FHSS scheme there are 1600 hops per second, which is a hop every 625 µs. Part of this hop timing is taken up by the guard time of 220 µs allowing the synthesizer time to settle. The frequency hopping implements time division multiplexing as shown in Figure 2. The basis of the scheme has the Master device transmitting in the first 625 us slot, k, and here the Slave receives. In the next slot k = 1 the Slave is permitted to transmit and the master listens.

Fig: Frequency hopping,master and  slave interact of corresponding slots

 

The radio must be able to retune and stabilise on a new frequency within tight time constraints. This is pushed further when establishing a connection; the hop rate can be shortened to every 312.5 us. As the radios are constantly hopping to different radio channels, this ensures that packets affected by interference on one channel can be retransmitted on a different frequency channel. To further enhance resilience both ARQ (Automatic Repeat reQuest) and FEC (Forward Error Correction) form part of the specification.

One drawback with the normal hop sequence is the time taken for production testing. Bluetooth ensures adequate frequency coverage with a test sequence allowing the radios to be tested at a faster rate

v  The Protocol Stack

The Bluetooth specifications define not only a radio system but cover the underlying structure. The Core Specification contains a software protocol stack similar to the more familiar Open Systems Interconnect (OSI) standard reference model for communication protocol stacks. It permits applications to discover devices, the services they offer and permission to use these services. The stack is a sequence of layers with features crossing single or multiple layered boundaries. Figure 4 outlines the stack with each block corresponding to a Core Specification chapter. Other remaining chapters relate to compliance requirements, test modes and test control interface.

                                    fig :  The Bluetooth protocol stack

If we ascend the stack, we first come across the fundamental component, the radio. The radio modulates and demodulates data for transmitting and receiving over the air. The operating band of the radio is divided into 1 MHz spaced channels with a chosen modulation scheme of Gaussian Frequency Shift Keying (GFSK). Each channel is specified to signal at 1mega symbols per second, equivalent to 1 Mb/s. Above the radio are the Baseband and Link Controller, they are responsible for controlling the physical links via the radio, assembling the packets and controlling the frequency hopping.

Progressing through the layers, the Link Manager (LM) controls and configures links to other devices. The Host Controller Interface (HCI) is above the             LM layer and is probably one of the most important layers to consider as a designer. It handles communication between host and the module. The standard defines the HCI command packets that the host uses to control the module, the event packets used by the host to inform lower protocol layers of changes, the data packets for voice and data traffic between host and module and the transport layer used by the HCI packets. The transport layer can be USB (H2), RS232 (H3), UART (4) or a robust proprietary standard such as BCSP (BlueCore Serial Protocol).

           

The Logical Link Control and Adaptation (L2CAP) is a multiplexor, adapting data from higher layers and converting between different packet sizes. The next 4 layers could be loosely grouped as communication interfaces. These are RFCOMM (Radio Frequency COMMunication port) which provides an RS232 like serial interface. Wireless Application Protocol (WAP) and OBject  EXchange (OBEX) are responsible for providing interfaces to other Communications Protocols. The final member of this rough grouping is the Telephony Control protocol Specification (TCS) providing telephony services. Service Discovery Protocol (SDP) lets devices discover the services available on another Bluetooth device.

            The application layer is probably obvious, but the standard provides Profiles laying out rules for how applications use the protocol stack, ensuring interoperability at application level.

v  The Profiles—A Hierarchy of Groups

The Bluetooth specification defines a wide range of profiles, describing many different types of tasks, some of which have not yet been implemented by any device or system.. For information on other profiles, including those still in development, see the Bluetooth specification.                                                                                               

At a minimum, each profile specification contains information on the following topics:                                                                                                                 Dependencies on other profiles. Every profile depends on the base profile, called the generic access profile, and some also depend on intermediate profiles.Suggested user interface formats. Each profile describes how a user should view the profile so that a consistent user experience is maintained.                                             Specific parts of the Bluetooth protocol stack used by the profile. To perform its task, each profile uses particular options and parameters at each layer of the stack. This may include an outline of the required service record, if appropriate

