EP2074775A2

EP2074775A2 - Mobile radio system, method for transmitting a us er datastream and for detecting a transmission mode in a mobile radio system and mobile station

Info

Publication number: EP2074775A2
Application number: EP07825455A
Authority: EP
Inventors: Andreas Arnold; Ralf Heddergott; Hanguang Wu; Wen Xu
Original assignee: Palm Inc
Current assignee: Qualcomm Inc
Priority date: 2006-08-16
Filing date: 2007-08-15
Publication date: 2009-07-01
Also published as: WO2008020320A3; DE102006038142A1; WO2008020320A2

Abstract

The invention relates to devices and methods for transmitting a user datastream in a mobile radio system (100) with a transmitter (101) with a first and a second transmitting antenna (104a, 104b), spatially separated from one another, to a receiver (102) with a first and a second receiving antenna (110a, 110b), spatially separated from one another. The invention additionally relates to a method (700) of detecting a transmission mode (204, 205) of a receiver (102) with a receiving antenna (110) in a mobile radio system (100).

Description

Mobile radio system, method for transmitting a user datastream and for detecting a transmission mode in a mobile radio system and mobile station

The invention relates to devices and methods for the transmission of a user datastream in a mobile radio system with a transmitter with a first transmitting antenna and with a second transmitting antenna, which is spatially separated from the first transmitting antenna, to a receiver with a first receiving antenna and with a second receiving antenna, which is spatially separated from the first receiving antenna.

Mobile radio systems with a plurality of antennas, in particular at the base station end, are known from e.g. so-called "transmission diversity" systems, in which a plurality of antennas at the transmitting end and/or the receiving end are used to achieve improved transmission reliability by exploiting spatial diversity.

Mobile stations with a plurality of antennas are also being developed, however, in the course of the development of existing mobile radio systems, such as GSM and the associated EGPRS Standard in connection with the so-called 3GPP-GERAJSf Project ("Feasibility study for evolved GSM/EDGE Radio Access Network

(GERAN)", TR 45.912 V.0.4.0, January 2006), and also as part of the development of future mobile radio systems .

Mobile radio systems with antenna arrays at the transmitting and receiving ends , known as "Multiple Input Multiple Output" (MIMO) systems, are, in addition to improving error correction, capable of increasing transmission capacity. A spatial selectivity is used here for the common transmission of a plurality of datastreams via a common physical medium, in particular the air interface.

An object of the invention is further to improve mobile radio systems of the above-mentioned kind. In particular, the data transmission rates or error susceptibility of new mobile stations is to be improved without extensive interventions into existing mobile radio systems becoming necessary for this purpose .

The object is achieved by means of a mobile radio system, a method for transmitting a user datastream and a mobile station according to claims 1, 6 and 10.

The object is likewise achieved by means of a mobile radio system and a method for detecting a transmission mode of a receiver according to claims 3 and 9, which enable, in particular, the integration of the transmission method according to the invention into existing mobile radio systems, wherein existing network equipment and mobile telephones may continue to be used in the conventional manner.

According to one embodiment of the invention, assigned to a training sequence used for encoding a first partial transmit datastream is an associated partner training sequence, which is matched to the training sequence in respect of its correlation properties and which is used for encoding a second partial datastream. The encoding may thereby be undertaken either jointly with or independently of a modulation used. First and second modulated transmit signals generated in this manner are transmitted via a first and a second transmitting antenna from a transmitter to a receiver. The receiver comprises a first and a second receiving antenna and a decoder unit, and is set up to decode a first receive signal from the first receiving antenna and a second receive signal from the second receiving antenna jointly using the training sequence and the associated partner training sequence in a first and a second partial receive datastream, and to combine these to form a user receiver datastream.

Owing to the use of training sequences and partner training sequences with predetermined correlation properties, the data transmission in MIMO systems can be improved.

In an advantageous embodiment, the mobile radio system comprises a further transmission mode in addition to the transmission mode described above. The further transmission mode may be either e.g. a conventional transmission mode with just one partial datastream or a future transmission mode. To ensure a reliable distinction between the first and the second transmission modes at the receiver end, the receiver attempts to decode part of the first modulated receive signal in a first direction and another part of the receive signal in a second modulation direction. Since in the case of e.g. GSM systems, it is known from the GSM Standard which training sequence a transmitter has used in encoding the transmit signal, the modulation direction used by the transmitter is derived by correlation of the decoded receive datastreams with the known training sequence. The modulation direction can here be used to detect one of two operating modes .

According to a further advantageous embodiment of the invention, the user transmit datastream is apportioned without overlap to the first and second partial transmit datastreams. In this manner, it is achieved that the first and second partial transmit datastreams are free from redundancies, so the transmission rate is maximised.

According to another embodiment of the invention, at least parts of the user transmit datastream are apportioned by e.g. timing-based and/or spatial channel encoding to both the first and the second partial transmit datastream so that redundant information is contained in the transmitted transmit signals . At the receiver end, this redundant information can be used for error correction.

Further advantageous embodiments are described in the sub-claims .

Further details of the invention will emerge from the following description of an embodiment which is shown in the accompanying drawings, in which:

Fig. 1 shows a mobile radio system according to an embodiment of the invention.

Fig. 2 shows a first quantity of training sequences for a first transmission mode and a second quantity of training sequences for a second transmission mode.

Fig. 3 shows autocorrelation functions of partner training sequences used according to the invention.

Fig. 4 shows cumulative distribution functions of the simulated SNIR degradations.

Fig. 5 shows probability density functions of the cross-correlation of training sequences and partner training sequences .

Fig. 6 is a schematic representation of a method for transmitting a user datastream. Fig. 7 is a flowchart for a method for the detection of a transmission mode of a receiver.

Fig. 1 shows a mobile radio system 100 according to one embodiment of the invention. The mobile radio system 100 comprises a transmitter 101 and a receiver 102 in a mobile radio network 106, such as a GSM network. For example, the transmitter 101 may be a base station, and the receiver 102 may be a mobile station, wherein the transmitter 101 transmits data to the receiver 102 in what is known as the downlink direction. Naturally, data transmission in the opposite direction, known as the uplink, i.e. from a mobile station to a base station, is also possible.

The transmitter 101 contains an encoding unit 103 and two transmitting antennas 104a and 104b. The encoding unit 103 is connected to a data input 105 via which a user transmit datastream is prepared for encoding by the encoding unit 103 and subsequent transmission via the transmitting antennas 104a and 104b. The two transmitting antennas are spatially separated from one another. For example, they may be two rod or dipole antennas arranged in parallel or orthogonally relative to one another. An individual plane antenna with two polarisation directions, orthogonal relative to one another, can, however, also act as the first and second transmitting antennas 104a and 104b.

The encoding unit 103 comprises a distributing device 107 and two modulation devices 108a and 108b, which are connected to the first transmitting antenna 104a and the second transmitting antenna 104b respectively. The distributing device 107 may be e.g. a multiplexer, which passes information units received via the data input 105, such as data packets with voice, video or other data, either to the first modulation device 108a or the second modulation device 108b. It is, however, also possible by means of suitable channel encoding for the distributing device 107 to pass at least part of the data both to the first modulation device 108a and the second modulation device 108b in order to generate a controlled redundancy between the modulated transmit signals generated by the modulation devices 108a and 108b.

In the embodiment shown, the encoding unit 103 also contains a memory 109, in which are stored at least one training sequence, also known as a "Training Sequence Code", TSC, and one partner training sequence PTSC assigned to the training sequence TSC. Naturally, the training sequence TSC and the partner training sequence PTSC do not have to be stored locally in the encoding unit 103, but may, for example, be provided via a SIM card integral to a mobile station or via a data network connected to a base station.

The training sequence TSC and the associated partner training sequence PTSC have predetermined, matched correlation properties. The training sequence TSC is used by the first modulation device 108a to generate a first transmit signal based on a first partial transmit datastream generated by the distributing device 107. The associated partner training sequence PTSC is used by the second modulation device 108b to generate a second transmit signal based on a second partial transmit datastream generated by the distributing device 107.

The receiver 102 contains a first receiving antenna 110a, a second receiving antenna 110b and a decoding unit 111. The decoding unit 111 is set up to receive a first receive signal from the first receiving antenna 110a and a second receive signal from the second receiving antenna 110b, to decode them jointly and to make available via a data output 112 a user datastream generated therefrom. To this end, the decoding unit 111 comprises a first demodulation device 113a, a second demodulation device 113b and a combining device 114. In addition, in the embodiment shown, the decoding unit 111 comprises a memory 115 in which both the training sequence TSC and the partner training sequence PTSC assigned thereto are stored.

Normally, the first demodulation device 113a and the second demodulation device 113b will be components of a common demodulator 116. By means of a close linkage of the decoding process of the first demodulation device 113a and of the second demodulation device 113b, in particular by the joint estimation of channel coefficients used, the improved decoding of the first and second receive signals can be achieved.

Joint demodulation processes of this kind are known, for example, from the articles by B. Steiner and P.

Jung "Optimum and suboptimum channel estimation for the uplink CDMA mobile radio systems with joint detection" from the European Transactions on

Telecommunications, Vol. 5, pages 19 to 50, Jan. 1994 and by P. Nickel, W. Gerstacker, R. Schober and W. Koch: "Analysis of MIMO Transmission for GSM/EDGE" from the Proceedings of the 43rd Allerton Conference on Communication, Control and Computing, Monticello, IL, September 2005.

