KR101330603B1 - Communication method using relay-based cooperative mac protocol - Google Patents

Abstract

A communication method using a cooperative MAC protocol is disclosed. The communication method comprises: detecting, by a source node, whether a channel is idle in a network and reserving the channel; transmitting, from a relay node to the source node, a relay response including the presence of the relay node and the capacity of a transfer rate after the channel is reserved; selecting, by the source node, two optimal relay nodes for data transmission and backup transmission whose transmission performance is better than direct source to destination node transmission based on the relay response; and cooperatively transmitting, by the source node, data to the destination data using the two optimal relay node. [Reference numerals] (210) Detecting, by a source node, whether a channel is idle in a network and reserving the channel;(220) Transmitting from a relay node to the source node;(230) Selecting, by the source node, two optimal relay nodes whose transmission performance is better than direct source to destination node transmission based on the relay response;(240) Cooperatively transmitting, by the source node, data to the destination node using the two optimal relay nodes;(AA) Start;(BB) End

Description

Communication method using relay-based cooperative MAC protocol

The present invention relates to a relay-based cooperative MAC protocol, and in particular, by utilizing a relay node that supports communication from a source node to a target node in a wireless ad hoc network, wireless nodes constituting the network cooperate with each other. A method of performing communication and a recording medium recording the method.

Ad hoc network is a communication network in which all communication terminals with similar characteristics communicate with each other directly through a wireless channel, unlike a wireless LAN that communicates with a mobile communication network or an access point (AP). It is a network composed autonomously by nodes. The nodes constituting the ad hoc network communicate with each other using a wireless interface, overcome the limitations of communication distance of the wireless interface by the multi-hop routing function, and move the nodes freely. topology) is dynamically changed. In addition, the ad hoc network may be configured as completely standalone, or may be interworked with an underlying network such as a general Internet via an Internet gateway.

Despite the above advantages, most wireless networks, including ad hoc networks, have a critical limitation of bandwidth limitation compared to wired networks. For this reason, one of the important challenges to be solved in a wireless communication network is to increase system performance, and to achieve this, it is most important to increase the frame rate of the data link layer. To increase the frame rate, the signal-to-noise ratio (SNR) value at the receiver side must be improved or the reception performance can be improved. Currently, the standard widely used in the physical layer and data link layer is IEEE 802.11 WLAN. This specification is due to the fact that DCF techniques based on the CSMA / CA protocol provide very good performance on a single hop, while flexibly solving hidden or exposed nodes.

On the other hand, the increasing demand for higher throughput and lower latency in wireless ad hoc networks has led to extensive research into new techniques, algorithms and techniques, and different modulation / demodulation techniques and channel coding techniques depending on the channel quality of the wireless communication network. A cooperative communication technique has been proposed to further improve system performance based on link adaptation, which is a transmission rate adjustment scheme using a DMA. This cooperative communication uses the broadcast nature of wireless channels to reduce channel failures (average path loss and fading), improve the network's processing power, and reduce the spatial diversity of independent paths (retransmission delays). Take advantage of spatial diversity. In a cooperative communication paradigm, nodes cooperate with source and target nodes at either the physical (PHY) layer or the MAC layer to improve throughput, delay, and coverage. Non-patent documents cited below describe the diversity characteristics of such cooperative communications.

 J. Laneman, G. Wornell, and D. Tse, “An Efficient Protocol for Realizing Cooperative Diversity in Wireless Networks,” in Proc. IEEE International Symposium on Information Theory (ISIT), USA, pp. 294, Jun. 2001.  A. Sendonaris, E. Erkip, and B. Aazhang, “User Cooperation Diversity Part I: System Description,” IEEE Trans. Commun., Vol. 51, No. 11, pp. 1927-1938, 2003.

The technical problem to be solved by the embodiments of the present invention is to overcome the limitation of the data rate and throughput constraints in the conventional ad hoc network, the reliability of data transmission is deteriorated due to signal interference or interference in the ad hoc network based on the wireless communication method It is intended to solve the technical problem that it is difficult to simultaneously provide higher throughput with higher success rate of data transmission, especially under fading conditions.

