|Title of Invention||
"A SYSTEM ADAPTED FOR COMMUNICATION IN A TWO-HOP WIRELESS COMMUNICATION NETWORK"
|Abstract||The present invention relates to wireless networks using relaying. In the method according to the present invention of performing communication in a two-hop wireless communication network, a transmitter 210, a receiver 220 and at least one relay station 215 are engaged in a communication session The relay station 215 forwards signals from a first link between the transmitter 210 and the relay station 215 to a second link between the relay stations 215 and the receiver 220. The forwarding performed by the at least one relay station 215 is adapted as a response to estimated radio channel characteristics of at least the first link. Preferably the forwarding is adapted as a response to estimated radio channel characteristics of both the first and second link.|
|Full Text|| Method and system for wireless communication networks using relaying
Field of the invention
The present invention relates to relay supported wireless communication to enhance communication performance. In particular the invention relates to a method and a system for performing communication in a two-hop wireless communication network
Background of the invention
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. At the same time, the cost aspect of building and maintaining the system is of great importance and is expected to become even more so in the future. As data rates and/or communication distances are increased, the problem of increased battery consumption is another area of concern.
Until recently the main topology of wireless networks has been fairly unchanged, including the three existing generations of cellular networks. The topology characterized by the cellular architecture with the fixed radio base stations and the mobile stations as the transmitting and receiving entities in the networks, wherein a communication typically only involves these two entities. An alternative approach to networks are exemplified by the 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-emd (ETE) users.
Attention has recently been given to another type of topology that has many features and advantages in common with the multihop networks but is limited to only two (or a few) hop relaying. In contrast to multihop networks, aforementioned topology exploits aspects of parallelism and also adopts themes from advanced antenna systems. These networks, utilizing the new type of topology, have cooperation among multiple stations as a common denominator, hi recent research literature, it goes under several names, such as cooperative relaying, cooperative diversity, cooperative coding, virtual antenna arrays, etc. hi the present application the terms "cooperative relaying" and "cooperative schemes/methods" is meant to encompass all systems and networks utilizing cooperation among multiple stations and the
¥chemes/methods used in these systems, respectively. A comprehensive overview of cooperative communication schemes are given in . Various formats of a relayed signal may be deployed. 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, whereas 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 .
The general benefits of cooperative relaying in wireless communication can be summarized as higher data rates, reduced outage (due to different forms of diversity), increased battery life, extended coverage (e.g. for cellular).
Various schemes and topologies utilizing cooperative relaying has been suggested, as theoretical models within the area of information theory, as suggestions for actual networks and in a few cases as laboratory test systems, for example. Examples are found in  pages 37-39,41-44. The various cooperation schemes may be divided based on which entities have data to send, to whom and who cooperates. In FIGs. la-f (prior art) different topologies are schematically illustrated, showing where traffic is generated, who is the receiver and the path for radio transmissions.
The classical relay channel, illustrated in FIG. la, consists of a source that wishes to communicate with a destination through the use of relays. The relay receives the signal transmitted by the source through a noisy channel, processes it and forwards it to the destination. The destination observes a superposition of the source and the relay transmission. The relay does not have any information to send; hence the goal of the relay is to maximize the total rate of information flow from the source to the destination. The classical relay channel has been studied in , and in  where receiver diversity was incorporated hi the latter. The classical relay channel, in its three-station form, does not exploit multiple relay stations at all, and hence does not provide the advantages stated above.
