WO2007096809A1 - Réseau de communication - Google Patents

Réseau de communication Download PDF

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Publication number
WO2007096809A1
WO2007096809A1 PCT/IB2007/050481 IB2007050481W WO2007096809A1 WO 2007096809 A1 WO2007096809 A1 WO 2007096809A1 IB 2007050481 W IB2007050481 W IB 2007050481W WO 2007096809 A1 WO2007096809 A1 WO 2007096809A1
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WO
WIPO (PCT)
Prior art keywords
frequency
link
network
terminal
data
Prior art date
Application number
PCT/IB2007/050481
Other languages
English (en)
Inventor
Franciscus M. J. Willems
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2007096809A1 publication Critical patent/WO2007096809A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
    • H04W16/02—Resource partitioning among network components, e.g. reuse partitioning
    • H04W16/10—Dynamic resource partitioning
    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria

Definitions

  • the invention relates to a communication network comprising two or more transmitter-receiver pairs, and in particular relates to a method for increasing the robustness of the communication network and an apparatus for use in such a network.
  • a transmitting terminal transmits data to a receiving terminal using a certain frequency or a set of frequencies.
  • the transmitted signal reaches the receiving terminal through several different paths by reflecting off different obstacles, with the result that the receiving terminal receives several 'echoes' of the signal. This is called multipath reception.
  • Figure 1 shows a communication network in which two terminals 2, labeled Tl and T2, are transmitting data to respective terminals 2, labeled Rl and R2, in a closed environment, such as a room 4.
  • the room 4 is richly scattering, so the signal from each transmitting terminal 2 takes several paths to the respective receiving terminal 2, some of which are indicated by the dotted arrows.
  • the first communication link (transmitting terminal Tl and receiving terminal Rl) is operating at a frequency /i and the second communication link (transmitting terminal T2 and receiving terminal R2) is operating at frequency /j-
  • the network is defined to be out if one or more links are out.
  • the network outage probability is denoted P N .
  • a method for increasing the robustness of a communication network comprising a plurality of links, each link using a respective frequency for transmitting data between a respective pair of terminals; wherein, in the event that at least a first link is unable to reliably transmit data between its respective pair of terminals, the method comprising exchanging the frequencies used for transmission of data by at least two of the links, such that the first link transmits data at a frequency previously used by another link in the network.
  • a terminal for use in a communication link in a communication network comprising means for transmitting data to a receiving terminal at a first frequency; means for determining whether the data has been successfully received by the receiving terminal; and means for exchanging the first frequency with a frequency in use by another link in the network, in the event that it is determined that data has not been reliably received by the receiving terminal.
  • a communication network comprising at least two links, each link comprising a respective pair of terminals, each terminal being as described above.
  • Fig. 1 shows a communication network with two links
  • Fig. 2 is a block diagram of a terminal in accordance with the invention
  • Fig. 3 is a flow chart illustrating the steps in the method according to the invention
  • Fig. 4 is a signaling diagram illustrating a frequency-swapping protocol in accordance with an embodiment of the invention
  • Fig. 5 is a signaling diagram illustrating a frequency-swapping protocol in accordance with an alternative embodiment of the invention
  • Fig. 6 is a flow chart illustrating the steps in the method according to an alternative embodiment of the invention.
  • Fig. 7 is a flow chart showing the steps in a method for determining the optimum frequency distribution in accordance with the embodiment of the invention shown in Fig. 6;
  • Figs. 8a to 8d show the network outage capacity in accordance with the invention in networks with one, two, three and four links respectively;
  • Fig. 9 shows channel coefficients for four transmitter-receivers pairs; and Fig. 10 shows the network outage capacity in accordance with the invention in a network with four links that use multi-carrier modulation.
  • the network outage P N ' is p ⁇ - p '+p '_p ' p ⁇ where Pi' is the outage probability of the first link, now at frequency f 2 , and P 2 ' is the outage probability of the second link, now at frequency fi.
  • the new communication links are assumed to be independent of each other and of the links at the original frequencies. This assumption is reasonable if the room 4 is not too small and the frequencies fi and f 2 are not too close together.
  • the network outage probability is approximately the sum of the link outage probabilities.
  • the two transmitter-receiver links are provided with a functionality to allow them to swap transmission frequencies in the event that one or both of the transmission links are unable to successfully convey data, then the resultant network outage probability is
  • At least two communication links in a communication network are provided with functionality to allow the links to exchange the frequency used for transmission with a frequency previously used by another link in the network, in order to improve the robustness of the network.
