KR20080049557A - Method for time synchronization in wireless communication system and device using the same - Google Patents

Abstract

A method for time synchronization in a wireless communication system and a device using the same are provided to perform an additional time synchronization process by transmitting data packets periodically. A coordinator transmits a beacon signal including time information periodically. The coordinator transmits a data packet including the time information periodically. A peripheral device receives the beacon signal and performs a time synchronization process for the beacon signal and the coordinator. The peripheral device receives the data packet including the time information and performs the time synchronization process for the data packet and the coordinator when the peripheral device does not receive the beacon signal.

Description

Method for time synchronization in wireless communication system and device using the same}

1 is a block diagram of a TDMA based short range communication system.

2 is a diagram illustrating a communication method of a TDMA-based short-range wireless communication system according to a conventional method over time.

3 is a diagram showing a data transmission and reception process according to the present invention over time.

4 illustrates a structure of a data packet TSEPB including time information according to the present invention.

The present invention relates to a method and a communication device capable of synchronizing time between respective communication devices in a short range wireless communication system using a time division multiple access (TDMA) scheme.

More specifically, in the TDMA wireless communication system, the present invention periodically transmits a data packet including time information and schedule information in addition to the beacon signal during communication between a coordinator for generating and transmitting a beacon signal and a peripheral device. A synchronization method and a communication device capable of synchronizing time even when a peripheral device loses a beacon signal.

The present invention can be particularly useful in a communication system using Ultra Wide Band (UWB) (IEEE 802.15.3) and mmWave (millimeter wave) (IEEE 802.15.3c), which are short-range wireless communication methods for home or office.

In addition to wireless LAN, high-throughput wireless technology standards such as UWB (IEEE 802.15.3) and mmWave (IEEE 802.15.3c) technologies have been proposed and developed for HD-class wireless transmission in homes or offices.

The MAC (Media Access Control) layer of such a short range wireless network system adopts a time division multiple access (TDMA) based channel access method for high throughput.

 In a TDMA communication system, time synchronization of all devices participating in the communication is required.

1 is a block diagram of a TDMA based short range communication system, and FIG. 2 illustrates a communication method of a TDMA based short range wireless communication system according to a conventional method.

As shown in FIG. 1, the coordinator communicates with the peripheral devices A and B in a TDMA manner. In addition to transmitting data packets, the coordinator generates and transmits a beacon signal at a beacon interval, and peripheral devices synchronize time based on the beacon signal received from the coordinator.

Referring to FIG. 2, the coordinator generates and transmits a beacon signal containing various pieces of information required for performing a communication of a wireless communication system such as time information and information schedule information at periodic time intervals. Receive a beacon signal to synchronize the time of each device with the coordinator.

As shown in Fig. 2, if the peripheral device A does not receive the beacon signal due to a communication failure or other reasons after receiving the data 1 during wireless communication, the peripheral device A temporarily waits until the next beacon signal is received. You will not be able to synchronize, and you will not be able to use the time slot assigned to you during the second beacon interval.

In this case, since data can be communicated only after receiving a beacon signal following a lost beacon signal, when a plurality of beacon signals are missed continuously, communication cannot be performed because a long time synchronization cannot be achieved.

This usually means failure of multiple data packet transmissions in high-performance wireless networks where the beacon intervals are much longer than the packet transmission time. Therefore, the impact on MAC efficiency is lower than that of one data packet loss.

Conventionally, when a beacon signal is missed, an algorithm for retransmitting time information by transmitting a request signal requesting a beacon signal from peripheral devices is also considered, but an algorithm for sending a request signal and retransmitting a beacon signal has been gradually accelerated. This is too difficult to apply and requires a new time synchronization method.

It is an object of the present invention to provide a method and apparatus capable of recovering time synchronization when a beacon signal is lost in a TDMA based wireless communication system.

It is an object of the present invention to provide a method and apparatus capable of guaranteeing time synchronization in addition to a beacon signal by periodically transmitting a data packet including time information and schedule information in a TDMA based wireless communication system.

An object of the present invention is to provide a method and apparatus for recovering time synchronization when a beacon signal is lost in a TDMA-based wireless communication system without transmitting a request signal for recovery to a coordinator communication device.

According to an embodiment of the present invention, a time synchronization method includes: periodically transmitting a beacon signal including time information in a coordinator; Periodically transmitting a data packet including time information; Receiving the beacon signal at a peripheral device and time synchronizing with the coordinator; And receiving a data packet including the time information and time synchronizing with the coordinator when the peripheral device does not receive the beacon signal.

The communication apparatus for a wireless communication coordinator according to an embodiment of the present invention is characterized by periodically generating and transmitting a beacon signal including time information and a data packet including time information.

The communication device for a wireless communication peripheral device according to an embodiment of the present invention receives a beacon signal from a coordinator communication device to synchronize time, and if the beacon signal is not received, receives the data packet to synchronize time. It is characterized by.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

3 is a diagram showing a data transmission and reception process according to the present invention over time.

1 and 3, the coordinator generates and transmits a beacon signal periodically for each beacon interval. Between the beacon interval intervals, the coordinator and the peripherals transmit and receive data packets (data 1, 2 ..., 7) to each other.

The coordinator and peripheral devices communicate using time slots assigned to beacon signals based on the TDMA communication method, and the peripheral devices synchronize time based on time information included in the beacon signal received from the coordinator, and schedule information Allocates time slots based on

The beacon signal includes a MAC header, beacon control information, variable information field, and schedule elements.

The MAC header is necessary for MAC data transmission and includes a MAC transmission address, a reception address, error protection information, and ACK information.

