Technology ATSC-M/H

1 technology

1.1 protocol stack
1.2 transport stream data structure
1.3 error protection
1.4 signaling
1.5 signaling of video- , audio coding
1.6 single-frequency network (sfn)

technology

atsc-m/h bandwidth consumes fixed chunks of 917kbit/s out of total atsc bandwidth. each such chunk called m/h group. data pipe called parade collection of 1 8 m/h groups. parade conveys 1 or 2 ensembles logical pipes of ip datagrams. datagrams in turn carry tv services, system signaling tables, oma drm key streams , electronic service guide. atsc-m/h has improved design based on detailed analyses of experiences other mobile dtv standards.

atsc-m/h layer model


protocol stack

atsc-m/h protocol stack umbrella protocol uses oma esg, oma drm, mpeg-4 in addition many ietf rfcs.

transport stream data structure

the atsc-m/h standard defines fixed transport stream structure, based on m/h frames, establishes location of m/h content within vsb frames , allows easier processing m/h receiver. contrary legacy atsc transport stream, defined in a/53, in there no fixed structure establish phase of data relative vsb frames.

one m/h frame equivalent in size 20 vsb frames , has offset of 37 transport stream (ts) packets relative beginning of vsb frame. each m/h frame, has fixed duration of 968 ms, divided 5 m/h sub-frames , each sub-frame further subdivided sixteen m/h slots. each slot equivalent amount of time needed transmit 156 ts packets. slot may either carry main atsc data (a/53) or 118 packets of m/h data , 38 packets of main data. collection of 118 m/h packets transmitted within slot called m/h group. each of 118 m/h packets within m/h group encapsulated inside special ts packet, known mhe packet.

an m/h parade collection of m/h groups , can carry 1 or 2 m/h ensembles. these ensembles logical pipes ip datagrams. datagrams in turn carry tv services , signaling of mobile content. m/h groups single parade placed within m/h slots according algorithm defined in a/153 part 2. number of groups per m/h sub-frame (nog) m/h parade ranges 1 8 , therefore number of groups per m/h frame parade ranges 5 40 step of 5. data of parade channel coded , distributed interleaver during m/h frame.

mobile data protected additional fec, interleaving , convolutional codes. improve reception in receiver, training sequences introduced atsc-m/h signal allow channel estimation on receiver side.

time slicing technique used atsc-m/h provide power savings on receivers. based on time-multiplexed transmission of different services.

error protection

atsc-m/h combines multiple error protection mechanisms added robustness. 1 outer reed–solomon error correction code corrects defective bytes after decoding outer convolutional code in receiver. correction improved additional crc checksum since bytes can marked defective before decoded (erasure decoding).

the number of rs parity symbols can represent 24, 36 or 48. symbols , additional checksum form outer elements of data matrix allocated payload of m/h ensemble. number of lines fixed , number of columns variable according how many slots per subframe occupied.

the rs frame partitioned several segments of different sizes , assigned specified regions. m/h data in these regions protected sccc (series concatenated convolutional code), incorporating code rate of 1/2 or 1/4, , specific each region in group. 1/4 rate pccc (parallel concatenated convolutional code) employed inner code m/h signaling channel, includes fic (fast information channel) , tpc (transmission parameter channel). tpc carries various fec modes , m/h frame information. once tpc extracted, receiver knows code rates being employed , can decode each region @ specified rate.

a modified trellis encoder employed backwards compatibility legacy a/53 receivers.

the time interleaving of atsc-m/h 1 second.

signaling

atsc m/h signaling , announcement defines 3 different layers of signalling. layers organized hierarchically , optimized characteristics of transmission layer.

transmission signaling system lowest layer , uses transmission parameter channel (tpc). provides information receiver needed decode signal
transport signaling system second layer, uses fast information channel (fic) in combination service signaling channel (ssc). main purpose of fic deliver essential information allow rapid service acquisition receiver. service signaling channel (ssc), consists of several different signaling tables. information carried within these tables can compared psip information of atsc. ssc provides basic information, logical structure of transmitted services , decoding parameters video , audio.
announcement / electronic service guide (esg) highest layer of signaling. uses open mobile alliance (oma) broadcast service enabler suite (oma bcast) electronic service guide (esg). esg delivered file data session file delivery on unidirectional transport (flute), , used delivery protocol. esg consists of several xml sections. structure, program guide , enabled interactive services can realized.

signaling of video- , audio coding

each video- or audio decoder needs information used coding parameters, instance resolution, frame rate , idr (random access point) repetition rate. in mpeg-4/avc, mobile tv systems receiver uses information session description protocol file (sdp-file). sdp-file format describes streaming media initialization parameters. in atsc-m/h, sdp-file transmitted within smt-table. of information coded in binary, coded in original ascii text format. smt-table combines information typically in different tables , reduces complexity network , receivers. in case of signaling esg, complete sdp-file transmitted.

single-frequency network (sfn)

in sfn, 2 or more transmitters overlapping coverage send same program content simultaneously on same frequency. 8vsb modulation used atsc allows sfn transmissions. allow regular channel approximation, atsc-m/h provides additional training sequences. atsc a/110 defines method synchronize atsc modulator part of transmitter. a/110 standard sets trellis coder in pre-calculated way transmitters of sfn. in such sfn, atsc-m/h multiplexer , atsc-m/h transmitter synchronized gps reference. atsc-m/h multiplexer operates network adapter , inserts time stamps in mpeg transport stream. transmitter analyzes time stamp, delays transport stream before modulated , transmitted. eventually, sfn transmitters generate synchronized signal.