Abstract:
Provided are a channel time allocation method and apparatus adopting the same. The channel time allocation method includes: (a) receiving a request of registering in a network from a device; (b) determining whether the network supplying a service required by the device exists; and (c) if the network supplying the requested service exists, performing a procedure of registering in the network, and if the network supplying the requested service does not exist, generating a new network. Since existing MAC protocols can be used in the channel time allocation method, an optimum service is provided in a network environment in which different kinds of services coexist.

Description:
BACKGROUND OF THE INVENTION 
   This application claims the priority of Korean Patent Application No. 2003-64725, filed on Sep. 18, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   1. Field of the Invention 
   The present invention relates to a wireless communication system, and more particularly, a channel time allocation method and apparatus according to characteristics of applications. 
   2. Description of the Related Art 
   A medium access control (MAC) protocol used in wireless communication systems adopts a carrier sense multiple access with collision avoidance (CSMA/CA) method and a time division multiple access (TDMA) method, in which a frequency band is shared between a plurality of users, according to its application. The CSMA/CA method includes generating a random number for each terminal, selecting a channel after a time equivalent to the random number, and using the channel if other terminals are not using the channel. Therefore, quality of service (QoS) does not depend on a terminal type or a transmission data type. However, the TDMA method allocates unique time slots with equal periods to each terminal on a given channel. Therefore, QoS does not depend on a terminal type or a transmission data type. 
     FIG. 1  illustrates a network topology according to the IEEE 802.15.3 standard. 
   A network includes a plurality of devices  101  through  104  and a piconet coordinator (PNC)  105  which relays and manages data and commands among the devices  101  through  104 . A piconet is a network made up of a plurality of devices and a PNC. The devices may be home appliances, such as TVs and camcoders, and any of the devices can be the PNC  105 . However, in general, an audio/video (AV) receiver or a computer is the PNC  105 . The PNC  105  receives a channel time request command from each of the devices  101  through  104  and allocates a channel time to each of the devices  101  through  104 . Each of the devices  101  through  104  directly transmits data to other devices at the allocated channel time. The PNC  105  also performs power save mode management and authentication management. Through the authentication management, the PNC  105  distributes a key for protecting a payload, and each of the devices  101  through  104  transmits and receives encrypted data using the allocated timeslot and the distributed key. 
   Each device used in the IEEE 802.15.3 standard smoothly enters and withdraws from a network, and in particular, it is preferable that a network entry time is less than one second. A MAC protocol of the IEEE 802.15.3 standard uses the TDMA method to guarantee QoS of streaming data. 
     FIG. 2  illustrates a configuration of a superframe to which a channel time is allocated. 
   The superframe includes a beacon  201 , a contention access period (CAP)  202 , two management channel time allocations (MCTAs)  203  and  204 , and a plurality of channel time allocations (CTAs)  205  through  207 . The beacon  201  is control information (an overhead) for transmitting data. The CAP  202  represents allocation of a channel time by contention, and a random access control based on the CSMA/CA is performed in the CAP  202 . The MCTAs  203  and  204  are used for managing the plurality of CTAs  205  through  207 . Payloads to be transmitted are allocated to the plurality of CTAs  205  through  207 . Since one device can transmit several kinds of streams, a plurality of CTAs can exist. Synchronous data, such as an A/V stream, can be transmitted by obtaining a timeslot in a CTA, and asynchronous data can also be transmitted in a required band according to data size. 
   Since a TDMA MAC protocol is designed to be suitable for transmitting/receiving multimedia data, the TDMA MAC protocol cannot properly allocate existing asynchronous data. That is, when the existing asynchronous data should be transmitted, the asynchronous data can only be transmitted in a CAP field or a CTA field allocated during a contention free period (CFP). 
   On the other hand, since a CSMA/CA TDMA MAC protocol is designed to be suitable for transmitting/receiving asynchronous data, the CSMA/CA TDMA MAC protocol cannot properly allocate multimedia data. That is, when isochronous data should be transmitted, since the isochronous data is transmitted in a CAP field, QoS of jitter or delay is not guaranteed. 
   The IEEE 802.15.3 standard provides a method of handling a dependent piconet, such as a child piconet and a neighbor piconet. Accordingly, a private time that allocates a portion of a timeslot to each group and makes each group using the dependent piconet use the timeslot is used. However, in the dependent piconet, except for a PNC, no member of the dependent piconet can perform communication with any member of a parent piconet. 