  • the terms “swap” and “exchange” as used herein are considered to have the same meaning, and are both intended to cover the situation in which two links in the network change frequencies such that the first link is using the frequency previously used by the second link and the second link is using the frequency previously used by the first link, and also the situation in which three or more links in the network change frequencies such that the frequency allocation between the links is changed or permuted (for example the first link could use the frequency previously used by the second link, the second link could use the frequency previously used by the third link and the third link could use the frequency previously used by the first link).
  • FIG. 2 shows a terminal 2 in accordance with the invention.
  • the terminal 2 comprises transceiver circuitry 6 for converting data into an appropriate format for transmission via an antenna 8 and for converting data received via antenna 8 into a format suitable for processing, a controller 10 connected to the transceiver circuitry 6 for controlling the operation of the terminal 2, a memory 12 connected to the controller 10 and a user interface 14 connected to the controller 10 for receiving inputs from, and providing outputs to, a user of the terminal 2.
  • FIG. 3 is a flow chart illustrating the method carried out by one of the terminals 2 (e.g. Tl) in a link of the communication network in accordance with one embodiment of the invention.
  • the controller 10 of the transmitting terminal Tl selects a frequency from the available frequency band and establishes a communication link at that frequency between the transmitting terminal Tl and the receiving terminal Rl using the transceiver circuitry 6.
  • the link may use any communication protocol known in the art, and the link is established using any methods appropriate to the protocol being used.
  • the controller 10 checks that the frequency is not in use by any other communication link in the network, so that direct interference with another link is avoided. Any conventional method for selecting a frequency for transmission can be used by the terminal Tl .
  • the protocol in use in the network is such that each link uses a single frequency for transmission.
  • the transmitting terminal Tl transmits data over the link at the selected frequency.
  • the data to be transmitted may be divided into packets or may be transmitted as a continuous stream, depending on the communication protocol being used.
  • the receiving terminal Rl When data is successfully received by the receiving terminal Rl (i.e. it is received without any errors or with any number of errors that can be corrected by an error correcting code used in the transmission), the receiving terminal Rl issues a positive acknowledgement to the transmitting terminal Tl in step 105. If data is not received successfully by the receiving terminal Rl (i.e. it is received with errors or errors that cannot be corrected by an error correcting code), the receiving terminal Rl issues a negative acknowledgement to the transmitting terminal Tl in step 105.
  • step 103 If the data transmission was successful, the process returns to step 103 and further data is transmitted to the receiving terminal Rl using the selected frequency.
  • step 107 a request to swap the selected transmission frequency is sent by the transmitting terminal Tl to other terminals (e.g. T2) in the communication network.
  • the request may be sent at the frequency used for transmission by the link, in which case each terminal in the network must continuously or periodically monitor all available frequencies used in the network for request messages.
  • the request must be sent at a lower data rate than that used previously to transmit the data in order for the request to stand a better chance of being received by the other terminals.
  • the terminals send the requests over a dedicated control link which uses a certain reserved frequency, or any other link having high robustness.
  • the transmitting terminal Tl receives a message from a terminal
  • this message can be sent at the frequency used for transmission by terminal T2 in the other link in the network, or alternatively it can be sent over a dedicated control link using a reserved frequency.
  • the terminal Tl exchanges its transmission frequency for the frequency of the other link in the network indicated in the message received in step 109.
  • Terminal T2 exchanges its transmission frequency for the frequency previously used by transmitting terminal Tl.
  • terminal Tl begins transmitting data to receiving terminal Rl using the new frequency. The process then returns to step 105 where it is determined whether or not the data transmission was successful.
  • Figure 4 is a signaling diagram illustrating a frequency-swapping protocol in accordance with an embodiment of the invention.
  • link 1 comprising terminals Tl and Rl
  • link 2 comprising terminals T2 and R2.
  • data is being transmitted from the T terminals to the R terminals, although a person skilled in the art will appreciate that the invention is equally applicable to links in which there is transmission of data in the opposite or both directions.
  • step 201 communication link 1 is established between Tl and Rl at a frequency fi.
  • Transmission of data begins in step 203 as Tl transmits a packet of data to Rl over link 1.
  • step 205 the data is received successfully by Rl, and a positive acknowledgement (ack(yes)) is sent to Tl.
  • ack(yes) a positive acknowledgement
  • the invention is described herein as relating to the transmission of packets of data, and to the transmission of acknowledgements when packets have been received successfully, it will be appreciated by a person skilled in the art that the invention is applicable to other types of network in which data is not divided into packets for transmission and/or to networks in which successful receipt of data by Rl is determined by means other than sending a positive acknowledgement message to the transmitter.
  • step 301 communication link 2 is established between T2 and R2 at a frequency f 2 .
  • link 2 is shown as being established at the same time as link 1, it will be appreciated that link 2 may be established before or after link 1.
