Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2000-02-22
2003-05-27
Baker, Stephen M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S774000, C714S780000, C714S790000
Reexamination Certificate
active
06571366
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for packet transmission using an ARQ protocol on transmission channels in a digital transmission system, in which, for channel coding, turbo coding is carried out. This turbo coding is carried out a turbo coder at the transmitter end and turbo decoding is carried out in a turbo decoder at the receiver end using soft-decision output signals, with a return channel, being provided, by the way of which the receiver re-quests the information from faulty packets.
2. Description of the Related Art
The use of turbo codes for digital transmission systems is investigated in P. Jung “Comparison of Turbo-Code Decoders Applied to Short Frame Transmission Systems”, IEEE Journal on Selected Areas in Communications, Volume 14 (1996) pages 530-537, with both coders and decoders being investigated for the turbo codes in the transmission path. Decoding of the turbo codes is based on the use of soft-input/soft-output decoders, which can be produced using either MAP (Maximum a-posteriori) symbol estimators or MAP sequence estimators, for example, an estimator using an a-priori soft-output Viterbi algorithm (APRI-SOVA). This publication describes four different decoder arrangements and their capabilities to process specific error rates. Furthermore, the performance of these decoders is investigated for different applications. It has been found that the turbo codes and their iterative decoding are an effective measure against packet errors.
ICC '95, Seattle, Wash., Jun. 18-22, 1995, “Turbo Codes for BCS Applications”, D. Divsalar and F. Pollara, proposes turbo codes to achieve error correction virtually as far as the Shannon limit. The use of relatively simple component codes and large interleavers are considered for this purpose. In this publication, the turbo codes are produced in a coder using multiple codes, and are decoded in a suitable decoder. The turbo codes were introduced by Berrou et al. 1993 (see C. Berrou, A. Glavieux and P. Thitimayshima, “Near Shannon limit area correction coding: Turbo codes” Proc. 1993 IEE International conference on communications, pages 1064-1070). On the one hand, this method allows very good error correction to be achieved.
Turbo equalization is known from ETT European Transactions on Telecommunications, Vol. 6, No. 5, September-October 1995, “Iterative Correction of Intersymbol Interference: Turbo-Equalization”, Catherine Douillard et al., whose use is intended to overcome the disadvantageous effects of intersymbol interference in digital transmission systems which are protected by convolution codes. The receiver makes two successive soft-output decisions, which are made in an iterative process by a symbol detector and a channel decoder. Each iteration makes use of extrinsic information from the detector and the decoder for the next iteration, as with turbo decoding. Douillard, et al. found that intersymbol interference effects in multipath channels can be overcome by turbo equalization.
The publication “A Novel ARQ Technique using the Turbo Coding Principle”, Narayanan et al., IEEE Communications Letters, Volume 1, No. 2, March 1997, pages 49-51 describes an ARQ-III method using punctured turbo codes, in which the bits which were punctured for the first transmission are transmitted after the occurrence of faulty data packets. The receiver then combines the punctured code and the punctured bits, and thus obtains the unpunctured code.
Future transmission systems, for example the European UMTS (Universal Mobile Telecommunications System), require the support of a large number of co-existing carrier services with carrier data rates of up to 2 Mbit/s in a flexible manner, with the best-possible spectral efficiency being desirable. An MA (Multiple Access) scheme has been developed in the ACTS (Advanced Communications Technologies and Services) project AC090 FRAMES (Future Radio Wideband Multiple Access Systems), which is called FRAMES Multiple Access (FMA) and satisfies the UMTS requirements. As a third-generation transmission system, which covers a wide range of application areas, carrier services and widely differing scenarios, FMA must to comply with present and future developments of UMTS radio interface standards. FMA comprises two operating modes, namely WB-TDMA (Wideband Time Division Multiple Access) with and without spreading and compatibility with GSM (Global System for Mobile Communications) and WB-CDMA (Wideband Code Division Multiple Access). Although, essentially, a system based on FMA is considered here, it is also possible to include other transmission systems using multiple access methods, for example FDMA (Frequency Division Multiple Access) MC-CDMA (Multicarrier-CDMA) or combinations of the said transmission systems.
With regard to the high performance of turbo codes, it is desirable to use these codes in digital transmission systems. The complex requirements, for example for FMA, mean, however, that it is necessary when using such turbo codes to ensure that the data transmission makes full use of the capabilities of the turbo codes.
SUMMARY OF THE INVENTION
The invention is based on the object of providing a method for packet transmission using an ARQ protocol on transmission channels in a digital transmission system in which turbo coding is used for channel coding, in which the channel loading from ARQ can be kept as low as possible by way of a new turbo code and puncturing matched to it.
The present invention implements a method for packet transmission using an ARQ (Automatic Repeat ReQuest) protocol on transmission channels in a digital transmission system, comprising the steps of turbo coding, for channel coding, in a turbo coder at a transmitter end, utilizing a punctured turbo code with a variable coding rate, wherein said coding rate is chosen as a function of a Quality of Service of a transmission channel which is one of the transmission channels, turbo decoding in a turbo decoder at a receiver end, requesting coded packets incorrectly sent, by the receiver via a return channel, transmitting a portion of information suppressed by a puncturing of turbo code in a previous transmission, constituting additionally transmitted information, when an incorrectly coded packet is re-transmitted, inserting said additionally transmitted information into already existing information at said receiver end, and decoding resultant completed information again.
When the RCPTC is used, the coding rate can be set by suitable puncturing of the systematic or non-systematic information at the output of the turbo encoder. An increase in the coding rate, i.e., more information being punctured, in this case means that the decoding result is worse for a given channel quality. This means that the bit error rate BER increases. The use of the RCPTC for channel coding means that it is not necessary to transmit the entire packet once again in packet-switching services when an ARQ is initiated. The first transmission of the packet is carried out using a high coding rate, with little error protection. If the packet is identified as being faulty, then an ARQ is initiated. After this, rather than transmitting the entire packet again, only the information which was punctured in the first transmission, or a portion of this punctured information, is transmitted. The coding rate is thus compatibly matched to the channel as a result of which, overall, less data need be transmitted over the channel. The advantage of this method is thus that the total load on the channel is reduced.
In this document, the term Quality of Service is used as follows. Specific QoS criteria (QoS=Quality of Service) apply to various services, and the definitions of the QoS criteria for various carrier services have been worked out in the course of FRAMES. One important component of a QoS criterion is the carrier data rate R. The QoS criterion also includes a maximum permissible error rate P
b
G
or a packet loss rate P
l
G
in conjunction with a maximum failure probability P
out
G
. In the case of line-swi
Berens Friedbert
Doetsch Markus
Jung Peter
Plechinger Jörg
Baker Stephen M.
Siemens Aktiengesellschaft
Staas & Halsey , LLP
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