Abstract:
A method and apparatus are described for applying a narrow band FH link for low-rate and medium-rate communications, and a stationary wide band channel for high-speed (HS) communications. A master and one or more slaves sharing the same FH link may form a piconet. Master and slaves may hop synchronously according to a pseudo-random hop sequence. A master may control traffic on the FH link. An HS link can be established between a master and one or more slaves or between two slaves. An appropriate band of the radio spectrum is selected adaptively based on lowest RSSI measurements both in master and slave to establish the HS link without making use of a hopping scheme. A master shares its time between the HS slave on the HS link and the slaves remaining on the FH link using Time Division multiplexing. If the HS link uses a part of the band over which the piconet hops, the master controls the traffic such that the HS link is never visited by the FH link. If the HS link and the FH link do not overlap, then hop avoidance is not required. The HS slave-pair remains in contact with the master by a beacon signal used on the FH link. Periodically, HS slaves interrupt HS communications to listen the FH link. The beacon protocol includes slaves returning from the HS link to the piconet channel. In an alternative embodiment, slaves communication over HS link for a time interval. Slaves automatically return to FH link after the expiration of the time interval.

Description:
This application claims priority under 35 U.S.C. §§119 and/or 365 to Provisional Patent Application No. 60/133,404 filed in U.S. Patent and Trademark Office on May 10, 1999; the entire content of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     The present invention relates to radio communication systems. In particular, the present invention is related to communication systems which use frequency hopping in unlicensed frequency carriers. 
     In the last decades, progress in radio and VLSI technology has fostered widespread use of radio communications in consumer applications, portable devices, such as mobile radios, can now be produced having acceptable cost, size and power consumption. 
     Although wireless technology is today focused mainly on voice communications (e.g. with respect to handheld radios), this field will likely expand in the near future to provide greater information flow to and from other types of nomadic devices and fixed devices. More specifically, it is likely that further advances in technology will provide very inexpensive radio equipment which can be easily integrated into many devices. This will reduce the number of cables currently used. For instance, radio communication can eliminate or reduce the number of cables used to connect master devices with their respective peripherals. 
     The aforementioned radio communications will require an unlicensed band with sufficient capacity to allow for high data rate transmissions. A suitable band is the ISM (Industrial, Scientific and Medical) band at 2.4 GHz, which is globally available. The ISM band provides about 83.5 MHZ of radio spectrum. 
     To allow different radio networks to share the same radio medium without coordination, signal spreading is usually applied. In fact, the FCC in the United States currently requires radio equipment operating in the 2.4 GHz band to apply some form of spreading when the transmit power exceeds about 0 dBm. Spreading can either be at the symbol level by applying direct-sequence (DS) spread spectrum or at the channel level by applying frequency hopping (FH) spread spectrum. The latter is attractive for the radio applications mentioned above since it more readily allows the use of cost-effective radios. A system called Bluetooth was recently introduced to provide pervasive connectivity especially between portable devices like mobile phones, laptops, PDAs, and other nomadic devices. This system applies FH to enable the construction of low-power, low-cost radios with a small footprint. The system supports both data and voice, the latter being optimized by applying fast FH with a nominal rate of 800 hops/s through the entire ISM band in combination with a robust voice coding. The system concept includes piconets consisting of a master and a limited number of slaves sharing the same 1 MHZ channel. The system also features low-power modes like HOLD and PARK where the slaves can be put in a temporary suspend or low duty cycle tracking mode, respectively. For additional information regarding the Bluetooth system, see “Bluetooth, the Universal Radio Interface for Ad Hoc wireless connectivity”, J. C. Haartsen, Ericsson Review, Telecommunications Technology Journal, No. 3, 1998. 
     In an FH system deploying transmit power above 0 dBm, the channel bandwidth may be limited to 1 MHZ. Limiting bandwidth correspondingly restricts data rates to the 1-2 Mb/s range. However, especially for data services like file transfer or file download, ever-increasing data rates are desirable. In a FH system with a limited hop bandwidth (e.g. 1 MHZ), high data rates are difficult to obtain. In a DS system, high data rates are also difficult to obtain at reasonable costs. DS systems have the additional disadvantage of the near-far problem which becomes more serious in uncoordinated scenarios for which the Bluetooth system was optimized. In scenarios where a Bluetooth system is used, communications over short distances (e.g. cable replacement applications) is common practice. In these applications, a data rate in excess of 2 Mb/s would be highly desirable. Yet, by its nature, the system must operate in unlicensed bands where interference cannot be controlled. 
