Abstract:
An active antenna system and algorithm is proposed that provides for dynamic tuning and optimization of antenna system parameters for a MIMO system that will provide for greater throughput. As one or multiple antennas are loaded or de-tuned due to environmental changes, corrections to correlation and/or isolation are made by tuning the active antenna. A null-steering technique is implemented to alter the near-field and far-field characteristics to aid in modifying correlation and isolation in the multi-antenna system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation in part (CIP) of U.S. Ser. No. 14/560,173, filed Dec. 4, 2014, and titled “ACTIVE MIMO ANTENNA CONFIGURATION FOR MAXIMIZING THROUGHPUT IN MOBILE DEVICES”; 
         [0002]    which is a continuation (CON) of U.S. Ser. No. 13/674,115, filed Nov. 12, 2012, and titled “ACTIVE MIMO ANTENNA CONFIGURATION FOR MAXIMIZING THROUGHPUT IN MOBILE DEVICES”, now U.S. Pat. No. 8,928,541; 
         [0003]    which said Ser. No. 13/674,115 is a CIP of U.S. Ser. No. 13/029,564, filed Feb. 17, 2011, and titled “ANTENNA AND METHOD FOR STEERING ANTENNA BEAM DIRECTION”, now U.S. Pat. No. 8,362,962; which is a CON of U.S. Ser. No. 12/043,090, filed Mar. 5, 2008, titled “ANTENNA AND METHOD FOR STEERING ANTENNA BEAM DIRECTION”, now issued as U.S. Pat. No. 7,911,402; and 
         [0004]    which said Ser. No. 13/674,115 is a CIP of U.S. Ser. No. 13/227,361, filed Sep. 7, 2011, and titled “MODAL ANTENNA WITH CORRELATION MANAGEMENT FOR DIVERSITY APPLICATIONS”; 
         [0005]    the contents of each of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0006]    1. Field of the Invention 
         [0007]    This invention relates generally to the field of wireless communication. In particular, the invention relates to Multiple Input Multiple Output (MIMO) antenna implementations capable of improved data throughput performance for use in such wireless communications. 
         [0008]    2. Description of the Related Art 
         [0009]    Commonly owned U.S. Pat. No. 7,911,402 describes a beam steering technique wherein a single antenna is capable of generating multiple radiating modes; the entire contents of which are hereby incorporated by reference. The multiple modes are effectuated with the use of offset parasitic elements that alter the current distribution on the driven antenna as the reactive load on the parasitic is varied. This beam steering technique where multiple modes are generated is referred to as a modal antenna technique, and an antenna configured to alter radiating modes in this fashion will be referred to here as a modal antenna. 
         [0010]    A receive diversity application using modal antennas as described in commonly owned U.S. Ser. No. 13/227,361, filed Sep. 7, 2011, and titled “MODAL ANTENNA WITH CORRELATION MANAGEMENT FOR DIVERSITY APPLICATIONS”; wherein a single modal antenna can be configured to generate multiple radiating modes to provide a form of switched diversity; the entire contents of which are hereby incorporated by reference. Certain benefits of this technique include the reduced volume required in the mobile device for a single antenna instead of a two antenna receive diversity scheme, reduction in receive ports on the transceiver from two to one, and the resultant reduction in current consumption from this reduction in receive ports. 
         [0011]    With MIMO (Multiple Input Multiple Output) systems becoming more prevalent in the access point and cellular communication fields, the need for two or more antennas collocated in a mobile device or small form factor access point are becoming more common. These groups of antennas in a MIMO system need to have high, and preferably, equal efficiencies along with good isolation and low correlation. For handheld mobile devices the problem is exacerbated by antenna detuning caused by the multiple use cases of a device: hand loading of the cell phone, cell phone placed to user&#39;s head, cell phone placed on metal surface, etc. For both cell phone and access point applications, the multipath environment is constantly changing, which impacts throughput performance of the communication link. 
       SUMMARY OF THE INVENTION 
       [0012]    An active antenna system and algorithm provides for dynamic tuning and optimization of antenna system parameters for a MIMO system that will provide for greater throughput. As one or multiple antennas are loaded or de-tuned due to environmental changes, corrections to correlation and/or isolation are made by tuning the active antenna. A null-steering technique is implemented to alter the near-field and far-field characteristics to aid in modifying correlation and isolation in the multi-antenna system. 
         [0013]    In one embodiment, an active MIMO antenna system comprises: a first active modal antenna capable of selective operation about a plurality of modes, wherein each of said plurality of modes generates a distinct antenna radiation pattern resulting from the first active modal antenna; a second antenna; each of the first active modal antenna and the second antenna being individually coupled to a respective transceiver selected from a first and second transceiver; and a processor coupled to at least the first active modal antenna and configured to select the mode from the plurality of modes associated with the first modal antenna such that correlation of the two antenna system is altered for optimal performance. 
         [0014]    In another embodiment, the second antenna is an active modal antenna capable of selective operation about a plurality of modes, wherein each of said plurality of modes generates a distinct antenna radiation pattern resulting from the first active modal antenna; the processor is further coupled to the second modal antenna and configured to select the mode from the plurality of modes associated with the second modal antenna such that the correlation of the two-antenna system is altered for optimal performance. 
         [0015]    In another embodiment, the first active modal antenna comprises: a radiating structure disposed above a circuit board and forming an antenna volume therebetween; a parasitic element positioned adjacent to the radiating structure; and an active element coupled to the parasitic element; wherein said active element is configured for one or more of: adjusting a reactance of the parasitic element, or shorting the parasitic element to ground. 
         [0016]    In certain embodiments, the active elements may individually comprise: a voltage controlled tunable capacitor, voltage controlled tunable phase shifter, field-effect transistor (FET), tunable inductor, switch, or any combination thereof 
         [0017]    In another embodiment, the active MIMO antenna comprises three or more antennas. 
         [0018]    In some embodiments, at least one passive antenna having a fixed radiation pattern. 
         [0019]    In another embodiment, an active MIMO antenna system comprises: three or more active modal antennas, each of the active modal antennas being adapted for operation at a plurality of antenna modes, and each of said antenna modes having a distinct antenna radiation pattern. A processor coupled to the modal antennas and configured to select a mode from the plurality of modes associated with each of the modal antennas such that the correlation of the multi-antenna system is altered for optimal performance. 
         [0020]    In certain embodiments, one or more of the antennas of the active MIMO antenna system comprises a passive antenna with a fixed radiation pattern. 
         [0021]    In yet another embodiment, an active MIMO antenna system comprises: a plurality of antennas, each of the antennas configured to produce a distinct radiation pattern with respect to each other; one or more of said plurality of antennas comprising an active modal antenna configured for multimode operation, wherein the active modal antenna comprises a distinct radiation pattern in each of the multiple modes; and a processor configured to select the mode of the one or more active modal antennas by sending control signals to respective active elements; wherein the active MIMO antenna system is adapted to optimize correlation of the antenna system for optimal antenna performance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The invention can be further understood upon review of the following detailed description in conjunction with the appended drawings, wherein: 
           [0023]      FIG. 1  illustrates a four antenna Multi-Input Multi-Output (MIMO) antenna system in an access point, wherein the antennas comprise passive antenna structures with fixed radiation patterns. 
           [0024]      FIGS. 2(A-C)  illustrate a correlation matrix for six antennas in a MIMO system, each of the antennas is configured for a single radiating mode. 
           [0025]      FIG. 3  illustrates a four antenna MIMO antenna system, each of the four antennas comprises “n” modes of operation, wherein the antenna produces a distinct radiation pattern at each of the “n” modes. 
           [0026]      FIGS. 4(A-C)  illustrate a correlation matrix for six antennas in a MIMO system, each of the antennas is configured for operation at two distinct radiating modes. 
           [0027]      FIGS. 5(A-C)  illustrate a correlation matrix for “m” antennas in a MIMO system, each of the antennas is configured for operation at “n” distinct radiating modes. 
           [0028]      FIG. 6  illustrates a process for selecting the optimal set of modes from an antenna system containing one or more active modal antennas. 
           [0029]      FIG. 7  illustrates a two antenna system where the antennas are conventional, passive antennas. 
           [0030]      FIGS. 8(A-B)  illustrate plots of return loss, isolation, and correlation for a two antenna system as illustrated in  FIG. 7 . 
           [0031]      FIG. 9  illustrates a two antenna system where the antennas are active modal antennas. 
           [0032]      FIG. 10(A-B)  illustrate plots of return loss, isolation, and correlation for a two active modal antenna system of  FIG. 9 . 
           [0033]      FIG. 11  illustrates a two antenna system wherein a first antenna is an active modal antenna and a second antenna is a conventional, passive antenna. 
           [0034]      FIG. 12  illustrates a two antenna system wherein the first and second antennas are both active modal antennas. 
           [0035]      FIG. 13  illustrates a two antenna system wherein the first and second antennas are both active modal antennas and a first of the modal antennas is coupled to a processor and first switch for controlling a second switch associated with a second of the modal antennas. 
           [0036]      FIG. 14  illustrates a 4×4 modal antenna MIMO configuration with respective switches for configuring the antenna. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    In the following description, for purposes of explanation and not limitation, details and descriptions are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these details and descriptions. 
         [0038]    Commonly owned, U.S. Pat. No. 7,911,402, titled “ANTENNA AND METHOD FOR STEERING ANTENNA BEAM DIRECTION”, and U.S. Pat. No. 7,830,320, titled “ANTENNA WITH ACTIVE ELEMENTS”, disclose antenna systems capable of beam steering, band switching, active matching, and other active tunable characteristics; the contents of each of which are hereby incorporated by reference. These antennas utilize a radiating element and one or more parasitic elements coupled to active elements in a manner for enabling switching, variable reactance, and other tuning of the antenna components. The resulting structure is an active tunable antenna capable of operating in multiple modes, otherwise termed an “active modal antenna” or “modal antenna”. The referenced patents disclose active modal antennas and thus details of these structures will not be discussed in detail herein. 
         [0039]    An “active modal antenna” as referred to herein includes an antenna capable of selective operation about a plurality of modes, wherein each of said plurality of modes generates a distinct antenna radiation pattern resulting from the first active modal antenna. In this regard, the active modal antenna can be reconfigured as necessary to provide an optimal radiation pattern. This is accomplished by one or more of: band-switching, beam steering, and active impedance matching as environmental effects detune the antenna. In representative examples, an active modal antenna comprises a radiating structure disposed above a circuit board and forming an antenna volume therebetween; a parasitic element positioned adjacent to the radiating structure; and an active element coupled to the parasitic element; wherein the active element is configured for one or more of: adjusting a reactance of the parasitic element, or shorting the parasitic element to ground. 
         [0040]    As referenced herein, an “active element” may comprise at least one of: a voltage controlled tunable capacitor, voltage controlled tunable phase shifter, field-effect transistor (FET), tunable inductor, switch, or any combination thereof 
         [0041]    In certain embodiments, an antenna system comprises: a first active modal antenna adapted for operation at a plurality of antenna modes, each of the antenna modes having a distinct antenna radiation pattern; a second antenna with a fixed radiation pattern; and a processor coupled to the first modal antenna and configured to select the mode from the plurality of modes associated with the modal antenna such that the correlation of the two antenna system is altered for optimal performance. 
         [0042]    In other embodiments, the second antenna comprises an active modal antenna adapted for operation at a plurality of antenna modes, each of the antenna modes having a distinct antenna radiation pattern; and a processor is coupled to the first and second modal antennas and configured to select each mode from the plurality of modes associated with the modal antennas such that the correlation of the two antenna system is altered for optimal performance. 
         [0043]    In another embodiment, the active modal antenna may further comprise a primary radiator, at least one parasitic element disposed adjacent to the primary radiator, and one or more active elements coupled to the at least one parasitic element; wherein the modal antenna is adapted to switch between two or more antenna modes by actively adjusting said at least one parasitic element and one or more active elements coupled therewith. The active elements can be used to vary a reactance on the parasitic element for causing a frequency shift, or rotation of the antenna radiation pattern depending on location of the parasitic element relative to the antenna radiator. 
         [0044]    In certain embodiments, an antenna system comprises: three or more modal device antennas, each adapted for operation at a plurality of antenna modes, each of said antenna modes having a distinct antenna radiation pattern; and a processor coupled to the modal antennas and configured to select the mode from the plurality of modes associated with the modal antennas such that the correlation of the multi-antenna system is altered for optimal performance. 
         [0045]    In various embodiments, one or more of the multiple antenna radiators is not a modal antenna and may comprise any passive antenna radiator in the art. 
         [0046]    Now turning to the drawings,  FIG. 1  illustrates a wireless access point  10  with a four-antenna Multiple Input Multiple Output (MIMO) system, the four antennas labeled as A; B; C; D, respectively. The access point  10  is used to communicate with multiple wireless users simultaneously, with three users shown (User  1 ; User  2 ; and User  3 ). The radiation patterns for each of the respective four antennas of the MIMO antenna system are denoted as  11 ;  12 ;  13  and  14 , respectively. Because the antennas are passive, the respective radiation patterns are fixed. 
         [0047]      FIG. 2A  illustrates a six-antenna MIMO system integrated into the wireless access point  20 . The antennas are conventional, passive antennas, with each antenna possessing a single radiation pattern or mode. The six antennas are labeled  1 ;  2 ;  3 ;  4 ;  5 ; and  6 , respectively.  FIG. 2B  shows a chart indicating a single radiating mode for each passive antenna of the six antennas. In  FIG. 2C , a correlation matrix is shown for the six-antenna system, with the correlation between antennas being characterized by a fifteen-value matrix. 
         [0048]      FIG. 3  illustrates a wireless access point  30  with a four-antenna MIMO system, with the four antennas being active modal antennas  35 (A-D), respectively. Each modal antenna is capable of generating several unique radiation patterns or modes. Three radiation patterns or modes (MODE  1 ; MODE  2 ; MODE  3 ) are shown for one of the antennas in breakout view  36 . As further illustrated in  FIG. 3 , an access point  30  comprising one or more modal antennas will be adapted for multiple modes (represented as “n” modes herein), wherein each of the “n” antenna modes generates a distinct radiation pattern. 
         [0049]      FIG. 4  illustrates a six-antenna MIMO system integrated into the wireless access point  40 . The antennas are active modal antennas, labeled A 1 ; A 2 ; A 3 ; A 4 ; A 5 ; and A 6 , respectively, where each modal antenna is capable of generating two radiation patterns or modes. In this example, as illustrated in  FIG. 4B , each modal antenna is capable of generating two modes; for example antenna Al can generate Modes A 1 , 1  and A 1 , 2 .  FIG. 4C  shows a correlation matrix for the six-antenna system, each antenna having two respective modes, with the correlation between antennas being characterized by a thirty-value matrix. It should be recognized that the modal antennas can be configured for up to “n” modes, where “n” is an integer between one and infinity. Thus, the correlation matrix will be increased with the number of antenna modes provided by the active modal antennas. 
         [0050]      FIG. 5  illustrates an “m”-antenna MIMO system integrated into the wireless access point; the antennas are labeled Al thru Am, respectively. In accordance with  FIG. 5B , the antennas are active modal antennas, where each modal antenna is capable of generating a plurality of modes, or “n” respective radiation patterns or modes.  FIG. 5C  shows a correlation matrix is shown for the “m” modal antenna system. 
         [0051]      FIG. 6  illustrates a process used to select the optimal set of modes from an antenna system containing one or multiple Modal antennas. The process includes: (i) iterating through all combinations of Modes and monitor system performance; the metric for system performance can be any of: channel correlation; throughput; signal to noise ratio (SNR); received signal strength indicator (RSSI); among others; (ii) selecting the best combination of Modes and initiate data transmission and reception; and (iii) periodically monitoring performance of available combinations of Modes and select a best combination. 
         [0052]      FIG. 7  illustrates a two antenna system where the antennas are conventional, passive antennas. Antenna  1  is connected to transceiver  1  (TXCR  1 ), and antenna  2  is connected to transceiver  2  (TXCR  2 ). A baseband processor interfaces with the pair of transceivers. With antennas  1  and  2  being passive antennas, parameters such as efficiency, isolation, return loss, and correlation are fixed and cannot be adjusted dynamically to optimize for different use conditions or changes to the multipath environment. These parameters vary as a function of local environment, i.e. hand loading of the device. System throughput and SNR varies and can degrade as the environment changes. 
         [0053]      FIGS. 8(A-B)  illustrate plots of return loss, isolation, and correlation for a two antenna system as illustrated in  FIG. 7 . The two antennas are passive which results in a fixed response of these parameters as a function of frequency. 
         [0054]      FIG. 9  illustrates a two antenna system where the antennas are active modal antennas. Modal antenna  1  is connected to transceiver  1  (TXCR 1 ), and modal antenna  2  is connected to transceiver  2  (TXCR 2 ). A baseband processor interfaces with the pair of transceivers and also provides control signals to modal antennas  1  and  2 . With antennas  1  and  2  being modal antennas, parameters such as efficiency, isolation, return loss, and correlation can be adjusted dynamically to optimize for different use conditions or changes to the multipath environment. Thus, the active Modal two antenna system has variable efficiency, isolation, and pattern correlation. Dynamic optimization of pattern correlation and isolation results in improved system throughput and SNR. 
