Performance Evaluation of Six-Sectored Configuration in Hexagonal WCDMA (UMTS) Cellular Network Layout

Transcription

1 LAPPEENRANTA UNIVERSITY OF TECHNOLOGY DEPARTMENT OF INFORMATION TECHNOLOGY Shyam Babu Mahato Performance Evaluation of Six-Sectored Configuration in Hexagonal WCDMA (UMTS) Cellular Network Layout Master of Science Thesis Subject approved by the department council on Examiner: D.Sc. Jouni Ikonen Supervisor: Prof. Jukka Lempiäinen

2 ii ABSTRACT Lappeenranta University of Technology Department of Information Technology Shyam Babu Mahato Performance Evaluation of Six-Sectored Configuration in Hexagonal WCDMA (UMTS) Cellular Network Layout Master of Science Thesis, 2007, 78 pages Examiner: D.Sc. Jouni Ikonen Supervisor: Prof. Jukka Lempiäinen Keywords: Performance, Coverage, Capacity, Radio Network Planning, WCDMA, UMTS, Hexagon The objective of this master s thesis is to evaluate the optimum performance of sixsectored hexagonal layout of WCDMA (UMTS) network and analyze the performance at the optimum point. The maximum coverage and the maximum capacity are the main concern of service providers and it is always a challenging task for them to achieve economically. Because the optimum configuration of a network corresponds to a configuration which minimizes the number of sites required to provide a target service probability in the planning area which in turn reduces the deployment cost. The optimum performance means the maximum cell area and the maximum cell capacity the network can provide at the maximum antenna height satisfying the target service probability. Hexagon layout has been proven as the best layout for the cell deployment. In this thesis work, two different configurations using six-sectored sites have been considered for the performance comparison. In first configuration, each antenna is directed towards each corner of hexagon, whereas in second configuration each antenna is directed towards each side of hexagon. The net difference in the configurations is the 30 degree rotation of antenna direction. The only indoor users in a flat and smooth semi-urban environment area

3 iii have been considered for the simulation purpose where the traffic distribution is 100 Erl/km 2 with 12.2 kbps speech service having maximum mobile speed of 3 km/hr. The simulation results indicate that a similar performance can be achieved in both the configurations, that is, a maximum of 947 m cell range at antenna height of 49.5 m can be achieved when the antennas are directed towards the corner of hexagon, whereas m cell range at antenna height of 54 m can be achieved when the antennas are directed towards the side of hexagon. However, from the interference point of view the first configuration provides better results. The simulation results also show that the network is coverage limited in both the uplink and downlink direction at the optimum point.

4 iv FOREWORD The research work for this Master of Science thesis was carried for the Laboratory of Communication Engineering, Department of Information Technology, Lappeenranta University of Technology, with kind support of Institute of Communication Engineering, Tampere University of Technology. First of all, I would like to thank the IMPIT program of Lappeenranta University of Technology for selecting me as a M.Sc. student and providing funding for the study period. I would like to express my deepest and sincere gratitude to my supervisor Prof. Jukka Lempiäinen, Institute of Communication Engineering, for his invaluable support and providing deep knowledge during the course Radio Network Planning. I would also like to thank Institute of Communication Engineering, Tampere University of Technology, for accepting me as a JOOPAS student for the course Radio Network Planning and providing the best environment for my research work. I am grateful to my thesis examiner D.Sc. Jouni Ikonen, Department of Information Technology, for his excellent comments and encouragements during the research work. I would like to thank M.Sc. Oleg Chistokhvalov, Department of Information Technology, for his kind and valuable discussions about the pre-task of the research work. I am most grateful to M.Sc. Jarkko Itkonen and M.Sc. Balázs P. Tuzson of European Communications Engineering (ECE) for their constant discussions about the research work on net meeting, providing simulation parameters, technical support and encouragements during the research work. I wish to thank M.Sc. Panu Lädekorpi, M.Sc. Tero Isotalo, D. Sc. Jarno Niemelä and my colleague Jussi Turkka, all of Institute of Communication Engineering, for their kind discussions and providing the license of installing Nokia NetAct Planner Tool.

5 v Finally, I would like to express my deepest love to my parents for their parenting, guidance, and love throughout the early days of my life. Tampere Shyam Babu Mahato

6 vi TABLE OF CONTENTS ABSTRACT ii FOREWORD iv TABLE OF CONTENTS vi LIST OF ABBREVIATIONS viii LIST OF SYMBOLS x 1 INTRODUCTION 1 2 UMTS NETWORK ARCHITECTURE Core Network(CN) UMTS Terrestrial Radio Access Network (UTRAN) Radio Network Controller (RNC) Node-B User Equipment (UE) 8 3 RADIO PROPAGATION Multipath Propagation Angular Spread Delay spread and Coherence Bandwidth Fast Fading and Slow Fading Propagation Slope 14 4 RADIO NETWORK PLANNING Pre-Planning (Dimensioning) Radio Link Budget (RLB) COST-231-Hata Model Cell Capacity and Cell Range (Coverage Area) Estimation Cell Capacity Estimation Cell Range (Coverage Area) Estimation Detailed Planning Planning Tool Coverage Planning 35