  • Transmission of data over link 2 begins in step 303 as T2 transmits a packet of data to R2.
  • step 305 R2 sends a positive acknowledgment signal (ack(yes)) to T2 to indicate that the data packet has been successfully received.
  • ack(yes) positive acknowledgment signal
  • Tl sends a data packet to Rl (step 207) and Rl sends a negative acknowledgement (ack(no)) to Tl (step 209).
  • ack(no) a negative acknowledgement
  • terminal Tl Upon receiving the negative acknowledgement message, terminal Tl sends a "request to swap frequency fi" message to terminals in other links in the network.
  • This message indicates to other terminals in the network that Tl wishes to swap frequency fi for another available frequency.
  • this request may be sent at frequency fi (possibly at a lower data rate than that used to transmit the data packets now that the link is unreliable) if each terminal in the network monitors other frequencies for request messages, or preferably, the message can be sent at a dedicated control frequency.
  • T2 sends an "okay to swap frequency f 2 " message to Tl. This message indicates to terminal Tl that terminal T2 is willing to swap frequency f 2 for frequency fi.
  • Each transmitting terminal Tl and T2 then notifies their respective receiving terminal Rl and R2 of their new frequencies in steps 213 and 313.
  • step 215 the terminals in link 1 switch to using the new frequency f 2
  • step 315 the terminals in link 2 switch to using the new frequency fi.
  • Figure 5 is a signaling diagram illustrating a frequency-swapping protocol in accordance with an alternative embodiment of the invention.
  • link 1 comprising terminals Tl and Rl
  • link 2 comprising terminals T2 and R2.
  • data is being transmitted from the T terminals to the R terminals, although a person skilled in the art will appreciate that the invention is equally applicable to links in which there is transmission of data in the opposite or both directions.
  • steps 201 to 211 in link 1 and steps 301 to 309 are as described above in relation to Figure 4.
  • terminal Tl has sent a "request to swap frequency ft" message, which is received by terminal T2 in link 2.
  • Terminal T2 stores the request message in its memory 12 and continues to transmit data packets to terminal R2 in step 351.
  • Terminal T2 continues transmitting data packets to R2 and receiving acknowledgements until a packet is not successfully received by the receiving terminal R2 (steps 353, 355 and 357).
  • terminal T2 Upon receipt of the negative acknowledgement from R2 (step 357), terminal T2 retrieves the "request to swap frequency ft" message from memory 12 and sends an "okay to swap frequency f 2 " message to terminal Tl in step 359.
  • Each transmitting terminal Tl and T2 then notifies their respective receiving terminal Rl and R2 of their new frequencies in steps 251 and 361.
  • step 253 the terminals in link 1 switch to using the new frequency f 2
  • step 363 the terminals in link 2 switch to using the new frequency ft.
  • Transmission of data in each link starts in steps 255 and 365 respectively, followed by respective acknowledgements in steps 257 and 367.
  • Figure 6 is a flow chart illustrating the method carried out by one of the terminals 2 (e.g. Tl) in a link of the communication network in accordance with an alternative embodiment of the invention.
  • Steps 101 to 107 are as described above with reference to Figure 3.
  • another link e.g. the link comprising terminal T2
  • the links in the network instead of another link (e.g. the link comprising terminal T2) directly swapping its frequency with that of the link containing terminal Tl so that Tl uses the frequency previously used by T2 and T2 uses the frequency previously used by Tl, some or all of the links in the network determine an optimum frequency distribution (or a frequency distribution that is better than the current frequency distribution), and then reallocate the relevant frequencies between the links to achieve this optimum (or better than the current) frequency distribution.
  • the terminals determine how the frequencies available in the network could be reallocated in order for the network to have the lowest possible outage probability (in the optimum case) or a lower outage probability (in the case where the frequency distribution is better than the present frequency distribution).
  • the invention will be described with reference to determining and achieving the optimum frequency distribution, although a person skilled in the art will appreciate that the methods described are adaptable to determining a suboptimal frequency distribution that is better than the present frequency distribution.
  • terminal Tl determines an optimum frequency allocation between the available links in the network.
  • the available links in the network are the links that are able to participate in the frequency exchange process. In the following, it is assumed that every link in the network is able to participate, although it will be appreciated that it is possible that only a subset of the links in the network may be available at a particular time.
  • Figure 7 illustrates one method of determining an optimum frequency allocation between the available links in accordance with the invention.
  • a terminal starts the process to determine an optimum frequency allocation by measuring one or more signal characteristics (for example signal strength or a signal-to-noise ratio) on each of the frequencies used by the available links in the network (step 151). That is, if there are N available links in the network with a particular link n using a frequency f n (where 1 ⁇ n ⁇ N), terminal Tl cycles through each of the frequencies f n and measures one or more signal characteristics at each of these frequencies. The measured signal characteristics are stored in the memory 12 of the terminal Tl.
  • the terminals in each of available links in the network perform the same procedure as terminal Tl as set out in Figure 7.
