Multichannel radio transmission system

State of the art

The present invention relates to a multi-channel radio transmission system in which the frequency channels are transmitted or received in the frequency and spatial multiplexing over an antenna array, wherein the individual antenna elements of the antenna array are a beamforming network so controlled that each frequency channel oriented in a particular direction in space antenna characteristic assignable is.

Such multichannel Funkübertragunssystem as is known from DE 195 35 441 A1. According to this publication, a multiple access is used in the spatial multiplexing in a point-to-multipoint radio relay system in addition to a multiple access frequency multiplexed. An array antenna with several antenna elements transmits and receives the bezgl. The frequency and space-multiplexed signals. By suitable mutual propagation delay of the individual antenna elements feeding signals the emission or reception of signals can be space-directionally controlled. The antenna characteristic of the antenna array can be so variable shapes. In the literature, for example by filtering or spatial beamforming or Spatial Division Multiple-Access (SDMA) is used in this context. The use of both frequency division multiplex and space division leads to a considerable increase in the communication capacity because frequency channels of the same frequency position in different spatial directions can be repeatedly transmitted.

In the known multi-channel radio communication system each frequency channel is subjected to a beam forming network of a complex weighting, so that creates a separate antenna pattern with a predetermined spatial direction for each frequency channel. Here each frequency channel is divided on to as many weighting elements as there are antenna elements. The weighting elements can also be referred to as a filter having a certain amplitude and phase response. The radio transmission system according to the prior art required at a number of K frequency channels and a number of N antenna elements K * N filter. In a large number of frequency channels (eg 150) and a correspondingly very high number of antenna elements, the beamforming network must contain an extremely large number of filters. As a result, a very extensive combiner or branching network is also required for the signal distribution to the individual antenna elements.

Another multi-channel radio communication system is described in the document "Channel individual adaptive beam forming for Mobile Satellite Communications", Gebauer et al, IEEE, 1 February 1995.

The invention is therefore based on the object to provide a multi-channel radio transmission system of the type mentioned, in which the circuit scale compared to the prior art as far as possible reduced.

ADVANTAGES OF THE INVENTION

The object is achieved with the features of claim 1, characterized in that the frequency channels in frequency division multiplexing summarized in several frequency channel groups and each frequency channel group is divided into equal performance shares to as many filters in the beam forming network as there are antenna elements. In this case, each filter to all the frequencies of its assigned frequency channel group comprising transmission bandwidth. The transfer function of each filter can be adjusted so that an individual antenna characteristic can be generated for each frequency channel of the filter assigned frequency channel group on its coefficients.

By combining a plurality of frequency channels in frequency channel groups reduces the number of filters in the beam forming network over the prior art, in which each frequency channel as many filters are assigned as there are antenna elements. The reduction of the number of the filter also leads to a reduction of the filter signals processing circuit means.

In order to reduce filtering requirements, it is advantageous so to divide the frequency channels to the frequency channel groups in that the spacings of the frequency channels are as large as possible within the individual frequency channel groups.

Advantageous developments of the invention will become apparent from the dependent claims.

A more flexible allocation of frequency channels to different spatial directional antenna characteristics can be achieved in that first means are provided which combine the frequency channel groups by frequency division multiplexing into a single frequency channel bundle, and in that second means are present which separate the frequency channel bundle back into frequency channel groups, in order then the supply beamforming filtering.

As a filter, for example, such a finite impulse response (FIR) filter or infinite impulse such response (IIR) filter may be used. The FIR filter can be implemented using fast convolution.

drawing

With reference to several illustrated in the drawings, exemplary embodiments, the invention is explained in detail below. Show it:<ul><li>Figure 1 is a block diagram of a multi-channel radio transmission system,</li><li>Figure 2 is a classification of frequency channels in frequency channel groups,</li><li>Figure 3 shows a block diagram of a multichannel radio communication system, wherein a plurality of frequency channel groups are bundled and</li><li>4 more summarized in a frequency bundle frequency channel groups.</li></ul>

Description of embodiments

The block diagram shown in Figure 1 is intended to illustrate the principle of a multi-channel radio transmission system. Such a multi-channel message transmission takes place, for example, between a central station and a plurality of subscriber stations place within a point-to-multipoint microwave radio system. The operation of the multi-channel radio transmission system shown in Figure 1 will be described in more detail for the transmit mode. A separate exposition of the reception operation is unnecessary because it is the inverse of the transmit mode and only if necessary for the transmission mode required Kombinatorschaltungen now have namely as branch circuits the opposite function in the receive mode.

