Abstract:
A wireless telecommunications terminal employing both an IEEE 802.11 radio and a Bluetooth radio is disclosed. The illustrative embodiment employs a novel preemption scheme that ensures that Bluetooth preemptions of the 802.11 radio are not fatal to the 802.11 media access control (MAC) error-correction mechanism. The illustrative embodiment thus enables what appears to be concurrent 802.11 and Bluetooth activity by a single wireless telecommunications terminal. The preemption scheme does not require any changes to the 802.11 and Bluetooth protocols, or to the radios. It will be clear to those skilled in the art how to make and use alternative embodiments of the present invention for protocols other than IEEE 802.11 and Bluetooth that might interfere with each other.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of: 
     1. U.S. provisional application Serial No. 60/409,356, filed Sep. 9, 2002, entitled “A Mechanism For Collaboration And Interference Prevention Between 802.11 And Bluetooth Using The 802.11 Power Save Mechanism,” and 
     2. U.S. provisional application Serial No. 60/411,848, filed Sep. 18, 2002, entitled “Coordinating A Plurality Of Medium Access Control Protocols That Share A Common Communications Channel,” 
     both of which are also incorporated by reference. 
     The following patent application is incorporated by reference: 
     1. U.S. patent application, entitled “Multi-Protocol Interchip Interface,” application Ser. No. 10444,383. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to telecommunications in general, and, more particularly, to a telecommunications terminal with two radios operating in accordance with competing respective protocols (i.e., respective protocols that might interfere with each other. 
     BACKGROUND OF THE INVENTION 
       FIG. 1  depicts a schematic diagram of a portion of wireless communication system  100  in the prior art. Wireless communication system  100  comprises wireless terminals  101 - 1  through  101 - 6 , all communicating with each other by using one or more air interfaces in the same, shared radio frequency band. As an example, IEEE 802.11 (i.e., “802.11”) wireless terminals  101 - 1 ,  101 - 2 , and  101 - 4  communicate using an 802.11 air interface, Bluetooth wireless terminals  101 - 5  and  101 - 6  communicate using a Bluetooth air interface, and 802.11/Bluetooth wireless terminal  101 - 3  communicates using either an 802.11 or a Bluetooth air interface. 
     As depicted in  FIG. 1 , wireless terminal  101 - 2  is transmitting a signal with wireless terminal  101 - 3  as the intended recipient. Also, wireless terminal  101 - 6  is transmitting a signal with wireless terminal  101 - 5  as the intended recipient. Wireless terminals  101 - 2  and  101 - 6  can transmit simultaneously, although in order to do so, either (1) their respective transmissions have to be coordinated, or (2) wireless terminals  101 - 2  and  101 - 6  have to be situated far enough apart from each other to minimize interference. If, however, a wireless terminal supports two air interface protocols (e.g., wireless terminal  101 - 3 , etc.), a mechanism must exist to prevent interference (i.e., the effect of two radios transmitting simultaneously in the same frequency band), since spatial separation of two air interfaces within the same wireless terminal is not an option. 
     In accordance with a first technique in the prior art,  FIG. 2  depicts a block diagram of the salient components of wireless terminal  101 - 3 . Wireless terminal  101 - 3  comprises host  201 , A/B switch  202 , 802.11 radio  203 , Bluetooth radio  204 , antenna switch  205 , and antenna  206 . Host  201  comprises a microprocessor. At any given time, host  201  communicates with 802.11 radio  203  or Bluetooth radio  204 , both not both, by means of A/B switch  202 . 802.11 radio  203  communicates in accordance with the 802.11 air interface, and Bluetooth radio  204  communicates in accordance with the Bluetooth air interface. Antenna switch  205  directs a signal to be transmitted to antenna  206  from either 802.11 radio  203  or Bluetooth radio  204 . Antenna switch  205  also directs a received signal from antenna  206  to either 802.11 radio  203  or Bluetooth radio  204 . Antenna switch  205  is coordinated with A/B switch  202 . 
     The first technique in the prior art controls contention for the shared frequency band through A/B switch  202 . In addition to providing contention-free access to the shared frequency band, the first technique provides a low-cost solution. As a disadvantage, however, the air interface in use must remain in either 802.11 or Bluetooth mode for relatively long periods of time. Also, contention resolution requires manual intervention on the part of a user whenever wireless terminal  101 - 3  has to make a transmission over the air interface that is not presently active. Finally, the inactive air interface might miss a transmission by some other wireless terminal. 
     In accordance with a second technique in the prior art,  FIG. 3  depicts a block diagram of wireless terminal  101 - 3 . Wireless terminal  101 - 3  comprises host  301 , 802.11 radio  302 , Bluetooth radio  303 , antenna switch  304 , and antenna  305 . Host  301  comprises a microprocessor. At any given time, host  301  communicates with 802.11 radio  302  or Bluetooth radio  303 , but not both, by means of an internal switch. Typically, the internal switch requires the user of wireless terminal  101 - 3  to select the air interface to be used (e.g., from a menu, etc.). Alternatively, host  301  chooses between the air interfaces based on the type of communication it needs to send or expects to receive. 802.11 radio  302  communicates in accordance with the 802.11 air interface, and Bluetooth radio  303  communicates in accordance with the Bluetooth air interface. Antenna switch  304  directs a signal to be transmitted to antenna  305  from either 802.11 radio  302  or Bluetooth radio  303 . Antenna switch  304  also directs a received signal from antenna  305  to either 802.11 radio  302  or Bluetooth radio  303 . Antenna switch  304  is coordinated with the selection of the air interface. 
