Generation of positioning information of radio device

Field

The invention relates to a method of generating positioning information of a radio device in a wireless telecommunication system, a transceiver, and to a computer program implementing the method.

Background

Positioning of radio devices in wireless telecommunications systems is typically based on the use of stationary positions of base stations and time- of-arrival measurements of signals transmitted between a base station and a radio device. In radio environments with high complexity, signals transmitted between the base station and the radio device typically diverge both spatially and temporally, thus giving rise to a complex receive signal structure with a large amount of delayed components.

The delayed components reduce the accuracy of the positioning, and therefore it is useful to consider means for improving the reliability of positioning information in a wireless telecommunication system.

Brief description of the invention

An object of the invention is to provide an improved method, transceiver and a computer program. According to a first an aspect of the invention, there is provided a method of generating positioning information of a radio device in a wireless telecommunication system, the method comprising: determining receive polarization characteristics of radio transmission, the radio transmission having known transmit polarization characteristics; performing a search for a line-of-sight component of the radio transmission by using the known transmit polarization characteristics and the receive polarization characteristics; and determining a positioning information element relating to the position of the radio device on the basis of the search.

According to a second aspect of the invention, there is provided a computer program of instructions for executing a computer process for gener- ating positioning information of a radio device in a wireless telecommunication system, comprising: determining receive polarization characteristics of radio transmission, the radio transmission having known transmit polarization characteristics; performing a search for a line-of-sight component of the radio transmission by using the known transmit polarization characteristics and the

receive polarization characteristics; and determining a positioning information element relating to the position of the radio device on the basis of the search.

According to another aspect of the invention, there is provided a transceiver of a wireless telecommunication system, the transceiver compris- ing: determining means for determining receive polarization characteristics of a radio transmission, the radio transmission having known transmit polarization characteristics; searching means for performing a search for a line-of-sight component of the radio transmission by using the known transmit polarization characteristics and the receive polarization characteristics; and positioning in- formation means for determining a positioning information element relating to the positioning of the radio device on the basis of the search.

The invention provides several advantages.

In an embodiment of the invention, the invention provides detection of a line-of-sight component for positioning a radio device, and thus improved positioning accuracy. Further, the invention enables the positioning accuracy to be assessed on the basis of the search for the line-of-sight component.

List of drawings

In the following, the invention will be described in greater detail with reference to embodiments and the accompanying drawings, in which Figure 1 shows an example of propagation of radio transmission in a radio environment;

Figure 2 shows an example of a structure of a wireless telecommunication system;

Figure 3 shows a first example of a structure of a transceiver; Figure 4 shows a second example of a structure of a transceiver;

Figure 5 shows a third example of a structure of a transceiver; Figure 6 shows a first example of a correlation curve; Figure 7 shows a second example of a correlation curve; and Figure 8 shows an example of a methodology according to em- bodiments of the invention.

Description of embodiments

Figure 1 illustrates a situation where radio transmission is transmitted from a radio device (RD) 102 to a transceiver (TRX) 104 through a radio environment 100.

The radio transmission is characterized by radio signals 1 12A, 1 12B, 1 12C with transmit polarization characteristics 1 10A, 1 10B, 1 10C, respectively. For the ease of illustration, the transmit polarization characteristics 1 10A to 1 10C are shown with polarization ellipses indicated with dashed lines. A transmit polarization characteristic 1 10A to 1 10C may be associated with a radio resource, such as coding, frequency, time slot, space-time modulation, or antenna configuration. The association may be used in reception in order to separate different receive polarization components in reception. Outmost radio signals 1 12A, 112C reach obstructions 106, 108, such as walls or buildings, and the transmit polarization characteristics 1 10A, 1 10B change to receive polarization characteristics 1 14A, 1 14C due to interaction between the obstruction 106, 108 and the electromagnetic field associated with the radio signal 112A, 1 12B. The interaction results in scattering, reflection and/or diffraction of the outmost signal 1 12A, 112C. The outmost signals 1 12A, 1 12C arrive at the transceiver 104 with the receive polarization characteristics 1 14A, 114C.

