Low latency data encoder

Details Low latency data encoder Low latency data encoder

2000-08-15

2004-04-20

Decady, Albert (Department: 2133)

Error detection/correction and fault detection/recovery

Pulse or data error handling

Digital data error correction

Reexamination Certificate

active

06725412

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to audio signal processing. In particular, the invention relates to the reduction of latency (i.e., time delay) in the digital encoding of audio information.
BACKGROUND OF THE INVENTION
Various methods of data transmission and storage require mechanisms to detect (or detect and conceal) errors. In order to do so, data is often partitioned into portions, packets, or segments such that for a given segment, appropriate error detection or concealment information is generated. This information, typically a codeword or parity word, may be associated with the segment in a known position by an encoding or transmission process. A decoding or receiving system uses the codeword and its associated segment at least to detect the presence of errors, and, possibly to conceal errors. In the prior art, generation of the codeword requires prior knowledge of the entire segment. Consequently, the latency, that is, the time delay, between the receipt of information included in the segment and the segment's transmission by an encoder or transmitter is a function of the position of the codeword in the transmitted segment. As explained below, latency resulting from codeword positioning in a data format is least when the codeword follows the other data; it is greatest when the codeword precedes the other data.
FIGS. 1-3
illustrate latency with respect to three examples of codeword positions. For simplicity of explanation of the effect of codeword position on latency in these and other figures throughout this document, the data applied to an encoder or transmitter along with any auxiliary data (including null or “stuffing” bits, if any) applied to or generated within the encoder or transmitter is shown already formatted into a block, frame or packet (in
FIGS. 1-5
, it is referred to as a “message segment”). It will be understood that such a block, frame, packet or message segment is, in practice, built incrementally as incoming information is received and that doing so involves other latency considerations that form no part of the present invention.
In
FIG. 1B
, a received message segment
2
is shown.
FIG. 1A
shows the transmitted data format in which the message segment
2
is followed by a codeword
6
. Ignoring all latency considerations other than those arising from the codeword location, the minimum latency between the onset of reception of the information that becomes message segment
2
and the earliest time at which transmission may begin is at least the sum of: (1) the time required to calculate the codeword, (2) the time required to insert the codeword into its location in the data format (which usually is very short), and (3) the time to transmit the codeword (times 1 and 2 are represented by an arrow
4
in FIG.
1
A). It is possible to begin transmission well prior to generating the codeword. This codeword position is optimum from a codeword-position-caused latency standpoint because the onset of transmission does not require knowledge of the entire message. As explained further below, the present invention cannot improve latency when a codeword follows a message segment, such as in this example. Indeed, it will be seen that the invention strives to achieve the effect of such an optimum codeword position in systems in which the codeword position is not optimum (but which must remain in such a position because of compatibility or other requirements).
In order to provide a sense of the relative latencies in
FIG. 1
(and in the following
FIGS. 2-5
) between the received information and the transmitted information, latency is indicated as the time lapse between the schematic rendition of the formatted received information (FIG.
1
A and
FIGS. 2A
,
3
A,
4
A,
5
A,
6
A, and
7
B) and the schematic rendition of the transmitted information (
FIG. 1B
, and
FIGS. 2B
,
3
B,
4
B, SB,
6
B, and
7
C, respectively).
FIGS. 2 and 3
show codeword positions for which the codeword-position-caused latency can be reduced by the present invention.
In
FIG. 2A
, a format is shown in which a received message segment is divided into two received message segments
8
and
10
.
FIG. 2
is idealized, schematic and not to scale (likewise, other figures herein are idealized, schematic and not to scale). For transmission, as shown in
FIG. 2B
, at least one error detection or concealment codeword
14
appropriate to the message segments
8
and
10
is generated and inserted in a codeword location in between message segments
8
and
10
. Thus, relative to its optimum position after the message segment as shown in
FIG. 1
, the codeword position is toward the beginning of the message segment in the
FIG. 2
format. The codeword position
14
is intended to show any codeword position between the beginning and end of a message segment. Again, ignoring all latency considerations other than those arising from the codeword location, the minimum latency between the onset of reception of the information that becomes message segment
8
and the earliest time at which transmission may begin is the sum of: (1) the time to receive the information that becomes the second part
10
of the message segment (
FIGS. 2A and 2B
assume that this is the same as the time period of segment
10
in the assembled data format and in the transmission), (2) the time required to calculate the codeword, (3) the time required to insert the codeword into its location in the data and format (the arrow
12
in
FIG. 2
represents times 2 and 3), and (4) the time to transmit the codeword. It is possible to transmit the message portion that appears before the codeword before the codeword is generated, but the codeword or codewords in location
14
cannot be transmitted until the entire message segment is known, thus causing an additional latency at least as great as the time to receive the information that is transmitted as the second message segment
10
. Thus, although it is possible to begin transmission prior to generating the codeword, transmission cannot begin as early as in the optimum end-of-message codeword position of FIG.
1
.
In
FIG. 3A
, a received message segment
16
is shown. For transmission, as shown in
FIG. 3B
, an error detection or concealment codeword
20
appropriate to the message segment
16
is generated and inserted in a codeword location preceding the message segment. Once again, ignoring all latency considerations other than those arising from the codeword location, the minimum latency between the onset of reception of the information that becomes message segment
16
and the earliest time at which transmission may begin is the sum of: (1) the time to receive all the information that is transmitted as the message segment
16
(
FIGS. 3A and 3B
assume that this is the same as the time period of segment
16
in the assembled data format and in the transmission), (2) the time required to calculate the codeword, (3) the time required to insert the codeword into its location (an arrow
18
in
FIG. 3
represents times 2 and 3), and (4) the time required to transmit the codeword.
FIG. 3
illustrates the worst case codeword position from the standpoint of encoder latency.
Thus, in all of the three codeword locations illustrated in
FIGS. 1-3
, the latency is at least the sum of:
the time to calculate the codeword,
the time to insert the codeword into its location,
the time to transmit the codeword, and
the time to receive the information that is transmitted as the message segment (if any) or portion of the message segment (if any) that follows the codeword position in the transmission.
The requirement in the prior art that the codeword cannot be generated and transmitted until the entire message is known does not cause a latency problem if the codeword follows the entire message segment. The further the codeword position is from the end of the transmission, the greater the encoder latency. Thus, from an encoder latency reduction standpoint, it is desirable to locate the codeword at the entire end of the message segment or as close thereto as possible. When desig

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