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TX networkadapter Distribution network

SFNadapter

MPEG2re-

multiplexer

MPEG2TS analysis

MPEG2 TS

analysis

MIPinsertion

GPS

10 MHz 1 pps

RX networkadapter

RX networkadapter

DVB-Tmodulator

Syncsystem

GPS

10 MHz 1 pps

MIPevaluation

DVB-Tmodulator

Syncsystem

GPS

10 MHz 1 pps

MIPevaluation

MPEG2

TS analysis

Following its successful implementation in satellite and cable systems, digitaltransmission of TV signals is now also making its entry into terrestrial networks.Besides efficient data compression and flexible multiplexing in line with MPEG2

standards, single-frequency networks (SFNs) allow the best possible utilization ofscarce terrestrial frequencies. Such networks are controlled by MIPs (megaframeinitialization packets, see box). Prerequisites for the working of an SFN are correctMIP generation and transmission plus continuous monitoring to avoid malfunctionsor network failures.

MIP monitoring: an innovativeadd-on

Both Rohde & Schwarz instrumentsMPEG2 Realtime Monitor DVRM [1]and MPEG2 Measurement Decoder

DVMD [2] can monitor MIPs in real-time an innovative extra to the manymeasurement parameters already sup-ported. Each incoming MIP is subjectedto twelve individual tests for transmis-sion time, structure and content as rec-ommended by the DVB MeasurementGroup.

Every error detected immediately pro-duces an alarm signal that is displayedby LEDs on the front panel of the

instruments and signalled on one oftwelve selectable alarm lines. Plus, theerror is registered in error statistics andincluded in a measurement report withdetails of its cause.

Here comes Stream Explorerwith new functions

Stream Explorer [3, 4] for DVMD/DVRM is an innovative computer soft-ware option. The extended control and

display functions including a table inter-preter are supplemented by a newoperating mode specially for MIP moni-toring. Stream Explorer reproducesthe complete and interpreted content ofthe incoming MIP in realtime and thusallows in-depth insight into the opera-tion routines irrespective of compliancewith error criteria.

This means that DVRM, DVMD andStream Explorer guarantee opera-

tional reliability also in new terrestrialSFNs. The first nationwide SFN in Spainis proof of this reliability, where all high-power transmitters are monitored by aDVMD (see Newsgrams p 44).

Michael Fischbacher

SFN and MIP

In single-frequency networks (FIG),neighbouring transmitters with iden-tical program content use exactlythe same channel. This is only fea-sible if all transmitters operate syn-chronized and simultaneously. Herethe global positioning system (GPS)serves as a time reference. The trans-port stream to be transmitted is pro-vided with additional informationallowing exact assignment of thetransmit signal to this time reference

in the TV transmitters and thus anappropriate time shift. The extrainformation is transmitted in mega-frame initialization packets (MIPs).Any error in the structure or con-tent of a MIP could cause failure ofthe complete transmitter network,making overall MIP monitoring indis-pensable.

MIP monitoring in single-frequency networks

Structure of single-frequency network

REFERENCES[1] Fischbacher, Michael: MPEG2 Realtime

Monitor DVRM Digital broadcastnetworks: operation secured. Newsfrom Rohde & Schwarz (1999) No. 165,pp 1415

[2] Fischbacher, Michael; Weigold, Harald:MPEG2 Generator DVG and MPEG2 Mea-surement Decoder DVMD Test equipmentfor digital TV in line with MPEG2. Newsfrom Rohde & Schwarz (1996) No. 152,pp 2023

[3] Fischbacher, Michael; Rohde, Werner:PC software for MPEG2 dream teamDVG/DVMD. News from Rohde & Schwarz(1997) No. 154, p 29

[4] Finkenzeller, Richard; Fischbacher, Michael:MPEG2 transport stream analysis in net-worked DVB monitoring system usingStream Explorer software. News fromRohde & Schwarz (1998) No. 159,pp 2425

Reader service card 168/10

News from Rohde& Schwarz Number 168 (2000/III) 35

Application notes