WO2008149304A2 - Appareil et procédé pour effectuer une adaptation de liaison dans des systèmes sans fil - Google Patents

Appareil et procédé pour effectuer une adaptation de liaison dans des systèmes sans fil Download PDF

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Publication number
WO2008149304A2
WO2008149304A2 PCT/IB2008/052193 IB2008052193W WO2008149304A2 WO 2008149304 A2 WO2008149304 A2 WO 2008149304A2 IB 2008052193 W IB2008052193 W IB 2008052193W WO 2008149304 A2 WO2008149304 A2 WO 2008149304A2
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WIPO (PCT)
Prior art keywords
link
reception device
optimum
transmission rate
signal strength
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PCT/IB2008/052193
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English (en)
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WO2008149304A3 (fr
Inventor
Hongqiang Zhai
Chun-Ting Chou
Richard Chen
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Koninklijke Philips Electronics, N.V.
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Publication of WO2008149304A2 publication Critical patent/WO2008149304A2/fr
Publication of WO2008149304A3 publication Critical patent/WO2008149304A3/fr

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Classifications

    • 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
    • H04L1/0023—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the signalling
    • H04L1/0026—Transmission of channel quality indication
    • 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
    • H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
    • 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
    • H04L1/0006—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission format
    • H04L1/0007—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission format by modifying the frame length
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/0001—Arrangements for dividing the transmission path
    • H04L5/0003—Two-dimensional division
    • H04L5/0005—Time-frequency
    • H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT

Definitions

  • WLANs wireless local area networks
  • WPANs wireless personal area networks
  • WLANs and WPANs may operate according to a number of different available standards, including the WiMedia Alliance Ultra- Wideband (UWB) standard.
  • UWB WiMedia Alliance Ultra- Wideband
  • FIG. 1 is a block diagram showing a conventional wireless network 100, including multiple terminals configured to communicate with one another over exemplary WPAN 125.
  • the wireless terminals may include any electronic devices or nodes configured to communicate with one another.
  • FIG.1 depicts a home network in which the electronic devices include a personal computer 120, a digital television set 121, a digital camera 122 and a personal digital assistant (PDA) 123.
  • the network 100 may also include an interface to other networks, such as modem 130, to provide connectivity of all or some of the wireless devices 120-123 to the Internet 140, for example.
  • modem 130 such as modem 130
  • beacons typically exchange information, such as control information, using beacons.
  • Beacons may be included in periodic superframes of respective transmissions, and are usually broadcast so that all devices in the transmission range of the beaconing device can receive the beacons.
  • an access point periodically sends out beacons so that wireless devices around the access point can associate with the access point and communicate.
  • Beacons (or beacon frames) may include information such as the medium access control (MAC) address of the beaconing device, data rates, signal strengths and the like.
  • MAC medium access control
  • wireless UWB systems In wireless networks, link quality changes with time and distance between transmitters and receivers based on various conditions, such as movement of the transmitters/receivers, obstructions, multipath fading, and the like. Therefore, different transmission rates may be appropriate over the same transmission link and various times, depending on the corresponding link quality. For example, in order to accommodate various network conditions, wireless UWB systems support multiple different transmission rates.
  • the WiMedia standard for UWB systems for example, defines eight data rates, shown in Table 1 :
  • a high transmission data rate should be used when link quality is good, otherwise a low transmission data rate should be used.
  • a transmitter moves toward its intended receiver from a relatively far distance, thus improving the link quality, the transmitter should gradually increase its transmission rate to achieve higher throughput. Accordingly, it would be desirable to link adaptation in a wireless system that reliably and efficiently controls adjustments to transmission rates and/or other parameters to adapt to variations in link quality.
  • a method for improving throughput of a forward communications link between a source device and a reception device.
  • the method includes receiving a beacon frame from the reception device; determining a link quality associated with the forward communications link based on information obtained from the received beacon frame; determining an optimum transmission rate based on the link quality; and transmitting a signal to the reception device using the optimum transmission rate.
  • an apparatus is provided for improving throughput of a forward communications link with a reception device.
  • the apparatus includes a receiver, a processor and a transmitter.
