Blind rate detection in a multiplexed transmission system

Details Blind rate detection in a multiplexed transmission system Blind rate detection in a multiplexed transmission system

2000-09-08

2004-05-04

Iqbal, Nadeem (Department: 2184)

Error detection/correction and fault detection/recovery

Data processing system error or fault handling

Reliability and availability

C714S004110, C714S025000, C714S701000, C714S758000

Reexamination Certificate

active

06732302

ABSTRACT:

BACKGROUND
The present invention relates generally to radio communication and, more particularly, to the format of transport channels and control channels within a frame of a radio communication system.
Radio communication systems conventionally multiplex data channels and control channels within a transmission frame. For example, Third Generation Partnership Project (“3GPP”) standardization for Wideband Code Division Multiple Access (W-CDMA) multiplexes three different data channels (e.g., transport channels) within a transmission frame of a fixed length.
FIG. 1
illustrates a conventional frame format in accordance with the 3GPP standards. As shown, a frame
100
includes a first field A
105
for holding data associated with a first transport channel. The frame
100
additionally includes second fields B
115
and C
120
for conveying information associated with second and third transport channels, respectively. Because the A field
105
typically carries important information (e.g., in the case of voice coding, information that is most important for recreating intelligible speech), Cyclic Redundancy Check (CRC) bits
110
are additionally attached to the first field A
105
for providing error detection capability in connection with the first transport channel. The information carried by the B and C fields
115
,
120
is typically of lesser importance, so these fields are not associated with CRC bits.
Each of the fields within the frame
100
shown in
FIG. 1
may be designed to have a single, fixed beginning and ending location within the frame
100
, thereby making each field easy to locate and decode. In this case, the length of each field must be large enough to accommodate the highest expected bit rate associated with the corresponding transport channel. Fixed field positions, however, use the system capacity in an inefficient way whenever a transport channel provides insufficient data to fill its associated field within the frame
100
.
The use of variable field lengths (e.g., increasing or diminishing the length of the A, B, and/or C fields to accommodate more or less available data traffic) can alleviate the inefficiencies that can result from fixed field positions. For example, the length of the A field
105
is often permitted to be any one of a number of predefined lengths, thereby permitting information to be transmitted at a variable rate. To determine the actual length of a received A field
105
, a process called “blind rate detection” is used, in which the actual data rate is determined without the need for rate information to be expressly inserted into the frame. In one blind rate detection strategy, the receiver hypothesizes one of these predefined lengths, such as the shortest one. Using the hypothesized length, the A field
105
is decoded, and its CRC field
110
(which must, by definition, immediately follow the A field
105
) determined. If the CRC field
110
indicates that no errors were detected, then the hypothesized length is presumed to have been correct. Otherwise, another one of the predefined lengths is hypothesized (e.g., the next largest length) and the process is repeated until a CRC field
110
indicates an absence of errors. At this point, the A field
105
is presumed to have been decoded correctly, and its length is known to be the last hypothesized length.
As mentioned earlier, fields B
115
and C
120
typically do not have attached CRC bits. Since, as defined in accordance with the 3GPP standards, the frame
100
is of a known length, the length of the B
115
and C
120
fields must be set to accommodate the length of the A field
105
. Typically, for each of the predefined lengths of the A field
105
, lengths for each of the B and C fields
115
,
120
are predefined as well. Thus the lengths, as well as the starting positions, of the B and C fields
115
,
120
are known once the length of the A field
105
is known.
In addition to the A
105
, CRC
110
, B
115
and C
120
fields described above, a variable length control channel DCCH is sometimes transmitted in the frame
100
. Because it is transmitted only occasionally, it would be inefficient to define a frame format that always included the DCCH field. Consequently, the frame format is defined in a way that permits the DCCH field to “steal” bits from the C field
120
. The DCCH field is also permitted to vary in length, however. This creates the problem of not knowing how many bits have been “stolen” from the C-field.
As shown in
FIG. 2
, it has been proposed to locate the DCCH field
203
(which includes an associated CRC field) at the end of the frame
200
, with bits that make up the DCCH field
203
being “stolen” from the C field
201
. The lengths of the A and B fields
105
,
115
are determined in the same manner as described above. To determine the length of the C field
201
, it is necessary to know the length of the DCCH field
203
. In the proposal, this is done by hypothesizing a first one of the possible DCCH lengths (e.g., a shortest DCCH length), and decoding the DCCH field
203
from the end of the frame
200
. This is illustrated in
FIG. 2
by means of the backwards arrow
205
. If the DCCH's CRC field fails to detect any errors in the decoded result, then the hypothesized length of the DCCH field
203
is presumed to have been correct. Otherwise, another DCCH length is hypothesized, and the process is repeated until either the DCCH field
203
is correctly decoded, or until a failure to decode any DCCH field indicates that the DCCH field
203
is not present in the frame
200
(i.e., no bits were stolen from the C field
201
). Once the length of the DCCH field
203
is known, the length of the C field can also be determined.
The proposed solution presents a number of problems. To begin with, it is very difficult to implement a format in which the bits are transmitted and received backwards. Furthermore, the proposed format is very different from other formats. This would require that a completely new kind of multiplexing be standardized.
SUMMARY
It is therefore an object of the present invention to provide a multiplexing technique that permits a variable length DCCH field to be intermittently included in a frame having a fixed length.
In accordance with one aspect of the present invention, data is multiplexed in a frame having a fixed bit length in a telecommunication system. This is achieved by transmitting a first transport channel comprising a first number of bits; transmitting first error detection bits associated with the first transport channel and comprising a second number of bits; transmitting a second transport channel comprising a third number of bits; transmitting a third transport channel comprising a fourth number of bits; and selectively transmitting a control channel comprising a fifth number of bits. Furthermore, the control channel is transmitted after the first error detection bits and before transmission of the third transport channel; whenever the control channel is transmitted as part of the frame, a sum of the first, second, third, fourth and fifth number of bits equals the fixed bit length; and whenever the control channel is not transmitted as part of the frame, a sum of the first, second, third and fourth number of bits equals the fixed bit length.
In other aspects of the invention, the control channel may be transmitted between the first error detection bits and the second transport channel. Alternatively, the control channel may be transmitted between the second and third transport channels.
In another aspect of the invention, the fifth number of bits may further include error detection bits associated with the control channel.
In still another aspect of the invention, multiplexed data that is received as a frame in a telecommunication system is decoded, wherein the frame has a fixed bit length. This is achieved by decoding a first transport channel contained in the frame, wherein the decoding step includes determining a first length of the first transport channel; decoding a second group of bits having a second

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