Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J1/00—Frequency-division multiplex systems
  • H04J1/02—Details
  • H04J1/12—Arrangements for reducing cross-talk between channels
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L1/00—Arrangements for detecting or preventing errors in the information received
  • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
  • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
  • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
  • H04L1/1829—Arrangements specially adapted for the receiver end

Definitions

• the present invention relates to a method of reducing interference between two communication systems operating in adjacent frequency bands, and more particularly, to a method of reducing interference between two communication systems operating in adjacent frequency bands and coexisting in a device with a limited space.
• WiMAX and WiFi systems operates on adjacent frequency bands, which are the 2.4 GHz Industrial Scientific and Medical (ISM) band and the licensed 2.3GHz and 2.5GHz bands. Most WiMAX systems use Time Division Duplex (TDD) to allocate radio resources because TDD has higher spectral efficiency and can be implemented with lower complexity.
• TDD Time Division Duplex
• a TDD frame is divided into a downlink sub frame and an uplink sub frame.
• a WiFi system is a contention-based system without dedicated radio resource and uses a technique called carrier sense multiple access with collision avoidance (CSMA/CA).
• CSMA/CA carrier sense multiple access with collision avoidance
• a WiFi station monitors the wireless medium and decides when to transmit packets. When the wireless medium is detected to be idle, the WiFi station is permitted to transmit; and when the wireless medium is detected to be busy, the WiFi station defers its transmission for a random period following the wireless medium turns to be idle again.
• a WiMAX-WiFi coexistence device 100 is a combination of a WiMAX system and a WiFi system, which can be a WiMAX-WiFi portable router or a WiMAX-WiFi customer- premises equipment (CPE) and performs as a WiMAX router connecting with a WiMAX base station 102 and a WiFi access point (AP) connecting with WiFi stations 104 as laptops or multimedia players. Therefore, the WiFi stations 104 are able to access the WiMAX network and communicate with WiMAX subscriber stations 106 via the WiMAX-WiFi coexistence device 100.
• a WiMAX-WiFi coexistence device 100 is a combination of a WiMAX system and a WiFi system, which can be a WiMAX-WiFi portable router or a WiMAX-WiFi customer- premises equipment (CPE) and performs as a WiMAX router connecting with a WiMAX base station 102 and a WiFi access point (AP) connecting with WiFi stations 104 as laptops or multimedia players. Therefore
• the guard band between the 2.4GHz band for WiFi and the 2.3/2.5GHz band for WiMAX are narrow and the portable WiMAX-WiFi coexistence device has limited dimensions, mutual interference between WiMAX and WiFi systems in the portable WiMAX- WiFi coexistence device is hard to be reduced.
• the WiFi transmitter interferes with the WiMAX receiver and decreases efficiency of WiMAX downlink reception, which has to be improved because the WiMAX system uses licensed bands and the waste of bandwidth is not acceptable.
• the WiFi system is receiving packets during a WiMAX uplink subframe, the WiMAX transmitter interferes with the WiFi receiver and WiFi packets cannot be received successfully, which causes a problem that the WiFi station may use the lower MCS (Modulation and Coding Scheme) rate according to its rate adaptation mechanism, and finally, interference is getting more serious until the WiFi stations and the WiFi system are disconnected.
• MCS Modulation and Coding Scheme
• the WiMAX-WiFi coexistence device uses conventional arbitration procedure to try to reduce interference
• the WiMAX-WiFi coexistence device does not take WiFi station connecting with WiMAX-WiFi coexistence device into consideration.
• the WiFi station cannot get information about the interference inside the WiMAX-WiFi coexistence device, and may still send packets to the WiMAX-WiFi coexistence device and wait for acknowledgements.
• the WiFi system of the WiMAX-WiFi coexistence device may not receive packets successfully due to the mutual interference and does not send acknowledgement as response.
• the WiFi station will use the lower MCS (Modulation and Coding Scheme) transmission rate according to its rate adaptation mechanism, and channel utilization between the WiMAX-WiFi coexistence device and the WiFi station is getting worse due to the retransmissions and inefficiency MCS.
