U.S. patent application number 12/161396 was filed with the patent office on 2011-03-17 for localized and distributed transmission.
Invention is credited to Erik Dahlman, Stefan Parkvall, Lei Wan.
Application Number | 20110065468 12/161396 |
Document ID | / |
Family ID | 37895979 |
Filed Date | 2011-03-17 |
United States Patent
Application |
20110065468 |
Kind Code |
A1 |
Parkvall; Stefan ; et
al. |
March 17, 2011 |
LOCALIZED AND DISTRIBUTED TRANSMISSION
Abstract
The available transmission resources on a downlink-shared
channel are divided into resource blocks, each resource block
comprising a predetermined number of sub-carriers during a
predetermined time period. The resource blocks are subdivided into
localized resource blocks and distributed resource blocks. A user
requiring sufficient resources can be allocated a plurality of said
localized resource blocks. A user who would require only a small
number of said localized resource blocks can instead be allocated
subunits of a plurality of said distributed resource blocks.
Inventors: |
Parkvall; Stefan;
(Stockholm, SE) ; Dahlman; Erik; (Bromma, SE)
; Wan; Lei; (Beijing, CN) |
Family ID: |
37895979 |
Appl. No.: |
12/161396 |
Filed: |
January 18, 2007 |
PCT Filed: |
January 18, 2007 |
PCT NO: |
PCT/EP07/00433 |
371 Date: |
March 25, 2010 |
Current U.S.
Class: |
455/509 |
Current CPC
Class: |
H04W 72/042 20130101;
H04W 72/04 20130101; H04B 7/06 20130101; H04L 5/0039 20130101; H04L
5/0007 20130101; H04W 72/1263 20130101; H04L 5/0041 20130101; H04L
5/0032 20130101; H04W 72/087 20130101 |
Class at
Publication: |
455/509 |
International
Class: |
H04B 7/00 20060101
H04B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 18, 2006 |
SE |
0600106-9 |
Claims
1. A method of allocating resources amongst users on a
downlink-shared channel of a telecommunication system, the method
comprising: dividing the available resources into a plurality of
resource blocks, each resource block comprising a predetermined
number of sub-carriers during a predetermined time period;
subdividing the resource blocks into localized resource blocks and
distributed resource blocks; and for at least one user, allocating
subunits of a plurality of said distributed resource blocks.
2. A method as claimed in claim 1, comprising allocating subunits
of each of said distributed resource blocks to a plurality of
respective users.
3. A method as claimed in claim 1, further comprising, for at least
one other user, allocating a plurality of said localized resource
blocks.
4. A method as claimed in claim 3, further comprising, for at least
one user: determining the amount of resources required by said
user; if the amount of resources is less than a predetermined
threshold, allocating to said user subunits of a plurality of said
distributed resource blocks; and if the amount of resources is
greater than a predetermined threshold, allocating to said user a
plurality of said localized resource blocks.
5. A method as claimed in claim 1, wherein each resource block
contains the same number of sub-carriers.
6. A method as claimed in claim 1, wherein each resource block
comprises a predetermined number of consecutive sub-carriers.
7. A method as claimed in claim 1, wherein the distributed resource
blocks are located at intervals amongst said resource blocks.
8. A method as claimed in claim 7, wherein the distributed resource
blocks are located at substantially regular intervals amongst said
resource blocks.
9. A method as claimed in claim 1 comprising: for a first user,
allocating a first subunit of each of a plurality of said
distributed resource blocks; and for a second user, allocating a
second subunit of each of said plurality of said distributed
resource blocks.
10. A method as claimed in claim 9, wherein said each of said first
and second subunits comprise similar numbers of sub-carriers during
a predetermined time period.
11. A method as claimed in claim 1, comprising: determining in a
network node how many of said resource blocks should be allocated
as localized resource blocks and how many of said resource blocks
should be allocated as distributed resource blocks; and
transmitting information to a user indicating how many of said
resource blocks should be allocated as distributed resource blocks,
such that said user can determine which of said resource blocks are
to be allocated as distributed resource blocks.
12. A network node, adapted to allocate resources amongst users on
a downlink-shared channel of a telecommunication system, wherein
said node comprises a controller, said controller being adapted to:
divide the available resources into a plurality of resource blocks,
each resource block comprising a predetermined number of
sub-carriers during a predetermined time period; subdivide the
resource blocks into localized resource blocks and distributed
resource blocks; and for at least one user, allocate subunits of a
plurality of said distributed resource blocks.
