U.S. patent application number 11/122216 was filed with the patent office on 2005-11-24 for system and method for channel time reservation in distributed wireless personal area network.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Arunan, Thenmozhi, Choudhary, Manoj, Dilipkumar Jogi, Sunil, Srinivas Holur, Balagi, Wason, Prashant.
Application Number | 20050259617 11/122216 |
Document ID | / |
Family ID | 36944064 |
Filed Date | 2005-11-24 |
United States Patent
Application |
20050259617 |
Kind Code |
A1 |
Wason, Prashant ; et
al. |
November 24, 2005 |
System and method for channel time reservation in distributed
wireless personal area network
Abstract
Disclosed are a channel time reservation system and method, and
a data slot reservation method for transmitting data in a medium
access control for a mobile ad-hoc wireless personal area networks.
A reservation conflict, which may occur during a data slot
reservation process, can be detected and solved. For this purpose,
the system exchanges various types of information. Thus, a slot
reservation for communication between devices can be completed in a
shorter period of time. Also, capacity of the network can be
improved by spatial reuse of channel time.
Inventors: |
Wason, Prashant; (Bangalore,
IN) ; Dilipkumar Jogi, Sunil; (Bangalore, IN)
; Srinivas Holur, Balagi; (Bangalore, IN) ;
Choudhary, Manoj; (Bangalore, IN) ; Arunan,
Thenmozhi; (Bangalore, IN) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
|
Family ID: |
36944064 |
Appl. No.: |
11/122216 |
Filed: |
May 5, 2005 |
Current U.S.
Class: |
370/329 ;
370/278 |
Current CPC
Class: |
H04W 74/04 20130101;
H04W 84/18 20130101; H04W 74/002 20130101 |
Class at
Publication: |
370/329 ;
370/278 |
International
Class: |
H04Q 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 30, 2004 |
KR |
2004-116188 |
May 6, 2004 |
IN |
418/CHE/2004 |
Claims
What is claimed is:
1. A method of reserving a channel time in a distributed wireless
network including at least one device, the method comprising:
issuing a reservation request to a destination device with respect
to at least one common free slot, wherein the common free slot is a
data slot which is not used by a beacon group of a source device,
and is a data slot having no data transmitter in a beacon group of
the destination device; and transmitting data after sending an
acknowledgement in response to an acceptance response of the
destination device to a reservation request for a slot, for which
no reservation conflict is found during the source's reservation
request.
2. The method as claimed in claim 1, wherein the distributed
wireless network is configured to be employed in ultra wide band
ad-hoc wireless personal area networks.
3. The method as claimed in claim 1, further comprising: receiving
a data slot reservation indicator, wherein at least one device
within the distributed wireless network broadcasts a status of data
slots, which is derived from its own beacon group; and determining
at least one common free slot according to the data slot
reservation indicator.
4. The method as claimed in claim 3, wherein the data slot
reservation indicator is updated by at least one device each
corresponding to the status of data slot, either when a desired
period comes or when having received a data slot reservation
indicator, which is broadcast by at least one device.
5. The method as claimed in claim 3, wherein the data slot
reservation indicator includes a status information on data slots
of one superframe within a beacon group, to which the respective
device broadcasting the data slot reservation indicator, and the
data slot reservation indicator is broadcasted through a beacon of
at least one device.
6. The method as claimed in claim 5, wherein the status information
indicates, from the view point of the device broadcasting the data
slot reservation indicator, a state where each of the data slot is
either vacant to be used or unavailable.
7. The method as claimed in claim 6, wherein the unavailable state
is either a state where at least one device broadcasting the data
slot reservation indicator corresponds to either a transmitter or a
receiver of a unicast or multicast communication mode, or a state
where either the transmitter or the receiver of the communication
mode exists in the beacon group.
8. The method as claimed in claim 7, wherein the data slot
reservation indicator indicates the status information in every
data slot, using at least one bit.
9. The method as claimed in claim 1, wherein, within the
destination's beacon group, the free slot corresponds to either a
slot vacant without communication or a slot where only a receiver
of multicast communication mode exists, and, within the beacon
group of the source device, the free slot corresponds to a slot
vacant without communication.
10. The method as claimed in claim 1, wherein, if the reservation
request of the source device is for a unicast communication, the
free slot is a vacant slot without communication within the beacon
group of the destination device.
11. The method as claimed in claim 1, wherein the response means a
rejection of the reservation request of the source device, in case
where a reservation other than the reservation request of the
source device is carried out within the beacon group of he
destination device with respect to at least one common free
slot.
12. The method as claimed in claim 1, wherein the acceptance
response is sent in case of a higher priority decided in a desired
manner, when the destination device has received from a neighbor
device within the beacon group of the destination device a separate
reservation request other than the reservation request of the
source device, with respect to the common free slot.
13. The method as claimed in claim 12, wherein the acceptance
response is sent in case of a higher priority, which is determined
based on an arbitrary number contained in the reservation requests,
even if the priority of the different reservation request is the
same as for same slot(s).
14. The method as claimed in claim 1, further comprising canceling
a reservation with the destination device, in spite of an
acceptance response of the destination device, on reception of
another reservation request having a higher priority from other
device(s) within the beacon group of the source device with respect
to the same common free slot(s), after the reservation request of
the source device.
15. The method as claimed in claim 1, wherein the destination
device cancels the reservation request of the source in spite of
the acknowledgement, when the destination device becomes aware,
after the acceptance response, that another acceptance response
having a higher priority for the same common free slot is sent from
other device within the beacon group of the destination device.
16. The method as claimed in claim 15, wherein the destination
device becomes aware of another acceptance response having the
higher priority, through a data slot reservation indicator which is
broadcast on a status of data slot in each beacon group by at least
one device of the distributed wireless network.
17. A system for reserving a channel time in a distributed wireless
network including at least one device, the system comprising: a
destination device configured to receive a reservation request and
to send an acceptance response on reception of the reservation
request for at least one common free slot for which no reservation
has been made within a beacon group of the destination device
during the reservation request; and a source device configured to
send the reservation request as a reservation request of the source
device for at least one common free slot, and to receive the
acceptance response, to send an acknowledgement for the acceptance
response and transmit data, the common free slot being a data slot
having no data transmitter in the beacon group of the destination
device and is not used in a beacon group of the source.
18. The system as claimed in claim 17, wherein the distributed
wireless network is configured to be employed in ultra wide band
ad-hoc wireless personal area networks.
19. The system as claimed in claim 17, wherein the source device
receives a data slot reservation indicator in which at least one
device within the distributed wireless network, which includes
information of respective beacon groups of the at least one device,
and determines at least one free slot according to the data slot
reservation indicator.
20. The system as claimed in claim 19, wherein the data slot
reservation indicator is updated by at least one device each
corresponding to the status of a data slot, either when a desired
period comes or on reception of a data slot reservation indicator,
which is broadcasted by at least one device.
21. The system as claimed in claim 19, wherein the data slot
reservation indicator includes status information on data slots of
one superframe within a beacon group, to which the respective
device broadcasting the data slot reservation indicator belongs,
and the data slot reservation indicator is broadcast through a
beacon of at least one device.
22. The system as claimed in claim 21, wherein the status
information indicates, from the view point of the device
broadcasting the data slot reservation indicator, a state where
each of the data slot either is vacant and available to be used or
is unavailable.
