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 illustrates a transmitter in a Localized FDMA (LFDMA) system,
which is a type of SC-FDMA system. While the transmitter is configured so as
to
use Discrete Fourier Transform (DFT) and Inverse Fast Fourier Transform (IFFT)
in FIG. 1, any other configuration is available to the transmitter.
Referring to FIG 1, the use of DFT and IFFT facilitates change of
LFDMA system parameters with minimal 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 including
successive subcarriers. A mapper 104 functions to map the transmission
modulated symbols to an actual frequency band.
FIG. 2 illustrates a 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
more subcarriers in frequency and one or more SC-FDMA symbols in time. For
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data transmission, two RUs indicated by the diagonal lines are allocated to
LTE1
and three RUs indicated by the dots are allocated to UE2.
The RUs in which UE1 and UE2 transmit data are fixed in time and
successive in set frequency bands. This scheme of resource allocation or data
transmission 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 blocks with the diagonal lines offer better radio
channel characteristics to UE1 than in other frequency bands, whereas the
dotted
blocks offer better radio channel characteristics to UE2 than in other
frequency
bands. 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 diagonal lines and dots
represent resources in which the Node B transmits data to UE1 and UE2,
respectively.
However, the frequency selective scheduling is not always effective. For a
UE that moves fast and thus experiences a fast change in channel status, the
frequency selective scheduling is not easy. To be more specific, 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 an already significantly changed channel
environment when it 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 a 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 substantial. In this case, it is more effective to use
frequency
hopping rather than the frequency selective scheduling.
FIG 3 illustrates frequency hopping in a conventional FDMA system.
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Referring to FIG. 3, frequency resources allocated to a UE for data
transmission change in 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 in time, the data has different
channel
characteristics and is interfered by a different UE in a neighbor cell 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 disclosed to substitute for the frequency hopping, and is
illustrated in
FIG. 4.
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 successively hop, 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
RU hopping pattern is available. Therefore, even when a plurality of cells
exists,
each cell cannot have a different pattern.
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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-diagonal lines is allocated to a
UE
in Cell B for a period of 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 Cell A, it causes substantial interference to LTEs in Cell
A. As a
result, the UE of Cell A using RLTs 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.
An 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.
An aspect of the present invention is to provide a method for determining
whether to turn 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 the present invention, there is provided a method for
allocating resources to a UE in an SC-FDMA communication system, in which is
determined on a cell basis whether to turn or off inter-subband hopping and
whether to turn on or off mirroring for a resource unit for the UE on a
frequency
axis along which at least two subbands are defined, at each hopping time, and
a
resource unit is selected by selectively performing inter-subband hopping and
mirroring on the resource unit for the UE according to the determination and
allocated to the UE.
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In accordance with the present invention, there is provided a method for being
allocated resources from a Node B in an SC-FDMA communication system, in which
it
is determined whether to turn or off inter-subband hopping and whether to turn
on or off
mirroring for a resource unit for the UE on a frequency axis along which at
least two
subbands are defined, at each hopping time, a resource unit is selected by
selectively
performing inter-subband hopping and mirroring on the resource unit for the UE
according to the determination, and data is transmitted in the selected
resource unit to the
Node B.
In accordance with 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 determines on a cell basis whether to turn or off inter-subband
hopping and
whether to turn on or off mirroring for resource units for the UEs on a
frequency axis
along which at least two subbands are defined, at each hopping time, and
selects resource
units to be allocated for the UEs by selectively performing inter-subband
hopping and
mirroring on the resource units for the UEs 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 the present invention, there is provided an apparatus of a
UE
for transmitting data to a Node B in a SC-FDMA communication system, in which
a data
transmission controller determines on a cell basis whether to turn or off
inter-subband
hopping and whether to turn on or off mirroring for a resource unit for the UE
on a
frequency axis along which at least two subbands are defined, at each hopping
time, and
a mapper maps data to a resource unit selected by selectively performing inter-
subband
hopping and mirroring on the resource unit for the UE according to the
determination and
transmits the mapped data to the Node B.
According to an aspect of the present invention, there is provided a method
for
transmitting data by a User Equipment (UE) in a communication system, the
method
comprising:
receiving resource allocation information from a Node B;
determining whether hopping is enabled or disabled;
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determining whether mirroring is enabled or disabled;
determining a frequency resource for data transmission based on whether the
hopping is enabled or disabled and whether the mirroring is enabled or
disabled; and
transmitting the data using the frequency resource for data transmission;
wherein whether the hopping and the mirroring are enabled or disabled is
determined at a Transmit Time Interval.
According to another aspect of the present invention, there is provided a
method
for receiving data by a Node B in a communication system, the method
comprising:
transmitting resource allocation information to a User Equipment (UE);
determining a resource used for receiving the data from the UE;
receiving the data through the determined resource; and
decoding the data;
wherein the resource used for receiving the data from the UE is determined
according to whether hopping and mirroring are enabled or disabled; and
wherein whether the hopping and the mirroring are enabled or disabled is
determined at the Transmit Time Interval.
According to a further aspect of the present invention, there is provided an
apparatus for a User Equipment (UE) for transmitting data to a Node B, the
apparatus
comprising:
a data transmission controller for receiving resource allocation information
from
the Node B, determining whether hopping and mirroring are enabled or disabled,
and
determining a frequency resource for data transmission based on whether the
hopping is
enabled or disabled and whether the mirroring is enabled or disabled; and
a mapper for mapping the data to the frequency resource and transmitting the
data
to the Node B,
wherein the data transmission controller determines whether the hopping and
the
mirroring are enabled or disabled at a Transmit Time Interval.
According to a further aspect of the invention, there is provided an apparatus
of a
node B for receiving data from a User Equipment (UE), the apparatus
comprising:
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a scheduler for allocating resources for the UE and determining resources used
for
receiving data from the UE;
a demapper for dernapping the data received through the resources from the UE;
and
a decoder for decoding the data,
wherein the scheduler determines the resources used for receiving the data
according to whether hopping and mirroring are enabled or disabled, and
wherein the scheduler determines whether the hopping and the mirroring are
enabled or disabled at a Transmit Time Interval.
According to a further aspect of the invention, there is provided a method for
transmitting data in a subframe including two slots in a communication system,
the
method comprising:
receiving resource allocation information at a User Equipment (UE);
detemiining, by the UE, a resource for data transmission based on the resource
allocation information, whether hopping is enabled, whether mirroring is
enabled, and
whether hopping is intra-subframe and inter-subfrarne hopping or inter-
subframe
hopping; and
transmitting data via the determined resource from the UE to a Node B.
According to a further aspect of the invention, there is provided an apparatus
of a
User Equipment (UE) for transmitting data in a subframe including two slots in
a
communication system, the apparatus comprising:
a data transmission controller configured to receive resource allocation
information, determine a resource for data transmission based on the resource
allocation
information, whether hopping is enabled, whether mirroring is enabled, and
whether
hopping is intra-subfrarne and inter-subframe hopping or inter-subframe
hopping; and
a transmitter configured to transmit data via the determined resource to a
Node B.
According to a further aspect of the invention, there is provided a method for
receiving data in a subframe including two slots in a communication system,
the method
comprising:
transmitting resource allocation information at a Node B;
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determining, by the Node B, a resource for data reception based on the
resource
allocation infomiation, whether hopping is enabled, whether mirroring is
enabled, and
whether hopping is intra.-subframe and inter-subframe hopping or inter-
subframe
hopping; and
receiving data via the determined resource from a User Equipment (UE) at the
Node B.
According to a further aspect of the invention, there is provided an apparatus
of a
Node B for receiving data in a subframe including two slots in a communication
system,
the apparatus comprising:
a scheduler configured to receive resource allocation information, determine a
resource for data reception based on the resource allocation information,
whether
hopping is enabled, whether mirroring is enabled, and whether hopping is intra-
subframe
and inter-subframe hopping or inter-subfiame hopping; and
a receiver configured to receive data via the determined resource from a User
Equipment (OE).
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 form the following
detailed description taken in conjunction with the accompanying drawings, in
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which:
FIG. 1 illustrates a transmitter in a conventional LFDMA system;
FIG. 2 illustrates a data transmission from UEs in their allocated resources
in a
conventional SC-FDMA SYSTEM;
FIG. 3 illustrates frequency hopping in a conventional FDMA system;
FIG. 4 illustrates conventional mirroring;
FIGs. 5A and 5B illustrate a method according to a first embodiment of the
present invention;
FIG. 6 illustrates an operation for selecting RUs in a UE or a Node B
according to
the present invention;
FIG. 7 illustrates a UE according to the present invention;
FIG. 8 illustrates the Node B according to the present invention;
FIG. 9 illustrates a channel structure according to the present invention;
FIGs. 10A to 10D illustrate a method according to a second embodiment of the
present invention;
FIG. 11 illustrates an operation for selecting RUs in the UE or the Node B
according to the second embodiment of the present invention;
FIG. 12 illustrates a channel structure according to the third embodiment of
the
present invention.
