U.S. patent application number 14/009534 was filed with the patent office on 2014-02-13 for receiver, transmitter and radio communication method.
This patent application is currently assigned to NTT DOCOMO, INC.. The applicant listed for this patent is Yoshihisa Kishiyama. Invention is credited to Yoshihisa Kishiyama.
Application Number | 20140044091 14/009534 |
Document ID | / |
Family ID | 47217159 |
Filed Date | 2014-02-13 |
United States Patent
Application |
20140044091 |
Kind Code |
A1 |
Kishiyama; Yoshihisa |
February 13, 2014 |
RECEIVER, TRANSMITTER AND RADIO COMMUNICATION METHOD
Abstract
Provided are a receiver, a transmitter and a radio communication
method capable of using non-orthogonal multiple access while
suppressing cost increase and processing delay. A mobile station
200A includes a target user control signal detector 230 and an
interfering user control signal detector 240 which are configured
to receive a control signal to be used to cancel a non-orthogonal
signal by interference canceller. The control signal includes
control information containing a radio resource block allocated to
the non-orthogonal signal addressed to another mobile station. The
mobile station 200A demodulates and cancels the radio signal
addressed to the other mobile station on the basis of the control
signal.
Inventors: |
Kishiyama; Yoshihisa;
(Chiyoda-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kishiyama; Yoshihisa |
Chiyoda-ku |
|
JP |
|
|
Assignee: |
NTT DOCOMO, INC.
Chiyoda-ku
JP
|
Family ID: |
47217159 |
Appl. No.: |
14/009534 |
Filed: |
May 17, 2012 |
PCT Filed: |
May 17, 2012 |
PCT NO: |
PCT/JP12/62647 |
371 Date: |
October 3, 2013 |
Current U.S.
Class: |
370/330 ;
370/329 |
Current CPC
Class: |
H04L 5/0014 20130101;
H04B 17/336 20150115; H04B 1/123 20130101; H04J 11/004 20130101;
H04W 52/143 20130101 |
Class at
Publication: |
370/330 ;
370/329 |
International
Class: |
H04L 5/00 20060101
H04L005/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 20, 2011 |
JP |
2011-114032 |
Oct 14, 2011 |
JP |
2011-227149 |
Claims
1. A receiver comprising: a radio signal reception unit configured
to receive radio signals including a plurality of non-orthogonal
signals which are not orthogonal to each other; an interference
cancelation unit configured to extract the non-orthogonal signal
addressed to the receiver from the plurality of non-orthogonal
signals received by the radio signal reception unit, by
demodulating and cancelling the radio signal addressed to another
receiver; and a control signal reception unit configured to receive
a control signal to be used by the interference cancelation unit to
demodulate and cancel the radio signal; and a demodulation unit
configured to demodulate the signal extracted by the interference
cancelation unit and addressed to the receiver, wherein the control
signal includes control information containing a radio resource
block allocated to the non-orthogonal signal addressed to the other
receiver, and the interference cancelation unit demodulates and
cancels the radio signal addressed to the other receiver on the
basis of the control information.
2. The receiver according to claim 1, wherein the control signal
reception unit receives a control signal including control
information for a receiver at least at a higher or lower level than
the receiver in a non-orthogonal multiplex domain, and the
interference cancelation unit demodulates and cancels the radio
signal addressed to the other receiver on the basis of the control
signal received by the control signal reception unit.
3. A transmitter comprising: a radio signal transmission unit
configured to transmit radio signals to a plurality of receivers
located within a cell, the radio signals including a plurality of
non-orthogonal signals which are not orthogonal to each other; and
a control signal transmission unit configured to transmit a control
signal to the plurality of receivers, the control signal being to
be used by any of the receivers to demodulate and cancel the radio
signal addressed to another one of the receivers from the plurality
of received non-orthogonal signals, wherein the control signal
includes control information containing a radio resource block
allocated to the non-orthogonal signal addressed to the other
receiver.
4. The transmitter according to claim 3, wherein a radio resource
block allocated to the non-orthogonal signals is defined in a
frequency domain, a time domain and a non-orthogonal multiplex
domain, the non-orthogonal multiplex domain has a plurality of
levels corresponding to the number of interference cancellations in
the receivers, and the control signal transmission unit transmits a
control signal including the levels of the radio resource block
allocated to the non-orthogonal signals addressed to the plurality
of receivers.
5. The transmitter according to claim 4, wherein the control signal
transmission unit transmits a control signal in which the control
information for the plurality of receivers is collectively
coded.
6. The transmitter according to claim 4, wherein the control signal
transmission unit transmits a control signal including the control
information for a receiver at a certain level in the non-orthogonal
multiplex domain and the control information for a receiver at a
lower level than the certain level in the non-orthogonal multiplex
domain.