23. The system as claimed in claim 22, wherein the unavailable
state is either a state where at least one device broadcasting the
data slot reservation indicator corresponds to either a transmitter
or a receiver of a unicast or multicast communication mode, or a
state where either the transmitter or the receiver of the
communication mode exists in the beacon group.
24. The system as claimed in claim 22, wherein the data slot
reservation indicator indicates the status information in each data
slot, using at least one bit.
25. The system as claimed in claim 17, wherein, within the beacon
group of the destination device, the free slot corresponds to
either a slot vacant without communication or a slot where only a
receiver of multicast communication mode exists, and, within the
beacon group of the source device, the common free slot corresponds
to a slot vacant without communication.
26. The system as claimed in claim 17, wherein, if the reservation
request of the source device is for a unicast communication, the
common free slot is a slot vacant within the beacon group of the
destination device without communication.
27. The system as claimed in claim 17, wherein the destination
device rejects the reservation request of the source device, in
case where a reservation other than the reservation request of the
source device is carried out within the beacon group of the
destination device with respect to the common free slot.
28. The system as claimed in claim 17, wherein the destination
device sends an acceptance response to a reservation request having
a higher priority decided in a certain desired manner, when the
destination device has received from a neighbor device within the
beacon group of the destination device a different reservation
request other than the reservation request of the source device for
the same common free slot.
29. The system as claimed in claim 28, wherein the destination
device sends an acceptance response to a single reservation
request, based on an arbitrary number contained in reservation
requests, even if multiple reservation requests having same
priority as that of the reservation request of the source
device.
30. The system as claimed in claim 17, wherein the source device
cancels a reservation with the destination device, in spite of an
acceptance response of the destination device, on reception of a
higher priority reservation for the same common free slot, after
the reservation request of the source device.
31. The system as claimed in claim 17, wherein the destination
device cancels the reservation request of the source device in
spite of the acknowledgement, when the destination device becomes
aware, after the acceptance response, that another acceptance
response having a higher priority for the same common free slot is
sent from other device within the beacon group of the destination
device.
32. The system as claimed in claim 31, wherein the destination
device becomes aware of another acceptance response having the
higher priority, through a data slot reservation indicator which is
broadcasted by at least one device of the distributed wireless
network.
33. A medium access control method in a distributed wireless
network including at least one device, the method comprising:
receiving, at a source device, a data slot reservation indicator
from a beacon group of the source device, and broadcasting a data
slot reservation indicator to the beacon group of the source
device; and determining at least one common free slot based on the
data slot reservation indicator, wherein the common free slot is
not used within the beacon group of the source device and is a data
slot having no data transmitter in a beacon group of a destination
device.
34. The medium access control method as claimed in claim 33,
further comprising a step of broadcasting the data slot reservation
indicator updated corresponding to the status of the data slot,
either when the data slot reservation indicator is being
broadcasted, received or at a certain desired interval.
35. The medium access control method as claimed in claim 33,
wherein the data slot reservation indicator includes status
information on 256 slots of one superframe, and the data slot
reservation indicator is broadcasted through a beacon of at least
one device.
36. The medium access control method as claimed in claim 35,
wherein the status information indicates a state of the data slot
as either vacant and can be used or unavailable, from the view
point of the device, which is broadcasting the data slot
reservation indicator.
37. The medium access control method as claimed in claim 36,
wherein the data slot reservation indicator includes the status
information of the 256 slots, and the status information is
constituted of at least one bit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit under 35 U.S.C. .sctn. 119
from Indian Patent Application No. 418/CHE/2004 filed on May 6,
2004, and Korean Patent Application No. 2004-116188, filed on Dec.
30, 2004, the entire contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a system for and a method
of making a channel time reservation as part of a medium access
control in a distributed wireless personal area network, which is
based on a wireless mobile ad-hoc network.
[0004] 2. Description of the Related Art
[0005] A wireless personal area network is defined as a network
working within a personalized area of about 10 meters. IEEE
(Institute of Electrical and Electronics Engineers) prescribes
standards for such a wireless personal area network. An ultra wide
band (UWB) communication technology can provide a transmission rate
of over several hundreds mega bits per second (Mbps) in this
personalized area. In such wireless personal area network, the
wireless medium is shared among all the devices for communication.
Therefore, it requires a medium access method for controlling the
access to the medium by the devices. In a broad sense of meaning,
it includes how to access the network, how to transmit data to
other devices at a desired transmission rate, and how to use the
medium optimally.
[0006] A medium access control for the wireless personal area
network can be designed in two access methods, i.e., a centralized
access mode and a distributed access mode. In the centralized
access, one of the devices acts as a coordinator for the whole
network in order to manage and coordinate a medium access for all
the devices. All the devices request assistance from the
centralized coordinator for a medium access such as participation
to the network or allocation of channel time. In the distributed
access, the medium access is uniformly distributed through all the
devices of the network. In addition, all the devices share the
burden of managing medium access with each other.
[0007] FIG. 1 shows one example of a conventional wireless personal
area network with centralized coordinator.
[0008] The network shown in FIG. 1 includes a centralized network
called a `piconet,` while supporting a centralized medium access
mode based on IEEE802.15.3. One device, which is called a PNC
(Piconet Coordinator) operates as a coordinator in the piconet. A
PNC, such as PNC 10 of FIG. 1, allows other devices to be connected
to the network, and provides a function of allocation and
synchronization of the channel (time slot), through which data is
transmitted to other devices. This is an ad-hoc centralized
wireless personal area network.
[0009] FIG. 2 shows a wireless personal area network having no
centralized coordinator.
[0010] Referring to FIG. 2, a plurality of devices are included and
marked by a dot. Circles made about each device indicate the
communication range for each device.
[0011] The network of FIG. 2 supports a distributed medium access
control mode. Each device cooperates with the other devices, allows
a new device to participate in the network, and shares information
required for performing a medium access control, such as channel
time allocation and synchronization for transmitting data to other
devices, and electric power saving. Therefore, no device in the
network acts as a dedicated coordinator. This is a distributed
ad-hoc WPAN system.
[0012] The distributed medium access control mode relies on a
timing concept called `superframe.` The superframe has a fixed
length in time, and is divided into a plurality of time windows
called a `time slot.` In addition, the time slot is also called a
`medium access slot (MAS).` Some of the time slots are used for the
devices to send a beacon. The remaining slots are used to send
data. The slot where beacons are sent may be called a `beacon slot`
and the slot where data is sent may be called a `data slot.` The
length of a beacon period (BP) may be smaller than that of data
period. The beacon slots may be distributed over the slots of a
superframe, or they may appear together in the starting portion of
a superframe. Furthermore, the number of beacons and beacon slots
may be fixed and may vary.
[0013] FIG. 3 shows the structure of a conventional superframe.
[0014] The superframe structure shown in FIG. 3 is basically
defined in the Multiband OFDM (Orthogonal Frequency Division
Modulation) Alliance MAC (Medium Access Control) draft v0.5. This
includes 256 medium access slots (including a11, a12, and a21).
Some of the medium access slots (including a11 and a12) constitute
a beacon period a10, which is constructed of beacon slots. The
remaining medium access slots (including a21) form a data section
a20 constituted of medium access slots, which can be used by other
devices of the network in order to transmit data to other devices
in the network.
