Abstract:
In a duplex link ( 40, 60, 90, 116 ) coupling first and second frequency hopping wireless communication devices, either or both of the frequency hopping patterns that are respectively used in the downlink and the uplink can be selectively and dynamically extended. Extension of the frequency hopping pattern associated with the uplink ( 55, 74 ) can compensate for a power imbalance between the uplink and the downlink by improving the gain of the uplink. By extending the frequency hopping pattern associated with the downlink ( 106, 129 ), strong interfering frequencies that would otherwise interfere with many downlink frequencies can be avoided.

Description:
This application claims the priority under 35 U.S.C. 119(e)(1) of copending U.S. provisional application No. 60/185,936, filed on Feb. 29, 2000. 

   CROSS REFERENCE TO RELATED APPLICATION 
   This application contains subject matter that is related to subject matter in copending U.S. Ser. No. 09,507,134 filed on Feb. 22, 2000, incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The invention relates generally to wireless communications and, more particularly, to wireless communications that employ frequency hopping techniques. 
   BACKGROUND OF THE INVENTION 
   Present telecommunication system technology includes a wide variety of wireless networking systems associated with both voice and data communications. An overview of several of these wireless networking systems is presented by Amitava Dutta-Roy,  Communications Networks for Homes , IEEE Spectrum, pg. 26, December 1999. Therein, Dutta-Roy discusses several communication protocols in the 2.4 GHz band, including IEEE 802.11 direct-sequence spread spectrum (DSSS) and frequency-hopping (FHSS) protocols. A disadvantage of these protocols is the high overhead associated with their implementation. A less complex wireless protocol known as Shared Wireless Access Protocol (SWAP) also operates in the 2.4 GHz band. This protocol has been developed by the HomeRF Working Group and is supported by North American communications companies. The SWAP protocol uses frequency-hopping spread spectrum technology to produce a data rate of 1 Mb/sec. Another less complex protocol is named Bluetooth after a 10 th  century Scandinavian king who united several Danish kingdoms. This protocol also operates in the 2.4 GHz band and advantageously offers short-range wireless communication between Bluetooth devices without the need for a central network. 
   The Bluetooth protocol provides a 1 Mb/sec data rate with low energy consumption for battery powered devices operating in the 2.4 GHz ISM (industrial, scientific, medical) band. The current Bluetooth protocol provides a 10-meter range and an asymmetric data transfer rate of 721 kb/sec. The protocol supports a maximum of three voice channels for synchronous, CVSD-encoded transmission at 64 kb/sec. The Bluetooth protocol treats all radios as peer units except for a unique 48-bit address. At the start of any connection, the initiating unit is a temporary master. This temporary assignment, however, may change after initial communications are established. Each master may have active connections of up to seven slaves. Such a connection between a master and one or more slaves forms a “piconet.” Link management allows communication between piconets, thereby forming “scatternets.” Typical Bluetooth master devices include cordless phone base stations, local area network (LAN) access points, laptop computers, or bridges to other networks. Bluetooth slave devices may include cordless handsets, cell phones, headsets, personal digital assistants, digital cameras, or computer peripherals such as printers, scanners, fax machines and other devices. 
   The Bluetooth protocol uses time-division duplex (TDD) to support bi-directional communication. Spread-spectrum technology or frequency diversity with frequency hopping permits operation in noisy environments and permits multiple piconets to exist in close proximity. The frequency hopping scheme permits up to 1600 hops per second over 79 1-MHZ channels or the entire ISM spectrum. Various error correcting schemes permit data packet protection by ⅓ and ⅔ rate forward error correction. Further, Bluetooth uses retransmission of packets for guaranteed reliability. These schemes help correct data errors, but at the expense of throughput. 
   The Bluetooth protocol is specified in detail in  Specification of the Bluetooth System , Version 1.0A, Jul. 26, 1999, which is incorporated herein by reference. 
   In many Bluetooth applications, it is desirable to improve the slave-to-master link. For example, in a cordless phone application, the base unit (master) can be plugged into a power outlet, so a 20 dBm power amplifier can be used, while the cordless phone (slave) itself must rely on battery power and therefore can only transmit at about 0 dBm. Such a power imbalance can be disadvantageous, because the slave-to-master link can be expected to have a higher error rate than the master-to-slave link, thereby increasing the likelihood that communications between the master and the slave will fail prematurely. 
