U.S. patent application number 13/742513 was filed with the patent office on 2013-05-23 for control apparatus to divide other communication apparatuses into multiple groups for slots allocated.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. The applicant listed for this patent is Canon Kabushiki Kaisha. Invention is credited to Eiji Imaeda, Ichiro Kato.
Application Number | 20130128804 13/742513 |
Document ID | / |
Family ID | 39153746 |
Filed Date | 2013-05-23 |
United States Patent
Application |
20130128804 |
Kind Code |
A1 |
Imaeda; Eiji ; et
al. |
May 23, 2013 |
CONTROL APPARATUS TO DIVIDE OTHER COMMUNICATION APPARATUSES INTO
MULTIPLE GROUPS FOR SLOTS ALLOCATED
Abstract
A communication control apparatus that performs wireless
communication with a plurality of communication apparatuses, the
communication control apparatus comprises: a grouping unit adapted
to group the plurality of communication apparatuses based on the
relative positions of each of the plurality of communication
apparatuses; a notification unit adapted to notify each of the
plurality of communication apparatuses of the group to which that
communication apparatus belongs and of a communication slot
allocated to that group; and a transmission unit adapted to
transmit transmission data at a predetermined timing.
Inventors: |
Imaeda; Eiji; (Kawasaki-shi,
JP) ; Kato; Ichiro; (Kawasaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Canon Kabushiki Kaisha; |
Tokyo |
|
JP |
|
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
39153746 |
Appl. No.: |
13/742513 |
Filed: |
January 16, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11939069 |
Nov 13, 2007 |
|
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13742513 |
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Current U.S.
Class: |
370/315 |
Current CPC
Class: |
H04W 72/04 20130101;
H04W 68/00 20130101; H04W 72/048 20130101; H04L 43/0852 20130101;
H04L 41/0893 20130101; H04W 72/005 20130101; H04L 43/00 20130101;
H04L 41/12 20130101 |
Class at
Publication: |
370/315 |
International
Class: |
H04W 72/04 20060101
H04W072/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 17, 2006 |
JP |
2006-312132 |
Claims
1. A control apparatus that performs communication with a plurality
of communication apparatuses including a first communication
apparatus, a second communication apparatus, and a third
communication apparatus, the control apparatus comprising: an
allocation unit configured to allocate: a first communication slot
for the first, second, and third communication apparatuses to
receive first data directly transmitted from a data source, a
second communication slot for the second and third communication
apparatuses to receive second data transmitted from the first
communication apparatus, the second data being obtained by
performing a relay transmission of the first data in the first
communication apparatus, and a third communication slot for the
third communication apparatus to receive third data transmitted
from the second communication apparatus, the data being obtained by
performing maximum likelihood processing based on the first data
transmitted from the data source in the first communication slot,
the second data transmitted from the first communication apparatus
in the second communication slot, and the third data transmitted
from the second communication apparatus in the third communication
slot; and a notification unit configured to notify at least the
first, the second, and the third communication apparatuses of the
communication slots allocated by the allocation unit.
2. The control apparatus according to claim 1, further comprising:
a determination unit configured to determine a relative position of
each communication apparatus of the plurality of communication
apparatuses, wherein the allocation unit allocates communication
slots based on the relative position of each communication
apparatus of the plurality of communication apparatuses as
determined by the determination unit.
3. The control apparatus according to claim 1, wherein the
allocation unit allocates communication slots in order from a
communication apparatus positioned nearest to the control apparatus
to a communication apparatus positioned farthest from the control
apparatus.
4. The control apparatus according to claim 1, further comprising:
a dividing unit configured to divide the plurality of communication
apparatuses into a plurality of groups, wherein a quantity of
groups is configured to be represented by a number, wherein the
allocation unit allocates a communication slot during which
communication apparatus of a group transmits data to other
communication apparatus of another group, and wherein the
allocation unit does not allocate a communication slot to the group
positioned farthest from the control apparatus when the number of
groups is three or more.
5. The control apparatus according to claim 1, wherein data
includes data of each communication apparatus of the plurality of
communication apparatuses.
6. The control apparatus according to claim 1, further comprising:
a transmission unit configured to transmit data to the plurality of
communication apparatuses at a predetermined communication
slot.
7. The control apparatus according to claim 2, wherein the
determination unit determines the relative position of each
communication apparatus of the plurality of communication
apparatuses based on a strength of a transmitted signal, on a
transmission delay of an acoustic signal or an ultrasonic signal
from the communication apparatus, or on an imaging result by an
optical imaging unit.
8. A communication apparatus, comprising: a receiving unit
configured to receive data in the course of a first communication
slot, a second communication slot, and a third communication slot,
wherein, in the course of the first communication slot, the
receiving unit receives first data, which is directly transmitted
from a first other communication apparatus to the communication
apparatus, wherein, in the course of the second communication slot,
the receiving unit receives second data, which is obtained by
performing a relay transmission of the first data in a second other
communication apparatus, and wherein, in the course of the third
communication slot, the receiving unit receives third data from a
third other communication apparatus, the third data being obtained
by performing maximum likelihood processing based on the first data
transmitted in the first communication slot and the second data
transmitted in the second communication slot; and a first maximum
likelihood processing unit configured to perform maximum likelihood
processing based on the first data received in the course of the
first communication slot, the second data received in the course of
the second communication slot, and the third data received in the
course of the third communication slot.
9. The communication apparatus according to claim 8, wherein the
receiving unit performs communication using Time Division Multiple
Access, Code Division Multiple Access, Frequency Division Multiple
Access, and/or Space Division Multiple Access techniques.
10. The communication apparatus according to claim 8, further
comprising: a control unit configured, in response to a request
from a control apparatus in a communication system to which the
communication apparatus belongs, to generate information for
estimating a distance to another communication apparatus based on
communication with that another communication apparatus and to
control transmission of that information to the control
apparatus.
11. A communication system, comprising: a plurality of
communication apparatuses including a first communication
apparatus, a second communication apparatus, and a third
communication apparatus; a control apparatus including: an
allocation unit configured to allocate: a first communication slot
for the first, second, and third communication apparatuses to
receive first data directly transmitted from a data source, a
second communication slot for the second and third communication
apparatuses to receive second data transmitted from the first
communication apparatus, the second data being obtained by
performing a relay transmission of the first data in the first
communication apparatus, a third communication slot for the third
communication apparatus to receive third data transmitted from the
second communication apparatus, the data being obtained by
performing maximum likelihood processing based on the first data
transmitted from the data source in the first communication slot
and the second data transmitted from the first communication
apparatus in the second communication slot; and a notification unit
configured to notify at least the first, second, and third
communication apparatuses of the communication slots allocated by
the allocation unit, wherein each of the plurality of communication
apparatuses includes: a receiving unit configured to receive a
plurality of the data in the course of the first, second, and third
communication slots, and a maximum likelihood processing unit
configured to perform maximum likelihood processing based on the
first data received in the course of the first communication slot,
the second data received in the course of the second communication
slot, and the third data received in the course of the third
communication slot.
12. A control method for a control apparatus that performs
communication with a plurality of communication apparatuses
including a first communication apparatus, a second communication
apparatus, and a third communication apparatus, the control method
comprising: allocating: a first communication slot for the first,
second, and third communication apparatuses to receive first data
directly transmitted from a data source, a second communication
slot for the second and third communication apparatuses to receive
second data transmitted from the first communication apparatus, the
second data being obtained by performing a relay transmission of
the first data in the first communication apparatus, and a third
communication slot for the third communication apparatus to receive
third data transmitted from the second communication apparatus, the
data being obtained by performing maximum likelihood processing
based on the first data transmitted from the data source in the
first communication slot, the second data transmitted from the
first communication apparatus in the second communication slot, and
the third data transmitted from the second communication apparatus
in the third communication slot; and notifying at least the first,
second, and third communication apparatuses of the communication
slots.
13. A control method for a communication apparatus, the control
method comprising: receiving data in a course of a first
communication slot, a second communication slot, and a third
communication slot, wherein, in the course of the first
communication slot, first data is received, which is directly
transmitted from a first other communication apparatus to the
communication apparatus, wherein, in the course of the second
communication slot, second data is received, which is obtained by
performing a relay transmission of the first data in a second other
communication apparatus, and wherein, in the course of the third
communication slot, third data is received, which is obtained by
performing a maximum likelihood processing based on the first data
transmitted in the first communication slot and the second data
transmitted in the second communication slot; and performing
maximum likelihood processing based on the first data received in
the course of the first communication slot, the second data
received in the course of the second communication slot, and the
third data received in the course of the third communication
slot.
14. A non-transitory computer readable storage medium storing a
program that, when executed by a computer, causes the computer to
perform the control method according to claim 12.
15. The control apparatus according to claim 6, wherein the
transmission unit transmits the data using Time Division Multiple
Access, Code Division Multiple Access, Frequency Division Multiple
Access, and/or Space Division Multiple Access techniques.
16. The control apparatus according to claim 6, wherein the
notification unit uses a first modulation scheme and the
transmission unit use a second modulation scheme that is different
from the first modulation scheme.
