Radio communication system, radio communication apparatus and radio communication method for UWB impulse communication

Provided is a radio communication system for ultra wideband (UWB) impulse communications and a radio communication apparatus and method thereof. The present patent provides a radio communication system that can minimize power consumption by eliminating a need for carrier detection and sharing transmission/reception time information in UWB impulse communications. The system includes a network coordinator; and one or more devices communicating on a superframe basis in subordination to the network coordinator. The devices perform data transmission/reception in predetermined time slots and then they are inactivated to thereby reduce power consumption.

TECHNICAL FIELD

The present invention relates to a radio communication system for ultra wideband (UWB) impulse communications, a radio communication apparatus, and a radio communication method thereof; and, more particularly, to a radio communication system that can be applied to a sensor network using UWB impulse signals or a low-rate Wireless Personal Area Network (WPAN) environment, a radio communication apparatus, and a radio communication method thereof.

BACKGROUND ART

According to Carrier Sensing Multiple Access/Collision Avoidance (CSMA/CA), which is a conventional multiple access method, transmission is performed when an idle channel is detected through carrier sensing, or when the channel is busy, transmission is postponed through backoff, which is revealed in the IEEE 802.15.4 Low-Rate WPANs Specification.

However, since the CSMA/CA method uses UWB impulse signals as short as less than several nanoseconds, the signal acquisition time taken for searching and determining accurate timing information of an impulse signal becomes long, compared to conventional systems using narrow band signals and when judging the presence of a signal, the probability of false alarm is high. Therefore, when the conventional CSMA/CA method is applied for multiple access in the ultra wideband impulse communication system, there is a problem that the performance of the CSMA/CA method is degraded remarkably.

Devices of a sensor network or a low-rate Wireless Personal Area Network (WPAN) should be designed to minimize power consumption when a communication scheme is designed because they are usually operated with small batteries. However, when the CSMA/CA method is used for multiple access in the ultra wideband (UWB) impulse communication system, the transmitting part of each device can begin transmission only when a channel is in an idle state. Thus, it should be in an active state while it monitors the channel. Also, since the receiving part of each device cannot know when the transmitting part begins transmission, it also has to remain in the active state while the channel is monitored. In short, since the transmitting and receiving parts of each device should remain in the active state while the channel is monitored, there is a problem of high power consumption.

Therefore, required are multiple access and communication methods that can minimize power consumption in the sensor network using UWB impulse communications or the low-rate WPAN environment and perform transmission and reception in a simple structure.

Since the sensor network can consist of more than hundreds to thousands devices, it is hard to support all the devices with the CSMA/CA technology which uses one channel. Therefore, a method for managing devices in a simple structure is needed.

Furthermore, since symbol-based Binary Exponential Backoff used in the conventional CSMA/CA method cannot relieve collisions between the devices, a hierarchical backoff method, which is an extended form of the symbol-based Binary Exponential Backoff, is required.

Compared to the conventional narrow band system using a band of several MHz, a band of 3.1 GHz to 10.6 GHz is split into bands of 500 MHz to bands of several GHz and each multi-piconet uses each split band in the ultra wideband impulse communication system. Thus, there is a problem that each sensor is too small to accommodate the transmitting and receiving parts having complicated functions to support bands of 500 MHz to bands of several GHz. This calls for the development of a method that can reduce the complexity in the transmitting and receiving structure and operate the multi-piconets in a simple method.

In addition, when an arbitrary time hopping pattern is determined and used between transmission and reception to apply an ultra wideband impulse signal to a time hopping system, it becomes more complicated to manage the time hopping pattern when there is a great deal of devices operated in the system. Therefore, a method that can simply manage the time hopping pattern in a simple manner is required.

DISCLOSURE

Technical Problem

The first objective of the present invention is to provide a radio communication method without carrier detection in an ultra wideband (UWB) impulse communication system.

The second objective of the present invention is to provide a radio communication system that can reduce power consumption by activating radio communication apparatuses to transmit/receive data in a predetermined time slot and by inactivating them in the other time slots in a radio network formed of a plurality of radio communication apparatuses and a coordinator which communicates with the radio communication apparatuses on a superframe basis.

The third objective of the present invention is to provide a radio communication apparatus that can operate in a radio network in a radio communication environment where a plurality of radio networks are operated under control of the network coordinators.

The other objectives and advantages of the present invention can be understood by the following description and become apparent with reference to preferred embodiments of the present invention. Furthermore, it is apparent that the objectives and advantages of the present invention can be easily realized by the means as claimed and combinations thereof.

