AU699049B2

AU699049B2 - Station for SDMA mobile radio system

Info

Publication number: AU699049B2
Application number: AU27117/95A
Authority: AU
Inventors: Rupert Rheinschmitt; Michael Tangemann; Bernd X. Weis
Original assignee: Alcatel NV
Current assignee: Alcatel Lucent NV
Priority date: 1994-08-05
Filing date: 1995-07-21
Publication date: 1998-11-19
Anticipated expiration: 2015-07-21
Also published as: EP0696112A3; NO953064L; DE59510960D1; NO953064D0; EP0696112A2; FI953724A0; DE4427755A1; AU2711795A; FI953724A; ATE279817T1; EP0696112B1

Abstract

The static or mobile radio station (BTS) has a number of complex weighted transmission signals provided via respective transmission paths with corresponding HF transmission stages (TX), connected to respective antenna elements of an antenna array. A modulation stage (MOD) and an associated control (CTR) are inserted in the transmission path for complex weighting of the transmitted signals, via respective phase shifts and/or amplitude weightings.

Description

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ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: *999 "STATION FOR SDMA MOBILE RADIO SYSTEM" The following statement is a full description of this invention, including the best methtod-,of performing it known to us:- -i .7J

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11~ i i This invention relates to a radio station for an SDMA mobile radio system which, for the generation of N complex-weighted transmission signals, has N transmitting branches with N RF transmitter stages which feed N aerial elements of an aerial array with the N complex-weighted transmission signals, so that the radio station radiates at least one directional radio signal.

An SDMA mobile radio system with radio stations for SDMA radio transmission (SDMA: Space Division Multiple Access) is known from the specification of Australian Application No. 31454/93. The SDMA radio transmission, with which multiple 10 access to a frequency channel becomes possible because of beam formation, is there carried out by the following means: In order to transmit beamed radio signals on a single frequency, the radio i. stations of the SDMA mobile radio system, at least the fixed radio stations, contain N 10 transmitting branches with N RF transmitter stages which feed N complex- .5 weighted transmission signals to the N aerial elements of an aerial array. These are generated from modulated baseband signals by a so-called "Spatial Multiplexer" which is connected between the RF transmitter stages and the modulators and which varies the amplitude and phase of each modulated baseband signal as 9" predetermined by a so-called "SDMA Controller". This controls the "Spatial Multiplexer" 20 via a so-called "SDMA Processor" so that the radiation beams follow the mobile radio stations.

The receiving section of the fixed radio station contains N receiving branches for receiving N complex-weighted reception signals, which correspond to the superposit on of radio signals sent out by the mobile radio stations on one carrier frequency f om different directions. Additionally, the fixed radio station contains a socalled "Spatial Demultiplexer" which is connected before the demodulators and which, from the N reception signals by complex weighting, forms the baseband signals to be demodulated.

Thus the known SDMA mobile radio system consists of radio stations which require costly signal processing stages, the so-called "Spatial Multiplexers" and "Spatial Demultiplexers", for the purpose of SDMA radio transmission.

An object of the invention is to provide radio stations of simpler construction for 0 C IE 1 1 1 i i 11 1 0 itl i 7.i i~~A' I I *e* ae a a a a a a.

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o io eo SDMA transmission in an SDMA mobile radio system.

According to the invention, there is provided a radio station for an SDMA mobile radio system which, for the generation of N complex-weighted transmission signals, has N transmitting branches with N RF transmitter stages which feed N aerial elements of an aerial array with the N complex-weighted transmission signals, so that the radio station radiates at least one directional radio signal, wherein a modulator stage in which the modulation and at least a part of the complex weighting of the transmission signals is carried out, either in the baseband or at an intermediate frequency.

