Radio Resource Management in MBMS Enabled 3G Mobile Cellular Networks: A New Handover Control

Approach

Christophoros Christophorou and Andreas Pitsillides Department of Computer Science

University of Cyprus 75 Kallipoleos Street, P.O.Box.20537, CY-1678 Nicosia, Cyprus

{cs98cc2 & Andreas.Pitsillides}@cs.ucy.ac.cy Abstract – Radio Resource Management (RRM) algorithms are needed to guarantee Quality of Service (QoS), to maintain the planned coverage area, and to offer high capacity. The family of RRM algorithms can be divided into Handover Control, Power Control, Admission Control, Load Control and Packet Scheduling functionalities. Using the existing RRM algorithms in 3rd Generation (3G) Cellular Networks supporting multicast and broadcast multimedia services (MBMS) might prove inefficient due to the new aspects introduced. Here, we focus our research on Handover Control. We investigate and highlight the inefficiencies caused when a mobile terminal is receiving an MBMS service and performs a handover using the existing Handover Control approach. We therefore propose and evaluate a specific MBMS Handover approach to compensate for the issues highlighted in our analysis. In this paper, using a different approach, we extend previous work to Non-homogeneous cell boundaries and Non-Line of Sight transmission.

I. INTRODUCTION

Multimedia Broadcast Multicast Service (MBMS) [1] is a new unidirectional (downlink only) Point-to-Multipoint service introduced in UMTS (Universal Mobile Telecommunication System) Release 6 specifications [2] in which the same data is transmitted from a single source entity to multiple recipients. The novelty with MBMS architecture is that it enables the efficient usage of radio-network and core-network resources by allowing the network resources to be shared. With MBMS bearer services (See Figure 1), the Core Network will send only one stream of data to the Radio Network Controller (RNC) despite the number of Base Stations (BSs) or User Equipments (UEs) that want to receive it. Then it is RNC’s jop to replicate and distribute the MBMS content to the UEs in the Cells as efficient as possible. According to [1], MBMS bearer services can be provided in each cell by either Point to Multipoint (P-t-M) or by Point to Point (P-t-P) transmission, but requires a decision to be made between the two approaches. This decision is made by the RNC. With the P-t-M transmission one Forward Access Channel (FACH) is established and shared by all the UEs in the Cell while with the P-t-P transmission one Dedicated Channel (DCH) is established for each UE in the Cell. The fundamental selection criterion of transmission mode is the amount of Base Station (BS) power required to transmit to a

group of MBMS users camping in that cell. As a P-t-M transmission (FACH) needs cover the cell perimeter and be received by all the UEs in the Cell, also those near the Cell’s border, it requires more radio resources (power) than a DCH. Therefore, few DCHs might outperform one FACH in terms of radio resource efficiency. Thus, in some cases where there are few MBMS users in the Cell it could be preferable to transmit the required service adopting P-t-P transmission using DCH’s. However if we have a Cell with considerable number of MBMS users, establishing a common FACH for all users could in many ways be the best solution, since it requires less cell resources and decreases the transmit complexity in a way that the service is transmitted for all users in the cell in a unique common channel avoiding multiple transmissions of the same content.

Figure 1 Core and Radio Network use of resources with MBMS

Bearing in mind the aforementioned, the mobile users that

are on the move and receive an MBMS Service may have to deal with the following four types of handovers when crossing the Cell edge: From P-t-P to P-t-P Cell; From P-t-M to P-t-M Cell; From P-t-M to P-t-P Cell; and From P-t-P to P-t-M Cell. The first type of handover (from P-t-P to P-t-P Cell) can be efficiently executed using the Soft Handover Control approach [3][4][5][6], while the second type of handover (from P-t-M to P-t-M Cell) can be executed using the Selective or Soft Combining as described in [1]. The last two types of handovers (from P-t-M (FACH) to P-t-P (DCH) Cell and vice versa) have to do with dynamic changes of network resources, an issue considered in [7] and [8], but only for

homogeneous cell boundaries and Line-of-Sight transmission. Note that this dynamic change may also be triggered within a cell due to dynamic variations of power consumption caused by the mobility of the UEs in that Cell. In that case a UE Counting threshold [9] can be used, but this is beyond the scope of this paper.