A more promising approach, parallel relay channel, is schematically illustrated in FIG Ib, wherein a wireless systems employing repeaters (such as cellular basestation with supporting repeaters) with overlapping coverage, a receiver may benefit of using super-positioned signals received from multiple repeaters. This is something that happens automatically in systems when repeaters are located closely. Recently, information theoretical studies have addressed
this case. A particular case of interest is by Schein,  and . Schein has performed information theoretical study on a cooperation-oriented network with four nodes, i.e. with one transmitter, one receiver and only two intermediately relays. A real valued channel with propagation loss equal to one is investigated. Each relay employs non-regenerative relaying, i.e. pure amplification. Thanks to the simplistic assumption of real valued propagation loss, the signals add coherently at the receiver antenna. Under individual relay power constraints, Schein also indicates that amplification factors can be selected to maximize receiver SNR, though does not derive the explicit expression for the amplification factors. One of the stations sends with its maximum power, whereas the other sends with some other but smaller power. The shortcoming of Schein's schemes is that it is; only an information theoretical analysis, limited to only two relay stations, derived in a real valued channel with gain one (hence neglecting fundamental and realistic propagation assumptions), lacks the means and mechanisms to make the method practically feasible. For example, protocols, power control and RRM mechanisms, complexity and overhead issues are not addressed at all. With respect to only addressing only two relay stations, the significantly higher antenna gains and diversity benefits, as would result for larger number of relays, are neither considered nor exploited.
The concept of Multiple-access Channel with Relaying (a.k.a. as Multiple access channels with generalized feedback) has been investigated by several researchers lately and is schematically illustrated in FIG. Ic. The concept involves that two users cooperate, i.e. exchange the information each wants to transmit, and subsequently each user sends not just its own information but also the other users information to one receiver. The benefit in doing so is that cooperation provides diversity gain. There are essentially two schemes that have been investigated; cooperative diversity and coded cooperative diversity. Studies are reported in , for example. With respect to diversity, various forms has bee suggested, such as Alamouti diversity, receiver diversity, coherent combining based diversity. Typically the investigated schemes and topologies rely on decoding data prior to transmission. This further means that stations has to be closely located to cooperate, and therefore exclude cooperation with more distant relays, as well as the large number of potential relays if a large scale group could be formed. An additional shortcoming of those schemes is that is fairly unlikely having closely located and concurrently transmitting stations. These shortcomings indicates that the investigated topology are of less practical interest. The broadcast channel with relaying, illustrated in FIG. Id, is essentially the reverse of the topology depicted in FIG Ic, and therefore shares the same severe shortcomings.
"*k further extension of the topology depicted in FIG. Ic is the so-called interference channel
with relaying, which is illustrated in FIG. le, wherein two receivers are considered. This has e.g. been studied in  and  but without cooperation between the receivers, and hence not exploiting Hie possibilities possibly afforded by cooperative relaying.
Another reported topology, schematically illustrated in FIG. If, is sometimes referred to as Virtual Antenna Array Channel, and described in for example . In this concept, (significant) bandwidth expansion between a communicating station and adjacent relay nodes is assumed, and hence non-interfering signals can be transferred over orthogonal resources that allows for phase and amplitude information to be retained. With this architecture, MIMO (Multiple Input Multiple Output) communication (but also other space-time coding methods) is enabled with a single antenna receiver. The topology may equivalently be used for transmission. A general assumption is that relay stations are close to the receiver (or transmitter). This limits the probability to find a relay as well as the total number of possible relays that may be used. A significant practical limitation is that very large bandwidth expansion is needed to relay signals over non-interfering channels to the receiver for processing.
Cooperative relaying has some superficial similarities to the Transmit diversity concept in (a.k.a. Transmit diversity with Rich Feedback, TDRF), as described in  and is schematically illustrated in FIG. Ig. Essential to the concept is that a transmitter with fixed located antennas, e.g. at a basestation in a cellular system, finds out the channel parameters (allowing for fading effects and random phase) from each antenna element to the receiver antenna and uses this information to ensure that a (noise free) signal, after weighting and phase adjustment hi the transmitter, is sent and adds coherently at the receiver antenna thereby maximizing the signal to noise ratio. While transmit diversity, with perfectly known channel and implemented in a fixed basestation, provides significant performance benefits, it also exist practical limitations in terms of the number of antenna elements that can be implemented in one device or at one antenna site. Hence, there is a limit in the degree of performance gain that can be attained. A disadvantage for basestation oriented transmit diversity is also that large objects between transmitter and receiver incur high path loss.
Thus, it is in the art demonstrated that cooperative relaying have great potentials in providing high capacity and flexibility, for example. Still, the in the art proposed topologies and methods do not take full advantage of the anticipated advantages of a network with cooperative relaying.
