LTE-Advanced Compatibility with Digital Broadcasting Receiver at 800 MHz

Zaid Ahmed Shamsan Dept. of Communications and Computer, Faculty of Engineering and Information Technology, Taiz University, Taiz, Yemen

Deanship of Scientific Research, Al Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh, Saudi Arabia shamsan22@gmail.com.com

Abstract—Coexistence between IMT-Advanced system and existing digital broadcasting is a matter of considerable when operating in a same or adjacent frequency channel within the band 790-862 MHz, which is recently allocated for mobile IMT-Advanced Systems represented by LTE-Advanced system. This can cause intersystem interference that affects on the coexisting feasibility between LTE-Advanced and digital broadcasting Receiver. In this paper, an efficient, simplified and graphical scheme for spectral emission mask and interference power level is proposed to investigate different channel overlapping scenarios between the two systems. A range of significant factors such as bandwidth, propagation distance, losses due to clutter, and antenna discrimination losses that can affect on the compatibility feasibility of the two systems are employed. The results demonstrate that using co-channel may unworkable unless some intersystem interference mitigation techniques are applied.

Index Terms—Coexistence, spectrum sharing, bandwidth overlapping, interference, LTE-Advanced.

I. INTRODUCTION Recently, several mobile communication carriers around

the world have begun arranging for 4G of mobile systems which are called international mobile telecommunications-advanced (IMT-Advanced). LTE (Long Term Evolution)-Advanced is one of the systems that proposed to reach and even surpass the requirements on IMT-Advanced, as being defined by ITU-R [1]. IMT-Advanced systems are supposed to support high data rate of 100 Mbit/s and 1 Gbit/s for high and low mobility, respectively, within a wide range of frequency bands from 800 MHz to 3.5 GHz and beyond [2-4].

The frequency band 790-862 MHz is one of the bands that recently allocated for use by IMT-Advanced systems. This band is certainly in the ‘sweet spot’ of frequencies with high wave-length enough to offer fulfilled coverage with comparatively less number of transceivers. In addition, supportive bandwidths are large enough to supply capacity for mass market services such as cell phone connections. Accordingly, the sweet spot frequencies in ultra high frequency (UHF) band are occupied by several and dissimilar services including digital broadcasting service [5]. The ITU recommendation for use 790-862 MHz band by the existing service, digital broadcasting [6], and the new service, IMT-Advanced, is on the co-primary operation basis which may lead to harmful intersystem interference between the two services.

This paper proposes an unsophisticated but general and efficient approach applied for spectrum coexistence investigating and coordinating between non co-sited systems. The proposed new method is based on spectral emission mask to investigate several intersystem interference scenarios with various overlapping possibilities; (1) full overlapping (co-channel), (2) partial overlapping (adjacent channel), (3) non overlapping adjacent channel with no protection band and (4) non overlapping adjacent channel with a protection band. In this method, different channel bandwidths can be applied for both systems under consideration, separation distance, frequency offset, and additional loss due to antenna discrimination are suggested to mitigate intersystem interference effects.

This paper is organized as follows. In Section II, the proposed intersystem interference coexistence method is introduced. Coexistence assumptions and parameters are presented in Sections III. In Section IV, results and discussion are introduced. Finally, the paper is concluded in Section V.

II. INTERSYSTEM INTERFERENCE COEXISTENCE METHOD Interference between dissimilar systems can be evaluated

based on the level of allowable interference at the interfered system receiver. For both LTE-Advanced and digital broadcasting receiver systems, this relies on coexistence and spectrum sharing criteria that is the broadcasting receiver threshold; The minimum signal level of digital receiver that can be detected is -116 dBm has been assumed as an interference protection criteria, Ipc, according to [6] and CEPT Rep. 24 [7]. This value is adopted because that if the interference power level is lesser than the minimum detection signal, then the television receiver will not be influenced by the interferer system. While if the interferer power level is greater than that limit and the carrier to interference ratio is not enough, then the condition of receiving is worse. The interference power level, I, [3] is given by (1):

( ) ( ) pbfattrtt LCfMGGPfI −+Δ+++=Δ (1) where Pt is the power of interferer (LTE-Advanced) in dBm, Gt and Gr denote the gains of interferer and victim receiver (TV receiver) antenna, in dBi, Matt is the attenuation due to interferer spectrum emission mask shift, Δf, from carrier

978-1-4673-6195-8/13/$31.00 ©2013 IEEE

frequency. The correction band factor is denoted by Cbf based on bandwidth of the transmitter and receiver. Lp is the channel propagation losses. The contributed loss is an aggregation of signal propagation in free space and local clutter due to modified plane earth characterizations of the mobile radio path loss, which is agreed by ITU and CEPT for spectrum sharing studies.

