WO2006070997A1

WO2006070997A1 - Method for media access controlling and system and method for channel time reservation in distributed wireless personal area networks

Info

Publication number: WO2006070997A1
Application number: PCT/KR2005/003727
Authority: WO
Inventors: Prashant Wason; Balaji Srinivas Holur; Manoj Choudhary; Sunil Dilipkumar Jogi; Thenmozhi Arunan
Original assignee: Samsung Electronics Co., Ltd.
Priority date: 2004-12-30
Filing date: 2005-11-04
Publication date: 2006-07-06

Abstract

Disclosed are a method for Media access controlling and channel time reservation system and methodin distributed wireless personal area networks. A method of Media access controlling for a distributed wireless network including at least one device, includes a device of the distributed wireless network, generating a data slot reservation indicator for devices of the same beacon group,andthe device, broadcasting the generated data slot reservation indicator. 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.

Description

METHOD FOR MEDIA ACCESS CONTROLLING AND SYSTEM AND METHOD FOR CHANNEL TIME RESEVATION IN DISTRIBUTED WIRELESS PERSONAL AREA NETWORKS

Technical Field

[1] The present invention relates to a system for and a method of making a channel time reservation as part of a media access control in a distributed wireless personal area network, which is based on a wireless mobile ad-hoc network. Background Art

[2] A wireless personal area network is defined as a network working within a personalized area of about 10m. 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 Mbps in this personalized area. In such wireless personal area network, the medium is shared among all the devices for communication. Therefore, it requires a medium access method for controlling the medium access of the devices. In a broad sense of meaning, it includes how to access the network, how to transmit data to other device in a desired transmission rate, and how to use optimally the medium.

[3] 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, each device is operated for the whole network in order to manage and coordinate a medium access for all the devices. All the devices request assistance from a 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.

[4] FIG. 1 shows one example of a conventional wireless personal area network.

[5] The network shown in FIG. 1 includes a network called 'piconet,' while supporting a centralized medium access mode based on IEEE802.15.3. In the piconet, one device can be operated as a coordinator, which is called PNC (Piconet Coordinator) 10. PNC 10 allows other device to be connected to the network, and provides a function of allocating and synchronizing a channel (time slot), through which data is transmitted to other devices. This is an ad-hoc centralized wireless personal area network.

[6] FIG. 2 shows a wireless personal area network having no centralized coordinator.

[7] Referring to FIG. 2, a plurality of devices is included, each of which is marked by a dot. Circles made about each device indicate the communication range for each affected device.

[8] The network of FIG. 2 supports a distributed medium access control mode. All the devices cooperates with each other, allows a new device to participate in, 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, any device included in the network is not a dedicated coordinator. This is a distributed ad-hoc WPAN system.

[9] The distributed medium access control mode relies on a timing concept called

'superframe.' The superframe has a fixed length of time, and is divided into a plurality of time windows called 'time slot.' In addition, the time slot is also called a 'medium access slot (MAS).' Most of the time slots are used for the devices to send a beacon. The remaining slots are used to send data. The slot where the beacon is sent is called a 'beacon slot' and the slot where data is sent is called a 'data slot.' The length of a beacon period (BP) may be smaller than that of data section. The beacon slots may be distributed over the slots of a superframe, or appeared together in the starting portion of a superframe. Furthermore, the number of beacons may be fixed and may be varied.

[10] FIG. 3 shows the structure of a conventional superframe.

[11] The superframe structure shown in FIG. 3 is basically defined in the Multiband

OFDM (Orthogonal Frequency Division Modulation) Alliance draft vθ.5. This includes 256 medium access slots (including al l, al2, and a21). Some of the medium access slots (including al 1 and al2) constitute a beacon period alO, which is constructed of beacon slots. The remaining medium access slots (including a21) forms 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 device in the network.

[12] Each medium access slot (including al 1, al2, and a21) forms a superframe of

64ms, and each medium access slot (including al l, al2, and a21) is 256ms.

[13] Information on 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).

[14] 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 each other. In order to reserve such a data slot, a transmitter 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 any device is not operated as a central coordinator for various medium access works. [15] Once a beacon slot is reserved, it is used by the affected device as long as the device is part of the network. 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. Any device cannot reserve a slot already reserved by other device. Disclosure of Invention Technical Problem

[16] A conventional system cannot detect and solve a reservation conflict, which may occur between two devices waiting to reserve a same data slot at the same time. Cosequently, there needs an efficient and reliable method of performing a slot reservation in the distributed wireless personal area network. Technical Solution

[17] 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 ultra wide band WPAN having a distributed network topology.