In order that the invention may be readily carried into effect, embodiments thereof will now be described in relation to the accompanying drawings, in which: Figure 1 shows schematically the transmitting section of a (mobile or fixed) radio station which radiates a directional radio signal; 15 Figure 2 shows the time variation of phase shifts and amplitude weightings for a TDMA radio signal to be transmitted and for its direction of radiation; Figure 3 shows the block diagram of a fixed radio station which radiates at least two directional radio signals; Figure 4 shows an SDMA mobile radio system with one fixed radio station 20 shown as a block diagram; Figure 5 shows schematically a module for complex weighting of I/Qmodulated signals and Figure 6 shows the block diagram of a fixed radio station with such arrangements for complex weighting in the transmitting branches.

Figure 1 shows the transmitter section of a radio 'tation BTS according to the invention, which radiates complex-weighted transmission signals at a frequency fc, via N aerial elements Al, A2, to AN of an aerial array. By means of the complex weighting, the transmission signals are superposed to form a radio signal S which propagates in some direction q from the aerial array, which here is a linear group aerial. The design version shown in Figure 1 is restricted to transmitting a radio signal, in order to describe a first example which applies equally to a mobile as well as to a fixed radio station and which demonstrates the invention very clearly. It is i i I i r l i, :i c: i iiY1~ I 1 Li+ 4* 4 4r 9 9.

based on a fixed radio station BTS which radiates the radio signal S as a TDMA signal in a direction q which changes from time slot to time slot. Thus the fixed radio station BTS shown in Figure 1 is, for instance, suitable for TDMA radio transmission according to the GSM standard (GSM: Global System for Mobile Communications).

The radio station BTS according to Figure 1 contains a control circuit CTR and a modulator stage MOD connected to it for generating N complex-weighted transmission signals f, f2 to f, by means of digital phase modulation and N-fold complex weighting of an input signal Furthermore, the radio station BTS contains 10 N RF transmitter stages TX which are connected after the modulator stage MOD and S each of which converts one of the N transmission signals to the carrier frequency fc 935 MHZ and amplifies it for feeding into the N aerial elements. In order to control S the N-fold complex weighting, the control circuit CTR presets N phase shifts f fN S and N amplitude weights a, aN for the modulator stage MOD via a data bus, 15 with the clock timing T of the digital phase modulation. These phase shifts and S amplitude weights are the complex weightings for the N transmission signals and determine the directional pattern of the group aerial. The calculation of the complex S weights is not described here in detail. It can, for example, be achieved as described in the aforementioned Australian Patent Application No. 31454/93.

The modulation stage MOD shown here contains a digital signal processor DSP and a fixed-value store I/Q-ROM by means of which the inphase and quadrature components of the N transmission signals are produced, as follows: From the sample values of the signal through filtering and integration, the signal processor DSP derives a modulating signal j[s] for a GMSK modulation (GMSK: Gaussian Minimum Shift Keying).

The modulating signal, therefore, represents the time variation of a phase angle For each of the N transmitter stages, through binary addition of the phase angle j[s] and one cf the N phase shifts f, to fN, the digital signal processor continuously calculates a sum as'nput value (address) for the fixed-value store I/Q- ROM The latter contains values for sine and cosine functions for the generation of inphase and quadrature components of the N transmission signals. Through bitshifting of the output values of the fixed-value store, the digital signal processor i i 1 1 I i r n c L "i-1" I :I i produces an amplitude change for each of the N transmission signals corresponding to the appropriate preset amplitude weight. Thus for, say, the first of the N transmitting branches the complex-weighted transmission signal f, is generated with inphase component a, sin[j fl] and with quadrature component a 1 cos[j fj], where a, is the amount and f, is the phase of the complex weight.

For each of the N transmitting branches, the control circuit presets a complex weight so that, after transmission by the N aerial elements Al to AN, the N transmission signals interfere and are superposed to form the radio signal S with carrier frequency fc and direction q. The radiation pattern of the aerial arrangement is determined by the complex weighting with amplitude weights a, to aN and the phase shifts fl to fN.

In this example the signal and the radio signal S which it modulates, are both TDMA signals as shown in Figure 2. For each time slot T1, T2, T3, of the TDMA frame, the control circuit CTR presets N complex weights, so that the direction q of the radio signal can change from time slot to time slot, depending on the current Ilcations of the mobile radio stations which successively access these time slots.

The principle of SDMA signal pre-processing for the transmitting direction, as described with the aid of Figure 1 and 2, is readily transferred by the expert to the 20 receiving direction application.

In the following, the design example of a fixed radio station is described which, S! in accordance with this principle, transmits at least two radio signals on one carrier Sfrequency in different directions, which corresponds to an SDMA radio transmission with multiple use of frequencies.

Figure 3 shows schematically the transmitter of a fixed radio station BTSm for an SDMA mobile radio system. Similarly to that of Figure 1, this radio station contains a modulator stage MOD, a control circuit CTR controlling it and N RF transmitter stages with a group aerial following them. Furthermore, this radio station BTSm contains a time-division multiplex stage MUX which is connected before the modulator stage and applies two input signals S[t] and to the modulator stage MOD for modulation and complex weighting. For each of N transmitting branches 1 to N, the modulator stage generates an /Q signal in accordance with the previously described i I =I

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*pS 6 principle. In this example, for each I/Q component a multiplex signal is generated, which corresponds to the interleaving of two component signals f j and f' which the modulator stage produces by means of the two signals S and In each transmitting branch, a series connection of a demultiplexer DEMUX, two digital/analogue converters and an adder form, from each multiplex signal, an analogue transmission signal which corresponds to the sum of the two analogue component signals. For example, for the first transmitting branch 1 the circuit according to Figure 3 produces a transmission signal f, f' with the inphase component: a 1 cos[j fl] cos[j' f 1

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and with the quadrature component: i sin[j f] a sin[j' fi'].

S. The first component signal which is modulated by the signal S[t] is complex S weighted with the amplitude weight a, and the phase shift fl. The second component 1 5 signal which is modulated by the signal is complex weighted with the amplitude weight and the phase shift For each of the transmitting branches 1 to N the control circuit CTR presets the S complex weights in such a way that the RF transmitter stages TX send out, via the group aerial and at the carrier frequency transmission signals which are composed of 2 N complex-weighted component signals. These 2 N are superposed in such a way that the group aerial radiates two radio signals S and S' in different directions q and Since here the two radio signals are TDMA signals, the control circuit CTR presets the complex weights afresh for each TDMA time slot. The directions of radiation q and q' of the radio signals are pointed by beam steering at the moving terminals (here mobile radio stations), by having the control circuit recalculate the complex weights, as a result of reception signal evaluations, at intervals of a TDMA frdme duration.

Figure 4 shows schematically the construction of the transmitter and receiver of the fixed radio station BTSm, for use in an SDMA mobile radio system MRS. The fixed radio station BTSm is in radio communication with two mobile radio stations MS and MS', via the traffic channels TCH. For this purpose, the fixed radio station BTSm transmits, at a carrier frequency fc= 935 MHZ, a radisignal S in the direction of )r r~ I I~ -s one mobile radio station, and a radio signal S' in the direction of the other. The mobile radio stations MS and MS' in turn, at a carrier frequency of 980 MHZ, each transmit a radio signal S or S' to the fixed radio station BTSm. Furthermore, over a service channel BCCH the fixed radio station transmits nondirectional radio signals, which the mobile radio stations listen to before a link is established. A mobile radio station MSO is shown in Figure 4 whose receivers monitor this service channel BCCH.

If the mobile radio station has, say, a circular group aerial, then a symmetrical complex weighting is preset which produces a reception radiation pattern with omnidirectional characteristics.

