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WO2010028687A1 - Réseau de communication ofdm amélioré - Google Patents

Réseau de communication ofdm amélioré Download PDF

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Publication number
WO2010028687A1
WO2010028687A1 PCT/EP2008/062022 EP2008062022W WO2010028687A1 WO 2010028687 A1 WO2010028687 A1 WO 2010028687A1 EP 2008062022 W EP2008062022 W EP 2008062022W WO 2010028687 A1 WO2010028687 A1 WO 2010028687A1
Authority
WO
WIPO (PCT)
Prior art keywords
prefix
node
relay node
data symbol
relay
Prior art date
Legal status (The legal status 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 status listed.)
Ceased
Application number
PCT/EP2008/062022
Other languages
English (en)
Inventor
Haifeng Wang
Bin Zhou
Jing Xu
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nokia Solutions and Networks Oy
Original Assignee
Nokia Siemens Networks Oy
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 Nokia Siemens Networks Oy filed Critical Nokia Siemens Networks Oy
Priority to PCT/EP2008/062022 priority Critical patent/WO2010028687A1/fr
Publication of WO2010028687A1 publication Critical patent/WO2010028687A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • H04L27/2605—Symbol extensions, e.g. Zero Tail, Unique Word [UW]
    • H04L27/2607—Cyclic extensions
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
    • H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
    • H04B7/2603—Arrangements for wireless physical layer control
    • H04B7/2606—Arrangements for base station coverage control, e.g. by using relays in tunnels