[18] The above object can substantially be achieved by a method of reserving a channel time in a distributed wireless network including at least one device according to the present invention, the method comprising steps of: a device of the distributed wireless network, making a data slot reservation indicator of devices existing in the same beacon group that the device belongs to; and the device, broadcasting the data slot reservation indicator.

[19] The data slot reservation indictor preferably contains a reservation availability status information regarding data slots of a super frame of the beacon group that the device belongs to.

[20] Preferably, the super frame includes 256 data slots, and the reservation availability status information is about the 256 data slots.

[21] Preferably, the reservation availability status information regarding one data slot is one bit, the reservation status information regarding the data slots that can be reserved by the devices within the beacon group is one bit, and the reservation status information regarding the data slots that cannot be reserved by the devices within the beacon group is zero bit.

[22] The data slot reservation indicator further comprises a length information of the reservation availability status information regarding data slot reservation indicator ID and the data slots of the super frame.

[23] The data slot reservation indicator ID is one byte, and the length information is one byte.

[24] The data slot reservation indicator comprises an information representing the data slots that can be reserved by the devices existing within the beacon group.

[25] The data slot reservation indicator comprises an information representing the data slots that cannot be reserved by the devices existing within the beacon group.

[26] According to the present invention, a method of reserving a channel time in a distributed wireless network including at least one device comprises step of: a device existing in the distributed wireless network, broadcasting a data slot reservation indicator of devices existing in the same beacon group that the device belongs to.

[27] Meanwhile, according to the present invention, a method of reserving a channel time in a distributed wireless network including at least one device comprises steps of: all devices existing in the distributed wireless network, making a data slot reservation indicator of devices existing in the same beacon group that the devices belong to; and said all devices, broadcasting the data slot reservation indicator simultaneously.

[28] Meanwhile, according to the present invention, a method of reserving a channel time in a distributed wireless network including at least one device comprises: 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.

[29] Preferably, the distributed wireless network is configured to be employed in ultra wide band ad-hoc wireless personal area networks.

[30] Preferably, further provided are the operations of: 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.

[31] Preferably, 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.

[32] Preferably, 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.

[33] Preferably, 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. 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.

[34] The data slot reservation indicator indicates the status information in every data slot, using at least one bit, and said at least one bit preferably contains the status in- formtaion of 256 bits about the superframe which includes 256 data slots each being of l bit.

[35] Preferably, 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.

[36] 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.

[37] Preferably, 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.

[38] Further, 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.

[39] Further, 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).

[40] Preferably, further provided operation comprises 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.

[41] Preferably, 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.

[42] It is preferable that 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.

[43] Furthermore, a system for reserving a channel time in a distributed wireless network including at least one device, comprises: 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.

[44] Preferably, the distributed wireless network is configured to be employed in ultra wide band ad-hoc wireless personal area networks.

[45] Preferably, 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.

[46] Preferably, 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.

[47] Preferably, 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.

[48]

[49] *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. 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.

[50] Furthermore, the data slot reservation indicator indicates the status information in each data slot, using at least one bit.

[51] Preferably, 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.

[52] 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.

[53] Preferably, 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.

[54] 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.

[55] 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.

[56] Preferably, 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.

[57] Furthermore, 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.

[58] 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.

[59] Meanwhile, according to the present invention, a medium access control method in a distributed wireless network including at least one device, comprises: 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. [60] Further provided is 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. [61] The data slot reservation indicator preferably 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. [62] The status information preferably 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. [63] Furthermore, the data slot reservation indicator includes the status information of the 256 slots, and the status information is constituted of at least one bit.

Advantageous Effects

[64] 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 or support of a central coordinator device.

[65] 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 a data slot.

[66] For this purpose, the system of the invention can determine a free slot, which is common in both a source device and a counter device. This decision procedure can be varied, depending on whether the device of the system tries a multicast communication or attempts a unicast communication.

[67] 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 network.

[68] Furthermore, the present invention establishes a reservation priority for various types of data traffic, thereby improving the QoS (quality of service) of a network.