7. The transmitter according to claim 4, wherein the control signal
transmission unit transmits, in the control information for a
receiver at a certain level in the non-orthogonal multiplex domain,
a control signal necessary to demodulate the control information
for another receiver at the next lower level than the certain
level.
8. The transmitter according to claim 4, wherein the control signal
transmission unit transmits a control signal with which the
plurality of receivers are enabled to demodulate the control
information for a receiver at a low level in the non-orthogonal
multiplex domain.
9. The transmitter according to claim 4, wherein the control signal
transmission unit changes the number of blind decodes to be used
for blind demodulation of the control signal, depending on the
level in the non-orthogonal multiplex domain.
10. A radio communication method comprising the steps of:
receiving, by a communication device, radio signals including a
plurality of non-orthogonal signals which are not orthogonal to
each other; receiving, by the communication device, a control
signal to be used to demodulate and cancel the radio signal
addressed to another receiver from the plurality of received
non-orthogonal signals; demodulating and cancelling the radio
signal addressed to the other receiver by the communication device;
and demodulating, by the communication device, the signal extracted
by the cancelling step and addressed to the communication device,
wherein the control signal includes control information containing
a radio resource block allocated to the non-orthogonal signal
addressed to the other receiver, and in the step of cancelling the
non-orthogonal signal, the radio signal addressed to the other
receiver is demodulated and cancelled on the basis of the control
information.
Description
TECHNICAL FIELD
[0001] The present invention relates to a receiver, a transmitter
and a radio communication method which are adapted to
non-orthogonal multiple access.
BACKGROUND ART
[0002] Mobile communication systems, for example, Long Term
Evolution (LTE) standardized by the 3GPP, widely use orthogonal
multiple access in which multiple orthogonal signals not
interfering with each other are used between a base station and
user terminals (mobile stations). On the other hand, there has been
proposed non-orthogonal multiple access using non-orthogonal
signals to increase the capacity of a mobile communication system
(for example, see Non-patent document 1).
[0003] The non-orthogonal multiple access is based on the premise
of signal separation (interference canceller) through non-linear
signal processing. For example, in the case of downlink, a base
station concurrently transmits non-orthogonal signals to multiple
user terminals. Each of the user terminals performs signal
processing to remove, from the received non-orthogonal signals, a
signal addressed to a user terminal (at a cell edge) having a
larger path loss than the user terminal itself, and then
demodulates the resultant signal.
PRIOR ART DOCUMENT
[0004] Non-Patent Document [0005] Non-patent document 1: D. Tse and
P. Viswanath, "Fundamentals of Wireless Communication", Cambridge
University Press, 2005, <http://www.eecs.berkeley.edu/ to
dtse/book.html>on the Internet.
SUMMARY OF THE INVENTION
[0006] As described above, in the case of non-orthogonal multiple
access, each user terminal, i.e., each mobile station needs to
perform demodulation after signal processing of removing the signal
addressed to a mobile station having a larger path loss than the
mobile station itself. For this reason, the processing load in the
mobile station is so high that problems of cost increase and
processing delay of the mobile station may occur. A possible
solution to these problems is to introduce hybrid
orthogonal/non-orthogonal multiple access in which orthogonal
multiple access and non-orthogonal multiple access are used in
combination. With this introduction, the problems of cost increase
and processing delay of the mobile station can be expected to
reduce to some degree.
[0007] In the implementation point of view, however, it is
preferable that each mobile station be able to recognize the
conditions of mobile stations multiplexed in non-orthogonal
multiple access in order to achieve further cost and processing
delay reductions.
[0008] Therefore, the present invention has been made in
consideration of the above circumstances, and has an objective to
provide a receiver, a transmitter, and a radio communication method
capable of using non-orthogonal multiple access while suppressing
cost increase and processing delay.
[0009] In summary, a first feature of the present invention is a
receiver (for example, a mobile station 200A) including: a radio
signal reception unit (physical channel segmentation unit 210)
configured to receive radio signals including multiple
non-orthogonal signals which are not orthogonal to each other; an
interference cancelation unit (data demodulating/decoding units
220) configured to extract the non-orthogonal signal addressed to
the receiver from the multiple non-orthogonal signals received by
the radio signal reception unit, by demodulating and cancelling the
radio signal addressed to another receiver; a control signal
reception unit (a target user control signal detector 230 and an
interfering user control signal detector 240) configured to receive
a control signal to be used by the interference cancelation unit to
demodulate and cancel the radio signal; and a demodulation unit
(the data demodulating/decoding units 220) configured to demodulate
the signal extracted by the interference cancelation unit and
addressed to the receiver. The control signal includes control
information containing a radio resource block allocated to the
non-orthogonal signal addressed to the other receiver. The
interference cancelation unit demodulates and cancels the radio
signal addressed to the other receiver on the basis of the control
information.