   It is therefore desirable to provide suitable gains in the slave-to-master link in order to balance the duplex link between the slave and the master. 
   Another problem that is commonly encountered in Bluetooth applications is the presence of a strong interferer, for example a microwave oven. In many conventional applications, microwave oven interference can make as many as 10 frequencies unusable half of the time. 
   It is therefore desirable to provide capabilities for avoiding strong interferers. 
   In wireless communications according to the present invention, either or both of the frequency hopping patterns that are respectively used in a master-to-slave link (downlink) and a slave-to-master link (uplink) can be selectively and dynamically extended. Extension of the slave-to-master frequency hopping pattern can advantageously compensate for a power imbalance between the links by improving the gain of the slave-to-master link. Strong interfering frequencies can be advantageously avoided by extending the master-to-slave frequency hopping pattern. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  diagrammatically illustrates an example of extending the frequency hopping pattern of a slave-to-master link according to the invention. 
       FIG. 2  diagrammatically illustrates an exemplary state diagram of the master device of  FIG. 1 . 
       FIG. 3  diagrammatically illustrates an exemplary state diagram of the slave device of  FIG. 1 . 
       FIG. 4  diagrammatically illustrates exemplary embodiments of the master device of  FIG. 1 . 
       FIG. 5  illustrates exemplary operations which can be performed by the master device of  FIG. 4 . 
       FIG. 6  diagrammatically illustrates exemplary embodiments of the slave device of  FIG. 1 . 
       FIG. 7  illustrates exemplary operations which can be performed by the slave device of  FIG. 6 . 
       FIG. 8  diagrammatically illustrates an extension of the frequency hopping pattern of a master-to-slave link according to the present invention. 
       FIG. 9  diagrammatically illustrates exemplary embodiments of the master device of  FIG. 8 . 
       FIG. 10  illustrates exemplary operations which can be performed by the master device of  FIG. 9 . 
       FIG. 11  diagrammatically illustrates exemplary embodiments of the slave device of  FIG. 8 . 
       FIG. 12  illustrates exemplary operations which can be performed by the slave device of  FIG. 11 . 
       FIG. 13  diagrammatically illustrates simulation results comparing the slave-to-master link performances associated with conventional frequency hopping and with frequency hopping extension in the slave-to-master link. 
       FIG. 14  diagrammatically illustrates simulation results comparing the slave-to-master link performances with conventional frequency hopping and with frequency hopping extension in both the slave-to-master link and the corresponding master-to-slave link. 
   

   DETAILED DESCRIPTION 
   According to the present invention, gains on the slave-to-master link can be achieved by extending the frequency hopping pattern in the slave-to-master link when channel conditions are favorable. Such an extension of the frequency hopping pattern of the slave-to-master link is also herein referred to as HES (hop extension for slave). The frequency hopping pattern of the slave-to-master link can be extended according to the present invention by commanding the slave to transmit its current packet to the master using the same frequency that the slave used to transmit the immediately preceding packet to the master.  FIG. 1  diagrammatically illustrates one example of the above-described operation. In HES operation, the frequency hopping pattern of the master-to-slave link remains unchanged, retaining the conventional master-to-slave frequency hopping pattern (e.g., the Bluetooth frequency hopping pattern). 
   In the example of  FIG. 1 , the master transmits to the slave a hopping extension for slave bit (HESB) indicative of the frequency that the slave should use to transmit the next slave-to-master packet. If HESB=0, then the slave simply uses the frequency specified by its normal frequency hopping pattern. However, if the master transmits HESB=1, this commands the slave to transmit the next packet on the same frequency that was used to transmit the immediately preceding slave-to-master packet. In particular, in response to transmission by the master of HESB=1 on frequency f 13 , the slave transmits its current packet to the master on the same frequency that it used to transmit its previous packet, namely frequency f 8 , rather than frequency f 14  of the slave&#39;s normal frequency hopping pattern. Thereafter, in its next transmission on frequency f 19 , the master transmits HESB=0, which the slave responds to by transmitting its current packet on the frequency f 20  dictated by the normal frequency hopping pattern. The master&#39;s decision to transmit HESB=1 and thereby command the slave to repeat its immediately preceding frequency can be based, for example, on a channel quality measurement, such as a measurement that indicates that frequency f 8  has a high E b /(N O +I O ) or a high RSSI (received signal strength indicator). 
