cell to switch assinment (2)

7/30/2019 Cell to Switch Assinment (2)

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Cell to switch assignment in UMTS

Contains page

1. Introduction 2

1.1 Introduction to the wireless cellular network (WCN)

1.2 Evolution of WCN

1.3 Introduction to First generation

1.4 Introduction to Second generation

1.5 Introduction to third generation

1.6 Handoff

2

4

4

6

8

11

2. Literature survey 12

2.1 Handoff in PCN2.2 Complex handoff

2.3 Simple handoff

2.4 Handoff in UMTS

2.5 Horizontal and vertical handoff in overlay network

2.6 Complex and Simple handoff in UMTS

2.7 Cell two Switch Assignment

2.8 Single homing

2.9 Dual homing

2.10 Cost function generation for Single homing cell to switch assignment in

PCN

2.11 Cost function generation for Dual homing cell to switch assignment in

PCN2.12 single homing in UMTS

2.13 Dual Homing in UMTS

2.14 Heuristic method

2.15 Tabu search

1212

13

13

15

15

16

16

17

18

19

20

2323

23

3. Future work 24

4. Reference 25


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1. IntroductionOver the recent years, telecommunication has been a fast growing industry. Because it draws a

great deal of attention since it was introduced. Several warless technologies were developed in

different times. They have different characteristics and different applications.

Before going into detail of cell to switch assignment for UMTS network, however, it is

appropriate to review mobile communication in general, as well as first and second generation

systems

The first generation mobile system was introduce in 1978 in Chicago as Advanced Mobile Phone

Services (AMPS), operating in 800-MHz and again it re-launch in 1983 for public use in Chicago.

Meanwhile many other country introduce their own 1st

generation mobile system, so, at a gross

1st

generation system experience success far greater than anyone had expected. But the main

problem with the 1

st

generation technology is its limited capacity.

Unlike 1st

generation system which is analog 2nd

generation comes with digital system. The

most successful 2nd

generation technologies are

1. Interim Standard 136 (IS-136) TDMA.

2. IS-95 CDMA

3. Global System for Mobile communication (GSM)

In third generation mobile system comes under 3GPP group. UMTS support high speed data as

well as voice communication that is why it is a popular chooses among people.

So as the demand increases services provider need to increases their services area. So there is a

cost for routing the call through their company network and which they have to bear.

Throughout this article, how could a services provider can minimize the cost associated with

the call routing through their network by optimally assigning its cells and switches, is disused


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1.1 Introduction to Wireless Cellular Networks (WCN)The WCN is a telephone system which provides wireless connection to a large number of users

over a large geographical area with a limited frequency spectrum. In WCN, the whole converge

area is divided into a number of hexagonal cells so that the same radio channels may be reused

by another base station located some distance away

Now, each cell contains a base station,a fixed station in a mobile radio system used for radio

communication with mobile stations ,Base stations are located at the center or on the edge of a

coverage region and consist of radio channels and transmitter and receiver antennas mounted

on a tower [1]. So base stations are the responsible for channel allocation of the users in that

particular cell. A portion of the total number of available channels is allocated to each BSC and

ne nearby BSCs is assigned different groups of channels so that there is no interference

between neighboring BSCs. channels of each BSC are well separated so the simultaneous

communication is possible and this increase the capacity. Spectrum reuse technique protectsthe services provider from buying more spectrum band which is too costly.

A group of cell is connected with a switch which is known as MSC or mobile switch center,

Switching center which coordinates the routing of calls in a large service area. In a cellular

radio system, the MSC connects the cellular base stations and the mobiles to the PSTN. An MSC

is also called a mobile telephone switching office (MTSO).[1] So basically MSC routed the call

trough out the company network. MSC is interconnected with the PSTN via Landline trunks line

and a switch. The inter communication between MSC is done by some dedicated channel for

exchanging of information like location update, validation, cell signaling information shown in

fig.1. In cellular telephone systems, voice traffic carried on the PSTN and the signaling

information is carried on the SS7 network. MSC is also connected with HLR (home location

register) i.e. it keeps track of the user of that particular MSC or cells. MSC is also connected

with VLR (visitor location resistor) and AuC(Authentication center) .by this MSC can keep track

the new subscriber in that cell and authenticated him or her

The global cellular network is required to keep track of all mobile users that are register

throughout the network. So that it is possible to forward incoming calls to rooming users at any

location. When the user roams the new market with completely new service provider the

wireless network must register the new user and cancel the previous one for the sleek of the

routing calls through the new network because it is in different MSC coverage area.