   SUMMARY OF THE INVENTION 
   The present invention provides a channel time allocation method and apparatus adopting a CSMA/CA or TDMA method according to characteristics of an application and guaranteeing a QoS suitable for the characteristics by grouping a plurality of devices according to QoS characteristics of applications supplied by the devices. 
   The present invention also provides a channel time allocation method and apparatus which allow for a CSMA/CA method and a TDMA method to coexist in a network, and in which a suitable MAC protocol is used according to characteristics of applications using the CSMA/CA and TDMA methods. 
   According to an aspect of the present invention, there is provided a channel time allocation method comprising: (a) receiving a request of registering in a network from a device; (b) determining whether the network supplying a service required by the device exists; and (c) if the network supplying the requested service exists, performing a procedure of registering in the network, and if the network supplying the requested service does not exist, generating a new network. 
   In an exemplary embodiment, the network is a piconet and the new network is a neighbor piconet of a parent piconet. 
   In an exemplary embodiment, in step (c), the neighbor piconet is generated by obtaining a channel time allocation (CTA) from the parent piconet. 
   In an exemplary embodiment, the method furthermore comprises playing a role of a piconet coordinator (PNC) of the neighbor piconet by the device after the neighbor piconet is generated. 
   In an exemplary embodiment, the neighbor piconet uses a medium access control (MAC) protocol different from that used in the parent piconet. 
   According to another aspect of the present invention, there is provided a channel time allocation apparatus comprising: a allocating unit which receives a register request from a device and performs a registering procedure; a piconet generator which generates a neighbor piconet when a piconet supplying a service required by the device does not exist; a PNC operator which makes the device play a role of a PNC of the neighbor piconet after the neighbor piconet is generated and operate as a PNC; and a MAC operator which makes the PNC of the neighbor piconet apply a MAC protocol suitable for characteristics of the service. 
   In an exemplary embodiment, the piconet generator generates the neighbor piconet by obtaining a CTA from a parent piconet. 
   In an exemplary embodiment, the MAC operator uses a MAC protocol different from that used in the parent piconet. 
   According to another aspect of the present invention, there is provided a computer readable medium having recorded thereon a computer readable program for performing the method. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  illustrates a network topology according to the IEEE 802.15.3 standard; 
       FIG. 2  illustrates a configuration of a superframe in which a channel time is allocated; 
       FIG. 3  is a timing diagram illustrating a configuration of a frame used in a CSMA/CA MAC protocol; 
       FIG. 4  illustrates configurations of superframes of a parent piconet and a neighbor piconet; 
       FIG. 5  illustrates a relationship between a parent piconet and a neighbor piconet; 
       FIG. 6  illustrates a CSMA/CA piconet frame operation in a private CTA; 
       FIG. 7  is a flowchart illustrating a channel time allocation method according to an embodiment of the present invention; and 
       FIG. 8  is a block diagram of a channel time allocation apparatus according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, the present invention will be described with reference to the accompanying drawings, in which an exemplary embodiment of the present invention is shown. 
     FIG. 3  is a timing diagram illustrating a configuration of a frame used in a CSMA/CA MAC protocol. 
   When a neighbor piconet cannot use a physical channel, the neighbor piconet uses frequency bands of two piconets (the neighbor piconet and a parent piconet). The neighbor piconet has an independent piconet ID (PNID) and operates independently, but relies on a private CTA of the parent piconet. 
   Referring to  FIG. 3 , a case where a source device  310  intends to transmit data to a destination device  320  will now be described. 
   The source device  310  transmits the data using a channel time allocated by a channel PNC. The destination device  320  receives the data and transmits an acknowledge (ACK) message to the source device  310 . Other station  330 , i.e., any other devices in the same network, waits during the communication time. 
     FIG. 4  illustrates configurations of superframes of a parent piconet and a neighbor piconet. 
   In communication between piconet devices, asynchronous data is transmitted during a CAP. Also, communication between the piconet devices is performed during channel periods of isochronous streams and channel times for the asynchronous data allocated to a contention free period (CFP). 
