DEVICE NECESSARY BANDWIDTH PHY RATE Device Avallability Info
A 1Mbps 50Mbps 000011110000000011111110000 000
B 2Mbps 100Mbps 000011110000000011111110000 000
C 10Mbps 200Mbps 000011110000000011111110000 000
D 4Mbps 100Mbps 000011110000000011111110000 000

[0020] :
Device Availability Info includes a field which has a length of 256 bits, where a MAS that can be executed by a WUSB device is represented in a bitmap format. That is, for a MAS corresponding to the position of a bit indicating "1" in the Device Availability Info field, a corresponding device serves as a target of transaction scheduling. [0021]
In .normal WUSB, one or more MASs reserved in accordance with the DRP are copied to each entry in the device information management table (for example, see Non-Patent Document 2) . Thus, Device Availability Info of all the devices has an identical value. This means, that, one or more MASs reserved in accordance with the DRP are to be equally used by all the WUSB devices (or individual pipes). Fig. 3 schematically shows the use statuses of MASs in a superframe for WUSB. The use statuses of the MASs are represented by the Device Availability Info shown in Table 1. , In this
figure, in bands represented by oblique lines, all the WUSB
i
devices A to D within a WUSB cluster serve as transaction

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candidates. [0022]
Obviously, in the WUSB specification, the priority relationship between transfer modes is defined {as described above). Thus, a bandwidth reserved by a WUSB host is not necessarily equally assigned to the individual WUSB devices. However, unlike USB 2.0, which uses a wired cable, in WUSB, the communication speed in the physical layer varies due,to the instability of a transmission channel relating to a communication distance, a communication status, or the like. Thus, the amount of data that can be transmitted during the same period of time continuously varies. Therefore, in order to ensure the amount of data to be transmitted in the isochronous transfer mode, complicated control, such as making a reservation of another MAS or ensuring the stability of a transmission chanhel by using Link Adaptation, is necessary. [0023]
In addition, in the case of executing a transaction for a MAS, an algorithm for determining a transaction schedule is equally applied to individual devices serving as candidates (that is, communications using individual pipes are equally handled).. Thus, under the totally identical conditions (relating to the transfer rate of a physical layer, a transfer mode, a desired bandwidth, and the like),

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equal services can be provided to the individual WUSB
devices.
[0024]
Due to such factors, there is a problem in that it is difficult to reliably ensure a bandwidth in the isochronous transfer mode. In addition, complicated control is necessary for implementing the isochronous transfer mode as hardware, thereby increasing the circuit scale and increasing the time necessary for inspection of a product. Thus, initial WUSB products might not support isochronous transfer. Even the subsequent WUSB products might not
support isochronous transfer, from the point of view of cost
if reduction. In such a case, a mechanism for .causing a device
to perform communication using a !bandwidth more
preferentially than other devices is not available.
[0025]
Patent Document 1: Japanese Unexamined Patent Application
Publication No. 2006-216015
Non-Patent Document 1: Wireless 'Universal Serial Bus
Specification (May 12, 2005, Revision 1.0)
Non-Patent Document 2: Wireless Host Controller Interface
(WHCI) Specification for Certified Wireless Universal Serial
Bus (June 16, 2006, Revision 0.95)
Disclosure of Invention
Technical Problem

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[0026]
An object of the present invention is to provide an excellent communication system, an excellent communication apparatus, an excellent communication method, and an excellent computer program in which communication can be suitably performed between a host and a device by using WUSB that adopts application of UWB, which is a wireless technology using an ultra-wide band, and adopts a multiband OFDM method promoted by Wimedia Alliance as standards for a physical layer and a MAC layer. [0027]
Another object of the present invention is to provide an excellent communication system, an excellent communication apparatus, an excellent communication method, and an excellent computer program in which priority communication can be suitably performed in units of devices in a WUSB communication environment in which isochronous transfer cannot be used. Technical Solution [0028]
The present invention has been made taking into account the above-described problems. According to a first aspect of the present invention, a communication system in which a band is reserved in units of predetermined time slots for each superframe and in.which within a cluster including a