   In low Doppler environments, the master can use one or more conventional techniques to keep track of the quality of the channel from each slave for all of the frequencies, so the master will know which frequencies are currently in a fade for each user (i.e., each slave). The master can then instruct the slave to use the frequencies that are not in a fade. In higher Doppler environments, the master can direct the slave to use normal hopping frequencies until a good frequency is encountered, at which time the master can instruct the slave to continue to use this good frequency until it starts to fade. The master can detect a fading frequency by monitoring conventionally available information. For example, a lowered sync word correlation or an increase in packet errors can be indicative of a fading frequency in a Bluetooth system. 
     FIG. 2  diagrammatically illustrates an exemplary state transition diagram for the master device illustrated in  FIG. 1 . Because the master uses its normal frequency hopping pattern, the slave will always know the hopping frequency that the master is using. However, if one or more packets from the master to the slave or from the slave to the master are lost, the master may not know the state of the slave for one or more transmissions. This uncertainty as to the state of the slave is illustrated by the transition states  21  and  22  in  FIG. 2 . When the master transmits HESB=1 to the slave, the master transitions from the state  20 , namely knowing that the slave is in its normal frequency hopping mode, into the transition state  21  of  FIG. 2 . If the master receives a packet from the slave on the extended hopping frequency, for example frequency f 8  of  FIG. 1 , then the master transitions into state  24 , namely knowing that the slave is in the extended hopping mode. 
   On the other hand, if no packet is received from the slave on the extended hopping frequency, the master remains in the transition state  21  and continues transmitting HESB=1 until a packet is received from the slave on the extended hopping frequency, or until a suitable timeout period has expired. Upon expiration of the timeout period, the master transmits HESB=0, thereby transitioning from transition state  21  to transition state  22 . In transition state  22 , the master continues to transmit HESB=0 until a packet is received from the slave on the normal hopping frequency, at which time the master transitions from state  22  back to state  20 . Referring again to state  24 , the master can continue transmitting HESB=1 for as long as it is desired to keep the slave in the extended hopping mode. When it is desired to return to the normal hopping mode, the master transmits HESB=0 to the slave, whereupon the master transitions from state  24  into transition state  22 . 
     FIG. 3  illustrates an exemplary state diagram for the slave of  FIG. 1 . As shown in  FIG. 3 , the slave remains in its normal frequency hopping pattern state until it receives HESB=1 from the master, whereupon the slave transitions from the normal frequency hopping state into the extended frequency hopping state. The slave remains in the extended frequency hopping state until it receives HESB=0 from the master, whereupon the slave transitions from the extended hopping state back to the normal hopping state. 
     FIG. 4  diagrammatically illustrates pertinent portions of exemplary embodiments of the master device of  FIG. 1 . The master device of  FIG. 4  could be provided, for example, in the base unit of a Bluetooth cordless phone system. Other examples of the master device are mentioned above. The master device of  FIG. 4  includes a packet processor  41  coupled for communication with a wireless communications interface  42  and a communications application  43 . The packet processor  41  receives communication information from the communications application  43 , and assembles this communication information into packets. The packet processor  41  then forwards the assembled packets to the wireless communications interface  42  for transmission to one or more slave devices (e.g., Bluetooth cordless phones) by signaling over a wireless communication link  40 , for example a Bluetooth radio link. Similarly, the wireless interface  42  receives packets from one or more slave devices via the wireless communication link  40 . The wireless interface forwards the received packets to the packet processor  41 , which disassembles the received packets and forwards them to the communications application  43 . The above-described operations of the packet processor  41  and wireless communications interface  42  are conventional operations that are well known in the art. 
