mobile communication computing

8/22/2019 Mobile Communication Computing

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MOBILE COMMUNICATION / COMPUTING

By-Vipul Patel and Milind Desai (T.E. Extc.),s.s.p.m.coe

ABSTRACT :

Mobile communication are changing peoples life style in many ways. The

tremendous demand from social are pushing to booming development of mobile

communication faster man ever advanced techniques emerging. This paper studies basic

concepts of mobility for mobile communication. A conceptual discussion is made on

mobility in the contexts of both computation & communication leading to the illustration

of mobile computing. The concept of mobility management for mobile communication

are introduced. The concept & operation of CDMA-based-digital cellular system for

mobile communication are also introduced. New challenges arises in future mobile

communication system with diversity as the key feature, which leads to the definations of

classified mobility according to different cells.

Keywords: Mobile communication, Mobility, Mobile Management, Wireless Networks.

1.INTRODUCTION

Mobility is humans nature. To the field of computing & communication

technologies, to be able to communicate with other persons & access & process

information simultaneously while moving has been as long expectation that causes great

deal of efforts having been made to turn the fancy into fact. The underlying vision for the

emerging mobile communication with a person, at any time, at any place and in any form,

as illustrated in fig. 1 Dial Patels personal number

At Any Location

Home

Office

In public

Using Any Device

Cellular / PCS phone

Office wired phone

Personal digital assistant

Multimedia terminal


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Mobile communication will continue to greatly change the way of peoples life.

Next generation mobile systems need the support of all the advances on new theories,

algorithms, architectures, standards and protocols. In the near future, more and more

internet based services like web service can be smoothly accessed with various mobile

devices through the wide deployed wireless networks.

Enabling concepts for mobility & mobile computing:-

Mobility is the characteristic of an object that can be mobile. In the field of

computing technology, the mobile object can be in both computation and communication,

according to which we get mobile computation & communication by extending the

features of the objects in these two areas with mobility. This two feature mobile

computation & communication helps us to construct the new research field Mobile

Computing. This extension is illustrated in fig.2

Mobility Mobile Communication

Mobile ServiceMobile Computation Mobile N/w

Mobile TerminalMobile Computing Mobile User

Mobile Agent

Communication

Mobile Process

Computation


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Fig. 2 Mobility & Mobile computing

Computation & Communication are always interdependent instead of independent.

Many mobile objects can be distinguish in the field of mobile computing. For mobile

computation, objects that can be of mobility are usually some logical computer critics

( code, data, or state):-

1. Mobile process :- Mobile process is a concept in the area of Operating system

(OS). A process is the abstraction of a running application that consist of the code, data,

& OS state, which can be transfer between systems.

2. Mobile Agent :- The main role of mobile agent is to improve performance &

reliability. It extends the concept of software object; which can carry both code & data &

the thread of control.

As to mobile communication, mobile objects are mostly physical components. Mobility

scenario include:-

1. Terminal mobility :- It is the ability of user device that can roam within a network

or between network with on going communication within the radio coverage area. Eg :

Laptop & Cellular phone.

2. Personal mobility :- It, means that end-users can access personal services

regardless of moving to any network or using any terminal, through unique user

identification like a Universal personal telecommunication ( UPT ) number.

3. Services mobility :- It means that a personalized service available to the user with

one mobile device in a N/w can still be accessible by another mobile device &/or in

another N/w of different region or operator.


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The Cellular ConceptThe cellular concept was developed & introduced by the Bell Laboratories in the early

1970s. The principle of cellular systems is to divide a large geographic service area into

cells with diameter from 2 to 50 Km, each of which is allocated a number of radio

frequency (RF) channels. Transmitters in each adjacent cell operate on different

frequencies to avoid interference. As the demand grows in a given area, cells can be split

to accommodate the additional traffic. Cells that are sufficiently far apart can reuse the

same set of frequencies without causing cochannel interference. Fig. 3 illustrate an

idealized view of a cellular mobile system, where cells are depicted as perfect hexagons.

Cells using the same RF channels

Fig.3 Concepts of frequency reuse in cellular system

System Architecture:

As mentioned earlier, the coverage area of a cellular system is partitioned into a

number of smaller area or cells with each cells served by a base station (BS) for radio

coverage. The base station are connected through fixed links to a mobile switching center

(MSC), which is a local switching exchange with additional features to handle mobility

management requirements of a cellular system. MSC also interconnect with the PSTN,


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because of majority of calls in a cellular mobile system either originate from or terminate

at fixed N/w terminals

Base station

HLR

VLR

T O O T H E R

MSC

MSC S

F I G 2.3 T Y P I C A L C E L L U L A R S Y S T E M A R C H I T E C T U R E

T O PSTN

Mobility Management for mobile

communication :-Mobility management is the essential technology that supports roaming user with

mobile terminal to enjoy their services through wireless N/ws when they are moving into

a new service area. Mobility mainly contains two distinct but related components :-

Location Management

Handoff Management


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Location management is to locate roaming terminals in order to deliver data packets

despite that the location of them may change from time to time.

Handoff management is to control the change of a mobile nodes attachment point to

n/w in order to maintain connection with the moving node during active data

transmission.

