Abstract:
Techniques are provided for frequency coordination among two different wireless network protocols, such as the IEEE 802.11 and Bluetooth protocols, operating in proximity with one another. Coordination is accomplished by the use of a first radio transceiver operating in accordance with a first communication protocol (which may be the 802.11 protocol) and using a frequency band (which may be the 2.4 GHz band), a base station connected to a wired network and operating in accordance with the first communication protocol, a second radio transceiver operating in accordance with a second communication protocol (which may be the Bluetooth protocol) and using the frequency band, and a coordinator associated with the base station for, in turn, activating the first radio transceiver, deactivating the first radio transceiver, activating the second radio transceiver, and deactivating the second radio transceiver.

Description:
BACKGROUND OF THE INVENTION 
   This application claims the benefit of provisional application Ser. No. 60/175,262, filed Jan. 10, 2000 and Ser. No. 60/196,979, filed Apr. 13, 2000. This invention relates to wireless data communications networks, and in particular to arrangements for ensuring coexistence between wireless networks that share the same frequency band with different operating protocols. 

   Wireless devices communicate with one another using agreed-upon protocols that are transmitted in predefined frequency bands. Often, devices using one or more wireless protocols may operate by transmission within the same frequency band. It is therefore necessary to develop coordination techniques in order for devices using one or more wireless protocols to efficiently operate in the same band of frequencies at the same time. 
   For example, the assignee of the present invention supplies wireless data communications systems known as the Spectrum 24® System that follows the communications protocol of IEEE 802.11 Standard (802.11), which is hereby incorporated by reference. In the system as implemented, mobile units (MUs) are in data communication with a central computer through one or more access points (APs). The APs may communicate with a computer directly or over an Ethernet wired network. Each of the MUs associates itself with one of the APs. As defined in 802.11, this communications protocol uses the 2.4 GHz ISM frequency band. 
   As currently designed, 802.11 devices may use several predefined methods for transmission within the 2.4 GHz band to perform as a wireless local area network. One method is to use a frequency hopping spread spectrum (FHSS) mechanism wherein data is transmitted for a certain period of time in a particular channel and, following a pseudorandom sequence, continues transmission at a different channel for the same predetermined length of time. As currently designed, 802.11 devices operate at a frequency hopping rate of 10 hops/second. Another method is to use a direct sequence spread spectrum (DSSS) mechanism wherein the data is transmitted in a predetermined frequency channel and is multiplied by a pseudorandom chipping sequence during transmission. 
   As all 802.11 devices use the same ISM frequency band, interference among these devices is minimized by use of a Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) protocol. Under CSMA/CA, an 8021.11 device listens for another&#39;s devices transmission prior to initiating its own transmission. If no other transmission is detected, the device transmits its information and waits for an acknowledgment (ACK) from the receiving device. If no acknowledgment of receipt is received after a pre-determined time interval, the device will retransmit after waiting for a randomly chosen interval of time. Thus, if two or more devices began transmitting coincidentally at the same time and the resulting interference blocks all of the transmissions, each device will wait a random amount of time to attempt a retransmission. This allows the devices to transmit at different times. 
   Another example of a wireless specification that also uses the 2.4 GHz ISM frequency band is Bluetooth™, which is designed for communication among devices within a short range transmitting at a lower power level. The Bluetooth specification, version 1.1, which would be known to one of ordinary skill in the art, is fully incorporated herein by reference. As currently designed, Bluetooth operates using a frequency hopping spread spectrum mechanism at a rate of 1600 hops/second. Bluetooth uses a master/slave system of communication. One example of a Bluetooth network may be a mobile device attached to the user&#39;s belt that communicates with a cordless scanner for reading bar codes and worn by the user as a ring. In this case, the mobile device would operate as the master and the cordless ring scanner would operate as the slave. In this system for data transmission, the master and slave only communicate at predefined intervals. At the first interval, the master may communicate to a first slave device, which may only respond during the second interval. At the third interval, a master may communicate to a second slave device, which may only respond during a fourth interval. By using this system, it is ensured that only one device within a particular Bluetooth “piconet” is transmitting at any particular time. Thus, interference is minimized. 