The combining device 114 combines the two partial datastreams generated by the first and second decoding devices 113a and 113b to form a user receive datastream, which is made available via the data output 112 of the receiver 102. If redundant information has been introduced by means of channel encoding into the two partial datastreams by the transmitter 101, it is removed by the combining device 114 by appropriate channel decoding.

Fig. 2 shows a first quantity 200 of training sequences TSC, which are used in a first transmission mode 204, also referred to below as dual-stream mode. The first quantity 200 contains elements 201, which each contain a set comprising a training sequence TSC and an associated partner training sequence PTSC. Also shown in Fig. 2 is a second quantity 202 of training sequences TSC. The second quantity 202 contains elements 203, which each contain just one individual training sequence TSC. The second quantity 202 is used in a second transmission mode 205, known as the single-stream mode.

Fig. 2 also shows identifiers 206, to each of which an element 201 of the first quantity 200 and an element

203 of the second quantity 202 are assigned. Because an element 201 or 203 is assigned to the same identifier 206 for the two operating modes 204 and 205 respectively, existing means may be used unmodified for the signalling of TSCs in the two operating modes

204 and 205.

In the example shown, both the first quantity 200 and the second quantity 202 each comprise eight elements 201 and 203 respectively. This corresponds to the training sequences TSC used in the GSM Standard, wherein the second transmission mode 205 corresponds to the normal GSM transmission mode. In the embodiment example, the training sequences TSC of the first quantity 200 are the same training sequences TSC contained in the associated elements 203. The associated partner training sequences PTSC are, however, contained only in the elements 201 of the first quantity 200. Partner training sequences PTSC, which possess especially good correlation properties in respect of their assigned training sequences TSC, may, for example, be generated by a method described in the German patent application with application number 10 2006 017 296.5. Here, substantially by multiplying the training sequences TSC known from the GSM Standard by a row from a Hadamard Matrix of order 16, new partner training sequences PTSC having the same autocorrelation properties as the training sequences TSC are generated. In addition, they have especially low cross-correlation properties relative to the standard-conformal training sequences TSC on which they are based, so they can be used jointly with these training sequences TSC.

Alternatively, partner training sequences PTSC can also be obtained by searching through all possible 16- bit sequences by selecting the 16-bit sequences that fulfil the following properties as well as possible:

At least 5 successive zero places after the autocorrelation maximum.

Exclusion of all 16-bit sequences that can be mapped onto already known 16-bit sequences, in particular the GSM Standard training sequences TSC, by shifting or negation.

Minimal SNIR degradation between the possible 16- bit sequences and existing training sequences .

Here, the SNIR degradation between two possible 16-bit sequences constitutes a measure of the interference to a datastream encoded with the first bit sequence from a datastream encoded with the second bit sequence as the interference source . It provides a measure of the degradation of the transmission channel in dB in the event of joint channel detection for a transmission channel of order L.

The following Table contains the bit sequences of eight partner training sequences PTSC, which are assigned to the eight training sequences TSC according to the GSM Standard for GMSK (Gaussian Minimum Shift Keying) modulation and which are used in the embodiment example of the present invention: Identif Partner training sequence (PTSC) bits ier

#0 0 0 0 1 1 1 0 1 1 0 1 1 1 1 0 1 0 0 0 1 1 1 0 1 1 0

#1 0 0 0 1 0 0 0 1 1 1 1 0 1 0 0 1 0 0 0 1 0 0 0 1 1 1

#2 0 0 1 0 0 0 1 0 0 1 0 1 1 1 1 0 0 0 1 0 0 0 1 0 0 1

#3 1 1 0 1 1 0 1 1 1 0 0 0 1 0 1 1 1 1 0 1 1 0 1 1 1 0

#4 0 1 0 0 1 1 1 1 1 1 0 0 1 1 0 1 0 1 0 0 1 1 1 1 1 1

#5 1 0 1 1 1 1 1 0 0 1 0 0 0 1 1 0 1 0 1 1 1 1 1 0 0 1

#6 1 1 1 1 0 0 1 0 1 0 1 1 0 0 1 1 1 1 1 1 0 0 1 0 1 0

#7 0 0 0 1 0 0 1 1 1 1 1 0 1 0 1 1 0 0 0 1 0 0 1 1 1 1

The following Table contains the eight symbol sequences of partner training sequences PTSC, which are assigned to the eight training sequences TSC according to the GSM Standard for 8-PSK (8 Phase Shift Keying) modulation and which are used in the embodiment example of the present invention:

Partner training sequence (PTSC)

Identif symbols ier

#0 111 111 111 001 001 001 111 001 001

111 001 001 001 001 111 001 111 111

111 001 001 001 111 001 001 111

#1 111 111 111 001 111 111 111 001 001

001 001 111 001 111 111 001 111 111

111 001 111 111 111 001 001 001

#2 111 111 001 111 111 111 001 111 111

001 111 001 001 001 001 111 111 111

001 111 111 111 001 111 111 001

#3 001 001 111 001 001 111 001 001 001

111 111 111 001 111 001 001 001 001

111 001 001 111 001 001 001 111

#4 111 001 111 111 001 001 001 001 001

001 111 111 001 001 111 001 111 001

111 111 001 001 001 001 001 001

#5 001 111 001 001 001 001 001 111 111

001 111 111 111 001 001 111 001 111

001 001 001 001 001 111 111 001

#6 001 001 001 001 111 111 001 111 001

111 001 001 111 111 001 001 001 001

001 001 111 111 001 111 001 111 #7 111 111 111 001 111 111 001 001 001 001 001 111 001 111 001 001 111 111 111 001 111 111 001 001 001 001

The standardised autocorrelation properties of the eight partner training sequences PTSC are shown in Fig. 3. One important property exists in the fact that the autocorrelation maximum is followed by five zero places, i.e. when the partner training sequences of up to five bits are shifted, e.g. by echoes or multipath transmission of a radio signal, no interference to the receive signal occurs.

Fig. 4 shows the cumulative distribution functions of the simulated SNIR degradation for different channel orders . The SNIR degradation indicates the degradation of the Signal to Noise plus Interference Ratio (SNIR) whilst the channel order indicates the degree of multipath propagation or degree of delay dispersion of the transmission channel, expressed in symbol duration. These variables are described in e.g. the above-mentioned article by B. Steiner and P. Jung.

As is apparent from Fig. 4, the SNIR degradation increases both with the use of a multiplicity of possible pairs of training sequences TSC and partner training sequences PTSC, and with increasing channel order. Nevertheless, it can be recognised that the SNIR degradation for any given channel order lies within a comparable order of magnitude.

In GSM systems in general, the inter-channel interference dominates over other types of interference. In the EGPRS data transmission mode in particular, data transmission frequently takes place in a range with high SNIR values . The reason is that this transmission takes place preferentially on the frequency of the Broadcast Control Channels (BCCH) , which is transmitted at full power and also exhibits a low level of re-use in adjacent cells. This range and this operating mode are therefore especially suited to the dual-stream transmission mode. For example, in a first time slot of the BCCH channel, signalling data for the configuration of a cell of a mobile radio network can be transmitted, and in subsequent time slots, further data can be transmitted in EGPRS mode with full transmission power.

Fig. 5 shows the probability density distribution of the cross-correlation of training sequences and partner training sequences . It shows that the interference between the training sequences TSC according to the GSM Standard (broken line) is on average higher than that between the training sequences TSC and the partner training sequences PTSC

(continuous line) . Higher cross-correlation functional values, which indicate poorer transmission properties, occur more frequently in the case of the GSM Standard than in the case of the dual-stream mode disclosed here. Accordingly, degradation of the transmission properties in existing GSM systems through communication with a partner training sequence PTSC instead of a standard-conformal training sequence TSC does not occur .

Nevertheless , the partner training sequences PTSC described above are just one possible example, since different 16-bit sequences can be selected in the manner described above .

Fig. 6 shows a schematic representation of a method 600 for transmitting a user datastream in a mobile radio system 100.

In a first step, a user transmit datastream 601, e.g. digitalised voice, sound or image data, is divided by a distributing device 107 into a first partial transmit datastream 602a and a second partial transmit datastream 602b.

This division may take place symmetrically or asymmetrically, e.g. as a function of a previously defined transmission quality or anticipated transmission rate of a physical transmission channel assigned to the partial datastreams .

Information units, such as individual symbols or entire data packets of the user transmit datastream 601, may here be assigned to either one or other of the partial transmit datastreams 602a or 602b, in order to allow maximum data transmission rates. Alternatively, it is also possible to encode at least parts of the user transmit datastream into the two partial transmit datastreams 602a and 602b, in order to create a controlled redundancy between the partial transmit datastreams 602a and 602b. This enables reliable data transmission, in particular in the case of poor channel quality, since the redundant information is available for error correction at the receiver end. In a further step, the first partial transmit datastream 602a is encoded and modulated, using a training sequence TSC, by a first modulation device 108a. A resultant first transmit signal 603a is then emitted via a first transmitting antenna 104b.

