Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
  • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
  • H04B7/2628—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA]
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/69—Spread spectrum techniques
  • H04B1/713—Spread spectrum techniques using frequency hopping
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W76/00—Connection management
  • H04W76/10—Connection setup
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/69—Spread spectrum techniques
  • H04B1/713—Spread spectrum techniques using frequency hopping
  • H04B1/715—Interference-related aspects
  • H04B2001/7154—Interference-related aspects with means for preventing interference
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W24/00—Supervisory, monitoring or testing arrangements
  • H04W24/10—Scheduling measurement reports ; Arrangements for measurement reports
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W48/00—Access restriction; Network selection; Access point selection
  • H04W48/08—Access restriction or access information delivery, e.g. discovery data delivery
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W72/00—Local resource management
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W72/00—Local resource management
  • H04W72/02—Selection of wireless resources by user or terminal
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W84/00—Network topologies
  • H04W84/18—Self-organising networks, e.g. ad-hoc networks or sensor networks
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W92/00—Interfaces specially adapted for wireless communication networks
  • H04W92/16—Interfaces between hierarchically similar devices
  • H04W92/18—Interfaces between hierarchically similar devices between terminal devices

Definitions

• the present invention relates to radio communication systems.
• the present invention is related to communication systems which use frequency hopping in unlicensed frequency carriers.
• 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.
• 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.
• 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
• the system 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 realtime 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 beacon signal.
• 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.
• 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
• 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.
• FIG 10 is a diagram illustrating beacon tracking of slaves B and C according to a further exemplary embodiment of the present invention.
• a preferred embodiment of the system described herein utilizes a FH radio interface as described in greater detail in U.S. Patent Application No. 08/685,069 "SHORT-RANGE RADIO COMMUNICATIONS SYSTEM AND METHOD OF USE", by P.W. Dent and J.C. Haartsen, filed July 23, 1996, (hereinafter "Dent") the disclosure of which is incorporated herein by reference.
• Bluetooth the Universal Radio Interface for Ad Hoc wireless connectivity
• 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.
• the unit that initiates the commumcations 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 08/932,911 by J.C. Haartsen, entitled "FREQUENCY HOPPING PICONETS INAN UNCOORDINATED MULTI-USER SYSTEM", filed September 18, 1997 and incorporated herein by reference.
• 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.
• 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.
• 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.
• 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 slace 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 110a, channel 110b, and channel 110c, respectively.
• master 120 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 110a, channel 110b, and channel 110c, 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 110a, send packets 121, 123, and 125 in respective master-to-slave time slots 201, 205, and 209 at respective frequencies h ⁇ 221, h ⁇ +4 225 h ⁇ +8 229 to slave A 130.
• 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 ⁇ +1 222, h ⁇ +5 226 h ⁇ +9 230.
• master 120 may, over channel 110b, send packet 122 in master-to-slave time slot 203 at frequency h ⁇ +2 223 to slave B 140.
• slave B 140 may respond with packet 141 only in the alternate slave-to-master time slot 204 at frequency h ⁇ +3 224.
• Master 120 may further, over channel 110c, send packets 124 and 126 in respective master-to-slave time slots 207 and 211 at respective frequencies h ⁇ +6 227 and h ⁇ +10 231 to slave B 140.
• 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 ⁇ +7 228 and h ⁇ +1] 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 particulary FH link.
• Packet header 320 may carry general control information, for example, identifying payload 330 and indicating error correction mechanisms.
• 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.
• an exemplary hop rate is 1600 hops/s resulting in exemplary time slots 201-212 being of about 625 ⁇ s 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.
• channel 110 associated with piconet 100 may have a maximum instantaneous rate of 1 Mb/s.
• regulatory bodies like the Federal Communications Commission
• 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.
• the laptop or slave B 440 may desire to download a print job to the printer or slave C 450.
• 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 IMb/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.
• 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 IMb/s. An even higher data rate can be obtained in accordance with the present invention.
• slave C 450 is in close proximity, for example 3-10m, 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.
• HS high-speed
• HS link such as channel 510a between master 420 and slave C 450, as illustrated in FIG 4A
• HS link such as channel 510b between two or more slaves, such as slave B 440 and slave C 450 as illustrated in FIG 4B.
• master 420 time multiplexes between slave C 450 associated with channel 510a, the HS link, and the other slaves, such as slave A 430 and slave B 440 in piconet 400.
• channel 420 jumps between channel 510a and the FH link associated with, for example, channel 410a and 410 b for slave A 430 and slave B 440 respectively. If the effective data rate on the HS link, channel 510a 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 510a 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 410a, 410b, and 410c respectively.