The construction and method of operation of the fixed radio station BTSm is described in the following: SIn the transmitting section input signals S, S' and the control signals are 'I applied, via a time-division multiplex stage, to a modulator stage which, in accordance with the previously described principle, generates complex-weighted transmission signals for the transmitting branches which feed N aerial elements Al to AN of a group aerial. For this, each transmitting branch also contains a demultiplexer i stage (not shown) followed by a D/A converter, and an adder, an RF transmitter stage S TX and a diplexer DIP.

.20 For reception, the diplexers DIP are followed by a receiving section which contains N receiver stages RX, a demodulator stage DEM and a demultiplexer.

The receiving section operates according to the same principle as the transmitting section, i.e. the complex weighti to determine the aerial pattern now takes place in the demodulator stage DEM. For this purpose a control circuit CTR also controls the demodulator stage, by presetting the complex weights (fl, fN), (al, aN) in order to "unweight" the reception signals. The calculation of the complex weights is carried out by the control circuit CTR by means of an evaluation of the reception signals as follows: while the demodulator stage DEM detects the training sequence in the N receiving branches in the respective reception signals, the control circuit CTR compares amplitude levels and phase values of the N reception signals in order to determine the complex weights and thus the receiving direction.

Figure 5 shows a module CWS which complex weights angle-modulated Pi 7i 8 signals f and which are each separated into an inphase component cos[j] or cos[j'], and a quadrature component sin[j] or sin[i']. The simply constructed module CWS can be used in a transmitting branch or in a receiving branch, by inserting it after an I/Q modulator or inserting it before an 1/Q demodulator. The module is especially suitable when transmission signals or reception signals are to be weighted at the intermediate frequency, without modulation or demodulation.

Figure 5 shows schematically a circuit for complex weighting of the transmission signal in one of the transmitting branches of an SDMA radio station. The circuit contains the module CWS which complex weights the quadrature components of the two angle-modulated signals f and f that are being transmitted. The module i CWS is followed by two adders, one of which adds the complex-weighted inphase components, and the other adds the quadrature components. The adders are followed by an RF transmitter stage which applies the superposed transmission signals 1 5 to an element of a group aerial. For each one of the signals, the module CWS has an I/Q phase shifting stage PS and an I/Q amplitude weighting stage AS to produce the complex weighting. In the following, the method of operation of the module CWS is described, using the example of the complex weighting of the signal f: The quadrature components cos[j] and sin[j] are altered by a phase shift f in :20 the phase shift stage PS. For this purpose, it contains function generators to form harmonic functions sin[f], cos[f] and -sin[f], mixers to multiply the quadrature components with the harmonic functions, and adders to sum the different mixing products, in accordance with the following addition theorems: 1) cos[i f] cos[j] cos[f] sin[j] (-sin[f]) 2) sin[j f] sin[j] cos[f] cos[j] sin[f] Thus the I/Q phase shift stage PS generates the phase-shifted quadrature components cos[j f] and sin[j These are then weighted in the amplitude weighting stage AS with the quantity a and, as an output signal of the module CWS, each one is applied to one of the adders. At the output of one of the adders, the inphase component I of the transmission signal appears, which corresponds to the sum of the two complex-weighted inphase components: I a cos[i f] a' cosi' f] 4 ai~- A .f Si

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At the output of the other adder, the quadrature component Q of the transmission signal appears: Q a sin[j f] a' sin[i' f] The module CWS shown in Figure 5 is also suitable for the complex weighting of angle-modulated reception signals, in order to pre-process these for demodulation.

The term 'angle-modulated' is here understood to mean all methods of modulation in which the signal content is determined by a phase value, a phase difference or a phase shift, such as, for example, PSK, GMSK or FM. With the circuit described 10 according to Figure 5, an SDMA radio station can be constructed very easily. This is described now, using the example of the transmitting section of a fixed radio station S BTSx, in accordance with Figure 6.

SThe fixed radio station BTSx contains two I/Q modulators IQM, which each generate a GMSK modulated signal f (or from an input signal S (or In addition, 1 5 the fixed radio station BTSx contains N transmitting branches, each having a module CWS which complex weights the signals f and and each having an RF transmitter stage TX which feeds one aerial element of a group aerial.

