Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2001-05-24
2004-02-24
Ton, David (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S748000, C714S751000
Reexamination Certificate
active
06697988
ABSTRACT:
PRIORITY
This application claims priority to an application entitled “Data Transmission Apparatus and Method for an HARQ Data Communication System” filed in the Korean Industrial Property Office on May 24, 2000 and assigned Ser. No. 2000-29121, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a data transmission apparatus and method in a radio communication system, and in particular, to an apparatus and method for managing retransmission of data which is subjected to transmission error during data transmission.
2. Description of the Related Art
A radio communication system chiefly uses convolutional codes, turbo codes or linear block codes, for channel coding. Such a radio communication system may employ an HARQ (Hybrid Automatic Repeat Request) Type I using an ARQ (Automatic Repeat Request) scheme which requests retransmission of data packets upon completion of decoding and CRC error check. HARQ scheme is generally applicable to a satellite system, an ISDN (Integrated Services Digital Network) system, a digital cellular system, a CDMA-2000 (Code Division Multiple Access-2000) system, a UMTS (Universal Mobile Telecommunication System) system or an IMT-2000 (International Mobile Telecommunication-2000) system, and HARQ scheme includes the convolutional codes and the turbo codes.
The above-stated hybrid ARQ scheme is generally divided into HARQ Type I, HARQ Type II and HARQ Type III. At present, most of the multi-access schemes and the multi-channel schemes using the convolutional codes or the turbo codes employ the HARQ Type I. That is, the multi-access and multi-channel schemes of the radio communication system using the above-stated channel coding scheme, employ the HARQ Type I as an ARQ scheme for increasing the data transmission efficiency, i.e., throughput of the channel coding scheme and improving the system performance.
A principle of the HARQ Type I is based on the fact that the channel encoder using the convolutional code, the turbo code or the linear block code has a constant code rate.
FIGS. 1A and 1B
illustrate a conceptional data process flow by the HARQ Type I.
Commonly, a transmitter of the radio communication system combines L-bits transmission data with a CRC (Cyclic Redundancy Check) code for error detection and then encodes the combined data, L+CRC, through channel coding. The transmitter transmits the encoded data through an assigned channel. Meanwhile, a receiver of the radio communication system acquires the original L-bits data and the CRC code through a reverse operation of the transmitter, and transmits a response signal ACK/NAK to the transmitter according to the CRC check results.
This will be described in more detail with reference to
FIG. 1A. A
CRC encoder
110
receives an L-bits source data packet and encodes the received data using a CRC code, creating a FEC input data block, L+CRC. Commonly, CRC bits are added to the source data before channel encoding. A channel encoder
112
performs channel coding on the FEC input data block, L+CRC, creating a channel-coded data block, (L+CRC)×R
−1
. The channel-coded data block, (L+CRC)×R
−1
, is provided to a specific channel through other functional blocks
114
necessary for multiplexing.
Other inverse functional blocks
124
necessary for demultiplexing in the receiver receiving the channel-coded data block through the specific channel, demultiplex the received coded data block and output a channel-coded data block, (L+CRC)×R
−1
. A channel decoder
122
then performs channel decoding on the channel-coded data block, (L+CRC)×R
−1
, and outputs a channel-decoded data block, L+CRC. A CRC decoder
120
performs CRC decoding on the channel-decoded data block, L+CRC, to acquire the original data, i.e., the L-bits source data packet. After completion of CRC decoding, the CRC decoder
120
performs CRC checking using the CRC decoding results, thereby to determine whether the source data packet has transmission errors.
If no error is detected through the CRC check, the receiver provides the source data packet to an upper layer and transmits a confirm signal ACK (Acknowledgement) acknowledging the source data packet to the transmitter. However, upon detecting an error through the CRC check, the receiver transmits a confirm signal NAK (Not-Acknowledgement) requesting retransmission of the channel coded data packet to the transmitter.
After transmitting the channel-coded data block, the transmitter receives the confirm signal ACK/NAK from the receiver in response to the transmitted channel-coded data block. Upon receipt of the confirm signal NAK, the transmitter retransmits the corresponding channel-coded data block in the above-described operation. The transmission scheme includes Stop-and-Wait ARQ, Go-Back-N ARQ, and Selective-Repeat ARQ schemes. The detailed description of the retransmission schemes will be omitted.
FIG. 1B
illustrates a conceptual transmission procedure of the channel-coded data packet between the transmitter and the receiver.
FIG. 1B
shows that the transmitter retransmits the channel-coded data block upon every receipt of m NAKs from the receiver.
As an example of such a procedure, in an air interface of the 3GPP-2 (3
rd
Generation Partnership Project-2; a standard for a synchronous CDMA system) mobile communication system (hereinafter, referred to as “CDMA-2000” system), the multi-access scheme and the multi-channel scheme of the system employ the HARQ Type I in order to increase data transmission efficiency of the channel coding scheme and to improve the system performance. In addition, in an air interface of the 3GPP (3
rd
Generation Partnership Project; a standard for an asynchronous CDMA system) mobile communication system (hereinafter, referred to as “UMTS system”), the multi-access scheme and the multi-channel scheme of the system also employ the HARQ Type I in order to increase data transmission efficiency of the channel coding scheme and to improve the system performance.
However, the HARQ Type I has the following disadvantages.
First, the HARQ Type I has higher throughput, compared with a pure ARQ scheme. However, as a signal-to-noise ratio (S/N) of a signal is increased more and more, the throughput becomes saturated to a code rate R of the FEC code, thus resulting in a reduction in the throughput as compared with the pure ARQ. That is, the throughput cannot approach 1.0 (100%) even at very high S/N. Such a problem is shown by a characteristic curve of the HARQ Type I in FIG.
2
. That is, as for the HARQ Type I, the throughput is saturated to the code rate R (<1.0) as shown in
FIG. 2
, so that it cannot approach 1.0.
Second, the HARQ Type I improves the throughput by performing error correction using the FEC code, compared with the pure ARQ. However, since the HARQ Type I uses a constant redundancy, i.e., constant code rate regardless of variation in S/N, it has low transmission efficiency. Therefore, the HARQ Type I cannot adaptively cope with variations in the channel condition, thus causing limitation of throughput.
To solve such problems, the HARQ Type II or the HARQ Type III is used. The HARQ Type II and the HARQ Type III have an adaptive structure which adaptively determines an amount of redundancies used for the FEC code according to how good the channel condition is. Therefore, the HARQ Type II and the HARQ Type III have improved throughput, compared with the HARQ Type I. That is, the adaptive structure reduces the amount of redundancies to a minimum, so that as the S/N of the signal is increased more and more, the code rate R of the FEC code approaches 1, thereby enabling the throughput to approach 1. Meanwhile, the adaptive structure performs optimal error correction such that if the S/N of the signal is decreased, the amount of redundancies is increased to a maximum to enable the code rate R of the FEC code to approach 0, or the redundancies are repeated so as
Kim Beong-Jo
Kim Min-Koo
Dilworth & Barrese LLP
Samsung Electronics Co,. Ltd.
Ton David
LandOfFree
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