Wireless Networking

05/EC/42 WIRELESS NETWORKING

WIRELESS NETWORKING

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Main Topic Sub Topic

1 Wireless LANs introduction peer-to-peer mode infrastructure mode WLAN Equipment access point outdoor LAN bridges IEEE 802.11 architecture IEEE 802.11 layers

2 Bluetooth introduction & history basic system architecture overview of protocol stack radio layer base band link manager protocol logical link control adoption protocol host controller interface security Why the Bluetooth way it is? significance of PINCODE in Bluetooth

3 The cellular concept introduction frequency reuse channel assignment strategies handoff strategies e. prioritizing handoffs

4 The multiple access techniques for wireless communication

introduction narrowband system wideband system frequency division multiple access time division multiple access code division multiple access Access schemes Coding Codes The spreading process Power control Hand over Multipath and rake receivers CDMA 2000 is 3G CDMA 2000 :delivering on 3G Advantage of CDMA 2000

5 GSM Architecture CDMA development Advantage of CDMA

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05/EC/42 WIRELESS NETWORKING Main switching center Visitor location resistor AnC EIR GIWU Geographical area of GSM network GSM function Transmission Management of GSM GSM services

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WIRELESS NETWORKING

Introduction:Over recent years the market for wireless communications has enjoyed tremendous growth. Wireless technology now reaches or is capable of reaching virtually everyLocation on the face of the earth. Hundreds of millions or is capable exchange information Everyday using pagers, cellular telephones, and the other wireless Communication products. With the tremendous success of wireless telephony and messaging Services, it is hardly surprising that Wireless communications is begging to be applied to the realm of personnel and business Computing. No longer bound by the harnesses of wired networks, peoples will be able to access and share information nearly anywhere they Venture. This article will try to answer some basic questions of why and where wireless local area networks can be used and present brief description of some one protocol that have been Developed with emphasis on IEEE802.11.

1. Wireless LANs:1. Wireless LANs:

The Wireless local area network is a flexible data communications system that can either replace or extend a wired LAN to provide added functionality. Using radio frequency (RF) technology, WLANs transmit & receive data over the air, through walls, ceilings & even cement structures, without wired cabling

A WLAN provides all the features & benefits of traditional LAN technologies like Ethernet and token ring, but without the limitations of being tethered to a cable. This provides greatly increased the freedom and flexibility the importance of WLAN technology however goes far beyond just the absence of wires. The advent of the WLAN opens up a whole few definition of what a network infrastructure can be instead it can move with the user and change as fast as the organization does.

For example business people stay connected us they move through out campus easily tapping into the resources of the wired network. Student and instructor can wirelessly access instant information during field trips or lab project .organization leasing temporary office space can setup a WLAN and they easily take the infrastructure with them when they move.

Just as wired LANs use copper or fibreoptic cable WLANs also use a medium: radio frequencies. Data is superimposed on to a radio wave through a process called modulation and this “carrier wave” then acts as the transmission medium taking the place of wire.

A WLAN can be configured in two basic ways: 1) peer-to-peer (ad hoc mode): This mode consists of two or more PCs equipped with Wireless adopter card but with no connection of wired network.

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2) client/server (infrastructure networking): offering fully distributed data Connectivity this mode typically consist of multiple PCs linked to a central hub That acts as a bridge to the resources of the wired network.

Introduction to LAN adopters:

Wireless adopters are made in the same basic from factors as their wired counter parts PCMCIA, card bus, PCI, and USB. They also serve the same Function enabling end users to access the network. In a wired LAN adopters provide the interface between the network operating system and the wire. In a WLAN they provide the interface between the network operating system and antenna to create Connection to the network.

Access point:

Essentially the access point is the wireless equipment of LAN hub. It receives buffers and transmits data between the WLAN and wired network, supporting a group of wireless user’s devices and access point is typically connected with the wireless devices by means of an antenna. The access point or the antenna connected to it is generally mounted high on a wall or on the ceilings .like the cell in a cellular phone network, multiple access point can support hand-off from one access point to another as the user moves from the area to area.Access points have range from under 20 meters to 500mts. And a single access point can Support between 15 and 250 users depending on the technology configuration and use. It is relatively easy to scale Weans by adding more access point.

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Server

Intel® PRO/Wireless 2011B LAN PC Card


Outdoor LAN bridges:

Out door LAN bridges are use to connect LANs in different building. When the cost of burying a fiber optic cable between buildings is considered especially if there are barriers such as highway or bodies of water in the way a WLAN bridges can be an economical alternative to recurring lease line charges. LAN bridges products support fairly high data rates and ranges pf several miles with the issue of the line-of-sight directional antennas. Some access point can also be used as a bridge between buildings of relatively close proximity.

Introduction to IEEE 802.11:

In IEEE’s proposed standard of wireless LANs (IEEE 802.11) there are two different ways to configure a network.

1. ad hoc network2. infrastructure as explain above

The IEEE 802.11 standard places specification on the parameters of the both physical (PHY)and medium access control(MAC) of the network .The PHY layer which actually handles the transmission of data between nodes can use either direct sequence spread spectrum, frequency hopping spread spectrum or infrared (IR) pulse position modulation. IEEE 802.11 makes provisions for data rates of either 1Mbps or 2Mbps & calls for the operation in the 2.42.4835GHz frequency band (in the case of spread spectrum transmission) which is an unlicensed band for industrial scientific and generally medical (ISM) application and 300-428000 GHz for IR transmission. Infrared is generally considered to be more secure to eavesdropping because IR transmissions require absolute of link of site links(no transmission is possible outside simply connected space or around corners ) as opposed to RF transmissions which can penetrate walls and be intercepted by third party’s knowingly. However infrared transmission can be adversely affected by sunlight and the spread spectrum protocol of 802.11 does provide some rudimentary security for typical data transfers.

The MAC layer is a set of protocols which is responsible for maintaining order in the use of a shared medium. The 802.11 standard specifies a carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In this protocol when a node receives a packet to be transmitted it first listens to ensure no other node is transmitting. If the channel is clear it then transmits the packet. Otherwise it chooses a random “back off factor” which determines the amount of time the node must wait until it is allowed to transmit its packet. During periods in which the channel is clear the transmitting node decrement it back off counters. (When the channel is busy it does not decrement its back off counter). When the back off counter reaches zero the node transmit the packet. Since the probability that two nodes will choose the same back off factor is small collision between packets are minimized. Collision detection as is employed is in Ethernet can not be used for the RF transmission of IEEE 802.11. The reason for this is that when a node is transmitting it can not hear any other node in the system which may be transmitting since its own signal will be drawn out any others arriving at the node. Whenever a packet is to be transmitted the transmitting node first sends out a short ready to send (RTS) packet

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05/EC/42 WIRELESS NETWORKINGcontaining information on the length of the packet. If the receiving node hears the RTS it responds with a short clear to send (CTS) packet. After this exchange the transmitting node its packet. When the packet is received successfully as determined by a cyclic redundancy check (CRC) the receiving node transmits an acknowledgement (ACK) packet. This back and forth exchange is necessary to avoid “hidden node” problem .as shown below node A can communicate with node B and node B connected with node C. However node a can not connected with node C. Thus for instance although node A may sense the channel to be clear node C may in affect be transmitting to the node B. the protocol described above alerts node A that node B is busy and hence it must wait before transmitting its packet.

2. Bluetooth2. Bluetooth6

Intel® PRO/Wireless 2011B LAN Access point

Intel® PRO/Wireless 2011B LAN PC Card

TheHiddenNode Problem


Bluetooth is the name given to technology standard using short range radio links instead to replace the cable connecting portable and\or fix electronic devices. The Standard defines uniform structure for wide range devices the communicate with each other with minimal user effort. Its key features are robustness low complexity low power & low cost which make it especially suited to mobile hand held devices. The technology also offers wireless access to LANs, PSTN, the mobile phone network and the internet for a host of home appliances and portable hand held interfaces.