   Referring to  FIG. 4 , channel timing is divided into a NONE division  410  in which communication is not performed, an N-P division  420  in which communication between a parent PNC and a neighbor PNC is performed, an N-N division  430  in which communication between devices of the neighbor PNC is performed, and an N-P division  440  in which communication between the parent PNC and the neighbor PNC is performed. 
     FIG. 5  illustrates a relationship between a parent piconet and a neighbor piconet. 
   Referring to  FIG. 5 , a network includes a parent piconet  510  and a neighbor piconet  520 . Since the two piconets have a parent/neighbor relationship, the two piconets share a frequency band. By sharing the frequency band, a parent PNC  511  operates using the TDMA method, and one CTA is allocated to a neighbor PNC  521 . The PNC  521  operates using the CSMA/CA method in the allocated CTA. 
   A first device  512  communicates with isochronous data suitable for the TDMA method, and is thus a member of the parent piconet  510 . A third device  522  communicates with asynchronous data suitable for the CSMA/CA method, and is thus a member of the neighbor piconet  520 . A second device  513  simultaneously communicates with the isochronous/asynchronous data, and is thus a member of the two piconets  510  and  520 . 
     FIG. 6  illustrates a CSMA/CA piconet frame operation in a private CTA. 
   Referring to  FIG. 6 , a parent piconet operates using the TDMA method and allocates one CTA (a private CTA) of a superframe to a neighbor PNC. The neighbor PNC operates using the CSMA/CA method using the allocated CTA. Each device can be registered in the parent piconet or a neighbor piconet according to characteristics of an application to which the device is applied. 
     FIG. 7  is a flowchart illustrating a channel time allocation method according to an embodiment of the present invention. 
   A device requests to become a member of a piconet using the TDMA method in step S 710 . Since a service required by the device can be an asynchronous data service or an isochronous data service, the device must be a member of each piconet according to the service required. In other words, service is classified according to characteristics of application data and the device is grouped according to a quality of service (QoS) of the service. 
   In step S 720 , it is determined whether a piconet providing the requested service exists. If a piconet providing the requested service exists, a procedure of registering in the piconet is performed in step S 730 . If the piconet of the requested service does not exist, a neighbor piconet is generated in step S 740 . That is, the neighbor piconet is generated using a CTA allocated from a parent piconet. Then, the device becomes a PNC of the neighbor piconet in step S 750 . 
   The PNC of the neighbor piconet uses a MAC (for example, CSMA/CA) protocol suitable for characteristics of a new service group in step S 760 . When the device withdraws, the neighbor piconet withdraws according to a conventional method. 
     FIG. 8  is a block diagram of a channel time allocation apparatus according to an embodiment of the present invention. 
   The channel time allocation apparatus includes an allocating unit  810 , a piconet generator  820 , a PNC operator  830 , and a MAC operator  840 . The allocating unit  810  receives a request to join a piconet from a device. Since a service required by the device can include an asynchronous data service and an isochronous data service, the device must be made a member of piconets according to a requested service. The allocating unit  810  determines whether a piconet providing the requested service exists. If the piconet providing the requested service exists, the allocating unit  810  performs a procedure of making the device a member of the piconet. 
   The piconet generator  820  generates a neighbor piconet when a piconet supplying the requested service does not exist. That is, the neighbor piconet is generated using a CTA allocated by a parent piconet. The PNC operator  830  sets the device as a PNC of the neighbor piconet after the neighbor piconet is generated and operates as a PNC. The MAC operator  840  assigns a MAC protocol to the PNC of the neighbor piconet (for example, CSMA/CA) suitable for characteristics of a service group. 
   The present invention can use a combination of hardware and software components. The software can be embodied as computer readable code on a computer readable medium. The computer readable medium is any data storage device that can store data that can thereafter be read by a computer system. Examples of the computer readable medium include read-only memory, random-access memory, CD-ROMs, magnetic tape, optical data storage devices. The computer readable medium can also be distributed over a network coupled computer system so that the computer readable code is stored and executed in distributed fashion. Code and code segments required for embodying the present invention can be easily deducted by a programmer of ordinary skill in the art. 
   As described above, according to the present invention, since a suitable MAC protocol can be implemented according to a requested service, optimum performance is achieved. Since a method according to the present invention can use existing MAC protocols, the method can supply a proper service in a network environment in which different kinds of services coexist. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.