Abstract:
By using switches ( 110 ) that are synchronously controlled, the present invention permits connection of a plurality of antennae ( 130 ) to a plurality of radio front end units (radios  120 ) so that at any time any of the radios ( 120 ) may be assigned to any of the antennae ( 130 ) without leaving any radio ( 120 ) unconnected. A controller ( 140 ) arbitrarily assigns, at any time, any of the radios ( 120 ) to any of the antennae ( 130 ) while keeping every radio ( 120 ) connected to an antenna ( 130 ).

Description:
[0001]    This application claims the priority under 35 U.S.C. §119(e)(1) of copending U.S. provisional application No. 60/301,402, filed on Jun. 27, 2001 and copending U.S. provisional application No. 60/344,896, filed on Dec. 31, 2001. The aforementioned patent applications are incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates generally to wireless communication systems and, more particularly, to an antenna to radio connection and switching for transit and receive diversity.  
         BACKGROUND OF THE INVENTION  
         [0003]    Transmission properties, such as gain and phase, of wireless communication channels are time-varying statistical quantities. Therefore, in a wireless communication system characterized by one (1) transmit antenna and one (1) receive antenna, transmission of information can be unreliable because the wireless channel that exists between the two (2) antennae is constantly changing. In digital wireless systems, the degrading effects of statistical channel variations are particularly evident and are manifested as packet errors. This degradation occurs whether or not there is relative movement between the transmit antenna and the receive antenna because it is still possible for the environment to change. Wireless channels are also rendered unreliable because the signal at the receive antenna is the superposition of many waves that travel paths of different lengths to the receive antenna and add constructively or destructively. When the waves add destructively, deep fades are experienced. When these fades occur, it is difficult to equalize the channel and decode the data correctly.  
           [0004]    One of the most effective ways to overcome this degradation in channel reliability is by employing receive diversity (the deployment of multiple receive antennae). In many scenarios, when the receive antennae are spatially separated by more than half a wavelength, the different receive signals are essentially uncorrelated and independent of the other received signals. Therefore, at an instant in time when the signal-to-noise ratio (SNR) at the output of one antenna is low, there is a good chance that the SNR at the output of at least one of the other antennae is high.  
           [0005]    There are several well-known diversity reception techniques that either combine the signals from multiple antennae in different ways or periodically sample the signal from each of the receive antennae and then connect the antenna with the strongest signal to the receiver. It has recently been shown that the benefits of diversity reception can also be obtained from diversity transmission, where multiple transmit antennae simultaneously send differently-encoded versions of the same information. Multiple radios are required to employ diversity transmission. The general case for diversity would then consist of T transmit antennae and R receive antennae.  
           [0006]    When N different radios must share N antennae, diversity transmission and/or reception becomes more difficult to implement. This case may be encountered when, for example, N independent wireless communication systems, each using a different modulation scheme (therefore requiring separate radios), must share N common receive antennae due to limitations such as space constraints. For the implementation of receive diversity, it is problematical to determine how to connect the antennae to the radios so that at any time any of the radios may be assigned to any of the antennae without leaving any radio unconnected. An identical problem arises for the implementation of transmit diversity when several communication systems share N common transmit antennae and at least one of the systems implements M-transmit diversity (M&lt;N), If, for example, exactly one (1) system implements M-transmit diversity, then a total of N−M+1 simultaneous transmit systems can be supported by N transmit antennae. Periodically, for a finite length of time, the system implementing M-transmit diversity will require that its M radios be simultaneously connected to M antennae. A problem also exists in determining the radio-antennae connection configuration if the M radio-antennae connections are required to be mutable.  