• MCS Modulation and Coding Scheme
• a method of reducing interference between two communication systems operating in adjacent frequency bands and coexisting in a communication device including a first communication system using Time Division Duplex (TDD) and a second communication system which is contention-based.
• TDD Time Division Duplex
• the method includes deciding whether to perform an arbitration procedure on a downlink subframe of the first communication system according to a carrier to noise plus interference ratio (CINR) of the first communication system and a received signal strength indicator (RSSI) value of the second communication system, wherein the first communication system is set to have a higher priority than the second communication system in the arbitration procedure; deciding whether to perform the arbitration procedure on an uplink subframe of the first communication system according to a transmit power of the first communication system and a RSSI value of the second communication system; and when deciding to perform the arbitration procedure on the downlink or uplink subframe, further deciding whether to send a specific packet to request one or more stations not to send packets to the second communication system.
• CINR carrier to noise plus interference ratio
• RSSI received signal strength indicator
• FIG. 1 is a diagram of a WiMAX network according to the prior art.
• FIG. 2 is a schematic diagram of a 4G-WiFi coexistence device according to an embodiment of the present invention.
• FIG. 3 is a flowchart of a process according to an embodiment of the present invention.
• FIG. 4A and FIG. 4B are timing diagrams illustrating the CTS-to-self packet and the CF-End packet based on the process of FIG. 3.
• FIG. 5 is a flowchart of a process according to an embodiment of the present invention.
• FIG. 6 is a flowchart of a process according to an embodiment of the present invention.
• FIG. 7 is a timing diagrams illustrating interference reduction by performing the process of FIG. 6.
• FIG. 2 is a schematic diagram of a 4G-WiFi coexistence device 20 according to an embodiment of the present invention.
• the 4G-WiFi coexistence device 20 comprises a 4G system 200 (including a transmitter and a receiver), a WiFi system 202 (including a transmitter and a receiver) and an interference reduction unit 204.
• The4G-WiFi coexistence device 20 can be a 4G-WiFi portable router or a 4G-WiFi consumer-premises equipment (CPE), and can replace the 4G-WiFi coexistence device 10 in FIG. 1.
• the WiFi system 202 performs as a WiFi access point (AP) and the 4G system
• the 200 performs as a 4G router to route data packets to 4G base station or to the con necting WiFi Stations.
• the 4G-WiFi coexistence device 20 is one of embodiments of the present invention.
• the 4G-WiFi coexistence device 20 can be referred to any other coexistence device including two communication systems operating in adjacent frequency bands, in which one communication system uses Time Division Duplex (TDD) to allocate radio resources, and the other communication system is a contention-based system.
• TDD Time Division Duplex
• the interference reduction unit 204 is software- implemented, capable of executing program code.
• the present invention does not give the limitation that to implement the interference reduction unit 204 by software; it is also possible to implement the interference reduction unit 204 by hardware.
• FIG. 3 and FIG. 5 are flowcharts of a process 30 and a process 50 according to embodiments of the present invention, which can be compiled into program code and performed by the interference reduction unit 204, for reducing interference between the 4G system 200 and the WiFi system 202.
• the interference reduction unit 204 is able to acquire system parameter values from the 4G system 200 and the WiFi system 202, e.g. received signal strength indicator (RSSI), transmit power, in-band noise/interference power, carrier to noise plus interference ratio (CINR) and so on, which are used in the processes 30 and 50.
• RSSI received signal strength indicator
• CINR carrier to noise plus interference ratio
• the process 30 is utilized for reducing interference on 4G downlink reception caused by the WiFi transmitter at 4G downlink subframes.
• the process 30 comprises the following steps:
• Step 300 Start (when 4G system and WiFi cannot operate at the same time without interfering each other).