Technical Solution

In accordance with one aspect of the present invention, there is provided a radio communication system, which includes: a network coordinator for operating a network; and one or more devices participating in communication on a superframe basis in subordination to the network coordinator, wherein the superframe includes: a beacon period in which the network coordinator transmits a beacon; a contention access period in which the devices contend with each other for multiple access; and a contention-free period in which the network coordinator allocates time slots to devices in need of time slots among the devices and the devices with time slots allocated thereto can make an access without contention, and the network coordinator divides the devices into one or more groups and allocates time slots of the contention period to each group.

In accordance with another aspect of the present invention, there is provided a radio communication system, which includes: a plurality of radio networks each of which includes a plurality of radio communication apparatuses; and a network coordinator communicating with the radio communication apparatuses on a superframe basis, wherein the superframe includes an active period in which the radio communication apparatuses of a network participate in communication while maintaining an active state; and an inactive period in which the radio communication apparatuses of the network remain in an inactive state, and the network coordinator operating a radio network controls the active period of the radio network to appear in the inactive period of another radio network.

In accordance with another aspect of the present invention, there is provided a radio communication method in a radio network including a plurality of radio communication apparatuses and a network coordinator communicating with the radio communication apparatuses on a superframe basis, which includes the steps of: a) dividing the radio communication apparatuses into a predetermined number of groups and allocating time slots to each group in a contention access period in the network coordinator; and b) transmitting data in each radio communication apparatus by randomly accessing to time slots allocated to a group to which the radio communication apparatus belongs, wherein the superframe includes: a beacon period in which the network coordinator transmits a beacon; a contention access period in which the radio communication apparatuses contend with each other for multiple access; and a contention-free period in which the network coordinator allocates time slots to radio communication apparatuses in need of time slots among the radio communication apparatuses and the radio communication apparatuses with time slots can make an access without contentions.

In accordance with another aspect of the present invention, there is provided a radio communication method in a radio communication environment including a plurality of radio networks operating under control of a network coordinator, which includes the steps of: a) establishing a superframe period including an active period and an inactive period and transmitting beacon information in the active period in a network coordinator of any one radio network; and b) controlling the active period of the superframe to appear in the inactive period based on the beacon information in a network coordinator of another radio network.

In accordance with another aspect of the present invention, there is provided a radio communication method in a radio network including a plurality of radio communication apparatuses and a network coordinator communicates with the radio communication apparatuses on a superframe basis, which includes the steps of: a) acquiring a beacon broadcasted by the network coordinator through channel scanning in any one radio communication apparatus; and b) accessing to arbitrary time slots of the contention access periods and transmitting association request information to the network coordinator in the radio communication apparatus, wherein the superframe includes: a beacon period in which the network coordinator transmits the beacon; a contention access period in which the network coordinator divides the radio communication apparatuses into one or more groups and allocates available time slots to each group; and a contention-free period in which the network coordinator allocates time slots to radio communication apparatuses in need of time slots among the radio communication apparatuses and the radio communication apparatuses with the time slots allocated thereto can make an access without contentions.

In accordance with another aspect of the present invention, there is provided a radio communication apparatus operating as a network coordinator in a radio communication environment where a plurality of radio networks operate under control of the network coordinator, which includes: a transmitting means for modulating and transmitting data to outside; a clock providing means for providing clocks based on a predetermined superframe period; and a controlling means for generating beacon information based on the clocks and transmitting the beacon information to outside through the transmitting means, wherein the beacon information includes: group management information on one or more groups of radio communication apparatuses which are obtained by grouping a plurality of radio communication apparatuses of the radio network; and time slot allocation information on time slots in a contention access period of the superframe, the time slots allocated to each group.

In accordance with another aspect of the present invention, there is provided a radio communication apparatus operating in a radio communication environment where a plurality of radio networks operate under control of a network coordinator, which includes: a transmitter for modulating and transmitting data to outside; a receiver for receiving beacon information from outside; a controller for setting up a superframe period based on the beacon information; and a clock providing unit for providing clocks based on the superframe period of the controlling means, wherein the beacon information includes: superframe timing information; group management information on one or more groups of radio communication apparatuses which are obtained by grouping a plurality of radio communication apparatuses of the radio network in the network coordinator; and time slot allocation information on time slots in a contention access period of the superframe, the time slots allocated to each group.

Advantageous Effects

The technology of the present invention can minimize power consumption and transmit/receive data in a simple structure in a sensor network or a low-rate Wireless Personal Area Network (WPAN) using an ultra wideband (UWB) impulse signal.

Also, the technology of the present invention can decentralize traffic of devices and relieve collisions between the devices by using a pre-arbitrated slot allocation-based Media Access Control (MAC) Protocol where a plurality of devices are divided into a predetermined number of groups and a predetermined number of slots are allocated to each group.

Also, since the technology of the present invention does not need carrier detection, it works in a network not capable of detecting carriers or an environment where carrier cannot be detected, i.e., in a network using a physical layer such as ultra wideband impulse communication.

