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WO2006121381A1 - Procede et dispositif utilises dans des reseaux de communication sans fil a relais - Google Patents

Procede et dispositif utilises dans des reseaux de communication sans fil a relais Download PDF

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Publication number
WO2006121381A1
WO2006121381A1 PCT/SE2005/001143 SE2005001143W WO2006121381A1 WO 2006121381 A1 WO2006121381 A1 WO 2006121381A1 SE 2005001143 W SE2005001143 W SE 2005001143W WO 2006121381 A1 WO2006121381 A1 WO 2006121381A1
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WIPO (PCT)
Prior art keywords
relaying
node
nodes
cyclic
ofdm symbols
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PCT/SE2005/001143
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English (en)
Inventor
Peter Larsson
Afif Osseiran
Andrew Logothetis
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Ericsson AB
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Ericsson AB
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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
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/02—Channels characterised by the type of signal
    • H04L5/023—Multiplexing of multicarrier modulation signals, e.g. multi-user orthogonal frequency division multiple access [OFDMA]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/022—Site diversity; Macro-diversity
    • H04B7/026—Co-operative diversity, e.g. using fixed or mobile stations as relays
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0667—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal
    • H04B7/0671—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal using different delays between antennas
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/155—Ground-based stations
    • H04B7/15592—Adapting at the relay station communication parameters for supporting cooperative relaying, i.e. transmission of the same data via direct - and relayed path
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0667—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal
    • H04B7/0676—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal using random or pseudo-random delays
    • 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

Definitions

  • the present invention relates to wireless communication systems wherein relaying is used to enhance performance.
  • the invention relates to a method and arrangement for applying cyclic delay diversity in such wireless communication system.
  • a main striving force in the development of wireless/ cellular communication networks and systems is to provide, apart from many other aspects, increased coverage or support of higher data rate, or a combination of both.
  • the cost aspect of building and maintaining the system is of great importance and is expected to become even more so in the future.
  • the problem of increased battery consumption is another area of concern.
  • the topology of existing wireless communication systems is characterized by the cellular architecture with the fixed radio base stations and the mobile stations as the only transmitting and receiving entities in the networks typically involved in a communication session.
  • OFDM Orthogonal Frequency Domain Multiplexing
  • the OFDM receiver is relative simple, since the multiple data streams are transmitted over a number of parallel flat fading channels. In fact, equalization is not done in the time domain; instead, one-tap filters in the frequency domain are sufficient.
  • uncoded OFDM transmission lacks inherent diversity that greatly helps to combat loss in the radio propagation environment, i.e. path loss, fast fading, etc.
  • One way to introduce diversity in the received signal is to utilize multiple antennas at the transmitter and possibly also at the receiver.
  • MIMO Multiple-Input Multiple-Output
  • Cooperative relaying systems have many features and advantages in common with the more well-known multihop networks, wherein typically, in a wireless scenario, a communication involves a plurality of transmitting and receiving entities in a relaying configuration. Such systems offer possibilities of significantly reduced path loss between communicating (relay) entities, which may benefit the end-to-end (ETE) users.
  • the cooperative relaying systems are typically limited to only two (or a few) hop relaying.
  • a typical cooperative relaying system comprises of an access point, for example a radio base station which communicates with one or more user equipments, for example a mobile station, via a plurality of relaying nodes.
  • cooperative relaying systems exploits aspects of parallelism and also adopts themes from advanced antenna systems. These systems have cooperation among multiple stations or relaying nodes, as a common denominator.
  • several names are in use, such as cooperative diversity, cooperative coding, and virtual antenna arrays.
  • cooperative relaying system and “cooperative schemes /methods” is meant to encompass all systems and networks utilizing cooperation among multiple stations and the schemes/methods used in these systems, respectively.
  • the term “relaying system” is meant to encompass all systems and networks utilizing relying in any form, for example multihop system and cooperative relaying systems.
  • a signal may be decoded, re-modulated and forwarded, or alternatively simply amplified and forwarded.
  • the former is known as decode-and- forward or regenerative relaying
  • the latter is known as amplify- and- forward, or non-regenerative relaying.
