Abstract:
A Bluetooth-enabled terminal having a radio manager for minimizing frequency collisions between channel hopping patterns transmitted over plural channels established between such terminal and correspondent Bluetooth devices is described. The radio manager extracts successive sets of projected future N—time slot segments of the respective Bluetooth channel hopping patterns. Each extracted set is tested to detect a time slot, if any, where frequency hops of the segments of the set coincide, indicating a frequency collision. When a collision time slot is detected, the radio manager generates a marker which triggers an alteration of the frequency hops that would otherwise be exhibited by a subset of the generated channel hopping patterns in such detected time slot. Such terminal may optionally be provided with an additional network interface to define a collision-resistant Bluetooth access point.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to packet transmission systems operating with Bluetooth transmission protocols and more particularly to Bluetooth-enabled devices employed in the implementation of such systems. 
     As is well known, devices utilizing Bluetooth communication protocols have evolved in recent years to facilitate instantaneous short-range wireless digital communications among a wide range of dissimilar devices in a robust and secure manner. 
     Bluetooth-enabled devices utilize spread-spectrum frequency hopping techniques to exchange data with other Bluetooth-enabled devices after establishment of a radio connection between radio modules associated with the transmitting and receiving devices. Pursuant to Bluetooth protocols, the device initiating the connection (the master) establishes and controls communication with other connected devices (the slaves) in a piconet by transmitting packets in a unique channel hopping pattern whose frequency hops in each successive time slot are distributed in a quasi-random manner. The time slots used by the master and the slaves in a piconet for the common channel hopping pattern are synchronized. 
     A Bluetooth master using a single radio module cannot form simultaneous connections with devices on separate piconets. Nor has it been practical, up to now, to simultaneously operate separate radio modules that are co-located on a single device. One reason for this is that the simultaneously transmitted channel hopping patterns would be statistically subject to frequency “collisions” in certain time slots and thereby to an attendant loss of transmitted information. 
     SUMMARY OF THE INVENTION 
     The present invention provides a unitary Bluetooth-enabled terminal that includes a plurality of independent radio interfaces associated with radio modules that provide collision-free simultaneous connections with Bluetooth-enabled device(s) on separate piconets. In a first embodiment, each radio interface is coupled to a baseband controller which generates, from a common system clock, a unique channel hopping pattern that is used by that radio interface to determine transmission frequencies used in subsequent time slots. Each radio interface simultaneously sends radio signals in frequencies determined by its own independent channel hopping pattern. 
     If two or more of such radio interfaces send information at the same time and on the same frequency, frequency collision occurs. In accordance with the invention, frequency collision on the respective channels is avoided by providing the terminal with a radio manager that extracts segments of the respective channel hopping patterns occurring over a selectable number of future time slots. The radio manager generates, from a comparison of the respective extracted segments, a marker indicative of a time slot(s), if any, where a collision between frequency hops on the respective channels will occur. An adjustment circuit responsive to the marker causes the baseband controller to alter the frequency hops that would otherwise be exhibited by a subset of such channels in such predicted time slot, thereby avoiding the collision that would otherwise occur. 
     Advantageously, the terminal may be implemented as a multiple-interface Bluetooth access point. This is accomplished by incorporating an additional interface (wired or wireless) to a backbone network, thereby permitting the establishment of a connection through the terminal between a selected one of the radio modules and the backbone network. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention is further illustrated in the following detailed description taken in conjunction with the appended drawing, in which: 
         FIG. 1  is a block diagram of an exemplary prior art Bluetooth-enabled device; 
         FIG. 2  is a block diagram of a unitary, multiple-interface Bluetooth-enabled terminal in accordance with the invention; 
         FIG. 3  is a block diagram of a radio manager employable in the terminal of  FIG. 2  for preventing collision of the frequency hops present at the multiple interfaces of such terminal; 
         FIGS. 4A and 4B  are time diagrams showing illustrative channel hopping segments that are expected to occur over a succession of future time slots at the respective radio interfaces in the terminal of  FIG. 2 ; 
         FIG. 5  is a flow chart of a typical sequence of operations used to implement a broad aspect of the invention; and 
         FIG. 6  is a block diagram of an alternate embodiment of the terminal of  FIG. 2  in the form of a Bluetooth access point. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings,  FIG. 1  shows a conventional Bluetooth-enabled device  10  having a radio interface  11  which couples packets to and from an external Bluetooth radio module  12 . The module  12  is adapted to transmit frequencies within the ISM band. The interface  11  is connected to a baseband controller  13 , which implements known Bluetooth baseband protocols by modulating packets to be transmitted in a FH-CDMA channel hopping pattern after a connection is made between the module  12  and a Bluetooth-enabled slave device (not shown). Each successive time slot of such channel hopping pattern illustratively exhibits a quasi-randomly selected one of 79 different 1 MHz frequency hops within the ISM band. 