     The second technique in the prior art integrates the switch into host  301 , so the intervention by the user is more convenient, even though the intervention is still possibly manual. In addition to providing contention-free access to the shared frequency band, the second technique provides a more convenient way of allowing the user to change between air interfaces. As a disadvantage, however, the air interface in use must remain in either 802.11 or Bluetooth mode for relatively long periods of time. Also, contention resolution still possibly requires manual intervention on the part of a user whenever wireless terminal  101 - 3  has to make a transmission over the air interface that is not presently active. Finally, the inactive air interface might miss a transmission by some other wireless terminal. 
     In accordance with a third technique in the prior art,  FIG. 4  depicts a block diagram of wireless terminal  101 - 3 . Wireless terminal  101 - 3  comprises host  401 , 802.11/Bluetooth radio  402 , antenna switch  403 , and antenna  404 . Host  401  comprises a microprocessor. Host  401  maintains an interface with the 802.11 part of 802.11/Bluetooth radio  402  and an interface with the Bluetooth part of 802.11/Bluetooth radio  402 . 802.11/Bluetooth radio  402  is a single integrated circuit that communicates in accordance with the 802.11 air interface and with the Bluetooth air interface. 802.11/Bluetooth radio  402  coordinates transmissions to some extent between its 802.11 part and its Bluetooth part. Antenna switch  403  directs a signal to antenna  404  to be transmitted from either the 802.11 part of 802.11/Bluetooth radio  402  or the Bluetooth part of 802.11/Bluetooth radio  402 . Antenna switch  403  also directs a received signal from antenna  404  to either the 802.11 part of 802.11/Bluetooth radio  402  or the Bluetooth part of 802.11/Bluetooth radio  402 . 
     In the prior art, approaches of integrating and dynamically coordinating multiple wireless protocols on a single platform have focused on integration into a single integrated circuit. This control necessitates coordinating the contention for the same frequency band between the two air interfaces. If the two air interface protocols are 802.11 and Bluetooth, the control must be imposed on the two air interfaces, since there is no standardized interoperability between the two air interface protocols. When the individual wireless technologies, however, are on a rapid evolutionary path, “same chip” integration can increase cost and can cause the integrated circuit development to lag behind that of separate circuits. Also, the market demand for a dual-interface solution within a single integrated circuit can be considerably smaller than the demand for either integrated circuit supporting a single protocol only (i.e., 802.11 or Bluetooth, but not both). Furthermore, even same chip integration by itself does not inherently guarantee a tight, efficient contention control between the two air interfaces. 
     Therefore, the need exists for multiple radios supporting different air interface protocols, possibly on separate integrated circuits, to coordinate the use of a shared frequency band. 
     SUMMARY OF THE INVENTION 
     The present invention enables both an IEEE 802.11 radio and a Bluetooth radio to be employed in a single wireless telecommunications terminal (e.g., wireless telephone, personal digital assistant (PDA), etc.) without interference. In particular, the illustrative embodiment enables standard “off-the-shelf” 802.11 and Bluetooth radios to work in concert in a single telecommunications terminal. 
     In the illustrative embodiment, the Bluetooth radio distinguishes between more “time-critical” packets that have a lower latency tolerance (for example, synchronous connection-oriented [SCO] packets, as are well-known in the art), and packets with a higher latency tolerance (for example, some asynchronous connection-less [ACL] packets, as are well-known in the art). The Bluetooth radio “preempts” the operation of the 802.11 radio to transmit the former, and waits until the 802.11 radio is in power-save mode, which is an inactive “sleep” mode employed to conserve power, to transmit the latter. By coordinating the occurrence and duration of the Bluetooth preemptions, the illustrative embodiment ensures that the preemptions are not fatal to the 802.11 medium access control (MAC) error-correction mechanism, thereby enabling what appears to be concurrent operation of 802.11 and Bluetooth by the wireless telecommunications terminal. 
     In this specification, the illustrative embodiment is disclosed in the context of the IEEE 802.11 and Bluetooth protocols; however, it will be clear to those skilled in the art how to make and use alternative embodiments of the present invention for other combinations of competing protocols (i.e., protocols that might interfere with each other). In addition, although the illustrative embodiment is disclosed in the context of radios, it will be clear to those skilled in the art how to make and use alternative embodiments of the present invention for non-RF wireless radios and/or wireline transceivers that might interfere with each other. 
     The illustrative embodiment comprises: a first transmitter for transmitting a first data block through a communications band in accordance with an automatic-repeat-request error-correction mechanism; and a second transmitter for (i) preventing the first transmitter from outputting at least a portion of the first data block into the communications band while the second transmitter transmits a second data block through the communications band, and (ii) allowing the first transmitter to output into the communications band before the error-correction mechanism for the first data block fails. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a schematic diagram of wireless telecommunications system  100  in the prior art. 
         FIG. 2  depicts a block diagram of a dual protocol wireless terminal that uses a first technique in the prior art. 
         FIG. 3  depicts a block diagram of a dual protocol wireless terminal that uses a second technique in the prior art. 
         FIG. 4  depicts a block diagram of a dual protocol wireless terminal that uses a third technique in the prior art. 
         FIG. 5  depicts a block diagram of wireless terminal  500  in accordance with the first illustrative embodiment of the present invention. 
         FIG. 6  depicts a block diagram of multi-radio card  600  in accordance with the second illustrative embodiment of the present invention. 
         FIG. 7  depicts a diagram of the salient components of radio  502 - 1  in accordance with the third illustrative embodiment of the present invention. 