The standard has achieved global acceptance such that any Bluetooth anywhere in the world can connect to other Bluetooth devices in proximity regardless of brand. Bluetooth enabled electronic devices Connect & communicate wirelessly via short-range, ad hoc networks called Pico nets. Each unit can simultaneously belong to several Pico nets. These Pico nets are established dynamically and automatically as Bluetooth devices enter and leave the proximity.

Bluetooth history:

L.M. Eric son of Sweden invented Bluetooth in 1984. The standard is named after Herald Blaatand “Bluetooth” II king of Denmark 940 to 981 AD. A runic stone has been erected in his capital city Jelling that depicts the chivalry of herald and the “runes” say:

Herald Christianized the Danes.Herald controlled Denmark and Norway.Herald thinks notebook and cellular phones should seamlessly communicate. The

Bluetooth special interest group was founded by ericsson, IBM, Intel, Nokia, Toshiba in February 1998 to develop an open specification for short range wireless connectivity. The group is now also promoted by 3com Microsoft; agree system (formula lucent) and Motorola more than 2500 companies have joined the SIG.

Bluetooth Architecture:

The system architecture for Bluetooth is briefly described here the system design has been segmented in to various almost independent layer for conceptual ease of description. These layers are describing in detail in the core Bluetooth specification. The design specification also describes certain properties for certain common classes of application to be implemented over Bluetooth to achieve uniformity across diverse manufactures. These are described in the profile of the Bluetooth specification.

Overview of the protocol stack:

The protocol stack consists of a radio layer at the bottom that forms the physical connection interface. The base band and link manager protocol (LMP) that resides over it are basically meant to establish and control link between Bluetooth devices. These three bottom layer are typically implemented in hardware &firm ware. The host control layer is required to interface to the Bluetooth hardware to the upper protocol L2CAP (logical link

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05/EC/42 WIRELESS NETWORKINGcontrol & adoption protocol) . The host controller is required only when the L2CAP resides in software in the host if the L2CAP is also on the Bluetooth module this layer may not be required as than the L2CAP can directly communicate with the LMP and Base band. Application resides above L2CAP.The following subsection gives a brief description of each layer .

Radio layer:

This link operate in the unlicensed ISM around 2.4GHz and uses spread spectrum communication the band extend from 2400-2483.5MHz in a vast majority of countries and this whole range is utilized for optimizing the spectrum spreading .However for some countries with a small ISM band a down scaled version is also provided spread spectrum the frequency hopping technique is used. As multiple uncoordinated networks may be exist in this band cause interference, fast FH & short data packets are used. This is because error rate may be high especially due to strong interference from micro wave ovens that operate at this frequency. CVSD coding has been adopted for voice which can withstand high bit error rates. Also the packet headers are protected by a highly redundant error correction scheme to make them robust to error.

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Application

TCS, SDP, RECOMM

Base band

L2cap

HCL

LMP

Radio

Data Data

Figure 1: The Bluetooth protocol Stack.

05/EC/42 WIRELESS NETWORKINGThe Frequency hops are Fixed at 2402+ K MHz Where K=0, 1……… 78.The nominal hop rate is 1600hops/sec. This gives a single hop slot of 625 micro seconds. The modulation used is Gaussian prefiltered binary FSK (frequency Shift Keying). The Gaussian filter has BT= 0.5

The transmitter power is fixed at 0dBm for a 10m range while it can be increased to 200dBm for 10m range while it can be increased to 200dBm for a 100m range. Various restrictions are specified on clock accuracies and drift, spurious emissions and radio frequency tolerance.

The Base band is the layers that control the radio. The frequency hop sequences

are provided by the layer. Base band also takes care of lower level encryption for secure links. The packets handling over the wireless link is the responsibility of Base band. Two types of links can be

Base band:

Synchronous connection less. These links are meant for synchronous data typically Voice.

Asynchronous connection oriented. These links may be used for data transfer applications which do not require a synchronous link.

The Base band provides the functionalities required for devices to synchronized their clocks and establish connection. Inquiry procedures for discovering the address of devices in proximity are also provided. Error connection for packets is provided depending on the type of packets. Various packet types are specified for some common application deferring in their data capacity and error correction overheads. Five different channel types are provided for control information, link management information, user synchronous data, user asynchronous data, and is synchronous data. Data whitening is also carried out of this layer. The function required for generating encryption keys and link keys are defined.

Link manager protocol:

The basic Function of LMP can be classified as;a) Pico net managementb) Link configurationc) Security Functions

A Pico net is a group of devices connected to a common channel which identified with its unique hop sequences. One of the devices usually the one which first initiated the connection is the master. Up to seven other devices usually the one which first initiated the connection is the master. And many more could be connected in the low power “parked” state. The devices on the Pico net can communicate with each other over SCO or ACL links. The channel sharing is managed by the master with the help of link manager on each device. Any two or more devices that need to communicate must

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05/EC/42 WIRELESS NETWORKINGestablish a Pico net among themselves. Devices can be part of many Pico nets at same time.

Pico net and scatter net:

a) a Pico net between two devicesb) a Pico net between many devices c) A scatter net, a Combination of Pico nets with some devices common the

Pico nets.

The LMP Provides the functionality to attach and detach slaves, switch roles between a master and a slave to establish ACL/SCO links. LMP also handles the low power modes-hold, sniff and park, designed to save power, when the device does not have data to send.Link configuration tasks include setting link parameters, quality of service and power control if the device supports it. Authentication of devices to be linked and managing link keys is also taken care by LMP.

Logical link control adoption protocol:

This is the protocol with which most applications would interact unless a host controller is used. The basic functions of the L2CAP are:

a) MULTIPLEXING:The protocol must allow multiple applications to user link between to devices simultaneously.

b) SEGMENTATION AND RESSEMBLY:The protocol must reduce the size of packets provided by applications to the size of packets accepted by base band. L2CAP it self Accepts packets size up to 64kb but the Base band Packets can accept a payload of at

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M

S

M

S

S

S

M S

M

S

S

S

M

05/EC/42 WIRELESS NETWORKINGmost 2745bits. The reverse procedure that combining the segmented packets in the proper order has to be carried out for received packets.

c) QUALITY OF SERVICE:L2CAP allows applications to demand QoS on the certain parameters like peak bandwidth latency and delay variation. L2CAP checks if the link is capable of providing it and provides it if possible.

Basically L2CAP provides the network layer functions to application and higher protocol

Host controller interface:

The basic structure showing the host controller layers are fitted into the protocol stack is shown in fig shown below:

For many devices the blue tooth enabling module may be added as a separate card for instance or a PC or a laptop the Bluetooth hardware May be added as a PCI card or a USB adapter. Hardware modules usually implement the lower layers radio Base band and LMP. Then the data to be sent to LMP and Base band travels over the physical bus like USB. A driver for this bus is required on the “host” that the PC and a “host controller interface “the required on the Bluetooth layers L2CAP and above are in software and the lower ones in hardware the following Extra layers are at least Required:

Bluetooth host

Other higher Layer driver

HCL driver

Physical bus driver (USB, PCcard, other)

Bluetooth host

Other higher Layer driver

HCL driver

Physical bus driver (USB, PCcard, other)

Bluetooth Hardware

Base band Controller

Firmware link manager

HCL firmware

Bluetooth Hardware

Base band Controller

Firmware link manager

HCL firmware

Physical firmware

Physical firmware

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HCI Driver:

This is the drive for host controller interface. It resides in the above the Physical Bus and Formats the data to be accepted by the host controller on the Bluetooth hardware. Host controller interface:

This resides on the Bluetooth hardware and accepts communication over the physical bus.

