Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Reexamination Certificate
2000-06-05
2002-03-05
Trost, William (Department: 2683)
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
C455S456500, C455S562100, C370S347000, C370S349000
Reexamination Certificate
active
06353731
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the telecommunications field. More specifically, the invention relates to a method for measuring the characteristics of radio channels, in which the signals are received by a total of M
1
receiving sensors in a linear antenna array, wherein the respective received signals are composed of wave elements of a transmitted signal with a different incidence direction and different delay. The invention furthermore relates to a measurement configuration for measuring the characteristics of radio channels having a linear antenna array, having a number of antenna sensors. Each antenna sensor is followed (in a signal flow direction) by analog/digital sampling, a filter matched to the signal, a stage for discrete Fourier transformation, and at least one signal processor is provided for the reception stages.
In a large number of applications, such as sonar, radar, satellite communication and mobile radio, high-resolution radio channel measurements, which also supply directional information, are desirable. A mobile radio channel represents the connection between a base station and mobile stations, and deep knowledge of the channel characteristics is required in order to allow propagation and channel models to be developed and used. Such models are required by system providers to plan their networks, and the propagation environment is an essential basis for designing mobile radio systems.
Increasing numbers of subscribers and a limited number of available frequencies necessitate improved spectral efficiency. A significant improvement is obtained by using intelligent antenna arrays, such as those described in German patent application DE 195 11 751 A, for example. There, use is made of the spatial diversity inherent in the radio channel. The design and provision of radio systems with intelligent antennas necessitate high-resolution measurements of the direction information on radio channels.
Two methods, in particular, for channel investigation have become known in order to solve the problem, and these methods estimate both the delay and the azimuth of the dominant wave fronts, that is to say the most powerful wave fronts for example, which arrive at an antenna configuration. Both methods furthermore use a test signal which consists of a pulse sequence modulated by means of a pseudo-random sequence.
The following two articles are of interest: U. Martin, “Modeling the mobile radio channel by echo estimation,” Frequenz, vol. 48, pp. 198-212, 1994; and U. Martin, “Echo estimation—Deriving simulation models for the mobile radio channel,” in Proc. IEEE Vehicular Techn. Conf., vol. 1, pp. 231-35, Chicago Ill., July 1995. They describe how the parameters of certain statistical channel models can be obtained from the results of propagation measurements. The author describes a measurement configuration in which estimates of the path delay times are made with high resolution in the frequency domain by estimation of superimposed exponential oscillations.
Alternatively, it is possible to use a method which has generally become known by the name ESPRIT, such as the 1D unitary ESPRIT method, which is disclosed in German patent application DE 195 11 752 A. If the receiving antenna of that channel measurement configuration is replaced by a centrally symmetrical antenna array, a two-dimensional (2D) unitary ESPRIT method can automatically provide estimates of both the incidence angle and the delay time for dominant signal paths. Such high-resolution direction measurements of radio channels make it easier to develop realistic channel models which include the dominant incidence directions at the base station. The 2D unitary ESPRIT method, in conjunction with this channel measurement configuration and uniform linear antenna array, has been proven in a number of field measurements, and it automatically supplies pairs of estimates of the incidence angle and of the delay time for the dominant paths, as described in U. Martin, “Charakterisierung und Simulation des richtungsabhängigen Funkkanals” [Characterization And Simulation Of The Directional Radio Channel], ITG Workshop on Smart Antennas, Zurich, October 1996.
The second method for channel investigation, described Fleury, Dahlhaus, Heddergott, and Tschudin, in “Wideband Angle Of Arrival Estimation Using The SAGE Algorithm” in Proc. IEEE ISSSTA, vol. 1, pp. 79-85, Mainz, September 1996, is based on the SAGE (space-alternating generalized expectation maximization) algorithm. This iterative method provides an estimate of the parameters based on the highest probability. This method involves considerably more computation complexity than the 2D unitary ESPRIT method mentioned above, since it is based on various 1D optimization processes and requires an additional algorithm, for example that from the 2D unitary ESPRIT method to solve its initial value problem. The channel investigation method based on the 2D unitary ESPRIT algorithm (and which is also required in order to understand the invention) will therefore be explained in more detail in the following text further below.
In addition, a method which also allows the incidence direction of received wave fronts to be estimated is known from Roy and Kailath, “ESPRIT—Estimation of Signal Parameters Via Rotational Invariance Techniques” in IEEE Transactions on Acoustics, Speech and Signal Processing, vol. 37, No. 7, July 1989, pages 984-995.
Finally, Josef Fuhl, et al., “High-Resolution 3-D Direction-of-Arrival Determination for Urban Mobile Radio,” IEEE Transactions on Antennas and Propagation, vol. 45, No. 4, April 1997, pages 672-682 describes a method for estimating the direction of electromagnetic waves arriving at a receiver, with the azimuth and elevation angles being determined at the same time once the propagation time delays of the electromagnetic waves have previously been determined.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method and a device for measuring the characteristics of radio channels which overcome the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and which method supplies pairs of values for the azimuth propagation time delay of the incident wave fronts with higher accuracy and less computation complexity—and thus more quickly as well.
With the above and other objects in view there is provided, in accordance with the invention, a method of measuring characteristics of radio channels, which comprises:
transmitting a transmission signal containing a preselected test sequence;
receiving signals with a plurality of receiving sensors in a linear antenna array, wherein respective received signals are composed of wave elements of the transmission signal with a different incidence direction and different delay;
demodulating the received signals and sampling to obtain samples;
supplying the samples for calculation of eigen vectors corresponding to dominant eigenvalues, and deriving a signal subspace matrix from the calculated eigen vectors;
producing invariance equations dependent on the signal subspace matrix; and
simultaneously determining estimated values for an incidence direction and delays of dominant wave fronts by solving the invariance equations.
Compared with the prior art methods, the invention allows the accuracy to be considerably increased and the computation complexity to be reduced. The invention can be used particularly expediently in the mobile radio field, but is not limited to this. Its advantages are also applicable, for example, to sonar applications and in radar technology.
When the azimuth and delay are being estimated, a data matrix contains a spatial invariance and a time invariance superimposed for each wave front.
The spatial frequency can be converted very easily to the incidence direction of the wave fronts at the measurement station (azimuth), and the associated time frequency can be converted very easily into the associated delay at the measurement configuration.
The invention determines the spatial and time invaria
Brunner Christopher
Haardt Martin
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
Tran Congvan
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