         FIG. 8  depicts a block diagram of wireless terminal  800  in accordance with the fourth illustrative embodiment of the present invention. 
         FIG. 9  depicts a graph of signals transmitted and their interrelationship in the illustrative embodiment of the present invention. 
         FIG. 10  depicts a diagram of the salient components of radio  502 - 1  in accordance with another variation of the third illustrative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 5  depicts a block diagram of wireless terminal  500  in accordance with the first illustrative embodiment of the present invention. Wireless terminal  500  is a computer that supports two distinct wireless air interface protocols concurrently for the purpose of sending and receiving data over the air on a shared frequency band. The frequency band, when used for communications purposes, is also referred to as a “communications band,” comprising one or more “channels” of communication. The object referred to generically as a “data block” conveys data across a transmission medium (e.g., air, wire, etc.). A data block constitutes a message, in which the message typically comprises a header part and the data in a payload part. A data block can be also referred to as a “frame” or as a “packet.” The term “frame,” as is known in the art, is commonly used in an IEEE 802.11 protocol context when referring to the medium access control data blocks that are communicated across over the air. The term “packet,” as is known in the art, is commonly used in a Bluetooth protocol context when referring to the data blocks that are communicated over the air. 
     A wireless telecommunications terminal, or “wireless terminal,” as described in this specification (e.g., wireless terminal  500 , etc.), is a type of telecommunications terminal. The wireless protocols supported by wireless terminal  500  can be, for example, 802.11 and Bluetooth. Wireless terminal  500  comprises host  501 , radio  502 - 1 , radio  502 - 2 , antenna switch  503 , and antenna  504 , interconnected as shown. 
     Host  501  is a computing platform (e.g., laptop, workstation, wireless terminal, etc.) comprising a general-purpose or special-purpose processor that is capable of storing data into a memory, retrieving data from a memory, and executing programs stored in a memory. The memory constituting host  501  might be random-access memory (RAM), flash memory, disk drive, etc. Host  501  processes higher-layer applications that use data that are transmitted over the air and data received over the air. Alternatively, host  501  can be the motherboard of a computer comprising a processor. Host  501  provides overall control of wireless terminal  500 , and the remainder of wireless terminal  500  provides the wireless communication function of host  501 . It will be clear to those skilled in the art how to make and use host  501 . 
     Host  501  also comprises an output device and an input device. The output device (e.g., display, speaker, etc.) is a transducer that receives signals from the processor and converts the received signals to an output signal (e.g., visual, auditory, etc.) in well-known fashion. The input device receives input from a user and sends the input to the processor. As is well-known in the art, the input device can take on a variety of forms, such as a keypad, pressure-sensitive touch screen, etc. 
     Radio  502 - 1  provides the channel-access control for communicating in accordance with a first air interface (e.g., 802.11, etc.). Radio  502 - 1  provides this service for data blocks arriving from host  501  via host data link  506  that are to be transmitted over the air and for data blocks arriving from antenna switch  503  via path  510 - 1 - 1  that are to be sent to host  501 . Radio  502 - 1  also receives data blocks from radio  502 - 2  and transmits data blocks to radio  502 - 2 . Radio  502 - 1  exchanges data blocks with radio  502 - 2  via collateral radio data link  507 , which will be described later. Radios  502 - 1  and  502 - 2  comprise a receiving function and a transmitting function and, as such, are transceivers. 
     Radio  502 - 1  receives signals from radio  502 - 2  and transmits signals to radio  502 - 2 . Radio  502 - 1  exchanges signals with radio  502 - 2  via signaling link  508 - 1 , a bus comprising M lines, and signaling link  508 - 2 , a bus comprising N lines. Signaling links  508 - 1  and  508 - 2  will be described later. 
     Radio  502 - 1  interfaces with host  501  through host data link  506 . Host data link  506  is a peripheral bus providing signaling, messaging, and control between those devices connected to the bus. It will be clear to those skilled in the art how to make and use the bus constituting host data link  506 . In the illustrative embodiment, host  501  is one such device connected to the bus, and radio  502 - 1  is another device. Radio  502 - 1  can interface with the bus mechanically, as well as electrically, through a removable circuit card designed for such an application. Alternatively, radio  502 - 1  can be hardwired directly to host  501  via the bus constituting host data link  506 . Examples of standardized busses include PCI, MiniPCI, and CardBus, all well known in the art. It will be clear to those skilled in the art how to make and use an interface that constitutes host data link  506 . 
     Radio  502 - 2  provides the channel-access control for communicating in accordance with a second air interface (e.g., Bluetooth, etc.). Radio  502 - 2  provides this service for data blocks arriving from host  501 —via host data link  506 , radio  502 - 1 , and collateral radio data link  507 —to be transmitted over the air and for data blocks arriving from antenna switch  503  via path  510 - 2 - 1  to be sent to host  501 . Radio  502 - 2  exchanges data blocks with radio  502 - 1  via collateral radio data link  507 . 
     Radio  502 - 2  receives signals from radio  502 - 1  and transmits signals to radio  502 - 1 . Radio  502 - 2  exchanges signals with radio  502 - 1  via signaling link  508 - 1  and signaling link  508 - 2 . Each of radios  502 - 1  and  502 - 2  might or might not constitute its own integrated circuit. 
