Localized and distributed transmission

[0001] The present invention relates to methods and systems in mobile communication systems, such as cellular mobile communication systems, and in particular relates to the allocation and separation of resource blocks in shared downlink channels.

BACKGROUND OF THE INVENTION [0002] The present invention in one particular embodiment relates to a localized, block-based transmission resource in a downlink shared channel, an improved UMTS Radio Access Network (E-UTRA). Localized transmission makes the shared transmission channel to a particular UE limited to a set of (physical) resource blocks, each resource block containing a number of consecutive LRB subcarriers during one subframe. The specific set of resource blocks to use, for transmission to a specific UE, is selected by a Node B, e.g. based on knowledge of the downlink channel status. (Eg. channel-dependent scheduling).

[0003] Channel-dependent scheduling provides a very effective means to combat frequency-selective fading in a radio channel by simply dynamically avoiding a portion of the spectrum that becomes subject to momentary deep fades. However, in some cases, channel-dependent scheduling is, for various reasons, impossible or unattractive. One reason may be that data can be addressed to more than one UE, in which case there is no single channel on which channel dependent scheduling could be based. Another reason may be that the channel can change so quickly over time, e.g. due to high mobility that tracking of the current channel status is not possible. Yet another reason considered may be that the signaling overhead on the downlink and / or uplink that is associated with channel-dependent scheduling is too "expensive". This can happen, e.g. for small loads, such as voice services. If channel-dependent scheduling cannot be used, it may be important to use frequency diversity to achieve good link performance.

[0004] For localized transmission, frequency diversification can easily be achieved by broadcasting on blocks of resources that are sufficiently scattered in the frequency domain.

SUMMARY OF THE INVENTION [0005] However, it has been observed that there is a problem that in some cases the payload may not be large enough to fill more than one or several resource blocks, which leads to reduced resource-based distribution, and sufficient frequency diversification is not achieved.

[0006] Hence, the object of the present invention is to achieve the benefits of frequency diversification also for transmissions with relatively small charges. Therefore, there is a need in the art for providing a transmission scheme in which such payloads can be distributed to many distributed resource blocks, and consequently, for the efficient use of the entire time / frequency grid, data for multiple users can be transmitted in the same physical resource block.

[0007] EP-A-1526674 discloses a subcarrier allocation method directed to the use of a transmission that is matched to the preferred receiving capabilities of each terminal. This requires extensive

Signaling between the network and terminals, before the resources are divided into one or two logical blocks or frequency subsets (SU1 or SU2), depending on the terminal response. The feedback is determined whether the response is (1) information about whether the channel is predictable or not, (2) information about whether the terminal wants to be scheduled using frequency-selective subcarrier allocation or not, and (3) approximate channel transfer function. In addition, there is described a "two-step" approach to signaling and scheduling, in which the terminal first returns information (1) and (2), then the network divides resources into SU1 and SU2, then the terminal returns a response (3) and finally the network schedules the terminals. However, the subcarriers found in logical blocks are not just a single subcarrier for the resource block described. Furthermore, only SU1 refers to a frequency selective allocation scheme, while SU2 refers to a frequency interleaving scheme.

[0008] The present invention provides a direct transmission scheme supporting a mix of localized and distributed transmission on a shared channel to meet these requirements.

[0009] In one exemplary embodiment, available resources are divided among a plurality of resource blocks, each resource block having a predefined number of subcarriers during a predetermined period of time. Resource blocks are divided between localized resource blocks and distributed resource blocks, and at least one user may have subunits allocated to many of these distributed resource blocks.

[0010] The present invention provides the benefits of a fully distributed transmission scheme used as a complement to localized transmission to implement the long-term evolution of downlink radio access schemes with minimal impact on the transmission scheme and with minimal additional signaling.

BRIEF DESCRIPTION OF THE DRAWINGS [0011]

Fig. 1 illustrates part of a cellular communication network in accordance with one embodiment of the present invention.