17. The communication apparatus according to claim 8, further
comprising: an acquisition unit configured to acquire a
communication slot, which is allocated to that communication
apparatus, and during which that communication apparatus transmits
the data; and a transmission unit configured to transmit the data,
on which the maximum likelihood processing has been performed by
the maximum likelihood processing unit, to other communication
apparatuses, during the communication slot that is allocated to
that communication apparatus.
18. The communication apparatus according to claim 17, wherein the
acquisition unit further acquires a group to which that
communication apparatus belongs.
19. The control apparatus according to claim 1, wherein the data
source is the control apparatus.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a communication control
apparatus and a control method thereof, a communication apparatus
and a control method thereof, a wireless communication system, a
program, and a storage medium.
[0003] 2. Description of the Related Art
[0004] Technology that aims to configure plural connection links
through relay transmission and carry out wireless transmission with
a remote communication terminal is known (Japanese Patent Laid-Open
No. H8-97821; Japanese Patent Laid-Open No. 2001-189971).
Specifically, a wireless communication system is known in which
address information, relay information, and the like are added to
communication data and transmitted to multiple addresses, and relay
terminals relay the data in accordance with the address
information, relay information, and the like.
[0005] Furthermore, a wireless communication scheme that aims to
expand the communication range of a receiving terminal through
plural senders transmitting identical data is known (Japanese
Patent Laid-Open No. H11-122150). Specifically, a scheme is known
in which plural transmission signals, to which have been added
respectively differing amounts of delay, are transmitted from
plural transmission terminals; on the receiving side, the received
signal unaffected by interference is selected, equalization
processing is performed thereon, and the original data is thereby
estimated.
[0006] Furthermore, as technology for efficiently transmitting data
wirelessly to a remote communication terminal, a scheme is known in
which a relay terminal having a good condition of communication is
selected and data is distributed to peripheral communication
terminals by way of that relay terminal, thereby realizing
efficient data transfer (Japanese Patent Laid-Open No.
2003-332977).
[0007] However, in recent years, where data communication
functionality has become widespread, demand has increased for what
is known as "real-time" communications, in which video data, audio
data, and the like is transmitted from a data storage device
through a communication line and is received and reproduced by a
video display device, an audio reproduction device, or the
like.
[0008] Schemes such as the above-mentioned conventional schemes
respond to the occurrence of disconnections and interruptions in
the communication path caused by some kind of problem in the
communication path by performing retransmission, changing paths,
and so on. However, the retransmission processing, processing for
changing paths, and so on are performed asynchronously, and thus
transmission delay cannot be guaranteed. For this reason, when
stream data that is temporally continuous, such as video or audio,
is transmitted and continuously reproduced on the receiving side,
and disconnections or interruptions occur in the communication
path, there are situations where data underruns occur on the
receiving side. Therefore, there is a problem that the reproduced
video is unstable, the reproduced audio cuts out intermittently,
and so on.
[0009] In the abovementioned conventional schemes, by using plural
paths, reception can be carried out properly even if disconnections
or interruptions occur in a single path. However, these processes
assume predetermined plural transmission terminals and a single
receiving terminal, and does nothing more than implement the
connection of plural paths by eliminating signal interference from
the plural transmission terminals. For this reason, when performing
data transfers in unison to plural receiving terminals, such as
with multi-channel stream data, mutual interference arises when
data is transmitted to the respective receiving terminals over
plural paths.
SUMMARY OF THE INVENTION
[0010] Having been conceived in light of the aforementioned
problems, it is an object of the present invention to provide a
technique for reducing the occurrence of disconnections and
interruptions when transmitting data such as stream data that is
temporally continuous, such as video or audio. It is furthermore an
object of the present invention to provide a technique for avoiding
mutual interference even when simultaneously sending plural pieces
of data to plural receiving terminals.
[0011] According to one aspect of the present invention, a
communication control apparatus that performs wireless
communication with a plurality of communication apparatuses, the
communication control apparatus comprises:
[0012] a grouping unit adapted to group the plurality of
communication apparatuses based on the relative positions of each
of the plurality of communication apparatuses;
[0013] a notification unit adapted to notify each of the plurality
of communication apparatuses of the group to which that
communication apparatus belongs and of a communication slot
allocated to that group; and
[0014] a transmission unit adapted to transmit transmission data at
a predetermined timing.
[0015] According to another aspect of the present invention, a
communication apparatus that performs wireless communication in a
wireless communication system that includes a plurality of
communication apparatuses and a communication control apparatus,
the communication apparatus comprises:
[0016] a notification receiving unit adapted to receive, from the
communication control apparatus, a notification of the group to
which the communication apparatus belongs and a communication slot
allocated to that group;
[0017] a data receiving unit adapted to receive transmission data
from an external apparatus and store the received data in a storage
device;
[0018] a maximum likelihood processing unit adapted to perform
maximum likelihood processing on the transmission data stored in
the storage device; and
[0019] a transmission unit adapted to transmit the transmission
data on which the maximum likelihood processing has been performed
using the communication slot allocated to the group to which the
communication apparatus belongs.
[0020] According to still another aspect of the present invention,
a wireless communication system comprising a plurality of
communication apparatuses and a communication control
apparatus,
[0021] wherein the communication control apparatus includes:
[0022] a grouping unit adapted to group the plurality of
communication apparatuses based on the relative positions of each
of the plurality of communication apparatuses;
[0023] a notification unit adapted to notify each of the plurality
of communication apparatuses of the group to which that
communication apparatus belongs and of a communication slot
allocated to that group; and
[0024] a transmission unit adapted to transmit transmission data at
a predetermined timing, and
[0025] each of the communication apparatuses includes:
[0026] a notification receiving unit adapted to receive, from the
communication control apparatus, a notification of the group to
which the communication apparatus belongs and a communication slot
allocated to that group;
[0027] a data receiving unit adapted to receive the transmission
data from an external apparatus and store the received data in a
storage device;
[0028] a maximum likelihood processing unit adapted to perform
maximum likelihood processing on the transmission data stored in
the storage device; and
[0029] a transmission unit adapted to transmit the transmission
data on which the maximum likelihood processing has been performed
using the communication slot allocated to the group to which the
communication apparatus belongs.
[0030] According to yet another aspect of the present invention, a
control method for a communication control apparatus that performs
wireless communication with a plurality of communication
apparatuses, the method comprises:
[0031] grouping the plurality of communication apparatuses based on
the relative positions of each of the plurality of communication
apparatuses;
[0032] notifying each of the plurality of communication apparatuses
of the group to which that communication apparatus belongs and of a
communication slot allocated to that group; and
[0033] transmitting transmission data at a predetermined
timing.
[0034] According to still yet another aspect of the present
invention, a control method for a communication apparatus that
performs wireless communication in a wireless communication system
that includes a plurality of communication apparatuses and a
communication control apparatus, the method comprises:
[0035] receiving, from the communication control apparatus, a
notification of the group to which the communication apparatus
belongs and a communication slot allocated to that group;
[0036] receiving transmission data from an external apparatus and
storing the received data in a storage device;
[0037] performing maximum likelihood processing on the transmission
data stored in the storage device; and
[0038] transmitting the transmission data on which the maximum
likelihood processing has been performed using the communication
slot allocated to the group to which the communication apparatus
belongs.
[0039] Further features of the present invention will become
apparent from the following description of exemplary embodiments
(with reference to the attached drawings).
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 is a diagram illustrating an example of a
configuration of a network that includes a wireless communication
apparatus.
[0041] FIG. 2 is a block diagram illustrating an internal
configuration of a control terminal.
[0042] FIG. 3 is a block diagram illustrating an internal
configuration of a node.
[0043] FIG. 4 is a diagram schematically illustrating the
difference in the signal transmission range between the DSSS and
OFDM techniques.
[0044] FIG. 5 is a diagram illustrating a detailed configuration of
a wireless transmission unit and a wireless receiving unit of a
control terminal.
[0045] FIG. 6 is a diagram illustrating a detailed configuration of
a wireless transmission unit and a wireless receiving unit of a
node.
[0046] FIG. 7 is a flowchart illustrating an operational procedure
performed by a control terminal.
[0047] FIGS. 8A and 8B are time slot diagrams illustrating
operations of a control terminal.
[0048] FIG. 9 is a flowchart illustrating a processing procedure
performed by each node.
[0049] FIGS. 10A, 10B, 10C, and 10D are diagrams conceptually
illustrating the change over time of the transmission of stream
data by the control terminal and nodes.
[0050] FIG. 11 is a diagram illustrating transmission of stream
data by the control terminal and nodes on the time axis.
[0051] FIG. 12 is a diagram illustrating procedures for node
topology determination processing performed by a control terminal
and by nodes.
[0052] FIG. 13 is a diagram schematically illustrating a
relationship between the strength of a received training signal and
the distance between nodes.
[0053] FIG. 14 is a diagram schematically illustrating the
estimation of a positional relationship through the triangulation
method.