  • Both regenerative and non-regenerative relaying is well known, e.g. by traditional multihopping and repeater solutions respectively.
  • Various aspects of the two approaches are addressed in "An Efficient Protocol for Realizing Distributed Spatial Diversity in Wireless Ad-Hoc Networks", J. N. Laneman and G. W. Wornell, Proc. of ARL FedLab Symposium on Advanced Telecommunications and Information Distribution (ATIRP-2001), (College Park, MD), March 2001.
  • Diversity gain is particularly attractive since it offers increased robustness of communication performance as well as allowing reduction of experienced average SNR for the same BER.
  • the cooperative relaying may provide other positive effects such as beamforming (or directivity) gain, and spatial multiplexing gain.
  • the general benefits of the mentioned gains include higher data rates, reduced outage primarily due to different forms of diversity, increased battery life, and extended coverage.
  • Alamouti diversity based cooperative relaying requires a receiver to perform signal processing in accordance with the Alamouti code. A relay with this capacity will be complex. This is also true for other space-time codes similar to Alamouti diversity. In addition, the Alamouti diversity order is limited to two. Higher order space-time codes cannot be constructed without reducing the code rate.
  • Coherent combining based cooperative relaying requires some sort of feedback to estimate channel phase and amplitude. This increases the control signalling in the system, which in turn may reduce the user data rate. As the phase and amplitude measure, feedback and application of gain-weights are generally associated with some smaller errors, the optimum performance will not be reached.
  • the desired signal is amplified at the RN at the expense of amplifying the interference.
  • the signal of interest is coherently added whereas noise and interferers are added non-coherently.
  • the decode-and-forward schemes if the signal is erroneously decoded, the error will be propagated.
  • relaying have great potentials in providing high capacity and flexibility, for example.
  • the in the art proposed arrangements and methods have significant drawbacks in that they require complex receiver/ transmitters in the relaying node, and/ or introduces extensive control signalling in the systems.
  • the object of the invention is to provide a method, a relay station and a system that overcomes the drawbacks of the prior art techniques. This is achieved by the method as defined in claim 1, the method in a relaying node as defined in claim 16 and the relaying node as defined in claim 22.
  • the present invention provides a method and a relaying node giving distributed delay diversity among relay stations.
  • Distributed delay diversity is achieved by that the relaying nodes in their forwarding between the access point and the user equipment applies dissimilar cyclic shifts to their respective forwarded OFDM symbols.
  • the method comprises the steps of: -the transmitting communication node transmitting encoded data to the relaying nodes; -the relaying nodes receives, and decodes the received OFDM symbols;
  • the relaying nodes applies a cyclic shift to the OFDM symbols and adds a cyclic prefix after encoding and before retransmitting the OFDM symbols to the receiving communication node; and -the receiving communication node receiving and decoding the data.
  • the method can be used in both regenerative and non-regenerative relaying.
  • the individual cyclic shifts can be generated randomly at each relaying node, or alternatively distributed to the relaying nodes.
  • the relaying nodes may in addition be provided with multiple antennas and apply cyclic delay diversity between their antenna branches. Cyclic delay diversity may also be used in the transmission between the transmitting node and the relaying nodes.
  • the relaying node comprises a transmitter provided with a cyclic shift module for applying a cyclic shift to an OFDM symbol, and a cyclic prefix module for adding a cyclic prefix to the OFDM symbol.
  • the receiver may comprise a cyclic prefix removal module for removing a cyclic prefix from a received OFDM symbol.
  • the relaying mode may also comprise means for generating cyclic shifts, for example randomly.
  • the relaying node comprises means for receiving cyclic shifts that are generated elsewhere in the system and distributed to the relaying nodes.
  • a system utilizing the method and arrangement according to the invention can take full advantage of the combined advantages of (artificial frequency) diversity introduced in (coded) OFDM and cooperative relaying.
  • One advantage of the invention is that antenna specific pilots are not required.
  • a further advantage is that a relay assisted micro-diversity gain is obtained by exploiting FEC while increasing the frequency selectivity.
  • a further advantage is that the signal processing in the relaying nodes, as well as receiving node, can bee kept relatively simple.