[0015] Each medium access slot (including a11, a12, and a21) forms
a superframe having a length of approximately 65 ms, and each
medium access slot (including a11, a12, and a21) is 256 .mu.s.
[0016] Information of the superframe is broadcast within a beacon,
which is broadcast by each device in the beacon period. Thus,
neighbor devices of that device can use the information for a
subsequent processing. The start time of a superframe is determined
by the start-up of a beacon period, and defines a beacon period
start time (BPST).
[0017] A device must find a free slot in the beacon slot in order
to send a beacon. The device, which sends its own beacon
periodically, is considered as part of the network. Furthermore,
devices need a free data slot for communication with another
device. In order to reserve such a data slot, a source device and a
receiver device must know that a particular data slot is free. The
reservation of data slot is carried out in a completely distributed
manner in the devices, which share information and assist in the
slot reservation with each other. Dissimilar to the centralized
WPAN, it is noted here that none of the devices are operated as a
central coordinator for various medium access tasks.
[0018] Once a beacon slot is reserved, it is used by the device for
sending a beacon as long as the device is part of the network. If
required, a device may change the slot of sending beacon during its
operation. On the contrary, data slots become free if devices stop
using them. Such free data slots are added to a free data slot
pool, and may be reserved for other devices. A device cannot
reserve a slot already reserved by another device.
[0019] A conventional system cannot detect and solve a reservation
conflict proactively, which may occur between two devices wanting
to reserve a same data slot at the same time. Consequently, there
is a need for an efficient and reliable method of performing a slot
reservation in the distributed wireless personal area network.
SUMMARY OF THE INVENTION
[0020] Therefore, it is an object of the present invention to
provide a channel time reservation system and method, which can
make a slot reservation in a completely distributed manner in an
ad-hoc ultrawide band WPAN having a distributed network
topology.
[0021] In order to accomplish the above object, according to one
aspect of the invention, there is provided a method of reserving a
channel time in a distributed wireless network including at least
one device. The method of the invention comprises a step of making
a source's reservation request to a destination device with respect
to at least one common free slot, wherein the common free slot is
not used within a source's beacon group to which the device
belongs, and is a data slot having no data transmitter in a
destination's beacon group which is a beacon group of the
destination device within the source's beacon group, and a step of
transmitting data after sending an acknowledgement in response to
an acceptance response of the destination device to a reservation
request for a slot, for which no reservation is processed within
the destination's beacon group, during the source's reservation
request for the common free slot.
[0022] An example of the distributed wireless network topology may
be implemented for ultrawide band ad-hoc wireless personal area
networks.
[0023] The method of the invention may further comprise a step of
receiving a data slot reservation indicator, wherein at least one
device within the distributed wireless network broadcasts a status
of data slot of its own beacon group, and a step of determining at
least one common free slot according to the data slot reservation
indicator. The data slot reservation indicator represents
availability of the data slots for the purpose of reservation in
order to have data exchanges.
[0024] Preferably, but not necessarily, the data slot reservation
indicator is updated by at least one device each corresponding to
the status of data slot, either when a desired period comes or when
having received a data slot reservation indicator, which is
broadcast by at least one device.
[0025] The data slot reservation indicator is preferred to include
status information of data slots of one superframe within a beacon
group. The data slot reservation indicator can be broadcasted
through the beacon of at least one device.
[0026] Preferably, but not necessarily, the status information
indicates, from the viewpoint of the device broadcasting the data
slot reservation indicator, a state where each of the data slots is
either vacant and available to be used or unavailable. The
unavailable state is either a state where at least one device in
the neighborhood is acting as either a transmitter or a receiver of
a unicast or multicast communication mode, or a state where either
the transmitter or the receiver of the communication mode exists in
the beacon group.
[0027] The data slot reservation indicator indicates the status
information of each data slot, using at least one bit or more
bits.
[0028] Preferably, but not necessarily, for a destination, the
common free slot corresponds to either a slot vacant without
communication in its beacon group or a slot where only a receiver
of multicast communication mode exists in its beacon group. For a
source, the common free slot corresponds to a slot vacant without
communication in its beacon group.
[0029] In addition, if the reservation request is for a unicast
communication, the common free slot is a slot vacant in the
destination's beacon group without communication.
[0030] The response can reject the reservation request, in case
where a reservation other than this reservation request is carried
out by the destination for requested slots.
[0031] In addition, the acceptance response is sent for a higher
priority request, decided in a certain desired manner, when
multiple simultaneous requests received from different devices for
the same common free slots.
[0032] Furthermore, the acceptance response is sent for a higher
number, which is determined based on an arbitrary number contained
in the reservation requests, even if the priorities of the received
multiple simultaneous reservation requests are the same.
[0033] The method of the invention may further comprise a step of
canceling of the reservation, in spite of an acceptance response
from the destination device, when there is received a reservation
request from another device with a higher priority for the same
common free slot after the source's reservation request.
[0034] Preferably, but not necessarily, the destination device
cancels the reservation request in spite of the acceptance
response, when the device receives another acceptance response
having a higher priority for the same common free slot.
[0035] In addition, the destination device may know about another
acceptance response having the higher priority, through a data slot
reservation indicator.
[0036] According to another aspect of the invention, there is
provided a system for reserving a channel time in a distributed
wireless network. The system of the invention comprises: a
destination device, that receives a reservation request and sends
an acceptance response to a reservation request for a slot, for
which no reservation conflict exists due to reservations in the
destination's beacon group during the reservation procedure; and a
source device that sends the reservation request for at least one
common free slot, and receives the acceptance response, and sends
an acknowledgement for the acceptance response and transmits the
data, wherein the common free slot is a slot that is not used by a
transmitter or for communication in the destination's beacon group
and is not used in the source's beacon group to which it
belongs.
[0037] Preferably, but not necessarily, the distributed wireless
network includes an ultra wide band ad-hoc wireless personal area
networks.
[0038] Preferably, but not necessarily, the source device receives
a data slot reservation indicator in which at least one device
within the distributed wireless network broadcasts a status of data
slot of its own beacon group, and determines at least one free slot
according to the data slot reservation indicator.
[0039] Preferably, but not necessarily, the data slot reservation
indicator is updated by at least one device each corresponding to
the status of data slot, either when a desired period comes or when
having received a data slot reservation indicator, which is
broadcast by at least one device.
[0040] The data slot reservation indicator is preferred to include
a status information on data slots of one superframe within a
beacon group, to which the respective device broadcasting the data
slot reservation indicator belongs. The data slot reservation
indicator is broadcast through a beacon of at least one device.
[0041] Preferably, but not necessarily, the status information
indicates, from the viewpoint of the device broadcasting the data
slot reservation indicator, a state where each of the data slot is
either vacant to be used or unavailable. The unavailable state is
either a state where at least one device broadcasting the data slot
reservation indicator corresponds to either a transmitter or a
receiver of a unicast or multicast communication mode, or a state
where either the transmitter or the receiver of the communication
mode exists in the beacon group.
[0042] In addition, the data slot reservation indicator indicates
the status information in every data slot, using at least one
bit.
[0043] Preferably, but not necessarily, within the second beacon
group, the common free slot corresponds to either a slot vacant
without communication or a slot where only a receiver of multicast
communication mode exists. Within the first beacon group, the
common free slot corresponds to a slot vacant without
communication.
