Abstract:
A method for multi-band ultra wide band (UWB) communication of a frequency hopping type. The method includes requesting a piconet coordinator (PNC) of a piconet to allocate a time, at which data is transmitted, according to a predetermined PNC sequence using frequency hopping. Information regarding the time, which is allocated by the PNC for data transmission, is received according to the PNC sequence using the frequency hopping. Then, data is transmitted to a predetermined device according to the information regarding the time allocated by the PNC for data transmission. Since a mechanism needed by a medium access control (MAC) layer for the multi-band UWB communication of the frequency hopping type is provided, the multi-band UWB communication of the frequency hopping type is accomplished.

Description:
[0001]     This application claims priority of Korean Patent Application No. 10-2003-0072783 filed on Oct. 18, 2003 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a medium access control (MAC) mechanism for supporting a multi-band ultra wide band (UWB) communication system, and more particularly, to a method of generating a piconet suitable for multi-band UWB communication of a frequency hopping type, and associating and communicating with a new device.  
         [0004]     2. Description of the Related Art  
         [0005]     With the rapid development of communication technology, ad-hoc communication or ubiquitous networks have been vigorously researched and developed. Currently, technology relating to a wireless personal area network (WPAN) is getting much attention in an ad-hoc or ubiquitous network environment. In communications over the WPAN, every device within a piconet defined by an Institute of Electrical and Electronics Engineers (IEEE) 802.15.3 standard can access a wireless medium (WM) according to information provided by a piconet coordinator (PNC). In other words, a single piconet includes a PNC and one or more devices, and data can be transmitted between the PNC and a device or between the devices using an ad-hoc method.  
         [0006]     UWB communication systems have been implemented in a field of a physical layer (PHY) under a WPAN environment. Initially, UWB technology was used for military purposes. Since 1994, the UWB technology has been researched and developed by some venture companies and laboratories for commercial use. In 2002, the Federal Communications Commission in the United States permitted the commercial use of the UWB technology. At present, the IEEE 802.15 Working Group (WG) is working on standardization. A UWB communication system is compatible with existing wireless communication services without securing additional frequency resources and allows high-speed communication with low power since a UWB communication system uses very short pulses. In addition, since a bandwidth of a UWB signal is very wide, e.g., a several GHz, in a frequency domain, the UWB signal is detected in a level lower than a noise level in the frequency domain and thus rarely affects other devices. Moreover, since the UWB signal has a pulse of a very small duty cycle, it offers various advantages including a high transfer rate, multiple access implementation, and low multipath interference.  
         [0007]     Although the current UWB technology is divided into a single-band mode and a multi-band mode, recently, the multi-band mode has been increasingly researched and developed. Unlike an initial single-band system, a multi-band UWB system uses a UWB signal containing a carrier wave and adopts a lot of conventional technology relating to communication systems. A multi-band UWB system can be constructed using devices having less bandwidth than a single-band system and uses a frequency hopping type of communication, and therefore, the multi-band UWB system has spectral flatness compared to the single-band system.  
         [0008]     However, the existing IEEE 802.15.3 standard lacks a mechanism for multi-band UWB communication. Therefore, a need exists for a method for multi-band UWB communication in the WPAN environment.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides a mechanism needed by a medium access control (MAC) layer for multi-band ultra wide band (UWB) communication.  
         [0010]     According to an exemplary embodiment of the present invention, there is provided a method for multi-band UWB communication of a frequency hopping type, the method including (a) requesting a piconet coordinator (PNC) of a piconet to allocate a time, at which data is transmitted, according to a predetermined PNC sequence using frequency hopping; (b) receiving information regarding the time, which is allocated by the PNC for data transmission, according to the PNC sequence using the frequency hopping; and (c) transmitting data to a predetermined device according to the information regarding the time allocated by the PNC for data transmission.  
         [0011]     The method may further comprise associating a device with the piconet using a predetermined scheme. Here, the associating with the piconet may comprise determining available channels by scanning channels, acquiring information regarding the PNC sequence from the PNC that uses some or all of the scanned channels, transmitting an association request to the PNC, the association request comprising information regarding the available channels, and receiving an association reply permitting the association from the PNC. The determining of the available channels may comprise determining the available channels based on a channel environment. Also, the acquiring of the information may comprise finding the PNC sequence in information regarding the PNC sequence, which is transmitted by the PNC through a particular channel among the determined available channels. The information regarding the PNC sequence is preferably a PNC sequence number representing the PNC sequence or a series of channel numbers according to the PNC sequence. The transmitting of the association request may comprise transmitting the association request comprising the information regarding the available channels to the PNC according to the PNC sequence using the frequency hopping.  
