U.S. patent application number 13/732800 was filed with the patent office on 2013-05-16 for reference signal multiplexing and resource allocation.
This patent application is currently assigned to NEC CORPORATION. The applicant listed for this patent is NEC Corporation. Invention is credited to Takamichi INOUE, Yoshikazu KAKURA, Shousei YOSHIDA.
Application Number | 20130121305 13/732800 |
Document ID | / |
Family ID | 38938288 |
Filed Date | 2013-05-16 |
United States Patent
Application |
20130121305 |
Kind Code |
A1 |
KAKURA; Yoshikazu ; et
al. |
May 16, 2013 |
REFERENCE SIGNAL MULTIPLEXING AND RESOURCE ALLOCATION
Abstract
A reference signal of a user equipment to which a resource
(LB#1) is allocated for a L1/L2 control signal, is allocateda
resource (SB#1) that is closer on the time axis to the resource
(LB#1), which the L1/L2 control signal is allocated, within the
same frequency band as the L1/L2 control signal. A reference signal
for CQI estimation, independent of a data signal and a L1/L2
control signal, is allocated a resource with which at least one of
a reference signal for demodulation of a data signal and a
reference signal for demodulation of a L1/L2 control signal is not
transmitted at the same timing within the transmission band. The
types of bandwidths of the reference signals multiplexed in a same
short block within a same band are reduced, whereby restrictions as
to the number of reference signal sequences that can be secured are
diminished.
Inventors: |
KAKURA; Yoshikazu; (Tokyo,
JP) ; YOSHIDA; Shousei; (Tokyo, JP) ; INOUE;
Takamichi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NEC Corporation; |
Tokyo |
|
JP |
|
|
Assignee: |
NEC CORPORATION
Tokyo
JP
|
Family ID: |
38938288 |
Appl. No.: |
13/732800 |
Filed: |
January 2, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11841021 |
Aug 20, 2007 |
|
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|
13732800 |
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Current U.S.
Class: |
370/330 |
Current CPC
Class: |
H04L 27/2613 20130101;
H04L 5/0007 20130101; H04L 5/0048 20130101; H04L 5/0053 20130101;
H04W 72/042 20130101; H04L 27/2602 20130101; H04L 1/20
20130101 |
Class at
Publication: |
370/330 |
International
Class: |
H04W 72/04 20060101
H04W072/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 22, 2006 |
JP |
2006-225932 |
Claims
1. A mobile station, comprising: a control signal transmission unit
which transmits an ACK/NACK control signal for a downlink data
signal; a data signal transmission unit which transmits an uplink
data signal; a reference signal generating unit which generates a
demodulation reference signal and a quality estimation reference
signal based on a CAZAC sequence; a reference signal transmission
unit which transmits the demodulation reference signal and the
quality estimation reference signal generated at the reference
signal generating unit; and a resource allocation unit which
allocates a time resource and a frequency resource to the
demodulation reference signal, the quality estimation reference
signal, the ACK/NACK control signal and the uplink data signal
respectively, wherein the resource allocation unit allocates, to
the quality estimation reference signal, the time resource and the
frequency resource which are difference from the time resource and
the frequency resource allocated to the ACK/NACK control signal and
the uplink data signal, and wherein the reference signal
transmission unit transmits the quality estimation reference signal
based on at least one preset subcarrier which is among subcarriers
in the frequency resource allocated to the quality estimation
reference signal.
2. The mobile station according to claim 1, wherein at least one
preset subcarrier is arranged for a preset interval.
3. A wireless communication method in a mobile station, comprising:
transmitting an ACK/NACK control signal for a downlink data signal;
transmitting an uplink data signal; generating a demodulation
reference signal and a quality estimation reference signal based on
a CAZAC sequence; transmitting the demodulation reference signal
and the quality estimation reference signal; allocating a time
resource and a frequency resource to the demodulation reference
signal, the quality estimation reference signal, the ACK/NACK
control signal and the uplink data signal respectively; allocating,
to the quality estimation reference signal, the time resource and
the frequency resource which are difference from the time resource
and the frequency resource allocated to the ACK/NACK control signal
and the uplink data signal; and transmitting the quality estimation
reference signal based on at least one preset subcarrier which is
among subcarriers in the frequency resource allocated to the
quality estimation reference signal.
4. The wireless communication method according to claim 3, wherein
at least one preset subcarrier is arranged for a preset interval.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2006-225932, filed on
Aug. 22, 2006, the disclosure of which is incorporated herein in
its entirety by reference.
[0003] The present invention relates to a radio communications
system and, more particularly, to a radio communications system
employing a scheme of multiplexing reference signals (also referred
to as pilot signals) with transmission signals, as well as a
technique for multiplexing reference signals, and radio
communication equipment using the technique.
[0004] 2. Description of the Related Art
[0005] In general, since transmission signals are under the
influence of radio channel fading, radio communications systems
employ a scheme of multiplexing a reference signal with a
transmission signal. That is, a reference signal received is used
to perform channel estimation for correct modulation/detection
(hereinafter, "modulation/detection" will mean modulation,
detection, or modulation and detection), and to perform channel
quality (CQI: Channel Quality Indicator) measurement for link
adaptation or scheduling.
[0006] Particularly in a mobile communications system in which a
base station carries out channel-dependent scheduling for a
plurality of mobile stations, since a resource is generally
allocated to a mobile station exhibiting the best CQI, CQI
measurement is performed in the entire frequency band where data
may be transmitted, with respect to those mobile stations waiting
for resource allocation. For CQI measurement, utilized is a
reference signal multiplexed on an uplink that the base station
receives from each mobile station. In the case where a reference
signal for demodulation of an uplink data signal or uplink control
signal is multiplexed, this reference signal can also be utilized
for CQI measurement.
[0007] To perform channel estimation and the like by using a
reference signal, the receiving side also needs to know in advance
a reference signal sequence to be transmitted. For such a sequence,
CAZAC (Constant Amplitude Zero Auto-Correlation) sequence has been
attracting attention in recent years. The CAZAC sequence has the
characteristics that the peak-to-average power ratio (PAPR) can be
kept low because the amplitude is constant in time domain, and that
excellent channel estimation in frequency domain is possible
because the amplitude is constant also in frequency domain (for
example, see Fazel, K., and Keiser, S., "Multi-Carrier and Spread
Spectrum Systems," John Willey and Sons, 2003). Therefore, the
CAZAC sequence is used as uplink reference-signal sequences also in
the 3GPP Long Term Evolution (see 3GPP TR 25.814 v2.0.0, June,
2006).
[0008] Such a reference signal is periodically multiplexed in every
frame so that variations due to channel fading can be accurately
estimated. In general, for a single channel, a plurality of
reference signals transmitted at discrete timings is used to
perform channel estimation and CQI measurement.
[0009] FIG. 1A is a format diagram showing an example of a frame
structure described in 3GPP R1-051033, Motorola, "Further Topics on
Uplink DFT-SOFDM for E-UTRA," Oct. 10-14, 2005. In this example,
one frame (sub-frame) has a frame length of 0.5 msec and includes
six long blocks LB#1 to LB#6 for transmitting control and data
signals and two short blocks SB#1 and SB#2 for transmitting
reference signals, with a cyclic prefix (CP) added to each block.
That is, the reference signals are time-multiplexed with control
and data signals in a frame. The number of short blocks SB to be
allocated for reference signals is dependent on the length of a
frame. As for the timings of the short blocks SB#1 and SB#2 within
a frame, it is sufficient to determine the timings so that the
reference signals will function effectively, and the timings shown
in the frame structure of FIG. 1A are not limitative.
[0010] Moreover, regarding the reference signals, which are
allocated the short blocks SB#1 and SB#2, a plurality of orthogonal
reference signals can be frequency-multiplexed within a certain
frequency band, allowing transmission in a single short block, and
these orthogonal reference signals can be allocated to different
user equipments respectively. However, the reference-signal
bandwidth required by each user equipment is not always the same as
that required by another user equipment, and suitable transmission
bandwidths differ depending on what purpose a reference signal is
used for (such as for modulation/detection of a data signal, for
modulation/detection of a L1/L2 control signal, or for CQI
measurement).
[0011] For example, when a data signal or L1/L2 (physical
layer/data link layer) control signal with a transmission bandwidth
of 5 MHz is transmitted in a frequency bandwidth of 10 MHz, it is
desirable to use a reference signal with the same transmission
bandwidth of 5 MHz in order to achieve highly reliable
demodulation/detection. However, in the case of a reference signal
for CQI measurement, the restriction as to the transmission
bandwidth is relaxed because the reference signal is not used for
demodulation/detection.