Also, since the technology of the present invention uses a superframe based binary exponential backoff method and time slot based backoff method simultaneously when a collision occurs in a contention access period, it can relive the collisions better than the conventional method.

Also, since the technology of the present invention specifies transmission and reception roles of time slots in a contention access period and guaranteed time slots in a contention-free period, it can reduce protocol complexity and reduce power consumption compared to conventional Carrier Sensing Multiple Access (CSMA) method to thereby lengthen communication time through a power management where constitutional elements wake up in corresponding slots to perform data transmission and reception and they are inactivated in the other time slots.

Also, the technology of the present invention can reduce the number of transmissions and receptions and simplify the communication scheme not by transmitting acknowledgement information for data transmission from the constitutional devices or responses to requests from the constitutional devices individually in the corresponding slots, but by informing them all at once by putting them in a beacon and transmitting the beacon.

Also, the technology of the present invention can manage hopping patterns simply by defining a time hopping pattern according to each time slot and each guaranteed time slot and using a hopping pattern corresponding to a slot in data transmission/reception while sharing the hopping pattern information in a network. In other words, it is easy to receive data and detect collisions, as the data are received based on a predefined hopping pattern. Also, the technology of the present invention can relieve spectral characteristics in conformity to a spectrum regulation in the UWB communication system and suppress the interference signal to another networks.

Also, the technology of the present invention can operate multi-piconets by not overlapping active periods of superframes for each piconet temporally when multi-piconets are operated by simply controlling superframe and timing information, such as active period and inactive period. When the multi-piconets are operated without active periods of piconets overlapped with each other temporally and data need to be transmitted between piconets, the data are relayed through a repeater in communication between two piconets to both of which it belongs. Thus, the technology of the present invention can extend a network by relaying data between piconets.

Also, the technology of the present invention can be applied to a physical layer suggestion based on ultra wideband communication in an activity for standardizing a physical layer for a low-rate WPAN based on the IEEE 802.15.4a, i.e., a group for standardization.

BEST MODE FOR THE INVENTION

Other objectives and aspects of the invention will become apparent from the following description of preferred embodiments, and the technological concept of the present invention will be easily implemented by those skilled in the art of the present invention. Also, when it is determined that the detailed description of prior art may blur the point of the present invention unnecessarily, the description will not be provided herein. Hereinafter, the preferred embodiments of the present invention will be described with reference to the accompanying drawings, which is set forth hereinafter.

FIG. 1is a diagram illustrating a network in accordance with an embodiment of the present invention. A network100is a Wireless Personal Area Network (WPAN) or a piconet but it can be a wireless Local Area Network (WLAN) or another type of radio network in which a plurality of users share bandwidths.

As described inFIG. 1, the network100includes one network coordinator105and one or more devices110. The network coordinator105can be a predetermined device or just one of devices selected to function as a coordinator.

The network coordinator105communicates with the devices110based on various control operations within the network, and the devices110acquire information needed for communication by receiving control information from the network coordinator105. The devices110basically communicate (see115) with the network coordinator105and also communicate (see120) with each other. Each of the devices110communicates (see120) with a reference device to acquire distance information and provide a positioning service to users.

FIG. 2is a diagram describing a superframe in accordance with an embodiment of the present invention. A superframe is a basic unit for communication in the present invention.

As shown inFIG. 2, each of consecutive superframes200is divided into an active period205where the network coordinator105and the devices110are activated to communicate with each other and an inactive period210where the network coordinator105and the devices110are inactivated. Herein, the active period205is divided into a beacon period215, a Contention Access Period (CAP)220, and a Contention-free Period (CFP)225.

In the beacon period215, the network coordinator105puts control information needed to operate the network and messages for the devices110into a beacon and broadcasts the beacon throughout the network. The devices110synchronize the time of the time slots based on the time when the beacon is received, and prepare for data transmission/reception based on the control information and the messages in the beacon.

The contention access period220is formed of one or more time slots (TS), i.e., TS1, TS2, TS3, . . . , TSnwhere 1≦n. The network coordinator105classifies the devices110of the network100into one or more groups, i.e., G1, G2, . . . , Ggwhere 1≦g, and allocates one or more time slots230to be used for each group in advance. Each of the devices110randomly accesses to the allocated slots to reduce collisions between the devices110of its group. Each of the devices110selects one or more time slots230among the time slots allocated for the group to which the device110belongs. Each device100randomly accesses to slots allocated to its group in such a manner that collisions between the device and the other devices110in its group can be reduced. The device110selects one or more time slots among the time slots allocated to a group to which the device belongs and transmits data through contention with the other devices of its group. The multiple access method is referred to as a Pre-arbitrated Slot Allocation Based MAC Protocol.

