Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2000-08-28
2003-09-02
Dildine, R. Stephen (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
Reexamination Certificate
active
06615382
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for controlling errors in a link layer during wideband wireless communication, and more particularly, to a method for controlling the errors in a wireless link layer using a simultaneous multiple copy scheme and an adaptive forward error control scheme for a real time service during wideband wireless communication. The present application is based on Korean Application No. 99-35839.
2. Description of the Related Art
In wideband communication using an optical cable, transmission error ratio is very low due to the stability of communication media. However, in the case of wireless communication, the transmission error ratio is higher than in communication through wire and the distribution of the error ratio is very variable, due to the characteristics of media. Therefore, the error controlling scheme is very important to wideband wireless communication.
The error controlling scheme in the conventional wireless link layer is classified into a forward error correction (FEC) scheme for correcting errors in a wireless channel, an automatic repeat request (ARQ) scheme for performing re-transmission when errors are detected in received data, and a hybrid ARQ scheme where the above two methods are combined with each other. The ARQ scheme will be described first.
FIG. 1
schematically shows processes of controlling errors in the link layer by the conventional ARQ method. In general, the ARQ scheme or a sliding window method is used for controlling the errors in the link layer. There are various types of ARQ schemes. Here, a selective repeat method, which is a representative ARQ scheme, will be described.
As shown in
FIG. 1
, a receiver
12
feeds back an acknowledgment (ACK) to a transmitter
10
when each cell (the transmission unit of the link layer) transmitted by the transmitter
10
is successfully received and feeds back a negative acknowledgment (NAK), which indicates that a cell has been corrupted, when a cell transmitted by the transmitter
10
is not successfully received. A time delay taken to receive the ACK or the NAK from the receiver
12
after the transmitter
10
transmits the cell is defined as a round trip delay (RTD)
14
. The receiver
12
generally uses a checksum in order to determine that a cell has been corrupted. A cyclic redundancy code (CRC) is used for the representative method for calculating the checksum.
In
FIG. 1
, the receiver
12
finds error in a third cell
16
and feeds back the NAK with respect to the corresponding cell to the transmitter
10
. After the RTD, the transmitter
10
which received the NAK re-transmits “one” copy
16
a
of the third cell
16
to the receiver
12
. Also, a corresponding cell
17
a
is re-transmitted with respect to a seventh cell
17
in which an error occurs. As a result, it is noted that a corresponding cell
19
is successfully received by the receiver
12
.
However, errors may occur in the re-transmitted cells
16
a
and
18
. In this case, the receiver
12
feeds back the NAK and the transmitter
10
re-transmits the corresponding cell
18
a.
In the FEC scheme, when the receiver finds an error in a cell, the receiver does not request the transmitter to re-transmit the cell, but recovers or corrects the cell. However, severe overhead is caused by encoding all information required for recovering the error and inserting the encoded information in a transmitted cell. It is difficult to apply the FEC scheme as the size of the cell increases. Therefore, a hybrid ARQ scheme, which first recovers or corrects a certain number of errors by the FEC and then determines whether an error exists by the CRC is generally used, instead of the pure FEC scheme.
FIG. 2
schematically shows the structure of a wireless cell according to the conventional hybrid ARQ scheme. The cell received through wire (a wire ATM cell), which is a protocol data unit (PDU)
20
of an upper layer, is encapsulated to a PDU
25
of the link layer for the wireless channel and then transmitted. Here, an asynchronous transfer mode (ATM) cell will be described.
A wire ATM cell
20
, including a header
21
of 5 bytes and a payload
22
of 48 bytes, has a fixed length of 53 bytes. The header
21
and the payload
22
of the wire ATM cell
20
are converged as they are to a header
21
a
and a payload
22
a
of the PDU of a wireless data link control layer (wireless DLC-PDU), and then the CRC
23
and the FEC
24
in order to control the error in the wireless channel are added for constituting the wireless DLC-PDU. Here, it is assumed that the wireless ATM DLC-PDU has a fixed length of 64 bytes, as proposed currently. Therefore, when it is assumed that the length of the CRC is 2 bytes, the length of the FEC is fixed to 9 bytes. Namely, a fixed encoding ratio is used regardless of the state of a channel.
Since a time delay corresponding to at least the RTD is required for the transmitter
10
to be informed of the error in the cell transmitted by the transmitter
10
from the receiver
12
and to re-transmit the cell to the receiver
12
, the number of times of the re-transmission is extremely restricted in a real time service. However, resources can be wasted without successful transmission of a cell if only one copy of a cell containing errors is re-transmitted to provide an opportunity to correct the errors. This is because the conventional method related to the ARQ error control scheme is mainly used for a non-real time service.
Since a uniform encoding ratio is used regardless of the state of a channel in the conventional hybrid ARQ scheme, the efficiency of resources may be deteriorated in a case where the conventional hybrid ARQ scheme is used in the wireless channel in which the state of the channel changes relatively often.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a method for controlling errors in a link layer using a simultaneous multiple copy scheme and an adaptive forward error control scheme, which is capable of satisfying quality of service (QOS) such as a cell propagation delay time and a cell loss ratio (CLR) for a real-time service as well as a non-real time service in a wideband wireless communication.
It is another object of the present invention to provide recording media therefor.
Accordingly, to achieve the first object, according to an aspect of the present invention, there is provided a method for controlling errors in a link layer in wideband wireless communication using an automatic repeat request (ARQ) scheme, in which a wideband wireless channel is used for communication between a first node and a second node, comprising the steps of (a) estimating the error ratio of a forward (a direction in which a cell is transmitted from the first node to the second node) channel using the state of a backward (a direction in which a cell is transmitted from the second node to the first node) channel, and transmitting a cell, in which a forward error correction (FEC) code having an encoding ratio that varies depending on the estimated error ratio is included in a protocol data unit (PDU) of a wireless link layer, through the forward channel and (b) re-transmitting the copy of a cell transmitted in the step (a), when feedback information that indicates that an error exists in the cell transmitted in the step (a) is received through the backward channel.
The PDU of the wireless link layer in the step (a) preferably has a fixed length regardless of the variable encoding ratio of the FEC code.
In the step (b), a plurality of copies of the cell to be transmitted in the step (a) are preferably re-transmitted using a simultaneous multiple copy method in the same frame.
According to another aspect of the present invention, there is provided a method for controlling errors in a link layer in wideband wireless communication using an ARQ scheme, in which a wideband wireless channel is used for communication between a first node and a second node, comprising the steps of (a) estimating the error rati
Ahn Chang-wook
Jang Kyung Hun
Kang Chung-gu
Kang Woo-shik
Dildine R. Stephen
Samsung Electronics Co,. Ltd.
Sughrue & Mion, PLLC
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