Abstract:
First and second wireless transceiver units operate in the same portion of the RF spectrum. An arbitration device controls when the first and second wireless transceiver units can operate. An interface connects the first transceiver unit to the arbitration device and receives requests for operation. The interface permits the transceiver unit o use one of N possible priority levels for requests. The transceiver associates a transceiver priority level to a series of packets which is chosen from a range of M possible priority levels. The transceiver unit sends a sequence of requests to operate to the arbitration device, each request in the sequence having a priority level chosen from the range of N possible priority levels. The average value of the priority levels used in the sequence depends on the associated transceiver priority level.

Description:
FIELD OF THE INVENTION 
   This invention relates to methods and devices for setting a priority level in a wireless communication apparatus as well to telecommunications systems using the methods and devices and software for use with the methods and devices. 
   BACKGROUND TO THE INVENTION 
   One band of the RF spectrum which is being increasingly used for wireless communications is the unlicensed Industrial Scientific &amp; Medical (ISM) band at 2.4 GHz. Currently, two types of wireless technology operate in this part of the spectrum. 
   Firstly, there is Wireless Local Area Network (WLAN) technology which is standardized under IEEE 802.11. One variant of IEEE 802.11 uses a frequency-hopping spread spectrum (FHSS) technique with 1 MHz channel separation and pseudorandom hops across 79 channels. Another variant (IEEE 802.11b) uses direct sequence spread spectrum (DSSS) techniques, with 22 MHz channels. WLAN technology is widely used in offices, homes and public places to support networking between users. 
   Secondly, there is Wireless Personal Area Network (WPAN) technology, which is standardized in IEEE 802.15.1. This is a 1 Mbit/s FHSS system which uses the same 79, 1 MHz-wide channels that are used by the FHSS version of IEEE 802.11. IEEE 802.15.1 hops pseudorandomly at a nominal rate of 1600 hops/second. IEEE 802.15.1 is intended as a low power, short range (&lt;3 m) technology for interconnecting devices such as mobile phones, portable computers and wireless handsfree headsets with fixed devices or other portable devices. One commercial implementation of IEEE 802.15.1 is known as ‘Bluetooth™’. 
   Since both IEEE 802.11 and IEEE 802.15.1 operate in the same 2.4 GHz unlicensed frequency band, there is mutual interference between the two wireless systems which may result in severe performance degradation. The interference is of most concern with IEEE 802.11b as this uses a static channel (i.e. no frequency hopping). Factors which determine the level of interference include the separation between the WLAN and WPAN devices, the amount of data traffic flowing over each of the two wireless networks, the power levels of the various devices, and the data rate of the WLAN. Also, different types of information being sent over the wireless networks have different levels of sensitivity to the interference. For example, a voice link may be more sensitive to interference than a data link being used to transfer a data file. 
   The IEEE has produced a Draft Recommended Practice IEEE P802.15.2/Dec. 20, 2002; “Telecommunications and Information exchange between systems—Local and metropolitan area networks Specific Requirements—Part 15.2: Coexistence of Wireless Personal Area Networks with Other Wireless Devices Operating in Unlicensed Frequency Bands.” This document outlines the interference problem and provides some guidance for how WLAN and WPAN equipment can coexist. Two categories of coexistence mechanisms are proposed: collaborative and non-collaborative. Collaborative coexistence mechanisms exchange information between two wireless networks.  FIG. 1  shows an example piece of equipment  100  which includes a WPAN transceiver TX 1  and a WLAN transceiver TX 2 . Equipment  100  can be, for example, a portable computer with the WLAN supporting a connection  40  with a WLAN base station  45  and the WPAN supporting a connection  30  with a WPAN device which, in this example, is a wireless headset  35 . Some of the possible sources of interference are shown: WLAN transmissions from BS  45  may interfere with reception of WPAN traffic at TX 1 , or WPAN transmissions from TX 1  may interfere with WLAN reception at the base station  45  (path  32  ); WPAN transmissions from head set  35  may interfere with reception of WLAN traffic at TX 2 , or WLAN transmissions from TX 2  may interfere with WPAN reception at the head set  35  (path  42  ). 
   One solution proposed by the IEEE Draft Recommended Practice Document is to provide a packet traffic arbitration (PTA) control entity which communicates with both the WLAN station and WPAN station and provides per-packet authorization of all transmissions.  FIG. 2  shows an apparatus  100  with an arbitration device  130 . Both transceivers TX 1 , TX 2  must request permission to transmit or receive and, in response, the arbitration device  130  will either grant or deny the permission to access the shared spectrum to transmit or receive a data packet. The recommended interface between a WPAN transceiver and an arbitration unit is shown in  FIG. 2  as lines  151 - 154 .
     The Bluetooth device and the WLAN may not be placed really close to each other (maybe 10 cm distance) in this case increasing the number of the pin in the coexistence interface increase the complexity of routing them in the board and most likely it increases the board size.   The pin count of both chips will increase and this is a problem especially for the Bluetooth which is a very small chip and there is very little room for adding pins.   