  • Fig. Ia is a schematic illustration of the transmitter diversity technique according to prior art, and Ib schematically illustrates the principles of cyclic delay according to prior art;
  • Fig 2a and 2b illustrates schematically a cellular system using cooperative relaying wherein the method and arrangement according to the present invention may be advantageously implemented
  • Fig. 3 is a flowchart of the method according to the invention.
  • Fig. 4 illustrates schematically a method and arrangement according to one embodiment of the present invention wherein relaying nodes are provided with multiple antennas.
  • Fig. 5 is a schematic illustration of a relaying node according to the invention.
  • Fig. 6 is a schematic illustration of a the present invention employed in a multihop communication system.
  • an artificial diversity which mimics the effects of spatial diversity, can be introduced in an OFDM system by the use of cyclic delays diversity (CDD).
  • CDD cyclic delays diversity
  • Methods for introducing artificial delay with the use of cyclic delays are described in for example US 6,842,487 and "Antenna Diversity for OFDM using Cyclic Delays" K. Witrisal et al Proc. SCVT-2001 (8th Symp. on Commun. and Vehic. Technol. in the Benelux), Oct. 2001, pp. 13-17.
  • a prior art transmitter diversity technique is depicted in FIG. Ia.
  • IFFT inverse FFT
  • cyclic delays of m samples or ti seconds
  • a cyclic delay means that the n, samples shifted beyond the effective part are transmitted in the beginning of that part of the symbol, as illustrated in FIG. Ib.
  • An alternative term for cyclic delay is the term cyclic shift.
  • the cyclic prefix (guard interval) is transmitted prior to the effective part. The signals are then up-converted from the base-band into the RF-band and transmitted.
  • artificial frequency selectivity and spatial diversity is provided in a cooperative relaying wireless communication system by introducing distributed delay diversity among relay stations.
  • Distributed delay diversity is provided by that the relaying nodes in their forwarding between the access point and the user equipment applies dissimilar cyclic shifts to their respective forwarded OFDM symbols.
  • the network outlined in FIG. 2 is an example of a cooperative relaying network wherein the present invention advantageously is implemented.
  • the figure shows one cell 205 of the wireless network comprising a transmitting communication node, the access point (AP) 210, a plurality of relaying nodes (RN) 215 and a plurality of receiving communication nodes or user equipment (UE) 220.
  • the access point is typically a radio base station (RBS) providing the point of access to and from the core network to the radio access network.
  • RBS radio base station
  • User equipments include, but are not limited to for example, mobile stations, laptop computers and PDAs equipped with wireless communication means and vehicles and machinery equipped with wireless communication means.
  • the relay stations 215 are mounted on masts, but may also be mounted on buildings, for example.
  • Fixed relaying nodes may be used as line of sight conditions can be arranged, directional antennas towards the basestation may be used in order to improve SNR (Signal-to-Noise Ratio) or interference suppression and the fixed relay may not be severely limited in transmit power as the electricity supply network typically may be utilized.
  • mobile relays, 221 and 222 such as mobile user terminals, may also be used, either as a complement to fixed relaying nodes or independently.
  • the user terminal 220 is in active communication with the base station 210.
  • the radio communication as indicated with arrows, is essentially simultaneously using a plurality of paths, characterized by two hops, i.e. via at least one relaying node 215.
  • the first part, from the access point 210 to at least one relaying node 215, will be referred to as the first link
  • the second part, from the relaying node or nodes to the user terminal 220 will be referred to as the second link.
  • direct communication between the access point 210 and the user terminal 220 may be utilized, in the figure indicated with a dashed arrow.
  • some basic low rate signalling between AP 210 and UE 220 may be required for setting up a relay supported communication channel.
  • a cellular system function such as paging may not use relaying as the RN to UE channels are not a priori known, instead preferably, a direct AP to UE communication is used during call setup and similar procedures.
  • the communication system may simultaneously set up and maintain a large plurality of communication sessions between the AP 210 and user terminals 220, and in the different communication sessions using different sets of relaying nodes 215.
  • the relaying nodes engaged in a specific communication may change during the session as the user terminal moves or the radio environment changes for other reasons.
  • Different aspects of optimising a cooperative relaying communication system are taught in WO2004/ 107693.