In order to solve the above technical problem, data is transmitted from a source node to a target node in a network including a source node, a destination node, and a relay node according to an embodiment of the present invention. The communication method may include: detecting, by the source node, whether a channel of the network is idle and reserving the channel; After the reservation of the channel, the relay node sending a relay response to the source node including its presence and rate capacity; Selecting, by the source node, two best relay nodes having better transmission performance than direct transmission between the source and target nodes from the transmitted relay response; And the source node cooperating to transmit the data to the target node using the selected two best relay nodes, wherein a first best relay node of the two best relay nodes transmits the data. A primary node, the second best relay node of the two best relay nodes is a back-up node for auxiliary transmission of the data.

In the communication method according to an embodiment, the selecting of the best relay node may include: a combined transfer rate value indicating a transfer rate when passing through a relay node based on the transmitted relay response is greater than a source-target transfer rate; Selecting a first best relay node having; Dividing the combined rate value by the source-target rate value; And selecting a second best relay node having a relay-target rate value greater than a predetermined magnification of the source-target rate based on the divided value and having a source-relay rate value greater than that of the first best relay node. It includes; step.

In the communication method according to an embodiment, the two best relay nodes may include a transmission time between the source node and the first best relay node, a transmission time between the first best relay node and the target node, and the second. The sum of the transmission times between the best relay node and the target node is selected to be less than the direct transmission time between the source node and the target node.

In the communication method according to an embodiment, the step of cooperatively transmitting the data to the target node may include: transmitting, by the source node, the data to the target node through the first best relay node; And when the source node receives a confirmation message indicating the normal reception of the data after the data is transmitted, the source node completes the data transmission, and the best relay nodes clear the buffer. It includes; step.

In the communication method according to an embodiment, the step of cooperatively transmitting the data to the target node may include: transmitting, by the source node, the data to the target node through the first best relay node; And if the source node does not receive an acknowledgment message indicating the normal reception of the data after the data is transmitted, the source node auxiliaryly transmitting the data through the second best relay node.

In the communication method according to an embodiment, the step of cooperatively transmitting the data to the target node may include: transmitting, by the source node, the data to the target node through the first best relay node and the second best relay node. Transmitting sequentially; And when the source node does not receive any acknowledgment message indicating the normal reception of the data after transmission of the data, the best relay nodes clear the buffer and the source node exponential back-off. Retrying the data transfer using a procedure).

In the communication method according to an embodiment, the reserving of the channel may include: sending, by the source node, a request-to-send (RTS) packet for the channel reservation to the target node; And after the target node receives the RTS packet, the target node responding to the source node with a clear-to-send packet.

In the communication method according to an embodiment, the relay node monitors data transmission of neighboring nodes and updates a network allocation vector (NAV) table for identifying a transmission interval through the network. The network allocation vector table further includes a data rate estimated using the average path loss.

In order to solve the technical problem, a communication method for transmitting data from a source node to a target node in a network including a source node, a target node and a relay node according to another embodiment of the present invention, the source node of the network Detecting whether a channel is idle and reserving the channel; After the reservation of the channel, the relay node sending a relay response to the source node including its presence and rate capacity; Selecting, by the source node, only one best relay node having better transmission performance than the direct transmission between the source and target nodes from the transmitted relay response; And the source node cooperatively transmitting the data to the target node using the selected one best relay node, wherein the source node directly transmits the data to the target node. The best relay node is a backup node for auxiliary transmission of the data.

In the communication method according to another embodiment, the selecting of the best relay node may include: a combined transfer rate value indicating a transfer rate when passing through a relay node based on the transmitted relay response is greater than a source-target transfer rate; The relay node having the same is selected as the best relay node.

In the communication method according to another embodiment, the step of cooperatively transmitting the data to the target node includes: transmitting, by the source node, the data directly to the target node; And if the source node does not receive a confirmation message indicating the normal reception of the data after the data is transmitted, the source node auxiliaryly transmitting the data through the best relay node.