[0044] In addition, if the first reservation request is for a
unicast communication, the common free slot is a slot vacant within
the second beacon group without communication.
[0045] Preferably, but not necessarily, the destination device may
reject the first reservation request, in case where a reservation
other than the first reservation request is carried out within the
second beacon group with respect to at least one common free
slot.
[0046] In addition, the counter device may make an acceptance
response to a reservation request having a higher priority decided
in a certain desired manner, when the counter device has received
from a neighbor device within the second beacon group a separate
reservation request other than the first reservation request, with
respect to the common free slot.
[0047] Furthermore, the counter device may make an acceptance
response to a single reservation request, based on an arbitrary
number contained in the reservation requests, even if the separate
reservation request has the same priority as that of the first
reservation request.
[0048] Preferably, but not necessarily, the source device cancels a
reservation with the counter device, in spite of an acceptance
response of the counter device, when having received from other
device within the first beacon group another reservation request
having a higher priority with respect to the common free slot,
after the first reservation request.
[0049] Furthermore, the counter device cancels the first
reservation request in spite of the acknowledgement, when the
counter device becomes aware, after the acceptance response, that
another acceptance response having a higher priority with respect
to the common free slot is made from other device within the second
beacon group.
[0050] Preferably, the counter device becomes aware of the another
acceptance response having the higher priority, through a data slot
reservation indicator which is broadcast on a status of data slot
in each beacon group by at least one device of the distributed
wireless network.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] The above aspects and features of the present invention will
be more apparent by describing certain embodiments of the present
invention with reference to the accompanying drawings, in
which:
[0052] FIG. 1 shows one example of a conventional centralized
wireless personal area network;
[0053] FIG. 2 shows a wireless personal area network having no
centralized coordinator;
[0054] FIG. 3 shows the structure of a conventional superframe;
[0055] FIG. 4 illustrates a network including a channel time
reservation system in a distributed wireless personal area network
according to one embodiment of the invention;
[0056] FIG. 5 shows one example of a data slot reservation
indicator according to the invention;
[0057] FIG. 6 shows a data slot reservation indicator including
one-bit unit status information according to the invention;
[0058] FIG. 7 illustrates one example of a data slot request
information element according to the invention;
[0059] FIG. 8 shows one example of a data slot response information
element according to the invention;
[0060] FIG. 9 shows one example of a data slot acknowledge
information element according to the invention;
[0061] FIG. 10 shows one example of a data slot negative
acknowledge information element according to the invention;
[0062] FIG. 11 is a flow chart showing a method of calculating and
updating a data slot reservation indicator according to the
invention;
[0063] FIG. 12 is a flow chart explaining a method of determining a
free slot according to the invention;
[0064] FIG. 13 is a message sequence chart explaining a data slot
reservation method according to the invention;
[0065] FIG. 14 is a message sequence chart explaining a scenario of
generation of data slot negative acknowledge information element
according to one embodiment of the invention; and
[0066] FIG. 15 is a message sequence chart explaining a scenario of
generation of data slot negative acknowledge information element
according to another embodiment of the invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0067] The present invention is described more fully hereinafter
with reference to the accompanying drawings, in which embodiments
of the invention are shown.
[0068] FIG. 4 illustrates a network including a channel time
reservation system in a distributed wireless personal area network
according to one embodiment of the invention.
[0069] The network in FIG. 4 is a distributed wireless personal
area network (WPAN) that is based on a wireless mobile ad-hoc
network and does not have a central coordinator.
[0070] The network of FIG. 4 is preferred to be an ultra wide band
(UWB) wireless personal area network.
[0071] The system of the invention includes a distributed medium
access control (MAC) means containing a superframe, which is
constructed of a time slot. Also, the system of the invention
provides a method of reserving a channel time using a slot for
communication between devices belonging to the network.
[0072] Referring to FIG. 4, the system of the invention includes
plural devices, along with a device S and a device D. The circle
around each device shows a communications range of the device and
devices in that circle represents the beacon group of the
device.
[0073] The device S (source device) can reserve a data slot for
communication with device(s) within the beacon group, through a
data slot reservation procedure according to the invention, and can
transmit data in a multicast or unicast mode, in a case where the
device S wants to communicate with the device D (destination
device).
[0074] In order to reserve a channel time, the system of the
invention transmits different information elements through the
beacon. Information elements are data slot reservation indicator
(DSRI), data slot request information element (DS-req IE), data
slot response information element (DS-res IE), data slot
acknowledge information element (DS-ACK JE), and data slot negative
acknowledge information element (DS-NACK LE). Each of the above
information elements are explained below and following that the
operation of the whole system is described.
[0075] The system of the invention is one of medium access control
means within a distributed wireless personal area network, and
provides a method where each device in a network can share
information as to whether a data slot is free or occupied, or as to
whether a data slot is allocated for communication. For this
purpose, the system of the invention includes an information
element frame called a "data slot reservation indicator." Using the
data slot reservation indicator, the system of the invention can
reserve a data slot.
[0076] The data slot reservation indicator includes status
information of all data slots with respect to the possibility of
reservation of a data slot, from the viewpoint of a device
transmitting DSRI. Each device determines a slot to be reserved
with a destination device, using DSRI. This reservation is
performed through a data slot reservation procedure, which is
hereinafter described.
[0077] FIG. 5 shows one example of a data slot reservation
indicator according to the invention.
[0078] Referring to FIG. 5, the data slot reservation indicator
includes a status information of 3 bits (including b01, b02), which
represents the status of a data slot. For example, in the case,
where a superframe has 256 data slots, the data slot reservation
indicator has a size of 96 bytes, as shown in FIG. 5. If the
superframe has 128 data slots, the size of the data slot
reservation indicator is reduced to 48 bytes. However, an element
ID field indicating the DSRI information element's ID and a length
field indicating the length of the DSRI are omitted here.
[0079] The data slot reservation indicator is contained in a
beacon, which is sent to the beacon group by each device. The data
slot reservation indicator includes information on all data slot,
which is based on information as to occupation and communication
status of data slots by devices (hereinafter, referred to as a
"neighbor device") within the beacon group of a device broadcasting
the data slot reservation indicator.
[0080] The following table 1 presents one example of the status
information of 3 bits in a data slot reservation indicator for a
single slot.
1TABLE 1 Status information Meaning 000 Free slot 001 Reserved (for
future use) 010 Reserved (for future use) 011 Reserved (for future
use) 100 A multicast recipient is present in the neighbor.
(Receiver Only in neighborhood) 101 A transmitter
(unicast/multicast) or unicast recipient is present in the
neighbor. 110 Receiving multicast data. (Receiver Only) 111
Operating as a transmitter, or a recipient for unicast data.
[0081] In table 1, the status information `100` indicates that only
a neighbor device currently operating as a recipient of multicast
communication mode exists in the neighbor.
[0082] In the case where there are two or more neighbor devices
present in beacon group, then larger value of status information is
used as status information. For example, when a device transmitting
a data slot reservation indicator has a transmitter in the neighbor
(status information 101) and the device itself is a recipient for
unicast data (status information 111); larger status information
111 can be used as a value indicating the status of the data
slot.
[0083] The data slot reservation indicator is used for determining
a free slot for reservation among devices.