[0054] FIG. 15 is a diagram schematically illustrating a
configuration of a network when there is a single group.
[0055] FIG. 16 is a diagram schematically illustrating a
configuration of a network when there are two groups.
[0056] FIG. 17 is a flowchart illustrating a procedure for
processing performed by the control terminal to determine groups
and time slots.
[0057] FIG. 18 is a diagram illustrating transmission of stream
data by the control terminal and nodes on the time axis in the case
where control information has been added to a beacon signal.
DESCRIPTION OF THE EMBODIMENTS
[0058] Hereinafter, embodiments of the present invention shall be
described in detail with reference to the appended drawings. Note
that the constituent elements denoted in the following embodiments
are only examples, and the scope of the present invention is not
intended to be limited thereto.
Embodiment 1
Network Configuration
[0059] FIG. 1 is a diagram illustrating an example of a
configuration of a network that includes a wireless communication
apparatus according to the present embodiment. In FIG. 1, 101-109
are nodes (communication apparatuses) a through i, which are the
wireless communication apparatuses according to the present
embodiment; 110 is a control terminal (communication control
apparatus), which is a wireless communication apparatus; and 111 is
a data source that outputs AV (audio-visual) data. 112 is a group
1, made up of nodes a to c; 113 is a group 2, made up of nodes d to
f; and 114 is a group 3, made up of nodes g to i.
[0060] The data source 111 is an apparatus that outputs AV data to
be processed in real time. The data source 111 continuously outputs
AV data, such as multi-screen video data, multi-channel audio data,
and so on.
[0061] The control terminal 110 mutually exchanges control signals,
control data, and the like wirelessly with the nodes a 101 to i
109. Furthermore, the control terminal 110 converts AV data from
the data source 111 into stream data and wirelessly transmits the
result.
[0062] The nodes a 101 to i 109 mutually communicate control
signals, control data, and the like with the control terminal 110
wirelessly. Furthermore, the nodes a 101 to i 109 wirelessly
receive stream data from the control terminal 110 and from plural
other nodes, and wirelessly transmit the received stream data.
[0063] Group 1 (112) to group 3 (114) are groups configured of
plural nodes. Group allocation is determined by the control
terminal 110, and each node is notified thereof by the control
data. As shall be explained later, nodes within the same group each
transmit stream data wirelessly at the same timing.
[0064] (Control Terminal)
[0065] FIG. 2 is a block diagram illustrating an internal
configuration of the control terminal 110. In FIG. 2, 201 is a
wireless transmission unit, 202 is a wireless receiving unit, 203
is a control unit that controls the overall operations of the
control terminal 110, 204 is an encoding unit, 205 is a memory, 206
is a cycle timer, and 207 is an antenna.
[0066] The control unit 203 sends control data to the wireless
transmission unit 201 via the memory 205, and controls the wireless
transmission unit 201 to modulate the control data into a wireless
signal and wirelessly transmit the resultant from the antenna 207.
Additionally, AV data from the data source 111 is converted into
stream data by the encoding unit 204 and is temporarily stored in
the memory 205. Then, in accordance with instructions from the
control unit 203, and in synchronization with the cycle timer 206,
the control terminal 110 converts the stream data into frames, the
units of transmission data, and the resultants are sent from the
memory 205 to the wireless transmission unit 201. After this, in
accordance with instructions from the control unit 203, and in
synchronization with the cycle timer 206, the wireless transmission
unit 201 modulates the data from the memory 205 into a wireless
signal, and wirelessly transmits the resultant from the antenna
207.
[0067] In accordance with instructions from the control unit 203,
the wireless receiving unit 202 receives the wireless signal from
the antenna 207, demodulates the wireless signal into received
data, and sends the received data to the control unit 203. In
addition to performing overall control, the control unit 203 writes
a synchronization signal, for controlling the synchronization of
wireless communication with other nodes, into the memory 205, and
performs control so that the synchronization signal is transmitted
from the wireless transmission unit 201 at a prescribed timing.
Furthermore, the control unit 203 converts the transmission data
into frames in accordance with terminal information communicated
from other nodes as control data.
[0068] Detailed descriptions of the wireless transmission unit 201
and the wireless receiving unit 202 shall be provided later. In the
present embodiment, the wireless transmission unit 201 of the
control terminal 110 includes a DSSS type modulation unit and an
OFDM type modulation unit. These two techniques utilize techniques
compliant with IEEE 802.11 and IEEE 802.11a, as standardized by the
IEEE, and thus detailed descriptions thereof shall be omitted. Note
that "DSSS" is an abbreviation of "Direct Sequence Spread
Spectrum", whereas "OFDM" is an abbreviation of "Orthogonal
Frequency Division Multiplexing". "IEEE" is an abbreviation of
"Institute of Electrical and Electronics Engineers".
[0069] In addition, the wireless receiving unit 202 of the control
terminal 110 includes a DSSS type demodulation unit. The OFDM type
modulation unit is used when stream data stored in the memory 205
is transmitted from the encoding unit 204. When transmitting and
receiving other data, the DSSS type modulation unit and
demodulation unit are used.
[0070] (Nodes)
[0071] FIG. 3 is a block diagram illustrating an internal
configuration of the node a 101. Nodes b 102 to i 109 have the same
configuration. In other words, although the node a 101 shall be
described hereinafter, these descriptions also apply to the nodes b
102 to i 109. In FIG. 3, 301 is a wireless transmission unit, 302
is a wireless receiving unit, 303 is a control unit that controls
the operations of the node, 304 is a memory, 305 is a maximum
likelihood processing unit, 306 is a decoding unit, 307 is a cycle
timer, and 308 is an antenna.
[0072] The wireless receiving unit 302 transmits, to the wireless
transmission unit 301, a synchronization signal notifying the
symbol synchronization timing of the received data. Additionally,
in accordance with instructions from the control unit 303, and in
synchronization with the cycle timer 307, the wireless receiving
unit 302 stores the received data in the memory 304.
[0073] The control unit 303 selects the data addressed to its own
node from among the received data stored in the memory 304, and
sends this data to the decoding unit 306 via the maximum likelihood
processing unit 305. The maximum likelihood processing unit 305
estimates the most likely data from among plural pieces of input
data, and generates output data. The decoding unit 306 receives the
most likely data from the maximum likelihood processing unit 305,
decodes the received data, and outputs AV data. The AV data output
from the decoding unit 306 is used in processing such as video
reproduction and display, audio reproduction, or the like.
[0074] Furthermore, the control unit 303 passes plural pieces of
received data stored in the memory 304 to the wireless transmission
unit 301 via the maximum likelihood processing unit 305; this
received data is wirelessly transmitted from the wireless
transmission unit 301 in synchronization with the cycle timer 307.
Further still, the control unit 303 passes terminal information of
its own node to the wireless transmission unit 301 as control data
to be communicated to the control terminal 110; this terminal
information is wirelessly transmitted to the control terminal 110.
The terminal information is an individual ID (identifier) value set
in advance for identification of the own node, capability
information of the decoding unit 306, capability information of the
wireless receiving unit 302 and wireless transmission unit 301, or
the like.
[0075] The wireless transmission unit 301 and the wireless
receiving unit 302 of the node a 101 include DSSS type and OFDM
type modulation units and demodulation units. In the present
embodiment, these two techniques utilize techniques compliant with
IEEE 802.11 and IEEE 802.11a, and thus detailed descriptions
thereof shall be omitted. The node a 101 communicates using the
OFDM type modulation unit when transmitting stream data and using
the DSSS type modulation unit when transmitting other control data.
In addition, the node a 101 communicates using the OFDM type
demodulation unit when receiving stream data and using the DSSS
type demodulation unit when receiving other control data, control
signals, and so on. Detailed descriptions of the wireless
transmission unit 301 and the wireless receiving unit 302 shall be
provided later.
[0076] (DSSS and OFDM Techniques)
[0077] Next, explanations shall be provided regarding the
characteristic differences between the DSSS and OFDM techniques
utilized in the present embodiment.
[0078] The DSSS technique utilized by the control terminal 110 and
the nodes a 101 to i 109 is a modulation technique that directly
spreads data with spread code using the Differential Binary Phase
Shift Keying (DBPSK) modulation technique. This can be implemented
by a simple circuit, and thus is a data communication technique
capable of low-delay processing. While the transmission rate is a
low 1 Mbps, the technique is highly resistant to errors, and can
properly transmit data over long distances even in communication
environments having poor transmission conditions.
[0079] Additionally, the OFDM technique of the present embodiment
utilizes an advanced modulation technique called the 64-position
Quadrature Amplitude Modulation (64QAM) technique. While this
technique has a heavier processing load and higher delay than the
stated DSSS technique, it is capable of realizing a high 54 Mbps
bitrate. However, the error resistance is low compared to the
stated DSSS technique, and the signal transmission range in which
information can be properly transmitted is smaller than that of the
DSSS technique.