[0012] To multiplex as many reference signals as possible while
ensuring the orthogonality between the reference signals with
different transmission bandwidths as described above, several
multiplexing methods have been proposed.
1) Distributed Frequency Division Multiplexing
[0013] FIG. 1B is a diagram of a reference-signal structure showing
an example of distributed frequency division multiplexing
(distributed FDM) of reference signals. Here, it is assumed that a
frequency bandwidth of 10 MHz includes four 2.5-MHz frequency
blocks, in each of which six subcarriers can be
frequency-multiplexed. Moreover, it is assumed that two of the six
subcarriers in each frequency block are assigned to each of three
transmission bandwidths .DELTA.f(a), .DELTA.f(b), and
.DELTA.f(c).
[0014] In this example, a set of distributed reference signals
corresponding to the transmission bandwidth .DELTA.f(a) of 10 MHz
is allocated to a set of user equipments (UEs) 1a and 2a, in each
2.5-MHz frequency block. Taking the case of the UE 1a as an
example, the subcarriers allocated to the UE 1a in the four
respective frequency blocks, occupying a four-toothed comb-shaped
spectrum, provides one frequency resource. Similarly, two sets of
distributed reference signals corresponding to the transmission
bandwidth .DELTA.f(b) of 5 MHz are respectively allocated to two
sets of UEs: UEs 1b and 2b, and UEs 3b and 4b. Further, four sets
of distributed reference signals corresponding to the transmission
bandwidth .DELTA.f(c) of 2.5 MHz are respectively allocated to four
sets of UEs: UEs 1c and 2c, UEs 3c and 4c, UEs 5c and 6c, and UEs
7c and 8c. That is, in distributed FDM, the orthogonality between
reference signals with different transmission bandwidths can be
ensured because even if reference signals have different
transmission bandwidths, the reference signals are distributed
across the frequency axis.
[0015] However, distributed FDM has a demerit that the number of
CAZAC sequences that can be secured decreases as the number of
reference signals that are multiplexed in a certain frequency band
increases. This is because the maximum number of CAZAC sequences
that can be secured is obtained by subtracting one (1) from the
sequence length (sequence length-1), and the sequence length of
each reference signal decreases as the number of reference signals
multiplexed in a certain frequency band increases.
[0016] For example, in the case where the total of six distributed
reference signals with three types of transmission bandwidths
.DELTA.f of 10 MHz, 5 MHz, and 2.5 MHz (two signals to each type)
are multiplexed in each 2.5-MHz bandwidth (frequency block) as
shown in FIG. 1B, a frequency component to be allocated to one
distributed reference signal is one sixths of a frequency component
allocated in the case of a reference signal occupying a continuous
2.5-MHz frequency block (in the case of localized reference
signals). Since the sequence length of a reference signal depends
on the number of subcarriers, the sequence length of a reference
signal is reduced to 1/6 when a frequency component allocated is
1/6. In proportion to this, the number of CAZAC sequences that can
be secured is also reduced. Such a reduction in the number of
sequences means that the probability of the same sequence being
selected by adjacent cells increases when this scheme in question
is applied to a mobile communications system.
2) Hybrid Scheme (Cdm+Distributed FDM)
[0017] To overcome the above-described restrictions as to the
number of CAZAC sequences in distributed FDM, a hybrid scheme of
code division multiplexing (CDM) and distributed FDM has been
proposed (see 3GPP R1-060319, NTT DoCoMo et al., "Orthogonal Pilot
Channel Structure for E-UTRA Uplink," February, 2006). According to
this scheme, CDM is used to multiplex reference signals with the
same transmission bandwidth, and distributed FDM is used only to
multiplex those with different transmission bandwidths. With this
scheme, as a whole, the sequence length of each reference signal
can be made longer than in the case of using distributed FDM only.
Accordingly, the restrictions as to the number of CAZAC sequences
can be diminished.
[0018] FIG. 1C is a diagram of a reference-signal structure showing
an example of the hybrid scheme of CDM and distributed FDM.
According to the hybrid scheme, even if the total of six reference
signals with three types of transmission bandwidths .DELTA.f of 10
MHz, 5 MHz, and 2.5 MHz (two signals to each type) are multiplexed
in each 2.5-MHz frequency block as in FIG. 1B, since distributed
reference signals with the same transmission bandwidth (here,
corresponding to "1a and 2a," "1b and 2b," etc.) are
code-multiplexed, the number of frequency components that can be
allocated to one distributed reference signal is, at the maximum,
twice the number in the case of using distributed FDM only as in
FIG. 1B. Accordingly, the sequence length becomes twice, and hence
the number of CAZAC sequences that can be secured is also
proportionately increased.
[0019] However, according to the above-described hybrid scheme,
since the sequence length is increased by code-multiplexing
reference signals with the same transmission bandwidth, this merit
cannot be exploited when reference signals are of many types with
different transmission bandwidths. That is, when there are a large
number of different types of distributed reference signals with
different transmission bandwidths, the sequence length of each
reference signal is short, and the restrictions as to the number of
sequences that can be secured cannot be satisfactorily
diminished.
SUMMARY OF THE INVENTION
[0020] An object of the present invention is to provide a novel
resource allocation method and reference signal multiplexing method
that can diminish the restrictions as to the number of reference
signal sequences that can be secured.
[0021] According to the present invention, a resource allocating
method in a radio communications system performing allocation of a
reference resource, includes: a) allocating a first resource to a
reference signal which is used at least for either of demodulation
and detection, wherein the first resource is at least part of the
reference resource; and b) allocating a second resource to an
independent reference signal which is used for processing other
than demodulation and detection, wherein the second resource is at
least part of the reference resource other than allocated to the
reference signal which is used at least for either of demodulation
and detection.
[0022] As described above, according to the present invention,
reference signals may be frequency-multiplexed and/or
time-multiplexed depending on the usage purpose and importance of
the reference signals, whereby a reduction can be achieved in the
number of reference signals that are multiplexed by distributed FDM
at the same timing in the transmission band of the reference
signals. Correspondingly to this reduction, an increase can be
achieved in the number of reference signal sequences that can be
secured. That is, it is possible to sufficiently diminish the
restrictions as to the number of reference signal sequences that
can be secured.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1A is a format diagram showing an example of a frame
structure described in 3GPP R1-051033, Motorola, "Further Topics on
Uplink DFT-SOFDM for E-UTRA," Oct. 10-14, 2005.
[0024] FIG. 1B is a diagram of a reference-signal structure showing
an example of distributed frequency division multiplexing
(distributed FDM) of reference signals.
[0025] FIG. 1C is a diagram of a reference-signal structure showing
an example of a hybrid scheme of code division multiplexing and
distributed FDM.
[0026] FIG. 2 is a diagram schematically showing an example of a
method for multiplexing reference signals, according to a first
exemplary embodiment of the present invention.
[0027] FIG. 3 is a diagram schematically showing an example of a
method for multiplexing reference signals, according to a second
exemplary embodiment of the present invention.
[0028] FIG. 4 is a block diagram showing a fundamental
configuration of a base station in a radio communications system
according to an example of the present invention.
[0029] FIG. 5 is a block diagram showing a fundamental
configuration of a mobile station in the radio communications
system according to this example.
[0030] FIG. 6 is a schematic diagram of a system architecture for
describing operations in the radio communications system according
to this example.
[0031] FIG. 7 is a flowchart showing an operation of the mobile
station in this example.
[0032] FIG. 8 is a flowchart showing an operation of the base
station in this example.
[0033] FIG. 9A is a diagram of a frame structure showing the
resource allocation in FIG. 2.
[0034] FIG. 9B is a sequence diagram showing an allocation of a
resource for a reference signal to a mobile station transmitting
data.
[0035] FIG. 9C is a sequence diagram showing an allocation of a
resource for a reference signal to a mobile station transmitting a
L1/L2 control signal.
[0036] FIG. 9D is a sequence diagram showing an allocation of a
resource for a reference signal to a mobile station transmitting an
independent reference signal.
[0037] FIG. 10 is a flowchart showing resource allocation control
to allocate a resource for a CQI estimation reference signal,
according to this example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
1. First Exemplary Embodiment
1.1) Resource Allocation
[0038] FIG. 2 is a diagram schematically showing an example of a
method for multiplexing reference signals according to a first
exemplary embodiment of the present invention. In this example, it
is assumed that the frame structure shown in FIG. 1A is used, in
which one frame (sub-frame) includes long blocks LB#1 to LB#6,
short blocks SB#1 and SB#2, and cyclic prefixes (CP), with the
short block SB#1 being inserted between the long blocks LB#1 and
LB#2, and the short block SB#2 being inserted between the long
blocks LB#5 and LB#6. In addition, it is assumed that L1/L2 control
signals are allocated the long block LB#1, that reference signals
(also referred to as pilot signals) are allocated the short blocks
SB#1 and SB#2, and that data signals are allocated the long blocks
LB#2 to LB#6. A time interval between the short blocks SB#1 and
SB#2, which reference signals are allocated, is set so that fading
variance in each channel during data transmission can be followed.
Note that in FIG. 2, illustration of the cyclic prefixes (CP) shown
in FIG. 1A is omitted.
[0039] Incidentally, the bandwidth of a subcarrier in each short
block SB is twice as wide as that in each long block LB. The number
of reference signals to be multiplexed by distributed FDM is set so
that a sufficient number of reference signal sequences will be
provided. It is desirable that the number of reference signals to
be multiplexed by distributed FDM be set to two.
[0040] Additionally, to simplify the description here, a resource
allocated for any one of a L1/L2 control signal, reference signal,
and data signal of a certain user equipment will be referred to as
a "resource block," and a resource allocated in the frequency
domain in one short block will be referred to as a "frequency
resource." For example, in FIG. 1B, the set of subcarriers
allocated to the UE 1a in four frequency blocks (spectrum in a
shape like a four-toothed comb) is a "frequency resource."
[0041] Moreover, a L1/L2 control signal, reference signal, and data
signal are multiplexed in the time direction in each frame.
Resources allocated for these L1/L2 control signal, reference
signal, and data signal in one frame FR will be referred to as a
control resource, reference resource, and data resource,
respectively. Incidentally, a L1/L2 control signal in this example
is an uplink control signal regarding a downlink data signal, which
is called "data non-associated control signaling," and contains
ACK/NACK indicative of whether or not a downlink CQI or a downlink
packet has been fully received, and the like.
1.2) Reference Signal for Demodulation/Detection
[0042] A reference signal for demodulation/detection (hereinafter,
also referred to as a demodulation/detection reference signal) is
multiplexed in any one or both of the short blocks SB#1 and SB#2.
If a corresponding transmission signal is spread over a sub-frame
in time domain and variances in channel quality in time domain
cannot be ignored within the period of a sub-frame (for example,
like data signals of user equipments UE1 and UE2 in FIG. 2), then
the demodulation/detection reference signal is multiplexed in both
the short blocks SB#1 and SB#2, across the entire transmission
bandwidth of this transmission signal. On the other hand, if a
corresponding transmission signal is spread over part of a
sub-frame in time domain and variances in channel quality in the
time domain can be ignored within the period of part of a sub-frame
(for example, like L1/L2 signals of user equipments UE3 to UE6 in
FIG. 2), then the demodulation/detection reference signal is
multiplexed in only one of the short blocks SB#1 and SB#2. In FIG.
2, the demodulation/detection reference signal is multiplexed in
the short block SB#1.
[0043] For example, when an uplink L1/L2 control signal or uplink
data signal is transmitted, a demodulation/detection reference
signal is also transmitted. Therefore, to a user equipment to which
a control resource is allocated in a frequency block, a reference
resource is also allocated in the same frequency block. To a user
equipment to which a data resource is allocated in a frequency
block, a reference resource is also allocated in the same frequency
block.
[0044] Referring to FIG. 2, it is assumed that frequency bandwidths
BW1 and BW2 (for example, 6.25 MHz and 3.75 MHz, respectively) for
data signals are allocated to mobile stations (user equipments) UE1
and UE2, respectively. In this case, a distributed
demodulation/detection reference signal of the mobile station UE1
is multiplexed in both of the short blocks SB#1 and SB#2 within the
same frequency bandwidth BW1, and a distributed
demodulation/detection reference signal of the mobile station UE2
is allocated both of the short blocks SB#1 and SB#2 within the same
frequency bandwidth BW2. Incidentally, in the drawings, the
numerals in the short blocks SB#1 and SB#2 represent the mobile
stations' numbers (the same holds true with the long block
LB#1.)
[0045] Moreover, it is assumed that mobile stations UE3 and UE4 are
allocated the same frequency bandwidth BW3/4 in the long block LB#1
for L1/L2 control signals, which are multiplexed by distributed FDM
within the same bandwidth BW3/4. In this case, corresponding
distributed demodulation/detection reference signals of the mobile
stations UE3 and UE4 are allocated a short block that is closer to
the long block LB#1 (here, the short block SB#1), within the same
bandwidth BW3/4.
[0046] The L1/L2 control signals of the mobile stations UE3 and UE4
are multiplexed by distributed FDM within a same bandwidth BW3/4,
and, if the maximum number of signals that can be multiplexed by
CDM in the short block SB#1 is not smaller than two, the
distributed reference signals of the mobile stations UE3 and UE4
are multiplexed by CDM in the short block SB#1 (denoted by "3/4" in
FIG. 2), within the same frequency bandwidth BW3/4.
[0047] Similarly, L1/L2 control signals of mobile stations UE5 and
UE6 are multiplexed by distributed FDM within a same bandwidth
BW5/6, and, if the maximum number of signals that can be
multiplexed by CDM in the short block SB#1 is not smaller than two,
corresponding distributed reference signals of the mobile stations
UE5 and UE6 are multiplexed by CDM in the short block SB#1 (denoted
by "5/6" in FIG. 2), in a distributed manner within the same
frequency bandwidth BW5/6.
1.3) Reference Signal for Channel Quality Estimation
[0048] A reference signal for channel quality (CQI) estimation
(hereinafter, also referred to as a CQI estimation reference
signal), which is transmitted independently of a
demodulation/detection reference signal, is multiplexed in any one
of three types of frequency resources in a short block, which are
generalized as follows:
[0049] (1) a frequency resource that is never allocated to a
demodulation/detection reference signal;
[0050] (2) a frequency resource that can be allocated to a
demodulation/detection reference signal and has not been currently
occupied by (not currently allocated for) a demodulation/detection
reference signal; and
[0051] (3) a frequency resource that can be allocated to a
demodulation/detection reference signal and has been currently
occupied by (currently allocated for) a demodulation/detection
reference signal but satisfies both of the following conditions A
and B: [0052] Condition A) the transmission bandwidth of a CQI
estimation reference signal is the same as that of the
demodulation/detection reference signal; and [0053] Condition B)
the number of reference signals to be multiplexed by CDM is smaller
than the maximum number of multiplexing.
[0054] The above-described item (1), "a frequency resource that is
not and will not be allocated for a demodulation/detection
reference signal," is defined as a frequency resource that is
unoccupied in a short block and will be allocated neither for a
reference signal for demodulation/detection of a data signal nor
for a reference signal for demodulation/detection of a L1/L2
control signal.
[0055] For example, in the case where frequency resources in the
short blocks SB#1 and SB#2 are allocated to the mobile stations UE1
and UE2 for reference signals for demodulation/detection of their
data signals, and to the mobile stations UE3, UE4, UE5, and UE6 for
reference signals for demodulation/detection of their L1/L2 control
signals as shown in FIG. 2, then an unoccupied resource is a
frequency resource with a 10-MHz frequency bandwidth, labeled "7"
in FIG. 2. However, this frequency resource with the 10-MHz
frequency bandwidth, labeled "7" in FIG. 2, cannot be allocated for
another demodulation/detection reference signal, because the two
mobile stations UE1 and UE2 are already allocated the short blocks
SB#1 and SB#2 for their data signals and the mobile stations UE3 to
UE6 are already allocated the short block SB#1 for their L1/L2
control signals.
[0056] Accordingly, this unoccupied frequency resource, applying to
the above-described item (1), is allocated to a mobile station UE7
for CQI estimation, as shown in FIG. 2. Thereafter, it is checked
whether or not there is an unoccupied frequency resource applying
to the above-described item (2), and then a frequency resource
applying to the above-described item (3). If such a frequency
resource is available, the resource is allocated for a CQI
estimation reference signal. Hereinafter, specific examples will be
shown.