ð  The Base Profile

At the base of the profile hierarchy is the generic access profile (GAP), which defines a consistent means to establish a baseband link between Bluetooth devices. In addition to this, the GAP defines:

ü  Which features must be implemented in all Bluetooth devices

ü  Generic procedures for discovering and linking to devices

ü  Basic user-interface terminology

All other profiles are based on the GAP. This allows each profile to take advantage of the features the GAP provides and ensures a high degree of interoperability between applications and devices. It also makes it easier for developers to define new profiles by leveraging existing definitions

ð  Other Profiles

            The service discovery application profile describes how an application should use the SDP (described in “The Bluetooth Protocol Stack”) to discover services on a remote device. As required by the GAP, any Bluetooth device should be able to connect to any other Bluetooth device. Based on this, the service discovery application profile requires that any application be able to find out what services are available on any Bluetooth device it connects to.         

          The human interface device (HID) profile describes how to communicate with a HID class device using a Bluetooth link. It describes how to use the USB HID protocol to discover a HID class device’s feature set and how a Bluetooth device can support HID services using the L2CAP layer.                                                             

         

Figure 1-2  The Bluetooth profiles

As its name suggests, the serial port profile defines RS-232 serial-cable emulation for Bluetooth devices. As such, the profile allows legacy applications to use Bluetooth as if it were a serial-port link, without requiring any modification. The serial port profile uses the RFCOMM protocol to provide the serial-port emulation.                 

The dial-up networking (DUN) profile is built on the serial port profile and describes how a data-terminal device, such as a laptop computer, can use a gateway device, such as a mobile phone or a modem, to access a telephone-based network. Like other profiles built on top of the serial port profile, the virtual serial link created by the lower layers of the Bluetooth protocol stack is transparent to applications using the DUN profile. Thus, the modem driver on the data-terminal device is unaware that it is communicating over Bluetooth. The application on the data-terminal device is similarly unaware that it is not connected to the gateway device by a cable.            

 The headset profile describes how a Bluetooth-enabled headset should communicate with a computer or other Bluetooth device (such as a mobile phone). When connected and configured, the headset can act as the remote device’s audio input and output interface.

The hardcopy cable replacement profile describes how to send rendered data over a Bluetooth link to a device, such as a printer. Although other profiles can be used for printing, the HCRP is specially designed to support hardcopy applications.

The generic object exchange profile provides a generic blueprint for other profiles using the OBEX protocol and defines the client and server roles for devices. As with all OBEX transactions, the generic object exchange profile stipulates that the client initiate all transactions. The profile does not, however, describe how applications should define the objects to exchange or exactly how the applications should implement the exchange. These details are left to the profiles that depend on the generic object exchange profile, namely the object push, file transfer, and synchronization profiles.

The object push profile defines the roles of push server and push client. These roles are analogous to and must interoperate with the server and client device roles the generic object exchange profile defines. The object push profile focuses on a narrow range of object formats for maximum interoperability. The most common of the acceptable formats is the vCard format. If an application needs to exchange data in other formats, it should use another profile, such as the file transfer profile.

The file transfer profile is also dependent on the generic object exchange profile. It provides guidelines for applications that need to exchange objects such as files and folders, instead of the more limited objects supported by the object push profile. The file transfer profile also defines client and server device roles and describes the range of their responsibilities in various scenarios. For example, if a client wishes to browse the available objects on the server, it is required to support the ability to pull from the server a folder-listing object. Likewise, the server is required to respond to this request by providing the folder-listing object.

The synchronization profile is another dependent of the generic object exchange profile. It describes how applications can perform data synchronization, such as between a personal data assistant (PDA) and a computer. Not surprisingly, the synchronization profile, too, defines client and server device roles. The synchronization profile focuses on the exchange of personal information management (PIM) data, such as a to-do list, between Bluetooth-enabled devices. A typical usage of this profile would be an application that synchronizes your computer’s and your PDA’s versions of your PIM data. The profile also describes how an application can support the automatic synchronization of data—in other words, synchronization that occurs when devices discover each other, rather than at a user’s command.

v  Piconet,and Scatternet

ð  Master and Slave Operation.

