Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1998-08-27
2001-11-13
Hunter, Daniel (Department: 2684)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S452200, C370S329000
Reexamination Certificate
active
06317612
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and a means for the estimation of spatial parameters of transmission channels for connections between radio stations in communication systems. More specifically, the present invention relates to a method for the estimation of spatial parameters of transmission channels between mobile radio telephone networked with spatial subscriber separation, in particular in mobile radiotelephone networks with spatial subscriber separation.
BACKGROUND OF THE INVENTION
In communication systems, for example, mobile radiotelephone networks or wireless subscriber line systems, methods for spatial subscriber separation are known, e.g. from DE 197 13 666. In such SDMA (space division multiple access) systems, several communication connections can be supported in a common channel, whereby the channel in FDMA/TDMA systems (frequency-/time-division multiple access) is described by a frequency band and a time slot. For this purpose, adaptive antennas are used at the transmission side, e.g. in base stations of mobile radiotelephone networks. By means of these adaptive antennas, radiation or beam shaping can be used to form several radiation lobes coordinated with the respective position of the receiving radio station, e.g. mobile stations of mobile radiotelephone networks. The spatial resolution used for the separation of subscriber signals takes place by means of these radiation lobes, which are independent of one another.
The transmission path from a base station to a mobile station is called the downward path, and the transmission path from a mobile station to a base station is called the upward path. The spatial subscriber separation by means of radiation shaping is used to particular advantage in the downward path, since for reasons of cost it is preferable to provide only the base station with an antenna means consisting of several individual sensors.
A spatial subscriber separation results in increased capacity in mobile communication systems, since, in addition to other subscriber separation methods TDMA, FDMA or CDMA, a larger number of communication connections can be supported, for the same required bandwidth.
In addition, in communication systems with SDMA subscriber separation the problem occurs with the selection of a suitable channel for an additional connection due to a connection setup or due to a handover procedure from an adjacent cell. For this purpose, it must be assessed whether and to what extent several subscribers operating in the same channel can be spatially separated by means of radiation shaping, i.e. whether for example their dominant directions of incidence are not located too close to one another.
Both for the assessment of the spatial separability of several subscriber connections and also for the calculation and updating of the radiation shaping coefficients after the channel allocation, estimated values concerning spatial parameters of the transmission channels between the subscribers and the base station are required. One possibility for modeling spatial transmission channels is to postulate the existence of a finite number of discrete propagation paths between the mobile and the base stations. The corresponding spatial parameters are given alongside the number of paths by means of the directions of incidence and complex-valued transmission factors of each path. A method for the estimation of these parameters is known from DE 195 11 752; further algorithms of this type can be found in the relevant literature under the trade names MUSIC, ESPRIT and Unitary ESPRIT.
However, the aforementioned methods lead to a high computing expense and high sensitivity to antenna flaws, and fail completely in spatially diffuse scenarios that can no longer be described by a finite number of discrete propagation paths, but rather only by a continuous spectrum of incidence.
SUMMARY OF THE INVENTION
Therefore, an underlying object of the invention is to provide a method for the accurate and reliable estimation of spatial parameters of transmission channels that can be carried out with a low computing-related expense.
In addition, another object of the present invention is to provide an accurate and reliable means for carrying out the method is indicated.
In the inventive method for the estimation of spatial parameters in communication systems, it is assumed that the subscriber-specific spatial covariance matrices represent the decisive spatial parameters both for the radiation shaping and for the assessment of the spatial separability. If the subscriber-specific directions of incidence and path attenuations are known, these matrices can be calculated; however, the goal of the inventive method is the direct calculation of these matrices from the sampled values measured at the base station in the upward direction, without having to make a detour via the estimation of the direction, which is expensive and subject to model error.
The determination of the spatial covariance matrices for the downward path from the receive data in the upward path is based on the knowledge that in most current mobile radiotelephone systems, given corresponding chronological averaging or mean value formation, these matrices differ only inessentially from one another in the upward and in the downward path. No model assumptions concerning the type of incidence spectra at the base station (e.g. discrete/continuous, many/few directions of incidence) are required.
This type of determination of the relevant spatial parameters forms the foundation for a reliable channel allocation and radiation shaping of a connection that is not susceptible to small estimation errors. Estimation errors that may occur lead only to a continuous degradation in performance (graceful degradation) and not to an abrupt collapse of the radiation shaping. In a mobile radiotelephone environment, this is particularly important for the practical realization.
According to the method, spatial parameters are obtained directly, without an expensive estimation of direction. If a spatial reciprocity in both directions of transmission can be assumed in such communication systems, then, with the aid of the spatial parameters, control signals are produced for the opposite direction of transmission. This is likewise possible if there is a frequency offset between the two directions of transmission, and if the group responses in the two frequency bands differ only slightly. Given greater deviations, a modification of the spatial parameters is required.
For the execution of the inventive method, a reception matrix is preferably formed from an arbitrarily determinable number of scanned values, which are measured at the individual sensors of the base station and which originate from signals radiated by one or more mobile apparatuses.
In a specific embodiment of the method that is particularly advantageous if only a single subscriber is transmitting, the spatial covariance matrix to be estimated is easily determined by multiplication of the receive matrix with its complex conjugate transpose.
If the transmission power in the upward path of this subscriber (or, respectively, an estimated value thereof) is known, it is useful to norm the spatial covariance matrix obtained in this way by means of division by this transmission power.
The estimation of the covariance matrix can advantageously be optimized by means of adaptation of the number of sampled values to the time variance of the channel. When the number increases, the reaction to rapid channel modifications improves, and when it decreases the averaging characteristics improve via the rapid fading, so that brief disturbances of the transmission channel are better compensated.
It is particularly advantageous to form the receive matrices segment by segment for several times, and to superpose the estimated values of several times to form a common covariance matrix. In this way, each determination of the spatial parameters is stabilized by means of already-existing experimental values from the previous determination, and is thus made more reliable.
Corsaro Nick
Hunter Daniel
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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