Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND METHOD FOR ALLOCATING RESOURCES IN A
SINGLE CARRIER-FREQUENCY DIVISION MULTIPLE ACCESS
SYSTEM
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for efficiently
allocating control channel transmission resources when a packet data channel
and
a control channel are transmitted in the same transmission period in a Single
Carrier-Frequency Division Multiple Access (SC-FDMA) wireless
communication system.
2. Description of the Related Art
FIG 1 is a block diagram of a transmitter in a Localized FDMA (LFDMA)
system being a kind of SC-FDMA system. While the transmitter is configured so
as to use Discrete Fourier Transform (DFT) and Inverse Fast Fourier Transform
(IFFT) in the illustrated case of FIG 1, any other configuration is available
to the
transmitter.
Referring to FIG 1, the use of DFT and IFFT facilitates changing LFDMA
system parameters with low hardware complexity. Concerning the difference
between Orthogonal Frequency Division Multiplexing (OFDM) and SC-FDMA
in terms of transmitter configuration, the LFDMA transmitter further includes
a
DFT precoder 101 at the front end of an IFFT processor 102 that is used for
multi-carrier transmission in an OFDM transmitter. In FIG 1, Transmission (TX)
modulated symbols 103 are provided in blocks to the DFT precoder 101. DFT
outputs are mapped to IFFT inputs in a band comprised of successive
subcarriers.
A mapper 104 functions to map the transmission modulated symbols to an actual
frequency band.
FIG. 2 illustrates an exemplary data transmission from User Equipments
(UEs) in their allocated resources in a conventional SC-FDMA system.
Referring to FIG 2, one Resource Unit (RU) 201 is defined by one or
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more subcarriers in frequency and one or more SC-FDMA symbols in time. For
data transmission, two RUs marked with slashed lines are allocated to UE1 and
three RUs marked with dots are allocated to UE2.
The RUs in which UE1 and UE2 transmit data are fixed in time and
successive in predetermined frequency bands. This resource allocation scheme
or
data transmission scheme selectively allocates frequency resources that offer
a
good channel status to each UE, to thereby maximize system performance with
limited system resources. For example, the slashed blocks offer relatively
better
radio channel characteristics to UE1 than in other frequency bands, whereas
the
dotted blocks offer relatively better radio channel characteristics to UE2.
The
selective allocation of resources with a better channel response is called
frequency selective resource allocation or frequency selective scheduling. As
with
uplink data transmission from a UE to a Node B as described above, the
frequency selective scheduling applies to downlink data transmission from the
Node B to the UE. On the downlink, the RUs marked with slashed lines and dots
represent resources in which the Node B transmits data to UEl and UE2,
respectively.
However, the frequency selective scheduling is not always effective. For a
UE that moves quickly and thus experiences a fast change in channel status,
the
frequency selective scheduling is not easy. More specifically, although a Node
B
scheduler allocates a frequency band in a relatively good channel status to a
UE at
a given time, the UE is placed in a channel environment that has already
changed
significantly when the UE receives resource allocation information from the
Node
B and is to transmit data in the allocated resources. Hence, the selected
frequency
band does not ensure the relatively good channel status for the UE.
Even in a Voice over Internet Protocol (VoIP)-like service that requires a
small amount of frequency resources continuously for data transmission, if the
UE reports its channel status for the frequency selective scheduling,
signaling
overhead can be huge. In this case, it is more effective to use frequency
hopping
rather than the frequency selective scheduling.
FIG. 3 illustrates an exemplary frequency hopping in a conventional
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FDMA system.
Referring to FIG 3, frequency resources allocated to a UE for data
transmission change over time. The frequency hopping has the effect of
randomizing channel quality and interference during data transmission. As data
is
transmitted in frequency resources that vary over time, the data has different
channel characteristics and a different UE in a neighbor cell interferes with
the
data at each time point, thus achieving diversity.
However, the frequency hopping is not viable when RUs hop in
independent patterns in the SC-FDMA system as illustrated in FIG 3. For
instance, if RUs 301 and 302 are allocated to different UEs, it does not
matter. Yet,
if both the RUs 301 and 302 are allocated to a single UE, they hop to the
positions of RUs 303 and 304 by frequency hopping at the next transmission
point. Since the RUs 303 and 304 are not successive, the UE cannot transmit
data
in these two RUs.
In this context, to achieve frequency diversity in the SC-FDMA system,
mirroring is proposed to substitute for the frequency hopping.
FIG 4 illustrates mirroring.
Conventionally, an RU moves symmetrically with respect to the center
frequency of a total frequency band available for data transmission. For
example,
an RU 401 is mirrored to an RU 403 and an RU 402 to an RU 404 at the next
transmission time in Cell A. In the same manner, an RU 405 is mirrored to an
RU
406 at the next transmission time in Cell B. The mirroring enables successive
RUs to hop as successive, thereby satisfying the single carrier property
during
frequency hopping.