Bluetooth devices exist in small ad-hoc network configuration with the ability to operate as either master or the slave; the specification also allows a mechanism for master and slave to switch their roles. The configurations can be single point, which is the simplest configuration with one master and one slave. Multipoint, called a Piconet, based on up to 7 slaves clustered around a single Master. And a third type called a Scatternet, this is a group of Piconets effectively hubbed via a single Bluetooth device acting as a master in one Piconet and a slave in the other Piconet. The Scatternet permits either larger coverage areas or number of devices than a single Piconet can offer. Figure 5 outlines the different master and slave topologies permitted for networks in the standard.

             fig : point to point ,piconet & scatternet

The role of the master is to control the available bandwidth between the slaves, it calculates and allocates how often to communicate with each slave and locks them into the appropriate frequency hopping sequence. The specification describes an algorithm that calculates the hop sequence, the seed being based on the master’s device address and clock. In addition to hop sequence control, the master is responsible for transmit control by dividing the network into a series of time slots amongst the net members, as part of a Time Division Multiplexing (TDM) scheme. These time slots can consist of data and potentially additional voice traffic i.e. you will always need a data channel before you can add a voice channel. The time slot is defined as 625 µs and all packet traffic is allocated 1, 3 or 5 slots, grouped together in transmit and receive pairs. Prior to connection some operations such as inquiry, paging and scanning operations may sometimes occur on half slots.

 v  bluetooth Security

Ø  Bluetooth guarantees security at the bit level. Authentication of any device is controlled by the user by using a 128 bit key. Radio signals can be coded with 8 bits or anything up to 128 bits.

Ø  Bluetooth protocol has these components:

ü  Random Number Generation

ü  Encryption (128-bit WEP)

ü  Encryption Key Management

ü  Authentication

Ø  Devices can be assigned a PIN which must be verified before others can access it

Ø  Devices have unique 48 bit Bluetooth address

Ø  Bluetooth uses Frequency Hopping Spread Spectrum (FHSS) techniques in order to improve its immunity from interference. .

Ø  Fast frequency hopping provides some security

ü  Only synchronised nodes can follow transmissions

Ø  Uses checksums & FEC (Forward Error Correction) to detect & fix corruption of data & limits the impact of random noise on long-distance links.

v  comparison with infrared and  802.11b

ð  Infrared vs. Bluetooth

Ø  The infrared beams have a major disadvantage because it is all done by line of sight. 

Ø  Line of sight is exactly how your eyes function; if you can not see an object you do not know it’s there.

Ø  The infrared transmitter must be in direct sight of the device. 

Ø  This means the user can not use the device in other rooms and it has a weaker signal since it always has to be in direct sight of the transmitter.

Ø   Since Bluetooth uses radio signals, the devices do not have to be in direct sight of the Bluetooth transmitter

ð  BLUETOOTH AND 802.B  

                                                                                                                                                                                                     

Bluetooth's biggest perception problem has nothing to do with Bluetooth itself. The meteoric rise in popularity of IEEE 802.11b (WiFi) wireless networking devices has left many users wondering if they need Bluetooth at all. IEEE 802.11b offers faster speeds and greater range than Bluetooth. To further confuse matters, the two systems share space in the unlicensed 2.4 GHz radio spectrum, and it is possible for Bluetooth and IEEE 802.11b systems to interfere with one another.

There's also a public perception that IEEE 802.11b and Bluetooth compete with one another. While both can be used to connect computers into an ad-hoc network, the two systems are really complementary technologies that meet very different needs. Refer to the table below for important fundamental differences between Bluetooth and IEEE 802.11b.