   Additionally, it is desirable for one Bluetooth piconet to operate in close proximity with another, separate Bluetooth piconet. Because there are 79 different frequency channels used by Bluetooth, different Bluetooth networks are unlikely to be operating on the same frequency at the same time. Interference between the separate Bluetooth piconets is thus minimized. This allows, for example, multiple individuals working in close proximity with one another to each have his or her own mobile unit along with a cordless ring scanner. 
   Along with the need to operate multiple networks of the same protocol in close proximity, there is also a recognized need in the art to coordinate the transmissions of devices operating under different protocols that use the same frequency band. For example, it may be desirable to use a cordless ring scanner that communicates with belt-mounted terminal using the Bluetooth protocol while the same belt mounted terminal communicates with an access point using the 802.11 protocol. For example, once the user scans a bar code using the cordless ring scanner, the bar code information may be sent to the belt-mounted terminal. That bar code information may then be transmitted to the 802.11 AP. Then an acknowledgment, and possibly a message, may need to be sent from the AP back to the belt-mounted terminal. The terminal may also need to communicate with other Bluetooth enabled peripherals like a printer or a headset. Although communication protocols such as 802.11 and Bluetooth are designed to ensure that devices using the same protocol may operate in the same frequency band with a minimum of interference, there has heretofore been no method of coordination for the use of these wireless devices in the same frequency operating under different communication protocols. 
   It is additionally desirable to provide voice service using the Bluetooth communications protocol, for example, between a belt-mounted terminal and a headset worn by the user. Bluetooth supports voice communications using Synchronous Connection Oriented (SCO) voice packets which are transmitted every 3.75 ms. The requirement for such frequent Bluetooth packet transmission makes it difficult to coordinate voice transmission using the Bluetooth SCO packets with 802.11 communications. 
   It is therefore an object of this invention to utilize coordination techniques to ensure that, for example, both Bluetooth and 802.11 enabled devices, may operate robustly in the same frequency band at the same time. 
   SUMMARY OF THE INVENTION 
   An embodiment of the present invention includes a first radio transceiver operating in accordance with a first communication protocol (which may be the 802.11 protocol) and using a frequency band (which may be the 2.4 GHz ISM band), a base station operating in accordance with the first communication protocol, a second radio transceiver operating in accordance with a second communication protocol (which may be the Bluetooth protocol) and using the frequency band, and a coordinator associated with the base station for, in turn, activating the first radio transceiver, deactivating the first radio transceiver, activating the second radio transceiver, and deactivating the second radio transceiver. 
   The first radio transceiver and the second radio transceiver may be mounted together in a housing, which may be suitable for wearing on a belt or a laptop computer or a PDA. One or more slave devices may be associated with the second transceiver and operate in accordance with the second communication protocol. The slave devices may include a scanner, worn on a user&#39;s finger and capable of transmitting bar code information to the second transceiver, a printer, or a personal data managing device. 
   In one arrangement wherein the first and second transceivers are mounted together in a housing, they may include orthogonally polarized antennas. In another arrangement a Bluetooth protocol transceiver transmits at power level of about 0 dBm. In still another arrangement, two or more sub bands within the frequency band are provided and the 802.11 protocol transceiver uses one of the two or more sub-bands and the Bluetooth protocol transceiver uses another of the two or more sub-bands. In still another arrangement in the second radio transceiver is equipped with a look-ahead function for determining whether two or more sub-bands are being used by the first radio transceiver that will also be used by the second transceiver. In still another arrangement, a coordinator is associated with the first radio transceiver for deactivating the second radio transceiver while the first radio transceiver is in use. 
   According to the invention, there is provided a method for operating a portable data communications device using first and second wireless data communications protocol. The data communications device is operated in a power saving mode of the first communication protocol, whereby the device has active time periods for transmitting and receiving data communications signals using the first communications protocol and dormant time periods during which the device neither transmits nor receives data communications signals using the first protocol. The data communications device is operated as a master device according to the second communications protocol whereby the data communication device controls operation of slave devices communicating therewith. The operation according to the second data communications protocol is controlled to operate only during the dormant time periods of the first protocols. 
   In one embodiment, a signal indicating that the active time period will commence following a predetermined time interval is provided to terminate operation according to the second data communication protocol during the predetermined time interval. The first wireless data communications protocol may be the 802.11 protocol. The second wireless communication protocol may be Bluetooth. 