  • the real world cellular system outlined in FIG. 2a is for simplicity modeled by system model shown in FIG. 2b, here with focus on a single pair of transmitter and receiver, utilizing an arbitrary number M of relay stations.
  • the notation is adapted to an access point 210 as a transmitter and a user terminal 220 as a receiver, but not limited thereto.
  • the communication between the access point 210 and the user terminal 220 can be described as comprising two main parts: the transmissions from the access point 210 to the relaying nodes 215:m, m e ⁇ l,2,...,M ⁇ , referred to as the first link, and the transmissions from the relaying nodes 215:m to the user terminal 220 referred to as the second link.
  • the radio paths on the first link are characterized by the respective channel impulse response I 1n , and the radio paths on the second link by the respective channel impulse response h m .
  • each of the relaying nodes 215: m is provided with of one or more antennas.
  • the AP 210 transmits to K RNs 215 and possibly also directly to the UE 220.
  • the relaying nodes 215 forward the information received from a first node (e.g. AP) to a second node (e.g. UE) using cycle delay diversity (CDD). This can be done in either with "amplify and forward"
  • Each relaying node 215:m encodes the data and applies an individual cyclic shift and adds the cyclic prefix (CP) before transmitting the signals.
  • the second node e.g. the UE 220, receives the combined signals and decodes the data that may be combined with a signal directly received from the AP 210.
  • CP cyclic prefix
  • the receiver operation i.e. i) combining/ non-combining with direct and forwarded signal, ii) maximum ratio combining when the receiver is equipped with multiple antennas.
  • the set of relaying nodes 215:m that are going to be used in the communication session between the AP 210 and the UE 215 is selected.
  • the selection when performed, is exemplary and preferably based on channel characterisation measurements, for example with the use of pilots. Alternatively, all relaying nodes in a cell are continuously active.
  • Each relaying node 215:m of the selected set receives, retrieves or generate at least one cyclic shift to use in the communication session.
  • the choice/ generation of cyclic shifts, and their distribution, then applicable, will be further discussed below.
  • the AP transmits data to each of the selected relay stations 215:m. This transmission may be performed in many different ways, including but not limited to the use of beamforming antennas, OFDM with or without CDD.
  • 320 The relaying nodes 215:m receives, demodulate and/or decode the data from the AP 210.
  • the relaying nodes 215:m forwards the data with the use of cycle delay diversity (CDD). Each relaying node uses its individual cyclic shift.
  • CDD cycle delay diversity
  • the UE 215 receives the combined signal from the plurality of relaying nodes 215:m, demodulate and remove the cyclic prefix and decode the forwarded data. By combining the signal from the relaying nodes the positive effects of the artificial diversity is utilized.
  • CDD is used on the second link, with each relaying node typically provided with a single antenna.
  • the combined signal as experienced by the UE 220 will in a sense be similar to the signal from a prior art transmitter with multiple antennas, utilizing CDD, but with the added benefits with regards to gain and coverage associated with cooperative relaying.
  • CDD is utilized also on the first link. Hence the AP needs to be equipped with multiple antenna. This will further increase the frequency diversity gain.
  • relaying nodes in the set of selected relaying nodes 215:m necessarily are able to receive and forward every data transmission from the AP 210. On occasion a transmission will fail due to changes in the radio environment, error or faults in the equipment etc.
  • the control of cyclic delays can be managed in different ways according to the invention, such as: -Assigning a fixed cyclic shift at relay deployment.
  • the value may be pre-calculated preferably taking into account the relation to other relaying nodes e.g. the geographic distribution of the relaying nodes.
  • the cyclic shifts may be randomly assigned.
  • the AP, RN or possibly the UE may control this.
  • the setting should preferably attain as rich artificial frequency selectivity as possible, and hence together with coded OFDM attain a coding diversity gain. This suggests that the cyclic shifts in neighbouring relaying nodes are preferably set to dissimilar (but proximate) values. The cyclic shift values should not change rapidly in order to allow the channel estimator (such as the LMMSE) to track the channel impulse response.
  • the channel estimator such as the LMMSE
  • the receiving step 320 comprises the substeps of:
  • 320:4 Equalize to give one data estimate.