     The time slots of the channel hopping pattern are established by a system clock  14  coupled to the controller  13 . The clock  14  may be illustratively embodied as a 28 bit counter with a clock rate in a range centered at 3.2 KHz. Each of the possible quasi-random frequency hopping patterns that may be generated by the controller  13  for use in the transmission link or channel associated with the radio module  12  illustratively corresponds to a unique count, or “tick”, of the clock  14 . 
     Packets to be transmitted by the device  10  through the radio module  12  are incident on the device through a host interface  16 . Such incident packets are applied to the controller  13  through a conventional CPU core  17  that is associated with a memory  18 . 
     The co-location of a plurality of radio interfaces in a single device to control a plurality of Bluetooth piconets with separate channel hopping patterns has not been practical in the past, since the Bluetooth devices that would be connected to each of the resulting multiple channels are independent and do not coordinate. Consequently, the simultaneous transmission of packets over the multiple channels established by such device would statistically exhibit identical frequency hops in certain future time slots. Because the co-located radio modules would be in close proximity to each other and therefore well within Bluetooth range, the collisions caused by the simultaneous occurrence of such frequency hops would cause a loss of packet communication during the time slots in question. 
     This drawback is minimized with the use of a unitary, Bluetooth-enabled terminal in accordance with the invention. In the illustrative embodiment shown in  FIG. 2 , such terminal is represented at  20 . The terminal  20  has a plurality of independent radio interfaces, two of which are shown and identified with the numerals  11 A and  11 B, respectively. Each of the interfaces  11 A and  11 B is in communication with the output of a common baseband controller  13 A, and is coupled to at least one external Bluetooth radio module. In the particular arrangement shown in  FIG. 2 , the interfaces  11 A and  11 B are respectively associated with a pair of radio modules  12 A and  12 B. The controller  13 A, which receives data to be transmitted through a host interface  16 A and a core  17 A, modulates the frequencies of the radio modules  12 A and  12 B with separate channel hopping patterns that may be transmitted by such radio modules to associated “slave” devices (not shown) in different piconets in a collision-free manner as described below. 
     In particular, the controller  13 A responds to different counts of a system clock  14 A by generating, for the two-interface arrangement shown in  FIG. 2 , a pair of unique channel hopping patterns of the type indicated above. (The characteristics of the clock  14 A may correspond to those of the clock  14  of  FIG. 1 .) The time slots of such patterns are illustratively synchronized by the clock  14 A ( FIG. 2 ). The patterns appear on outputs  21  and  22  of controller  13 A and are respectively applied to the radio modules  12 A and  12 B through the interfaces  11 A and  11 B. 
     As indicated above, such patterns are susceptible to collision in certain time slots. In further accordance with the invention, the terminal  20  is provided with facilities including a radio manager for predicting in which future time slots a collision between the corresponding channel hopping patterns will occur and for taking preemptive measures to avoid such collision. 
       FIG. 3  shows an illustrative implementation of such a radio manager, represented at  31 , for the assumed case where the terminal  20  exhibits the two interface arrangement of  FIG. 2 . The radio manager  31  includes a prediction circuit  32  ( FIG. 3 ) that is coupled to the clock  14 A and to the outputs  21  and  22  of the baseband controller  13 A. The prediction circuit  32  illustratively includes a replicator unit  33  that extracts, for each of a selectable and incrementable number (illustratively N) of successive future time slots, corresponding segments F 1 (t) and F 2 (t) of the channel hopping patterns applied to the outputs  21  and  22 . The respective segments occur over synchronized time slots T( 0 ), T( 1 ), T( 2 ) . . . T(N−1) as shown in  FIGS. 4A and 4B . Each frequency hop of each segment shown in  FIGS. 4A and 4B  is represented with a mark “X”. The N-slot pattern segments F 1 (t) and F 2 (t) appear on outputs  36  and  37  of the replicator unit  33  ( FIG. 3 ). 
