KR100645868B1 - A method of multimedia medium access control for high-speed powerline communication - Google Patents

Abstract

A multimedia access control method for very high speed power line communication is provided to considerably improve a buffer overflow phenomenon of a video or data node and lower a frame loss rate in very high speed power line communication. After nodes, which are currently performing transmission, finishes the transmission of frames, all of the nodes having frames to be transmitted detect a carrier on a medium. If no carrier of a medium is sensed during a certain time, priority levels of each frame to be transmitted are determined. A node having a frame of the highest priority level transmits the frame, and in this case, the node transmits the frame selected according to a back-off counter value determined between 0 and a CW(Contention Window). The CW value is determined according to the number of standby frames accumulated in a standby queue of each node.

Description

A method of multimedia medium access control for high-speed powerline communication

1A is a diagram schematically illustrating steps of performing a conventional HomePlug 1.0 and a media access control method according to the present invention.

FIG. 1B is a diagram illustrating interframe spacing in a conventional HomePlug 1.0 and a media access control method according to the present invention.

2 is a flowchart illustrating in detail the operation of the voice node according to the medium access control method according to the present invention.

3 is a flowchart illustrating in detail the operation of a video node and a data node according to the method for controlling media access according to the present invention.

4 is a simulation graph comparing the throughput of the method used in the conventional HomePlug 1.0 and the method according to the present invention.

5 is a simulation graph comparing the average delay of the method used in the conventional HomePlug 1.0 and the method according to the present invention.

6 is a simulation graph comparing the queue overflow of the method used in the conventional HomePlug 1.0 and the method according to the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a medium access control (MAC) method, and more particularly, a medium that solves a problem of information collision that occurs when a plurality of network users share information in a power line communication network environment. It relates to a connection control method.

To date, a lot of researches have been conducted on the method and protocol of media access control, and representative examples are Carrier Sense Multiple Access with Collision Detection (CSMA / CD) and mainly wireless. Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA), which is used in a local area network, may be used. These two methods of operation basically use the CSMA scheme, which detects the carrier signal of the medium and attempts transmission only when no signal is detected (ie, when no node is in use).

However, the CSMA / CD method attempts to transmit immediately if the medium is not in use, and checks whether there is a collision with another node when attempting the transmission, and cancels the transmission immediately after detecting the collision. When the carrier signal is not detected for a sufficient time, the transmission is attempted, and before the transmission, the short request / response control signal is checked to see if it is normally exchanged with the receiving node to avoid collision. Therefore, the CSMA / CA method is known to be useful in an environment where the transmission medium is not stable, such as in a wireless communication or power line communication environment.

On the other hand, HomePlug 1.0 medium access control protocol developed by HomePlug, a research group for powerline communication standardization, is used to modify the CSMA / CA scheme. It includes a Priority Resolution mechanism and a backoff algorithm.

The prioritization mechanism of the Homeplug 1.0 media access control protocol provides preferential access to media in a highly distributed manner. Because this mechanism is distributed, there is no need for the central node to coordinate access to the media as in other networking technologies. HomePlug 1.0 allows four different priority classes, and the core of the prioritization mechanism is Priority Resolution Slots (PRS) and prioritization signals. After each transmission is finished, two slots are allocated for prioritization, and prioritization signals are generated. After prioritization slots, there is only contention between the nodes with the highest priority in the network. For example, if there are four priority classes in the network, priority 3 and priority 2 nodes send a priority determination signal to PRS0, the first priority slot (i.e., priority 3 and priority 2). Nodes will assert PRS0, and priority 1 and priority 0 nodes detect this signal and are deferred for high priority traffic. When priority 3 nodes send a priority determination signal within PRS1, priority 2 nodes are detected and held by priority 2 nodes. Thus, only priority 3 nodes will compete in the race.