In this paper, we extend previous work [7] [8] using a different approach, and deal with the dynamic change of network resources during handover (from FACH to DCH and vice versa) considering non-homogeneous cell boundaries and Non-Line of Sight (NLOS) transmission. Throughout this paper we will refer to these types of handovers as MBMS Handovers. Since Soft Handover [6] cannot be utilized between different kinds of resources, the new types of MBMS Handovers are dealt using Hard Handover [6].

The paper is organized as follows: Section II analyses the inefficiencies caused when a UE is performing an MBMS Handover using the existing Hard Handover approach, highlighting the need for a specific MBMS handover approach for mobile users receiving an MBMS service. In Section III the proposed MBMS Handover Control approach is described while the Performance Evaluation is presented in Section IV. Finally in Section V we provide our conclusions.

II. REASONS FOR A NEW MBMS HANDOVER APPROACH

In this section the inefficiencies caused when the existing Hard Handover approach is employed during an MBMS Handover are analysed and illustrated. Before going into that analysis, a brief description of the channels characteristics that take part in these types of handover (DCH and FACH) and the existing Hard Handover control approach is given.

The FACH channel can be shared by several UEs. Power control is not used on FACH. The amount of transmission power allocated to FACH is that required to achieve coverage at the cell edge, despite the number and the location of the users that are receiving it at any particular point in time. Since FACH ‘guarantees’ the required QoS only within the coverage of the cell, leaving its coverage area will result in signal strength degradation and even worse the loss of the connection.

The DCH channel is dedicated to one UE and allows the use of fast power control. Fast power control is a crucial aspect of WCDMA because it improves link performance and enhances downlink capacity by reducing the average required transmission power. The transmission power allocated for this channel is variable and increasing exponentially while the UE distance from the BS is increasing in order to compensate for the pathloss, shadowing, fading and interference.

According to the existing Hard Handover control approach [6], the mobile station performs a handover when the Common Pilot Channel (CPICH) signal strength of a neighbouring cell exceeds the CPICH signal strength of the current cell within a predefined threshold (AS_Rep_Hyst - Replacement Hysteresis Threshold).

Taking into consideration the FACH and DCH characteristics described above, it is obvious that in order to guarantee the QoS of the MBMS Service throughout the

handover process, and reduce the total downlink power in the P-t-P Cell to the minimum required the handover should be executed on the coverage limit of the P-t-M Cell. By doing this, the UE will still be inside the coverage of the P-t-M Cell (thus the FACH will be received with the required signal strength) and also when the handover occurs it will be as close as possible to the P-t-P BS (thus the minimum power required will be used by the P-t-P BS in order to reach the UE).

The existing hard handover control approach as described above has been implemented considering only the DCH characteristics and it is based on a comparison between the CPICH signal strength transmitted from the BSs taking part in the handover procedure. Adopting this approach to execute an MBMS Handover might result in inefficiencies since it does not guarantee the MBMS handover execution on the coverage limit of the P-t-M Cell. These inefficiencies are illustrated using Scenario 1 depicted in Figure 2.

In this scenario a UE is moving in a “Pedestrian Outdoor” environment with a speed of 6 Km/h from a P-t-M Cell (FACH) towards a P-t-P Cell (DCH) receiving an MBMS streaming video of ~60 Kbits/sec and performing a handover adopting the existing handover approach using a Replacement Hysteresis Threshold of 0dB. A variety of other threshold values (-3dB – +3dB) have been tested with different scenarios resulting also in similar inefficiencies. This is to be expected due to the fixed nature of the threshold value whose aim is not to trigger handover at the edge but rather when the CPICH power ratio between the two cells reaches a certain predefined value (which depends on the loading of the two cells; see below). The coverage of both cells is 1000 meters while the distance between the two BSs is ~1800 meters (giving a space of ~200 meters overlap). Two instances of the same scenario have been simulated. In the first instance the P-t-P Cell has been configured to be high loaded (High Noise (No)) while in the second instance to be low loaded (Low Noise (No)). Simulation results concerning these two instances have been collected, illustrated and described below.

