International Conference on Computer and Communication Engineering (ICCCE 2010), 11-13 May 2010, Kuala Lumpur, Malaysia

978-1-4244-6235-3/10/$26.00 ©2010 IEEE

Sensitive and Non- Sensitive DVB-T Mask for Coordination with IMT-Advanced Systems

Zaid A. Shamsan, Tharek Abd Rahman, Muhammad R. Kamarudin Wireless Communication Centre, Faculty of Electrical Engineering

Universiti Teknologi Malaysia (UTM) Johor Bahru, Malaysia

shamsan22@gmail.com

Abstract— As a result of frequency spectrum scarcity and emerging various wireless applications, coexistence and sharing between wireless systems become a recently significant issue. At WRC-07, 790-862 MHz is allocated for IMT-Advanced systems on a co-primary basis in company with existing digital video broadcasting- terrestrial (DVB-T). Therefore, coexistence and sharing requirements must be achieved in terms of both co-channel and adjacent channel frequencies. Coexistence situation is analyzed by using sensitive and non-sensitive spectral emission mask (SEM) of DVB-T. Possible intersystem interference mitigation techniques are recommended.

Keywords- IMT-Advanced, DVB-T, intersystem interference, coexistence, SEM

I. INTRODUCTION The latest potential capabilities of these International

Mobile Telecommunications (IMT)-Advanced systems are envisioned to handle a wide range of supported carrier bandwidth. This range is around 20 MHz up to 100 MHz to be able to deliver targeted peak data rates of up to approximately 100 Mbps for high mobility such as mobile access and up to say 1 Gbps for low mobility such as nomadic/local wireless access [1]. 790-862 MHz band is one of the bands, which are allocated by ITU-R at World Radiocommunication Conference 2007 (WRC-07) for IMT-Advanced service in several countries in Asia with regulatory and technical constraints [2], meanwhile, this frequency band is currently used by broadcasting services in most of the world countries including Malaysia. This means that interference probability due to frequency sharing between these two systems is bound to happen if the two systems operate in adjacent areas with same carrier frequency (co-channel frequency) or in the same area with an adjacent carrier frequency. A few studies were done between terrestrial systems around the said band and some of them are under way. In our study the concept of SEM is presented such that the effect of T-DVB transmitter on IMT-Advanced will be addressed.

The reminder of this paper is organized as follows. In Sections II and III, coexistence scenarios and interference analysis methods, IMT-Advanced and DVB-T services parameters, spectral emission mask, protection criteria, propagation models, are explained in details. Section IV is devoted to the coexistence results, analysis and compatibility

between the services. Finally, the conclusion is presented in Section V.

II. COEXISTENCE METHODOLOGY In order to examine coexisting and sharing issues, it is

necessary to clarify the intersystem interference method assessment, permissible interference level criterion, propagation model, and parameters of both IMT-Advanced and DVB-T systems that will affect the interference level and criterion.

A. Method and Procedure The method consists in determining the INR or I/N ratio

and then comparing it with the necessary I/N at the victim receiver. Firstly, the interference level I (dBm) is computed at the victim receiver by assessing the level of emissions from the interferer falling within the victim receiver bandwidth for both co-channel frequency and adjacent frequency situations according to [3]:

(1) where, Pt: transmitted power of the interferer in dBm, Gt: gain of the interferer transmitter in dBi Gr gain of the victim receiver antenna in dBi Mask(∆f): attenuation of adjacent frequency due to mask where (∆f) is the difference between the carriers of interferer and the victim. Cor_Fac: correction factor of band ratio, where Cor_Fac= 0 dB if BWinterference < BWvictim or Cor_Fac=-10log(BWinterference/BWvictim), if not, where BWinterference and BWvictim represent channel bandwidth of interferer and victim receiver, respectively. LFs+Clutter: attenuation due to the wave propagation, it includes free space and clutter loss attenuation (model in ITU-R P.452 is used). Secondly, the thermal noise floor of victim receiver is determined according to the following formula: (2) where NF is the noise figure of receiver in dB and BWvictim represent victim receiver bandwidth in MHz. Finally, the

difference between I and N is compared to the coexistence and sharing criterion at the IMT-Advanced receiver.

B. Coexistence and Sharing Criterion The interference protection criteria are necessary for

coexistence fulfillment, it can be defined as an absolute interference power level I, interference-to-noise power ratio I/N, or carrier-to-interfering signal power ratio C/I [3]. ITU-R Recommendation F.758-2 details two generally accepted values for the interference–to–thermal-noise 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 limit that is independent of most characteristics of the victim receiver, apart from noise figure. IMT-Advanced 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 considered criterion for coexistence [4]. This can be justified as (3):

C. Propagation Model 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. WiMAX has a specific usage as it may be fixed or mobile and to operate in line or non-line of sight environment. The standard model agreed upon in CEPT and ITU for a terrestrial interference assessment at microwave frequencies is clearly marked in ITU-R P.452-12 [5]. This is model which is used for this coexistence study includes the attenuation due to clutter in different environments.

AhfdL ClutterFs AC log20log205.92 (4) where d is the distance between interferer and victim receiver in km, f is the carrier frequency in GHz, and Ah is loss due to protection from local clutter or called clutter loss, it is given by the expression:

33.0625.06tanh125.10 011 666 0ta1a

d

hheAh k (5)

where dk is the distance (km) from nominal clutter point to the antenna, h is the antenna height (m) above local ground level, and ha is the nominal clutter height (m) above local ground level. In [5], clutter losses could be evaluated for different categories: trees, rural, suburban, urban, and dense urban, etc.

D. System Parameters In order to study and examine coexisting and sharing

issues, it is necessary to clarify the parameters of both IMT-Advanced and broadcasting that will affect the interference level and criterion. These parameters are shown in Table 1.

TABLE I IMT-ADVANCED AND DVB-T SERVICES PARAMETERS

Parameter Value

IMT-Advanced

DVB-T Transmitter

Frequency of operation (MHz) 800 EIRB (dBm) ------ 72.15 Transmitted Power (dBm) 43 Base station antenna gain (dBi) 15 ------ Base station antenna height (m) 20 100 Interference limit power (dBm) -109 ------ Channel bandwidth (MHz) 5, 20 8 Spectral Emission Mask Not

Available DVB-T GE06

Permissible interference to noise ratio I/N (dB)

-6 ------

Noise Figure dB 4 7

E. Spectrum Emission Mask The spectral emission mask (SEM) is a set of rules that

apply to the spectral emissions of radio transmitters. Such rules are set forward by regulatory bodies such as FCC and ETSI. It is defined as the spectral power density mask, within ± 250% of the relevant channel separation, which is not exceeded under any combination of service types and any loading. The masks vary with the type of radio equipment, their frequency band of operation and the channel spacing for which they are to be authorized. DVB-T masks (sensitive and non-sensitive cases) according to [6] are depicted and tabulated, where spectrum masks for DVB-T is declared in Table 2 and Fig. 1 for a channel bandwidth of 8 MHz.

TABLE II CRITICAL AND NON CRITICAL SPECTRUM EMISSION MASK BREAK

POINTS OF DVB-T (GE06 FINAL ACTS, SECTION 3.6.2) [6]

Relative frequency (DVB-T)

DVB-T Sensitive

case

DVB-T Non-Sensitive case

(MHz) (dB) (dB)

-12 -87.2 -77.2 -9 -74.7 -64.7 -6 -62.2 -52.2 -5 -55.5 -45.5

-4.2 -50.2 -40.2 -4 -25.2 -20.1

-3.9 0 0 0 0 0

Malaysia Communication and Multimedia Commission (MCMC).

Figure 1. Critical and non-critical spectrum emission mask of 8MHz DVB-T

The spectral emission mask is considered in this study because it may be used to generate a “worst case” power spectral density for worst case interference analysis purposes. Where, the coexistence study can be applied by spectrum emission mask as an essential parameter for adjacent frequency sharing analysis to evaluate the attenuation of interference signal power in the band of the victim receiver. To carry out this study the spectral emissions masks in the Fig. 1 are applied for coming interference from DVB-T systems.

III. COEXISTENCE SCENARIOS In this study, three intersystem interference scenarios are

proposed. These are co-channel frequency interference, zero-guard band interference, and adjacent channel frequency interference scenarios. Both co-channel and zero-guard band cases require a physical separation distance, while both spectral frequency separation (guard band) and physical separation distance are required for adjacent channel coordination case. A clutter loss of 20 dB is assumed to be in the path of the interfering signal.