     It would therefore be appreciated that a need exists in the art for a method and apparatus for providing low-rate, medium-rate, and high-rate data communications concurrently between communications entities over the same unlicensed frequency carrier. 
     SUMMARY 
     It is therefore an object of the present invention to provide a communications system for conducting low, medium and high rate communications over a shared communications channel. 
     It is a further object of the present invention to provide such a communications system having a narrow and wide band communication link over the same shared communication channel. 
     In accordance with one aspect of the present invention, the foregoing and other objects are achieved in a method and apparatus which applies a narrow band FH link for low-rate and medium-rate communications, and a stationary wide band link for high-speed (HS) communications. The system, generally, may include a master and one or more slaves which all share the same FH link. The master and slaves may form a piconet. Master and slaves may hop synchronously according to a pseudo-random hop sequence. The sequence may be determined by the master identity, the phase in the sequence may be determined by the master real-time system clock. The master may control the traffic on the link. An HS link can be established between the master and one or more slaves or between two slaves. 
     The high-speed link need not make use of a hopping scheme, and instead an appropriate band of the radio spectrum may be selected to establish the HS link. The selection is based on RSSI measurements both in master and slave, preferably carried out during the low-rate communications in the piconet. The HS link may be placed on the radio band carrying, on average, the lowest amount of interference. The selection is adaptive in the sense that the system avoids using a radio band with much interference for the HS link. If the master is involved in communications with one or more slaves over an HS link, the master has to share its time between the HS slave on the HS link and the slaves remaining on the FH link. Time division multiplexing may be applied where the master, during a certain time interval, resides on an HS link and during the remaining time resides on the FH link. If the master is not involved in communications over an HS link, e.g. two slaves establish an HS link, then piconet communications over an FH link may progress in parallel with the HS link. If the portion of the shared radio band which the HS link uses, is part of the band over which the piconet hops, the master may control traffic such that the HS link is never visited by the FH link. If the HS link and the FH link do not overlap, then such hop avoidance is not required. 
     The HS slave-pair may further remain in contact with the master by a beacon signal which may be used on the FH link. Periodically, HS slaves may interrupt their HS communications and temporarily listen to the master on the FH link. This beacon also provides a means for the slaves to return from the HS link to the FH link. In an alternative embodiment, the two slaves are directed to the HS link for a limited amount of time. After the time interval has expired, slaves engaged in communications over the HS link may automatically return to the FH link. If required, slaves may be sent to the HS link again. If the HS link experiences interference, the units participating in the HS link return to the FH link and a new HS link can be negotiated. New RSSI measurements will show where the HS link can best be placed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and advantages of the invention will be understood by reading the following detailed description in conjunction with the drawings in which: 
     FIG. 1 is a diagram illustrating an exemplary piconet having a master and one or more slaves in accordance with an exemplary Bluetooth system; 
     FIG. 2 is a diagram illustrating exemplary timing in an exemplary piconet channel having a master and one or more slaves in accordance with an exemplary Bluetooth system; 
     FIG. 3 is a diagram illustrating an exemplary packet format in accordance with an exemplary Bluetooth system; 
     FIG. 4A is a diagram illustrating exemplary FH links and an exemplary high-speed link between a master and exemplary slave devices; 
     FIG. 4B is a diagram illustrating exemplary FH links between an exemplary master and exemplary slave devices and an exemplary high-speed link between exemplary slave devices; 
     FIG. 5 is a diagram illustrating FH links between a master and slaves A, B and C and a high-speed link between a master and a slave device in accordance with an exemplary embodiment of the present invention; 
     FIG. 6 is a diagram illustrating a high-speed link between slaves B and C in accordance with another exemplary embodiment of the present invention; 
     FIG. 7 is a diagram illustrating exemplary RSSI measurement results and the exemplary selection of an HS link; 
     FIG. 8 is a diagram illustrating frequency interaction between a FH link and a HS link in accordance with an exemplary embodiment of the present invention; 
     FIG. 9 is a diagram illustrating carrier allocations on a FH link and a HS link using the same radio band in accordance with an exemplary embodiment of the present invention; and 
     FIG. 10 is a diagram illustrating beacon tracking of slaves B and C according to a further exemplary embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     The various features of the invention will now be described with respect to the figures, in which like parts are identified with the same reference characters. A preferred embodiment of the system described herein utilizes a FH radio interface as described in greater detail in U.S. patent application Ser. No. 08/685,069 “SHORT-RANGE RADIO COMMUNICATIONS SYSTEM AND METHOD OF USE”, by P. W. Dent and J. C. Haartsen, filed Jul. 23, 1996, (hereinafter “Dent”) the disclosure of which is incorporated herein by reference. 