In accordance with the already described principle, the modules CWS generate the complex-weighted transmission signals for the N transmitting branches from the 20 modulated signals f and f. For this, a control circuit CTR controls the modules CWS by presetting two complex weights, for each transmitting branch, i.e. the amplitude weights a i and a i as well as the phase shifts fi and in order to weight the two modulated signals f and P. The fixed radio station BTSx shown in the figure transmits two correspondingly modulated radio signals S and S' with a carrier frequency fc in different directions q and q' determined by the complex weightings. In order to guarantee coherent operation of the RF transmitter stages TX, the radio station BTSx contains a frequency generator GEN which produces the carrier frequency fc, and RF transmission lines over which the carrier signal is supplied to the RF transmitter stages TX. The line lengths are so adjusted that the carrier signal arrives at the inputs of the RF transmitter stages in the same phase. The adjustment of the line lengths can also be carried out electronically, for example by the use of phase shifters.

The invention has been described by means of particularly advantageous t tf t 4 ~1 n" i: i design examples for fixed radio stations, The application of the invention to mnobile Sadio stations, such as mobile stations for motor cars or mobile telephones is possible without any restrictions. Moreover, the invention can be applied in digital as well as in analogue mobile radio systems. These can either be associated with public systems such as, for example, GSM or DECT (Digital European Cordless Telephone), or the) can be associated with non-public systems such as, for example, TETRA (Transeuropean Trunked Radio).

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Claims

1. A radio station for an SDMA mobile radio system which, for the generation of N complex-weighted transmission signals, has N transmitting branches with N RF transmitter stages which feed N aerial elements of an aerial array with the N complex-weighted transmission signals, so that the radio station radiates at least one directional radio signal, wherein a modulator stage in which the modulation and at least a part of the complex weighting of the transmission signals is carried out, either in the baseband or at an intermediate frequency.

2. A radio station as claimed in Claim 1, wherein the radio station contains a S.o*o control circuit which is connected to the modulator stage and controls it for the complex weighting of the N transmission signals, by presetting N phase shifts an. 2 /or N amplitude weights for a modulating signal which the modulator stage applies to the N transmission signals.

3. A radio station as claimed in Claim 2, wherein the modulating signal ind: tes the variation of a phase angle, that the modulator stage distributes the modulc.,, signal to the N transmitting branches and that, for each of the transmitting branches in the modulator stage, the control circuit causes a change in the phase angle by one of the N preset phase shifts so that the radio station radiates an angle-modulated radio signal in a direction. 0 4. A radio station as claimed in Claim 2, wherein the modulating signal represents the variation of an amplitude, that the modulator stage distributes the modulation signal to the N transmitting branches and that, for each of the transmitting branches in the modulator stage, the control circuit causes a weighting of the amplitude with one of the N preset amplitude weightings so that the radio station radiates an amplitude-modulated radio signal in some direction. A radio station as claimed in Claims 3 or 4, wherein the modulator stage contains a digital signal processor which is connected to the control circuit and which, for each of the N transmitting branches, binarily adds to the phase angle one of the N phase shifts, or-weights the amplitude with one of the amplitude weiph!, .f y bit shifting.

6. A radio station as claimed in Claim 2, wherein the modulator stage derives the L:0i i 4 i t B. O'Connor Date j(Authorized Signatory) P5/1/1703 C 0278 1 7 21JUL95 172"95 id ~r~r 1 I I 9