Summary of the invention
In the state of the art methods, the quality of the first link, the second link or a combination thereof is not considered in adapting any transmission parameters. This has the consequence that performance may degrade and resources are inefficiently utilized.
Hence, a significant shortcoming of the above discussed prior art is that they do not adapt transmit parameters of the relays hi response of the quality of a link or combination of links (first and second) involved in the forwarding procedure. Whereby, the prior art has not been able to fully take advantage of the anticipated advantages of a cooperative relaying network.
Obviously an unproved method and system for a cooperative relaying network is needed, which consider the quality of the first link, the second link or a combination thereof in adapting transmission parameters is needed, to whereby have the ability to better take advantage of the anticipated advantages of a cooperative relaying network.
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 relay station as defined in claim 12 and the system as defined in claim 16.
The problem is solved by that the present invention provides a method, a relay station and a system that makes it possible to use estimated radio channel characteristics of both the first and second link for adapting the forwarding of signals from a first link to a second link performed by the relay station.
In the method, according to the present invention of perfonmng communication in a two-hop wireless communication network, a transmitter, a receiver and at least one relay station are engaged in a communication session. The relay station forwards signals from a first link between the transmitter and the relay station to a second link between the relay stations and the receiver. The forwarding performed by the at least one relay station is adapted as a response to estimated radio channel characteristics of at least the first link. Preferably the forwarding is adapted as a response to estimated radio channel characteristics of both the first and second link.
The relay station according to the present invention is adapted for use in a two-hop wireless communication network, wherein the network comprises a transmitter, a receiver and at least one relay station. The relay station is adapted to forward signals from a first link between the
transmitter and the relay station to a second link between the relay stations and the receiver. The relay station is provided with means for adapting the forwarding based on characterization of both the first and second link.
Thanks to the invention it is possible to better adjust the forwarding on the second link to the actual conditions present during a communication session. In addition the forwarding can be better adjusted to changes in the conditions.
One advantage afforded by the present invention is that the more precise and reliable characterization of the individual radio paths may be used to determine and optimize different transmission parameters. Whereby, the capabilities of a cooperative relaying network, for example, may be more fully exploited.
A further advantage is that characterisation of the first and second link advantageously is performed in the relay stations. Hence, the method according to the invention fascilitates a distribution of functionalities in the network allowing an increase in the number of relay stations in a communication session without any significant increase in the amount of protocol overhead that is needed for the transmission of data from the transmitter to the receiver.
A yet further advantage further advantage of the method and system according to the present invention is that the improved characterization of the first and second link facilitate to take full advantage of the anticipated advantages of a network with cooperative relaying that comprises a larger number of relaying stations. With the invention used in a coherent combining setting, the directivity gain and diversity gain increases with increasing number of relay stations. The directivity gain itself offers increased SNR that can be used for range extension and/or data rate enhancement. The diversity gain, increases the robustness of the communication, providing a more uniform communication quality over time. While directivity and diversity gain can be provided by various traditional advanced antenna solutions, where the antennas are placed either at the transmitter or the receiver, the proposed solution is generally not limited to the physical space constraints as is seen in basestations or mobile terminals. Hence, there is indeed a potential to use a larger number of relays, than the number of antennas at a basestation or a mobile station, and hence offer even greater directivity and diversity gains.
Embodiments of the invention are defined in the dependent claims. Other objects, advantages and novel features of the invention will become apparent from the following detailed
description of the invention when considered in conjunction with the accompanying drawings and claims.
Brief description of the figures
The features and advantages of the present invention outlined above are described more fully below in the detailed description in conjunction with the drawings where like reference numerals refer to like elements throughout, in which:
Fig. la-g are schematic illustrations of the topologies of some prior art utilizing cooperative relaying;
Fig 2. schematically illustrates a cellular system using cooperative relaying according to the present invention;
Fig. 3 is a schematic model used to describe the parameters and terms used in the present invention;
Fig. 4 is a flowchart over the method according to the invention;
Fig. 5a and 5b are a schematic illustrations of two alternative logical architectures for the cooperative relaying network according to the present invention;
Fig. 6 is a flowchart over one embodiment of the method according to the invention;
Fig. 7 is a schematic illustration of an alternative embodiment of the invention utilizing relay stations with multiple antennas;
Fig. 8 is a schematic illustration of an alternative embodiment of the invention utilizing direct transmission between the transmitter and the receiver;
Detailed description of the invention
Embodiments of the invention will now be described with reference to the figures.