In order to solve the technical problem, a communication method for transmitting data from a source node to a target node in a network including a source node, a target node and a relay node according to another embodiment of the present invention, the source node is the network Detecting whether the channel is idle and reserving the channel; After the reservation of the channel, the relay node sending a relay response to the source node including its presence and rate capacity; Searching, by the source node, the best relay node having better transmission performance than direct transmission between the source and target nodes from the transmitted relay response; If the best relay node is not found as a result of the search, selecting one alternative relay node having the best transmission performance based on the relay response; And the source node cooperatively transmitting the data to the target node using the selected one alternate relay node, wherein the source node directly transmits the data to the target node. The alternate relay node is a backup node for auxiliary transmission of the data.

In the communication method according to another embodiment, the step of cooperatively transmitting the data to the target node, the source node directly transmitting the data to the target node; And if the source node does not receive a confirmation message indicating normal reception of the data after the data is transmitted, the source node auxiliaryly transmitting the data through the substitute relay node.

On the other hand, the following provides a computer-readable recording medium recording a program for executing a communication method for transmitting data from a source node to a target node in a computer in a network including the source node, the target node and a relay node described above. .

Embodiments of the present invention maximize the data rate and throughput in an ad hoc network by selecting the best relay node with better transmission performance than direct transmission between source and target nodes, and adaptively performing cooperative communication according to the detected network state. In addition, the reliability of data transmission can be improved by utilizing relay node which performs backup communication, and data transmission under fading condition by using direct transmission between source and target node and indirect transmission method using best relay node. It is possible to simultaneously provide higher throughput with higher success rates.

1 is a diagram illustrating a method for performing cooperative communication through an ad hoc network in which embodiments of the present invention are implemented and nodes constituting the same.
2 is a flowchart illustrating a communication method of transmitting data using two best relay nodes in an ad hoc network according to an embodiment of the present invention.
3 is a diagram illustrating a structure of a relay response frame adopted by embodiments of the present invention.
4 is a flowchart illustrating a process of selecting the best relay node in more detail in the communication method of FIG. 2 according to an embodiment of the present invention.
5 is a flowchart illustrating a process of cooperatively transmitting data to a target node using two best relay nodes in the communication method of FIG. 2 according to an embodiment of the present invention.
6 is an exemplary diagram for explaining a cooperative transmission process of FIG. 5 using two best relay nodes according to an embodiment of the present invention.
7 is a flowchart illustrating a communication method of transmitting data using one best relay node in an ad hoc network according to another embodiment of the present invention.
FIG. 8 is a flowchart illustrating a process of cooperatively transmitting data to a target node using one best relay node in the communication method of FIG. 7 according to another embodiment of the present invention.
9 is an exemplary view for explaining a cooperative transmission process of FIG. 8 using one best relay node according to another embodiment of the present invention.
10 is a flowchart illustrating a communication method of transmitting data by using one alternative relay node in an ad hoc network according to another embodiment of the present invention.
FIG. 11 is a flowchart illustrating a process of cooperatively transmitting data to a target node using one alternate relay node in the communication method of FIG. 10 according to another embodiment of the present invention.
12 is an exemplary diagram for describing a data transmission process when a relay response is not received in the embodiments of the present invention.

Prior to describing the embodiments of the present invention, after briefly introducing a cooperative communication technique utilized in the field of ad hoc network communication, the technical means adopted by the embodiments of the present invention to solve problems that may occur under such a communication environment. To be presented sequentially.

1 is a diagram illustrating a method for performing cooperative communication through an ad hoc network in which embodiments of the present invention are implemented and nodes constituting the same. In FIG. 1, an identifier 'S' means a source node, an identifier 'D' means a destination node, and r _n (where n is a positive integer) is a relay node. ) Means.