The beacon control information includes information on the beacon interval, and includes information on whether the base station transfer or association (association).

The variable information field is a variable data area that can contain various information according to an embodiment.

The schedule element is variable information data for schedule access, and includes a number of reserved transmissions, a reserved transmission address, a sender tank, a receiver tank, and transmission time information allocated to the corresponding data transmission.

In a wireless communication scheme based on the TDMA scheme, if a beacon signal is lost, data cannot be transmitted or received during the beacon interval in which the beacon signal is lost. In addition, when a plurality of beacon signals are not continuously received, the communication becomes incapable of communication for a long time.

In the time synchronization method and apparatus according to the present invention, in addition to a beacon signal transmitted periodically, a data packet including time information and schedule information is transmitted between beacon signals, every predetermined number of beacon signals, or a predetermined number of transmitted and received signals. By periodically generating and transmitting a data packet (TSEPB) containing time information for each data packet periodically, it provides a means for additionally guaranteeing time synchronization.

4 illustrates a structure of a data packet TSEPB including time information according to the present invention.

Unlike regular data packets, an extension field is provided between the header and the MAC Packet Data Unit (MPDU), and the extension field includes a TSE indication field, a remaining time field, and a schedule information field indicating that the extension field is TSE. do.

The remaining time field indicates the time remaining until receiving the next beacon signal in the corresponding beacon interval. According to an embodiment, the time required from the lost beacon signal to the time when the TSEPB is received may be included in the remaining time field instead of the remaining time.

The last 1 bit of the TSE display field indicates whether to indicate the remaining time or the time required. The schedule information field includes information on the time slot to be allocated in the TDMA communication.

As shown in FIG. 3, when the peripheral device A does not receive the second beacon signal due to an error or the like, data transmission and reception cannot be performed during the second beacon interval, and thus data 5 cannot be received. However, when the peripheral device A receives the data packet TEPB including the time information, the time is synchronized using the information included in the extended field of the packet and data can be transmitted and received using the schedule information.

In the conventional system without this TSEPB, once time synchronized with the coordinator, there is also a clock device in the peripheral devices, so if there is no change in the schedule information for allocating time slots, a small amount of one or two beacon signals is lost. Only data packets are lost and communication can be resumed. However, if several beacon signals are lost in succession, or if communication must be performed without beacon signals, an error may occur in the coordinator's clock and the clock in the peripheral device, which may cause time synchronization to be lost.

If communication is to be performed without a long beacon signal, the TSEPB according to the present invention may be transmitted every predetermined number, for example, 100 beacon intervals. The number of beacon intervals that become the period of TSEPB transmission may vary according to embodiments, and when communication is performed without a beacon signal, it is preferable to allow the TSEPB to be transmitted before an error occurring between the coordinator clock and the clock in the peripheral device exceeds an acceptable range. Do.

In another embodiment, one TSEPB according to the present invention may be inserted one at every beacon interval to assist the beacon signal to transmit time information and schedule information.

In another embodiment, the TSEPB according to the present invention may set the number of data packets to be transmitted or received regardless of the beacon signal, and may be transmitted once for each set number of data packets.

In this case, the number of data (MaxTSE), which is the period of TSEPB transmission, is set, and a variable (PckCnt) indicating the number of data transmitted / received to the memory in the coordinator device is assigned, and the value of the variable each time data is transmitted or transmitted. Increase by one, and if the variable value PckCnt exceeds the transmission period MaxTSE, TSEPB is embedded in the data packet to be transmitted and transmitted. Peripherals support the role of the beacon signal by receiving TSEPB-embedded data packets, synchronizing the time when the beacon signal is lost, and recovering the beacon interval.

In the TDMA-based wireless communication system, even when a beacon signal is lost, time synchronization can be restored to maintain communication.

According to the wireless communication system of the present invention, by periodically transmitting a data packet including time information and schedule information, time synchronization can be additionally ensured even when a beacon signal cannot be used.

According to the present invention, when the beacon signal is lost, time synchronization can be restored without transmitting a request signal for recovery to the coordinator communication device.

The present invention can be applied not only to the wireless local area network system of the 60Ghz band but also to all wireless network systems requiring time synchronization, for example, a communication system such as IEEE 802.11a, IEEE 802.15.3, IEEE 802.15.4, 3GPP, 4G, etc. There is this.

Claims (9)

Periodically transmitting a beacon signal including time information in the coordinator; Periodically transmitting a data packet including time information; Receiving the beacon signal at a peripheral device and time synchronizing with the coordinator; And Receiving a data packet including the time information and time synchronizing with the coordinator when the peripheral apparatus does not receive the beacon signal; Time synchronization method comprising a. The method of claim 1, Periodically transmitting the data packet including the time information, Transmitting a data packet including the time information each time a predetermined number of general data packets are transmitted. The method of claim 1, Periodically transmitting the data packet including the time information, And each time a predetermined number of beacon signals are transmitted, transmitting a data packet including the time information. And a beacon signal including time information and a data packet including time information are periodically generated and transmitted. The method of claim 4, wherein And the coordinator transmits a data packet including the time information each time a predetermined number of general data packets are transmitted. The method of claim 4, wherein And the coordinator transmits a data packet including the time information each time a predetermined number of beacon signals are transmitted. The method of claim 4, wherein The communication device for the coordinator is a communication device for a wireless communication coordinator, characterized in that the communication with the peripheral devices in a time division multiple access (TDMA). And receiving a beacon signal from the coordinator communication device to synchronize time, and if not receiving the beacon signal, receiving the data packet to synchronize the time. The method of claim 8, And said communication device for wireless communication peripheral devices communicates by time division multiple access (TDMA).

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