     Antenna switch  503  exchanges signals with radio  501 - 1  via paths  510 - 1 - 1  and  510 - 1 - 2 , with radio  502 - 2  via paths  510 - 2 - 1  and  510 - 2 - 2 , and with antenna unit  504 . Antenna switch  503  enables antenna unit  504  to be shared, or switched, between radios  501 - 1  and  502 - 2 , reducing the required number of antennas. Antenna unit  504  provides coupling for transmitted and received signals between antenna switch  503  and the air. Antenna unit  504  can consist of a single antenna or it can consist of multiple antennas (e.g., one antenna for transmit, two antennas for receive, etc.). Antenna unit  504  can support receive diversity, transmit diversity, or both. Radio  501 - 1 , radio  502 - 2 , or host  501  can control the antenna switching.  FIG. 5  depicts radio  501 - 1  providing control of antenna switching via path  511 - 1 . It will be clear to those skilled in the art how to make and use antenna switch  503  and antenna unit  504 . It will also be clear to those skilled in the art how to make and use a wireless terminal (e.g., wireless terminal  500 , etc.,) without antenna switch  503 . 
     Collateral radio data link  507  provides a path through which radio  502 - 2  exchanges data blocks with host  501 . Essentially, collateral radio data link  507  provides the host interface for radio  502 - 2 . This “daisy-chaining” of host  501 , radio  502 - 1 , and radio  502 - 2  is necessary, since multiple integrated circuits with host interfaces that use certain bus standards, such as PCI, cannot be located on the same card because of the loading requirements of the bus. PCI, however, supports a multiple function model, in which more than one logical host interface is combined into a single physical integrated circuit. Radio  502 - 1  uses the ability to host more than one logical host interface and uses collateral radio data link  507  to provide radio  502 - 2  with access to host  501 . It will be clear to those skilled in the art how to host more than one logical host interface for a given physical interface. 
       FIG. 6  depicts a block diagram of wireless terminal  600  in accordance with the second illustrative embodiment of the present invention. Wireless terminal  600  supports two distinct wireless air interface protocols concurrently. The wireless protocols supported by wireless terminal  600  can be, for example, 802.11 and Bluetooth. Wireless terminal  600  comprises host  501 , radio  502 - 1 , radio  502 - 2 , antenna switch  503 , and antenna unit  504 , interconnected as shown. 
     Radio  502 - 1 , radio  502 - 2 , antenna switch  503 , antenna unit  504 , and printed circuit board  602  constitute multi-radio card  601 . Each of radios  502 - 1  and  502 - 2  might or might not constitute its own integrated circuit. Multi-radio card  601  is mechanically separable from host  501  and is electrically connected to host  501  using a card bus standard, in well-known fashion. The set of possible standards comprises PCI, MiniPCI, and CardBus. Printed circuit board  602 , constituting multi-radio card  601 , plugs into a card bus interface that electrically connects host  501  and radio  502 - 1 , and can be physically removed from that interface as needed. It will be clear to those skilled in the art how to make and use printed circuit board  602  as part of multi-radio card  601 . 
     The relationship and interaction between the elements depicted in  FIG. 6  differ from that in  FIG. 5  only in that the elements constituting multi-radio card  601  are mechanically separable from (i.e., not hardwired to) host  501 . Elements common to both  FIGS. 5 and 6  have been described above. 
       FIG. 7  depicts a block diagram of radio  502 - 1  in accordance with the third illustrative embodiment of the present invention. As is well known in the art, radio  502 - 1  might or might not constitute its own integrated circuit. Channel-access controller  701  provides the medium access control (MAC) functionality for communicating in accordance with a first air interface (e.g., 802.11, etc.). Note that the term “medium access control,” as used in this specification, denotes the functionality that determines which wireless terminal transmits next on a multi-access (shared) channel, constituting a communications band, for a given air interface. Channel-access controller  701  accepts host data from multi-radio host interface  702  via path  711 . It provides data from host  501  to baseband controller  703  via path  712  for preparation for transmission. Channel-access controller  701  also provides data received over the air from baseband controller  703  via path  712  to host  501  through path  711  and multi-radio host interface  702 . Channel-access controller  701  can track whether it has control or radio  502 - 2  has control of the frequency band at any given moment. Consequently, channel-access controller  701  can control antenna switching at antenna switch  503  via path  511 - 1 . Alternatively, channel-access controller  701  can operate uninformed of the status of radio  502 - 2 . 
     Channel access controller  701  can pass to radio  502 - 2  via signaling link  508 - 1  information representative of receiver  704 - 1  and transmitter  705 - 1 , received through path  715 . Channel access controller  701  can pass to receiver  704 - 1  and transmitter  705 - 1  via path  715  information representative of radio  502 - 2 , received through signaling link  508 - 2 . It will be clear to those skilled in the art how to make and use channel-access controller  701 . 
     In accordance with the illustrative embodiment of the present invention, multi-radio host interface  702  provides the interface between host  501  and radio  502 - 1 . Multi-radio host interface  702  accepts data blocks from host  501  via host data link  506 . Multi-radio interface  702  then determines whether it should (1) transfer each data block to channel-access controller  701  via path  711 , if the data block is meant for radio  502 - 1 , or (2) relay the data block over to radio  502 - 2  via link collateral radio data link  507 . Multi-radio host interface  702  accepts data blocks from channel-access controller  701  and transfers them to host  501 . In other words, multi-radio host interface  702  provides multiple logical channel interfaces on a single physical channel interface to host  501 . After reading this specification, it will be clear to those skilled in the art how to make and use multi-radio host interface  702 . 