  • the receiver is configured to receive a beacon frame from the reception device.
  • the processor is configured to determine a signal strength associated with the forward communications link based on information obtained from the received beacon frame, and to determine an optimum transmission rate based on the signal strength.
  • the transmitter is configured to transmit a signal to the reception device using the optimum transmission rate.
  • a method for improving throughput.
  • the method includes sending an information element request from a source device to a reception device in a first transmission over a wireless communications link, and subsequently receiving a beacon frame from the reception device, the beacon frame having a link feedback information element in response to the information element request, the link feedback information element indicating a feedback rate corresponding to the first transmission over the communications link.
  • An optimum transmission rate associated the communications link is determined based on at least the link feedback information from the received beacon frame.
  • a second transmission is sent over the wireless communications link from the source device to the reception device using the determined optimum transmission rate.
  • FIG. 1 is a block diagram of a conventional wireless communications network.
  • FIG. 2 is a functional block diagram of wireless devices communicating over a wireless network according to one embodiment of the invention.
  • FIG. 3 is a diagram of sample frames for communication by unsynchronized wireless devices in a wireless network according to an embodiment of the invention.
  • FIG. 4 is a flow chart of a basic adaptation process according to various embodiments.
  • FIG. 5 is a flow chart of an enhanced adaptation process according to various embodiments.
  • FIG. 6 is a flow chart of an enhanced adaptation process according to various embodiments.
  • FIG. 7 is a flow chart of an enhanced adaptation process according to various embodiments.
  • FIG. 8A-8D show graphs showing simulation results according to various embodiments.
  • wireless network 230 may be a UWB network and wireless devices 210 and 220 may be adapted to operate using a UWB protocol in accordance with WiMedia specifications.
  • the wireless network 230 may represent a communications link between the wireless devices 210 and 220.
  • the wireless devices 210 and 220 may be adapted to operate using other communications protocols, although the protocols must provide for appropriate information elements to accommodate certain embodiments, discussed below.
  • the WiMedia UWB protocol for example, provides a link feedback information element (IE), which can be used to send link quality information to a requesting device to achieve better performance of link adaptation.
  • IE link feedback information element
  • FIG. 2 may be physically implemented using a software-controlled microprocessor, hard-wired logic circuits, or a combination thereof. Also, while the parts are functionally segregated in FIG. 2 for explanation purposes, they may be combined variously in any physical implementation.
  • source device 210 and reception device 220 are intended to be descriptive for purposes of discussion, and thus it is understood that both the source device 210 and reception device 220 are capable of transmitting information to and receiving information from one another, as well as other devices within the wireless network 230.
  • Source device 210 includes transceiver 214, processor 216, memory 218, and antenna system 212.
  • Transceiver 214 includes a receiver 213 and a transmitter 215, and provides functionality for source device 210 to communicate with other wireless devices, such as reception device 220, over wireless communication network 230 according to the appropriate standard protocols.
  • Processor 216 is configured to execute one or more software algorithms, including the link adaptation process algorithms of the embodiments described herein, in conjunction with memory 218 to provide the functionality of source device 210.
  • the enhanced link adaptation processes may be software implemented in the MAC layer.
  • Processor 216 may include its own memory (e.g., nonvolatile memory) for storing executable software code that allows it to perform the various functions of source device 210, discussed herein. Alternatively, the executable code may be stored in designated memory locations within memory 218.
  • antenna system 212 may include a directional antenna system that provides a capability for the source device 210 to select from multiple antenna beams for communicating with other wireless devices in multiple directions.
  • antenna system 212 may include multiple antennas, each corresponding to one antenna beam, or antenna system 212 may include a steerable antenna that can combine multiple different antenna elements to form a beam in different directions.
  • antenna system 212 may include a single antenna, and/or a non-directional or omnidirectional antenna system.
  • reception device 220 may be substantially the same as source device 210, for ease of explanation. Accordingly, reception device 220 includes transceiver 224, processor 226, memory 228 and antenna system 222. Transceiver 224 includes a receiver 223 and a transmitter 225, and provides functionality for reception device 220 to communicate with other wireless devices, such as source device 210, over wireless communication network 230, according to the appropriate standard protocols.