A shortcoming with the frequency hopping with frequency diversity is that
the hopping pattern is fixed because there is no way to move RUs without
mirroring with respect to a center frequency. This means that frequency
diversity
is achieved to a certain degree but interference randomization is difficult.
As an
RU hopped to the opposite returns to its original position by mirroring, only
one
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RU hopping pattern is available. Therefore, even when a plurality of cells
exist,
each cell cannot have a different pattern.
Referring to FIG. 4, if the RU 402 marked with dots is allocated to a UE in
Cell A and the RU 405 marked with single-slashed lines is allocated to a UE in
Cell B for a predetermined time, the UE of Cell A interferes with the UE of
Cell
B because only one hopping pattern is available in the mirroring scheme. If
the
UE of Cell B is near to Cell A, it causes great interference to UEs in Cell A.
As a
result, the UE of Cell A using RUs marked with dots suffers from reception
quality degradation.
SUMMARY OF THE INVENTION
An aspect of the present invention is to address at least the problems
and/or disadvantages and to provide at least the advantages described below.
Accordingly, an aspect of the present invention is to provide a method and
apparatus for allocating resources to randomize interference between neighbor
cells when mirroring is adopted to achieve frequency diversity.
Another aspect of the present invention is to provide a method for
determining whether to turn on or off mirroring at each hopping time according
to
a different mirroring on/off pattern for each cell, and a
transmitting/receiving
apparatus using the same.
A further aspect of the present invention is to provide a method for
determining whether to turn on or off frequency hopping and mirroring at each
hopping time according to a different pattern for each cell, and a
transmitting/receiving apparatus using the same, when frequency hopping can be
supported to increase a frequency diversity effect.
In accordance with an aspect of the present invention, there is provided a
method for allocating resources to a UE in an SC-FDMA communication system,
in which inter-subband hopping is performed on a resource unit for the UE on a
frequency axis along which at least two subbands are defined, at each
predetermined hopping time, it is determined whether to turn on or off
mirroring
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in a subband having the hopped resource unit on a cell basis at the each
hopping
time, and a resource unit is selected by selectively mirroring the hopped unit
according to the determination and allocated to the UE.
In accordance with another aspect of the present invention, there is
provided a method for being allocated resources from a Node B in an SC-FDMA
communication system, in which inter-subband hopping is performed on a
resource unit for a UE on a frequency axis along which at least two subbands
are
defined, at each predetermined hopping time, it is determined whether to turn
on
or off mirroring in a subband having the hopped resource unit at the each
hopping
time according to scheduling information received from the Node B, a resource
unit is selected by selectively mirroring the hopped unit according to the
determination, and data is transmitted in the selected resource unit to the
Node B.
In accordance with a further aspect of the present invention, there is
provided an apparatus of a Node B for allocating resources to UEs in an SC-
FDMA communication system, in which a scheduler performs inter-subband
hopping on resource units for the UEs on a frequency axis along which at least
two subbands are defined, at each predetermined hopping time, determining
whether to turn on or off mirroring in subbands having the hopped resource
units
on a cell basis at the each hopping time, and selects resource units by
selectively
mirroring the hopped units according to the determination, a mapper separates
data received from the UEs according to information about the selected
resource
units received from the scheduler, and a decoder decodes the separated data.
In accordance with still another aspect of the present invention, there is
provided an apparatus of a UE for transmitting data to a Node B in an SC-FDMA
communication system, in which a data transmission controller performs inter-
subband hopping on a resource unit for the UE on a frequency axis along which
at
least two subbands are defined, at each predetermined hopping time, and
determines whether to turn on or off mirroring in a subband having the hopped
resource unit at the each hopping time according to scheduling information
received from the Node B, and a mapper maps data to a resource unit selected
by
selectively mirroring of the hopped resource unit according to the
determination
and transmits the data in the mapped resource unit to the Node B.