So from the previous discursion we can see that whenever one user moving from one cell to

other cell a new channel is allocated for that particular user. Before BSC allocated some channel

MSC must aware about the call and then finally handed over that call from one cell to another

cell


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Fig.1. Block diagram of a cellular radio network [1]

1.2 Evaluation of WCNWCN has gradually improved since it was initiated as most advanced technologies have been

introduced. The demand of WCN increases with rapid worldwide growth in cellular telephonesubscribers. The wide spread success of WCN has led to the development of advanced WCN

systems

1.3 First Generation (1G)This is the one of the most prolific voice communication platforms that has been deployed

within the last two decades. In this generation some key concept employed in wireless

communication such as

1. Frequency reuse

2. Mobility of the subscriber

3. Handoff

There are several 1st

generations mobile system were develop but among them two most

popular system was advance mobile phone system (AMPS) & total access communication

services (TACS).


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AMPS TACS

Base Tx MHZ 869-894 935-960

Base Rx MHZ 824-849 890-915

Multiple access method FDMA FDMA

Modulation FM FM

Radio channel spacing KHZ 30 25

Number channels 832 1000

Spectrum allocation MHZ 50 50

Comparative study between AMPS and TACS

So as discus previously BSCs are connected with MSCs and two MSCs connected with the land

line via PSTN & for signaling porous SS7 was there. HLR, VLR and AuC are there for user

registration and authentication

Some key features of 1st

generation architecture is

Analog traffic channel.

Frequency modulation (FM) technique is used.

Operated on FDMA/FDD.


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It can handle only voice signal

Use circuit switching

MSC serves

Call processing

Power control

Hand off control

Billing

The main disadvantages are

Very low in capacity

High load on MSC

1.4 Second generation (2G)Second generation design is generalize used to describe the advantage of the digital mobile

communication for cellular mobile system.

The issues regarding 2G deployment are as follows:

Capacity

Spectrum utilization

Infrastructure change Subscriber unit upgrades

Subscriber upgrade penetration rates

The fundamental binding issues with 2G are the utilization of digital radio technology for

transporting the information content.

The digital techniques for cellular communication can be deviled into two major groups, AMPS

and TACS. For AMPS TDMA or CDMA are use for TACS GSM is preferred. Other then

AMPS/TACS, IDEN radio access platform is available and in the SMR (specializes mobile redio)

band, which is neither cellular nor PCS. In the table below represent some of the specificationof different technology used in second generation WCN


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IS-136 IS-95 GSM

Base Tx MHZ 869-894 869-894 925-960

Base Rx MHZ 824-849 869-894 880-915

Multiple Access

Method

TDMA/FDMA CDMA/FDMA TDMA/FDMA

Modulation Pi/4DPSK QPSK .3 GMSK

Radio Channel

Spacing KHZ

30 1.25 200

Users /Channel 3 64 8

Number Channels 832 9(A)

10(B)

124

Spectrum Allocation

MHZ

50 50 50

Comparative study for different technology

From the fig.3 we can see that one ISDN (Integrated System Digital Network) is connected with

GMSC (Gateway MSC) for data communication.


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Some key features are

Digital network

Use digital voice coding

Digital modulation

Higher Capacity

Higher security

Caller identification , short Massaging Service(SMS)

It is designed to provide voice & other data services.

Operated on TDMA/FDD or CDMA/FDD.

Network controlling structure is more distributed

Hand off process is mobile control (MAHO).

Introduce Base Station Controller(BSC)

Higher Mobility

Lower power radio signal require.