Cooperative communication is a signal based on a distance in a wireless communication network composed of a source node, a target node, and a relay node (or sometimes referred to as a helper node in terms of helping communication), in order to transmit data directly from a source node to a target node. In addition to the weakening of the strength, poor channel conditions may cause delays in transmission time and degradation of transmission quality. In particular, when there are certain obstacles between nodes deployed in the ad hoc network or factors that may degrade the wireless communication quality, communication performance may deteriorate although the physical distance is close.

Therefore, rather than transmitting data directly from a source node to a target node, transmitting data through a relay node may help to improve communication quality. In view of this, the proposed technique is a cooperative communication technique. For example, in FIG. 1, it is faster to utilize a path Sr3-r3D that indirectly transmits data through the relay node 'r3', rather than a path SD that directly transmits data from the source node to the target node. Can provide a transfer rate.

Furthermore, when the fading of the received signal power changes with time due to the change of the transmission medium or the path, the necessity of such cooperative communication becomes more important. In particular, in a mobile environment in which one of the antennas of the transmitting side and the receiving side moves relative to the other, the relative position of various obstacles changes over time, resulting in an unexpected transmission effect, resulting in a deterioration in the quality of communication services. Can be. Considering frequent movements in an urban environment, a rapid change in signal strength occurs as the mobile terminal passes a distance, which causes fast fading.

In view of the above problems, the single-hop ad hoc network cooperative MAC protocol adopted by the embodiments of the present invention described below can achieve performance improvement through the following two main approaches.

First, when the transmission time through the relay path is better than the direct path, the relay node is used, which corresponds to the basic idea of the cooperative protocol.

Second, when direct transmission fails due to fading or interference, a backup transmission is performed by using a relay node, which corresponds to an approach for improving transmission reliability of an ad hoc network.

The first approach examines the channel state or packets on the network and analyzes the transmission path from the source node to the target node. Then, the communication may be performed by selecting either a direct path between the source and target nodes or an indirect path using a relay node having better performance. Although the source-target node can communicate directly at a rate, cooperative communication can be used with multi-hop communication in that relay nodes can still be utilized to achieve improved data rates. Is different. Relay nodes cooperating at the MAC layer simply forward the received packets to another node for improved throughput and coverage reliability. In particular, when the source-target nodes are separated by a distance that prevents the source node from transmitting directly to the target node at a high data rate, MAC layer cooperation improves the performance of data transmission.

However, although this first method has an advantage in that it can provide better transmission performance and speed, it does not provide appropriate countermeasures for extreme signal strength degradation in a fading environment. Although relay paths can provide higher data rates, they are more susceptible to transmission failures due to independent fading between source-relay links and relay-target links. For this reason, an approach that utilizes the first relay path can provide higher throughput, but has the disadvantage of having a lower packet success rate.

The second approach uses the direct path between the source and target nodes as the main path of data communication, and the indirect path through the relay node as a secondary backup path in case of transmission failure. That is, the second approach utilizes the diversity of relay paths for backup transmission. Thus, data throughput can be improved under network conditions such as Rayleigh fading. In particular, Rayleigh fading is known to conform to the signal propagation models of the convective and ionic layers of the earth, as well as the radio signal effect in urban environments with high buildings, and thus is suitable for the technical field in which embodiments of the present invention are utilized.

As a result of comparing the advantages and disadvantages of the two approaches that can be considered in a collaborative communication environment, we conclude that each approach lacks the ability to simultaneously provide higher throughput and higher throughput under fading conditions. Reached. With this in mind, embodiments of the present invention described below intend to propose a hybrid cooperative communication method in which the above two approaches are appropriately combined. The hybrid cooperative communication method adopted by the embodiments of the present invention utilizes spatial diversity through two best relay paths that provide higher data rates compared to the direct path. In addition, when only one relay path is available according to the network condition, the source node directly transmits data to the target node, grasps the reception status, and adaptively utilizes the relay node for backup transmission.