Figure 2 Scenario 1: Illustrating the inefficiencies caused when the existing Hard Handover approach is applied on MBMS Handovers

Figure 3 Received CPICH signal strength (Ec/No): High Noise (No)

in the P-t-P Cell. Handover is executed outside of the P-t-M cell Coverage

Figure 4 Received CPICH signal strength (Ec/No): Low Noise (No) in the P-t-P Cell. Handover is executed away before the UE leaves

the Coverage of the P-t-M Cell Adopting the existing Hard Handover approach in the first

instance where the noise (load) in the P-t-P Cell is high, will result, as illustrated in Figure 2 & Figure 3, in the execution of handover close to the P-t-P BS at a point outside of the P-t-M cell coverage (Handover Point 1). This is caused due to the degradation that the high noise (No) causes on the received CPICH signal strength (Ec/No) transmitted from the P-t-P BS, forcing the UE to get closer to the P-t-P BS before the handover condition is met. The Ec/No denote the Energy per Chip (Ec) to Noise Spectral Density (No) ratio for one user. Since the transmission power allocated for FACH is at a level aimed to ensure the requested QoS only within the coverage of the P-t-M Cell, once outside the coverage area (at ~400th second of the simulation) the signal strength of the FACH will start degrading, resulting initially in the loss of packets and later on in the loss of the connection (see Figure 5), until the handover’s condition is met and the UE is handed over to the P-t-P Cell (at ~480th second of the simulation).

Figure 5 Traffic Received (bits/sec) when the existing handover

approach is applied

On the other hand, as shown in Figure 2 & Figure 4, when the load (noise) in the P-t-P Cell is low, the execution of handover happens away before the UE leaves the P-t-M Cell coverage (Handover Point 2). In this case we do not have any degradation on the QoS of the received traffic since the UE is still inside the coverage of FACH. But, considering that the requested QoS can be supported up to the coverage limit of the cell (that is ~1000 meters from the P-t-M BS) this results in inefficient use of common (FACH) resources. This inefficiency becomes clearer if we consider both Figure 6 and Figure 7. The black discontinued line shown in Figure 6 indicates the point in time (at a distance equal to ~885 meters from the P-t-M BS) where the handover was actually executed while in Figure 7 indicates the total downlink power that was actually used in the P-t-P Cell (0.46 watts) after handover. On the other hand, the green discontinued line in Figure 6 indicates the point in time where the handover should be executed (point in time where the UE is at ~1000 meters distance from the P-t-M BS), considering that FACH can be utilized up to the coverage limit of the P-t-M cell. This would result in a much lower power consumption (0.26 watts) in the P-t-P Cell (depicted by the green discontinued line in Figure 7) since the handover will be triggered closer to the P-t-P BS, providing a gain of about 2.5 dB for the presented case.

Figure 6 UE distance (meters) from attached Base Station.

Figure 7 Downlink power used in P-t-P Cell (watts) after handover.

The results illustrated above highlight the reason why a

specific MBMS handover approach is essential for mobile users receiving an MBMS service. A vital aspect for the efficient execution of these types of handover is the consideration of the FACH capacity and coverage characteristics, a feature not considered in the existing handover control approach. In the following section the proposed MBMS handover approach is described, extending previous work [7] and [8], taking into account all the aforementioned in order to compensate for the inefficiencies described above.

III. PROPOSED MBMS HANDOVER CONTROL ALGORITHM

With any communication system, the received signal strength defers from the transmitted signal strength due to various channel impairments. In cellular communication system the most significant impairments are distance dependent path loss; location dependent shadowing; multi-path fading dependent on the speed and environment of the mobile; and interference level dependent on cell position and neighbouring cell activity. These impairments introduce various random modifications that degrade the signal quality during signal propagation. They can be efficiently compensated with channels supporting fast power control (e.g. DCH) by adjusting the downlink transmission power of the signal in order to reach the terminal with the requested SIR (Signal to Interference Ratio). Since fast power control cannot be applied with FACH channel, these impairments cannot be efficiently compensated resulting in non-homogeneous dispersion of the signal quality along the perimeter of the cell coverage giving the impression of non-homogeneous circle Cells (Figure 8).

Figure 8 P-t-M Cell coverage and FACH effective coverage

Thus, in order to achieve efficient execution of MBMS

Handover the handover should be executed (switch channels) at a point as close as possible to the P-t-P BS (thus minimizing as much as possible the power consumption in the P-t-P Cell) but not outside of the FACH effective coverage (once outside its coverage area will result in degradation of the FACH signal strength and even worse the loss of the connection). Logically, this switching point can be described as the coverage limit of the P-t-M Cell. But, considering the non-homogeneous dispersion of FACH throughout the Cell coverage, it can be better described as the point where the FACH provides the required quality with minimum Required Eb/No (measured in dB) essential for correctly detecting the signal (See Figure 8). Throughout the rest of the paper we will refer to this point as the “Efficient switching point”. The Required Eb/No for a service denotes the value that the signal energy per bit (Eb) divided by the interference and noise power density (No) should have for achieving a certain BER (Bit Error Rate) so as to satisfy the required QoS of a service. The Eb/No can be measured at the input of the receiver and is used as the basic measure of how strong the signal is. Let us consider the case where a 12.2 kbps speech service is spread over a 5 MHz Carrier and an Eb/No of 5.0 dB is required to achieve a 0.01 BER performance. After the de-spreading in the receiver, the signal power needs to be typically a few decibels (dB) above