Simultaneously with this, the second partial transmit datastream 602b is encoded and modulated, using a partner training sequence PTSC assigned to the training sequence TSC, by a second modulation device 108b. A resultant second transmit signal 603b is then emitted via a second transmitting antenna 104a.

The two transmit signals 603a and 603b are transmitted via the same transmission medium, in particular an air interface . The interference arising as a result between the first transmit signal 603a and the second transmit signal is represented by the connection 604 and the mixers 605a and 605b. In addition, the two data transmission channels are affected by further interference signals 606a and 606b, e.g. transmit signals 603 from other transmitters 101 in the mobile radio system, or other electromagnetic interference sources . In a further step, a first receive signal 607a is received via a first receiving antenna 110a and fed to a first demodulation device 113a. Simultaneously, a second receive signal 607b is also fed via a second receiving antenna 110b to a second demodulation device 113b.

The first and the second demodulation devices 113a and 113b are part of a common demodulator 116, and exchange data via an interface 608 during the decoding of the first and second receive signals 607a and 607b. This may be e.g. probability information relating to symbols to be decoded.

Since the receiver 102 receives modulated receive signals 607a and 607b via two spatially separated receiving antennas 110a and 110b, it is rather improbable that interference in the medium will affect both transmission paths in the same manner. The manner in which one of the propagation paths is subject to interference will differ in the case of the other transmission path. For example, through Maximum Ratio Combining (MRC) , decoding is undertaken in a manner such that the overall error probability is minimised. The first receive signal 607a is demodulated and decoded into a first partial receive datastream 609a using the training sequence TSC. The second receive signal 607b is demodulated and decoded into a second partial receive datastream 609b using the partner training sequence PTSC.

In a further step, the two partial receive datastreams 609a and 609b are directed to a combining device 114. The combining device 114 generates a user receiver datastream 610 from the information from the two partial receive datastreams 609a and 609b. Under favourable conditions, the user receiver datastream 610 is identical with the user transmit datastream 601. Transmission errors arising from e.g. a channel decoding undertaken by the combining device can be eliminated. In the case of severe interference to transmission channels, user transmit and user receiver datastreams 601 and 610 may, however, differ from one another, which can be compensated either from the application level by error-correction or error-masking devices, which are not shown in Fig. 6, or by repeat transmission of the data transmitted unsuccessfully.

In order to permit a reliable and delay-free distinguishing between a first transmission mode 204 and a second transmission mode 205 on the part of the receiver 102 without the exchange of additional control signals between the transmitter 101 and the receiver 102 becoming necessary for this purpose, a signalling operation is performed, according to a further embodiment of the present invention, on the basis of the applied modulation itself.

Fig. 7 shows a flowchart for a method 700 for the detection of a transmission mode of a receiver 102.

In a first step 701, a training sequence TSC is selected by the receiver 102. For example, the GSM Standard defines which training sequences may be used by a transmitter 101. The training sequence TSC used for a specific data transmission is here selected by a base station and, using appropriate control information, signalled to a mobile station, e.g. by transmitting an associated identifier 206, so the receiver 102 can select the training sequence TSC from the quantity of training sequences contained in the Standard.

In an advantageous embodiment, assigned to an identifier 206 in the first transmission mode 204 is a set of training sequences TSC and associated partner training sequences PTSC, and assigned to an identifier 206 in the second transmission mode 205, is only a training sequence TSC. In all cases, therefore, only one identifier has to be transmitted, so that existing signalling means can be used unmodified in the two modes .

In a second step 702, the receiver 102 receives a modulated receive signal from a receiving antenna 110. At this point, the receiver 102 does not know whether a transmitter 101 is being operated currently in the first transmission mode 204 or the second transmission mode 205.

In the further steps 703 and 704 respectively, the receiver 102 decodes at least a first part of the modulated receive signal in a first modulation direction and a second part of the receive signal in a second modulation direction. This gives rise to a first part of a decoded receive datastream and a second part of a decoded receive datastream.

The decoding of steps 703 and 704 may be undertaken simultaneously by different demodulation devices, e.g. the first demodulation device 113a and the second demodulation device 113b. Here, the two demodulated parts may be identical. Alternatively, it is also possible to decode parts of a modulated receive signal successively by means of one and the same demodulation device 113.

In steps 705 and 706 respectively, a first conformity of the first part of the receive datastream with the selected training sequence TSC is determined and a second conformity of the second part of the receive datastream with the selected training sequence TSC is determined. Since the modulated receive signal contains a training sequence TSC both in the first transmission mode 204 and in the second transmission mode 205, a relatively great conformity must exist, at least in one of the two modulation directions, between the selected training sequence TSC and the first/second parts of the receive datastream, which enables a differential recognition of the modulation direction used.

To this end, in a step 707, the conformities of the first and second receive datastreams determined in steps 705 and 706 respectively are compared with the selected training sequence TSC. Through a direct comparison of the two conformities, it can be ensured, even under unfavourable reception conditions, that the correct modulation direction, and thus the correct transmission mode, is recognised. An absolute degradation of the conformity is unimportant for the differential recognition.

It is determined in step 708, on the basis of the comparison from step 707, which transmission mode has been used by the transmitter 101. If the first conformity is greater than the second conformity, i.e. the modulated receive signal has been modulated by the transmitter 101 in the first modulation direction, the receiver 102 is switched into the first transmission mode 204. If, conversely, the second conformity is greater than the first conformity, the receiver 102 is switched into the second transmission mode 205.

In a subsequent, optional step 709, a decoding of further data, in particular user data, may then be undertaken by the receiver 102, either in the first transmission mode 204 or in the second transmission mode 205. For example, further data bits from a so- called burst, which also contains the training sequence TSC, may be decoded. It is unimportant whether this subsequent decoding is undertaken in the first or the second modulation direction.

For purposes of integration with existing GSM systems, it is advantageous to assign the conventional, single- stream mode, i.e. the second transmission mode, to the standard-conformal modulation direction, i.e. the forwards direction. For easier distinguishing of the dual-stream mode, i.e. the first transmission mode 204 according to the invention, the modulation direction for the first transmit signal modulated by the transmitter 101 may be reversed.

In the case of phase-modulation processes normal in GSM systems, this corresponds with the reversal of phase shifting, which is expressed by a negative preceding sign in the mathematical formulae that form the basis. However, other symmetrical modifications of the modulation, e.g. the shifting of a phase by a predetermined amount, are also possible.

According to the GSM Standard, e.g. GMSK modulation comprises the following steps: Step 1: Differential encoding

Every data bit di = [0,1] is differentially encoded. The output value of the differential encoder is: d_t=d_t ⁽Bd_1^1 (J,- e {0,1}) _^

wherein Θ indicates the modulo-2 addition.

The modulating data value ax, which is supplied to the modulator, is then:

«,=1-2.?, (α,e {-1,+1})_

Step 2 : Filtration and output phase

The modulating data value ax in a Dirac impulse representation activates a linear filter with an impulse response gr(fc) defined in the GSM Standard, so the output phase of the modulated signal is as follows:

t'-iT jg(ιι)du wherein the modulation index h has a value of 1/2, which corresponds to a maximum phase change of π/2 per symbol interval .

Step 3 : Modulation

With the exception of the start and end of a TDMA burst interval, the modulated high-frequency carrier signal therefore looks as follows:

x(t') = ij-jr ■ cos(2τr/₀ t'+φ(t') + φ₀)

where Ec corresponds to the energy per modulated bit, f0 to the carrier frequency and φO to a random phase shift, unchanged during the transmission interval .

According to one possible embodiment of the invention, in dual-stream mode the output phase is modified as follows in Step 2, at least for the first partial datastream, using the training sequence TSC:

r-ιτ

<p(*')=-∑«,^ jg(u)du This corresponds to a reversal of the modulation direction by comparison with standard-conformal modulation, without the output spectrum being changed thereby. In addition, values needed for developing amplifiers of transmitters, such as e.g. the ratio between maximum and average power, remain the same.

An equivalent reversal of modulation direction by adaptation of the output phase in Step 2 is also possible for 8 -PSK modulation, in which, however, the phase change per modulated symbol is only 3π/8.

Although the method 700 for detection of a transmission mode of a receiver 102 is here used to select between a single-stream mode and a dual-stream mode, a detection of this kind may also be used for signalling other operating modes and parameters orcontrol information. In particular, the application of the method 700 is not restricted to MIMO systems, i.e. transmitter 101 and receiver 102 with a plurality of transmitting antennas 104 and receiving antennas 110 respectively.

Likewise, the properties of transmission diversity can of course be combined with those of spatial selectivity in order to improve both data transmission rates and error correction. For example, a transmitter 101 with more than four transmitting antennas 104 may use two antennas per user datastream. Likewise, it is possible to transmit more than two partial transmit datastreams 602 provided a corresponding number of transmitting and receiving antennas 104 and 110 respectively are available.

