Digital signal transmission system in radio subscriber connection network

A wireless subscriber access network is a - typically nationwide - System of radio cells, each one - in usually possible central - stationary base station contain around which in a radius of z. B. 1 km be distributed more or less homogeneous, the Termi Network nations (NTs) of the radio stations are located. Such radio cell is in the drawing <b>Fig.</b> 1 outlines, in which the base station BS and the mobile subscriber (or its Network Termination) are denoted by NT. Since in a radio system the path loss increases quadratically with the distance, is the radio field strength at the cell edge is substantially smaller than inside the cell; in<b>Fig.</b> 1 is this attenuation with concentric 's illustrates circles around the base station around. at related example by rain, also entfernungsabhän dependent additional losses can at the network terminations available at the cell border receive power additional Lich reduce greatly.

In such a radio system which, in principle, a point-to-Mul tipunkt system represents (the transmitter of the base station can the recipient of many participants reach), the signal transmission from the base station down to the Funkteilneh numbers out in time division multiplex (TDM - Time Division Multiplex) in go a 155-Mbit / s bitstream over and the signal About transmission upstream of the radio subscribers towards the basestation in a TDMA (Time Division Multiple Access) -Zugriffsverfah ren.

In such a system, the Shannon channel capacity not optimally exploited in two ways: All network terminations (NT in <b>Fig.</b> 1) process the full Total bit rate of 155 Mbit / s of the down-time-division multiplex signal, although only a small part of this bitrate usually the respective network termination is determined. The high band width of the time division multiplexed signal leads to a corre accordingly poor signal / noise ratio at the partici performance merindividuellen receiver.

The transmission power in particular the base station (BS in <b>Fig.</b> 1) is from telecommunications law and / or technical limited reasons, resulting in as given parameters RF transmission frequency, total bit rate, antenna gain, S / N Ratio of the maximum cell radius results; at denje Nigen network terminations (NT in <b>Fig.</b> 1) that is closer to the Base station are, the reception performance - and thus the signal / noise ratio - in this case greater than This is necessary for a given bit error rate, so that far "away" transmit power.

The - usual in TDM - uniform distribution of the Ver Bundling standing overall performance over time t and the Fre frequency f illustrates the in <b>image</b> called 2 illustrated. "Water-filling" diagram for a channel having a bandwidth B, a time duration T and a transmission power P_s, Such uniform power distribution, as in the in <b>Fig.</b> 2 hatched planar surface of the diagram expressed comes, is ideal in a radio system, in which all Network Termination the same constant distance from the base have station.

Taking the time T to be constant, so that they in Chart does not have to be shown, and leads to the Distance r from the base station as a third variable, then is obtained for the constant for a bit error rate required Transmission power P in <b>Fig.</b> 3 shaded applied curved Surface, which is obtained by one for each point of the Level the required power P for a predetermined Bitfeh error rate (z. B. 10⁻⁹) Plotting. With negligible Multi patheffekten P is hardly dependent on the frequency. In the <b>Fig.</b> 2 depicted power distribution according to the "water-fil ling "algorithm, ie, the distance r independent power P_s, Is in <b>Fig.</b> 3 again shown hatched. The distance between the curved and the straight Oberflä che is then a measure of the above so primed, at a given distance r "gave away" performance.

To optimize the power distribution in the upward direction (Of the radio subscribers (NT) for base station BS back) can one within a radio cell in each case the received power at measure the individual network terminations NT and as a measure of use the respective pathloss, according to its then the transmission power of the respective Network Termination is adjusted accordingly; such an arrangement is 96/31014 A1, WO.

To optimize the power distribution in a downward direction (From the base station BS to the radio subscribers (NT) towards) Kings NEN with adaptive antennas each network terminations NT a radio cell are driven in succession, the higher profit such antennas towards omnidirectional Antennas with the same transmission power corre bridging accordingly greater distances allowed; a corresponding radio system is set out in DE 195 06 439 A1. Adaptive antennas are However, only at the beginning of development.