• Step 302 Determine whether a 4G CINR value CINR 4G is larger than a 4G CINR threshold CINR T hi_4G and a WiFi RSSI value RSSIW I R is larger than a WiFi RSSI threshold RSSIih DL WiFi- If CINR4G is larger than CINRihi 4G and RSSIwiFi is larger than RSSIih DL WiFi, perform Step 304; else, perform 306.
• Step 304 Decrease WiFi transmit power and not to perform an arbitration procedure.
• Step 306 Determine whether CINR 4G is larger than another 4G CINR threshold CINRih2_4G. If CINR4G is not larger than CINRih2 4G, perform Step 308; else, perform 312.
• Step 308 Perform the arbitration procedure and notify the WiFi system to send a CTS- to-self packet.
• Step 310 When 4G downlink reception is completed earlier than the end of duration of the CTS-to-self packet, stop the arbitration procedure and send a CF-End packet.
• Step 312 Perform the arbitration procedure and decrease WiFi transmit power.
• the process 30 includes three mechanisms, an arbitration procedure, reserve channel procedure by sending CTS-2-Self packet and a power control procedure, which are performed under different conditions of system parameters.
• the arbitration procedure handles each transmit attempt from two systems and can be realized in various ways, e.g. packet traffic arbitration (PTA) in IEEE 802.15 standard, which is well- known to those skilled in the art.
• PTA packet traffic arbitration
• the process 30 does not aim at how the arbitration procedure performs but when the arbitration procedure performs and thus detail of the arbitration procedure is omitted herein.
• the 4G system is set to a higher priority than the WiFi system.
• a 4G CINR value CINR 4G that the interference reduction unit 204 acquires is compared with a predefined 4G CINR threshold CINRihi 4G, and this comparison intends to know if 4G downlink reception quality is good enough to sustain certain level of interference from the WiFi transmitter; in addition, a WiFi SSI value RSSIwi F ithat the interference reduction unit 204 acquires is compared with a predefined WiFi RSSI threshold RSSIih DL WiFi, and this comparison intends to know if a WiFi station connecting with the 4G-WiFi coexistence device 20 is near the 4G-WiFi coexistence device 20.
• the interference reduction unit 204 decreases WiFi transmit power to be lower than the original power and decides not to perform the arbitration procedure. In merit of a lower WiFi transmit power, interference on 4G downlink reception is reduced. As a result, 4G system and WiFi can perform transmission and reception simultaneously in this case.
• CINR 4 G is not larger than CINR Th i 4 c or RSSIwi F i is not larger than RSSIi h DL WiFi
• CINR4G is further compared with a 4G CINR threshold CINRih2_4G smaller than CINRihi 4G-
• the interference reduction unit 204 performs the arbitration procedure and notifies the WiFi system 202 to send a CTS (clear-to-send)-to-self packet, which is received by all the WiFi stations connecting with the WiFi system 202 and thus the WiFi stations are informed of not to transmit packets to the WiFi system 202 during the given period.
• Timing to send the CTS-to-self packet can be controlled by a timer.
• the timer can be set to start (or expire) 1ms earlier than the end of each 4G uplink sub frame to trigger the CTS-to-self packet.
• a reservation period indicated in CTS-to-self packet can be set to a length equal to the 4G downlink subframe or the 4G downlink reception, so that the 4G downlink reception is well-protected as much as possible.
• the WiFi system 202 receives no packets and does not need to respond an acknowledgement (ACK) packet. Interference caused by transmitting ACK packages is avoided.
• ACK acknowledgement
• Step 310 when the interference reduction unit 204 detects that 4G downlink reception is completed earlier than the end of the reservation duration indicated in the CTS-to-self packet, the interference reduction unit 204 stops the arbitration procedure and sends a CF (contention-free)-End packet.
• the CF-End packet is received by all the WiFi stations connecting with the WiFi system 202, so that the WiFi stations are informed that the previous reservation specified in WiFi system 202 is released and the contention-based service begins.
• the WiFi system 202 can provide services more efficiently, which are illustrated in FIG. 4A and FIG. 4B more clearly. In FIG. 4A and FIG.