FIG 13. illustrates a method for performing mirroring irrespective of Hybrid
Automatic Repeat reQuest (HARQ) according to the third embodiment of the
present
invention;
FIG. 14 illustrates a method for performing mirroring for each HARQ process
according to the third embodiment of the present invention; and
FIG. 15 illustrates a method for performing mirroring for each HARQ process
according to a fourth embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The matters defined in the description such as a detailed construction and
elements are provided to assist in a comprehensive understand of preferred
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 of the invention. Also,
descriptions of well-known functions and constructions are omitted for the
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sake of clarity and conciseness.
Preferred 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 include 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.
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
Embodiment 1 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.
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FIGs. 5A and 5B illustrate a method according to the first embodiment of
the present invention. FIG 5A illustrates slot-based mirroring irrespective of
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-subfTame 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 a 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+1). 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+1), UE B uses an RU 509 in
slot (k+1). At hopping time (k+3), mirroring is on and thus LTE 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).
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 their 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 Cell A, LTE A is likely to be significantly interfered with by UE B.
However, since LTE A turns on mirroring at the next hopping time (k+1), UE A
transmits data in the RU 505 in slot (k+1), 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
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FIG. 5A in that different cells use different mirroring on/off patterns and
the
former differs from the latter in that in FIG. 5B, 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, as in FIG 5A.
In FIG. 5B, 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 initial transmission time when a response for transmitted data
is
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 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 ls.
(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 that
RUs hop in the same manner in different cells. In the context of the PN
sequence-
based method, the present invention will be described below.
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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 infoimation. The timing infonnation 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 illustrates an operation for determining mirroring on/off in a UE
according to the first 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 LIE determines to turn mirroring
off in
step 604. If the PN sequence value is 1, the UE determines to turn mirroring
on in
step 603. In step 605, the UE determines an RU position for the next data
transmission according to the mirroring-on/off determined in step 603 or 604.
The
UE transmits data in the determined 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 in
Equation (1) as
MO= N FH 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. II(r) denotes an RU to which the mirroring
base is mirrored in a slot. N FH denotes the total number of RUs in the FH
band.
FIG 7 illustrates the UE according to the first 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
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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 aforementioned 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 illustrates the Node B according to the first 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
LTEs based on RU allocation information about each UE detenained by an uplink
scheduler 802. The uplink scheduler 802 generates the RU information for each
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
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
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total system frequency band are divided into an FH band and an FS band, and a
channel structure which offers a sufficient frequency hopping gain in the FH
band
and achieves a sufficiently available frequency band in the FS band is
disclosed.
FIG 9 illustrates the channel structure according to the second
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.
Next, a description will be.m.ade of 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,
considering the single carrier property in the disclosed channel structure. As
in the
first embodiment, inter-sub-FH band hopping is on/off and mirroring is on/off
at
each hopping time according to a cell-specific pattern.
Four combinations of inter-sub-FH band hopping on/off and mirroring
onJoff are available as illustrated in Table 1. At each hopping time, one of
the
combinations is selected and hopping and/or 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
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FIGs. 10A to 10D illustrate the method according to the second
embodiment of the present invention.
FIGs. 10A and 10B 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 10B, combinations 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+1). At the next hoping time (k+2), Cell A perfothis 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+1), 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
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 FIGs. 10C and 10D, inter-sub-FH band hopping and mirroring are
performed 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 10C, 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 hopping 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
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hopping time k. At hopping time (k-I-1) for which combination 3 is set, the RU
1013 is inter-sub-FH band-hopped and mirrored to an RU 1012.
Next, a description will be made of a method for selecting combinations
of inter-sub-FH band hopping on/off and mirroring on/off using a sequence.
(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,
not 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 its detailed
description 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
increases randomization between cells and thus minimizes the phenomenon that
RUs hop in the same manner in different cells. In the context of the PN
sequence-
based method, the second 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 illustrates an operation of the UE according to the second
embodiment of the present invention. The same operation applies to the Node B
when it receives data from the UE.
