Planning Of Single Frequency Networks

Transcript

TITU/EBU workshop on Digital Broadcasting TSofia 8-10 June 2004 Planning of Single Frequency Networks J. Doeven Subjects Single Frequency Network “A network of synchronised transmitting stations radiating identical signals in the same RF channel” • General aspects • Network gain • Internal network interference • Practical cases • References TITU/EBU workshop Sofia General aspects Pros and Cons of SFNs Pro Con • Spectrum efficient due to power distribution • Network gain due to simultaneous reception of multiple useful signals • No need to retune when travelling through area (mobile reception) • No option for local windows in programming • Reduced bitrate due to long guard interval • Relay transmitters more complicated • More complicated frequency planning • MFNs and SFNs are based in principle on the same network topology (main transmitters with auxiliary gap fillers if necessary) TITU/EBU workshop Sofia Example DVB-T 64QAM D/Tu Mbit/s 1/4 19.9 1/8 22.1 1/16 23.4 1/32 24.1 • SFNs can be used in small and large areas – Extent of area is limited by internal network interference • SFNs can be used with all reception modes – Most applications are in relation to indoor and mobile reception • SFNs can be used in a mixed configuration with MFNs, e.g. – Main transmitters in MFN and additional fill-in transmitters in SFN mode – Main transmitter supplemented by lower power transmitters in towns to improve indoor reception TITU/EBU workshop Sofia General aspects Application of SFNs • Network gain consists of two components – Statistical gain due to higher change to receive a signal. Location variation of the field strength is the dominating factor – Additive gain due to the increase in field strength because of the incidence of two or more signal at the receiving antenna • Network gain varies: – From point to point depending on the relative field strength values – Location variation for which the coverage is calculated TITU/EBU workshop Sofia Network gain Network gain 3 equal signals 80 total statistical additive single 75 field strength / dB(uV/m) 70 65 60 55 50 45 40 0.01 0.1 1 5 10 20 30 40 50 60 70 80 90 95 cumulative distribution function / % TITU/EBU workshop Sofia 99 99.9 99.99 Network gain Example 1 100 Field strength (dBuV/m) 90 80 70 37.5 m 37.5 m network statistical 60 50 40 30 0 5 10 15 20 25 Distance (km) TITU/EBU workshop Sofia 30 35 40 Network gain Example 2 Network gain as function of distance between two equal transmitters 1 transmitter T10 kW Splitting of one transmitter into two with same total power to improve coverage 2 transmitters T5 kW TITU/EBU workshop Sofia Practical case 1 Amsterdam coverage 246 µsec • Length of guard interval • Delay between signals – Transmitter separation distance – Artificial delays – Delays in distribution links • Nuissance field of interfering signal – Propagation path – ERP – C/N (system variant) TITU/EBU workshop Sofia Example DVB-T 8k D/Tu µsec km 1/4 224 67 1/8 112 34 1/16 56 17 1/32 28 8 Internal network interference Aspects regarding internal network Example interference (1) T-DAB • In most cases in frequency planning the following measures are possible: – – – – – Increase guard interval (one of the 4 options) Adding artificial delay at one of tx Reducing power Add fill-in transmitter Remove tx from SFN (that is: use different frequency) • Some times it is possible: – Chose alternative site (with delay inside guard interval) – Use obstructions in propagation path TITU/EBU workshop Sofia In general internal network interference is not a major problem with DAB Internal network interference Solving internal network interference T1% time Internal network interference Internal network interference TITU/EBU workshop Sofia Practical case 2 SFN CH 34 Additional fillin station T1% time Artificial delay 5 µsec Other SFN Artificial delay 15 µsec TITU/EBU workshop Sofia Practical case 2 SFN CH 34 TITU/EBU workshop Sofia Practical case 2 SFN CH 34 TUseful signals: 50% time TAll interferers: 1% time References • EBU report BPN 003. Technical bases for T-DAB services network planning and compatibility with existing broadcasting services - third issue. February 2003 • EBU report BPN 005. Terrestrial digital television planning and implementation considerations - edition 3. August 2003 • EBU report BPN 018. ERC/EBU report on planning and introduction of terrestrial digital television (DVB-T) in Europe. February 1999 • EBU report BPN 059. Impact on coverage of inter-symbol interference and FFT window positioning in OFDM receivers. August 2003 TITU/EBU workshop Sofia