• a signal PTA indicates when the arbitration procedure is ongoing or stopped, and a signal CTS2Self_DU indicates the CTS-to-self packet duration.
• the arbitration procedure is started (PTA from low to high) and the CTS-to- self packet is sent at the beginning of the 4G downlink subframe, and the end of original CTS- to-self packet duration is depicted in dashed-line.
• the arbitration procedure is stopped (PTA from high to low), the CF-End packet is sent, and the CTS-to-self packet duration is stopped (CTS2Self_DU from high to low) as depicted in solid-line.
• a time period "A" is saved by use of the CF-End packet.
• FIG. 4B somehow transmission of the CTS-to-self packet is delayed, e.g. due to medium is busy and the CTS-to-self packet duration starts late.
• the CF-End packet is sent and the CTS-to-self packet duration is stopped at as the depicted in solid-line in replace of the original end depicted in dashed-line. Consequently, a time period "B" is saved.
• Step 310 after the 4G downlink reception is completed, the WiFi system 202 returns to provide services with the WiFi stations without waiting until the end of CTS-to-self packet duration.
• Step 308 and Step 310 are performed when 4G downlink reception is interfered seriously.
• the interference reduction unit 204 determines that CINP G is larger than CINPTh2 _AG, the interference on 4G downlink reception may be acceptable. In other words, interference caused by transmission of WiFi ACK packets is acceptable. In this situation, the interference reduction unit 204 performs the arbitration procedure and decreases WiFi transmit power. No that, in this situation, the interference reduction unit 204 does not send the CTS-to-self to the WiFi stations; when the WiFi stations transmit packets to the WiFi system 202, the WiFi system 202 transmits ACK packets with a lower power in response.
• the process 30 provides three modes for reducing interference and every time the interference reduction unit 204 performs the process 30, one of the three modes is decided to be used according to values of system parameters.
• the first mode is using the power control procedure only as illustrated in Step 302 and Step 304.
• the power control procedure in the process 30 only includes decreasing WiFi transmit power, which is an embodiment and not a restriction.
• the second mode is using the arbitration procedure combined with transmission of the CTS-to-self and CF-End packets as illustrated in Steps 302, 306, 308 and 310.
• the third mode is using the arbitration procedure combined with the power control procedure and with no transmission of CTS-to-self packet, as illustrated in Steps 302, 306 and 312.
• the CTS-to-self packet in the process 30 can be replaced with another packet which can inform the WiFi stations that not to send packets, such as a null packet including only preamble, signal symbol and MAC header, or a dummy protocol data unit (PDU) including only header and no user data.
• a null packet including only preamble, signal symbol and MAC header
• PDU protocol data unit
• the process 50 is performed by the interference reduction unit 204, for reducing interference on the WiFi receiver caused by 4G uplink transmission at 4G uplink subframes.
• the process 50 comprises the following steps:
• Step 500 Start (when WiMAX and WiFi cannot operate at same time without interfering each other).
• Step 502 Determine whether a 4G transmit power value P 4G is larger than a 4G transmit power threshold P3 ⁇ 4 JG and a WiFi SSI value RSSIwiFi is smaller than a WiFi RSSI threshold RSSIih uL WiFi- If P 4 G is larger than P T h c and RSSIwiFi is smaller than RSSIih uL WiFi, perform Step 504; else, perform 508.
• Step 504 Perform an arbitration procedure and notify the WiFi system to send a CTS- to-self packet.
• Step 506 When 4G uplink transmission is completed earlier than the end of duration of the CTS-to-self packet, stop the arbitration procedure and send a CF-End packet.
• Step 508 Not to perform the arbitration procedure.
• Step 510 End
• a 4G transmit power value P 4G is compared with a predefined 4G transmit power threshold P Th _ 4G and a WiFi RSSI value RSSIwi F i is compared with a predefined WiFi RSSI threshold RSSIih UL WiFi- This comparison intends to know if the WiFi receiver is interfered with 4G uplink transmission.
