Pulse or digital communications – Repeaters – Testing
Patent
1997-11-07
2000-04-04
Chin, Stephen
Pulse or digital communications
Repeaters
Testing
375206, 375349, 370342, 370344, 370347, H04B 1500
Patent
active
060470208
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a receiving method in which a received signal comprises several summed signal components, at least some of which being unknown, and the received signal being sampled, said samples forming an information vector, and in which the received signals are estimated with one or more multidimensional filters.
PRIOR ART
In planning and implementing communication systems, one of the fundamental problems is concurrent transmission and reception of signals by several simultaneous users so that the signals would interfere with one another as little as possible. For the above reason, and because of other interference caused by the transmission channel, as well as the transmission capacity being employed, a number of different transmission protocols and multiple access methods have been developed. Particularly in mobile communication systems, the most common of these include the FDMA and TDMA methods, and lately also the CDMA method.
In all the above methods, interference is present in somewhat different forms, and different kinds of methods have been employed in these methods to overcome interference-related problems. In TDMA, a significant source of interference is intersymbol interference (ISI), and in CDMA, multiple access interference (MAI). Generally speaking, in detection of a desired signal, the aim is to find the desired symbols in a signal to which surplus information has been summed. The different multiple access methods pursue this aim in different ways. For CDMA, simultaneous detection of a plurality of users, and for TDMA different types of equalizers have been suggested.
The equalizers, which seek to alleviate signal distribution in time domain, come in two basic types: linear and non-linear. The linear equalizers, such as Wiener filters, are simple to implement but do not perform well enough in all situations due to a modulated waveform being characteristically non-linear. Non-linear equalizers are represented by e.g. a Viterbi equalizer and decision-feedback equalizers.
Correspondingly in the CDMA, the MUD methods are either linear or non-linear. Of the former, a decorrelating receiver, and of the latter, a Viterbi and decision feedback coupling method may be mentioned. A closer description of decorrelating receivers may be found in e.g. A. Hottinen: Self-organizing multiuser detection, Proc. of IEEE ISSSTA '94, Oulu, Finland.
Also known in prior art is the use of so-called blind adaptive algorithms in the equalizers and detection. A blind algorithm refers to a adaptation rule that does not take into account the polarities of the signals, i.e. a training sequence is not required to bring the receiver in a correct state. Blind methods are described in association with CDMA, for example in the reference S. Verdu: Adaptive multiuser detection, Proc. of IEEE ISSSTA '94, Oulu, Finland.
All the above methods, including the non-linear ones, share the drawback that as the number of interfering signals increases, which means that the dimension of the computation space increases, a steep increase occurs in the computation amount required for carrying out optimal detection. As the optimal detection has thus turned out to be difficult, suboptimal methods have been employed, which has resulted in loss of received information, manifest at the detector as deteriorated signal quality.
CHARACTERISTICS OF THE INVENTION
It is consequently an object of the present invention to implement a method by means of which a received signal containing interference may be detected suboptimally even in case the signal model is unknown. The invention further aims at implementing an adaptive method which requires little information on the interfering signals and noise and which is able to detect the desired signal reliably with a smaller amount of information even in a disturbed propagation environment.
These objects are achieved by a method of the type set forth in the introduction, characterized in that signal filtering takes place adaptively by forming a model for the signal by mea
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Hottinen: "Self-Organizing Multiuser Detection", IEEE, 1994, pp. 152-156.
Verdu:. "Adaptive Multisuer Detection", Department of Electrical Engineering, Princeton University, pp. 43-50.
Chin Stephen
Fan Chieh M.
Nokia Telecommunications Oy
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