Project Report Prasanta Pdf

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 the handoff algorithm can have the knowledge of achievable bandwidths from both access networks to make handoff decisions with QoS consideration. Moreover, power of the mobile station is controlled to maintain the SINR so that number handoff can be minimized due to ping pong effect. 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 popularity of wireless communication is increasing quite rapidly through out the world after the introduction of cellular and broadband [2] technologies. 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. The demand of broadband and cellular technology is increasing due to its superior quality of services (QoS), greater coverage area as well as low cost effectiveness. The success of Wi-Fi network with IEEE 802.11x technology makes it possible to access broadband anywhere with low cost. 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. 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 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. In case WiMAX

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becomes the major broadband service provider to the metropolitan area and GPRS (General packet radio service)[10] the major cellular service provider, users must be able to easily roaming among different technologies without interruption. The success will depend 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.

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[10] (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 802.16 broadband network, 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 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 and vice versa. But the main issue will be to provide fast vertical handover between these heterogeneous access networks of larger coverage area, considering the quality of service (QoS), continuous service as well as cost effectiveness. Therefore, better algorithm is necessary in the handover procedure instead of the received signal strength (RSS) based algorithm. It has been experimented that SINR is better than the RSS based since, it considers the noise and interference factors in the background of the networks. Vertical handoff is work of my thesis using SINR based approach. Moreover step is taken to control the transmission power of the mobile to maintain the SINR for reducing the number of handoff and saving the battery power depending on the noise and interference present.

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Chapter 1

1. Aim of the work

Vertical handoff process is always associated with two networks of different technologies. 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 Chapter 6 includes the simulation result

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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 bring in 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-filter method for power control is proposed for broadband, packet-switched TDMA wireless networks. By exploiting the temporal correlation of co-channel interference, a Kalman filter 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-filter method. The condition generalizes the existing one for a fixed path-gain matrix, as for circuit-switched networks. Specifically, 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 rates up to several megabits per second. The advantage of the Kalman filter 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 filters have been applied successfully to many systems [BH97]. As for wireless networks, [DJM96] proposes using a Kalman filter for call admission in CDMA networks. But, here in this report it is shown that Kalman filtering is also useful for power control in TDMA networks.

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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 (γAP) from both WLAN and WCDMA (γBS) makes the SINR based vertical handoff method applicable, in which the receiving SINR from WCDMA γBS is being converted to the equivalent γAP 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

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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 unified 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-tointerference-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 filtering, in which transmitted waveforms are either amplified 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

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packet error rate (PER) between a node and each of its first 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 different flows 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 defining an efficient user-driven vertical and over 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-plusNoise Ratio (SINR) level and channel occupancy respectively. Then they propose a novel algorithm which embeds two independent triggers: the first 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-effective scheme for fast handoff between mobile WiMax and cdma2000 networks. The smoothly

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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 MobileWiMax 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 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 categories—hard and soft handoffs. Usually, the hard handoff can be further divided into two different types intra and intercell 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.

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Figure 1: Hard Handoff

Figure 2: Soft Handoff

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.

GPRS

GPRS

Figure 3: Horizontal Handoff

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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.

GPRS

WiMaX

Figure 4: Vertical Handoff 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 eliminated. Figure 5 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 Figure 5 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.

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BS1 Signal

BS2 Signal

h T1 T2

BS1

A

B

C

D

BS2

Figure: 5 Movement of a mobile station in the handoff zone

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 5 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 5 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

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users. Thus, this scheme may create overlapping cell coverage areas. A threshold is not used alone in actual practice 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. 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 (advanced mobile phone

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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 handoff features Maximize

Maintain

Minimize

Reliability

Seamless

Interference

Performance

Load balancing

No of handoff

Figure 6: Desirable handoff features

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

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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.

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.

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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 technology’s 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. 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 user’s 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.

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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 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. Figure 7 shows the flow chart of a mobile station showing its process of association to a foreign network to make continuation of packet receiving during and after the vertical handoff process.

