U.S. patent application number 11/389164 was filed with the patent office on 2007-05-24 for wireless communication system, weight control apparatus, and weight vector generation method.
Invention is credited to Hideo Kasami, Shuichi Obayashi.
Application Number | 20070117513 11/389164 |
Document ID | / |
Family ID | 18809317 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070117513 |
Kind Code |
A1 |
Kasami; Hideo ; et
al. |
May 24, 2007 |
Wireless communication system, weight control apparatus, and weight
vector generation method
Abstract
Signals received by a plurality of antenna elements are supplied
to a beam forming circuit via a distributor. The beam forming
circuit weights and combines the signals to output a reception
signal corresponding to a beam having a predetermined
directionality pattern. A weight used to control weighting and
combining is set by a weight controller. Upon receiving a
registration request from an unregistered terminal, the weight
controller calculates a weight vector used to form a beam having
null directionality toward that terminal, and maximum
directionality toward the range of an area other than an area where
the terminal is located of a plurality of areas obtained by
dividing the area covered by the antenna elements in accordance
with direction.
Inventors: |
Kasami; Hideo;
(Yokohama-shi, JP) ; Obayashi; Shuichi;
(Yokohama-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
18809317 |
Appl. No.: |
11/389164 |
Filed: |
March 27, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09984713 |
Oct 31, 2001 |
7042860 |
|
|
11389164 |
Mar 27, 2006 |
|
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Current U.S.
Class: |
455/63.4 ;
455/562.1 |
Current CPC
Class: |
H04W 16/24 20130101;
H04W 16/28 20130101 |
Class at
Publication: |
455/063.4 ;
455/562.1 |
International
Class: |
H04B 1/00 20060101
H04B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2000 |
JP |
2000-333202 |
Claims
1-9. (canceled)
10. A wireless communication system for making packet transmission
control based on carrier sense, comprising: a plurality of cells
each of which includes a plurality of wireless base stations which
use radio channels that do not interfere with each other, and at
least one wireless terminal for communicating with the wireless
base station, each wireless base station includes: a transmission
adaptive array for making transmission beam control; and a
reception adaptive array for making reception beam control, said
reception adaptive array reducing an interference wave from the
wireless base station in a neighboring cell that uses a radio
channel which becomes an interference source to not more than a
carrier sense level, and an arbitrary location in the cell being
covered by a transmission beam formed by said transmission adaptive
array and a reception beam formed by said reception adaptive array
of at least one wireless base station.
11. A system according to claim 10, wherein the neighboring cells
use different radio channels.
12. A system according to claim 10, wherein an arbitrary location
in the cell is covered by transmission beams formed by the
transmission adaptive arrays and reception beams formed by the
reception adaptive arrays of at least two wireless base
stations.
13. A method of controlling an adaptive array for a wireless base
station, wherein after a wireless terminal which communicates with
the wireless base station roams to another wireless base station,
and the wireless terminal which communicates with a wireless base
station in a neighboring cell that uses a radio channel which
becomes an interference source roams to another wireless base
station, a reception adaptive array of the wireless base station
makes beam control to suppress reception power after combining of
the reception adaptive array to less than a carrier sense level
while the wireless base station in the neighboring cell that uses
the radio channel which becomes the interference source sends a
packet.
14. A method according to claim 13, wherein suspension of packet
transmission by the wireless base station for a predetermined
period of time makes the radio terminal, which communicates with
the wireless base station, roam to another wireless base
station.
15. A method of controlling an adaptive array for a wireless base
station, wherein a reception adaptive array of a wireless base
station makes beam control to suppress reception power after
combining of the reception adaptive array to not more than a
carrier sense level while a wireless base station in a neighboring
cell that uses a radio channel which becomes an interference source
sends a multi-cast packet.
16. A method according to claim 15, wherein the wireless base
station in the neighboring cell that uses the radio channel which
becomes the interference source sends the multi-cast packet while
setting the reception adaptive array not to receive any packet.
17. An adaptive array connected to a wireless base station for
making packet transmission control based on carrier sense,
comprising: a plurality of antenna elements that receive signals; a
reception beam forming circuit to form a beam by weighting
reception signals received by said plurality of antennas; a
reception level suppression unit configured to suppress an output
level of said reception beam forming circuit to not more than a
predetermined value, and to provide the output thereof to the
wireless base station; a transmission level suppression unit
configured to suppress an output level from the wireless base
station to not more than a predetermined value; a transmission beam
forming circuit to form a beam by weighting the output from said
transmission level suppression unit; and an interference generation
unit configured to generate an interference for sending a packet
irrespective of the reception signals received by said plurality of
antenna elements.
18. An adaptive array according to claim 17, wherein said
interference generation unit comprises: a reception disconnector
configured to control said reception level suppression unit to
suppress the output level of said reception beam forming circuit to
not more than the predetermined value; and a multi-cast packet
transmission controller configured to issue a command to the
wireless base station to send a multi-cast packet.
19. An adaptive array connected to a wireless base station for
making packet transmission control based on carrier sense,
comprising: a plurality of antenna elements that receive signals; a
reception beam forming circuit to form a beam by weighting
reception signals received by said plurality of antennas; a
reception level suppression unit configured to suppress an output
level of said reception beam forming circuit to not more than a
predetermined value, and to provide the output thereof to the
wireless base station; a transmission level suppression unit
configured to suppress an output level from the wireless base
station to not more than a predetermined value; a transmission beam
forming circuit to form a beam by weighting the output from said
transmission level suppression unit; and an interference
suppression unit configured to calculate and set a weight to be set
in said reception beam forming circuit on the basis of the output
from said reception beam forming circuit while no packet is sent
from said plurality of antenna elements.
20. An adaptive array according to claim 19, wherein said
interference suppression unit comprises: a transmission
disconnector configured to control said transmission level
suppression unit to suppress the output level from the wireless
base station to not more than the predetermined value; and a weight
controller configured to calculate and set the weight to be set in
said reception beam forming circuit on the basis of the output form
said reception beam forming circuit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No.
2000-333202, filed Oct. 31, 2000, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a wireless communication
system for making space-division multiple access, a weight control
apparatus, and a weight vector generation method.