In the contention access period220, it is the characteristics of a sensor network that most of the communication is an up-link communication from the devices110to the network coordinator105. The purpose of this communication method is to reduce power consumption by activating the devices110and transmitting data at the corresponding time slots when there are data to be transmitted, or maintaining the inactive mode when there are no data to be transmitted.

In the contention access period220, it is possible to perform downlink communication from the network coordinator105to the devices110. The downlink communication includes unicast where the network coordinator105broadcasts data to a device110in the network, multicast where the network coordinator105broadcasts data to a group of devices110in the network, and broadcast where the network coordinator105broadcasts data to all the devices110in the network. In this case, the network coordinator105puts information of time slots230to be used for downlink communication among the time slots230of the contention access period220within a corresponding superframe200into a beacon and broadcasts the beacon. Herein, the devices110of the network receive the beacon, check out the time slots230for downlink communication upon receipt of the beacon information, make the time slot230be used only for the downlink communication by restricting that the predetermined groups use the time slots230which are allocated to the predetermined groups for up-link communication in the time slots230, and activate the time slots230for the downlink communication to receive needed information.

A contention-free period225is formed of one or more guaranteed time slot (GTS), e.g., GTS1, GTS2, . . . , GTSmwhere 1≦m. The devices110of a network request the network coordinator105for use of guaranteed time slots235in a contention access period220to use the guaranteed time slots235. The network coordinator105allocates the guaranteed time slots235of a contention-free period225of the next superframe200to the devices110which have requested the use of the guaranteed time slots235including the network coordinator105itself through scheduling in consideration of request information transmitted from the devices110and whether the network coordinator105itself is used or not. In other words, the network coordinator105puts information on the devices110allocated with the guaranteed time slot allocation information, i.e., GTSiwhere iε{1, 2, . . . , m}, into a beacon in a beacon period215and broadcasts the beacon, while the devices110receive the beacon information and use the allocated guaranteed time slots235.

As described above, multiple access is carried out based on time division in the contention-free period225. In the guaranteed time slots235of the contention-free period225, the devices110including the network coordinator105can communicate with each other, and the devices can be used for relaying, positioning, and transmission of a higher quality of service (QoS) according to usage.

Just as the contention access period220, guaranteed time slots235for downlink communication can be allocated and used in a contention-free period225. If necessary, the network coordinator105can establish one or more guaranteed time slots235for downlink communication in a contention-free period225, inform the network of them by using a beacon so that those devices110in need can be activated in the time slots for downlink communication and receive data. In short, it is possible to perform downlink communication in all the beacon period215, the contention access period220, and the contention-free period225, and the period to be used is determined based on the conditions of the network.

The structure of a superframe and parameters for an algorithm, which will be described later, are established according to a network operation policy and stored in a storage305ofFIG. 3. A controller301ofFIG. 3controls the data transmission/reception based on the parameters by using timing information of a system clock unit302.

FIG. 3is a block diagram showing a radio communication apparatus operated in a network in accordance with an embodiment of the present invention. The radio communication apparatus ofFIG. 3performs the operation of the network coordinator105which are shown inFIG. 1and an general device110.

As shown inFIG. 3, the controller301of the radio communication apparatus transmits data in a transmission buffer303to a transmitter304based on the timing information of the system clock unit302. The transmitter304modulates the data in the transmission buffer303and transmits them to the outside through an antenna308. Meanwhile, when a receiver306receives a radio frequency (RF) signal from the outside through the antenna308, it demodulates the RF signal based on the timing information of the system clock unit302under the control of the controller301and stores the received data in a reception buffer307.

Herein, the controller301controls data transmission and reception based on a communication protocol function of an execution program stored in the storage305. The storage305includes the structure of a superframe and system parameters therefor, operation procedures, transmission and reception structures needed for modulation and demodulation and parameters therefor, and protocol algorithm functions needed for communication.

When the radio communication apparatus ofFIG. 3functions as the network coordinator105, the storage305includes functions needed for controlling the network as well as contents included in the general devices110. Thus, beacon information is generated in the controller301in the radio communication apparatus operated by the network coordinator105, and the generated beacon information is transmitted in the transmitter304according to a timing of a predetermined superframe period generated from the system clock unit302.

Meanwhile, when the radio communication apparatus functions as a general device110, it receives the beacon information transmitted from the network coordinator105in the receiver306according to the timing of the predetermined superframe period, establishes the superframe period, periods within the superframe, and timing information of time slots based on the beacon information, and operates in subordination to the network coordinator105.

FIG. 4is a flowchart describing a process of transmitting data between a general device and a network coordinator in a contention access period in accordance with an embodiment of the present invention. An operation algorithm in a contention access period and parameters therefor are included in the storage305of the network coordinator105and the general device110and executed by the controller301.