   The WPAN can support multiple simultaneous links, which can be voice, data or control information. One of the lines between the WPAN transceiver and arbitration device  130  is a status line  152  which can be used to indicate the priority level of the link. The priority can take the value ‘1’ or ‘0’. The arbitration device uses the priority level to decide whether the WPAN should be granted access to the shared RF band. Links with a priority ‘1’ can be granted access to the band in preference to the WLAN, while the links with priority ‘0’ are not. One problem with this arrangement is that, during a long period of WLAN activity, such as a file transfer, the WPAN links with priority ‘0’ will be refused. The Bluetooth protocol requires transceivers to make one TX/RX operation within a predetermined timeout period to maintain synchronization. In an environment where the Bluetooth device shares the RF band with a WLAN, this can be difficult. 
   SUMMARY OF THE INVENTION 
   The present invention seeks to provide a way of improving the operation of a wireless device in a shared environment. 
   An advantage of the present invention is that there is no requirement to increase the number of pins of the chips used for implementation. 
   A first aspect of the present invention provides a method of operating a first wireless transceiver unit which operates in the same portion or has an overlapping portion of an RF spectrum as a second wireless transceiver unit, there being an arbitration device which controls when the first and second wireless transceiver units can access the shared portion of the RF spectrum and an interface connecting the first transceiver unit to the arbitration device, the interface carrying access requests, each request having one of N possible interface priority levels, the method comprising: 
   associating a transceiver priority level with a series of packets which are intended for transmission, the transceiver priority level being chosen from a range of M possible priority levels, where M&gt;N; and 
   sending a sequence of access requests to the arbitration device, each access request in the sequence having an interface priority level chosen from the range of N possible interface priority levels, wherein the average value of the interface priority levels used in the sequence depends on the associated transceiver priority level. 
   By associating a priority level taken from a range of M possible levels, the first transceiver unit is able to provide a greater degree of granularity to its requests. For high priority traffic, the transceiver unit can continue to send a sequence of access requests to the arbitration unit with the highest of the N possible interface priority levels. However, other traffic which is of a lower priority, but which must be sent on an occasional basis (such as periodic traffic for maintaining synchronization) can be associated with a priority level at the transceiver which will send an occasional access request at the highest one of the N interface priority levels. 
   In one embodiment the interface between the first transceiver unit and the arbitration device supports a high priority level and a low priority level (N=2) and the number of high priority level access requests sent during the sequence corresponds to the associated transceiver priority level. 
   The transceiver priority level (taken from the range of M possible levels) which is to be associated with the packets can be determined by an entity external to the first transceiver unit, such as a host of the first transceiver unit. Alternatively, the transceiver priority level (taken from the range of M possible levels) which is to be associated with the packets can be chosen by the wireless transceiver unit, based on the type of packet. 
   The first wireless transceiver unit can be part of a Wireless Personal Area Network (WPAN), such as one based on IEEE 802.15.1 or Bluetooth™, and the second wireless transceiver unit can be part of a Wireless Local Area Network (WLAN), such as one based on one of the IEEE 802.11 family of protocols. In such cases the first and second wireless transceiver units may be close to each other e.g. less than 1 meter from each other or less than 0.5 meter from each other. This can be typical of an application on a laptop or PC in which the two transceivers are close together. Such an application is said be a collocation of the two units. 
   The present invention also provides a first wireless transceiver unit which operates in the same portion or has an overlapping portion of an RF spectrum as a second wireless transceiver unit, and an arbitration device which controls when the first and second wireless transceiver units can access the shared portion of the RF. spectrum and an interface connecting the first transceiver unit to the arbitration device, the interface carrying access requests, each request having one of N possible interface priority levels, comprising: 
   means for associating a transceiver priority level to a series of packets which are intended for transmission, the transceiver priority level being chosen from a range of M possible priority levels, where M&gt;N; and 
   means for sending a sequence of access requests to the arbitration device, each access request in the sequence having an interface priority level chosen from the range of N possible interface priority levels, wherein the average value of the interface priority levels used in the sequence depends on the associated transceiver priority level. 
   The present invention may also provide a communications system with a first wireless transceiver unit which operates in the same portion or has an overlapping portion of an RF spectrum as a second wireless transceiver unit, there being an arbitration device which controls when the first and second wireless transceiver units as described above. The first and second wireless transceiver units may be close to each other e.g. less than 1 meter from each other or less than 0.5 meter from each other. This can be typical of an application on a laptop or PC in which the two transceivers are close together. Such an application is said be a collocation of the two units. 
   The functionality described here can be implemented in software, hardware or a combination of these. Accordingly, another aspect of the invention provides software for performing the method when executed on a processing engine. The software may be installed on the transceiver unit at the time of manufacture, or it may be installed onto an existing transceiver unit at a later date as an upgrade. The software may be stored on an electronic memory device, hard disk, optical disk or other machine-readable storage medium. The software may be delivered as a computer program product on a machine-readable carrier or it may be downloaded directly to the transceiver unit via a network connection. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will be described with reference to the accompanying drawings in which: 
       FIG. 1  shows an apparatus with two co-located wireless transceivers operating in a common RF band; 
       FIG. 2  shows the apparatus of  FIG. 1  with an arbitration unit for coordinating access to the common RF band; 
       FIG. 3  shows one of the transceivers in more detail in accordance with an embodiment of the present invention; 
       FIG. 4  shows a sequence of requests for packet transmission as used in embodiments of the present invention. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   The present invention will now be described with reference to certain embodiments and with reference to the above mentioned drawings. Such description is by way of example only and the invention is not limited thereto. In particular the present invention will be described with reference to radio communications network but the present invention is not limited thereto. The term “wireless” should be interpreted widely to cover any communications system which does not use fixed wireline communications for some of its transmissions. Alternative wireless communications systems include optical systems such as those operating with diffuse infra-red. It should also be noted that the term “wireless” also includes so-called cordless systems. General aspects of cordless communications systems are described for instance in the book by W. Tuttlebee, “Cordless Telecommunications Worldwide”, Springer, 1997. Cordless systems are generally local, uncoordinated radio communications networks having a limited range. 
   Referring again to  FIG. 2 , this shows an apparatus in which a transceiver TX 1  of a first wireless system, e.g. a WPAN, such as a WPAN based on a IEEE 802.15.1 protocol, e.g. Bluetooth, and a transceiver TX 2  of a second wireless system, e.g. a WLAN, such as a WLAN based on IEEE 802.11b are co-located with one another at an apparatus  100 . An arbitration device  130  communicates with TX 1  via an interface  151 - 154  and with TX 2  via an interface  161 . The interface between the WPAN transceiver TX 1  and the arbiter  130  comprises four lines  151 - 154 . TX 1  uses line  151  (TX Request) to send a request to access the shared RF band. The priority of the request is indicated by setting line  152  (Status) high (high priority) or low (low priority) at a similar time to making the request. The Frequency line  153  (FREQ) is an optional line, and can be used to indicate that TX 1  intends to ‘hop’ into one of the restricted (shared) channels during the next transmission/reception slot. The arbiter may or may not decide to let the Bluetooth transmit/receive even in shared channels. This is dependent on the implementation of the arbiter which is vendor dependent. The present invention is not dependent upon any particular arbiter implementation. 
   The arbiter  130  uses line  154  (TX CONFIRM) to indicate whether TX 1  is allowed to operate in the next slot. If TX 1  is not allowed to operate, it must not transmit during the next slot. 
   In a similar manner to TX 1 , TX 2  of the WLAN uses an interface  161  to indicate when it wishes to access the shared RF band and receives a signal indicating permission or denial to transmit from the arbiter  130 . 
   Each attempt to transmit by either TX 1  or TX 2  is submitted to the arbiter  130  for approval. The arbiter  130  may deny a transmit request that would result in a collision. The arbiter  130  provides a permission/denial signal to both TX 1  and TX 2  on a per packet/slot basis. When a collision would occur, the arbiter  130  prioritizes transmissions of TX 1  and TX 2  based on the priorities of the transmissions that it receives on line  152  and interface  161 . 
     FIG. 3  shows transceiver TX 1  in more detail. An interface  210  communicates  115  with a host  110 . The host can provide the data which is to be transmitted by the transceiver TX 1 , such as voice data or data for a file transfer. A baseband processing unit  220  packetizes the data, if necessary, and issues transmission requests which are sent to the arbiter interface unit  240  for transmission along lines  151 - 153 . A permission/denial signal is received from interface unit  240 . An RF processing unit  250  modulates to RF for transmission via antenna  252 . As noted above, TX 1  can support multiple (e.g. 7) simultaneous connections, called links. As an example, one link may carry voice data between unit  100  and handsfree headset  35 , while another link may carry data between unit  100  and another portable device. Bluetooth defines a number of different types of link, including Synchronous Connection-oriented (SCO) links which carry constant bite rate data, such as voice data, and Asynchronous Connection-oriented (ACL) links which carry data or control data (ACL-C). SCO links generate a series of packets at regular time intervals whereas ACL links generate packets at irregular time intervals. 
   A priority setting unit  230  is used to set the priority of the traffic on each link. Fore every link, a priority is associated with that link which is taken from a possible range of 8 priority levels. The levels range from priority level 7 (maximum priority) to priority level 0 ( minimum priority). The priority level can be assigned, within transceiver TX 1 , using a table in priority setting unit  230 . The priority level can be set based on the type of traffic, e.g. voice-priority 7; file transfer data-priority 3; parked connections sync data-priority 1. Alternatively, the priority can be set by the host and is received, via link  115 , from the host  110 . 
   As described above, line  152  (STATUS) between transceiver TX 1  and arbiter  130  has only one line (STATUS) which can be used to indicate the priority, and the priority can take one of two values: high (1) or low (0). A priority level in the range 0 . . . 7is achieved by the following the following table of priority levels to a sequence of requests: 
   
     
       
             
             
             
           
         
             
                 
                 
             
             
                 
               Priority 
               Sequence 
             
             
                 
                 
             
           
           
             
                 
               7 
               1111111 
             
             
                 
               6 
               0111111 
             
             
                 
               5 
               1011101 
             
             
                 
               4 
               1010101 
             
             
                 
               3 
               0101010 
             
             
                 
               2 
               0100010 
             
             
                 
               1 
               0000001 
             
             
                 
               0 
               0000000 
             
             
                 
                 
             
           
        
       
     
   
   In the table it is preferred to distribute the zeros and the ones uniformly. To explain this table, consider that the transceiver TX 1  supports a link (ACL  1  ) which is given the priority level 3. The link has a stream of packets associated with it which carry the data for that link. For every packet, the transceiver TX 1  makes a transmission request just before the time it is scheduled to transmit that packet. For the first packet, the transceiver TX 1  makes a request with priority ‘0’. For the second packet, the transceiver TX 1  makes a request with priority ‘1’. After seven packets, the transceiver TX 1  has made a total of 3 requests with priority ‘1’ and 4 with priority ‘0’.  FIG. 4  shows a sequence of access requests and their priority levels, together with the packets for other links ACL 2 , ACL 3  and SCO 1 . A priority level of 7—the maximum priority level—is translated into a sequence of requests which all have the priority level equal to 1 (full protection). A priority level of 0—the lowest priority level—is translated into a sequence of requests with the priority level of 0. A priority level of 4—medium—is translated into a sequence of requests in which 4 out of 7 requests have the priority level of 1 and 3 requests have the priority level of 0. In general, a priority level m (out of a total range of M priority levels) is translated into m requests having a value of 1 in each sequence of M requests. 
   PWAN links which are not currently carrying data, but which need to be periodically used to maintain synchronization, can be allocated a priority level of 1 (in the range 0 . . . 7) to ensure that at least one out of every eight requests is granted. 
   This mechanism is completely transparent at the level of the algorithm used by arbiter  130  since, for each transaction, the arbiter  130  sees only a request of priority level 1 or a priority level 0. 
   If there is priority 0 and the arbiter lets the Bluetooth transmitter operate (because for instance the WLAN is not doing anything) then the Bluetooth transmitter will make the transmit/receive (TX/RX). If the arbiter denies the operation, the Bluetooth transmitter will not do the TX/RX and it will try to do it in the next available slot (always requiring permission before doing so). 
   In this embodiment, the status line  152  signals one of two priority levels. The invention can be applied to apparatus in which the interface can support more than two priority levels (e.g. N priority levels), with transceiver TX 1  having M priority levels (where N&lt;M). In this case, each of the M transceiver priority levels is associated with a sequence of requests which are spread across the range of N levels. As the transceiver priority level increases, the average value of interface priority levels in the sequence increases. In the following example, the transceiver has seven priority levels, the interface to the arbiter  130  has 4 priority levels (0, 1, 2, 3) and the sequence lasts for only two periods. It can be seen that the average value of the priority levels used in the sequence varies according to the transceiver priority level. 
   
     
       
             
             
             
           
         
             
                 
                 
             
             
                 