First Example
[0057] It is assumed that demodulation/detection reference signals
are multiplexed as described above in the section 1.2. In this
state, for example, if the mobile station UE7 makes an entry for
channel-dependent scheduling with its CQI estimation range set as a
bandwidth BW7=10 MHz, then a reference signal for estimation of the
channel quality of the mobile station UE7 should be allocated a
short block.
[0058] In this case, first, it is checked whether or not an
unoccupied frequency resource is present in the short block SB#2,
which is subsequent to the short block SB#1. This is because the
possibility of the presence of an unoccupied frequency resource
applying to the above-described item (1), "a frequency resource
that is not and will not be allocated for a demodulation/detection
reference signal," or an unoccupied frequency resource applying to
the above-described item (2), "a frequency resource that can be
allocated for a demodulation/detection reference signal and is not
currently occupied by a demodulation/detection reference signal,"
is higher in the short block SB#2 than in the short block SB#1. In
the short block SB#2, frequency resources are allocated only to the
mobile stations UE1 and UE2 for the reference signals for
demodulation/detection of their data signals, and an unoccupied
frequency bandwidth is present that is not allocated for at least
one of a reference signal for demodulation/detection of a data
signal and a reference signal for demodulation/detection of a L1/L2
control signal. Accordingly, if this unoccupied frequency bandwidth
is not smaller than the required bandwidth, a CQI estimation
reference signal of the mobile station UE7 can be allocated this
unoccupied frequency bandwidth. For example, if the unoccupied
frequency bandwidth in the short block SB#2 is 10 MHz as shown in
FIG. 2, a CQI estimation reference signal of the mobile station UE7
can be allocated the unoccupied frequency bandwidth in the short
block SB#2.
[0059] Alternatively, it is also possible to check the presence of
an unoccupied frequency resource first in the short block SB#1. In
this case, the whole short block SB#1 is occupied by the reference
signals for demodulation/detection of data and control signals, and
none of the transmission bandwidths of these demodulation/detection
reference signals match with the bandwidth BW7 (=10 MHz) required
by the mobile station UE7. That is, this fact does not meet the
above-described condition A, and therefore the short block SB#1 has
no room to be allocated for a CQI estimation reference signal of
the mobile station UE7.
Second Example
[0060] For example, it is assumed that the bandwidth BW7, which is
the CQI estimation range for the mobile station UE7, is 6.25 MHz,
the same as the frequency bandwidth BW1 for the mobile station UE1.
If an unoccupied frequency resource as required is not present in
the short block SB#2, then it is checked whether or not an
unoccupied frequency resource is present in the short block SB#1.
Although the whole short block SB#1 is occupied by the reference
signals for demodulation/detection of data and control signals, the
transmission bandwidth BW1 of the reference signal for
demodulation/detection of the data signal matches with the
transmission bandwidth BW7 required by the mobile station UE7, and
the maximum number of signals that can be multiplexed by CDM in the
short block SB#1 is not smaller than two. This fact meets the
above-described condition A. Accordingly, a CQI estimation
reference signal of the mobile station UE7 is allocated a frequency
resource by being multiplexed by CDM with the
demodulation/detection reference signal of the mobile station UE1
in the short block SB#1.
Third Example
[0061] For example, it is assumed that bandwidths BW7 and BW8,
which are the CQI estimation ranges for two mobile stations UE7 and
UE8 respectively, are each 10 MHz. In the short block SB#2,
frequency resources are allocated only to the mobile stations UE1
and UE2 for the reference signals for demodulation/detection of
their data signals, and an unoccupied frequency bandwidth of 10 MHz
is present that is not allocated for at least one of a reference
signal for demodulation/detection of a data signal and a reference
signal for demodulation/detection of a L1/L2 control signal.
Therefore, in this case, if the maximum number of signals that can
be multiplexed by CDM in the short block SB#2 is not smaller than
two, CQI estimation reference signals of the mobile stations UE7
and UE8 can be allocated this unoccupied frequency bandwidth by
CDM.
1.4) Advantages
[0062] According to the above-described first exemplary embodiment
of the present invention, it is possible to set a small number of
reference signals that are multiplexed by distributed FDM in a same
short block, within a frequency band in which the reference signals
are to be transmitted. For example, if the number of reference
signals that are multiplexed by distributed FDM is set to two, then
the sequence length of a reference signal is half the length when a
reference signal occupies the entire frequency in the same band.
Accordingly, it is possible to set a large number of reference
signal sequences that can be secured.
[0063] In addition, a reference signal for demodulation/detection
of a L1/L2 control signal is allocated the short block SB#1, which
is closer in the time direction to the long block LB#1 which the
L1/L2 control signal is allocated. Therefore, channel estimation
used for demodulation of the L1/L2 control signal can be performed
with high accuracy.
[0064] Further, if an independent reference signal for CQI
estimation cannot be allocated the short block SB#1, then the
independent reference signal is allocated the short block SB#2,
which is closer to the next frame on the time axis. Therefore, the
measurement of the channel quality of a mobile station UE in
question is less susceptible to a processing delay.
2. Second Exemplary Embodiment
[0065] In the above-described first exemplary embodiment,
description has been given of the cases where independent reference
signals for CQI estimation have the same frequency bandwidths.
However, according to the present invention, resources can be
allocated even to independent reference signals with different
frequency bandwidths.
2.1) Interframe Multiplexing of CQI Estimation Reference
Signals
[0066] FIG. 3 is a diagram schematically showing an example of a
method for multiplexing reference signals according to a second
exemplary embodiment of the present invention. In this example, it
is assumed that independent reference signals for CQI estimation
have two types of frequency bandwidths. Specifically, it is assumed
that the CQI estimation range for a mobile station UE7 is a
frequency bandwidth BW7 (=10 MHz, for example) as in the first
exemplary embodiment, and that the CQI estimation ranges for mobile
stations UE8 to UE11 are equal frequency bandwidths BW8 to BW11
(=2.5 MHz each, for example), respectively.
[0067] In this case, resource allocation in a first frame FR1 is
the same as in FIG. 2. That is, an independent reference signal of
the mobile station UE7 is allocated a short block SB#2 in the frame
FR1, as in FIG. 2.
[0068] However, as for independent reference signals of the mobile
stations UE8 to UE11, the frequency bandwidth thereof (2.5 MHz)
matches neither with transmission bandwidths BW1 and BW2 of
reference signals for demodulation/detection of data signals of
mobile station UE1 and UE2, nor with the transmission bandwidth BW7
of the independent reference signal of the mobile station UE7.
Accordingly, since the independent reference signals of the mobile
stations UE8 to UE11 do not meet the condition A described earlier,
these independent reference signals cannot be allocated either of
the short blocks SB#1 and SB#2.
[0069] However, channel quality does not need to be consecutively
measured for the mobile station UE7, to which the short block SB#2
is allocated in the frame FR1. Accordingly, in this case, it is
possible to allocate a short block SB#2 in the next frame FR2, for
the independent reference signals of the mobile stations UE8 to
UE11. A short block SB#1 in the frame FR2 cannot be allocated
because the condition A is not met.
[0070] As described above, it is possible to allocate resources
even to a plurality of independent reference signals with different
transmission bandwidths, by multiplexing the independent reference
signals in the time direction.
2.2) CQI Measurement Period
[0071] As mentioned above, channel quality (CQI) does not need to
be measured in every frame. Nevertheless, as a CQI measurement
period becomes shorter, accurate scheduling for mobile stations
moving faster can be achieved, although the overhead is increased.
Conversely, as a CQI measurement period becomes longer, accurate
scheduling for mobile stations moving faster becomes difficult to
achieve, but the overhead can be reduced. Therefore, it is
desirable to determine the CQI measurement period with
consideration given to what moving speed of mobile stations the
optimization is based upon.
[0072] For example, assuming that a coherent time is a supposed
length of time during which channel variance of a mobile station
can be considered constant, the effects of channel-dependent
scheduling cannot be obtained as expected when the CQI measurement
period is longer than the coherent time. Therefore, it is desirable
to set the CQI measurement period to be equal to or smaller than
the supposed coherent time.
2.3) Advantages
[0073] As described above, according to the present embodiment,
resources can be allocated even to a plurality of independent
reference signals with different transmission bandwidths, by
multiplexing the independent reference signals in the time
direction.