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plurality of devices, one or more time slots reserved for the cluster are shared between the plurality of devices, is characterized by including time-slot reservation means for reserving the one or more time slots within the,superframe for the cluster; and time-slot assigning means for assigning the reserved one or more time slots to the plurality of . devices within the cluster in such a manner that different transaction opportunities are provided to the plurality of devices. [0029]
However, "system" used here :represents a logical collection of a plurality of apparatuses (or functional modules implementing particular functions). It is not particularly relevant whether or not individual apparatuses or individual functional modules are provided in a single casing {the same applies to the description below). [0030]
USB, which is widely used as the general-purpose bus interface standard, supports a plurality of transfer modes for which the priority relationship is defined, and different transfer modes can be designated for individual pipes. In addition, recently, the development of expanded wireless USB using a UWB wireless technology has been conducted. WUSB, which is designed and managed by USB-IF, is a typical wireless USB.

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[0031]
Normally, in WUSB, communications using pipes in the same transfer mode are equally handled. For example, data can be transmitted at the same speed in bulk transfer to a WUSB device A and in bulk transfer to a WUSB device B. This is realized when a WUSB host collectively obtains MASs and equally performs scheduling of communications with pipes. Normally, a round-robin method or the like is used for scheduling. [0032] .
Meanwhile, in WUSB, the error rate and transfer speed of communication continuously vary due to a variation in a communication status. Thus, in order to reliably ensure a bandwidth required by a pipe using the isochronous transfer mode, a problem in which complicated processing is necessary occurs. [0033]
In contrast, in the communication system according to the present invention, a WUSB host reserves one or more MASs to be used by the WUSB cluster in a superframe, which is used at the same time by a plurality of network upper layers adopting a physical layer and a MAC layer designed by WiMedia Alliance. The WUSB host also assigns the reserved one or more MASs to a plurality of devices in the cluster in such a manner that different transaction opportunities are

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provided to the plurality of devices. [0034]
More specifically, the WUSB :host performs assigning of a band of the reserved one or more MASs in the superframe by using a device information management table, in which device information entries (Device Availability Info) each describing, in a bitmap format, a MAS for which a transaction can be executed are each provided for a WUSB device in the WUSB cluster. The WUSB host assigns at least some of the reserved one or more MASs only to a particular WUSB device. In other words, the details of the MASs reserved for the WUSB cluster are not copied to the device information entries each provided for a corresponding WUSB device. All the MASs reserved for the WUSB" cluster are not shared among all the WUSB devices. [0035]
Each of the WUSB devices serves as a target of transaction scheduling for a MAS marlced in the corresponding device information entry for the WUSB device. That is, when one of the one or more- time slots in the superframe reserved
L
for the WUSB cluster is reached, the device information management table is referred to, and transaction scheduling for starting'execution of a transaction for a WUSB device for which information indicating that the device is capable of executing the transaction is described in a corresponding

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device information entry is performed. [0036]
Consequently, in the communication system according to the present invention, by adopting a configuration in which the details of a device information entry in the device information management table are changed for each WUSB device, different transaction opportunities can be provided to a plurality of devices in a WUSB cluster. [0037]
Now, the WUSB host receives a request for a transaction from an application or a class driver using each WUSB device, The WUSB host determines the number of time slots necessary for the WUSB cluster in accordance with the total bandwidth necessary■for transactions for the individual WUSB devices in the WUSB cluster and reserves the time slots in the superframe. [0038]
The WUSB host performs registration of device information entries for the individual WUSB devices in accordance with the number of time slots necessary for the transactions for the individual WUSB devices in the WUSB cluster. For example, if the number of necessary time slots is different for each WUSB device, as in a case where some of pipes use the isochronous transfer mode, the WUSB cluster assigns at least some of the reserved MASs only to a

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particular WUSB device. Accordingly, different transaction
opportunities can be provided to the WUSB devices.
[0039]
Furthermore, according to a second aspect of the present invention, a computer program described in a computer-readable format in such a manner that processing for reserving a band within a cluster including a plurality ?f devices is executed by a computer in a communication environment in which a plurality of network upper layers use a superframe at the same time, is characterized by causing the computer to execute the processing including a time-slot reservation step of reserving one or more time slots within the superframe for the cluster and a time-slot assigning step of assigning the reserved one or more time slots to the plurality of devices within the cluster in such a manner that different transaction opportunities are provided to the plurality of devices. . [0040]
The computer program according to the second aspect of the present invention defines a computer program that is described in a computer-readable format in such a manner that predetermined processing is performed by a computer. In other words, when the computer program according to the second aspect of the present invention is installed into the computer, a cooperative function is implemented on the

