Analysis and study of compatibility between digital broadcasting and the mobile communication LTE

Muratbek Dzhamanshalov Kazakh National University (KazNTU)Almaty, Kazakhstan muratbek_1981@mail.ru

Abstract-Co-existence between mobile and digital broadcast television, generally focus on one system that has to be protected, providing the operational constraints for the other system, which is considered as interferer. In article, an analysis of the coexistence of primary services is presented, focusing on the study of mutual interference between DVB T2 broadcasting and 3GPP Long Term Evolution (LTE) mobile systems.

Index Terms-Mobile communications, digital TV, LTE, DVB-T2.

I.INTRODUCTION.

       In today’s world mobility is highly valued. That is why the last 15years were characterized by rapid development of mobile technologies. There is an avalanche  increase in the number of mobile users. There are third network, and now the 4th generation is able to provide a huge variety of services to users. Approved standards for CDMA, UMTS, LTE, in the terminology of the International Telecommunication Union (ITU) has been generally termed IMT.

       Especially important is the evaluation of EMC PC and PS in this band, the more appear in both services and develop new standards, such as digital TV standards DVB-T and DVB-T2, standards of IMT WCDMA and LTE. We propose a versatile methodology to take into account both the interference originated from the mobile radio systems to the broadcast system and the interference generated from the TV transmitters to the cellular system from a performance degradation point of view. The LTE network works in Kazakhstan in the range of frequencies of 1800 MHz.

       We present the simulated scenario; describe the assumptions made on the two interfering systems, and on the propagation model. The proposed methodology is based on the evaluation of the cumulative distribution of the Signal-to-Interference plus Noise-Ratio (SINR) and of the consequent degradation of DVB T and LTE system performance due to the mutual interference. The analyzed scenario comprises a mobile radio system and a DVB T transmitter. Two different aspects have been considered (Fig.2):

-         case study 1: interference generated by a certain number of base stations (BSs) versus DVB T receivers;

-         case study 2: one DVB T transmitter (of height hTx) which acts as extermal interferer versus several LTE Base Stations (BSs)

It is worth noting that in case study 2 we decided  to take into account the uplink because it is the most critical link. This may not seem obvious, but it is due to the fact that cellular base stations are considerably higher than mobile terminals, hence they can receive a larger amount of interference from the DVB-T transmitter .The downlink analysis is left for further studies.

Also the interference caused by mobile terminals over the DVB T receivers will be addressed in future works, owing to the low height and transmitted power of the mobile terminals.

II. EMC ASSESSMENT

       EMC assessment when sharing RES RS and IMT systems in the band 790-862 MHz may performed in two ways-a deterministic assessment and statistical of EMC.

Based on deterministic estimates EMC develop relevant standards frequency-spatial spacing (CHTR) RES. For example, the development of such standards CHTR include[3].It is known that traditionally focused on the definition of the mutual influence of the two RECs with fixed parameters and can not always take into account the complex dynamics of change the RES in the real world.

In accordance with [7] field strength Edef, permissible interfering television signal for general mobile service calculated the formula:

        Edef=-37+F-Gi+LF+10log (Bi)+Po+20 logf-KdB(mV/m), (1)

where: F:receiver noise or mobile base stations in the land mobile service (SPS) (dB)

Bi: the bandwidth of the terrestrial broadcasting station (MHz);

GI: receiving antenna feeder cable (dBi);

LF: losses in the antenna feeder cable (dB);

f: center frequency of the interfering station (MHz);

Po: man-made noise (dB) (typical value of 0 dB for UHF);

K:correction factor of overlap (in DVB-T) (dB).

Allowable field strength interference from IMT for RES stations broadcasting service is de-fined by the following formula:

Einter=Emin-PR-Kloc +Asel                     (2)

where:Emin-minimum median field strength for a given type of modulation and reception of the broadcasting service dBmkV/m;

PR- defensive attitude broadcasting system from interfering signals, IMT,dB;

Asel-spatial selectivity of the  receiving antenna RES broadcasting service, dB;

Kloc-combined ratio by location, taking into account the random distribution of the electro-magnetic field in the territory.

The calculations are performed for the case interference from IMT one interfering station and two of layouts receiving DVB-T antenna and interfering station IMT:

-Interference from a transmitting station IMT misses the main lobe of the receiving antenna DVB-T(ie, selectivity  of Asel=0 dB).

-Interference from a transmitting station IMT comes from  the direction opposite to the direction of the main lobe of the receiving antenna DVB-T (ie, selectivity  of Asel=16dB).

 

A statistical approach to the evaluation of EMC based on statistical distributions of the parameters specifying RES (coordinates, frequency, power, radiation,  etc.),calculating the statistical characteristics of EMI and statistical evaluation of the impact of EMCO on RES.  For statistical evaluation of EMC for the IMT becomes the most appropriate method of statistical modeling, called the Monte Carlo method. Monte Carlo method- is a numerical method for solving mathematical problems by simulating random numbers. It allows you to simulate any process, which influence on the course of random factors. A feature of this method is the simplicity of the structure of the computational algorithm. Applied to problems of EMC Monte Carlo method allows to simulate the real situation when setting change network settings as appropriate distribution of random numbers, which to some extent reflects the random behavior of these parameters. Simulations result is random and is expressed in terms of probability of  probability of interference.

III.SIMULATION SCENARIO

Cellular system parameters

       We assumed a channel bandwidth of 5 MHz for LTE, as for this bandwidth the whole BS transmitted power is in in band transfer function of the victim DVB T receiver. Therefore, in case study 1, as the power spectrum of a DVB T signal is approximately flat in its 8 MHz channel, the interference generated on the 5 MHz chanell can be assimilated to AWGN. The adopted cellular layout is shown in Fig.3.It comprises 99 base station, but the statistics are collected only in the innermost 42 of them (enclosed in the smaller square in the figure). To avoid border effects.

      We simulated the Link Adaptation behavior of LTE mobile system as a function of the SINR, which for the purpose of this work is assumed equivalent to Signal to-Noise-Ratio (SNR), owing to the assumption that the interferer behaves like an AWGN source.

DVB-T system parameters

Different DVB T transmitter configurations have been considered in the simulations by varying the Effective Radiated Power (ERP) and the antenna height. The cell radius varies with the configuration and it is determined according to the Reference Planning   Configurations (RPCs) defined in ITU-R (2006), assuming:

-Location Probability (LP):95%

-Emed:58.2 dB V/m(ITU-R,2006, Annex 3.4)

Note that in order to obtain a 95% LP at the cell edge, 9.05 dB must be added to the receiver minimum required SNR.

In each simulation run the TV receiver positions have been randomly generated within  the DVB-T coverage area.

IV.SIMULATION RESULTS

Mobile interferer victim DVB-T

Different configurations of DVB-T transmitter height and ERP have been considered and the effect of the co-channel interference has been evaluated varying the distance between the broadcasting and mobile service areas. Fig.4 shows the Cumulative Distribution Functions (CDF) of the SNR and the SINR of the received DVB-T signal obtained with hTx=100 m and ERP=50 dBm and for various distances between the edge of the DVB-T coverage area edge and the centre of area served by the LTE network. We clearly notice the effect of the distance, with a serious interference when the distance is 30 Km. Increasing the distance causes a reduction of interference, and as expected the CDFs quickly approach the  nointerference case for higher distances.

From the CDFs.we are able to compute the performance degradation in the DVB-T broadcasting service. For instance, since the required minimum SNR for the TV receiver is 21 dB, as stated in Table III. The degradation of SNR due to the neighbouring mobile interfering system causes the reduction of the service coverage area.

TABLE III.Main Simulation parameters

Television tower

 

ERP

50 dBm or 70 dBm

Antenna height

100 m or 200 m

Antenna pattern

Omnidirectional in azimuth

Operating frequency

800 MHz

Receiver

 

Antenna gain

14.15 dBi

Antenna height

10m

Antenna pattern

Mask taken from International Telecommunication Union-Radio communication sector [ITU-R] (1992)

Receiver minimum

SNR 21 dB

Noise equivalent bandwidth

8MHz

Number of TV receivers generated for each Monte Carlo simulation

200

 

 

                                                                            

DVB-T interferer vs victim mobile network

The effect of the interferer is evaluated in terms of the percentage of mobile users that are able to access a certain modulation type, which is, of course, a function of the received SINR. The interference originated from the DVB-T transmitter has been estimated using ITU-R P.1546, considering the interference  originated both at 50% and 1% of time. The DVB-T interference contribution has been added to the internal interference contribution of the LTE system considering a cluster size equal to 3.The results are shown in Fig.5 and Fig.6. Obviously worst cases are obtained for higher-T transmitter ERP and antenna heights, as this causes the increase of the interferer signal strength and the reduction of the guard distance, and for a percentage of time equal to 1%, as this corresponds to lower attenuation values in the ITU-R P.1546 propagation model. As a matter of facts, the performance degradation is evident for higher interference from the DVB T transmitter (i.e.ERP=70 dBm), while with ERP=50 dBm the impact of the DVB T system is lower. In particular, with hTx=100 m the performance degradation is negligible. This is due to the low interference generated on the BSs antennas with ERP=50 dBm, as in this case this value is negligible with respect to the internal interference of the mobile system (this is especially evident with the attenuation values at 50% of time).

      The proposed methodology takes into account both the interference originated from the mobile  radio network on the broadcasting system and the interference generated from the TV transmitted on the cellular system. The aim is to assess the reciprocal interference in order to compare the different behaviors of the two radio links, thus identifying  the most critical situations. The document proposes a versatile methodology, which can be easily adapted to different configurations, for protecting either DVB-T or mobile service. 

Another item of future investigation deals with adjacent channel interference between mobile radio and digital television operating in adjacent frequency bands.

REFERENCES

[1] The Radio Regulations.Geneva, ITU,2008

[2] Detailed results of field study of compatibility between DVB-T and UMTS.European Broadcasting Union/ Free TV Australia Ltd

[3] Faizullaev A.N.Development of norms frequency-spatial separation of radio equipment operating in the frequency range of 450MHz.Magazin “Infocommunications; Networking-Technology-Solutions”

[4] Assessing the conditions of EMC accounting system features a radio interface UMTS. Skrynnikov VG/T-Comm, ¹2,2008

[5] Measurements on the performance of DVB-T Receivers in the presentce of interference from the mobile service (especially from LTE)/Marseille,June2010/ECC Report 148.

[6] Chaiko Y.V   Dzhamanshalov M.U Evaluation of digital broadcasting and the mobile communication