1.5 Third generation (3G)Analog cellular phones were the first generation while digital marked the second generation.

3G is loosely defined, but generally includes high data speeds, always-on data access, and

greater voice capacity. The high data speeds are possibly the most prominent feature and

currently most hyped. They enable such advanced features as a live streaming video

3G and all it is meant to be are defined in ITU specification International Mobile

Telecommunication- 2000 (IMT-2000). IMT-2000 is a radio and network access specification

defining several method or technology platforms that meet the overall goals of thespecification.

When the International Telecommunication Union solicited solutions meet the requirement

laid down for IMT-2000, a number of technology were proposed by various stander groups.


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The European Telecommunications Stander Institute (ETSI) agreed on a WCDMA solution using

FDD. In Japan, WCDMA solution is also proposed, with both TDD and FDD option. In Korea two

different type of CDMA solution were proposed. So a number of groups working on the very

similar technology and it were fairly obvious that the most effective way forward was pool

resource. This led to the creation of two group 3GPP (Third generation partnership project) :works on UMTS and other one is 3GPP2 works on CDMA200 .

UMTSis aimedto be a system capable ofproviding a variety of mobile services (up to 2Mbps)

offered by (dedicated) paging, cordless, and cellular Communications systems separately. UMTSis tobe operational in domestic, business, vehicular, and (multi-operator) public environments.

For UMTS architecture two new units are added, those are RNC (Radio Network Controller):

between BSC and MSC & SGSN (serving GPRS support node): work as an internet gate way

The major tasks of RNCs:

management of radio resources

channelization code allocation

QoS monitoring

handover of users between cells on the same site (softer handover)

handover of users between cells on different sites (soft handover)

handover of users between different UMTS carriers (hard handover)

handover of users to GSM networks (hard handover)

power control management of user and Node B equipment

network alarm correlation


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The optimal cellular architecture is determined by traffic and mobility characteristics. In a

certain coverage area the traffic and mobility characteristics are varying. Rather than defining

a conventional cellular architecture to cope with this mixed traffic, a mixed cell layout

consisting of an over levering of micro and Pico cells by macro (umbrella) cells is being

considered [2]. The following advantages are foreseen:

highly mobile traffic may be allocated to macro cells thus reducing the handover

signaling load

Macro cells can cover black spotsnot covered by Pico or microcells

Macro cells introduce some redundancy thus increasing system availability

Macrocells can accommodate. for microcell handover failures

The disadvantage of macro cells isreduced spectrum efficiency.

Fig.5. micro and umbrella cell [1]

So the some key feature of 3G:

Generate one world standards.

CDMA use as air interface.

Provide better system capacity both in terms of user & bandwidth

Support multimedia services with high speed.

o Telephony(voice)

o Internet

o Location service

o Video conferencing


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o Live streaming

Better Power Control.

1.6 Handoff

From the figure we can see that cell-1, 2 are connected with MSC-1 and cell-4,3 are connected

with MSC-2. Now consider some subscriber is moving from cell-1 to cell-4 while taking with

someone over phone (that call is now served by BSC-1). Now, BSC-1 can measure the signal

strength of that call & inform MSC-1 about it. MSC-1 has also knowledge about the signal

strength of cell-1 and cell-4. So, when ever MSC-1 can sense that the signal strength of that

particular call goes down below some pre define threshold and simultaneously the signals

strength of cell-4 became more prominent, MSC-1 can understand that the vehicle is now

entering cell-4 and BSC-1 cannot serve that call. So for the sleek of continuing the call MSC-1

transfers all the data regarding that call to MSC-2. MSC-2 registers the subscriber and finally

BSC-2 allocated some channel.

So, in short MSC-1 handed over that call from cell-1 to cell-4 and this is known as handoff


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2 Literature surveyWe were motivated to work in the field of wireless networks as we have gone through some

published literatures. Different types of works were done in this field by many researchers in

different times. Lots of Journals, transaction papers were published and are available in this

context. We got information required to start our work through some literature survey. We

explain about our survey in the following sections

2.1 Handoff in PCNSo in one line the handoff is the process of transferring a mobile station from one channel or

base station to another.