[0004] 2. Description of the Related Art
[0005] In an FWA (Fixed Wireless Access) system, a base station and
fixed terminal station make wireless, high-speed communications. In
a point-to-multipoint (P-MP) system, a base station communicates
with a plurality of terminal stations. In the P-MP system,
space-division multiplex access (SDMA) is known as means for
increasing the subscriber capacity. As shown in FIG. 16, an
adaptive array 1002 arranged in a base station 1001 forms
orthogonal beams that do not interfere with each other. These beams
allow simultaneous communications of a plurality of terminals
1003.
[0006] FIG. 17 shows an arrangement of the adaptive array 1002 when
the multiplexing degree=2. In beam forming circuits 1051 and 2051,
appropriate weight vectors are set in weighting devices 1501 to
1504 and 2501 to 2504. These weighting devices and combiners 1512
and 2512 weight and combine the outputs from antenna elements 1011
to 1014, thereby forming orthogonal beams having maximum
directionality toward one terminal, and null directionality toward
the other terminal.
[0007] The same applies to a case wherein the multiplexing degree
is more than 3. That is, orthogonal beams are formed to have
maximum directionality toward the objective terminal, and null
directionality toward a plurality of remaining terminals.
[0008] In the conventional system, weights for forming orthogonal
beams used to attain space-division multiplex access are
individually calculated and held in correspondence with all
combinations of terminals while considering the multiplexing degree
for a given number of base stations. For example, when the
multiplexing degree=2 and the total number of terminals=n, the
number of combinations of weights to be calculated and held as
combinations of terminals is n.times.(n-1). Therefore, the number
of combinations of weights to be held becomes huge with increasing
number of registered terminals which must undergo space-division
multiplex access.
[0009] A wireless communication system that makes packet
communications by CSMA/CA is known.
[0010] FIG. 22 shows the arrangement of an IEEE802.11 wireless LAN
system using CSMA/CA. A base station 900 senses carriers before
transmission of packets to a terminal 911. Upon receiving packets
containing channel reserve information from a terminal 913, the
base station 900 postpones packet transmission during that reserved
period. After that, the base station 900 waits for a random time
period (back-off process) calculated by a controller 901, and
transmits packets addressed to a target terminal 911. If the
received data is correct, the target terminal 911 transmits an
acknowledge response packet (ACK) to the base station after an
elapse of a predetermined period of time. If the base station 900
fails to receive ACK from the target terminal 911 after an elapse
of a predetermined period of time, it executes the back-off process
using the controller 901 and transmits data again.
[0011] On the other hand, an adaptive array can improve
communication quality by forming beams that reduce interference
from a neighboring cell, as shown in FIG. 23.
[0012] The adaptive array generally makes beam control on the basis
of a received signal. For example, a direction-constrained power
minimization method suppresses all received signals as interfering
signals while holding the gain in a specific direction. Therefore,
if a situation in which only an interference wave from a
neighboring cell arrives is formed, and the direction-constrained
power minimization method is used in this situation, beams that can
cover a specific area in the self cell and can remove the
interference wave can be formed.
[0013] However, in order to suppress all co-channel interference
waves from a neighboring cell, the number of antenna elements must
be increased, resulting in a large apparatus scale.
[0014] Since the IEEE802.11 wireless LAN system using CSMA/CA does
not make integrated control of packet transmission, as described
above, it is difficult to form a situation in which only terminals
or base stations to be suppressed transmit packets. As a result, a
terminal of the self cell transmits packets in place of the
terminal or base station to be suppressed, and unwanted beams that
suppress such packets are formed.
BRIEF SUMMARY OF THE INVENTION
[0015] The present invention has been made in consideration of the
above situation, and has as its object to provide a wireless
communication system, weight control apparatus, and weight vector
generation method, which can prevent the number of weights to be
held from increasing abruptly even when the number of terminals
increases, since orthogonal beams are not prepared in
correspondence with combinations of terminals upon space-division
multiplex access.
[0016] It is another object of the present invention to reduce the
apparatus scale by limiting the number of interference waves to be
suppressed in a wireless communication system that makes packet
communications using CSMA/CA, and to form a situation in which only
interference waves to be suppressed are present so as to form beams
which remove these interference waves.
[0017] According to one aspect of the present invention, there is
provided a wireless communication system which allows simultaneous
communications with a plurality of terminals by space-division
multiplex access, comprising: a plurality of antenna elements that
receive a signal transmitted from the terminals; a plurality of
beam forming units configured to output reception signals
corresponding to beams having predetermined directionality patterns
by weighting and combining reception signals received by the
plurality of antenna elements; and a controller configured to set
weight vectors used to control weighting and combining in the
plurality of beam forming units, wherein when the controller
receives a registration request from an unregistered terminal, the
controller calculates and stores at least one of the weight vectors
used to form a beam having null directionality toward the
unregistered terminal and maximum directionality toward a specific
area other than an area where the unregistered terminal is located
of areas obtained by dividing a cover area covered by the wireless
communication system.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0018] FIG. 1 is a view for explaining an FWA system according to
the first embodiment of the present invention;
[0019] FIG. 2 is a block diagram showing an example of the
arrangement of an adaptive array according to the first
embodiment;
[0020] FIG. 3 shows a cover area of a base station according to the
first embodiment, which is divided into a plurality of areas;
[0021] FIG. 4 is a block diagram showing an example of the
arrangement of a terminal classification unit of the adaptive array
according to the first embodiment;
[0022] FIG. 5 shows beams formed by initial weights according to
the first embodiment;
[0023] FIG. 6 is a flow chart showing an example of a registration
sequence of a terminal according to the first embodiment;
[0024] FIG. 7 shows beams formed by initial weights according to
the first embodiment;
[0025] FIG. 8 shows beams having null directionality toward
terminals according to the first embodiment;
[0026] FIG. 9 shows beams having null directionality toward
terminals according to the first embodiment;
[0027] FIG. 10 is a table showing an example of the storage
contents of a correspondence storage unit according to the first
embodiment;
[0028] FIG. 11 is a flow chart showing an example of a
space-division multiplex access sequence for two terminals
according to the first embodiment;
[0029] FIG. 12 shows beams upon space-division multiplex access for
two terminals according to the first embodiment;
[0030] FIG. 13 is a block diagram showing an example of an adaptive
array according to the second embodiment of the present
invention;
[0031] FIG. 14 is a flow chart showing an example of a registration
sequence of a terminal according to the second embodiment;
[0032] FIG. 15 is a table showing an example of the storage
contents of a correspondence storage unit according to the second
embodiment;
[0033] FIG. 16 is a view for explaining a conventional
point-to-multipoint system;
[0034] FIG. 17 is a block diagram showing an example of the
arrangement of a conventional adaptive array when the multiplexing
degree is 2;
[0035] FIG. 18 is a diagram for explaining a wireless communication
system according to the third embodiment of the present
invention;
[0036] FIG. 19 is a flow chart showing a control method of an
adaptive array for a wireless base station according to the third
embodiment;
[0037] FIG. 20 is a diagram for explaining the internal arrangement
of a controller of the adaptive array according to the third
embodiment of the present invention;
[0038] FIG. 21 is a diagram for explaining a wireless communication
system according to the fourth embodiment of the present
invention;
[0039] FIG. 22 is a diagram for explaining a conventional
IEEE802.11 wireless LAN system using CSMA/CA; and
[0040] FIG. 23 is a diagram for explaining conventional adaptive
array antennas.