     In Dent, an air interface is described based on the transmission of short packets on a FH link. The air interface therein described, forms the basis for a new air interface referred to as Bluetooth, which is intended to provide unlimited radio connectivity between devices of any kind, see “Bluetooth, the Universal Radio Interface for Ad Hoc wireless connectivity”, J. C. Haartsen, Ericsson Review, Telecommunications Technology Journal, No. 3, 1998. The Bluetooth concept includes a piconet which is created on a FH link. One of the units on the channel acts as a master and other units are slaves. Any unit can take on the master role or the slave role. The role of master and slave may be assigned when the piconet is established. By default, the unit that initiates the communications, e.g. creates the piconet, is the master. The master controls all traffic over the FH link in a manner using centralized control. A more thorough description of the use of master and slave units in an FH communication system using centralized control may be found in U.S. patent application Ser. No. 08/932,911 by J. C. Haartsen, entitled “FREQUENCY HOPPING PICONETS IN AN UNCOORDINATED MULTI-USER SYSTEM”, filed Sep. 18, 1997 and incorporated herein by reference. 
     In piconet  100 , a star configuration may be used as is illustrated in FIG.  1 . Master  120  is the center of the star: all communications flow via master  120 . When a slave, such as, for example, slave A  130 , slave B  140 , and slave C  150  joins piconet  100 , a slave address may be assigned. The slave address assignment may be temporary since slave units may enter and exit piconet  100 . Slave addresses may be included in packets exchanged between, for example, slave A  130 , slave B  140 , and slave C  150  and master  120 . In accordance with U.S. patent application Ser. No. 08/685,069 mentioned above, piconet  100  may generally include FH link  200  using a series of time slots: each slot being assigned a different frequency as is illustrated in FIG.  2 . Accordingly, on exemplary FH link  200 , master  120  may alternate transmit and receive single packets  121 - 126  and, for example, packets  131 - 333  associated with slave A  130 , packet  141  associated with slave B  140 , and packets  151  and  152  associated with slave C  150  across time slots  201 - 212 , each having a hop frequency  221 - 232 . Frequencies on exemplary FH link  200  may be assigned according to a pseudo-random hopping sequence as would be known to one skilled in the art. Alternate communications between master  120  and, for example, slave A  130 , slave B  140 , and slave C  150  may be conducted over corresponding links, preferably Time Division duplex links represented in FIG. 2 as channel  110   a , channel  110   b , and channel  110   c , respectively. It may accordingly be preferable for master  120  to communicate with slave A  130 , slave B  140 , and slave C  150  using, for example, a polling scheme to avoid two slaves transmitting simultaneously. Only that slave which is addressed in a master-to-slave slot corresponding to, for example, a TDD link, may respond in the following slave-to-master slot. Polling may be better understood with reference to channel  110   a , channel  110   b , and channel  110   c , for establishing communications between master  120  and slave A  130 , slave B  140 , and slave C  150  as is illustrated. Master  120  may, over channel  110   a , send packets  121 ,  123 , and  125  in respective master-to-slave time slots  201 ,  205 , and  209  at respective frequencies h K    221 , h K+4    225  h K+8    229  to slave A  130 . In response, slave A  130  may respond respectively with packets  131 ,  132 , and  133  only in the respective alternate slave-to-master time slots  202 ,  206 , and  210  at respective frequencies h K+1    222 , h K+5    226  h K+9    230 . Similarly, master  120  may, over channel  110   b , send packet  122  in master-to-slave time slot  203  at frequency h K+2    223  to slave B  140 . In response, slave B  140  may respond with packet  141  only in the alternate slave-to-master time slot  204  at frequency h K+3    224 . Master  120  may further, over channel  110   c , send packets  124  and  126  in respective master-to-slave time slots  207  and  211  at respective frequencies h K+6    227  and h K+10    231  to slave B  140 . In response, slave C  150  may respond respectively with packet  151  and  152  only in the respective alternate slave-to-master time slots  208  and  212  at respective frequencies h K+7    228  and h K+11    232 . 