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computer and the computer is capable of operating as a host generalizing the operations within a cluster in the communication system according to the first aspect of the present invention. Advantageous Effects [0041] '
In a communication system according to the present invention, a scheduling mechanism of a WUSB host is set in such a manner that only a particular WUSB device is capable of using some of the MASs obtained by the WUSB host. Thus, a pipe belonging to the particular WUSB device can be preferentially implemented. Consequently, according to the present invention, an excellent communication system, an excellent communication apparatus, an excel'lent communication method, and an excellent computer program in which priority communication can be performed in units of devices in a WUSB communication environment in which isochronous transfer cannot be used can be provided. [0042]
Other objects, features, and advantages of the present invention will become apparent from the,more detailed description based on embodiment's of the present invention described below and the attached drawings. Brief Description of Drawings [0043]

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I ■ ■ [Fig. 1] Fig. 1 is an illustiration showing a functional
block diagram for performing comm!unication management by
i
using a MAS management table and 'a device information
management table in a WUSB commuhication system.
;i [Fig. 2] Fig. 2 is, an illustration schematically
showing the use statuses of MASs fin a superframe for WUSB,
the use statuses of the MASs being represented by Device
Availability Info shown in Tablets,
[Fig. 3] Fig. 3 is an illustration schematically
showing the use statuses of MASsij in a superf rame for WUSB,
the use statuses of the MASs being represented by Device
Availability Info shown in Table? 1.
Best Modes for Carrying Out the Invention
[0044] ; i|
Hereinafter, embodiments of^the present invention will"
J be explained in detail with reference to the drawings.
[004 5] ,-;
■i
The present invention relat'es to a WUSB communication system utilizing multiband OFDMJUWB. WUSB adopts a physical
I
layer .and a MAC layer designed by WiMedia Alliance and is
^1 capable of using other upper layers in Wireless 1394, WiNet,
f and the like at the same time. jIn WiMedia Alliance, a
network is operated for each superframe having a
.[ ii
predetermined period 'of time. Each superframe is further
I divided into 256 MASs, and upper layers reserve MASs to be
'L

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used for themselves. A WUSB host reserves the number of
necessary MASs and performs transaction scheduling for each
WUSB device within a WUSB cluster.
{0046] .
Fig. 1- shows a functional block diagram for performing communication management by using a MAS management table and a device information management table in a WUSB communication system. Individual functional blocks shown in this figure are implemented in, for example, a WUSB host that generalizes a certain WUSB cluster. [0047]
A class driver is software for implementing a function unique to each device {for example, in the case ot a printer, a function of feeding and printing data), For example, an application, such as a spreadsheet application, calls a i^ class driver for a printer to perform printing or calls a class driver for mass storage to perform reading and writing of a file. An upper layer, such as a class driver or an application, requires a transaction for performing communication with a WUSB device. [0048]
A MAS management table iS|ia table in which reservation
■I
Statuses of MASs in a superframe for a plurality of network upper layers in WUSB, wireless 1394, WiNet, and the like using multiband OFDM UWB at the same time are described.

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performs control, such as analysis of a transaction request from an upper layer, calculation of the number of MASs necessary for communication with a WUSB device, and registration of reserved MASs by referring to a MAS management table. The reserved MASs are assigned to each WUSB device and are registered into the above-mentioned device information management table. In normal WUSB, the same MAS information (that is, all the MASs reserved for a WUSB cluster) is registered in all the entries of a device information management table (as described above). [0053]
A transaction scheduler performs, for each superframe, management of scheduling of a transaction for each WUSB device. More specifically, when:a MAS in a 'superframe reserved by a WUSB host is reached, one of a plurality of devices for which transaction requests exist in a queue is selected, and a corresponding transaction is executed. Here, the device information management table is referred to, and a WUSB device that is not capable of using the MAS {that is, a device for which. "1" is not described in the position of a bit corresponding to the MAS and thus which does not serve as a target of transaction scheduling) is excluded. In addition, in a case where a plurality of WUSB devices that are capable of using the MAS {that is, a plurality of devices for which "1" is described in the position of the

