Project Report Final11

8/14/2019 Project Report Final11

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Abstract

To provide quality of services to the end users during vertical handoff period,

heterogeneous wireless networks have to be aware of quality of services (QoS)

within each access network. The traditional vertical handoffs algorithms are

based on received signal strength (RSS) are not of QoS concerned and hence

cannot fulfill the requirements of the users. Here, I propose a new vertical

handoff algorithm which uses received signal to inference plus noise ratio (SINR)

from various access networks as the handoff criteria. In this algorithm, the SINR

from one network is converted to the equivalent SINR of the target, so that thehandoff algorithm can have the knowledge of achievable bandwidths from both

access networks to make handoff decisions with QoS consideration. It has been

observed that SINR based vertical handoff algorithm can consistently offer the

end users with maximum available bandwidth during vertical handoff contrary to

the RSS based vertical handoff algorithms. Also, it is observed that the

performance of RSS based handoff is different in different network conditions as

against the SINR based algorithm. System level simulations also reveal the

improvement of overall system throughputs using SINR based vertical handoff,

compared to the RSS based vertical handoff.


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Introduction

The real potential of broadband wireless networks lies with mobility. A hot debate

is centered on building metropolitan area networks using WiMAX (Worldwide

Interoperability for Microwave Access)[1] technology based on the IEEE 802.16

standards. Good mobility management schemes enable it to become the

disruptive solution that fulfills the promises of ubiquitous computing with

broadband access everywhere that was left unsatisfiable with the Wi-Fi and 3G

cellular solutions. The wide area coverage and co-existence of multiple wireless

access technologies pose a challenge to mobility in the metropolitan network.

The success of Wi-Fi network with IEEE 802.11x technology makes it possible toaccess broadband anywhere with low cost. However, WiFi suffers from two

drawbacks: limited coverage and restricted scalability. Existing propriety solutions

to extend its coverage or interconnection are not scalable. Cellular based 3G

network provide extended coverage, however, limitations on bandwidth and high

costs on infrastructure equipments prohibit its growth. The introduction of

broadband wireless WiMAX solution based on IEEE 802.16 technology makes it

possible a standard based low cost solution for the last mile. In particular, with its

coverage of 30 miles and non line of sight technology based on OFDM, it will be

able to construct a metropolitan network where broadband access from

anywhere within the area is possible. The current version is based on IEEE

802.16a that specifies a fixed wireless environment. It is expected that within the

next few years, we will observe an explosive growth in this area. It will be based

on the IEEE 802.16e standard. It extends the 802.16a specification with the

capability to support mobile users in the region. With the inclusion of mobility,

WiMAX could become the ultimate solution that provides a low latency, high

bandwidth, and wide area connectivity to mobile users which is long sought after

by the industry. A metropolitan network will cover an area of up to 30 miles.

Current study shows that the effective range for broadband coverage under

IEEE802.16a is 4 to 5 miles. The eventual network might be composed of many


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base stations connected together to provide broadband connectivity to hundreds

of stationary and mobile users. The intended applications of such a network are

real-time media streaming and VOIP. The network must guarantee that the

continuous services will not be disrupted while a mobile user switched its

connectivity from one station to another due to signal fading or change of

provider. The effectiveness of mobility depends on whether a moving node can

maintain continuous connectivity with the base station without packet loss or

delay during handoff. One characteristic is the handoff distance which specifies

the minimum coverage between adjacent base stations for a moving node at

maximum specified speed. Due to the proliferation of existing wireless

technologies, a metropolitan network will consist of various wireless accessing

technologies with different link speed and mobility support. It might include Wi-Fifor short distance WLAN, UMTS and CDMA2000 for broadband on 3G cellular

networks. It is bound to be a multimode environment. In case WiMAX becomes

the major broadband service provider to the metropolitan area, users should be

able to easily roaming among different technologies without interruption. Its

success depends on the integration of mechanisms to deal with handoffs. Within

a metropolitan network, a mobile user could switch between different access

technologies due to coverage and provider changes, like GPRS (General packet

radio service).

WiMax and GPRS are viewed as the future complementary access technologies.

From one side, UMTS (Universal Mobile Telecommunication System) core

network GPRS that uses GSM (Global System for Mobile Communication)

technology is capable of providing data transmission with medium speed over

wide area, supporting high numbers of mobile users. On the other side, IEEE

802.16a broadband network[2], WiMax can offer high data rates relatively in large

geographical areas as well as high data rate as compared to the cellular GPRS

and are expected to be widely deployed in the future network generation.

The services running over a GPRS link experience a dramatic decrease in

bandwidth and increase in latency, but keep up and running. This can be even


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more signicant if we consider that most of the time users connect to non real-

time services, like web or email. The main problem of next generation network is

to seamlessly transfer the connection of a mobile host exiting the coverage of the

GPRS to another access network with larger coverage area like WiMax. In other

words, interoperability is needed to support the mobile users between

GPRS, with mobile internet access, keeping the connection on line when

moving to WiMax access network, thus providing always on connectivity. But

the main issue will be to provide fast vertical handover between these

heterogeneous access networks taking into consideration the quality of service

(QoS), service continuity, security as well as cost effectiveness. The chapter1

includes what is vertical handoff, aim of the work, organization of rest of the

thesis.


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Chapter 1

1. Aim of the work

Vertical handoff process is always associated with two networks of differenttechnologies. Maintaining continuous and quality of service to a mobile user is

more challenging task in a vertical handoff process. The aim of the work is to

make vertical handoff between WiMaX and GPRS without compromising the

continuity and quality of service to the users. Normally, received signal strength

(RSS) from a mobile user is considered as the means of handoff decision. But, it

has a lot of pitfalls. Therefore, instead of RSS, another approach known as

Signal to noise plus interference ratio (SINR) has been used as the means of

handoff decision between WiMaX and GPRS to reduce the inefficiency

associated with RSS based approach. Moreover, transmission power control

mechanism has been introduced for the mobile to maintain its SINR for effective

throughput of the system. The calculation of SINR in mobile station needs the

amount of noise and interference associated with the background.

