Abstract:
The invention relates to a device for receiving signals in a MIMO system comprising:
       m signal receiver channels, where m is greater than 1;   an antenna system constituted either by n directive antennae n&gt;m, each antenna being able to receive signals in one of its own angular sectors, the angular sectors of the n antennae essentially not overlapping each other and together thrilling a total angular sector of 360 degrees, or a multi-sector antenna with n angular sectors n&gt;m the n angular sectors essentially not overlapping each other and having a distinct access; and   switching means to associate with each signal receiver channel an antenna from among the n antennae according to a switching schema selected by control means, the switching schema being selected from a plurality of switching schemas of a switching matrix according to a criterion representing the quality of the reception of the signals by said signal receiver channels.

Description:
This application claims the benefit, under 35 U.S.C. §365 of International Application PCT/FR2011/052894, filed Dec. 7, 2011, which was published in accordance with PCT Article 21(2) on Jun. 14, 2012 in English and which claims the benefit of French patent application No. 1060241, tiled Dec. 8, 2010. 
     TECHNICAL FIELD 
     The present invention relates to the transmission and the reception of signals in a MIMO (Multiple Input Multiple Output) type wireless multi-antenna transmission system. The present invention applies more specifically to broadband multimedia home networks. 
     PRIOR ART 
     The increasing development of digital multimedia devices has given rise to the concept of the home network ensuring the simultaneous distribution of multiple data streams, such as HD (High Definition) video streams, audio streams and computer data streams at any point in the home environment. Such a network, whose structure is dependent on the distribution of rooms within the building (apartment, house with or without a second floor, etc.) in which it is installed, can be deployed using different technologies such as cable, Power Line Carrier (PLC), optical fiber or WiFi type wireless devices complying with the standards 802.11a/big or 11n. The latter standard enables the use of MIMO technology which is a multi-antenna technique enabling transmission performances to be improved in terms of bitrate and robustness in environments dominated by interferences. 
     The MIMO technology consists in transmitting or receiving signals by using a plurality of transmission channels having different characteristics in order to obtain independent signals and thus increase the probability that at least one of the signals is not affected by fading. When the system uses several transmission and/or reception antennae, this is referred to as spatial diversity or antenna diversity. This diversity contributes to improving the MIMO gain by attenuating the interferences due to multi-paths on the one hand, and by increasing the transmission bitrate, the system reliability and the coverage zone on the other hand. 
     Most MIMO systems use standard 802.11n and a majority of products available on the market rely on 2×2 MIMO type links, that is to say, a system comprising, on the transmission side, 2 transmitters and, on the reception side, 2 receivers. Each transmitter and each receiver is connected to its own omnidirectional antenna. Each transmitter can transmit a single data stream in order to increase the global bitrate or the same stream as the other transmitter in order to increase redundancy and thus improve reception with a nonetheless lower bitrate. It is possible to increase the diversity in transmission or in reception by increasing the number of antennae so as to increase the transmission or reception performances. 
     One example of a 2×2 MIMO system with a diversity of order 2 in reception is shown by  FIG. 2 . The system comprises, on the transmission side, two transmission channels  100  and  101  each connected to an omnidirectional antenna, respectively  110  and  111 , and on the reception side, two receiver channels  120  and  121  connected to four omnidirectional antennae,  130  to  133 , via switching means  140 . The switching means are intended to associate with each receiver channel  120  or  121  an antenna from among the  4  antennae  130  to  133  according to a switching schema selected by control means  150 . The switching schema is selected from a plurality of switching schemas of a switching matrix according to a criterion representing the quality of the reception of the signals by receiver channels  120  and  121 . 
     If antennae  130  to  133  are also connected by switching means  23  to transmission channels (not shown in  FIG. 1 ), the switching schema selected for the reception can also be used to connect the transmission channels to antennae  130  to  133 . 
     The antennae being omnidirectional, they either transmit or receive signals in all directions and the receiver channels are therefore subjected to many interferences coming from all directions. In transmission, they also create a lot of interferences affecting neighboring devices. This is harmful to the global performance of the MIMO system. Thus, in order to limit the problems due to interferences and improve the quality of the transmitted/received signal, it is also known in the art to use techniques known as “beam forming”. A technique of this type is described in U.S. Pat. No. 6,438,389. 