[0010] In summary, a second feature of the present invention is a
transmitter (base station 100) including: a radio signal
transmission unit (a hybrid orthogonal/non-orthogonal multiplexer
130 and a physical channel multiplexer 160) configured to transmit
radio signals to multiple receivers located within a cell, the
radio signals including multiple non-orthogonal signals which are
not orthogonal to each other; and a control signal transmission
unit (a control signal generator 140, a control signal resource
allocator 150 and a physical channel multiplexer 160) configured to
transmit a control signal to the multiple receivers, the control
signal being to be used by any of the receivers to demodulate and
cancel the radio signal addressed to another one of the receivers
from the multiple received non-orthogonal signals. The control
signal includes control information containing a radio resource
block allocated to the non-orthogonal signal addressed to the other
receiver.
[0011] In summary, a third feature of the present invention is a
radio communication method including the steps of: receiving, by a
communication device, radio signals including multiple
non-orthogonal signals which are not orthogonal to each other;
receiving, by the communication device, a control signal to be used
to demodulate and cancel the radio signal addressed to another
receiver from the received multiple non-orthogonal signals;
demodulating and cancelling the radio signal addressed to the other
receiver by the communication device; and demodulating, by the
communication device, the signal extracted by the cancelling step
and addressed to the communication device. The control signal
includes control information containing a radio resource block
allocated to the non-orthogonal signal addressed to the other
receiver. In the step of cancelling the non-orthogonal signal, the
radio signal addressed to the other receiver is demodulated and
cancelled on the basis of the control information.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a diagram of an overall schematic configuration of
a mobile communication system 1 according to an embodiment.
[0013] FIG. 2 is a diagram illustrating radio resource allocation
images in orthogonal multiple access, non-orthogonal multiple
access, and hybrid orthogonal/non-orthogonal multiple access.
[0014] FIG. 3 is a diagram of a functional block configuration of a
transmission unit of a base station 100 according to the embodiment
of the present invention.
[0015] FIG. 4 is a diagram of a functional block configuration of a
reception unit of a mobile station 200A according to the embodiment
of the present invention.
[0016] FIG. 5 is a diagram illustrating an example of scheduling of
non-orthogonal signals for mobile stations in the base station 100
according to the embodiment of the present invention.
[0017] FIG. 6 is a diagram illustrating a radio resource block
allocation example according to the embodiment of the present
invention.
[0018] FIG. 7 is a diagram illustrating a configuration example 1
of a control signal according to the embodiment of the present
invention.
[0019] FIG. 8 is a diagram illustrating a configuration example 2
of a control signal according to the embodiment of the present
invention.
[0020] FIG. 9 is a diagram illustrating a configuration example 3
of a control signal according to the embodiment of the present
invention.
[0021] FIG. 10 is a diagram illustrating a configuration example 4
of a control signal according to the embodiment of the present
invention.
MODES FOR CARRYING OUT THE INVENTION
[0022] Hereinafter, embodiments of the present invention will be
described. Note that, in the following description of the drawings,
same or similar reference numerals denote same or similar elements
and portions. In addition, it should be noted that the drawings are
schematic and ratios of dimensions and the like in the drawings are
different from actual ones.
[0023] Therefore, specific dimensions and the like should be
determined in consideration of the following description. Moreover,
as a matter of course, the drawings include portions having
different dimensional relationships and ratios from each other.
[0024] FIG. 1 is a diagram of an overall schematic configuration of
a mobile communication system 1 according to this embodiment. As
illustrated in FIG. 1, the mobile communication system 1 includes a
base station 100 and mobile stations 200A, 200B.
[0025] The base station 100 transmits radio signals to the mobile
stations 200A, 200B, more specifically to the inside of a cell C1.
In addition, the base station 100 receives radio signals from the
mobile stations 200A, 200B. In this embodiment, the base station
100 configures a transmitter and the mobile stations 200A, 200B
each configure a receiver.
[0026] The mobile station 200A is located within the cell C1 but is
located at a cell edge of the cell C1 where a path loss of a radio
signal from the base station 100 is large. The mobile station 200B
is located in the center within the cell C1. For this reason, the
path loss of a radio signal from the base station 100 in the mobile
station 200B is smaller than the path loss in the mobile station
200A.
[0027] In this embodiment, the base station 100 transmits radio
signals to the mobile stations 200A, 200B located in the cell C1,
the radio signals including multiple orthogonal signals that are
orthogonal to each other, and multiple non-orthogonal signals that
are not orthogonal to each other. In other words, the mobile
communication system 1 uses a combination of orthogonal multiple
access for implementing concurrent communications with multiple
mobile stations using orthogonal signals, and non-orthogonal
multiple access for implementing concurrent communications with the
multiple mobile stations using non-orthogonal signals (hereinafter
referred to as hybrid orthogonal/non-orthogonal multiple
access).