Definitions

  • the invention relates to a wireless communication network applying relays in an orthogonal frequency division multiple access (OFDMA) transmission.
  • OFDMA orthogonal frequency division multiple access
  • FIG. 1 illustrates a cellular communica- tion system applying relay nodes.
  • a relay node 106 providing coverage to a cell 104 is placed at the edge of a cell 100 covered by a central node 102 in order to extend the coverage area of the central node 102 and to increase the capacity/throughput at the cell-edge.
  • the relay node 106 may be applied to reduce the average radio transmission power of user equipment 110 attached to the relay node 106.
  • An amplify-and-forward protocol is a simple and promising relaying scheme.
  • the amplify-and-forward relay node first receives a signal from a source node, then scales the power of the signal up or down and finally for- wards the signal towards a target node.
  • Another exemplary relaying protocol applies a detect-and-forward method in which the transmitted signal is detected at the relay node and re-transmitted using the same processes as in the original transmission at the source node.
  • OFDM is a modulation technique in which the data is carried in a large number of closely separated orthogonal sub-carriers. Each sub-carrier is modulated with a conventional modulation method. In order to combat inter- symbol interference in OFDM, a guard interval exceeding an estimated maximum channel delay spread is inserted prior to the OFDM symbol. Further, typically a cyclic prefix is transmitted during the guard interval. The cyclic prefix is a repeat of the end of the symbol enabling circular convolution at the receiver side. OFDM may be combined with a multiple access leading to an orthogonal frequency division multiple access (OFDMA), in which different, orthogonal, sub-carriers may be assigned to different users in order to distinguish them.
  • OFDMA orthogonal frequency division multiple access
  • spectral efficiency is the key to efficient data transmission.
  • the spectral efficiency is not optimized and, thus, novel methods are needed to improve the throughput of the transmission.
  • An object of the invention is to provide improved efficiency in a communication system applying relay nodes and orthogonal frequency division multiplexing.
  • Figure 1 presents a communication system applying relay nodes (PRIOR ART);
  • Figure 2 shows a relay enhanced communication system
  • Figure 3 shows how prefixes are added to data symbols, according to an embodiment of the invention
  • Figure 4 illustrates a method performed at the source node, accord- ing to an embodiment of the invention.
  • Figure 5 illustrates method performed at the relay node, according to an embodiment of the invention. Description of embodiments
  • the relay nodes may be applied, for example, in an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN).
  • E-UTRAN is also known as the 3.9G or the Long Term Evolution (LTE) in 3 rd generation partnership project (3GPP).
  • LTE Long Term Evolution
  • 3GPP 3 rd generation partnership project
  • a telecommunication system may have a fixed infrastructure providing wireless services to subscriber terminals.
  • LTE E-UTRAN
  • Figure 1 illustrates a relay enhanced communication system, wherein the relay node 106 may forward a signal from a source node to a target node.
  • the relay node 106 may be located at some specific point within the cell 100 covered by the central node 102.
  • the relay node 106 may increase the capacity at shadowed areas in the cell 100 as well as in the locations where the traffic demand is high such as in airports or other hot spots, for example.
  • the source node may be, in a downlink transmission, a central node 102 such as a base station, an evolved node B as in E-UTRAN, a radio network controller (RNC) or any other apparatus capable of controlling a radio communication within the cell 100.
  • the target node may be, for example, any user equipment 110 such as a mobile phone, a palm computer, or any other apparatus capable of interacting with a radio communication network.
  • the user equipment 110 may be the source node and the central node 102 may be the target node.
  • the relay node 106 may be the amplify-and-forward relay node, although other types of relay nodes, such as the detect-and-forward relay node, are also possible.
  • the user equipment 110 may transmit information to the relay node 106 as shown in Figure 1 with reference number 114.
  • the connection between the user equipment 110 and the relay node 106 may be an access link 114.
  • the relay node 106 may amplify and forward the information to the central node 102 via a relay link 112.
  • the actual channel response between the user equipment 110 and the central node 102 may be a linear convolution of the channel responses of the relay link 112 and the access link 114. Therefore, the estimated maximum delay spread of the equivalent channel between the user equipment 110 and the central node 102 may be the sum of the maximum delay spreads of the relay link 112 and the access link 114.
  • the longer maximum delay spread leads to lower spectrum efficiency due to the longer duration of an OFDM prefix, such as a guard interval or a cyclic prefix.
  • the user equipment 110 may be located at a spot in the cellular communication network, which is covered by the relay node 106 (i.e. in cell 104) but not by the central node 102. Thus, from the point of view of the central node 102, it may be called remote user equipment (RUE) 110. Unlike, the remote user equipment 110, the user equipment 108 may be located inside the cell 100 covered by the central node 102. For this reason, from the central node's 102 point of view, the user equipment 108 may be called local user equipment (LUE) 108, which may communicate with the central node 102 via a direct link 116.
  • RUE remote user equipment
  • the LUE 108 may have a direct access via the direct link 116 to the central node 102, whereas the RUE 110 may have to access the central node 102 via the access link 114, the relay link 112 and the relay node 106.
  • Embodiments of the invention may be applied, for example, in a re- lay enhanced communication network applying OFDMA as a multiple access method.
  • the central node 102 may be accessed by the LUE 108 via direct link 116 and by the RUE 110 via the relay node 106 in the OFDMA manner, i.e. the signals from the LUE 108 and the RUE 110 (via the relay node 106) may be orthogonally occupying the different sub-carriers of the same OFDM data symbol. For this reason, they may need to have prefixes of equal duration in the time domain prior to the data symbol.
  • the RUE 110 is forced to add a prefix equal to or longer than the sum of the maximum delay spreads of the radio frequency propagation channel between the RUE 110 and the relay node 106 and the channel be- tween the relay node 106 and the central node 102
  • the LUE 108 is also forced to add a prefix with equal length prior to the data symbol. This might decrease the spectral efficiency of the communication network, compared to an embodiment of the invention in which the duration of the prefix may be significantly reduced, as will be explained below.
  • the invention is not limited to such a communication net- work, but may be applied in any relay enhanced communication network where the prefix of the data symbol limits the efficiency of the network.
