Co-sited and Non Co-sited Coexistence Analysis between IMT- Advanced and FWA Systems in Adjacent Frequency Band

Transcription

1 Co-sited and Non Co-sited Coexistence nalysis between IMT- dvanced and FW Systems in djacent Frequency Band ZID. SHMSN, LWY FISL, THREK BD RHMN Wireless Communication Center, Faculty of Electrical Engineering Universiti Teknologi Malaysia UTM, Skudai, Johor Bahru MLYSI bstract: - In this paper, coexistence study of the future fourth generation IMT-dvanced with fixed wireless access systems is analyzed. Co-sited the two base stations and non co-sited coexistence and interference are investigated. The interference analysis model, adjacent channel interference ratio CIR is applied in the band 30- MHz to extract the additional isolation needed to protect adjacent channel interference. lso interference to noise ratio as a standard interference criteria is introduced and possible engineering solutions are explained at last. Key-Words: - CIR, CLR, CS, additional isolation, co-sited and non co-sited coexistence, FW systems, IMT-dvanced system, interference. 1 Introduction Interference between two wireless communication systems occurs when these systems operate at overlapping frequencies, sharing the same physical environment, at the same time with overlapping antenna patterns. ITU-R recommends expressing the level of interference in terms of the probability that reception capability of the receiver under consideration is impaired by the presence of an interferer. Concerning the different systems of International Mobile Telecommunication (IMT- dvanced) and Fixed Wireless ccess (FW) systems, it is natural to conclude that those technologies will work in the same environment that leads to occurrence of performance degradation. Main mechanisms of coexistence are: co-sited (colocated) and non co-sited (non co- located). 30- MHz band is allocated for FW band and Fixed Satellite Service (FSS) downlink part. Meanwhile, the said frequency band is identified at WRC-07 for IMT-dvanced in several countries in sia with regulatory and technical constraints [1], which means that frequency sharing between these systems is bound to happen. few studies were done between terrestrial systems in the said band because this band did not use for mobile as the bands lower than 3 GHz as in WCDM up to 2690 MHz. The studies which carried out in this band are in [2] and [3]. In [2] the study implemented by using dvanced Minimum Coupling Loss (-MCL) between beyond 3G systems and fixed microwave services to get the minimum separation distance and frequency between the two systems. Whereas in the [3], BW system represented by FW is studied to share the same band with p-to-p fixed link system also to determined the minimum separation distance and frequency separation. In our study the concept of djacent Channel Leakage ratio and djacent Channel Selectivity is presented such that the effect of both of transmitter and receiver are taking into account. The reminder of this paper is organized as follows. In Section 2 interference model used is described in detail. Section 3 is devoted to describing the systems parameters. Protection criteria, propagation models, scenarios executions, and analysis are presented in Sections 4 to 8. Finally, the conclusions are presented in Section 9. 2 Interference Model and Scenarios When a system IMT-dvanced of other is considered, main type of interference is intrasystem interference, including interference coming from given cell, adjacent cell, and thermal noise. Whereas two systems coexist in the same geographic area, the interference includes not only intrasystem interference, but also intersystem interference. The only form of interference modeled in this paper is CI that arises from the adjacent channel leakage (CLR) from base station transmissions in the IMT- dvanced and FW systems and the adjacent channel selectivity (CS) of the base station, receivers in the IMT-dvanced and FW systems ISBN: ISSN:

2 and the ability of these receivers to reject power legitimately transmitted in the adjacent channel. The level of interference received depends on the spectral leakage of the interferer s transmitter and the adjacent channel blocking performance of the receiver. For the transmitter, the spectral leakage is characterized by the CLR, which is defined as the ratio of the transmitted power to the power measured in the adjacent radio frequency (RF) channel at the output of a receiver filter. Similarly, the adjacent channel performance of the receiver is characterized by the CS, which is the ratio of the power level of unwanted CI to the power level of co-channel interference that produces the same bit error ratio (BER) performance in the receiver. In order to determine the composite effect of the transmitter and receiver imperfections, the CLR and CS values are combined to give a single adjacent channel interference ratio (CIR) value using the following equation [4], 1 CIR= (1) CLR CS 3 IMT-dvanced and Fixed Services s Describtion In order to examine coexisting and sharing issues, it is necessary to clarify the parameters of IMT- dvanced and FW that will affect the interference level and criterion as clarified in equation (1). The following tables 1 and 2 present the parameters for the two systems. 3.1 IMT-dvanced parameters The term IMT-dvanced has been introduced for beyond IMT-00 system [5]. The target peak data rates are 100 Mbps for high mobility systems and 1 Gbps for low mobility of fixed and nomadic systems. The required channel bandwidths ranging between -100 MHz where 50 MHz for suburban and 100 MHz for urban coverage [6]. Table 1 contains the IMT-dvanced parameters assumed for the comparison of the different studies. Where 5 MHz and 10 MHz are offset of 1 st adjacent channel and 2 nd adjacent channel separation from center frequency, respectively. 3.2 FW system parameters In Malaysia the frequency range GHz is allocated for FW systems, it is divided into subbands for duplex use (non duplex systems can still be used in this band), MHz paired with MHz as well as MHz paired with MHz. These FW bands are to be used for direct radio connection in the last mile between a fixed radio central station and subscriber terminal stations in a point-to-point and/or point-tomultipoint configuration. Countries have various frequency channel spacing within the 3.5 GHz bands 1.25, 1.75, 3.5, 7, 8.75, 10, 14, and 28 MHz can be used according to capacity needs [7]. FW parameters are shown in Table 2. Table 1: IMT-dvanced system parameters (macro cell) Value Center frequency of operation (MHz) 3500 Base station transmitted power (dbm) 43 Minimum Coupling Loss ( (db) 30 Base station antenna gain (dbi) 18 Base station antenna height (m) 30 Interference Limit Power (dbm) -109 CLR Offset 5 MHz Offset 10 MHz 50 CS Offset 5 MHz Offset 10 MHz 50 Table 2: FW system parameters (macro cell) Value Center frequency of operation (MHz) 3500 Base station transmitted power (dbm) 36 Minimum Coupling Loss (db) 30 Base station antenna gain (dbi) 18 Base station antenna height (m) 30 Interference Limit Power (dbm) -109 CLR Offset 5 MHz Offset 10 MHz 66 CS Offset 5 MHz Offset 10 MHz 70 4 Protection Criteria In the deterministic analysis, the interference thresholds of -109 (dbm) is used as the maximum interference s that can be tolerated by both of the IMT-dvanced and FW equipment. This threshold is specified in Report ITU-R [6] and the RF parameters specified by the WiMX Forum [8] for the IMT-dvanced and FW equipment, respectively. For discussion of various sharing scenarios, it is necessary to develop appropriate rules for sharing. Intersystem interference can be described as short term or long-term. It is referred to ISBN: ISSN:

3 as long term interference for percentage of time of greater than % While a small percentage of the time in range of 0.001% to 1.0% is referred to short-term interference which is rarely evaluated in the coordination literature as it is very much statistical in nature and not found for many services and will be specific to the cases considered [9], [10]. In this paper we consider long term interference only. The interference protection criteria can be defined as an absolute interference power level I, interference-to-noise power ratio I/N, or carrier-tointerfering signal power ratio C/I [10]. ITU-R Recommendation F details two generally accepted values for the interference to thermalnoise ratio (I/N) for long-term interference into fixed service receivers. When considering interference from other services, it identifies an I/N value of 6 db or 10 db matched to specific requirements of individual systems. This approach provides a method for defining a tolerable that is independent of most characteristics of the victim receiver, apart from noise figure. Each fixed service accepts a 1 db degradation (i.e., the difference in decibels between carrier-to-noise ratio (C/N) and carrier to noise plus interference ratio C/(N + I) in receiver sensitivity. In some regard, an I/N of 6 db becomes the fundamental criterion for coexistence [11], so it should be that [12]: I N α (2) Where α is the protection ratio in db and here has value of -6 db. 5 Propagation models In particular, there is no single propagation model used for different sharing studies because the particular deployment of the systems requires using specific propagation model relevant to the specific system. For co-sited base stations, a coupling loss value of 30 db is assumed between co-sited antennas, which was also a value measured by llgon [13] for horizontally separated antennas of the order of 1 meter. When the base stations are not co-sited but separated by some distance, the path loss between the two base stations can be evaluated using the free space propagation model that can be defined as L 43.3 log10 ( d freespace = + ) (3 Where d is the distance in meters between the transmitting and receiving antennas. For example, with a base station-to-base station separation of 1,000 m, the path loss between two isotropic antennas is db, assuming free space path loss and an operating frequency of 3.5 GHz. This represents a worst case scenario, in which a LOS path exists between the two base stations. Table 3: nalysis for co-sited microcellular base station, where the FW is the interference victim Offset 5 MHz 10 MHz Transmit Power (dbm) Coupling Loss (db) CIR (db) Interference power at receiver input (dbm) llowed interference power (dbm) dditional isolation needed (db) Table 4: nalysis for co-sited microcellular base station, where the IMT-dvanced is the interference victim Offset 5 MHz 10 MHz Transmit Power (dbm) Coupling Loss (db) CIR (db) Interference power at receiver input (dbm) llowed interference power (dbm) dditional isolation needed (db) Co-sited Macrocellular Base Stations nalysis In order to get additional isolation which is required to prevent adjacent channel interference for a collocated systems the following formula should be calculated. = Pt CL CIR I (4) Where is additional Isolation (db) required to prevent adjacent channel interference, P t is the transmitter power, and I is the Interference Limit. CL is the antenna coupling loss which has practical ISBN: ISSN:

4 values for macro, micro, and pico cell types, for base station-to-base station macro interference the antenna coupling loss is 30 db [13]. The additional isolation needed when the interference is generated from an IMT-dvanced base station to a FW base station is shown in Table3. Similarity, the additional isolation needed when the interference is generated from a FW base station to an IMT-dvanced is tabulated in Table 4. 7 Not Co-sited Macrocellular Base Stations nalysis The dditional isolation needed for certain distances can be extracted and expressed by = Pt+ G+ G L CIR I (5) t r p Where G t is transmitter antenna gain, G r is victim receiver antenna gain, L p is propagation path loss, and I is Interference Limit. The equation (4) can be represented by the following expression. = CI I (6) Where CI is adjacent channel interference which it should be minimum as much as possible. Figure 1 clarify the additional isolation needed when interference from IMT-dvanced on FW. Furthermore, the required additional isolation when interference from FW on IMT-dvanced is depicted in Figure 2. s mentioned earlier, the interference to noise ratio is the considered protection criteria here, it is shown in the Figures 3 and 4 that the amount of interference noise compare to distance i.e. there is no communication possibility for the assumed scenario between the two base stations. of by 29.7 db is needed. Furthermore, the additional isolation needed is increased to 36.7 db if the interference victim is the FW base station. The effect of high power for IMT-dvanced clearly appears from Fig. 1 and 3, in these figures additional isolation required is larger and Interference to noise I/N ratio is greater than the target value (-6 db). It is expected that high values CLR and CS can improve the I/N and thus the performance level of both coexisting systems in the same area will be high. In addition, the frequency carrier separation is going to enhance quality of service. dditional isolation (db ) MKHz 10 MHz Separation distance between interferer and victim base stations (m) Fig.1: dditional isolation when interference from IMT-dvanced on FW (non co-sited case) MHz 10 MHz 8 Compatibility and Simulation nalysis With equipment that just conforms to the standards, it is unlikely to be possible to use a macrocellular IMT-dvanced base station in the same area as a macrocellular FW base station if LOS path exists between the two antennas and each site is in the main beam of the other site s antenna (i.e., a worst case scenario), without mitigation techniques. If the base stations are separated by 1 km and they operate on radio channels that are separated by 10 MHz (i.e., the second adjacent channel), an additional isolation between the two base stations dditional isolation (db) Separation distance between interferer and victim base stations (m) Fig.2: dditional isolation when interference from FW on IMT-dvanced (non co-sited case) ISBN: ISSN:

5 I/N (db) MHz Freq. offset 5 MHz Freq. offset Interference Criteria Separation distance between transmitter and receiver base stations (m) Fig.3: Interference from IMT-dvanced (50MHz) into FW (7MHz) I/N (db ) MHz Freq. Offset 5 MHz Freq. Offset Interference Criteria Separation distance between transmitter and receiver base stations (m) Fig.4: Interference from FW(7MHz) into IMT- dvanced (50 MHz) 9 Conclusion From above analysis, the additional isolation required to protect adjacent channel interference is calculated and simulated. The most severity interference appears at co-located base station to base station scenario. way for enabling the coexistence of both systems would be to introduce a large geographical offset between two systems and improve CLR and CS of equipment. Co-located and non co-located base stations will require additional filtering and site engineering to facilitate coexistence between the two systems. References: [1] IST WINNER II D , The WINNER Role in the ITU Process Towards IMT-dvanced and Newly Identified Spectrum, Vo1.0, Nov. 07 [2] J. H-Shin, Y. H-Goo, L. Jaewoo, C. Woo-Ghee, Y. Jong-Gwan, P. Han-Kyu, The Coexistence of OFDM-Based Systems Beyond 3G with Fixed Service Microwave Systems, Journal of Communications and Networks, Vol. 8, No. 2, 06, pp [3] CEPT ECC Report 100, Compatibility Studies in the Band MHz between Broadband Wireless ccess (BW) Systems and other Services, 07. [4] 3GPP, Radio Frequency system scenarios, 3GPP TS Version 6.4.0, March 05. [5] I. Ferdo, 4 GHz for 4G: Why, How and When?, IEEE Conference, 06, pp [6] ITU-R Document 8F/1015-E, Sharing Studies between FSS and IMT-dvanced Systems in the 30- and MHz Bands, 06. [7] MCMC SRSP 507a, Requirements for FW Systems Operating in the Frequency Band from 30 MHz to 3700 MHz, Issue 1, 01. [8] Report ITU-R M. [LMS.CHR.BW], Characteristics of Broadband Wireless ccess Systems Operating in the Mobile Service for Frequency Sharing and Interference nalyses. [9] P. Gardenenier, Mansoor Shafi, Robert B. Vernall, and Murray Milner,Sharing Issues between FPLMTS and Fixed Services, IEEE Comm. Mag., Vol. 32, No. 6, 1994, pp [10] NTI Report , Interference Protection Criteria Phase1- Compilation from Existing Sources, 05. vailable: [11] IEEE Std , IEEE Recommended Practice for Local and Metropolitan rea Networks Coexistence of Fixed Broadband Wireless ccess Systems, 04. [12] ITU-R Recommendation F.12, Frequency Sharing Criteria between a Land Mobile Wireless ccess System and a Fixed Wireless ccess System Using the Same Equipment Type as the Mobile Wireless ccess System, [13] llgon, ntenna to ntenna Isolation Measurements, 3GPP TSG RN WG4 Meeting No. 8, TDOC 631/99, ISBN: ISSN: