KR100697828B1 - A low-power consumption traffic control method for wireless sensor network using media access control protocol - Google Patents

Abstract

The present invention relates to a low-power traffic control method in a wireless sensor network using a medium access control method. In detail, the present invention can extend network life time and guarantee quality of service (QoS) of wireless terminals in a wireless sensor network. The present invention relates to a traffic control method using media access control. Such a traffic control method includes allocating a designated backoff time for specifying an access order in advance to at least one real-time terminal to which a real-time packet is to be transmitted, and performing a backoff procedure to generate a real-time packet with a backoff time of zero. Allowing a non-real time terminal to transmit a non-real time packet by performing a backoff procedure on at least one non-real time terminal to which the non-real time packet is to be transmitted, and transmitting the non real time packet. If the real-time packet transmission fails, allocating an arbitrary backoff time to the corresponding non-real time terminal and retrying to transmit the non-real time packet after the allocated backoff time has elapsed. .

Medium access control, traffic control

Description

A low-power consumption traffic control method for wireless sensor network using media access control protocol

1 is a conceptual diagram of a superframe for media access control according to an embodiment of the present invention;

2 is a bandwidth allocation table for a guaranteed service according to an embodiment of the present invention.

3 is an exemplary view for explaining a method of transmitting a real-time packet according to an embodiment of the present invention.

The present invention relates to a low power communication method in a wireless sensor network using a medium access control method.

More specifically, the present invention relates to a traffic control method using a media approach that can extend network life time and guarantee quality of service (QoS) of wireless terminals in a wireless sensor network.

In general, data transmitted and received in a communication system includes not only simple data but also data requiring simultaneous real-time and survivability such as control signals and signaling data, and multimedia data such as video and audio.

Since all such data is transmitted through one physical transmission path, a technique is needed to distinguish each data and to transmit the data appropriately. That is, since different Quality of Service (QoS) is required for each data, in order to support them effectively, the transmission path must be controlled according to the characteristics of the data.

The traffic can be classified into Guaranteed Service, Predictive Service, and Best-Effort Service, depending on the degree of strictness of satisfaction with the QOS request. It is required to fully satisfy the end-to-end latency conditions, packet loss rate, etc., so that sufficient resources must be allocated to guarantee this. In general, data requiring real time and survivability at the same time as data related to control or signaling related data require such a guaranteed service.

On the other hand, various functions are implemented on the network to support guaranteed services. The functions include routing function, resource reservation function, call admission control function, and packet scheduling. Scheduling, and policing functions, among which routing, resource reservation, and lock control functions are required before the call is set up. This function is applied during transmission.

The packet scheduling function corresponds to a function that operates on a packet basis to determine whether the next packet to be transmitted is in an input path, and block other input paths even if there is a packet to be transmitted.

The present invention is particularly for providing a guaranteed service in a wireless sensor network, the wireless sensor network is a technical field that can be applied in various fields such as environmental monitoring, medical systems, robot exploration. In such a network, many distributed terminals (or nodes) generally configure the network in a multi-hop form by themselves. Each terminal has several sensors, an embedded processor, a low-power radio communication interface, and is primarily battery powered. Typically these terminals are intended to cooperate with each other for a common task.

As with all shared media networks, Media Access Control (MAC) is an important technology element for successful operation of the network. The most basic role of media access control is to prevent two or more terminals from starting transmission at the same time to avoid collisions, and there are many media access control protocols developed for wireless voice or wireless data networks. There are competition based protocols such as TDMA, CDMA and IEEE802.11.

In particular, it is important to improve energy efficiency for media access control suitable for wireless sensor networks. The wireless sensor terminal uses a battery power supply method, and in some cases, it is difficult to replace or recharge the battery, and in such a case, when the end of life instead of replacing or recharging the battery by lowering the manufacturing cost of the sensor terminal is discarded This is because there are many cases. For this reason, the present invention is designed to provide a traffic control method for smoothly providing guaranteed services while improving energy efficiency.

An object of the present invention is to provide a traffic control method of a wireless sensor network that can provide a guaranteed service while simultaneously reducing energy consumption of each terminal of the wireless sensor network.