  • 320:5 Combine the data estimate.
  • a maximum ratio combining method may advantageously and preferably be used.
  • 320:6 Store the coded data in order to be further processed and forwarded in the next transmitting time slot.
  • the forwarding procedure will depend on if non-regenerative relaying or regenerative relaying is used. If non-regenerative, the coded output data is Modulated (the modulation is implemented using IFFT) and Forwarded. If regenerative, the coded output data is Decoded, Re-Encoded, Modulated, and Forwarded.
  • the forwarding step 325 comprises of the substeps of: 325: 1 A cyclic shift ⁇ is applied to the OFDM symbol. 325:2 A cyclic prefix (CP) is added.
  • CP cyclic prefix
  • the signal is up-converted to the RF-band and fed to the antenna.
  • At least one of the relaying nodes is equipped with a multiple antenna and transmitting in a CDD fashion.
  • the relaying nodes 215:2 and 215:4 are equipped with multiple antennas.
  • the UE will experience an increased spatial diversity, without any increased complexity in the receiving operations. The situation is equivalent of having more relaying nodes.
  • cyclic shifts can in this embodiment be managed similarly to above described.
  • Fixed cyclic delays may assigned for each relaying node and for each antenna of the relaying nodes with multiple antennas antenna 215:2 and 215:4 at relay deployment.
  • a range of cyclic shifts are distributed to the relaying nodes and the individual relaying nodes generate cyclic shifts within that range for its antenna branches.
  • Random generation of cyclic shifts provides a simple and effective way of providing the relaying nodes with individual cyclic shifts.
  • the probability that two relaying nodes choose the same cyclic shift is very small, and even if the same cyclic shift is used by two relaying nodes, the benefits of the method will only be slightly diminished. Therefore, given the simplicity of implementation a random generation of cyclic shifts may be an attractive alternative compared to a more elaborated and optimized distribution.
  • the embodiments of the invention have been exemplified with cyclic shifts, which represent a preferred solution.
  • the methods and arrangement according to the invention is not limited to the use of cyclic shift, on the contrary, all methods introducing artificial frequency selectivity could advantageously be combined with the present invention.
  • Artificial frequency selectivity is for example introduced also with for example linear delays. Linear delays are less favourable as Inter Symbol Interference (ISI) is introduced and typically large prefix needs to be added, but could be used if minor ISI is found to be acceptable and the number of antennas /relaying nodes is small.
  • ISI Inter Symbol Interference
  • CDD allows for large number of transmit antennas with different delays as it does not introduce ISI, and hence together with coded OFDM a large diversity order.
  • FIG. 5 An arrangement according to the present invention in a relaying node, suitable for effectuating the above described embodiments is schematically illustrated in FIG. 5.
  • the modules and blocks according to the present invention described above are to be regarded as functional parts of a sending and/ or receiving node in a communication system, and not necessarily as physical objects by themselves.
  • the modules and blocks are at least partly preferably implemented as software code means, to be adapted to effectuate the method according to the invention.
  • the receiver 550 of a relaying node comprises receiving means 555, which provides the necessary functionalities for performing the actual reception of radio signals and is well known for the skilled person.
  • a down conversion module 560 In connection to the receiving means 555 is a down conversion module 560.
  • the receiver 550 is provided with a cyclic prefix removal module 565 wherein the cyclic prefix (or guard interval) is removed before the signal is conventionally processed by a FFT module 570, an equalizer 575 and a module for inverse FFT 580.
  • the transmitter 500 of a relaying node comprises transmitting means 505, which provides the necessary functionalities for performing the actual transmission and is well known for the skilled person.
  • a up conversion module 520 In connection to the transmitting means 505 is a up conversion module 520.
  • the transmitter 500 is provided with cyclic shift module 510 wherein a cyclic shift ⁇ is applied to the incoming OFDM symbol after the IFFT module 580.
  • the cyclic prefix module 515 the cyclic prefix is added before the signal is fed to the up conversion module 520, and transmitted.
  • the relaying node is provided with means for generating cyclic shifts, or alternatively means for receiving distributed cyclic shift, which are used by the cyclic shift module 510.