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BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of certain exemplary
embodiments of the present invention will be more apparent from the following
detailed description taken in conjunction with the accompanying drawings, in
which:
FIG 1 is a block diagram of a transmitter in a conventional LFDMA
system, which is a type of SC-FDMA system;
FIG 2 illustrates an exemplary data transmission from UEs in their
allocated resources in a conventional SC-FDMA system;
FIG 3 illustrates an exemplary frequency hopping in a conventional
FDMA system;
FIG. 4 illustrates mirroring;
FIGs. 5A and 5B illustrate a method according to an exemplary
embodiment of the present invention;
FIG 6 is a flowchart of an operation for selecting RUs in a UE or a Node
B according to the exemplary embodiment of the present invention;
FIG 7 is a block diagram of the UE according to an exemplary
embodiment of the present invention;
FIG 8 is a block diagram of the Node B according to an exemplary
embodiment of the present invention;
FIG 9 illustrates a channel structure according to another exemplary
embodiment of the present invention;
FIGs. 1 OA to 1 OD illustrate a method according to the second exemplary
embodiment of the present invention;
FIG. 11 is a flowchart of an operation for selecting RUs in the UE or the
Node B according to the second exemplary embodiment of the present invention;
FIG 12 illustrates a channel structure according to a third exemplary
embodiment of the present invention;
FIG 13 illustrates a method for performing mirroring irrespective of
Hybrid Automatic Repeat reQuest (HARQ) according to the third exemplary
embodiment of the present invention;
FIG 14 illustrates a method for performing mirroring for each HARQ
process according to the third exemplary embodiment of the present invention;
and
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FIG 15 illustrates a method for performing mirroring for each HARQ
process according to a fourth exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The matters defined in the description such as a detailed construction and
elements are provided to assist in a comprehensive understanding of exemplary
embodiments of the invention. Accordingly, those of ordinary skill in the art
will
recognize that various changes and modifications of the embodiments described
herein can be made without departing from the scope and spirit of the
invention.
Also, descriptions of well-known functions and constructions are omitted for
clarity and conciseness.
Exemplary embodiments of the present invention provide a method for
increasing the randomization of interference between cells when data is
transmitted in a different RU at each predetermined time by a general
frequency
hopping or mirroring scheme to achieve frequency diversity while satisfying
the
single carrier property in an uplink SC-FDMA system.
For a better understanding of the present invention, data channels are
defined as follows:
Frequency Scheduling (FS) band: a set of RUs allocated by frequency
selective scheduling. They are successive or scattered.
Frequency Hopping (FH) band: a set of RUs transmitted to achieve
frequency diversity. These RUs are not allocated by frequency selective
scheduling. They are successive or scattered. An FH band can be comprised of
one or more sub-FH bands.
Mirroring: RUs are symmetrically hopped from left to right and from right
to left with respect to a center subcarrier or a center RU in a sub-FH band.
Hopping time: a time at which an allocated RU hops or is mirrored.
Depending on how hopping or mirroring applies, the RU has the following
period.
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1. When intra-subframe hopping and inter-subframe hopping are
supported, the period is a slot.
2. When only inter-subframe hopping is supported, the period is one sub-
frame.
Embodiment 1
An exemplary embodiment of the present invention provides a method for
turning mirroring on or off according to a different mirroring on/off pattern
for
each cell. Using different mirroring on/off patterns for different cells as
much as
possible and decreasing the probability of mirroring-on in cells at the same
time
maximize the effect of randomizing interference between cells.
FIGs. 5A and 5B illustrate a method according to the exemplary
embodiment of the present invention. FIG. 5A illustrates slot-based mirroring
irrespective of Hybrid Automatic Repeat reQuest (HARQ) and FIG. 5B illustrates
independent mirroring for each HARQ process.
Referring to FIG 5A, there are cells 501 and 502 (Cell A and Cell B). As
intra-subframe hopping is assumed, the hopping period is a slot. On a slot
basis,
mirroring is performed at each hopping time in a pattern 503 of on, on, on,
off, on,
off, off, off ... in Cell A, and in a pattern 512 of on, off, on, on, off,
off, on,
on, ... in Cell B.
In Cell A, an RU 504 is allocated to UE A at hopping time k. Since
mirroring is on for UE A at the next hopping time (k+1), UE A uses an RU 505
in
slot (k+l). Mirroring is off at hopping time (k+3) and thus UE A transmits
data in
an RU 506 identical to an RU used in the previous slot (k+2) in slot (k+3).
Similarly, since mirroring is off at hopping time (k+6), UE A transmits data
in an
RU 507 identical to an RU transmitted in the previous slot (k+5) in slot
(k+6).
In the same manner, an RU 508 is allocated to UE B in slot k in Cell B.
Since mirroring is off at the next hopping time (k+l), UE B uses an RU 509 in
slot (k+1). At hopping time (k+3), mirroring is on and thus UE B uses an RU
510
in slot (k+3). Similarly, since mirroring is on at hopping time (k+6), UE B
uses an
RU 511 in slot (k+6).
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Mirroring is on or off at each hopping time in a different pattern in each
cell. Therefore, while UEs within different cells may use the same RU in a
given
slot, the probability of the different cells using the same RU in the next
slot
decreases due to the use of different mirroring on/off patterns. For example,
the
RUs 504 and 508 are allocated respectively to UE A in Cell A and UE B in Cell
B
in slot k. If UE B is near to Cell A, UE B will likely significantly interfere
with
UE A. However, since UE A turns on mirroring at the next hopping time (k+l),
UE A transmits data in the RU 505 in slot (k+l), whereas mirroring is off for
UE
B and thus UE B transmits data in the RU 509 identical to that used in the
previous slot. Thus, UE A and UE B use different RUs in slot (k+1).