A line-of-sight (LOS) radio signal 1 12B encounters an obstruction 1 10. However, the polarization characteristics 1 10B of the LOS radio signal 1 12B remain substantially unaltered, while the signal strength may change. The LOS radio signal 1 12B is also referred to as a LOS component 1 12B of the radio transmission.

At least some of the transmit polarization characteristics 1 10A to 1 10C are known and may include transmit weights of a polarization component or a transmit polarization angle of a transmit component. The transmit weights may be defined as absolute or as relative weights. The transmit polarization angles may be defined as absolute polarization angles or as relative polarization angles.

The transmit weights are factors which define absolute of relative magnitudes of each polarization component in a radio signal 112A to 1 12C. In reception, the outmost radio signals 1 12A, 1 12C give rise to various delayed components due to an increased signal path, while the LOS component 1 12B gives rise to undelayed components. The outmost radio signals 1 12A, 1 12B are also referred to as non-LOS components 1 12A, 1 12C.

A time of propagation of the LOS component 1 12B from the radio device 102 to the transceiver 104 is defined by the speed of light and the distance between the radio device 102 and the transceiver 104. Thus, the LOS

component 1 12B provides accurate information for measuring the distance between the radio device 102 and the transceiver 104.

With reference to Figure 2, a typical wireless telecommunication system 200 comprises a plurality of base stations (BS) 202A, 202B, 202C, 202D with known spatial positions and a common time reference, and a mobile station (MS) 204 with a non-stationary location. The wireless telecommunication system 200 may further include a positioning unit (PU) 206 connected to the base stations 202A to 202D.

In an embodiment of the invention, the mobile station 204 transmits radio transmission 208A, 208B, 208C, 208D. The radio transmission 208A may include a pilot having a predetermined symbol sequence. In this case, the mobile station 204 represents the radio device 102 of Figurei , and the base station 202A to 202D represents the transceiver 104 of Figure 1.

The base station 202A to 202D receives the radio transmission 208A to 208D and generates a positioning information element relating to the position of the mobile station 204 on the basis of the reception of the radio transmission 208A to 208D.

A positioning information element is a piece of information which characterizes the position of the mobile station 204 relative to the base station 202A, 202D.

The positioning information element may be proportional to the distance between the mobile station 204 and a base station 202A to 202D. In such a case, the positioning information element is the distance itself or a time delay corresponding to the distance. In an embodiment of the invention, the positioning information element includes information on the accuracy of the position of the mobile station 204 relative to the base station 202A to 202D. The accuracy may be expressed as an estimated error of the distance between the mobile station 204 and a base station 202A to 202D. The positioning information element or information on the positioning information element is transmitted to the positioning unit 206 in a positioning communication signal 210A, 210B, 210C, 210D.

The positioning information element is received in the positioning unit 206. The positioning unit 206 determines the position of the mobile station 204 relative to a reference on the basis of the positioning information ele-

merits and the positions of the base stations 202A to 202D. The positioning unit 206 may also determine the accuracy of the position of the mobile station 204. The position may be signaled to the mobile station 204 via a base station 202A to 202D. In an embodiment of the invention, the accuracy is signaled to the mobile station 204 via a base station 202A to 202D.

In an embodiment of the invention, the mobile station 204 possesses position information on the positions of the base stations 202A to 202D. The position information on the positions of the base stations 202A to 202D may be signaled to the mobile station 204, or the mobile station 204 may in- elude a data base including the positions.

The base stations 202A to 202D may transmit radio transmission 208A to 208D, which is received by the mobile station 204. In this case, the base station 202A to 202D represents the radio device 102 of Figure 1 , and the mobile station 204 represents the transceiver 104 of Figure 1. The mobile station 204 may derive its position on the basis of the time characteristics of received radio transmissions 208A to 208D and the position information on the base stations 202A to 202D.

In an embodiment of the invention, the transceiver 104 is a relay station of a wireless telecommunication system, and the radio device 102 is a mobile station of a wireless telecommunication system.