     The prediction circuit  32  further illustratively includes a test circuit  38  which compares the frequency hops of the segments F 1 (t) and F 2 (t) in the successive associated time slots to determine which, if any, of the time slots reflects a coincidence of the hops. The output of the test circuit  38  exhibits a marker indicative of the time slot where the corresponding frequency hops coincide and therefore collide. For example, such marker would appear at the time slot T(X) in  FIGS. 4A and 4B , since the respective then-occurring frequency hops (represented at  39  in  FIG. 4A  and at  40  in  FIG. 4B ) are both illustratively centered at 2420 MHz. 
     The output of the prediction circuit  32  is coupled to a pattern adjustment circuit  41 . The circuit  41  responds to a marker from the test circuit  38  by directing the controller  13 A to alter the prospective frequency hop on one of the colliding channels that would normally occur during the predicted time slot T(X). The adjustment circuit  41  may be implemented in several ways. For example, the circuit  41  may direct the controller  13 A ( FIG. 3 ) to mute transmission from one of the colliding channels during the time slot T(X). Alternatively, where the channel hopping patterns being transmitted employ packet sizes that encompass a selectable number of time slots as permitted by Bluetooth protocols, the adjustment circuit  41  may be implemented to direct the controller  13 A to change the packet size of the transmitted data on the channel that is selected for alteration. (It will be appreciated that a collision would have to be predicted far enough in advance to afford sufficient time for the radio modules servicing the affected channel to negotiate and execute the packet size change.) 
     The replicator unit  33  may be arranged, with the aid of a memory  18 A that may also be associated with the core  17 A ( FIG. 2 ), to extract successive N-slot segments F 1 (t) and F 2 (t) of the channel hopping patterns on the baseband controller outputs  21  and  22 . In this way, the pattern of extraction, comparison testing and alteration just described can be repeatedly applied to a moving succession of future time slots and thereby to a corresponding moving succession of future collisions. 
     The radio manager  32  just described, and the methods implemented thereon, are readily extensible to the general case of a K-interface terminal (not shown), where K is at least two. Such extension is depicted in the flow diagram of  FIG. 5 , wherein K sets of corresponding N-time slot segment are extracted in sequence from each of K independent Bluetooth channel hopping patterns generated by the such terminal. Each successive set is tested to predict the occurrence of a possible colliding time slot(s) during the N-time slot interval defining such set. If no collision between frequency hops is predicted during an interval corresponding to a currently extracted set, the next set is extracted and tested. If, on the other hand, a collision is predicted for the current set, the predicted time slot is employed as a parameter in the alteration of the frequency hops that would otherwise occur during such time slot in a subset of the K channel hopping patterns from which the segments were extracted. Preferably, such subset includes all but one, or (K−1), of such patterns. The K channel hopping patterns from the terminal, including the K−1 patterns that have ben altered as indicated, may be conventionally transmitted over the appropriate Bluetooth channels to the associated correspondent devices. 
       FIG. 6  shows a modification of the unitary Bluetooth-enabled terminal  20  of  FIG. 2  wherein the modified terminal may serve as an enhanced Bluetooth access point. (Corresponding elements in  FIGS. 2 and 6  have been given corresponding reference numerals). The access point of  FIG. 6 , represented at  43 , is similar to and shares the above-mentioned advantages with the terminal  20  of  FIG. 2 . In addition, however, the access point  43  ( FIG. 6 ) includes a network interface  44  which is coupled to the core  17 A for supporting transmission between the access point  43  and a conventional wired backbone network (not shown). The interface  44  permits connectivity between such backbone network and a selected one of the radio modules  12 A and  12 B. 
     The interface  44  may conventionally be embodied for wired connection to such backbone network. Alternatively, the interface  44  may be embodied in wireless form in order to connect to the backbone network through a separate wireless network (not shown). 
     In the foregoing, the invention has been described in connection with illustrative embodiments thereof. While the specific embodiments of a unitary Bluetooth terminal shown in  FIGS. 2 and 6  are provided with two radio interfaces, it will now be evident to those skilled in the art that any reasonable number of such interfaces may be employed without departing from the spirit and scope of the invention. Many other variations and modifications will also occur to those skilled in the art. For example, while the radio manager  31  has been illustrated in  FIG. 3  in connection with one arrangement for effecting collision-resistant transmission of packets through such radio interfaces, it will be understood that other equivalent means may be employed for this purpose. It is accordingly desired that the scope of the appended claims not be limited to or by the specific disclosure herein contained.