9. 9 #99 #*4 9 *CI 4#4#: modulating signal from a TDMA signal which has K time slots, and that the control circ.jit presets, for each of the time slots, the N phase shifts and/or the N amplitude weights in such a way that the radio station radiates a TDMA radio signal in a direction which can be varied from time slot to time slot. 7. A radio station for an SDMA mobile radio system which, for the evaluation of N complex-weighted reception signals, contains N receiving branches with N RF receiver stages which are fed from N aerial elements of an aerial array with the N complex- weighted reception signals, if the radio station receives at least one radio signal, wherein a demodulatce stage in which the demodulation and at least a part of the complex weighting is carried out, in the baseband or at an intermediate frequency. 8. A radio station as claimed in Claim 7, wherein the radio station contains a S control circuit which is connected to the demodulator stage and which controls this stage for the evaluation of the N complex-weighted reception signals by presetting N 15 phase shifts and/or the N amplitude weights for the N reception signals being demodulated. 9. A radio station as claimed in Claims 1 or 7, wherein in order to establish a directional radio connection with another radio station, the control circuit controls the complex weightings so that the aerial array transmits and receives with an 20 omnidirectional pattern.

10. A radio station as claimed in Claim 1, wherein the radio station radiates at least two modulated radio signals synchronously on a single carrier frequency in different directions, that the fixed radio station contains a time-division multiplex stage which precedes the modulator stage and which, for the purpose of modulation, applies to that stage at least two digital signals, or modulating signals derived from them, and that the fixed radio station contains N demultiplexer stages and N adders after the~iodulator stage, so that for the N transmitting branches N transmission signals are generated which each correspond to a sum signal which contains at least two complex-weighted component signals.

11. A radio station for an SDMA mobile radio system which contains at least one I/Q modulator for generating an angle-modulated transmission signal, which contains N transmitting branches with N RF transmitter stages for supplying the #6e98 9i 9 i 9 -I B. O'Connor 13 transmission signal to N aerial elements of an aerial array, wherein the N modules which are connected between the I/Q modulator and the RF transmitter stages for the complex weighting of the quadrature components of the transmission signal, and which contain harmonic function generators, multipliers and adders, by means of which each one of the N modules varies one phase angle, which is the argument of the quadrature components, varies by a phase shift for one of the N transmitting branches according to the addition theorems of trigonometrical functions.

12. A radio station for an SDMA mobile radio system which contains at least one I/Q modulator for evaluating an angle-modulated reception signal, and which contains N receiving branches with N RF receiver stages for receiving the reception signal from N aerial elements of an aerial array, wherein N modules which are connected between the I/Q demodulator and the RF receiver stages for the complex weighting of the quadrature components of the reception signal, and which contain harmonic function generators, multipliers and adders, by means of which each one of the N modules varies one phase angle, which is the argument of the quadrature components, varies by a phase shift for one of the N receiving branches according to the addition theorems of trigonometrical functions. S 13. A radio station as claimedin any one of the Claims 1, 7, 11 or 12, wherein a carrier frequency generator which is connected to the N transmitter stages and the N 2o O receiver stages via a distribution network that compensates for different signal propagation times resulting in a clock-synchronous and phase-constant carrier I/Q*i: frequency supply. DATED THIS NINTH DAY OF OCTOBER 1998 ALCATEL N.V. A 1 0 ca sinlfo eraolmnso a eilaryweenNmdle hc r tteadiintermoftiooeicl fntos ABSTRACT Fixed or Mobile Radio Station for an SDMA Mobile Radio System For the complex weighting of transmission or reception signas in an SDMA mobile radio system (Space Division Multiple Access), costly arrangements are known which, at the intermediate frequency position, alter the transmission or reception signals by means of amplitude weighting or phase shifts. A simple radio station (BTS) is proposed for SDMA radio transmission which, in the transmitting section, contains a modulator stage (MOD) connected to a control I'4 circuit (CTR) which, by presetting complex weights (f fN;al aN), affects the modulation in such a way that the modulator stage generates N modulated and complex-weighted transmission signals. These are radiated by the radio station (BTS) ;a via an N-element group aerial, which causes the transmission signals to be superposed to form a directionally radiated radio signal :o I For the receiving direction, a receiving section is proposed which operates according to the same principle. (Figure 1) 4i e 4 1 i 'I