         [0012]     Also, the method may further comprise receiving information regarding channels available to member devices in the piconet from the PNC. Here, the transmitting of data may comprise transmitting the data to the predetermined device using channels common to a set of the determined available channels and to a set of channels available to the predetermined device. In this case, the data may be transmitted to the predetermined device according to the PNC sequence using the frequency hopping. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The above and other features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:  
         [0014]      FIG. 1  illustrates members included in a single piconet;  
         [0015]      FIG. 2  illustrates a spectrum of a signal of a multi-band ultra wide band (UWB) communication system in a frequency domain;  
         [0016]      FIG. 3  illustrates frequency hopping sequences for minimizing interference between piconets performing multi-band UWB communication of a frequency hopping type;  
         [0017]      FIG. 4  illustrates frequency hopping sequences of devices transmitting data in a single piconet, according to an embodiment of the present invention;  
         [0018]      FIGS. 5A and 5B  illustrate states before and after, respectively, a device associates with a piconet having a particular piconet coordinator (PNC) sequence;  
         [0019]      FIG. 6  illustrates a structure of a frame made by a device to transmit an association request command to a PNC, according to an embodiment of the present invention;  
         [0020]      FIG. 7  illustrates a structure of a device information field that is included in a PNC information command frame made by a PNC to indicate that a new device is associated with a piconet, according to an embodiment of the present invention;  
         [0021]      FIG. 8  is a flowchart of a procedure in which a device is associated with a piconet, according to an embodiment of the present invention;  
         [0022]      FIG. 9  is a flowchart of a procedure in which one device transmits data to another device; and  
         [0023]      FIG. 10  illustrates a structure of a superframe defined by an Institute of Electrical and Electronics Engineers (IEEE) 802.15.3 standard. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings.  
         [0025]      FIG. 1  illustrates members included in a single piconet.  
         [0026]     According to an Institute of Electrical and Electronics Engineers (IEEE) 802.15.3 standard, a piconet is a group of one or more devices (DEVs) that share a single piconet coordinator (PNC) and locally associate with each other. The PNC has a DEV function, a coordination function, and functions for quality of service (QoS), synchronization, and association. The PNC provides a beacon for basic timing for a piconet. In addition, the PNC manages QoS, power curtailment, and piconet access control. Since a standard piconet is generated only when necessary, it is referred to as an ad-hoc network.  
         [0027]      FIG. 2  illustrates a spectrum of a signal of a multi-band ultra wide band (UWB) communication system in a frequency domain.  
         [0028]     A multi-band UWB has about several sub-bands through several tens of sub-bands. As shown in  FIG. 2 , the multi-band UWB may have 15 sub-bands. Of those sub-bands, one or some sub-bands may be reserved to avoid collision with household appliances other than a UWB system, for example, wireless local area network (LAN) DEVs defined by an 802.11a standard. The frequency domain for a UWB signal shown in  FIG. 2  is divided into a group consisting of seven low-frequency sub-bands  0  through  6  and a group consisting of high-frequency sub-bands  8  through  14 .  
         [0029]      FIG. 3  illustrates frequency hopping sequences for minimizing interference between piconets performing multi-band UWB communication of a frequency hopping type.  
         [0030]     The multi-band UWB communication uses frequency hopping to flatten frequency characteristics and reduce an influence of fading. Frequency hopping sequences may be variously set like piconet 1 , piconet 2 , and piconet 3  shown in  FIG. 3 . A system may be embodied such that the low-frequency sub-band group and the high-frequency sub-band group are subjected to frequency hopping in the sequences as shown in  FIG. 3 . To construct a piconet, a PNC performs a channel scan and determines available channels according to a channel state. In an exemplary embodiment of the present invention, a channel indicates a sub-band. If the channel state is good, all channels are available, as shown for piconet 1 . However, if the channel state is poor, only some of the channels are available, as shown for piconet 2  and piconet 3 . Whether the state of a channel is good or poor can be determined according to a level of noise in the channel. For example, in a place where a 2.4 GHz wireless LAN is available, a 2.4 GHz channel may not be available. Meanwhile, if the number of channels available in a single piconet is determined, the PNC selects an appropriate PNC sequence in accordance with the channel state. The PNC sequence indicates order in which frequency hopping is performed on channels available to a piconet. The channels available to the piconet are channels available to the PNC. Some DEVs or all of the DEVs included in the piconet can use channels that are not used by the PNC. For example, the piconet 2  uses channels  0 ,  1 ,  2 ,  3 ,  4 , and  6  while a DEV on the piconet 2  can use channels  0 ,  1 ,  5 , and  6 . This will be later described in detail with reference to  FIG. 4 . Where there is another piconet influencing a current piconet, the PNC sequence can be selected such that different channels are used for a same chip, as shown in  FIG. 3 , in order to minimize interference. Meanwhile, since important data such as a beacon is transmitted through a channel used by the piconet, it is determined which channels can be used by all DEVs associated with the piconet as channels that are used by the piconet. Generally, members included in the piconet are separated from one another by a distance of less than about 10 m, and therefore, channels available to each of the members are similar to those available to other members.  