The transmitter spectral emission mask is one of the main factors that influence the ability of two non co-sited systems to concurrently operate with no interference risk created to one another since it limits the allowable power radiation levels as a function of the frequency. Usually, power masks are designed based on the type of systems for each channel bandwidth. In this proposed method different intersystem interference scenarios, as shown in Fig. 1, where each two systems sharing a frequency band can go under one of the following cases.

A. Full Overlapping (Co-Channel) Scenario Full overlapping scenario occurs once the signal of

interference at the corresponding 0 MHz frequency offset (∆f) is equal to the Ipc (the horizontal dotted line in Fig. 1). This means that co-channel scenario is possible if (2) is achieved.

[ ] .0)( IpcdBMHzffI ==ΔΔ (2)

Fig. 1. The proposed intersystem interference analysis scheme

B. Partial Overlapping Scenario This scenario takes place when the channel of interferer

system overlaps with the channel of victim system by a frequency shift in the range of greater than 0 MHz and less than the minimum frequency shift at witch coexistence between the two systems is feasible with no overlapping. The minimum frequency shift is equal to half of the summation bandwidths (BW) of interferer and victim systems, 0.5SBW, (the vertical dashed line in Fig.1indicated by overlapping and non overlapping border). Therefore, partial overlapping scenario occurs according to (3).

[ ] .0)( IpcdBMHz0.5SfMHzfBW

I =<Δ<Δ (3)

The value of overlapping bandwidth, OB, can be obtained,

from Fig.1, by calculating the difference between 0.5SBW value and the frequency shift ∆fLCP at which interference signal intersects Ipc line at the left side of 0.5SBW line (at the left cross point, LCP, on Fig.1), i.e.

[ ] .LCPf0.5SMHzOB BW Δ= − (4)

C. Non Overlapping (Adjacent Channel with no Protection Band) Scenario In this case, the two systems can coexist by an adjacent

channel with zero additional bandwidth between the two system channels. This scenario can be occurred according to (5).

[ ] .)( IpcdBMHz0.5SffBW

I ==ΔΔ (5)

Value of the frequency shift, ∆f, at which this scenario can

be take placed is typically corresponding to 0.5SBW. Graphically, this value is equivalent to the point at which three factor lines cross jointly; interference power signal, Ipc and 0.5SBW.

D. Non Overlapping (Adjacent Channel with Protection Band) Scenario In worst cases, spectrum regulators force service providers

to add a protection band, PB, between their service frequency and other service providers. This scenario is the easiest to make two systems peacefully operating with no harmful interference; however, it leads to inefficient spectrum utilization. From Fig. 1, this scenario can be a case according to the following.

[ ] IpcdBMHzffMHz0.5SfRCPBW

I =Δ<Δ<Δ )( (6)

where ∆fRCP represents the frequency shift at which interference power level intersects Ipc line at the right side of 0.5SBW line (at the right cross point, RCP, on Fig.1). Consequently, the size of protection band can be calculated by (7).

[ ] .BW0.5SfMHzPB RCP −Δ= (7)

III. COEXISTENCE ASSUMPTIONS The intersystem interference scenario that should be taken

in consideration when LTE-Advanced as a new technology in the 800 MHz band, that is dedicated for broadcasting services,

is the interference from LTE- Advanced base station (BS) into digital TV receiver. This is, as mentioned by previous studies, due to that interference from a system user (such LTE-Advanced user) to another system user will cause insignificant effect on the performance of a system when averaged over the system. Consequently, the radiation of LTE-Advanced BS to TV receiver scenario is evaluated as the major sever interference link. This as it is relatively static but affects a large number of customers. Additionally, LTE-Advanced BS radiates higher transmitted power than LTE-Advanced user. In this scenario, it is assumed that a TV digital receiver device is located at cell edge coverage for LTE-Advanced BS. Such that, the distance between LTE-Advanced BS and TV receiver device is 1, 2, 3, 4, 5 and 6 km. This scenario is shown in Fig. 2. Table I lists the intersystem interference factors for the two systems.

Fig. 2. The proposed intersystem interference scenario between LTE-

Advanced and TV digital receiver

TABLE I. LTE-ADVANCED AND TV DIGITAL RECEIVER COEXISTENCE PARAMETERS (NR= NOT REQUIRED) [4, 6, 7-10]

Parameter Value LTE-Advanced TV Receiver

Centre carrier frequency 800 MHz Channel bandwidth 5, 10, 20 MHz 8

EIRP 53 dBm NR BS transmitted power 36 dBm NR

BS antenna gain 17 dBi NR BS antenna heigh 30 m 3 m

SEM requirements ETSI-EN301021 (Type G) NR

Correction band factor 0 dB if BWLTE-A <BWTV-R -10log(BWLTE-A/BWTV-R) dB

if BWLTE-A ≥BWTV-RClutter factor (dB) –40

Receiver antenna gain NR 30 dB Receiver noise figure NR 7 dB

Receiver thermal-noise floor NR -101 dBm

Allowable interference at receiver NR -116 dBm (for 8 MHz)

IV. RESULTS AND DISCUSSION Various LTE-Advanced channel bandwidths of 5, 10 and

20 MHz have been utilized for the interference from LTE-Advanced BS into 8 MHz digital TV receiver. Usually, the strongest interference signal is completely mysterious from

which side it arrives. This consideration is significant since it indicates that the antenna discrimination in the direction of the great circle path, which contains the overriding interference path between interferer and victim, can not necessarily be relied upon.