List of reference characters

100 Mobile radio system

101 Transmitter

102 Receiver 103 Encoding unit

104 Transmitting antenna

105 Data input

106 Mobile radio network

107 Distributing device 108 Modulation device

109 Memory

110 Receiving antenna

111 Decoding unit

112 Data output 113 Decoding device 114 Combining device

115 Memory

116 Common demodulator

200 First quantity

201 Element (of the first quantity)

202 Second quantity

203 Element (of the second quantity)

204 First transmission mode 205 Second transmission mode

206 Identifier

600 Method of transmitting a user datastream

601 User transmit datastream 602 Partial transmit datastream

603 Modulated transmit signal

604 Connection

605 Mixer

606 Interference signal 607 Modulated receive signal

608 Interface

609 Partial receive datastream

610 User receiver datastream

700 Method of detecting a transmission mode 701 - 709 Method steps

TSC Training sequence PTSC Partner training sequence

Claims

1. Mobile radio system (100) with a first transmission mode (204) for the transmission of at least two transmit signals (603) simultaneously and at the same frequency, equipped with a transmitter (101) with an encoding unit (103) and two spatially separated transmitting antennas (104a, 104b) , wherein the encoding unit (103) comprises a distributing device (107) to split a user transmit datastream (601) into two partial transmit datastreams (602a, 602b) and a first and a second modulation device (108a, 108b) , which each generate a modulated transmit signal (603a, 603b) , each based on a partial transmit datastream (602a, 602b) , and is set up to encode a user transmit datastream (601) into two modulated transmit signals (603a, 603b) and to transmit them via the two transmitting antennas (104a, 104b) , and a receiver (102) with a decoding unit (111) and at least two receiving antennas (110a, 110b) wherein the decoding unit (111) comprises a first and a second demodulation device (113a, 113b) , which each demodulate a modulated receive signal (607a, 607b) into a partial receive datastream (609a, 609b) and a combining device (114) to combine two partial receive datastreams (609a, 609b) into a user receiver datastream (610) , and is set up to decode two modulated receive signals (607a, 607b) received by the receiving antennas (110a, 110b) jointly into a user receiver datastream (610) by means of the decoding unit (111) , wherein, in the first transmission mode (204) , the first modulation device (108a) uses a training sequence (TSC) during modulation of the first partial transmit datastream (602a), so that a first modulated transmit signal (603a) contains the training sequence (TSC) , the second modulation device (108b) uses a partner training sequence (PTSC) assigned to the training sequence (TSC) during modulation of the second partial transmit datastream (602b) , which partner training sequence (PTSC) is matched to the training sequence

(TSC) in terms of its quality criterion, so that a second modulated transmit signal (603b) contains the partner training sequence (PTSC) , and the first and the second demodulation devices (113a, 113b) use the training sequence (TSC) and the partner training sequence (PTSC) respectively during demodulation of a first and a second partial receive datastream (609a, 609b respectively) in order to decode a first and a second modulated receive signal (607a, 607b) jointly into a user receiver datastream (610) by exploiting the correlation properties .

2. Mobile radio system (100) according to claim 1, characterised in that the mobile radio system (100) comprises a second transmission mode (205) , wherein the transmitter (101) and the receiver (102) can be switched into the first or the second transmission mode (204, 205) , the first modulation device (108a) and the first demodulation device (113a) are set up to undertake the modulation and demodulation respectively in a first modulation direction in the first transmission mode (204) , and the modulation and demodulation respectively in a second modulation direction in the second transmission mode (205) , and the first and/or second demodulation device (113a, 113b) is set up to undertake a first demodulation in the first direction and a second demodulation in the second direction, and to identify the modulation direction used by the transmitter (101) by comparing demodulated signals with the training signal (TSC) or the partner training signal (PTSC) , so that the receiver (102) can be switched into the first or second transmission mode (204, 205) on the basis of the identified modulation direction.

3. Mobile radio system (100) according to claim 2, characterised in that the transmitter (101) is set up to transmit an identifier (206) for selection of the training sequence (TSC) used by the transmitter, the receiver (102) is set up to recognise a transmitted identifier (206) for selection of a training sequence (TSC) , and to use, in the first transmission mode (204) , a training sequence (TSC) assigned to the received identifier (206) and the associated partner training sequence (PTSC) and, in the second transmission mode (205) , only the training sequence (TSC) assigned to the received identifier (206) .

4. Mobile radio system (100) equipped with a transmitter (101) with an encoding unit (103) to encode a user transmit datastream into a modulated transmit signal, and with a transmitting antenna (104) to transmit a modulated transmit signal, and a receiver (102) with a decoding unit (111) to decode a modulated receive signal into a user receive datastream and with a receiving antenna (110) to receive a modulated receive signal wherein the transmitter (101) is set up to encode, in a first transmission mode (204) , at least part of a user transmit datastream in a first modulation direction and to emit it via the transmitting antenna (104) , and to encode, in a second transmission mode (205) , at least part of the user transmit datastream in a second modulation direction and to emit it via the transmitting antenna (104) , and the receiver (102) is set up to recognise a modulation direction of a part of a modulated receive signal received by the receiving antenna (110) and to decode the part of the received modulated receive signal in the first modulation direction into a user receiver datastream if the first modulation direction is recognised, and to decode the part of the received modulated receive signal in the second modulation direction into a user receiver datastream if the second modulation direction is recognised.

