Localized and distributed transmission

[0001] The present invention relates to methods and systems in a mobile communication system, such as a cellular mobile communication system, and in particular relates to the allocation and separation of resource blocks on 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 means that the shared transmission channel to a specific UE is limited to a set of (physical) resource blocks, each resource bioc containing a certain L number_rb subsequent subcarriers during one subframe. The specific set of resource blocks to use, for transmission to a particular UE, is selected by the Node B, e.g. based on knowledge of the status of the downlink channel. (e.g., channel-based scheduling).

[0003] Channel-dependent scheduling provides a very effective means to combat frequency-selective fading in a radio channel by simply dynamically avoiding parts of the spectrum that become 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 the current status of the channel is not possible. Yet another reason taken into account may be that the downstream and / or uplink signaling overhead that is associated with channel-dependent scheduling is too "expensive"¹. 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. [0005] 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 the terminals before the resources are divided into one or two logical blocks or frequency subsets (SU1 or SU2), depending on the terminal's response. This method determines whether the response is (1) information as to whether the channel is predictable or not, (2) information as to whether the terminal wants to be scheduled using frequency selective subcarrier allocation or not, and (3) an approximate channel transfer function. What's more, 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 the answer (3) and finally the network schedules the terminals. However, the subcarriers found in logical blocks are not just a single subcarrier per block described

EP-1974579B1PL resources. Furthermore, only SU1 refers to the selective frequency scheme of this allocation, while SU2 refers to the frequency interleaving scheme.

SUMMARY OF THE INVENTION [0006] 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 there may be several resource blocks, which leads to reduced resource-based distribution, and sufficient diversification frequency is not reached.

[0007] Therefore, the object of the present invention is to achieve the benefit of frequency diversification also for relatively low-charge transmissions. Therefore, there is a need in the art to provide a transmission scheme in which such payload can be distributed to many distributed resource blocks, and as a consequence, in order to effectively use the entire time / frequency grid, data for multiple users can be transmitted in the same physical resource block.

[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, the available resources are divided among a plurality of resource biocides, each resource block having a predefined number of subcarriers during a predetermined time interval. 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 attacked blocks of resources in a frequency domain to achieve frequency diversity in accordance with an aspect of the method of Fig. 2.

Fig. 4 illustrates an example of mapping distributed virtual resource blocks into 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.

EP-1974579B1PL

As shown in Fig. 1, the Node B includes a controller 20, while UE 12, 14, 16 include respective controllers 22, 24, 26. These controllers, for determining resource allocation, follow the methods described in more detail below.

[0013] The band 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 specific UE is in in this embodiment, the node B selects, 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 partitioning .

[0014] Fig. 2 illustrates a method in accordance with a further aspect of the invention. In this illustrated embodiment, the method is performed on the node B 10, although, for its implementation, some or all of the steps may be performed on other network nodes, with the result which is communicated to the node B. [0015] In step 30, physical resources available for downlink transmission from node B 10 to various 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 biocomposition may contain a predefined number of subcarriers and a predefined period of time. Again, these parameters can be determined in advance by the system specification. In one illustrated embodiment of the invention, each block of physical resources contains twelve consecutive subcarriers, and lasts for a subframe period (T_sf) 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 critical to this particular discussion, for simplicity it is assumed that the physical resource blocks 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] One possible non-limiting example of implementation is described below an algorithm to more accurately determine which physical resource blocks should be assigned as distributed physical resource blocks. More specifically, it is assumed that there is a number N_RB blocks of physical resources, indexed, e.g. 0, 1,2, ..., (N_RB"1), of which a number N_Drb is assigned to the distributed sides of physical resources, Number N_DRB it can be determined independently by the B10 node or by another network node. Indexes N_Drb distributed blocks of physical resources that are assigned

For distributed transmission, data is given by the expression / * C, where / denotes the values ​​in the sequence 0, 1,2, .... (Ndrb-1). and the integer C is given by the expression

ΛΤ -1 L 'DRB ^lJ [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., N_RB = 10 and N_Drb = 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 physical blocks of physical resources.