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 basestation 210 (BS), a plurality of relay stations 215 (RS) and a plurality of mobile stations (MS) 220-223. As shown in the figure, the relay stations 215 are mounted on masts, but may also be mounted on buildings, for example. Fixed relays 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. However, mobile relays, such as users mobile terminals, may also be used, either as a complement to fixed relays or independently. The mobile stations 221 and 222 are examples of mobile relays, i.e. mobile stations that temporarily functions also as relays. The mobile station 220 is in active communication with the base station 210. The signalling, as indicated with arrows, is essentially simultaneously using a plurality of paths, characterized by two hops, i.e. via a relay station 215 or a mobile station acting as a mobile relay 221,222. The transmission will experience interference from for example adjacent cells, and the effect of the interference will vary over the different paths.
It should be noted that although relay based communication is used to enhance communication, direct BS to MS communication may still be used. In fact, some basic low rate signalling between BS and MS may be required for setting up a relay supported communication channel. For example, a cellular system fiinction such as paging may not use coherent combining based relaying as the relay to MS channels are not a priori known, instead preferably, a direct BS to MS communication is used during call setup and similar procedures.
The real world cellular system outlined hi FIG. 2 is modeled by system model shown in FIG. 3, here with focus on a single pair of transmitter and receiver, with an arbitrary number K of relay stations. The notation is adapted to a basestation 210 as a transmitter and a mobile station 220 as a receiver, but not limited thereto. The communication between the basestation 210 and the mobile station 220 can be described as comprising two main parts: the transmissions from the base station 210 to the relay stations 215:k referred to as Link 1, and the transmissions from the relay stations 215:fcto the mobile station 220 referred to as Link 2.
The transmitter, i.e. BS 210 transmits with a power PBS. Each relay station 2l5:k, wherein k e (l,2,..., K} and K is the total number of relay stations, receive the signal and re-transmits with a total power Pk. The aggregate transmit power of all relay stations 2l5:k is denotedPj®. h^k is the complex path gain from the basestation 210 to relay station k2l5:k, and h^/c is the complex path gain from the relay station k to the mobile station, i.e. h^k and /72)4 characterizes the individual signal paths. The receiver, i.e. MS 220, receives a total signal denoted Cr and experience the total noise Nr.
Typically, hi a realistic scenario a BS in a cell is simultaneously engaged in communication with a plurality of mobile stations. This can be envisaged by considering each communication as modeled in accordance to FIG. 3. For clarity only a communication session involving one
Us, one MS and a plurality of relay station will be considered in the present application. However, as will be apparent for the skilled in the art the inventive architecture and method/scheme is easily applied also in the case with a plurality of simultaneous communications between the base station and mobile stations.
As realized by the skilled in the art, in a network according to the above model, a large number of parameters need to be set and preferably optimized in order to fully take advantage of the possibilities and capacity offered by such a network. This is also, as previously discussed, there the prior art systems display their shortcomings as multi-relay systems, due to their presumed complexity, are not discussed. Parameter that needs to be considered and preferably optimized include, but is not limited to, transmit power of the basestation 210 and each relay station 2\5:k, which relay stations that should be used in the communication, phase control (if coherent combining is used), coding, delay (in the case of delay diversity), antenna parameters (bearnforming, spatial multiplexing), etc. The parameters needed to control and optimize the transmission will be referred to as transmission parameters (TP). A preferred optimization includes, but is not limited to, optimizing the transmit powers of the base station 210 and the relay stations 215:k in order to obtain a specific SNR at the receiving mobile station, which in turn correspond to a certain quality of service or capacity, for example, with regards to power consumption of the different entities and the interference level in the cell and adjacent cells, for example.