According to the backoff algorithm of the Homeplug 1.0 media access control protocol, as in other CSMA / CA algorithms, the random integer between the backoff slot is 0 and the contention window (CW) value. If the backoff value is decremented by 1 and then transmits its frame when it becomes 0, as long as the medium continues to be idle, the medium is not idle (i.e. itself When a node with a lower backoff value transmits a frame, it attempts to suspend its frame transmission attempt.

On the other hand, the HomePlug 1.0 media access control protocol was developed for relatively low-speed powerline communications, while the HomePlug organization has adopted the HomePlug A / V specification to seamlessly accommodate multimedia traffic in powerline communications at 200Mbps. Currently under development but not yet announced.

However, according to the Homeplug 1.0 media access control protocol, the multimedia traffic is divided into a priority class and a high priority traffic is transmitted first. At the same priority level, the open competition is performed as described above. Since the transmission node is determined with the same probability, the quality of service (QoS) of the multimedia traffic is poor, such as flexibility and delay depending on the situation or overflow of a waiting queue. There is a problem that cannot be guaranteed.

That is, according to the conventional Homeplug 1.0 media access control protocol, for example, when a plurality of voice nodes and video nodes attempt to transmit, the voice nodes transmit first because voice traffic belongs to a higher priority class than video traffic. There is a chance, because video nodes have to wait until the end of the transmission of the voice nodes, so that many frames are accumulated in the waiting queue of the video nodes. When the transmission of the voice node is finished and the transmission of the video node starts, the transmission node is determined by the open competition with the same probability regardless of the number of frames accumulated in the waiting queue. There arises a problem that the overall delay time is increased. In addition, when the waiting queue becomes full while waiting for a transmission opportunity and overflow occurs, there is a problem that frames may need to be discarded.

The present invention has been made to solve the above-mentioned problems, and even in the same video node, a node having a large number of waiting frames can have a chance of transmission earlier than a node having a small number of waiting frames, thereby reducing the overall delay time, thereby making high-speed power line communication possible. It is an object of the present invention to provide a medium access control method having a high performance by significantly improving a buffer overflow phenomenon of a video or data node and lowering a frame loss rate.

In addition, according to the HomePlug 1.0 media access protocol, when a node has a transmission opportunity, only one frame is transmitted. However, the present invention determines the number of frames that can be transmitted at one time by considering not only the priority but also the number of waiting frames. It is an object of the present invention to provide a medium access control method capable of determining a more efficient number of transmission frames.

In accordance with one aspect of the present invention, there is provided a method for controlling access to a multimedia medium, comprising: a first step of detecting a carrier on a medium after all nodes having a frame desired to be transmitted are finished transmitting; Determining a priority of a frame to be transmitted if a carrier on the medium is not detected for a predetermined time (CIFS); And a node having the highest priority frame transmits the frame, and the node having the highest priority frame has a value of the backoff counter BC, which is a random value determined between 0 and the contention window value. And a third step of transmitting the selected frame according to the step, wherein the contention window (CW) value is individually determined according to the number of waiting frames accumulated in the waiting queue of each of the nodes, preferably the contention. The value of the window CW is determined to be smaller as the number of idle frames increases.

In addition, according to the multimedia media access control method of the present invention, when the transmitted frame is related to video or data traffic, one or more frames are continuously transmitted. Preferably, the number of the transmitted frames is a priority class of the frame, and It is determined by the number of waiting frames accumulated in the waiting queue of the node.

Hereinafter, a method of controlling a medium connection in power line communication according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1A is a block diagram illustrating the step-by-step functionality of a HomePlug 1.0 and media access control method according to an embodiment of the invention, and FIG. 1B is a diagram illustrating interframe spacing in this method.