13. A network node as claimed in claim 12, wherein said controller
is further adapted to: determine how many of said resource blocks
should be allocated as localized resource blocks and how many of
said resource blocks should be allocated as distributed resource
blocks; and transmit information to a user indicating how many of
said resource blocks should be allocated as distributed resource
blocks, such that said user can determine which of said resource
blocks are to be allocated as distributed resource blocks.
14. A network node as claimed in claim 12, wherein the network node
is a Node B of a cellular communications system.
15. A user equipment, for use in a telecommunication system,
wherein the user equipment is adapted to receive transmissions from
a network node on a downlink-shared channel, said channel
comprising resources divided into a plurality of resource blocks,
each resource block comprising a predetermined number of
sub-carriers during a predetermined time period, and wherein the
user equipment comprises a controller, said controller being
adapted to: receive information from the network node, in order to
determine how many of said resource blocks should be allocated as
distributed resource blocks, and to determine which of said
resource blocks are to be allocated as distributed resource
blocks.
16. A method for achieving frequency diversity for scheduled
transmissions of resource blocks on a downlink-shared channel of a
telecommunication system, comprising: subdividing resource blocks
into localized and distributed virtual resource blocks, mapping the
localized resource blocks one-to-one to the set of physical
resources that are assigned for localized transmission, mapping the
distributed resource blocks to all of the remaining physical
resource blocks assigned for distributed transmission.
17. The method according to claim 16, whereby the mapping of a
distributed resource block is done by splitting the distributed
resource block into a number of parts, and mapping said parts to
the physical resource blocks.
18. The method according to claim 17, wherein said number of parts
corresponds to the number of physical resource blocks assigned for
distributed transmission.
19. An arrangement in a network node of a telecommunication system,
comprising means for performing the method according to claim 17.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to methods and arrangements in
mobile communication systems, such as cellular mobile communication
systems, in particular to resource block allocation and
distribution on downlink shared channels.
BACKGROUND OF THE INVENTION
[0002] The present invention refers in one particular embodiment to
localized, resource-block-based transmission on the downlink shared
channel of an enhanced UMTS Radio Access Network (E-UTRA).
Localized transmission implies that the shared-channel transmission
to a certain UE is confined to a set of (physical) resource blocks,
where each resource block consists of a certain number L.sub.RB of
consecutive sub-carriers during one sub frame. The specific set of
resource blocks to be used for transmission to a certain UE is
selected by the Node B, e.g., based on knowledge of the downlink
channel conditions (i.e. channel-dependent scheduling).
[0003] Channel-dependent scheduling provides a very efficient means
to combat frequency-selective fading on the radio channel by simply
dynamically avoiding parts of the spectrum that are subject to
momentary deep fades. However, in some cases, channel-dependent
scheduling is, for different reasons, not possible or not
attractive. One reason can be that data may be targeting more than
one UE, in which case there is not one single channel on which the
channel-dependent scheduling can be based. Another reason might be
that the channel may vary so fast in time, e.g. due to high
mobility, that tracking of the instantaneous channel conditions is
not possible. Yet another considerable reason might be that the
downlink and/or uplink signaling overhead that is associated with
channel-dependent scheduling is too "expensive". This could be the
case, e.g., for small payloads such as for voice services. If
channel-dependent scheduling cannot be used, an exploitation of
frequency diversity may be important in order to achieve good link
performance.
[0004] In the case of localized transmission, frequency diversity
can be achieved by simply transmitting on a set of resource blocks
that are sufficiently spread in the frequency domain.
SUMMARY OF THE INVENTION
[0005] However, it has been observed to be a problem that in some
cases the payload may not be large enough to fill more than one or
perhaps a few resource blocks, which leads to a limitation of the
distribution on a resource-block basis, such that sufficient
frequency diversity is not achieved.
[0006] Thus, it is an object of the present invention to achieve
the benefits of frequency diversity also for transmissions with
relatively small payloads. There is thus a need for a transmission
scheme where such payloads can be distributed over multiple
distributed resource blocks and, as a consequence, in order to
efficiently utilize the overall time/frequency grid, data to
multiple users can be transmitted within the same physical resource
block.
[0007] The present invention addresses a straightforward
transmission scheme supporting a mix of localized and distributed
shared-channel transmission in order to fulfil these
requirements.
[0008] In one embodiment, the available resources are divided into
a plurality of resource blocks, each resource block comprising a
predetermined number of sub-carriers during a predetermined time
period. The resource blocks are subdivided into localized resource
blocks and distributed resource blocks and at least one user can be
allocated subunits of a plurality of said distributed resource
blocks.