Handoff is broadly divided into two categories- hard handoff and soft handoff. In hard handoff

current resources are released before the new resources are used, that is when two MSCs

involve in handoff. In case of soft handoff the current and new resources are used

simultaneously while handoff takes place, i.e. when handoff occurs between two different cellbut both are connected with same MSC. Handoff can be further divided into intra-cell handoff

and Inter-cell handoff. The soft handoff can also be divided into multi way soft handoff and

softer handoff.

2.2 Complex hand off


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As the vehicle move from cell-1 to cell-4, two MSCs involve in the process. So this type of handoff needs

transferring data from one MSC to other MSC so it is respectively costly. This type o f hand off is known

as complex handoff

2.3 Simple handoff

In case of simple handoff, consider the case when vehicle moving from cell-1 to cell-2. In this case as the

both cell are connected with the same MSC, there is no need of data transferring so this type of handoff

is known as simple handoff

In [3] they calculated handoff for PCN like this way .The rate of calls originated in each cell was

generated from a Gamma distribution with mean one and coefficient of variation 0.25. The

holding time of a call within each cell was taken to be exponentially distributed with mean one.

If a cell had ICneighbors, then we divided the range (0, 1) into K+ 1 interval by selecting K

random numbers from a uniform distribution between 0 and 1. The length of the ith intervalrepresented the probability of handoff from the cell to its ith neighbor for i= 1, 2. . .Katthe

end of the holding time. With probability equal to the length of the K+ 1st interval, the call ends

2.4 Handoff in UMTSUMTS is a 3 layer architected system. In UMTS, there are 3 different types of handover, as follow.


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Hard handoff: involving two different MSCs

Soft handoff : involving two different RNCs and both are connected with same MSC

Softer handoff: handoff between two cells connected with same RNC

Fig.11. hard handoff


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2.5 Horizontal and Vertical Handoff in Overlay Networks

Fig.12. horizontal and vertical handoff

Horizontal handoff is a system which allows an active user to move between different = access

points (AP) of same network technology without any interruption on the ongoing call. Its

shown in fig.12 Vertical handoff is a system which allows active user to roam between different

wireless networks in wireless overlay network.

Vertical handoff happens between the BSC of different wireless network technologies. there

are two type of vertical handoff describe in [13] ,

upward vertical handoff

downward Vertical handoff

When vertical handoff occurs from network with lower cell size and higher bandwidth, it is

called upward vertical handoff. And when it happens to a network of lower cell size and higher

bandwidth from higher cell size and low bandwidth network, then it is called downward Vertical

handoff.

Vertical handoff may happen between two immediately higher and lower networks or hopping

of an overlay may possible. The downward vertical handoff is less time-critical because it could

always be connected to an upper layer while handoff takes place.

2.6 Complex and simple handoff in UMTSSome Literatures [9] describe this type of handoff in UMTS network for making an analogy with

PCN simple and complex handoff.


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Simple handoff: in this type of hand off both soft and softer handoff included. In this

type of handoff two RNCs or two BSC may involve but both are connected with same

MSC & SGSN. So this is basically horizontal handoff

Complex handoff: in this type of handoff hard hand off is included. so this is basically it is

vertical type of handoff

2.7 Cell to switch assignmentIn [5], Merchant and Sengupta define the problem as We are given a group of cells and a

group of switches (whose locations are known). The problem is to assign the cells to switches in

an optimum manner. We would like to do the assignment in an attempt to minimize a cost

criterion. The cost has two components. One is the cost of handoffs which involve two switches

and the other is the cost of cabling (or trucking).

2.8 Single homing

Fig.13. single home cell to switch assignment


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If we have only one user behavior pattern trough out the day then assigning each cell to a

switch would make sense. That Is in this type of arrangement each cell can be assign only one

switch

2.9 Dual homing

Fig.14. dual homing

Consider a situation, say at the evening many subscriber are moving form cell-7 to cell-2 by cell-

8 and cell-8 is connected with MSC-2 and cell-2 & & are connected with MSC-1 (as in the fig.14).