[0028] Parts (a) to (c) of FIG. 2 illustrate radio resource
allocation images in the orthogonal multiple access, the
non-orthogonal multiple access, and the hybrid
orthogonal/non-orthogonal multiple access. As illustrated in part
(a) of FIG. 2, in the orthogonal multiple access, radio resources
allocated to mobile stations (users) do not overlap each other in
the bandwidth in a frequency domain/time domain/space domain. For
this reason, in principle, the orthogonal multiple access does not
need to remove interferences from the radio resources allocated to
the other mobile stations. The orthogonal multiple access is also
used in Long Term Evolution (LTE) standardized by the 3GPP.
[0029] As illustrated in part (b) of FIG. 2, in the non-orthogonal
multiple access, radio resources allocated to mobile stations
(users) overlap each other in the bandwidth mentioned above. For
this reason, each mobile station needs to remove all the multiple
access interferences through signal processing. The specific signal
processing therefor can use the technique described in Non-patent
document 1 mentioned above.
[0030] As illustrated in part (c) of FIG. 2, in the hybrid
orthogonal/non-orthogonal multiple access, radio resources
allocated to mobile stations (users) partly overlap each other in
the bandwidth mentioned above. For this reason, each mobile station
only has to remove multiple access interferences of a prescribed
number or less according to the number of multiplexed radio
resources.
[0031] This embodiment reduces a signal processing load associated
with removal of multiple access interferences by introducing the
aforementioned hybrid orthogonal/non-orthogonal multiple access,
and specifies a radio interface enabling a mobile station to
recognize the number of multiple access interferences to be
removed.
(2) Functional Block Configuration
[0032] Next, a functional block configuration of the mobile
communication system 1 is described. FIG. 3 is a diagram of a
functional block configuration of a transmission unit of the base
station 100. FIG. 4 is a diagram of a functional block
configuration of a reception unit of the mobile station 200A.
(2.1) Base Station 100
[0033] As illustrated in FIG. 3, a transmission unit of the base
station 100 includes coding/data modulating units 110, a base
station scheduler 120, a hybrid orthogonal/non-orthogonal
multiplexer 130, a control signal generator 140, a control signal
resource allocator 150 and a physical channel multiplexer 160.
[0034] The coding/data modulating units 110 perform division of
transmission data, channel coding/data modulation, transmission
power setting, and resource block allocation for their respective
predetermined users (user k). In this embodiment, in particular,
the coding/data modulating units 110 allocate radio resource blocks
to orthogonal signals and non-orthogonal signals included in radio
signals to be transmitted to the mobile stations 200A, 200B.
[0035] The base station scheduler 120 controls the coding/data
modulating units 110, the hybrid orthogonal/non-orthogonal
multiplexer 130 and the control signal generator 140 on the basis
of information such as feedbacks of Circuit State Information (CSI)
from the mobile stations 200A, 200B, and the path loss between the
base station 100 and each of the mobile stations 200A, 200B.
[0036] In this embodiment in particular, the base station scheduler
120 schedules signals multiplexed as non-orthogonal signals for
multiple mobile stations (for example, the mobile stations 200A,
200B), on the basis of the path losses of the signals multiplexed
as non-orthogonal signals to the respective multiple mobile
stations, in such a way that the signals can have a large
difference in the path loss among them.
[0037] FIG. 5 illustrates an example of scheduling of
non-orthogonal signals for mobile stations in the base station 100.
The example illustrated in FIG. 5 uses non-orthogonal signals with
which at maximum four users (mobile stations) are multiplexed. As
illustrated in FIG. 5, in the case of non-orthogonal signals,
multiple signals are not orthogonal to each other, in other words,
the same radio resource block in the frequency domain or time
domain is allocated to the multiple signals.
[0038] In this embodiment, signals are multiplexed as
non-orthogonal signals sequentially from a signal addressed to a
mobile station having the smallest path loss to a signal addressed
to a mobile station having the largest path loss. A signal
addressed to a mobile station having a small path loss only needs
low transmission power to surely obtain a desired SNR, and
therefore accounts for a small share in a vertical axis
(transmission power) direction in FIG. 5. On the other hand, a
signal addressed to a mobile station having a large path loss needs
high transmission power to surely obtain a desired SNR, and
therefore accounts for a large share in the vertical axis
(transmission power) direction in FIG. 5.
[0039] In the case of using such non-orthogonal signals, for
example, the user (mobile station) having the second smallest path
loss needs to remove interferences from the signals allocated to
the two mobile stations having the larger path losses than the user
(see explanation in the drawing).