  • Processor 226 is configured to execute one or more software algorithms in conjunction with memory 228 to provide the functionality of reception device 220.
  • Processor 226 may include its own memory (e.g., nonvolatile memory) for storing executable software code that allows it to perform the various functions of wireless device 220, discussed herein.
  • the executable code may be stored in designated memory locations within memory 228.
  • Antenna system 222 may include a directional antenna system and provide a capability for the reception device 220 to select from multiple antenna beams for communicating with other wireless devices (e.g., source device 210) in multiple directions.
  • antenna system 222 may be a non-directional or omnidirectional antenna system.
  • both antenna system 212 of source device 210 and antenna system 222 of reception device 220 are directional antenna systems, the antennas must be aligned in order for the devices to discover and communicate with one another.
  • Link adaptation adapts transmission rates to changing link quality to improve throughput performance. Link adaptation is thus intended to maximize the throughput seen by the networking layer, which is above the medium access control (MAC) and physical (PHY) layers.
  • the embodiments enable the source and reception devices 210, 220 to maintain and optimize communication quality through varying network conditions, for example, by optimizing rate and/or frame payload sizes based on actual or estimated signal to noise ratios (SNRs) of transmission links. Examples are provided for illustration purposes and are not to be construed as limiting the scope of the teachings of this specification, or the claims to follow.
  • FIG. 3 shows timing diagrams corresponding to examples of different connections between wireless devices, according to UWB specifications.
  • Each frame transaction includes an optional ready to send (RTS) frame/clear to send (CTS) frame exchange, a single frame, and an associated acknowledgement (ACK) frame, if requested by the ACK policy.
  • RTS ready to send
  • CTS clear to send
  • ACK acknowledgement
  • the payload in each MAC frame may consist of multiple trunks of six OFDM symbols, for example. Different rates, such as those indicated by Table 2A above, have different information bits N 1 in each trunk of six OFDM symbols, as shown in Table 2B:
  • the number of trunks of six OFDM symbols U 1J may be determined as follows, where function
  • the MAC payload can be transmitted at any rate supported by both the source device 210 (transmitter) and the reception device 220 (receiver). Other portions of the transaction, such as RTS, CTS, ACK, PHY and MAC headers, are transmitted at the lowest rate supported by the PHY layer. Therefore, throughput s( ⁇ j) for various rates and frame payload sizes may be determined as follows:
  • t over is the frame transaction time excluding the payload transmission time
  • / is the frame payload size in bits
  • t sym is the transmission time of one OFDM symbol
  • T 1 is the transmission rate in bits per second (bps).
  • t over may be fixed. Therefore, the relative protocol overhead becomes larger, as the frame payload size / becomes smaller. When choosing different rates, the protocol overhead must be taken into consideration.
  • the effective throughput S(T 1 J) may be determined as follows, where p r is the packet error rate: P 1 )
  • the packet error rate P 1 may be determined by the signal to noise ratio (SNR) and the payload size, for example.
  • SNR signal to noise ratio
  • the corresponding error rate of each may be denoted by p ⁇ ,i.
  • the packet error rate may then be determined as follows, where H 1 1 is the number of trunks of six OFDM symbols for transmission rate T 1 and payload size /.
  • p t accounts only for the error of the payload. It is assumed that the error rate for other portions of the frame transaction may be neglected because they are transmitted at the lowest PHY rate, as stated above. Thus, p ⁇ ,i may be determined given a rate T 1 and SNR. According to the above equation, the larger the payload size, the larger the packet error rate is. A transmission rate may be optimized by maximizing the throughout, discussed above. Optimizing the transmission rate is determined differently, depending on whether the frame payload size is fixed or adjustable.
  • the throughput s( ⁇ ,l) is determined by the following equation, discussed above, where the fixed payload size is indicated by / and the transmission rate is indicated by r ⁇ .
  • Rate r is the transmission rate corresponding to maximized throughput based on a fixed payload size, determined according to Equation (1):
  • the frame payload size and/or n t t can be adjusted, a higher throughput may be obtained, where the frame transaction transmits n t , trunks of six OFDM symbols.