1.1 Organization of the dissertation

The rest of the thesis is organized in the following way:

Chapter 2 includes related works

Chapter 3 includes background works of a handoff process

Chapter 4 includes a brief description about GPRS and WiMaX Technology

Chapter 5 includes the proposed algorithm


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Chapter 6 includes the simulation result

Chapter 2

1. Related work

This work consists of the summary of different papers of different authors,

related to the work carried out by me. The main aim of this chapter is to bringin to focus the related topics of my work. Following are the related work taken

into consideration for carrying out work.

a) Power Control by Interference Prediction for Broadband Wireless

Packet Networks [3]: A Kalman-lter method for power control is proposed

for broadband, packet-switched TDMA wireless networks. By exploiting the

temporal correlation of co-channel interference, a Kalman lter is used to

predict future interference power. Based on the predicted interference and

estimated path gain between the transmitter and receiver, transmission power

is determined to achieve a desired signal-to-interference-plus-noise ratio

(SINR). A condition to ensure power stability in the packet-switched

environment is established and proven for a special case of the Kalman-lter

method. The condition generalizes the existing one for a xed path-gain

matrix, as for circuit-switched networks. Specically, power control has been

shown to be a useful technique to improve performance and capacity of time-

division-multiple-access (TDMA) wireless networks. In addition to

performance improvement, power control is actually essential in solving the

near-far problem in code-division-multiple-access (CDMA) networks. In this

paper, we focus on broadband packet-switched TDMA networks with data


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rates up to several megabits per second. The advantage of the Kalman lter

is that it is simple, due to its recursive structure and robust over a wide range

of parameters, and it possibly provides an optimal estimate in the sense of

minimum mean square error. Kalman lters have been applied successfully to

many systems [BH97]. As for wireless networks, [DJM96] proposes using a

Kalman lter for call admission in CDMA networks. But, here in this report it is

shown that Kalman ltering is also useful for power control in TDMA networks.

b) Combined SINR Based Vertical Handoff Algorithm for Next

Generation Heterogeneous Wireless Networks [4]: Next generation

heterogeneous wireless networks offer the end users with assurance of QoS

inside each access network as well as during vertical handoff between them.For guaranteed QoS, the vertical handoff algorithm must be QoS aware,

which cannot be achieved with the use of traditional RSS as the vertical

handoff criteria. In this paper, the author of this paper proposes a vertical

handoff algorithm which uses received SINR from various access networks as

the handoff criteria. This algorithm considers the combined effects of SINR

from different access networks with SINR value from one network being

converted to equivalent SINR value to the target network, so the handoff

algorithm can have the knowledge of achievable bandwidths from both

access networks to make handoff decisions with QoS consideration. His

analytical results confirm that the new SINR based vertical handoff algorithm

can consistently offer the end user with maximum available bandwidth during

vertical handoff contrary to the (received signal strength) RSS based vertical

handoff, whose performance differs under different network conditions.

System level simulations also reveal the improvement of overall system

throughputs using SINR based vertical handoff, comparing with the RSS

based vertical handoff. Having the relationship between the maximum

achievable data rate and the receiving SINR ( AP) from both WLAN and

WCDMA ( BS) makes the SINR based vertical handoff method applicable, in

which the receiving SINR from WCDMA BS is being converted to the


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equivalent AP required to achieve the same data rate in WLAN, and

compared with the actual receiving SINR from WLAN. With the combined

effects of both SINR being considered, handoff is triggered while the user is

getting higher equivalent SINR from another access network. It means that

given the receiver end SINR measurements of both WLAN and WCDMA

channel, the handoff mechanism now has the knowledge of the estimated

maximum possible receiving data rates a user can get from either WLAN or

WCDMA at the same time within the handover zone, where both WLAN and

WCDMA signal are available. This gives the vertical handoff mechanism the

ability to make handoff decision with multimedia QoS consideration, such as

offer the user maximum downlink throughput from the integrated network, or

guarantee the minimum user required data rate during vertical handoff.

c) SINR Estimation for Power Control in Systems with Transmission

Beamforming [5]: The author of this paper takes a unied approach to the

downlink transmission power control, while a transmission beamforming is

applied in the base station. The proposed scheme is based on the estimation

of signal-to-interference-and-noise-ratios (SINRs) by antenna array

measurement and using this estimate in transmission power control. Hence

power control algorithms needing SINR-levels can be applied instead of the

simple relay power control. The SINR estimation technique does not require

any additional measurements compared to a separate adaptive beamforming

and power control, since the required measurements are needed for the

adaptive beamforming update. The estimation is based on the knowledge of

the level of caused interference to the multiple access links in the same cell,

and the utilization of relay power control commands in SINR estimation.

Adaptive beamforming is an antenna array technique used to reduce the

interference experienced by the receivers. Antenna array is a group of

antennas in the transmitter or in the receiver of a radio link This method

considers systems with transmission beamforming in base stations. The

interference reduction of transmission beamforming is based on spatial


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ltering, in which transmitted waveforms are either amplied or cancelled

depending on the directions of departure to the antenna array.

d) On the Use of SINR for Interference-aware Routing in Wireless Multi-

hop Networks [6]: This work considers the problem of mitigating interference

and improving network capacity in wireless multi-hop networks. An ongoing

aim of this research is to design a routing metric which is cognizant of

interference. To address this issue, and based on the measurement of the

received signal strengths, we propose a 2-Hop interference Estimation

Algorithm .With the use of the received signal level, a node can calculate the

signal to interference plus noise ratio (SINR) of the links to its neighbors. The

calculated SINR is used to infer the packet error rate (PER) between a nodeand each of its rst tier interfering nodes set. Then, the residual capacity at a

given node is estimated using the calculated PERs. Based on the capacity

estimation analysis, a new routing metric, EBC (Estimated Balanced

Capacity), is proposed. EBC uses a cost function at the aim of load-balancing

between the di erent ows within the network. Extensive simulations show

that EBC improves tremendously the network capacity and also enhances the

VoIP calls quality.