     Packets exchanged within piconet  100  may conform generally to exemplary packet format  300  as illustrated in FIG.  3 . Each packet sent according to packet format  300  may include access code  310 , header  320 , and payload  330  as shown. Access code  310  may be used to identify, for example, a particular FH link. Each separate instance of piconet  100  may use a different access code  310 . Access code  310  may be derived, for example, from the identity of master  120 . It is to be noted that all packets on, for example, the same FH link may carry the same access code  310 . Access code  310  may further be used for frequency and timing recovery in addition identifying the particularly FH link. Packet header  320  may carry general control information, for example, identifying payload  330  and indicating error correction mechanisms. It is to be noted that payload  330  may, for example, be identified as contain data or voice information. It is important to note that in accordance with the present invention, a high speed link may be established in addition to a more conventional FH link on piconet  100 . It may be desirable in the context of the high speed link to use a modified packet format  300  to improve overall data transfer figures. Since it is in accordance with the present invention to support both FH and high speed links, packet format  300  may be optimized to suit each link type. 
     To better understand the desirability associated with providing the high speed link in accordance with the present invention, it may be useful to analyze exemplary bandwidth constraints associated with piconet  100 . In a typical Bluetooth system, an exemplary hop rate is 1600 hops/s resulting in exemplary time slots  201 - 212  being of about 625 μs in length. GFSK modulation results in a data rate of 1 Mb/s. The frequency carrier used for a typical Bluetooth system is the unlicensed ISM band at 2.4 GHz, with the bandwidth occupied by a single hop specified at 1 MHZ. The number of hops used in Europe and the US is 79, providing a spreading of about 80 MHZ in the 2.4 GHz ISM band. 
     Thus in accordance with the information above, channel  110  associated with piconet  100  may have a maximum instantaneous rate of 1 Mb/s. For systems using the 2.4 MHZ ISM band, regulatory bodies like the Federal Communications Commission (FCC) and European Telecommunications Standards Institute (ETSI) restrict the bandwidth of a single hop to 1 MHZ for system using an average transmit power larger than 0.75 mW. A problem arises however in that such bandwidth restrictions limit the maximum possible data rate achievable on channel  110 . Given a bandwidth limitation of 1 MHZ, reliable data communications at rates higher than 2-3 Mb/s becomes unfeasible. For conventional operations on piconet  100 , the data rate is accordingly limited to a maximum of around 1 Mbps. 
     Many applications however require a higher data rate, and are often accompanied by a shorter range limitation. Such a scenario is illustrated in FIG.  4 A. Piconet  400  may be established in, for example, an environment including LAN  400 . LAN access point  420 , which may be a LAN server, telephonic device, cellular or wireless communication base station, or the like, may act as a master and will be referred to hereinafter as master  420 . Cordless phone  430 , laptop  440 , and printer  450  may act as exemplary slaves and may hereinafter be referred to respectively as slave A  430 , slave B  440 , and slave C  450 . All devices may be synchronized to a FH link. 
     The operation of a FH link and HS link on a common channel according to the present invention may best be described by an example. At some point in time, for example, the laptop or slave B  440  may desire to download a print job to the printer or slave C  450 . Since piconet  100  is configured as a star network, slave B  430  may normally only reach slave C  450  via the LAN access point or master  420 . Since the FH link operates at the maximum practical limit of 1 Mb/s and is used in this example both for communication between master  420  and slave B  440  and between master  420  and slave C  450 , the maximum effective data rate for the download operation is limited to 500 kb/s. Preferably, slave B  440  may temporarily leave piconet  100  controlled by master  420  and create its own piconet to slave C  450 . In such a hypothetical case, slave B  440  would support a FH link to slave C  450  directly, resulting still in a maximum effective rate of only 1 Mb/s. An even higher data rate can be obtained in accordance with the present invention. Assuming slave C  450  is in close proximity, for example 3-10 m, to slave B  440 , it would suffice to cover such a distance using 0 dBm transmit power. Accordingly, a link between slave B  440  and slave C  450  may be created with a much larger bandwidth than 1 MHZ. Data rate may be increased to 5-10 Mb/s using a high speed connection as will be described in greater detail hereinafter. 