Application:

The L2CAP may be accessed directly by the applications or thought certain support protocols like RFCOMM, TCS and SDP mentioned earlier. The applications may themselves run PPP (point to point protocol) FTP (file transfer protocol) or other specific protocols as required by the application. An application many usage models have been proposed by several manufacturers. Some of these:Three in one phone:

A single handset Works as an intercom in the office (no call charges) as a PSTN phone whenever an access point to the PSTN is available and as a mobile otherwise.

The briefcase link:

The RF link does not need line of sight. So a mobile could connect to a laptop even while it is in the briefcase and allow access to its facilities like email.

The Automatic synchronize:Seamless connectivity between the user’s PDA’s laptop and mobile will allow

applications to automatically update and synchronize schedules and the other data when modifications are made on one device.

Car kits:

Hands free devices will allow users to access their phones without letting their hands off the steering wheel.

Apart from these a large variety of other applications in home automation data sharing during meeting without the use of extra equipments, testing Factory devices over a wireless hand held while Walking through, toddler alarms, security system, network access at public places and hidden computing have been suggested some of Which have been successfully demonstrated.

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Bluetooth security:

The Bluetooth system is intended to be used as uniform interface to on off person’s information sources and thus be expected to transfer sensitive personal data. Security of the data is thus understandably an important issue. Further Bluetooth devices are expected to be omnipresent and at some places the access to these devices by public users may have to be restricted. This calls for authentication procedure to be provided. AsThe channel used in wireless and the packets being transmitted are available to all members of a Pico net the security initialization Communication should not send any information that can allow an authorized device to know the secret authentication keys. Further the mechanisms should be appropriate for a peer- to-peer environment. The method s adopted by the Bluetooth Standards care of these issues. This scheme used refereed to as the challenge Response scheme.

The application may itself encrypt its data for added security. This can add to the safety of the data but most of the authentication is based on the link level security procedures, as it is difficult to achieve uniformity in this step at the application level.

The Basic Structure:

The procedure for security use four values: the device address (which is public), a private authentication (128 bites), private encryption key (8-128 bits, configurable) and a random number. As the key have to be secret they can not be obtained by inquiry. The exchange procedure will be described below. The security procedure requires a secret PIN to be known to the user (or stored by his application) for accessing a particular device. The main steps in the procedure are:

An initialization key is generated using the PIN the length of the PIN, a random number and a device address. The dependence on the device address makes it more difficult for a fraudulent device to try a large number of PINs as each has now to be a tired with different device addresses.

An authentication procedure is carried out using the challenges response scheme. The verifier unit sends random numbers generated by a specific process for the authentication. This random number is such that a claimant device that has the correct initialization key (or a link key if the devices had exchanged that during an earlier communication) and required device address will be able to produce a response number that is known to the verifier. This response number is sent back and checked by the verifier.

The claimant may also carry out verification on the verifier using the similar procedure as above.

Each Bluetooth units has a unit key, installed in its non volatile memory. The device is treated as the devices are capable of handling this. Otherwise the unit key of one of initialization key to encrypt this unit key and sends it to the other device that decrypts it using the initialization key exchange earlier.

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05/EC/42 WIRELESS NETWORKINGThe second device may add its own unit’s key to the unit key of the First device

and generates a combination link key if both the devices are capable of handling this. Otherwise the unit key of one of initialization key is discarded.

An encryption key is now generated from the link key, a random number and another number obtained from a fix procedure. Both the device can generate this encryption key as all the required information is known to both the devices. This key with some modification as described later is used to encrypt data pay loads.

The link key is remembered. If another link is to be established between the two devices at a later time, this link key can be directly used. This eliminates the need to send keys over the channel again. Thus, data can be transmitted securely with minimum user interaction.Why Bluetooth the way it is?

This section attempt to explain some of the design and technology tradeoffs in Bluetooth and the main consideration in the wireless link design are explored.

Ad the connectivity: Most wireless communication systems like the public cellular phone networks-

GSN, DAMPS, IS-95 other private networks like Hiperlan 2, DECT or personal handy phone networks –GSN, Damps, IS-95 or other private network like Hiperlan 2 ,DECT or personal handy phone system, use a network architecture in which the radio units: Base stations and mobile terminals are strictly distinct. This advantageous in design as channel access, channel allocation, traffic control, interference minimization etc. can be taken care by the base station, making the design of mobile terminals simpler. In ad hoc networks, there is no difference between radio units. Communication is peer to peer with no central controllers. Conventionally in ad hoc Wireless network, all devices in Bluetooth usage models however even this is not sufficient as the numbers of Bluetooth devices. In given region of space may be very large and only a few of them may need to communicate among themselves making mutual coordination among them very difficult and unlikely .this has led to the concept of scatter nets: a group of networks in the same space but communicating over different channels, with some overlapping devices. There need not be any coordination among devices belonging to different networks with in the scatter nets.

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Base station

Mobile admit

Figure:a) a cellular network with squares representing stationary base stationb) a conventional ad hoc system c) Scatter ad hoc network.

Thus it is clear that the Bluetooth system due to its very nature of application will have to use scatter net kind of ad hoc connectivity. The major consideration in this design is:

a) Choice of the radius spectrum b) Connection establishment and determining units in range that can be connected.c) Choice of the multiple access Schemed) Channel allocation e) Medium access control f) Service prioritization. Voice may have higher priority over data.g) Interference, mutual and from other Sources.h) Power Consumption.i) Production of data over the channel

The choice of the radius spectrum:

The issues to be considered here are:There will not be any coordination between operators as in a cellular

network. The spectrum must be available world wide without the need for licenses. This will make the interoperability truly global. This is important, as mobility is one main advantage of Bluetooth devices.

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05/EC/42 WIRELESS NETWORKINGThis consideration encourages the adoption of the ISM band around 2.45 GHz.

that is globally available. It is governed by different regulation in different parts of the world and hence the system must be designed considering the minimum common availability.

Medium access control:

The choice of the medium, access scheme must take into account the lack of coordination among devices in the ISM band. FDMA (Frequency division multiple access) can not be used, as it dose not satisfy the frequency spreading characteristics of the ISM spectrum. TDMA (time division multiple access) can not be used, as it dose nit satisfy the frequency spreading characteristics of the ISM spectrum. TDMA (time division multiple access) require a strict timing synchronization that is rather cumbersome for ad hoc connections. CDMA (code division multiple access) is the clear choice as it fulfills the spreading requirements and can work with uncoordinated systems. The next question in DS (direct sequence) of FH (frequency hopping). DS suffers from certain disadvantages like the requirement of a common timing reference which is not good idea in the scatter net ad hoc scenario. Further due to the near far problem a coordinated power control is required. Finally high data rates will require higher chip rates which is not advisable due to the wide bandwidth and the resulting interference and due to excessive current drain. FH, apart from taking care of these problems, offers other advantages. The average signal is spread over a large bandwidth but the in instantaneous signal is only in a narrow band making it easy to filter out a lot of potential interference. Bluetooth thus uses FH-CDMA. To keep interference effects minimal and to make the data robust very short brackets are used and the Frequency hop rate is kept is kept high 1600 hops/sec.Connection establishment:

The environment of a Bluetooth will change dynamically with fair amount of rapidity. Further the number of devices will be quite large and new devices will usually be had to access whenever the user takes its device outside his usual work place. Then how to do the device Find each other and establish links over the CDMA channel? It is important that the devices should not depend on manual command to establish connections. So the standard must provide for procedures using which a device can discover the address of the other Bluetooth devices in its proximity without any user support. Further there synchronization to be achieved between the two devices.