[0084] A process for obtaining a status information corresponding
to each slot (hereinafter, referred to as "calculation of a data
slot reservation indicator") is periodically carried out, and also
performed on beacon reception from a neighbor device. The
calculation of a data slot reservation indicator constitutes an
important part of the beacon frame processing in each device. Each
device sends a data slot reservation indicator as part of its own
beacon to thereby help updating other devices' data slot
reservation indicator.
[0085] The data slot reservation indicator presents the
availability status of a slot, including action that can be
performed by the device in the slot.
[0086] A data slot reservation indicator may be expanded to include
information for multi-channel for the purpose of spatial reuse.
This is possible in the case where those rules are enabled by
physical layer.
[0087] In addition, the calculation of a data slot reservation
indicator may be called the `formation of a data slot reservation
indicator.` As shown in Table 1, the bit value of a data slot
reservation indicator may be varied, and also the number of bits
used may be varied.
[0088] The data slot reservation indicator may have status
information of two bits for each slot. In this case, the status
information may present an availability of a device with respect to
data slot reservation of a single channel. The following table 2
shows one example of a two-bit status information.
2TABLE 2 Status information Meaning 00 Free slot 01 Busy because of
multicast Rx in a neighbor 10 Busy because of multicast Tx in a
neighbor 11 Busy because of unicast Tx/Rx in a neighbor or Busy
because a device is in Tx/Rx in the slot
[0089] In addition, a data slot reservation indicator may have a
one-bit status information for each slot. In this case, the status
information represents the availability of device in the slot of a
single channel. The following table 3 and FIG. 6 show one example
of a one-bit status information and a data slot reservation
indicator of that case.
3TABLE 3 Status information Meaning 0 A slot is vacant 1 A slot is
not vacant for a certain reason
[0090] In Table 3, the status information `0` means that the slot
is available in a position of the device broadcasting the data slot
reservation indicator and the status information `1` indicates that
the slot is not available. Those skilled in the art would
appreciate that one can achieve the same objectives even when the
meanings of a `0` and `1` are reversed from that written in Table
3, without deviating from the invention.
[0091] FIG. 6 shows a data slot reservation indicator including a
one-bit unit status information according to the invention.
[0092] The data slot reservation indicator illustrated in FIG. 6 is
related to a superframe having 256 data slots, and includes 256
status information of one-bit unit indicating the status of a data
slot. Dissimilar to FIG. 5, FIG. 6 illustrates an `element ID`
field and a `length` field.
[0093] The data slot reservation indicator may be sent in each
superframe or some superframes, voluntarily by the device or by
request from some devices. In addition, it may be sent in the form
of an information element through a beacon, or in other forms
through other frames.
[0094] According to the invention, a data slot reservation for
communication between a source device and a destination device is
initiated by the source device. The source device sends a data slot
request information element to the destination device through a
beacon every time when a reservation is required.
[0095] Referring to FIG. 7, the data slot request information
element of the invention will be described below.
[0096] The data slot request information element is used by a
source device in order to initiate a reservation for a free slot(s)
with destination device(s). The data slot request information
element includes all information requested for reservation, such as
a destination device ID, slot, priority, and a stream ID.
[0097] FIG. 7 illustrates one example of the data slot request
information element according to the invention.
[0098] The data slot request information element includes a
destination ID field (c01), the number of slots field (c02), the
number of options field (c03), a slot number field (c04), a format
field (c05), a priority field (c06), a random number field (c07),
and a stream ID field (c08). Each field may be formed of at least
one bit.
[0099] The destination ID field (c01) is the ID of a destination
device of the reservation to be formed.
[0100] The number of slots field (c02) represents the number of
slots to be requested for reservation.
[0101] The number of options field (c03) represents the number of
options that a source device provides to a destination device in
order to select a lot. The number of slots requested to be selected
is given by the number of slots field (c02). A source device may
select plural slots for reservation. A source device may provide a
multiple selection such that a destination device can solve a
reservation conflict in a speedy manner. For example, if the source
device wants a reservation of a single slot and plural slots are
determined as free slots for reservation, the number of slots to be
reserved must be one (1).
[0102] The slot number field (c04) is a list of slots, which is
determined by a source device as being free for reservation with a
destination device. The entire number of slots to be listed is
given by the number of options field (c03).
[0103] The format field (c05) represents a reservation format. The
following table 4 shows one example of the format field (c05).
4TABLE 4 Format Meaning 0000 Isochronous unicast stream 0001
Asynchronous unicast stream 0010 Multicast stream 0011 Back-up . .
. Back-up 1111 Back-up
[0104] Here, the values and meanings of the format field (c05) are
not limited to those illustrated in Table 4. However, other types
of reservations having other purposes may be performed using other
types or bit values.
[0105] The priority field (c06) represents a priority order of
reservation in eight steps of 0-7. A higher number indicates a
higher priority. A stream having a higher priority may be
preferentially selected in the case of reservation conflicts. The
priority of reservation can be a QoS parameter, and can be defined
by a higher layer.
[0106] The random number field (c07) is used to solve a reservation
conflict, which may be caused due to a multiple reservation with
the same priorities. A reservation having a higher random number
has a preference.
[0107] The stream ID field (c08) is used as a sole certificate for
the reservation between a source device and a destination device.
In the case where multiple reservations for streams between a
source device and a destination device are being simultaneously
processed, the stream ID field can be used to identify a special
request for reservation.
[0108] Since every device hears a beacon of all the neighbor
devices present in the network, all the devices including the
destination device receive a data slot request information element
for a slot reservation from the source device. The data slot
request information element requests a response from a destination
device, which is defined by the destination ID field contained in
the data slot request information element. The devices other than
the destination device should also pay attention to the data slot
request information element, in order to detect and solve a
reservation conflict.
[0109] The data slot request information element may be sent as
part of a beacon, or, for the same purpose, may be transmitted
having a different name and as part of a different frame.
[0110] A data slot response information element will be described
below, which is used for responding to a request for slot
reservation from a source device through a data slot request
information element.
[0111] The data slot response information element is used by a
destination device in order to respond to a data slot request
information element, which is sent by a source device for a request
for reservation. The data slot response information element
includes an acceptance and a rejection as the response of the
destination device. In the case where the destination device
accepts the request, a response including a destination device ID,
slots, a priority, a stream format, or the like is required.
[0112] FIG. 8 shows one example of a data slot response information
element according to the invention.
[0113] Referring to FIG. 8, a data slot response information
element includes a destination ID field (d01), a response field
(d02), an allowed number of slots field (d03), a slot number field
(d04), a format field (d05), a priority field (d06), a random
number field (d07), and a stream ID field (d08). Each field is
preferred to be constituted of at least one bit.
[0114] The destination ID field (d01) is the ID of a device, which
had requested the reservation.
[0115] The response field (d02) includes a response of the
destination device to a source device. The following table 5 shows
one example of the response field (d02).
5TABLE 5 Response value Meaning Ox00 Accepted Ox01 Rejected, No
free slot Ox02 Rejected, Conflict Ox03 Rejected, Power Save Ox04
Rejected, Going for power off . . . Reserved for future use OxFF
Rejection, No reason specified
[0116] The response values are not limited to those illustrated in
Table 5, but may have a different value for representing a response
of different purpose.
[0117] The allowed number of slots field (d03) represents the
number of slots accepted by the destination device. The destination
device may select less than the requested number of slots for
various reasons. In the case where the response field (d02) has a
value other than an acceptance (0.times.00), the allowed number of
slots is zero (0) and thus the value of the allowed number of slots
field (d03) is preferred to be 0.times.00.