[69] In addition, the present invention provides a method of spatially re-using a channel, when multiple channels are simultaneously formed in a spatial region having the same physical medium, without a co-channel interference. Brief Description of the Drawings

[70] FIG. 1 shows one example of a conventional wireless personal area network; [71] FIG. 2 shows a wireless personal area network having no centralized coordinator;

[72] FIG. 3 shows the structure of a conventional superframe;

[73] 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; [74] FIG. 5 shows one example of a data slot reservation indicator according to the invention;

[75] FIG. 6 shows a data slot reservation indicator including a one-bit unit status information according to the invention; [76] FIG. 7 illustrates one example of a data slot request information element according to the invention; [77] FIG. 8 shows one example of a data slot response information element according to the invention; [78] FIG. 9 shows one example of a data slot acknowledge information element according to the invention; [79] FIG. 10 shows one example of a data slot negative acknowledge information element according to the invention; [80] FIG. 11 is a flow chart showing a method of calculating and updating a data slot reservation indicator according to the invention; [81] FIG. 12 is a flow chart explaining a method of determining a free slot according to the invention; [82] FIG. 13 is a flow chart explaining a data slot reservation method according to the invention;

[83] FIG. 14 is a flow chart showing creation of a data slot negative acknowledge information element according to one embodiment of the invention; and [84] FIG. 15 is a flowchart showing creation of a data slot negative acknowledge information element according to another embodiment of the invention.

Best Mode for Carrying Out the Invention [85]

Mode for the Invention [86] The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. [87] 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. [88] 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. [89] The network of FIG. 4 is preferred to be an ultra wide band (UWB) wireless personal area network.

[90] The system of the invention includes a distributed media 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 a network.

[91] Referring to FIG. 4, the system of the invention includes plural devices, along with a device S and a device D. The circle about each device shows a communicable range of the affected device and represents a beacon group for the affected device.

[92] The device S can reserve a data slot for communication with devices within the beacon group, through a data slot reservation procedure according to the invention, and can transmit data in a multicast or unicast mode. Considering a case where the device S wants to communicate with the device D, a device such as the device S, which starts a communication with a device in the group in a unicast or multicast mode, is called a "source device." The device D is called a "counter device."

[93] In order to reserve a channel time, the system of the invention carries out a process of transmitting through a beacon one of a data slot reservation indicator (DSRI), a data slot request information element (DS-req IE), a data slot response information element (DS-res IE), a data slot acknowledge information element (DS-ACK IE), and a data slot negative acknowledge information element (DS-NACK IE). First, each of the above information elements will be explained below and then the operation of the whole system will be described.

[94] The system of the invention is one of media 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 a mark called a "data slot reservation indicator." Using the data slot reservation indicator, the system of the invention can reserve a data slot. Furthermore, by using this information, the communication efficiency can be enhanced in a contention environment not assuming a reservation of data slot, such as an enhanced distributed channel access (EDCA).

[95] The data slot reservation indicator includes status information of all data slots with respect to the possibility of reservation of data slot, from the viewpoint of a device transmitting this mark. Each device determines a slot to be reserved with a counter device, using the data slot reservation indicator. This reservation is performed through a data slot reservation procedure, which will be hereinafter described.

[96] Meanwhile, it may well be understood that the data slot reservation indicator is the information representing data slots which can, or cannot be reserved by the devices of the beacon group.

[97] FIG. 5 shows one example of a data slot reservation indicator according to the invention.

[98] [99] *Ref erring to FIG. 5, the data slot reservation indicator includes a status information of 3 bits (including bθl, bO2), 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 ID of the device broadcasting the data slot reservation indicator and a length field indicating the length of the data slot reservation indicator are omitted here.

[100] The data slot reservation indicator is contained in a beacon, which is sent into 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 affected data slot reservation indicator.

[101] The following table 1 presents one example of a status information of 3 bits in a data slot reservation indicator for a single slot. [102] Table 1

[103] In the 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.

[104] In the case where two or more status information can be used for indicating the status of a device, a larger value of status information is used. 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), a larger status information 111 can be used as a value indicating the status of the affected data slot.

[105] The data slot reservation indicator is used for determining a free slot for reservation among devices.

[106] 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 ever time when a beacon is received 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.

[107] In detail, a deice in network generates data slot reservation indicator of the other devices of the same beacon group it belongs to, and braodcasts it to the network.

[108] In here, 'all' devices of the network may generate data slot reservation indicator of the other devices within the beacon group of themselves, and braodcast the generated data slot reservation indicator 'simultaneously'.

[109] Meanwhile, devices existing in the network may broadcast data slot reservation indicator of the devices of the same beacon group they belong to.