Fig. 2 is a flow diagram illustrating a method in accordance with one embodiment of the present invention.

Fig. 3 illustrates the scattering of allocated resource blocks in a frequency domain to achieve frequency diversity according to an aspect of the method of Fig. 2.

Fig. 4 illustrates an example of mapping distributed virtual resource blocks to physical resource blocks, in accordance with an aspect of the method of Fig. 2.

DESCRIPTION OF THE INVENTION [0012] Fig. 1 illustrates part of a mobile communication system according to the invention. In the illustrated embodiment, the system is part of the improved UMTS Radio Access Network (E-UTRA) using an Orthogonal Frequency Domain Multiplexing (OFDM) Access Scheme, but the invention can also be used in other types of networks, as will be shown later. In the illustrated part of the system, a network node is shown, which in this case is a B 10 node being in wireless communication with the three illustrated user devices (UE) 12, 14, 16. As shown in Fig. 1, node B contains controller 20, while UE 12, 14, 16 contain respective controllers 22, 24, 26. These controllers perform the methods described in more detail below to determine resource allocation.

[0013] The bandwidth available for transmission from node B 10 is divided into the number of subcarriers, and transmission from node B 10 to UE 12, 14, 16 can take place on specific subcarriers. The specific set of subcarriers to be used for transmission to a particular UE is in this embodiment selected by node B, although this selection can be made by another network node if desired. The term subcarrier is used herein to mean any small part of the available spectrum, and it will be obvious that the invention can be applied to modulation schemes in which the band is explicitly divided into predefined subcarriers, or modulation schemes in which there is no such predefined division .

[0014] Fig. 2 illustrates a method in accordance with a further aspect of the invention. In this illustrated embodiment, the method is performed at node B 10, although, to implement it, some or all of the steps may be performed at other network nodes, with the result being communicated to node B.

[0015] In step 30, downlink physical resources from node B 10 to different EU 12, 14, 16, etc. are determined. For example, physical resources may include a specific frequency band that is divided into a number of subcarriers. . The number of subcarriers can be determined in advance by the system specification.

[0016] In step 32, available physical resources are divided between physical resource blocks. For example, each physical resource block may contain a predefined number of subcarriers and a predefined time interval. Again, these parameters can be determined in advance by the system specification. In one illustrated embodiment of the invention, each physical resource block contains twelve consecutive subcarriers, and lasts for a subframe period (Tsf) of 0.5 ms. More generally, the physical resource block may contain the number of L consecutive subcarriers and, as a consequence, may contain M = n * L time / frequency symbols per subframe, where n is the number of OFDM symbols in the subframe (and hence, in the illustrated embodiment, M = 7 * L symbols, or M = 6 * L symbols for long cyclic prefix). Although this is not crucial for this particular discussion, for simplicity it is assumed that the blocks of physical resources constitute the entire subcarrier space, e.g. each subcarrier belongs to the physical resource block.

[0017] Fig. 3 illustrates the distribution of available physical resources between physical resource blocks.

[0018] In step 34, physical resource blocks are divided between localized physical resource blocks and distributed physical resource blocks, the use of which will be described in greater detail below. For reasons that will be explained below, it is advantageous for distributed physical resource blocks if they are not consecutive physical resource blocks, but are located in the intervals between said physical resource blocks.

[0019] Hereinafter, one possible non-limiting embodiment of the algorithm for more accurately determining which physical resource blocks should be assigned as distributed physical resource blocks is described below. More specifically, it is assumed that there are a number of NRB blocks of physical resources, indexed, e.g. 0, 1, 2, ..., (NRB-1), of which a number of NDRBs are assigned to distributed physical resource blocks. The number of NDRBs can be determined independently by the B10 node or by another network node. NDRB indexes of distributed physical resource blocks that are assigned to distributed transmission are given by the expression i * C, where i denotes the values ​​in the sequence 0, 1, 2, ... (NDRB-1), and the integer C is given by expression

N -1 ^7V DRB ¹

[0020] Thus, in the illustrative embodiment of the invention in which there are 10 physical resource blocks and 3 of them are assigned as physical resource blocks, i.e., NRB = 10 and NDRB = 3, C = 4 , physical resource blocks indexed 0, 4, 8 are assigned as distributed physical resource blocks. Other physical resource blocks indexed 1, 2, 3, 5, 6, 7, 9 are assigned as localized physical resource blocks.