[0074] Accordingly, as in the above-described first exemplary
embodiment, it is possible to set a small number of reference
signals that are multiplexed by distributed FDM in a same short
block, within a frequency band in which the reference signals are
to be transmitted. For example, if the number of reference signals
that are multiplexed by distributed FDM is set to two, then the
sequence length of a reference signal is half the length when a
reference signal occupies the entire frequency in the same band.
Accordingly, it is possible to set a large number of reference
signal sequences that can be secured.
[0075] In addition, a reference signal for demodulation/detection
of a L1/L2 control signal is allocated the short block SB#1, which
is closer in the time direction to the long block LB#1 which the
L1/L2 control signal is allocated. Therefore, channel estimation
used for demodulation of the L1/L2 control signal can be performed
with high accuracy.
[0076] Further, if an independent reference signal for CQI
estimation cannot be allocated the short block SB#1, then the
independent reference signal is allocated the short block SB#2,
which is closer to the next frame on the time axis. Therefore, the
measurement of the channel quality of a mobile station UE in
question is less susceptible to a processing delay.
3. Radio Communications System
3.1) Base Station and Mobile Station
[0077] FIG. 4 is a block diagram showing a fundamental
configuration of a base station in a radio communications system
according to an example of the present invention. Here, it is
assumed that a base station 10 accommodates a plurality of mobile
stations UE1, UE2, . . . . Major components of the base station 10
related to the present example include a radio transceiver (Tx/Rx)
101, a reception processing section R, a control section 106, a
resource management section 107, and a transmission processing
section T.
[0078] The radio transceiver (Tx/Rx) 101 transmits and receives
radio signals to/from the plurality of mobile stations UE through
respective channels, by using the frequency/time-multiplexing
structure as shown in any one of FIGS. 2 and 3. The radio
transceiver 101 outputs a multiplexed reception signal S.sub.RX
from the plurality of mobile stations UE to the reception
processing section R, and also converts a multiplexed transmission
signal S.sub.TX inputted from the transmission processing section T
into a radio transmission signal.
[0079] The reception processing section R includes a signal
demultiplexing section 102, a data signal reproduction section 103,
a L1/L2 control signal reproduction section 104, and a channel
quality measurement section 105.
[0080] The signal demultiplexing section 102 removes cyclic
prefixes (CP) and demultiplexes, in time domain, data signals in
the long blocks LB#2 to LB#6, L1/L2 control signals in the long
block LB#1, and reference signals in the short blocks SB#1 and
SB#2, from the reception signal S.sub.RX multiplexed by TDM as
shown in FIG. 2. Further, in accordance with uplink resource
allocation information S.sub.RAL.sub.--.sub.U from the resource
management section 107, the signal demultiplexing section 102
identifies a resource block or resource blocks allocated to each
mobile station UE, and demultiplexes the multiplexed reception
signal S.sub.RX received from the mobile stations UEs back to
reception data signals S.sub.RDATA, reception L1/L2 control signals
S.sub.RCTL, and three types of reference signals: reference signal
S.sub.DREF for demodulation/detection of the reception data;
reference signal S.sub.CREF for demodulation/detection of the
reception L1/L2 control signal; and independent reference signal
S.sub.IREF for CQI estimation.
[0081] The data signal reproduction section 103 inputs the
reception data signal S.sub.RDATA and corresponding
demodulation/detection reference signal S.sub.DREF of each mobile
station UE, demodulates/detects reception data S.sub.DATA, and
outputs the reception data S.sub.DATA to the control section 106.
The L1/L2 control signal reproduction section 104 inputs the
reception L1/L2 control signal S.sub.RCTL and corresponding
demodulation/detection reference signal S.sub.CREF of each mobile
station UE, demodulates/detects a L1/L2 control signal S.sub.CTL,
and outputs the L1/L2 control signal S.sub.CTL to the control
section 106.
[0082] The channel quality measurement section 105 inputs the three
types of reference signals (reference signal S.sub.DREF for
demodulation/detection of the reception data, reference signal
S.sub.CREF for demodulation/detection of the reception L1/L2
control signal, and independent reference signal S.sub.IREF for CQI
estimation), measures uplink channel quality S.sub.CQI.sub.--.sub.U
of each mobile station UE by using a reference signal sequence
maintained by itself, and outputs the measured uplink channel
quality S.sub.CQI.sub.--.sub.U to the control section 106 and
resource management section 107.
[0083] The resource management section 107 inputs the respective
uplink channel qualities S.sub.CQI.sub.--.sub.U of the mobile
stations UE and compares them, thereby generating uplink resource
allocation information S.sub.RAL.sub.--.sub.U indicating which
resource blocks are allocated to which mobile stations UE, with
respect to each of the data signal, L1/L2 control signal, and
reference signals. As mentioned above, the signal demultiplexing
section 102 performs signal demultiplexing in accordance with this
uplink resource allocation information S.sub.RAL.sub.--.sub.U.
[0084] The transmission processing section T includes a data signal
generation section 108, a L1/L2 control signal generation section
109, a reference signal generation section 110, and a signal
multiplexing section 111.
[0085] The data signal generation section 108 generates a downlink
data signal S.sub.TDATA for a mobile station UE to which downlink
data should be transmitted, in accordance with downlink resource
allocation information S.sub.RAL.sub.--.sub.D inputted from the
resource management section 107, and outputs the generated downlink
data signal S.sub.TDATA to the signal multiplexing section 111. The
L1/L2 control signal generation section 109 generates a downlink
L1/L2 control signal S.sub.TCTL for a mobile station UE to which a
downlink L1/L2 control signal should be transmitted, in accordance
with the downlink resource allocation information
S.sub.RAL.sub.--.sub.D inputted from the resource management
section 107, and outputs the generated downlink L1/L2 control
signal S.sub.TCTL to the signal multiplexing section 111. The
reference signal generation section 110 generates a reference
signal S.sub.TREF in accordance with the downlink resource
allocation information S.sub.RAL.sub.--.sub.D received as input
from the resource management section 107 and outputs the generated
reference signal S.sub.TREF to the signal multiplexing section 111.
As described above, in accordance with the downlink resource
allocation information S.sub.RAL.sub.--.sub.D, the reference signal
generation section 110 generates a demodulation/detection reference
signal for a mobile station UE to which a downlink data signal or
downlink L1/L2 control signal is to be transmitted, and generates a
CQI estimation reference signal for a mobile station UE which has
made an entry for channel-dependent scheduling. The resource
management section 107 inputs downlink channel qualities
S.sub.CQI.sub.--.sub.D respectively measured by the mobile stations
UE and then generates the downlink resource allocation information
S.sub.RAL.sub.--.sub.D, which will be described later.
[0086] The signal multiplexing section 111 multiplexes in FDM
and/or TDM the thus generated downlink data signals S.sub.TDATA,
downlink L1/L2 control signals S.sub.TCTL, and reference signals
S.sub.TREF for the mobile stations UE, in accordance with the
downlink resource allocation information S.sub.RAL.sub.--.sub.D,
thereby generating a transmission signal S.sub.TX and transmitting
it from the radio transceiver 101.
[0087] Incidentally, the uplink resource allocation information
S.sub.RAL.sub.--.sub.U and downlink resource allocation information
S.sub.RAL.sub.--.sub.D generated by the resource management section
107 are contained in a L1/L2 control signal generated by the L1/L2
control signal generation section 109 and are transmitted to each
mobile station UE, under the control of the control section 106.
Each mobile station UE receives these uplink resource allocation
information S.sub.RAL.sub.--.sub.U and downlink resource allocation
information S.sub.RAL.sub.--.sub.D and determines resource blocks
to use respectively for uplink and downlink communications with the
base station 10 in accordance with the received uplink resource
allocation information S.sub.RAL.sub.--.sub.U and downlink resource
allocation information S.sub.RAL.sub.--.sub.D.
[0088] Moreover, the control section 106 controls the entire
operation of the base station 10. The functions of the resource
management section 107 can also be implemented by executing a
resource management program on a program-controlled processor, or a
computer.
[0089] FIG. 5 is a block diagram showing a configuration of a
mobile station in the radio communications system according to the
present example. Since mobile stations do not perform resource
management, resources for the mobile station itself to use in
transmission and reception are determined in accordance with the
uplink resource allocation information S.sub.RAL.sub.--.sub.U and
downlink resource allocation information S.sub.RAL.sub.--.sub.D
received from the base station 10. Hereinafter, the configuration
of a mobile station will be described briefly.