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MN

FA

HA

CN Packet dropping

Gets subnet info

IP Registration Request Send Request

Authenticates Assigns IP Tunnel Establishment Transmitting Tunnel Establishment Delivered

MN HA FA CN

Mobile Node Home Agent Foreign Agent Correspondent Node

Figure 7: Registration flow chart of a mobile node in a foreign network

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 device’s exact locality when calls/packets need to be delivered to the mobile device. Some key research issues for location management include:

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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. 3.8 Handoff management It means controlling the changes required during the handoff in order to maintain the connection with the mobile node. Operations of handoff management include: 3.8.1 Handoff triggering Initiating of handoff process is according to some conditions. Possible conditions may include e.g. signal strength, workload, bandwidth, cost, network topology change etc. 3.8.2 Connection re-establishing It means establishing new connection between the mobile node and the new access point. 3.8.3 Packet routing It means routing the data through the new connection path after establishment of the connection to the target access point.

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Chapter 4 4. GPRS System GPRS (General Packet Radio Service) is rapidly becoming a global standard for sending and receiving high-speed data across the GSM network. It is also known as GSM-IP (Internet Protocol) because it connects users directly to Internet Service Providers. It uses existing GSM network to transmit and receive TCP/IP based data to and from GPRS mobile devices. GPRS now makes it possible to deploy several new devices that have previously not been suitable over traditional GSM networks due to the limitations in speed (9600bps), message length of the Short Message Service (160 characters), dial up time and costs. These applications include Point Of Sale Terminals, Vehicle tracking systems, and monitoring equipment. It's even possible to remotely access and control in-house appliances and machines. Since, GPRS is a Radio Service, like a radio, a GPRS enabled device is "always on", so as long one’s 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. 

Efficient - GPRS mobile devices only use the GSM network when data is transferred. The GSM connection is not dedicated to each user; therefore it can be shared with many users resulting in efficient use of the network.



Fast - 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.



Payment based on data usage - Billing is not based on time, but on the amount of data actually transferred.

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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:

Circuit Switched GSM

X.25 network

Internet

PSTN

GPRS

GGSN

AUC

HLR

MSC

GGSN

Internal Backbone Network

EIR

SGSN

SGSN

BSC

Signaling Circuit Switched GSM Packet Switched Data Signaling

Figure 8: GPRS Network Architecture

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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 cards for laptop computers. These mobile stations are backward compatible for making voice calls using GSM. 4.1.2 GPRS Base Station Subsystem 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 new components, 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 information connected to the use of the external data networks and can act as a packet filter for incoming traffic.

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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 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 Interoperability for Microwave Access is based on wireless broadband technology. WiMAX technology based on the IEEE 802.16 specifications to enable the delivery of last-mile wireless broadband 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 OFDM-based physical layer The WiMAX physical layer (PHY) is based on orthogonal frequency division multiplexing, 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. 24 Evaluation notes were added to the output document. To get rid of these notes, please order your copy of ePrint 5.0 now.

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 downlinkto-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 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 such that 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 FDD 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.

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4.2.8 Orthogonal frequency division multiple access (OFDMA) 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 Flexible and dynamic per user resource allocation 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.

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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. 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 architecture relying 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.

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MS

MS

BS

BS

MS

BS

Access Network IP Network

ASN GW

ASP

IP Network Internet

AAA Connectivity Service Network (CSN)

PSTN

BSS

3GPP

Gateway

Figure 9: IP Based WiMaX Network Architecture

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The WiMAX Forum has defined an architecture that defines how a WiMAX network connects with other networks, and a variety of other aspects of operating such a network, including address allocation, authentication, etc. An overview of the architecture is given in the illustration. This defines the following components: 

ASN: the Access Service Network



BS: Base station, part of the ASN



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



CSN: the Connectivity Service Network



AAA: AAA Server, part of the CSN



NAP: a Network Access Provider



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).

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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 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.

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Chapter 5 5. Proposed System It has been observed that the traditional received signal strength (RSS) based algorithm suffers from major drawbacks which made us to choose another one which provide better service quality to the users during handoff. This new approach not only provide enhance service quality but also more efficient as compared to RSS based. This new approach is based on signal to noise plus interference ratio (SINR). This algorithm is proposed for vertical handoff between those different networks which supports time division multiple access multiplexing (TDMA). The proposed algorithm is SINR based and also controls the transmission power of the transmitter. This algorithm will provide better quality of services as well better system throughput as compared to RSS based algorithm because SINR is adaptive to noisy and overload condition and controlling transmission power minimizes the energy consumption and reduces the interference as well as increases the system capacity. In this proposed algorithm, the power required for the transmitter is calculated based on the required target SINR for the receiver. Since the algorithm is for TDMA systems, prior to the power calculation, interference and noise is measured using Kalman filter method for the slot n. In TDMA the interference and noise measures of the previous slot can be used to determine the transmission power required for the next slot to maintain the target SINR at the receiver. Therefore the measure of SINR of the slot n is used to adjust the power of the transmitter for the slot n+1 for achieving the required SINR at the receiver even when the user keeps moving. The SINR received by the mobile station from other networks is being converted equivalent SINR value of the current network required to achieve the same data rate in the current network. With this combined effects, handoff is triggered when the receiver receives greater SINR from another network. So the handoff algorithm can have the knowledge of achievable bandwidths from both access networks to make handoff decisions with QoS consideration.

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5.1 Major advantages of SINR based algorithm over RSS based

 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.

 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.

 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.

 SINR based vertical handoff algorithm can consistently offer the end user with maximum available bandwidth during vertical handoff contrary to the RSS based vertical handoff, whose performance differs under different network conditions.

 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.

 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

 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

 The channel gain between a mobile station and its base station is measured as follows: Gain (or loss) = Pr / Pt , Pr is the received power and Pt is the transmitted power.

 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.

 Base stations do not exchange control information among themselves on a per packet basis in real time due to the large volume of data.

 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-filter method A Kalman-filter method for power control is proposed for broadband, packet-switched TDMA wireless networks. By exploiting the temporal correlation of co-channel interference, a Kalman filter 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-plusnoise ratio (SINR). Performance results reveal that the Kalman-filter method for power control provides a significant performance improvement.

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Although the Kalman-filter method is applicable to both the uplink (from terminal to base station) and the downlink (from base station to terminal) we will focus on the downlink here. 5.4 Interference prediction by Kalman Filter method We apply the Kalman-filter 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 I (n ) be the actual interference-plus-noise power in dBm received at a given base station in time slot n. In fact, I (n ) is required to be estimated by the Kalman filter. Assume that the noise power, which depends on the channel bandwidth, is given and fixed. 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: I ( n )  I ( n  1)  F ( n )

Where F (n ) represents the fluctuation of interference power when terminals start new transmissions and/or adjust their transmission power in the time slot. Let Z (n ) be the measured interference power plus noise power in dBm for slot n then Z (n )  I (n )  E (n )

By the Kalman filter theory, the time and measurement update equations for the interference power are: ~ I (n  1) 

Iˆ ( n )

~ P ( n  1 )  Pˆ ( n ) 

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~ K (n )  P (n Iˆ ( n ) 

Pˆ ( n ) 

~ I (n )  K (n

~ P (n

Pˆ ( n ) 

- 1 ~ Z (n )  I (n )]