[0009] The present invention offers the advantage of a fully
distributed transmission scheme to be used as a complement to
localized transmission for introduction into the long-term
evolution of downlink radio-access schemes with minimum impact on
the transmission scheme and with minimum additional signaling.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 illustrates a part of a cellular communications
network in accordance with an embodiment of the present
invention.
[0011] FIG. 2 is a flow chart, illustrating a method in accordance
with an embodiment of the present invention.
[0012] FIG. 3 illustrates the spreading of allocated resource
blocks in the frequency domain in order to achieve frequency
diversity, in accordance with an aspect of the method of FIG.
2.
[0013] FIG. 4 illustrates an example of a mapping of distributed
virtual resource blocks to physical resource blocks, in accordance
with an aspect of the method of FIG. 2.
DESCRIPTION OF THE INVENTION
[0014] FIG. 1 illustrates a part of a cellular telecommunications
system in accordance with the invention. In the illustrated
embodiment, the system is part of an enhanced UMTS Radio Access
Network (E-UTRA), using an Orthogonal Frequency Division Multiple
(OFDM) Access scheme, but the invention can be used in other types
of network, as will be apparent. In the illustrated part of the
system, there is shown a network node, which, in this case, is a
Node B 10, which is in wireless communication with three
illustrated user equipments (UEs) 12, 14, 16. As shown in FIG. 1,
the Node B 10 includes a controller 20, while the UEs 12, 14, 16
include respective controllers 22, 24, 26. These controllers
perform the methods described in more detail below, for determining
the allocation of resources.
[0015] The bandwidth available for transmissions from the Node B 10
is divided into a number of sub-carriers, and transmissions from
the Node B 10 to the UEs 12, 14, 16 can take place on particular
ones of these sub-carriers. The specific set of sub-carriers to be
used for transmission to a certain UE is selected by the Node B
itself in this embodiment, although this selection can be made by
another network node, if desired. The term sub-carrier is used to
mean any small part of the available spectrum, and it will be noted
that the invention is applicable to modulation schemes in which the
bandwidth is explicitly divided into predefined sub-carriers, or to
modulation schemes in which there is no such predefined
division.
[0016] FIG. 2 illustrates a method in accordance with an aspect of
the invention. In this illustrated embodiment, the method is
performed in the Node B 10, although some or all of the steps can
be performed in other nodes of the network, with the results being
communicated to the Node B 10 for implementation.
[0017] In step 30, the physical resources available for
transmission on the downlink from the Node B 10 to the various UEs
12, 14, 16, etc are determined. For example, the physical resources
may include a particular frequency bandwidth, which is divided into
a number of sub-carriers. The number of sub-carriers may be
determined in advance by the system specification.
[0018] In step 32, the available physical resources are divided
into physical resource blocks. For example, each physical resource
block may include a predetermined number of sub-carriers and a
predetermined time period. Again, these parameters may be
determined in advance by the system specification. In one
illustrated embodiment of the invention, each physical resource
block includes twelve consecutive sub-carriers, and lasts for a
sub-frame period (T.sub.sf) of 0.5 ms. More generally, a physical
resource block may consist of a number L of consecutive
sub-carriers and, as a consequence, may contain M=n.times.L
time/frequency symbols per sub-frame, where n is the number of OFDM
symbols in a sub-frame (and hence, in the illustrated embodiment,
M=7.times.L symbols, or M=6.times.L symbols in the case of a long
cyclic prefix). Although not of importance for this specific
discussion, for simplicity we assume that physical resource blocks
make up the entire sub-carrier space, i.e. each sub-carrier belongs
to a physical resource block.
[0019] FIG. 3 illustrates the division of the available physical
resources into physical resource blocks.
[0020] In step 34, the physical resource blocks are subdivided into
localized physical resource blocks and distributed physical
resource blocks, the uses of which will be described in more detail
below. For reasons that will become apparent below, it is
advantageous for the distributed physical resource blocks not to be
consecutive physical resource blocks, but to be located at
intervals amongst said physical resource blocks.
