Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Reexamination Certificate
1999-09-27
2001-05-01
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S382000
Reexamination Certificate
active
06225948
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the field of electronic signal processing. More specifically, the invention relates to a method for estimating a direction of incoming wave elements of a received signal, for example in base stations for mobile radio networks or in applications for radar or sonar systems and for seismic measurement systems.
One or more subscriber signals can be caused by transmitting from one or more communication subscribers to a common receiving station, by transmitting from one or more transmitters with superimposed measurement signals or by reflections of a measurement signal on obstructions or geological layers.
Estimation methods for determining the directions of arrival of various signals are described by Roy and Kailath, “ESPRIT—Estimation of Signal Parameters via Rotational Invariance Techniques,” IEEE Trans. Acoustics, Speech, and Signal Processing, Vol. ASSP-37, pp.984-95, July 1989. For example, a direction estimation method which is known from German patent application DE 195 11 752 and used as the UNITARY-ESPRIT method leads to the direction of wave elements being determined directly from the received signals.
Direction estimation is very important, by way of example, in the context of mobile radio application and the novel method of direction estimation will be discussed in the following in the context of mobile radio.
With mobile radio or methods similar to mobile radio, a new field of application has been opened up for direction estimation. When signals propagate in a propagation medium, they are subject to interference caused by noise. Owing to diffraction and reflections, signal components pass through different propagation paths and are superimposed at the receiver. This leads to superposition cancellation effects. Furthermore, if there is more than one signal source, this leads to the signals being superimposed. Frequency-division multiplex (FDMA), time-division multiplex (TDMA) or a method which is known as code division multiplex (CDMA) are used to distinguish between the signal sources, and thus to evaluate the signals.
If, for example, a CDMA (code division multiple access) method is used for subscriber separation, a plurality of subscriber signals can be transmitted in one frequency channel at the same time. The individual signals are separated in the receiver.
Mathematical descriptions, the method of operation, and the structure of CDMA (Code Division Multiple Access) radio transmission systems are described by Jung and Blanz in “Joint Detection With Coherent Receiver Antenna Diversity in CDMA Mobile Radio Systems,” IEEE Transactions on Vehicular Technology, Volume VT-44, 1995, pages 76-88. When such systems are used for mobile communication, there is a radio interface between fixed-position base stations and moving mobile stations. The transmission path from a base station to a mobile station is called the downlink path, and the transmission path from a mobile station to a base station is called the uplink path.
The Jung and Blanz article furthermore shows that the transmission quality in such radio transmission systems can be improved since it is possible to use an arrangement of a plurality of receiving sensors instead of a single receiving sensor. In accordance with the terminology used in the above-mentioned document, K denotes the number of subscriber signals which are transmitted from a base station at the same time in the same frequency channel, for example of supplied mobile stations. Ka denotes the number of receiving sensors which are assigned to a receiving device, for example the base station. In one such scenario, there are, therefore, K--Ka radio channels in the uplink path between the K mobile stations and the Ka receiving sensors in the base station. Each of the radio channels is characterized by a discrete-time baseband equivalent of its channel pulse response g
(k) (ka)
where k=1 . . . K, ka=1 . . . Ka. These channel impulse responses g
(k) (ka)
are used for channel modeling in data detection. That method does not take into consideration any statements relating to the directions in which wave elements arrive.
International PCT publication WO 95/09490 describes a mobile radio system with spatial subscriber separation, in which two different channel classes with a different capacity are used. After determining the position of the mobile station, narrow directional polar diagrams are used for transmission.
European Patent Application EP 0 701 334 A2 discloses a method for determining impulse responses of a radio channel in a cellular radiotelephone system.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an improved method for direction estimation, which overcomes the above-mentioned disadvantages of the heretofore-known methods of this general type and which results in a reduction in the influence of interference signals on the direction estimation, with little calculation complexity.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for direction estimation for wave elements of one or more subscriber signals. The method comprises the following steps:
assigning to a receiving device a number Ka of receiving sensors;
receiving Ka signals caused by at least one subscriber signal having impressed thereon a transmitter-specific fine structure, wherein a k
th
subscriber signal, with k=1 . . . K, is transmitted by means of Kd wave elements having mutually differing directions of arrival at the receiving sensors;
determining channel impulse responses assigned to the Ka receiving sensors from the received signals; and
determining the direction of arrival of at least one of the wave elements from the channel impulse responses.
In other words, in the method for direction estimation of wave elements of at least one subscriber signal, a plurality of receiving sensors are assigned to one receiving device. The same plurality of received signals are received via the receiving sensors, being caused by at least one subscriber signal which has a transmitter-specific fine structure impressed on it, in which case a k
th
subscriber signal, k=1 . . . K, is transmitted by means of Kd wave elements whose directions of arrival at the receiving location differ. Channel impulse responses assigned to the Ka receiving sensors are determined from the received signals, and the direction of arrival of at least one wave element is determined from the channel impulse responses.
The accuracy of the direction estimation is improved since the channel impulse responses already take account of the characteristics of the channels as raw information for the direction estimation. Knowledge relating to the received signal, in the form of the transmitter-specific fine structure, can be used for channel estimation in the receiving device. The direction estimation is thus more accurate than when using unknown data which are still to be detected.
In accordance with an added feature of the invention, the channel impulse responses are determined from training sequences of the subscriber signals, wherein the training sequences form the transmitter-specific fine structures. Such training sequences are known from mobile radio, for example as midambles in GSM useful channels. These training sequences can be used in a simple manner for the method according to the invention. The method according to the invention can thus be implemented in mobile radio networks with little complexity.
In accordance with an additional feature of the invention, the signals arriving in the receiving device are superimposed subscriber signals from a plurality of transmitters or reflectors, the signals being transmitted concurrently in one frequency channel. That is, the subscriber signals (which can be separated by the transmitter-specific fine structures) from a plurality of transmitters or reflectors arrive at the receiving device and are superimposed to form the received signals, in which case these signals are transmitted at the s
Baier Paul Walter
Blanz Josef
Haardt Martin
Schmalenberger Ralph
Greenberg Laurence A.
Lerner Herbert L.
Phan Dao L.
Siemens Aktiengesellschaft
Stemer Werner H.
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