[0080] FIG. 4 is a diagram schematically illustrating the
difference in the signal transmission range between the DSSS and
OFDM techniques. In FIG. 4, 401 schematically indicates the concept
of the distance that data can be properly transmitted using the
OFDM technique, while 402 schematically indicates the concept of
the distance that data can be properly transmitted using the DSSS
technique. In other words, FIG. 4 conceptually illustrates that the
control terminal 110 and the nodes a 101 to i 109 are capable of
data communication at 1 Mbps using the DSSS technique. Furthermore,
FIG. 4 conceptually illustrates that the control terminal 110 and
the nodes a 101 to c 103 and e 105 are capable of data
communication at 54 Mbps using the OFDM technique.
[0081] However, here, nodes outside of the transmission range 401
are also capable of data communication using the OFDM technique if
errors of a certain degree can be overcome. The probability of an
error occurring generally increases as the transmission distance
increases. Forward Error Correction (FEC) code is added to the
transmitted data frames for error correction on the receiving side.
Therefore, due to error correction, it is possible to estimate the
original data if the transmission conditions are favorable and the
degree of the error is small, even if the node is outside of the
transmission range 401; thus correct data reception is possible
with communication using the OFDM technique.
[0082] Although the above descriptions discuss the case of the
control terminal 110 transmitting data, the same applies in the
case where any of the nodes a 101 to i 109 transmit data using the
OFDM technique. In other words, 54 Mbps communication using the
OFDM technique is possible between nearby nodes, and 1 Mbps
communication using the DSSS technique is possible between faraway
nodes, the control terminal, and so on.
[0083] (Wireless Transmission Unit/Wireless Receiving Unit of the
Control Terminal)
[0084] Next, the wireless transmission unit 201 and wireless
receiving unit 202 of the control terminal 110 shall be described
with reference to FIG. 5. FIG. 5 is a diagram illustrating a
detailed configuration of the wireless transmission unit 201 and
wireless receiving unit 202 of the control terminal 110.
[0085] 501 is a scrambling unit for randomizing a bit string and
reducing its correlation with an unrelated bit string; 502 is a
modulation unit that performs DBPSK modulation; and 503 is a
spreading unit that performs spectrum spreading using spread code.
A DSSS type modulation unit 521 is configured of the scrambling
unit 501, modulation unit 502, and spreading unit 503.
[0086] 504 is a convolutional encoding unit that performs redundant
encoding for error correction processing. 505 is a modulation unit
that divides input data among 48 subcarriers and performs 64
Quadrature Amplitude Modulation (QAM). 506 is an Inverse Fast
Fourier Transform (IFFT) unit that performs an inverse Fast Fourier
Transform on each modulated subcarrier signal. 507 is a Guard
Interval (GI) adding unit that adds a guard interval for canceling
the influence of delay interference waves. 508 is a shaping unit
that performs waveform shaping in order to reduce out-of-band
power. An OFDM type modulation unit 522 is configured of the
convolutional encoding unit 504, modulation unit 505, IFFT unit
506, GI adding unit 507, and shaping unit 508.
[0087] 509 is a modulation unit that performs orthogonal modulation
at an intermediate frequency. 510 is a multiplier that converts a
signal input from the modulation unit 509 into a wireless carrier
frequency. 511 is a power amplifier (PA) that amplifies the
wireless transmission power.
[0088] Only one of the DSSS type modulation unit 521 and the OFDM
type modulation unit 522 operates. In other words, the transmitted
data is processed by either the scrambling unit 501 or the
convolutional encoding unit 504. The processed data is then output
from either the spreading unit 503 or the shaping unit 508, and
input into the modulation unit 509.
[0089] 512 is an oscillator that generates an intermediate
frequency, whereas 513 is an oscillator that generates a wireless
carrier frequency. 514 is a low noise amplifier (LNA) that
amplifies a received signal. 515 is a multiplier that extracts a
signal tuned by the wireless carrier frequency. 516 is an automatic
gain control (AGC) that automatically adjusts the signal strength
to a predetermined amplitude strength. 517 is a detection unit that
converts the frequency of the signal to an intermediate frequency
and performs quadrature detection.
[0090] 518 is a despreading unit that multiplies the spread signal
by spread code and produces the original signal. 519 is a
demodulation unit that generates the original data from the
DBPSK-modulated signal. 520 is a descrambling processing unit that
returns the scrambled data to its original state. The DSSS type
demodulation unit 523 is configured of the despreading unit 518,
the demodulation unit 519, and the descrambling processing unit
520.
[0091] (Wireless Transmission Unit/Wireless Receiving Unit of the
Nodes)
[0092] FIG. 6 is a diagram illustrating a detailed configuration of
the wireless transmission unit 301 and wireless receiving unit 302
of the node a 101. The same applies to nodes b 102 to i 109.
[0093] 601 is a scrambling unit for randomizing a bit string and
reducing its correlation with an unrelated bit string; 602 is a
modulation unit that performs DBPSK modulation; and 603 is a
spreading unit that performs spectrum spreading using spread code.
A DSSS type modulation unit 629 is configured of the scrambling
unit 601, modulation unit 602, and spreading unit 603.
[0094] 604 is a convolutional encoding unit that performs redundant
encoding for error correction processing. 605 is a modulation unit
that divides input data among 48 subcarriers and performs 64QAM
modulation. 606 is an IFFT unit that performs an inverse Fast
Fourier Transform on each modulated subcarrier signal. 607 is a GI
adding unit that adds a guard interval for canceling the influence
of delay interference waves. 608 is a shaping unit that performs
waveform shaping in order to reduce out-of-band power. An OFDM type
modulation unit 630 is configured of the convolutional encoding
unit 604, modulation unit 605, IFFT unit 606, GI adding unit 607,
and shaping unit 608. Additionally, the modulation unit 605 and GI
adding unit 607 perform symbol synchronization in accordance with
the synchronization signal from the wireless receiving unit
302.
[0095] 609 is a modulation unit that performs orthogonal modulation
at an intermediate frequency.
[0096] 610 is a multiplier that converts a signal into a wireless
carrier frequency. 611 is a PA that amplifies the wireless
transmission power.
[0097] Only one of the DSSS type modulation unit 629 and the OFDM
type modulation unit 630 operates. In other words, the transmitted
data is processed by either the scrambling unit 601 or the
convolutional encoding unit 604. The processed data is then output
from either the spreading unit 603 or the shaping unit 608, and
input into the modulation unit 609.
[0098] 612 is an oscillator that generates an intermediate
frequency, whereas 613 is an oscillator that generates a wireless
carrier frequency. 614 is an LNA that amplifies a received signal.
615 is a multiplier that extracts a signal tuned by the wireless
carrier frequency. 616 is an automatic gain control (AGC) that
automatically adjusts the signal strength to a predetermined
amplitude strength. 617 is a detection unit that converts the
frequency of the signal to an intermediate frequency and performs
quadrature detection.
[0099] 618 is a despreading unit that multiplies the spread signal
by spread code and produces the original signal. 619 is a
demodulation unit that generates the original data from the
DBPSK-modulated signal. 620 is a descrambling processing unit that
returns the scrambled data to its original state. A DSSS type
demodulation unit 632 is configured of the despreading unit 618,
the demodulation unit 619, and the descrambling processing unit
620.
[0100] 621 is an automatic frequency control (AFC) unit that
corrects errors in the wireless carrier frequency. 622 is a GI
removal unit that removes the guard interval added at the time of
transmission. 623 is a timing detection unit that detects, from the
received signal, the synchronization timing between the frequency
synchronization of the wireless carrier frequency, the frequency
synchronization of the intermediate frequency, and the frequency
symbol. 624 is a FFT unit that performs a Fast Fourier Transform
for dividing the received data into each of the subcarriers. 625 is
a channel estimation unit that estimates transmission path
distortion of the subcarrier signal, and 626 is an equalization
unit that removes transmission path distortion from the received
data in accordance with the estimation of the transmission path
distortion. In other words, the processing performed by the channel
estimation unit 625 and equalization unit 626 is maximum likelihood
processing that estimates the original data from the received data
including a multipath signal and the like. 627 is a demodulation
unit that restores the original data per subcarrier. 628 is a phase
detection correction unit that detects the phase of each subcarrier
and generates a correction signal, and 641 is a Viterbi decoding
unit that performs error correction on the convolutionally encoded
data and restores the original data. An OFDM type decoding unit 631
is configured of the stated functional processing units from the
AFC unit 621 to the Viterbi decoding unit 641.
[0101] The timing detection unit 623 and the phase detection
correction unit 628 synchronize a detected timing with the
synchronization cycle of the overall system, and hold that
synchronization; the timing detection unit 623 and the phase
detection correction unit 628 operate spontaneously even during
periods where there is no received data, and continue to generate a
cyclical synchronization signal. By providing the synchronization
signal to the modulation unit 605 and the GI adding unit 607 of the
wireless transmission unit 301, the operations of the wireless
transmission unit 301 and the wireless receiving unit 302 are
synchronized. In other words, operations are carried out so that
the synchronization timing of the own node is synchronized with the
synchronization timing of the received data, and the data is
transmitted in accordance with that synchronization timing. In this
manner, nodes operate in synchronization with one another, and thus
synchronization of the entire communication network, in which nodes
are communicating with one another, is established.