DETAILED DESCRIPTION OF THE INVENTION
[0041] Embodiments of the present invention will be described
hereinafter with reference to the accompanying drawings.
First Embodiment
[0042] FIG. 1 shows an example of an FWA (Fixed Wireless Access)
system including a base station 1 to which the first embodiment of
the present invention is applied.
[0043] A base station 1 comprises an adaptive array (wireless
communication system) 2, and can make simultaneous communications
with a plurality of terminals 3 via a single channel by avoiding
interference between terminals using the adaptive array 2. Note
that FIG. 1 illustrates a 90.degree. sector, but the present
invention is not limited to this.
[0044] Note that this embodiment will exemplify space-division
multiplex access (SDMA) of two terminals using an adaptive array
consisting of four antenna elements.
[0045] FIG. 2 shows an example of the arrangement of the adaptive
array arranged in the base station according to this
embodiment.
[0046] As shown in FIG. 2, the adaptive array of this embodiment
comprises m (m is a plural number; m=4 in FIG. 2) antenna elements
11 to 14, m amplifiers (low noise amplifiers) 21 to 24, m frequency
converters 31 to 34, m distributors 41 to 44, n (n is a plural
number; n=2 in FIG. 2) beam forming circuits 51 and 52, n receivers
61 and 62, and a weight controller 7.
[0047] The beam forming circuit 51 includes m weighting devices
5111 to 5114, and a combiner 512. Likewise, the beam forming
circuit 52 includes m weighting devices 5211 to 5214 and a combiner
522.
[0048] Furthermore, the weight controller 7 includes a terminal
classification unit 71, terminal storage unit 72, weight
calculation unit 73, weight storage unit 74, and weight selection
unit 75.
[0049] Note that the base station may comprise a plurality of
adaptive arrays shown in FIG. 2. For example, when the adaptive
array shown in FIG. 2 covers a 90.degree. sector, the base station
can cover 360.degree. full directions if it comprises four adaptive
arrays.
[0050] In the adaptive array shown in FIG. 2, reception signals
received by the antenna elements 11 to 14 are respectively input to
the corresponding amplifiers 21 to 24. The amplifiers 21 to 24
respectively amplify the reception signals.
[0051] The reception signals amplified by the amplifiers 21 to 24
are respectively input to the corresponding frequency converters 31
to 34. The frequency converters 31 to 34 respectively convert the
frequency bands of the reception signals from radio frequency (RF)
to intermediate frequency (IF) or baseband (BB).
[0052] The reception signals frequency-converted by the frequency
converters 31 to 34 are respectively input to the corresponding
distributors 41 to 44. The distributors 41 to 44 distribute the
reception signals and output them to the beam forming circuits 51
and 52.
[0053] In this way, the beam forming circuit 51 receives the
reception signals received by the antenna elements 11 to 14 from
the distributors 41 to 44. The same applies to the beam forming
circuit 52.
[0054] The reception signals input to the beam forming circuit 51
are respectively weighted by the weighting devices 5111 to 5114,
and are then combined by the combiner 512. The combined signal is
sent to the receiver 61. The same applies to the beam forming
circuit 52.
[0055] The weights in the weighting devices 5111 to 5114 and 5211
to 5214 are appropriately set by the weight controller 7.
[0056] In the above description, the reception signals are analog
signals. Also, using A/D converters and the like, weighting can be
done in a digital signal domain.
[0057] The weight controller 7 will be described in detail
below.
[0058] Note that this embodiment will examine a case wherein the
cover area (by the adaptive array in FIG. 2) of the base station is
divided into a plurality of areas in accordance with direction
viewed from the base station, as shown in FIG. 3, and a given
terminal belongs to one of the plurality of areas. FIG. 3
exemplifies a case wherein when the cover area of the base station
is divided into seven areas A1 to A7, a terminal T1 belongs to the
area A2, and a terminal T2 belongs to the area A5. The area
configuration shown in FIG. 3 will be taken as an example in the
following description. Of course, the present invention may be
applied even when the cover area is divided into another number of
areas, or when the cover area is divided unequally.
[0059] The terminal classification unit 71 in the weight controller
7 estimates one of the plurality of areas obtained by dividing the
cover area of the base station, where the target terminal 3 is
located (one of the areas A1 to A7 in FIG. 3) on the basis of the
reception signal from the terminal 3.
[0060] After the area to which the terminal 3 belongs is estimated,
a correspondence between identification information for identifying
the terminal 3, and identification information for identifying the
area to which the terminal 3 belongs, and which is estimated by the
terminal classification unit 71 is stored as terminal-area
correspondence information in a correspondence storage unit 72 (see
FIG. 10; FIG. 10 shows an example of the contents after the
terminals T1 and T2 have been registered, as will be described
later).