7 vii Capacity Planning Optimization 46 5 SIMULATION AND ANALYSIS Simulation Methodology Network Configuration Simulation Environment and Parameters Analysis Method Analysis Results 55 6 CONCLUSIONS 65 REFERENCES 67

8 viii LIST OF ABBREVIATIONS 2G Second Generation 3G Third Generation AUC Authentication Center BCH Broadcast Channel BS Base Station BSC Base Station Controller BTS Base Transceiver CDMA Code Division Multiple Access CIR Carrier to Interference Ratio CN Core Network CPICH Common Pilot Channel DL Downlink EIR Equipment Identity Register EIRP Effective Isotropic Radiated Power GGSN Gateway GPRS Support Node GMSC Gateway MSC GPRS General Packet Radio Service GSM Global System of Mobile Communication HLR Home Location Register IM Interference Margin IMEI International Mobile Station Equipment Identity ISDN Integrated Services Digital Network ISI Inter-Symbol Interference KPI Key Performance Indicator LNA Low Noise Amplifier ME Mobile Equipment MGW Media Gateway MS Mobile Station MSC Mobile Switching Center NF Noise Figure P1 Publication 1 P-CCPCH Primary-Common Control Physical Channel PCH Physical Channel PCH Gain Power Control Headroom Gain PR Power Rise P-SCH Primary-Sysnchronisation Channel P-SCH Primary-Synchronization Channel

9 ix PSTN QoS RAN RLB RNC RX S-CCPCH SCH SfHO SGSN SHO SIM SIR SNR S-SCH STD TX TXP UE UL UMTS UTRA UTRAN U u WCDMA VLR Public Switched Telephone Network Quality of Service Radio Access Network Radio Link Budget Radio Network Controller Receiver Secondary-Common Control Physical Channel Synchronization Channel Softer Handover Serving GPRS Support Node Soft Handover Subscriber Identity Module Signal-to-Interference Ratio Signal-to-Noise Ratio Secondary- Synchronization Channel Standard Deviation Transmitter Transmitted Power User Equipment Uplink Universal Mobile Telecommunication System UMTS Terrestrial Radio Access UMTS Terrestrial Radio Access Network UMTS air interface Wideband CDMA Visitor Location Register

10 x LIST OF SYMBOLS B C B D B S C c D S E b /N o E c /I o f G LNA G r G t h b h m i L CABLE L p N n N 0 NF BS NF LNA N s P r P t R T C T S W α α (h m ) β η η UL λ ν ξ Coherence bandwidth Doppler bandwidth Signal bandwidth Area correction factor Light speed Delay spread Energy received per chip to the total power spectral density Energy received per chip to the total interference power Frequency LNA gain Receiver gain Transmitter gain Base station antenna height Mobile station antenna height Other-to-own cell interference Cable loss Path loss Number of terminals Propagation exponent Thermal noise density Noise figure of BS Noise figure of LNA Number of sectors Received power Transmitted power User bit rate Coherence time Symbol period Chip rate Orthogonality factor Mobile station antenna gain function Bearer control overhead factor Loading factor Uplink load Wavelength Activity factor Sectorization gain

11 1 1 INTRODUCTION The coverage and the capacity are the significant issues in the planning process of cellular mobile networks. In WCDMA (UMTS) systems, coverage and capacity planning are taken in account simultaneously because capacity requirements and traffic distributions influence the coverage. Since UMTS radio interface is based on WCDMA technology, each user in the network directly affects the others. This means, each user s signal is treated as interference to others. Hence, an important part of radio network planning in WCDMA system is to simultaneously optimize the coverage and control the interference to maximize the capacity. The target of the thesis is to evaluate the maximum performance of hexagon layout having six-sectored sites. Figure 1.1 Three-Sectored Site Layouts The hexagon shape has been traditionally used as a basis of the network layout design for cellular networks [1-3]. Two basic network layouts (Fig. 1.1(a) & (b)) with three-sectored

12 2 sites have become widely used during the cellular evolution [6]. The demand of cellular service is increasing day by day which in turn has forced the network operator to update their existing services so that they can provide the needs of market. Increasing sectors in the existing site is one way of increasing the capacity of the network. A third network layout (Fig. 1.1(c)) with three-sectored site has been designed in [4-6] as an alternative network layout with the concept of dividing a hexagon in 6-cell. The network performances of three-sectored site designs (Fig.1.1) with hexagon divided in 1-cell, 3-cell and 6-cell have been evaluated in [4-6] and it is seen that the 6-cell alternative design has comparatively better performance. Though the 6-cell design with three-sectored site can provide double coverage and capacity than the 3-cell design with three-sectored site, it can be easily noticed that to implement a 6-cell hexagon (Fig 1.1(c)), we must need six sites which in turn increases the implementation cost. Figure 1.2 Six-Sectored Site Layouts In this thesis, a network layout was designed by six-sectored site (Fig. 1.2) with hexagon divided in 6-cell and its performance was evaluated. Two topology layout designs have

13 3 been considered for the comparison. The first topology layout was considered by pointing each antenna towards each corner of the hexagon (Fig.1.2 (a)), whereas the second topology layout was considered by pointing each antenna towards each face of the hexagon (Fig.1.2 (b)). In each topology, the site is located at the center of the hexagon. The only difference between the topologies is the 30 degree rotation of the antenna directions. However, the shape of cell s dominance area is different which leads to a different behavior when considering coverage and interference properties. The main parameters in a network topology are cell size, site location, cell layout, antenna type, antenna azimuth and antenna height [5-6]. For the simulation purpose, a total of 19 sites with 6-sectored have been considered to find the optimum point regarding the cell size and the base station antenna height. The optimum performance of a network configuration is achieved when a given planning area can be covered with minimum number of cells offering the required service of quality and the capacity. This optimization minimizes the cost of the network which is driven by the number of cells and the sites.