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bit corresponding to the MAS) exist, one of the plurality of WUSB devices is selected in accordance with a predetermined algorithm and the corresponding transaction is executed. For example, the specification for a WUSB controller chip, such as a WHCI (for example, see Non-Patent Document 2), defines that a round-robin method is used for bulk transfer. [0054]
In normal WUSB, a WUSB host directly copies the details
of MASs reserved in a MAS management table to Device
Availability Info of all the entries in a device information
management table. In this case, a bitmap representing MASs
assigned for a WUSB cluster in the MAS management table is
identical to a bitmap of Device Availability Info of each
device in the WUSB cluster in the device information
management table. Thus, equal transaction opportunities are
provided to all the devices in the WUSB cluster.
[0055] Meanwhile, in this embodiment, the communication manager does not cause MASs reserved in the MAS management table to be shared among all the WUSB devices. At least some of the reserved MASs are assigned only to a particular WUSB device (more specifically, a device using higher priority communication). That is, the communication manager does not simply copy the details of MASs reserved in the MAS management table to Device Availability Info of all the

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entries in the .device information management table. The details of Device Availability Info are changed for each device.
[0056]
For example, the communication manager performs processing for registering one-fifth of the MASs reserved in the MAS management table into only Device Availability Info of a device A, registering another one-fifth of the MASs reserved in the MAS management table into Device Availability Info of a device B, and registering the remaining MASs into Device Availability Info of all the other devices in the WUSB cluster. By setting the device information management table as described above, some of the MASs are not shared among all the WUSB devices in the WUSB cluster. Thus, only a particular WUSB device is construed ' as being capable of executing a transaction. When selecting a communication device for the some of the MASs, the transaction scheduler inevitably selects the particular WUSB device.
[0057]
In Table 3 below, an example of the configuration of the device information management table in a case where the details of Device Availability Info are changed for each device is shown.
[0058']

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[Table 3]

DEVICE NECESSARY BANDWIDTH PHY RATE Device Avallabi1ity (nfo
A IMbps 50Mbps 111111110000000011111110000 000
B 2Mbps 100Mbps 000011110000000011111111110 000
C 10Mbps 200Mbps 000011111111000011111110000 000
D 4Mbps 100Mbps 000011110000000011111111110 000
[0059]
Each WUSB device serves as a target of transaction
ii scheduling for a MAS that is marked in a Device Availability
Info field of the WUSB device (as described above) . Thus,.
in some MASs, only a particular device serves as a target of
transaction scheduling. In the example shown in Table 3, in
MASS marked only for a device A, only the device A serves as
a target of transaction scheduling. In MASs marked only for
a device C, only the device C serves as a target of
transaction scheduling. In MASs marked for devices B and D,
both the devices B and D serve as targets of transaction
scheduling.
[0060]
Fig. 2 schematically shows :the use statuses of MASs in
a superframe for WUSB. The use!?statuses of the MASs are
represented by the Device Avail'ability Info shown in Table 3.
In the example shown in this figure, in a time-slot group #1,
only the device A serves as a transaction candidate. In■
time-slot groups #2-1 and #2-2, each of the devices A to D

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serves as a transaction candidate. In a time-slot group #3,
only the device C serves as a transaction candidate. In a
time-slot group #4, the devices B and D serve as transaction
candidates.
[0061] '■;
As shown in Table 3, a configuration in which, in the device information management table, the details of Device Availability Info are changed for each device is adopted. Thus, it should be fully understood that different transaction opportunities can be provided to a plurality of devices in a WUSB cluster. [0062]
However, the device information management table describes transaction schedules in a WUSB cluster. There is no chan'ge in the MAS management table, which manages the reservation statuses of MASs between WUSB and other upper layers. That is, a bitmap obtained by ORing Device Availability Info of individual entries .in the device information management table must be equal to the details of the entry for the WUSB cluster in the ^4AS management table. Table 4 shows the details of a MAS management table corresponding to the device information management table shown in Fig. 2. [0063] [Table 4]

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UPPER LAYER RESERVATION STATUS OF MAS
WUSB 111111111111000011111110000 000
OTHER 000000000000011000000000011 000
[0064]
A procedure for performing communication management by using a MAS management table and a device information management table while changing the details of Device Availability Info for each device in a WUSB cluster is as described below. [0065]
(1) At the initialization of a WUSB device, the
communication manager adds an entry for the WUSB device into
the device information management table.
[0066]
(2) An application or a class driver using the WUSB
device specifies a bandwidth necessary for communication.
If a bandwidth is not specified/ the communication manager
estimates a necessary bandwidth .jby referring to the length
of a queue holding a transaction to be processed and the
like. In a case where a plurality of endpoints are used at
the same time, the total sum of the specified or estimated
bandwidths is obtained. The communication manager registers
the total bandwidth into the entry in the device information
management table.