     When any two communication units participating in communications over piconet  400  desire to increase the speed of communications, they may request a high-speed (HS) link. It is important to note that a distinction may be made between an HS link, such as channel  510   a  between master  420  and slave C  450 , as illustrated in FIG.  4 A and an HS link, such as channel  510   b  between two or more slaves, such as slave B  440  and slave C  450  as illustrated in FIG.  4 B. When a HS link, such as channel  510   a  is established between master  420  and slave C  450  in accordance with one exemplary embodiment of the present invention, master  420  time multiplexes between slave C  450  associated with channel  510   a , the HS link, and the other slaves, such as slave A  430  and slave B  440  in piconet  400 . Master  420  jumps between channel  510   a  and the FH link associated with, for example, channel  410   a  and  410   b  for slave A  430  and slave B  440  respectively. If the effective data rate on the HS link, channel  510   a  is important, master  420  should allocate many time slots as to slave C  450  for traffic and just enough time slots for traffic to slave A  430  and slave B  440  to enable FH synchronization to be maintained. Maximum data rate may be achieved on channel  510   a  by allocating all time slots to the HS link, however, FH synchronization will likely be lost. 
     FIG. 5 illustrates this concept in more detail, wherein master  420  supports three slaves: slave A  430 , slave B  440 , and slave C  450  over channels  410   a ,  410   b , and  410   c  respectively. An HS link may be established, for example, between master  420  and slave C  450  over channel  510   a . An HS link between master  420  and slave A  430  reflects the configuration illustrated in  4 A. As can be seen from FIG. 5, master  420  may communicate packet  421  to slave A  430  over channel  410   a  on time slot  201  at frequency h K    221 . Slave A  430  may respond in a manner as described above by responding with packet  431  in the next time slot  202  at frequency h K+1    222 . Similarly, master  420  may communicate packet  422  to slave B  440  over channel  410   b  on time slot  203  at frequency h K+2    223 . Slave B  440  may respond in a manner as described above by responding with packet  441  in the next time slot  204  at frequency h K+3    224 . With regard to slave C  450 , master  420  may, at point x, shift from FH communications on link  410   c  to HS communications on channel  510   a  and may shift back to FH communications, releasing channel  510   a , at point y. It should be noted that, while FIG. 5 illustrates point x and y as occurring within frequency hopping periods represented by traversing, for example, frequencies h K    221  to h K+11    232 , master  420  may maintain HS communications with, for example, slave C  450  through several frequency hopping iterations through the entire range of frequencies h K    221  to h K+11    232 . 
     Accordingly, master  420  conducts HS communications with slave C  450  over channel  510   a  by communicating on frequency carrier f HS    510 . Once the HS channel is established in a manner described in greater detail hereinafter, master  420  may send variable length packet  423  to slave C  450 . Slave C  450  may send variable length packet  424 . Master  420  may send additional variable length packet  424  which may or may not be responded to by slave C  450 . It is important to note that the data rate for the HS link is adaptive in that, for example, by reducing the scope of communications between, for example, master  420  and slave A  430  and slave B  440 , the data rate associated with the HS link may be increased. At point y, master  420 , for example, may resume FH communications with slave C  450  over channel  410   c  by, for example, transmitting packet  425  on time slot  211  at frequency h K+10    231 . In response, slave C  450  may send packet  452  in the next time slot  212  at frequency h K+11    232 . 