Contrasting Technologies
Here are important fundamental differences between Bluetooth and IEEE 802.11b
	Bluetooth	IEEE 802.11b
Access	Doesn't typically have an access point--devices on a Bluetooth PAN communicate directly with one another.	IEEE 802.11b allows mobility over a very large area. When out of range of one IEEE 802.11b access point, another takes over.
Use of Radio Band/Spectrum	2.4 GHz radio band/Frequency Hopping Spread Spectrum (FHSS)	2.4 GHz radio band/Direct Sequence Spread Spectrum (DSS)
QOS Features	Yes	A proposed extension will add this feature, paving the way for wireless IP telephones
Radio Signal	Weaker signal provides for more conservative use of battery power (designed for PDAs, wearable headsets, cell phones)	Stronger signal provides more power but uses 10 to 100 more power than Bluetooth (designed for notebook computers, where the additional current drain is negligible

 

v  Advantages & Disadvantages

ü  Advantages

1.      It eliminates the need of cables or wires for connecting various devices.

2.      The capital cost is low .

3.      Chips are available in very small size having area 0.9 cm square, and much smaller chip versions are in development.

4.      Almost  any electronic device can be connected.

5.      Unlike infra-red, Bluetooth does not require line-of-sight positioning of connected devices.

ü  Disadvantages

1.      The maximum range for this technology is 10 meter, which limits the space of PAN and/or limits the connection accessibility needed by other electronic devices to perform an action.

2.      The maximum capacity of data transmission with this technology one mega bit per second, which makes the information exchange very slow when handling large size files or folders.

v  Applications

Automatic communication between various devices within a small area makes it possible to provide unique and innovative services to the professional  workers using portable devices. Bluetooth technology has this potential and is coming along fast and quick. It will replace clumsy wires, make information transfer automatic and introduce many new applications, as follows

1.      The Bluetooth technology connects all office peripherals wirelessly. We can connect  PC or notebook to printers, scanners and faxes without cable attachments. 

2.      If digital camera is  Bluetooth enabled, we can send  video images from any location to any location without the hassle of connecting the camera to the mobile phone on the wire line phone.

3.      Bluetooth allows us to have three way phones. At home, your phone functions as a portable phone (fixed line charge). When you're on the move, it functions as a mobile phone (cellular charge). And when your phone comes within range of another mobile phone with built-in Bluetooth wireless technology it functions as a walkie-talkie (no telephony charge).

4.       We can connect wireless headset to mobile phone, mobile computer or any  wired connection to keep our hands free for more important tasks when we're    at the office or in car.

5.      

Automatic Message Delivery : Compose e-mails on  portable PC while you're on an airplane. As soon as you've landed and switched on your mobile phone, all messages are immediately sent.

6.      Upon arriving at the home, the door automatically unlocks, the entry way lights come on, and the heat is adjusted to pre-set preferences.

7.      There are in automobile’s navigation system, when the driver opens the car door with his or her palm pilot, the palm and navigation system automatically communicate and transfer driving instructions. 

v  Conclusion

This was an overview of Bluetooth giving insight to the key features and potential challenges of the technology. The technology occupies the 2.4 GHz ISM band sharing the bandwidth with potential competing standards. It defines a Personal Area Network (PAN) whereas others advocate a Wide Area Network (WAN) approach. It is best positioned as a short-range wireless standard designed with the same cost goals and similar or greater reliability and performance as the cable it replaces. Based on a frequency agile FHSS scheme it leverages hopping to avoid interference and it was not intended as a replacement for wireless LAN in a WAN scenario, because as yet it does not fully specify a hand over mechanism.

The importance of the Bluetooth SIG and how its specifications aid development of applications was highlighted, especially through the profiles, and their interoperability is assured through the qualification process. A flavour of the applications was explored through the functionality and where particular attention must be paid to the protocol stack for system segmentation. But to thoroughly investigate Bluetooth a list of further reading and applicable websites is given in the reference section. The latest specifications including the profiles are available from the Bluetooth SIG website. Reading specifications can seem a little ‘one dimensional’ but read in conjunction with a good book, whilst using a development tool from one of the Bluetooth silicon vendors, then the jigsaw pieces to really start to fit.

Still, with its all advantages, the Bluetooth technology is in its primary stages. Hence, we hope that, through the impending development phases, it will have the potential to address most of its current shortcomings.

v  rererences

ð  http://www.opengroup.org/bluetooth

ð  http://www.bluetooth.com

ð  http://www.palowireless.com

ð  http://grouper.ieee.org/groups/802/11/main

ð  J. Bray and C.F. Sturman, “Bluetooth: Connect Without Cables”, Prentice Hall.