e) Vertical handover criteria and algorithm in IEEE 802.11 and 802.16

hybrid network [7]: Hybrid networks based, for instance, on systems such as

WiMAX and WiFi can combine their respective advantages on coverage and

data rates, offering a high Quality of Service (QoS) to mobile users. In such

environment, WiFi/WiMAX dual mode terminals should seamlessly switch

from one network to another, in order to obtain improved performance or at

least to maintain a continuous wireless connection. This paper proposes a

new user centric algorithm for vertical handover, which combines a trigger to

continuously maintain the connection and another one to maximize the user

throughput (taking into account the link quality and the current cell load). This

aims of this paper are dening an efcient user-driven vertical and over


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mechanism which does not require any change on network and protocol

architecture, and that can furthermore e easily applied in current WiFi/WiMAX

hybrid systems. To is purpose, the author has introduced the estimation of

two common network performance parameters, data rate and network load,

based on a measurement of Signal to Interference-plus-Noise Ratio (SINR)

level and channel occupancy respectively. Then they propose a novel

algorithm which embeds two independent triggers: the rst one aims at

maintaining the wireless connection, the second one at maximizing the

network performance.

f) A Performance Evaluation of Vertical Handoff Scheme between Mobile

WiMax and Cellular Networks [8]: This paper proposes a cost-effectivescheme for fast handoff between mobile WiMax and cdma2000 networks. The

smoothly integration scheme proposed in this paper adopts the advantages of

both loosely integration and tightly integration schemes: cdma2000 and

Mobile WiMax networks provide their own services independently and, on

vertical handoff between them, support seamless services by fast handoff.

Since we present protocol stacks as well as operation flows considering

cdma2000 and Mobile-WiMax standard specifications, the proposed scheme

can be implemented with minimal modification of existing Mobile WiMax and

cdma2000 networks. As result of simulation, the performance of the proposed

scheme is proved compared with others.


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Chapter 3

3. Background of the work

The background of the work covers those which involves in carrying out the

handoff between two networks. Before performing handoff it is important to know

these activities to carry out the handoff operation smoothly.

3.1 Handoff in Wireless Mobile Networks

Mobility is the most important feature of a wireless cellular communication

system. Usually, continuous service is achieved by supporting handoff (or

handover) from one cell to another. Handoff is the process of changing the

channel (frequency, time slot, spreading code, or combination of them)

associated with the current connection while a call is in progress. It is often

initiated either by crossing a cell boundary or by deterioration in quality of the

signal in the current channel. Handoff is divided into two broad categories hard

and soft handoffs. They are also characterized by break before make and

make before break. In hard handoffs, current resources are released before

new resources are used; in soft handoffs, both existing and new resources are


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used during the handoff process. Poorly designed handoff schemes tend to

generate very heavy signaling traffic and, thereby, a dramatic decrease in quality

of service (QoS). The reason why handoffs are critical in cellular communication

systems is that neighboring cells are always using a disjoint subset of frequency

bands, so negotiations must take place between the mobile station (MS), the

current serving base station (BS), and the next potential BS. Other related

issues, such as decision making and priority strategies during overloading, might

influence the overall performance.

3.2 Types of Handoffs

Handoffs are broadly classified into two categorieshard and soft handoffs.

Usually, the hard handoff can be further divided into two different types intra andintercell handoffs known as horizontal as well as vertical handoff respectively.

The main topic of our discussion is the vertical handoff between WiMaX and

GPRS systems.

3.2.1 Horizontal Handoff

In this handoff process, the handoff of a mobile terminal takes place between

base stations supporting the same network technology. For example, the

changeover of signal transmission due to the mobility of the mobile terminal from

an IEEE 802.11b base station to a neighboring IEEE 802.11b base station is

considered as a horizontal handoff process. Signal strength and channel

availability are needed to consider in horizontal handoffs.


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3.2.2 Vertical handoff:

The vertical handover was introduced with the development of different wireless

technologies and the coexistence of their networks including GSM, GPRS, and

UMTS as cellular networks and WiFi, WiMAX as broadband access networks.This handoff process of a mobile terminal takes place among access points

supporting different network technologies. For example, the changeover of signal

transmission from an IEEE 802.16 WiMax base station to a cellular GPRS

network is considered as a vertical handoff process. Due to the different

technologies of the networks, more than one interface is required during the

handoff process.

3.3 Handoff Initiation [9]

A hard handoff occurs when the old connection is broken before a new

connection is activated. It is assumed that the signal is averaged over time, so

that rapid fluctuations due to the multipath nature of the radio environment can be


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eliminated. Figure 1 shows a MS moving from one BS (BS1) to another (BS2).

The mean signal strength of BS1 decreases as the MS moves away from it.

Similarly, the mean signal strength of BS2 increases as the MS approaches it.

This figure is used to explain various approaches described in the following

subsection.

3.3.1 Relative Signal Strength

This method selects the strongest received BS at all times. The decision is based

on a mean measurement of the received signal. In Figure1 the handoff would

occur at position A. This method is observed to provoke too many unnecessary

handoffs, even when the signal of the current BS is still at an acceptable level.