Medium access control and Channel allocation:

As noted earlier a large number of independent channels need to exist in the same space each serving its own participants on the modulation scheme used the data rate available is the same space each serving its participants on the modulation Scheme used the data rate available is 1 Mbps. So to conserve capacity, only the units that need to transfer data among themselves should be put on a particular channel. For this reason the concept of

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05/EC/42 WIRELESS NETWORKINGPico nets has been introduced. Each channel is identified with identified with a unique hop sequence and the clock of one coordinating devices on that channel refer to as a master. This channel called a Pico net and multiple Pico nets that overlap in terms of devices connected are referred to as a scatter net. To simplify implementation of duplex communication TDD has been applied. Each device transmits in alternate slots and uses the intermediate slots to receive.

Further a 1/3 rate Forward Error Check (FEC) is applied Which repeats each bit three times For protection of data various levels of redundancy are supported differing in their overheads.

The required packet type may be used by an application as per its requirement. For the synchronous Voice link is difficult to retransmit a packet in case of error hence the CVSD voice coding is employed which are robust to high bit error rates.

Modulation scheme used:

In the ISM band the band width of signals is limited to 1 mega hertz.For robustness a binary modulation scheme has been chosen. This is what places the data rate limit of Mbps. For FH systems and support for burst data traffic a non coherent detection scheme is most appropriate. A Gaussian profiteered frequencyShift keying (FSK) is used with a nominal modulation index of 0.3. The time band width product of the Gaussian pre filter is 0.5. Logical ones are sent as positive frequency deviational and Zeros as negative frequency deviations. In this technique demodulation can be simply accomplished by a limiting FM discriminator thus enabling the implementation of low cost radio units.

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FIG: 2 The TDD scheme in Bluetooth

6.25 Ps

Stave

Master

F (k) F (k < 1) F (k < 2)


Protection of data:

Blue tooth devices will usually carry and transmit a person’s very personal data as they will be the interface to most of her valuable information resources. Thus it is essential that no compromise on security be made while shifting from the wired interfaces to wireless ones. For this reason it is necessary to provide data encryption facility. Further services offered through blue tooth excess points may have to be limited to a certain setoff authorized users. This means that the standard should provide some mechanism to allow restricted excess and identification of registered devices. Keeping both this requirements in mind Bluetooth provides both link level encryption and authentication. These are controlled by providing a PIN to user this number must be known to the users if he has to secured device. Thus access control can be implemented. To ensure safety of encryption keys are used. Further these keys are not transmitted over the wireless channel rather other parameters are limited using which in combination with the information specifically Known to authenticated devices, the keys can be generated. Different type of keys has been provided to allow for varying computing power on non uniform devices .Apart from encryption at link level which uses 128 bit keys regarded as fairly safe currently there is always an option to further encrypt at the application layer itself. Link level encryption however allows a universal standard.

The master of the Pico net manages which devices transmit when. Thus the channel can be effectively shared. One may note that there are 79 Frequencies in the hop sequence opening the possibility for 79 orthogonal frequency hop sequences that can provide 80 Mbps of data transfer capacity within a local space. However as the Bluetooth device

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Zero Crossing Error

Ideal Zero Crossing

Time

FDD scheme in Bluetooth

05/EC/42 WIRELESS NETWORKINGdose not coordinate the hop sequences will not be orthogonal 80 Mbps will not be reached.

Service prioritization:

Bluetooth devices intend to provide both voice communications as in mobile phones head sets on voice browsers and also data communications to access networks in the traditional way. The voice channel must be synchronous and provide guaranties on delay and latency for acceptable voice quality .thus a separate link to support Voice is required which must be given priority over asynchronous data. Hence Bluetooth uses two Kinds of links, Asynchronous connectionless ACL Synchronous connection oriented – SCO

The SCO link is a point to point linking in which resources are reserved TDD slots at regular intervals are reserved to guarantee the Continuity of the voice channel. The remaining slots can be used by ACL links. The SCO links is such that even during paging inquiry and scan procedures, which may be require for some parallel application the synchronous packets can be transferred at their fixed slots.

Interference:

The ISM band being an unnerved band will have a variety of heterogeneous transmitter in its frequency range. Further microwave ovens and lighting sources emit in this band which was in fact the original reasons for unlicensing this band. Another source that may be expected to be present in the same areas as the Bluetooth environment would be the 30d Bm WALN transmitters. Thus the Bluetooth devices must be immune to such interference. Two common approaches are suppression and avoidance.

Suppression, which can be obtained by coding or DS spreading, makes less sense For Bluetooth because the near far ratios may be too high to handle with practical attainable coding gains. Interference avoidance is more attractive because the desired signal is transmitted at points in frequency and/or time where interference is low or absent. Avoidance in frequency is more practical because most radio systems are band limited and it should be possible to find some band where the interference is fairly low, further robustness to errors is required as interference in short bursts due to collision at higher layers above the physical link. For this purpose Bluetooth has chosen to provide an acknowledgement based scheme with automatic repeat request (ARQ). The header information in packets that is very critical to the link operation is protected first by a cyclic redundancy check and

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05/EC/42 WIRELESS NETWORKINGWhat is the significance of PINCODE TO Bluetooth?

The PINCODE is a secret code provided for security applications. This number has to be manually entered by the user or stored by his application. Once the devices Knows the PIN of the device it wants to connect to it can start the security procedures relevant to authentication and encryption. In some devices like access points or head sets which do not have an interface good enough to allow the users to enter a PIN the PIN is preferred and used by other devices to connect to it.

3. The cellular concept:3. The cellular concept:

Introduction:

The cellular concept was a major break through in solving the problem of spectral congestion and user capacity. It offered very high capacity in a limited spectrum allocation without any major technological changes. The cellular concept is a system level idea which calls for replacing a single, high power transmitter with many low power transmitters each providing coverage to only a small portion of the service area. Each base station is allocated a portion of the total number of channels available to the entire system and nearby base stations is assigned different groups of channels so that all the available channels are assigned to a relatively small number of neighboring base station neighboring base station are assigned different groups of channel so that the interference between base station (and the mobile user under their control) is minimized. By systematically spacing base station and their channel groups throughout a market the available channels are distributed throughout the geographic region and may be reused as many times as necessary so long as the interference between co channel stations is kept below acceptable levels.

As the demand for service increases (i.e. as more channels are needed within a particulars market) the number of base stations may be increased (along with a corresponding decrease in transmitter power to avoid added interference) thereby providing additional radio capacity with no additional increase in radio spectrum. This fundamental principle is the foundation for all modem wireless communication systems, since it enables a fix number of channels to serve an arbitrarily large number of subscribers by reusing the channels throughout the coverage region. Further more the cellular concept allows never piece of subscriber equipment within a country or a continent to be manufactured with the same set of channels so that any mobile may be used anywhere within the region.

Reuse:

Cellular radio systems rely on an intelligent allocation and reuse of channels throughout a coverage region. Each cellular base station is allocated groups of radian channels to be used within a small graphic area called a cell. Base station in adjacent cells assigned channel groups which contain completely different channels than neighboring cell. The base station antennas are designed to achieve the desire coverage within a

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05/EC/42 WIRELESS NETWORKINGparticular cell. By limiting the coverage area to within the boundaries of a cell the same group of channels may be used to cover different cells that are separated from one another by distances large enough to keep interference levels within tolerable limits. The design process of selecting and allocating channels groups for all of the cellular base stations within a system u\is called frequency reuse or frequency planning.