So it would make sense if we connect cell-8 with MSC-1 for that time period. Because it will

reduce the handoff cost i.e. connecting with MSC-1 the handoff between cell-2 and cell-8 and

cell-8 and cell-7 is became simple handoff. So for the evening time cell-8 connects with MSC-1

and rest of the day it connected with MSC-2, i.e. cell-8 connects with two different MSCs but

only one is active in a particular time. So this is known as dual homing.


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So, if we have two different users behavior patterns throughout the day then we could assign

each cell to one or two MSCs but only one MSC is active for a particular time is known as dual

homing problem

2.10Cost function for single homing cell to switch assignment in PCNIn [5], Merchant and Sengupta well define about the cost function .some assumptions are as follow

There are n {1,2,n} cells to be assigned to m{1,2,m} switch

hij is the handoff cost between cells i & j

cik be the amortized cost of cabling per unit time for ith cell with kth switch

i denote the number of calls that cell i handles per unit time

Mk denote the call handling capacity of switch k

We are interested min. cabal costing as well as cost due to complex handoff. we shall not

consider the simple handoff cause cost due to it respectively chip

Now consider we arrange our cells and switch in some way and it is look like fig.13.

Now define

(1)

Constrain on the call handling capacity

For k=1 m (2)

This prove is obvious say consider k=2 then equation (2) shows

(3)

I.e. the left hand side of the inequality (3) gives the sum of call handle capacity per unit time of

those cells which are connected with MSC-2 and the RHS shows that the call handling capacity

per unit time for MSC-2 . so it is obvious that for successfully handling a call inequality (2) must

hold true

For I, j=1 n (4)

The cabling cost for ith cell is

1 ' ' ' '

0ik

x if cell i is assigned to switch k

otherwise

1

n

i ik k

i

x M

53 4 6 2M

1 ' ' & ' '

0

ijy if i j connected with a common switch

otherwise

1

m

ik ik

k

C c x


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(5)

This is also very obvious like (2)

Handoff cost from ith cell can be express as

(6)

For proving it 1st notice that

( ) If i and j are connected with same MSC

( ) Otherwise

I.e. we eliminate the simple handoff from cost function.

So

(

) if there is simple handoff and

(

)

if there is complex hand

off

So the RHS of (6) shows the total cost due to complex handoff from cell i to other cell in the

network

So the total cost is (7)

2.11Cost function for dual cell to switch assignment in PCNAccording to the principal of double homing, a cell could be connected to one or two switch,but in each pattern only one switch is active at a time. We must then find two assignment

patterns for each part of the day, by indicating whether it is cost-effective to have a cell

connected to two switches or to have a cell connected with one switch

Some assumptions are

For some time in a day the parameters are

For some other time it is

are constant

So we have two single home problem in the cost function but we can/t simply write them side

by side because we may over calculated the cabling cost . So we define ne variable as

(8)

1

(1 )n

ij ij

j

H h y

1 1 1 1

(1 )n m n n

ik ik ij ij

i k i j

c x h y


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Here is the or operation

So the cost function is

' '

1 1 1 1 1 1

(1 ) (1 )ij ij

n m n n n n

ik ik ij ij

i k i j i j

c w h y h y

(9)

2.12Single homing in UMTSThe basic problem is that UMTS is three layer, so we cannot simply formulated its cost function

Here complex handoff is hard handoff and soft and softer are called simple handoff as discuss

before

Fig.15. typical UMTS architecture

The assumptions are

There are I{1,2,n} cells , J{1,2,r} RNC, K{1,2,m} MSCs and L{1,2,s} SGSN

12

ijc cabling cost between ith BSC and jth RNC

23jkc cabling cost between jth RNC and Kth MSC

24

jlc cabling cost between jth RNC and lth SGSN

2

vjw circuit switching cap. For of jth RNC


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2djw packet switching cap. For of jth RNC

3

vkw capacity of MSC k

4dl

w capacity of SGSN l

12vif amount of voice traffic of node B

12dif amount of data traffic of node B

23vj

f amount of voice traffic of RNC j

24dj

f amount of data traffic of RNC j

'

3

iih complex handoff involving MSCs

'