   According to the present invention, the packet processor  41  inserts the bit HESB in the outgoing packets of the master-to-slave link. In  FIG. 4 , the value of HESB is determined by a slave-to-master (SM) hop extension determiner  45  whose function is to determine whether or not the frequency hopping pattern of the slave-to-master link should be extended. If the SM hop extension determiner  45  determines that the frequency hopping pattern of the slave-to-master link should be extended, then the determiner  45  outputs a value of HESB=1. Otherwise, the determiner  45  outputs a value of HESB=0. In addition to being provided in the outgoing packets on the master-to-slave link, HESB is also used to control a selector  44  whose output provides to the wireless interface  42  frequency information for the next slave-to-master packet. If HESB=0, then selector  44  indicates to the wireless interface  42  that the next slave-to-master packet is to be transmitted on the normal frequency hop. On the other hand, if HESB-1, then the selector  44  indicates to the wireless interface  42  that the frequency used to transmit the previous slave-to-master packet will be repeated for transmission of the next slave-to-master packet. The selector  44  thus serves as an indicator of the frequency that will be used for transmission of the next slave-to-master packet. 
   The SM hop extension determiner  45  determines the value of HESB in response to an input  46 , which receives information indicative of the condition of the slave-to-master link. As mentioned above, examples of this information include conventionally available channel quality measurement information, conventionally available sync word correlation information and conventionally available packet error information. The information received at  46  is considered by the determiner  45  along with information (received at an input  47 ) indicative of both the next frequency of the normal SM frequency hopping pattern and the previous frequency at which the immediately preceding SM packet was transmitted. The determiner  45  determines from the condition information at  46  whether the next hop frequency in the normal frequency hopping pattern is more or less desirable than the previous frequency at which the immediately preceding SM packet was transmitted. If the next frequency hop is more desirable, then the determiner  45  outputs HESB=0, but if the previous SM transmit frequency is more desirable, then the determiner  45  outputs HESB=1. In one exemplary embodiment, if the condition information at  46  indicates that the previous SM transmit frequency has a higher E b /(N O +I O ) than does the next frequency in the normal hopping pattern, then the determiner  45  outputs HESB=1, and otherwise outputs HESB=0. The condition information at  46  may also indicate the presence of a strong interferer, (for example a microwave oven or an IEEE 802.11b interferer) at the next frequency. 
     FIG. 5  illustrates exemplary operations which can be performed by the master device of  FIG. 4 . After initially setting HESB=0 at  51 , the jth master-to-slave packet (including HESB) is transmitted at  52  on the normal hopping frequency for the jth packet on the master-to-slave link, which frequency is designated in  FIG. 5  as MS j . Thereafter, if HESB=0 at  53 , then the jth slave-to-master packet is received at  54  on the normal hopping frequency for the jth packet of the slave-to-master link, which frequency is designated as SM j  in  FIG. 5 . If IESB=1 at  53 , then the jth slave-to-master packet is received at  55  on the frequency SM j−1 , namely the frequency that was used in the immediately preceding (j−1)th slave-to-master transmission. After the jth SM packet is received at  54  or  55 , the index j is incremented at  56 , and it is then determined at  57  whether SM j  (the normal hopping frequency for the jth SM packet) or SM j−1  (the frequency that was used for the (j−1)th SM packet) is more desirable. If the frequency SM j−1  is more desirable, then HESB is set to 1 at  58 . On the other hand, if the normal hopping frequency SM j  is more desirable at  57 , then HESB is set to 0 at  59 . After HESB is determined at  58  or  59 , the above-described operations at  52 – 59  are repeated. 
     FIG. 6  diagrammatically illustrates pertinent portions of exemplary embodiments of the slave device illustrated in  FIG. 1 . The slave device of  FIG. 6  could be provided, for example, in a mobile phone unit of a Bluetooth cordless phone system. Other examples of the slave device are mentioned above. The slave device of  FIG. 6  includes a packet processor  61  coupled between a wireless communications interface  62  and a communications application  63 , similar to the arrangement at  41 – 43  in the master device of  FIG. 4 . The components  61 – 63  of  FIG. 6  can cooperate together using the well known conventional operations mentioned above with respect to  FIG. 4  to permit the slave device of  FIG. 6  to engage in bidirectional wireless packet communication with a master device (such as shown in  FIG. 4 ) via a suitable wireless communication link  60 . 