As illustrated inFIG. 4, the device110initializes a parameter R indicating the number of re-transmissions in step400, when data to be transmitted to the network coordinator105are generated. In step401, the device110determines whether data can be transmitted at a time point when the data are generated.

When the data are not generated in a contention access period220or although the data are generated in a contention access period220, when the allocated time slot of the device110is not available, that is, when the time of the corresponding time slots has passed by, or when the time slot cannot be used because it is reserved for downlink communication by the network coordinator105, the device110remains in an inactive state until the next contention access period220in step402. When the new contention access period220begins, the device determines again whether the data can be transmitted or not in the step401.

When the data are generated in a contention access period220and there are more than one time slot allocated for the device110, the device110makes a random selection among the available time slots in step403. When available time slots are selected, data are transmitted to the network coordinator105in step404at time corresponding to the time slots.

In step405, after data are transmitted to the network coordinator105, it is checked in step405whether acknowledgement information is needed for the transmitted data. When the acknowledgement information is not needed, the data transmission is completed in step406. Otherwise, if the acknowledgement information is needed, it is checked whether or not the beacon information broadcasted in the network in the next beacon period includes acknowledgement information in steps407and408.

When the acknowledgement information is received, it is determined in the step406that the data transmission is completed. Otherwise, the number of data re-transmissions, R is increased by one and re-transmission is prepared in step409. When the data re-transmission is prepared, the increased number of data re-transmissions is compared with the maximum available number of retransmissions, RMAXin step410. When it is turned out that R exceeds RMAX, the transmission of that data is regarded as a failure in step411. Otherwise, a backoff process is performed in step412. After the backoff, a time slot available in the corresponding contention access period is selected and transmitted repeatedly.

In the time slot230of the contention access period220, each of the devices110can transmit not only data but also request information, such as a request for guaranteed time slot235of a contention-free period220, to the network coordinator105. The transmission of the data and the request information goes through the same process as the data transmission in the contention access period220, which is described before. Just as acknowledgement information for the data transmission is confirmed in a subsequent beacon, the network coordinator105puts response information for the request information into a beacon and transmits the beacon to the devices so that the devices can receive a response to their request information.

Backoff relieves collisions in a contention access period220. A backoff process can be divided into an inter-superframe backoff based on a superframe unit and an intra-superframe backoff based on a time slot unit in a contention access period of a superframe. The two-step backoff process can effectively relieve collisions in which a plurality of users use the same time slot at the same time.

When a collision occurs in the superframe-based backoff, the next superframe to be transmitted is determined based on binary exponential backoff. When a collision occurs, a device selects a predetermined integer number k from a backoff window [1,2BE-1] where BE is an exponential parameter of the backoff window size, and attempts a message transmission in the kthsuperframe apart from the corresponding superframe. Herein, if collisions occur repeatedly, backoff is carried out with an increased value of BE, and the value of BE is limited by defining the maximum value of BE, BEMAX.

The superframe-based backoff is useful for relieving the collision effect, when circumstances require the superframe-based backoff, for instance, when there is one time slot allocated to each group, when the only one time slot in a predetermined group is available since the other time slots allocated to a predetermined group are used for downlink communication in the network coordinator105, or when the collision probability is high because the allocated time slots are not enough to accommodate data transmissions due to an increase in the quantity of data to be transmitted within a group.

As described above, a plurality of time slots can be allocated to a group including a plurality of devices in a contention access period220. In the time slot-based backoff in a contention access period220, the devices110of a group select time slots randomly among the allocated time slots. The backoff can reduce the number of recurring collisions in a time slot.

FIG. 5is a flowchart describing a backoff method in accordance with an embodiment of the present invention. A collision occurs in a contention access period220when more than two devices110select the same time slot230to transmit data. Due to the collision, the receiver306of the network coordinator105cannot demodulate the received signals properly, and the controller301of the network coordinator105cannot transmit acknowledgement information for the data transmission of the devices110in a corresponding time slot230. Thus, the devices110which have transmitted data cannot receive the acknowledgement information and recognize the occurrence of a collision and executes a backoff algorithm stored in the storage305.

As described inFIG. 5, when the device110is ready to transmit data in step500, it initializes the value of BE into 1 in step501and performs data transmission by selecting a time slot in step502. In short, a backoff is performed on a time slot basis. Subsequently, the presence of collisions is checked based on the acknowledgement in step503. If there is no collision, it is regarded in step504that the data transmission is completed successfully. If there is a collision, the value of BE is increased by one and compared with the maximum value of BE, BEMAXin step505. If the BE value is larger than the BEMAXvalue, the transmission is regarded as a failure in step506, or if the BE value is equal to or smaller than the BEMAXvalue, an integer number is selected from a superframe backoff window [1,2BE-1] in step507and the superframe-based backoff is performed in step508.