[0102] (Control Terminal Operations)
[0103] Next, operations of the control terminal 110 shall be
described with reference to FIGS. 7, 8A, and 8B. FIG. 7 is a
flowchart illustrating an operational procedure performed by the
control terminal 110. FIGS. 8A and 8B are time slot diagrams
illustrating operations of the control terminal 110.
[0104] In FIG. 7, first, the control terminal detects the plural
nodes present in the surrounding area, and furthermore performs
processing for determining the node topology (Step S1) in order to
determine the positional relationships between the nodes. Details
of the node topology determination processing shall be provided
later.
[0105] Next, in accordance with the determined node topology, or in
other words, in accordance with the relative positions of the
nodes, the timeslot configuration and node group allocation for
synchronized communication is determined, and the resultant is
communicated to all nodes by the wireless transmission unit 201
using the DSSS technique (Step S2). In the case of the present
embodiment, the nodes a 101 to i 109, as shown in FIG. 1, are
detected. Then, in accordance with the positional relationship
between the nodes and the control terminal 110, the nodes are
divided into groups 1 (112), 2 (113), and 3 (114), from the nearer
nodes outward. Next, the timeslots are allocated as indicated by
FIG. 8A. 801 is a time interval Tf of the repeat cycle of
synchronized transfer. 802 is a shared slot, slot 0, capable of
being used in common by the control terminal 110 and the nodes, and
the time interval thereof is Tc. 803 is a slot, slot 1, capable of
transmission by the control terminal 110. 804 is a slot, slot 2,
capable of transmission by the nodes of group 1 (112). 805 is a
slot, slot 3, capable of transmission by the nodes of group 2
(113). 806 is a slot, slot 4, capable of transmission by the nodes
of group 3 (114). The time intervals for slots 1 to 4 are each the
same Ts.
[0106] Next, the cycle timer 206 starts timer operations at the
cycle Tf of the time division communication in accordance with the
stated time slot configuration (Step S3). When the cycle timer 206
reaches the starting time of the synchronization cycle Tf (YES in
Step S4), the procedure moves to Step S5.
[0107] In Step S5, the control terminal 110 transmits beacon
signals for notifying all nodes of the synchronization timing, as
indicated by 807 to 810 in FIG. 8A. These beacon signals (807, 808,
809, and 810) are transmitted from the wireless transmission unit
201 using the DSSS technique, which is capable of long-distance
communication.
[0108] Next, the control terminal 110 determines whether or not
control data to be transmitted through the shared slot, slot 0
(802), is present (Step S6). In the case where such control data is
present (YES is Step S6), the procedure moves to Step S7, and the
control data to be transmitted is transmitted from the wireless
transmission unit 201 using the DSSS technique at the timing of
slot 0 (802) indicated by the cycle timer 206. The procedure then
moves to Step S8. In the case where the control data is not present
(NO in Step S6), the procedure moves to Step S8.
[0109] Furthermore, the control terminal 110 determines whether or
not control data to be received at the timing of the shared slot,
slot 0 (802), as indicated by the cycle timer 206, is present (Step
S8). In the case where control data to be received is present (YES
in Step S8), the procedure moves to Step S9, and the control data
is received by the wireless receiving unit 202 using the DSSS
technique. The procedure then moves to Step S10. In the case where
control data to be received is not present (NO in Step S8), the
procedure moves to Step S10.
[0110] Next, the control terminal 110 determines whether or not
stream data to be transmitted is present (Step S10). In the case
where such stream data is present (YES in Step S10), the procedure
moves to Step S11, whereas in the case where such stream data is
not present (NO in Step S10), the procedure returns to Step S4 and
the process repeats.
[0111] In Step S11, transmission is performed from the wireless
transmission unit 201 using the OFDM technique, at the timing of
the slot 1 (803) indicated by the cycle timer 206, the slot 1 being
a slot usable by the control terminal. The stream data frame
transmitted at this time is indicated by 815 in FIG. 8B. The stream
data frame 815 is configured of stream data D1 (816) to D9 (824)
addressed to the respective nodes.
[0112] D1 (816), which makes up part of the stream data frame, is
stream data addressed to the node a 101. Additionally, D2 (817) is
stream data addressed to the node b 102. D3 (818) is stream data
addressed to the node c 103. In the same manner, D4 (819) to D9
(824) are pieces of stream data addressed to the nodes d 104 to i
109 respectively. The frame configuration of the transmitted stream
data frame 815 is communicated in advance to all nodes in Step S2.
Therefore, each node can identify the data portion addressed to
itself from among the received stream data frame 815.
[0113] When the stream data frame is transmitted in Step S11 in
this manner, the control terminal 110 once again returns to Step
S4, waits until the starting time of the next synchronization cycle
Tf, and repeats the abovementioned operations.
[0114] Therefore, the control terminal 110 transmits the beacon
signals (811, 812, 813, and 814) per cycle Tf, and transmits the
stream data frames (815, 825, 826) through slot 1 (803) per cycle
Tf. FIG. 8B illustrates the transmission operations of the control
terminal 110 performed at this time.
[0115] (Node Operations)
[0116] Next, the operations of the nodes shall be described with
reference to FIG. 9. FIG. 9 is a flowchart illustrating a
processing procedure performed by each node. Note that the
descriptions explicitly provided here discuss the case of the
operations of the node a 101 as an example; however, the nodes b
102 to i 109 also operate with the same procedure.
[0117] First, a single or plural nodes present in the area
surrounding the node a 101 are detected, and inter-node information
necessary for the control terminal 110 to perform the processing
for determining the node topology is transmitted to the control
terminal 110 (Step S21). The processing for detecting the
surrounding nodes performed by the control terminal 110 shall be
described later in detail in the descriptions of the processing for
determining the node topology.
[0118] Next, control data transmitted from the control terminal
110, including information of the synchronized communication
timeslot configuration and the node group allocation, is received
by the wireless receiving unit 302 using the DSSS technique (Step
S22). Node a (101) acquires the timeslot configuration in
accordance with the received control data, identifies the frame
configuration of the stream data frame 815, and identifies the
layout of the data D1 (816) addressed to itself. In addition, the
node a (101) acquires information of the group to which it belongs,
in accordance with the received control data, and identifies the
slot through which it performs transmission.
[0119] Next, the node a (101) determines whether or not a beacon
signal has been received (Step S23), and in the case where a beacon
signal has been received (YES in Step S23), the procedure moves to
Step S24, whereas in the case where a beacon signal has not been
received (NO in Step S23), the procedure moves to Step S26. In Step
S24, the cycle timer is restarted. Through this restarting process
(Step S24), the cycle timer 206 of the control terminal 110 and the
cycle timer 307 of the node a (101) are synchronized, and
determination of the cycle Tf and slots 0 to 4 becomes possible on
the node side.
[0120] Next, the node a (101) extracts plural pieces of stream data
D1 addressed to itself from among the plural stream data frames
stored in the memory 304, and sends the stream data D1 to the
maximum likelihood processing unit 305; the data on which maximum
likelihood processing has been performed is sent to the decoding
unit 306 and decoded into AV data (Step S25). However, when there
is only a single piece of stream data D1 in the memory 304, the
maximum likelihood processing is bypassed, and the stream data D1
is sent to the decoding unit 306. Additionally, storage of the
received stream data within the memory 304 occurs in Step S27,
which shall be described later.
[0121] Next, the node a 101 determines whether or not the wireless
receiving unit 302 is receiving stream data (Step S26). In the case
where receiving is being carried out (YES in Step S26), the
procedure moves to Step S27, whereas in the case where receiving is
not being carried out (NO in Step S26), the procedure moves to Step
S28. In Step S27, the stream data frame is received by the wireless
receiving unit 302 using the OFDM technique, and is stored in the
memory 304. Here, the node a 101 has, within a single Tf cycle,
three receiving slots, or the slots 1 (803), 3 (805), and 4 (806),
which are slots aside from the node a 101's own transmission slot.
Therefore, although processing for storing the stream data frame
occurs three times within a single Tf cycle, these are stored
independently in the memory 304 and are used in the maximum
likelihood processing of the aforementioned Step S25.
[0122] Next, it is determined whether or not the time indicated by
the cycle timer 307 is the transmission slot of the node itself
(Step S28). The transmission slot is slot 2 if the node is in group
1 (112), slot 3 if the node is in group 2 (113), and slot 4 if the
node is in group 3 (114). Then, if the current time is the starting
timing of the transmission slot (YES in Step S28), the procedure
moves to Step S29, whereas in other cases (NO in Step S28), the
procedure returns to Step S23.