In an embodiment of the invention, the transceiver 104 is a mobile station of a wireless telecommunication system, and the radio device 102 is a relay station of a wireless telecommunication system. The relay station may be fixed or mobile. In an embodiment of the invention, the wireless telecommunication system 200 is a cellular telecommunication system, such as a GSM (Global System for Mobile Communications), GERAN (GSM/EDGE Radio access network), GPRS (General Packet Radio Service), E-GPRS (EDGE GPRS), UMTS (Universal Mobile Telecommunications System), CDMA2000 (CDMA, Code Division Multiple Access), US-TDMA (US Time Division Multiple Access), TDS- CDMA (Time Division Synchronization CDMA), 3GPP LTE (3 ^rd Generation Partnership Project Long Term Evolution), 4G or IMT-Advanced (International Mobile Telecommunications).

In an embodiment of the invention, the wireless telecommunication system 200 is WLAN (Wireless Local Area Network), WiMAX (Worldwide Interoperability for Microwave Access), or car-to-car communication.

In an embodiment of the invention, the wireless telecommunication system 200 utilizes multi-antenna communication, such as MIMO (Multiple- Input Multiple-Output), which is based on the use of at least two transmit antennas in the radio device 102 and at least two receive antennas in the trans- ceiver 104. The two antennas in the radio device 102 may be configured to transmit orthogonally polarized electromagnetic waves. The two antennas in the transceiver 104 may be configured to receive orthogonally polarized electromagnetic waves.

With reference to Figure 3, the transceiver 300 typically comprises a polarization antenna 310, a radio frequency unit (RF) 302 connected to the polarization antenna 310, a digital signal processor (DSP) 304, and a memory unit (MEM) 306. The memory unit 306 comprises computer programs of instructions for executing computer processes in the digital signal processor 304. The transceiver 300 may further include a user interface (Ul) 308. With reference to an example of Figure 4, a transceiver (TRX) 400 comprises a polarization antenna unit 310 for receiving radio signals 112A to 112C with arbitrary receive polarization characteristics 110B, 114A, 114C.

The polarization antenna 310 is coupled to a receiver unit (RXU) 402, which converts the radio signals 112A to 112C into digital receive signals 410.

The digital receive signals 410 are fed into a polarization analyser (POL) 404, which determines the receive polarization characteristics 110B, 1 14A, 1 14C of the radio signals 1 12A to 1 12C.

Information 412 on the receive polarization characteristics 1 10B, 1 14A, 1 14C is fed into a searching unit (SU) 406, which performs a search for a LOS component of the radio signals 1 12A to 112C by using known transmit polarization characteristics 1 10A to 1 10C and the receive polarization characteristics 1 10B, 1 14A, 1 14C.

In an embodiment of the invention, the search for the LOS compo- nent of the radio signals 112A to 1 12C is based on a comparison between the receive polarization characteristics 1 10B, 1 14A, 1 14C and the transmit polarization characteristics 11 OA to 1 10C. Furthermore, an assumption is used that the polarization characteristics of the LOS radio signals substantially remain in a LOS radio path. The receive polarization characteristic 1 10B, 1 12A, 1 12C may include receive weight of a polarization component or a receive polarization an-

gle. The receive weight may be defined as an absolute or as a relative weight. The receive polarization angle may be defined as an absolute polarization angles or as a relative polarization angle.

A search result 414 is inputted into a position information unit 408, which determines a positioning information element relating to the position of the radio device 102 on the basis of the search result 414.

The search result 414 may be indicative of the presence of a LOS component 1 12B in the radio signals 1 12A to 112C. In such a case, the positioning information unit 408 may determine the timing of the reception of the LOS component 1 12B relative to a time reference, in which case the timing may be interpreted as an positioning information element. Information on the timing may be transmitted to the positioning unit 206 to be used in a calculation of the position of the radio device 102. Furthermore, if the search result is indicative of the LOS component 1 12B, a positioning information element may indicative an accuracy of the timing so that the positioning unit 206 may evaluate the overall accuracy of the position of the radio device 102.

If the search result 414 indicates the absence of a LOS component 1 12B in reception, the positioning information unit 408 may determine the position information element from a non-LOS component 1 12A, 112C. In such a case, the positioning information unit 408 may further generate accuracy information characterizing the accuracy of the positioning information element when the non-LOS component 1 12A, 1 12C is used. In this case, the accuracy information may be transmitted to the positioning unit 206.