1 

~ Where, I (n Iˆ(n) are the a priori and a posteriori estimates of I (n ) . ~ P (n) , Pˆ (n) are the a priori and posteriori estimate error variances respectively. K (n ) is the Kalman gain, and Q (n) and R (n ) are the variances for the process

noise F (n ) and measurement noise E (n ) respectively. Q (n) is estimated based on the interference measurements in the last W slots

as follows:  Z ( n)  1 / W

n

 Z (i)

i  n W 1

Q (n)  1 W  1)

n

[ Z (i)  Z (n

2

i n W 1

W is used to capture the non stationary interference

 Z (n) is the average measured interference with noise over the last W slots. Also R (n ) can be given by R ( n)   Q ( n )

Where,  is a given constant between 0 and 1

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5.5 Determination of Transmission power Let  is the target SINR, p (n ) is the transmission power and g (n ) the path gain from the transmitting base station to the mobile station for slot n, respectively. I (n ) and ~ I (n) represent the actual and predicated interference power in dBm and let i (n ) and ~ ~ i (n) denote the respective value in mW. Based on I (n) the base station transmits in slot n with power

~ p( n)   ( i ( n) / g ( n)

The goal of this of transmission power is to choose just enough power to achieve the target SINR  . When p(n) is the power of the base station selected by (11) for slot n, the actual receiving SINR  (n) at the mobile station is

~

 ( n )  p ( n ) g ( n ) / i ( n )   i ( n ) / i( n )

Where i (n ) is the actual interference power in mW for the slot n. ~ Thus (12) implies that when predicted interference i (n) is accurate to actual interference i (n ) , the target SINR is achieved. Even if i (n ) is not exactly equal to i (n ) , the method helps in reducing the spread ~ of  (n ) as long as i (n ) and i (n) are correlated.

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Steps for the Kalman Filter The Kalman Filter method for power control is summarized below: 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 I (n  1) in slot n+1. 3. Based on the MAC protocol in use, the base station tracks the path gain g ( n  1) 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 p ( n  1) 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 Rij received by the user i from the base station j is given by: R W

2

(1   i j /  )

Where, W is the bandwidth.

 i j is SINR received at user i when associated with GPRS or WiMaX B j .  is the gap between uncoded QAM and capacity, minus the coding gain. Thus the if R

and 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:

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R

W

R W

Where, 

2

2

(1  

(1  

/ ) / )

is SINR received from WiMaX on High Speed Downlink Packet

Access (HSDPA) Channel and  and 

relationship between 





1 

/ )

/

is SINR received from GPRS on HSDP. The 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  i j received by user i from WiMaX base station

j

can be represented

as:

 i j  G Pj /

 k

G

Pk

,k# j

Pj is the transmitting power of

j

G is the channel gain between user i and

j

is the background noise power at user receiver end. The SINR  i j received by user i from GPRS base station

j

can be

represented as:

 i j  G Pi j

  G P k G Pi j ) k

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P k is the total transmitting power of Pi j is the transmitting power of

j

k

to user j

G is the channel gain between user i and

j

5.6.3 Throughput calculation In this analysis, consider a point to point model, in which a user is moving at speed v from

( X 1 ) to

( X 2 ), as shown in the following figure. The vertical

handoff has shown to be taken place at point X h . R

R

X2

X

X1

Xh

1

Figure 10: Point to point model

The total downlink throughputs ө can be represented as  



X X

Where

h

R

(x)X



1



X X

2

R

( x) X

h

is cell residence time, and R and R is maximum data rate received

from WiMaX and GPRS. •

For the RSS based vertical handoff, the X h is dependent on the minimum required receiving power Pj from WiMaX base station

•

j

In SINR based vertical handoff, X h is calculated based on the receiving SINR from WiMaX and GPRS.

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•

So, It will be possible to compare the average throughputs for different vertical handoff algorithm with different X h . GPRS network

WiMaX network

Gateway Gateway MSC BS

BS

MS

N

Internet P A C K E T S

Gateway

P A C K E T S

MSC

BS

CN

Corresponding network Figure 11: Integration of GPRS and WiMax networks 40 Evaluation notes were added to the output document. To get rid of these notes, please order your copy of ePrint 5.0 now.

References 1. “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 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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