[0123] In Step S29, it is determined whether or not the group to
which the node itself belongs is group 1 (112). To rephrase, in
Step S29, it is determined whether a stream data frame is being
received a plurality of times at the starting time of the
transmission slot of the node itself. In the case where the node
belongs to group 1, the stream data frame is received directly from
the control terminal 110; thus, the same data is not being received
a plurality of times, and the maximum likelihood processing is
therefore unnecessary. As opposed to this, in the case where the
node does not belong to group 1, the same data is received a
plurality of times from plural nodes, and therefore it is necessary
to carry out the maximum likelihood processing. In the case where
the node has been determined not to belong to group 1 (112) (NO in
Step S29), the procedure moves to Step S30, whereas in the case
where the node has been determined to belong to group 1 (112) (YES
in Step S29), the procedure moves to Step S31.
[0124] In Step S30, the stream data frames within the memory 304
are sent to the maximum likelihood processing unit 305, and the
stream data frame obtained by performing the maximum likelihood
processing is transmitted from the wireless transmission unit 301
using the OFDM technique. The stream data frame transmitted at this
time is a frame in which the stream data D1 (816) to D9 (824) of
all nodes are included. On the other hand, in Step S31, one of the
stream data frames within the memory 304 and received from the
control terminal 110 is transmitted as-is from the wireless
transmission unit 301 using the OFDM technique.
[0125] In the manner described thus far, upon transmitting the
stream data in Step S30 or Step S31, the node a 101 once again
returns to Step S23, and the abovementioned processing is repeated.
Accordingly, each node repeats the following process within a Tf
cycle: receiving stream data a plurality of times; performing
maximum likelihood processing on and decoding the data addressed to
itself from among the received data; and performing maximum
likelihood processing on and transmitting the received stream
data.
[0126] (Cooperative Operations Between Control Terminal and
Node)
[0127] FIGS. 10A, 10B, 10C, 10D, and 11 illustrate the operations
of the control terminal 110 and the nodes 101 to 109 as described
above. FIGS. 10A, 10B, 10C, and 10D are diagrams conceptually
illustrating the change over time of the transmission of stream
data by the control terminal 110 and the nodes. FIG. 11 is a
diagram illustrating transmission of stream data by the control
terminal 110 and nodes on the time axis.
[0128] First, in the time of slot 1 (803) shown in FIG. 11, the
control terminal 110 transmits a stream data frame, as shown in
FIG. 10A. At this time, the signal that reaches the nearby nodes a
101, b 102, and c 103 is strong, and thus the stream data frame can
be received with a low rate of error. However, as the position of
the node grows more distant, the signal that reaches that node
grows weaker, and thus distant nodes receive the stream data frame
with a high rate of error. The stream data frame transmitted by the
control terminal 110 at this time is the data frame indicated by
815 in FIG. 11. As shown in FIG. 8B, the data frame 815 includes
data addressed to all of the nodes a 101 to i 109.
[0129] Next, in the time of slot 2 (804), the nodes a 101 to c 103
of group 1 (112) transmit stream data frames, as shown in FIG. 10B.
At this time, the signal that reaches the nearby nodes d 104 to f
106 is strong, and thus the stream data frames can be received with
a low rate of error. However, as the position of the node grows
more distant, the signal that reaches that node grows weaker, and
thus distant nodes receive the stream data frames with a high rate
of error. The stream data frames transmitted by the nodes a 101 to
c 103 at this time are the frame data indicated by 901 to 903 in
FIG. 11. In other words, the nodes a 101, b 102, and c 103 transmit
the data frames they received in slot 1 (803) as-is, and therefore
the same data is transmitted from three points simultaneously. When
the same data is transmitted simultaneously from plural points, it
can be handled in the same way as a multipath wave, as far as the
receiving nodes are concerned; accordingly, maximum likelihood
processing and estimation of the original data can be performed by
the channel estimation unit 625 and the equalization unit 626 of
the wireless receiving unit 302 in each node.
[0130] Next, in the time of slot 3 (805), the nodes d 104 to f 106
of group 2 (113) transmit stream data frames, as shown in FIG. 10C.
At this time, the signal that reaches the nearby nodes a 101 to c
103 and g 107 to i 109 is strong, and thus the stream data frames
can be received with a low rate of error. However, as the position
of the node grows more distant, the signal that reaches that node
grows weaker, and thus distant nodes receive the stream data frames
with a high rate of error. The stream data frames transmitted by
the nodes d 104 to f 106 at this time are the frame data indicated
by 904 to 906 in FIG. 11. In other words, the nodes d 104 to f 106
perform maximum likelihood processing on the data frames received
in slot 1 (803) and slot 2 (804) and transmit the data frames, and
therefore the same data is transmitted from three points
simultaneously. When the same data is transmitted simultaneously
from plural points, it can be handled in the same way as a
multipath wave, as far as the receiving nodes are concerned;
accordingly, maximum likelihood processing and estimation of the
original data can be performed by the channel estimation unit 625
and the equalization unit 626 of the wireless receiving unit 302 in
each node.
[0131] Lastly, in the time of slot 4 (806), the nodes g 107 to i
109 of group 3 (114) transmit stream data frames, as shown in FIG.
10D. At this time, the signal that reaches the nearby nodes d 104
to f 106 is strong, and thus the stream data frames can be received
with a low rate of error. However, as the position of the node
grows more distant, the signal that reaches that node grows weaker,
and thus the stream data frames are received with a high rate of
error. The stream data frames transmitted by the nodes g 107 to i
109 at this time are the frame data indicated by 907 to 909 in FIG.
11. In other words, the nodes g 107 to i 109 perform maximum
likelihood processing on the data frames received in slot 1 (803),
slot 2 (804), and slot 3 (805), and transmit the data frames, and
therefore the same data is transmitted from three points
simultaneously. When the same data is transmitted simultaneously
from plural points, it can be handled in the same way as a
multipath wave, as far as the receiving nodes are concerned;
accordingly, maximum likelihood processing and estimation of the
original data can be performed by the channel estimation unit 625
and the equalization unit 626 of the wireless receiving unit 302 in
each node.
[0132] Through the stated process, within the repeating cycle Tf,
each node receives the same stream data frames from plural nodes
and stores the stream data frames in the memory 304. Then, upon
receiving the next beacon signal 812, each node extracts plural
pieces of data addressed to the node itself from the plural stream
data frames stored in the memory 304, performs maximum likelihood
processing through the maximum likelihood processing unit 305, and
reproduces the original data. The reproduced data is sent to the
decoding unit 306.
[0133] (Node Topology Determination Processing)
[0134] Next, node topology determination processing executed by the
control terminal 110 in Step S1 of FIG. 7 shall be described using
FIG. 12. FIG. 12 is a diagram illustrating procedures for node
topology determination processing performed by the control terminal
and by the nodes. Note that the control terminal 110 and the nodes
use the DSSS technique when transmitting/receiving wireless signals
in this node topology determination process.
[0135] First, the control terminal 110 carries out processing for
recognizing nodes present in the surrounding area (Step S41).
Recognizing nodes is performed through a repeating procedure, in
which the control terminal 110 broadcasts an inquiry signal, and
the nodes that receive the inquiry signal add an individual ID
value, provided individually to each node in advance, to a response
signal and broadcast the response signal. The nodes randomly change
the transmission timing of the response signal within a range up to
a maximum wait time Tmax so as to avoid having their response
signals interfere with the response signals from other nodes. The
control terminal 110 repeatedly transmits the inquiry signal until
response signals cease to arrive within the maximum waiting time
Tmax, thereby receiving a response signal from all of the nodes. In
this manner, the control terminal 110 acquires the individual ID
values of all nodes present in the surrounding area.
[0136] Next, the control terminal 110 allocates node numbers,
corresponding to the individual ID numbers, to all the recognized
nodes, and notifies the nodes of these node numbers (Step S42).
Numbers such as node 1, node 2, and node 3, . . . , node 9 are
dealt to each node a.about.i in this manner.
[0137] Next, the control terminal 110 instructs all nodes to begin
measuring the signal strength of a training signal (Step S43). All
nodes that receive this instruction move to a status in which they
measure the signal strength of the training signals transmitted in
order from the other nodes, including the control terminal, and
create measurement result lists (Step S50).
[0138] Then, first, the control terminal 110 commences transmission
of the training signal (Step S44). Note that this training signal
has a preset transmission power strength, and is transmitted at the
same signal strength from the control terminal 110 and all the
nodes.
[0139] Next, the control terminal 110 sequentially requests each
node to transmit a training signal of a preset transmission power
strength (Step S45). That is, the control terminal 110 selects each
node sequentially, and requests the select node to transmit the
training signal. The nodes that receive the request instruction
transmit the training signals (Steps S51, S52, and S53). During
this time, the control terminal 110 measures the signal strengths
of the training signals transmitted by each node (Step S46). Here,
as described above, each node is performing the measurement
processing of the signal strength of the training signals (Step
S50) on receiving the instruction from the control terminal 110 at
step S43. When the transmission of the training signal has finished
for all nodes, the control terminal 110 then inquires to each node
and receives the measurement result list from each node (Step
S47).
[0140] The received signal strength of the training signals
received by the control terminal 110 and the nodes is inversely
proportional to the distance between nodes, as illustrated in FIG.