  • the largest information bits or payload size / transmitted in the transaction is H 1 1 ⁇ N 1 , and therefore the throughput s may be determined by the following equation:
  • Link adaptation processes implemented by the source device 210 (and/or reception device 220) determine the optimal transmission rate, maximizing throughput according to the link quality, based on Equation (1) (e.g., when the frame payload size is fixed) or Equation (2) (e.g., when the frame payload size is adjustable).
  • Equation (1) the error rate of trunks of six OFDM symbols must be provided given a link quality in order to perform the link adaptation processes. This can be accomplished through estimations and/or simulations. Accordingly, an analysis of how to obtain accurate estimates of throughput and error rate of trunks of six OFDM symbols p ⁇ i through simulations is provided below.
  • Simulations may be conducted to estimate packet error rate p t given a packet length or payload size I 1 for each rate r u Basically, simulations are run for N p packets. If N e error packets are found, then the estimated packet error rate p lX ' is determined as follows:
  • the packet error rate for payload size I 2 isp l2 , which may be determined as follows:
  • the number of packets N p effectively determines the accuracy of the estimated p t and p 61 . Since the intent is to maximize throughput, an accurate estimate of the throughput is necessary.
  • the following lemma and theorem gives the number of packets N p :
  • « 1 " » gi ven P acket error rate/?,, u, and I- a confidence interval s(r t , /)(1 -u) ⁇ s(r t , I)' ⁇ s(r t , /)(1 + u) .
  • Theorem 2 For — > M 1 or p l+l ⁇ q t , s( ⁇ , l opt ⁇ ) ⁇ s( ⁇ , / max ) ⁇ s(r i+l , / max ) ⁇ s(r i+l , l opt ⁇ + ⁇ )
  • Eb error rate for interval ⁇ M is sufficient for rater, as indicated in the following
  • Simulations may be run for any allowed payload size, although this approach would require a significant amount of time.
  • simulations were run for one payload size and the packet error rates for other payload size were derived, as discussed above.
  • the following lemmas and theorem are provided to indicate how large estimation error is if throughput is calculated for any packet size based on the result for a given size:
  • N 6sym, ⁇ ,l* ⁇ ⁇ sym, i, I* approximation error e ( e U 1 -U 1 ) satisfies: (1) e ⁇ au r , ⁇ U 1 ; (2)
  • Theorem 3 illustrates that the change of u is independent of packet error rates and only decided by the change of number of trunks of six OFDM symbols.
  • the foregoing discussion addresses how to obtain accurate estimations of throughput based on simulation results of packet error rate.
  • the throughput accuracy is represented by the confidence interval and its probability.
  • Preliminary simulation results may be used to determine the lower bound.
  • the simulation was run for a small number of packets (setting of this number is discussed below) to obtain the SNR values SNR 1 , t (1 ⁇ i ⁇ 7) , at which the rate changes to maximize the throughput.
  • the lower bound for each rate is set as the obtained SNR value minus a constant C L , as follows:
  • the upper bound is the minimum value of SNR ⁇ t and SNR ⁇ t ' :
  • the turning point of SNR values SNR T l (l ⁇ i ⁇ 7) is calculated for rate changes according to the previously described throughput analysis to maximize throughput and determine the SNR intervals, e.g., [SNR 11 , SNR ⁇ 1 ](I ⁇ i ⁇ 7) .
  • N ' is set according to the estimated p t for each SNR value found in the first step and the simulations are run.
  • FIGs. 8A-8D show results of a sample simulation, in which the packet size was 1024 bytes.
  • FIGs. 8A-8D depict packet error rate, throughput, optimum packet size and optimum rate index, respectively.
  • the turning points of SNR values for rate changes at optimum size are indicated in FIG. 8D, and summarized in Table 3, below:
  • the corresponding optimum frame payload sizes (in bytes) for rate indexes 1 through 8 are shown in Table 4.
  • the asterisk (*) indicates the rate index and payload size that are the optimum at each SNR value, thus maximizing throughput.
  • the illustrative optimum frame payload sizes and rates shown in Table 4 coincide with the simulation results depicted in FIGs. 8C and 8D, respectively.