14 4 2 UMTS NETWORK ARCHITECTURE The Universal Mobile Telecommunication System (UMTS) is one of the third-generation (3G) mobile phone technologies. It uses WCDMA as the underlying standard for air interface and is standardized by the 3 rd Generation Partnership Project (3GPP). The UMTS network is based on GSM and GPRS network [7-11]. The UMTS network elements and their interfaces are shown in Figure 2.1. It consists of three main sections: 1. Core Network (CN) 2. UMTS Terrestrial Radio Access Network (UTRAN) 3. User Equipment (UE) 2.1 Core Network (CN) The Core Network is a backbone network of telecommunication system that provides connections among different devices. The basic 3G CN architecture is based on GSM

15 5 network with GPRS. The main functions of the CN are to provide switching, routing and transit for user traffic. The 3G Core Network is divided into two domains: circuit switched and packet switched domains [9, 13]. The circuit switched domain elements are: Mobile Switching Center (MSC) A Mobile Switching Center is a telecommunication switch or exchange within a cellular network architecture which is capable of interworking with location databases. The main task of MSC is to route, switch and transmit the circuit switched data received from Radio Network Controller (RNC) to the PSTN / ISDN networks via GMSC and vice versa. MSC is the core element of GSM network. Visitor Location Register (VLR) The Visitor Location Register is a network database which keeps the information about all the roaming mobile customers required for call handling and mobility management. Whenever an MSC detects a new mobile subscriber, in addition to creating a new record in the VLR, it also updates the HLR (Home Location Register) of the mobile subscriber [3]. Gateway MSC (GMSC) The Gateway MSC is the main routing element for the circuit switched data from the UMTS network to the PSTN/ ISDN network or vice-versa. A GMSC is the MSC that determines which visited MSC the subscriber who is being called currently located. All mobile-to-mobile calls and PSTN to Mobile calls are routed through GMSC. It terminates the PSTN signaling and traffic formats and converts this to protocols employed in mobile networks. For mobile terminated calls, it interacts with HLR to obtain routing information.

16 6 The packet switched domain elements are: Serving GPRS Support Node (SGSN) A Serving GPRS Support Node (SGSN) is responsible for the delivery of packet switched data received from Radio Network Controller (RNC) to the Gateway GPRS Support Node or vice-versa. Its main tasks include packet routing and transfer, mobility management, logical link management. Gateway GPRS Support Node (GGSN) Like GMSC is the main routing element for circuit switched data to the PSTN or ISDN network, GGSN is the main routing element for the packet switched data of UMTS network to the Ethernet network. Besides the circuit switched and the packet switched elements, the shared elements of both the domains are: Equipment Identity Register (EIR) The Equipment Identity Register is a database that keeps a list of mobile phones (identified by their IMEI), which are to be banned from the network or monitored. When a mobile requests services from the network, its IMEI (International Mobile Equipment Identity) is checked against the EIR and then decides whether to allow the service or banned. Home Location Register (HLR) The Home Location Register is a central database that contains information of each mobile phone subscriber that is authorized to use the network. More precisely, the HLR

17 7 stores the information of every SIM card issued by the mobile phone operator. It is responsible for the maintenance or user subscription information. Authentication Center (AUC) The function of AUC is to authenticate each SIM card that attempts to connect the GSM network. Once the authentication is successful, the HLR is allowed to manage the SIM and services. 2.2 UMTS Terrestrial Radio Access Network (UTRAN) The Radio Access Network (RAN) is also called UMTS Terrestrial RAN (UTRAN) and the radio access (radio interface) is also called UMTS Terrestrial Radio Access (UTRA) [7]. UTRAN is the main section of the mobile network evolution. The main changes are occurring in this section for the evolution of new technology. UTRAN consists of two elements: 1. Radio Network Controller (RNC) 2. Node B Radio Network Controller (RNC) The RNC is the governing element in the UMTS radio access network (UTRAN) which is responsible for controlling the Node-Bs. The RNC in UMTS networks functions equivalent to the Base Station Controller (BSC) functions in GSM/GPRS networks. The RNC connects to the Circuit Switched Core Network through MSC (which is also known as Media Gateway, MGW) and Packet Switched Core Network through SGSN. The main function of the RNC is management of radio channels (Uu-, or Air-, interface) and terrestrial channels (towards the MGW and SGSN) and mobility management. The

18 8 resource and the mobility management functionality includes: radio resource control, admission control, channel allocation, power control settings, handover control, load control, macro diversity, broadcast signaling, packet scheduling, security functions, open loop power control [13] Node B The Node B is that element in the UMTS network which provides the physical radio link between the User Equipment (UE) and the network. The Node B in UMTS networks provides functions equivalent to the Base Transceiver Station (BTS) in GSM/GPRS networks. Node B is typically physically co-located with existing GSM BTS to reduce the cost of UMTS implementation. The Node B is responsible for air interface processing and some Radio Resource Management functions such as: air interface transmission / reception, modulation /demodulation, CDMA physical channel coding, micro diversity, error handling, closed loop power control [13]. 2.3 User Equipment (UE) The terminal is known as the user equipment. The UMTS UE is based on the same principles as the GSM MS, i.e., the separation between mobile equipment (ME) and the UMTS subscriber identity module (SIM) card (USIM) [7]. The USIM card contains the subscriber-related information such as authentication, encryptions.