The figure shown below illustrates the concept of cellular frequency reuse where cells labeled with the same letter use the same groups of channels. The frequency reuse plan is overlaid a map to indicate where different frequency channels are used. The hexagonal shape shown in the figure is conceptual and is a simplistic model of the radio coverage for each base station but it has been universally adopted since the hexagon permits easy and manageable analysis of a cellular system. The actual radio coverage of a cell is known as the footprint is amorphous in nature a regular cell shape is needed for systematic system design and adaptations for future growth. While it might seem natural to choose a circle to represent the coverage area of base station adjacent circles can not be overlaid upon a map without leaving gaps or creating overlapping regions. Thus when considering geometric shapes which cover an entire region overlap and with equal area there are these sensible choices – a square, an equilateral triangle. And a hexagon. A cell must be designed to serve the weakest mobiles within the footprint and these are typically located at the edge of the cell. For a given distance between the centre of the polygon and its farthest perimeter points the hexagon has the larges area of the three. Thus by using the hexagon

Geometry the fewest number of cells can cover a geographic region and the hexagon closely approximates a circular radiation pattern which would occur for an omni directional base station antenna and free space propagation. Of course the actual cellular footprint is determined by the contour in which the given transmitter serves the mobiles successfully.

When using the hexagons to model coverage areas base station transmitters are depicted as either being in the centre of the cell or on three of the six cell vertices normally omni directional antennas are used in centre excited cells and sectored directional antennas are used in corner excited cells. Practical consideration usually donor allows base station to be places exactly as they appear in the hexagonal layout. Most system designs permit a base station to be positioned up to one for the of the cell radius away from the idea location.

To understand the Frequency reuse concept consider a cellular system which has a total of S duplex channels available for use. If each cell is allocated a group of k channels (k<S) and if the of S duplex channels are divided among N cells into unique and disjoint

21

B

C D

A E

D

C

E

F

A

G F

B G

A E

D

C

F

B

G

05/EC/42 WIRELESS NETWORKINGchannel groups which each have the same number of channels, the total number of available radio channels can be expressed as S=k*N

The N cells which collectively use the complete set of available frequencies is called cluster. If a cluster is replicated M times within the system the total umbers of duplex channels C can be used as the measure of capacity and is given byC=M*S

As seen from the above equation the capacity of a cellular system is directly proportional to the number of times a cluster is replicated in the fix service area. The factor N is called the cluster size and is typically equal to 4, 7, or 12. If the cluster size N is reduced while the cell size is kept constant more cluster are required to cover a given area and hence more capacity is achieved. A large cluster size indicates that the radio between the cell radius and the distance between co located much closer together. The value for N is a function of how much interference or base station can tolerate while maintaining sufficient quality of communications. For a design view point the smallest possible value of N is minimum useable signal for acceptable voice quality at the base station receiver (normally taken as between 90 dBm to 100 dBm) a slightly stronger signal level is used as between 90 dBm to 100 dBm) a slightly stronger level is used as a threshold at which a handoff is made. This margin given by = phandoff – P minimum useable cannot be too large or to small. If is too large or a small. If is too large unnecessary handoffs which burden the MSC may occur and if too small there may be insufficient time to complete handoff before a call is lost due to weak single condition therefore is chosen carefully to make this conflicting requirements the Figure shown below illustrate a handoff situation the first demonstrates the case where a handoff is not made and the signal drops below the minimum Acceptable level to keep the channel active. This dropped call event can happen when there is an excessive delay by the MSC in a assigning a handoff or when the threshold is set to small for the handoff time in the system. Excessive delays may occur during high traffic conditions due to computational loading at the MSC or due To the fact that no channels are available on any of the nearby base stations (thus Forcing the MSC to wait until a channel in a nearly cell becomes Free)

In deciding when to handoff it is important to ensure that the drop in the measured signal level is not due to momentarily fading and that the mobile is actually moving away from the base station. In order to ensure this the base station monitors the signal level for a certain period of time before a handoff is initiated. This running average measurement of single strength should be optimized so that unnecessary handoffs are avoided. While ensuring that necessary a handoffs are avoided. While ensuring that a handoff is completed before a call is terminated due to a poor single level. The length of time needed to decide if a handoff is necessary depends on the speed at which the vehicle is moving. If the slope of the short term average received signal level in a given time interval is steep the handoff should be made quickly. Information about the vehicle speed which can be useful in handoff decisions can also be computed from the statistics of the received short term Fading single at the base station.

22


Figure 3.2 method of locating co-channel cell in a cellular system. In this example N = 19 (i.e... I =3, j=2). (Adapted from [Oet83] c IEEE.)

The time over which a call may be maintained within a cell without handoff is called the dwell time. The dwell time of a particular user is governed by number of factors including propagation, interferences, distance between the subscriber and the base station, and other time varying effects. The statistics of dwell time vary greatly depending on the speed of the user and the type of radio coverage. For e.g. in mature cells which provides coverage for vehicular highway users Desirable in order to maximize capacity over a given coverage area. The frequency reuse factor of a cellular system is given by 1/N. since each cell within a cluster is assigned 1/N of the total available channel in the system.

Channel assignment strategies:For efficient utilization of the radio spectrum a frequency reuse scheme i.e.

consistent with the objectives of increasing capacity and minimizing interference is required. A variety of channel assignment strategies have been developed to archive these objectives. Channel assignment strategies can be classified as either fixed or dynamic. The choice of channel assignment strategy impacts the performance of the system particularly as to how calls are managed when a mobile user is handed off from one cell to another.

In a fix channel assignment strategy each cell is allocated a predetermined set of voice channels. Any call attempt within the cell can only be served bay the unused channels in that particular cell. If all the channels in that cell are occupied the cell is blocked and the subscriber does not receive service. Several variations of the channels in the fixed assignment strategy exist. In one approach called the borrowing strategy a cell is allowed to borrow channels from a neighboring cell if all of its own channels are already occupied. The mobile switching center (MSC) supervises such borrowing procedures and ensures that the borrowing of a channel does not disrupt or interfere with any of the cells in progress in the donor cell.

In a dynamic channel assignment strategy voice channel are not allocated to different cells permanently. Instead each time a call request is made the service base station request a channel from the MSC. The switch then allocated the channel to requested cell following an algorithm that takes into account the likelihood of future

23

A

05/EC/42 WIRELESS NETWORKINGblocking within the frequency of use of candidate channel the reuse distance of the channel and other cost function.

Accordingly the MSC only allocates a given frequency if that frequency is not presently in use in the cell or any other cell which falls within the minimum restricted distances of frequency reused to avoid co channel interference. Dynamic channel assignments the like hood of blocking which increases the trucking capacity of the system since all the available channels on a market are accessible to all the cells. Dynamic channel assignment strategy is require the MSC to collect real time data on channel occupancy, traffic distribution and radio signal strength indication (RSSI) of all channels on a continues basis. This increases the storage and computational load on the system but provides the advantage of increased channel utilization and decreased probability of a blocked call.

Hand Of Strategist:

When a mobile moves into a different cell while a conversation is in progress the MSC automatically transfer the cell to a new channel belonging to the new base station. This hand off operation not only involves identifying the new base station but also requires that the voice and control signals to channels associated with the new base station.

Processing handoffs in an important task in any cellular radio system. Many handoff strategies priorities handoff request over call initiation requests when allocating unused channels in a cell site. Handoff must be performed successfully and as infrequently as possible and be imperceptible to the users. In order to meet these requirements system designers must specify an optimum signal level at which to initiate a handoff. Once a particular signal level is specified as the most users tend to have a relatively constant speed and travel along fixed and well defined paths with good radio coverage in such instances the dwell time for an arbitrary user is random variables with a distribution that is highly concentrated above the mean dwell time. On the other hand for users in dense cluttered micro cells environments there is typically a large variation of dwell time about the mean and the dwell times are typically shorter than the cell geometry would otherwise suggest. It is apparent that the statistics of dwell time are important in the practical design of handoff algorithms.