Low power traffic control method in a wireless sensor network according to an embodiment of the present invention for achieving the above object is

Allocating a designated backoff time to predetermine an access order to at least one real-time terminal to which a real-time packet is to be transmitted, and performing a backoff procedure to allow a real-time terminal having a backoff time of 0 to transmit real-time packet data And performing a backoff procedure on at least one non-real time terminal to which the non-real time packet is to be transmitted, allowing the non-real time terminal having a backoff time of 0 to transmit the non-real time packet; If the packet transmission fails, allocating an arbitrary backoff time to the corresponding non-real time terminal, and retrying the transmission of the non-real time packet after the allocated backoff time has elapsed. .

According to the configuration as described above, it is possible to efficiently transmit data while smoothly performing real-time packet transmission for the guaranteed service.

In addition, the low-power traffic control method in the wireless sensor network according to another embodiment of the present invention performs carrier detection for data transmission, and for this purpose, when the network allocation vector value is inspected, a predetermined time when data transmission is impossible While deactivating the communication interface of the associated terminal.

According to the above-described configuration, the power supply for the communication interface is cut off during the time when data transmission is impossible, thereby reducing energy consumption and increasing the survival time of the wireless sensor network terminal.

In addition, the low power traffic control method in the wireless sensor network according to another embodiment of the present invention is to be variably determined according to the result of comparing the channel utilization rate of the medium with the activation / deactivation period of the at least one wireless sensor network terminal. It is characterized by one.

According to the configuration as described above, by optimizing the period of activation according to the channel utilization rate of the medium, it is possible to prevent unnecessary activation of the communication interface of the terminal to further reduce the power consumption.

In the medium access control method for the preferred embodiment of the present invention, the terminal (or nodes) constituting a PAN (Personal Area Network) or a virtual cluster basically accesses the medium as in the existing IEEE802.15.4 MAC or S-MAC. Has a superframe structure. This superframe is composed of an active period in which nodes can transmit and receive and an inactive period in which a node sleeps or stands in a state where power consumption is minimized. Activation intervals are contention free periods (CFPs) used for the transport of real time traffic (rt-traffic), which in turn require guaranteed services, and nrt-traffic, which typically requires the best service. It is divided into Contention Access Period (CAP) which is used for transmission of non-real time traffic.

In the non-competition period, the media is accessed in a contention free manner so that collisions do not occur between real-time terminals (or nodes: rt-nodes) requiring the transmission of real-time traffic according to the procedure of the present invention. It is configured to transmit data, and in the contention period is configured to access the medium competitively in the so-called CSMA / CA method.

Terminals constituting the virtual cluster according to the embodiment of the present invention repeat activation and deactivation of the same period. The duty cycle of activation / deactivation is variably determined according to the utilization rate of the channel. Details thereof will be described later.

Each terminal selects its own schedule and exchanges schedule information with neighbors before starting periodic activation and deactivation, and each terminal manages a schedule table that stores schedules of neighbors it knows. Details of schedule management in this regard follow a publicly-known procedure, and a detailed description thereof will be omitted.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, if it is determined that a detailed description of related known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

1 is a conceptual diagram of a superframe for media access control according to an embodiment of the present invention.

According to Fig. 1, updating of a schedule consists of sending a synchronization packet. The synchronization packet is configured to include the sender's address, the time required to start the next contention interval (t _cap ) and the time required to start the next inactivity interval (t _sleep ), and through this information, each terminal (or node) can Will be synchronized.

In order for each terminal to receive a synchronization packet or a data packet, the super frame is divided into three parts, the first part for the synchronization packet, the second part for the non-competition part (CFP), and the third part for the contention part ( CAP).

The transmission of real-time packets authorized only to real-time terminals for providing guaranteed service in a non-competition period performs a backoff procedure with a pre-defined backoff time value corresponding to a pre-assigned unique access order. Nodes occupy the medium in turn and begin transmitting real-time packets. That is, only one terminal, which is given a small value according to a unique access order, becomes a winner, and as a result, data can be transmitted in a non-competitive manner.