[0090] Referring to FIG. 5, major components of a mobile station 20
related to the present example include a radio transceiver (Tx/Rx)
201, a reception processing section R, a control section 206, and a
transmission processing section T. The radio transceiver 201
transmits and receives radio signals to/from the base station 10
through a designated channel. The reception processing section R
includes a signal demultiplexing section 202, a data signal
reproduction section 203, a L1/L2 control signal reproduction
section 204, and a channel quality measurement section 205.
[0091] The signal demultiplexing section 202 identifies a resource
block or resource blocks allocated to the mobile station 20, in
accordance with downlink resource allocation information
S.sub.RAL.sub.--.sub.D designated by the control section 206, and
demultiplexes a reception data signal S.sub.RDATA, a reception
L1/L2 control signal S.sub.RCTL, and three types of reference
signals: reference signal S.sub.DREF for demodulation/detection of
the reception data; reference signal S.sub.CREF for
demodulation/detection of the reception L1/L2 control signal; and
independent reference signal S.sub.IREF for CQI estimation.
[0092] The data signal reproduction section 203 inputs the
reception data signal S.sub.RDATA and corresponding
demodulation/detection reference signal S.sub.DREF,
demodulates/detects reception data S.sub.DATA, and outputs the
reception data S.sub.DATA to the control section 206. The L1/L2
control signal reproduction section 204 inputs the reception L1/L2
control signal S.sub.RCTL and corresponding demodulation/detection
reference signal S.sub.CREF, demodulates/detects a L1/L2 control
signal S.sub.CTL, and outputs the L1/L2 control signal S.sub.CTL to
the control section 206. The channel quality measurement section
205 inputs the three types of reference signals (reference signal
S.sub.DREF for demodulation/detection of the reception data,
reference signal S.sub.CREF for demodulation/detection of the
reception L1/L2 control signal, and independent reference signal
S.sub.IREF for CQI estimation), measures downlink channel quality
S.sub.CQI.sub.--.sub.D of the mobile station 20 itself, and outputs
the measured downlink channel quality S.sub.CQI.sub.--.sub.D to the
control section 206.
[0093] When a L1/L2 control signal S.sub.CTL received from the base
station 10 contains uplink resource allocation information
S.sub.RAL.sub.--.sub.U and downlink resource allocation information
S.sub.RAL.sub.--.sub.D, the control section 206 controls the signal
demultiplexing section 202 in accordance with the downlink resource
allocation information S.sub.RAL.sub.--.sub.D as described above,
and controls the transmission processing section T in accordance
with the uplink resource allocation information
S.sub.RAL.sub.--.sub.U as described below.
[0094] The transmission processing section T includes a data signal
generation section 207, a L1/L2 control signal generation section
208, a reference signal generation section 209, and a signal
multiplexing section 210.
[0095] The data signal generation section 207, when transmitting
uplink data, generates an uplink data signal S.sub.TDATA in
accordance with the uplink resource allocation information
S.sub.RAL.sub.--.sub.U inputted from the control section 206 and
outputs the generated uplink data signal S.sub.TDATA to the signal
multiplexing section 210. The L1/L2 control signal generation
section 208, when transmitting an uplink L1/L2 control signal,
generates an uplink L1/L2 control signal S.sub.TCTL in accordance
with the uplink resource allocation information
S.sub.RAL.sub.--.sub.U and outputs the generated uplink L1/L2
control signal S.sub.TCTL to the signal multiplexing section 210.
The reference signal generation section 209 generates a reference
signal S.sub.TREF in accordance with the uplink resource allocation
information S.sub.RAL.sub.--.sub.U and outputs the generated
reference signal S.sub.TREF to the signal multiplexing section 210.
As described above, in accordance with the uplink resource
allocation information S.sub.RAL.sub.--.sub.U, the reference signal
generation section 209 generates a demodulation/detection reference
signal when the mobile station 20 has an uplink data signal or
uplink L1/L2 control signal to transmit, and generates a CQI
estimation reference signal when the mobile station 20 has made an
entry for channel-dependent scheduling.
[0096] The signal multiplexing section 210 multiplexes the thus
generated uplink data signal S.sub.TDATA, uplink L1/L2 control
signal S.sub.TCTL, and/or reference signal S.sub.TREF in the
resource blocks designated by the uplink resource allocation
information S.sub.RAL.sub.--.sub.U, thereby generating a
transmission signal S.sub.TX and transmitting it from the radio
transceiver 201 to the base station 10.
3.2) Operation
[0097] FIG. 6 is a schematic diagram showing system architecture
for describing operations in the radio communications system
according to the present example. Here a transmitting device T
corresponds to the mobile station 20 shown in FIG. 5, and a
receiving device R corresponds to the base station 10 shown in FIG.
4. Blocks having the same functions as those in FIGS. 4 and 5 are
denoted by the same reference numerals as those in FIGS. 4 and 5,
and the description thereof will be omitted. Hereinafter,
operations of the transmitting device T and receiving device R will
be described with reference to the block diagram of FIG. 6 and
flowcharts of FIGS. 7 and 8. Note that in FIG. 6, a signal is
transmitted from the transmitting device T to the receiving device
R, and therefore uplink resource allocation information
S.sub.RAL.sub.--.sub.U and downlink resource allocation information
S.sub.RAL.sub.--.sub.D are simply referred to as "resource
allocation information S.sub.RAL."
[0098] FIG. 7 is a flowchart showing an operation of the mobile
station according to the present example. First, the control
section 206 of the mobile station sets resource allocation
information S.sub.RAL received from the base station 10 (step
S301), and then determines whether or not a resource for a data
signal is allocated (step S302). If a resource for a data signal is
allocated (YES in step S302), the control section 206 controls the
data signal generation section 207 and reference signal generation
section 209 to generate a data signal S.sub.DATA and a reference
signal S.sub.REF (step S303). If a resource for a data signal is
not allocated (NO in step S302), the control section 206 does not
carry out the step S303.
[0099] Subsequently, the control section 206 determines whether or
not a resource for a L1/L2 control signal is allocated (step S304).
If a resource for a L1/L2 control signal is allocated (YES in step
S304), the control section 206 controls the L1/L2 control signal
generation section 208 and reference signal generation section 209
to generate a L1/L2 control signal S.sub.CTL and a reference signal
S.sub.REF (step S305). If a resource for a L1/L2 control signal is
not allocated (NO in step S304), the control section 206 does not
carry out the step S305.
[0100] Subsequently, the control section 206 determines whether or
not a resource for a CQI estimation reference signal (independent
reference signal) is allocated (step S306). If a resource for an
independent reference signal is allocated (YES in step S306), the
control section 206 controls the reference signal generation
section 209 to generate an independent reference signal S.sub.REF
(step S307). If a resource for an independent reference signal is
not allocated (NO in step S306), the control section 206 does not
carry out the step S307.
[0101] The signals thus generated by the data signal generation
section 207, L1/L2 control signal generation section 208, and/or
reference signal generation section 209 are multiplexed by FDM
and/or TDM in accordance with the resource allocation information
S.sub.RAL as described already, whereby a transmission signal
S.sub.TX is generated (step S308). The transmission signal S.sub.TX
is transmitted to the base station 10 via the radio transceiver 201
(step S309).
[0102] FIG. 8 is a flowchart showing an operation of the base
station according to the present example. First, when the base
station 10 receives a multiplexed signal from a plurality of mobile
stations UE (step S401), the control section 106 of the base
station 10 controls the signal demultiplexing section 102, using
resource allocation information S.sub.RAL. Thereby, the signal
demultiplexing section 102 identifies a resource block or resource
blocks allocated to each mobile station UE and demultiplexes a
reception data signal S.sub.RDATA, a reception L1/L2 control signal
S.sub.RCTL, and three types of reference signals (reference signal
S.sub.DREF for demodulation/detection of the reception data,
reference signal S.sub.CREF for demodulation/detection of the
reception L1/L2 control signal, and independent reference signal
S.sub.IREF for CQI estimation) of each mobile station UE (step
S402).
[0103] Subsequently, the control section 106 controls the resource
management section 107, which then determines, with respect to each
mobile station UE, whether or not a resource for a data signal is
allocated (step S403). If a resource for a data signal is allocated
to the mobile station UE (YES in step S403), the control section
106 controls the data signal reproduction section 103 to have it
reproduce an uplink data signal S.sub.DATA sent from the mobile
station UE in question, and controls the channel quality
measurement section 105 to have it measure channel quality
S.sub.CQI of the mobile station UE in question from the reference
signal S.sub.DREF for demodulation/detection of that reception data
(step S404). For a mobile station UE to which a resource for a data
signal is not allocated (NO in step S403), the control section 106
does not carry out the step S404.