[0118] The slot number field (d04) is a list of slots, which is
determined by a source device as being free for reservation with
the destination device. The entire number of listed slots is given
by an allowed number of slots field (d03).
[0119] The format field (d05) represents a reservation format. This
field must have the same value as the format field (c05) of a
corresponding data slot request information element.
[0120] The priority field (d06) represents a priority order of
reservation in eight steps of 0-7. A higher number indicates a
higher priority. A stream having a higher priority may be
preferentially selected in the case of reservation conflicts. The
priority of reservation can be a QoS parameter, and can be defined
by a higher layer.
[0121] The random number field (d07) is used to resolve a
reservation conflict, which may be caused due to a multiple
reservation with the same priorities. A reservation having a higher
random number has given a preference.
[0122] The stream ID field (d08) is used as a sole certificate,
which is identical to the stream ID field (c08) sent as part of a
corresponding data slot request information element. In the case
where multiple reservations for streams between a source device and
a destination device are being simultaneously processed, the stream
ID field is requested for identifying a special request for
reservation.
[0123] After receiving a data slot request information element from
a source device, a data slot response information element is sent
as part of a beacon of a destination device in the subsequent
superframe. As described above, every device hears a beacon of all
the neighbor devices present in a network. Therefore, all the
devices including the source device, which has sent a data slot
request information element in the previous superframe, receive a
response for a slot reservation. A device, which is defined by the
destination ID field (d01) contained in the data slot response
information element, must respond to the data slot response
information element. The other devices except for this device must
pay attention to the data slot response information element for the
purpose of detection and resolution of a reservation conflict.
[0124] The data slot response information element may be sent as
part of a beacon, or, for the same purpose, may be transmitted
having a different name and as part of a different frame.
[0125] Hereafter, a data slot acknowledge information element will
be described, which is a confirmation indicator sent by a source
device as a response to a data slot response information element
received from a destination device.
[0126] In order to establish a three-way handshake for a slot
reservation between a source device and a destination device, a
confirmation indicator called a data slot acknowledge information
element is used. The data slot acknowledge information element is
used by a device, which sends a data slot request information
element, receives a data slot response information element
corresponding thereto, and acknowledges it. Therefore, a three-way
handshake required for a successful slot reservation can be
achieved.
[0127] The data slot acknowledge information element sent by a
source device to a destination device indicates that the source
device has accepted the reservation and data transmission can be
started. A data slot acknowledge information element is sent, only
when a source device is satisfied with a reservation in response
from the destination device. Furthermore, if the source device, the
initiator of the reservation, is not satisfied with the reservation
response sent by the destination device, an acknowledgement to the
data slot response information element is not sent.
[0128] FIG. 9 shows one example of a data slot acknowledge
information element according to the invention.
[0129] Referring to FIG. 9, a data slot acknowledge information
element includes a destination ID field (e01), a format field
(e02), and a stream ID field (e03).
[0130] The destination ID field (e01) constitutes a field for
indicating the ID of a device to which the acknowledgement is
directed.
[0131] The format field (e02) is a field for defining a reservation
format.
[0132] The stream ID field (e03) is a field for defining a sole
authenticator, which is identical to the stream ID field (c08) sent
as part of a data slot request information element that has
generated this response. This is required in order to identify a
particular reservation request, in the case where plural
reservations for streams are performed simultaneously between a
source device and a destination device.
[0133] A slot reservation by a source device is completed by
transmitting a data slot acknowledge information element in a
superframe subsequent to a superframe through which a data slot
response information element has been received. Then, the source
device prepares for transmitting data in the reserved slots, which
starts from the superframe where the data slot acknowledge
information element is sent.
[0134] After source device has received a data slot response
information element from destination device, a data slot
acknowledge information element is sent as part of a beacon of a
source device in a subsequent superframe. As described above, each
device hears a beacon of all the neighbor devices present in a
network. Therefore, all the devices including the device, which has
sent a data slot response information element in the previous
superframe, receive an acknowledge for a slot reservation. The
destination device, which is defined in the destination ID field
(e01) of the data slot acknowledge information element, must
prepare for reception of data in the acknowledged slot. Devices
other than the destination device must pay attention to the data
slot acknowledge information element for the purpose of detection
and resolution of a reservation conflict.
[0135] The data slot acknowledge information element may be sent as
part of a beacon, or, for the same purpose, may be transmitted
having a different name and as part of a different frame.
[0136] Hereafter, a data slot negative acknowledge information
element will be explained, which means a cancellation of
reservation procedures.
[0137] In order to indicate a cancellation or termination of a slot
reservation between a source device and a destination device, a
data slot negative acknowledge information element can be used by
either one of the two device. During a reservation procedure, a
data slot negative acknowledge information element sent by a device
means a cancellation of reservation of the indicated reservation
for some reason. The reason may be unavailability of reservation
due to reservation conflict or some other device specific
reason.
[0138] In addition, after a successful reservation, a data slot
negative acknowledge information element sent from a device means
an intention to terminate the stream. In general, termination is
initiated by a source device. No acknowledgement is required for a
data slot negative acknowledge information element, it results in
termination of the reservation.
[0139] If a data slot negative acknowledge information element
appears during a reservation procedure, it means that the
reservation being processed is cancelled. After a reservation is
successfully performed and while a communication is carried out, a
data slot negative acknowledge information element means a formal
termination of stream.
[0140] FIG. 10 shows one example of a data slot negative
acknowledge information element according to the invention.
Referring to FIG. 10, a data slot negative acknowledge information
element includes a destination ID field (f01), a stream ID field
(f02), and a format field (f03).
[0141] The destination ID field (f01) represents the ID of a
device, to which a negative acknowledgement is directed, and the
stream ID field (f02) is a sole authenticator for indicating which
stream or reservation is to be terminated. The format field (f03)
represents a reservation format.
[0142] The data slot negative acknowledge information element plays
an important role in resolving a conflict. The data slot negative
acknowledge information element is transmitted by an affected
device as part of a beacon. All the devices, including a device
defined in the destination ID field (f01), hear the beacons of
neighbor devices in the network, and receive a data slot negative
acknowledge information element for the reservation. A device
defined in the destination ID field (f01), which is one field of a
data slot negative acknowledge information element, is requested to
cancel the reservation, or to terminate the stream defined in the
stream ID field (f02). All other devices except for that device may
simply ignore the data slot negative acknowledge information
element.
[0143] The data slot negative acknowledge information element may
be sent as part of a beacon, or, for the same purpose, may be
transmitted having a different name and as part of a different
frame.
[0144] The types of information sent and received through the
beacon of each device are explained above. Prior to transmit data
within a network, a data slot reservation performed among devices
is constituted of a process for exchanging this information.
[0145] A method of data slot reservation according to the invention
is hereafter explained. The method of data slot reservation
includes a calculation of a data slot reservation indicator and a
slot reservation process. The slot reservation process includes a
determination of free slot and a reservation process.
[0146] FIG. 11 is a flow chart showing a method of calculating and
updating a data slot reservation indicator according to the
invention.
[0147] All the devices include a data slot reservation indicator in
their beacons. Each device updates its own data slot reservation
indicator, based on its own status during a data slot and also
using the data slot reservation indicator of a neighbor device.