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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 determines an RU for data transmission by mirroring and/or
hopping according to the selected combination. The UE transmits data in the
determined RU in step 1108.
A transmitter and a receiver according to the second embodiment of the
present invention have the same configurations as those according to the first
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
FIG. 12 illustrates a channel structure according to a third embodiment of
the present invention.
For a system where a plurality of sub-FH bands exist as illustrated in FIG
12 and hopping always occurs between the sub-FH bands, a method is disclosed
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 performing mirroring at the same time in the different cells,
thus
resulting in maximized randomization of inter-cell interference.
FIGs. 13 and 14 illustrate a method according to the third 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.
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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 perfatmed 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 because inter-sub-FH band hopping always
applies 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. Specifically, 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 embodiment of the present invention reduces the
probability of selecting the same RU at the next hopping time in the two
cells.
For instance, when the same RUs 1302 and 1312 are allocated
respectively to UE A in Cell A and UE B in Cell B for a period of time, if UE
B is
near Cell A, UE A is likely to be significantly interfered with by UE B at
hopping
time k. However, since Cell A perfothis 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+1), whereas inter-sub-FH band hopping is on and mirroring is off for
'GE
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+1), 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 in FIG.
14, rather than with respect to an RU used at the previous transmission time
as in
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FIG. 13.
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 detelmines mirroring on/off in the same manner as in the first
embodiment of the present invention, except that inter-sub-FH band hopping
occurs all the time in selecting an RU.
To realize the third 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, and is shown as follows:
Os f _s ¨N 0 =12(t), Os= Os mod N _RB
if 0.0,<N,
f h p(i) = N0 = h(i)+0s+I(Ns ¨1)¨ 2 x (Os mod(N))lx m(i)
fhop(i)= fhop(i)mod N RB
else if Ns..03
f 1,0= N = 40+ 0 + {(N0 ¨1)¨ 2 x ((Os ¨ Ns)mod(No))}x in(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), fh0p(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 resource blocks that can be scheduled for
UEs that perform hopping.
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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, N, 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, No and N, are computed by Equation (3), as follows:
No=1-N N, = N RB¨(M ¨1)x No
...................................................................... (3)
In Equation (2), 1/(i) denotes a cyclic shift degree, being one of 10, 1, . .
M I selected according to a bit value of a random sequence. 40)=0. m(i) is a
parameter that determines mirroring on/off at hopping time (i), being one of
{0,
1}. in(i) is selected according to a bit value of a random sequence, or by
h(i)= x/2 and in(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, mirroring is on.
Specifically, in Equation (2) the offset 0, at the scheduling time of the
scheduled resource block is first calculated by the first line of Equation
(2).
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 No than the number N, of resources blocks of each
of the other subbands and 0, is used to indicate the subband having the fewer
number of resource blocks to the LTE in the third embodiment of the present
invention.
For example, 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 0, is less than 4, the
UE is
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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
N5-1 according to the offset 0, and then mirrored within N, resource blocks.
If m(i)=0, mirroring is off.
If Os is larger than Nõ 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 subband configuration, it can further be contemplated that a
plurality of subbands each have Ns resource blocks and a plurality of
remaining
subbands each have 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.
Embodiment 4
If mirroring is on or off according to a random pattern in each cell,
successive mirrorings on/off increases 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 embodiment of
the
present invention discloses a limited use of a method for generating a random
mirroring pattern and deteimining 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 paftern for the other hopping scheme.
FIG. 15 illustrates a method for always turning on mirroring for inter-
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subframe hopping and determining mirroring on/off according to a random
mirroring on/off pattern for intra-subframe hopping according to the fourth
embodiment of the present invention.
As in the second 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 embodiment of the present invention.
Referring to FIG 15, mirroring occurs at each intra-subframe hopping
time according to a pattern of on, off, off, . . . in a cell 1500 (Cell A) and
according to a pattern of off, off, 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+1). 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
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+1), 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+1),
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
pattem
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
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the next HARQ transmission time, an RU 1510 is selected at hopping time k. At
hopping
time (k+1), mirroring is an 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+1),
mirroring is on according to the mirroring on/off pattern and thus an RU1513
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 maybe made therein
without
departing from the scope of the present invention as defined by the appended
claims and
their equivalents.