In the media access control method according to an embodiment of the present invention, in step 11, the node having the frame to be transmitted continues to detect the channel after the transmission of the node currently being transmitted, and the schedule defined in the CSMA / CA media access control scheme. If no carrier signal is detected on the medium during the Coordination Inter Frame Space (CIF), that is, when no node is transmitting, go to the Priority Resolution Period (PRP) step 12, The transmission will be made first. As a result of step 12, the nodes with the highest priority among the nodes waiting for transmission determine the random value through the backoff process of step 13, and only one node having the lowest random value transmits the frame. Then wait for a response (steps 14 and 15). The remaining nodes, which did not transmit, repeat the initial process in step 11, step 12, and step 13, respectively, to create a transmission opportunity.

2 is a flowchart illustrating in detail the operation of a voice node of a method for controlling a multimedia medium access according to an embodiment of the present invention, which is a voice node, a data node, and a video node of a Homeplug 1.0 medium access control protocol except for step 25. Same as the operation flowchart of all nodes, including.

3 is a flowchart illustrating a method for controlling access to a medium according to an embodiment of the present invention, in which a video node and a data node except a voice node follow the operation flowchart of FIG. 3.

Hereinafter, the operation flowcharts of FIGS. 2 and 3 will be described together, and the same reference numerals are used for the same or similar steps.

If in step 21 the transmission of the node that is already transmitting is terminated and the channel is idle, then the channel is not used for a certain period of time (CIFS) in step 22, the node with the highest priority among the nodes In step 23, the node verifies the PRS0 and PRS1 slots to confirm that its frame has a higher priority than the frames of other nodes.

Then, in step 24, the value of the backoff counter (BC) of the nodes having the highest priority frames is checked, and if it is 0, the process goes to step 25 and assigns each new contention window (CW) value. At the same time, a new backoff counter (BC) is determined, and the value of the backoff counter corresponds to a random value between 0 and the CW value. In the CSMA / CA or HomePoug 1.0 media access control protocol, all nodes apply the same contention window value, which is the maximum value of the backoff counter, but according to an embodiment of the present invention, the number of frames accumulated in the transmission wait queue of each node. The contention window value is applied differently for each node according to the number of waiting frames. That is, a node having a large number of idle frames allocates a contention window value smaller than that of a node that does not, so that the number of backoff counters randomly determined between 0 and CW has a relatively small value.

According to the above embodiment of the present invention, first, all nodes participating in the backoff have a Backoff Counter (BC), a Deferral Counter (DC), and a Backoff Procedure Event (BPE) parameter defined differently according to their priority class. This will be used as the initial value of 0. And CW is defined differently according to BPE in a node with DC. Here, BPE refers to the case of setting a new BC due to a transmission error or when DC becomes 0. DC represents the degree of transmission hold and is selected as an appropriate value according to the value of BPE. For example, if BPE is 0, CW = 7, DC = 0, BPE is 1, CW = 15, DC = 1, BPE is 2, CW = 15, DC = 3, and BPE is 3 or more. In the same way, CW = 31 and DC = 15 are defined by the user according to the priority support level.

 Subsequently, nodes of the same priority participating in the transmission contention each set a random BC value using the contention window value based on the number of frames to be transmitted as described above, and then set the BC value at a predetermined time (slot time). Decrease by one and continue to check if the medium is in use (steps 26, 27 and 29). At this time, when the medium is not still in use and the BC value reaches 0, the node starts transmitting in step 30, but if it detects that the medium is in use before reaching 0, it is already transmitted by a node with a lower backoff counter than itself. Is started, so the process is interrupted through step 28 and the like and returns to the first process. Nodes returning to the initial process are allowed to use the reduced backoff counter value until then as the backoff counter value in the next step, so that they have a chance to gradually transmit preferentially (see steps 24 and 24 ').