  • each terminal measures a different frequency during a particular time period. For example, as terminal Tl is measuring the one or more signal characteristics at frequency f ⁇ , a terminal T2 is measuring the signal characteristics at frequency f 2 , a terminal T3 is measuring the signal characteristics at frequency f3, and so on. Once the measurements at these frequencies have been carried out, each terminal switches to the next frequency and measures the signal characteristics at that frequency. For example, terminal Tl can then measure the signal characteristics at frequency f 2 , while terminal T2 measures the signal characteristics at frequency f 3 , and so on until each of the terminals has stored measurements for each of the frequencies available in the network.
  • Each terminal then transmits its respective set of measured characteristics to all of the terminals in the available links in the network (step 153). This transmission may be carried out in turn by each terminal over a dedicated control channel or at any other frequency available in the network. On receipt of the measurements from each of the terminals in the other links in the network (step 155), the results are stored. Thus, each terminal now has a set of signal characteristics for each of the available terminals in the network at each of the available frequencies.
  • Each terminal then executes an algorithm on the stored results to determine the optimum frequency distribution (step 157).
  • the algorithm will determine which particular allocation of frequencies to the links will result in the lowest network outage probability. It will be appreciated that it will not always be possible for each link to use the frequency that provided it with the best signal characteristics, as there is a good chance that that frequency may have the best characteristics for more than one link. Algorithms that are suitable for determining the lowest network outage probability from a set of signal characteristics are known in the art, and will not be described further herein.
  • step 123 the frequencies are exchanged as necessary between the available links in accordance with the determined allocation.
  • a message can be sent from a terminal in each link that is changing its frequency to the link to which that frequency has been reallocated, indicating that it is ready to release the frequency.
  • the links that are changing frequency can all change in a given time period, without transmitting messages beforehand.
  • Figure 8 shows the network outage capacity under Rayleigh fading in bits per transmitted symbol as a function of the signal-to-noise ratio (SNR) for: (a) a single link network; (b) a two-link network in which the links can swap frequencies; (c) a three-link network in which the links can swap frequencies; (d) a four-link network in which the links can swap frequencies.
  • SNR signal-to-noise ratio
  • each communication link may have use of a set of frequencies for transmitting data.
  • the way in which the links use the set of frequencies is determined by the communication protocol being used in the network. If a link is not able to reliably transmit data, one or more of the frequencies in the set can be exchanged with one or more of the frequencies used by another link in the network as appropriate. This allows the sets of frequencies used by all transmitter-receiver pairs in the network to be optimized.
  • a random vector of 64 channel coefficients can be generated as shown in Figure 9.
  • One of the four frequency bands out of this spatial link can be chosen for the communication link for this transmitter-receiver pair. Note, however that a certain frequency band can only be chosen once.
  • the four random channel coefficients determine the 16 relevant capacities and it is possible to determine the allocation that yields the largest minimal communication- link capacity. Generating many quadruples of channel coefficient vectors yields the graph in Figure 10.
  • Figure 10 shows that to achieve a minimal link capacity of 5 bits with a link outage probability of 1%, a signal-to-noise ratio of 28.5 dB is needed in the no-swap case and 21.5 dB when frequency swapping is allowed. Therefore, the gain in the network according to the invention is approximately 7 dB. A larger delay spread will result in a better outage behavior, and the gain from swapping will become smaller. On the other hand a smaller delay spread will result in more correlation between the four frequency bands and this will lead to a smaller swap gain as well. Additional transmitter-receiver pairs will increase the swap gain since the number of effective uncorrelated pairs will also increase. In another embodiment of the invention, the robustness of the network can be further improved by providing the network with one or more escape frequencies.
  • the escape frequency is a frequency or frequencies that are held in reserve by the network and not initially used by any links in the network. If the reliability of a link deteriorates, and a frequency swap, if carried out, is unsuccessful in restoring the reliability of the data transmission, then the link can switch to using the escape frequency for data transmission.
  • a transmitting terminal 2 in the network can store details of the escape frequency in its memory 12.
  • the controller 10 of the terminal 2 selects whether to transmit a request to swap frequency message to other terminals in the network as described above, or whether to switch transmission to the escape frequency.
  • the controller 10 can select the escape frequency for use if the terminal 2 does not receive a response to a request to swap frequency message within a given time limit.
  • the controller 10 can select the escape frequency for use if a frequency swap has been performed and the link is still unreliable, or if a frequency swap has been performed, and the link becomes unreliable within a predetermined period of the swap being performed.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Data Exchanges In Wide-Area Networks (AREA)