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[0067]
(3) The communication manager registers the present speed (physical layer rate) of communication with the WUSB device into the corresponding entry in the device information management table. [0068]■
(A) In accordance with the physical layer rate and the necessary bandwidth of the WUSB device, the communication manager calculates the number of MASs necessary for the
i
device. At the same time, the communication manager also calculates the total number of necessary MASs.
[0069]
{5} The communication manager refers to- the MAS management table, and obtains the number of reserved MASs.
[0070]
(6) The communication manager compares the number of necessary MASs with the number of reserved MASs. If the number of MASs is short, the communication manager, reserves a non-reserved MAS in accordance with the DRP. Meanwhile, if an unwanted MAS exists, the communication manager cancels the unwanted MAS. The result of such reservation or cancellation is reflected in the'MAS management table.
[0071]
(7.) The communication manager sets the position of a MAS that can be used by the device in Device Availability

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Info of the entry in the device information management table If there is a particular device that is to start a transaction preferentially, one or more MASs that can be used only by the particular device are prepared in accordance with the number of MASs necessary for the particular device. [0072]
(8) If a new device is connected, the communication
manager returns to {1).
[0073]'
(9) If a device is disconnected, the communication
manager deletes the entry for the corresponding device from
the device information management table. Then, the
communication manager returns to (2).
[0074], ;
(10) In parallel to distributing transactions, which
are generated by an application, to queues, the
communication manager regularly repeats the processing of
(2) and the subsequent processing.
[0075]
Note that in procedure (7) mentioned above, an algorithm for assigning, by a WUSB host, each MAS reserved in the MAS management table to a corresponding device in the WUSB cluster is not particularly limited.
[0076]

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For example, a class driver notifies the communication
manager of a bandwidth necessary for requiring a transaction^
and the communication manager calculates the number of MASs
necessary for transmission of the bandwidth and sets Device
Availability Info. The position of a MAS to be marked may
be selected at random. In this case, independent of
communication of a transaction request, a necessary
bandwidth may be reported. Alternatively, a method in which
a bandwidth that is originally associated with a transaction
request in the isochronous transfer mode is used may be
employed. In the latter case, a state in which bulk
transfer is actually used although it appears to the class
driver as if the isochronous transfer mode was used, can be
implemented.
[0077] In addition, in a case where a plurality of devices capable of using a MAS exist, ahy method can be used for determining which device should execute a transaction preferentially. For example, ai device that executes a transaction preferentially can be determined in accordance with any one of the methods described below. [0078]
Method 1: An application or a class driver transmits to the communication manager a message indicating that "priority communication is.requested".

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Method 2: The administrator of a WUSB host sets, by using a management tool, information indicating which device should have priority in the communication manager.
Method 3: A predetermined algorithm is incorporated in the communication manager- For example, an algorithm for providing a priority communication system to a device having a queue length of a predetermined value or more is adopted. Industrial Applicability [0079]
The present invention has been explained above in detail with reference to particular embodiments. However, it is obvious that those skilled in the art can make modifications or substitutions to the foregoing embodiments without departing from the gist of the pres'ent invention.
-s
[0080]'
In this description, embodiments applied to WUSB have been mainly explained. However, the gist of the present invention should not be limited to the foregoing embodiments The present invention can also be applied, in a similar manner, to various communication systems in which a band is reserved in units of time slots for each predetermined time and in which a reserved time slot is shared between devices within a cluster (or a network). Furthermore, the application area should not be limited to wireless communication and should include various communication

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techniques. [0081]
In short, the present invention has been disclosed by way of exemplary embodiments, and the description should not be construed in a limited manner. The gist of the present invention should be determined with reference to the claims.