DVB-T2/LTE Interference Challenges at UHF

Transcription

1 DIGITAG Workshop Istanbul November 2013 DVB-T2/LTE Interference Challenges at UHF Mats Ek

2 Content of presentation MHz LTE Downlink interference examples o LTE Base Station interference DVB-T/T2 2. The 700 MHz Uplink interference example o LTE Terminals (UE) interference DVB-T/T2 3. What about MHz sharing? o DVB-T/T2 interference LTE uplink 4. Mobile services vs. DTT in 700 MHz band 2

3 MHz interference issues Interference Guard band 1 MHz Downlink Duplex gap Uplink x 5 MHz 11 MHz 6 x 5 MHz Broadcasting 790 MHz Mobile communications 862 MHz Main issue: LTE Downlink interfering into DVB-T/T2 Relatively easy to mitigate 3

4 MHz- Easy to calculate impact 800 MHz: LTE downlink problem: DVB-T2/T Receiver overload (Oth) Not fulfilled Protection ratios (PR) ITU-R BT.2033 established- defining protection criteria for T2 Measured overload thresholds (dbm) for a DVB-T2 signal (defined in Table 1) Interfered with by an LTE BS signal in adjacent channels for silicon tuners DTT LTE Channel Offset N (8 MHz channels) Cochannel AWGN Cochannel LTE Centre frequen cy offset (MHz) Numbe r of receive rs tested 0% BS traffic loading PR (db) 50% BS traffic loading PR (db) 100% BS traffic loading PR (db) Percentile Percentile Percentile 50 th 90 th 50 th 90 th 50 th 90 th Interference Situation can be evaluated before and after implementation 4

5 MHz - Interference calculations DVB-T near Edge of Coverage area Rooftop Reception LTE BS at 60 dbm LTE Site Direction to DVB-T Direction Transmitter to DVB-T Transmitter LTE antenna height 50 m First DL frequency Interference areas In red (maximum 1-3 km) 5

6 MHz - Interference calculations Direction To DVB-T2 Transmitter City of Norrköping, Sweden Rooftop reception DVB-T2 CH60 interfered with by LTE Base stations LTE EIRP is about 50 dbm (= 100W) Interference up to 1 km Protection Ratio (PR) not fulfilled! Planning parameters 6

7 MHz DTT receiver overload-example Direction To DVB-T2 Transmitter Rooftop reception City of Norrköping, Sweden Example DVB-T2 CH60 interfered with by LTE Base station Interference up to m DVB-T2 Receiver overload! 7

8 MHz mitigation Mitigation: o Use as orthogonal polarisation o Filters at DTT Receiver o VRP and antenna height of LTE base station o ERP of LTE base station BUT Portable DTT reception - often overlooked! 8

9 2. Proposals for LTE band MHz As discussed in CEPT PTD Interference DTT CH48 9

10 2. The 700 MHz uplink interference 700 MHz: Mainly LTE uplink interference DTT High Out of Band (OOB) suppression (ACLR) at LTE terminal (UE) to avoid loss of further broadcast spectrum (CH48, 690 MHz) Studies in ITU (JTG) and CEPT PTD (using MCL and Monte Carlo) Frequency offset: j channels N Rx N+j Tx P I ACLR ACS Transmitter mask ACLR: Adjacent channel leakage ratio, characterises the out of band emission of the interfering signal (base station or mobile terminal) Receiver filter P 1 P 2 ACS: Adjacent channel selectivity, characterises the selectivity of the victim receiver (DTT receiver) Frequency 10

11 MHz- uplink interference example DTT near edge of coverage area- Denmark DTT- CH MHz LTE base station with 30 meter antenna height, 3 sectors 2km 11

12 MHz- uplink interference example Existing LTE 800 MHz site at edge of DTT coverage in Denmark Suburban area One LTE sector Antenna height = 30 meters Radius =2 km 12

13 MHz- uplink interference example UE can be positioned almost anywhere inside LTE cell 2km DTT Antennas at Rooftop height on most of houses LTE terminals far away from BS will use higher power More likely to interfere with DTT 13

14 2. The 700 MHz - uplink interference issue Example based upon a OOB UE of -26 dbm /5MHz (according to 3GPP ) The OOB emission limits for LTE terminals (UE) important OOB requirement about -55 dbm/5mhz Interference radius up to 100 meters 14

15 3. Can DTT and MS share spectrum in MHz? Discussion ongoing to make mobile services co-primary with broadcast in MHz: o o o Different situation: MS LTE interfered by DTT? In particular LTE uplink is sensitive to interference interference Reduced coverage radius of LTE base Interference from DTT into LTE uplink Large interference distance > km LTE UE Antenna Height m DTT site LTE Base station 15

16 3. Co-channel sharing LTE vs DTT CH50 France 16

17 3. Co-Channel Sharing between DTT and LTE in MHz o Large frequency reuse km o Interference will reduce the coverage radius of the Mobile service! o However some mitigation is possible Orthogonal polarization to broadcast Vertical radiation pattern at MS (more difficult at lower frequencies!) 17

18 4 What happens if 700 MHz is allocated to Mobile services? Allocation of the 700 MHz band to Mobile service (LTE) would: o Reduce the available capacity (Mbit/s) for DTT at UHF ( MHz: total of 4-5 DTT multiplexes providing national coverage OR Total 5-7 muxes providing lower degree of coverage Additional cost for DTT infrastructure in order to maintain capacity Study in European Country A ( km2) 4 Muxes: Additional 50 sites needed to maintain coverage 5 Muxes: More than 100 new DTT sites (medium power) Renovation of DTT antennas replanning of frequencies Investment and operational cost 18

19 o o o o 4. DTT or LTE in 700 MHz? Are there alternatives to allocation of MS in 700 MHz band? How important is the 700 MHz band to reach the mobile broadband targets? 900 MHz 800 MHz 700 MHz? High speed mobile broadband in rural areas Cost saving Licensing fee Capacity enhancement using additional LTE sites Cost of LTE vs. cost of modifying Broadcast network Study in Denmark ongoing:? Maintain a living and profitable DTT platform Cost of LTE deployment vs. additional cost of Broadcast to provide enough DTT capacity Broadcast Mobile 19

20 MHz DTT vs LTE Key Question is: Will DTT survive the loss of the 700 MHz band? Can DTT develop in the future and provide also: o o o o HDTV and UHDTV, 3D TV? Mobile TV reception? More programs? 20

21 Thank you for listening! 21