   In another aspect of the invention, there is provided a method for operating a wireless data communications system having an access point and at least one mobile unit associated with said access point using a first wireless protocol (which may be 802.11), wherein said mobile unit is arranged to conduct wireless data communications with other units using a second wireless protocol (which may be Bluetooth). Periodic beacon signals are transmitted from the access point according to the first wireless protocol. Global clear to send signals are transmitted from the access point according to the first wireless protocol, whereby the global clear to send signals prevent mobile units from transmitting signals using the first data communications protocol during an allocated time interval within the beacon signal period. The access point is controlled to avoid transmissions during the allocated time interval, and the mobile unit is operated in response to the global clear to send signal to conduct wireless communications acting as a master unit using the second wireless protocol during the allocated time interval. 
   In one embodiment, the beacon signal period is divided into three time intervals, wherein the access point conducts power saving mode data communications during a first time interval, wherein the access point conducts data communications using the second communications protocol during the second time interval and wherein the access point conducts data communications using the first wireless protocol during a third time interval. The first time interval may immediately following the beacon signal. In another embodiment, the first time interval may not be utilized. 
   In accordance with another aspect of the invention, there is provided a method of operating a data communications system using a master-slave protocol (such a Bluetooth), wherein a master transceiver transmits to slave units during first even time slots and wherein slave units transmit to the master unit during odd time slots, and wherein the transmissions follow a predetermined frequency hop pattern at a hop rate corresponding to the time slots. The master unit is operated during a first time period of each time slot to detect interfering signals at a frequency corresponding to the following time slot. Transmission by the master transceiver is inhibited during even time slots if interfering signals have been detected during either of the current or previous time slots. 
   In a preferred practice, the operating step includes tuning the master unit to receive signals corresponding to the frequency allocated to the next following time slot; detecting the strength of signals received and retuning the master unit to send or receive signals corresponding to the frequency allocated to the current time slot. 
   In another aspect of the invention, there is provided a method for providing voice communications in a wireless data communications system having a mobile unit arranged to communicate with an access point using a first data communications protocol (such as 802.11) and arranged to communicate with other devices using a second data communications protocol (such as Bluetooth). Data corresponding to the voice communication is communicated between the access point and the mobile unit using the first data communications protocol. The data corresponding to the voice communications is communicated between the mobile unit and a portable device using the second data communication protocol. The communication is arranged at time intervals which avoid interference with the communicating using the first data communications protocol. Voice signals are converted to data corresponding to the voice signals and data signals corresponding to voice signal are converted into voice signals in the portable device. 
   In a preferred arrangement, the data corresponding to voice signals comprises compressed voice signal data. The communication between the mobile unit and the portable device preferably uses a Bluetooth ACL link. 
   According to a further aspect of the invention, there is provided a method for operating a mobile unit arranged to communicate using first and second data communication protocols operating in the same frequency band (such as 802.11 and Bluetooth) wherein the mobile unit associates with an access point and receives therefrom beacon signals demarcating time intervals according to the first communications protocol. Signals are received from the access point (such as CTS signals) designating a portion of one of the time intervals during which mobile units associated with the access point refrain from transmissions using said first data communications protocol. The mobile unit is operated as a master unit using the second data communications protocol to communicate with slave units during the designated portion of the time interval. 
   According to a further aspect of the invention, there is provided a method for operating a wireless data communications network having at least one access point and at least one mobile unit, including a mobile unit arranged to communicate with the access point using a first wireless data communication protocol (such as 802.11) in a first frequency band and to communicate with other devices using a second wireless data communication protocol (such as Bluetooth) in the first frequency band. Signals (such as CTS) as sent from the access point in the first communications protocol, which designate a time period wherein mobile units associated with the access point refrain from transmitting using the first data communications protocol. The mobile units operate as a master unit to conduct wireless data communications with the other devices operating as slave units using the second data communications protocol during the designated time period. 
   According to still another aspect of the invention, a method is provided for operating a mobile unit arranged to communicate using first and second data communications protocols operating in the same frequency band (such as 802.11 and Bluetooth), wherein the mobile unit associates with an access point. The mobile unit receives first and second control signals using the first data communications protocol. The mobile units are operated in response to the first control signals to act as a master unit and conduct data communications with slave units using the second data communications protocol. Communications by the mobile unit using the second data communications protocol is discontinued in response to the second control signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a wireless communications system using 802.11 and Bluetooth devices. 