     One purpose of the invention is to propose a device for receiving or transmitting/receiving signals in a MIMO environment which, in reception, is less affected by interferences. 
     In the 2×2 MIMO system of  FIG. 2 , the switching matrix comprises C 2   4 =6 switching schemas. Each switching schema is tested so as to determine which enables the best reception for signals transmitted by the transmitting antennae  110  and  111 . This involves quite a long processing time. 
     This processing time increases with the MIMO system ranking. If, for example. a 4×4 MIMO system with a degree of diversity of order 2 in reception and using 8 antennae is considered, each receiver channel must be able to choose an antenna from among the 8. If all combinations of 4 antennae from S are considered, C 4   8 =70 possible switching schemas are obtained. This clearly leads to a processing time incompatible with a dynamic management of the antenna device according to the variations in the environment and more specifically in a home network rich in multi-paths. 
     Another purpose of the present invention is to propose a multi-antenna device for receiving or transmitting/receiving, enabling the reduction of this processing time. 
     Moreover, the switching means comprise switching elements leading to losses in the reception of the signals by receiver channels  120  and  121 . For example, in the case of the 2×2 MIMO system of  FIG. 2 , the switching means comprise for example 4 single-pole double-throw switches  141  and 2 single-pole four-throw switches  142  as shown in  FIG. 2 . 
     Switches  141  and  142  generate a loss of approximately 0.5 dB and 2 dB respectively at 6 GHz. 
     Another purpose of the invention is to propose a multi-antenna device for receiving or transmitting/receiving enabling the use of a reduced number of switches in the switching means or the use of switches creating fewer losses. 
     SUMMARY OF THE INVENTION 
     According to the invention, the reception device of a MIMO system is equipped with a plurality of directive antennae each covering one of its own angular sectors, the angular sectors of the antennae essentially not overlapping and together forming a total angular sector of 360 degrees. 
     For this purpose, the present invention relates to a device for receiving signals in a MIMO system comprising:
         m signal receiver channels, where m is greater than 1;   an antenna system;   switching means in order to associate with each signal receiver channel an antenna from among n antennae according to a switching schema selected by control means, the switching schema being selected from a plurality of switching schemas of a switching matrix according to a criterion representing the quality of the reception of the signals by said signal receiver channels,       

     characterized in that the antenna system is constituted by either n directive antennae n&gt;m, each antenna being able to receive signals in one of its own angular sectors, the angular sectors of the n antennae essentially not overlapping each other and together forming a total angular sector of 360 degrees, or by a multi-sector antenna with n angular sectors n&gt;m, the n angular sectors essentially not overlapping each other and each possessing a distinct access. 
     According to a specific embodiment, the switching matrix comprises p switching schemas, where 
               p   &lt;       n   !         m   !     ⁢       (     n   -   m     )     !           ,         
and the control means control the switching means so as to select one of said switching schemas p according to said quality criterion.
 
     The use of directive antennae each covering its own angular sector or of a multi-sector antenna enables the number of switching schemas in the switching matrix to be reduced and to make this number less than c n   m . Indeed, in a home network context, there is always a main path and therefore a privileged propagation direction. The result is that the probability that opposite sectors contribute to the MIMO multi-path is low. In other words, if a first sector correctly receives MIMO signals, there is a low probability that the opposite sector also correctly receives the MIMO signals. The switching schemes corresponding to these cases can therefore be deleted from the switching matrix, 
     According to a specific embodiment, the switching matrix comprises at least the n switching schemes, each selecting m antennae having consecutive angular sectors. In this embodiment, the switching matrix comprises a limited number of switching schemes, namely m switching schemes instead of c n   m , resulting in a much reduced processing time for the dynamic management of the antennae. 
     According to another embodiment, the switching matrix also comprises the switching schemes, each selecting m antennae having their angular sectors comprised in a set of m+1 consecutive angular sectors, with at most two antennae from among the m selected antennae having opposite angular sectors. In this embodiment, the switching matrix comprises a larger number of switching schemes, which increases the processing time but enables a response to a larger number of multi-path configurations. 
