Multichannel radio transmission system

State of the art

The present invention relates to a multi-channel Radio transmission system in which the frequency channels in the Frequency and spatial multiplexing over an antenna array be sent or received, the individual Antenna elements of the antenna array via a Beam forming network can be controlled so that each Frequency channel in a certain one direction in space oriented antenna characteristic is assignable.

Such multichannel Funkübertragunssystem is eg 195 35 441 A1 known from DE. According to this document is in a point-to-multipoint microwave radio system next to a Multiple access frequency multiplexed a Multiple access used in space division. A Array antenna with multiple antenna elements and sends 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 are space-directionally controlled. The Antenna characteristics of the antenna array can be so variable shapes. The literature in this Connection example of spatial filtering or Beamforming or Spatial Division Multiple Access (SDMA) spoken. The use of both frequency division multiplexing as and spatial multiplexing results in a considerable increase in the Message transmission capacity because frequency channels the same frequency position in different spatial directions can be retransmitted.

is In the known multi-channel radio transmission system each frequency channel in a beam forming network subjected to a complex weighting so that, for each Frequency channel a separate antenna pattern with a predetermined spatial direction arises. This means that each Frequency channel for on so many weighting elements divided, as there are antenna elements. The Weighting elements can also be referred to as a filter, the have a certain amplitude and phase response. The requires radio transmission system according to the prior art in 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 accordingly very high number of antenna elements has the Beamforming network an extremely large number of filters contain. As a consequence, also for the signal division to the individual antenna elements to a very long Combiner or branching network required.

The invention is therefore based on the object, a multichannel radio transmission system of the above specify the type in which the circuit scale compared to the prior art as much as possible reduced.

ADVANTAGES OF THE INVENTION

This object is with the features of claim 1 achieved in that the frequency channels in the frequency multiplex summarized into several groups and each frequency channel Frequency channel group to the same power units at so many filter is divided in beamforming network as there are antenna elements. Here each filter has an all Frequencies of the assigned frequency channel group comprehensive transmission bandwidth on. The Transfer function of each filter is about his Coefficients adjustable such that for each frequency channel of the filter frequency assigned to a channel group individual antenna characteristics can be generated.

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

Advantageous developments of the invention emerge from the Among claims.

To reduce the amount of filtering, it is expedient that Frequency channels should be allocated between the frequency channel groups, that the spacings of the frequency channels within the individual Frequency channel groups are as large as possible.

A more flexible assignment of frequency channels to different space directional antenna characteristics can be achieved in that first means are provided which Frequency channel groups by frequency division at a single frequency channel bundle together, and that second Means are provided which the frequency channel bundle again separated in frequency channel groups they then supply beamforming filtering.

As filter for example, those having finite impulse response (FIR) filter or infinite impulse response such with (IIR) filter may be used. The FIR-filter can be realized by fast convolution.

drawing

With reference to several illustrated in the drawing Embodiments will now be the invention in detail explained. Show it:<sl><li>Figure 1 shows a block diagram of a multichannel 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 transmission system in which a plurality Frequency channel groups are bundled and</li><li>4 more summarized in a frequency bundle Frequency channel groups.</li></sl>

Description of embodiments

The block diagram shown in Figure 1 is this Principle of a multi-channel radio transmission system clarify. Such a multi-channel Communication takes place as between a Central station and a plurality of subscriber stations instead of within a point-to-multipoint microwave radio system. The operation of the shown in Figure 1 multichannel radio transmission system is then for the transmission operation described in detail. A separate Exposition of the reception operation is unnecessary, because he is merely the converse of the transmit mode and at most required Kombinatorschaltungen now for the transmission mode in receive mode, the opposite function namely as have branch circuits.

The radio transmission system shown has a Variety of modems, which separate frequency channels Ckm (k = 1, ..., K and m = 1, ..., M) are assigned. With Frequency channels are meant modulated carrier frequencies. All available frequency channels are Ckm in m Frequency channel groups divided. are In the figure 2 some examples of frequency channel groups FG1, FG2 and FGM shown, in which different Ckm frequency channels that have different bandwidths can, are summarized. The summary of the Frequency channels in frequency channel groups via Combiner K1 to KM. In the allocation of frequency channels Ckm is it to the frequency channel groups FG1 to FGM eighth, that within each frequency channel group Frequency channels Ckm not overlap each other and have sufficiently large frequency spacing. With others Words carried the constitution of each frequency channel group by frequency division of the existing frequency channels.

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

go to each antenna element to an adder ADDn the from the output signals of all to the nth Ante Name element to associated filter forms the sum mn and this sum signal to the antenna element to supplies. As Figure 1 can be seen, therefore forms the adder ADD1 from the output signals of the filter F11 to FM1 and the Adder ADDN from the outputs of all filters to F1N FMN sum signals for the antenna element A1 or AN. Each Fmn filter has a transfer function which the entire Bandwidth fmin to fmax the frequency channel groups FGM includes. 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 undergoes amplitude and phase so that the An antenna elements of the antenna array for each Frequency channel an individual antenna characteristic produce. In this way, it is possible frequency channels in same frequency positions on antenna characteristics with differently oriented directions in space from one another to separate. The multi-channel described So radio transmission system carries out a separation of Frequency channels by both frequency division multiplex and by Space division.

The frequency channel-specific shaping of Transfer function of each filter F mn via a corresponding adjustment of the filter coefficients. The Filter coefficients may be fixed or be adjusted via a processor PR adaptively so that the optimal decoupling of frequency channels with equal Frequency location antenna characteristics with significantly different direction in space are formed. As Criterion for the setting of the filter coefficients for example, could receive signals from the antenna elements An and their mutual locking or decoupling the processor PR are evaluated.

For broadband radio transmission systems with many, very closely juxtaposed frequency channels Ckm within each frequency channel group FGM can Implementation effort for the transfer functions of Filter mn be reduced by the fact that very closely adjacent frequency channels to a plurality of frequency channel groups be split so that a large distance between the individual frequency channels within the Frequency channel groups results. As a result, the need Filter transfer functions not extremely high exhibit slew rates, which filtering requirements and the signal processing times of the filter decreases.

As filter mn possible to use conventional filters with limited Impulse response (FIR) filter for example, as in the textbook D. Achilles: The Fourier transform in the Signal Processing, Second Edition, 1985, Springer-Verlag Chapter 5.hervorgeht, by means of fast convolution are realized. Or it can filter unlimited Impulse response (IIR) filters are used.

In the embodiment shown in Figure 3 a multi-channel radio transmission system are the Frequency channel groups FG1 to FGM by a multiplexer MUX joined to form a frequency channel bundle FB. Figure 4 illustrates how the individual frequency channel groups FG1, FG2 to FGM frequency multiplexed to the frequency channel bundle FB will be running together. While the bandwidth of the Frequency channel groups fmin and fmax by the frequencies is limited, now has the frequency channel bundle FB a according to the number M of the frequency channel groups multiplied bandwidth between the frequencies and F'min F'max. The frequency channel bundle FB is a network for FS Selection of frequency channels supplied. This network FS contains for each newly formed frequency channel group FG'1 to FG'M a mixer Mm (m = 1, ..., M), a LO Lom, of the reference frequency for the Mixer Mm forms, and the mixer downstream Mm Bandpass filter, BPM. With the help of these circuits Frequency channel groups from the frequency channel bundle FB in any frequency positions are implemented so that it new Frequency channel groups FG'1 to FG'M arise. After all this new frequency channel groups FG'1 to FG'M be the Beam forming network BF supplied, in which the already above described processing of frequency channels takes place.