       FIG. 2  is a block diagram of a wireless communications system using 802.11 and Bluetooth devices at the same time along with a connect button switch and connected indicators. 
       FIG. 3  is a schematic diagram of an embodiment of the present invention illustrating a coordinated time line between the operation of 802.11 and Bluetooth devices. 
       FIG. 4  is a schematic diagram of an embodiment of the present invention illustrating another coordinated time line between the operation of 802.11 and Bluetooth devices. 
       FIG. 5  is a diagram showing a modified Bluetooth operating method for avoiding interference. 
       FIG. 6  is a drawing showing one example of orthogonally polarized antennas. 
       FIG. 7  is a drawing of a wireless headset arranged for voice communications. 
       FIG. 8  is a block diagram of the headset of  FIG. 7 . 
   

   DESCRIPTION OF THE INVENTION 
   Turning to  FIG. 1 , shown are a plurality of base stations or Access Points (APs)  20 ,  30  that are physically connected  40 ,  50  to a wired network  10 . While a wired network with multiple access points connected to a CPU  12  is a typical installation, the system may use a single computer and single AP. Each AP contains apparatus  60 ,  70  for the transmission and reception of radio frequency (RF) signals under the 802.11 protocol. Also using the 802.11 protocol, a plurality of radio transceivers or mobile units (MUs)  120 ,  140  communicate using apparatus  80 ,  90  for the transmission and reception of RF signals. Each MU  120 ,  140  may also be associated with a radio transceiver which is a Bluetooth Master (BTM) device  130 ,  150 , which together make up a dual mode devices  100 ,  110 . The association between the MU and BTM may be, for example, by way of being physically housed in the same unit. An example of a dual mode device  100 ,  110  may be portable terminal worn on a belt. 
   Each BTM  130 ,  150  communicates with one or more Bluetooth Slave (BTS) devices  160 ,  170 ,  180 ,  190 ,  200 ,  210  via the Bluetooth protocol. The Bluetooth protocol is established such that each BTS is uniquely associated with a BTM. Thus, as illustrated, BTSIA  160 , BTS 1 B  170 , and BTS 1 C  180  communicate using RF signals  220 ,  230 ,  240  only with BTM 1   130 . This forms a piconet  280 . Correspondingly, BTS 2 A  190 , BTS 2 B  200 , and BTS 2 C  210  communicate using RF signals  250 ,  260 ,  270  with BTM 2   150 . This forms a piconet  290 . An example of a BTS may be a cordless ring scanner, a printer, or personal data managing device. 
   With no coordination, there will be times when the BTM  130 ,  150  and the associated MU  120 ,  140  attempt to operate at the exact same time. Since the two devices operate in the same 2.4 GHz ISM frequency band the BTM  130 ,  150  and the MU  120 ,  140  may severely interfere with one another, especially if they are housed in a dual mode device  100 ,  110 . Therefore, there is a need for coordination between the two devices. One such coordination scheme is primarily based on time multiplexing of the 802.11 and BT radios, which is especially suitable for a controlled environment (e.g., the 802.11 and BT radios are housed in the same terminal or dual mode device). In one embodiment, the Bluetooth systems are enabled or disabled according to a global/central signal from the 802.11 AP as described herein. The central signal may also be coordinated among the two devices without coordinating with the AP. 
   In a further embodiment, the dual mode devices  100 ,  110  may be designed such that the 802.11 antennas  80 ,  90  have orthogonal polarization with respect to the Bluetooth antennas used to generate RF signals  220 ,  230 ,  240 ,  250 ,  260 ,  270 . This technique may provide additional protection from 802.11 Bluetooth interference and does not require the need for centralized control. 
     FIG. 6  shows one example of orthogonally polarized antennas that can be used to reduce interference. The antenna structure of  FIG. 6  includes a vertically polarized monopole antenna  502 , which is connected to a transmitter/receiver by an unbalanced transmission line  510 . The structure also includes a horizontally polarized dipole antenna having dipole arms  504 ,  506  which are connected to a transmitter/receiver by balanced transmission line  508 . Those skilled in the art will recognize that many other orthogonal-polarized antenna configurations may be used. In a further embodiment, the BTMs  130 ,  150  may be designed to transmit at a relatively low power level such as lower than 0 dBm. This technique may provide additional protection from 802.11 Bluetooth interference and may be used with other antenna or frequency coordination methods discussed herein. 