19 9 3 RADIO PROPAGATION The mobile communication uses air interface for transmission and reception of signal. The interface between the base station (Node B) and the mobile station (UE) in UMTS is known as U u -interface (UMTS radio interface) which is the propagation path of radio signal between the mobile station and the network. This interface in UMTS is based on WCDMA technology. The UMTS radio interface has different behaviors for different propagation environments. The propagation environment can be classified into outdoor and indoor environment. The outdoor environment can be further classified into macrocellular environment and microcellular environment. Depending on the buildings or other obstacles density, a macrocellular environment contains an urban, suburban and rural type of area. Detailed knowledge of radio propagation and characterization of the propagation medium is an essential step required for successful performance analysis. Propagation model plays an important role in modeling the behavior of radio signal in different propagation environment. There are many propagation models such as Okumura- Hata model, Ray Tracing model, COST-231-Hata model which help in modeling the radio propagation. The COST-231-Hata model is used in this simulation which is described in later chapter. Each propagation environment has its own propagation characteristics, which can be defined by the following parameters: [12] Multipath Propagation Angular Spread Delay spread and Coherence Bandwidth Fast Fading and Slow Fading Propagation Slope 3.1 Multipath Propagation Multipath propagation occurs due to reflections, diffractions, and scatterings from different obstacles such as buildings, street lamps, trees in the radio path [14-16]. The

20 10 multipath waves coming from different directions combine at the receiver antenna to give a resultant signal which can vary widely in amplitude and phase depending on the distribution of the intensity and the relative propagation time of the component waves. Figure 3.1 Cellular Environment The path exhibit differing attenuations and have different lengths, so that the receiver observes several relatively delayed and attenuated versions of the signal. The effect of different time delays is to introduce relatively phase shifts between the component waves. As a result, the superposition of the different components induces either destructive or constructive addition, depending on the relative phases. As the mobile moves around in space, or in case of stationary mobile unit, due to moving obstacles such as cars, people, etc., the structure of the multipath medium changes and spatial variations appear as timevariation in the received signal. The Figure 3.1 illustrates the described propagation scheme in a macrocellular radio environment, where the base station antennas are typically located above the average roof-top level.

21 Angular Spread Angular spread describes the deviation of the signal incident angle. It can be calculated in two planes, horizontal or vertical. The received power from the horizontal plane is still the most important because of obstructing constructions: most of the reflecting surfaces are related to the horizontal propagation and thus multiple BTS to MS propagation paths exist more in horizontal plane. The horizontal angular spread is around 5-10 [12] degree in macrocellular and very wide in microcellular and indoor environments because the reflecting surfaces surround the base station antenna. The angular spread has a significant effect on antenna installation direction and on the selection and implementation of traditional space diversity reception. The vertical angular spread influences, additionally, the base station antenna array tilting angle. The angular spread is also a key parameter when the performance of the adaptive antennas is discussed because the optimization of the Carrier-to-Interference Ratio (CIR) depends strongly on the incident angles of the carrier and on the interference signals. Thus, the performance of the adaptive antennas is lower or more difficult to achieve in the microcellular environments than in the macrocellular environments. 3.3 Delay Spread and Coherence Bandwidth Due to multipath propagation of the radio signal, the same signal arrives at the receiver end at different times with different angles of arrival which causes the signal to spread in time. The arrival time difference between the first multipath signal and the last one is called the delay spread (D S ), as shown in Figure 3.2. The delay would be unimportant if the entire signal components arrived at the receiver with the same delay. However, the signal actually becomes spread in time, and the symbol arrives at the receiver with duration equal to the transmitted duration plus the delay range of the channel. The symbol

22 12 is therefore still arriving at the receiver when the initial energy of the next symbol arrives, and this energy creates ambiguity in the demodulator of the new symbol which is known as inter-symbol interference (ISI). [15] P Ds t Figure 3.2 Delay Spread The bandwidth over which the channel s transfer function remains virtually constant is called the coherence bandwidth. In other words, the maximum bandwidth over which two frequencies of a signal are likely to experience comparable or correlated amplitude fading is called coherence bandwidth. Coherence bandwidth ( ) is related to delay spread as: 1 2. (3.1) The channel is wideband when the signal bandwidth is large compared with the coherence bandwidth. 3.4 Fast Fading and slow Fading A channel can be classified either as a fast fading or slow fading channel depending upon how rapidly the transmitted radio signal changes as compared to the rate of change of the channel [3]. Figure 3.3 depicts an example of fading channel. We can note that the signal strength varies rapidly as time elapsed. It is because either mobile station or the surrounding object is moving due to which multipath effects occurred and the receiver receives different components of same signals at different times.

23 Signal Strength (db) Elapsed Time (ms) Figure 3.3 An Example of Fading Channel [3] In fast fading channel, the impulse response of the channel changes rapidly within the symbol duration. That is, the coherence time of the channel is smaller than the symbol period of the transmitted signal. This causes frequency dispersion (also called time selective fading) due to Doppler spreading, which leads to signal distortion. The signal distortion due to fast fading increases with the increase of Doppler spread relative to the bandwidth of the transmitted signal. Therefore, a signal undergoes fast fading if [3], 3.2 where, is the symbol period, is the coherence time, is the bandwidth of the transmitted signal and is the Doppler spread bandwidth. In slow fading channel, the impulse response of the channel changes at a rate much slower than the transmitted radio signal. In this case, the channel may be assumed to be a static over one or several reciprocal bandwidth intervals. In the frequency domain, this implies that the Doppler spread of the channel is much less than the bandwidth of the transmitted signal. Therefore, a signal goes slow fading if [3], 3.3

24 14 It should be emphasized that the fast fading and the slow fading deal with the relationship between the time rate of change in the channel and the transmitted signal, and not with the path loss models. Fast fading is quite similar in all environments but depends on the speed of the receiver. 3.5 Propagation Slope The propagation slope characterizes the behavior of propagation environment. It indicates that by how much a radio signal is attenuated over a distance in an environment. Attenuation due to propagation limits the usability of the radio signal for the communication purposes. The received power at a distance r from the isotropic radiator in an environment is given by [17]:, 3.4 where, is signal wavelength in meters, n is the path loss exponent, is the transmitted power, is the receiving antenna gain and, is the transmitting antenna gain where, are the angles measured in the vertical and horizontal directions respectively. The path loss in db can be written as: 1 10log, log. 10 log, 3.5 where, f is the system frequency given by The path loss exponent (n) in case of free space is 2, i.e. the propagation slope is 20. But the path loss exponent changes with the environment according to the values given in Table 1.

25 15 Table 1: An Example of Path Loss Exponents According to Environment Type [3] Environment Path Loss Exponent Free Space 2 Ideal Specular Reflection 4 Urban Cells Urban Cells with shadowing 3-5 In building, LOS In building, obstructed path 4-6 In factory, obstructed path 2-3

26 16 4 RADIO NETWORK PLANNING The radio network planning process for WCDMA is nearly the same as for GSM with consideration of some parameters during the planning. The radio network planning process can be divided into three phases [7, 9, 10, and 12]: Pre-planning phase (also called system dimension) Detailed planning phase and Post-planning or optimization phase Each of the phases requires additional considerations such as propagation conditions, traffic distributions. The process of 3G radio network planning is illustrated as shown in Figure 4.1. Figure 4.1 Radio Network Planning Process [9] The planning of the radio network starts from the pre-planning phase. In the pre-planning phase, a rough number of network elements with its configuration are estimated for the target planning area based on the user traffic demand and the coverage requirements. The radio link budget and a suitable propagation model are used for the estimation of cell range for a certain base station antenna height. The number of the base stations required to

27 17 achieve the desired coverage and quality is also dependent on the capacity of the base stations. After the estimation of cell range and antenna height, the planning process goes to the detailed planning phase. The network is configured in detail such as site location, antenna direction, antenna type, antenna beam width, antenna downtilt, cable loss, antenna gains and so on. All the parameters from the link budget are assigned to the elements in a radio planning tool. A virtual network is built on the digital map by the help of a suitable radio network planning tool. The network is simulated and the results of the coverage predictions are analyzed on each pixel of the planning area on digital map. The detailed planning is first done in the simulator and the real site survey is investigated for the deployment of service. In the optimization phase, the result from the network performance is verified and compared with the required target. If the result is not satisfied, then some parameters such as site location, antenna height etc are changed until the result is within the reasonable limit. Actually, optimization phase starts from the beginning of the preplanning phase and last to the life of the network. 4.1 Pre-Planning (Dimensioning) In the dimensioning phase, an approximate number of base stations and their configurations are estimated to cover a certain area and to serve a certain capacity based on operator s requirement and the radio propagation in the area as well as network layout. Moreover, one critical parameter for a detailed planning phase is the base station antenna height, which must be defined in order to be able to define the characteristics of the radio propagation channel [12]. Pre-planning phase includes radio link budget (RLB) and coverage analysis, capacity estimation and lastly estimation of the amount of base station hardware and sites. The Figure 4.2 illustrates the coverage and capacity dimensioning process used in the following sections. The link budget and the propagation model form an important part of prediction of cell range. The cell coverage is estimated based on the type of the cell

28 18 layout. On the other hand, the cell capacity is calculated based on the load and the interference in the system. The cell area occupied by the cell capacity is then estimated based on the traffic distribution. Finally, the cell coverage obtained from the coverage and capacity planning is synchronized by tuning the base station antenna height in the propagation model. In this way, we can get the initial dimensioning of cell coverage and cell capacity with a base station antenna height. Figure 4.2 Dimensioning Process Radio Link Budget (RLB) The radio link budget gives the path loss between the base station and the mobile station. It is needed for the estimation of maximum path loss between the base station and the mobile station. The RLB calculations help in defining the cell range along with the coverage thresholds. The coverage threshold is a downlink power budget that gives the signal at the cell edge (border of the cell) for a given location probability. Link budget calculations are done for both the uplink and the downlink. As the power transmitted by the mobile station antenna is less than the power transmitted by the base station antenna, the uplink power budget is more critical than the downlink power budget. Due to this

29 19 reason, the path loss in the limited direction is used for the calculation of cell range. A general approach to calculate the path loss is described as below [9]: Uplink (UL) Path Loss (PL) Calculations: where, 4.1 = = Uplink Downlink BS MS Figure 4.3 Path Loss direction Downlink (DL) Path Loss (PL) Calculations: where, 4.2 = =

30 20 A practical example of radio link budget calculation used in the simulation is shown in table 2. The descriptions of parameters apply to both the uplink and downlink directions unless specifically stated otherwise. For the downlink direction, the base station is the transmitting end and the mobile station is the receiving end. For the uplink direction, the mobile station is the transmitting end and the base station is the receiving end. The frequency is set to 2140 MHz which is the middle frequency of European UMTS downlink frequency band. The chip rate of WCDMA is 3.84 Mcps. The data rate of spreading code is called the chip rate. The network load is assumed to be 60 % in uplink and 50 % in downlink direction. The speech users with 12.2 kbps bit rate are observed. The calculation of link budget is described as below. (g) Thermal Noise Density (dbm/hz): Thermal noise density, No, is defined as the noise power per Hertz at the receiver input which is given by the logarithmic of the product of Boltzmann s constant and the temperature. The thermal noise density at 20 is calculated as: 10 log / where, (h) Receiver Noise Figure (db): Receiver noise figure is the noise of the receiving system to the receiver input. The noise figure of Node B was set to 4 db and of UE to 8 db.

31 21 Table 2: An Example of Radio Link Budget Used in Simulation GENERAL INFO Units Value Downlink Frequency MHz 2140 a Chip Rate Mcps 3.84 b Temperature K 293 c Boltzmann's Constant J/K 1.38E-23 d SERVICE INFO UPLINK DOWNLINK Units Value Value Load % e Bit Rate kbps f RECEIVING END BS MS Thermal Noise Density dbm/hz g = 10*log(d*c) Receiver Noise Figure db h Receiver Noise Density dbm/hz i = g+h Receiver Noise Power dbm j = 10*log(b)+i Interference Margin (Noise Rise) db k = -10*log(1-e) Total Interference Level dbm l = j+k Required Eb/No db m Processing Gain db n = 10*log(b/f) Receiver Sensitivity dbm o = l+m-n Rx Antenna Gain dbi p LNA Noise Figure db q LNA Maximum Gain db r LNA Insertion Loss db s NF Improvement using LNA linear scale t = h*x/(q+1/r*(h*x-1)) ( in UL) db t = -s ( in DL) Feeder/Cable Loss db/m u Feeder/Cable Length m v Connector Loss db w Total Feeder/Cable Loss db x = u*v+w Antenna Diversity Gain db y (included in Eb/No) Soft Handover Diversity Gain db z Power Control Headroom db A Required Signal Power dbm B = o-p-t+x-y-z+a

32 22 TRANSMITTING END MS BS TX Power per Connection dbm C Cable/Feeder Loss db D TX Antenna Gain dbi E Peak EIRP dbm F = C-D+E ISOTROPIC PATH LOSS db G = F- B PLANNING THRESHOLD SHO Gain db H Body Loss db I Propagation Slope db/dec J Outdoor Coverage Probability % K Outdoor Slow Fading STD db L Outdoor Slow Fading Margin db M Outdoor Planning Threshold dbm N = B+I+M Indoor Coverage Probability % O Indoor Slow Fading STD db P Indoor Slow Fading Margin db Q Building Penetration Loss db R Indoor Planning Threshold dbm S = B+I+Q+R MAXIMUM PATHLOSS Outdoor db T = F-N Indoor db U = F-S (i) Receiver Noise Density (dbm/hz): Receiver noise density is the noise power per Hertz including the thermal noise and the receiver noise figure of the system at the receiver input /. 4.4 (j) Receiver Noise Power (dbm): Receiver noise power is the total noise power seen at the receiver input within the noise bandwidth. That is,

33 23 ( 10 log 10 log where, W is the chip rate. (k) Interference margin or Nose Rise (db): Interference margin is also called noise rise. It is the margin due to loading in the system. The interference margin is needed in the link budget because the loading of the cell, the load factor, affects the coverage. The more loading is allowed in the system, the larger is the interference margin needed in the uplink, and the smaller is the coverage area. For coverage-limited cases a smaller interference margin is suggested, while in capacitylimited cases a larger interference margin should be used in the link budget. Typical values for the interference margin in the coverage-limited cases are db, corresponding to 20-50% loading [7]. 14 Interference Margin (db) Loading (%) Figure 4.4 Loading Effect The interference margin is calculated as 10 log 1 where, η is the loading factor. 10 log

34 24 Using equation (4.6), a graph of interference margin vs. loading is plotted in Figure 4.4. We can notice that the interference margin is increases rapidly when the load in the system increases. If the load in the system is too high, say 90%., we need 10 db margins to balance the interference. This means we are using more power to control the interference only. If the load increases ideally 100%, then the system cannot work at all. Hence, loading plays a vast role in the system performance. (l) Total Interference Level (dbm): Total interference level is the total noise power seen at the receiver input including the noise rise. Hence, (m) : is the KPI of the QoS. It is the ratio of the received bit energy to the thermal noise. is the received energy per bit multiplied by the bit rate. is the noise power density divided by bandwidth. Typically, E N values of 5 db in UL and 8 db in DL are used for speech connection. (n) Processing Gain (db): The ratio between the transmitted modulation bandwidth and the information signal bandwidth is called spreading factor and the logarithmic value of the spreading factor is known as processing gain. If the data rate is smaller than the chip rate, then it provides a gain to the signal to interference ratio after dispreading in both directions. Processing gain is WCDMA-specific parameter. 10 log log where, W is the chip rate and R is the user bit rate.

35 25 (o) Receiver Sensitivity (dbm): Receiver sensitivity is the minimum signal level needed at the receiver input which just satisfies the requirements over the total interference level That is, dbm is the receiver sensitivity of base station and dbm is the receiver sensitivity of mobile station. (p) Rx Antenna Gain (dbi): Rx antenna gain is the receiving antenna gain compared to isotropic radiator (an antenna which radiates equally in all directions). Typically, antenna gains in base station are high because of directional antenna. A value of 18 dbi is used for the base station receiving antenna gain in the simulation. Antenna used in the mobile stations is presumed Omnidirectional and therefore their gain is assumed to be 0 dbi. (q) LNA Noise Figure (db), (r) LNA Maximum Gain (db), (s) LNA Insertion Loss (db), (t) Total LNA Gain or Improvement (db): Low Noise Amplifier (LNA), also called Mast Head Amplifier (MHA), is used as an effective method to improve the cell coverage in uplink direction. This is achieved by amplifying the received signal by LNA before the receiver losses. It is used just after the receiving antenna. Figure 4.5 depicts the situation how LNA is used. The noise figure of a system having cascade amplifiers is calculated by Friis formula: The improvement of noise figure in the system after using LNA is calculated as the ratio between the NF without LNA and with LNA. That is,

36 26 where, is the noise figure of base station, is the cable loss, is the noise figure of LNA, is the gain of LNA. Using given parameters, the improvement of noise figure in the system after LNA is db. Hence, using LNA in this simulation, a db gain is achieved in uplink direction. Besides the gain improvement in uplink direction, LNA has negative effect in downlink direction. It produces some insertion loss in downlink direction. Hence, in power budget, we have used the insertion loss of 0.1 db in downlink direction. (x),(d) Cable, Connector, and the Combiner Loss (db): These are the combined losses of all the transmission system components between the transmitter output and the antenna input. Combiner loss is taken in account only in downlink direction. Typically, cable loss depends on the frequency and its diameter. Thin cable has more loss than thick cable. Cable loss is higher at higher frequency. The cable loss in the base station side is assumed to be A 100 m cable length is used in the simulation. The net cable loss in base station side is 1.22 db. The cable loss in mobile side is assumed to be 0 db. In this simulation, there are no connector and combiner losses. (y) Antenna Diversity Gain (db): It is the gain provided by the receiver diversity or transmitter diversity antenna. Antenna diversity gain has to be taken in account separately only if the diversity is used and it is not included in the requirements.

37 27 (z) Soft Handover Diversity Gain (db): It is defined as the macro-diversity gain against fast fading caused by the multi path propagation. The soft handover diversity gain is the different in the uplink and the downlink directions due to a different macro-diversity combining method. (A) Power Control Headroom (db): This is commonly known as the fast fading margin. Some margin is needed in the mobile station transmission power for maintaining adequate closed-loop fast power control in unfavorable propagation conditions such as near the cell edge. This applies specially to pedestrian users, where to be maintained is more sensitive to the closed-loop power control [10]. Power control headroom is taken into account in the uplink power budget. It is taken into account because at the cell edge, the mobile station transmitter is transmitting continuously at full power and thus cannot follow the fading according to the uplink power control commands. (B) Required Signal Power (dbm): This is the required signal power needed at the receiving end for the connection.. The required signal power in UL is dbm and in DL is dbm (C) Tx Power per Connection (dbm): It is the maximum transmitter power per traffic channel at the transmitter output for a single traffic channel. A traffic channel is defined as the communication path between a mobile station and a base station used for user and signaling traffic. (F) Peak EIRP (dbm): Peak Effective Isotropic Radiated Power is the resultant output power of the transmitter ready to transmit after system losses and the transmitter antenna gain