FIG. 6is a diagram describing a backoff method in accordance with an embodiment of the present invention. As described inFIG. 6, it is assumed that devices #a and #b transmit data at the same time slot TS602in a superframe1601to thereby cause a collision.

When a collision occurs, the devices select a predetermined integer number k among the backoff window [1,2BE-1] and attempt to transmit data in the kthsuperframe apart from the current superframe, i.e., the superframe1. Herein, since the initial value of BE is 1, the backoff window becomes [1] in the initial collision. Thus, the predetermined integer number k is 1, and the devices #a and #b attempt to transmit data in the first superframe2603from the superframe1601.

In the superframe2603, when the device #a selects a time slot TSj604for a data transmission and the device #b selects the time slot TSj604for a data transmission and, as a result, a collision occurs, the BE value is increased by one. Then, the backoff window becomes [1, 2BE-1]=[1,2] (BE=2), and the devices #a and #b transmit a message by randomly selecting one of the values of the backoff window [1,2]. When the device #a selects ‘1’ and the device #b selects ‘2,’ no collision occurs.

However, when both devices #a and #b ofFIG. 6select ‘2’ and attempt data re-transmissions in a superframe4605and then the devices #a and #b select the same time slot TSk606in the superframe4605, a collision occurs again. Thus, both devices #a and #b increase their backoff windows into [1, 2BE-1]=[1, 4] (BE=3).

Subsequently, as shown inFIG. 6, the device #a selects ‘2’ while the device #b selects ‘3’ and the devices #a and #b perform a backoff in a superframe6607and a superframe7608, respectively. In the superframes6and7, a time slot-based backoff scheme is performed. The device #a selects a time slot TS1609whereas the device #b selects a time slot TSm610and they transmit data without a collision. Although both devices #a and #b select ‘3’ in the superframe-based backoff and perform backoff in the superframe7608, when the device #a performs the time slot-based backoff by selecting a time slot TSn611(n≠m) and the device #b performs the time slot-based backoff by selecting a time slot TSm610(n≠m), a collision does not occur either.

FIG. 7is a flowchart illustrating a process for transmitting data between a general device and a network coordinator105in a contention-free period in accordance with an embodiment of the present invention. In the contention-free period, an operation algorithm and parameters are stored in the storage305of the general device110and the network coordinator105and executed by the controller301.

As illustrated inFIG. 7, when data to be transmitted in the contention-free period225are generated, a device110initializes a parameter Rrindicating the number of requests for a guaranteed time slot235and a parameter R indicating the number of data re-transmissions and prepares for a transmission in step700.

When the devices110need the guaranteed time slot235in a contention-free period225, they randomly select a time slot among the times slots allocated for their groups in the contention access period220and request the network coordinator105for a guaranteed time slot in step701. This process goes through data transmission in a contention access period220, which is described with reference toFIG. 3.

The network coordinator105schedules the guaranteed time slots235of the contention-free period225based on the guaranteed time slot request information transmitted from the devices110in the contention access period220, puts the result in a beacon, and broadcasts the beacon to the devices of the network. Thus, in step702, the device checks out a beacon transmitted after it requests for the guaranteed time slot235to see whether there is a guaranteed time slot235allocated thereto.

If no guaranteed time slot235is allocated to the device, the device increases the Rrvalue of requesting for a guaranteed time slot235by one in step703. Then, it compares it with the Rr—MAXvalue for guaranteed time slot requests in step704and, if the obtained Rrvalue is larger than the Rr—MAXvalue, the request is regarded as a failure in step705. If it is equal to or smaller than the Rr—MAXvalue, the logic flow goes back to the step701where it requests for a guaranteed time slot.

Meanwhile, when there is a guaranteed time slot235allocated to the device, the device transmits data by using the guaranteed time slot235in step706. After it transmits data in the allocated guaranteed time slot235, it determines whether the acknowledgement information is needed or not in step707. If it does not need the acknowledgement information, it regards that the transmission is completed successfully in step708. Otherwise, when it requires the acknowledgement information, it enters an inactive mode and waits in step709until it receives the acknowledgement in one time slot or a beacon including the acknowledgement information.

It waits for the acknowledgement information and checks out the presence of the acknowledgement information in step710. When the acknowledgement information is received, it completes the data transmission in the step708. When the acknowledgement information is still absent, it prepares to re-transmit the data in step711. When it prepares for the data re-transmission, it increases the R value by one, compares it with the RMAXvalue in step712. When the R value is larger than the RMAXvalue, it is regarded as a transmission failure in the step705, or when R is equal to or smaller than RMAX, the Rrvalue is initialized in step713and the re-allocation for guaranteed time slot235is requested for data re-transmission in the step701.