In first generations analogue cellular systems signal strength measurements are made by the base station and supervised by the MSC. Each base station constantly monitors the signal strength of all of its reverse voice channels to determine the relative location of each mobile user with respect to the base station tower. In addition to measuring the RSSI of calls in progress within the cell a spare receiver in each base station called the locater receiver is used to scan and determine signal strengths of mobile users which are in neighboring cells. The locator receiver is controlled by the MSC and is used to monitor the signal strengths of users in neighboring cells which appear to be in

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05/EC/42 WIRELESS NETWORKINGneed of handoff and reports all RSSI values to the MSE. Based on the locater receiver signal strength information from each base station. The MSC decides if a handoff is necessary or not.

In today's second generation system handoff decision are mobile assisted. In mobile assisted handoff (MAHO) every mobile station measures the received power from surrounding base stations and continually reports the result of three measurements to the serving base station a handoff is initiated when the power received from the base station of the neighboring cell begins to accede the power received from the current base station by a certain level or for a certain period of time. The MAHO method enables the cell to be handed over between base stations at a much faster rate than in first generation analog systems since the handoff measurements are made by each mobile and the MSC no longer constantly monitors signal strength. MAHO particularly suited for micro cellular environments where handoff is more frequent.

During the course of a call if a mobile moves from on cellular system to a different cellular system controlled by a different MSC and intersystem handoff becomes necessary. An MSC engages in an intersystem handoff when a mobile signal becomes weak in a given cell and the MSC cannot find another cell within its system to which it can transfer the cell in progress. There are many issues that must be addressed while implementing an intersystem handoff. For instance a local call may become a long distance call as mobile moves out of its home system and becomes a roamer in a neighboring system. Also capability between the two MSC s must be determined implementing an intersystem handoff.

Different system has different policies in methods for managing handoff requests. Some systems handle handoff request in the same way they handle originating calls. In such systems the probability that a handoff request will not be served bay new base station is equal to the blocking probability of incoming calls. However from the user’s point of view having a call abruptly terminated while in the middle of the conversation is more annoying than being blocked occasionally on a new call attempt. To improve the quality of service as perceived by the users. Various methods have been device to priorities handoff request over call initiasition request when allocating voice channels.

Title:One method for giving priority to handoff is called the guard channel concept

whereby a fraction of the total available channels in a cell is received exclusively for handoff request from ongoing calls which may be handed off into the cell. This method has the disadvantages of reducing the total carried traffics as fewer channels are allocated to originating cells. Guard channels however offer efficient spectrum utilization when dynamic channel assignment strategies which minimize the number of required guard channels by efficient channels based allocation are used.

Queuing of handoff request is another method to decrease the probability of forced termination of a call due to lack of available channels. There is a trade off between the decrees in probability of forced termination and total carried traffic. Queuing of handoff is possible due to the fact that there is a finite time interval between the time received signal levels. The delay time and size of the queue is determined from the traffic pattern of the traffic pattern of the particulars service area. It should be noted that queuing does not guarantee a zero probability of forced termination.

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4. Multiple access techniques for wireless communication:4. Multiple access techniques for wireless communication:

Introduction to Multiple Accesses:Frequency division multiple access (FDMA) time division access (TDMA) code

division multiple access (CDMA) are the three major access techniques used to share the available bandwidth in a wireless communication system. These techniques can be grouped as narrow band and wide band system depending upon how the available bandwidth is allocated to the depleting technique of a multiple access system is usually described along with the multiple access schemes.

Title:The term narrow band is used to relate the bandwidth of a single channel to the

expected coherence bandwidth of the channel. In a narrow band multiple access system the available radio spectrum is divided into a large number of narrow band channels. The channels are usually operated using FDD. To minimize interference between forward and reverse links on each channel the frequency separation is made as great as possible within the frequency spectrum while still allowing in inexpensive duplexers and a common transceiver antenna to be used in each subscribe unit in narrow band FDMA a user is assigned a particular channels which is not shared by other user in the vicinity and FDD is used (each duplex channel has forward and reverse simplex channels) than the system is called FDMA/FDD. Narrow band TDMA on the other hand allow users to share the same radio channel but allocates a unique time slough to each user is a cyclic fashion on the channel. Thus separating a small number of users in time on a single channel. For narrow band TDMA systems there generally are a large numbers of radio channels allocates using either FDD or TDD and each channel is shared using TDMA such systems are called TDMA/FDD or TDMS/TDD excess systems.

In wide band systems the transmission bandwidth of a single channel is much larger that the coherence bandwidth of the channel. Thus multipart fading does not greatly very the received signal power within a wide band channel and frequency selective fades occur in only a small fraction of the signal bandwidth at any instance of time. In wide band multiple access system a large number of transmitter are allowed to transmit on the same channel. TDMA allocates time sloughs to the many transmitters on the same channel and allows only one transmitter to access the channels at the instance of time whereas spread spectrum CDMA allows the entire transmitter to access the channels at the sometime. TDMA and CDMA systems may use either FDD or TDD multiplexing techniques.

Frequency division multiple accesses (FDMA) assign individual to individual users. IT can be seen from the figure below that each user is allocated a unique frequency band or channel. These channels are assigned on demand to users who request service. During the period of the call no other user can share the same channel. In FDD systems the users are assigned a channel as a pair of frequencies. One frequency is used for forward channel while the other frequency is used for the reverse channel. The features of FDMA are as follows.

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05/EC/42 WIRELESS NETWORKINGa) The FDMA channels carries only one phone circuit at a timeb) If an FDMA channel is not in uses than it sits idle and cannot be used by other

users to increase or shares capacity. It is essentially a wasted resource.c) After the assignment of a voice channel the base station and the mobile

transmit simultaneously and continuously.

d) The bandwidths of FDMA channels are relatively narrow (30 kHz) as each channel supports only one circuit per carrier i.e. FDMA is usually implemented in narrow band systems.

e) The symbol time of a narrow band signal is large as compared to the average delay spread. These implies that the amount of inter symbol interference is low and thus little or no equations is required in FDMA narrow band systems.

f) The complexity of FDMA mobile system is lower than compared to TDMA systems. Through this is changing as digital signal processing methods improved for TDMA

g) FDMA systems have higher sell site system cost as compared to TDMA systems.

h) The FDMA mobile units use duplexers since both the transmitter and receiver operator at the same time. This result in increases in the cost of FDMA subscriber units and base stations.

i) FDMA requires tight RF filtering to minimize adjacent channel interference.