     If on the other hand, for example, slave B  440  and slave C  450  desire to establish an HS link as is illustrated in FIG. 4B, the situation is quite different. In an alternate embodiment of the present invention, master  420  may establish an FH link with slave A  430 , slave B  440 , and slave C  450 . At some point, denoted as point x in FIG. 6, slave B  410  and slave C  450  may establish HS communications on a separate link, such as channel  510   b . Accordingly, communications over the FH link and HS link may proceed in parallel provided that different frequencies are used for the FH and HS links. Collisions may occur if frequencies for channel  510   b  conflict with FH frequencies associated with link  410  at the same point in time. Master  420  may communicate over channel  410   a , for example, packet  421  to slave A  430  over time slot  201  at frequency h K    221 . Slave A  430  may respond in a manner as described above by responding with packet  431  in the next time slot  202  at frequency h K+1    222 . Similarly, master  420  may communicate packet  422  to slave B  440  over channel  410   b  on time slot  203  at frequency h K+2    223 . Slave B  440  may respond in a manner as described above by responding with packet  441  in the next time slot  204  at frequency h K+3    224 . Master  420  may further send packets  427 ,  428 , and  429  over channel  410   a  to slave A  430  on time slots  205 ,  207 , and  209  respectively using respective frequencies h K+4    225 , h k+6    227 , and h k+8    229 . In response, slave A  430  may send respective packets  432 ,  433 , and  434  over channel  410   a  in respective time slots  206 ,  208 , and  210  which correspond respectively to the next slots after packets  427 ,  428 , and  429  are sent. Packets  432 ,  433 , and  434  may further be sent over frequencies h k+5    226 , h k+7    228 , and h k+9    230 , respectively. 
     Meanwhile, HS communications may proceed between slave B  440  and slave C  450 . Packet  442 , for example may be sent on channel  510   b  from slave B  440  to slave C  450  on the frequency carrier allocated for the HS link, referred to as f HS    510 . Packet  451  may further be sent from slave C  450  to slave B  440 . It is important to note that channel  510   b  is established on HS frequency carrier f HS    510 . Details of the establishment of the HS link and associated frequency carrier f HS    510 , are described in greater detail hereinafter. In accordance with an exemplary embodiment of the present invention, master  420  may continue FH communications with slave C  450  on channel  410   c  by sending, for example, packet  425  over time slot  211  at frequency h k+10    231  to slave C  450 . Slave C  450  may respond over channel  410   c  with packet  452  in the next time slot  212  at frequency h K+11    232 . 
     It is important to note that once established, the HS link may be stationary and therefore does not frequency hop. Instead, a dynamic frequency channel selection scheme may be used. Before the HS link is established, signal strength measurements may be carried out by master  420  and/or any one or more of slave A  430 , slave B  440 , or slave C  450  in the radio spectrum available for the HS link as illustrated in FIG.  7 . HS radio spectrum  700  is not necessarily the same as the radio spectrum used for the FH link of piconet  100  (e.g. the 80 MHZ of the 2.4 GHz ISM band). In HS radio spectrum  700 , HS band  741  may be selected on which the lowest interference is measured. For example, frequency plot  700   a  represents RSSI  720  measurements  721  through  736  over HS radio spectrum  700 . The width of HS band  741  corresponds to the bandwidth required to support HS link  740 . As is illustrated, HS link  740  is selected to coincide with the RSSI  720  measurements  723  through  726  since they correspond to low RSSI  720  values. As the RSSI  720  measurements change over time the allocation of HS band  741  may change as will be described in greater detail hereinafter. 
     If HS radio spectrum  700  coincides with the FH radio spectrum in the 2.4 GHz ISM band, the width of HS band  741  is preferably smaller than 4 MHZ for the following reasons. For the operation of a FH system with a transmit power larger than 0.75 mW, the FCC requires the number of hop channels to be at least 75. In the Bluetooth standard, 79 hop channels are defined. If 4 consecutive hops can be used for HS link  740 , 75 hops are remaining to fully support the FH link of piconet  100  as is illustrated in FIG.  8 . In such an exemplary embodiment, HS link  740  may be established at four 1 MHz hop intervals wide, such as hop intervals  723 ,  724 ,  725 , and  726  of frequency plot  700   a , and, accordingly, the FH link  810  at the required 75 hops may co-exist within the same 80 MHZ band of the 2.4 GHz ISM band without interfering with each other. As is shown, hops may be centered at hop carriers  812   a - 812   d  and may be surrounded by 1 MHz envelopes  811   a - 811   d  with negligible guard bands separating each hop. Interference may only occur when HS link  740  is present between, for example slave B  440  and slave C  450 , as illustrated in FIG.  4 B and in FIG.  6 . In contrast, the exemplary embodiment shown in FIG.  4 A and FIG. 5, where an HS link is established between master  420  and, for example, slave C  450 , only one unit can transmit at a time and no collisions take place irrespective of frequency allocation between HS and FH links. Frequency carrier allocation  921  for hop carriers  812   a - 812 “ n ” of the FH link and the semi-stationary carrier allocation  911  for carriers  742   a - 742 “ n ” of the HS link may both use a 1 MHZ spacing but may be staggered by 0.5 MHZ as is shown in FIG.  9 . As a result, HS link  740  for example, can exactly replace 4 hops of the FH link. 