  • H 1n F H D(Fh 1n )F (2)
  • D(x) is a diagonal matrix with x on its main diagonal
  • F is the unitary discrete Fourier transform matrix of size NxN .
  • the (n,m) th. element of F is given by
  • P k is a right circulant matrix with e I+(] _ ⁇ ) mod N as the first row i.e.
  • Fy 0 D(Fh 0 )Fx
  • Fy 1 D(Fh n )Fx (5)
  • the signals can be combined using MRC method. Note that the channels from each antenna do no need to be explicitly estimated.
  • the effective channel impulse response and the channel response from the AP can be estimated using a common time-frequency pilot pattern, which are not antenna specific. The same conclusion is reached when multiple transmit antennas are used in the AP and/ or the RNs.
  • the invention has in the above embodiments been envisaged in a two hop cooperative relaying scenario.
  • the method and arrangement according to the present invention may advantageously be utilized also in other systems wherein a plurality of nodes are engaged in a communication session, for example a multihop system.
  • a majority of the nodes are user equipment of various kinds, but the system may also comprise fixed nodes, such as access points.
  • Preferably all nodes have the capability of receiving and forwarding data.
  • An example of a multihop system utilizing the method of the invention is schematically illustrated in FIG. 6, wherein an originating node 610 communicates with the destination node 620, via the intermediate nodes 615: 1-4, acting as relaying nodes, in a three hop scenario.
  • the CDD scheme according to the invention can be used in all hops, or in a selection of hops, depending on, for example, the capabilities of the involved nodes, and the presence of suitable nodes.
  • the novel CDD scheme is utilized on the second hop, wherein intermediate nodes 615: 1 and 615:3 applies individual cyclic shifts and adds the cyclic prefix prior to the transmission to nodes 615:2 and 615:4, which receives the combined signal from nodes 615: 1 and 615:3.
  • CDD is utilized by the nodes 615: 1 and 615:3 for the retransmission to the destination node 620.

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

Abstract

La présente invention concerne des systèmes de communication sans fil dans lesquels sont utilisés des relais pour améliorer leur efficacité. Le procédé et le dispositif de l'invention permettent d'obtenir une sélectivité de fréquence et une diversité spatiale artificielles par introduction d'une diversité de retard distribuée parmi les stations relais. La diversité de retard distribuée est obtenue grâce à l'application, par les noeuds de relais dans leur transmission entre le point d'accès et l'équipement utilisateur, de décalages cycliques sur les symboles OFDM transmis correspondants.
PCT/SE2005/001143 2005-05-06 2005-07-08 Procede et dispositif utilises dans des reseaux de communication sans fil a relais Ceased WO2006121381A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US67818505P 2005-05-06 2005-05-06
US60/678,185 2005-05-06
SE2005000799 2005-05-26
SEPCT/SE2005/000799 2005-05-26

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Cited By (22)

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WO2008133447A1 (fr) * 2007-04-27 2008-11-06 Samsung Electronics Co., Ltd. Procédé permettant de faire suivre un message direct dans un système de relais ofdma à fonction partielle
WO2008098093A3 (fr) * 2007-02-06 2008-11-20 Qualcomm Inc Transmission entrée multiple sortie multiple (mimo) à retards cycliques explicites et implicites
JP2009049937A (ja) * 2007-08-22 2009-03-05 Nippon Telegr & Teleph Corp <Ntt> 無線通信システム及び中継無線装置
WO2009074936A1 (fr) * 2007-12-11 2009-06-18 Koninklijke Philips Electronics N.V. Système et procédé pour relayer des signaux dans un réseau coopératif asynchrone
WO2009158542A1 (fr) * 2008-06-27 2009-12-30 Qualcomm Incorporated Procédé et appareil de sélection et de traitement de signaux provenant d'une station source et de stations relais
WO2010021597A1 (fr) * 2008-08-18 2010-02-25 Agency For Science, Technology And Research Procédé et appareil de relais espace-temps analogique pour canal de relais de communication sans fil
WO2010028687A1 (fr) * 2008-09-11 2010-03-18 Nokia Siemens Networks Oy Réseau de communication ofdm amélioré
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