T1

T2

BS1 BS2 A B DC

Fig: 1 Movement of an MS in the handoff zone

BS1 Signal BS2 Signal

h


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This method allows a MS to hand off only if the current signal is sufficiently weak

(less than threshold) and the other is the stronger of the two. The effect of the

threshold depends on its relative value as compared to the signal strengths of the

two BSs at the point at which they are equal. If the threshold is higher than this

value, say T1 in Figure 1 this scheme performs exactly like the relative signal

strength scheme, so the handoff occurs at position A. If the threshold is lower

than this value, say T2 in Figure 1 the MS would delay handoff until the current

signal level crosses the threshold at position B. In the case of T3, the delay may

be so long that the MS drifts too far into the new cell. This reduces the quality of

the communication link from BS1 and may result in a dropped call. In addition,

this results in additional interference to co-channel users. Thus, this scheme may

create overlapping cell coverage areas. A threshold is not used alone in actualpractice because its effectiveness depends on prior knowledge of the crossover

signal strength between the current and candidate BSs.

3.3.2 Relative Signal Strength with Hysteresis

This scheme allows a user to hand off only if the new BS is sufficiently stronger

(by a hysteresis margin, h in Figure 1) than the current one. In this case, the

handoff would occur at point C. This technique prevents the so-called ping-pong

effect, the repeated handoff between two BSs caused by rapid fluctuations in the

received signal strengths from both BSs. The first handoff, however, may be

unnecessary if the serving BS is sufficiently strong.

3.3.3 Relative Signal Strength with Hysteresis and Threshold

This scheme hands a MS over to a new BS only if the current signal level drops

below a threshold and the target BS is stronger than the current one by a given

hysteresis margin. In Figure 1, the handoff would occur at point D if the threshold

is T3.


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3.4 Handoff Decision

The decision-making process of handoff may be centralized or decentralized (i.e.,

the handoff decision may be made at the MS or network). From the decision

process point of view, one can find at least three different kinds of handoff

decisions.

3.4.1 Network-Controlled Handoff

In a network-controlled handoff protocol, the network makes a handoff decision

based on the measurements of the MSs at a number of BSs. Network-controlled

handoff is used in first-generation analog systems such as AMPS (advancedmobile phone system), TACS (total access communication system), and NMT

(advanced mobile phone system).

3.4.2 Mobile-Assisted Handoff

In a mobile-assisted handoff process, the MS makes measurements and the

network makes the decision. In the circuit-switched GSM (global system mobile),

the BS controller (BSC) is in charge of the radio interface management.

3.4.3 Mobile-Controlled Handoff

In mobile-controlled handoff, each MS is completely in control of the handoff

process. MS measures the signal strengths from surrounding BSs and

interference levels on all channels. A handoff can be initiated if the signal

strength of the serving BS is lower than that of another BS by a certain threshold.

3.5 Desirable features of handoff

An efficient handoff algorithm can acquire many desirable features. Some of the

major desirable features of any handoff algorithm are described below.

Desirable f eatures of handoff


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Maximize Maintain Minimize

3.5.1 Reliability

A handoff algorithm should be reliable. This means that the call should have

good quality after a handoff. Many factors help in determining the potential

service quality of a candidate base station. Some of these factors include signal-to-interference ratio (SIR), signal-to-noise ratio (SNR), received signal strength

(RSS), and bit error rate (BER).

3.5.2 Seamless

A handoff algorithm should be fast so that the mobile device does not

experience service degradation or interruption during the handoff process.

Service degradation may be due to a continuous reduction in signal strength or

an increase in co-channel interference (CCI).

3.5.3 Interference

A handoff algorithm should avoid high interference. The Co-channel and

interchannel interferences can degrade the transfer rate of a wireless network.

Co-channel interference is caused by devices transmitting on the same channel

and on the other hand, interchannel interference is caused by devices

transmitting on adjacent channels.

3.5.4 Load balancing

A handoff algorithm should balance traffic in all cells, whether of the same or

different network type. This helps to eliminate the borrowing of channels from the

neighboring cells to reduce the probability of new call blocking.

R eliability Seamless Inter f erence

Per formance Load balancing No of h andoff


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3.5.5 Minimizing the no of handoff

The number of handoffs should be minimized in a handoff scenario, because

more the number of handoff attempted, the greater the chances that a call will be

denied access to a channel, resulting in a higher handoff call dropping

probability.

3.6.2 Vertical handoff decision

In vertical handoffs, whether a handoff should take place or not depends on

many network characteristics. Following characteristics are particularly important

for this type of decision in addition to the two in the horizontal decision.

3.6.2.1 Quality of Service

Handing over to a network with better conditions and higher performance would

usually provide improved service facility. Transmission rates, error rates, and

other characteristics have to be measured in order to decide which network can

provide a higher assurance of continuous connectivity.

3.6.2.2 Cost of Service

The cost of the different services to the user is a major issue, and could

sometimes be the decisive factor in the choice of a network. The cost of service

of new network set by the internet provider may be higher than the previous one.

3.6.2.3 Security

Risks are inherent in any wireless technology. Perhaps the most significant

source of risks in wireless networks is the technologys underlying

communications medium. That is the airwave which is open to intruders.

3.6.2.4 Power Requirements

Wireless devices have limited battery power. When the level decreases, handing

off to a network with low power may require much time.


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3.6.2.5 Proactive Handoff

In proactive handoff, the users are involved in the vertical handoff decision. By

permitting the user to choose a preferred network, the system is able to

accommodate the users special requirements.

3.6.2.6 Velocity

The velocity of the mobile device has a greater effect on vertical handoff decision

than in horizontal handoffs. Because of the heterogeneous networks, handing off

to an embedded network when traveling at high speeds is discouraging since a

handoff back to the original network would occur very shortly afterward.

3.6.2.7 Radio Link Transfer

Radio link transfer, the second part of the handoff process, is the task of

establishing links to a call at the new base station. The radio link is transferred

from the old to the new base station.

3.6.2.8 Channel Allocation

The final handoff stage is channel assignment which consists of the allocation of

channels at the new base station.