[110] In other words, the data slot reservation indicator represents availability of the slot including the job proceeded by the device in the slot.

[I l l] A data slot reservation indicator may be expanded to include information for multichannel for the purpose of spatial reuse. This is possible in the case where those rules are enabled by physical layers.

[112] 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.

[113] The data slot reservation indicator may have a 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.

[114] Table 2

Status inMeaning formation

[115] 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.

[116] Table 3

[117] In Table 3, the status information '0' means that the affected slot is available in a position of the device broadcasting the affected data slot reservation indicator, and the status information T indicates that the affected slot is not available.

[118] FIG. 6 shows a data slot reservation indicator including a one-bit unit status information according to the invention. [119] 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.

[120] The data slot reservation indicator may be sent from every superframe or some su- perframes, voluntarily by an affected 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.

[121] According to the invention, a data slot reservation for communication between a source device and a counter device is initiated by the source device. The source device sends a data slot request information element to the counter device through a beacon every time when a reservation is required.

[122] Referring to FIG. 7, the data slot request information element of the invention will be described below. [123] The data slot request information element is used by a source device in order to initiate a reservation for a free slot of a counter device. The data slot request information element includes all information requested for reservation, such as a counter device ID, a slot, priority, and a stream form.

[124] FIG. 7 illustrates one example of the data slot request information element according to the invention. [125] The data slot request information element includes a destination ID field (cOl), the number of slots field (cO2), the number of options field (c03), a slot number field (cO4), a format field (c05), a priority field (cO6), a random number field (cO7), and a stream ID field (c08). Each field may be formed of at least one byte.

[126] The destination ID field (cOl) is the ID of a counter device to be reserved. [127] The number of slots field (cO2) represents the number of slots to be requested for reservation.

[128] The number of options field (c03) represents the number of options that a source device provides to a counter device in order to select a slot. The number of slots requested to be selected is given by the number of slots field (cO2). A source device may select plural slots for reservation. A source device may provide a multiple selection such that a counter 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).

[129] The slot number field (cO4) is a list of slots, which is determined by a source device as being free for reservation with a counter device. The entire number of slots to be listed is given by the number of options field (c03).

[130] The format field (c05) represents a reservation format. The following table 4 shows one example of the format field (c05). [131] Table 4

[132] 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.

[133] The priority field (cO6) represents a priority order of reservation in eight steps of 1-8. 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 is a QoS parameter, and is defined by a higher layer. Each device must not use a priority higher than that required for reservation.

[134] The random number field (cO7) is used to solve a reservation conflict, which may be caused due to a multiple reservation among the same priorities. A reservation having a higher random number is given a preference.

[135] The stream ID field (cO8) is used as a sole certificate for the reservation between a source device and a counter device. In the case where multiple reservations for streams between a source device and a counter device are being simultaneously processed, the stream ID field can be used for certifying a special request for reservation.

[136] Since every device hears a beacon of all the neighbor devices present in a network, all the devices including the counter device receives 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 counter device, which is defined by the destination ID field contained in the data slot request information element. The other devices except for the counter device must pay attention to the data slot request information element, in order to detect and solve a reservation conflict.

[137] 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.

[138] 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.

[139] The data slot response information element is used by a counter 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 a counter device. In the case where the counter device accepts the request, a response including a counter device ID, slots, a priority, a stream format, or the like is required.

[140] FIG. 8 shows one example of a data slot response information element according to the invention.

[141] Referring to FIG. 8, a data slot response information element includes a destination

ID field (dOl), a response field (dO2), an allowed number of slots field (dO3), a slot number field (dO4), a format field (dO5), a priority field (dO6), a random number field, and a stream ID field (dO8). Each field is preferred to be constituted of at least one byte.

[142] The destination ID field (dOl) is the ID of a device, which is requested to respond. [143] The response field (dO2) includes a response of a counter device to a source device. The following table 5 shows one example of the response field (dO2). [144] Table 5

[145] 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. [146] The allowed number of slots field (dO3) represents the number of slots accepted by a counter device. The counter device may select less than requested number of slots for various reasons. In the case where the response field (dO2) has a value other than an acceptance (OxOO), the allowed number of slots is zero (0) and thus the value of the allowed number of slots field (dO3) is preferred to be OxOO.

[147] The slot number field (dO4) is a list of slots, which is determined by a source device as being free for reservation with a counter device. The entire number of listed slots is given by an allowed number of slots field (dO3).