     Baseband controller  703  exchanges signals with channel-access control  701  via path  712 . It also exchanges signals with receiver  704 - 1  and transmitter  705 - 1  via paths  713  and  714 , respectively. In the receive direction, baseband controller  703  accepts the demodulated signal from receiver  704 - 1  and converts the signal into a format that can be used by channel-access controller  701 . In the transmit direction, baseband controller  703  takes the signal from channel-access controller  701  and converts the signal into a format that is ready for modulation to the transmit frequency, the modulation being performed by transmitter  705 - 1 . It will be clear to those skilled in the art how to make and use baseband controller  703 . 
     In addition to exchanging signals with baseband controller  703 , receiver  704 - 1  and transmitter  705 - 1  exchange signals with antenna switch  503  via paths  510 - 1 - 1  and  510 - 1 - 2 , respectively. Transmitter  705 - 1  provides part of the functionality of the physical layer of communication—that is, modulation of the baseband signals, representing data blocks, received from baseband controller  703  to characteristics consistent with the particular air interface protocol supported by radio  502 - 1 . Transmitter  705 - 1  can accomplish modulation through an intermediate frequency (IF) section, or stage, and a radio frequency section. It then amplifies the signal to be transmitted via a power amplifier section. Transmitter  705 - 1  transmits the modulated and amplified signal over the air through antenna switch  503  and antenna unit  504 . Receiver  704 - 1  receives, amplifies, and demodulates signals from antenna switch  503  and antenna unit  504 , providing the signals to baseband controller  703 . Respectively, receiver  704 - 1  and transmitter  705 - 1  receives and transmits signals at a radio frequency communications band, such as, for example, the 2.4 GHz Industrial, Scientific, and Medical (ISM) band or the 5.0 GHz ISM band. It will be clear to those skilled in the art how to make and use receiver  704 - 1  and transmitter  705 - 1 . 
     Radio  502 - 1  communicates with radio  502 - 2  via collateral radio data link  507 , signaling link  508 - 1 , and signaling link  508 - 2 . Collateral radio data link  507  serves to exchange data blocks between host  501  and radio  502 - 2 , in well-known fashion. In accordance with the illustrative embodiment of the present invention, signaling link  508 - 1  and signaling link  508 - 2  provide the signaling interface between radio  502 - 1  and radio  502 - 2 , conveying transmitting/receiving status and specifying control. Signaling link  508 - 1  provides inter-MAC messaging from radio  502 - 1  to radio  502 - 2 . Similarly, signaling link  508 - 2  provides inter-MAC messaging from radio  502 - 2  to radio  502 - 1 . 
     Signaling links  508 - 1  and  508 - 2  comprise a communication and coordination protocol. Signaling links  508 - 1  and  508 - 2  also provide time synchronization functions between radio  502 - 1  and  502 - 2  for the purposes of determining time intervals corresponding to transmit opportunities for either air interface (i.e., the air interface served by radio  502 - 1  and the air interface served by radio  502 - 2 ). These characteristics are described below. 
     Signaling link  508 - 1  conveys a first set of signals from radio  502 - 1  to radio  502 - 2 . In some embodiments, this first set of signals comprises a first transmitting indication signal, a first receiving indication signal, and a first idle indication signal. The transmit indication signal indicates when radio  502 - 1  is transmitting signals over the air. The receive indication signal indicates when radio  502 - 1  is receiving (or attempting to receive) signals from over the air. The idle indication signal indicates when radio  502 - 1  is neither in transmit mode nor in receive mode (but is still powered on). The idle indication signal, for example, can be used to indicate when radio  502 - 1  is in a power save mode, possibly an opportunity in time when radio  502 - 2  can control the shared frequency band. It will be clear to those skilled in the art how to determine which signal levels indicate what condition. 
     Signaling link  508 - 2  transfers a second set of signals from radio  502 - 2  to radio  502 - 1 . In some embodiments, this second set of signals comprises a first transmit inhibit signal. The transmit inhibit signal specifies that radio  502 - 2  is commanding radio  502 - 1  to inhibit transmitter  705 - 1  of radio  502 - 1 . In an illustrative scenario, radio  502 - 2  has time-critical information to transmit over the air and needs to “cut in” to radio  502 - 1 &#39;s usage of the communications band. Use of the transmit inhibit signal in this scenario forces the radio frequency and intermediate frequency sections of transmitter  705 - 1  (within radio  502 - 1 ) out of transmit mode or turns off the power amplifier section or both, whatever ensures that no signal is transmitted by transmitter  705 - 1 . It will be clear to those skilled in the art how to turn off the transmitter  705 - 1  of radio  502 - 1  so that no signal is radiated over the air. It will be clear to those skilled in the art how to determine which signal levels indicate which conditions. 
     In some other embodiments, radio  502 - 2  also uses signaling link  508 - 2  to send a polite request signal to radio  502 - 1  as part of the second set of signals. The polite request signal indicates to radio  502 - 1  that radio  502 - 2  has a data block to transmit, but does not necessarily have to send it at that moment. Correspondingly, radio  502 - 1  understands that it does not have to turn off its transmitter the moment it receives a polite request signal. The polite request signal can also be used to indicate level of urgency or importance of the data block requiring transmission, the time by which the data block has to be transmitted (i.e., latency tolerance), or other time-sensitive characteristics of the data blocks. The particular usage of the polite request signal depends on the relationship of the respective air interfaces of radios  502 - 1  and  502 - 2 . It will be clear to those skilled in the art how to customize the usage of the polite request signal. It will be clear to those skilled in the art how to determine which signal levels indicate which conditions. 