[0021] The following describes one possible, non-limiting, example
embodiment of an algorithm for determining more exactly which
physical resource blocks should be assigned as distributed physical
resource blocks. More specifically, it is assumed that there are a
number N.sub.RB of physical resource blocks, indexed, e.g., 0, 1,
2, . . . , (N.sub.RB-1), of which a number N.sub.DRB are assigned
to be distributed physical resource blocks. The number N.sub.DRB
can be determined by the Node B 10 itself, or by another network
node. The indices of the N.sub.DRB distributed physical resource
blocks that are assigned for distributed transmission are then
given by the expression i*C, where i denotes a value in the
sequence 0, 1, 2, . . . , (N.sub.DRB-1), and the integer C is given
by the expression
C = N RB - 1 N DRB - 1 . ##EQU00001##
[0022] Thus, in an illustrative example, where there are 10
physical resource blocks and 3 of them are assigned to be physical
resource blocks, that is, N.sub.RB=10 and N.sub.DRB=3, C=4, and so
the physical resource blocks indexed 0, 4, 8 are assigned to be
distributed physical resource blocks. The other physical resource
blocks, indexed 1, 2, 3, 5, 6, 7, 9 are assigned to be localized
physical resource blocks.
[0023] In step 36, a new user is considered by the Node B.
Specifically, in step 38, it is determined whether the user is
suitable for distributed transmission or localized transmission.
The method of the present invention seeks, in particular
embodiments, to achieve frequency diversity for the transmissions
to each user equipment. Where the transmissions to a user equipment
will occupy a reasonably large number of resource blocks, that user
can be assigned to localized transmission, and more specifically
the transmissions to that user can be assigned to multiple physical
resource blocks that are located at intervals amongst the available
physical resource blocks.
[0024] This is illustrated in FIG. 3, in which the resource blocks
allocated to one specific UE, which has been assigned to localized
transmission, are shown cross-hatched. Thus, during a sub-frame
period T.sub.A, transmissions to that UE are assigned three
non-consecutive physical resource blocks. This provides an
acceptable degree of frequency diversity for the transmissions to
this UE.
[0025] However, where the transmissions to a user equipment will
occupy only one or a small number of resource blocks, if that user
is assigned to localized transmission, then frequency diversity
will not be achieved. Embodiments of the invention therefore
provide a way of achieving this frequency diversity, even in this
case.
[0026] Thus, if it is determined that the user is suitable for
localized transmission, the process passes to step 40, in which
localized virtual resource blocks are assigned. Each localized
virtual resource block also consists of M symbols. Furthermore,
each localized virtual resource block is mapped one-to-one to the
set of physical resource blocks that are assigned to localized
transmission. The number of physical resource blocks assigned to
localized transmission (denoted N.sub.LRB) is thus equal to the
number of localized virtual resource blocks.
[0027] Thus, in step 42, the physical resource blocks corresponding
to the allocated localized virtual resource blocks are assigned to
that user.
[0028] If it is determined in step 38 that the user is suitable for
distributed transmission, the process passes to step 44, in which
distributed virtual resource blocks are assigned. Then, in step 46,
the physical resources corresponding to the allocated distributed
virtual resource blocks are assigned to that user. Each distributed
virtual resource block also consists of M symbols. Each of a total
of N.sub.DRB=N.sub.Rb-N.sub.LRB distributed virtual resource blocks
are mapped to the remaining N.sub.DRB physical resource blocks (the
physical resource blocks assigned for distributed transmission).
However, in contrast to localized virtual resource blocks, this
mapping is not one-to-one. Instead, each distributed virtual
resource block is mapped to a plurality of the physical resource
blocks assigned for distributed transmission. Thus, subunits of a
plurality of the distributed physical resource blocks are allocated
to that user, as described in more detail below.
[0029] In this illustrated embodiment, every one of the N.sub.DRB
distributed virtual resource blocks is mapped to every one of the
plurality of the physical resource blocks assigned for distributed
transmission.
[0030] The mapping of a distributed virtual resource block to the
N.sub.DRB physical resource blocks assigned for distributed
transmission is as follows:
[0031] 1) Each distributed virtual resource block is split into a
number N.sub.DRB of parts P.sub.i,j of almost equal size, where i
is the resource-block number and j is the part number. Each
physical resource block assigned for distributed transmission is
similarly divided into subunits S.sub.k,l. For example, where, as
here, each physical resource block includes 12 sub-carriers and
there are 3 resource blocks assigned for distributed transmission,
each of these subunits includes 4 sub-carriers.
[0032] 2) In this illustrated embodiment, the part P.sub.i,j (part
j of distributed virtual resource block i) is mapped to the subunit
S.sub.k,l (subunit l of distributed physical resource block k),
where the distributed physical resource blocks are indexed
sequentially 0, 1, . . . , N.sub.DRB, and where k=[(i+j)mod
N.sub.DRB] and l=j.