[148] The format field (dO5) represents a reservation format. This field must have the same value as the format field (cO5) of a corresponding data slot request information element.

[149] The priority field (dO6) represents a priority order of reservation in eight steps of 1-8. 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 is a QoS parameter, and is defined by a higher layer. Each device must not use a priority higher than that required for reservation.

[150] The random number field (dO7) is used to solve a reservation conflict, which may be caused due to a multiple reservation among the same priorities. A reservation having a higher random number is given a preference.

[151] The stream ID field (dO8) is used as a sole certificate, which is identical to the stream ID field (cO8) 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 counter device are being simultaneously processed, the stream ID field is requested for certifying a special request for reservation.

[152] After receiving a data slot request information element from a certain source device, a data slot response information element is sent as part of a beacon of a counter 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 solution of a reservation conflict.

[153] 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.

[154] 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 counter device.

[155] In order to establish a three-way handshake for a slot reservation between a source device and a counter 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 acknowledge it. Therefore, a three-way handshake required for a successful slot reservation can be achieved.

[156] The data slot acknowledge information element sent by a source device to a counter device defines that the source device has accepted a reservation parameter and data transmission will be started instantly. A data slot acknowledge information element needs to be sent, only when a source device is satisfied with a reservation parameter such as a response from a counter device. Furthermore, if the source device, the initiator of the reservation, is not satisfied with the reservation parameter accepted by the counter device and responded through a data slot response information element, an acknowledgement to the data slot response information element is not required.

[157] FIG. 9 shows one example of a data slot acknowledge information element according to the invention.

[158] Referring to FIG. 9, a data slot acknowledge information element includes a destination ID field (e01), a format field (eO2), and a stream ID field (e03).

[159] The destination ID field (e01) constitutes a field for indicating the ID of a device to which the acknowledgement is directed. [160] The format field (eO2) is a field for defining a reservation format.

[161] 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 define solely a particular reservation request, in the case where plural reservations for streams are performed simultaneously between a source device and a counter device.

[162] 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.

[163] After a source device has received a data slot response information element from some device, a data slot acknowledge information element is sent as part of a beacon of a source device beacon in a 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 device, which has sent a data slot response information element in the previous superframe, receive an acknowledge for a slot reservation. A counter device, which is defined in the destination ID field (e01) of the data slot acknowledge information element, must prepare for receiving data in the acknowledged slot. The other devices except for this device must pay attention to the data slot acknowledge information element for the purpose of detection and solution of a reservation conflict.

[164] 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.

[165] Hereafter, a data slot negative acknowledge information element will be explained, which means a cancellation of reservation procedures or an end of data transmission.

[166] In order to indicate a cancellation or termination of a slot reservation between a source device and a counter 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 certain device means a cancellation of reservation for a certain reason. The reason includes unavailability of reservation for other reasons such as a reservation conflict or a matter of device.

[167] In addition, after a successful reservation, a data slot negative acknowledge information element sent from a certain device means an intention to terminate the stream. In general, termination is initiated by a source device. With respect to a data slot negative acknowledge information element, any acknowledge is not required. A stream or a reservation is cancelled or terminated promptly. [168] If a data slot negative acknowledge information element is appeared 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.

[169] 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 (fO2), and a format field (f03).

[170] The destination ID field (f01) represents the ID of a device, to which a negative acknowledgement is directed, and the stream ID field (fO2) is a sole authenticator for indicating which stream or reservation is to be terminated. The format field (f03) represents a reservation format.

[171] The data slot negative acknowledge information element plays an important role in solving a conflict. The data slot negative acknowledge information element is transmitted by an affected device as part of a beacon. All the device including a device defined in the destination ID field (f01) hears the beacons of neighbor devices in the network, and receives a data slot negative acknowledge information element for a slot 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 (fO2). All other devices except for that device may simply ignore the data slot negative acknowledge information element.

[172] 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.

[173] 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 these information.

[174] A method of making a data slot reservation according to the invention will be hereafter explained. The method of making a 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.

[175] FIG. 11 is a flow chart showing a method of calculating and updating a data slot reservation indicator according to the invention.

[176] All the devices include a data slot reservation indicator in their beacons. Each device updates its own data slot reservation indicator, based on the matters occurring in the data slot and also using the data slot reservation indicator of a neighbor device. [177] 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 contain the updated data slot reservation indicator in its own beacon.