[0061] The weight calculation unit 73 calculates a weight for
forming a beam having null directionality toward the terminal 3 and
maximum directionality toward the range of a specific area other
than the area to which the terminal 3 belongs, on the basis of the
contents of the terminal-area correspondence information stored in
the correspondence storage unit 72 using the reception signal from
the terminal 3 (null directionality points to that terminal, while
maximum directionality points to (one of directions) the range of
the corresponding area). This weight is calculated for a case
wherein each of all areas other than the area to which the terminal
3 belongs or each of areas that satisfy a predetermined condition
other than the area to which the terminal 3 belongs is assumed to
be the specific area. In the example of the arrangement shown in
FIG. 2, the weight is a four-dimensional vector.
[0062] The weights calculated by the weight calculation unit 73 are
stored in the weight storage unit 74 so that the corresponding
terminal (i.e., a terminal to which null directionality is pointed)
and the corresponding area (an area to which maximum directionality
is pointed) can be specified.
[0063] Upon making space-division multiplex access (SDMA) for two
terminals, when the weight used to form a beam having null
directionality toward the second terminal and maximum
directionality toward the range of the area to which the first
terminal belongs, and the weight used to form a beam having null
directionality toward the first terminal and maximum directionality
toward the range of the area to which the second terminal belongs,
are stored in the weight storage unit 74, the weight selection unit
75 sets these two weights respectively in the weighting devices
5111 to 5114 of the beam forming circuit 51 and the weighting
devices 5211 to 5214 of the beam forming circuit 52. In this
fashion, even when an identical channel is used, the beam forming
circuit 51 can supply the reception output from the first terminal
to the receiver 61, and the beam forming circuit 52 can supply the
reception output from the second terminal to the receiver 62 (of
course, correspondence between the terminals and the beam forming
circuits/receivers may be reversed). In the example of FIG. 3,
these two weights correspond to a weight used to form a beam having
null directionality toward the terminal T2 and maximum
directionality toward the range of the area A2 to which the
terminal T1 belongs, and a beam having null directionality toward
the terminal T2 and maximum directionality toward the range of the
area A5 to which the terminal T2 belongs.
[0064] The arrangement of the terminal classification unit 71 will
be described in more detail below.
[0065] FIG. 4 shows an example of the internal arrangement of the
terminal classification unit 71.
[0066] An initial weight storage device 711 stores a weight used to
form a beam having maximum directionality toward the corresponding
area (in a direction of, e.g., its central portion), as an initial
weight for each of the plurality of areas obtained by dividing the
cover area of the base station. For example, in case of FIG. 3,
seven different initial weights, i.e., an initial weight used to
form a beam having maximum directionality toward the area A1, . . .
, an initial weight used to form a beam having maximum
directionality toward the area A7, are stored. Note that the
initial weights do not particularly consider the directions of null
directionality.
[0067] B1, B2, B3, . . . , B7 respectively represent beams having
maximum directionality toward the areas A1, A2, A3, . . . , A7, and
W1, W2, W3, . . . , W7 represent weights used to form these beams
B1, B2, B3, . . . , B7.
[0068] FIG. 5 exemplifies the states of the beams B1, B2, B3, . . .
, B7 formed using the weights W1, W2, W3, . . . , W7.
[0069] A reception state observation device 712 observes a signal
from the terminal 3 when upon setting the initial weights stored in
the initial weight storage device 711 in the weighting devices 5111
to 5114 of the beam forming circuit 51, and determines an area to
which maximum directionality of a beam that can assure the best
reception state of the signal from the terminal 3 (i.e., an area
pointed by maximum directionality of a beam formed by the initial
weight used in that state) is pointed as an area to which the
terminal 3 belongs. The reception state observation device 712
outputs, as the observation result, identification information of
the terminal, and that of the area to which that terminal belongs,
to the correspondence storage unit 72.
[0070] Note that the "best reception state" evaluated by the
reception state observation device 712 is a reception state with
maximum reception power. Alternatively, for example, the best
reception state may be defined as a reception state with a maximum
signal to noise power ratio.
[0071] In the above description, the beam forming circuit 51 is
used in observation. Of course, the beam forming circuit 52 may be
used. Also, one of the beam forming circuits 51 and 52 may be
fixedly used, or may be selected by a predetermined method in each
observation. Furthermore, different initial weights may be set in
the two beam forming circuits to observe signals parallel to each
other. In this way, the time required for evaluation can be
shortened.
[0072] With the aforementioned arrangement, an area in which the
terminal is currently located can be estimated using only the
output from the beam forming circuit 51 or 52.
[0073] The weight calculation unit 73 will be explained below.
[0074] The weight calculation unit 73 makes predetermined
repetitive calculations based on the reception signal from the
terminal 3 using the initial weight (i.e., an initial weight used
to form a beam having maximum directionality toward a given area)
stored in the initial weight storage device 711 as an initial
value, thus calculating a weight used to form a beam (having
maximum directionality toward a given area and) having null
directionality toward the terminal 3 (i.e., the unit 73 repeats
calculations of a weight value to converge the direction of null
directionality to that of the terminal 3).
[0075] In a practical process for this purpose, a weight vector
used to form a beam having a directionality gain in a desired
direction is set as an initial value, and null directionality is
set in an incoming wave direction while this gain is maintained.
Required information is only output power of the beam forming
circuit.
[0076] The operation sequence for making space-division multiple
access (SDMA) for two terminals by the base station of this
embodiment will be explained below.
[0077] A case will be examined below wherein the two terminals
newly subscribe to a service in the order of terminal
T1.fwdarw.terminal T2. As shown in FIG. 3, the terminal T1 is
located within the area A2, and the terminal T2 is located within
the area A5.
[0078] A registration process when a new terminal subscribes will
be explained first, and a process upon making space-division
multiple access (SDMA) for two terminals will be explained.
[0079] FIG. 6 shows an example of the registration sequence of a
new terminal.
[0080] The registration sequence when the terminal T1 subscribes as
a new terminal will be explained.
[0081] The terminal T1 sends a registration request signal to the
base station (step S1).
[0082] The base station receives the signal from the terminal T1.
When the base station recognizes that the received signal is a
registration request, it assigns an empty channel to the terminal
T1, and instructs the terminal T1 to send a signal with
predetermined power in that assigned channel (step S2). The
predetermined power value must be appropriately set to eliminate
the influence of overreach interference from a neighboring
cell.
[0083] The terminal T1 sends a signal using the assigned channel
and instructed transmission power (step S3).
[0084] During this interval, in the base station, the reception
state observation device 712 checks the reception power from the
terminal T1 upon setting the initial weights W1, W2, W3, . . . , W7
stored in the initial weight storage device 711 in the weighting
devices 5111 to 5114 of the beam forming circuit 51, respectively,
and stores in the corresponding storage unit 72 the area A2 (FIG.
7) to which maximum directionality of the beam B2 corresponding to
the maximum reception power is pointed as an area to which the
terminal T1 belongs (step S4).
[0085] After that, the weight calculation unit 73 calculates a
weight used to form a beam having null directionality toward the
terminal T1. At this time, in this example, as for an area to which
maximum directionality is pointed, a condition that areas except
for the area A2 to which the terminal T1 belongs must be separated
a predetermined angle or more from the area to which the terminal
T1 belongs is imposed. Also, as another condition, such area is
separated one or more areas from the area to which the terminal T1
belongs. Under these conditions, areas to which maximum
directionality are pointed are four areas A4, A5, A6, and A7.
[0086] More specifically, as shown in FIG. 8, weights W_A4_T1 ,
W_A5_T1 , W_A6_T1 , and W_A7_T1 used to form beams B_A4_T1,
B_A5_T1, B_A6_T1, and B_A7_T1 having null directionality toward the
terminal T1 and maximum directionality toward the areas A4, A5, A6,
and A7, which are separated a predetermined angle or more from the
area A2 to which the terminal T1 belongs, of those except for the
area A2 are calculated (steps S5 and S6).
[0087] In this case, upon calculating the weight W_A4_T1, a weight
used to form a beam having null directionality toward the terminal
T1 is calculated by repetitive calculations based on the reception
signal from the terminal T1 using the initial weight W4 stored in
the initial weight storage device 711 as an initial value.
Likewise, the weights W_A5_T1, W_A6_T1, and W_A7_T1 are calculated
using the initial weights W5, W6, and W7 as initial values.
[0088] These weights W_A4_T1, W_A5_T1, W_A6_T1, and W_A7_T1
calculated by the weight calculation unit 73 are stored in the
weight storage unit 74 (steps S5 and S6).
[0089] When maximum directionality is separated a predetermined
angle or more from null, as described above, the gain difference
between maximum directionality and null can be set to be a
predetermined value or more.
[0090] With the aforementioned processes, since registration of the
terminal T1 is complete, the base station instructs the terminal T1
to end signal transmission (step S7).
[0091] Subsequently, assume that the terminal T2 newly subscribes
to this service.
[0092] In this case as well, the same sequence as in FIG. 6 is
executed. That is, the area A5 to which maximum directionality of
the beam B5 corresponding to the maximum reception power from the
terminal T2 is pointed is stored as an area to which that terminal
belongs in the correspondence storage unit 72. After that, as shown
in FIG. 9, weights W_A1_T2, W_A2_T2, W_A3_T2, and W_A7_T2 used to
form beams B_A1_T2, B_A2_T2, B_A3_T2, and B_A7_T2 having null
directionality toward the terminal T2 and maximum directionality
toward the areas A1, A2, A3, and A7, which are separated a
predetermined angle or more from the area A5 to which the terminal
T2 belongs, of those except for the area A5 are calculated. In this
case, the initial weights W1, W2, W3, and W7 are used as initial
values. The weights calculated by the weight calculation unit 73
are stored in the weight storage unit 74. With the aforementioned
process, since registration of the terminal T2 is complete, the
base station instructs the terminal T2 to end signal
transmission.
[0093] FIG. 10 shows an example of the storage contents of the
correspondence storage device 72 upon completion of registration of
the terminals T1 and T2.
[0094] In this embodiment, the registration sequence for other
terminals T3, T4, . . . when these terminals T3, T4, . . . newly
subscribe to the service after the terminals T1 and T2 is executed
in the same manner as described above.
[0095] A process upon making space-division multiplex access (SDMA)
for the two terminals T1 and T2 will be explained below.
[0096] FIG. 11 shows an example of the processing sequence in this
case.
[0097] The terminals T1 and T2 send communication request signals
to the base station (step S8).
[0098] The base station receives the signals from the terminals T1
and T2. When the base station recognizes that these signals are
communication requests, since the weight W_A5_T1 used to form the
beam B_A5_T1 having. null directionality toward the terminal T1 and
maximum directionality toward the area A5 to which the terminal T2
belongs, and the weight W_A2_T2 used to form the beam B_A2_T2
having null directionality toward the terminal T2 and maximum
directionality toward the area A5 to which the terminal T1 belongs
are stored in the weight storage device 74, the weight selection
unit 75 sets, e.g., the weight W_A5_T1 in the weighting devices
5111 to 5114 of the beam forming circuit 51, and the weight W_A2_T2
in the weighting devices 5211 to 5214 of the beam forming circuit
52 (step S9). Of course, the correspondence between the weights and
beam forming circuits may be different from (reversed to) that
described above.
[0099] FIG. 12 exemplifies the states of the beams at that
time.
[0100] After that, an identical channel is assigned to the
terminals T1 and T2 (step S10).
[0101] In this way, signals from the terminals T1 and T2 can be
respectively received by the receivers 62 and 61 without
interfering with each other (of course, when the correspondence
between the weights and beam forming circuits is reversed to that
described above, signals from the terminals T1 and T2 are
respectively received by the receivers 61 and 62).
[0102] When a communication is made with only one terminal (e.g.,
T1) after the weights that consider null directionality are
calculated, the communication may be made using the initial weight
(e.g., W2) used to form a beam having maximum directionality toward
the area A2 to which the terminal T1 belongs, or using one of
weights (e.g., W_A2_T2) used to form a beam having maximum
directionality toward the area A2 to which the terminal T1 belongs
and null directionality toward a terminal in another area.
Second Embodiment
[0103] Since this embodiment is basically the same as the first
embodiment, differences between this embodiment and the first
embodiment will be mainly explained below.
[0104] FIG. 13 shows an example of the arrangement of an adaptive
array arranged in a base station according to this embodiment.
[0105] As shown in the example of the arrangement of the adaptive
array in FIG. 13, this embodiment is different from the first
embodiment in that an initial value selection unit 76 is added to
the example of the arrangement of the adaptive array of the first
embodiment shown in FIG. 2.
[0106] This initial value selection unit 76 selects the weight
stored in the initial weight storage device 711 of the terminal
classification unit 71 or that (used to form a beam having null
directionality toward a given terminal and maximum directionality
toward the range of a given area) stored in the weight storage unit
74 on the basis of the registration record (terminal-area
correspondence information) stored in the correspondence storage
unit 72, and inputs the selected weight as an initial value to the
weight calculation unit 73.
[0107] When the weight storage unit 74 stores a plurality of
weights that can be selected, one of these weights can be selected
based on a predetermined criterion (e.g., random or appropriate
order, a weight generated first, a weight generated latest, or the
like).
[0108] A process executed when a terminal T3 which belongs to the
same area as the terminal T2 newly subscribes to a service after
registration of the terminals T1 and T2 will be explained
below.
[0109] The process at that time is basically the same as that in
the registration sequence of the terminals T1 and T2 mentioned
above, except that the initial value selection unit 76 selects an
initial value of a weight in weight calculations as needed.
[0110] FIG. 14 shows an example of the processing sequence in such
case (which has basically the same flow of sequence as in FIG.
6).
[0111] The terminal T3 sends a registration request signal to the
base station (step S11).
[0112] The base station receives the signal from the terminal T3.
When the base station recognizes that the received signal is a
registration request, it assigns an empty channel to the terminal
T3, and instructs the terminal T3 to send a signal with
predetermined power (step S12).
[0113] The terminal T3 sends a signal with the designated power in
the assigned channel (step S13).
[0114] The base station stores the area A5 to which maximum
directionality of the beam B5 corresponding to the maximum
reception power from the terminal T3 in the correspondence storage
unit 72 is pointed as an area to which that terminal belongs (step
S14).
[0115] FIG. 15 shows an example of the storage contents of the
correspondence storage unit 72 upon completion of registration of
the terminal T3.
[0116] After that, the initial value selection unit 76 selects an
initial value of a weight to be input to the weight calculation
unit 73. Initially, the initial value selection unit 76 looks up
the contents of the correspondence storage unit 72. When the unit
76 detects that the terminal T2 has already been registered in the
area A5 to which the terminal T3 belongs, it inputs weights
W_A1_T2, W_A2_T2, W_A3_T2, and W_A7_T2, which are stored in the
weight storage unit 74 and have null directionality toward the
terminal T2, to the weight calculation unit 73 as initial values of
weights. If a plurality of terminals have already been registered
in the area A5 to which the terminal T3 belongs, a weight
corresponding to a minimum reception signal from the terminal T3
may be used as an initial value.
[0117] If the terminal T3 belongs to an area different from those
of the already registered terminals T1 and T2, it is detected that
no terminal has been registered yet in the area to which the
terminal T3 belongs. In such case, the initial weights W1, W2, W3,
and W7 stored in the initial weight storage device 711 of the
terminal classification unit 71 are input to the weight calculation
unit 73 as initial values of weights (in this case, the same
calculations as in the first embodiment are consequently made).
[0118] After that, the weight calculation unit 73 calculates
weights W_A1_T3, W_A2_T3, W_A3_T3, and W_A7_T3 used to form beams
B_A1_T3, B_A2_T3, B_A3_T3, and B_A7_T3 having null directionality
toward the terminal T3 and maximum directionality toward the areas
A1, A2, A3, and A7, which are separated a predetermined angle or
more from the area A5 to which the terminal T3 belongs, of those
except for the area A5 (steps S15 and S16).
[0119] The weights calculated by the weight calculation unit 73 are
stored in the weight storage unit 74 (steps S15 and S16).
[0120] With the aforementioned processes, since registration of the
terminal T3 is complete, the base station instructs the terminal T3
to end signal transmission (step S17).
[0121] In this manner, when another terminal has already been
registered in an identical area, the weights calculated for that
already registered terminal can be used as initial values. In this
case, since beams having null directionality toward the vicinities
of the direction of the terminal T3, have already been formed while
the initial values of the weights are set, the number of repetitive
calculations required to calculate weights used to form beams
having null directionality toward the terminal T3 and maximum
directionality toward the areas A1, A2, A3, and A7, can be reduced.
Therefore, channels to be assigned to the terminal T3 for null
control can be reduced.
[0122] Note that the operation sequence upon making space-division
multiplex access (SDMA) for two terminals by the base station of
this embodiment is the same as that in the first embodiment.
[0123] For example, upon making space-division multiplex access
(SDMA) for the two terminals T1 and T3, the weight W_A5_T1 used to
form the beam B_A5_T1 having null directionality toward the
terminal T1 and maximum directionality toward the area A5 to which
the terminal T2 belongs, and the weight W_A2_T3 used to form the
beam B_A2_T3 having null directionality toward the terminal T3 and
maximum directionality toward the area A5 to which the terminal T1
belongs, are used.
[0124] In the examples described in the first and second
embodiments, the multiplexing degree is 2. Of course, the present
invention can be applied to a case wherein the multiplexing degree
is 3 or more. Even in such case, the number of weights to be held
can be smaller than that in the prior art.
[0125] For example, when the multiplexing degree is 3, assuming
that terminals T1 to T3 simultaneously make communications using a
single channel, and respectively belong to areas A1, A3, and
A5,
[0126] for the terminal T1, a weight W_A1_T2_T3 used to form a beam
having null directionality toward the terminals T2 and T3 and
maximum directionality toward the area A1 to which the terminal T1
belongs,
[0127] for the terminal T2, a weight W_A3_T1_T3 used to form a beam
having null directionality toward the terminals T1 and T3 and
maximum directionality toward the area A3 to which the terminal T2
belongs, and
[0128] for the terminal T3, a weight W_A5_T1_T2 used to form a beam
having null directionality toward the terminals T1 and T2 and
maximum directionality toward the area A5 to which the terminal T3
belongs,
[0129] can be respectively set in three beam forming circuits.
[0130] Even when the multiplexing degree are 3 or more, the same
effect can be obtained when the initial value selection unit 76 of
the second embodiment selects initial values for weight
calculations.