13. FIG. 13 is a diagram schematically illustrating a relationship
between the strength of a received training signal and the distance
between nodes. Accordingly, the control terminal 110 is provided
with a list in which the corresponding relationship between the
received signal strengths and the distances is pre-measured, and
from this measurement result list, determines the distance between
the nodes. If the distance between the nodes can be determined, it
is possible to estimate the positional relationship between each of
the nodes using a publicly known triangulation method such as that
illustrated in FIG. 14 (Step S48). FIG. 14 is a diagram
schematically illustrating the estimation of a positional
relationship through the triangulation method. The distance between
the control terminal 110 and the nodes (for example, the distance
between the control terminal and the nodes a and b) can be
estimated based on the training signal received in Step S46. In
addition, the distance between nodes (for example, the distance
between the nodes a and b) can be estimated based on the
measurement results received in Step S47 (for example, the
measurement results from nodes a and b).
[0141] The control terminal 110 first determines the length of the
necessary stream data frame 815 based on the total number of nodes,
and then determines the beacon cycle Tf 801 based on the bitrate of
the stream data frame. The control terminal 110 then determines the
number of group divisions based on the beacon cycle Tf, the data
frame length, and the total number of nodes. In this manner, the
time slot configuration such as that shown in FIGS. 8A and 8B is
determined; adjacent nodes positioned close to the control terminal
110 are configured into the same group based on the positional
relationships between the nodes; and the layout map shown in FIG. 1
is created. Then, in accordance with the layout map, the groups to
which the nodes belong and the time slot configuration are
determined, and the determination is communicated to the nodes
(Step S49).
[0142] In the configuration according to the present embodiment as
described thus far, plural communication terminals make up a
synchronized-type network; within each synchronization cycle,
plural transmission terminals transmit data of a predetermined
length, and receiving terminals perform maximum likelihood
processing on the plural pieces of received data and finalize the
received data. Thus, according to the configuration of the present
embodiment, plural communication devices redundantly transmit the
same data within the same cycle; therefore, an abnormality arising
in a single communication connection is solved through the other
communication connections, and the data can be transmitted to all
of the communication devices within the same cycle. Additionally,
all of the terminals are temporally synchronized, which makes it
possible to avoid transmissions from interfering with one another.
Accordingly, it is possible to realize communication in which data
disconnections and interruptions do not occur, even when handling
stream data that is temporally continuous, such as video or audio.
It is also possible to carry out communication in which plural
transmission terminals simultaneously transmit plural data streams
without interfering with one another.
Embodiment 2
[0143] In the previously described embodiment, nodes belonging to
the final group also transmit stream data frames. However, in order
to effectively utilize the communication bandwidth, the nodes of
the final group may operate so as not to carry out transmission
when the redundancy of the received data of each of the nodes is
ensured. For example, in the case where the number of groups is
three, as in the first embodiment, slot 4 becomes unnecessary, and
thus it is possible to reduce the bandwidth used by all nodes
within the repeating cycle Tf by omitting communication through
slot 4.
[0144] Under these conditions, the method of allocating the time
slots in accordance with the number of groups may be performed as
follows. Descriptions shall first be provided regarding the case
where there is a single group. In this case, as illustrated in FIG.
15, all nodes receive data directly from the control terminal, and
thus the nodes in group 1 (112) do not need to transmit the
received data further on. FIG. 15 is a diagram schematically
illustrating a configuration of a network when there is a single
group. Therefore, the only timeslots required are two slots, or the
shared slot, slot 0, and the transmission slot, slot 1. In this
case, the redundancy in each node is only 1; however, because the
data transmitted from the control terminal 110 is the most correct
data, a higher redundancy is not necessary. If a node within the
group has a poor reception state, that node may be separated into a
difference group.
[0145] Next, descriptions shall be provided regarding the case
where there are two groups. In this case, when the nodes of group
2, which is the final group, do not carry out transmission, the
data path through which the nodes carry out reception is as
illustrated in FIG. 16. FIG. 16 is a diagram schematically
illustrating a configuration of a network when there are two
groups. The nodes in group 1 (112) only receive the transmission
data from the control terminal 110, and thus the redundancy thereof
is 1. The nodes in group 2 (113) receive the transmission data from
the control terminal 110 and the transmission data from the nodes
of group 1 (112), and thus the redundancy thereof is 2. Therefore,
if the nodes of group 2 (113) carry out transmission further on,
the redundancy of the nodes in group 1 (112) can be set at 2. At
first glance, having group 1 (112) receive the transmission data of
group 2 (113) appears to be meaningless. However, for example, due
to the transmission performed by group 2 (113), the node a 101
receives data on a direct path from the control terminal 110, and
furthermore receives the data sent on a path from the control
terminal 110 via the node c 103 and the node e 105. Accordingly, it
is possible to set the redundancy with data received from differing
paths at 2, making it possible to expect a reduction in errors
through the maximum likelihood processing.
[0146] Detailed descriptions of the process for determining groups
and timeslots (Step S49 in FIG. 12) performed by the control
terminal 110, which carries out the above-described operations,
shall be provided with reference to FIG. 17. FIG. 17 is a flowchart
illustrating a procedure for processing performed by the control
terminal 110 to determine groups and time slots in the present
embodiment.
[0147] First, the control terminal 110 finalizes the layout and
number of all nodes, in the same manner as the process from Step
S41 to Step S48 in the aforementioned first embodiment (Step S61).
Then, the control terminal 110 determines the length of the
necessary stream data frame 815 based on the total number of nodes,
and then determines the beacon cycle Tf (801) based on the bitrate
of the stream data frame (Step S62). The control terminal 110 then
determines the number of group divisions N based on the beacon
cycle Tf, the data frame length, and the total number of nodes
(Step S63).
[0148] Next, in the case where the number of group divisions N is 1
(YES in Step S64), the number of slots into which the cycle Tf is
divided is set to N+1 (Step S65). In other words, the cycle Tf is
divided by two slots: slot 0, which is the shared slot, and slot 1,
which is the transmission slot of the control terminal 110. The
procedure then moves to Step S70.
[0149] Next, in the case where the number of group divisions N is 2
(YES in Step S66), the number of slots into which the cycle Tf is
divided is set to N+2 (Step S67). In other words, the cycle Tf is
divided by four slots: slot 0, which is the shared slot; slot 1,
which is the transmission slot of the control terminal 110; slot 2,
which is the transmission slot of group 1; and slot 3, which is the
transmission slot of group 2. The procedure then moves to Step
S70.
[0150] In the case where the number of group divisions N is three
or more (YES in Step S68), the number of slots into which the cycle
Tf is divided is set to N+1 (Step S69). In other words, the cycle
Tf is divided by N+1 slots: slot 0, which is the shared slot; slot
1, which is the transmission slot of the control terminal 110; and
slots 2 to N, which are the transmission slots of groups 1 to
(N-1). The procedure then moves to Step S70.
[0151] In this manner, the time slot configuration such is
determined in accordance with the number of group divisions N;
adjacent nodes positioned close to the control terminal 110 are
configured into the same group based on the positional
relationships between the nodes; and a layout map identical to that
shown in FIG. 1 is created. Then, in Step S70, in accordance with
the layout map, the groups to which the nodes belong and the time
slot configuration are determined, and the determination is
communicated to the nodes.
[0152] As described thus far, according to the configuration of the
present embodiment, groups that do not need to transmit data
further on, such as the final group to receive the data within each
time interval of the repeating cycle, do not carry out
communication. For this reason, according to the configuration of
the present embodiment, it is possible to allocate the groups
necessary for communication to a longer time interval, and thus it
is possible to increase the speed of data transfer.
Embodiment 3
[0153] In the first and second embodiments, the beacon signal is
used only as a signal that communicates the timing of the repeating
cycle Tf. However, by adding control information to this beacon
signal, the control terminal 110 may communicate the timings of
each of the slots, specify the node that uses the shared slot, and
so on.
[0154] FIG. 18 is a diagram illustrating transmission of stream
data by the control terminal 110 and nodes on the time axis in the
case where control information has been added to the beacon signal.
In FIG. 18, 921 is the repeating cycle Tf, 922 is the shared slot,
slot 0, and 923 is the transmission slot, slot 1, of the control
terminal 110. 924 to 926 are transmission slots, slots 2 to 4, of
groups 1 to 3 respectively. 927 to 932 are beacon signals to which
control information has been added. 933 is a stream data frame
transmitted by the control terminal 110, whereas 934 to 942 are
stream data frames transmitted by the nodes a 101 to i 109
respectively.
[0155] Information indicating the start of the cycle Tf and
information indicating that node a 101 is permitted to use the
shared slot, slot 0, is added to the beacon signal indicated by
927. If, at this time, node a 101 has information to be
communicated to the control terminal 110, node a 101 transmits
control data. When node a 101 does not have information to be
communicated, node a 101 simply stands by for reception. Nodes b
102 to i 109 also simply stand by for reception.
[0156] Information indicating that authority to transmit stream
data frames has been given to the control terminal 110 is added to
the beacon signal indicated by 928. In response to the beacon
signal 928, the control terminal 110 transmits the stream data
frame 933.