[0021] In step 36, a new user is considered by node B. More specifically, in step 38, it is determined whether the user matches the distributed transmission or localized transmission. The method of the present invention seeks, in particular embodiments, for possibilities to achieve frequency diversity for transmission to each user equipment. When transmissions to a user's device occupy a reasonably large number of resource blocks, this user can be assigned to a localized transmission, and more specifically, the transmission to this user device can be assigned to multiple physical resource blocks that are located at intervals between available physical resource blocks.

[0022] This is illustrated in Fig. 3, in which the resource blocks are allocated to one specific UE that has been assigned to the localized transmission, they are shown as dashed. Thus, during the TA subframe period, three non-consecutive physical resource blocks are assigned to this UE. This leads to an acceptable degree of diversification for transmission to this EU.

[0023] However, when the transmission to the user equipment will only occupy one or a small number of resource blocks, if such a user is assigned to a localized transmission, then frequency diversification will not be achieved. Embodiments of the invention thus provide a way to achieve this frequency diversification, even in this case.

[0024] Hence, if it is determined that the user matches the localized transmission, the process proceeds to step 40, in which the localized virtual resource blocks are assigned. Each localized block of virtual resources also contains M symbols. In addition, each localized block of virtual resources is mapped one to one to a set of blocks of physical resources that are assigned to localized transmission. The number of blocks of physical resources assigned to localized transmission (denoted NLRB) is therefore equal to the number of blocks of localized virtual resources.

[0025] Hence, in step 42, physical resource blocks corresponding to the allocated localized virtual resource blocks are assigned to this user.

[0026] If it is determined in step 38 that the user matches the distributed transmission, the process proceeds to step 44, in which the distributed virtual resource blocks are assigned. Then, in step 46, physical resources corresponding to the allocated distributed virtual resource blocks are assigned to this user. Each distributed virtual resource block also contains M symbols. Each of the NDRB = NRB - NLRB distributed virtual resource blocks is mapped to the remaining NDRB physical resource blocks (physical resource blocks assigned to distributed transmission). However, unlike localized blocks of virtual resources, this mapping is not performed one-to-one. Instead, each distributed block of virtual resources is mapped to multiple blocks of physical resources assigned to distributed transmission. Therefore, subunits of many distributed blocks of physical resources are allocated to this user, as described in greater detail below.

[0027] In this illustrated embodiment, each of the NDRBs of distributed virtual resource blocks is mapped to each of a plurality of blocks of physical resources assigned to the distributed transmission.

[0028] The mapping of the distributed virtual resource block to the NDRB of the physical resource blocks assigned to the distributed transmission is as follows:

1) Each distributed virtual resource block is divided into the number of NDRBs of the Pi part, almost equal in size, where i is the resource block number and aj is the part number. Each block of physical resources assigned to distributed transmission is similarly divided into Sk, 1 subunits. For example, when, as here, each physical resource block contains 12 subcarriers and there are 3 resource blocks assigned to distributed transmission, each of these subunits contains 4 subcarriers.

2) In this illustrated embodiment, the part Pi, j (part j of the distributed virtual resource block i) is mapped to the sub-unit Sk, 1 (the sub-unit l of the distributed physical resource block k), where the distributed physical resource blocks are indexed sequentially 0, 1, ..., NDRB, and where k = [(i + j) mod NDRH] and 1 = j.