[0131] As described above, according to this embodiment, an area to
which a given terminal belongs of a plurality areas obtained by
dividing the cover area of the base station in accordance with
direction is estimated in place of preparing for orthogonal beams
in correspondence with combinations of terminals, and weights used
to form a beam having null directionality toward a terminal and
maximum directionality toward a given area are held, thus reducing
the number of weights to be held.
[0132] Also, according to this embodiment, weights used to form
beams having maximum directionality toward a plurality of areas
obtained by dividing the cover area of the base station are
pre-stored, and an area to which maximum directionality of a beam
which allows reception of a signal from a terminal with the highest
reception power or signal to noise ratio upon setting these weights
in the weighting devices is pointed is determined as an area to
which the terminal belongs. Hence, an area to which the terminal
belongs can be estimated using only the output from the beam
forming means.
[0133] Furthermore, according to this embodiment, upon calculating
weights used to form beams having null directionality toward a
terminal and maximum directionality toward a given area, since
weights used to form beams having maximum directionality toward the
given area are set as initial values, the number of required
repetitive calculations can be reduced.
[0134] Moreover, according to this embodiment, upon calculating
weights used to form beams having null directionality toward a
terminal and maximum directionality toward a given area, since
weights used to form beams having null directionality toward the
vicinities of the direction of the terminal are set as initial
values, the number of required repetitive calculations can be
reduced.
[0135] In addition, according to this embodiment, since weights
used to form beams having null directionality toward a terminal and
maximum directionality toward areas which are separated by the area
to which the terminal belongs of those except for the area to which
the terminal belongs are calculated, maximum directionality is
separated a predetermined angle or more from null, thus setting the
gain difference between maximum directionality and null to be a
predetermined value or more.
Third Embodiment
[0136] In the third embodiment, the present invention is applied to
an IEEE802.11 wireless LAN system using CSMA/CA. Since the
conventional IEEE802.11 wireless LAN system using CSMA/CA does not
make integrated control of packet transmission, as described above,
it is difficult to obtain a situation in which only a terminal to
be suppressed or base station transmits packets. As a result, a
terminal of the self cell transmits packets in place of the
terminal or base station to be suppressed, and unwanted beams that
suppress such packets are formed. This embodiment solves this
problem.
[0137] FIG. 18 shows an example of a wireless communication system
according to the third embodiment of the present invention.
[0138] Base stations (AP) 111 to 114, 211 to 214, and 311 to 314
respectively comprise transmission adaptive arrays (transmission
SA) 131 to 134, 231 to 234, and 331 to 334 and reception adaptive
arrays (reception SA) 141 to 144, 241 to 244, and 341 to 344, which
share array antennas 101 to 104, 201 to 204, and 301 to 304.
[0139] In FIG. 18, the transmission and reception adaptive arrays
share the array antennas. Alternatively, the transmission and
reception adaptive arrays may use independent array antennas.
[0140] An arbitrary location in a cell is covered by transmission
and reception beams formed by the adaptive arrays of at least one
AP. With this arrangement, terminals (STA) 121 to 124, 221 to 224,
and 321 to 324 located at arbitrary locations in cells can
communicate with corresponding APs.
[0141] This embodiment will exemplify a case wherein interference
waves from the APs 312 and 212, which become interference sources
for the AP 112 that uses Ch7, are reduced lower than the carrier
sense level by the reception SA 142.
[0142] The reason why objects to be suppressed are limited to APs,
and the suppression level is limited to the carrier sense level is
to reduce the required number of antenna elements, and to reduce
the apparatus scale. Although the objects to be suppressed are
limited, if the AP traffic is heavier than the STA, as packet
transmission delay of the AP due to carrier sense of packets sent
from a neighboring AP mainly deteriorates the throughput of the
entire system, the effect of improving the throughput according to
the present invention is great.
[0143] FIG. 19 shows a beam control method of the SA 142 in the
third embodiment of the present invention.
[0144] A transmission beam of the transmission SA 132, a reception
beam of the reception SA 142, a transmission beam of the
transmission SA 131, and a reception beam of the reception SA 141
are set to cover a single area.
[0145] Also, a transmission beam of the transmission SA 232, a
reception beam of the reception SA 242, a transmission beam of the
transmission SA 231, and a reception beam of the reception SA 241
are set to cover a single area.
[0146] Furthermore, a transmission beam of the transmission SA 332,
a reception beam of the reception SA 342, a transmission beam of
the transmission SA 331, and a reception beam of the reception SA
341 are set to cover a single area (step 101).
[0147] With this arrangement, roaming of the STAs 122, 222, and 322
to the APs 111, 211, and 311 can be made.
[0148] Subsequently, packet transmission from the transmission SAs
132, 232, and 332 is suspended for time T (step 102). In this way,
since the STAs 122, 222, and 322 cannot communicate with the APs
112, 212, and 312, they roam to the APs 112, 212, and 312 after a
predetermined period of time.
[0149] It is checked if the STAs 122, 222, and 322 respectively
roam to the APs 112, 212, and 312 (step 103). This operation can be
made if the MAC layer can be monitored.
[0150] After confirmation of roaming to the STAs 122, 222, and 322,
packet transmission from the transmission SA 132 is suspended (step
104). In this manner, since the AP 112 whose beam control is
underway sends no beacon, roaming from the STAs to the AP 112 can
be prevented.
[0151] The reception SAs 242 and 342 are set not to receive any
packets (step 105). More specifically, the reception SAs 242 and
342 may be disconnected from the APs 212 and 312 by switches.
Alternatively, the reception gains of the reception SAs 242 and 342
may be lowered. In this way, since the back-off process of the APs
212 and 312 due to carrier sense can be avoided, a problem of
packet transmission delay can be solved.
[0152] The transmission SAs 232 and 332 send multi-cast packets
(step 106). In this manner, since the multi-cast packets do not
require any ACK reception from the STAs, and the back-off process
due to ACK non-reception can be avoided, a problem of packet
transmission delay can be solved. Especially, this embodiment is
effective when the reception SAs 242 and 342 are set not to receive
any packets.
[0153] The gain of the reception beam of the reception SA 142 in
the main lobe direction is constrained (step 107).