[178] A data slot reservation indicator includes, from its own point of view, all information on the status of all the data slots of a superframe. In this way, what the affected device does in the slot is simply recorded in the status information (triplet) of the slot of the data slot reservation indicator. If the device does not do anything, what its neighbor device does is recorded. If the neighbor device too does not do any work, the value of status information will become '000.' The calculation procedure of a data slot reservation indicator is simple as explained below.

[179] In a data slot reservation indicator, the status information for each slot x may have one value among the five status information as shown in Table 1.

[180] In order to calculate the status information of a data slot reservation indicator for a slot x, a device determines if itself is a sender of unicast or multicast, or a receiver of a unicast stream (Sl 101). If so, the device indicates, using the status information of the slot x, that itself is a sender of unicast or multicast, or a receiver of a unicast stream. Preferably, it is updated to '111' according to Table 1 (Sl 103).

[181] If the device itself is not a sender and a unicast receiver, it determines if itself is a multicast receiver in the slot x (Sl 105). If so, the device indicates, using the status information of the slot x, that itself is a multicast receiver. Preferably, the status information of the slot x is updated to '110' according to Table 1 (Sl 107).

[182] As the result of determination in step Sl 105, if the device is not a sender or a unicast or multicast receiver, it receives a data slot reservation indicator from a neighbor device in order to update the data slot reservation indicator through a neighbor device information (S 1109).

[183] First, after understanding all the information corresponding to the slot x from the data slot reservation indicator of all neighbor devices, which are received through the beacon at the beacon period, a status information having a maximum value is searched from the status information on the slot x, which is found out from all neighbor devices (Sl l l l).

[184] Using the above-found status information, from the affected device point of view, a status information of the data slot reservation indicator of the slot x is obtained and updated. From the affected device point of view, the status information of slot x found out from a neighbor device is not the status of the slot x, and thus a mapped status information is obtained using a desired mapping table (Sl 113).

[185] The mapped status information is a value to be recorded in the data slot reservation indicator of this device for the slot x. The following table 6 shows one example of a desired mapping table. [186] Table 6

[187] That is, in the case where the neighbor device itself is not a sender and a multicast or unicast receiver (in case of one of 000, 100, 101), the affected device corresponds to the case where there is no sender or multicast receiver in the neighbor and thus is mapped into '000.'

[188] Through the above-described processes, the calculation and update of a data slot reservation indicator by each device in a network are carried out. The data slot reservation indicator is calculated and updated every time when a new beacon is received. In addition, the calculation and update of a data slot reservation indicator must be periodically performed, and the period may be equal to the superframe, or larger or smaller than that.

[189] Hereafter, a data slot reservation procedures based on the updated data slot reservation indicator according to the invention will be explained, with reference to FIGS.4 to 12.

[190] It is explained assuming that, in FIG. 4, the device S (hereinafter, referred to as a 'source device S') makes a data slot reservation in order to communicate with the device D (hereinafter, referred to as a 'counter device D').

[191] In the system of the invention, the source device S and the counter device D can distinguish between a multicast stream and a unicast stream, and the data slot reservation procedures may vary with the types of stream.

[192] Two multicast streams share a two-hop region neighbor, and exist without interference to each other. It is because the multicast stream in a single slot is perfectly unidirectional and an acknowledgement for a receiver is not requested as part of a multicast transmission.

[193] In contrast, two unicast streams cannot exist in a two-hop region neighbor in a single slot. It is because of interference by a transmitter or a receiver. This is, a transmitter requests a normal acknowledgement from a receiver, and the acknowledgement may be broadcast into a two-hop region neighbor as well as a sender in the same slot. Therefore, again it can be interfered with other unicast streams present in the two-hop region neighbor. This is, it is because of the bi-directionality of the unicast stream.

[194] The first step of a data slot reservation is to determine a free slot, which is common and vacant in both devices (hereinafter, referred to as a 'common free slot') such that a source device S can transmit and a counter device D can receive.

[195] FIG. 12 is a flow chart explaining a method of determining a free slot according to the invention.

[196] Since a slot reservation procedure is initiated in a source device, a method of the f ree slot determination describes a procedure in the source device.

[197] The source device S first is to determine a free slot in order to transmit to the counter device D in a data section. As shown in the status information table of a data slot reservation indicator, a slot having a status information value '000' will be free such that the source device can transmit (S 1201).

[198] Next, the source device S is to determine a free slot, in which the counter device D does not receive. This is controlled differently, due to a difference between the two streams of multicast and unicast. This is, a multicast stream does not require an acknowledgement through the same slot.