The mirroring method illustrated in FIG 5B is similar to that illustrated in
FIG 5A in that different cells use different mirroring on/off patterns and the
former method illustrated in 5B differs from the latter method illustrated in
5A in
that an RU is mirrored with respect to an RU in the same HARQ process rather
than with respect to an RU in the previous slot. In FIG 513, mirroring is on
for a
UE in a cell 513 (Cell A) at hopping time k. Thus, the UE uses an RU 518 to
which an RU 517 used in the previous slot (k-RTT+1) of the same HARQ process
is mirrored, instead of an RU to which an RU used in the previous slot (k-1)
is
mirrored. RTT represents Round Trip Time, defined as the time` taken for an
initial transmission in the case where a response for transmitted data is a
Negative
ACKnowledgment (NACK) and a response for retransmitted data is an ACK.
Therefore, data transmitted in RUs 518 and 519 are retransmission versions of
data transmitted in RUs 516 and 517 or belong to the same HARQ process as the
data transmitted in the RUs 516 and 517. The HARQ RTT-based mirroring
facilitates defining a mirroring on/off pattern in which different RUs are
used for
initial transmission and retransmission. Despite this advantage, management of
a
different mirroring on/off pattern for each HARQ process increases complexity.
In this context, a mirroring on/off pattern is determined as follows.
(1) Mirroring is on/off at each hopping time according to a predetermined
sequence. The sequence is needed to indicate whether mirroring is on or off,
not
to indicate the position of an RU for hopping. Therefore, the sequence is
composed of two values. In general, a binary sequence is composed of Os or 1
s.
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(2) A plurality of sequences are generated and allocated to cells such that
different patterns are applied to at least neighbor cells to thereby minimize
RU
collision among them. For example, a set of orthogonal codes such as Walsh
codes are allocated to respective cells and each cell determines mirroring
on/off
according to a code value 0 or 1 at each hopping time. Alternatively, each
cell can
determine mirroring on/off according to a Pseudo Noise (PN) sequence having a
seed specific to the cell. As compared to the former method, the latter method
increases randomization between cells and thus minimizes the phenomenon in
which RUs hop in the same manner in different cells. In the context of the PN
sequence-based method, the exemplary embodiment of the present invention will
be described below.
For generation of a PN sequence, a cell-specific seed is used and to
achieve the same PN sequence, UEs within the same cell should receive the same
timing information. The timing information can be represented as the
difference
between an absolute time and a current time or as a common time frame count
such as a System Frame Number (SFN).
FIG 6 is a flowchart of an operation for determining mirroring on/off in a
UE according to the exemplary embodiment of the present invention. To receive
data from the UE, a Node B can perform the same operation.
Referring to FIG. 6, when the Node B schedules an RU for the UE, the UE
generates a PN sequence value in step 601 and checks the PN sequence value in
step 602. If the PN sequence value is 0, the UE turns mirroring off in step
604. If
the PN sequence value is 1, the UE turns mirroring on in step 603. In step
605,
the UE selects an RU for the next data transmission according to the mirroring-
on/off decided in step 603 or 604. The UE transmits data in the selected RU in
step 606.
Mirroring results in a symmetrical RU hopping with respect to the center
of a total FH band. A new RU for use in the next slot can be detected based on
information about an RU used in a previous slot. The mirroring is expressed as
Equation (1):
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H(r)=NFH -r
.....(1)
where r denotes an RU being a mirroring base. The mirroring base is an
RU used in the previous slot in FIG. 5A and an RU used in the previous slot of
the
same HARQ process in FIG. 5B. H(r) denotes an RU to which the mirroring
base is mirrored in a slot. NFH denotes the total number of RUs in the FH
band.
FIG 7 is a block diagram of the UE according to the exemplary
embodiment of the present invention.
Referring to FIG 7, a data symbol generator 703 generates data symbols
to be transmitted. The amount of data transmittable in each Transmission Time
Interval (TTI) is determined by Node B scheduling. A Serial-to-Parallel (S/P)
converter 704 converts the sequence of the data symbols to parallel symbol
sequences. A DFT processor 705 converts the parallel symbol sequences to
frequency signals, for SC-FDMA transmission. A DFT size is equal to the number
of the data symbols generated from the data symbol generator 703. A mapper 706
maps the frequency signals to frequency resources allocated to the UE based on
RU information received from a data transmission controller 702.- The data
transmission controller 702 generates the RU information based on scheduled RU
information and mirroring on/off information. Each cell has a different
mirroring
on/off pattern according to a PN sequence. Hence, a PN sequence generator 701
is required. An RU to be used is decided using the output of the PN sequence
generator 701 in the afore-described method. An IFFT processor 707 converts
the
mapped signals to time signals. A Parallel-to-Serial (P/S) converter 708
converts
the time signals to a serial signal for transmission.