     Radio  502 - 1  continually monitors the second set of signals sent on signaling link  508 - 2 . Radio  502 - 1  uses the signals to make decisions as to when to transmit, when not to transmit, and when to communicate status or control or both back to radio  502 - 2  along signaling link  508 - 1 . 
     In some embodiments, all signals sent across signaling links  508 - 1  and  508 - 2  apply bi-directionally—that is, each signal described thus far can also be sent in the direction opposite to what has been described. Signaling link  508 - 1  can also send, as the first set of signals, a second transmit inhibit signal and a polite request signal. Furthermore, signaling link  508 - 2  can also send, as the second set of signals, a second transmitting indication signal, a second receiving indication signal, and a second idle indication signal. This fully reciprocal sharing between radios  501 - 1  and  501 - 2  of status and control signals can be used, for example, in applications where master control of the radios—functionality essentially residing in radio  502 - 1  in the illustrative embodiments has to be reassigned to a different radio (e.g., radio  502 - 2 , etc.). 
       FIG. 8  depicts a block diagram of wireless terminal  800  in accordance with the fourth illustrative embodiment of the present invention. Wireless terminal  800  supports two distinct wireless air interface protocols concurrently. The wireless protocols supported by wireless terminal  800  can be, for example, 802.11 and Bluetooth. Wireless terminal  800  comprises host  501 , radio  502 - 1 , radio  502 - 2 , antenna switch  503 , and antenna unit  504 , interconnected as shown. Radio  502 - 1  comprises receiver  704 - 1 , transmitter  705 - 1 , and host interface  801 - 1 . Radio  502 - 2  comprises receiver  704 - 2 , transmitter  705 - 2 , and host interface  801 - 2 . Other elements constituting radios  502 - 1  and  502 - 2  have been depicted earlier and for clarity are not depicted in FIG.  8 . 
     Each of host data links  802 - 1  and  802 - 2  is a peripheral bus providing signaling, messaging, and control between those devices connected to the bus. It will be clear to those skilled in the art how to make and use the bus constituting each of host data links  802 - 1  and  802 - 2 . In the illustrative embodiment, host  501  is one such device connected to the bus, radio  502 - 1  is another device regarding host data link  802 - 1 , and radio  502 - 2  is yet another device regarding host data link  802 - 2 . Each of radios  502 - 1  and  502 - 2  can interface with its bus mechanically, as well as electrically, through a removable circuit card designed for such an application. Examples of standardized busses include PCI, MiniPCI, and CardBus, all well known in the art. It will be clear to those skilled in the art how to make and use an interface that constitutes host data link  802 - 1  and an interface that constitutes host data link  802 - 2 . 
     Host interface  801 - 1  provides the interface between host  501  and radio  502 - 1 , in well-known fashion. Host interface  801 - 1  accepts data blocks from host  501  via host data link  802 - 1 . Host interface  801 - 1  is also connected to channel-access controller  701  (described earlier) in radio  705 - 1  via a path equivalent to path  711  and accepts data blocks from channel-access controller  701 , transferring them to host  501 . Note that host interface  801 - 1  is identical to multi-radio host interface  702 , except that host interface  801 - 1  does not have to sort out data blocks for or from radio  502 - 2 . It will be clear to those skilled in the art how to make and use host interface  801 - 1 . 
     Host interface  801 - 2  provides the interface between host  501  and radio  502 - 2 , in well-known fashion. Host interface  801 - 2  accepts data blocks from host  501  via host data link  802 - 2 . Host interface  801 - 2  is also connected to channel-access controller  701  (described earlier) in radio  705 - 2  via a path equivalent to path  711  and accepts data blocks from channel-access controller  701 , transferring them to host  501 . It will be clear to those skilled in the art how to make and use host interface  801 - 2 . 
       FIG. 9  depicts a timing diagram of an exemplary communication sequence for receiver  704 - 1 , transmitter  705 - 1 , and transmitter  705 - 2 , in accordance with the illustrative embodiment of the present invention. This timing diagram serves to illustrate the operation of radio  502 - 1  and radio  502 - 2  in accordance with the fifth illustrative embodiment of the present invention. For illustrative purposes, radio  502 - 1  operates in accordance with the 802.11 air interface protocol and radio  502 - 2  operates in accordance with the Bluetooth air interface protocol. It will be clear, however, to those skilled in the art that radios  502 - 1  and  502 - 2  can operate in accordance with other protocols. 
       FIG. 9  shows two sequences related to transmitter  705 - 1 . Signal stream  901  represents the input signal into transmitter  705 - 1  provided on path  714 , and signal stream  902  represents what actually is transmitted by transmitter  705 - 1  (i.e., the transmitter&#39;s “output” on path  510 - 1 - 2 ). The distinction between transmitter  705 - 1 &#39;s input and its output will be made clear below. 
     The first frame intended for transmission is frame  911 , provided to transmitter  705 - 1 . Since transmitter  705 - 1  is active, transmitted frame  921  (corresponding to frame  911 ) is equivalent to frame  911  (i.e., all of frame  911  reaches antenna unit  504 ), except for the fact that frame  911  is an unmodulated signal while frame  921  is modulated. 
     The next transmission in the sequence is acknowledgement frame  931  of signal stream  903 , which is received, in well-known fashion, by receiver  704 - 1  from the station to which frame  921  was directed. 