  • Table 5 when the transmitting device does not want to or is unable to change the frame payload size, Table 5 may be used instead of Table 4 to obtain the optimum rate for a given SNR, based on the fixed frame payload size. More particularly, Table 5 provides the turning points (dB) for rate changes at different packet sizes.
  • SNR ⁇ ,o may be set to equal - ⁇ and SNR ⁇ .8 is set to equal + ⁇ .
  • SNR 11 ⁇ SNR ⁇ SNR 1 ⁇ 1+1 , where (0 ⁇ i ⁇ 7)
  • the optimum rate index is i.
  • the link may then be adapted accordingly.
  • the link adaptation process runs once in the beacon period of each super frame, for example.
  • the link adaptation process is robust, and reduces complexity and implementation cost.
  • Each device e.g., source device 210 and reception device 220
  • maintains a neighbor table which records the link quality information for corresponding links between the device and each neighboring device.
  • the neighbor table may be arranged in columns and rows, such that each row corresponds to a different neighbor device.
  • the neighbor devices may be tracked, for example, based on the corresponding MAC address or other identifying information contained in beacon frames.
  • the link adaptation process may include a basic link adaptation process, discussed with respect to FIG. 4, and an enhanced link adaptation process, discussed with respect to FIGs. 5-7.
  • the basic link adaptation process enables a transmitting device to adapt its transmission rate to measured SNR of a received beacon frame. No additional information is required to be exchanged between the transmitter (e.g., source device 210) and the receiver (e.g., reception device 220).
  • the source device 210 utilizes the physical layer information of an incoming beacon frame, including the link quality indication (LQI) or measured SNR, to obtain the link quality of the reverse link, which is the transmission link from the reception device 220 to the source device 210.
  • the source device 210 then regards the reverse link quality information as that of its forward link, which is the transmission link from the source device 210 to the reception device 220. Accordingly, the source device chooses the best rate and frame payload size based on this link quality information.
  • LQI link quality indication
  • the source device chooses the best rate and frame payload size based
  • FIG. 4 is a flow diagram showing the basic link adaptation process, according to one embodiment of the invention.
  • the depicted process may be a program stored in the memory 218 and executed by the processor 216 of the source device 210, for example.
  • the source device 210 receives an incoming frame, for example, from the reception device 220 at S410. It is assumed for purposes of explanation that the reception device 220 is a neighboring device, so that the source device 210 already has a neighbor table (e.g., Table 6, below) corresponding to the reception device 220.
  • the received information may include a PHY-RX- START. confirm signal, for example, which includes information such as data rate, length, received signal strength indication (RSSI), and the like.
  • RSSI received signal strength indication
  • the source device 210 analyzes the information in the incoming frame, such as RXVECTOR, at S412. Based on the analysis, the source device 210 determines whether the incoming frame is a beacon frame at S414. When the incoming frame is not a beacon frame (S414: NO), the process ends, and the source device 210 awaits another frame. When the incoming frame is a beacon frame (S414: YES), the source device 210 obtains the SNR of the reverse link, for example, from the link quality indication (LQI) field of the beacon frame at S416 and obtains the address of the reception device 220, for example, from the MAC Header field, at S418. The source device 210 is thus able to identify the appropriate set of entries in neighbor table, Table 6, based on the address.
  • LQI link quality indication
  • the source device 210 obtains the optimum rate corresponding to the SNR of the reverse link.
  • the optimum rate may be obtained from Table 4 or Table 5, both of which may be stored in the memory 218 of the source device 210.
  • Table 4 is consulted. For example, if the SNR of the reverse link is 3 dB, a rate index of 4 (e.g., corresponding to 160.0 Mbps) and a payload size of 2660 bytes are selected for subsequent transmission.
  • the optimized combinations of rate and payload size may be determined as discussed above with respect to the simulation results, e.g., as shown in FIGs. 8C and 8D. If the SNR of the reverse link falls between two values listed in Table 4, the lower SNR entry may be used, or the SNR may be rounded to the nearest SNR entry.
