UMTS Spectrum Allocation: Technical Aspects and Suggestions for Mobile Operators

UMTS Spectrum Allocation: Technical aspects and suggestions for mobile operators

IOANNIS KOSTOPOULOS Information and Communications Department Siemens S.A Athens, GREECE

CONSTANTINOS GIANNARIS Department of Information Systems London School of Economics London, U.K

Abstract: The aim of this paper is to present the spectrum allocation for third generation mobile communication, UMTS (Universal Mobile Telecommunication System) which is the key enabler to bring multimedia services into the mobile environment. UMTS provides an attractive solution for Greenfield operators as well as for established operators.

Keywords: Interference, handover, frequency band, carrier spacing, co-location.

1 Introduction According to the ERC/DEC (99)25 [1] the As a working assumption ETSI SMG /3GPP has following assumptions have to be taken in assumed that the core band location for UMTS account when defining the spectrum for UMTS the sub-bands 1920 - 1980 MHz and 2110 - 2170 operators: MHz will be the paired band used for FDD, and the range 1900 - 1920 MHz and 2010 - 2025  The frequency band 1920-1980 MHz is paired MHz will be unpaired bands used for TDD. with 2110-2170 MHz for FDD operation; Figure1 shows the frequency bands of operation  The duplex direction for FDD carriers in these for both modes FDD and TDD. bands is mobile transmit within the lower band and base transmit within the upper band;  The channel raster is 200 KHz and the frequency is an integer multiple of 200 KHz;

FDD carrier spacing between public operators is a minimum of 5 MHz. FDD carrier spacing within a public operators spectrum is variable, based on a 200 KHz raster, and may be less than 5.0 MHz; Figure 1 - European spectrum allocation for UTRA  The frequency bands 1900-1920 MHz and 2010-2025 MHz are unpaired bands for TDD;  TDD carrier spacing between public and self provided applications is a minimum of 4.8 MHz;  TDD carrier spacing between public operators is a minimum of 5.0 MHz. TDD carrier spacing within public operators spectrum is variable, based on a 200 KHz raster, and may be less than 5.0 MHz; Figure 2 Outer guard bands  Carrier spacing between TDD and FDD carriers is a minimum of 5.0 MHz between public operators; 2 Underlying Technical Aspects  TDD carrier spacing between self-provided When defining the frequency channels allocated applications is a minimum of 4.4 MHz, based to each operator many inbound factors have to be on a 200 KHz raster; taken in account, in order to avoid interferences  The carrier nearest to 1900 MHz should be between operators and technologies (e.g., TDD, centered at 1902.4 MHz or above;1 FDD, etc).  The carrier nearest to 1980 MHz should be The following points have to be evaluated: centered at 1977.2 MHz or below;2  The carrier nearest to 2010 MHz should be  Inter-operator FDD/FDD co-location centered at 2013.0 MHz or above;  Inter-operator TDD/FDD co-location  The carrier nearest to 2025 MHz should be  Inter-operator TDD/TDD co-location centered at 2022.2 MHz or below;  Intra-operator FDD/FDD co-location  The carrier nearest to 2110 MHz should be  Intra-operator TDD/FDD co-location centered at 2112.8 MHz or above;  Inter-system DCS1800/FDD collocation  The carrier nearest to 2170 MHz should be  Inter-system DECT/TDD co-location centered at 2167.2 MHz or below;  Border coordination

From the above statements a preliminary draft For each case different solutions are available, can be drawn (Figure 2), regarding the outer that allow operators to flexibly design their guard bands between TDD, FDD and MSS. network and define strategies towards the sharing of sites.