When a band allocation request for guaranteed service is received from each terminal, the network management terminal determines whether to accept or reject the request from the band allocation table and selects and specifies the minimum value that can be taken in the band allocation table as illustrated in FIG. Allocate a backoff time. At this time, the device address (device address) of the terminal requesting the assignment is recorded and the state is changed to the assignment. The backoff time value is determined according to how many guaranteed services will be accommodated. In a typical wireless sensor network, the number of terminals requesting guaranteed services is not large. In the case of IEEE802.15.4, up to seven can be accommodated.If the number of guaranteed services is excessively increased, the proportion of non-competition periods increases, and the proportion of contention periods decreases, thereby reducing the transmission opportunities of general data, thereby reducing data transmission efficiency. The chances are high.

The process of performing the backoff procedure by the real-time nodes after the synchronization packet is transmitted will be described with reference to FIG. 3 (a).

3 (a), three real-time terminals are assigned. The real time terminal (#AAAA) has a backoff time value of 1, the real time terminal (#BBBB) has a backoff time value of 2, and the real time terminal (#CCCC) has a backoff time value of 3 You can see that it is assigned. After the synchronization packet is transmitted and 1 t _BackoffSlot elapses, the backoff time of the real-time terminal (#AAAA) becomes 0 and packet transmission can be started. However, other nodes remain in the backoff state because the backoff time value remains, that is, not zero. When the real-time terminal (#AAAA) starts transmission, other nodes set the network allocation vector (NAV) based on the value of the duration field of the transport packet, and the backoff timer value is maintained at the current value state. When the network allocation vector time expires, the nodes decrement the backoff timer again after 1 t _BackoffSlot and the real-time terminal #BBBB acquires a transmission right. This causes the network allocation vector to be set when the real-time terminal (#BBBB) starts transmission and the real-time terminal (#CCCC) remains in the backoff state. You will have a chance to send. In this case, other terminals except the terminal having the transmission opportunity check whether the receiver of the packet to be transmitted is their own, and if the terminal is not the receiver, set the network allocation vector and avoid overhearing.

FIG. 3 (b) shows a traffic control method on a medium assuming that a real time terminal #BBBB having a backoff time value of 2 is deallocated. Even when the terminal having the backoff time value of 2 is deallocated, the real-time terminal #AAAA is able to transmit the synchronization packet after 1 t _{BackoffSlot irrespective of} this. In the case of a real-time terminal (#CCCC), as the real-time terminal (#BBBB) is _deallocated , the transmission opportunity is obtained immediately after 2 t _BackoffSlot after the transmission of the real-time terminal (#AAAA) is completed.

Through such a configuration, all real-time terminals are provided with one transmission opportunity in each superframe, thereby providing stable guaranteed service.

When the transmission of the real time packet is completed, the transmission of the non-real time packet is started during the contention period. In order to transmit a non-real time packet, a carrier is sensed to acquire a use right of a medium through a backoff procedure. In one embodiment of the present invention, the broadcast packet of the real time packet and the non-real time packet is transmitted without RTS / CTS, but the unicast packet is transmitted according to the RTS / CTS / DATA / ACK procedure. To perform the backoff procedure, the backoff counter decrements the counter while the channel is idle and stops counting while the channel is busy. When the backoff counter reaches zero, that is, the backoff time has elapsed, the node will begin transmitting. At this time, the collision of data transmission does not occur, and when the receiving terminal receives the packet, the transmission procedure is terminated. However, if a terminal to transmit a packet fails in carrier sensing, it determines an arbitrary backoff time and designates it as the backoff time of the related terminal. When the value of the backoff time counter becomes 0 according to the designated backoff time, Attempt to retransmit.

Equation for determining the back off time for the embodiment of the present invention is as shown in Equation 1 below

Here, a = 0, b = b _min x 2 ^r <b _{max ,} and b _{min = 32 and} b _{max = 1024} in the embodiment of the present invention. r represents the number of retransmissions, and Backoffslot_Time is the sum of the time each terminal detects the packet, the transmission delay time, the time required to switch from the reception state to the transmission state, and the time required to notify the state of the channel to the MAC layer. Value.