The radio transmission system illustrated comprises a plurality of modems, where separate frequency channels Ckm (k = 1, ..., K and m = 1, ..., M) are assigned. With frequency channels modulated carrier frequencies are meant. All available frequency channels are divided into Ckm m frequency channel groups. 2 shows examples of some frequency channel groups FG1, FG2 and FGM are shown, in which different frequency channels Ckm, which may also have different bandwidths, combined. The summary of the frequency channels in frequency channel groups via combiner K1 to KM. In the allocation of frequency channels Ckm on the frequency channel groups FG1 to FGM is to ensure that within each frequency channel group the frequency channels Ckm not mutually overlap and have sufficiently large frequency spacing. In other words, the structure of each frequency channel group is carried out by frequency-division multiplexing of available frequency channels.

The total M frequency channel groups FG1 to FGM are supplied to a beam forming network BF. In the beamforming network BF are several filters F mn (m = 1, ..., M and n = 1, ..., N). The division of the filter F mn is such that for each of the m = 1, ..., M frequency channel groups FGM many filter F mn are present, such as an array antenna the antenna elements An (n = 1, ..., N). Each frequency channel group FGM is divided between the N filter its associated filter group to the same power components. For example, the frequency channel group is divided FG1 to the filter F11 to F1N and the frequency channel group FGM on the filter FM1 to FMN.

there is an adder ADDn of all to the nth element Ante call to belonging Filter mn constituting the sum of the output signals and this sum signal to the antenna element to at each antenna element to. As the figure 1 can be seen, therefore forms the adder ADD1 from the output signals of the filter F11 to FM1 and adder ADDN from the outputs of all filters F1N to FMN sum signals for the antenna element A1 or AN. Each filter has a transfer function F mn which fmin the entire range comprises to fmax the frequency channel groups FGM. The transfer function of each filter F mn has such amplitude and phase response that each frequency channel Ckm within the filter each assigned frequency channel group an individual weighting amplitude and phase learns so that the antenna elements generate a custom antenna pattern on the array antenna for each frequency channel , In this way it is possible to separate frequency channels in the same frequency positions on antenna characteristics with differently oriented directions in space from one another. Thus, the multi-channel wireless transmission system described performs a separation of frequency channels both by frequency division multiplexing and through spatial multiplexing.

The frequency channel-specific shaping of the transfer function of each filter F mn via a corresponding adjustment of the filter coefficients. The filter coefficients can be fixed or can be adjusted via a processor PR adaptively so as to define the optimal decoupling of frequency channels with the same frequency position antenna characteristics with significantly unterschiedlicher.Raumrichtung. The criterion for the setting of the filter coefficients, for example, received signals from the antenna elements to and their mutual locking or decoupling the processor PR may be evaluated.

For broadband radio transmission systems with very many, very closely spaced frequency channels Ckm within each frequency channel group FGM the implementation effort for the transfer functions of the filters F mn can be reduced by the fact that very closely spaced frequency channels are divided into a plurality of frequency channel groups so that the largest possible distance between the individual frequency channels within the frequency channel groups results. As a result, the filter transfer functions need not have extremely high slew rates, which reduces the filtering requirements and the signal transit times of the filter.

As filter mn possible to use conventional filters with finite impulse response (FIR) filter for example, as in the textbook by D. Achilles: 5.hervorgeht The Fourier transform in signal processing, second edition, 1985, Springer-Verlag chapter, by means of fast convolution are realized. Or it can filter with infinite impulse response (IIR) filters are used.

In the embodiment, a multi-channel radio transmission system shown in Figure 3, the frequency channel groups to be assembled FGM FG1 by a multiplexer MUX to a frequency channel bundle FB. Figure 4 illustrates how the single frequency channel groups FG1, FG2 are to FGM frequency multiplexed to the frequency channel bundle FB strung together. While the bandwidth of the frequency channel groups fmin by the frequencies and is fmax, then the frequency channel bundle FB has a correspondence with the number M of the frequency channel groups multiplied bandwidth between the frequencies and F'min F'max. The frequency channel bundle FB is supplied to a network FS for the selection of frequency channels. This network includes FS for each newly formed frequency channel group FG'1 to FG'M a mixer Mm (m = 1, ..., M), a local oscillator Lom, which forms the reference frequency for the mixer Mm, and the mixer Mm downstream bandpass filter, BPM. Using these circuits frequency channel groups can be converted from the frequency channel bundle FB in any frequency layers so that it new frequency channel groups are formed to FG'1 FG'M. Finally, this new frequency channel groups FG'1 to FG'M supplied to the beam forming network BF, locations where the further processing of the frequency channels already described above.