the interference and noise power. Since an Eb/No of 5.0 dB is enough for efficiently detecting the signal, the required wideband Signal to Interference Ratio (SIR) will be 5.0 dB minus the Processing Gain [10] of 25 dB that can be achieved for the corresponding service. The Processing Gain is equal to 10 x log (WCDMA Chip Rate/Bit Rate) and the WCDMA Chip Rate is equal with 3.84 Mcps. In other words, the signal power can be 20 dB under the interference and thermal noise power, and the WCDMA receiver can still efficiently detect and interpret the signal correctly.

Since some signalling delay is caused from the time the handover is triggered until the UE switches channels (Handover Delay, ∆t), triggering the handover on the point where the measured Eb/No quality of FACH channel is equal with the minimum required will result in the switching of channels at some distance (Handover Delay Distance (HDD)) away from the “Efficient switching point”. Therefore, in order to anticipate this HDD a parameter called Handover Delay Anticipator (HDA) will be considered. For example, if the UE is moving from a P-t-M cell towards a P-t-P cell (See Figure 9) the handover should be executed at a point where the measured signal quality of the FACH is equal to the Required Eb/No + Handover Delay Anticipator (HDA) (expressed in dB ). On the other hand, if the UE is moving from a P-t-P Cell towards a P-t-M cell (See Figure 10), the handover should be executed at that point where the measured signal quality of the FACH is equal to the Required Eb/No - Handover Delay Anticipator (HDA) (expressed in dB).

Figure 9 Moving from a P-t-M Cell towards a P-t-P Cell

Figure 10 Moving from a P-t-P Cell towards a P-t-M Cell

The aforementioned outlines the main concept of the proposed MBMS Handover approach. The estimation of the minimum Required Eb/No and the HDA values are described in the following sections.

A. Downlink Required Eb/No value estimation The Required Eb/No ensuring the required quality of a

service depends on the bit rate of the service, the type of service, the multipath profile, the receiver algorithms and the Base Station antenna structure. According to [11] the downlink Eb/No values can be derived using the following formula (1):

⎟⎟⎟⎟

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or

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ob

IIityOrthogonal

IEx

RateBitRateChip

reqNE

/11

__

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(1)

The Ec/Ior requirement and Ior/Ioc operation point can be retrieved from [12]. An orthogonality factor of 1.0 is assumed for a static channel and 0.5 for a multipath channel. The calculations of the downlink Eb/No values for a 64 kbps service are shown in Table I for a static and a multipath channel.

TABLE I REQUIRED DOWNLINK EB/NO FOR A 64 KBPS DATA SERVICE

Static channel Multipath channel Ec/Ior from [12] -12.8 dB -7.4 dB Ior/Ioc from [12] -1.0 dB -3.0 dB Eb/No from Eq. (1) 3.7 dB 5.7 dB

B. Estimation of Handover Delay Anticipator (HDA) value The concept of using the Handover Delay Anticipator

(HDA) is to anticipate the HDD and switch channels on the “Efficient switching point”. Therefore in order to estimate the HDA value the HDD has to be estimated first.

The HDD is variable and depends on the Handover Delay time (∆t), the Speed and the Direction (expressed in angle φ) of the UE. According to the type of handover that is executing a slightly different formula will be used. At the case where the UE is moving from a P-t-P Cell towards a P-t-M the formula shown in (2) will be used. At the case where the UE is moving from a P-t-M cell towards a P-t-P Cell the formula shown in (3) will be used.