         [0031]      FIG. 4  illustrates frequency hopping sequences of DEVs transmitting data in a single piconet, according to an embodiment of the present invention.  
         [0032]     A single piconet is determined by a single PNC sequence. Referring to  FIG. 4 , the PNC sequence is  0 ,  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  0 ′,  1 ′,  2 ′,  3 ′,  4 ′,  5 ′,  6 ′. DEV 1 , DEV 2 , and DEV 3  included in a piconet comply with the PNC sequence. While the DEV 1  can use all channels, the DEV 2  and the DEV 3  can use only some channels among all of the channels. The DEV 2  uses channels  0 ,  1 ,  4 , 5 , 0 ′,  2 ′,  3 ′,  4 ′,  5 ′, and  6 ′, and the DEV 3  uses channels  0 ,  2 ,  3 ,  5 , 6 , 0 ′,  1 ′,  2 ′,  3 ′, and  4 ′. Channels available to a PNC and each DEV are determined according to a channel environment. In other words, a DEV close to another DEV such as a microwave oven or a wireless LAN system does not use some of the channels in order to avoid interference with the other DEV.  
         [0033]     In  FIG. 4 , the shaded channel  5  is a control channel. The control channel is used by the PNC to send a control signal to DEVs included in the piconet and other DEVs wanting to associate with the piconet. The control channel may be one channel, e.g., a best channel (having least noise), among channels scanned by the PNC when the piconet is generated. A representative of the control signal is a frame (not shown) informing the PNC sequence. The frame informing the PNC sequence includes a header and a body, which contains information regarding the PNC sequence. The information regarding the PNC sequence may be expressed in the body as including a channel sequence. Alternatively, a sequence number representing particular PNC sequences may be expressed in the body. For example, where the sequence number is expressed in the body, if a PNC sequence of the piconet 1  shown in  FIG. 3  is represented by “ 1 ”, a PNC sequence of the piconet 2  is represented by “ 2 ”, and a PNC sequence of the piconet 3  is represented by “ 3 ”, “ 1 ” is recorded in a body of a frame informing the PNC sequence in the piconet including the DEV 1 , the DEV 2 , and the DEV 3  having the frequency hopping sequences shown in  FIG. 4 . Such PNC sequence may be embedded into a beacon to report the PNC sequence to DEVs. However, a separate frame containing the information regarding the PNC sequence may be periodically broadcasted through the control channel. Accordingly, a DEV wanting to associate with the piconet can recognize a frequency hopping pattern of the piconet through the control channel.  
         [0034]      FIGS. 5A and 5B  illustrate states before and after, respectively, a DEV associates with a piconet having a particular PNC sequence.  
         [0035]     Referring to  FIG. 5A , both of a PNC and DEV 1  that are included in a piconet use channels  1 ,  2 ,  3 ,  5 ,  6 , and  7 . In this situation, DEV 2  using channels  1 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8 ,  9 , and  10  will associate with the piconet to transmit data to and receive data from the DEV 1 . The DEV 2  associates with the piconet according to a predetermined association procedure, and  FIG. 5B  illustrates a result of the association. The DEV 2  transmits data to and receives data from the DEV 1  using the channels  1 ,  3 ,  5 ,  6 , and  7  common to both of the DEV 1  and the DEV 2 . Using the channels  1 ,  3 ,  5 ,  6 , and  7  may be performing frequency hopping using the channels  1 ,  3 ,  5 ,  6 , and  7  according to an arbitrary sequence. However, frequency hopping may be performed according to the PNC sequence. For example, if the PNC sequence is  1 ,  2 ,  3 ,  5 ,  7 ,  6 , one DEV among the DEV 1  and the DEV 2  transmits a UWB signal through the channel  1 , idles at a chip transmitting a signal of the channel  2 , and then transmits UWB signals sequentially through the channels  3 ,  5 ,  7 , and  6 . The other DEV among the DEV 1  and the DEV 2  receives the UWB signals according to a current frequency hopping sequence.  