In order to implement the hybrid cooperative communication method adopted by the embodiments of the present invention, a cooperative MAC protocol for a single channel, single hop ad hoc network is designed as follows. Since the channel is assumed to be symmetric, the communication will experience the same channel fading in any direction. Such a system may consist of evenly distributed nodes to act as potential relays. For convenience of description, in the embodiments of the present invention, source, target and potential relay nodes are always located within communication range with each other when a packet is transmitted at 1 Mbps, and all nodes transmit with a fixed power. Suppose As shown in FIG. 1 introduced above, in a system model for a general cooperative network, nodes manually receive data and update the relay table based on a path loss estimate (average signal loss).

In addition, embodiments of the present invention may consider an IEEE 802.11b physical layer capable of providing multiple data rates such as 1, 2, 5.5, and 11 Mbps. The specification uses a direct sequence spread spectrum (DSSS) at the 2.4 GHz frequency in the Industrial, Scientific and Medical (ISM) band. Differential modulation techniques can be used to achieve varying bit rates, with control packets and headers being transmitted at a fixed rate of 1 Mbps. The achievable data rate between the two nodes depends on the average of the received signal-to-noise ratio, which is to be utilized as one of the indicators of the main function of several factors such as distance, frequency, propagation environment, and total noise at the receiver. Can be.

Data packets transmitted at rates higher than achievable rates cannot be correctly decoded due to an increase in the bit error rate (BER), which results in packet loss. Furthermore, considering the use of an ad hoc network in an urban environment, it is assumed that embodiments of the invention are under fast fading channel conditions. Each packet transmission and each link (eg, will be SD, Sr3 and r3D in FIG. 1) may undergo independent and identically distributed (i.i.d.) Rayleigh fading.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Embodiments of the present invention described below are based on a network operating according to the IEEE 802.11 distributed coordination function (DCF) protocol, and a description thereof will be omitted for a basic configuration that may blur the nature of the present invention.

2 is a flowchart illustrating a communication method of transmitting data using two best relay nodes in an ad hoc network according to an embodiment of the present invention, in which one or two adaptively improves throughput in a fast fading state. Suggest ways to use the best relays.

As discussed above, embodiments of the present invention follow the basic IEEE 802.11 protocol procedure of the cooperative MAC protocols proposed. According to the IEEE 802.11 protocol, a source node wishing to transmit data discovers a channel by detecting a distributed interframe space (DIFS) section. If the channel is detected as idle, the source node randomly performs a back-off for a uniformly distributed time interval between 0 and the contention window (CW), and requests-to-request- to-send) Send the packet to the target. Here, the CW interval is included in the interval [CW _min , CW _max ]. After the short interframe space (SIFS) period has elapsed, the target receiver responds by transmitting a CTS control packet indicating a channel reservation, unless it is busy. This handshaking procedure addresses two important issues: First, the sender and receiver establish communication and initialize parameters. Second, neighboring nodes within the communication range of the sender or receiver do not initiate any transmission during the session.

Neighbor nodes update their network allocation vector (NAV) table for no transmission (called mute time) by extracting information from RTS or CTS packets. Once the reservation for channel use is complete, the source node sends a data packet after the SIFS interval has elapsed and waits for an ACK response from the target. This process consists of RTS + SIFS + CTS + SIFS + DATA + SIFS + ACK, and completes one basic transmission cycle. If the channel is detected to be congested during the DIFS period, the source node delays the transmission. If packet transmission fails due to fading or collision, the source node detects the DIFS interval and then backoff during any interval evenly distributed over the contention window interval [0, CW _i ] (where i is a positive integer). Perform Here, for the i th retransmission attempt, CW _i = 2 ⁱ CW _min and CW _i ∈ [CW _min , CW _max ]. This procedure is called binary exponential backoff.

Accordingly, the above-described communication method in performing a series of procedures according to the embodiment of FIG. The method may further include updating a network allocation vector (NAV) table. Specifically, idle nodes always passively monitor the transmission of their neighbors. The nodes update the network allocation vector table to identify the transmission interval, and the relay table is updated with the node identifier (node ID), entry time of entry and average transmission rate. In addition, the data rate can be estimated using the average path loss converted to the corresponding rate value using the physical mode table.