   In a further embodiment, the 802.11 APs  20 ,  30  and MUs  120 ,  140  may be designed to operate in one portion of the 2.4 GHz spectrum, while the BTMs  130 ,  150  and BTSs  160 ,  170 ,  180 ,  190 ,  200 ,  210  may be designed to operate in another portion of the 2.4 GHz spectrum. 
   In a further embodiment, the BTMs  130 ,  150  may be equipped with a look-ahead function to determine which frequencies within the 2.4 GHz band will be used for two or more future Bluetooth frequency hops to occur. If the BTM  130 ,  150  determines that one of the next two or more frequency hops will use the same frequency that the 802.11 system is using, the BTMs  130 ,  150  will blank their output, thus reducing the effect of the interference on the 802.11 transmissions. By using this method, interference between Bluetooth and 802.11 could be reduced or eliminated at the expense of dropping a couple of packets when channel overlap occurs. This approach may also be expanded to include the blanking of adjacent channels that may also interfere with the 802.11 transmissions. 
   Bluetooth uses a Frequency Hopping Spread Spectrum (FHSS) radio, which hops much faster than most IEEE 802.11 radios. Bluetooth sends a short packet as it dwells on a given frequency. Most IEEE 802.11 radios hop much slower and send much longer packets. Also there are versions of IEEE 802.11 WLANs that use Direct Sequence Spread Spectrum (DSSS) which do not hop and occupy a wide band. 
   As a result, during the transmission of an IEEE 802.11 packet the Bluetooth radio hops across many frequencies and potentially sends a packet on each frequency. These Bluetooth packets can interfere with the IEEE 802.11 packets and cause the IEEE 802.11 packet to be in error. The IEEE 802.11 packet needs to be retransmitted, and once again may be destroyed by the signal from the Bluetooth radio. 
   This technique shown in  FIG. 5  can be used in any Bluetooth radio and in any device that will operate in an IEEE 802.11 WLAN environment. Since it detects devices radiating in the 2.4 GHz ISM band it could also be used to prevent interference with other devices in that band. 
   A Bluetooth network consists of up to eight Bluetooth devices operating in a piconet. The piconet has one master and up to seven slaves. All the Bluetooth devices in the piconet hop in unison, at a rate of 1600 hops/second. The time that the frequency hopper dwells on a given frequency is called the slot time. At this hop rate the slot time is 625 microseconds. Typically packets are completed within one slot time, however, it is also possible to have 3 and 5 slot packets. The master and the slaves take turns transmitting, with the master transmitting on even slots and the slaves transmitting on odd slots. See also Bluetooth Specification, version 1.0, Dec. 1, 1999, which is hereby incorporated by reference in full. 
   There are two types of links between the master and each of the slave devices in a Bluetooth piconet. There is an asynchronous connection-less link (ACL) which is used to transfer data. There is also a synchronous connection oriented link (SCO) that is used to transfer voice data. The master in the picolink determines when data on an ACL link is transferred. Data is transferred when the master has data to send to a slave or the master wants to receive data from a slave. 
   Each Bluetooth device within a piconet frequency hops in unison, according to a pseudo random sequence.  FIG. 5  illustrates a device hopping along its sequence of frequencies: f( 1 ), f( 2 ), . . . f(n) . . . The figure also shows how the 625-microsecond slot time includes a 220-microsecond period for tuning the frequency synthesizer in the radio to a new frequency and a 405-microsecond data transmission period. 
   As stated above during even slots T(f) the master transmits to a slave and during odd slots R(f) the slave transmits back to the master. The master can transmit on any even time slot. The slave can only transmit to the master in a time slot if the master sent the slave a packet in the previous time slot. If the master does not send data to any slave in slot n then no slave can transmit in slot (n+1). The exception to this rule is for SCO link packets in which data is always transmitted in predefined periodic intervals. So for ACL links if the master does not transmit any data, the slaves do not send any data. 
   Currently the piconet master does not attempt to determine if any other devices are using the spectrum before it transmits. As a result, if there is an IEEE 802.11 packet currently being transmitted the Bluetooth master will not bother to check to see if this other system is transmitting and will itself transmit at the same time, and possibly on the same frequency. As a result it will interfere with the IEEE 802.11 packet possibly causing the packet to be received incorrectly. 