( ) ( ) CovaCovdaCovdHDD −×+×∆×−++∆= ϕcos121 22 (2)

aCov

aCovCovd −

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Speedta ×∆= & CellPtMOfCoverageCov ___=

The Coverage of the P-t-M Cell (measured in meters) and the Handover Delay time (measured in seconds) might vary. The Coverage of the P-t-M Cell varies according to the environmental setting (e.g. Pedestrian, Vehicular, Open Space) and user density (e.g. Hotspots, Rural area). The Handover Delay time varies according to the different delays that are caused during the handover signalling. Since it is impossible for the UE to know these two parameters without any feedback from the Network, the task of evaluating these parameters is assigned to the RNC. The RNC should periodically estimate these parameters and broadcast them to the UEs in the Cell through the MBMS Point-to-Multipoint Control Channel (MCCH) [1]. Due to the fact that the MCCH currently does not include these fields, we propose to enhance with two more fields for accommodating these two new parameters. On the other hand, the Speed and the Direction of the UE can be retrieved using for example GPS (Global Positioning System) technology, or any of the other positioning and speed detection methods [13] [14][15].

The Handover Delay Anticipator (HDA) value will depend on the P-t-M Cell environment. The formulas that estimate this value can be derived using the propagation models of the Cell environment [16] defined by the International Telecommunications Union (ITU). For example for a “Pedestrian Outdoor” environment the formula shown in (4) will be used in order to estimate the HDA when the UE is moving from a P-t-P Cell towards a P-t-M Cell and the formula shown in (5) will be used when the UE is moving from a P-t-M Cell towards a P-t-P Cell.

CellPtMofCoverageHDDCellPtMofCoverageHDA

______log40 10

+×= (4)

HDDCellPtMofCoverageCellPtMofCoverageHDA−

×=___

___log40 10 (5)

IV. PERFORMANCE EVALUATION

For the performance evaluation of the proposed scheme the OPNET Modeller 11.0.A UMTS module [17] was used as a base for building the MBMS simulator [18]. The performance was evaluated by comparing the amount of the total downlink power (capacity) that becomes available and the QoS level experienced when the proposed scheme is used instead of the existing one. Noting that the power used for Common Resources (FACH) is not affected by the number or the position of the UEs in the Cell, the evaluation will be focused on the P-t-P Cells. A series of 3 scenarios (Scenario 2 – Scenario 4) will be used in order to illustrate the feasibility, the performance and the usefulness of the proposed scheme. Scenario 2 and 3 are used in order to show any capacity gain that the proposed approach may have while Scenario 4 is used to show not only the capacity gain but also the ability of the proposed scheme to avoid the QoS degradation during handover.

Scenario 2 (Figure 11) considers the case where a group of 6 UEs are moving from a P-t-P Cell towards a P-t-M Cell with a

speed of 5 Km/h. All the UEs are expected to receive an MBMS Streaming video of ~60 Kbits/sec. The coverage of the cells is 1 Km and the pathloss model used is “Pedestrian Outdoor”. Two instances of this scenario have been simulated, one with the existing handover approach (using in this case a Replacement Hysteresis Threshold of 0 dB) and the other with the proposed handover approach applied.

Figure 11 Scenario 2: From P-t-P (DCH) to P-t-M (FACH) handover

Figure 12 Total downlink power required in P-t-P Cell (watts) –

Existing Vs Proposed Handover approach (Scenario 2) From Figure 12 we can deduce that the UEs moving from

the P-t-P towards the P-t-M Cell increase the demanded capacity (power) in the P-t-P cell. By using the proposed MBMS Handover approach instead of the existing one, a substantial decrease on the total power used is observed, thus reducing the maximum downlink power required in the P-t-P Cell from 0.86 watts to 0.45 watts (~47% decrease). This is caused due to the ability of the proposed scheme to release the DCH established in the P-t-P cell as soon as the FACH signal strength becomes adequate to ensure the detection of the signal with the requested BER. This results in the execution of handover as close as possible to the P-t-P Base Station thus reducing the interference caused in the P-t-P Cell and achieving less power consumption per subscriber. Moreover, the radio resources in the P-t-P Cell are released much sooner, thus making space for new admissions in the cell.

Scenario 3 (Figure 13) uses the same simulation parameters as scenario 2 but in this case a group of 6 UEs are moving from a P-t-M Cell towards a P-t-P Cell.