In an embodiment of the invention, existence of the LOS component 1 12B is evaluated for each link 208A to 208D and the positioning is calculated from those links which have the LOS component 112B. For example, if three out of four links 208A to 208D have a LOS component 1 12B it is enough for an accurate positioning.

In an embodiment of the invention, the transceiver 400 comprises a signaling transmitter (TXU) 418 for transmitting information on the known transmit polarization characteristics to the radio device 102.

The signaling transmitter receives information 416 on the known transmit polarization characteristics and transmits a corresponding radio signal 420 to the polarization antenna 310. The radio device 102 receives the information on the transmit polarization characteristics, and adjusts the transmission so as to make it comply

with the transmit polarization characteristics. In this arrangement, the transceiver 400 may choose an optimal polarization for the transmission on the basis of polarization diversity, for example, and instruct the radio device 102 to adjust the transmit polarization characteristics 110A to 110C accordingly. With reference to Figure 5, the radio signals 112A to 112C include at least two different transmit polarization components, which may give rise to at least two receive polarization components 502A, 502B in reception. A first polarization component 502A may be orthogonal with respect to the second polarization component 502B. Figure 5 shows signal conversion paths 516A, 516B, each comprising a down-converter 504A, 504B followed by an analogue-to-digital converter 508A, 508B.

A down-converter 504A, 504B receives the polarization component 502A, 502B, and converts the polarization component 502A, 502B into ana- logue signals 506A, 506B.

The analogue signal 506A, 506B is fed into the analogue-to-digital converter 508A, 508B, which converts the analogue signal 506A, 506B into a digital signal 510A, 510B.

The digital signal 510A, 510B is taken into a correlator (CORR1 , CORR2) 512A, 512B, which calculates a correlation 514A, 514B of the digital signal 510A, 510B with a symbol sequence 518A, 518B, which is also encoded into the radio signals 112A to 112C at transmission. The symbol sequences 518A, 518B may be spreading codes, for example. The correlation 514A, 514B includes a temporal structure of impulse responses of the radio signals 112A to 1 12C.

The correlations 514A, 514B are fed into the search unit 406, which searches the LOS components 112B of the radio signals on the basis of the correlations 514A, 514B.

With reference to an example of Figure 6, a first correlation 610 ex- emplifies a temporal structure of a first polarization component 502A, while a second correlation 612 exemplifies a temporal structure of a second polarization component 502B. In this example, it is assumed that the known ratio of the weights of the two polarization components is unity.

A horizontal axis 600 shows a delay in an arbitrary time unit, while a vertical axis 602 shows an impulse response in impulse response units. The

first correlation 610 and the second correlation 612 are shown relative to a reference level 604 and 606, respectively.

In an embodiment of the invention, the search unit 406 compares impulse responses 1A, 2A, 3A, 4A, 5A of the first correlation 610 with impulse responses 1B, 2B, 3B, 4B, 5B of the second correlation 612.

In an embodiment of the invention, the search unit 406 may calculate a receive ratio between impulse responses 1 A to 5B with a same time delay as follows: ^κ n,τ - ^~ r- ' V ^{) h} 2 wherein hi and h ₂ are impulse responses of the first correlation 610 and the second correlation 612, respectively.

The receive ratio may characterize a cross-correlation between the first polarization component 502A and the second polarization component 502B. The receive ratio may be compared with a known ratio, which deter- mines the relative weights of the two polarization components when transmitted from the radio device 102. If the receive ratio (1 ) agrees with the known ratio within a predetermined confidence limit, it can be assumed that the two polarization components 502A, 502B have passed via a LOS radio path. As a result, the impulse responses hi and h ₂ represent channel estimates of a LOS radio channel.

In an embodiment of the invention, the known transmit polarization characteristics include transmit polarization angular characteristics information on two transmit polarization components. The transmit polarization angular characteristics information may include the absolute or relative polarization angles of the transmit signals 112A to 112C.

The correlations 514A, 514B include information on polarization of a receive signal relative to a polarization element of the polarization antenna 310. The search unit 406 may compare the polarization angles of the receive signal with the known polarization angles of the transmit signal. In a LOS radio path, the relative polarization angle remains, while in a non-LOS radio path the relative polarization angle usually changes.

