Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1999-02-18
2002-02-05
Chin, Stephen (Department: 2634)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C375S347000, C375S349000, C708S304000, C455S039000, C455S063300, C370S902000, C342S359000
Reexamination Certificate
active
06345075
ABSTRACT:
TECHNICAL FIELD
The invention relates to a process for data transmission in a cellular mobile radio network in which at least one transmitter/receiver statuib a phase-controlled antenna group is provided which is supplied with a circuit for adaptively modifying the antenna signal weighting factors for producing a directional characteristic in which, for adaptation of the antenna signal weighting factors, a nonlinear structure is used for antenna signal processing, whereby the nonlinear structure is comprised of a forward filter, a feedback filter and a decision circuit and the antenna signals initially are fed over the forward filter, then supplied to the decision circuit and from the decision circuit are fed via the feedback filter, whereafter the output signal of the feedback filter is subtracted from the output signal of the forward filter. It relates also to a device for data transmission in a cellular mobile radio network in which a phase-controlled antenna group is provided which, for achieving a directional characteristic, is provided with a circuit for the adaptive influencing of the antenna signal weighting factors and wherein a nonlinear structure is used for antenna signal processing in the adaptation of the antenna signal weighting factors whereby the nonlinear structure is comprised of a forward filter, a feedback filter and a decision circuit and the individual antennae are connected at the inputs of the forward filter, the output of the forward filter is connected to a subtracter whose output is connected with the input of the decision circuit, the output of the decision circuit is connected with the input of the backward filter and the output of the backward filter is connected with the second input of the subtracter.
With such a process or such a device, one obtains a phase control antenna group provided with a circuit for adaptively influencing the antenna weighting factors so that a directional characteristic is produced. This circuit includes as is conventional a mixer, a time and value discretizing of all of the received signals of the individual antennae of the antenna group as well as a signal processing circuit.
STATE OF THE ART
The limited availability of the electromagnetic spectrum on the one hand and the rapid increase of the number of mobile radio subscribers and services on the other has mandated efficient utilization of the network drivers for those frequency bands which are utilized. Since known access processes, like FDMA, TDMA and CDMA have already reached their capacity limits (e.g. in GSM, Global System for Mobile Communications) and microcells in municipal high population density areas as well as half rate coders for GSM are already in use, new efficient access processes are highly desired for capacity increase. Directionally resolved reception represents a promising new technology for increasing the range, reducing the common channel interference and reducing the frequency repetition spacing, and thereby increasing the subscriber capacity of a mobile radio network.
The increase in the range is of interest in lightly settled regions and also for large umbrella cells in which overflow traffic from subordinate microcells must be absorbed. A further interesting field of application is radio access for fixed network subscribers (“radio in the local loop”, RLL, or “radio in the loop”, RITL).
The common channel interference is known to be the limiting influencing factor for well developed cellular mobile radio networks.
Directionally resolved reception, in which a maximum of the directional diagram of the receiving antenna is in the incident direction of the desired signal (of a subscriber) and/or zero locations of this directional diagram lie in incident direction of interference signals, reduces the common channel interference. These interference signals are, for example, signals which either derive from other subscribers in the same cell or from subscribers in foreign (distal) cells. With this mode of operation it is possible to so reduce the frequency repetition spacing that in an extreme case, reuse of the same frequency is possible in a neighboring cell (channel group number equal to one).
For the increase of the subscriber capacity of a mobile radio network it is however also a possibility to service multiple subscribers at one and the same frequency and the same time slot in the same radio cell. The usual designation for this, SDMA, Space Division Multiple Access, is unprecise: it should be designated Angle Division Multiple Access.
With the processes proposed to date for the directionally resolved reception, the lower limit of the angular separation at which the process breaks down is a significant problem. In the ideal case this lower limit should be 0°.
When more than one subscriber in a radio cell is serviced at the same frequency and the same time slot, the desired signal of one subscriber becomes an interference signal for all other subscribers and vice versa. SDMA enables a proper separation of the individual subscriber signals and in connection therewith the detection of the signals associated with each subscriber.
The current state of the art is described for example in T. Bull, M. Barrett, R. Arnott, “Technology in Smart Antennas for Universal Advanced Mobile Infrastructure (TSUNAMI R2108)—Overview”, Proc. RACE Mobile Telecommunications Summit, Cascais, Portugal, November 22-24, 1995, pp. 88-97; and in M. Tangemann, C. Hoeck, and R. Rheinschmitt, “Introducing Adaptive Array Antenna Concepts in Mobile Communication Systems”, RACE Mobile Communications Workshop, May 17-19, 1994, Amsterdam, pp. 714-727.
Here a group antenna with variable directional characteristics is used in which there is separation of desired subscriber signals and interference signals (referred to in total also as “interference”). The signal from each individual antenna element of the group is mixed at a lower frequency (intermediate frequency IF or base band BB). These IF or BB signals as time-discrete and value-discrete signals are used as input parameters for an efficient optimizing algorithm. The algorithm which determines the directional characteristic through the adaptive effect of the antenna weighting factors is realized by a signal processor or the like. This algorithm is either a “temporal-reference” algorithm as has been described for example in S. Ratnavel, A. Paulraj and A. G. Constantinides “MMSE Space-Time Equalization for GSM Cellular Systems”, Proc. Institute of Electrical and Electronics Engineers, IEEE, Vehicular Technology Conference 1996, VTC '96, Atlanta, Ga., pp. 331-335, E. Lindskog, A. Ahlen and Sternad, “Spatio-Temporal Equalization for Multipath Environments in Mobile Radio Applications”, Proc. Institute of Electrical and Electronics Engineers, Vehicular Technology Conference 1995, VTC '95, Chicago, Ill., USA, Jul. 25-28, 1995 pp. 399-403, and O. Munoz and J. Fernandez, “Adaptive Arrays for Frequency Non-selective and Selective Channels”, Proc. EUSIPCO '94, European Conference for Signal Processing, Edinburgh, pp. 1536-1539 or a “spatial-reference” algorithm as is described for example in M. Haardt and J. A. Nossek, “Unitary ESPRIT: How to Obtain an Increased Estimation Accuracy with a Reduced Computational Burden”, IEEE Trans. on Signal Processing, Bd. 43, Nr. 5, May 1995, pp. 1232-1242, R. Roy and R. Kailath, “ESPRIT”—Estimation of Signal Parameters via Rotational Invariance Techniques”, IEEE Trans. Acoust., Speech, Signal Processing, Bd. 37, July 1989, pp. 984-995.
“Temporal-reference” algorithms rely on the (previous) recognition of a part of the signal, for example, an intentionally introduced training sequence for identification of the subscriber. In the Global System for Mobile Communications (GSM) such a standard is provided and service for the estimation of the radio channel or for the identification of the base station. By contrast thereto “spatial-reference” algorithms require no previous knowledge of the subscriber signals since these algorithms utilize the spatial-geometric arrangement of the individual an
Bonek Ernst
Fuhl Josef
Chin Stephen
Ha Dac V.
Telekom Austria Aktiengesellschaft
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