   It is proposed to subdivide the 220 microsecond tuning time interval into several subintervals and to spend some of that time looking ahead into subsequent frequencies to see if there is any other devices transmitting in those channels. The reason to look ahead is that if the a master sends a message to slave #1 on frequency f(n), then the master has cleared slave #1 to transmit during the next time slot on frequency f(n+1). Therefore, the master needs to look ahead to the frequency that corresponds to the next slot. The 220 microsecond timing interval can be subdivided as follows. In the first 80 microseconds the frequency synthesizer in the master retunes to f(n+1), then in the next 60 microseconds the master listens for any signal in that band. This can be done using a standard Receive Strength Signal Indicator (RSSI) in the radio. Then in the next 80 microseconds the frequency synthesizer then retunes the radio to f(n).  FIG. 5  illustrates the new proposed time slot subdivision. 
   Just prior to receiving on frequency f(n−1) the master checks to see that the frequency band at f(n) is clear. Also, prior to transmitting on frequency f(n) the master also makes sure that the frequency band f(n) is clear. If frequency bands f(n) and f(n+1) are clear then the master will transmit on frequency band f(n) and as a result allow the slave to transmit on frequency band f(n+1), in the next time slot. 
   During a time slot R the master likewise checks the frequency band that it will use to transmit in the following time interval. If that time slot is occupied, it will not transmit. 
   Referring now to the schematic of  FIG. 3  in conjunction with the physical layout shown in  FIG. 1 . There is shown another technique to coordinate transmissions. Every 802.11 beacon time period, T  300 , may be divided into three time intervals: 802.11 communications in the power saving (PSP) mode—t 802.11PSP    310 , Bluetooth communications—t NAV    320 , and 802.11 communications in the active mode CAM—t 802.11CAM    330 . The duration of time intervals T, t 802.11PSP , t NAV , and t 802.11CAM  depend on traffic characteristics and application needs (e.g., time critical services). At the beginning of each beacon period  300 , AP  20  sends a beacon signal  350  to the 802.11 PSP MU&#39;s  120 ,  140  that wake up in this period (some PSP MU&#39;s may wake up in a different beacon). During this period the PSP MU&#39;s  120 ,  140  receive and transmit their packets according to the 802.11 protocol. Once all the PSP MU&#39;s  120 ,  140  receive their packets, the AP  20 , may optionally send a global Clear to Send (CTS) signal  430  to shut down all the 802.11 communications for a NAV (Network Allocation Vector) period. At this point the 802.11 MUs  120 ,  140  will enable their associated BTMs  130 ,  150  (which may be housed in the same dual mode devices  100 ,  110 ) so the piconets  280 ,  290  associated with these BTMs  130 ,  150  may begin BT communications  360 ,  370 . After completion of the NAV period  320  the BTM  130 ,  150  radios are disabled and all BT communications is ceased. The rest of the time (until the next beacon  380 ) is dedicated for 802.11 Continuously Aware Mode (CAM) MU&#39;s (not shown) that operate according to the 802.11 protocol. 
   In a further embodiment, the t 802.11PSP    310  time interval may be eliminated if the MUs do not operate in PSP mode. Here, the CTS signal  340  would trigger only t NAV    320  and t 802.11CAM    330  time intervals for every 802.11 beacon period, T  300 . 
   In a further embodiment, the t 802.11CAM    330  time interval may be eliminated if the MUs do not operate in CAM mode. Here, the CTS signal  340  would trigger only t NAV    320  and t 802.11PSP    310  time intervals for every 802.11 beacon period, T  300 . 
   In a further embodiment, the Bluetooth systems are enabled or disabled according to a global/central signal from the dual mode devices  100 ,  110  instead of from an AP  20 . 
   A further embodiment of the present invention may be demonstrated by referring to the schematic of  FIG. 4  in conjunction with the physical layout shown in  FIG. 1 . In this approach there is no need for the 802.11 APs to coordinate between Bluetooth and 802.11 transmission. Instead, the Bluetooth network operates in the ordinary course until a 802.11 MU instructs one or all of the Bluetooth masters to stop transmitting messages to the Bluetooth slaves. When using Asynchronous Connectionless (ACS) packets, the Bluetooth master controls access to the medium for its piconet. Thus, if the masters stops transmitting the slaves stop as well. Once the 802.11 MU has completed its communication, the Bluetooth masters are allowed to resume communicating with the Bluetooth slaves. This technique is especially useful when all the 802.11 MUs are in PSP mode, because these devices are in suspended mode during most of the time. 