           [0007]    It is therefore desirable to provide a solution that permits connection of a plurality of antennae to a plurality of radios (radio front end units) so that at any time any of the radios may be assigned to any of the antennae without leaving any radio unconnected. The present invention provides this through synchronously controlled switches that enable a controller to arbitrarily assign any of the radios to any of the antennae while keeping every radio connected to an antenna.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The above and further advantages of the invention may be better understood by referring to the following description in conjunction with the accompanying drawings in which corresponding numerals in the different figures refer to the corresponding parts, in which:  
         [0009]    [0009]FIG. 1 illustrates an N-radio-to-N-antenna switching arrangement with 2N switches in accordance with an exemplary embodiment of the present invention;  
         [0010]    [0010]FIG. 2 shows a table of simultaneous connections made by FIG. 1;  
         [0011]    [0011]FIG. 3 illustrates a 2-radio-to-2-antenna switching arrangement with four (4) single-pole-double-throw switches in accordance with an exemplary embodiment of the present invention;  
         [0012]    [0012]FIG. 4 illustrates a 2-radio-to-2-antenna switching arrangement with four (4) single-pole-double-throw switches in accordance with a further exemplary embodiment of the present invention;  
         [0013]    [0013]FIG. 5 illustrates a 3-radio-to-3-antenna switching arrangement with six (6) single-pole-triple-throw switches in accordance with an exemplary embodiment of the present invention;  
         [0014]    [0014]FIG. 6 illustrates a 3-radio-to-3-antenna switching arrangement with six (6) single-pole-triple-throw switches in accordance with a further exemplary embodiment of the present invention;  
         [0015]    [0015]FIG. 7 shows a table of simultaneous connections made by FIG. 6;  
         [0016]    [0016]FIG. 8 illustrates an N-radio-to-N-antenna switching arrangement with N switches in accordance with an exemplary embodiment of the present invention;  
         [0017]    [0017]FIGS. 9A and 9B illustrate N-radio-to-N-antenna switching arrangements with N single-pole-N-throw switches for N=2 and N=3, respectively, in accordance with exemplary embodiments of the present invention; and  
         [0018]    [0018]FIGS. 10A and 10B illustrate single-pole-N-throw switches constructed from single-pole-double-throw switches for N=3 and N=4, respectively, in accordance with exemplary embodiments of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0019]    While the making and using of various embodiments of the present invention are discussed herein in terms of specific switches and switch configurations, it should be appreciated that the present invention provides many inventive concepts that can be embodied in a wide variety of contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and are not meant to limit the scope of the invention.  
         [0020]    [0020]FIG. 1 illustrates N radio  120  to N antenna  130  switching arrangement  100  with 2N switches  110  in accordance with an exemplary embodiment of the present invention. The arrangement of FIG. 1 (and also FIGS.  2 - 10 B, below) can be implemented as a wireless transmitter system, a wireless receiver system, or a wireless transceiver system, such as an IEEE 802.11 system, a Bluetooth system or a Global System for Mobile Communication (GSM). Switching arrangement  100  does not use power splitters, each of which carries a 3 dB reduction in power delivered to a radio  120  or an antenna  130 . Therefore, switching arrangement  100  minimizes radio frequency (RF) power losses due to the connection and switching. FIG. 1 uses exactly 2N synchronously controlled single-pole-N-throw (SPNT) switches  110 . Each SPNT switch  110  is connected to a radio (a radio front end unit)  120  and has N outgoing contacts  125  that allow connection to N distinct antennae  130 . Likewise, each SPNT switch  110  connected to an antenna  130  has N incoming contacts  135  that allow connection to N distinct radios  120 . Since there are exactly (N!) 2N  possible ways to connect 2N SPNT switches  110 , by synchronously switching switches  110  through N possible states, each radio  120  can be connected to each antenna  130 . FIG. 2 shows a table of simultaneous connections made by simultaneously switching switches  110 , wherein x N ≡x mod N. Left-hand-side numerals are the radio indices; right-hand-side numerals are the antenna indices. The wiring shown in FIG. 1 makes the connections according to FIG. 2, but there are many other wiring configurations that also implement these connections.  
