Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Reexamination Certificate
1999-01-28
2001-11-13
Hunter, Daniel (Department: 2684)
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
C455S067700, C455S063300, C455S067700
Reexamination Certificate
active
06317586
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention lies in the telecommunications field. More specifically, the invention relates to a method and a base station for data transmission in a wireless communications system, wherein a base station has an associated antenna device with a plurality of antenna elements, so that spatial resolution in a beam formation can be carried out.
In wireless (radio) communications systems, messages (for example voice, video information or other data) are transmitted with the aid of electromagnetic waves via a radio interface between a transmitting and a receiving station (base station and mobile, respectively). The electromagnetic waves are thereby transmitted at carrier frequencies which are in the frequency band laid out for the respective system. In the case of GSM (Global System for Mobile Communication), the carrier frequencies are in the region of 900, 1800 or 1900 MHz. For future mobile radio networks using CDMA or TD/CDMA transmission methods via the radio interface, for example the UMTS (Universal Mobile Telecommunication System) or other 3rd generation systems, frequencies in the frequency band of about 2000 MHz are envisaged.
During their propagation in a propagation medium, signals are subject to interference from noise. As a result of diffraction and reflections, signal components flow over different propagation paths and are superimposed in the receiver, where they lead to mutual interference effects. Furthermore, if there is more than one signal source, the signals from these sources are superimposed. Frequency division multiplex (FDMA—frequency division multiple access), time division multiplex (TDMA—time division multiple access) or a method which is known as code division multiplex (CDMA—code division multiple access) are used to distinguish between the signal sources, and thus to evaluate the signals.
The GSM mobile radio system which is currently in existence is a wireless communications system using a TDMA component for subscriber separation (Time Division Multiple Access). Wanted information for the subscriber links is transmitted in time slots on the basis of a frame structure. Transmission takes place in blocks.
German patent application DE 195 49 148 discloses a mobile communications system which uses TDMA/CDMA subscriber separation (time division and code division multiple access) and uses a JD method (joint detection) at the receiving end in order to improve the detection of the transmitted wanted information on the basis of knowledge of the spread codes of a plurality of subscribers. Information from a plurality of wanted data links is transmitted simultaneously in one frequency channel (TCH traffic channel), and these links can be distinguished by their spread code.
German patent application DE 197 12 549 discloses the use of intelligent antennas (smart antennas) in order to increase the transmission capacity in the uplink (mobile to base station) direction. Various methods for space signal separation for the uplink (reverse—mobile to base station) and downlink (forward—base station to mobile) directions are known from Paulraj and Papadias, “Space-Time Processing For Wireless Communications,” IEEE Signal Processing Magazine, November 1997, pages 49-83.
For the downlink direction, that is to say from the base station to the mobile, particular difficulties occur since the beam forming must be carried out before the transmitted signals have been influenced by the radio channel. Beam forming in the downlink direction is known from Schmalenberger and Blanz, “A Comparison Of Two Different Algorithms For Multi Antenna C/I Balancing,” Proc. 2nd European Personal Mobile Communications Conference (EPMCC), Bonn, Germany, September 1997, pages 483-90, wherein a direct propagation path (line of sight) is assumed to exist between the radio stations involved, together with iterative calculation of beam forming vectors. Whenever the radio stations involved change, for example a link to or from a mobile station is set up or cleared, the entire calculation must be repeated.
2. Summary of the Invention
It is accordingly an object of the invention to provide an improved method and an improved base station for data transmission, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and in which the computation complexity for beam forming is considerably reduced.
With the foregoing and other objects in view there is provided, in accordance with the invention, a signal transmission method in a wireless communications system of the type having a base station with an antenna device provided with and a plurality of antenna elements, and having a plurality of wireless stations, which method comprises:
defining space covariance matrices for a k
th
link from the base station to a wireless station and for a sum of further wireless stations;
defining a beam forming vector w
(k)
in accordance with the condition
&LeftBracketingBar;
w
(
k
)
R
xx
(
k
)
w
(
k
)
w
(
k
)
R
I
(
k
)
w
(
k
)
&RightBracketingBar;
max
having a greatest intrinsic value &lgr;
max
(k)
in accordance with
R
xx
(k)
w
(k)
=R
I
(k)
w
(k)
&lgr;
max
(k)
for the link, where R
xx
and R
I
are the covariance matrices;
weighting transmission signals for the link with the beam forming vector; and
transmitting the transmission signals with the antenna elements.
In other words, the novel method for data transmission is used in a radio communications system with a base station and further radio stations. The further radio stations may be mobile stations, for example in a mobile wireless network, or fixed stations, for example in so-called subscriber access networks for wire-free subscriber access.
In a first step, space covariance matrices are defined for a k
th
link from the base station to a wireless station and for a sum of signals of further radio stations, that is to say, in the latter case, the sum of the interference for the link k.
In a second step, a beam forming vector w
(k)
is calculated for the link in such a manner that the relationship
&LeftBracketingBar;
w
(
k
)
R
xx
(
k
)
w
(
k
)
w
(
k
)
R
I
(
k
)
w
(
k
)
&RightBracketingBar;
is maximized, wherein the generalized intrinsic vector w
(k)
is defined for the greatest generalized intrinsic value &lgr;
max
(k)
by using R
xx
(k)
w
(k)
=R
I
(k)
w
(k)
&lgr;
max
(k)
.
Transmission signals for the link are then weighted with the beam forming vector, and are supplied to the antenna elements for transmission.
This method is used to maximize the power available for the link k in comparison with the interference power, in which case it is possible to dispense with iterations, since the use of the secondary condition R
xx
(k)
w
(k)
=R
I
(k)
w
(k)
&lgr;
max
(k)
for the calculation leads to the desired result in one step. The computation complexity is thus drastically reduced. Particularly in scenarios having a large number of subscribers and severely fluctuating channel conditions, beam forming in the downlink direction is considerably more economic according to the invention.
In accordance with an added feature of the invention, a transmission power is defined for the transmission signals for the link from the beam forming vector in accordance with P
k
=w
(k)H
w
(k)
, where H is a complex-conjugate vector and P
k
is the transmission power, and raising the transmission power to a predetermined minimum signal-to-noise ratio in the radio station. The transmission power is also raised to a predetermined minimum signal-to-noise ratio in the wireless station. The instantaneous signal-to-noise ratio is measured in the receiving wireless station and is reported to the base station, so that the latter can use an appropriate transmission power setting to guarantee the minimum signal-to-noise ratio.
In accordance with an additional feature of the invention, data are transmitted in an uplink direction and a downlink direction in a given frequency band, and at least one of the space covariance matric
Gantt Alan
Greenberg Laurence A.
Hunter Daniel
Lerner Herbert L.
Siemens Aktiengesellschaft
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