The Advanced Television Systems Committee (ATSC) published a Digital Television Standard in 1995 as Document A/53, hereinafter referred to simply as “A/53” for sake of brevity. Annex D of A/53 titled “RF/Transmission Systems Characteristics” is of particular relevance to this specification, defining many of the terms employed herein. In the beginning years of the twenty-first century, efforts were made to provide for more robust transmission of data over broadcast DTV channels without unduly disrupting the operation of so-called “legacy” DTV receivers already in the field. These efforts culminated in an ATSC standard directed to broadcasting data to mobile receivers being adopted on 15 Oct. 2009. This standard, referred to as “A/153” herein, is also relevant to this specification, defining many of the terms employed herein. The data for concatenated convolutional coding are commonly referred to as “M/H data” in reference to the mobile and handheld receivers that will receive such data.
Both A/53 and A/153 are directed to 8-VSB signals being used in DTV broadcasting. A radio-frequency (RF) 8-VSB signal is transmitted by vestigial-sideband amplitude modulation of a single carrier wave in accordance with an 8-level modulating signal that encodes 3-bit symbols descriptive of 2-bit symbols of the digital data to be transmitted. The three bits in the 3-bit symbols are referred to as Z-sub-2, Z-sub-1 and Z-sub-0 bits. The initial and final bits of each successive 2-bit symbol of the digital information are referred to as an X-sub-2 bit and as an X-sub-1 bit, respectively. The X-sub-2 bits are subjected to interference-filter pre-coding to generate the Z-sub-2 bits, which Z-sub-2 bits can be post-comb filtered in a DTV receiver to recover the X-sub-2 bits. The Z-sub-1 bits correspond to the X-sub-1 bits. The Z-sub-0 bits are redundant bits resulting from one-half-rate convolutional coding of successive X-sub-1 bits to provide two-thirds-rate trellis coding as prescribed by A/53.
A/53 prescribes (207, 187) Reed-Solomon forward-error-correction (RS FEC) coding of data followed by convolutional byte interleaving before two-thirds-rate trellis coding that employs one-half-rate convolutional coding of the less significant bits of successive two-bit symbols of data. It is a common practice in the digital coding arts to precede convolutional coding by RS FEC coding and byte interleaving of the RS FEC codewords. In a receiver the decoding of the convolutional coding is apt to contain burst errors caused by the decoding procedures stretching response to bit errors. De-interleaving the burst errors breaks protracted burst errors up into isolated byte errors that can often be corrected in reliance upon the RS FEC coding. Usual practice is to complete decoding of the convolutional coding before subsequent de-interleaving, to break up burst errors into isolated byte errors, and decoding of the RS FEC coding, to correct the isolated byte errors if there are not too many per RS FEC codeword.
A/153 prescribes serial concatenated convolutional coding (SCCC) of data transmitted to mobile receivers, which SCCC uses one-half-rate outer convolutional coding upon such data followed by symbol-interleaving and two-thirds-rate trellis coding similar to that prescribed by A/53. The one-half-rate convolutional coding incorporated within the two-thirds-rate trellis coding serves as one-half-rate inner convolutional coding in the SCCC. A/153 further prescribes additional forward-error-correction coding of the data transmitted to mobile receivers, which additional FEC coding comprises transverse Reed-Solomon (TRS) coding combined with lateral cyclic-redundancy-check (CRC) codes which an M/H can use to locate byte errors for the TRS coding. The principal design task for the transverse Reed-Solomon (TRS) coding used in the RS Frames prescribed by A/153 is overcoming drop-outs in received strength caused by reception nulls when the receiver is moved through an electromagnetic field subject to multipath signal propagation. The strongest TRS codes prescribed by A/153 can overcome momentary drop-outs in received signal strength that are as long as four tenths of a second. Furthermore, the shortened 255-byte Reed-Solomon (RS) codes used for TRS coding are very powerful codes for correcting shorter burst errors, especially when used together with codes for locating byte-errors.
A/153 prescribes that the M/H-service information be subjected to outer convolutional coding and symbol interleaving before encapsulation in 188-byte transport-stream (TS) packets called “MHE packets” that are subjected to non-systematic (207, 187) Reed-Solomon coding to generate selected segments of 8-VSB data fields. These segments of 8-VSB data fields are time-division multiplexed with other segments generated by systematic (207, 187) Reed-Solomon coding of 188-byte TS packets of main-service information. The bytes of the resulting 8-VSB data fields are convolutionally interleaved before being subjected to the 2/3 trellis coding that functions as inner convolutional coding of the SCCC used for transmissions to M/H receivers. All the segments of 8-VSB data fields have (207, 187) Reed-Solomon coding to insure that DTV receivers already in the field continue usefully to receive main-service information.