     In a variant, the switching matrix comprises, in addition to the n switching schemes each selecting m antennae with consecutive angular sectors, the switching schemes each selecting m antennae having their own angular sectors comprised in a set of m+2 consecutive angular sectors, the switching schemes selecting antennae having opposite angular sectors being excluded from said switching matrix. 
     The reduction of the number of switching schemes in the switching matrix (&lt;c n   m ) enables, in addition to the reduction in the processing time for the dynamic selection of the antennae, the use of a reduced number of switching elements in the switching means and/or the use of switching elements. 
     According to a preferred embodiment, the control means comprise additional means in order to replace the switching schema selected by said control means by another predefined switching schema of the switching matrix, when the reception quality criterion for at least one of the signal receiver channels is no longer met. 
     For each switching schema, a replacement switching schema is thus determined in advance when the quality of the reception of the switching schema selected by the control means is no longer good. The replacement can thus be made instantaneously and the processing time is thus reduced to its minimum. 
     According to a particular embodiment, the angular sectors of the antennae have identical sizes equal to 360/n degrees. The coverage domain of the device is thus divided into equal sectors. 
     According to a particular embodiment, the n antennae are formed by a multi-sector antenna with n angular sectors, each sector being able to be linked to a receiver channel via said switching means. 
     The invention is also applicable to the transmission of signals in a device for transmitting and receiving MIMO system signals. In this case, the invention relates to a device for transmitting and receiving signals in a MIMO system comprising:
         a reception device such as described previously, and   m signal transmission channels, each signal transmission channel being associated with a signal receiver channel,       

     wherein switching means are further able to associate with each transmission channel an antenna from among n antennae according to a switching schema selected by the control means, the switching schema being selected from a plurality of switching schemes of a switching matrix according to a criterion representing the quality of the reception of the signals by said associated signal receiver channels. 
     In this case, it is considered that the transmission channels of the MIMO system are reciprocal. The selection of antennae for the transmission of MIMO signals is then carried out by using the same switching matrix. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The invention will be better understood, and other aims, details, characteristics and advantages will appear more clearly over the course of the detailed description which follows in referring to the figures in the appendix, showing in: 
         FIG. 1 , a diagram showing a 2×2 NINO system with a diversity of order 2 in reception according to prior art; 
         FIG. 2 , a diagram of the reception device of the MIMO system of  FIG. 1 ; 
         FIG. 3 , a diagram of a reception device for a 2×2 MIMO system of order 2 in reception in accordance with the invention; 
         FIG. 4 , a diagram showing the switching schemes of a switching matrix which can be used by the device of  FIG. 3 ; 
         FIG. 5 , a diagram of a reception device for a 4×4 MIMO system of order 2 in reception in accordance with the invention; 
         FIG. 6 , a diagram showing the switching schemes of a switching matrix which can be used by the device of  FIG. 5 ; 
         FIGS. 7 and 8 , diagrams showing the replacement of the switching schemes of the switching matrix of  FIG. 6  by other switching schemes of the matrix; 
         FIG. 9 , a diagram of a reception device for a 3×3 MIMO system of order 2 in reception 
       in accordance with the invention; 
         FIG. 10 , a diagram showing the switching schemes of a switching matrix which can be used by the device of  FIG. 9 ; and 
         FIG. 11 , a diagram showing the replacement of a switching schema of the switching matrix of  FIG. 10  by another switching schema of the matrix. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The invention will be described within the scope of multi-antenna reception device of a MIMO system. 
     The invention is more specifically described using different examples of reception devices, namely a reception device for a 2×2 MIMO system of order 2 in reception, a reception device for a 4×4 MIMO system of order 2 in reception and a reception device for a 3×3 MIMO system of order 2 in reception. 
     2×2 MIMO System of Order 2 in Reception 
       FIG. 3  shows a reception device for a 2×2 MIMO system of order 2 in reception 
     The reception device comprises two receiver channels  220  and  221 , four antennae  230  to  233  and switching means  240  for associating with each receiver channel an antenna from among the four antennae  230  to  233 . The switching means are controlled by control means  250  selecting a switching schema from a plurality of switching schemes of a switching matrix according to a criterion representing the quality of the reception of the signals by receiver channels  220  and  221 . This criterion is, for example, a measurement of the received strength or RSSI (Received Signal Strength Information) or a measurement of the signal-to-noise ratio. 
     According to the invention, antennae  230  to  233  are directive antennae, meaning each antenna covers a specific angular sector of around 90°. In the example shown in  FIG. 3 , antenna  230  covers the 0°-90° sector (clockwise), antenna  231  covers the 180°-270° sector, antenna  232  covers the 90°-180° sector and antenna  233  covers the 270°-360° sector. Directive antennae  230  and  231  cover opposite sectors and are connected by a single-pole double-throw switch  241  to receiver channel  220 . Likewise, directive antennae  232  and  233  cover opposite sectors and are connected by a single-pole double-throw switch  241  to receiver channel  221 . The angular sectors able to be associated with receiver channel  220  are hatched and the angular sectors able to be associated with reception channel  221  are checkered. 
     According to a particular embodiment, antennae  230  to  233  are constituted by a single multi-sector antenna having 4 angular sectors of 90° essentially not overlapping and having 4 distinct sector accesses. 
     The switching matrix advantageously comprises a reduced number of switching schemes enabling a reduced processing time for the dynamic selection of antennae. 
     This switching matrix comprises for example the 4 switching schemes shown in  FIG. 4 , namely:
         the switching schema associating antenna  230  with receiver channel  220  and antenna  233  with receiver channel  221 ;   the switching schema associating antenna  230  with receiver channel  220  and antenna  232  with receiver channel  221 ;   the switching schema associating antenna  231  with receiver channel  220  and antenna  233  with receiver channel  221 ;   the switching schema associating antenna  231  with receiver channel  220  and antenna  232  with receiver channel  221 ;       

     Advantageously, the antennae associated with receiver channel  220  and the antennae associated with receiver channel  221  have orthogonal polarizations in order to improve the decorrelation of signals received in adjacent sectors. 
     In this embodiment, the control means  250  select for receiver channel  220  the antenna enabling the best reception from among the antennae corresponding to the hatched sectors and for receiver channel  221  the best antenna from among the antennae corresponding to the checkered sectors. 
     In order to achieve this, during a search phase, the control means test successively the  4  switching schemes of the switching matrix and memorize for each one a measurement of the received strength and/or a measurement of the signal-to-noise ratio. 
     Once the measurements are completed, the control means select the optimal switching schema. Then, the received strength and/or the signal-to-noise ratio are/is measured periodically on each receiver channel, for example every 100 ms. When one of the measurements falls below a predefined threshold value, a search phase is reinitiated. 
     In this embodiment, the use of one single-pole double throw switch  241  to connect each receiver channel to an antenna has the advantage of reducing the losses to 0.5 dB, compared with 2.5 dB for the device in  FIG. 2 . 
     4×4 MIMO System of Order 2 in Reception 
       FIG. 5  shows a reception device for a 4×4 MIMO system of order 2 in reception. 
     The reception device comprises four receiver channels  320  to  323 , eight antennae  330  to  337  and switching means  340  in order to associate with each receiver channel an antenna from among the four antennae  330  to  337 . Switching means  340  are controlled by control means  350  which select a switching schema from among a plurality of switching schemes of a switching matrix according to a criterion representing the quality of the reception of the signals by receiver channels  320  and  323 . 
     Antennae  330  to  337  are directive and each cover a specific angular sector of around 45°. In the example shown in  FIG. 5 , antenna  330  covers the 0°-45° sector, antenna  331  covers the 90°-135° sector, antenna  332  covers the 180°-225° sector and antenna  333  covers the 270°-315° sector, antenna  334  covers the 45°-90° sector, antenna  335  covers the 135°-180° sector, antenna  336  covers the 225°-270° sector and antenna  337  covers the 315°-360° sector. 
     Receiver channels  320  and  321  are selectively connected to directive antennae  330  to  333  via switching means  340 . Similarly, receiver channels  322  and  323  are selectively connected to directive antennae  334  to  337  via switching means  340 . 
     Switching means  340  comprise four single-pole double-throw switches  341  and two single-pole four-throw switches  342  for the connection of antennae  330  to  333  to the receiver channels  320  and  321 . They comprise four further single-pole double-throw switches  341  and two further single-pole four-throw switches  342  for the connection of antennae  334  to  337  to the receiver channels  322  and  323 . 
     In  FIG. 5 , the angular sectors which can be associated with receiver channels  320  and  321  are hatched and the angular sectors that can be associated with receiver channels  322  to  323  are checkered. 
     According to a particular embodiment, antennae  330  to  337  are constituted by one single multi-sector antenna having 8 angular sectors of 45° essentially not overlapping and having 8 distinct sector accesses, 
     The switching matrix advantageously comprises a reduced number of switching schemes enabling a reduced processing time by the dynamic selection of antennae. 
     This switching matrix comprises the 16 switching schemes shown in  FIG. 6 , including 8 switching schemes each selecting 4 reception antennae having consecutive angular sectors and 8 switching schemes each selecting 4 reception antennae having their angular sectors comprised in a set of 5 consecutive angular sectors, with at most two from among the 4 antennae selected having opposite angular sectors. 
     Advantageously, the antennae associated with receiver channels  320  and  321  and the antennae associated with receiver channels  322  and  323  have orthogonal polarizations in order to improve the decorrelation of signals received in adjacent sectors. 
     In this embodiment, the control means  350  select for receiver channels  320  and  321  the two best antennae from among the antennae corresponding to the hatched sectors and for receiver channels  322  and  323  the two best antennae from among the antennae corresponding to the checkered sectors. 
     In order to achieve this, during a search phase, the control means  350  test successively the  16  switching schemas of the switching matrix and memorize for each one a measurement of the received strength and/or a measurement of the signal-to-noise ratio. 
     Once the measurements are completed, the control means select the optimal switching schema. Then, the received strength and/or the signal-to-noise ratio are/is measured periodically on each receiver channel. When one of the measurements fails below a predefined threshold value, a search phase is reinitiated. 
     The duration of this initialization phase can nevertheless be long when the switching matrix comprises a large number of switching schemas. It is therefore advantageously provided to define in advance, for each switching schema, a switching schema called a replacement schema which replaces it when the reception quality criterion for at least one of the receiver channels is no longer met, that is to say when the is measurement of the received strength and/or the measurement of the signal-to-noise ratio of one of the receiver channels fall below the predefined threshold values. 
     This replacement operation is shown by  FIGS. 7 and 8 .  FIG. 7  shows the case where the quality criterion for one of the receiver channels is no longer met. The angular sector of the antenna associated with this receiver channel is represented in black in the figure. In this embodiment, the current switching schema is replaced by a predefined replacement switching schema of the switching matrix which does not use the sub-optimal receiver channel. This replacement operation is performed by means of a look-up table  351  (LUT) controlled by a replacement algorithm. This LUT is stored in the control means. In the example of  FIG. 8 , the current switching schema is replaced by the switching schema in which the sector in black is replaced by its opposite dual. 
       FIG. 8  shows the case where the quality criterion for two receiver channels is no longer met. In this case, the current switching schema is replaced by a predefined replacement switching schema of the switching matrix which does not use the defective sectors (sectors in black). 
     It should be noted that the use of one single-pole double-throw switch  341  and one single-pole four-throw switch  342  to connect each receiver channel to an antenna enables losses to be limited to 2.5 dB. In the prior art, a single-pole eight-throw switch is typically used for which losses are much higher. 
     3×3 MIMO System of Order 2 in Reception 
       FIG. 9  shows a reception device for a 3×3 MIMO system of order 2 in reception 
     The reception device comprises three receiver channels  420 ,  421  and  422 , six reception antennae,  430  to  435 , and switching means  440  for associating with each receiver channel an antenna from among the six antennae  430  to  435 . The switching means are controlled by control means  450  selecting a switching means from among a plurality of switching means of a switching matrix according to a criterion representing the quality of the reception of the signals by receiver channels  420  and  422 . 