3.7 Mobility management

Mobility in handoff means movement of a user from one location to another from

time to time. Mobility of a user in a wireless communication system has a big

impact on maintaining the continuity of the service to the users. Mobility

management has widely been recognized as one of the most important and

challenging problems for seamless handoff of a mobile device across wireless

networks. In this situation, such technology needs to be used so that mobile


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users receive their services without the disruption of communications. Two main

aspects need to be considered in mobility management are location management

and handoff management.

3.7.1 Location management

It means locating mobile terminals in order to deliver data packets to them.

Operations of location management include:

3.7.1.1 Location registration: Also know as location update or tracking, i.e.

the procedure that the mobile node informs the network and other nodes of its

new location by updating the corresponding location information entries stored

in some databases in the networks.

3.7.1.2 Location paging

Also know as locating or searching. In most cases location information stored in

databases is only the approximate position of a mobile device. Location paging is

the procedure that the network tries to find the mobile devices exact locality

when calls/packets need to be delivered to the mobile device.

Some key research issues for location management include:

3.7.1.3 Addressing

It means how to represent and assign address information to mobile nodes.

3.7.1.4 Database structure

It is for how to organize the storage and distribution of the location information of

mobile nodes. Database structure can be either centralized or distributed.

3.7.1.5 Location update time

It means when a mobile node should update its location information by renewing

its entries in corresponding databases.

3.7.1.6 Paging scheme

Paging means how to determine the exact location of a mobile node within a

limited time.


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GPRS enabled device is "always on", so as long ones equipment in switched on,

he has an open channel for sending and receiving data.

Being used the packet-switched technology, GPRS users are always connected,

always on-line, and may be charged only for the amount of data that is

transported. Voice calls can be made simultaneously over GSM-IP while a data

connection is operating, depending on the phone Class and Type. Thus GPRS is

efficient, fast and cost effective as compared to GSM technology as explained

follows.

y Efficient - GPRS mobile devices only use the GSM network when data is

transferred. The GSM connection is not dedicated to each user; thereforeit can be shared with many users resulting in efficient use of the network.

y F ast - GPRS gives speeds of upto 5 times faster than GSM. GPRS offers

maximum data rates of 56Kbps (down) and 14.4kbps (up); however, this is

shared bandwidth therefore actual data rates are potentially lower.

y Payment based on data usage - Billing is not based on time, but on the

amount of data actually transferred.

4.1 Architecture of GPRS [11]

GPRS provides packet radio access for Global System for Mobile

Communications (GSM) and uses time-division multiple access (TDMA) for

providing services to the users. GPRS is a data network that overlays a second-

generation GSM network. This data overlay network provides packet data

transport at rates from 9.6 to 171 kbps. Additionally, multiple users can share the

same air-interface resources simultaneously. Following is the GPRS Architecture

diagram:

PSTN


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Signaling

Circuit Switched GSM

Packet Switched Data Signaling

F igure: 2 GPRS Architecture

4.1.1 GPRS Mobile Stations

New Mobile Station are required to use GPRS services because existing GSM

phones do not handle the enhanced air interface or packet data. A variety of MS

can exist, including a high-speed version of current phones to support high-speed

data access, a new PDA device with an embedded GSM phone, and PC cardsfor laptop computers. These mobile stations are backward compatible for making

voice calls using GSM.

4.1.2 GPRS Base Station Subsystem

CircuitSwitched GPRSGSM

HLR

GGSNAUC

EIR

GGSN

SGSN SGSN

Internet X.25 network

BSC

MSC Internal Backbone Network


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Each BSC requires the installation of one or more Packet Control Units (PCUs)

and a software upgrade. The PCU provides a physical and logical data interface

to the base station subsystem (BSS) for packet data traffic. The BTS can also

require a software upgrade but typically does not require hardware

enhancements.

When either voice or data traffic is originated at the subscriber mobile, it is

transported over the air interface to the BTS, and from the BTS to the BSC in the

same way as a standard GSM call. However, at the output of the BSC, the traffic

is separated; voice is sent to the mobile switching center (MSC) per standard

GSM, and data is sent to a new device called the Serving GPRS support node

(SGSN) via the PCU over a frame relay interface. Following two newcomponents, called GPRS support nodes (GSNs), are added.

4.1.3 Gateway GPRS support node (GGSN)

The Gateway GPRS Support Node acts as an interface and a router to external

networks. The GGSN contains routing information for GPRS mobiles, which is

used to tunnel packets through the IP based internal backbone to the correct

Serving GPRS Support Node. The GGSN also collects charging informationconnected to the use of the external data networks and can act as a packet filter

for incoming traffic.

4.1.4 Serving GPRS support node (SGSN)

The Serving GPRS Support Node is responsible for authentication of GPRS

mobiles, registration of mobiles in the network, mobility management, and

collecting information for charging for the use of the air interface.

4.1.5 Internal Backbone

The internal backbone is an IP based network used to carry packets between

different GSNs. Tunneling is used between SGSNs and GGSNs, so that internal


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backbone does not need any information about domains outside the GPRS

network. Signaling from a GSN to a MSC, HLR or EIR is done using SS7.

4.1.6 Routing Area

GPRS introduces the concept of a routing area. This is much the same as a

Location Area in GSM, except that it will generally contain fewer cells. Because

routing areas are smaller than Location Areas, less radio resources are used

when a paging message is broadcast.

4.2 WiMaX System

WiMaX stands for Worldwide Inter operability for Micr owave Access is based on wireless br oadband technology. WiMAX technology based on the IEEE 802 .16

s pecif ications to enable the delivery of last-mile wireless br oadband access as an

alternative to cable and DSL. WiMAX has a rich set of features with a lot of flexibility

in terms of deployment options and potential service offerings. Some of the more

salient features that deserve highlighting are as follows:

4.2.2 O F DM-based physical layer

The WiMAX physical layer (PHY) is based on orthogonal frequency divisionmultiplexing, a scheme that offers good resistance to multipath, and allows

WiMAX to operate in (non line of sight) NLOS conditions. OFDM is now widely

recognized as the method of choice for mitigating multipath for broadband

wireless.