Figure 13 Scenario 3: From P-t-M (FACH) to P-t-P (DCH) handover

Figure 14 Total downlink power required in P-t-P Cell (watts) –

Existing Vs Proposed Handover approach (Scenario 3) From Figure 14, we can deduce that the UEs moving from

the P-t-M towards the P-t-P Cell increase the demanded capacity (power) in the P-t-P cell after handover. By using the proposed MBMS Handover approach instead of the existing one a substantial decrease on the total power used is observed, reducing the maximum downlink power required in the P-t-P Cell from 1.1 watts to 0.75 watts (~32% decrease). The reason for achieving this capacity gain is the ability of the proposed scheme to force the UE to stay tuned to the FACH channel as long as its signal strength is enough for detecting the signal with the requested BER. As in scenario 2, this will result in the execution of handover as close as possible to the P-t-P Base Station and reduce the demanded capacity in the P-t-P cell to the minimum. Moreover, the radio resources in the P-t-P Cell are allocated much later, thus not causing additional interference in the P-t-P cell during this period and giving space for other admissions.

Scenario 4 illustrated in Figure 15 is more complex than Scenario 2 and 3, and is used to show the feasibility and the performance of the proposed scheme in a multi-cell environment. In this scenario a total of 18 users are moving from the surrounding P-t-M cells towards a central P-t-P cell with a speed of 6 Km/hour and receiving an MBMS Streaming video of ~60 kbps. The coverage of the Cells is 1000 meters (with an overlap of ~200 metres) and the propagation model used is “Pedestrian Outdoor”. Two instances have been simulated using the existing (using a Replacement Hysteresis Threshold of 0dB) and the proposed MBMS handover approach respectively. The results collected are illustrated in Figure 16 - Figure 18.

Figure 15 Scenario 4: Group of UEs moving from surrounding P-t-M

Cells towards a P-t-P Cell

Figure 16 Total average downlink power required in P-t-P Cell

(watts) – Existing Vs Proposed Handover approach (Scenario 4)

Figure 17 Traffic Received (bits/sec) for the last UE entering the P-t-

P Cell – Existing Handover approach applied (Scenario 4)

Figure 18 Traffic Received (bits/sec) for the last UE entering the P-t-P Cell – Proposed MBMS Handover approach applied (Scenario 4) The collected results illustrated above reveal not only

capacity optimization (up to ~36% decrease on the average demanded capacity as shown in Figure 16) but also the ability of the proposed scheme to avoid the QoS degradation experienced when the existing handover approach is used (See Figure 17 & Figure 18). Figure 17 and Figure 18 illustrate the traffic received by the last UE (the 18th) entering the central P-t-P Cell.

V. CONCLUSIONS

In this paper we propose a new MBMS Handover approach which efficiently deals with the new aspects of handover introduced with MBMS, considering non-homogeneous cell coverage areas and Non-Line of Sight transmissions. This extends previous results in [7] [8]. The main concept of the proposed scheme is to minimize the interference caused in the P-t-P cells while at the same time satisfy the requested QoS, by taking full advantage of Common Resources (FACH). We show the importance of the Proposed MBMS Handover approach on the QoS of MBMS Services and also that it achieves enhanced Cell capacity (a reduction in power of up

to 47% was observed) during an MBMS Handover. In wireless/mobile environments where the radio resources are limited, any capacity increase is of major importance therefore the utility of the proposed algorithm for the MBMS system is evident. Future work will include a comprehensive evaluation of the proposed scheme and a sensitivity analysis.

ACKNOWLEDGEMENT

This work is partially supported by RPF CS-0104-12 VIDEO, and IST-2005 27423 C-MOBILE projects. The authors also thank OPNET Technologies Inc. for providing software licence to carry out the simulations of this research.

REFERENCES [1] 3GPP TS 25.346, “Technical Specification Group Services and System

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[5] I. A.Tomić, M. L. Dukić, “Soft Handover and Downlink Capacity in UMTS Network”, XII Telekomunikacioni forum TELFOR 2004.

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[12] 3GPP TS 25.101 V7.5.0, “Technical Specification Group Services and System Aspects; User Equipment (UE) Radio Transmission and Reception (FDD)”.

[13] H. Kaaramen, A. Ahtiainen, L. Laitinen, S. Naghian, V. Niemi. “UMTS Networks - Architecture, Mobility, and Services”. John Wiley & Sons Ltd, England, 2001.

[14] R. Narasimhan and D. Cox, “Speed Estimation in Wireless Systems Using Wavelets”, IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 47, NO. 9, SEPTEMBER 1999, pp. 1357-1364.

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[17] OPNET University Program: http://www.opnet.com/services/ university/ [18] B-BONE MBMS System Level simulator, http://www.NetRL.cs.ucy.cy