• P 4G is larger than Pi h _ 4G and SSIwi F i is smaller than RSSIi h DL WiFi, which indicates that the WiFi receiver is interfered and the received packets may fail to be successfully decoded
• the interference reduction unit 204 performs Step 504 and Step 506; otherwise, according to Step 508, the interference reduction unit 204 does not perform the arbitration procedure.
• the interference reduction unit 204 performs an arbitration procedure and notifies the WiFi system 202 to send a CTS-to-self packet, to inform the WiFi stations not to transmit packets. Note that transmission of the CTS- to-self packet is necessary because the WiFi receiver of the WiFi system 202 may unsuccessfully decode the received packet duo to the interference and cannot send an ACK packet as a response, or may decode the received packet successfully but cannot send an ACK packet since the arbitration procedure is already started (in which 4G System is set to a higher priority).
• Step 506 when the 4G system uplink transmission is completed earlier than the end of duration of the CTS-to-self packet, the interference reduction unit 204 stops the arbitration procedure and sends a CF-End packet, so that the WiFi stations are informed that the WiFi system 202 is released and the contention- based service begins.
• the arbitration procedures shown in the process 30 and the process 50 are the same.
• CTS-to-self packet can also be replaced with a null packet or a dummy PDU.
• the process 30 is utilized for reducing interference on 4G4G downlink reception caused by the WiFi transmitter at 4G downlink sub frames
• the process 50 is utilized for reducing interference on the WiFi receiver caused by 4G uplink transmission at 4G uplink subframes.
• the interference reduction unit 204 performs the processes 30 and 50 and thereby, for a long time, decides to perform the arbitration procedure and send the CTS- to-self packet at both of downlink and uplink subframes
• the WiFi system 202 may have no radio resource to transmit packets.
• a process 60 is provided and illustrated in FIG. 6.
• the process 60 can be compiled into program code and is performed by the interference reduction unit 204.
• the process 60 comprises the following steps:
• Step 600 Start (when WiMAX and WiFi cannot operate at same time without interfering each other).
• Step 602 Get values of system parameters.
• Step 604 Check whether a current sub frame is for downlink or uplink. When the current subframe is for downlink, perform Step 606; else, perform Step 614.
• Step 606 Perform an uplink protection process.
• Step 608 Check whether to perform the arbitration procedure and/or send the CTS-to- self packet at a next subframe. If yes, perform Step 610; else, perform Step 612.
• Step 610 Set a flag Fl to 1.
• Step 612 Set a flag Fl to 0.
• Step 614 Perform a downlink protection process.
• Step 616 Check whether to perform the arbitration procedure and/or send the CTS-to- self packet at a next subframe. If yes, perform Step 618; else, perform Step 620.
• Step 618 Set a flag F2 to 1.
• Step 620 Set a flag F2 to 0.
• Step 622 Check whether the current subframe is the last subframe in a frame. If yes, perform Step 624; else, perform Step 604.
• Step 624 Check whether the flags Fl and F2 are set to 1. If yes, perform Step 626; else, perform Step 628.
• Step 626 Increase the value of a counter.
• Step 628 Reset the value of a counter and return to perform Step 602.
• the interference reduction 204 acquires values of system parameters, such as RSSI, CINR and transmit power of the 4G system 200 and the WiFi system 202 used in the processes 30 and 50.
• system parameters such as RSSI, CINR and transmit power of the 4G system 200 and the WiFi system 202 used in the processes 30 and 50.
• system parameters used in processes 30 and 50 are embodiments and are not restrictions on the present invention. Those skilled can also use signal to signal to noise ratio (SNR), modulation and coding scheme (MCS) and any other system parameters representing conditions of 4G system 200 and WiFi system 202.
• SNR signal to signal to noise ratio
• MCS modulation and coding scheme
• the process 60 and the processes 30 and 50 included in the process 60 are performed frame by frame, so that the interference between the 4G system 200 and the WiFi system 202 can be preferably reduced according to the latest values of system parameter values.
• the interference reduction unit 204 checks whether a current subframe is a downlink subframe or an uplink subframe.