[0148] Regardless of whether or not a device is interested in a
data slot reservation, the device is required to update its own
data slot reservation indicator and broadcast the updated data slot
reservation indicator in its own beacon.
[0149] A data slot reservation indicator includes the status of all
the data slots of a superframe from the device's own point of view.
So, the status of the device in the slot is recorded in the status
information (triplet) in a data slot reservation indicator. If the
device does not communicate during the slot, then its neighbor
device(s)' status is (are) recorded as status information. If the
neighbor device(s) is (are) also silent during the slot, then the
value of status information becomes `000.` The calculation
procedure of a data slot reservation indicator is explained
below.
[0150] The status information for each slot can have one of the
values listed in Table 1.
[0151] In order to calculate the status information of a data slot
reservation indicator for a slot, a device determines if it is a
source of unicast or multicast, or a receiver of a unicast stream
(S1101). If so, the device indicates status as `111` according to
Table 1 (S1103).
[0152] If the device itself is not a unicast or multicast
transmitter and a unicast receiver, it determines if it is a
multicast receiver in the slot x (S1105). If so, the device
indicates status as `110` according to Table 1 (S1107).
[0153] As the result of the determination in step S1105, if the
device is not a source or a receiver, it receives a data slot
reservation indicator from neighbor device(s). It uses those data
slot reservation indicators in order to update its own data slot
reservation indicator (S1109).
[0154] After understanding all the information corresponding to a
slot from the data slot reservation indicator of all neighbor
devices, the status information having a maximum value is selected
for the slot, which is found out from all neighbor devices
(S1111).
[0155] Using the above selected status information, from the
neighbor device, a status information of the data slot reservation
indicator for the slot is obtained from mapping table (Table 6),
from the device's point of view and updated (S1113).
[0156] The mapped status information value is recorded in the data
slot reservation indicator of this device for the slot. The
following table 6 shows one example of a desired mapping table.
6 TABLE 6 Status information received from neighbor device Mapped
status information 000 000 100 000 101 000 110 100 111 101
[0157] That is, in the case where the neighbor device is not a
transmitter or receiver (status 000, 100 or 101), the affected
device corresponds to the case where there is no sender or receiver
in the neighbor and thus is mapped into `000.`
[0158] Through the above described processes, calculation and
updating of a data slot reservation indicator by each device in a
network are carried out. The data slot reservation indicator should
be calculated and updated every time that a new data slot
reservation indicator is received.
[0159] Hereafter, data slot reservation procedures based on the
updated data slot reservation indicator according to the invention
will be explained, with reference to FIGS. 4 and 12.
[0160] Referring to FIG. 4, device S (hereinafter, referred to as a
`source device S`) wants to reserve slots in order to communicate
with the device D (hereinafter, referred to as a `destination
device D`).
[0161] Data slot reservation procedures may vary with the types of
stream, i.e. multicast stream and unicast stream.
[0162] Two multicast streams share a two-hop region neighborhood in
the same slot(s), and exist without interference with each other.
It is because the multicast stream in a single slot is perfectly
unidirectional and an acknowledgement for the data is not
required.
[0163] In contrast, two unicast streams cannot exist in a two-hop
region neighborhood in the same slot(s) because of interference by
a transmitter or a receiver. Because the transmitter requests a
normal acknowledgement from a receiver, and the acknowledgement is
also broadcasted, there can again be interference with other
unicast streams present in the two-hop region neighborhood. This is
because of the bi-directionality of the unicast stream.
[0164] The first step of a data slot reservation is to determine a
free slot, which is common in both devices (hereinafter, referred
to as a `common free slot`) such that a source device S can
transmit and a destination device D can receive.
[0165] FIG. 12 is a flow chart explaining a method of determining a
free slot according to the invention.
[0166] Since a slot reservation procedure is initiated by the
source device, the method of the free slot determination describes
a procedure for the source device.
[0167] The source device S first is to determine a free slot in
order to transmit to the destination device D in a data section.
So, slot(s) having a status information value `000` will be free
such that the source device can transmit (S1201).
[0168] Next, the source device S is to determine a free slot, in
which the destination device D can receive. This is controlled
differently, due to a different nature of acknowledgement policies
of multicast and unicast streams.
[0169] If the source device S is interested in an initiation of a
multicast stream, it selects slot(s) having the status information
`000` or `100` in the data slot reservation indicator of the
destination device D. If the source device S is interested in an
initiation of a unicast stream, it selects a slot having the status
information `000` in the data slot reservation indicator of the
destination device D (S1203).
[0170] Then, a common free slot(s) is determined as the slot
selected in the above steps S1201 and S1203, i.e., a slot free with
respect to both the source device S and the destination device D.
This common free slot can be used for a reservation between the
source device S and the destination device D (S1205).
[0171] In the case where a common free slot is not found, the
source device S and the destination device D have no slot for a
reservation. In this case, the source device S should wait for a
certain period of time before retry for reservation.
[0172] After deciding a common free slot according to the above
mentioned procedures, the source device S initiates the data slot
reservation procedure with the destination device D, which is
described hereafter.
[0173] The slots in the data section of a superframe can be
reserved for an isochronous or asynchronous stream by means of a
request, response and acknowledgement, which is based on a
three-way handshake. If the source device S has received a data
slot response information element of acceptance from the
destination device D in response to a data slot request information
element then, those slots are considered to be reserved by the
source device S and the destination device D, and their data slot
reservation information elements are updated.
[0174] FIG. 13 is a flow chart that explains a data slot
reservation method according to the invention.
[0175] The data slot reservation procedure is configured such that
a common free slot between a pair of devices can be reserved for
the purpose of communication.
[0176] Once a common free slot is decided through the free slot
determination procedure (S1301), the source device S includes data
slot request information element in the beacon thereof (S1303).
[0177] In the case where at least one selectable slot is provided
as part of a reservation request, the destination device D checks
to see if the slot is reserved for another device (S1305).
[0178] If it is found that a neighbor device has not performed any
data slot reservation procedure for the same slot, the destination
device D accepts the request. If not, the destination device D may
select other slot(s) among plural options offered by the source
device. If any slot could not be selected, the destination device
rejects the request. An appropriate response (acceptance or
rejection) is sent as a data slot response information element of
the beacon of the destination device (S1307).
[0179] The destination device D updates its own data slot
reservation indicator, when it has transmitted an acceptance in the
data slot response information element. So, the selected slot(s) is
reserved and marked as unavailable according to its stream type
(Refer to Table 1) in its own data slot reservation indicator, so
that other pair of devices cannot reserve the same slot(s)
(S1309).
[0180] When the source device S receives an acceptance response
from the destination device D through a data slot response
information element, it decides on sending acknowledgement for the
reservation. If the source device S determines to send an
acknowledgement, the data slot reservation indicator is updated
(S1311).
[0181] If the source device S sends an acknowledgement in response
to the acceptance response of the destination device D by sending a
data slot acknowledgement information element in the subsequent
superframe (S1313), the source device S can start sending data in
the reserved slot.
[0182] Therefore, if the destination device D has received a data
slot acknowledgement information element from the source device S,
the destination device D waits for data to be received in the
reserved slot through the reserved channel. This is the case when
there are no conflicts of the reservation found either for the
source or destination devices, and successful communication is
performed on the reservation. Accordingly, a data slot reservation
procedure is completed (S1315).