               Priority 
               Sequence 
             
             
                 
                 
             
           
           
             
                 
               6 
               33 
             
             
                 
               5 
               32 
             
             
                 
               4 
               31 
             
             
                 
               3 
               12 
             
             
                 
               2 
               11 
             
             
                 
               1 
               01 
             
             
                 
               0 
               00 
             
             
                 
                 
             
           
        
       
     
   
   In the above described embodiment, transceivers TX 1 , TX 2  are co-located within the same physical unit as the arbiter  130 . For instance, the two transceivers TX 1 , TX 2  may be located less than 1 meter apart or for example less than 0.5 meter apart. This may occur if both units are in a PC or a laptop. Where one or more of the TX 1 , TX 2  and arbiter  130  are not housed within the same physical unit, an appropriate connection between the units carries the access requests and replies. 
   With reference to all the embodiments of the present invention the problem of having a priority mechanism based on one single line which may give only priority 0 or priority 1 to each packet can be solved. For example, conventionally the number of lines carrying the priority indication cannot be increased practically because two chips (for two different telecommunications protocols) may be placed far away from each other on the device. Having more lines for priority would increase the complexity of the routing in the device and increase its size. Hence, one priority line is an important practical restriction. Other mechanisms like shared memory, etc. suffer from the same type of problem. A solution to this problem proposed by the present invention is to use at least a single priority line to provide a generic level of priority to each connection link. A telecommunications device using a first protocol, e.g. a wireless protocol such as Bluetooth device, can have different links to the same device or to a different device at the same time. In case of coexistence with a device using a second, different, telecommunications protocol, e.g. a wireless protocol such as WLAN, it is preferred to assign different priority levels to each first protocol link, e.g. Bluetooth link, to avoid loss of performance in the system. For example: the first protocol device, e.g. Bluetooth device, may have one voice link to one device and one data link to another device. Without a mechanism in accordance with the present invention, the following might be used:
         i) set priority 1 to all voice packets and set priority 0 to all datapackets. In case the WLAN chip would be active this would result in a very good quality for the Bluetooth voice link and basically no throughput on the Bluetooth data link. This is clearly not acceptable.   ii) set priority 1 for all voice packet and priority 1 on all datapackets. This would result in very good Bluetooth links but basically no throughput on a WLAN link which would be not acceptable.
 
One aspect of the present invention is a mechanism to allow a variable priority of the different first protocol, e.g. Bluetooth, links. An example can be setting a priority between 0% and 100%, with a certain granularity. The coexistence of links with different protocols will then have a higher performance.
       

   The invention is not limited to the embodiments described herein, which may be modified or varied without departing from the scope of the invention. 
   Having thus described at least one illustrative embodiment of the invention, various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be within and scope of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention is limited only as defined in the following claims and the equivalents thereto.