IV. RESULTS AND DISCUSSIONS

A. Sensitive 8 MHz DVB-T interference to IMT-Advanced BS In this case, sensitive spectrum mask for DVB-T shown in

Fig. 1 is applied for the interference coming from DVB-T on IMT-Advanced. Figs. 2-4 describe the permissible interference for co-channel frequency, zero-guard band, and adjacent channel frequency scenarios to ensure the coexistence feasibility. Co-channel interference scenario is represented by 0 MHz frequency separation between carriers. It seems that 22,300 km, 19,030 km, and 1,3460 km are the required separation distance for coexistence coordination which is considered not feasible in these ranges. While, using zero-guard band scenario, which corresponds to 6.5 MHz, 9 MHz, and 14 MHz frequency offset from the carrier frequency for 5 MHz, 10 MHz and 20 MHz IMT-Advanced channel bandwidth respectively, looks feasible if the separation distance is 13 km, 3.5 km, and 588 m for the above mentioned channel

bandwidths. The adjacent channel frequency intersystem interference scenario is studied at guard bands of 5.5 MHz, 3 MHz and -2 MHz (overlapping by 2 MHz) for 5 MHz, 10 MHz and 20 MHz IMT-Advanced channel bandwidth, in that order. The results indicate that minimum separation distances are required in this scenario due to the frequency offset between IMT-Advanced as a victim receiver and DVB-T as interferer transmitter. These distances are reduced to be 929 m, 831 m, and 588 m. Generally, these results inform that as channel bandwidth receiver goes wider as interference effect goes down. Therefore, when IMT-Advanced has a channel bandwidth of 20 MHz the needed distance for coexistence coordination decreases more than that of IMT-Advanced with channel bandwidth of 10 MHz and 5 MHz. This is true, because wider receiver channel bandwidth means high thermal noise receiver, which again means the interference effects can be stronger or the separation distance to be closer.

Figure 2. Interference from 8MHz DVB-T transmitter into 5MHz IMT-Advanced BS

Figure 3. Interference from 8MHz DVB-T transmitter into 10MHz IMT-Advanced BS

B. Non-Sensitive 8 MHz DVB-T interference to IMT-Advanced BS

Figs 5-7 show the interference from non-sensitive T-DVB Transmitter into 5MHz, 10 MHz, and 20MHz IMT-Advanced BS, respectively, as a victim receiver is applied, where the minimum separation distance and frequency separation for the minimum I/N ratio of -6 dB are analyzed in a clutter loss

-10 -5 0 5 10 12-12

-80

-70

-60

-50

-40

-30

-20

-10

0

10

Frequency offset from the center frequency (MHz)

Att

enua

tion

(dB

)

Non-Critical cases

Critical cases

0 2 4 8 10 12 14 16 18 206.5-100

-80

-60

-40

-20

0

20

40

60

80

100

-6

Frequency seperation between carriers (MHz)

Inte

rfere

nce t

o no

ise ra

tio (d

B)0.929 km (Adj. Ch. scenario)

13 km (Zero-GB scenario)

22300 km (Co-Ch. scenario)

0 2 4 6 8 10 12 14 16 18 209-100

-80

-60

-40

-20

0

20

40

60

80

100

-6

Frequency seperation between carriers (MHz)

Inte

rfere

nce t

o no

ise ra

tio (d

B)

0.831 km (Adj. Ch. scenario)

3.5 km (Zero-GB scenario)

19030 km (Co-Ch. scenario)

Figure 4. Interference from 8MHz DVB-T transmitter into 20MHz IMT-Advanced BS

situation of 20 dB. For adjacent channel coexistence it can be observed that the minimum separation distance between the two services must be greater than 2.937 km, 2.627 km, and 1.858 km for bandwidth of 5MHz, 10 MHz, and 20 MHz, respectively, with frequency separation of 12 MHz from the carrier frequency.

For deploying the two systems with a null guard band, the separation distances must be greater than 41.1 km, and 11.1 km for IMT-Advanced bandwidth of 5MHz, and 10 MHz. The two systems can be overlapped with coexisting operation if the distance is more than 1.858 km at 20MHz channel bandwidth of IMT-Advanced. Zero (null) guard band is represented by a vertical line in the graphs.

Sharing the same channel (co-channel) is not feasible between the two systems under assumed scenario because huge and impractical separation distances are of the order of 21,300km, 19,030km, 13,400 km for 5MHz, 10 MHz, and 20MHz IMT-Advanced channel bandwidth, respectively, are required. The entire requirements are summarized in Table 2.

In general, sensitive spectrum mask for DVB-T is more stringent than the non-sensitive mask as shown in Fig. 1, so it provides more protection to the service using an adjacent channel and thus less required separation distances and less frequency offset from the carrier of the victim carrier frequency.