[199] If the source device S is interested in an initiation of a multicast stream, it selects a slot having the status information '000' or '100' in the data slot reservation indicator of the counter device D. In addition, 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 counter device D (S 1203).

[200] Then, a common free slot is determined as the slot selected in the above steps

S 1201 and S 1203, i.e., a slot vacant or free with respect to both the source device S and the counter device D. This common free slot can be used for a reservation between the source device S and the counter device D (S 1205).

[201] In the case where a common free slot is not found, the source device S and the counter device D have no slot for a reservation in-between. In this case, the source device S needs to wait for a certain period of time before retrying to find a free slot. If a free slot is found, a data slot reservation procedure is initiated again.

[202] According to the above-mentioned procedures, when a free slot to be used for a data slot reservation is determined, the source device S performs with the counter device D a data slot reservation procedure, which will be hereafter described.

[203] The slots in the data section of a superframe can be reserved for a synchronized or unsynchronized stream by means of a request response acknowledge, 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 counter device D with respect to a data slot request information element, such slots are to be reserved by the source device S and the counter device D, and their data slot reservation information element is to be updated.

[204] FIG. 13 is a flow chart explaining a data slot reservation method according to the invention.

[205] 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.

[206] Once a common free slot is decided through a free slot determination procedure

(S 1301), the source device S contains a data slot request information element in the beacon thereof (S 1303).

[207] In the case where at least one selectable slot is supplied as part of a reservation request, the counter device D checks to see if the slot is reserved for other device (S1305).

[208] If it is found that other neighbor device does not have performed any data slot reservation procedure for the same slot, the counter device D accepts the request. If not, the counter device D is to select other slot among plural options offered by the source device. If any slot cannot be selected, the counter device rejects the request. An appropriate response (acceptance or rejection) is returned as a data slot response information element of the beacon of the counter device (S 1307).

[209] The counter device D updates its own data slot reservation indicator, only when it has transmitted an acceptance in the data slot response information element. Due to the update, the affected slot is reserved in its own data slot reservation indicator, so that other pair of devices cannot reserve the same slot (S 1309).

[210] When the source device S receives an acceptance response from the counter device

D through a data slot response information element, it makes a decision as to whether an acknowledgement is sent or not. If the source device S determines to send an acknowledgement, the data slot reservation indicator is updated (S 1311).

[211] If the source device S determines to send an acknowledgement in response to the acceptance response of the counter device D, it is to make an acknowledgement by sending a data slot acknowledgement information element in the subsequent superframe. The acknowledgement is sent along with data in the data slot and channel reserved in the data section of the same superframe (S1313).

[212] Therefore, if the counter device D, which has received a data slot acknowledgement information element from the source device S, does not contain a data slot negative acknowledgement information element in its own beacon in the same superframe, the communication occurs in that slot. If it hears an acceptance response from the source device S, the counter device D waits for data to be transmitted in the reserved slot through the reserved channel. This is when any conflict between source and counter devices is not found and an effective and successful transmission is performed due to a reservation. Accordingly, a data slot reservation procedure is completed (S1315).

[213] Through the above-described processes, a data slot reservation for communication between two devices is completed. However, for various reasons, the reservation can be cancelled, and in this case the source device S or the counter device D may send a data slot negative acknowledge information element. A reservation conflict is detected and solved through these processes.

[214] Hereafter, a method of detecting and solving a possible reservation conflict in the system of the invention will be explained.

[215] If a counter device D hears plural requests for a slot reservation between pairs of devices, which have at least one request towards the counter device D, the counter device D will try a mechanism for solving a reservation conflict. In this case, first, the counter device D compares a request directed to it with other requests, based on the higher priority. Second, the comparison is carried out based on the higher random number. If a request from a source device S wins in this comparison, the counter device D accepts the reservation request of the source device S. Otherwise, the reservation request from the source device S is rejected. In addition, instead of rejection, if the source device S provides plural options for slots, the counter device D may accept a request for other slot, which has won in the comparison and no reservation in other pairs of devices.

[216] If the counter device D hears a data slot response information element from at least one neighbor device, together with a data slot request information element from the source device S, the counter device D can not 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 counter device D is free to accept a reservation request for other slot.

[217] FIG. 14 is a flowchart showing creation of a data slot negative acknowledge information element according to one embodiment of the invention.

[218] It is assumed that a source device Sl tries to reserve a slot n with a counter device

Dl and a source device S2 attempts to reserve the same slot n with a counter device D2.