Time division multiple access (TDMA):

Time division multiple access (TDMA) systems divide the ratio spectrum into time sloughs and each slough only one user is allowed to transmit or receive. It can be seen from the figure below that each user occupies a cyclically repeating time sloughs so the channel may be thought of as a particular time sloughs that reoccurs every frame when N time sloughs comprise the frame. TDMA systems transmit data in a buffer in a buffer and burst method. Thus the transmission of my user is no continues. This implies that unlike in FDMA systems which accommodate analog FM, digital data and digital

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Cha

nnel

1

Cha

nnel

2

Cha

nnel

3

Cha

nnel

N

Frequency

Code

05/EC/42 WIRELESS NETWORKINGdata and digital modulation must be used with TDMA. The transmission from various users is interred laced into a repeating frame structure as shown below. It can be seen that a frame consist of a number of sloughs. Each frame is made up of a preamble and information message would be and tail bits. In TDMA/TDD half of the time sloughs in the frame information message would be uses for the forward link channels and half would be used for the reverse link channels. In TDMA/FDD systems an identical or similar frame structure should be used solely for either forward or reverse transmission but the carrier frequencies would be used solely or either foreword or reverse transmission but the carrier frequencies would be different for the forward and reverse links. In general TDMA/FDD systems intentionally induce several time sloughs of delay between the forward and reverse time sloughs for a particular user so that duplexers are not required in subscriber units.The features of TDMA include the following

a) TDMA shares a single carrier frequency with users where each user makes use of non overlapping time sloughs. The number of time soughs per frame depends on several factors such as modulation technique, available band width etc.

b) Data transmission for users of a TDMA system is not continue but occurs in burst. This result in low battery consumption since the subscriber transmitter can be turned off when not in use.

c) Because of this continues transmission in TDMA the handoff process is much simpler for a subscriber unit since it is able to listen for other base station during the idle time sloughs. An chanced link control such as that provide by mobile assisted handoff (MAHO) can be carried out by a subscriber listening on idle sloughs in the TDMA frame.

d) TDMA uses different time sloughs for transmission and reception, Thus duplexers are not required to switch between the transmitter and receiver using TDMA.

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Channel 1

Channel N

Code

Frequency

Time

Channel 2Channel 3

05/EC/42 WIRELESS NETWORKINGe) Adaptive equalization is usually necessary in TDMA system since the

transmission rates are generally vary high as compared to FDMA channels. f) In TDMA the guard time should be minimized. If the transmitted signals at

the edges of a time slough are suppressed sharply in order to shorten the guard time the transmitted spectrum will expand and cause interference to adjacent channels.

g) High synchronization overhead is required in TDMA system because of bust transmissions. TDMA transmissions are sloughed and this requires the receivers to be synchronized for each data burst. In addition guard sloughs are necessary to separate users and this result in the TDMA system having larger overheads as compared to FDMA.

h) TDMA has an advantage in that it is possible to allocate different users by concatenating time sloughs based on priority.

Code division multiple access (CDMA):

Access schemes:

For radio system there are two resources frequency and time. Division of frequency so that each pair of communicators is allocated part of the spectrum for all of the time results in frequency division multiple accesses (FDMA). Division by time so that each pair of communicators is allocated all of the spectrum for part of the time results in time division multiple access (TDMA).in code division multiple access (CDMA)every communicator will be allocated the entire spectrum all of the time. CDMA uses codes to identify connections.

Coding:

CDMA uses unique spreading codes to spread the basement data before transmission. The signal is transmitted in a channel which is below noise level. The receiver than uses a correlate to dispread the wanted signal which is passed through a narrow band pass filter. Unwanted signal will not be dispread and will not pass through the filter. Codes take the form of carefully designed one/zero sequence produced at a much higher rate than that of the basement data. The rate of a spreading code is referred to as cheap rate rather than bit rate.

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Examples OVSE codes, used in channels coding.

Codes:

CDMA codes are not required to provide call security but create a uniqueness to enable call identification, codes or time shifted version of itself. Spreading codes are noise like pseudo-random codes channels codes are designed for maximum separation from each other and cell identification codes are balanced not to correlate to other codes of it.

The Spreading Process:

WCDMA uses direct spreading where spreading process is done by directly combining the base band information to high chip rate binary code. The spreading factor is the ratio of the chips (UMTS= 3.84 Chips/s) to base band information rate. Spreading factors vary from 4 to 512 in FDD UMTS. Spreading process gain can be expressed in dBs (spreading factor 128 = 21dB gain).

Spreading factor = Chip rate QPSK

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Data rate

C1 (1) =1

C2 (1) C2 (2)

C4 (1) C4 (2)

C8 (1) C8 (2)

C16 (1) C16 (2) C16 (3) C16 (4)

C32 (1) C32 (2) C32 (3) C32 (4)

C64 (1) C64 (2) C64 (3) C64 (4)

Layer 1

Layer 2

Layer 3

Layer 4

Layer 5

Layer 6

1 1 1 1 1 -1 1 -1 1 1 -1 -11 -1 -1 1

W3 =

W2 = 1 1 1-1


CDMA SpreadingPower control:

CDMA is interference limited multiple access system. Because all user Transmit on the same frequency internal interference generated by the systems is the most signification factor in determining system capacity and call quality. The Transmit power for each user must be reduced to however the power should be enough to maintain the required Eb\no (signal to noise ratio) for a satisfactory maximum is achieved when Eb\no of every user is at the minimum level needed for the acceptable channel performance. As the ms moves around the RF environment continuously changes due to fast and slow fading external interference shadowing and other factors. The aim of the dynamic power

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USER 1 DATA

USER 2 DATA

USER 3 DATA

POWER

USER 1 CODDING

USER 2 CODDING

USER 3CODDING

POWER

TIMEFREQUENCY

User 1Decoding

FREQUENCY

TIME

05/EC/42 WIRELESS NETWORKINGcontrol is to limit transmitted power on both the links while maintaining link quality under all condition. Additional advantages are longer mobile battery life and longer life span of BTS power amplifiers.

Handover:Handover occurs when a call has to be passed from one cell to another as the user

moves between cells. In a traditional "hard" handover the connection to the current cell is broken cell is broken and then the connection to the new cell is made. This is known as a "break-before-make" handover. Since all cells in CDMA use the same frequency it is possible to make the connection to the new cell before leaving the current cell. This is knows as a "make before break" or "soft" handover. Soft handover require less power which reduces interference and increases capacity. Mobile can be connected to more that two bits the handover. "Softer" handover is a special case of soft handover where the ratio links that are added and removed belong to the same node b.

Multi path and rake receivers:

One of the main advantages of CDMA systems is the capability of using signals that arrive in the receivers with different time delays. This phenomenon is called the multi path. FDMA and TDMA which are narrow band system can not discriminate between the multi path arrivals and resort to equalization to mitigate the negative effects of multi path. Due to its wide bandwidth the rake receiver’s CDMA uses the multi path signals and combines them to make an even stronger signal at the receivers. CDMA subscriber unit’s user rake receivers. This is essentially an ET of several receivers. One of the receiver’s consistently searches for different multi path and feeds the information to the other three fingers. Each finger then demodulates the signal corresponding to a strong multi path. The result are them combined together to make the signal stronger.

CDMA2000 is 3G:

3g is the to describe next generation mobile services which provide better Quality voice and high speed internet and multimedia services. While there are

many interpretations of what 3g represents the only definition accepted universally is the one published by the international telecommunication union (ITU). ITU working with standards well as the spectrum for 3g systems under the imt-2000 program.

The ITU requires that imt-2000 (3g) networks among other capabilities deliver improved system capacity and spectrum efficiency over the 2g systems and support data service at minimum transmission rates of 144 kbps in mobile (outdoor) and 2 mbps in fixed environments.

Based on these requirements in 1999, ITU approved five radio interfaces for IMT-2000 standards as a part of the ITU-R.M. 1457 recommendation. CDMA2000 is one the five standards. It is also known by its ITU name IMT-CDMA multi carrier.