FIG 8 is a block diagram of the Node B according to the exemplary
embodiment of the present invention.
Referring to FIG. 8, an S/P converter 807 converts a received signal to
parallel signals and an FFT processor 806 converts the parallel signals to
frequency signals. A demapper 805 demaps the frequency signals for different
UEs based on RU allocation information about each UE determined by an uplink
scheduler 802. The uplink scheduler 802 generates the RU information for each
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UE using scheduled RU information and mirroring on/off information based on a
mirroring on/off pattern. Since each cell has a different mirroring on/off
pattern, a
PN sequence generator 801 is needed. An RU from which data is to be extracted
is decided based on the output of the PN sequence generator 801 in the afore-
described method. An IDFT processor 804 converts the demapped signal of an
intended UE, UE 1 to time signals. A P/S converter 808 converts the time
signals
to a serial signal. A data symbol decoder 803 demodulates data received from
UE
1.
Embodiment 2
Inter-sub-FH band hopping on/off is combined with mirroring on/off, and
the position of an RU for data transmission is determined by selecting one of
the
combinations such that each cell has a different pattern. That is, the
resources of a
total system frequency band is divided into an FH band and an FS band and a
channel structure is proposed, which offers a sufficient frequency hopping
gain in
the FH band and achieves a sufficiently available frequency band in the FS
band.
FIG. 9 illustrates the channel structure according to the second exemplary
embodiment of the present invention.
Referring to FIG 9, sub-FH bands 901 and 903 are defined at either side
of a total frequency band and the center frequency band between the sub-FH
bands 901 and 903 is defined as an FS band 902. UEs using the FS band 902 can
hop to the sub-FH bands 901 and 903, thereby achieving a sufficient frequency
hopping gain. As the frequencies of the FS band 902 are successive to maximize
successive frequency allocation, a maximum data rate can be increased.
A method for performing inter-sub-FH band hopping and mirroring within
each FH band in order to achieve a sufficient frequency diversity gain and
simultaneously to enable variable RU allocation, taking into account the
single
carrier property in the proposed channel structure will now be described. As
done
in the first exemplary embodiment of the present invention, inter-sub-FH band
hopping is on/off and mirroring is on/off at each hopping time according to a
cell-
specific pattern.
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Four combinations of inter-sub-FH band hopping on/off and mirroring
on/off are available as illustrated in Table 1. At each hopping time, one of
the
combinations is selected and hopping or/and mirroring apply to each cell using
the selected combination in a different pattern.
Table 1
Combination FH band hopping Mirroring
1 On On
2 Off Off
3 Off On
4 On Off
FIGs. 10A to lOD describe the second exemplary embodiment of the
present invention.
FIGs. l0A and lOB are based on the assumption that intra-TTI hopping is
supported in cells 1001 and 1007 (Cell A and Cell B). Therefore, the hopping
period is a slot.
Referring to FIGs. 10A and lOB, combinations of inter-sub-FH band
hopping on/off and mirroring on/off according to Table 1 are selected in the
order
of 3-1-4-3-2-1-2-3 for Cell A and in the order of 3-4-2-1-3-2-1-4 for Cell B.
Although Cell A uses an RU 1002 at hopping time k, it selects an RU
1005 by inter-sub-FH band hopping and mirroring according to combination 1 at
hopping time (k+l). At the next hoping time (k+2), Cell A performs only inter-
sub-FH band hopping without mirroring according to combination 4 and thus
selects an RU 1003. Since combination 2 is set for hopping time (k+4), Cell A
selects an RU 1004 without inter-sub-FH band hopping and mirroring.
Cell B selects the same RU 1008 used for Cell A at hopping time k. At
hopping time (k+l), Cell B selects an RU 1009 through inter-sub-FH band
hopping only without mirroring according to combination 4, as compared to Cell
A that selects the RU 1005 through both inter-sub-FH band hopping and
mirroring according to combination 1. While another UE within Cell B may use
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the same RU as the RU 1005 in slot (k+1), interference from a different UE at
each time rather than collision with the same UE offers a better interference
randomization gain.
In the illustrated cases of FIGs. IOC and 10D, inter-sub-FH band hopping
and mirroring are carried out with respect to an RU used for the previous data
transmission of the same HARQ process, instead of an RU used at the previous
hopping time.
Referring to FIG. lOC, an RU 1013 is selected at hopping time k by inter-
sub-FH band hopping of an RU 1014 used for the previous data transmission of
the same HARQ process, not of an RU used at hopping time (k-1). Combination 4
is set for hoping time k, which means inter-sub-FH band hopping is on and
mirroring is off with respect to the RU 1014. Thus, the RU 1013 is selected at
hopping time k. At hopping time (k+l) for which combination 3 is set, the RU
1013 is inter-sub-FH band-hopped and mirrored to an RU 1012.
A method for selecting combinations of inter-sub-FH band hopping on/off
and mirroring on/off using a predetermined sequence will now be described.
(1) Since the sequence is needed to indicate combinations selected from
the four combinations of inter-sub-FH band hopping on/off and mirroring
on/off,
but the sequence is not needed to indicate the position of an RU for hopping,
four
values are available in forming the sequence. In general, a quaternary
sequence or
two binary sequences in combination serves the purpose of indicating selected
combinations. The sequence can be generated in a conventional method and thus
a detailed description of the method is not provided herein.
(2) A plurality of sequences are generated and allocated to cells such that
different patterns are applied to at least neighbor cells to thereby minimize
RU
collision among them. For example, a set of orthogonal codes such as Walsh
codes are allocated to cells in a one-to-one correspondence and each cell
selects a
combination according to a sequence value at each hopping time. Alternatively,
each cell can select a combination according to a PN sequence having a seed
specific to the cell. As compared to the former method, the latter method
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increases randomization between cells and thus minimizes RUs hopping in the
same manner in different cells. In the context of the PN sequence-based
method,
the exemplary embodiment of the present invention will be described below.
For generation of a PN sequence, a cell-specific seed is used and to
achieve the same PN sequence, UEs within the same cell should receive the same
timing information. The timing information can be represented as the
difference
between an absolute time and a current time or as a common time frame count
such as an SFN.
FIG 11 is a flowchart of an operation of the UE according to the second
exemplary embodiment of the present invention. The same operation applies to
the Node B when it receives data from the UE.
Referring to FIG 11, when the Node B schedules a specific RU for the UE,
the UE generates a PN sequence value in step 1101 and determines whether the
PN sequence value is 1, 2, 3, or 4 in step 1102. If the PN sequence value is
1, the
UE selects a combination of mirroring-on and inter-sub-FH band hopping-on in
step 1103. If the PN sequence value is 2, the UE selects a combination of
mirroring-off and inter-sub-FH band hopping-off in step 1104. If the PN
sequence
value is 3, the UE selects a combination of mirroring-off and inter-sub-FH
band
hopping-on in step 1105. If the PN sequence value is 4, the UE selects a
combination of mirroring-on and inter-sub-FH band hopping-off in step 1106. In
step 1107, the UE selects an RU for data transmission by mirroring and/or
hopping according to the selected combination. The UE transmits data in the
selected RU in step 1108.
A transmitter and a receiver according to the second exemplary
embodiment of the present invention have the same configurations as those
according to the first exemplary embodiment of the present invention, except
that
the PN sequence generators 701 and 802 generate one of four values 1 to 4 and
provide the generated value to the data transmission controller 702 and the
uplink
scheduler 802 so as to determine the position of an RU.
Embodiment 3
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FIG. 12 illustrates a channel structure according to a third exemplary
embodiment of the present invention.
For a system where a plurality of sub-FH bands exist as illustrated in FIG.
12 and where hopping always occurs between the sub-FH bands, a method is
proposed for determining mirroring on/off according to a different pattern for
each cell. The use of different mirroring on/off patterns for different cells
decreases the probability of perfonning mirroring at the same time in the
different
cells, thus resulting in maximized randomization of inter-cell interference.
FIGs. 13 and 14 describe a method according to a third exemplary
embodiment of the present invention. Specifically. FIG 13 illustrates a
mirroring
method independent of HARQ and FIG. 14 illustrates a method for performing
mirroring on an HARQ process basis.
Referring to FIG. 13, since it is assumed that both cells 1301 and 1311
(Cell A and Cell B) support intra-subframe hopping, the hopping period is a
slot.
Mirroring is performed at each hopping time in a pattern 1310 of on, on, off,
off,
on, off, off, off ... in Cell A, and in a pattern 1320 of on, off, off, on,
off, off, on,
on, ... in Cell B.
If an RU 1302 in sub-FH band #1 is allocated to a UE at hopping time k in
Cell A, it hops to sub-FH band #2 occurs because inter-sub-FH band hopping
applies always and is mirrored according to the mirroring pattern 1310. Hence,
the UE uses an RU 1303 in slot (k+1). At the next hopping time (k+2), the UE
selects an RU 1304 through hopping to sub-FH band #1 and mirroring-off. Since
hopping to sub-FH band #2 occurs and mirroring is off at the next hopping time
(k+3), the UE uses an RU 1305 in slot (k+3).
Compared to Cell A, a different mirroring on/off pattern is defined for
Cell B. In other words, mirroring is on/off in a different manner at each
hopping
time for each cell. Although Cell A and Cell B may select the same RU at a
given
hopping time, the third exemplary embodiment of the present invention reduces
the probability of selecting the same RU at the next hopping time in the two
cells.