         [0021]    In switching arrangement  100 , there are always exactly two (2) switches  110  between a radio  120  and the antenna  130  to which it is connected. Since each switch  110  has an associated insertion loss, switching arrangement  100  minimizes the number of switches  110  in the path between a radio  120  and the antenna  130  to which it is connected. Switching arrangement  100  also avoids leaving any radio  120  or antenna  130  unconnected or unterminated. Control of the switching can reside with a single antenna master controller  140  which could be a microprocessor that controls switches  110  to make the desired radio  120  to antenna  130  connections. Antenna master controller  140  can assign any antenna  130  to a particular radio  120 , and then simultaneously assign the remaining radios  120  to respective ones of the remaining antennae  130  depending on which of the (N!) 2N  wiring configurations is implemented and which radio  120  to antenna  130  assignment has already been made by the antenna master.  
         [0022]    For any one of the N switching states of FIG. 2, all switches  110  of FIG. 1 are in the same position, and each of the N switching states dictates a different (common) position for switches  110 . That is, switching state  1  requires all switches  110  to be in position  1 , switching state  2  requires all switches  110  to be in position  2 , etc., where position  1  corresponds to the top contact of the switch, position  2  corresponds to the contact immediately below the top contact, etc. This makes it particularly easy to control switches  110  since each switch  110  is controlled to the same position at any given time. For N=2, there are sixteen (16) possible ways to wire the four (4) SP2T switches  110 . One way, consistent with FIGS. 1 and 2, is shown in FIG. 3 which illustrates two-radio  120  to two-antenna  130  switching arrangement  300  with four (4) single-pole-double-throw switches  110  in accordance with an exemplary embodiment of the present invention. Each SP2T switch  110  is connected to a radio  120  and has two (2) outgoing contacts  125  that allow connection to two (2) distinct antennae  130 . Likewise, each SP2T switch  110  connected to an antenna  130  has two (2) incoming contacts  135 . Switches  110  are shown in one of two (2) possible switching states, that which implements the first row (switching state  1 ) of FIG. 2. The other possible switching state implements the last row (switching state N, for N=2) of FIG. 2.  
         [0023]    Another way to connect switches  110  for N=2 is shown in FIG. 4 which illustrates two-radio  120  to two-antenna  130  switching arrangement  400  with four (4) single-pole-double-throw switches  110  in accordance with an exemplary embodiment of the present invention. This configuration also implements FIG. 2, but the set of states of individual switches  110  which makes a specific radio  120  to antenna  130  connection is different from that of FIG. 3. Specifically, the four (4) switches  110  are never all in the same position for either of the two (2) possible switching states (i.e., radio 1           antenna 1  and radio 2           antenna 2  or radio 1           antenna 2  and radio 2           antenna 1 ). Therefore, in this configuration, switches  110  cannot all be driven by the same control signal unless the default state of switches  110  are different.  
         [0024]    For N=3, there are 46,656 possible ways to wire the six (6) SP3T switches. One way, consistent with FIGS. 1 and 2, is shown in FIG. 5 which illustrates three-radio  120  to three-antenna  130  switching arrangement  500  with six (6) single-pole-triple-throw switches  110  in accordance with an exemplary embodiment of the present invention. Each SP3T switch  110  is connected to a radio  120  and has three (3) outgoing contacts  125  that allow connection to three (3) distinct antennae  130 . Likewise, each SP3T switch  110  connected to an antenna  130  has three (3) incoming contacts  135 . Switches  110  are shown in one of three (3) possible switching states, that which implements the first row of FIG. 2. The other two (2) possible switching states implement the last two (2) rows, respectively, of FIG. 2 (for N=3 and j=2).  
         [0025]    Another way to connect switches  110  for N=3 is shown in FIG. 6 which illustrates three-radio  120  to three-antenna  130  switching arrangement  600  with six (6) single-pole-triple-throw switches  110  in accordance with an exemplary embodiment of the present invention. For this case, the set of switching states is different from those listed in FIG. 2 and is given, instead, by FIG. 7. It can be seen from FIG. 7 that, for the wiring connections depicted in FIG. 6, any radio  120  can still be assigned to any antenna  130 . Number sequence  610  shown above each switch  110  gives the sequence of positions (where 1 represents the top contact, 2 represents the middle contact and 3 represents the bottom contact) through which that particular switch  110  must progress in order to implement the connections in FIG. 7. It can thus be observed from FIG. 6 that individual SP3T switches  110  are never all in the same state and therefore cannot be driven by the same control signal. As is the case for FIG. 1, switching arrangement  600  allows all switches  110  to change positions at the same time. Sequences  610  of FIG. 6 can also be seen in FIG. 7 wherein, for each of the three (3) switching states, the switch positions of switches  110  associated with radio 1  (R 1 ), radio 2  (R 2 ), radio 3  (R 3 ), antenna 1  (A 1 ), antenna 2  (A 2 ) and antenna 3  (A 3 ) are shown in the “Switch Positions” column adjacent to the corresponding reference symbol R 1 , R 2 , R 3 , A 1 , A 2  and A 3 .  
         [0026]    Although FIG. 1 shows discrete SPNT switches  110 , pairs, triplets, quartets, etc. of these SPNT switches  110  could be combined (for example, in parallel) into 2PNT, 3PNT, 4PNT, etc. switches  110 , respectively, with MPNT representing an “M pole N throw” switch  110 . This would yield an implementation that uses fewer, but more complex, switches  110 .  
         [0027]    For the case where the switching circuit is fabricated as stripline or microstrip, and power splitters or power dividers are not used, it is possible to accomplish the general diversity switching arrangement with only N SPNT switches  110  as shown in FIG. 8 which illustrates N radio  120  to N antenna  130  switching arrangement  800  with N switches  110  in accordance with an exemplary embodiment of the present invention. In this configuration, there is only one switch  110  in the path between a radio  120  and an antenna  130 . Reflective losses from the N−1 possibly unterminated stubs at each radio  120  connection can be minimized if stub lengths are kept very short compared to the wavelength of the RF carrier. The N radios  120  can be wired to the N switches  110  in (N!) N  ways. FIGS. 9A and 9B illustrate N radio  120  to N antenna  130  switching arrangements  900 A and  900 B, respectively, with N single-pole-N-throw switches  110  for N=2 and N=3, respectively, in accordance with exemplary embodiments of the present invention. The configurations shown in FIGS. 9A and 9B implement the connections in FIG. 2.  
         [0028]    The SPNT switches  110  used in switching arrangement  100  can also be implemented as configurations of SP2T switches. The motivation for this is that SP2T switches are very common and allow simple binary control. It can be shown by mathematical induction that an SPNT switch can always be constructed from N−1 SP2T switches. It can also be shown that N−1 is the minimum number of SP2T switches required to construct an SPNT switch. FIGS. 10A and 10B illustrate single-pole-N-throw switches  1000 A and  1000 B, respectively, constructed from single-pole-double-throw switches for N=3 and N=4, respectively, in accordance with exemplary embodiments of the present invention. However, with SPNT switches constructed from the minimum number of SP2T switches, the number of switch contacts in the path between the SPNT input and one of its N outputs is variable. Therefore, the insertion loss will change according to the particular connection made in the SPNT switch. For example, there is a minimum of one (1) and a maximum of two (2) SP2T switch contacts in a path in SP3T switch  1000 A, while for SP4T switch  1000 B, there are always exactly two (2) SP2T switch contacts in each path. The minimum and maximum number of switch contacts in these SPNT constructions can be easily computed recursively.  
         [0029]    Although exemplary embodiments of the present invention have been described in detail, it will be understood by those skilled in the art that various modifications can be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.