3 Technical Suggestions From studies conducted by the standardization bodies some suggestions can be advanced in order to compensate the technical limitations above mentioned. 1 If the top DECT channel is used for DECT WLL, additional mitigation techniques might be necessary. 2 Use of the TDD here would require a greater frequency separation, or other mitigation techniques such as increased filtering, or a combination of these. 3.1 Multi-operator interference (FDD/FDD) Adjacent channel interference needs to be  Selection of the base station location considered, because it will affect all wideband spatially separated; systems, where large guard bands are not  Desensitization of the base station possible, and WCDMA is no exception. The use receiver (specially for the micro layer); of guard bands between operators has to be  Adjustment of the carrier spacing; carefully defined in order not to have very large  Inter-frequency handovers; guard bands that will waste spectrum bandwidth. Besides the definition of guard bands between As the operator has the liberty of defining it's operators, also spectrum mask requirements for own channel bandwidth and because the carrier the transmitter and high selectivity requirements spacing between intra-operator carriers could be for the receiver, both in the mobile station and as small as 4.0 MHz, is not up to the regulator to base station, will guarantee low adjacent channel define the guard bands between the channels of interference. each operator, and so in our technical suggestion we don't specify such guard bands. According to the 3GPP standards [2,3] the minimum required attenuation between adjacent carriers is: 3.3 Inter-system DCS1800/FDD Co-location Operators may share UMTS with 2G existing Adjacent carrier (5 MHz separation): Required base stations. For this reason GSM to FDD attenuation 33 dB interference should also be evaluated. Special Second adjacent carrier (10 MHz separation): reference has to be made to the DCS1800/FDD Required attenuation 43 dB co-location cases. General guidelines in order to avoid such conditions are: As defined by ERC/DEC(99)25 [1] FDD carrier spacing between public operators has a  Selection of the base station location spatially minimum of 5 MHz, while FDD carrier spacing separated; within a public operators spectrum is variable,  Addition of external filters (dual 1800 / UMTS based on a 200 KHz raster, and may be less than filters); 5.0 MHz. By using a larger carrier spacing, the  Spatial decoupling between the antennas adjacent channel interference can even be more (isolation >30 dB); reduced. In terms of definition of the frequency channels, TDD (+ DECT) is between the DCS1800 3.2 Intra-operator (FDD/FDD) co-location channels and the FDD uplink channels, so a If the operator has two carriers in the same base guard band is already required between TDD and station, the carrier spacing between them could FDD that will ensure minimum interference be as small as 4.0 MHz (< 5 MHz according to between DCS1800 and UMTS. Nevertheless, ERC/DEC (99)25 [1]), because the adjacent other mechanisms like out of band spurious channel interference problems are completely emissions and intermodulation effects should be avoided if the two carriers use the same base avoided by spatial decoupling and the filters station antennas, which will be the case for the mentioned above. second carrier used in the macro layer to expand the capacity in each site. If not the case, is up to the network planning to avoid this interference by applying different mechanisms like: 3.4 UTRA TDD Interference TDD and FDD uplink carriers the resulting Within TDD interference mechanisms we would filtering requirements in TDD base stations are like to refer TDD/TDD interference between expected to be very high and are not considered operators, and TDD/FDD interference. to be a technically and a commercially viable On the first scenario some theoretical solution. assumptions can be previewed when co-siting different TDD operators. In TDD, uplink and downlink share the same frequency channel so 3.5 UTRA DECT/TDD Interference main interference will arise if the base stations The interference between DECT and TDD are not synchronized. Also it is present if systems can be, in some points, compared with different asymmetry is used between the uplink TDD/TDD interference and on a first evaluation and downlink in adjacent cells even if the base can be reduced by the dynamic channel stations are frame synchronized. In order to allocation mechanism in both systems. Only for avoid such cases the following measures have to DECT WLL extra mitigation techniques have to be considered: be employed in other to avoid interference.

 Frame-level synchronization of each operator's UTRA TDD base stations is required; 3.6 Border Coordination  Frame-level synchronization of the base Special care has to be taken in account when stations of different TDD operators is also defining cross-border situations. Besides code recommended if the base stations are close to coordination, it will be advisable for the operator each other; to agree on a frequency coordination based on  Cell-independent asymmetric capacity preferential frequencies by ensuring a fair allocation between uplink and downlink is not treatment of different operators within a country. feasible for each cell in the coverage area; It will also be advisable for the operator to  Dynamic channel allocation is needed to establish, with their neighbor country operator reduce the interference problems within the partners, the same set of frequency channels has TDD band; preferential frequency bands in order to have more flexibility when doing the network The UTRA FDD and TDD have spectrum planning. allocations that meet at the border at 1920 MHz. On TDD/TDD co-location scenarios dynamic channel allocation can be used to avoid interference, but DCA is not effective between TDD and FDD, since FDD has continuous transmission and reception. In terms of the spectrum frequency channel allocation a larger guard band has to be defined between TDD and FDD uplink channels that will avoid part of the interference. Nevertheless, some points have to be considered, Figure 3 Illustration of preferential frequency the TDD base stations can be mainly used for scenario micro and pico coverage areas, so spatial decoupling is guaranteed in most of the co-siting cases. Also additional filters can be used to avoid such interference. For operators with adjacent services in the neighboring country using preferential frequencies.

4 Conclusions In this paper we described the UMTS spectrum allocation. We underlined some important technical aspects and we made suggestions to mobile operators in order to compensate system limitations.

Figure 4 Illustration of neutral frequency scenario References: [1] ERC/DEC/99) 25 – Harmonized utilization of spectrum for terrestrial UMTS operating In ERC/REC(01)01 [4] the following rules are within the bands 1900-1980 MHz, 2010-2025 applied for the coordination of frequency MHz and 2110-2170 MHz. channels between neighboring countries: [2] 3GPP TS 25.101 – UE Radio Transmission and Reception (FDD).  Preferential frequencies (figure 3) and neutral [3] 3GPP TS 25.104 – UTRA (BS) FDD; Radio frequencies (figure 4) shall be agreed between transmission and Reception. Administrations concerned. [4] ERC/REC/01(01) – Border Coordination of  Preferential frequencies may be used without UMTS/IMT-2000 Systems. coordination with a neighboring country if the predicted mean field strength of each carrier produced by the base station does not exceed a value of 65 dBµV/m/5 MHz at a height of 3m above ground at and beyond the border line between two countries;  Neutral frequencies may be used without coordination with a neighboring country if the predicted mean field strength of each carrier produced by the base station does not exceed a value of 45 dBmV/m/5MHz at a height of 3m above ground at and beyond the border line between two countries;  Non-preferential frequencies may be used without coordination with a neighboring country if the predicted mean field strength of each carrier produced by the base station does not exceed a value of 45 dBmV/m/5MHz at a height of 3m above ground at and beyond the border line between two countries;

Systems operating on non-preferential frequencies must accept interference from