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For instance, in the case where the same RUs 1302 and 1312 are allocated
respectively to UE A in Cell A and UE B in Cell B for a predetermined time, if
UE B is near to Cell A, UE A is probable to be interfered significantly by UE
B at
hopping time k. However, since Cell A performs both inter-sub-FH band hopping
and mirroring at the next hopping time (k+ 1), UE A transmits data in the RU
1303
in slot (k+l), whereas inter-sub-FH band hopping is on and mirroring is off
for
UE B and thus UE B transmits data in an RU 1313 in slot (k+1). Thus, UE A and
UE B use different RUs in slot (k+l), thus avoiding continual interference
from
the same UE.
The mirroring method illustrated in FIG 14 is similar to that illustrated in
FIG 13 in that mirroring follows inter-sub-FH band hopping and different cells
use different mirroring on/off patterns, and the former differs from the
latter in
that an RU is mirrored with respect to an RU in the same HARQ process rather
than with respect to an RU used at the previous transmission time.
That is, at hopping time (k+RTT), a UE in a cell 1401 (Cell A) uses an RU
1407 to which an RU 1406 used in slot (k+1) of the same HARQ process is
mirrored, instead of an RU to which an RU used in the previous slot (k+RTT- 1)
is
mirrored. The HARQ RTT-based mirroring facilitates defining a mirroring on/off
pattern in which different RUs are used for initial transmission and
retransmission,
thereby maximizing an interference diversity effect.
The UE determines mirroring on/off in the same manner as in the first
exemplary embodiment of the present invention, except that inter-sub-FH band
hopping occurs all the time in selecting an RU.
To realize the third exemplary embodiment of the present invention, a
hopping pattern formula is given as Equation (2), for example. The UE is aware
of a resource block to be used at each transmission time using the hopping
pattern
formula and the index of a scheduled resource block. Equation (2) uses sub-
band-
based shifting for inter-subband hopping.
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Os=f_s-Na-h(t), OS=OsmodN_RB
if 0<-Os <Ns
fhaP (i) = N. - h(i) + OS +{(NS - l) - 2 x(OS mod(Ns Ax m(i)
fhop(i) = f,op(i)modN_RB
else if Ns <- OS
f&,p(i)= Na -h(i)+Os +{(N -1) - 2 x ((Os -Ns)mod(No))}x m(i)
fhop (i) = fhop (i)mod N _ RB
.....(2)
where OS denotes an offset by which a resource block scheduled to the
UE is spaced from a cyclic shift reference point, f_s denotes the index of a
resource block allocated by a scheduling grant, h(t) denotes the degree to
which
the scheduled resource block is cyclically shifted at scheduling time (t),
fhop (i)
denotes the index of a resource block after hopping at hopping time (i), N_RB
denotes the total number of resource blocks available for data transmission,
and
No and Ns are maximum numbers of resources blocks that can be scheduled
for UEs that perform hopping.
If the total number of resource blocks N_RB is not a multiple of the
number of subbands M, a particular subband has a fewer number of resource
blocks, NS than that of the resource blocks of the other subbands each No.
Because Equation (2) assumes that only one subband has a fewer number of
resource blocks, N0 and Ns are computed by Equation (3):
N,, _rN RB1 Ns =N_RB-(M-1)xNa
.....(3)
In Equation (2), h(i) denotes a cyclic shift degree, being one of {0, 1, ...,
M} selected according to a bit value of a random sequence. h(0)=0. m(i) is a
parameter that determines mirroring on/off at hopping time (i), being one of
{0,
1}. m(i) is selected according to a bit value of a random sequence, or by
h(i)= x/2 and m(i) = xMod (2) where x is one of {0, 1, ..., M} selected
according to the bit value of the random sequence. If m(i)=0, mirroring is off
and
if m(i)=1, rriirroring is on.
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To describe Equation (2) in great detail, the offset Os at the scheduling
time of the scheduled resource block, is first calculated by the first line of
Equation (2). Os indicates how far a cyclically shifted resource block is
spaced
from the cyclic shift reference point.
OS is introduced for the following reason. When the total number of
resource blocks N_RB is not a multiple of the number of subbands M, the
subbands do not have the same amount of resources, causing failed inter-
subband
hopping. Therefore, subbands are formed such that one subband has a fewer
number of resource blocks N. than the number Ns of resources blocks of each
of the other subbands and O.s is used to indicate the subband having the fewer
number of resource blocks to the UE in the third exemplary embodiment of the
present invention.
For exainple, if N_RB is 22 and M is 4, subbands can be configured
so that a first subband has four resource blocks and each of the other
subbands
has six resource blocks. In this subband structure, if Os is less than 4, the
UE is
aware that the scheduled resource block resides in the smaller subband.