Meanwhile, according to the HomePlug 1.0 medium access protocol, when a node has a transmission opportunity, only one frame is transmitted. However, according to an embodiment of the present invention, when a video or data is to be transmitted rather than a traffic that is very sensitive to delay such as voice. Based on the concept applied in the IEEE 802.11e high-speed wireless communication protocol (that is, the number of frames that can be transmitted at one time depends on the priority), and the number of frames that can be transmitted at one time is the number of waiting frames. Consider it at the same time. That is, the node to start the transmission is allocated differently the TX_Counter value indicating the number of frames that can be transmitted at one time according to the number of transmission waiting frames accumulated in the waiting queue. For example, if the number of frames waiting to be transmitted is less than or equal to the first threshold, a plurality of frames can be transmitted at one time, such as one frame, two frames between the first and second thresholds, and three frames if the second threshold or more. An appropriate TX_Counter value is assigned (step 33 of FIG. 3).

After transmitting one frame in step 30 of FIG. 3, the node capable of transmitting a plurality of frames decreases TX_Counter by 1, waits for a response from the receiving node, and determines whether there is an error or collision. If there is no collision, the process continues to transmit a plurality of frames without going through the PRP and backoff stages until TX_Counter becomes 0.

4 to 6 show the results of analyzing the performance of the multimedia media access control method proposed in the present invention and the conventional HomePlug 1.0 media access control method through simulation.

4 compares the throughputs of the two methods. In this figure, the X-axis shows the number of nodes generating traffic. In the case of 3 nodes, the data, video, and voice nodes each have 3 nodes, that is, 9 nodes are considered. As shown in FIG. 4, when the number of nodes is smaller than 4, the throughput of the scheme proposed by the present invention for the data nodes is much higher than that of the HomePlug 1.0 scheme. In the case of voice and video, the result is almost similar to that of the HomePlug 1.0 scheme. Is showing.

In Figure 5, the average delay time for the voice and video nodes is shown, and the method proposed by the present invention and the method used in HomePlug 1.0 show almost similar results.

Finally, FIG. 6 shows the number of queue overflows. In the case of the data node, the method proposed by the present invention is much lower than the method used in HomePlug 1.0. This means that the number of frames discarded by the limited queue queue at each node can significantly reduce the overhead of memory management or retransmission of each node.

In the case of video nodes, when the number of nodes increases, the method proposed by the present invention generally shows better performance than the method used in HomePlug 1.0.

4 to 6, the method proposed by the present invention shows a result similar to that used in HomePlug 1.0 in terms of throughput or average delay time for the voice node having the highest priority. For video and data nodes, we see higher throughput and lower overflow rates.

According to the present invention, the same priority nodes can flexibly apply the transmission opportunities according to the number of frames stacked in the waiting queue, so that even if the same video node has a higher number of waiting frames, the nodes having the higher number of waiting frames are more likely to receive the transmission opportunities. This can reduce overall latency and significantly reduce overflow due to limited wait queue lengths.

In addition, according to the present invention, when the node to transmit traffic having a lower priority than voice traffic has a transmission opportunity, the number of frames that can be transmitted can be determined in consideration of not only the priority but also the number of waiting frames accumulated in the waiting queue. This makes it possible to efficiently transmit more than one frame.

Accordingly, the present invention can provide flexibility to efficiently accommodate multimedia traffic, and thus can be utilized as a new medium access control method for guaranteeing service quality of multimedia information in future high-speed power line communication.

Claims (3)

A multimedia medium access control method for high speed power line communication, Detecting a carrier on a medium after all nodes having a frame to be transmitted have finished transmitting the current node; Determining a priority of a frame to be transmitted if a carrier on the medium is not detected for a predetermined time (CIFS); And The node having the highest priority frame transmits the frame, but the node having the highest priority frame is assigned to the value of the backoff counter BC, which is a random value determined between 0 and the contention window value. In accordance with the third step of transmitting the selected frame according to, The contention window (CW) value is determined individually according to the number of waiting frames accumulated in the waiting queue of each of the nodes. The method of claim 1, And when the frame transmitted in the third step relates to video or data traffic, one or more frames are continuously transmitted according to the length of the waiting queue. The method of claim 2, And if the number of frames continuously transmitted is two or more, waits for a response from a receiving node after transmitting one frame, and continuously transmits the next frame if there is no error or collision.

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