         [0036]     Referring to  FIGS. 5A and 5B , the PNC and the DEV 1  use the same channels. However, the DEV 1  may not use some of the channels used by the PNC and use some of channels that are not used by the PNC. For example, the DEV 1  may use the channels  1 ,  3 ,  4 ,  5 ,  6 , and  7 . In this case, the DEV 1  can communicate with the DEV 2  according to frequency hopping using the channels  1 ,  3 ,  4 ,  5 ,  6 , and  7  common to both of the DEV 1  and the DEV 2 . Here, a frequency hopping sequence for data communication can be the PNC sequence.  
         [0037]      FIG. 6  illustrates a structure of a frame made by a DEV to transmit an association request command to a PNC, according to an embodiment of the present invention.  
         [0038]     The association request frame includes sequentially from a right most end a 2-octet command type field indicating a type of the frame (where 1 octet is 8 bits), a 2-octet length field indicating a length of a part of the frame succeeding the length field, an 8-octet DEV address indicating an address of the DEV wanting association, a 7-octet overall capabilities field, a 2-octet association timeout period (ATP) field, a 1-octet DEV utility field, and a 2-octet channel capabilities field. The command type field indicates a type of a command frame. The IEEE 802.15.3 standard uses a 0x0000 frame as an association request frame. According to the IEEE 802.15.3 standard, the length field indicates  18  octets. However, in the embodiment of the present invention, a value of 20 including 2 octets that is a length of the channel capabilities field is recorded in the length field. A DEV address is 64 bits in length. The overall capabilities field has 4 octets for PNC capabilities and 3 octets for DEV capabilities. A maximum number of DEVs that can be associated with a piconet by the PNC, maximum transmission power, etc. are recorded in the 4 octets for the PNC capabilities. Fields indicating whether the DEV can receive a signal through multicast and/or from a single source, a field indicating a desirable size of a fragment, etc. are recorded in the 3 octets for the DEV capabilities. An ATP expresses duration in milliseconds while association is maintained in a state where there is no communication between the PNC and the DEV. The DEV utility field includes a field indicating whether the DEV requests the PNC to send a piconet service command or a field indicating whether the DEV is designated as a neighboring PNC. The channel capabilities field indicates available channels. For example, in a UWB system using the above-described 15 channels, bits b 0  through b 14  indicate channels, respectively. If the DEV uses the channels  0 ,  1 ,  2 ,  4 ,  9 , and  10 , bits b 0 , b 1 , b 2 , b 4 , b 9 , and b 10  may be set to “1”, and the remaining bits may be set to “0”. An association acknowledgement frame corresponding to the association request complies with the IEEE 802.15.3 standard.  
         [0039]      FIG. 7  illustrates a structure of a DEV information field that is included in a PNC information command frame made by a PNC to indicate that a new DEV is associated with a piconet, according to an embodiment of the present invention.  
         [0040]     The DEV information field includes an 8-octet DEV address field indicating an address of the newly associated DEV, a 1-octet DEV 1 D field indicating an ID allocated to the newly associated DEV, a 1-octet DEV information (info) utility field indicating a membership state or the like expressing security or non-security, a 7-octet overall capabilities field, a 2-octet ATP field, a 1-octet system wake beacon interval field indicating a value that the new DEV transmits to the PNC using a synchronous power curtailment type request command, and a 2-octet channel capabilities field indicating available channels. DEVs that receive the PNC information command frame within the piconet can identify channels that are available to the new DEV. Due to the transmission of the PNC information command frame, each of the DEVs included in the piconet can have information regarding channels available to the other DEVs.  
         [0041]     Meanwhile, the PNC periodically broadcasts an information command containing information regarding all of the DEVs. Accordingly, each of the DEVs including the newly associated DEV can obtain information regarding channels available to the other DEVs through the information command broadcast by the PNC.  
         [0042]     The channel capabilities field shown in  FIGS. 6 and 7  has a different length depending on a total number of channels. For example, in a UWB communication system including 64 channels, the channel capabilities field is a minimum of 64 bits, i.e., 8 octets, in length.  