FIG. 8is a flowchart describing a method for a general device being associated with a network in accordance with an embodiment of the present invention. The algorithm and needed parameters are stored in the storage305of the network coordinator105and the general device110and executed by the controller301.

As described inFIG. 8, when the arbitrary device110searches to be associated with the network, it initializes a parameter RASSindicating the number of association requests in step800. It scans the channel and acquires a beacon transmitted by the network coordinator105in step801. The beacon includes various types of timing information needed for communication within the network, e.g., time duration of a superframe200, time duration of an active period205, an inactive period210, a beacon period215, a contention access period220and a contention-free period225, time duration of a time slot230of the contention access period220and a guaranteed time slot235of the contention-free period225, which are described with reference toFIG. 2.

The device110which desires to be associated with the network is not yet assigned with a device number (address used in the network) in the initial period and, since it does not belong to any group, it does not have any pre-allocated time slot. Thus, it acquires timing information included in the beacon and arbitrarily selects a time slot among all time slots within a contention access period in step802and it transmits association request information to the network coordinator105in a corresponding time slot in step803. After the association request information is transmitted, the device remains in the inactive mode to save power consumption until it acquires the next beacon information.

After the device110acquires the next beacon information, it checks out a response for an association request in step804and, if there is a response, it makes an association successfully in step805. Otherwise, it prepares for another association request in step806. That is, it increases the RASSvalue by one, and compares it with the maximum number of association requests, RASS—MAXin step807. When the RASSvalue is larger than the RASS—MAXvalue, it determines that the association fails in step808, or if it is equal to or smaller than the RASS—MAXvalue, it repeats the process of scanning channels and acquiring a beacon again in the step801.

FIG. 9is a diagram showing a frame structure of beacon information in accordance with an embodiment of the present invention.

As described inFIG. 9, the MAC frame900of a MAC layer includes an MAC header910, a MAC payload920and a frame check sequence (FCS)930, and the MAC payload920includes beacon information.

A frame of the beacon information in the MAC payload920includes various information fields, such as a superframe timing information field921, a guaranteed time slot allocation information field922, a data pending information field923, an acknowledgement information field924for data transmission, a response information field925for slot or control request information, a downlink slot allocation information field926, a group management information field927, a beacon payload field928, and a reserved field929.

The superframe timing information field921includes a time duration of a superframe, time duration of an active period205, an inactive period210, a beacon period215, a contention access period220and a contention-free period225, and time duration of a time slot of the contention access period220and a guaranteed time slot235of the contention-free period225.

The guaranteed time slot allocation information field922includes a transmitter address and a receiver address for each guaranteed time slot235of the contention-free period225allocated to a transmitter and a receiver only.

The data pending information field923shows that the current network coordinator105has data or control information to be transmitted to predetermined devices of the network and it includes address informations of the devices.

The acknowledgement information field924includes acknowledgement information when the device110transmits data to the network coordinator105in contention access and contention-free periods of a previous superframe and it includes address information of a transmitter.

The response information field925for slot or control request information includes response information when the device transmits a slot request or a control request information to the network coordinator105in a contention access period of a previous superframe, and it includes information such as address of a transmitter, a response to the request for a control, and a reason for rejection to the control request.

The downlink slot allocation information field926includes time slot information for downlink communication which will be used when there is a message to be transmitted from the network coordinator105to predetermined devices in contention access and contention-free periods of a superframe. With this information, the network coordinator105prevents a time slot from being used by a predetermined group to thereby make the time slot used without collision.

The group management information field927includes a classification method for grouping devices of the network, information on the time slots in contention access periods allocated to each group, and information to be used when the collision probability of a predetermined group exceeds a pre-defined threshold or when a group needs to be classified again upon a request from the network.

The beacon payload928includes security information, and control information and/or control request information to be transmitted from the network coordinator105to more than one device110.

The reserved field929is reserved to be used in case where it is needed for the network in future.

Hereinafter, a hopping pattern that can be applied to a time hopping system using an ultra wideband impulse signal in a time slot or a guaranteed time slot will be described.

FIG. 10is a diagram describing a time hopping pattern in a time slot and a guaranteed time slot in accordance with an embodiment of the present invention.

A time slot or a guaranteed time slot is formed of more than one chip, i.e., Tc—1and Tc—2, . . . , Tc—p(1≦p), and one chip is formed of more than one hop, i.e., Th—1and Th—2, . . . , Th—q(1≦q). A time hopping system is a system where information is transmitted at the only one hop in one chip, and the elements of the hopping pattern can be the same or random for each chip.

The hopping pattern of each slot is predetermined between the network coordinator105and the device so the transmitter and receiver using a predetermined slot communicate with each other by using the corresponding hopping pattern. The information on the hopping pattern is stored in the storage305of the radio communication device, and the controller301controls the transmitter and receiver304and306according to the timing information of the system clock unit and the hopping pattern stored in the storage305.