         [0055]      FIGS. 10(A-B)  illustrate plots of return loss, isolation, and correlation for a two antenna system of  FIG. 9 . The two antennas are modal antennas which results in multiple responses of these parameters being available for selection to provide the ability to dynamically adjust antenna system performance to optimize for different use conditions or changes to the multipath environment. Multiple tuning states from Modal antennas provide dynamic tuning capabilities, where correlation and isolation can be varied. 
         [0056]      FIG. 11  illustrates a two-antenna system where antenna  111  is a modal antenna and antenna  112  is a conventional, passive antenna. Antenna  111  is connected to a first transceiver  114  and antenna  112  is connected to a second transceiver  115 . Modal antenna  111  includes a parasitic element  111   b  positioned near a radiator element  111 A, and an active tuning element  111 C is associated with the parasitic element. A processor  113  provides control signals  116  to the active tuning element  111 C for configuring one of several modes of the modal antenna  111 . 
         [0057]      FIG. 12  illustrates a two-antenna system where both antennas  121  and  122  are modal antennas. Modal antenna  121  is connected to a first transceiver  124  and modal antenna  122  is connected to a second transceiver  125 . Each of the modal antennas comprises a radiator  121 A;  122 A positioned adjacent to a parasitic element  121 B;  122 B, respectively, and an active tuning element  121 C;  122 C associated with the respective parasitic element. A processor  123  provides control signals  126 ;  127  to the modal antennas. 
         [0058]      FIG. 13  illustrates a two antenna system where each of the antennas are active modal antennas. A first modal antenna  131  is connected to a first transceiver (TXCR 1 )  137 , and a second modal antenna  132  is connected to a second transceiver (TXCR 2 )  138 . The first modal antenna is further coupled to a first RF switch (S 1 )  134  for configuring a mode of the first modal antenna. The second modal antenna is further coupled to a second RF switch (S 2 ) for configuring a mode of the second modal antenna. In the illustrated example, a first processor (P) and the second RF switch (S 2 ) are each housed in an RF integrated circuit module  133  positioned adjacent to the second modal antenna  132 . A baseband processor  139  interfaces with the pair of transceivers  137 ;  138  and also provides signal information to an RF integrated circuit module  133  and second switch  134 . A transmission line  135  is shown extending between the RF integrated circuit module  133  and the first RF switch  134 , wherein the RF integrated circuit module  133  is configured to send control signals to the first RF switch  134  for configuring the first modal antenna in a preferred configuration mode. 
         [0059]    The signal information can be in the form of received signal strength indicator (RSSI) data or error vector magnitude (EVM) data. 
         [0060]    The processor is coupled to memory containing an algorithm configured to: sample the signal information received from a baseband processor of the antenna system, select a preferred configuration for each of the first and second modal antennas based on the signal information; and communicate control signals to the first and second RF switches for implementing the preferred configuration of the antenna system. 
         [0061]    The preferred configuration includes each of the modal antennas being selected in a respective mode that yields optimum data throughput. The first processor is used to set the preferred mode for each of the first and second modal antennas. 
         [0062]    The preferred mode can be selected based on the optimum data throughput amongst a plurality of client devices on a communication link. For example, the preferred mode can be a configuration of the first and second modal antenna which yields equal and optimum performance for each of the client devices; or alternatively, the preferred mode can be that which yields the optimum data throughput for one or more preferred clients on the communication link. 
         [0063]      FIG. 14  illustrates a four by four MIMO antenna system having a first modal antenna  141   a;  a second modal antenna  141   b;  a third modal antenna  141   c;  and a fourth modal antenna  141   d.  The fourth modal antenna  141   d  is shown coupled to an RF integrated circuit module  143  containing a first processor, memory, and a first RF switch. The first RF switch of the module  143  is coupled to a transceiver  146  via a trace or other transmission line. Each of the first thru third modal antennas  141   a;    141   b;    141   c,  are connected to one of a plurality of RF switches  142   a;    142   b;    142   c,  respectively. Each of the plurality of RF switches is further connected to the transceiver  146 . A baseband processor  147  is connected to the RF integrated circuit model  143  for communicating signal information. The first processor of the RF integrated circuit module  143  processes the signal information in accordance with a resident algorithm to determine a control state for controlling each of the RF switches for configuring the respective modal antennas in a preferred mode. The first processor samples a signal metric against stored antenna mode information to determine a preferred mode, then communicates signals to the RF switches to cause each modal antenna to be set in the preferred configuration mode. Dashed lines show transmission lines extending between the baseband processor and the RF integrated circuit module; and further show connection lines between the RF integrated circuit module and each respective RF switch. 
         [0064]    Other variations will be recognized by those having skill in the art.