  • the source device 210 accesses Table 5 instead of Table 4 to obtain the optimum rate. For example, if the frame payload size is fixed at 4095 bytes, then the optimum rate is determined to be the rate corresponding to the next SNR higher than the SNR of the reverse link (indicating the next turning point) recorded in Table 5. Therefore, if the SNR of the reverse link is 6 dB, a rate of 200.0 Mbps (corresponding to rate index 5) is selected for subsequent transmission, because column SNRr, j indicates the highest rate (corresponding to 6.8 dB for a 4095 byte payload) at which a 6 dB signal is reliably transmitted. In other words, referring to Table 5, the 200.0
  • Mbps rate is the optimum rate for a 4095 byte payload when the measured SNR is greater than 5.4 dB and less than or equal to 6.8 dB. Once the SNR exceeds 6.8 dB, the optimum rate increases to 320.0 Mbps (corresponding to rate index 6) for 4095 byte frame payload.
  • the source device 210 updates the entries in its (basic) neighbor table corresponding to the reception device 220, accordingly, at S422.
  • An example of a neighbor table for storing entries according to the basic link adaptation process of FIG. 4 is shown in Table 6, below: TABLE 6
  • the reception device 220 is identified by its MAC address, which is previously stored in the first column of Table 6. If this is the first beacon frame received from the reception device 220, a new row may be entered in Table 6 corresponding to the reception device 220.
  • the measured SNR is entered in the second column of Table 6, which is the SNR of the reverse link of the frame received by the source device 210 from the reception device 220, as discussed above.
  • the optimum rate as determined by referencing Table 4 or Table 5 in S420, is entered in the third column, and the optimum frame payload size, as determined by referencing Table 4 or which has been fixed to a particular value, is entered in the fourth column of Table 6. To the extent that the frame payload size is fixed, the optimum size entry may remain unchanged throughout communications with the reception device 220.
  • the source device 210 may transmit frames to the reception device 220 on its forward link, using the optimum rate and payload size retrieved from Table 6, which had been previously entered based on the reverse link information, according to the process depicted in FIG. 4.
  • Table 6 may be updated, enabling the source device 210 to adjust its transmissions in accordance with current network conditions.
  • the reception device 220 likewise executes the link adaptation process of FIG. 4, and thus maintains its own version of Table 6, which has a set of entries corresponding to transmissions to the source device 210 based on reverse link information received in beacon frames from the source device 210.
  • a transmitting device may alternatively adapt its transmission rate to actual SNR of its forward link based on previous transmission(s) using the enhanced link adaptation process.
  • the link quality of the reverse link may not always exactly represent that of the forward link over which a data frame is transmitted for a number of reasons. For example, interference and hence SNR are location sensitive. Therefore, obtaining link quality of the forward link itself typically achieves better performance of link adaptation.
  • the WiMedia MAC standard defines a link feedback IE, which may be used to perform this task.
  • the transmitting device e.g., source device 210 simply requests a link feedback IE according to the link quality information in Table 6, inserts the IE in outgoing beacon frame(s), and receives and analyzes a responsive Link Feedback IE constructed by the receiving device (e.g., reception device 220).
  • FIG. 5 is a flow diagram showing an example of a receiving device receiving an IE in a beacon frame transmitted by a transmitting source device, enabling the enhanced link adaptation process, according to an embodiment of the invention.
  • the depicted process may be a program stored in the memory 228 and executed by the processor 226 of the reception device 220, for example.
  • the reception device 220 receives an incoming beacon frame from the source device 210.
  • the beacon includes an IE for providing link feedback in subsequent beacon frames transmitted from the reception device 220.
  • the reception device 220 identifies the source device 210, for example, based on a MAC address in the received beacon frame, at S512.
  • the reception device 220 determines whether its Table 4 includes a valid entry for the source device 210.
  • the reception device 220 transmits its beacon without regard for the IE of the beacon received from the source device 210.
  • the reception device 220 constructs a link feedback IE according to an optimum rate at S516. For example, the reception device 220 is able to obtain information on the reverse link (i.e., from the source device 210 to the reception device 220), such as the SNR of the reverse link LQI field of the received frame. This information may be used to construct the link feedback IE, which is inserted in a subsequent beacon frame at S518 and transmitted at S520.