According to the above-described configuration, real-time packet traffic for guaranteed service and non-real-time packet traffic allocation for general data transmission are optimized, so that stable traffic control and power consumption are reduced, thereby extending the life of the wireless sensor network terminal. Will be.

Meanwhile, a carrier sensing method for transmitting a real time packet or a non-real time packet can be largely divided into virtual carrier sensing and physical carrier sensing. In general, a wireless network terminal listens to data transmissions from all neighboring terminals for virtual carrier detection. As a result, it receives packets that are not delivered to them, that is, overhearing, resulting in increased network traffic, resulting in increased energy waste. In an embodiment of the present invention, a duration field is included in a packet to be transmitted, so that terminals other than the receiving terminal can predict a time required until data transmission is completed. Therefore, when a terminal receives a packet transmitted to another terminal, the terminal may predict how long data transmission continues through the delay field value, and the delay field value is inputted into the network allocation vector to count. Done. Although the value of the input network allocation vector is gradually decreased, it is determined that the medium is in use until the value becomes 0, so that a communication operation such as data transmission is not performed. On the other hand, physical carrier detection that checks whether a channel can be transmitted in the physical layer is a publicly known technique, and a detailed description thereof will be omitted.

On the other hand, when it is determined that the medium is in use as a result of the inspection of the network allocation vector, the RF function of the wireless sensor network terminal may be stopped and deactivated to cut off the power, thereby further reducing power consumption.

On the other hand, in order to smoothly provide a guaranteed service in the wireless sensor network, it is important to determine the time that should be occupied in the non-competition period, that is, the time t _cap required to start the competition period. To this end, a non-competition period is obtained by summing all the bandwidths ( BW _i ) of terminals wishing to transmit real-time packets, divided by the data transmission rate ( S ) of the medium, and a value obtained by adding up the maximum value of the time required to perform the backoff procedure. This will determine how long you need to occupy. The maximum value of the time required to perform back-off procedures are to be determined by the product of the time (BackoffSlot .Time) allocated to the maximum value (max.BackoffTime.Value) and each back-off slots in the back-off time. This is summarized as in Equation 2.

Meanwhile, the activation / deactivation interval of the communication interface of the wireless sensor network terminal of the present invention is switched according to a specific cycle. According to the prior art, since the S-MAC method adopts a fixed cycle, it is not a method of reducing power consumption according to the situation, and as a result, the life of the terminal is shortened. In addition, in the so-called T-MAC method, the activation / deactivation cycle is determined adaptively or variably, but the control mechanism is complicated. In the embodiment of the present invention, in order to prolong the life of the wireless sensor network terminal by reducing power consumption, it is variably determined according to the channel utilization rate of the medium.

1) Control procedure to determine activation / deactivation cycle

First, the channel utilization ( U _CH ) of the previous superframe is calculated, and t _SLEEP is dynamically adjusted based on a certain threshold to be adaptively changed according to traffic characteristics and changes. To do this, the control method is summarized as follows.

if ( U _CH  < U _{lower _threshold} )

t _SLEEP  = t _{SLEEP *} α;

if ( U _CH  > U _{upper _threshold} )

t _SLEEP  = t _SLEEP  / α;

else

t _SLEEP  = t _SLEEP ;

Where 0 <a <1, and a is any weight. Any weight factor.

Thus channel utilization U _CH Is the reference value U Compare with _{lower _threshold} and if the utilization rate of the channel is greater than the reference value, the time required to start the activation period, that is, the deactivation period, because the traffic is heavy. T _SLEEP When the size of the channel is increased and the channel utilization is lower than the reference value, there is less traffic. Therefore, the time required to start the activation section or the deactivation section. T _SLEEP The size of the will be reduced.

2) Calculation of Channel Utilization

Channel utilization is monitored and collected at the network management terminal and can be obtained in one of several ways. As a method adopted by the present invention, a method of calculating a 'packet transmission time occupancy ratio' obtained by dividing the total packet transmission time, which is the sum of the transmission times of each packet on the medium, by the synchronization period may be used. Same as 3.