[0040] Note that, the example illustrated in FIG. 5 also uses
orthogonal signals to which different radio resource blocks in the
frequency domain and time domain are allocated, i.e., multiple
signals orthogonal to each other. Since the aforementioned
interference does not occur between the orthogonal signals, the
mobile stations do not have to remove the interference.
[0041] The hybrid orthogonal/non-orthogonal multiplexer 130
multiplexes the orthogonal signals and the non-orthogonal signals.
Specifically, the hybrid orthogonal/non-orthogonal multiplexer 130
multiplexes signals (radio resource blocks) outputted from the
multiple coding/data modulating units 110 under the control of the
base station scheduler 120. As a result, the multiplexed signals as
illustrated in FIG. 5 are generated.
[0042] The control signal generator 140 generates various kinds of
control signals to be broadcasted to the mobile stations 200A,
200B. In this embodiment, in particular, the maximum number of
signals multiplexed as non-orthogonal signals (for example, quad
multiplexing) is known to the base station 100 and the mobile
stations 200A, 200B. The control signal generator 140 generates a
control signal necessary for a mobile station to demodulate and
cancel radio signals addressed to other mobile stations (other
devices).
[0043] The control signal generator 140, for example, can generate
a signal including the following control information or reference
signal in order for the mobile station to demodulate and cancel
radio signals addressed to other mobile stations (other
devices):
(a) information indicating the number (including 0 or 1) of
multiple access interferences to be removed by a user (mobile
station); (b) information indicating the conditions (such as
allocated radio resource block, modulation scheme and channel
coding rate) of other users, which are needed by the user (mobile
station) to remove multiple access interferences; (c) a reference
signal necessary for coherent demodulation in the user (mobile
station); and (d) information (transport block, definition of a
radio resource block, transmission power control, feedback control
signal, and the like) necessary for allocation of radio resource
blocks in the hybrid orthogonal/non-orthogonal multiple access.
[0044] The control signal generator 140 may generate a control
signal including any one or any combination of the above (a) to
(d). The control signal generator 140 transmits the generated
control signal to the mobile stations 200A, 2003 via the control
signal resource allocator 150 and the physical channel multiplexer
160.
[0045] In this embodiment, the control signal generator 140, the
control signal resource allocator 150 and the physical channel
multiplexer 160 configure a control signal transmission unit to
send the mobile stations 200A, 200B a control signal to be used by
the mobiles stations 200A, 200B (multiple receivers) to cancel the
non-orthogonal signals addressed to the other receivers (for
example, the mobile station 200A).
[0046] The control signal resource allocator 150 allocates a radio
resource block to the control signal outputted from the control
signal generator 140.
[0047] The physical channel multiplexer 160 multiplexes baseband
signals outputted from the hybrid orthogonal/non-orthogonal
multiplexer 130 and the control signal outputted from the control
signal resource allocator 150 with each other in physical channels.
The signals outputted from the physical channel multiplexer 160 are
subjected to IFFT and Cyclic Prefix (CP) is added to the resultant
signals. Then, the signals are transmitted to the mobile stations
200A, 200B from a transmission antenna. In this embodiment, the
hybrid orthogonal/non-orthogonal multiplexer 130 and the physical
channel multiplexer 160 configure a radio signal transmission unit
to transmit orthogonal signals and non-orthogonal signals to
multiple mobile stations (receivers) located within the cell
C1.
(2.2) Mobile Station 200A
[0048] As illustrated in FIG. 4, the mobile station 200A includes a
physical channel segmentation unit 210, data demodulating/decoding
units 220, a target user control signal detector 230 and an
interfering user control signal detector 240. Note that the mobile
station 200B has the same functional block configuration as the
mobile station 200A.
[0049] The physical channel segmentation unit 210 receives radio
signals transmitted from the base station 100, and performs
segmentation of physical channels included in the radio signals. As
described above, the radio signals received by the physical channel
segmentation unit 210 are radio signals transmitted from the base
station 100 (one transmitter) and include orthogonal signals which
are orthogonal to each other and non-orthogonal signals which are
not orthogonal to each other. The segmented physical channels are
outputted to the data demodulating/decoding units 220, the target
user control signal detector 230 and the interfering user control
signal detector 240. In this embodiment, the physical channel
segmentation unit 210 configures a radio signal reception unit.
[0050] There are provided multiple data demodulating/decoding units
220. Specifically, the data demodulating/decoding units 220 are
provided for interfering users and a target user according to the
number of signals (users) multiplexed as non-orthogonal signals. In
this embodiment, since at maximum four users are multiplexed, it is
preferable to also provide four data demodulating/decoding units
220.
[0051] The data demodulating/decoding units 220 each execute radio
resource block extraction, interference canceller, channel
estimation, demodulation/decoding and decoded data combining.