• the interference reduction unit 204 performs an uplink protection process (Step 606) that is the process 50 of FIG. 5; otherwise, when the current subframe is an uplink subframe, the interference reduction unit 204 performs a downlink protection process (Step 614) that is the process 30 of FIG. 3.
• the interference reduction procedure (which is the arbitration procedure plus sending CTS-to-self packet or the power control procedure, for example) used for a current downlink/uplink subframe is decided in a preceding uplink/downlink subframe. That is, the interference reduction procedure for a next subframe is decided in advance.
• the interference reduction unit 204 checks whether the current subframe is the last subframe in a frame, and when the current subframe is the last subframe, the interference reduction unit 204 further checks whether both of the flags Fl and F2 are set to 1, which indicates that the arbitration procedure is performed and the CTS-to-self is sent in the downlink subframe and also the uplink subframe, and thus the WiFi system 202 has no resource to transmit/receive packets.
• Fl and F2 are set to 1
• the interference reduction unit 204 increases the value of a counter, wchich is counted by frames, for example.
• the counter is preferably used for counting the number of "continuous" times that Fl and F2 are set to 1; when any one of Fl and F2 are set to 0, according to Step 628, the counter is reset to 0. Therefore, the value of the counter, T c , indicates a continuous time during which the WiFi system 202 has no resource to transmit.
• the value of the counter Tc can be used to determine when the WiFi system 202 is able to transmit packets and how much time the WiFi system 202 can use for transmission.
• 4Ga scan mode is initiated by 4G mobile station to request a period of time for searching and monitoring suitability of neighbor base stations as targets for handover.
• a 4G mobile station may send a scan request message to request a 4G base station to allocate time intervals to the mobile station.
• the scan request message is the mobile station indicates an estimated scanning duration (by including recommended start frame of the scanning duration), which is the time the mobile station requires scanning for available base stations.
• the base station may comply with the recommended start frame and set "start frame" as recommended by mobile station in a scan response message, in response to the scan request message.
• the interference reduction unit 204 uses one or more threshold values to be compared with Tc and uses the scan request message as described above to determine when the WiFi system 202 is able to transmit packets. For example, when Tc is larger than a threshold T ls the interference reduction unit 204 notifies the 4G system 200 to send a scan request message to a 4G base station for requesting a scanning duration, in which 4G downlink reception and uplink transmission are stopped. Therefore, the WiFi system 202 can use the requested scanning duration to transmit packets.
• the interference reduction unit 204 is able to acquire a longer scanning duration corresponding to a larger Tc.
• the interference reduction unit 204 when performing the process 60, the interference reduction unit 204 also monitors the size of an output buffer queue of the WiFi system 202. The interference reduction unit 204 can request a duration having a length corresponding to the size of an output buffer queue.
• the mobile station as the 4G-WiFi coexistence device 20 can decide the scanning duration to be used for the scan mode, or for the transmission of the WiFi system 202 according to the present invention.
• the interference reduction unit 204 reserves an N% of a 4G frame for the WiFi system 202.
• the interference reduction unit 204 stops the arbitration procedure on the downlink subframe for a time duration or stops the arbitration procedure on the uplink subframe for a time duration, so that the WiFi system 202 can use those duration to transmit packets.
• FIG. 7 is a timing diagram illustrating how the interference reduction unit 204 performs the process 60 .
• a signal PTA indicates when the arbitration procedure is ongoing or stopped. PTA keeps in a high level for channel estimation or channel measurement from the beginning of the frame N to a time point "A", even there is no 4G data burst.
• a short 4G data burst generates at a time point "B".
• the interference reduction unit 204 may not perform the arbitration procedure.
• a CTS-to-self packet is sent at a time point "C", which is Kms earlier than the end of the downlink subframe, so that the WiFi stations can know not to send packets to the WiFi system 202 in advance.
• PTA transits from low to high and thus the arbitration procedure is performed.

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• 2010
  • 2010-12-07 WO PCT/CN2010/079535 patent/WO2011069442A1/en active Application Filing
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