Fundamental to all optimization and necessary for an efficient use of the radio recourses is an accurate characterization of the radio paths in the first and second link, and control over how any changes in any transmission parameter will affect the overall performance. The method according to the present invention provides a method wherein a relay station 2l5:k uses channel characteristics of both the first and second link to determine transmission parameters for the forwarding on the second link. In addition, according to the method, each relay station 215:k may optionally adapt its forwarding on the second link to a quality measure on the communication in full as perceived by the receiver 220, for example. The quality measure on the communication in full will be referred to as the common transmission parameter.
In the method according to the present invention of performing communication in a two-hop wireless communication network, a transmitter 210, a receiver 220 and at least one relay station 215 are engaged in a communication session The relay station 215 forwards signals from a first link between the transmitter 210 and the relay station 215 to a second link between the relay stations 215 and the receiver 220. The forwarding performed by the at least
one relay station 215 is adapted as a response to estimated radio channel characteristics of at least the first link. Preferably the forwarding is adapted as a response to estimated radio channel characteristics of both the first and second link.
The method according to the invention will be described with reference to the flowchart of FIG. 4 The method comprises the main steps of:
400: Send pilots on the k paths of link 1; 410: Characterize the k paths of link 1. 420: Send pilots on the k paths of link 2; 430: Characterize the k paths of link 2.
440: Determine relative transmission parameters for each relay station 215, wherein each relative parameter is based on the characterization of the respective paths of link 1 or a combination of link 1 and Iink2.
450: Each relay station 215:k adapts the forwarding on link 2 to the receiver 220 using its respective relative transmission parameter.
Optionally the method comprises the step of:
445: Determining a common transmission parameter reflecting the quality of the communication in full.
447: Distribute the common transmission parameter to the relay stations (215). and step 450 is subsequently replaced with:
450': Each relay station 2l5:k adapts the forwarding on the second link to the receiver 220 using its respective relative transmission parameter and the common transmission parameter,
"Pilots" and "sending pilots" should be interpreted as sending any kind of channel estimation symbols. "Hello messages" may also be used for this purpose.
It should be noted that the sending of pilots does not have to occur in the above order and may also be simultaneous on link 1 and 2.
The characterization of the radio paths in steps 410 and 430 is preferably adapted to the transmission technique used, and possibly also to the type of optimization which should utilize the characterization. The characterization may comprises of, but is not limited to:
estimating complex path gains hi and h2 characterizing each path of the first and second link, respectively.
As there are two links, transmitter to relay and relay to receiver, there are four possibilities of which station(s) transmit and which station(s) estimate the channel(s). The four possibilities are summarized in Table 1. The purpose is to illustrate that several different implementation approaches of the invention may be taken.
(Table Removed)Table 1
Given that channel estimation has been performed in some station, it is also an issue who perform processing of the collated information, i.e. determine the relative transmission parameters. Essentially, there are three choices, the transmitter BS 210, the receiver MS 220 or a set of relay stations RS 215. Since it is the relay stations that must perform the adjustments of the forwarding on link 2, this is the preferred place to determine the relative transmission parameters. If a relay station sends a pilot signal, a representation of the channel characterization needs to be reported back to the relay. If a relay station instead receives a pilot, the representation of the channel characterization does not need to be reported anywhere (corresponding to case 1). Case one is in many situations the preferred alternative, since it minimizes the overhead signalling. On the other hand, one may want to keep the relay stations as simple as possible and perform all calculations in the receiver and/or transmitter, or in entities in connection with the receiver or transmitter. If, so case 4 of tablel may be preferred, and all estimation and calculation is performed in other entities than the relay stations. The information needed for the relay stations to adjust their respective forwarding is sent to each relay station. As illustrated, many possible combinations exist and the invention is not limited to a specific one.