In operation 210, the source node detects whether a channel of the network is idle and reserves the channel. In this channel reservation process, the source node transmits a request-to-send (RTS) packet for the channel reservation to the target node, and after the target node receives the RTS packet, the target node receives a CTS ( clear-to-send) packet to the source node.

That is, when the source node has a data packet for transmission to the target, the source node detects a channel for an idle state. If the channel remains idle for the distributed interframe space (DIFS) interval, the source will perform back-off for the random interval. According to the IEEE 802.11 protocol, once the backoff counter reaches zero, the source node will send an RTS packet at 1 Mbps to the target node for channel reservation.

In step 220, after reserving the channel through step 210, the relay node transmits a relay response to the source node including its existence and a rate capacity. If the RTS packet is directly decoded at the target node, the target node responds to the source node with a clear-to-send (CTS) packet after a short interframe space (SIFS) interval has elapsed. In embodiments of the present invention, the CTS packet is sent before the relay response (RR) to allow the source and relay nodes to confirm the presence of the target node under fading conditions. Each relay node that has received both RTS and CTS packets responds with a single bit feedback in a relay response (RR) frame to inform the source node of the presence and rate capability of the relay node.

In general, the dynamics of relay nodes under high load and fast fading conditions require real-time updating of relay information. Furthermore, due to the presence of multiple relay nodes, the probability of collision also increases greatly. Accordingly, in order to manage relay contention and obtain rate information, embodiments of the present invention include response information of each relay node, and relay response (RR) frames that help manage each of them separately. I would like to propose.

FIG. 3 is a diagram illustrating the structure of a relay response frame adopted by embodiments of the present invention. The relay response frame is designed as an 8-slot frame having 7 bits per slot, and the size of the relay response frame is shown in FIG. Embodiments of the present invention may be appropriately modified or changed depending on the environment in which they are implemented. In order to identify the relay node, one collision-free bit may be utilized in one slot constituting the relay response frame, and each slot represents a different data rate category. The duration of the relay response frame can be fixed at 60 μs, and each relay node can be correctly synchronized after receiving the CTS bits, indicating the start bit time and the last bit time of the relay response frame.

By using such a relay response frame, embodiments of the present invention can estimate the transmission rate between the source-relay and the relay-target. Based on the estimated data rate, the relay node selects an appropriate data rate slot and transmits a single bit feedback at a randomly selected bit interval position. If the relays do not meet the preset rate requirement in the relay response frame slot, the relays remain idle. To this end, embodiments of the present invention assume that the source node receives a single bit set to '1' when no collision occurs during a particular bit interval. Each relay node stores the bit interval position of the corresponding relay node corresponding to the source node to which the response is sent.

In step 230, the source node selects the two best relay nodes having better transmission performance than the direct transmission between the source and target nodes from the relay response transmitted in step 220. Once a relay response is received during the relay response frame, the source node searches for the two best relays in the same or different slots starting from the rate category. A more detailed process of the source node deriving the two best relays will be described in detail later with reference to FIG. 4.

In step 240, the source node cooperatively transmits the data to the target node using the two best relay nodes selected in step 230. In this case, the first best relay node of the two best relay nodes is a main node transmitting data, and the second best relay node of the two best relay nodes is a back-up node for auxiliary transmission of data. . That is, the embodiments of the present invention secure a relay path through two best relay nodes having better transmission performance than direct transmission between the source and target nodes, and one path is a data communication path and the other path is for ensuring reliability. We propose a hybrid cooperative communication method utilized as a backup communication path.

FIG. 4 is a flowchart illustrating a process of selecting the best relay node in the communication method of FIG. 2 according to an embodiment of the present invention in detail, and focuses only on step 230 of FIG.