  • FIG. 6 is a flow diagram showing the enhanced link adaptation process, according to an illustrative embodiment, performed by the source device 210 upon receiving the beacon frame, containing the link feedback IE, transmitted from the reception device 220 at S520 of FIG. 5.
  • the depicted process may be a program stored in the memory 218 and executed by the processor 216 of the source device 210, for example.
  • the source device 210 receives an incoming frame, for example, from the reception device 220 at S610 of FIG. 6.
  • the received information may include a PHY-RX-START. confirm signal, for example, which includes information such as data rate, length, RSSI and the like.
  • the source device 210 analyzes the information in the incoming frame at S612.
  • the source device 210 determines whether the incoming frame is a beacon frame at S614. When the incoming frame is not a beacon frame (S614: NO), the process ends, and the source device 210 awaits another frame. When the incoming frame is a beacon frame (S614: YES), the source device 210 determines whether the incoming beacon frame includes a link feedback IE at S616. When the incoming beacon frame does not include the link feedback IE (S616: NO), the process ends, and the source device 210 awaits another frame. Alternatively, when there is no link feedback IE, which prevents implementation of the enhanced link adaptation process, the source device 210 may proceed with the basic link adaptation process using only reverse link quality information, as discussed with respect to FIG. 4.
  • the source device 210 obtains the feedback rate index and/or the corresponding feedback rate from the link feedback IE at S618, which is determined by the reception device 220 as the measured SNR of its reverse link (which coincides with the SNR of the previous forward link of the source device 210).
  • the address of the reception device 220 is obtained at S620, for example, from the MAC Header field of the beacon frame.
  • the source device 210 updates the entries in its (enhanced) neighbor table corresponding to the reception device 220.
  • An example of a neighbor table for storing entries according to the enhanced link adaptation process of FIG. 6 is shown in Table 7, below:
  • the reception device 220 may be identified by its MAC address, which is previously stored in the first column of Table 7.
  • the feedback rate retrieved from the link feedback IE (or corresponding to the feedback rate index retrieved from the link feedback IE) is entered in the second column of Table 7, which is based on the SNR of the reverse link of the reception device 220.
  • the source device 210 calls a link feedback process in order to determine the optimum rate and the optimum payload size (when not fixed) to be entered in the third and forth columns of Table 7, respectively.
  • the link feedback process is explained below with reference to FIG. 7.
  • the source device 210 updates the entries in its (enhanced) neighbor table, Table 7, corresponding to the reception device 220 accordingly at S626. Subsequent transmission(s) are performed using the updated entries.
  • FIG. 7 is a flow diagram showing the link feedback process called in S624 of FIG. 6, according to an embodiment of the invention.
  • the depicted process may be stored as a program in the memory 218 and executed by the processor 216 of the source device 210, for example.
  • initial SNR values corresponding to rate indexes are set to indicate turning points for rate changes at optimum frame sizes, as shown in Table 3, with respect to SNRr, t , where 1 ⁇ i ⁇ l.
  • SNRr, o is set to - ⁇
  • SNRr, s is set to +oo. It is understood that these initial SNR values need not be set each time the link feedback process is performed or executed. Rather, the initial values may be set once upon initiating the source device 210, or each time the source device 210 is powered on, etc., and stored, for example, in the memory 218.
  • the measured SNR corresponding to the address of the reception device 220 is obtained from Table 6, which is the reverse link SNR (indicated as SNR*) between source device 210 and reception device 220.
  • the feedback rate from the link feedback IE corresponding to the address of the reception device 220 is obtained from Table 7.
  • the measured SNR* is compared to the feedback rates in S716.
  • the optimum rate (or corresponding optimum rate index) and the frame payload size for transmissions to the reception device 220 are determined to be the same as those provided in Table 6 at S718.
  • the process then returns to S626 of FIG. 6, where Table 7 is modified by effectively copying the optimum rate and the frame payload size from Table 6 to Table 7.
  • SNR* is less than SNRr, z or greater than or equal to SNRy 2+ ; (S716: NO), the SNR is set to the following at S720:
  • the source device 210 obtains the optimum rate (or corresponding optimum rate index) corresponding to the calculated SNR.