[0052] In particular, in this embodiment, the interference
canceller of the data demodulating/decoding units 220 extracts the
non-orthogonal signal addressed to the mobile station 200A from the
multiple non-orthogonal signals by demodulating and cancelling the
radio signals addressed to the other mobile stations (receivers) by
use of the orthogonal signals (for example, the foregoing control
information and reference signal) included in the received radio
signals.
[0053] Specifically, the interference canceller demodulates and
cancels the radio signals addressed to the other mobile stations
(receivers) on the basis of the control signal received by the
physical channel segmentation unit 210 (control signal reception
unit). More specifically, the interference canceller cancels the
non-orthogonal signals addressed to the other mobile stations on
the basis of the control information included in the control signal
detected by the target user control signal detector 230 and the
interfering user control signal detectors 240.
[0054] In addition, since the maximum number of multiplexed
non-orthogonal signals is known (quad multiplexing in this
embodiment), the interference canceller demodulates and cancels the
radio signals addressed to the other receivers within the range not
exceeding the known maximum number of non-orthogonal signals. Note
that the interference cancelling method will be described
later.
[0055] In addition, the data demodulating/decoding unit 220
demodulates the signal included in the orthogonal signals and
addressed to the mobile station 200A and the signal extracted by
the interference canceller and addressed to the mobile station
200A.
[0056] The target user control signal detector 230 detects the
control signal addressed to the target user, i.e., the device
(mobile station 200A) itself. The target user control signal
detector 230 provides the detected control signal to the data
demodulating/decoding unit 220 (for the target user). Anyone or
combination of the above (a) to (d) is used as the control
signal.
[0057] The interfering user control signal detector 240 detects the
control signals addressed to the interfering users, i.e., the other
devices (for example, the mobile station 200B). As similar to the
target user control signal detector 230, the interfering user
control signal detector 240 provides the detected control signals
to the data demodulating/decoding units 220 (for the interfering
users). In this embodiment, the interfering user control signal
detector 240 configures a control signal reception unit to receive
the control signals to be used to cancel the non-orthogonal signals
by the interference canceller.
[0058] Here, the signal processing in the interference canceller in
the data demodulating/decoding units 220 is explained briefly.
First, when the mobile station 200A is located at the cell edge of
the cell C1 as illustrated in FIG. 1, the interference canceller
cannot remove the signal of the mobile station 200B located in the
center within the cell C1. For this reason, the data
demodulating/decoding units 220 perform the demodulation/decoding
directly. Specifically, the signal processing in the user 1 can be
explained based on the following computational expression:
##STR00001##
[0059] Here, the user 1 denotes the mobile station 200A located at
the cell edge of the cell C1, and the user 2 denotes the mobile
station 200B located in the center in the cell C1. P.sub.1 and
P.sub.2 are transmission powers of the user 1 and the user 2, and
h.sub.1 and h.sub.2 are channel gains of the user 1 and the user
2.
[0060] As described above, in the case where the mobile station
(user 1) is located at the cell edge, the received signals
(R.sub.1) include an interference from the mobile station (user 2)
located in the cell center, but the user 1 cannot remove the
interference from the user 2 because having a poorer SNR than the
user 2. Hence, the user 1 executes the demodulation/decoding
directly without removing the signal of the user 2.
[0061] On the other hand, the signal processing in the user 2 can
be explained based on the following computational expression:
##STR00002##
[0062] As described above, in the case where the mobile station
(user 2) is located at the cell center, the received signals
(R.sub.2) include an interference from the mobile station (user 1)
located at the cell edge. Since the user 2 has a better SNR than
the user 1, the user 2 removes the signal of the user 1 by decoding
it once, and then demodulates/decodes the signal of the user 2
after removing the signal of the user 1.
[0063] Note that this signal processing is the same as the method
described in above Non-patent document 1.
(3) Configuration Examples of Control Signals
[0064] Next, description is provided for configuration examples of
control signals. Specifically, configuration examples 1 to 4 of
control signals are described with reference to FIGS. 6 to 10.
(3.1) Configuration Example 1
[0065] To begin with, radio resource block allocation according to
this embodiment is described with reference to FIG. 6. FIG. 6
illustrates a radio resource block allocation example according to
this embodiment. In this embodiment, in addition to the
conventional frequency/time domain-based definitions of radio
resource blocks, a radio resource domain (level) for non-orthogonal
multiplexing is newly defined (hereinafter, referred to as a
non-orthogonal multiplex domain). In other words, a radio resource
blocks allocated to non-orthogonal signals is defined in the
frequency domain, the time domain and the non-orthogonal multiplex
domain.
[0066] The non-orthogonal multiplex domain has multiple levels
according to the number of interference cancellations in the mobile
station. Specifically, the levels are determined according to the
path losses between the base station 100 and the mobile stations
200A, 200B, and a radio resource block at a higher level is
allocated to the mobile station having a smaller path loss. In
other words, the coding/data modulating units 110 of the base
station 100 allocate, to non-orthogonal signals, a radio resource
block defined in the frequency domain, the time domain and the
non-orthogonal multiplex domain having the multiple levels
according to the number of interference cancellations in the mobile
stations 200A, 200b.