4iih complex handoff involving two SGSN

So as previously define

12 1ijx If I ith BSC is connected with jth MSC

12 0ijx Otherwise

231

0

jkx if jthRNCconnectwithKthMSC

otherwise

24 1

0

jlx if jthRNCconnect withlthSGSN

otherwise

Also define

' '

12 1 &

0

iiy if both i i conectedwithsameRNC

otherwise

' '

23 1 &

0

jjy if both j j conected withsameMSC

otherwise

''

241 &

0

jjy if both j j conected withsameSGSN

otherwise

Considering two classes of traffic, the traffic generated by all Nodes Bs connected with RNC j

cannot exceed the RNC capacities in term of voice and data traffic which is expressed as follow


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12 12 2

12 12 2

vi ij vj

i I

di ij dj

i I

f x w j J

f x w j J

(10)

Similarly, voice traffic from the RNCs to MSC k cannot exceed the MSC capacity, which is

express as follows:

23 23 3

vj jk vk

j Jf x w k K

(11)

Also, data traffic from the RNC to SGSN l cannot exceed the SGSN capacity, which is express as

follow

24 24 4

dj jl vl

j Jf x w l L

(12)

Like the previous solution we can express our cabling cost in similar way but the only problem is

we shod consider three case BSC RNC, RNCMSC and RNCSGSN

So our cabling cost is

12 12 23 23 24 24

ij ij jk jk jl jl

i I j J j J k K j J l L

C c x c x c x

(13)

Now in case of handoff cost again we three layer architecture now considering the liner

programming we can express the BSCRNCMSC handoff is as

'

' '

1 3 12 23(1 )(1 )i iii ii jj

i I j J i I j J

f h y y

(14)

Because 1st

consider the term'

3 12(1 )i iii ii

i I i I

h y

this is just like PCN network handoff cost

formulation. The only difference is that instead of BSC, MSC connection it is BSC, RNC

connection. Now'

23(1 )jjy is 1 if both the RNC doesnt control by the same RNC.

So the total term is express as like (14)

Similarly for the BSCRNCSGSN, the handoff cost is as

'

' '

2 4 12 24(1 )(1 )i iii ii jj

i I j J i I j J

f h y y

(15)

So the total cost function is express as


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' '

' ' ' '

1 2 12 12 23 23 24 24 3 12 23 4 12 24(1 )(1 ) (1 )(1 )i i i i

ij ij jk jk jl jl ii ii jj ii ii jj

i I j J j J k K j J l L i I j J i I j J i I j J i I j J

C f f c x c x c x h y y h y y

(16)

2.13

Dual homing in UMTSIn case of dual homing in we have two options

We may connect cells with one or two RNC but only one RNC is in action at a time

We may connect RNCs with one or two MSCs and SGSN but only one MSC and SGSN is in

action at a time

In [10] authors are formulated cost function for dual homing in RNC in UMTS network

2.14Heuristic MethodAssigning cell to switch is like Bin-picking problem in mathematics, so this is NP-hard problem

and can be solve by heuristic method. In [8] authors solve cell to switch assignment problem for

PCN network for both the single & dual home by greedy method & their own describe heuristic.

In [9],[14] authors solve the same problem by Tabu search method. In case of UMTS network

[9],[14] authors solve it by tabu and the use three level Tabu search for getting the better

solution. In [10] they compeer different Meta heuristic technique for giving us better

understanding

2.15Tabu searchTabu search is an adaptive technique used in combinatorial optimization problem the besic

Tabu search sis as follow

INITIALIZATION: choose an initial solution S in X

: = S ( )

nbiter: = 0 ( )

bestiter : = 0

( )

T := null (T is Tabu list)

Continue: = true

While Continue do

If (nbiter-bestiter>kmax) or (V-T=null)


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Then continue: = false

Else nbiter : = nbiter+1

Generate (N(S) is the neighborhoods of S)

Find the best solution S in

S: = S

Update T

If then

bestiter := nbiter

End if

end while

3 Future workSolving the cell to switch problem for UMTS network by some Meta heuristic method and also

involve kth step random walk model


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