     The next frame intended for transmission in the sequence is frame  912 , provided to transmitter  705 - 1 . As shown in  FIG. 9 , at time t 1  during transmission of corresponding frame  922 , transmitter  705 - 2  transmits, as part of signal stream  905 , lower latency-tolerant packet  951  (e.g., a synchronous connection-oriented [SCO] packet, etc.), while simultaneously, the transmit inhibit signal (described earlier), represented by signal  906 , is set high. The transmit inhibit signal is provided on signaling link  508 - 2 . 
     For the purposes of discussion of the illustrative embodiments of the present invention, it is assumed that setting a signal high indicates that control is being exercised and that resetting a signal low indicates that control is no longer being exercised by the particular signal line. It will be clear to those skilled in the art how to indicate control in a way that is suitable to the particular design. 
     The transmit inhibit signal indicated to radio  502 - 1  and, more particularly, to transmitter  705 - 1 , ultimately controls the signal radiated by radio  502 - 1 . In order to suppress radiation of a signal, it might be necessary to turn off or turn low the power amplifier and the RF/IF sections of transmitter  705 - 1 , as described earlier. It will be clear to those skilled in the art how to suppress output from transmitter  705 - 1 . 
     Setting the transmit inhibit signal prevents the remainder of frame  912  from reaching antenna unit  504 , as shown by frame  922 . When transmitter  705 - 2  completes lower latency-tolerant packet  951 , the transmit inhibit signal resets low, thereby allowing input to transmitter  705 - 1  to once again reach antenna unit  504 . The transmit inhibit signal, in combination with any intermediate logic gates required to format the control signal actually provided to transmitter  705 - 1 , acts as a preemption signal that effectively suppresses output from transmitter  705 - 1  during transmitter  705 - 2 &#39;s transmissions, thereby avoiding interference. 
     Meanwhile, transmitter  705 - 1 , unaware that frame  912  did not fully reach antenna unit  504 , waits for an acknowledgement in accordance with automatic repeat request (ARQ) error correction, as is well understood in the art. Since frame  912  was effectively interrupted, transmitter  705 - 1  does not receive such an acknowledgement, and, after a timeout in accordance with the protocol, retries frame  912  (in the form of frame  913 .) As illustrated in  FIG. 9 , as long as Bluetooth packet  951  is kept sufficiently short, transmitter  705 - 1  is no longer suppressed by transmitter  705 - 2  when transmitting frame  913 . Consequently, frame  913  in its entirety reaches antenna unit  504  (shown by frame  923 ), and receiver  704 - 1  subsequently receives acknowledgement  932 . Recalling the 802.11/Bluetooth nature of the example depicted by  FIG. 9 , the IEEE 802.11 ARQ error correction thus automatically compensates for sufficiently-short Bluetooth interruptions (i.e., interruptions that are not “fatal”) without any changes to the protocols. 
     It will be clear to those skilled in the art that ARQ error correction will also automatically compensate for sufficiently-short transmissions from transmitter  705 - 2  of radio  502 - 2  that overlap receiver  704 - 1 &#39;s receiving of data. In addition, it will be clear to those skilled in the art how to make and use alternative embodiments of the present invention for protocols that use other methods of error correction (e.g., forward error correction, etc.) In the case of forward error correction, for example, the interruption of a transmission is not fatal as long as the interruption is kept short enough so that the number of suppressed bits is below the particular error correction threshold. 
     So far throughout the exemplary sequence depicted in  FIG. 9 , radio  502 - 1  has been active, as shown by the “low” value of signal  904 , corresponding to the first idle indication signal of radio  502 - 1 , which is provided by signaling link  508 - 1  to radio  502 - 2 . After acknowledgement frame  932 , radio  502 - 1  enters power-save (i.e., idle) mode, as shown in  FIG. 9  by the transition of first idle indication signal (signal  904 ) from low to high. Transmitter  705 - 2 , upon detecting this transition, takes advantage of this situation by transmitting higher latency-tolerant packet  952  (e.g., an asynchronous connection-less [ACL] packet, etc.). Thus, instead of preempting transmitter  705 - 1 , as is done for transmissions with a lower latency tolerance (e.g., transmission  951 , etc.), transmitter  705 - 2  waits for radio  502 - 1  to enter power-save mode before initiating transmissions with a higher latency tolerance (e.g.,  952 , etc.). 
     When radio  502 - 1  exits power-save mode (i.e., “wakes up”), it executes a “warm-up sequence” before transmitting any frames, as is well known in the art. If radio  502 - 1  happens to wake up while transmitter  705 - 2  is still transmitting, radio  502 - 2 , which detects that radio  502 - 1  has awakened, terminates transmitter  705 - 2 &#39;s transmissions. As will be clear to those skilled in the art, the warm-up sequence of radio  502 - 1 , operating in the example in accordance with the Bluetooth protocol, gives transmitter  705 - 2  plenty of time to gracefully terminate any in-progress transmissions. Any “left-over” information that transmitter  705 - 2  was unable to transmit before radio  502 - 1  awoke is queued for the next time that radio  502 - 1  enters power-save mode; this postponement is not problematic since, by definition, the information has a higher latency tolerance. If, instead, this information had a lower latency tolerance, transmitter  705 - 2  would have previously preempted transmitter  705 - 1 , as described above; 
       FIG. 10  depicts a block diagram of radio  502 - 1  in another variation of the third illustrative embodiment of the present invention.  FIG. 10  is similar to  FIG. 7 , except that the signaling links between radios  502 - 1  and  502 - 2  are interfaced directly to multi-radio host interface  1002 . Consequently, channel-access controller  1001 , multi-radio host interface  1002 , and path  1005  are different from channel-access controller  701 , multi-radio host interface  702 , and path  705 , respectively. 