Sharing the hopping pattern makes the hopping pattern managed simply within the network, and the time hopping system can relieve the spectral characteristics in the ultra wideband impulse communication and suppress other interference signals from or to other networks.

In the conventional narrow band communication, a channel is divided into frequency channels based on frequencies and a different frequency channel is used for each piconet so that multi-piconets are operated. However, since the ultra wideband communication uses a wideband which is as wide as several GHz, compared to a band of several MHz, which is used in the conventional narrowband communication, there is a limit in dividing a channel based on frequencies and using frequency-based channels. That is, with the limited band of 3.1 to 10.6 GHz that can be used in the ultra wideband communication, the number of multi-picotnets that can simultaneously support is limited. Thus, a method where the multi-piconets are divided temporally and operated will be described.

FIG. 11is a diagram illustrating the operation of multi-piconets in accordance with an embodiment of the present invention.

As illustrated inFIG. 11, the piconet communicates with temporally continual superframes1100. As described above, one superframe1100is divided into an active period1101and an inactive period1102. In the active period1101, the network coordinator105and the devices of a piconet110are activated to communicate with each other. In the inactive period1102, all the devices in the piconet are inactivated and they do not communicate with each other.

Thus, it is possible to form the operation structure of multi-piconets by using the inactive period1102in which all the devices of a piconet are inactivated and activating the other piconets for communication. As shown inFIG. 11, it is possible to set up an active period1103of the piconet #b to be operated by using the inactive period1102of the piconet #a, and an active period1105of the piconet #c to be operated by using the inactive period1102of the piconet #a and an inactive period1104of the piconet #b. When a new piconet is formed to expand the superframe, the inactive periods1102,1104and1106of the piconets are checked out and the superframe is formed to be activated for communication within the inactive periods of the other piconets.

FIG. 12is flowchart describing a channel scanning process for generating a new piconet in accordance with an embodiment of the present invention.

As described inFIG. 12, the network coordinator105of the piconet #c, which desires to form a new piconet, requests a MAC layer1201for channel scanning in a prior upper layer1200in step1202. Then, the MAC layer1201scans a channel for a predetermined scanning time τ in step1203. The scanning time τ can be the size of a superframe, which is a basic communication unit of a network.

The network coordinator105of the piconet #c scanning a channel can receive beacons1205broadcasted by the network coordinator105of the piconet #a in a MAC layer1204and beacons1207broadcast by the network coordinator105of the piconet #b in an MAC layer1206. To receive the beacons without an error, the scanning process of the step1203is repeated.

As described above, since a beacon includes control information needed to operate a network and timing information such as the size of a superframe, the size of an active period, and the size of an inactive period, reception of a beacon makes it possible to reveal how the corresponding network is operated. Therefore, after the network coordinator105of the piconet #c receives the beacons of the piconets on service without an error, it informs that channel scanning is completed from the MAC layer1201to an upper layer1200in step1208. As described inFIG. 11, the network can be operated by forming the superframe, active period and inactive period of the piconet #c by using the inactive periods of the other piconets.

The algorithm and the channel scanning process, which are needed to form multi-piconets and described above with reference toFIGS. 11 and 12, are stored in the storage305of a radio communication apparatus with parameters set up according to a network operation policy, and executed based on timing information of the system clock unit302under control of the controller301.

FIG. 13is a diagram illustrating a process relaying data between piconets in accordance with an embodiment of the present invention.

As shown inFIG. 13, while the multi-piconets are temporally divided and operated, the superframe of the piconet #a, i.e., an active period1300and an inactive period1301, are operated continuously, and the superframe of the piconet #b, i.e., an active period1302and an inactive period1303are operated continuously. Herein, the network coordinator1304of the piconet #a transmits data through a repeater1306that can communicate between the piconet #a and the piconet #b, only when it has data to be transmitted to the network coordinator1305of the piconet #b. The data transmission process is as follows.

First, the network coordinator1304of the piconet #a transmits data to the repeater1306to relay in a guaranteed time slot1308of a contention-free period1307, assigned in advance. The repeater1306requests the network coordinator1305of the piconet #b for a guaranteed time slot1310of a contention-free period1309for data relaying. Thus, data are relayed from the network coordinator1304of the piconet #a to the network coordinator1305of the piconet #b.

The relaying algorithm between piconets is stored in the storage305of the radio communication apparatus and executed based on the timing information of a system clock unit302under the control of the controller301.

The method of the present invention, which is described above, can be realized as a program and stored in a computer-readable recording medium, such as CD-ROM, RAM, ROM, floppy disks, hard disks, magneto-optical disks and the like. Since the process can be easily implemented by those skilled in the art of the present invention, further description on it will not be provided herein.