In step 231, the source node selects a first best relay node having a combined transfer rate value indicating a transfer rate when passing through the relay node based on the relay response transmitted in operation 220 having a value greater than the source-target transfer rate. That is, a relay node having a combined transmission rate greater than that of direct transmission through the source-target node in the relay response frame is searched. This combined data rate may be expressed by Equation 1 below.

In Equation 1, R denotes a rate, and each subscript represents a link between nodes. That is, R _C1 represents the combined transmission rate of the entire path through the relay node, R _Sr1 represents the transmission rate of the path between the source and relay nodes, and R _r1D represents the transmission rate of the path between the relay and target nodes.

Therefore, in step 231, the first best relay node is selected as a relay node that satisfies the condition of R _C1 > R _SD . Here, RSD represents a transmission rate of the direct path between the source and target nodes.

와 같다. 앞서 231 단계에서의 조건을 고려할 때, α는 오직 1보다 큰 값으로 결정될 수 있음을 알 수 있다.In step 232, the source node divides the combined rate value by the source-target rate value. In other words, the divided result is

Same as Considering the conditions in step 231 above, it can be seen that α can only be determined to be greater than one.

In step 233, the source node has a value where the relay-target rate is greater than the specified magnification of the source-target rate based on the value divided by the step 232, and the source-relay rate is greater than the case of the first best relay node. Select the second best relay node with. That is, in step 233, the relay node satisfying the two conditions defined in Equation 2 at the same time is selected as the second best relay node.

In Equation 2, R _r2D represents the transmission rate of the path between the relay and target nodes, and R _Sr2 represents the transmission rate of the path between the source and relay nodes. Of course, the relay node at this time refers to the second best relay node that is not the first best relay node.

In summary, the two best relay nodes may include a transmission time between the source node and the first best relay node, a transmission time between the first best relay node and the target node, and the second best relay node and the target node. It is preferable that the sum of the transmission times between the two nodes is selected to be smaller than the direct transmission time between the source node and the target node. That is, by selecting two best relay nodes such that the sum of the total transmission time through the first best relay path and the second best relay path used for backup transmission is less than the direct transmission time, the reliability of data transmission under fading conditions is improved. Not only can it be improved, but also the mute time for other nodes in the network can be reduced.

5 is a flowchart illustrating a process of cooperatively transmitting data to a target node using two best relay nodes in the communication method of FIG. 2 according to an embodiment of the present invention.

In step 241, the source node sends data to the target node via the first best relay node.

After the transmission of the data in step 241, in step 242, the source node checks whether an acknowledgment (ACK) message indicating the normal reception of the data has been received. If the source node receives an acknowledgment message indicating the normal reception of the data, the process proceeds to step 243.

In step 243, since the confirmation message is received, the source node completes the data transmission process, and the best relay nodes clear their buffers. As described above, the first best relay node is always used as a path for transmitting data to the target node, and if the data is successful, it clears it without having to maintain a buffer anymore.

In step 244, the source node auxiliaryly transmits the data through the second best relay node. That is, after transmitting data through the first best relay node, when the source node does not receive a confirmation message indicating the normal reception of the data, the second best relay node may set a preset relay timeout. , And then jump to and transmit the data received from the source node to the target node. At this time, the relay timeout is longer than the SIFS interval, but much shorter than the DIFS interval, to detect the start of an ACK packet. In the embodiments of the present invention, the relay timeout was set to twice the SIFS interval, and the experiment was performed, and further improved transmission performance was confirmed.

If the source node sequentially transmits the data to the target node through the first best relay node and the second best relay node, as described in FIG. It may happen that no acknowledgment message is received indicating the normal reception of data. In this case, it is preferable that the best relay nodes clear their buffers and the source node retries the failed data transfer using an exponential back-off procedure.

That is, if the first best relay node does not receive a data packet due to fading, the second best relay node always jumps after the relay timeout and sends data to the target node. The two best relay message sequences described above are shown in FIG.

FIG. 6 is an exemplary diagram for describing a cooperative transmission process of FIG. 5 using two best relay nodes according to an embodiment of the present invention. An identifier 'S' means a source node and an identifier 'D' is a target node. It shows that there are a total of four relay nodes on the network.