Co-existence of IMT with T-DVB reception will require the application of the same available mitigation techniques and careful network planning. Possible ways to mitigate the intersystem interference, which may include limiting the maximum transmit power of the IMT terminal, Frequency polarization, antenna discrimination, site engineering, as well as improving the characteristics of future T-DVB receiver including T-DVB rejection performance at the adjacent channels.

It should also be observed that the results are more favourable for compatibility by using 20 MHz channel bandwidth for IMT-Advanced which means higher data rates. Since the higher BW means higher noise bandwidth in receiver, this again means higher noise floor level. This allows

the interfering signal to be stronger (in dBm) or the distance to be closer.

Figure 5. Interference from non-sensitive 8 MHz DVB-T transmitter into 5 MHz IMT-Advanced BS

Figure 6. Interference from non-sensitive 8MHz DVB-T transmitter into 10MHz IMT-Advanced BS

Figure 7. Interference from non-sensitive 8 MHz DVB-T transmitter into 20MHz WiMAX BS

0 2 4 6 8 10 12 14 16 18 2020-100

-80

-60

-40

-20

0

20

40

60

80

100

-6

Frequency seperation between carriers (MHz)

Inte

rfere

nce t

o no

ise ra

tio (d

B)

0.588 km (Overlapping by 2 MHz)

13460 km (Co-Ch. scenario)

0 2 4 86.5 10 12 14 16 18 20-100

-80

-60

-40

-20

0

20

40

60

80

100

-6

Frequency seperation between carriers (MHz)

Inte

rfere

nce t

o no

ise ra

tio (d

B)

2.937 km (Adj. Ch. scenario)

41.1 km (Zero-GB scenario)

21300 km (Co-Ch. scenario)

0 2 4 6 8 10 12 14 16 18 209-100

-80

-60

-40

-20

0

20

40

60

80

100

-6

Frequency seperation between carriers (MHz)

Inte

rfere

nce

to n

oise

ratio

(dB)

2.627 km (Adj. Ch. scenario)

11.1 km (Zero-GB scenario)

19030 km (CoCh. scenario)

0 5 10 15 20-100

-80

-60

-40

-20

0

20

40

60

80

100

-6

Frequency seperation between carriers (MHz)

Inte

rfere

nce

to n

oise

ratio

(dB)

1.858 km (Overlapping by 2 MHz)

13400 km (Co-Ch. scenario)

V. CONCLUSION In this paper, a coexistence study on the interference

coming from DVB-T to IMT-Advanced BS is investigated by using sensitive and non-sensitive spectral emission mask. Co- channel, zero-guard band, and adjacent interference scenarios are taken into account. The results showed that it is difficult to share the same frequency channel between IMT-Advanced and T-DVB services without mitigation techniques due to required high separation distance (which is considered impractical) to satisfy coexistence requirements. Methods for enabling the coexistence of both systems would be inevitable especially at small geographical offset between two systems and at co-channel, 1st and 2nd adjacent channels frequencies. For more coordination fulfillment, coexistence studies between mobile and DVB-T services at the frequency band 790-862 MHz are recommended especially when the victim receiver is the digital television.

ACKNOWLEDGMENT The authors would like to thank the Malaysia

Communication and Multimedia Commission (MCMC) for the financial support.

REFERENCES [1] ITU-R M.1645, Framework and Overall Objectives of the Future

Development of IMT 2000 and Systems Beyond IMT 2000, 2003. [2] Position Paper for WiMAX™ Technology in the 700 MHz Band,

WiMAX Forum, Mar 2008. [3] Z. A. Shamsan, A. M. Al-Hetar, and T. A. Rahman, “Spectrum sharing

studies of IMT-advanced and FWA services under different clutter loss and channel bandwidths effects,” Progress In Electromagnetics Research, vol. 87, pp. 331-344, 2008.

[4] Z. A. Shamsan, and T. A. Rahman, “Simulation model for compatibility of co-sited IMT-advanced and point to multipoint services,” Progress In Electromagnetics Research C, vol. 6, pp.127-144, 2009.

[5] ITU-R Recommendation P.452-12, “Prediction procedure for the evaluation of microwave interference between stations on the surface of the earth at frequencies above about 0.7 GHz,” 2005.

[6] Technical Options for the Use of a Harmonized Sub-Band in the Band 470 - 862 MHz for Fixed/Mobile Application (including Uplinks), CEPT Rep. 23, Jul 2008.