4.2.3 Very high peak data rates

WiMAX is capable of supporting very high peak data rates. In fact, the peak PHY

data rate can be as high as 74Mbps when operating using a 20MHz wide

spectrum. More typically, using a 10MHz spectrum operating using TDD scheme

with a 3:1 downlink-to-uplink ratio, the peak PHY data rate is about 25Mbps and

6.7Mbps for the downlink and the uplink respectively.

4.2.4 Scalable bandwidth and data rate support


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WiMAX has a scalable physical-layer architecture that allows for the data rate to

scale easily with available channel bandwidth. This scalability is supported in the

OFDMA mode, where the FFT (fast fourier transform) size may be scaled based

on the available channel bandwidth.

4.2.5 Adaptive modulation and coding (AMC)

WiMAX supports a number of modulation and forward error correction (FEC)

coding schemes and allows the scheme to be changed on a per user and per

frame basis, based on channel conditions. AMC is an effective mechanism to

maximize throughput in a time-varying channel. The adaptation algorithm

typically calls for the use of the highest modulation and coding scheme that can

be supported by the signal-to-noise and interference ratio at the receiver suchthat each user is provided with the highest possible data rate that can be

supported in their respective links.

4.2.6 Link-layer retransmissions

For connections that require enhanced reliability, WiMAX supports automatic

retransmission requests (ARQ) at the link layer. ARQ-enabled connections

require each transmitted packet to be acknowledged by the receiver;

unacknowledged packets are assumed to be lost and are retransmitted.

4.2.7 Support for TDD and F DD

IEEE 802.16-2004 and IEEE 802.16e-2005 supports both time division duplexing

and frequency division duplexing, as well as a half-duplex FDD are cost effective.

4.2.8 Orthogonal frequency division multiple access (O F DMA)

Mobile WiMAX uses OFDM as a multiple-access technique, whereby different

users can be allocated different subsets of the OFDM tones. OFDMA facilitates

the exploitation of frequency diversity and multiuser diversity to significantly

improve the system capacity.

4.2.9 F lexible and dynamic per user resource allocation


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Both uplink and downlink resource allocation are controlled by a scheduler in the

base station. Capacity is shared among multiple users on a demand basis, using

a burst TDM scheme. When using the OFDMA-PHY mode, multiplexing is

additionally done in the frequency dimension, by allocating different subsets of

OFDM subcarriers to different users. Resources may be allocated in the spatial

domain as well when using the optional advanced antenna systems (AAS). The

standard allows for bandwidth resources to be allocated in time, frequency, and

space and has a flexible mechanism to convey the resource allocation

information on a frame-by-frame basis.

4.2.10 Support for advanced antenna techniques

The WiMAX solution has a number of hooks built into the physical-layer design,which allows for the use of multiple-antenna techniques, such as beamforming,

space-time coding, and spatial multiplexing. These schemes can be used to

improve the overall system capacity and spectral efficiency by deploying multiple

antennas at the transmitter and/or the receiver.

4.2.11 Quality of service support

The WiMAX MAC layer has a connection-oriented architecture that is designed to

support a variety of applications, including voice and multimedia services. The

system offers support for constant bit rate, variable bit rate, real-time, and non-

real-time traffic flows, in addition to best-effort data traffic. WiMAX MAC is

designed to support a large number of users, with multiple connections per

terminal, each with its own QoS requirement.

4.2.12 Robust security

WiMAX supports strong encryption, using Advanced Encryption Standard (AES),

and has a robust privacy and key-management protocol. The system also offers

a very flexible authentication architecture based on Extensible Authentication

Protocol (EAP), which allows for a variety of user credentials, including

username/password, digital certificates, and smart cards.


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4.2.13 Support for mobility

The mobile WiMAX variant of the system has mechanisms to support secure

seamless handovers for delay-tolerant full-mobility applications, such as VoIP.

The system also has built-in support for power-saving mechanisms that extend

the battery life of handheld subscriber devices. Physical-layer enhancements,

such as more frequent channel estimation, uplink subchannelization, and power

control, are also specified in support of mobile applications.

4.2.14 IP based architecture

The WiMAX Forum has defined a reference network architecture that is based on

an all-IP platform. All end-to-end services are delivered over an IP architecturerelying on IP-based protocols for end-to-end transport, QoS, session

management, security, and mobility. Reliance on IP allows WiMAX to ride the

declining costcurves of IP processing, facilitate easy convergence with other

networks, and exploit the rich ecosystem for application development that exists

for IP.

4.3 Architecture of WiMaX System [12]

The network reference model describes the architecture of WiMaX developed by

the WiMAX Forum defines a number of functional entities and interfaces between

those entities is shown in the figure 3 given below. The design of WiMAX network

is based on the following major principles. They are spectrum, topology, inter-

working, IP connectivity and mobility management.

BB

M M M

Access


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Figure: IP based WiMaX Network Architecture

The WiMAX Forum has def ined an arc hitecture that def ines how a WiMAX netw ork

connects with o ther netw orks, and a variety of o ther as pects of op erating suc h a netw ork,

including address allocation, aut henticati on, etc. An overview of the architecture is given

in the illustrati on. This def ines the following com po nents:

y ASN: the Access Service Network

BSS

Gatewa


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y BS: Base station, part of the ASN

y ASN-GW: the ASN Gateway, part of the ASN

y CSN: the Connectivity Service Network

y AAA: AAA Server, part of the CSN

y NAP: a Network Access Provider

y NSP: a Network Service Provider

4.3.1 Base station (BS) [13]

The BS is responsible for providing the air interface to the MS. Additional

functions that may be part of the BS are micro mobility management functions,

such as handoff triggering and tunnel establishment, radio resource

management, QoS policy enforcement, traffic classification, DHCP (Dynamic

Host Control Protocol) proxy, key management, session management, and

multicast group management.