   When disassembling the packets received from the wireless interface  62 , the packet processor  61  provides the bit HESB to a selector  64  whose output provides to the wireless interface  62  information indicative of the frequency for the next slave-to-master packet. If HESB=0, then the selector  64  indicates to the wireless interface  62  that the frequency for the next slave-to-master packet will be the normal hop frequency from the slave-to-master frequency hopping pattern. On the other hand, if HESB=1, then the selector  64  indicates to the wireless interface  62  that the previous frequency used to transmit the immediately preceding slave-to-master packet is to be repeated for transmission of the next slave-to-master packet. The selector  64  thus serves as an indicator of the frequency that will be used for transmission of the next slave-to-master packet. 
     FIG. 7  illustrates exemplary operations which can be performed by the slave device of  FIG. 6 . After initially setting HESB=0 at  71 , the jth master-to-slave packet is received at  72  on frequency MS j . Thereafter, if HESB=1 at  73 , the jth slave-to-master packet is transmitted at  74  on frequency SM j−1 . Otherwise, if HESB=0 at  73 , then the jth slave-to-master packet is transmitted at  75  on frequency SM j . After the jth slave-to-master packet has been transmitted at  74  or  75 , the index j is incremented at  76 , and the above-described operations at  72 – 75  are repeated. 
     FIG. 8  diagrammatically illustrates an example of extending the frequency hopping pattern of a master-to-slave link according to the present invention. This hop extension for the master, also designated herein as HEM, can be advantageous in the presence of a strong interferer, for example a microwave oven. As shown in  FIG. 8 , the master transmits a hop extension for master bit (HEMB) which is indicative of the frequency that the master will use in its next transmission. If the master transmits HEMB=0, then the frequency of the master&#39;s next transmission will be the normal hopping frequency from its normal hopping frequency pattern. On the other hand, if the master transmits HEMB=1, this indicates that the master will repeat the frequency of the current transmission in its next transmission. In the example of  FIG. 8 , when the master is transmitting on frequency f 7 , it knows that there will be interference on the next frequency f 13  in its normal hopping pattern, so the master transmits HEMB=1, thereby indicating to the slave that the current frequency f 7  will be used for the next master-to-slave transmission instead of frequency f 13  from the normal frequency hopping pattern. In this manner, the master can avoid a strong interferer on frequency f 13 . 
     FIG. 9  diagrammatically illustrates pertinent portions of exemplary embodiments of the master device illustrated in  FIG. 8 . The master device of  FIG. 9  could be provided, for example, in the base unit of a Bluetooth cordless phone system. Other examples of the master device are mentioned above. The master device of  FIG. 9  includes a packet processor  91  coupled between a wireless communications interface  92  and a communications application  93 . These components can cooperate together in generally the same fashion as described above with respect to the components  41 – 43  of  FIG. 4  and the components  61 – 63  of  FIG. 6  to permit bidirectional packet communications between the master device of  FIG. 9  and slave devices (e.g., Bluetooth cordless phones) over wireless communication link  90  (e.g., a Bluetooth radio link). The packet processor  91  receives HEMB as in input, and inserts HEMB in the outgoing master-to-slave packets. Each time that a slave-to-master packet is received, the packet processor  91  outputs a slave-to-master (SM) packet received signal which clocks a latch  94  such that the HEMB transmitted in the most recent master-to-slave packet is latched through to the select input of a selector  99 . The output of the selector  99  provides to the wireless interface  92  information indicative of the frequency at which the next master-to-slave packet is to be transmitted. Thus, by operation of the latch  94 , the HEMB value that was included in the most recently transmitted master-to-slave packet is used to determine the frequency at which the next master-to-slave packet will be transmitted. If HEMB=0 in the most recently transmitted master-to-slave packet, then the selector  99  will indicate to wireless interface  92  that the normal hop frequency from the normal frequency hopping pattern will be used for transmission of the next master-to-slave packet. On the other hand, if HEMB=1 in the most recently transmitted master-to-slave packet, the selector  99  will indicate to the wireless interface  92  that the frequency at which the most recent master-to-slave packet was transmitted is to be repeated for transmission of the next master-to-slave packet. The selector  99  thus serves as an indicator of the frequency that will be used for transmission of the next master-to-slave packet. 