[0154] Beam control is made based on the direction-constrained
power minimization method, so that the reception power after
combining of the reception SA 142 becomes equal to or lower than
the carrier sense level (step 108).
[0155] This embodiment uses the direction-constrained power
minimization method as a beam control algorithm. This algorithm
suppresses all received signals as interference while maintaining a
gain in a specific direction. Therefore, when a situation in which
only interference waves from only the APs 212 and 312 arrive is
formed, and the direction-constrained power minimization method is
used, a beam that covers a specific area in the self cell and
removes interference waves from the APs 212 and 312 can be
formed.
[0156] With this control method, the number of interference waves
as objects to be suppressed can be limited to reduce the apparatus
scale, a situation in which only interference waves as objects to
be suppressed are present can be set, and a beam that removes these
interference waves can be formed.
[0157] Since the object to be suppressed is limited to a
neighboring AP, this embodiment is particularly effective when the
AP traffic is heavier than the STA. Since the suppression level is
set to be less than the carrier sense-level, packet transmission
delay of the AP due to carrier sense of packets sent from a
neighboring AP can be avoided, thus improving the throughput of the
entire system.
[0158] In this embodiment, setups of the APs and transmission and
reception SAs may be locally directly controlled or may be
controlled by a controller that makes integrated control. Upon
making integrated control, either wired or wireless control may be
used.
[0159] In this embodiment, a pair of transmission and reception SAs
are provided to each AP. Alternatively, a plurality of APs may
share a pair of transmission and reception SAs.
[0160] The internal arrangement of a controller of the adaptive
array will be described below using FIG. 20.
[0161] Reception signals received by an array antenna 400 are
respectively weighted by a reception beam forming circuit 404 to
form a beam. The output from the reception beam forming circuit 404
is input to a reception switch 405. When the reception switch is
ON, the output from the reception beam forming circuit 404 is input
to an AP 401.
[0162] A packet sent from the AP 401 is input to a transmission
switch 402. When the transmission switch 402 is ON, a signal sent
from the AP 401 is input to a transmission beam forming circuit
403. After the input signal is weighted, that signal is transmitted
from the array antenna, thus forming a beam.
[0163] An interference generation unit 407 comprises a reception
disconnector 408 and multi-cast packet transmission controller 409.
The reception disconnector 408 sets the reception switch 405 OFF.
The multi-cast packet transmission controller 409 sends a command
to the AP 401 to send a multi-cast packet.
[0164] With this arrangement, when another AP controls weights to
have the AP 401 as an interference source, since the AP 401 does
not execute a back-off process due to carrier sense or ACK
non-reception, a problem of packet transmission delay can be
solved.
[0165] An interference suppression unit 410 comprises a
transmission disconnector 411 and weight controller 412. The
transmission disconnector 411 sets the transmission switch 402 OFF.
The weight controller 412 calculates and sets weights in the
reception beam forming circuit 404 on the basis of the output from
the reception beam forming circuit 404.
[0166] With this arrangement, when another AP controls weights to
have the AP 401 as an interference source, since no beacon is sent
to a terminal, the terminal can be prevented from subscribing the
AP 401 whose beam control is underway by roaming. Therefore, a
situation in which no interference from the terminal is present can
be formed. Also, the transmission signal itself from the AP 401 can
be prevented from being received by the array antenna 400 to
adversely influence the beam control.
[0167] In this embodiment, the AP 401 is directly controlled by
only the multi-cast packet transmission controller, but may be
controlled via the backbone 406. In such case, the AP 401 does not
require any additional functions to implement this embodiment, and
an existing AP can be used. Also, the interference generation unit
407 and interference suppression unit 410 can be controlled via the
backbone 406.
Fourth Embodiment
[0168] Since this embodiment is basically the same as the third
embodiment, only a difference between this embodiment and the third
embodiment will be mainly explained below.
[0169] FIG. 21 shows an example of a wireless communication system
according to the fourth embodiment of the present invention.
[0170] As shown in FIG. 21, this embodiment is different from the
third embodiment in that neighboring cells use different radio
channels, and an arbitrary location in a cell is covered by
transmission and reception beams formed by adaptive arrays of at
least three APs.
[0171] Since neighboring cells use different radio channels, the
interference level from the neighboring AP lowers, resulting in a
small interference suppression amount and a small apparatus
scale.
[0172] Since each cell is covered by three beams, the STA can roam
to two APs upon beam control.
[0173] A case will be exemplified below wherein interference waves
from APs 211, 212, 311, and 312, which become interference sources
for an AP 412 that uses Ch5, are reduced to less than the carrier
sense level. STAs 422, 221, 222, 321, and 322, which are associated
with APs 412, 211, 212, 311, and 312, can roam to APs 421 or 413,
214, 213, 314, and 313.
[0174] According to the third and fourth embodiments of the present
invention, since the object to be suppressed is limited to a
neighboring AP, and the suppression level is limited under the
carrier sense level, the number of antenna elements can be reduced,
and the apparatus scale can become small. Although the objects to
be suppressed are limited, if the AP traffic is heavier than the
STA, as packet transmission delay of the AP due to carrier sense of
packets sent from a neighboring AP mainly deteriorates the
throughput of the entire system, the effect of improving the
throughput according to the present invention is great.
[0175] Since an arbitrary location in a cell is covered by
transmission and reception beams of at least two APs, and the
direction-constrained power minimization method is executed after
roaming of the STA, a beam that suppresses a packet to be sent from
the STA can be prevented from being formed. Also, the STA can
communicate with another AP even during beam control.
[0176] Since an AP whose beam control is underway does not send any
beacon, roaming of the STA can be prevented.
[0177] Since the reception SA of an interfering AP is set not to
receive any packet, the interfering AP can be prevented from
executing a back-off process due to carrier sense, thus solving a
problem of packet transmission delay.
[0178] Since an interfering AP sends a multi-cast packet, which
does not require ACK reception from the STA, and a back-off process
due to ACK non-reception can be avoided, a problem of packet
transmission delay can be solved.
[0179] Since neighboring cells use different radio channels, the
interference level from a neighboring AP lowers, resulting in a
small interference suppression amount and a small apparatus
scale.
[0180] Since an arbitrary location in a cell is covered by three
beams, the STA can roam to two APs during beam control.
[0181] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *