Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2000-02-22
2003-09-30
Dildine, R. Stephen (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S786000
Reexamination Certificate
active
06629286
ABSTRACT:
BACKGROUND OF THE INVENTION
1Field of the Invention
The invention relates to a method and a device for assessing the quality of service (QoS) on transmission channels in a digital transmission system, in which, for a channel coding, a turbo coding is carried out in a turbo coder at the transmitter end and a turbo decoding is carried out in a turbo decoder with soft-decision output signals at the receiver end.
The use of turbo codes for digital transmission systems is investigated in the article “Comparison of Turbo-Code Decoders Applied to Short Frame Transmission Systems”, by P. Jung, 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 configurations 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.
In the article “Turbo Codes for PCS Applications”, ICC '95, Seattle, Wash., Jun. 18-22, 1995, D. Divsalar and F. Pollara propose turbo codes to achieve an error correction virtually as far as the so-called Shannon limit. Relatively simple component codes and large interleavers are intended to be used 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.
So-called turbo equalization is known from the article “Iterative Correction of Intersymbol Interference: Turbo-Equalization”, by Catherine Douillard et al., ETT European Transactions on Telecommunications, Vol. 6, No. 5, September-October 1995. The use of turbo equalization 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. It was found that intersymbol interference effects in multipath channels can be overcome by turbo equalization.
M. Na
han et al. disclose in their article “New Results on the application of antenna diversity and turbo-codes in a JD-CDMA mobile radio system”, 5
th
IEEE International Sysposium on Personal, Indoor and Mobile Radio Communications (PIMRC '94), and ICCC Regional Meeting on Wireless Computer Networks/WCN), The Hague, The Netherlands, Vol. 2, Sep. 18-23, 1994, pages 524-528 how assessment of the system behavior (system performance) can be achieved in a JD (joint detection) -CDMA (code division multiple access) mobile radio system by long-term averaging of the variances of the soft-decision output signals (&sgr;
LLR
2
) from a turbo decoder.
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 (
F
uture
R
adio Wideb
a
nd
M
ultiple
A
ccess
S
ystems), 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 comply with present and future developments of UMTS radio interface standards. FMA includes 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 WBCDMA (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 transmission systems.
With regard to the high performance of turbo codes, it is desirable to use these 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 is not overloaded by transmission of error correction codes.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and a device for assessing the quality of service (QoS) on transmission channels in a digital transmission system which overcome the above-mentioned disadvantages of the heretofore-known methods and devices of this general type and which do not require any additional complexity or outlay.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for assessing a quality of service on transmission channels in a digital transmission system, which includes the steps of:
performing a turbo coding in a turbo coder for a channel coding at a transmitter end;
performing a turbo decoding in a turbo decoder with soft-decision output signals at a receiver end; and
determining a quality of service from instantaneous values of variances of the soft-decision output signals from the turbo decoder.
In other words, according to the invention, the method mentioned above is characterized in that the quality of service is determined from the instantaneous values of the variances of the soft-decision output signals from the turbo decoder.
In the following, 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
1
G
in conjunction with a maximum failure probability P
out
G
. In the case of line-switching services, the probability P{P
b
>P
b
G
} of the instantaneous bit error rate P
b
exceeding P
b
G
must not be greater than P
out
G
, that is to say
Pr{P
b
>P
b
G
}<P
out
G
For voice transmission, P
b
G
is equal to 10
−3
and P
out
G
is equal to 0.05. A similar condition for the instantaneous packet loss rate P
1
applies to packet services:
Pr{P
1
>P
1
G
}<P
out
G
Apart from the criteria relating to Pr, there are also other conditions relating to the QoS criterion. However, the QoS parameters P
b
G
, P
1
G
and P
out
G
will mainly be considered here, which relate directly to the choice of the error correction code (ECC). For the ECC, the coding rate R
c
is essentially governed by the multiple access method, the modulation and the packet parameters. In other words, the coding rate R
c
is directly related to the question as to whether a QoS criterion is or is not satisfied for a specific service.
It can be seen that determination of the quality of service in conjunction with the QoS criteria is important, wherein this determination is possible by using the method according to the invention without having
Berens Friedbert
Doetsch Markus
Jung Peter
Plechinger Jörg
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