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CDMA2000 delivering on do:

CDMA2000 represents a family of technologies that includes CDMA2000 IX and CDMA2000 IXEVa). CDMA2000 IX can double the voice capacity of cdmaone networks and delivers peak packet data speeds of 307 kbps in mobile environments.b). CDMA2000 IXEV includes: - CDMA2000 1xEV-DO i. CDMA2000 1xEV-DV delivers peak data speeds of 2.4 Mbps and support application such as MP3 transfer and video conferencing. - CDMA2000 1xEV-DV

i. CDMA2000 1xEV-DV provides integrated voice and simultaneous High-speed packet data multimedia services at speeds of up to 3.09 Mbps

- 1xEV-Do and 1xEv-DV are both backward compatible with CDMA2000

The Worlds first 3g Commercial systemize e in October 2000. Since them CDMA2000 1x has been deployed in asia, north and south America and Europe and the subscriber base is growing at 70000 subscribers per day.CDMA2000 1xEV-DV was launched in 2002 by SK Telecom and K T FreeCell. The commercial Success of CDMA2000 has made the IMT-2000 vision a reality.

CDMA2000 benefited from the extensive experiences acquired through several years of operation of CDMA one system. As a result CDMA2000 is a very efficient and robust technology. Supporting both voice and data the standard was devised and tasted in various spectrum bands including the new IMT-2000 allocation.

1) Increased voice capacity2) Higher data throughout 3) Frequency band flexibility4) Increased battery life 5) Synchronization6) Power control 7) Soft hand-off8) Transmit diversity9) Voice and data channels 10) Traffic channel11) Supplemental channel12) Turbo coding.13) Connectivity to ansi-41, GSM-MAP, and op network 14) Full backward compatibility15) Improved service multiplexing and QoS management 16) Flexible channel structure in support of multiple services with Various QoS and variable transmission rates.

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CDMA deployments:

The first 3g networks to be commercially deployed were launched in Korea in October 2000 using CDMA 2000 technology. CDMA2000 dominates the 3g market today and analysts forecast that will continue to lead in the future.

What are the advantages of CDMA?

1) Capacity increases 8 to 10 times that of an AMPS analog system and 4 to 5 times GSM

Because of CDMA's unique technology may users can share the same carrier frequency. This means that mobile phone services providers can handle more customers on a CDMA network than on a GSM network.

2) Improved call quality with better and more consistent sound: CDMA systems use precise power control that is the base station sends

commands to every mobile phone currently involved in a call turning down the power on the nearby ones and increasing the power of those further away. The result is a nice even level across the carrier with lower overall power levels and no spiky interference. In this civilized atmosphere, each station can easily pick out is own data frames decode them and deliver a clean end result.

Dropped calls are minimized by CDMA's unique ability to keep every sector of every cell on the same frequency so handoffs are "soft" as the mobile phone moves from one area to the next.

CDMA decodes interpret constant sound such as road notice as having no useful content and ignore them as much as possible.

3) Simplified systems planning through the use of the same frequency in every sector of every cell.

Other types of systems need to break up their frequency spectrum allotments so that each cell uses a different frequency. And since no two adjoining cells can use the same frequency a given cell has to be surrounded by a circle of six other cells all of which have to be on different frequencies. This translates to frequency re-use of only 1 in 7 and if you change one the effects ripple through the system. CDMA provides have no such planning headaches since every sector of every cell uses the same frequency.

4) Enhanced privacy5) Improved coverage characteristics allowing for the possibility of fewer cell site 6) Increased talk time for mobile phone7) Bandwidth on demand

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5. GSM architecture:5. GSM architecture:

MSC:It also stores the current location of these subscribers and the services to which

they have access. The location of the subscriber corresponds to the ss7 Address of the visitor location register (VLR) associated to the terminal.

Visitor location registers (VLR):The VLR contains information from a subscriber's HLR necessary in order to

provide the subscribed services to visiting users. When a subscriber enters the covering area of a new MSC, the VLR associated to this MSC will request information about the new subscriber to its corresponding HLR. The VLR will then have enough information in order to assure the subscribed services without needing to ask the HLR each time a communication is established.The VLR is always implemented together with a MSC, so the area under control of the MSC is also the area under control of the VLR.

The Authentication Centre (AuC):Te AuC register is used for security purposes. It provides the parameters needed

for authentication and encryption functions. These parameters help to verify the user's identity.

The Equipment identity Register (IMEI):The EIR is also used for security purposes. It is register containing information

about the mobile equipments. More particularly, it contains a list of all valid terminals. A terminal is identified by its international mobile equipment identity (IMEI). The EIR allows then to forbid calls from stolen or unauthorized terminals (e.g., a terminal which does not respect the specifications concerning the output RF power).

The GSM networking Unit (GIWU):

The GIWU corresponds to an interface to various networks for data communications. During these communications, the transmission of speech and data can be alternated.

The Operation and Support sub System:The OSS is connected to the different components of the NSS and to the BSC, n

order to control and monitor the GSM system. It is also in charge of controlling the traffic load of the BSS. However, the increasing number of base stations, due to the development of cellular radio networks, has provoked that some of the maintenance tasks are transferred to the BTS. This transfer decreases considerably the costs of the maintenance of the system.

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The figure 2 presents the different areas that from a GSM network. As it has already been explained a cell, identified by its cell globule identify number (CGI), corresponds to the radio coverage of a base transceiver station. A location area (LA), identified by its location area identity (LAI) number, is a group of cells served by a single MSC/VLR area. A Public Land Mobile network (PLMN) is the area served by one network operator.

Figure 2: GSM network areas

In this paragraph, the description of the GSM network is focused on the different function to fulfill by the network and not and not on its physical components.

In GSM, five main functions can be defined: Transmission. Radio resources management (RR). Mobility management (MM). Communication management (CM). Operation administration and maintenance (OAM).

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MSCBSC=BASE STATION CONTROLLERBTS= BASE TRANSCEIVER STATION MSC=MOBILE SWITCHING CENTREHLR=HOME LOCATION REGISTERVLR=VISITOR LOCATION REGISTEREIR=EQUIPMENT IDENTITY REGISTER


Transmission:The transmission function includes two sub functions:

(1) the first one is related to the means needed for transmission of user information.

(2) The second one is related to the means needed for the transmission of signaling information.

Not all the component of the GSM network is strongly related with the transmission function. The MS, The BTS are deeply concern with the transmission but other component concern with the transmission for their signaling needs with other component of the GSM network.Radio resource management:The role of RR function to establish , maintain and release communication links between mobile station and the MSC. The element that mainly concerned with the RR function are the mobile station and base station. the RR is also responsible for the management of frequency spectrum and the reaction of the network to changing radio environment condition some of the main RR procedure that ensure its responsibility are:(1) Channel assignment, change and release.(2) Handover.(3) Frequency hopping.(4) Power level control.(5) Discontinuous transmission and reception(6) timing advance.

Mobility management:The MM function is in charge of all aspects related with the mobility of user, specially the location management and the authentication and security.Communication management:The CM function responsible for:Call control.Supplementary service management.Short message service management.

The CC is responsible for Call establishing ,maintain and releasing as well as for selecting for type of service. One of the most important function of the CC is call routing. In order to reach a mobile subscriber , a user dials the mobile subscriber ISDN number which includes :

(1) A country code:(2) A national Destination code identifying the subscribers operator(3) A code corresponding to subscribers HLR..

Operation Administration and maintenance:The OAM function allows the operator to monitor and control the system as well as to modify the configuration of the element of the system.

Bibliography

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Books

1. MOBILE COMMUNICATION BY J. SCHILLER

2. MOBILE COMMUNICATION BY THEODORE RAPPARPART

3. MOBILE AND PERSONAL COMMUNICATION BY RAJ PANDAY

Web Sites

1. www.gsmworld.com

2. www.paloworeless.com

3. www.3Gtoday.com

4. www.etsi.com

5. www.wapforun.org

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http://www.wapforun.org/

http://www.etsi.com/

http://www.3Gtoday.com/

http://www.paloworeless.com/

http://www.gsmworld.com/

Wireless Networking

Documents

Transcript of Wireless Networking