Guidelines for the design of UMTS Access Networks

Transcription

1 August 2000 European Institute for Research and Strategic Studies in Telecommunications GmbH Project P921-PF Guidelines for the design of UMTS Access Networks Deliverable 2

2 Project P921 Goals The main target of this work was to develop recommendations and guidelines for UMTS network design and implementation. These guidelines and recommendations are to support planners and operators in designing and implementing efficient UMTS networks. Services, applications and Quality of Service UMTS is going to support a variety of services and applications, using both circuit and packet switched access. In the framework of EURESCOM project P921 three kinds of applications have been selected for Quality of Service analysis: audio retrieval, MPEG-4 video download applications, and IP-based appliobtained by means of a link level simulator to corrupt the application bit stream and to evaluate the degradation of the quality due to the radio interface. The results of the tests have shown a strong impact of the UTRA interface on the Quality of Application testing Link Level Simulator Error patterns Application Application performance Subjective Testing UTRA characterisation QoS cations (web browsing, ftp). The objective of the quality test was to assess the impact of the UTRA (UMTS Terrestrial Radio Access) interface on the selected applications. The test method applied was to use the error patterns Service. For example, real time streaming of high quality music over UMTS requires a highly protected channel, at least when the application is not using any error resilience tools. Cell coverage in UMTS Cell breathing: left lower, right higher cell traffic One of the fundamental characteristics of CDMA systems implemented in UMTS is that the coverage range is intrinsically linked to the capacity of the system: the more traffic is carried by a cell, the smaller the coverage area of the cell becomes. This phenomenon is known as cell breathing, which shows the service area of one base station with different traffic loads in the system. This dynamic behaviour makes cell planning and network dimensioning a very complex process. Traditional static prediction methods are not appropriate. Therefore simulation and statistical modelling techniques have to be used. However, the system is very complex, with so many interactions, that the simulation has been split into two parts: Link level, considering the effects of the radio channel on individual bits transmitted in a single communication. System level, considering a number of cells and mobiles, based on output parameters from individual link simulations produced at link level.

3 UTRAN characterisation UTRAN, the UMTS Terrestrial Radio Access Network, operates in two modes, the UTRA FDD and the UTRA TDD mode. The UTRAN link level simulation results of P921 are given for the voice service, circuit switched data service (LCD, Long Constrained Delay) and for packet switched data service (UDD Unconstrained Delay Data) over the ETSI / ITU propagation channels (vehicular A/B, outdoor to indoor A/B). The simulations include realistic algorithms for closed loop power control and pilot assisted channel estimation. For the up-link channel, the antenna diversity technique has been implemented by doubling the Rake receiver structure and using an equal gain combiner before decoding. Voice service was simulated at 8 kbits/s, and LCD and UDD services at 64, 144 and 384 kbits/s. Resulting system working point for the 8 kbit/s voice service as a function of mobile speed and number of users per slot (downlink Vehicular A channel) System working point BER = 0,1 %] Mobile speed [km/h] 8 users per slot 4 users per slot 1 user per slot Link budget and cell sizes The link budget is calculated by the following procedure: 1. Uplink path loss evaluation 2. Downlink power level evaluation at cell border 3. Downlink EIRP value evaluation per traffic channel (Effective Isotropic Radiated Power i.e. how much power you would be transmitting if transmitting in a perfect sphere) 4. Downlink power evaluation per traffic channel 5. Downlink path loss evaluation Link-level simulation results Cell radius [km] 2,0 1,5 1 0, Average power of the mobile station [dbm] UMTS speech GSM 1800 UMTS LCD384 (Long Constrained Delay 384kb/s) UMTS UDD480 (Unconstrained Delay Data 480kb/s) On the basis of the radio link results the UMTS (FDD component based on W-CDMA access) link budget has been evaluated for the case of an urban environment. The cell radius of the UMTS system has been compared with the one of GSM The figure presents results from link level simulations: The coverage range of UMTS services in the urban environment as a function of average power of the mobile station and offered service (70 % cell load). The UMTS cell radius is compared to the cell radius of a GSM 1800 system. It is worth noting that in the GSM 1800 case the cell radius is not related to the system load. The results show that, in the case of a voice service, the UMTS cell radius is greater than the one of GSM In contrast to this, the coverage in UMTS is smaller than in GSM 1800 systems for the other services. UTRAN architecture The UMTS Radio Access Network is built around two new nodes and three new interfaces (see the figure). The Node B is effectively a UMTS base station, while a Radio Network Controller (RNC) is comparable with a GSM Base Station Controller (BSC). Each RNC is connected to the Core Network (both packet and circuit domains) by the Iu interface; RNCs are connected together with the Iur interface. Each Node B is connected to an RNC by the Iub interface.there are some fundamental limits on the numbers of cells and RNCs that can be supported, due to the way that cells and RNCs are identified normally by the number of bits in the identities, but sometimes hidden elsewhere in the protocol definitions. There is currently no restriction of the numbers of Nodes B in a Radio Network Subsystem (RNS) or PLMN.