  • the optimum rate may be obtained from Table 4 or Table 5, each of which may be stored in the memory 218 of the source device 210.
  • Table 4 is consulted.
  • the source device 210 accesses Table 5 instead of Table 4 to obtain the optimum rate index.
  • the process then returns to S626 of FIG. 6, where Table 7 is modified by entering the rate and frame payload size corresponding to the reception device 220 into the third and fourth columns of Table 7, respectively.
  • the optimum size entry may remain unchanged throughout communications with the reception device 220.
  • the measured SNR* obtained from Table 6 at S712 is 3 dB and the rate index obtained from Table 7 at S714 is rate index 3 (corresponding to 106.7 Mbps)
  • SNR* (3 dB) is compared to SNR 7 -,* (2.8 dB) and SNR ⁇ (5.4 dB) at S716. Because 2.8 dB ⁇ 3 dB ⁇ 5.4 dB, the optimum rate index and frame payload size of Table 7 is set to equal the optimum rate index and frame payload size of Table 6 with respect to the reception device 220.
  • the optimum rate index is rate 4 and the optimum frame payload size is 4095 bytes.
  • Table 7 is updated with these values with respect to the reception device 220, accordingly.
  • the source device 210 may transmit frames to the reception device 220 on its forward link, using the optimum rate and payload size retrieved from Table 7.
  • Table 7 may be updated, enabling the source device 210 to adjust its transmissions in accordance with current network conditions.
  • the reception device 220 likewise executes the enhanced link adaptation process of FIGs. 6 and 7, and thus maintains its own version of Table 7, which has a set of entries corresponding to transmissions to the source device 210 based on link feedback IEs received in beacon frames from the source device 210.
  • neighboring wireless devices such as representative wireless devices 210 and 220 are able to communicate with one another over links adapted for current network conditions based on reverse link information and/or link feedback IEs exchanged in beacon frames. Examples are provided herein for illustration purposes and are not to be construed as limiting the scope of the teachings of this specification, or the claims to follow.

Abstract

L'invention concerne un procédé et un appareil qui améliorent le débit d'une liaison de communications aller entre un dispositif source et un dispositif récepteur. Le procédé comprend la réception d'une trame balise provenant du dispositif récepteur, la détermination d'une qualité de liaison associée à la liaison de communications aller sur la base d'informations obtenues à partir de la trame balise reçue, et la détermination d'un débit de transmission optimal sur la base de l'intensité du signal. Un signal est transmis du dispositif source au dispositif récepteur en utilisant le débit de transmission optimal.
PCT/IB2008/052193 2007-06-05 2008-06-04 Appareil et procédé pour effectuer une adaptation de liaison dans des systèmes sans fil WO2008149304A2 (fr)

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WO2010073143A2 (fr) * 2008-12-24 2010-07-01 Koninklijke Philips Electronics, N.V. Techniques pour réaliser une adaptation de liaison efficace dans des réseaux personnels sans fil
WO2010073143A3 (fr) * 2008-12-24 2010-08-19 Koninklijke Philips Electronics, N.V. Techniques pour réaliser une adaptation de liaison efficace dans des réseaux personnels sans fil
CN102265547A (zh) * 2008-12-24 2011-11-30 皇家飞利浦电子股份有限公司 在无线个人网络中执行高效的链路适配的技术
JP2012514368A (ja) * 2008-12-24 2012-06-21 コーニンクレッカ フィリップス エレクトロニクス エヌ ヴィ 無線パーソナルネットワークにおける効率的なリンク適合を実行するための技術
TWI487422B (zh) * 2008-12-24 2015-06-01 Koninkl Philips Electronics Nv 在無線個人網路中執行有效率的鏈路調適之技術
KR101531374B1 (ko) * 2008-12-24 2015-06-25 코닌클리케 필립스 엔.브이. 무선 개인 네트워크들 내에서 효율적인 링크 적응을 수행하기 위한 기술들
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CN106850130A (zh) * 2008-12-24 2017-06-13 皇家飞利浦电子股份有限公司 在无线个人网络中执行高效的链路适配的技术

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