[0033] FIG. 4 illustrates this mapping of distributed virtual
resource blocks to physical resource blocks by means of an example
embodiment assuming the values N.sub.DRB=3 and N.sub.RB=10. Thus,
the three distributed physical resource blocks, namely the physical
resource blocks indexed 0, 4, 8, are re-indexed 0, 1, 2 for these
purposes, and then, for example, the part P.sub.1,1 (part 1 of
distributed virtual resource block 1) is mapped to the subunit
S.sub.2,1 (subunit 1 of distributed physical resource block 2, that
is, the original physical resource block 8), and the part P.sub.2,2
(part 2 of distributed virtual resource block 2) is mapped to the
subunit S.sub.1,2 (subunit 2 of distributed physical resource block
1, that is, the original physical resource block 4).
[0034] Thus, when a user requires a data transmission capacity that
is equal to that of one resource block, and is therefore allocated
one virtual resource block, the transmissions occur in multiple
physical resource blocks, thereby achieving frequency diversity
even for such users.
[0035] In this example, each virtual resource block is partially
mapped to every one of the distributed physical resource blocks. In
other embodiments, where there are a larger number of distributed
physical resource blocks, it may be preferable to map each
distributed virtual resource block to only a subset of the
distributed physical resource blocks.
[0036] Thus, there is provided a method whereby a Node B, or other
network node, can determine which resources to allocate to a user.
Further, the same procedure can be performed simply in the relevant
user equipment, which only needs to know the value of N.sub.DRB,
i.e. the number of distributed virtual resource blocks, in order to
know exactly what physical resource blocks are assigned for
distributed transmission. Thus, in step 48 of the process shown in
FIG. 2, information is provided to the user equipment, allowing it
to determine which physical resource blocks are assigned for
distributed transmission. In one embodiment, this value of
N.sub.DRB is signaled to the user equipment via higher-layer
signaling. Based on a knowledge of the number of resource blocks
and of the number of distributed resource blocks, the user
equipment can then calculate the number of localized resource
blocks, and moreover can determine which of the resource blocks are
to be distributed resource blocks.
[0037] Alternatively, the relevant network node can signal to the
user equipment the number of localized resource blocks, allowing
the user equipment to calculate the number of distributed resource
blocks.
[0038] For signaling of dynamic scheduling information, it is
necessary to identify each localized and distributed virtual
resource block. It is assumed that each physical resource block has
an appropriate form of identity. According to one conceivable
embodiment this can be ordered numbers. For each localized virtual
resource block, the resource-block identity is the same as the
identity of the physical resource block to which the localized
virtual resource block is mapped to (physical resource block 1, 2,
3, 5, 6, 7, and 9 in FIG. 2). In case of distributed virtual
resource blocks the resource-block identity is the same as the
identity of the physical resource block to which the first part
P.sub.i,j of the distributed virtual resource block is mapped.
Referring to the example according to FIG. 4, the first resource
block thus gets an identity 0, the second resource block gets
identity 4, and the third gets identity 8. Note that these are
exactly the numbers missing from the sequence of localized virtual
resource blocks.
[0039] Once the process shown in FIG. 2 has been completed for one
user, it can be repeated for another user. If it is determined that
that user is also suitable for distributed transmission, then it
will be allocated a different distributed virtual resource block,
but it may be allocated sub-carriers in the same physical resource
blocks as the first user. For example, based on the illustrated
case shown in FIG. 4, and where each physical resource block
includes twelve consecutive sub-carriers, the first user may be
allocated sub-carriers 0-3 in physical resource block 0,
sub-carriers 4-7 in physical resource block 4, and sub-carriers
8-11 in physical resource block 8, while the second user may be
allocated sub-carriers 8-11 in physical resource block 0,
sub-carriers 0-3 in physical resource block 4, and sub-carriers 4-7
in physical resource block 8. Thus, each user is able to achieve a
desirable frequency diversity.
[0040] Moreover, the localized and distributed resource blocks
share the same "identity space" and the support for distributed
transmission can thus be introduced without adding any additional
dynamic signaling compared to what is anyway needed for localized
transmission.
[0041] It should be noted that, strictly speaking, nothing prevents
different UEs from assuming (being signaled) different values of
N.sub.DRB. That would simply imply that, for certain user
equipments, certain physical resource blocks are used for localized
transmission while, for other user equipments, the same physical
resource blocks may be used for distributed transmission. In this
case, the Node B dynamic scheduler must ensure that collisions do
not happen.
[0042] There is therefore provided a method for achieving frequency
diversity, even for users that require only a relatively small
transmission capacity.
* * * * *