[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 the transmission to the user's device occupies 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 many physical resource blocks that are located at intervals between available blocks physical resources.

[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. So during the subframe period T_AND , transmissions to this UE are assigned three non-adjacent blocks of physical resources. 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 localized blocks of virtual resources.

[0025] Hence, in step 42, physical resource blocks corresponding to the attacked 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 attacked distributed virtual resource blocks are assigned to this user. Each distributed virtual resource block also contains M symbols. Each of all Ndrb - Nrb - Nlrb ​​distributed virtual resource blocks is mapped to the remaining N_DRB physical resource blocks (blocks of physical resources 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 resource blocks

EP-1974579B1PL physical, 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 N_DRB distributed virtual resource blocks are mapped to each of the many physical resource blocks assigned to the distributed transmission.

[0028] Mapping the distributed virtual resource block to N_DRB blocks of physical resources assigned to distributed transmission are as below;

1) Each distributed block of virtual resources is divided into the number N_DRB nearly equal sized parts, where / 'is the resource block number and aj is the part number. Each block of physical resources assigned to distributed transmission is similarly divided into S_kt 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, part P_v (part j of the distributed virtual resource block /) is mapped to the S subunit_k1 ( subunit / distributed physical resource block k), where the distributed physical resource blocks are indexed sequentially 0, 1, .... N_DRB, and where k - [(/ '+ /) mod Ndrb] and f [0029] Fig. 4 illustrates the mapping of distributed virtual resource blocks to physical resource blocks, using the example embodiment, assuming N values_DRB = 3 and N_RB = 10. To this end, three distributed physical resource blocks, i.e. physical resource blocks with indexes 0, 4, 8, are reindexed to 0, 1, 2, and then, for example, part P_1T1 (part 1 of distributed virtual resource block 1) is mapped to the S subunit_2i1 (sub-unit 1 of the distributed physical resource block 2, i.e., the original physical resource block 8), and part P_2T2 (part 2 of distributed virtual resource block 2) is mapped to the S subunit₁₂ (sub-unit 2 of the distributed physical resource block 1, i.e., the original physical resource block 4).

[0030] Hence, when the user needs a data transmission capacity that is equal to the capacity of one block of resources, and therefore the allocation of one block of virtual resources occurs, the transmission occurs in many blocks of physical resources, 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 attack the user. Further, the same procedure can easily be performed on the appropriate user device, which, in order to find out exactly which blocks of physical resources are assigned to the distributed transmission, must only know the value of N_DRB e.g. the number of distributed virtual resource blocks. Therefore, in step 48 of the process shown in Fig. 2, information is provided to the user equipment that allows determining which physical resource blocks are assigned to the distributed transmission. In one embodiment, this N value_DRB is signaled to the user equipment by signaling a higher layer. Based on the knowledge of the number of resource blocks and the number of distributed resource biocons, the user's device can calculate

The number of localized resource blocks and, moreover, can determine which resource blocks are distributed resource blocks.

[0033] Alternatively, a suitable network node may signal to the user equipment the number of localized resource blocks, allowing the user equipment to calculate the number of distributed resource blocks. [0034] For signaling dynamic scheduling information, it is necessary to identify each located and distributed virtual resource block. 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 located virtual resource block, the resource block identifier is the same as the physical resource block identifier 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 Py portion of the distributed virtual resource block is mapped. Referring to the example of Fig. 4, the first resource block therefore 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 completed 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 allocated subcarriers 0-3 in physical resource block 0, subcarriers 4-7 in physical resource block 4, and subcarriers 8-11 in physical resource block 8, during when the second user may have allocated subcarriers 8-11 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 the uaiai transmission.

[0037] It should be noted that, strictly speaking, nothing prevents different UEs from assuming (signaled) different N values_DRB. This fact simply implies that, while, for certain 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.