A preferred system according to the invention, adapted to be able to effectuate the above-described case 1, will be described with reference to FIG. 5a. Each relay station 215:fchas means for performing channel characterization 216 and means for determining relative transmission parameters 217 based on the channel characterization and means for adjusting 218 the forwarding based on relative transmission parameters and optionally on a common transmission parameter. The receiver 220 has means for performing a quality measure of the collective signal 221 and optionally means for determining a common transmission parameter 222. The common transmission parameter is distributed from the receiver 220 to the relay stations 215:k either as a direct broadcast to the relay stations 215:^ or via the transmitter 210. The relay stations 2l5:k receive the common transmission parameter and in combination with their relative transmission parameters adjust their forwarding of the signal. This can be seen as comprising a logical control loop between the receiver 220 and the relay stations 215 :k. Typically another logical control loop exists between the receiver 220 and the transmitter 210, regulating the transmitter's transmission parameters such as output power, modulation mode etc. Hence, the preferred embodiment of the present invention comprises two logical control loops: a first control loop 505 between the receiver 220 and the relay stations 2l5:k, providing the relay stations with the common transmission parameter, and a second control loop 510 feed-backing transmission information from the receiver 220 to the transmitter 210.
In an alternative embodiment, adapted to be able to effectuate the above described cases 3-4, and described with reference to FIG. 5b., the means for performing channel characterization 216 and means for determining both the relative transmission parameters 217 and the common transmission parameters 222 is centralized located in the receiver 220, for example. The receiver receives the unprocessed results of the pilot from the relay station 215 and/or transmitter 210. The receiver performs the necessary estimations and sends information on the relative transmission parameters arid the common transmission parameter to the relay stations 215, either as a broadcasted message including all relative transmission parameters or as dedicated messages to each relay station. Alternatively may the transmitter perform the estimation of the radio paths of the first link (case 2), and hence, have the means therefore. A further alternative is that the characterization and the determination of transmission parameters is performed However, preferably the receiver and transmitter communicate to present a collected message, or messages, with all transmission parameter information to the relay stations, either as a broadcasted message to all relay stations or as dedicated messages to each relay station. A further alternative is that the characterization and the determination of
transmission parameters is performed elsewhere in the network, for example hi a radio network controller (RNC) or an entity with similar functionality.
As described the present invention makes it possible to more precise and reliable determine and optimize different transmission parameters. This is turn makes it possible to folly take advantage of the capabilities of a relaying network, in particular the capabilities of a cooperative relaying network.
The method according to the invention facilitates a distribution of functionalities in the network allowing an increase in the number of relay stations in a communication session without any significant increase in the amount of protocol overhead that is needed for the transmission of data from the transmitter to the receiver.
To efficiently implement the method according to the above, a procedure of taking the characterization of the radio paths of both the links, and possibly common quality measures, into account in determining the forwarding parameters is desirable. An efficient procedure is outlined below and a full derivation of included expressions "derivation of analytic expressions" is given at the end of the detailed description. How the procedure can be adapted to control and optimize transmitted power, phase and relay station activation, representing different embodiments, is also given below.
Each relay station k transmits with a total power defined by
,where P is the aggregate transmit power of all relay stations, ak is a un-normalized complex gain factor for relay station k e (l,2,..., K} and K is the total number of relay stations.
In "derivation of analytic expressions" it is shown that the maximum receiver SNR is attained (provided received signal is normalized to unit power) if,
and PBS is the transmit power of the basestation, is the noise plus interference level at
any relay station, 0$s me level at the mobile station, h2k is complex path gain from the basestation to relay station k, and finally h2k is complex path gain from the relay station k to the mobile station.
It is can be shown (see the detailed derivation) that a relay station k that receives a signal shall transmit the following signal
It should be noted that T^ fc refers to the radio paths of the first link and TMSik refers to the
radio paths of the second link. Hence, the radio characteristics of both links are taken into account in each relay stations forwarding, r^ and TMS>k are preferably, but not necessarily
calculated at each relay station.
The ]T \ak term act as a power normalization factor, denoted
corresponds to the
|Indian Patent Application Number||4852/DELNP/2005|
|PG Journal Number||12/2010|
|Date of Filing||24-Oct-2005|
|Name of Patentee||TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)|
|Applicant Address||S-164 83 STOCKHOLM, SWEDEN .|
|PCT International Classification Number||H04L 25/52|
|PCT International Application Number||PCT/SE2004/000825|
|PCT International Filing date||2004-05-27|