         [0043]      FIG. 8  is a flowchart of a procedure in which a DEV is associated with a piconet, according to an embodiment of the present invention.  
         [0044]     The DEV wanting association with the piconet scans channels. The DEV determines channels, e.g., channels  1 ,  2 ,  3 ,  6 , and  7 , that are in a satisfactory condition and available to the DEV by scanning the channels. Thereafter, the DEV acquires a channel sequence from a PNC of a piconet using the channel  3  as a control channel. If the piconet uses as the control channel a channel other than the determined available channels  1 ,  2 ,  3 ,  6 , and  7 , the DEV cannot find a PNC sequence and cannot associate with the piconet. The DEV that finds the PNC sequence requests the PNC for association according to the PNC sequence. For example, if the PNC sequence is  1 ,  2 ,  4 ,  6 , the DEV transmits an association request frame to the PNC through the channels  1 ,  2 , and  6  in sequence other than the control channel among the channels  1 ,  2 ,  3 ,  6 , and  7  available to the DEV. In response to the association request from the DEV, the PNC determines whether to permit the association. In the case where the association is not possible such as the case where a maximum number of DEVs that can be associated with the piconet have already been associated with the piconet, the PNC does not permit the association. Otherwise, the PNC permits the association. When the PNC permits the association, the PNC transmits a reply to the DEV and broadcasts information regarding the new DEV to the other DEVs included in the piconet. With such operations, the existing DEVs included in the piconet can obtain information regarding channels available to the new DEV.  
         [0045]      FIG. 9  is a flowchart of a procedure in which DEV 1  transmits data to DEV 2 .  
         [0046]     To transmit data to the DEV 2 , the DEV 1  requests a PNC to perform channel time allocation (CTA) in operation S 10 . In response to the CTA request, the PNC allocates a time slot at which the DEV 1  transmits data to the DEV 2 , and the DEV 1  receives a beacon that contains CTA information including the time slot and is broadcast by the PNC in operation S 20 . The DEV 1  obtains the CTA information from the beacon and transmits data at the time slot included in the CTA information through channels common to both of the DEV 1  and the DEV 2  in operation S 30 . In an exemplary embodiment of the present invention, frequency hopping is performed according to a PNC sequence when transmitting the data. Where the PNC sequence is  1 ,  2 ,  3 ,  4 ,  5 ,  6  and the channels  1 ,  2 ,  3 ,  5 , and  6  are common to both of the DEV 1  and the DEV 2 , UWB signals may be transmitted in a channel sequence of  1 ,  2 , and  3  using frequency hopping, a chip of the channel  4  may idle, and then UWB signals may be transmitted in a channel sequence of  5  and  6  using the frequency hopping.  
         [0047]      FIG. 10  illustrates a structure of a superframe defined by the IEEE 802.15.3 standard.  
         [0048]     A superframe is a frame between beacons and may include a beacon, a contention access period (CAP), a CTA, and a management CTA (MCTA). The beacon is used to communicate a time allocation, such as a CTA or an MCTA, and management information for a piconet. The CAP is used to communicate commands and asynchronous data. The CTA is used to communicate commands, isochronous streams, and asynchronous data. The MCTA is a kind of CTA and is used for communication between DEVs and a PNC. Where the DEV 1  transmits data to the DEV 2 , typically, the DEV 1  requests CTA of the PNC during the CAP. In response to the CTA request, the PNC performs an appropriate CTA and broadcasts a beacon containing information regarding the appropriate CTA. The DEV 1  receives the beacon and transmits data to the DEV 2  at a time slot corresponding to the appropriate CTA. In an exemplary embodiment of the present invention, frequency hopping is performed on channels available to both of the two DEVs when transmitting data. A frequency hopping sequence may be a PNC sequence.  
         [0049]     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and without changing any of its essential features. Therefore, it is to be understood that the above described embodiments are for purposes of illustration only and not to be construed as limitations of the invention. The scope of the invention is given by the appended claims, rather than the preceding description, and all variations and equivalents which fall within the range of the claims are intended to be embraced therein.  
         [0050]     The present invention makes the best of the conventional IEEE 802.15.3 standard that does not specifically define a mechanism for multi-band UWB communication and partially makes modification necessary for the multi-band UWB communication to the conventional IEEE 802.15.3 standard, so that the multi-band UWB communication can be performed in an almost similar manner to the conventional IEEE 802.15.3 standard.