According to the first conditional sentence of Equation (2), then, the
scheduled resource block is cyclically shifted with respect to resource blocks
0 to
Ns -1 according to the offset OS and then mirrored within Ns resource blocks.
If m(i)=0, mirroring is off.
If OS is larger than NS , which implies that the scheduled resource block
resides in a normal subband, a cyclic shift is performed according to the
second
conditional sentence of Equation (2) and then mirroring is performed within No
resource blocks. If m(i)=0, mirroring is off.
Depending on a subband configuration, a plurality of subbands may each
have Ns resource blocks with a plurality of remaining subbands each having
No resource blocks. For example, if four subbands are given, two subbands each
have five resources blocks and the other two subbands each include six
resource
blocks. This case can be easily realized by modifying the conditional
sentences of
Equation (2) that indicate a scheduled subband using an offset.
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Embodiment 4
If mirroring is on or off according to a random pattern in each cell,
successive mirroring ons/offs increase the probability of data transmission
from
UEs in the same RUs in different cells. Considering that it is preferred, in
terms
of channel quality, to achieve a sufficient frequency diversity at each
transmission
time when data is transmitted by an HARQ process, it is necessary to allow UEs
to select different RUs at least under a successive data transmission
situation such
as initial transmission and retransmission. To do so, a fourth exemplary
embodiment of the present invention proposes a limited use of a method for
generating a random mirroring pattern and determining mirroring on/off
according to the random mirroring pattern, when needed. When both intra-
subframe hopping and inter-subframe hopping are supported, mirroring is always
on at each hopping time for one of the two hopping schemes and mirroring is
on/off in a random mirroring on/off pattern for the other hopping scheme.
FIG 15 illustrates a method for always turning on mirroring for inter-
subframe hopping and determining mirroring on/off according to a random
mirroring on/off pattern for intra-subframe hopping according to the fourth
exeinplary embodiment of the present invention.
As in the second exemplary embodiment of the present invention, sub-FH
bands are positioned at either side of a system frequency band and an FS band
is
interposed at the center frequency band between the sub-FH bands. To achieve a
frequency diversity gain, an RU hops between the sub-FH bands at each hopping
time as in the third exemplary embodiment of the present invention.
Referring to FIG. 15, mirroring occurs at each intra-subfraine hopping
time according to a pattern of on, off, off, . . . in a cell 1500 (Cell A) and
according to a pattern of o f f , o f f , on, ... in a cell 1520 (Cell B).
When an RU 1502 is allocated to a UE at hopping time (k-RTT) in Cell A,
the UE selects an RU 1503 by mirroring according to the mirroring on/off
pattern
at the next hopping time (k-RTT+l). At hopping time k being the next
transmission time of the same HARQ process, mirroring is always on. To select
an RU at a different position from an RU transmitted at the previous
transmission
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time of the same HARQ process, an RU 1504 is selected by mirroring the RU
1502 used in the first slot (k-RTT) of the previous HARQ transmission time.
Since mirroring is off according to the mirroring on/off pattern at the next
hopping time (k+l), the UE selects an RU 1505. At hopping time (k+RTT) being
the next transmission time of the same HARQ process, mirroring is always on.
To
select an RU at a different position from an RU transmitted at the previous
HARQ
transmission time, the RU 1504 is mirrored to an RU 1506. Since mirroring is
off
according to the mirroring on/off pattern at the next hopping time (k+RTT+l),
the
UE selects an RU 1507.
In the same manner, an RU hops to another sub-FH band by turning on/off
mirroring according to a random mirroring on/off pattern at each intra-
subframe
hopping time in Cell B. That is, if an RU 1508 is used in slot (k-RTT), an RU
1509 is selected by turning off mirroring according to the mirroring on/off
pattern
at the next hopping time (k-RTT+1). Since mirroring is performed with respect
to
the RU 1508 used at the previous transmission time of the same HARQ process at
the next HARQ transmission time, an RU 1510 is selected at hopping time k. At
hopping time (k+l), mirroring is off according to the mirroring on/off pattern
and
thus an RU 1511 is selected. Since mirroring is performed with respect to the
RU
1510 used at the previous transmission time of the same HARQ process at the
next HARQ transmission time, an RU 1512 is selected at hopping time (k+RTT).
At hopping time (k+RTT+l), mirroring is on according to the mirroring on/off
pattern and thus an RU 1513 is selected.
As is apparent from the above description, the present invention
advantageously randomizes inter-cell interference, increasing a frequency
diversity effect, by turning on or off mirroring at each hopping time
according to
a different mirroring on/off pattern in each cell.
While the invention has been shown and described with reference to
certain exemplary embodiments of the present invention thereof, it will be
understood by those skilled in the art that various changes in form and
details
may be made therein without departing from the spirit and scope of the present
invention as defined by the appended claims and their equivalents.