• An HS link may be established, for example, between master 420 and slave C 450 over channel 510a.
• An HS link between master 420 and slave A 430 reflects the configuration illustrated in 4A.
• master 420 may communicate packet 421 to slave A 430 over channel 410a on time slot 201 at frequency h ⁇ 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 ⁇ +1 222.
• master 420 may communicate packet 422 to slave B 440 over channel 410b on time slot 203 at frequency h ⁇ +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 ⁇ +3 224.
• master 420 may, at point x, shift from FH communications on link 410c to HS communications on channel 510a and may shift back to FH communications, releasing channel 510a, at point y.
• FIG 5 illustrates point x and y as occuring within frequency hopping periods represented by traversing, for example, frequencies h ⁇ 221 to h ⁇ +n 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 ⁇ 221 to h ⁇ +11 232. Accordingly, master 420 conducts HS communications with slave C 450 over channel 510a 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.
• master 420 may resume FH communications with slave C 450 over channel 410c by, for example, transmitting packet 425 on time slot 211 at frequency h ⁇ +10 231.
• slave C 450 may send packet 452 in the next time slot 212 at frequency h ⁇ +11 232. .
• slave B 440 and slave C 450 desire to establish an HS link as is illustrated in FIG 4B, the situation is quite different.
• master 420 may establish an FH link with slave A 430, slave B 440, and slave C 450.
• slave B 410 and slave C 450 may establish HS communications on a separate link, such as channel 510b. 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 510b conflict with FH frequencies associated with link 410 at the same point in time.
• Master 420 may communicate over channel 410a, for example, packet 421 to slave A 430 over time slot 201 at frequency h ⁇ 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 ⁇ +1 222.
• master 420 may communicate packet 422 to slave B 440 over channel 410b on time slot 203 at frequency h ⁇ +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 ⁇ +3 224.
• Master 420 may further send packets 427, 428, and 429 over channel 410a to slave A 430 on time slots 205, 207, and 209 respectively using respective frequencies h ⁇ +4 225, h k+6
• slave A 430 may send respective packets 432, 433, and 434 over channel 410a 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
• HS communications may proceed between slave B 440 and slave C 450.
• Packet 442 for example may be sent on channel 510b 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 510b 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.
• master 420 may continue FH communications with slave C 450 on channel 410c 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 410c with packet 452 in the next time slot 212 at frequency h ⁇ +n 232.
• 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).
• HS band 741 may be selected on which the lowest interference is measured.
• frequency plot 700a 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.
• HS link 740 is selected to coincide with the RSSI 720 measurements 723 through 726 since they correspond to low RSSI 720 values.
• RSSI 720 measurements change over time the allocation of HS band 741 may change as will be described in greater detail hereinafter.
• the width of HS band 741 is preferably smaller than 4 MHZ for the following reasons.
• the FCC requires the number of hop channels to be at least 75.
• 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.
• HS link 740 may be established at four 1MHz hop intervals wide, such as hop intervals
• hops may be centered at hop carriers 812a-812d and may be surrounded by 1MHz envelopes 811a-811d 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 4B and in FIG 6.
• Frequency carrier allocation 921 for hop carriers 812a-812"n" of the FH link and the semi-stationary carrier allocation 911 for carriers 742a-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.
• HS link 740 for example can exactly replace 4 hops of the FH link.
• 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.
• slave B 440 and slave C 450 may temporarily leave piconet 100 to establish an HS link over, for example, HS channel 410d, again, as is illustrated in FIG 4B and FIG 6.
• master 420 maintains control of slave
• Slave B 440 and slave C 450 in one of, for example, two ways.
• Slave B 440 and slave C 450 and master 420 may agree on a fixed interval for which HS link 741 will last.
• slave B 440 and slave C 450 will automatically return to piconet 100, at, for example, point y as is illustrated in FIG 6.
• slave B 440 and slave C 450 may request HS link
• 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 No. 09/210,594, incorporated herein above.
• Master 420 may transmit beacon packets 1010a, 1010b, and 1010c at fixed intervals. Beacon packets 1010a, 1010b, and 1010c 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 No. 09/210,594 incorporated herein above. Accordingly, slave
• HS channel 1400 may also remain synchronized with FH channel 1200.
• slave B 440 and slave C 450 may be configured to "listen" for beacon packets 1010a, 1010b, and 1010c. If present, beacon packets 1010a, 1010b, and 1010c, may, for example, include a message ordering slave B
• 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.
• slave B 440 and slave C 450 may further interrupt communicating with each other over HS channel 1400.
• slave B 440 may send, for example, packets 1441, 1442, and 1543 to slave C 450 at frequency f HS 510.
• 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.
• the data link protocol on HS link 1500 may differ from the data link protocol on FH link 1200.
• a listen before-talk protocol may be applied to conform to the etiquette or protocols associated with communications in the 5 GHz band.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Mobile Radio Communication Systems (AREA)
• Small-Scale Networks (AREA)

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Cited By (7)

Citations (1)

• 2000
  • 2000-05-12 JP JP2001520967A patent/JP4523216B2/ja not_active Expired - Lifetime
  • 2000-05-12 WO PCT/EP2000/004323 patent/WO2001017136A1/en active Application Filing
  • 2000-05-12 AU AU49214/00A patent/AU4921400A/en not_active Abandoned

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