Some of those “legacy” DTV receivers place themselves in a “sleeping” mode if their decoders for (207, 187) R-S coding find a large enough portion of the segments of 8-VSB data fields to contain byte errors that cannot be corrected. The parity bytes of non-systematic (207, 187) Reed-Solomon coding of MHE packets was originally regarded to be a loss of digital payload that was unfortunately necessitated to accommodate these “legacy” DTV receivers. U.S. patent application Ser. No. 12/931,688 filed 8 Feb. 2011 by A. L. R. Limberg and titled “Utilization of non-systematic (207, 187) Reed-Solomon coding in mobile/handheld digital television receivers” describes the non-systematic (207, 187) Reed-Solomon coding being utilized during the turbo decoding of SCCC to recover M/H-service data.
U.S. patent application Ser. No. 12/928,186 filed 6 Dec. 2010 by A. L. R. Limberg and titled “Broadcasting of concatenated-convolutional-coded data by one or more digital television transmitters for diversity reception” advocates that the M/H-service signals be composed of X-sub-2, Z-sub-1 and Z-sub-2 bits. This, rather than being composed of Z-sub-2, Z-sub-1 and Z-sub-2 bits. The interference-filter pre-coding of the X-sub-2 bits to generate Z-sub-2 bits that A/53 and A/153 prescribe is selectively discontinued during the concatenated convolutional coding (CCC) used for transmission of M/H-service signals. This permits parallel concatenated convolutional coding (PCCC) of data transmitted to M/H receivers. This PCCC uses one-half-rate outer convolutional coding of M/H data followed by symbol-interleaving and two-thirds-rate trellis coding similar to that prescribed by A/53. The Z-sub-1 bits convey the M/H data in the PCCC. The X-sub-2 bits provide one of the two sets of parity bits for the PCCC, and the Z-sub-0 bits provide the other set of parity bits for the PCCC.
U.S. patent application Ser. No. 12/928,186 describes the X-sub-2 bits in the final 185 bytes of the MHE packets as not being subjected to interference-filter pre-coding. Just the X-sub-2 bits in the initial two bytes of the MHE packets are subjected to interference-filter pre-coding. This enables legacy DTV receivers to identify the MHE packets as being of a type those receivers are to disregard when assembling a transport stream (TS) of MPEG-2 data packets.
Utilization of the non-systematic (207, 187) RS coding during turbo decoding to recover M/H-service data from PCCC described in U.S. patent application Ser. No. 12/928,186 presents a different problem than its utilization to recover M/H-service data from SCCC, as prescribed by A/153. This is because the X-sub-2 bits in the MHE data packet are not subjected to interference-filter pre-coding to generate Z-sub-2 bits, when generating PCCC as described in U.S. patent application Ser. No. 12/928,186. So, contrary to what is described in U.S. patent application Ser. No. 12/931,688, the M/H receivers described in U.S. patent application Ser. No. 12/928,186 do not employ post-comb filtering of the baseband 8-VSB signal supplied for turbo decoding. Accordingly, M/H Group data temporarily stored in memory to support decoding of the inner convolutional coding of CCC, cannot be scanned with suitable addressing to supply useful input signal to a decoder for non-systematic (207, 187) RS coding. The problem is not with generating suitable addressing to supply byte de-interleaved bytes of input signal to the decoder for non-systematic (207, 187) RS coding. The problem is that signal read from the memory has not been post-comb filtered, as it would be post-comb filtered in a legacy DTV receiver. The signal will not comprise a series of non-systematic (207, 187) RS codewords susceptible of being decoded by the decoder for non-systematic (207, 187) RS coding.
Supposing that the decoder for non-systematic (207, 187) RS coding were supplied a series of non-systematic (207, 187) RS codewords susceptible of being decoded, a further problem is presented that does not arise when non-systematic (207, 187) RS coding is utilized during turbo decoding to recover M/H-service data from PCCC. This further problem concerns how to over-write the memory, supposing that the decoder for non-systematic (207, 187) RS coding is able to correct one or more erroneous bytes in a non-systematic (207, 187) RS codeword. This problem arises because the non-systematic (207, 187) RS codewords are recoverable from post-comb filtered baseband 8-VSB signal after its being de-interleaved in the receiver to complement the convolutional byte interleaving performed at the transmitter. However, the memory to support turbo decoding to recover M/H-service data from PCCC temporarily stores symbols of baseband 8-VSB signal that have not been post-comb filtered in the receiver, not needing to have been since there was no interference-filter pre-coding of the MHE packets at the transmitter.