[0157] Information indicating that authority to transmit stream
data frames has been given to group 1 is added to the beacon signal
indicated by 929. The nodes a 101 to c 103, which receive the
beacon signal 929, transmit the stream data frames 934 to 936.
[0158] Information indicating that authority to transmit stream
data frames has been given to group 2 is added to the beacon signal
indicated by 930. The nodes d 104 to f 106, which receive the
beacon signal 930, transmit the stream data frames 937 to 939.
[0159] Information indicating that authority to transmit stream
data frames has been given to group 3 is added to the beacon signal
indicated by 931. The nodes g 107 to i 109, which receive the
beacon signal 931, transmit the stream data frames 940 to 942.
[0160] Lastly, information indicating the start of the cycle Tf and
information indicating that node b 102 is permitted to use the
shared slot, slot 0, is added to the beacon signal indicated by
932.
[0161] Information of the control terminal 110, node a 101, node b
102, node c 103, and on up to node i 109 is specified repeatedly in
sequence, as information of terminals permitted to carry out
transmission, in the beacon signal sent at the beginning of the
cycle Tf.
[0162] In this manner, it is easier to achieve synchronization
between nodes by having the starting timing of each slot be
communicated by the beacon signal. Additionally, the number of the
node permitted to perform transmission may be specified rather than
the group number that is added to the beacon signal. Doing so makes
it acceptable to carry out transmission of the received data in
accordance with the node number specified in the beacon signal,
even if each node is not aware of the group to which it belongs.
Accordingly, it is possible to simplify the operational processing
of the nodes.
Embodiment 4
[0163] In the first embodiment, maximum likelihood processing is
performed on data transmitted simultaneously from plural nodes in
the same manner as with multipath communication by the estimation
unit 625 and the equalization unit 626, and the original data is
estimated. However, OFDM subchannels may be divided/allocated per
transmission node, the data may be stored as individual data in the
memories 304 of the nodes on the receiving side, and maximum
likelihood processing may be performed by the maximum likelihood
processing unit 305.
[0164] In this case, for example, the OFDM technique in the present
embodiment divided communication into 48 subchannels, and the
channels can be allocated for use by the nodes as follows:
[0165] channels 1 to 16: node a 101, node d 104, and node g
107;
[0166] channels 17 to 32: node b 102, node e 105, and node h
108;
[0167] channels 33 to 48: node c 103, node f 106, and node 109.
[0168] In this case, regarding the transmission data sent from the
control terminal 110, the same data is transmitted redundantly over
channels 1 to 16, 17 to 32, and 33 to 48, respectively.
[0169] By using such a configuration, it is possible for each node
to distinguish transmission nodes and receive the data; thus it is
possible to more accurately restore the original data through the
maximum likelihood processing.
Embodiment 5
[0170] In the above embodiments, descriptions are given assuming an
example in which the wireless scheme used by the wireless
transmission units 201 and 301 and the wireless receiving units 202
and 302 is the Time Division Multiple Access (TDMA) technique.
However, the wireless scheme used is not limited thereto. For
example, the Code Division Multiple Access (CDMA) technique may be
used. In this case, different spread code is allocated per node
that performs transmission at the same time as another node, and
the wireless transmission units modulate the transmission data
using the CDMA technique with the spread code allocated to their
own nodes, and transmit the data. On the other hand, the wireless
receiving units are provided with plural spread code correlation
devices; by performing plural correlations on received signals,
signals transmitted simultaneously from plural nodes are each
divided, received, and stored in the memories. Then, maximum
likelihood processing is performed on the respective pieces of
received data and the original data is estimated.
[0171] Alternatively, the wireless scheme used by the wireless
transmission units 201 and 301 and the wireless receiving units 202
and 302 may be the Frequency Division Multiple Access (FDMA)
technique. In this case, transmission frequencies are allocated per
node that simultaneously performs transmission. The wireless
receiving units are provided with plural receiving units in
parallel; data received simultaneously in parallel may be stored in
the memories per frequency, maximum likelihood processing performed
on the received data within the memories, and the original data
estimated.
[0172] Alternatively, the space-division multiple access technique
may be used. Or, a combination of the abovementioned communication
techniques may be used.
[0173] In this manner, by using wireless techniques as necessary,
it is possible to carry out communication appropriate for the
applications and goals of the communication.
Embodiment 6
[0174] In the stated embodiments, the layout of the nodes is
determined using the received signal strength of the wireless
signal (the strength of the signal transmitted from the nodes);
however, the layout may be determined using an optical device, an
acoustic device, or a different kind of measurement device, or,
alternatively, a combination of these.
[0175] For example, in the case of using an optical device (an
optical imaging device), the control terminal is provided with a
camera and a range finding unit for autofocus; the nodes are
identified from an image captured by the camera, and the distance
to each node is measured by the range finding unit. Through this,
the control terminal can determine the layout of the nodes.
[0176] Or, for example, in the case of using an acoustic device,
the control terminal and the nodes can be provided with a speaker
for outputting sound waves (an acoustic signal) or ultrasonic waves
(an ultrasonic signal) and a microphone for detecting those waves.
In this case, nodes are synchronized to one another; sound waves or
ultrasonic waves are output by the nodes in order in
synchronization with a reference time; the distance between the
nodes is measured based on the amount of delay time before the
sound wave reaches the node (the transmission delay); and thereby,
the control terminal can determine the layout of the nodes.
Alternatively, because ultrasonic waves have strong directivity, a
device that structurally scans the space may be provided; the
layout of the nodes is detected by measuring the delay of a
reflected ultrasonic wave, using publicly known sonar technology,
and the control terminal may determine the node layout thereby.
[0177] Furthermore, a publicly known Global Positioning System
(GPS) unit may be provided in each node; each node autonomously
detects its own position and communicates this to the control
terminal, and the control terminal may determine the node layout
thereby.
[0178] In this manner, the layout of the nodes can be accurately
detected by using an optical device, an acoustic device, or a
different kind of measurement device, or, alternatively, a
combination of these.
Embodiment 7
[0179] Although an embodiment of the present invention has been
described in detail above, it is possible for the invention to take
on the form of a system, apparatus, program or storage medium. More
specifically, the present invention may be applied to a system
comprising a plurality of devices or to an apparatus comprising a
single device.
[0180] It should be noted that there are cases where the object of
the invention is attained also by supplying a program, which
implements the functions of the foregoing embodiments, directly or
remotely to a system or apparatus, reading the supplied program
codes with a computer of the system or apparatus, and then
executing the program codes.
[0181] Accordingly, since the functions of the present invention
are implemented by computer, the program codes per se installed in
the computer also fall within the technical scope of the present
invention. In other words, the present invention also covers the
computer program itself that is for the purpose of implementing the
functions of the present invention.
[0182] In this case, so long as the system or apparatus has the
functions of the program, the form of the program, for example,
object code, a program executed by an interpreter or script data
supplied to an operating system, etc., does not matter.
[0183] Examples of storage media that can be used for supplying the
program are a floppy (registered trademark) disk, hard disk,
optical disk, magneto-optical disk, CD-ROM, CD-R, CD-RW, magnetic
tape, non-volatile type memory card, ROM, DVD (DVD-ROM, DVD-R),
etc.
[0184] As for the method of supplying the program, a client
computer can be connected to a website on the Internet using a
browser possessed by the client computer, and the computer program
per se of the present invention or a compressed file that contains
an automatic installation function can be downloaded to a recording
medium such as a hard disk. Further, the program of the present
invention can be supplied by dividing the program code constituting
the program into a plurality of files and downloading the files
from different websites. In other words, a WWW server that
downloads, to multiple users, the program files that implement the
functions of the present invention by computer also is covered by
the present invention.
[0185] Further, it is also possible to encrypt and store the
program of the present invention on a storage medium such as a
CD-ROM, distribute the storage medium to users, allow users who
meet certain requirements to download decryption key information
from a website via the Internet, and allow these users to run the
encrypted program by using the key information, whereby the program
is installed in the user's computer. Further, besides the case
where the aforesaid functions according to the embodiment are
implemented by executing the read program by computer, an operating
system or the like running on the computer may perform all or a
part of the actual processing so that the functions of the
foregoing embodiment can be implemented by this processing.
[0186] Furthermore, after the program read from the storage medium
is written to a memory provided in a function expansion board
inserted into the computer or a function expansion unit connected
to the computer, a CPU or the like mounted on the function
expansion board or function expansion unit performs all or a part
of the actual processing so that the functions of the foregoing
embodiment can be implemented by this processing.
[0187] In this manner, according to the abovementioned embodiments,
it is possible to provide a technique for reducing the occurrence
of disconnections or interruptions when transmitting/receiving
stream data that is temporally continuous, such as video or audio.
It is furthermore possible to provide a technique for avoiding
mutual interference even when simultaneously sending plural pieces
of data to plural receiving terminals.
[0188] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
[0189] This application claims the benefit of Japanese Patent
Application No. 2006-312132, filed Nov. 17, 2006, which is hereby
incorporated by reference herein in its entirety.
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