  • FIG. 2 A very general architecture of the relay enhanced communication system is shown in Figure 2.
  • Figure 2 shows only the elements and functional entities required for understanding the communication system. Other compo- nents have been omitted for reasons of simplicity. The implementation of the elements and functional entities may vary from that shown in Figure 2.
  • the connections shown in Figure 2 are logical connections, and the actual physical connections may be different. It is apparent to a person skilled in the art that the relay enhanced communication system also comprises other functions and structures.
  • the source node 200 (the user equipment in the uplink transmission and the central node in the downlink transmission) may comprise a transmitter 204, which may be used to access the radio channel by sending data via a radio communication data channel.
  • the transmitter 204 may comprise an antenna for transmitting information to an air interface.
  • the transmitter 204 may transmit orthogonal frequency division multiplexed data symbols to a target node 240 via a relay node 106.
  • the target node 240 may be the user equipment in the downlink transmission and the central node in the uplink transmission.
  • the OFDM data sym- bols may comprise a number of sub-carriers.
  • the source node 200 may further comprise a controller 202.
  • the controller 202 may add a first prefix to the orthogonal frequency division multiplexed data symbol, the duration of the first prefix being shorter than the sum of maximum delay spreads of radio frequency propagation channel between the source node 200 and the relay node 106 and the channel between the relay node 106 and the target node 240.
  • the duration of the first prefix may be shorter than the sum of the maximum delay spreads of the relay link 112 and the access link 114 of Figure 1.
  • the first prefix may be the cyclic prefix or the guard interval, of the orthogonal frequency division multiplexed data symbol.
  • the controller 202 may also perform other signal-processing operations, such as modulation, to the data symbol.
  • the duration of a prefix added by the source node 200 has been designed in such a way that the duration of the first prefix is equal to or longer than the sum of the maximum delay spreads of the radio frequency propagation channel between the source node 200 and the relay node 106 and the channel between the relay node 106 and the target node 240. It is, thus, longer than the first prefix according to an embodiment of the invention.
  • the controller 202 may further determine the duration for the first prefix based on the maximum delay spread of the radio frequency propagation channel between the source node 200 and the relay node 106. That is, the duration of the first prefix may be determined to be equal to or longer than the maximum delay spread of the radio frequency propagation channel between the source node 200 and the relay node 106. By doing this, intersymbol interference possibly occurring on the channel between the source node 200 and the relay node 106 may be prevented.
  • the communication system in Figure 2 may also comprise a relay node 106.
  • the relay node 106 may be, for example, the amplify-and-forward relay node.
  • the relay node 106 may be located at the edge of the cell covered by the central node.
  • the relay node 106 may comprise a receiver 224, which may be used to access the radio channel by receiving data via the radio communication data channel.
  • the receiver 224 may comprise an antenna for receiving information over the air interface.
  • the receiver 224 may further receive the orthogonal frequency division multiplexed data symbol including the first prefix from the source node 200.
  • the first prefix may be the cyclic prefix or the guard interval, of the orthogonal frequency division multiplexed data symbol.
  • the first prefix may have been inserted into the data by the source node 200.
  • the relay node 106 may further comprise a controller 222 that may remove the first prefix from the data symbol and add a second prefix to the data symbol.
  • the second prefix may be the cyclic prefix or the guard interval, of the orthogonal frequency division multiplexed data symbol.
  • the duration of the second prefix may be shorter than the sum of the maximum delay spreads of radio frequency propagation channel between the source node 200 and the relay node 106 and the channel between the relay node 106 and the target node 240.
  • the duration of the sec- ond prefix may be shorter than the sum of the maximum delay spreads of the relay link 112 and the access link 114 of Figure 1.
  • the controller 222 may further determine the duration of the second prefix based on the maximum delay spread of the radio frequency propagation channel between the relay node 106 and the target node 240. That is, the duration of the second prefix may be determined to be equal to or longer than the maximum delay spread of the radio frequency propagation channel between the relay node 106 and the target node 240. By doing this, the intersymbol interference possibly occurring on the channel between the relay node 106 and the target node 240 may be prevented.
  • the controller 222 may further perform signal-processing opera- tions, such as synchronization, analog-to-digital and digital-to-analog conversion, to the data symbol.
  • the relay node 106 may further comprise a transmitter 226, which may transmit the data symbol including the second prefix to the target node 240.
  • the transmitter 226 may comprise an antenna for transmitting the data symbol via the air interface.
  • the target node 240 may then receive the data symbol at a receiver 244.
  • the controller 242 of the target node 240 may remove the second prefix from the data symbol and demodulate the data symbol.
  • the controller 242 may also perform other signal-processing operations to the data symbol.
  • the controllers 202, 222 and 242 may be implemented with separate digital signal processors provided with suitable software embedded on a computer readable medium, or with separate logic circuits, such as an application specific integrated circuit (ASIC).
  • the controllers 202, 222, 242 may comprise input/output (I/O) interfaces such as computer ports for providing com- munication capabilities.
  • the input/output interfaces may perform signal- processing operations for enabling a physical channel connection, if needed.
  • Figure 3 illustrates how a prefix is added to the data symbol according to an embodiment of the invention.
  • the source node 200 may generate a data symbol 330 comprising a data part 301 to be transmitted to the target node 240.
  • the source node 200 may perform signal-processing operations, such as modulation, puncturing, interleaving, encoding, etc., to the data symbol 330.
  • the source node 200 may then add a first prefix 310 to the data symbol 330.
  • the duration of the first prefix 310 may only need to be equal to or longer than the maximum delay spread of the radio frequency propagation channel between the source node 200 and the relay node 106.
  • the duration of the first prefix 310 may be shorter than the sum of the maxi- mum delay spreads of the radio frequency propagation channel between the source node 200 and the relay node 106 and the channel between the relay node 106 and the target node 240.