[0104] Subsequently, the control section 106 controls the resource
management section 107, which then determines, with respect to each
mobile station UE, whether or not a resource for a L1/L2 control
signal is allocated (step S405). If a resource for a L1/L2 control
signal is allocated to the mobile station UE (YES in step S405),
the control section 106 controls the L1/L2 control signal
reproduction section 104 to have it reproduce an uplink L1/L2
control signal S.sub.CTL sent from the mobile station UE in
question, and controls the channel quality measurement section 105
to have it measure channel quality S.sub.CQI of the mobile station
UE in question from a reference signal S.sub.CREF for
demodulation/detection of that L1/L2 control signal (step S406).
For a mobile station UE to which a resource for a L1/L2 control
signal is not allocated (NO in step S403), the control section 106
does not carry out the step S406.
[0105] Subsequently, the control section 106 determines whether or
not a resource for a CQI estimation reference signal (independent
reference signal) is allocated (step S407). If a resource for an
independent reference signal is allocated (YES in step S407), the
control section 106 controls the channel quality measurement
section 105 to have it measure channel quality S.sub.CQI of the
mobile station UE in question from the independent reference signal
S.sub.IREF (step S408). For a mobile station UE to which a resource
for an independent reference signal is not allocated (NO in step
S407), the control section 106 does not carry out the step
S408.
[0106] Subsequently, the control section 106 controls the resource
management section 107 to determine which resources will be
allocated to which mobile stations UE (that is, resource allocation
information S.sub.RAL), based on the channel quality S.sub.CQI of
each mobile station UE inputted from the channel quality
measurement section 105 (step S409). Then, as described already,
corresponding resource allocation information S.sub.RAL is notified
to each mobile station UE (step S410).
3.3) Resource Allocation
[0107] Hereinafter, an operation of the base station to allocate a
resource for a reference signal will be described by using the
resource allocation shown in FIG. 2 as an example.
[0108] FIG. 9A is a diagram of a frame structure showing the
resource allocation shown in FIG. 2. FIG. 9B is a sequence diagram
showing allocation of a resource for a reference signal to a mobile
station transmitting data. FIG. 9C is a sequence diagram showing
allocation of a resource for a reference signal to a mobile station
transmitting a L1/L2 control signal. FIG. 9D is a sequence diagram
showing allocation of a resource for a reference signal to a mobile
station transmitting an independent reference signal.
[0109] Referring to FIG. 9B, it is assumed that, for example, a
mobile station UE1 has transmitted a CQI estimation reference
signal S.sub.IREF using an unoccupied frequency resource in a short
block SB#1 or SB#2 in accordance with resource allocation
information S.sub.RAL received from the base station 10, as
described in any one of the first to third examples in the section
1.3. The base station 10 measures channel quality S.sub.CQI of the
mobile station UE1 from this CQI estimation reference signal
S.sub.IREF. When the base station 10 determines to allocate a
resource for a data signal to the mobile station UE1 as shown in
FIG. 9A, the base station 10 notifies the mobile station UE1 of
resource allocation information S.sub.RAL indicative of a
transmission frequency bandwidth to be allocated and corresponding
frequency resources in short blocks SB#1 and SB#2. In accordance
with this resource allocation information S.sub.RAL, the mobile
station UE1 generates uplink data S.sub.DATA and a corresponding
demodulation/detection reference signal S.sub.REF, multiplexes in
distributed-FDM and TDM manner the demodulation/detection reference
signal S.sub.REF in each of the short blocks SB#1 and SB#2 as shown
in FIG. 9A, and then transmits the multiplexed signal to the base
station 10.
[0110] Referring to FIG. 9C, it is assumed that, for example, a
mobile station UE3 has transmitted a CQI estimation reference
signal S.sub.IREF by using an unoccupied frequency resource in a
short block SB#1 or SB#2 in accordance with resource allocation
information S.sub.RAL received from the base station 10, as
described in any one of the first to third examples in the section
1.3. The base station 10 measures channel quality S.sub.CQI of the
mobile station UE3 from this CQI estimation reference signal
S.sub.IREF. When the base station 10 determines to allocate a
resource for a L1/L2 control signal to the mobile station UE3 as
shown in FIG. 9A, the base station 10 notifies the mobile station
UE3 of resource allocation information S.sub.RAL indicative of a
transmission frequency bandwidth to be allocated and a
corresponding frequency resource in a short block SB#1. In
accordance with this resource allocation information S.sub.RAL, the
mobile station UE3 generates an uplink L1/L2 control signal
S.sub.CTL and a corresponding demodulation/detection reference
signal S.sub.REF, multiplexes in distributed-FDM and TDM manner the
demodulation/detection reference signal S.sub.REF in the short
block SB#1 as shown in FIG. 9A, and then transmits the multiplexed
signal to the base station 10.
[0111] Referring to FIG. 9D, it is assumed that a mobile station
UE7 has sent a request for data transmission to the base station 10
and has made an entry for channel-dependent scheduling with the
resource management section 107 of the base station 10. In this
case, the mobile station UE7 transmits a CQI estimation reference
signal S.sub.IREF by using an unoccupied frequency resource in a
short block SB#1 or SB#2 in accordance with resource allocation
information S.sub.RAL received from the base station 10, as
described in any one of the first to third examples in the section
1.3. Specifically, here, the base station 10 notifies the mobile
station UE7 of resource allocation information S.sub.RAL indicative
of the entire frequency bandwidth of a short block SB#2 as shown in
FIG. 9A. In accordance with this resource allocation information
S.sub.RAL, the mobile station UE7 generates a CQI estimation
reference signal S.sub.IREF,
distributed-frequency-division-multiplexes and
time-division-multiplexes the CQI estimation reference signal
S.sub.IREF in the short block SB#2, and then transmits the
multiplex signal to the base station 10.
3.4) Resource Allocation to CQI Estimation Reference Signal
[0112] Next, a procedure of allocating a resource to a CQI
estimation reference signal according to the present example will
be described. Note, however, that the under-mentioned order of
steps should be regarded as illustrative only and not
restrictive.
[0113] FIG. 10 is a flowchart showing resource allocation control
to allocate a resource to a CQI estimation reference signal
according to the present example. In the present example, the
operation of allocating resources for demodulation/detection and
CQI estimation reference signals in the short blocks SB#1 and SB#2
is repeated in every frame (S501).
[0114] In one frame, if a mobile station in course of communication
exists, a frequency resource with a transmission bandwidth required
for a reference signal used in that communication is allocated to
this mobile station (S502). Specifically, to a mobile station (UE)
that is communicating data, a frequency resource in both the short
blocks SB#1 and SB#2 is allocated to a reference signal for
demodulation/detection of the data, and to a mobile station that is
communicating a L1/L2 control signal, a frequency resource in the
short block SB#1 is allocated to a reference signal for
demodulation/detection of the L1/L2 control signal.
[0115] Subsequently, it is checked whether or not an unoccupied
frequency resource is present in the short block SB#2 (step S503).
The checking of the presence or absence of an unoccupied frequency
resource can be carried out as described already in the section
1.3. For example, the steps are as follows:
[0116] (1) It is checked whether or not a frequency resource is
never allocated to a demodulation/detection reference signal;
[0117] (2) When an unoccupied frequency resource applying to the
above item (1) is not present, it is checked whether or not a
frequency resource is present which can be allocated to a
demodulation/detection reference signal but has not been currently
occupied by (not currently allocated to) a demodulation/detection
reference signal; and
[0118] (3) When an unoccupied frequency resource applying to the
above item (2) is not present, it is checked whether or not a
frequency resource is present which can be allocated to a
demodulation/detection reference signal and has been currently
occupied by (currently allocated to) a demodulation/detection
reference signal but satisfies both of the following conditions A
and B: [0119] Condition A) the transmission bandwidth of a CQI
estimation reference signal is the same as that of the
demodulation/detection reference signal; and [0120] Condition B)
the number of reference signals to be multiplexed by CDM is smaller
than the maximum number of multiplexing.
[0121] If such a frequency resource is present in the short block
SB#2 (YES in step S503), then this frequency resource in the short
block SB#2 is allocated to, depending on the bandwidth of the
frequency resource, one or a plurality of the mobile stations
waiting for channel-dependent scheduling, for their CQI estimation
reference signals (step S504).