In Figs. 3-5, the effect of antenna discrimination loss on the distance required for compatibility between the two systems is applied for the different intersystem interference mechanisms that shown in Fig. 1.

Fig. 3. Additional isolation due to antenna discrimination for interference

between 5 MHz LTE-Advanced and TV digital receiver

Fig. 4. Additional isolation due to antenna discrimination for interference

between 10 MHz LTE-Advanced and TV digital receiver

For non overlapping scenario with no protection band, the frequency offset should be no less than 14, 9 and 6.5 MHz for LTE-Advanced system bandwidth of 20, 10 and 5 MHz, respectively. This means that the two systems can be in a partial overlapping scenario for frequency shift less of 6.5, 9 and 14 MHz for the corresponding LTE-Advanced channel bandwidth provided keeping the required additional isolation loss at each possible frequency shift. For example, in case 5 MHz LTE-Advanced with coverage area of 5 km, the required additional isolation is 30.9 dB for overlapping by 4 MHz, whereas, an isolation loss of 56.4 dB is required for partial overlapping of 2.5 MHz for same case.

For compatibility between the two systems by full overlapping scenario in case 5 MHz LTE-Advanced with

coverage area of 6 km, the required additional isolation must be not less than 62.9 dB. Moreover, LTE-Advanced system can also coexist with TV receiver by adjacent channel with a certain protection band. The smallest isolation should be greater than 12.9 dB for a protection band is equal to or greater than 3.5 MHz (frequency offset of ≥ 10 MHz).

Fig. 5. Additional isolation due to antenna discrimination for interference

between 20 MHz LTE-Advanced and TV digital receiver

From Figs. 3-5, it can be concluded that frequency efficiency in terms of frequency offset and the separation distance between LTE-Advanced BS and the TV receiver as a victim is significantly affected by the propagation path loss. That is, the farthest TV device path from the LTE-Advanced BS interferer requires lesser isolation level for coexistence compared to the isolation required for the closet TV device to the interferer which must be maximum.

By comparing the results in Figs. 3-5, it can be observed that the additional isolation (in dB), which can be gained by antenna discrimination, is the highest in case 5 MHz LTE-Advanced channel bandwidth, while 20 MHz LTE-Advanced requires the lowest additional isolation. This is a consequence of the correction band factor effect, which provides an attenuation loss of 4 and 1 dB for LTE-Advanced channel bandwidth of 20 and 10 MHz, respectively. Whereas, in case a channel bandwidth of 5 MHz, this factor does not affect on compatibility scenario due to that channel bandwidth of the victim receiver is wider than that of the interferer.

Furthermore, comparing Figs. 3-5, it can be observed the relation between isolation losses required for coexistence, represented by antenna discrimination loss, and the physical path between LTE-Advanced and TV receiver device. In General, keeping a fixed separation distance between the victim receiver and interferer, extra isolation is progressively reduced as the victim receiver goes further away from the interferer. E.g., for interference from 20 MHz LTE-Advanced into TV digital receiver case, it is easy to observe that at edge physical separation distances of 1, 2, 3, 4, 5 and 6 km the required additional losses at frequency offset of 20 MHz are 37.5, 31.5, 27.9, 25.5, 23.5, and 22 dB, correspondingly.

This means that a difference in the required loss of 6 dB between a TV receiver placed at a distance of 1 km and 2 km

must be managed. However, the difference in the required loss between a TV receiver placed at distance of 2 and 3 km is 3.6 dB. By comparing the difference in the isolation loss needed for coexistence purpose which must be employed for 5, 10 and 20 MHz LTE-Advanced, it is found that the difference in required loss results can be applied for every adjacent frequency offset plus every LTE-Advanced channel bandwidth. This leads us to realize that as separation distance between LTE-Advanced BS and TV receiver increases, the difference in additional loss becomes at its minimum levels. The need for a combination of interference mitigation strategies becomes more necessary for the two systems compatibility within very short distances.

V. CONCLUSION Compatibility investigation between LTE-Advanced and

digital TV receiver is presented using an efficient graphical method. The results show that coexistence between TV receiver and LTE-Advanced by full overlapping scenario may be not visible due to large isolation loss needed. This leads to the necessity for use some interference mitigation strategies such as antenna discrimination. Additionally, the results showed importance of propagation path factor which has a significant influence on coexistence condition, which means that a considerable interest should be paid for terrestrial area category and cellular design.

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