Patent Publication Number: US-2004053526-A1

Title: Receive diversity antenna system for use with multiple radios

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
     [0001] The present invention claims the benefit of U.S. Provisional Patent Application Serial No. 60/411741, entitled “Mechanism For Sharing A Diversity Antenna System Between Colocated 802.11 And Bluetooth Radios,” filed on Sep. 18, 2002, which application is also incorporated by reference. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] The present invention relates to telecommunications in general, and, more particularly, to a receive diversity antenna system for use with multiple radios.  
       BACKGROUND OF THE INVENTION  
       [0003] Before the 1980&#39;s, most computer users shared the resources of a single mainframe computer, and the centralized nature of the mainframe enabled those users to easily share information with each other. In the 1980&#39;s, increasing numbers of computer users used a personal computer, and the distributed nature of the personal computers hindered the users from sharing information with each other.  
       [0004] In fact, the most common way of transporting information from one personal computer to another in the early 1980&#39;s was by physically carrying a floppy disk from one machine to another. This was widely-known as, and facetiously called, a “sneaker net.” 
       [0005] To facilitate the sharing of information among personal computers, local area networks were born. The first local area networks had metal wires that directly connected the computers, but in the 1990&#39;s, local area networks that used radios, instead of wires, became popular.  
       [0006]FIG. 1 depicts a block diagram of the salient components of a network interface in the prior art for a host computer that is a member of two different local area networks—an 802.11 network and a Bluetooth network. Network interface  100  comprises: antenna  101 - 1 , antenna  101 - 2 , antenna  101 - 3 , single-pole, double-throw, single-break switch  102 , receive diversity controller  104 , IEEE 802.11-compliant radio  105 - 1 , and Bluetooth-compliant radio  105 - 2 .  
       [0007] When a computer is part of a wireless local area network, the computer uses an antenna and radio to communicate with the other computers. Some radios, for example radio  105 - 2 , only use one antenna, antenna  101 - 3 . In contrast, some radios, for example radio  105 - 1  uses two antennas, antenna  101 - 1  and antenna  101 - 2 . For a variety of reasons (e.g., to address Rayleigh fading, etc.), the ability of a radio to receive signals from other computers is usually improved when the radio uses two or more antennas rather than just one.  
       [0008] For example, the signals from antenna  101 - 1  and  101 - 2  are fed to receive diversity controller  104 , which based on a receive diversity algorithm, causes the stronger of the signals on antennas  101 - 1  and  102 - 1  to be fed to radio  105 - 1 .  
       [0009] The fact that radios  105 - 1  and  105 - 2  don&#39;t share antennas causes the cost of network interface  100  to rise, and, therefore, FIG. 2 depicts a block of the salient components of a network interface in which two radios do share antennas. In this arrangement, network interface  200  comprises: antenna  201 - 1 , antenna  201 - 2 , electrical connection mechanism  202 , IEEE 802.11-compliant radio  203 - 1 , and Bluetooth-compliant radio  203 - 2 . The electrical connection mechanism  202  monitors the strength of the signals on antenna  201 - 1  and  201 - 2 , and based on a receive diversity algorithm, feeds the stronger signal to radio  203 - 1  and radio  203 - 2 .  
       [0010]FIG. 3 depicts a block diagram of the salient components of electrical connection mechanism  202  in the prior art. Electrical connection mechanism  202  comprises single-pole, double-throw, single-break switch  302 , receive diversity controller  304 , and low noise amplifier  305 . As in FIG. 1, receive diversity controller  304  measures the strength of the signals on antenna  101 - 1  and  101 - 2  based on a receive diversity algorithm and causes switch  302  to feed the stronger signal to low noise amplifier  305  and then to both radios. Low noise amplifier is needed to boost the split signals going to both radios. Were it not for low noise amplifier  305 , each radio would receive only one-half of the signal from the stronger antenna, and this might prevent either or both of the radios from receiving an adequate signal. The cost of low noise amplifier is prohibitively expensive in some network interfaces, and, therefore the need exists for an improved network interface.  
       SUMMARY OF THE INVENTION  
       [0011] The present invention enables two or more radios to share two or more antennas in a receive diversity antenna system without some of the costs associated with the prior art. In particular, the illustrative embodiment eliminates the need for a low-noise amplifier.  
       [0012] The illustrative embodiment uses a switching matrix (e.g., a double-pole, double-throw, single-break switch, etc.) to feed the stronger signal from the two antennas to one radio and the weaker signal from the two antennas to the second radio. Although this causes the second radio to always receive a weaker signal than the first radio, embodiments of the present invention are acceptable when the second of the two radios is capable of receiving weaker signals than is the first radio.  