  • the first prefix 310 may be the cyclic prefix or the guard interval, of an orthogonal frequency division multiplexed data sym- bol 332.
  • the first prefix 310 may comprise several samples at the end of the data part 301 of the data symbol 330 (shown with diagonal lines) inserted prior to the data part 301 of the data symbol 332, as shown in Figure 3.
  • the source node 200 may further transmit the data symbol 332 including the first prefix 310 and the data part 301 to the relay node 106.
  • the relay node 106 may receive a data symbol 334 including a first prefix 312 and a data part 303.
  • the received data symbol 334 may be identical to the data symbol 332 or it may have suffered from severe channel conditions distorting the data symbol 332.
  • the data part 303 and the first prefix 312 may be identical to the data part 301 and the first prefix 310, respectively, or they may have been distorted due to severe channel conditions.
  • the relay node 106 may remove the first prefix 312 from the data symbol 334. Thus, the relay node 106 may cut and discard the first prefix 312 from the received data symbol 334. Without loss of generality, the relay node 106 may have knowledge regarding the duration of the first prefix 312 U, the duration of a second prefix 320 t 2 and the duration of the data part 303 in the received data symbol 334 t. After having received the data symbol 334, the relay node 106 may perform analog-to-digital conversion and synchronization of the data symbol 334. However, even in the amplify-and-forward relay nodes, a general synchronization may be required for inter/intra-interference coordina- tion.
  • the second prefix 320 may be the cyclic prefix or the guard interval, of an orthogonal frequency division multiplexed data symbol 338.
  • the second prefix 320 may comprise several samples at the end of the data part 303 (shown with diagonal lines) inserted prior to the data part 303 of the data symbol 338, as shown in Figure 3.
  • the duration of the second prefix 320 may be equal to or longer than the maximum delay spread of the radio frequency propagation channel between the relay node 106 and the target node 240. In any case, the duration of the second prefix 310 may be shorter than the sum of maximum delay spreads of the radio frequency propagation channel between the source node 200 and the relay node 106 and the channel between the relay node 106 and the target node 240.
  • the relay node 106 may further trans- mit the data symbol 338 comprising the data part 303 and the second prefix 320 to the target node 240.
  • the target node 240 may receive a data symbol 340 including a second prefix 322 and a data part 305.
  • the data symbol 340 may be identical to the data symbol 338 or it may have suffered from severe channel conditions distorting the data symbol 338.
  • the data part 305 and the second prefix 322 may be identical to the data part 303 and the second prefix 320, respectively, or they may have been distorted due to severe channel conditions.
  • the target node 240 may remove the second prefix 322 from the data symbol 340 in order to obtain a data symbol 342 without any prefix, and perform signal-processing operations, such as demodulation, de-interleaving, decoding, etc., to the data symbol 342.
  • Figure 4 shows a method performed at the source node according to an embodiment of the invention.
  • the method begins in step 400.
  • the method comprises utilizing orthogonal frequency division multiplexing in data transmission from a source node to a target node via a relay node.
  • the data transmission may comprise, for example, transmission of OFDM data symbols.
  • Step 404 comprises adding the first prefix to an orthogonal frequency division multiplexed data symbol at the source node, the duration of the first prefix being shorter than the sum of maximum delay spreads of radio frequency propagation channel between the source node and the relay node and the channel between the relay node and the target node.
  • the step 404 may further comprise determining the duration of the first prefix based on the maximum delay spread of the radio frequency propagation channel between the source node and the relay node.
  • the first prefix may be a cyclic prefix or a guard interval, of the orthogonal frequency division multiplexed data symbol.
  • the source node may be comprised in a central node or user equipment, depending on whether an uplink or a downlink transmission is concerned.
  • the relay node may be, for example, an amplify-and-forward relay node.
  • the method ends in step 406.
  • Figure 5 shows a method performed at the relay node according to an embodiment of the invention.
  • the relay node may be, for example, an amplify-and-forward relay node.
  • the method begins in step 500.
  • the method comprises receiving, at a relay node, the orthogonal frequency division multiplexed data symbol including the first prefix from the source node.
  • Step 504 comprises removing the first prefix from the data symbol at the relay node.
  • the relay node may cut and discard the first prefix from the received data symbol.
  • Step 506 of the method comprises adding the second prefix to the data symbol at the relay node.
  • the second prefix may be a cyclic prefix or a guard interval, of the orthogonal frequency division multiplexed data symbol.
  • the duration of the second prefix may be shorter than the sum of maximum delay spreads of radio frequency propagation channel between the source node and the relay node and the channel between the relay node and the target node.
  • Step 506 may further comprise determining the duration of the sec- ond prefix based on the maximum delay spread of the radio frequency propagation channel between the relay node and the target node.
  • Step 508 of the method comprises transmitting the data symbol including the second prefix from the relay node to the target node.
  • the method ends in step 510.
  • Embodiments of the invention may be implemented as computer programs in the source node and in the relay node according to the embodiments of the invention.
  • the computer programs comprise instructions for executing a computer process for improving the spectral efficiency of the relay enhanced communication network.
  • the computer program implemented in the source node may carry out, but is not limited to, the tasks related to Figures 2, 3 and 4.
  • the computer program implemented in the relay node may carry out, but is not limited to, the tasks related to Figures 2, 3 and 5.
  • the computer program may be stored on a computer program distribution medium readable by a computer or a processor.
  • the computer pro- gram medium may be, for example but not limited to, an electric, magnetic, optical, infrared or semiconductor system, device or transmission medium.
  • the computer program medium may include at least one of the following media: a computer readable medium, a program storage medium, a record medium, a computer readable memory, a random access memory, an erasable program- mable read-only memory, a computer readable software distribution package, a computer readable signal, a computer readable telecommunications signal, computer readable printed matter, and a computer readable compressed software package.