One can also for more distant a network terminations hand, and network terminations in the vicinity of the base station other use erseits different modulation methods, For example, 16QAM and QPSK for the inner for the outer Area of ​​the radio cell. The required signal / noise Behaves NIS (S / N) is smaller by 7 dB for QPSK than 16QAM. at 16QAM increase, however, especially in the amplifiers, the requirements for the linearity. Such a method is especially suitable for OFDM.

The object of the invention is now another way to to provide an optimization of power distribution within a radio cell.

The object is specified in claim 1. dissolved. Special embodiments of the invention are the subject of Subclaims.

In this case, in a further embodiment of the invention, a solid Number of frequency sub-bands, each with a fixed predetermined be provided transmission power of the base station, of which each link from the base station to a wireless subscriber out in accordance with its distance from the base station one or more frequency subbands of the each required Transmission power can be allocated.

Another embodiment of the invention may also transmit power of the base station with one or more ganzzahli gen harmonics of a sine wave of a predetermined frequency be modulated and each link from the base station to a mobile subscriber towards pursuant to its removal from the base station a time portion of the required transmission performance are assigned.

With such a power scaling in the frequency and / or Time domain, according to which the respective straight existing Ver connections between the base station and radio subscribers each a frequency band portion or period only with the respectively assigned required base station transmission power is, the invention advantageously enables opti male power distribution within the cell, whereby ent neither the total transmission power of the base station corresponding to can be reduced, or - at constant Total transmission power - the regenerated power to increase of the cell radius can be used.

The modulation of the transmission power with one or more Sine waves that are integer harmonics of a sine are vibration of a predetermined frequency, allowing the specific allocation of phases of large or small Sendelei Stung to individual links between the base station and the more or less remote radio subscribers by Basis of the distance. For sufficiently small modulation frequencies (eg., 10 kHz) is connected to a modulation of the transmission performance only an insignificant broadening of the RF-spotting spectrum connected.

In a breakdown of the total available frequency band in frequency subbands of different base station transmitter performance varies with z. B. 8 frequency sub-bands and a Scaled performance of example 3 dB respectively per Fre frequency sub-band, the transmission power by 24 dB. The benefits of Frequency sub-bands add up geometrically, ie Overall performance is substantially in the frequency Subbands with the highest performance. The Reichweitenerhö increase is correspondingly large.

The signal transmission from the base station down to the Radio subscribers can go again, if necessary, in any frequency Subband for themselves, go in time multiplex in front of him; as Modu tion techniques for the digital signals to be transmitted can be provided uniformly QPSK. Using zueinan the orthogonal carriers for the individual frequency-Teilbän avoids the otherwise in FDMA (Frequency Division Multiple Access) unavoidable filter losses.

Other features of the invention will become apparent from the fol ersicht lowing more detailed explanation of the drawings Lich. show case

<b>Fig.</b> 1 occur the typical picture of a radio cell with it the losses and

<b>Fig.</b> 2, the uniform distribution of data available Total transmission power with respect to time and frequency;

<b>Fig.</b> 3 illustrates the course of the constant for a Bitfeh error rate required transmission power depending on the Distance of the mobile subscriber from the sending base sta- tion.

<b>Fig.</b> 4 shows an allocation of the total transmit power in Fre frequency sub-bands of different transmission power, and

<b>Fig.</b> 5 illustrates an allocation of the total transmit power in time segments of different transmission power.

The painting <b>Fig.</b> 1, <b>Fig.</b> 2 and <b>Fig.</b> 3 were already above explained, so that further explanations on this Place unnecessary.

In <b>Fig.</b> 4 schematically an embodiment of an In division of the total transmission power of the base station (BS in <b>Fig.</b> 1) a radio cell (<b>Fig.</b> 1) in frequency sub-bands FK0, FK1. , , naturism different transmit power shown by where the digital signal transmission from the base station to the located in the radio cell of radio subscribers (NT in <b>Fig.</b> 1) towards each link from the base station to a radio Participants in the back in accordance with its distance from A base station or a plurality of frequency subbands of each be assigned required transmission power (s) so that the for located at a greater distance from the base station Radio subscriber specific digital signals in frequency Teilbän countries with a correspondingly higher transmission power of the base station are transmitted and the for a small distance away from Base station located radio subscriber specific Digitalsi signals in frequency sub-bands with correspondingly lower Transmission power.