   As shown in  FIG. 4 , when the MU  120  desires to initiate 802.11 communication, its sends a STOP signal  400  to the BTMs  130 ,  150 . The MU  120  then communicates  450  using the 802.11 protocol with the AP  20 . When the MU  120  is finished communicating for the period t 802.11    470  and is ready to resume its power save mode, the MU  120  communicates a START signal  410  to the BTMs  130 ,  150 . The BTMs  130 ,  150  may then proceed to communicate  430 ,  440  using the BT protocol with their respective BTSs  160 ,  170 ,  190 ,  200  during the period t BT    480 . When the MU  120  802.11 terminal “wakes up” to either send data or to listen for a 802.11 beacon from the AP  20 , the MU  120  sends a STOP signal  420  to the BTMs  130 ,  150  to inform then that the MU  120  is taking over access to the medium. The MU  120  may warn the BTMs  130 ,  150  before it needs exclusive use of the medium, and this warning may occur, for example, about 4 μsec before access is required. This allows the BTMs  130 ,  150  to complete several packet transfers and then stop communicating with their respective BTSs  160 ,  170 ,  190 ,  200 . Subsequently the MU  120  may communicate  460  with the AP  20  for a new period t 802.11    490 . 
   In a further embodiment, the periods t 802.11    490  and t BT    480  are at fixed, predetermined intervals throughout the communications process. In a further embodiment, the periods t 802.11    490  and t BT    480  are equal length of time. 
   In a further embodiment, a BTS  160 ,  170 ,  180 ,  190 ,  200 ,  210  may be, for example, a headset or voice transmission device designed to transmit voice data to the BTMs  110 ,  130 , which is then transmitted via the 802.11 network. Voice information is normally transmitted on a Bluetooth network using the periodic Synchronous Connection Oriented (SCO) protocol. This protocol is not conducive to the transmission interruptions required to coordinate with 802.11 operation. It would be more efficient, when using Bluetooth and 802.11, to transmit voice over the Bluetooth network using the ACL protocol that is normally reserved for data transmission. To use voice transmission over Bluetooth, when used in conjunction with the frequency coordination techniques disclosed herein, the Bluetooth piconet  280 ,  290  needs to compress and decompress the voice information in order to use the ACL protocol normally reserved for data transmissions. 
   Referring to  FIGS. 7 and 8 , there is shown a voice communication system  520  including a headset  521  having a BTS radio unit  210  which communicates with a dual mode mobile unit  110  using the BT protocol. The headset  521  includes an earphone in the same housing as radio unit  210  and a microphone  522 . Mobile unit  110  may be arranged to be worn on the belt of a user. As shown in  FIG. 8 , BTS  210  include microphone  522 , earphone  524 , and D to A and A to D converter  526  for converting sound signals to digital signals and vice versa. Digitized sound signals are compressed and arranged in packets in processor  528  and transmitted using RF module  530  and antenna  532 . The reverse process is used for received signals. RF module  530  communicates with MU  110  using BT protocol in the ACL mode. 
   Another issue that results from attempts to coordinate 802.11 and Bluetooth devices is ensuring that the lower power Bluetooth devices are actually operating in conjunction with the higher power 802.11 devices. In this regard, a further embodiment of the present invention may be demonstrated by referring to  FIG. 2 .  FIG. 2  is substantially similar to a portion of  FIG. 1 , with the addition of a connect button  500  that provided on MUs  140  of the 802.11 network and light  540 . The connect button  500 , may be physically mounted on a dual mode device  110 . When activated by the user, the connect button  500  instructs the mobile units  140  to stop transmitting (timeout) for a preset amount of time. For example, the timeout could last for 10 seconds. This timeout would allow the Bluetooth piconet  290  to establish operations free from interference from 802.11 devices for the timeout period. Once established, the piconet  290  may activate light  540  to assure the user that the Bluetooth piconet  290  has in fact, been established. Once the timeout period ends, other methods for frequency coordination as described herein may be utilized. 
   While there have been described what are believed to be the preferred embodiments of the present invention, those skilled in the art will recognize that other changes and modifications may be made thereto without departing from the spirit of the present invention, and it is intended to claim all such changes and modifications as fall within the true scope of the invention.