Multiple Access TechnologiesMultiple access system specify how signals from different sources can be

combined efficiently for transmission over a given radio frequency band & then separated

at the destination without mutual interference. The three basic multiple access methods

currently in use in the cellular system are :-

FDMA (Frequency Division Multiple Access)

TDMA (Time Division Multiple Access)

CDMA ( Code Division Multiple Access)

In case ofFDMA, users share the available spectrum in the frequency domains Analog

systems, which represent the initial implementations of the cellular concept, uses FDMA

techniques.

In case ofTDMA techniques that are utilized in many Digital cellular systems, the

available spectrum is partitioned into narrow frequency bands or frequency channels,

which in turn are divided into a number of time slots. In TDMA guard bands are needed

both between frequency channels & time slots.

The CDMA systems utilizes the spread spectrum technique, whereby spreading code

(with different pseudo-random noise) is used to allow multiple users to share a block of

frequency spectrum. No guard bands are necessary. (Ux - user slot, Fx

Frequency slot, Cx PN code slot, Tx time slot)


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U1 U2 U3 U4

FDMA F1 F2

F3 F4 frequencytime

TDMA t2 U2 U4

U6 U8

T1 U1 U3 U5 U6

F1 F2 F3 F4 frequencyPN code

CDMA cn

Un

C1 U1

F = f1 to f4 frequency

CDMA Based Digital Cellular SystemIS 95 standard for the CDMA common air interface was adopted in 1993. The

final assessment on the potential superiority of CDMA systems over TDMA systems in

terms of capacity, cost, & speech quality, will emerge only after both systems have being

in operation in dense, urban areas with full complements of subscriber & services.

Service Aspects: - Short message service (SMS)

Supplementary services (Call waiting, Call forwarding, Calling line ID,

etc)

Packet data etc.


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Forward link Structure in IS 95 or Base to

Mobile interaction: -A system is based on the spread spectrum concept is an example of a power

limited system that 8is not constrained by bandwidth. The CDMA common air interface

(CAI) specifies a forward physical channel design that uses a combination of frequency

division, pseudo multiple access techniques. Frequency division is achieved by

dividing the available cellular spectrum into nominal 1.23mhz channels which can be

increased from the initial single CDMA channel to multiple such channels as demand for

digital services increases. An example of a logic forward (base to mobile) w/f is shown

in fig.4

Pilot channel: - Base uses of the pilot channel are uniquely identifying sectors / cells,

providing phase/ time/ signal strength reference, identifying multipath components &

handoff candidates etc.

Synchronization channel: - System identification number (SID), N/w identification

number (NID), precise time of day information, PN offset of the associated pilot

channel.


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Paging channels: - A forward w/f transmitter by a base station to can have up to seven

paging channels, mobile, as well as necessary system parameters.

Forward Traffic channels: - The forward Traffic channels are used to transmit voice or

data to a mobile that is in a call. There may be up to 63 forward traffic channels,

depending on the numbers of paging channels and synchronization channels. Data rates

are flexible ( 1200,4800 or 9600 b/s.) to support variable-rate voice coders and this are

structured in 20 ms frames. Signally information from the base station to the mobile

during a call can be transmitted using blank and burst or dim and burst methods.

Reverse link structures in IS-95 :- The reverse CDMA channel is used by all the

mobiles in a cell coverage area to transmit to the base station. IS-95 CDMA System

capacity :- The key parameters that determines the capacity of a CDMA digital cellular

system are as follows :- Processing gain, ratio of energy per bit to noise power (Eb/No),

voice activity factor, frequency reuse efficiency. The theoretical capacity of the IS-95

CDMA cellular system in terms of calls per 1.25 MHz channel per cell is provided by

Np = (w/R)vS(Eb/No)F

Where, Np = capacity in terms of numbers of calls/1.25 MHz channels/cell

W/R = ratio of spreading code (1.2288 M cps) to maximum information rate (9600

b/s)

V = voice activity gain (approximately 2) , S = sectors per cell

(generally 3)

Eb/No = minimum ratio of bit energy to noise power (6 dB or factor of 4)

F = Frequency reuse efficiency factor ( approximately 3/2)

The theoretical estimated capacity is therefore in the order of 128 calls per 1.25 MHz channel

(i.e. practically 64 calls)


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Mobility in future mobile systems:-The future mobile system will provide capabilities constituting significant

improvements over the current mobile systems, especially in terms of global mobility for

the users and supports of services like high speed data, multimedia and internet. In scope,

future mobile service environments will address the full range of mobile and personal

communication applications shown in figure. In building (picocell), urban(microcell),

suburban(macrocell) and global(megacell/satellite) as well as communication types that

includes voice, data and image. Support of communication needs for developing

countries in the form of fixed wireless access (FWA) applications.

Conclusion:-This paper studies the basic concepts of mobility for mobile communication. Mobility is

definition in the context of computation and communication, which lead to the concept of

mobile computing. The impacts of mobility on mobile communication are analyses and

the main idea of mobile management are also introduced. The digital cellular system

based on CDMA technologies are fully specified and are being implemented at a rapid

rate around the world. The recognized need for a third - generation system that will

provide global roaming and service delivery as well as support for high speed data,

internet and multimedia service is playing a significant roll in the evolution of these

digital cellular systems.


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Reference:- Mobile communication systems and services.-By RAJPANDYA.

Fundamental of mobile communication and computing -From

IEEE PAPERS.

mobile communication computing

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