   The value of HEMB that will be transmitted in a given master-to-slave packet (and which will determine the frequency at which the next master-to-slave packet will be transmitted) is produced by a master-to-slave (MS) hop extension determiner  98 . The determiner  98  includes inputs  96  and  97 , and responds to these inputs to determine the value of HEMB. The input  96  receives information indicative of master-to-slave link conditions, for example information indicative of any strong interferers which may be operating on master-to-slave frequencies. Interference information, for example the frequency of interferers produced by a microwave oven, is typically readily available. The input  97  of the determiner  98  is coupled to the output of a latch  95  that is clocked by the SM packet received signal produced by the packet processor  91  when a new slave-to-master packet is received. Thus, the latch  95  is clocked together with the aforementioned latch  94 . Consequently, at the same time that the latch  94  is clocked to select (via selector  99 ) the frequency at which the next master-to-slave packet will be transmitted, the latch  95  is clocked to apply to the input  97  of the determiner  98  information indicative of the normal hopping frequency for the master-to-slave packet-after-next. 
   Based on the normal hopping frequency for the packet-after-next received at  97 , and also based on the master-to-slave link condition information received at  96 , the determiner  98  determines the value of HEMB that will be transmitted in the next master-to-slave packet. This value of HEMB is indicative of the frequency at which the master-to-slave packet-after-next will be transmitted. For example, if the information received at  96  indicates that the normal hop frequency for the master-to-slave packet-after-next coincides with a strong interferer, then the determiner  98  outputs HEMB=1, which means that the frequency of the next master-to-slave packet transmission will also be used for the master-to-slave packet transmission-after-next. On the other hand, if the determiner  98  determines that the normal hopping frequency for the packet-after-next does not coincide with a strong interferer, then the determiner  98  outputs HEMB=0, which indicates that the packet-after-next will be transmitted at the normal hopping frequency. 
     FIG. 10  illustrates exemplary operations which can be performed by the master device of  FIG. 9 . It is initially determined at  100  whether or not the normal hopping frequency associated with the (j+1)th packet, namely MS j+1 , is to be avoided, for example due to a conflict with a strong interferer. If the frequency MS j+1  is to be avoided, then HEMB j , namely the value of HEMB that will be sent with the jth master-to-slave packet, is set equal to 1 at  102 . Otherwise, HEMB j  is set equal to 0 at  103 . Thereafter, if HEMB j−1 , namely the value of HEMB that was sent with the (j−1)th master-to-slave packet, is 0 at  104 , then the jth master-to-slave packet is transmitted at  105  on the normal hopping frequency MS j  associated therewith. If HEMB j−1 , is equal to 1 at  104 , then the jth master-to-slave packet is transmitted at  106  on the frequency MS j−1 , namely the frequency at which the immediately preceding (the (j−1)th) master-to-slave packet was transmitted. After transmission of the jth master-to-slave packet (including HEMB j ) at  105  or  106 , the jth slave-to-master packet is received at  107  on frequency SM j . At  108 , the index j is incremented, and the above-described operations at  100 – 107  are thereafter repeated. 
     FIG. 11  diagrammatically illustrates pertinent portions of exemplary embodiments of the slave device illustrated in  FIG. 8 . The slave device of  FIG. 11  could be provided, for example, in a mobile phone unit in a Bluetooth cordless phone system. Other examples of the slave device are mentioned above. The slave device of  FIG. 11  includes a packet processor  111  coupled between a wireless communications interface  112  and a communications application  113 . These components can cooperate in generally the same fashion as described above with respect to components  41 – 43 ,  61 – 63  and  91 – 93  of  FIGS. 4 ,  6  and  9  respectively, to permit packet communications to and from a master device (such as shown in  FIG. 9 ) via a suitable wireless communication link  116 . When disassembling a received master-to-slave packet, the packet processor  111  outputs HEMB to a selector  118  whose output provides to the wireless interface  112  information indicative of the frequency at which the next master-to-slave packet will be transmitted. If HEMB=0, then the selector  118  indicates that the normal hop frequency will be used for the next master-to-slave packet transmission. On the other hand, if HEMB=1, then the selector  118  indicates that the frequency that was used for the most recent master-to-slave packet transmission will be repeated for the next master-to-slave packet transmission. The selector  118  thus serves as an indicator of the frequency that will be used for transmission of the next master-to-slave packet. 