4.3.2 Access service network gateway (ASN-GW)

The ASN gateway typically acts as a layer 2 traffic aggregation point within an

ASN. Additional functions that may be part of the ASN gateway include intra-ASN

location management and paging, radio resource management and admission

control, caching of subscriber profiles and encryption keys, AAA client

functionality, establishment and management of mobility tunnel with base

stations, QoS and policy enforcement, and foreign agent functionality for mobile

IP, and routing to the selected connectivity service network (CSN).

4.3.3 Connectivity service network (CSN)

The CSN provides connectivity to the Internet, ASP, other public networks, and

corporate networks. The CSN includes AAA servers that support authentication

for the devices, users, and specific services. The CSN is own by NSP also


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provides per user policy management of QoS and security. The CSN is also

responsible for IP address management, support for roaming between different

NSPs, location management between ASNs, and mobility and roaming between

ASNs. The CSN also provides per user policy management of QoS and security.

The CSN is also responsible for IP address management, support for roaming

between different NSPs, location management between ASNs, and mobility and

roaming between ASNs.

Chapter 5

5. Proposed System


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y Use of RSS based vertical handoff cannot provide the user with quality of

service (QoS) throughput, as the vertical handoff algorithm itself is not

QoS aware. But SINR can provide QoS since SINR takes into account the

interference and noise at the transmission end.

y Analysis results show that SINR based vertical handoff provides higher

average throughput for end users as compared to the RSS based vertical

handoff with various thresholds settings, and also can adapt to different

network conditions, such as different noise level and load factor.

Simulation results further confirm that the SINR based vertical handoff

improves the overall system throughputs.

y In real networks, interference power will depend on the user location as

well as the density of the users. Therefore, only the SINR based vertical

handoff can guarantee multimedia QoS specifying the achieved date rate

for end user inside vertical handover zone. This is also another important

reason that our SINR based vertical handoff can adapt to the network

conditions and can provide consistently maximum available throughputs to

the end user, which RSS based handoff cannot achieve.

y SINR based vertical handoff algorithm can consistently offer the end user

with maximum available bandwidth during vertical handoff contrary to theRSS based vertical handoff, whose performance differs under different

network conditions.

y SINR based does handoff actually when it is necessary. But RSS based

sometimes does unnecessary handoffs under interference and noisy

condition even though the signal strength in current network is still greater

than the threshold.

y SINR based handoff will be able reduce the ping pong effect as controlling

the power of transmission it will be able to provide the required SINR for

the mobile even if the mobile user is closed to the boundary of the

neighboring network.


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5.2 System assumptions for the algorithm

y In the networks time is divided into slots. Let each data message be

divided into a number of packets, each of which can be sent in one time

slot. Allows multiple, contiguous time slots to be used by the same

transmitter for sending a message, thus producing temporal correlation for

interference

y The channel gain between a mobile station and its base station is

measured as follows:

Gain (or loss) = t r P P / , r P is the received power and t P is the transmitted

power.

y The medium-access control (MAC) protocol used allows at most one

terminal in each sector or cell to send data at a time. Therefore, no data

contention occurs within the same sector or cell. Also, a terminal can

transmit in contiguous time slots. Moreover, the base station knows which

terminal is scheduled to transmit at different times.

y Base stations do not exchange control information among themselves on

a per packet basis in real time due to the large volume of data.y The interference power is equal to the difference between the total

received power and the power of the desired signal.

5.3 Power Control using Kalman-lter method

A Kalman-lter method for power control is proposed for broadband, packet-

switched TDMA wireless networks. By exploiting the temporal correlation of co-

channel interference, a Kalman lter is used to predict future interference power.Based on the predicted interference and estimated path gain between the

transmitter and receiver, transmission power is determined to achieve a desired

signal-to-interference-plus-noise ratio (SINR). Performance results reveal that the


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Kalman-lter method for power control provides a signicant performance

improvement.

Although the Kalman-lter method is applicable to both the uplink (from terminal

to base station) and the downlink (from base station to terminal) we will focus onthe downlink here.

5.4 Interference prediction by Kalman F ilter method

We apply the Kalman-lter method to predict interference power for predicting

SINR by adjusting transmission power. Using this method, each terminal

continuously measures the interference power for its assigned radio channel

(e.g., the same time slot of the consecutive TDMA frames). Let )(n I be the actual

interference-plus-noise power in dBm received at a given base station in time slot

n. In fact, )(n I is required to be estimated by the Kalman lter. Assume that the

noise power, which depends on the channel bandwidth, is given and xed. The

total interference is simply the thermal noise plus the measured interference. The

system dynamics of the interference plus noise power can be modeled as:

(1) )()1()( n F n I n I !

Where )(n

represents the uctuation of interference power when terminals start

new transmissions and/or adjust their transmission power in the time slot.

Let )(n Z be the measured interference power plus noise power in dBm for slot n

then

(2) )()()( n E n I n

!

By the Kalman filter theory, the time and measurement update equations for the

interference power are:

(3) )()1(~

n I n I !


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(4) Q(n))()1( ! n P n P

(5) 1-R(n)])()[()( ! n P n P n K

(6) ])()()[()()( n I n

n K n I n I !

(7) K (n)]1)[()( ! n P n P

Where, )(),(~ n I n I are the a priori and a posteriori estimates of )(n I .

)(n P , )( n P are the a priori and posteriori estimate error variances

respectively.

)(n

is the Kalman gain, and )(nQ and )(n R are the variances for the

process noise )(n

and measurement noise )(n

respectively.

)(n is estimated based on the interference measurements in the last W

slots as follows:

(8) )(/1)(1

!

!n

W ni

i Z W n Z X

(9) )]()([)1/(1)(1

2!

!

n

W ni

n

i

W n

W is used to capture the non stationary interference

)(n

Xis the average measured interference with noise over the last W

slots.