[0067] The mobile station 200A, 200B (user itself) removes signals
of mobile stations (interference removal target users) assigned to
lower levels than the mobile station itself in the non-orthogonal
multiplex domain, within the radio resource block in the
frequency/time domain to which the mobile station itself is
assigned (an arrow in the drawing indicates the radio resource
block allocated to non-orthogonal signals at low levels to be
removed by a mobile station at the highest level). In short, the
interference canceller of the mobile station 200A, 200B cancels the
non-orthogonal signals whose allocated radio resource block is at
lower levels than that of the mobile station itself.
[0068] Thus, with the definition of the non-orthogonal multiplex
domain, a mobile station (user) and a radio resource block targeted
for interference removal are automatically and uniquely determined
based on the radio resource block allocated thereto.
[0069] Moreover, each mobile station needs to recognize information
on radio resource block allocation, modulation scheme, coding rate
or the like of an interference removal target user. To this end,
this embodiment enables each mobile station to recognize these
kinds of information by using the control signal.
[0070] FIG. 7 is a diagram illustrating a configuration example 1
of a control signal. In the configuration example 1, the control
information on all the users is collectively coded. Specifically,
the control information on all the users is coded by Joint coding.
In the configuration example 1, the control signal generator 140 of
the base station 100 sends the mobile stations 200A, 200B a control
signal in which the control information on the multiple mobile
stations is collectively coded.
[0071] In addition, as illustrated in FIG. 7, the control signal
includes control information containing a radio resource block
allocated to a non-orthogonal signal addressed to another mobile
station (receiver), a modulation scheme, a transport block size
(coding rate), and a transmission power ratio. Note that the
transmission power ratio is a ratio between the transmission power
of the non-orthogonal signal to the mobile station itself and the
transmission power of the non-orthogonal signal to the other mobile
station. Moreover, the control information may contain other
control information and a mobile station identifier (UE ID). Then,
the modulation scheme, the transport block size (coding rate), and
the transmission power ratio are not necessarily essential, and the
control signal does not have to include these kinds of the control
information.
[0072] Further, as illustrated in FIG. 7, the control signal
generator 140 may send the control signal including the levels in
the non-orthogonal multiplex domain (non-orthogonal multiplex
levels) within the radio resource block allocated to non-orthogonal
signals addressed to multiple mobile stations. However, the
non-orthogonal multiplex levels may be omitted if the
non-orthogonal multiplex levels can be determined by blind
demodulation or the like.
[0073] The control signal generator 140 (control signal
transmission unit) may change the number of blind decodes according
to the level in the non-orthogonal multiplex domain. For instance,
the number of blind decodes may be increased as the level in the
non-orthogonal multiplex domain becomes higher.
[0074] The mobile station 200A, 200B acquires the control
information on another mobile station whose allocated radio
resource block is in the same frequency domain or time domain as,
but is at a lower level than that of the mobile station itself, and
cancels the non-orthogonal signal to which the radio resource block
at the lower level than that of the mobile station itself is
allocated, by using the acquired control information.
[0075] Such control information may be mapped in ascending order
(or descending order) of the level in the non-orthogonal multiplex
domain. Instead, information indicting the levels may be included
in the control information, and thereby the mobile station 200A,
200B may be directly notified of the levels.
(3.2) Configuration Example 2
[0076] Parts (a) and (b) of FIG. 8 are diagrams illustrating a
configuration example 2 of a control signal. In the configuration
example 2, the control information necessary to remove interference
of an interference removal target mobile station (user) is sent as
control information addressed to the user itself.
[0077] Part (a) of FIG. 8 illustrates a configuration example of a
control signal addressed to a user at a low level in the
non-orthogonal multiplex domain. Part (b) of FIG. 8 illustrates a
configuration example of a control signal addressed to a user at a
high level in the non-orthogonal multiplex domain.
[0078] As illustrated in part (b) of FIG. 8, the control signal
addressed to the user at the high level (certain level) is
multiplexed with the control information addressed to users at
lower levels in addition to the user at the high level. On the
other hand, as illustrated in part (a) of FIG. 8, the control
signal addressed to the user at the low level only includes control
information addressed to the user because there is no need to
remove an interference from another user.
[0079] In summary, in the configuration example 2, the control
signal generator 140 of the base station 100 transmits a control
signal including the control information on a mobile station at a
high level in the non-orthogonal multiplex domain and the control
information on a mobile station at a lower level than the high
level in the non-orthogonal multiplex domain.