The from the base station BS (in <b>Fig.</b> 1) with the individual emitted frequency-subband individual transmission powers Signals form an OFDM (Orthogonal Frequency Division Multi plex) signal with a few carriers, the actual Much is multiple access time division multiplexed (TDM) forward. By Using only a few (eg., 4 to 16) carrier remains on wall, however small for the OFDM. On the other hand, the Symbol duration so greatly extended that an otherwise in TDM / TDMA because of so-called. Multipathverzerrungen required elaborate can be dispensed with equalizer.

In OFDM systems, the crest factor is very unfavorable in itself, what after especially in highly nonlinear amplifiers makes pieces noticeable. ver The breakdown of the total fügbaren frequency band in frequency subbands unterschiedli cher base station transmit power add up the benefits the frequency sub-bands, however, geometrically, that the total power is substantially of the frequency sub-band with the greatest performance determined. The crest factor is therefore much cheaper than OFDM with constant Trägerampli amplitudes.

The breakdown of the total available frequency band in Frequency sub-bands of different base station transmission performance also allows an improvement in the frequency re-use. The co-channel interference from frequency sub-bands with smaller Transmission power is innately very low. The co-channel disturbance of the frequency sub-bands with high power are indeed as great as in the previous systems, limited Now, however, smaller on a substantial Frequency Ranges rich. In principle, the transmission system keeps the Störlei Stung as small as possible.

It can not even frequency sub-bands determined with each predetermined transmission power of the base station, but with kon be provided continuously controllable transmission power. A Such a configuration of the transmission system allows adaptively to each given in the radio cell Ratios (z. B. the rain-induced increase of pathloss during the existence of a connection, Number of active Radio subscriber).

The for a Network Termination (NT in <b>Fig.</b> 1) specific Different signals can also on frequency subbands Power are divided. The received bits are then each by frequency sub-band more or less reliable, with using a corresponding encoding method the less reliable bits are correct effectively.

The frequency band FK0 with the highest power can be used as Emergency channel for all connections from the base station (BS in <b>Fig.</b> 1) to the network terminations of the mobile subscriber (NT in <b>Fig.</b> 1) may be used, via the then at - for example, by star. ken rain conditional - greatly increased pathloss at least telephony traffic is still possible.

In <b>Fig.</b> 5 schematically shows a breakdown of total Sendelei Stung to the base station (BS in <b>Fig.</b> 1) of a radio cell (<b>Fig.</b> 1) in periods ZK0, ZK1,. , , CCC different transmission performance illustrates, one of which for digital signal transmission from the base station to the located in the radio cell Radio subscribers (NT in <b>Fig.</b> 1) out of each compound of the Base station to a wireless subscriber out in accordance with whose distance from the base station one or more time sections of the respective required transmit power (s) zugeord be net, so that the for of a greater distance Base station located radio subscriber specific Digitalsi signals in time periods with a correspondingly higher Sendelei Stung to the base station are transmitted and to dress for in dis- tance from the base station located Funkteilneh mer certain digital signals in periods of corre accordingly lower transmit power. In the<b>Fig.</b> 5 outlined Power modulation results from the superimposition the first and third harmonics of a (z. B. 10-kHz) -Si wave oscillation. In the receivers of radio subscriber can the power modulation by means of an opposite Modulation be rescinded.

The for a Network Termination (NT in <b>Fig.</b> 1) specific Signals on different time periods Power are divided. The received bits are then each more or less on time slot reliably, which with Aid of an appropriate coding the less reliable bits are correct effectively.

The period Z0 with the highest power can be used as Emergency channel for all connections from the base station (BS in <b>Fig.</b> 1) to the network terminations of the mobile subscriber (NT in <b>Fig.</b> 1) may be used, via the then at - for example, by star. ken rain conditional - greatly increased pathloss at least telephony traffic is still possible.

It should be particularly noted that a power scaling in the frequency range as above with reference to <b>Fig.</b> 4 explained was charged with a power scaling in time domain, as above on the basis of <b>Fig.</b> 5 was explained, also be combined may, without this still needs further explanation.