[0029] Fig. 4 this illustrates the mapping of distributed virtual resource blocks to physical resource blocks, using the example embodiment, assuming NDRB = 3 and NRB = 10. For this purpose, three distributed physical resource blocks, that is, physical resource blocks with indexes 0, 4 8 are reindexed to 0, 1 2 and then, for example, part P1,1 (part 1 of distributed virtual resource block 1) is mapped to sub-unit S2,1 (sub-unit 1 of distributed physical resource block 2, it is, the original physical resource block 8), and part P2.2 (part 2 of distributed virtual resource block 2) is mapped to sub-unit S1,2 (sub-unit 2 of distributed physical resource block 1, it is, the original physical resource block 4).

[0030] Hence, when the user needs a data transmission capacity that is equal to the capacity of one resource block, and therefore one virtual resource block is allocated, transmission occurs in many physical resource blocks, thereby achieving frequency diversification even for such users.

[0031] In this embodiment of the invention, each virtual resource block is partially mapped to each distributed physical resource block. In other embodiments, where there are more distributed physical resource blocks, it may be preferable to map each distributed virtual resource block to only a subset of distributed physical resource blocks.

[0032] Hence, a method is provided according to which a Node B, or other network node, can determine which resources to allocate to a user. Further, the same procedure can easily be performed in the appropriate user device, which, in order to find out which exactly blocks of physical resources are assigned to the distributed transmission, must only know the NDRB value, e.g. the number of distributed virtual resource blocks. Hence, in step 48 of the process shown in Fig. 2, information is provided to the user's device enabling determination of which blocks of physical resources are assigned to the distributed transmission. In one embodiment, this NDRB value is signaled to the user equipment by higher layer signaling. Based on the knowledge of the number of resource blocks and the number of distributed resource blocks, the user equipment can calculate the number of localized resource blocks and, moreover, can determine which resource blocks are distributed resource blocks.

[0033] Alternatively, the respective network node may signal to the user equipment the number of resource blocks located, allowing the user equipment to calculate the number of distributed resource blocks.

[0034] For signaling dynamic scheduling information, it is necessary to identify each localized and distributed block of virtual resources. The assumption is that each block of physical resources has the appropriate form of identifier. According to a possible embodiment, these may be ordered numbers. For each localized virtual resource block, the identifier of the resource block is the same as the identifier of the physical resource block to which the localized virtual resource block is mapped (physical resource block 1, 2, 3, 5, 6, 7, and 9 in Fig. 2). For distributed virtual resource blocks, the resource block identifier is the same as the physical resource block identifier to which the first Pi portion of the distributed virtual resource block is mapped. Referring to the example according to Fig. 4, the first resource block thus receives identifier 0, the second resource block receives identifier 4, and the third receives identifier 8. It should be noted that these are exactly the numbers that are missing in the sequence of localized blocks of virtual resources.

[0035] When the process shown in Fig. 2 is ended for one user, it can be repeated for another user. If it is determined that this user also matches distributed transmission, then another distributed virtual resource block will be allocated, but subcarriers may be allocated in the same physical resource block as for the first user. For example, based on the case illustrated in Fig. 4, and where each physical resource block contains twelve consecutive subcarriers, the first user may have subcarriers 0-3 allocated in the physical resource block 0, subcarriers 4-7 in the physical resource block 4, and subcarriers 8-11 in the physical resource block 8, during when the second user may have subcarriers 8-11 allocated in physical resource block 0, subcarriers 0-3 in physical resource block 4, and subcarriers 4-7 in physical resource block 8. Hence, every user is able to achieve the desired frequency diversification.

[0036] Furthermore, localized and distributed resource blocks share the same "identifier space" and support for distributed transmission can thus be implemented without adding any dynamic signaling, compared to what is still needed for localized transmission.

[0037] It should be noted that, strictly speaking, nothing prevents different UEs from establishing (signaled) different NDRB values. This fact simply implies that, while, for some user devices, certain physical resource blocks are used for localized transmission, for other user devices, the same physical resource blocks can be used for distributed transmission. In this case, node B, the dynamic dispatcher must ensure that no collisions occur.

[0038] Thus, a method of achieving frequency diversification is provided, even for such users who only need a relatively low transmission capacity.