Here, tx is a transmission time of each packet, and SI is a synchronization interval (Sync Interval).

As another method, a method of determining a channel utilization rate by normalizing the sum of the transmission queue (Tx queue) and the reception queue (Rx queue) of the network management terminal (PNC or Synchronizer) may be used. The transmission queue size of the network management terminal may be defined as the sum of message queues for each node or each terminal. This can be summarized as in Equation 4.

Since IEEE802.15.4 uses an indirect transmission method, the network management terminal (PNC) can determine the load of the network through the Tx queue and the Rx queue size.

In terms of the type of traffic generated by the network, if the network accepts only homogeneous traffic that periodically reports its status, the variation in channel utilization will remain very small and average. In this case t _tLEEP will not change.

However, if the event is reported asynchronously whenever the event occurs, several terminals detect the event at the same time and the report comes up, so it shows burst characteristics (correlated), especially in this case according to the present invention The adaptive activation / deactivation cycle setting method is very effective.

According to this method, in controlling traffic in a wireless sensor network, real-time packets are controlled by a designated backoff time, non-real-time packets are controlled by a random backoff time, and activation of a communication interface using a channel utilization rate. By controlling the / deactivation, it is possible to control the traffic at low power, and consequently, the effect of extending the survival time of the wireless sensor network terminal is generated.

As described above, according to the present invention, it is possible to smoothly designate a real-time packet transmission for a guaranteed service in a wireless sensor network, and furthermore, by limiting the activation of each wireless sensor network terminal to a necessary case, reducing unnecessary power consumption to survive. The effect of prolonging time is achieved.

On the other hand, the present invention has been described with reference to the embodiments shown in the drawings, which are merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention should be defined only by the appended claims.

Claims (9)

Allocating a designated backoff time for specifying an access order in advance to at least one real-time terminal to which a real-time packet is to be transmitted; and Performing a backoff procedure to allow a real time terminal having a backoff time of 0 to transmit real time packet data; and Performing a backoff procedure on at least one non-real time terminal to which a non-real time packet is to be transmitted, and allowing a non-real time terminal having a backoff time of 0 to transmit the non-real time packet; and Detecting the presence or absence of a packet carrier when allowing the transmission of the real time packet and the non real time packet, and transmitting the real time packet or the non real time packet only when the packet carrier exists; and Allocating a random backoff time to a corresponding non-real-time terminal when data transmission fails in the non-real time packet transmission; and Retrying to transmit a non-real time packet after the allocated backoff time has elapsed; Low power traffic control method in a wireless sensor network using a medium access control method comprising a. delete The method of claim 1, The carrier detection includes a virtual carrier detection for determining whether data can be transmitted according to a value of a network allocation vector (NAV) and a physical carrier detection for checking whether data can be transmitted in the physical layer. A low power traffic control method in a wireless sensor network using a medium access control method. The method according to claim 1 or 3, As a result of checking the network allocation vector value of each terminal, when data transmission is impossible, the low power traffic control method in a wireless sensor network using a medium access control method, characterized in that the communication interface of the terminal is deactivated for a predetermined time. . The transmission time of data allocated to the one or more real-time terminals for transmitting real-time data is the sum of the bandwidths of the real-time terminals divided by the transmission rate of the data transmission medium. Low power traffic control method in a wireless sensor network using a medium access control method, characterized in that the sum of the maximum time required to perform the off procedure. The method according to claim 1 or 3, The activation / deactivation period of the at least one wireless sensor network terminal is variably determined according to a result of comparing the channel utilization rate of the medium with a predetermined threshold. The method according to claim 1 or 3, In the wireless sensor network, a synchronization packet is configured to control traffic, wherein the synchronization packet includes a time t _cap required until the start of the next contention period and a time t _sleep until the start of the next deactivation period. Low power traffic control method. The method of claim 6, The channel utilization rate is calculated by the share of packet transmission time on the medium, low power traffic control method in a wireless sensor network. The method of claim 6, The channel utilization rate is normalized by summing the sizes of the transmission queue (Tx Queue) and the reception queue (Rx Queue) of the network management terminal (PNC).

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