[0122] If such a frequency resource is not present in the short
block SB#2 (NO in step S503), it is next checked whether or not an
unoccupied frequency resource is present in the short block SB#1
(step S505). The checking of the presence or absence of an
unoccupied frequency resource is similarly performed as in the
above-described procedure.
[0123] If such a frequency resource is present in the short block
SB#1 (YES in step S505), then this frequency resource in the short
block SB#1 is allocated to, depending on the bandwidth of the
frequency resource, one or a plurality of the mobile stations
waiting for channel-dependent scheduling, for their CQI estimation
reference signals (step S506). If such a frequency resource is not
present in the short block SB#1 either (NO in step S505), similar
processing is repeated in the next frame.
[0124] Note that after an unoccupied frequency resource in the
short block SB#2 is allocated to a CQI measurement reference signal
(step S504), the step S505 may also be subsequently performed, in
which it is checked whether or not an unoccupied frequency resource
is present in the short block SB#1.
3.5) Advantages
[0125] As described hereinabove, by applying the present invention
to mobile stations and base stations in a radio communications
system, it is possible to set a sufficiently small number of
reference signals that are multiplexed by distributed FDM in a same
short block, within a frequency band where the reference signals
are to be transmitted. Accordingly, it is possible to sufficiently
diminish the restrictions as to the number of reference signal
sequences that can be secured.
[0126] Moreover, a reference signal for demodulation/detection of a
L1/L2 control signal is allocated a short block SB#1, which is
closer in the time direction to a long block LB#1 which the L1/L2
control signal is allocated. Accordingly, it is possible to perform
channel estimation used for demodulation of the L1/L2 control
signal, with high accuracy.
[0127] Further, a CQI estimation reference signal, when it cannot
be allocated a short block SB#1, is allocated a short block SB#2,
which is closer to the next frame on the time axis. Accordingly,
the measurement of channel quality is less susceptible to a
processing delay.
[0128] Hence, the restrictions as to the number of reference signal
sequences that can be secured can be diminished to sufficiently low
level, while the accuracy with which a data signal or L1/L2 control
signal is demodulated and the accuracy with which channel quality
is measured are kept at high level.
[0129] The present invention can be applied to radio communications
systems and, more particularly, to mobile communications systems
employing a scheme of multiplexing reference signals (pilot
signals) with data and control signals, as well as to base and
mobile stations in such a system, and operation programs for the
base and mobile stations.
4. Various Aspects
[0130] As described before, the present invention provides a
resource allocation method and reference signal multiplexing method
that can diminish the restrictions as to the number of reference
signal sequences that can be secured, and that can prevent a
reduction in the number of reference signals multiplexed, as well
as a radio communications system using the methods.
[0131] The present invention also provides a resource allocation
method and reference signal multiplexing method that enable
reference signals with different transmission bandwidths to be
efficiently allocated a limited frequency band, as well as a radio
communications system using the methods.
[0132] The present invention is based on findings such that the
size of a resource allocated to a reference signal is changed
depending on its use purpose and degree of importance. According to
the present invention, high efficient multiplexing of reference
signals and diminishing the restrictions as to the number of
reference signal sequences can be achieved. For example, a
reference signal for demodulation/detection of a data signal or a
L1/L2 control signal is multiplexed by distributed FDM over the
same bandwidth as the transmission bandwidth of the data signal or
L1/L2 control signal. In addition, when a data signal is
transmitted, a reference signal for demodulation/detection is
multiplexed at a plurality of timings. When a L1/L2 control signal
is transmitted, a reference signal for demodulation/detection is
multiplexed at a single timing closer in time to the L1/L2 control
signal. It should be noted that hereinafter a reference signal for
demodulation/detection of a data signal and a reference signal for
demodulation/detection of a L1/L2 control signal are simply
referred to as "a reference signal for demodulation/detection."
[0133] In contrast, a reference signal for channel quality
estimation may be multiplexed, independently of data signal or
L1/L2 control signal, under the condition of timing and bandwidth
allowing effective channel quality measurement within a channel
quality measurement range.
[0134] In other words, the number of reference signals to be
multiplexed by distributed FDM at the same timing for each
predetermined frequency block is previously set to a small number
so that a sufficiently large number of reference signal sequences
can be ensured. Depending on the user purposes and degrees of
importance for reference signals, the respective reference signals
are multiplexed by time and/or frequency division in a plurality of
frequency resources in a plurality of reference signal timings,
which will be described later as short blocks SB#1, SB#2. Resource
allocation to reference signals at the plurality of reference
signal timings will be described hereinafter.
[0135] According to the present invention, a resource allocating
method in a radio communications system performing allocation of a
reference resource, includes: a) allocating a first resource to a
reference signal which is used at least for either of demodulation
and detection, wherein the first resource is at least part of the
reference resource; and b) allocating a second resource to an
independent reference signal which is used for processing other
than demodulation and detection, wherein the second resource is at
least part of the reference resource other than allocated to the
reference signal which is used at least for either of demodulation
and detection.
[0136] Hereafter, a reference signal that is used at least for
either of demodulation and detection will be referred to as "a
demodulation/detection reference signal." If variations in the
channel quality of a corresponding transmission signal within a
frame in time domain are not negligible, then the
demodulation/detection reference signal is multiplexed by time
division at a plurality of reference signal timings over the entire
transmission bandwidth of the transmission signal. If variations in
the channel quality of a corresponding transmission signal within a
frame in time domain are negligible, then the
demodulation/detection reference signal is multiplexed by time
division at any one of the plurality of reference signal
timings.
[0137] A channel-quality estimation reference signal which is
transmitted independently of demodulation/detection reference
signals is multiplexed at one or more timing of the plurality of
reference signal timings in one of the following resources:
[0138] (1) a frequency resource that is never allocated to a
demodulation/detection reference signal;
[0139] (2) a frequency resource that can be allocated to a
demodulation/detection reference signal and has not been currently
occupied by (not currently allocated for) a demodulation/detection
reference signal; and
[0140] (3) a frequency resource that can be allocated to a
demodulation/detection reference signal and has been currently
occupied by (currently allocated for) a demodulation/detection
reference signal but satisfies both of the following conditions A
and B: [0141] Condition A) the transmission bandwidth of a CQI
estimation reference signal is the same as that of the
demodulation/detection reference signal; and [0142] Condition B)
the number of reference signals to be multiplexed by CDM is smaller
than the maximum number of multiplexing.
[0143] According to another aspect of the present invention, a
reference signal which is transmitted independently of the presence
or absence of a data signal and a L1/L2 control signal, or an
independent reference signal, is allocated a resource in which at
least one of the demodulation/detection reference signals for the
data signal and the L1/L2 control signal is not transmitted at the
same timing within its transmission band.
[0144] More specifically, in a reference signal multiplexing
method, the demodulation/detection reference signals for the data
signal is allocated a plurality of reference signal resources which
are closer in time axis to a resource allocated to the data signal,
the demodulation/detection reference signals for the L1/L2 control
signal is allocated a single reference signal resource which is
closer in time axis to a resource allocated to the L1/L2 control
signal, and an independent reference signal is allocated a resource
in which at least one of the demodulation/detection reference
signals for the data signal and the L1/L2 control signal is not
transmitted at the same timing within its transmission band. The
demodulation/detection reference signals for the data signal, the
demodulation/detection reference signals for the L1/L2 control
signal and the independent reference signal are multiplexed in
frequency-division and/or time-division manner.
[0145] As described above, according to the present invention,
reference signals are multiplexed in frequency-division and/or
time-division depending on the usage purpose and importance of the
reference signals, whereby a reduction can be achieved in the
number of reference signals that are multiplexed by distributed FDM
at the same timing in the transmission band of the reference
signals. Correspondingly to this reduction, an increase can be
achieved in the number of reference signal sequences that can be
secured. That is, it is possible to sufficiently diminish the
restrictions as to the number of reference signal sequences that
can be secured.
[0146] The present invention may be embodied in other specific
forms without departing from the spirit or essential
characteristics thereof. The above-described exemplary embodiments
are therefore to be considered in all respects as illustrative and
not restrictive, the scope of the invention being indicated by the
appended claims rather than by the foregoing description, and all
changes which come within the meaning and range of equivalency of
the claims are therefore intended to be embraced therein.
* * * * *