     Channel-access controller  1001  provides the medium access control functionality for communicating in accordance with a first air interface (e.g., 802.11, Bluetooth, etc.). In this regard, it provides the same functionality as channel-access controller  701 . It accepts host data from multi-radio host interface  1002  via path  1005 . It provides data from host  501  to baseband controller  703  via path  712  for preparation for transmission. Channel-access controller  1001  also provides data received over the air from baseband controller  703  via path  712  to host  501  through path  1005  and multi-radio host interface  1002 . Channel-access controller  1001  can track whether it has control or radio  502 - 2  has control of the communications band at any given moment. Consequently, channel-access controller  1001  can control antenna switching at antenna switch  503  via path  511 - 1 . Alternatively, channel-access controller  1001  can operate uninformed of the status of radio  502 - 2 . 
     Channel access controller  1001  can pass to radio  502 - 2  via signaling link  508 - 1  information representative of receiver  704 - 1  and transmitter  705 - 1 , received through path  1006 . Channel access controller  1001  can pass to receiver  704 - 1  and transmitter  705 - 1  via path  1006  information representative of radio  502 - 2 , received through signaling link  508 - 2 . It will be clear to those skilled in the art how to make and use channel-access controller  1001 . 
     In accordance with the illustrative embodiment of the present invention, multi-radio host interface  1002  provides the interface between host  501  and radio  502 - 1 . Multi-radio host interface  1002  accepts data blocks from host  501  via host data link  506 . Multi-radio host interface  1002  then determines whether it should (1) transfer each data block to channel-access controller  1001  via path  1005 , if the data block is meant for radio  502 - 1 , or (2) relay the data block over to radio  502 - 2  via link collateral radio data link  507 . Multi-radio host interface  1002  accepts data blocks from channel-access controller  1001  and transfers them to host  501 . In other words, multi-radio host interface  1002  provides multiple logical channel interfaces on a single physical channel interface to host  501 . After reading this specification, it will be clear to those skilled in the art how to make and use multi-radio host interface  1002 . 
     Multi-radio host interface  1002  terminates one end of collateral radio data link  507 , as well as signaling links  508 - 1  and  508 - 2 . Collateral radio data link  507  and signaling links  508 - 1  and  508 - 2  can be different interfaces to radio  502 - 2  physically, or they can be the same interface. It will be clear to those skilled in the art how to combine collateral radio data link  507  and signaling links  508 - 1  and  508 - 2  into one interface. Each of the interfaces with radio  502 - 2  can be a serial interface or a parallel interface. It will be clear to those skilled in the art how to make and use a serial or parallel interface. If one or more of collateral radio data link  507  and signaling links  508 - 1  and  508 - 2  are serial, the serial interface characteristics can comprise SERDES, IEEE1394 style data/strobe encoding, or RFF( 2 , 5 ) coding, in well-known fashion. 
     The signaling information that is exchanged between radio  502 - 1  and  502 - 2  can be represented in any of a variety of formats. Signals from radio  502 - 1  can be communicated to radio  502 - 2  along signaling link  508 - 1  via a single high or low electrical signal, one signal value per state, in well-known fashion. For example, when radio  502 - 1  wants to indicate that it is transmitting, it can set the transmitting indication signal line to “high” and maintain that signal value for as long as radio  502 - 1  is in the transmitting state. When radio  502 - 1  stops transmitting, it can reset the transmitting indication signal line to “low”, and maintain that signal value for as long as radio  502 - 1  is not transmitting. Similarly, signals from radio  502 - 2  can be communicated to radio  502 - 1  along signaling link  508 - 2  via a single high or low electrical signal, one signal value per state, in well-known fashion. 
     Alternatively, signals can be communicated between radio  502 - 1  and radio  502 - 2  via a packet format (i.e., a format using blocks of data to represent information), as opposed to using individual electrical signal levels to directly represent information. For example, when radio  502 - 1  wants to indicate that it is transmitting, it can prepare and transfer a packet message to radio  502 - 2  indicating “transmitting” when the state change from “not transmitting” to “transmitting” occurs. When radio  502 - 1  stops transmitting, it can prepare and transfer a packet message to radio  502 - 2  indicating “not transmitting” when the state change from “transmitting” to “not transmitting” occurs. The packet message also specifies the type of message being sent, such as control (e.g., transmit inhibit, etc.), status (e.g., idle indication, etc.), or host interface-related (e.g., data message for radio  502 - 2  from host  501 , etc.). The packet format can be transferred in full-duplex, bidirectional fashion between radios  502 - 1  and  502 - 2 . It will be clear to those skilled in the art how to make and use a packet format to convey signals and to do so in full-duplex, bidirectional fashion. 
       FIG. 10  depicts signaling link  508 - 1  as comprising M lines and signaling link  508 - 2  as comprising N lines. This is for illustrative purposes only, since signaling links  508 - 1  and  508 - 2  can be combined with collateral radio data link  508  in practice. The values for M and N depend on several factors, including (in no particular order):
         1. Whether each of signaling link  508 - 1  and  508 - 2  is a serial or parallel interface;   2. How wide the parallel interface is;   3. If communication is full-duplex, bidirectional;   4. If the information is sent in packet format; and   5. If collateral radio data link  507 , signaling link  508 - 1 , and signaling link  508 - 2  are combined into one interface.
 
Values for M and N are determined in well-known fashion. If the three links are combined into one serial interface that is full-duplex, bidirectional with packet format, the number of lines required by that interface is as little as two, consistent with the notion of low cost, low complexity.
       
     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.