     As previously described, selection of a particular band for HS link  741  is adaptive. If the performance of HS link  741  deteriorates, units operating on HS link  741  may return to the FH link and new RSSI  720  measurements may be carried out to determine a better band in HS radio spectrum. In an alternate embodiment of the present invention, slave B  440  and slave C  450 , for example, may temporarily leave piconet  100  to establish an HS link over, for example, HS channel  410 d, again, as is illustrated in FIG.  4 B and FIG.  6 . To facilitate return to the FH link should HS link  741  deteriorate, master  420  maintains control of slave B  440  and slave C  450  in one of, for example, two ways. Slave B  440  and slave C  450  and master  420 , for example, may agree on a fixed interval for which HS link  741  will last. When the predetermined interval expires, slave B  440  and slave C  450  will automatically return to piconet  100 , at, for example, point y as is illustrated in FIG.  6 . If desired, slave B  440  and slave C  450  may request HS link  741  for an additional interval. In a different embodiment, slave B  440  and slave C  450  may track communications on the FH link with a relatively low duty cycle. Master  420  may additionally support, for example, a beacon signal  1010  on FH channel  1200  as is illustrated in FIG.  10  and further described in U.S. patent application Ser. No. 09/210,594, incorporated herein above. Master  420  may transmit beacon packets  1010   a ,  1010   b , and  1010   c  at fixed intervals. Beacon packets  1010   a ,  1010   b , and  1010   c  may be used respectively for slave A  430 , slave B  440 , and slave C  450  when one or more of slave A  430 , slave B  440 , and slave C  450  want to enter a low-power mode (e.g. PARK mode) where they may remain synchronized to FH channel  1200  of piconet  100  but do not exchange any packets. Slave A  430 , slave B  440 , or slave C  450  which are inactivated in the low-power mode may be re-activated and returned to piconet  100  as further described in U.S. patent application Ser. No. 09/210,594 incorporated herein above. Accordingly, slave B  440  and slave C  450  communicating on, for example, HS channel  1400  may also remain synchronized with FH channel  1200 . 
     At periodic intervals, slave B  440  and slave C  450  may be configured to “listen” for beacon packets  1010   a ,  1010   b , and  1010   c . If present, beacon packets  1010   a ,  1010   b , and  1010   c , may, for example, include a message ordering slave B  440  and slave C  450  to release HS channel  1400  and return to FH channel  1200  until further instructed and, in so doing, may interrupt communications on HS channel  1400 . During intervals in which slave B  440  and slave C  450  are listening for beacon packets  1010   a ,  1010   b , and  1010   c , slave B  440  and slave C  450  may further interrupt communicating with each other over HS channel  1400 . As illustrated, slave B  440  may send, for example, packets  1441 ,  1442 , and  1543  to slave C  450  at frequency f HS    510 . When slave B  440  and slave C  450  desire to return to piconet  100  and FH channel  1200 , they may do so via an access procedure supported by the beacon protocol. 
     It is important to note that the data link protocol on HS link  1500 , as suggested earlier, may differ from the data link protocol on FH link  1200 . Depending on the radio spectrum used for HS link  1400 , for example, if the radio spectrum associated with HS link  1400  is in the 5 GHz range, a listen before-talk protocol may be applied to conform to the etiquette or protocols associated with communications in the 5 GHz band. In other bands, other etiquette rules may apply and may be adopted on HS link  1400  to regulate the flow of, for example, data packets  1543  and  1552 . 
     The invention has been described with reference to a particular embodiment. However, it will be readily apparent to those skilled in the art that it is possible to embody the invention in specific forms other than those of the preferred embodiment described above. This may be done without departing from the spirit of the invention. The preferred embodiment is merely illustrative and should not be considered restrictive in any way. The scope of the invention is given by the appended claims, rather than the preceding description, and all variations and equivalents which fall within the range of the claims are intended to be embraced therein.