     Antennae  430  to  233  are directive antennae each covering a particular angular sector of around 60°. In the example shown by  FIG. 9 , antenna  430  covers the 0°-60° sector, antenna  431  covers the 180°-240° sector, antenna  432  covers the 60°-120° sector, antenna  433  covers the 240°-300° sector, antenna  434  covers the 120°-180° sector and antenna  435  covers the 300°-360° sector. In the figure, the sectors of antennae  430  and  431  are hatched and represent the sectors able to be associated with receiver channel  420 . The sectors of antennae  432  and  433  are represented by points and represent the sectors able to be associated with receiver channel  421 . The sectors of antennae  434  and  435  are checkered and represent the sectors able to be associated with receiver channel  422 . 
     The 6 antennae  430  to  435  can constitute one and the same multi-sector antenna having 6 angular sectors of 60° essentially not overlapping and 6 distinct sector accesses. 
     The switching means comprise three single-pole double-throw switches  441 , each selectively connecting two antennae to its own receiver channel. 
     The switching matrix advantageously comprises the 8 switching schemas shown in  FIG. 10 , including 6 switching schemas each selecting 3 antennae having consecutive angular sectors and 2 switching schemes each selecting 3 antennae having non-contiguous angular sectors. 
     In this embodiment, control means  450  select, for the 3 receiver channels the “best” antenna from among the antennae corresponding to the hatched sectors, the “best” antenna from among the antennae corresponding to the sectors represented by points and the “best” antenna from among the antennae corresponding to the checkered sectors. 
     As for the other systems, during a search phase, the control means test successively the 8 switching schemes of the switching matrix and memorize for each one a measurement of received strength and/or a measurement of the signal-to-noise ratio. Once the measurements are completed, the control means select the optimal switching schema. Then, the received strength and/or the signal-to-noise ratio are/is measured periodically on each receiver channel. When one of these measurements falls below a predefined threshold value, the switching schema is replaced by a predefined replacement switching schema. 
     This replacement operation is shown by  FIG. 11  This figure shows the case where the quality criterion for one of the receiver channels is no longer met. The angular sector of the antenna associated with this defective receiver channel is represented in black in the figure. In the example of  FIG. 11 , the current switching schema is replaced by the switching schema in which the sector in black is replaced by its opposite dual 
     It should be noted that the use of one single-pole double-throw switch  441  to connect each receiver channel to an antenna enables losses to be limited to 0.5 dB. In the prior art, a single-pole six-throw switch is typically used for which losses are much higher. 
     The invention is also applicable to the transmission of signals in a device for transmitting and receiving MIMO system signals. In this case, the device comprises, in addition to the means described previously, signal transmission channels, each signal transmission channel being associated with a signal receiver channel The switching means are further able to associate with each of the channels or the receiver channels an antenna from among the antennae of the device according to a switching schema selected by the control means. In this case, it is considered that the transmission channels of the MIMO system are reciprocal. 
     The switching schema selected to connect the transmission channels to the antennae and to transmit MIMO signals is the same as that used to receive the MIMO signals. 
     The invention is more specifically applicable within the scope of deployment of broadband multimedia home networks. The switching matrix topologies proposed here enable the implementation of directive antennae solutions associated with MIMO type multi-antenna transmission devices. They allow for a directivity gain while limiting the perturbation risk linked to the interferences in a home environment that is rich in multi-paths. The invention helps to discretize space and, as a result, adds a degree of spatial diversity via the sectorization of antennae. This concept associates a simplified architecture and considerably alleviates the process of switching schema selection. The reduction in processing time thus enables an effective dynamic control of the antennae in order to combat the harmful effects of multi-paths and interfering elements more efficiently, and to increase the system performances noticeably in terms of range and bitrate. 
     Although the invention has been described in relation to different particular embodiments, it is obvious that it is in no way restricted and that it comprises all the technical equivalents of the means described together with their combinations if the latter fall within the scope of the invention.