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

Abstract

L'invention concerne un procédé, un appareil et un programme informatique destinés à améliorer l’efficacité spectrale dans un réseau de communication renforcé par relais. Le procédé comporte les étapes consistant par exemple à recevoir, au niveau d’un nœud relais (106), un symbole de données multiplexé par répartition orthogonale de fréquence comprenant un premier préfixe (PRE310) et provenant d’un nœud source (200), à retirer le premier préfixe (PRE312) du symbole de données au niveau du nœud relais (106), à ajouter un deuxième préfixe (PRE320) au symbole de données au niveau du nœud relais (106) et à émettre le symbole de données comprenant le deuxième préfixe du nœud relais à un nœud (240) de destination.
PCT/EP2008/062022 2008-09-11 2008-09-11 Réseau de communication ofdm amélioré Ceased WO2010028687A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/EP2008/062022 WO2010028687A1 (fr) 2008-09-11 2008-09-11 Réseau de communication ofdm amélioré

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP2008/062022 WO2010028687A1 (fr) 2008-09-11 2008-09-11 Réseau de communication ofdm amélioré

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Publication Number Publication Date
WO2010028687A1 true WO2010028687A1 (fr) 2010-03-18

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006121381A1 (fr) * 2005-05-06 2006-11-16 Ericsson Ab Procede et dispositif utilises dans des reseaux de communication sans fil a relais
EP1850509A1 (fr) * 2006-04-24 2007-10-31 NTT DoCoMo Inc. Méthode et système de l'estimation de canal dans un système de communication sans fils, répéteur et récepteur
US20080112497A1 (en) * 2006-11-13 2008-05-15 Samsung Electronics Co., Ltd. Apparatus and method for providing relay service in an OFDM mobile communication system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006121381A1 (fr) * 2005-05-06 2006-11-16 Ericsson Ab Procede et dispositif utilises dans des reseaux de communication sans fil a relais
EP1850509A1 (fr) * 2006-04-24 2007-10-31 NTT DoCoMo Inc. Méthode et système de l'estimation de canal dans un système de communication sans fils, répéteur et récepteur
US20080112497A1 (en) * 2006-11-13 2008-05-15 Samsung Electronics Co., Ltd. Apparatus and method for providing relay service in an OFDM mobile communication system

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