In an embodiment of the invention, the search unit 406 applies a comparison procedure given above to impulse responses with the smallest delay. It is known that the LOS components have the smallest delay, and so the comparison between the receive ratio (1 ) and the known ratio may be used

to verify that the component with the smallest delay is a LOS component. In the example of Figure 6, the relevant impulse responses would be 1A and 1 B. The search unit 406 determines the delay of the impulse responses 1A, 1 B of the LOS components and feeds delay values to the positioning information unit 408.

Figure 7 shows a second example comprising a first correlation 704 exemplifying a temporal structure of a first polarization component 502A and a second correlation 706 exemplifying temporal structure of a second polarization component 502B. In this example, it is assumed that the known ratio of the weights of the two polarization components is unity.

In this example, the receive ratio (1 ) of the impulse responses 1 C, 1 D with the smallest delay does not agree with the known ratio. This indicates that the LOS component 7A, 7B is below a noise limit and cannot be used for positioning. In such a case, a positioning algorithm may select components 1 C, 1 D with the smallest delay for the positioning and assess the accuracy of the positioning on the basis of finding out that the components used for the positioning are in fact non-LOS components.

The accuracy information may indicate "accurate" if the LOS component is used in the positioning. The accuracy information may indicate "inaccurate" if the LOS component was not found, and non-LOS component was used in the positioning instead.

The indication of "inaccurate" may result in that a transceiver not finding a LOS component is not used in the positioning. This may be the case, when more than two other transceivers provide positioning information. In an embodiment, a K factor is used for evaluating the accuracy of positioning.

With further reference to Figures 3, 4, and 5, the polarization analyzer 404 may be implemented with software stored in the memory unit 306 and executed in the digital signal processor 304. Some tasks may be imple- mented with ASIC (Application-Specific-Integrated Circuit) and/or with FPGA (Field Programmable Gate Array).

The search unit 406 may be implemented with software stored in the memory unit 306 and executed in the digital signal processor 304. Some tasks may be implemented with ASIC and/or with FPGA.

The positioning information unit 408 may be implemented with software stored in the memory unit 306 and executed in the digital signal processor 304. Some tasks may be implemented with ASIC and/or with FPGA.

With reference to Figure 8, a methodology according to embodi- ments of the invention is shown with a flow chart.

In 800, the method starts.

In 802, information on the known transmit polarization characteristics is transmitted between the transceiver 104 and the radio device 102. In an embodiment of the invention, the information on the known transmit polariza- tion characteristics is transmitted from the transceiver 104 to the radio device 102. In an embodiment of the invention, the information on the known transmit polarization characteristics is transmitted from the radio device 102 to the transceiver 104.

In 804, the radio transmission is received from the radio device 102. In 806, at least two receive polarization components 502A, 504B are separated on the basis of an association between the at least two transmit polarization components and an orthogonal radio resource, such as coding, time slot or frequency.

In 808, receive polarization characteristics of a radio transmission having known transmit polarization characteristics are determined.

In 810, a search for a line-of-sight component of the radio transmission is performed by using the known transmit polarization characteristics and the receive polarization characteristics.

In 812, a positioning information element relating to the position of the radio device 102 is determined on the basis of the search.

In 814, the method ends.

The method may be implemented with a computer program executed in the digital signal processor 304. The computer program may be stored in the memory unit 306. The computer program may be encoded into a computer program product.

The computer program may be stored on a computer program distribution medium readable by a computer or a processor. The computer program medium may be, for example but not limited to, an electric, magnetic, optical, infrared or semiconductor system, device or transmission medium. The computer program medium may include at least one of the following media: a

computer readable medium, a program storage medium, a record medium, a computer readable memory, a random access memory, an erasable programmable read-only memory, a computer readable software distribution package, a computer readable signal, a computer readable telecommunications signal, computer readable printed matter, and a computer readable compressed software package.

Even though the invention has been described above with reference to an example according to the accompanying drawings, it is clear that the invention is not restricted thereto but it can be modified in several ways within the scope of the appended claims.