Also )(n R can be given by


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(10) )()( n n

^ !

Where, ^ is a given constant between 0 and 1

5.5 Determination of Transmission power

Let K is the target SINR, )(n p is the transmission power and )(n g the path gain

from the transmitting base station to the mobile station for slot n,

respectively. )(n I and )(n I represent the actual and predicated interference

power in dBm and let )(ni and )(~ ni denote the respective value in mW. Based

on )(n I the base station transmits in slot n with power

(11 ) )(/)(()( n g nin p K !

The goal of this of transmission power is to choose just enough power to achieve

the target SINR K .

When p(n) is the power of the base station selected by (11) for slot n, the actual

receiving SINR K (n) at the mobile station is

(12) )(/)(~)(/)()()( nininin g n pn K K !!

Where )(ni is the actual interference power in mW for the slot n. Thus (12)

implies that when predicted interference )(ni is accurate to actual interference

)(ni , the target SINR is achieved.

Even if )(ni is not exactly equal to )(ni , the method helps in reducing the spread

of )(nK as long as )(ni and )(ni are correlated.

Steps for the Kalman F ilter

The Kalman Filter method for power control is summarized below:


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1. For each slot n, each base station measures the interference power for the

time slot.

2. The interference measurements are used as input to the Kalman filter in

equation (3) to (10) to predict the interference power )1(~ n I in slot n+1.

3. Based on the MAC protocol in use, the base station tracks the path gain

)1(n g and selects the transmission power by (11) to meet a given target SINR

for the terminal that transmits in slot n+1.

4. The power level )1(n p is used for transmission to the mobile station in slot

n+1.

5.6 Calculation SINR at the mobile station from WiMaX and GPRS networks

5.6.1 Date rate using Shannon capacity formula

According to Shannon capacity formula, the maximum achievable data

rate R ij received by the user i from the base station j is given by:

Where, W is the bandwidth.

jiK is SINR received at user i when associated with GPRS or WiMaX

j B .X is the gap between uncoded QAM and capacity, minus the coding

gain.

Thus the if ws R and g s R are maximum achievable data rate from WiMaX

as well as from GPRS respectively, these can be represented in terms of the receiving SINR from the two networks as:

)/1(log 2 X K jiij W R !


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Where, wsK is SINR received from WiMaX on High Speed Downlink Packet

Access (HSDPA) Channel and g sK is SINR received from GPRS on

HSDP. The relationship between w sK and g sK is

5.6.2 Calculation for SINR at the mobile station

In this discussion, we consider the downlink traffic, as they normally require

higher bandwidth than uplink.

The SINR jiK received by user i from WiMaX base station jwb s can be

represented as:

! jk w sk

k ik jij jiP G P B P G

#,

/K

j P is the transmitting power of jw b s

ijG is the channel gain between user i and jw b s

P

is the background noise power at user receiver end.

The SINR jiK received by user i from GPRS base station j g b s can be

represented as:

)/1(log 2 wswswsws W R X K !

)/1(log 2 g s g s g s g s W R X K !

1)-)/1(( / W w sWg s g s g sw sw s X K X K !


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)/( jiij g sk

k ik jiij ji P G P G P

P G !K

k P is the total transmitting power of k b s

ji P is the transmitting power of jb s to user j

ijG is the channel gain between user i and jb s

5.6.3 Throughput calculation

In this analysis, consider a point to point model, in which a user is moving at

speed v from w b s ( 1 X ) to g b s ( 2 X ), as shown in the following figure. The

vertical handoff has shown to be taken place at point h

.

The total downlink throughputs can be represented as

g s

X

X g sw s

X

X w s

c rt X x Rc rt X x Rh

h ! 21

)()(U

Where c rt is cell residence time, and w s R and g s R is maximum data rate

received from WiMaX and GPRS.

1 X 2

X 1

X

ws R

h X

g s R

Figure: Point to point model


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For the RSS based vertical handoff, the h X is dependent on the minimum

required receiving power j P from WiMaX base station jwb s

In SINR based vertical handoff, h X is calculated based on the receiving

SINR from WiMaX and GPRS.So, It will be possible to compare the average throughputs for different

vertical handoff algorithm with different h X .

References1. A Mobile-IP Based Mobility System for Wireless Metropolitan Area Networks

--- by Chung-Kuo Chang.

2. www.wiremaxforum.org --- by WiMaX forum

3. Power Control by Interference Prediction for Broadband Wireless Packet

Networks ---by Kin K. Leung.

4. Combined SINR Based Vertical Handoff Algorithm for Next Generation

Heterogeneous Wireless Networks by --- Kemeng Yang, Iqbal Gondal, Bin Qiu

and Laurence S. Dooley, 2007.

5. SINR Estimation for Power Control in Systems with Transmission

Beamforming

---by Vesa Hasu, Student Member, IEEE, and Heikki Koivo, Senior Member,

IEEE, 2005.

6. On the Use of SINR for Interference-aware Routing in Wireless Multi-hop

Networks ---by Riadh M. Kortebi, Yvon Gourhant, Nazim Agoulmine.

7. Vertical handover criteria and algorithm in IEEE 802.11 and 802.16 hybrid

networks ---by Z. Daia, R. Fracchiaa, J. Gosteaub, P. Pellatia,G.Vivier.

8. A Performance Evaluation of Vertical Handoff Scheme between Mobile

WiMax and

Cellular Networks ---by Seongsoo Park, JaeHwang Yu, ,JongTae Ihm


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9. Handoff in Wireless Mobile Networks ---by Qing-An Zeng, Dharma P.

Agrawal

10. http://www.tutorialspoint.com/gprs/gprs_architecture.htm

11. http://www.en.wikipedia.org/wiki/WiMAX#Architecture

12. http://www.tutorialspoint.com/wimax/wimax_network_model.htm

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