(3.3) Configuration Example 3
[0080] FIG. 9 is a diagram illustrating a configuration example 3
of a control signal. In the configuration example 3, the control
signal addressed to the user itself includes information for
demodulating the control signal addressed to an interference
removal target user, specifically, a user lower by one level than
the user itself. To be specific, UE ID or information indicting the
position of a radio resource block (for example, Control Channel
Element (CCE) index, or the like) can be used.
[0081] In the case of the configuration example 3, the mobile
station 200A, 200B sequentially demodulates the control signals of
users at lower levels. For example, when the control information
for the mobile station 200B is at the level 2, the mobile station
200B sequentially demodulates the control signals for users (for
example, the mobile station 200A) at the level 1 and level 0.
[0082] In summary, in the configuration example 3, the control
signal generator 140 of the base station 100 transmits a control
signal in which the control information of a mobile station at a
high level in the non-orthogonal multiplex domain includes the
control information of another mobile station at the next lower
level than the high level.
(3.4) Configuration Example 4
[0083] Parts (a) and (b) of FIG. 10 are diagrams illustrating a
configuration example 4 of a control signal. The configuration
example 4 is configured such that the control information for a
user at a low level can be demodulated by all the users of
multiplexed non-orthogonal signals. The configuration example 4 is
effective in a case where the non-orthogonal multiplex domain only
has two levels.
[0084] Part (a) of FIG. 10 illustrates a configuration example of a
control signal addressed to a user at a high level (certain level)
in the non-orthogonal multiplex domain. Part (b) of FIG. 10
illustrates a configuration example of a control signal addressed
to a user at a low level in the non-orthogonal multiplex
domain.
[0085] Specifically, in the configuration example 4, the control
signal generator 140 of the base station 100 transmits a control
signal with which multiple mobile stations (all the mobile
stations) is enabled to demodulate the control information for a
mobile station at a low level in the non-orthogonal multiplex
domain. Here, the configuration that can be demodulated by all the
mobile stations (users) is, for example, to fix the radio resource
block (CCE index) where the control signal is multiplexed.
(4) Examples of Operations and Effects
[0086] In the mobile communication system 1 according to this
embodiment, the control signal used to cancel the non-orthogonal
signal in the mobile station 200A, 200B includes control
information containing the radio resource block allocated to a
non-orthogonal signal addressed to another mobile station, the
modulation scheme, the transport block size, and the transmission
power ratio. Hence, using the control information, the mobile
station 200A, 200B can reduce a processing load for removal of
multiple access interference due to use of the non-orthogonal
signals, and thereby cost increase and processing delay in the
mobile station or the like can be suppressed in the case where the
hybrid orthogonal/non-orthogonal multiple access is introduced.
(5) Other Embodiments
[0087] Although the content of the present invention is disclosed
through the embodiment of the present invention as described above,
it should not be understood that the description and drawings
constituting part of this disclosure limit the present invention.
From this disclosure, various alternative embodiments would be
obvious to those skilled in the art.
[0088] For example, in the foregoing embodiment of the present
invention, the examples of downlink from the base station 100 to
the mobile stations 200A, 200B are described. However, the present
invention can be applied to uplink. Moreover, the present invention
can be also applied to radio communications not only between the
base station and mobile stations, but also between base
stations.
[0089] Furthermore, the foregoing embodiments are described by
taking as the example the case where the hybrid
orthogonal/non-orthogonal multiple access is introduced. The
application range of the present invention, however, is not limited
to the hybrid orthogonal/non-orthogonal multiple access, but
obviously includes any mobile communication system using
non-orthogonal multiple access.
[0090] As described above, the present invention naturally includes
various embodiments which are not described herein. Accordingly,
the technical scope of the present invention should be determined
only by the matters defining the invention in the scope of claims
regarded as appropriate based on the foregoing description.
[0091] The entire contents of Japanese Patent Application No.
2011-114032 (filed on May 20, 2011) and Japanese Patent Application
No. 2011-227149 (filed on Oct. 14, 2011) are incorporated herein by
reference.
INDUSTRIAL APPLICABILITY
[0092] According to the features of the present invention, provided
are a receiver, a transmitter, and a radio communication method
capable of using non-orthogonal multiple access while suppressing
cost increase and processing delay.
EXPLANATION OF THE REFERENCE NUMERALS
[0093] 1 mobile communication system [0094] 100 base station [0095]
110 coding/data modulating unit [0096] 120 base station scheduler
[0097] 130 hybrid orthogonal/non-orthogonal multiplexer [0098] 140
control signal generator [0099] 150 control signal resource
allocator [0100] 160 physical channel multiplexer [0101] 200A, 200B
mobile station [0102] 210 physical channel segmentation unit [0103]
220 data demodulating/decoding unit [0104] 230 target user control
signal detector [0105] 240 interfering user control signal
detector
* * * * *
References