     FIG. 12  illustrates exemplary operations which can be performed by the slave device of  FIG. 11 . The jth master-to-slave packet (including HEMB) is received at  121  on frequency MS j . Thereafter at  122 , the jth slave-to-master packet is transmitted on frequency SM j . After incrementing the index j at  123 , the value of HEMB is inspected at  128 . If HEMB=0, then the jth master-to-slave packet is received at  121  on frequency MS j . Thereafter, the above-described operations at  122 ,  123  and  128  are repeated. On the other hand, if HEMB=1 at  128 , then the jth master-to-slave packet is received at  129  on frequency MS j−1 , after which the above-described operations at  122 ,  123  and  128  are repeated. 
     FIG. 13  illustrates simulation performance curves for conventional Bluetooth HV3 voice (High-quality Voice) over a conventional SCO (Synchronous Connection-Oriented) slave-to-master link and for conventional HV3 voice over an SCO slave-to-master link that employs the HES techniques described above relative to  FIGS. 1–7 . HES advantageously provides an E b /N O  gain of 16 dB. Although not shown in  FIG. 13 , HES can also be used in Bluetooth ACL (Asynchronous Connection-Less) links. 
   Referring again to  FIGS. 4 and 9 , the broken lines in the master device of  FIG. 4  indicate how the features of the master device of  FIG. 9  can be incorporated into the device of  FIG. 4 , thereby providing a master device which employs both the HES techniques of  FIG. 4  and the HEM techniques of  FIG. 9 . In particular, HEMB is provided to the packet processor  41  by the MS hop extension determiner  98  of  FIG. 9 , and the information indicative of the frequency for the next master-to-slave packet is provided to the wireless interface  42  by the selector  99  of  FIG. 9 . Similarly, and referring to  FIGS. 5 and 10 , the broken lines in  FIG. 5  illustrate how selected HEM operations from  FIG. 10  can be combined with the HES operations of  FIG. 5 . In particular, operations can proceed from  59  in  FIGS. 5 to 100  in  FIG. 10 , and thereafter from  106  in  FIGS. 10 to 53  in  FIG. 5  or from the “0” branch of  104  in  FIGS. 10 to 52  in  FIG. 5 . Of course, both HESB and HEMB j  would be included in the jth MS packet. 
   Referring again to  FIGS. 6 and 11 , the broken lines in  FIG. 6  indicate how the HEM capabilities of the slave device of  FIG. 11  can be combined with the HES capabilities of the slave device of  FIG. 6 . In particular, the packet processor  61  of  FIG. 6  can extract HEMB from received master-to-slave packets and provide HEMB to the select input of the selector  118  of  FIG. 11 , and the wireless interface  62  of  FIG. 6  can receive from the selector  118  of  FIG. 11  information indicative of the frequency at which the next master-to-slave packet will be transmitted. Similarly, and referring to  FIGS. 7 and 12 , the broken lines in  FIG. 7  indicate how selected HEM operations from  FIG. 12  can be combined with the HES operations of  FIG. 7 . In particular, operations can proceed from  76  in  FIGS. 7 to 128  in  FIG. 12 , and thereafter from  129  in  FIGS. 12 to 73  in  FIG. 7  or from the “0” branch of  128  in  FIGS. 12 to 72  in  FIG. 7 . 
     FIG. 14  illustrates simulation performance curves for two conventional slave-to-master links, one conventional master-to-slave link, one master-to-slave link using the above-described HEM techniques, and two slave-to-master links wherein the above-described HES and HEM techniques are employed together. The curves illustrated represent Bluetooth HV3 voice on SCO links, and they assume microwave oven interference that makes ten frequencies unusable half of the time. The master is assumed to be transmitting at +20 dBm. 
   Taking the Bluetooth protocol as an example, HESB and HEMB can be included in master-to-slave packets by, for example, substituting them for existing bits or adding them after the header. 
   It will be evident to workers in the art that the above-described embodiments of  FIGS. 1–12  can be readily implemented, for example, by suitable modifications in software, hardware, or a combination of software and hardware, in conventional frequency hopping wireless communication devices such as Bluetooth masters and slaves. 
   Although exemplary embodiments of the invention are described above in detail, this does not limit the scope of the invention, which can be practiced in a variety of embodiments.