[0183] Through the above described processes data slot reservation
for communication can be performed. However, for various reasons,
the reservation can be cancelled, and in this case the source
device S or the destination device D may send a data slot negative
acknowledge information element. A reservation conflict is detected
and resolved through those processes.
[0184] Hereafter, a method of detecting and resolving a reservation
conflict in the system of the invention is explained.
[0185] If a destination device D hears multiple requests for a
reservation from different devices, which have at least one request
towards the destination device D, the destination device D compares
all requests, based on the higher priority, and then comparison is
carried out based on the higher random number. If a request from a
source device S wins in this comparison, the destination device D
accepts the reservation request of the source device S. Otherwise,
the reservation request from the source device S will be rejected.
In addition, instead of rejection, if the source device S provides
multiple options for slots, the destination device D may accept the
request for other slot(s), which has won in the comparison and no
reservation in other pairs of devices.
[0186] If the destination device D hears a data slot response
information element from at least one of the neighbor device,
together with a data slot request information element from the
source device S for same slot(s) or reservation, the destination
device D cannot accept the reservation request for the slot. This
rule enables a `first-start-first-reserve` principle with respect
to reservations for a same slot. If a source device S offers plural
options, the destination device D is free to accept a reservation
request for other slot.
[0187] FIG. 14 is a message sequence chart showing creation of a
data slot negative acknowledge information element according to one
embodiment of the invention.
[0188] It is assumed that a source device S1 tries to reserve a
slot n with a destination device D1 and a source device S2 attempts
to reserve the same slot n with a destination device D2.
[0189] The source device S1 sends data slot request information
element 1 to the destination device D1 for the slot n (S1401).
Similarly, the source device S2 sends data slot request information
element 2 to the destination device D2 for the slot n. Here, the
data slot request information element 1 has a higher priority, as
compared with the data slot request information element 2
(S1403).
[0190] The destination device D1 and D2 can send a data slot
response information element 1 and 2 respectively. No reservation
conflict situation is identified between them (S1405, S1407).
[0191] The destination device D1 marks the reservation of the slot
n in its own data slot reservation indicator (S1409), and also the
destination device D2 marks the reservation of the slot n in its
own data slot reservation indicator. The respective data slot
reservation indicators are advertised through their own beacon
(S1411).
[0192] The source devices S1 and S2 receive a data slot response
information element 1, 2 respectively from the destination devices
D1 and D2, and then send data slot acknowledge information element
1, 2 to the destination devices D1 and D2 (S1413, S1415). However,
the destination device D2 recognizes the reservation processing of
the slot n through the data slot reservation indicator received
from the destination device D1, and also recognizes that the
priority is higher than its own reservation and thus a reservation
can not be continued. The destination device D2 cancels the
reservation by sending a data slot negative acknowledge information
element to the source device S2 (S1417).
[0193] FIG. 15 is a message sequence chart showing creation of a
data slot negative acknowledge information element according to
another embodiment of the invention.
[0194] Similar to FIG. 14, it is assumed that a source device S
tries to reserve a slot n with a destination device D1 and a source
device S2 attempts to reserve the same slot n with a destination
device D2.
[0195] The source device S1 sends data slot request information
element 1 to the destination device D1 for the slot n. This data
slot request information element 1 can be heard by the source
device S2 present in the same beacon group as the source device S1
(S1501).
[0196] Similarly, the source device S2 sends data slot request
information element 2 to the destination device D2 for the slot n.
Here, the source device S1 can hear the data slot request
information element 2. However, the data slot request information
element 1 has a higher priority, as compared with the data slot
request information element 2 (S1503).
[0197] The destination device D1 and D2 can send a data slot
response information element 1 and 2 respectively. Any reservation
conflict could not be identified by destination devices (S1505,
S1507).
[0198] The source device S1 compares the data slot request
information element 1 with the data slot request information
element 2 received from the source device S2. Since the data slot
request information element 1 has a higher priority, the source
device S1 can send a data slot acknowledge information element
after receiving a data slot response information element 1 from the
destination device D1 (S1509).
[0199] The source device S2 compares the data slot request
information element 2 with the data slot request information
element 1 received from the source device S1. However, the data
slot request information element 1 has a higher priority. Thus,
even if the source device S2 receives a data slot response
information element 2 from the destination device D2, it cannot
send a data slot acknowledge information element, but must send a
data slot negative acknowledgement information element (S1511).
[0200] In this way, the reservation conflict between the source
device S1 and the source device S2 can be resolved.
[0201] The methods as described above enable a data slot
reservation among devices in a distributed wireless personal area
network. In addition, they can detect and resolve a reservation
conflict, which may occur during the reservation process.
[0202] Furthermore, the reservation conflict resolution may occur
during the reservation process and then a new data slot reservation
can be carried out in a speedy manner. Since options for plural
slots are offered for reservation, the reservation can be more
rapidly processed. Therefore, the efficiency of the whole system
can be enhanced and the energy consumption can be reduced, thereby
extending the service life of the device.
[0203] The present invention can be embodied into a method, a
device or a system. In addition, in the case where the present
invention is embodied into a computer software, the constitutional
elements of the invention can be replaced by code segments required
for executing required actions. The program or the code segments
can be stored in a medium, which can be processed by a
microprocessor, and also can be transmitted through a transmission
medium or a communication network as a computer data combined with
carrier waves.
[0204] A medium, which can be processed by a microprocessor,
includes an electronic circuit, a semiconductor memory element, a
ROM, a flash memory, an EEPROM, a floppy disk, an optical disk, a
hard disk, an optical fiber, a wireless network, or the like, which
can transmit and store information. The computer data includes
data, which can be transmitted through an electrical network
channel, an optical fiber, an electromagnetic field, a wireless
network, and the like.
[0205] As described above, according to the present invention, in a
data slot reservation for data transmission in a distributed
wireless personal area network, all the devices within the wireless
personal area network can make a channel time reservation with a
data slot required for their communication, in a completely
distributed manner without help from or support of a central
coordinator device.
[0206] In addition, beyond detection of an already-occurred
reservation conflict, the invention can detect and solve a
potential reservation conflict, which may occur during the
reservation process of data slot(s).
[0207] For this purpose, the system of the invention can determine
a free slot, which is common in both a source device and a
destination device. This decision procedure can be varied,
depending on whether the device of the system tries a multicast
communication or attempts a unicast communication.
[0208] In addition, a data slot reservation for communication among
devices can be completed within a shorter period of time, by means
of the method of solving a reservation conflict according to the
invention. Therefore, the efficiency of the whole system can be
enhanced and the energy consumption can be reduced, thereby
extending the service life of the device.
[0209] Furthermore, the present invention establishes a reservation
priority for various types of data traffic, thereby improving the
QoS (quality of service) of a network.
[0210] In addition, the present invention provides a method of
spatially re-using the channel time, when multiple reservations are
simultaneously formed in a spatial region having the same physical
medium, without any interference.
[0211] The foregoing embodiment and advantages are merely exemplary
and are not to be construed as limiting the present invention. The
present concept can be readily applied to other types of
apparatuses. Also, the description of the embodiments of the
present invention is intended to be illustrative, and not to limit
the scope of the claims, and many alternatives, modifications, and
variations will be apparent to those skilled in the art.
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