4 According to standardisation the limits are as follows: Maximum number of Cells in a PLMN 26,435,456 Maximum number of RNCs in a PLMN 4,096 Maximum number of Cells in an RNS 65,536 Maximum number of Nodes B in an RNS No limit defined in the standards Maximum number of Cells in a Node B No limit currently defined in the standards UTRAN architecture Iu RNS RNC Iub Node B Node B Iur RNS Node B Iu RNC Iub Node B In practice, the maximum numbers supported by the vendors will vary and are likely to be lower than the absolute limit stated here. Infrastructure sharing Given the limited number of sites for new base stations, and the cost of errecting new masts, site sharing between 3G and GSM is likely to be of importance, especially for existing Hierarchical cell structures UMTS, as GSM, supports the deployment of micro cells within macro cells to provide increased capacity in traffic hot spots and coverage where previously none has existed. However, there is some concern that the limited dynamic range of the terminal power as operators. In contrast to the mechanical issues, there should be no problem with the co-location of W-CDMA and GSM900/1800 sites. It should be possible to share the same headframe between GSM and UMTS, assuming there is sufficient space for the additional specified in UMTS will result in a minimum obtainable cell radius, which is accentuated when good line of sight is achieved. There is also some doubt about the suitability of the currently specified soft handover mechanism for use in contiguous micro-cellular coverage areas. Therefore it could be that micro cells cannot be designed to perform optimally until antennas and feeders, and assuming that the structure is capable of withstanding the additional wind load. This has to be determined on a case by case basis. equipment designed to a later release of the standards is available. These issues require further investigation. There are two options for the choice of carrier for micro cells: Same carrier for micro/macro cells Different carriers for micro/macro cells Increasing the coverage area The UTRAN will support six sectored sites, which could maximise coverage and capacity of UMTS sites. The basic principle is that by using six narrow beam antennas, the coverage area of a cell will be extended due to the increased forward gain, and the capacity will be double that of a three-sectored cell. The use of six sectors can lead to an increase in the coverage area that is served by multiple cells (i.e. the soft handover region), depending on the local propagation conditions and the antenna pattern. The two figures show the overlap between the antenna patterns. This does not match the soft handover regions, but it shows, how the overlap can increase, given certain antenna beamwidths. 3 sectors 900 beamwidth (left) compared to 6 sectors 600 beamwidth (right)

5 Conclusions The number of services in a UMTS system is substantially higher compared to GSM, which makes the network design more complex. Packet switched mode allows costeffective transport of data, but requires QoS control. Some applications such as voice or real-time video require throughput with a guaranteed data rate and maximum delay. Mobile communication applications have to be designed according to the user mobility, the radio environment (user speed and coverage radius), the application topology, and the user terminal requirements. Current applications content, e.g. JPEG, does not allow missing data. UMTS radio interface has a strong impact on the QoS of applications, requiring an error-resistant mechanism to obtain the required QoS level. In a CDMA network coverage is intrinsically linked to the capacity of the system. Cells are breathing; the coverage range for voice varies between 200 m and 1.4 km, depending on the number of users. Traditional static prediction methods for network planning are not applicable. Two link level simulators (W-CDMA and TD- CDMA) have been developed in the project to evaluate the radio performance of UTRA. The main outcome of link level simulations is the system working point, the minimum Eb/No (ratio between energy per bit and noise). Voice services have an almost constant system working point with respect to the mobile speed in the range of km/h. Data services (LCD & UDD) are more sensitive to the mobile speed and to the propagation environment. The link performance of the TDD mode is more influenced by the mobile speed than the FDD mode. For the voice service, the UMTS cell radius is greater than the GSM 1800 one. Data services with data rates higher than 384 kbit/s have a lower cell radius compared to GSM The Project has reviewed available system level simulators, and established scenarios for system level simulations. A future project is envisaged to analyse these scenarios. A more detailed version of this deliverable is available at: public/projects/p900-series/ p921/p921.htm About P921 EURESCOM Project P921-PF started on 23 February 1999 with a planned duration of 18 months. The total budget was 100 MM. Additional information can be obtained from: public/projects/p900-series/ p921/p921.htm Publications resulting from this work: 1. D. Wake and R. E. Schuh, IEE Electronics Letters, vol. 36, no. 10, pp , D. Wake and R. E. Schuh, Technical Digest, International Topical Meeting on Microwave Photonics MWP 99, Post deadline paper, Session F-12, pp. 9-12, ISBN X, Melbourne, Australia, November 17 19, Ralf E. Schuh and David Wake, Proceedings, IEEE International Conference on Third Generation Wireless Communications, IEEE 3g Wireless'2000, San Francisco, Silicon Valley, USA, ISSN No (2000), pp , June 14-16, 2000 The Project team: Project Members Name Company Josef Noll (Project Leader) Telenor josef.noll@telenor.com Jon Harris BT jon.w.harris@bt.com Milan Jankovic Community of Yugoslav PTT ljiljamj@eunet.yu Borislav Odadzic zjptt@eunet.yu Armando Annunziato CSELT Telecom Italia Group armando.annunziato@cselt.it Enrico Buracchini enrico.buracchini@cselt.it Bruno Melis bruno.melis@cselt.it Anne-Gaële Acx France Télécom annegaele.acx@rd.francetelecom.fr Jean-Francois Chaumet jeanfrancois.chaumet@rd.francetelecom.fr Nicolas Guerin nicolas.guerin@rd.francetelecom.fr Georgos AgapiouOTE gagapiou@oteresearch.gr Dimitrios Xenikos dimitrios.xenikos@oteresearch.gr Amparo SanmateuT-Nova amparo.sanmateu@telekom.de Ignacio Berberabana Telefónica I+D ibfm@tid.es Héctor González hector@tid.es Fernando Martinez fvega@tid.es Jorge Montero jams@tid.es Arild Jacobsen Telenor arild.jacobsen@telenor.com Tor Jansen tor-magnus.jansen@telenor.com Tore Arthur Worren tore-arthur.worren@telenor.com Uwe Herzog (Project Supervisor) EURESCOM herzog@eurescom.de

6 What is EURESCOM? EURESCOM is the European institute for collaborative research and strategic studies in all areas of telecommunications. Currently there are 24 Operators from 23 European countries participating in EURESCOM. It acts as technical forum for sharing visions and concepts, as an initiator of targeted activities, and as facilitator for common undertakings on technical issues. EURESCOM is open to any European Network Operator or Service Provider who may wish to join. EURESCOM GmbH Schloss-Wolfsbrunnenweg 35 D Heidelberg, Germany Tel.: Fax: EURESCOM Participants in Project P921-PF