5. Mobile radio system (100) according to claim 4, characterised in that the encoding unit (103) is set up to modulate the part of the user transmit datastream using a predetermined training sequence

(TSC) , so that a transmit signal modulated by the encoding unit (103) contains the training sequence

(TSC) , and the decoding unit (111) is set up to decode part of the modulated receive signal in the first modulation direction into a first demodulated signal. and to decode part in the second modulation direction into a second demodulated signal, and to compare a conformity of the first demodulated signal with the predetermined training sequence (TSC) with a conformity of the second demodulated signal with the predetermined training sequence (TSC) , wherein a greater conformity is characteristic of the modulation direction to be recognised.

6. Mobile radio system (100) according to any one of claims 2 to 5 , characterised in that the encoding unit

(103) and the decoding unit (111) use phase modulation, wherein the phase direction used by the transmitter (101) for modulation is selected as a function of the selected first or second transmission mode (204, 205) .

7. Method (600) of transmitting a user datastream in a mobile radio system (100) from a transmitter (101) with a first transmitting antenna (104a) and a second transmitting antenna (104b) spatially separated from the first, to a receiver (102) with a first receiving antenna (110a) and a second receiving antenna (110b) spatially separated from the first, using the following steps: division of a user transmit datastream (601) into a first and a second partial transmit datastream (602a, 602b) ;

selection of a training sequence (TSC) from a first quantity of training sequences and a partner training sequence (PTSC) assigned to the selected training sequence (TSC) from the second quantity of training sequences;

encoding of the first partial transmit datastream

(602a) into a first transmit signal (603a) using the selected training sequence (TSC) and the second partial transmit datastream (602b) into a second transmit signal (603b) using the selected partner training sequence (PTSC) ;

simultaneous transmission of the first transmit signal (603a) via the first transmitting antenna (104a) and the second transmit signal (603b) via the second transmitting antenna (104b) at the same frequency;

reception of a first receive signal (607a) via the first receiving antenna (110a) and of a second receive signal (607b) via the second receiving antenna (110b) ; joint decoding of the first receive signal (607a) into a first partial receive datastream (609a) using the selected training sequence (TSC) , and the second receive signal (607b) into a second partial receive datastream (609b) using the selected partner training sequence (PTSC) ; and

combination of the first and second partial receive datastreams (609a, 609b) into a user receiver datastream (610) .

8. Method (600) according to claim 7, characterised in that in the step involving division, information units of the user transmit datastream (601) are assigned to either the first or the second partial transmit datastream (602a, 602b) , so that the first and the second partial transmit datastreams (602a, 602b) are free from redundancies.

9. Method (600) according to claim 7, characterised in that in the step involving division, information units of the user transmit datastream (601) are assigned to either the first, the second or both partial transmit datastream (602a, 602b) , so that the first and the second partial transmit datastreams (602a, 602b) contain redundant information, and in the step involving decoding or combination, the redundant information from the first and the second partial receive datastreams (609a, 609b) is used for error correction.

10. Method (700) of detecting a transmission mode (204, 205) of a receiver (102) with a receiving antenna (110) in a mobile radio system (100) with the following steps:

selection of a training sequence (TSC) ;

reception of a receive signal via the receiving antenna (110) ;

decoding of at least a first part of the receive signal in a first modulation direction into a first part of a receive datastream and a second part of the receive signal in a second modulation direction into a second part of the receive datastream;

determination of a first conformity of the first part of the receive datastream with the selected training sequence (TSC) and of a second conformity of the second part of the receive datastream with the selected training sequence (TSC) , and

selection of a first transmission mode (204) if the first conformity is greater than the second conformity, and of a second transmission mode (205) if the second conformity is greater than the first.

11. Mobile station for use in a mobile radio system (100) equipped with at least two antennas (110a, 110b) arranged with spatial separation, a decoding unit

(111) for the joint decoding and demodulation of two modulated receive signals (607a, 607b) received by means of the antennas (110) into a combined user receiver datastream (114) and a memory device (115) to store at least one training sequence (TSC) and one partner training sequence (PTSC) assigned to the training sequence (TSC) , wherein the mobile station is set up to execute the steps comprising selection, reception, decoding and combination according to any one of claims 6 to 8.

12. Mobile station according to claim 11, characterised in that the mobile station is additionally equipped with an encoding unit (103) to encode and modulate a first and a second transmit signal (603a, 603b) based on a user transmit datastream (601) wherein the mobile station is set up to execute the steps comprising division, encoding and transmission according to any one of claims 6 to 8.