Abstract

L'invention concerne un procédé servant à accroître la robustesse d'un réseau de communication. Ce réseau comprend plusieurs liaisons qui utilisent chacune une fréquence respective pour transmettre des données entre une paire de terminaux. Au cas où au moins une première liaison ne peut transmettre fiablement des données entre sa paire respective de terminaux, le procédé consiste à échanger les fréquences utilisées pour la transmission de données par au moins deux liaisons, afin que la première liaison transmette des données à une fréquence utilisée antérieurement par une autre liaison du réseau.
PCT/IB2007/050481 2006-02-20 2007-02-14 Réseau de communication WO2007096809A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP06110148.1 2006-02-20
EP06110148 2006-02-20

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WO2007096809A1 true WO2007096809A1 (fr) 2007-08-30

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PCT/IB2007/050481 WO2007096809A1 (fr) 2006-02-20 2007-02-14 Réseau de communication

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000074415A1 (fr) * 1999-05-28 2000-12-07 Ericsson Inc. Attribution automatique de frequences pour systemes de bureaux sans fil partageant le spectre avec des systemes publics
WO2002011455A2 (fr) * 2000-08-02 2002-02-07 Metric Systems Corporation Procede et appareil pour le reglage adaptatif de canaux de frequence dans un systeme de gestion de reseau multipoint sans fil

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000074415A1 (fr) * 1999-05-28 2000-12-07 Ericsson Inc. Attribution automatique de frequences pour systemes de bureaux sans fil partageant le spectre avec des systemes publics
WO2002011455A2 (fr) * 2000-08-02 2002-02-07 Metric Systems Corporation Procede et appareil pour le reglage adaptatif de canaux de frequence dans un systeme de gestion de reseau multipoint sans fil

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