[219] The source device Sl sends to the counter device DI a data slot request information element 1 for the slot n (S 1401). Similarly, the source device S2 sends to the counter device D2 a data slot request information element 2 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 (S 1403).

[220] The counter device Dl and D2 can send a data slot response information element 1 and 2 respectively. Any reservation conflict or other situation does not occur between them (S 1405, S 1407).

[221] The counter device Dl marks the reservation of the slot n in its own data slot reservation indicator (S 1409), and also the counter device D2 marks the reservation of the slot n in its own data slot reservation indicator. The respective data slot reservation indicators are transmitted to the counter devices D 1 and D2 respectively through their own beacon (S 1411).

[222] The source devices Sl and S2 receive a data slot response information element 1, 2 respectively from the counter devices Dl and D2, and then send a data slot acknowledge information element 1, 2 to the counter devices Dl and D2 (S1413, S1415). However, the counter device D2 recognizes the reservation processing of the slot n through the data slot reservation indicator received from the counter device Dl, and also recognizes that the priority is higher than its own reservation and thus a reservation procedure can not be performed. The counter device D2 cancels the reservation process by sending a data slot negative acknowledge information element to the source device S2 (S1417).

[223] FIG. 15 is a flowchart showing creation of a data slot negative acknowledge information element according to another embodiment of the invention.

[224] Similar to FIG. 14, it is assumed that a source device Sl tries to reserve a slot n with a counter device Dl and a source device S2 attempts to reserve the same slot n with a counter device D2.

[225] The source device Sl sends to the counter device DI a data slot request information element 1 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 Sl (S1501).

[226] Similarly, the source device S2 sends to the counter device D2 a data slot request information element 2 for the slot n. Here, the source device S 1 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).

[227] The counter device Dl and D2 can send a data slot response information element 1 and 2 respectively. Any reservation conflict or other situation does not occur between them (S 1505, S 1507).

[228] The source device Sl 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 Sl can send a data slot acknowledge information element after receiving a data slot response information element 1 from the counter device Dl and then (S 1509).

[229] 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 Sl. 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 counter device D2, it cannot send a data slot acknowledge information element, but must send a data slot negative acknowledgement information element (S 1511).

[230] In this way, the reservation conflict between the source device S 1 and the source device S2 can be solved.

[231] 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 solve a reservation conflict, which may occur during the reservation process.

[232] Furthermore, by solving a reservation conflict that may occur in the reservation process, the 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 network.

[233] 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 networks as a computer data combined with carrier waves.

[234] 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.

[235] The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching 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. Industrial Applicability

[236]

Sequence Listing [237]

Claims

[1] A method of reserving a channel time in a distributed wireless network including at least one device, the method comprising steps of: a device of the distributed wireless network, making a data slot reservation indicator of devices existing in the same beacon group that the device belongs to; and the device, broadcasting the data slot reservation indicator. [2] The method of claim 1, wherein the data slot reservation indictor contains a reservation availability status information regarding data slots of a super frame of the beacon group that the device belongs to. [3] The method of claim 2, wherein the super frame includes 256 data slots, and the reservation availability status information is about the 256 data slots. [4] The method of claim 2, wherein the reservation availability status information regarding one data slot is one bit, the reservation status information regarding the data slots that can be reserved by the devices within the beacon group is one bit, and the reservation status information regarding the data slots that cannot be reserved by the devices within the beacon group is zero bit. [5] The method of claim 1, wherein the data slot reservation indicator further comprises a length information of the reservation availability status information regarding data slot reservation indicator ID and the data slots of the super frame. [6] The method of claim 5, wherein the data slot reservation indicator ID is one byte, and the length information is one byte. [7] The method of claim 1, wherein the data slot reservation indicator comprises an information representing the data slots that can be reserved by the devices existing within the beacon group. [8] The method of claim 1, wherein the data slot reservation indicator comprises an information representing the data slots that cannot be reserved by the devices existing within the beacon group. [9] A method of reserving a channel time in a distributed wireless network including at least one device, the method comprising step of: a device existing in the distributed wireless network, broadcasting a data slot reservation indicator of devices existing in the same beacon group that the device belongs to. [10] A method of reserving a channel time in a distributed wireless network including at least one device, the method comprising steps of: all devices existing in the distributed wireless network, making a data slot reservation indicator of devices existing in the same beacon group that the devices belong to; and said all devices, broadcasting the data slot reservation indicator simultaneously.