Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1999-07-01
2002-04-02
Chung, Phung M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
Reexamination Certificate
active
06367045
ABSTRACT:
FIELD OF THE INVENTION
The present application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 60/110,444, filed Nov. 27, 1998.
The present invention generally relates to error handling in the field of communication systems and, more particularly, to error handling using both automatic repeat request (ARQ) and variable rate transmission techniques in digital communication systems.
BACKGROUND INFORMATION
Variable rate transmission in a radio communication system can be achieved using several methods. For example, in a CDMA (Code Division Multiple Access) system the information transmission rate changes as a function of the spreading factor used for transmissions. In a TDMA (Time Division Multiple Access) system, variable rate transmission is generally achieved by using different numbers of time slots. In a TDMA system the data transmission rate also varies as a function of the modulation and coding scheme used for mapping data bits to channel bits/symbols.
EDGE Enhanced Data Rates for Global Evolution) is an example of a system that uses different modulation and coding schemes, in addition to a variable number of time slots, to achieve different transmission rates of user data. The different modulation and coding schemes used in the EDGE system, MCS-
1
through MCS-
6
, have various payload sizes, differing for example in increments of 25 octets as shown in FIG.
1
.
FIG. 2
summarizes the different block sizes, code rates, and payload sizes for the different modulation and coding schemes MCS-
1
through MCS-
6
. As indicated in
FIG. 2
, the modulation schemes can include PSK (Phase Shift Keying) and GMSK (Gaussian Minimum Shift Keying).
A block numbering scheme depending upon a payload in a block is disclosed in co-pending U.S. patent application Ser. No. 09/120,163, entitled “Method and Apparatus for Minimizing Overhead in a Communication System”, which is hereby incorporated by reference. The basic principle of the numbering scheme is illustrated in FIG.
3
.
As shown in
FIG. 3
, the block sequence numbers (SNs) can be integer multiples of an identification number of a currently used modulation and coding scheme, or can be separated by a step equal in magnitude to the identification number. For example, as shown in
FIG. 3
, where the current modulation and coding scheme is MCS-
6
, blocks in a sequence can be assigned sequence numbers
6
,
12
and
18
. The round trip time (RTT) shown in
FIG. 3
refers to an amount of time that elapses between when one or more blocks are sent, and when acknowledgment for them is received. As shown in
FIG. 3
, the payload size of a block for a current modulation and coding scheme can be defined as a number of octets that is equal to a product of the identification number of the current modulation and coding scheme and a block size increment between modulation and coding schemes. For example, the block payload size of the MCS-
6
modulation and coding scheme can be defined as (6)(25) octets=150 octets large.
When blocks of data are to be retransmitted at a rate that is lower than a rate at which the blocks of data were initially transmitted, the initially transmitted data can be resegmented into different size blocks, or different blocks having different payload sizes, and the different size blocks can be renumbered accordingly. For example, as shown in
FIG. 3
, block
12
of the MCS-
6
scheme, containing a payload of 150 octets, can be resegmented into two blocks
9
and
12
each containing a payload of 75 octets, and then retransmitted in accordance with the MCS-
3
scheme.
This procedure can be repeated as necessary or appropriate. If, for example, as shown in
FIG. 3
, the retransmitted block
9
is not correctly received, then it can be resegmented into three blocks
7
,
8
and
9
each containing a payload of 25 octets in accordance with the MCS-
1
scheme, and resent as the new blocks
7
,
8
and
9
.
Using the technique illustrated in
FIG. 3
, data can be retransmitted using a modulation and coding scheme that is appropriate at the time of retransmission. For example, the data can be retransmitted using a modulation and coding scheme that is optimal, and/or better at the time of the retransmission than the scheme used for the initial or previous transmission of the data.
Multiple blocks of data can also be resegmented into a fewer number of blocks for retransmission. For example, as shown in
FIG. 4
, where two blocks
4
and
6
of the scheme MCS-
2
are corrupted and need to be retransmitted, and at the time of retransmission the scheme MCS-
4
is optimal or otherwise appropriate, the two blocks
4
and
6
of the MCS-
2
scheme can be combined to form the single block
6
of the scheme MCS-
4
and retransmitted accordingly. The payload of the MCS-
4
scheme block
6
can be formed by concatenating the payloads of the blocks
4
and
6
of the MCS-
2
scheme. Note that when the optimal initial coding scheme is changed from MCS-
2
to MCS-
4
and the two blocks are combined, the resulting concatenated block is identified with the sequence number
6
of the second block. Alternatively, when a series of blocks are combined, the resulting combined block can be identified with the sequence number of any appropriate block in the series. For example, the combined block can be identified with the sequence number of the first block in the series, or the sequence number of the middle block, and so forth.
As shown in
FIG. 5
, ACK/NACK (positive acknowledgment
egative acknowledgment) messages can include a Received Block Bitmap (RBB) field format
506
having a Start Sequence Number (SSN)
502
followed by a bitmap
504
. The bitmap
504
contains an acknowledgment for each possible sequence number in a sequence of data blocks starting with a block whose SN has the same value as that of the SSN
502
. Thus, when this technique is used, a receiver must positively or negatively acknowledge all sequence numbers represented in an RBB field having the format
506
, regardless of whether all of the sequence numbers are actually used to transmit data blocks.
FIG. 6
shows an RBB field
606
having the format
506
. A single bit in the bitmap
506
can be used to acknowledge a block. Block sequence numbers of blocks acknowledged in the bitmap
506
correspond to bits in the bitmap
506
in a left-to-right, top-to-bottom order. The bitmap
506
includes a bit for each possible sequence number between the beginning and ending block sequence numbers of an ordered sequence of blocks. In other words, bits in the bitmap represent or acknowledge blocks having sequence numbers that are separated by a minimum step, regardless of whether the step in a particular ordered sequence of blocks is greater than the minimum step. Thus, both used and unused SNs are represented or acknowledged in the bitmap
506
.
For example, as shown in
FIG. 6
, when the RBB field
606
is used to indicate the acknowledgment status of a 12-block sequence that is configured in accordance with the MCS-
3
scheme (so that the SNs of the blocks in the 12-block sequence are separated by a step of 3), every third bit in the bitmap
506
indicates the acknowledgment status of a block in a 12-block sequence. As shown in
FIG. 6
, the sequence starts (as indicated by the SSN
602
) with data block
15
, and includes blocks having SNs of 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45 and 48. As shown in
FIG. 6
, blocks having SNs of 15, 18, 30 and 39 are each represented by three bits having a zero value, indicating that the blocks having SNs of 15, 18, 30 and 39 are negatively acknowledged (NACKed) and need to be retransmitted. However, unused SNs of 16, 17, 19, 20, 22, 23, 26, 26, 28, 29, 31, 32, 34, 35, 37, 38, 40, 41, 43, 44, 46, 47, 49 and 50 are also acknowledged. Thus, a total of (3)(12)=36 bits in the bitmap
604
are required to indicate the acknowledgment status of a 12-block sequence configured in accordance with the MCS-
3
scheme. Other schemes can require even more bits in the bitmap. For example, if a 12-block sequence were
Furuskär Anders
Jäverbring Stefan
Khan Farooq
Wallman Mattias
Burns Doane Swecker & Mathis L.L.P.
Chung Phung M.
Telefonaktiebolaget LM Ericsson (publ)
Torres Joseph D.
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