       [0013] The illustrative embodiment comprises: a switching matrix comprising a first antenna terminal, a second antenna terminal, a first radio terminal, a second radio terminal, and a control terminal; and a receive diversity controller comprising an output terminal that is electrically connected to the control terminal; wherein the receive diversity controller causes the switching matrix to: (i) electrically connect the first antenna terminal to the first radio terminal, and (ii) electrically connect the second antenna terminal to the second radio terminal when the quality of a first signal on the first antenna terminal is stronger than the quality of a second signal on the second antenna terminal; and wherein the receive diversity controller causes the switching matrix to: (i) electrically connect the first antenna terminal to the second radio terminal, and (ii) electrically connect the second antenna terminal to the first radio terminal when the quality of the first signal is weaker than the quality of the second signal. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014]FIG. 1 depicts a block diagram of the salient components of a network interface in the prior art for a host computer that is a member of two different local area networks.  
     [0015]FIG. 2 depicts a block of the salient components of a network interface in which two radios do share antennas.  
     [0016]FIG. 3 depicts a block diagram of the salient components of electrical connection mechanism  202  in the prior art.  
     [0017]FIG. 4 depicts a block diagram of the salient components of the illustrative embodiment of the present invention.  
     [0018]FIG. 5 depicts a block diagram of the salient components of switching matrix  401  in accordance with illustrative embodiment of the present invention.  
     [0019]FIG. 6 depicts a schematic the double-pole double-pole single-break switch when it is configured to connect one configuration of antennas to radios.  
     [0020]FIG. 7 depicts a schematic the double-pole double-pole single-break switch when it is configured to connect a second configuration of antennas to radios.  
     [0021]FIG. 8 depicts a flow diagram of the salient tasks performed in accordance with the illustrative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
     [0022]FIG. 4 depicts a block diagram of the salient components of the illustrative embodiment of the present invention. Electrical connection mechanism  400  comprises: switching matrix  401  and receive diversity controller  402 , interconnected as shown.  
     [0023] Switching matrix  401  selectively connects the incoming signals from antennas  201 - 1  and  201 - 2  to radios  203 - 1  and  203 - 2  under the control of receive diversity controller  402 . The details of switching matrix  401  are described below and with respect to FIGS. 5, 6, and  7 .  
     [0024] Receive diversity controller  402  receives signals from antennas  201 - 1  and  201 - 2 . The strength of the signal on each antenna is determined by receive diversity controller  402  in accordance with a receive diversity algorithm optimized for IEEE 802.11 operation. Receive diversity controller  402  causes, via control signal  403 , switching matrix  401  to feed the stronger of the signals on antenna  201 - 1  and antenna  201 - 2  to radio  203 - 1 . Furthermore, receive diversity controller  402  causes, via control signal  403 , switching matrix  401  to feed the weaker of the signals on antenna  201 - 1  and antenna  201 - 2  to radio  203 - 2 .  
     [0025]FIG. 5 depicts a block diagram of the salient components of switching matrix  401  in accordance with illustrative embodiment of the present invention. Switching matrix  401  comprises double-pole, double-throw, single-break switch  501 . Double-pole, double-throw, single-break switch  501  receives signals from antennas  201 - 1  and  201 - 2  and feeds those signals to radios  203 - 1  and  203 - 2  under the control of receive diversity controller  402 .  
     [0026] As is well-known to those skilled in the art, a double-pole, double-throw, single-break switch has two states. In the first state, which is depicted in FIG. 6, the signal from antenna  201 - 1  is fed to radio  203 - 1  via contacts  601 - 1  and  602 - 1 , and the signal from antenna  201 - 2  is fed to radio  203 - 2  via contacts  601 - 2  and  602 - 3 . In the second state, which is depicted in FIG. 7, the signal from antenna  201 - 1  is fed to radio  203 - 2  via contacts  601 - 1  and  602 - 2 , and the signal from antenna  201 - 2  is fed to radio  203 - 1  via contacts  601 - 2  and  602 - 4 .  
     [0027]FIG. 8 depicts a flow diagram of the salient tasks performed in accordance with the illustrative embodiment of the present invention.  
     [0028] At task  801 , the illustrative embodiment determines whether the first signal at the first antenna is stronger than the second signal at the second antenna or not. When the first signal at the first antenna is stronger than the second signal at the second antenna, control passes to task  802 .  
     [0029] At task  802 , switching matrix  401  electrical connects a first antenna terminal to a first radio terminal and electrically connects the second antenna terminal to the second radio terminal. From task  802 , control passes to task  801 .  
     [0030] Back at task  801 , when the first signal at the first antenna is weaker than the second signal at the second antenna, control passes to task  803 .  
     [0031] At task  803 , switching matrix  401  electrical connects the second antenna terminal to the first radio terminal and electrically connects the first antenna terminal to the second radio terminal. From task  803 , control passes to task  801 .  
     [0032] It is to be understood that the above-described embodiments are merely illustrative of the present invention and that many variations of the above-described embodiments can be devised by those skilled in the art without departing from the scope of the invention. It is therefore intended that such variations be included within the scope of the following claims and their equivalents.