38 28 (G) Isotropic Path Loss (db): Isotropic path loss is the path loss between the transmitting and receiving end (H) SHO Gain (db): The soft handover phenomenon gives an additional gain against the fast fading that takes place in the network. Due to the soft handover phenomenon, mobile connectivity to a base station gives a better signal quality. Thus due to macro diversity combinations, the soft handover gain has a positive impact on the base station. The total soft handover gain is assumed to be between 2.0 and 3.0 [7], including the gain against slow and fast fading. (I) Body Loss (db): Body loss is the loss of signal by the user s body. The loss occurs when the user s body lies in the path of signal between the base station and the mobile station. That is, the body loss depends on how the mobile station antenna is oriented towards the base station antenna. Typical value of 3 db is assumed as body loss. (J) Propagation Slope (db/decade): Propagation slope characterizes the type of environment. It indicates that how much signal is attenuated by distance in an environment. The propagation slope of 35 db/decade is used. (K) Outdoor Coverage Probability (%), (L) Outdoor Slow Fading STD (db), (M) Outdoor Slow Fading Margin (db), (O) Indoor Coverage Probability (%), (P) Indoor Slow Fading STD (db), (Q) Indoor Slow Fading Margin (db), (R) Building Penetration Loss (db): These are the planning thresholds for the outdoor and indoor users. In this simulation, only indoor planning thresholds are used. Building penetration loss of 15 db with 9 db indoor slow fading margin is used in both the UL and DL direction

39 29 Maximum Path Loss: The difference between the required signal power and the peak EIRP is the maximum allowed path loss. The maximum allowed path loss of db is calculated for UL and db for DL. It is clear that UL direction is limited and due to this reason the cell was dimensioned based on UL path loss COST-231-Hata Model The COST-231-Hata model [18] is the extension of Hata s propagation model. It is used for the coverage calculation in macro-cell environment where the base station antenna height is above the average rooftop level of the buildings adjacent to the base station. The propagation model describes the average signal propagation in that environment, and converts the maximum allowed propagation loss in db to the maximum cell range in kilometers [7]. The COST-231-Hata Model in the form of propagation loss is given as: where is the path loss (db), is the frequency (MHz), is the base station antenna height (m), is the mobile station antenna height (m), is the mobile station antenna gain function (db), d is the distance between the base station and the mobile station (km), and C is the area correction factor (db). The mobile station antenna gain function is given as: For a medium or small city And for a large city

40 30 The area correction factor is given as: Cell Capacity and Cell Range (Coverage Area) Estimation The coverage and the capacity in UMTS have their direct impact on each other [19-25]. The more the users served by a network means the more capacity the system has but at the same time the load of the system increases beyond the limit in proportion of increasing users due to which the interference in the system increases which in turns degrades the service. In such a limiting case, the users at the far distance must have to move towards the base station to serve properly which means the cell range decrease which is also known as cell breathing. On the other hand, if the users want to get proper service without moving towards the base station, then they must have to use their full transmit powers to overcome the interference which consumes the power of the traffic channels that means there is the decrease of capacity. Hence, in UMTS we must have to take in account both the coverage and capacity planning simultaneously. To synchronize the cell range in both the coverage and capacity planning, let us first calculate the cell area from the capacity planning and then use this cell area in the coverage planning to find the base station antenna height and cell range Cell Capacity Estimation The capacity of a system means the total number of subscribers the system can serve at a time satisfying the required quality of service. Since WCDMA (UMTS) is interference limited, the capacity of such a system varies time to time which depends on the present

41 31 situation of the system. The main parameters affecting the capacity of WCDMA system are the present load of the system, the other-to-own cell interference which is also known as little i, the signal energy per bit divided by the noise spectral density, the activity factor of the users, the user s bit rate and the orthogonality of the users. The orthogonality 1 of the users affect only in the downlink direction. According to [10, Eq. (3.6), p78], the uplink load equation is given as where, 1 1 = the uplink load factor N = the total number of users = the signal energy per bit divided by the noise spectral density of user k W = the wideband chip rate = the bit rate of user k = the activity factor of user k = the other-to-own cell interference = the number of sectors and = the sectorisation gain. If the service in the system is only voice and all N users have the same rate of R, then the eq. (4.20) is reduced to The orthogonality represents how well the noise rejection is improved between traffic channel and cell. That is, how well the mobile station is able to decode its code.

42 32 Including the bearer control-overhead factor 2 ( in the speech service, the eq. (4.21) can be written as Based on the uplink load equation (4.22), the example of capacity calculation used in the simulation is shown in table 3. Table 3: An Example of Capacity Calculation based on Load Equation GENERAL INFO Units Value Frequency MHz 2140 a Chip Rate Mcps 3.84 b Tempereature K 293 c Boltzmann's Constant J/K 1.38E-23 d SERVICE INFO UPLINK DOWNLINK Units Value Value Load % e Bit Rate kbps f Required Eb/No db 5 8 g g = 10^(g/10) Activity Factor % h Other-to-Own Cell Interference % i Bearer Control-Overhead Factor % j Number of Sectors 6 6 k Sectorisation Gain l [10, Table 3.21, p132] Total Number of Users in Uplink Using eq.(4.22) The all terminals in the planning area are distributed uniformly having traffic density of 100 /. One erlang (Erl) is the equivalent of one call for an hour. Here, one 2 The bearer control overhead factor accounts for the fact that control channel power is transmitted even during the inactive periods of a call [21].

43 33 erlang represents one terminal or user. Then, the area occupied by the total number of terminals in a cell is calculated as Hence, from the capacity planning the cell area is km Cell Range (Coverage Area) Estimation The Figure 4.6 illustrates the cell dimensioning. The cell area (shaded area) is given by Figure 4.6 Cell Dimensioning From the right angled triangle ABC,