First, when the source node sends the RTS packet to the target node, the target node returns the CTS packet to the target node. Then, it can be seen that each relay node is sending a relay response (RR) message to the source node. Based on the relay response message, the source node selects two best relay nodes from a total of four relay nodes, performs data transmission through the first best relay node, and auxiliaryly performs backup data transmission through the second best relay node. Can be done. Of course, such backup data transfer is performed when the data transfer through the first best relay node fails.

FIG. 7 is a flowchart illustrating a communication method for transmitting data using one best relay node in an ad hoc network according to another embodiment of the present invention. Steps 710 and 720 include steps 210 and 2 described above with reference to FIG. Corresponds to step 220. Accordingly, in order to avoid duplication of description, the operation will be described by focusing on steps 730 and 740.

The biggest difference between the embodiment of FIG. 7 and the embodiment of FIG. 2 described above is the number of best relay nodes. It is best to use two best relay nodes to improve transmission speed and to ensure reliability. However, when searching for the best relay based on the relay response, only one best relay can be found that meets the given conditions. have. 7 proposes a method of effectively transmitting data in this case.

In step 730, the source node selects only one best relay node having better transmission performance than the direct transmission between the source and target nodes from the relay response transmitted in step 720. Of course, the selection process of the best relay node may select, as the best relay node, a relay node having a combined transfer rate value indicating a transfer rate when passing through a relay node based on the transmitted relay response, which is greater than a source-target transfer rate. Of course it is.

In step 740, the source node cooperatively transmits the data to the target node using the one best relay node selected in step 730. At this time, the source node directly transmits the data to the target node, and the one best relay node is utilized as a backup node for auxiliary transmission of the data. That is, unlike the embodiment of FIG. 2, the embodiment of FIG. 7 utilizes a direct path between the source and target nodes as a main path for data transmission, and still the best relay node is used as a backup node.

FIG. 8 is a flowchart illustrating in more detail a process of cooperatively transmitting data to a target node using one best relay node in the communication method of FIG. 7 according to another embodiment of the present invention. There is a major difference in path.

In step 710, the source node directly sends the data to the target node. In other words, there is only one best relay node that provides a combined throughput that is better than the rate utilizing the direct transmission path between the source and target nodes, and all other relay nodes have introduced Equation 1 and Equation 1 above. If the condition of 2 is not met, the source node selects the one best relay for the backup path and sends the packet directly to the target node.

After the transmission of the data, it is checked in step 742 whether the source node has received an acknowledgment message informing of the normal reception of the data. If the acknowledgment message is received, the process proceeds to step 743, and in step 744. .

In step 743, the source node auxiliaryly transmits the data through the best relay node. In contrast, in step 744 where the source node does not receive the confirmation message, the best relay node jumps after a preset relay timeout and transmits data received from the source node to the target node.

Furthermore, if the backup data transfer through one best relay node also fails, the source node may repeat the above transfer cycle. This one best relay message sequence is shown in FIG.

FIG. 9 is an exemplary diagram for describing a cooperative transmission process of FIG. 8 using one best relay node according to another embodiment of the present invention. Unlike FIG. 6 described above, only one best relay node is used. It can be seen that.

First, when the source node sends the RTS packet to the target node, the target node returns the CTS packet to the target node. Then, it can be seen that each relay node is sending a relay response (RR) message to the source node. Based on the relay response message, the source node selected one best relay node out of four relay nodes. Now, the source node may attempt to transfer data directly to the target node, and may secondaryly perform backup data transfer through the one best relay node previously selected. Of course, such backup data transfer is performed when the direct data transfer between the source and target nodes fails.

FIG. 10 is a flowchart illustrating a communication method for transmitting data by using one alternative relay node in an ad hoc network according to another embodiment of the present invention, in which steps 1010 and 1020 are described above with reference to FIG. And step 220. Accordingly, in order to avoid duplication of description, the operation will be described by focusing on steps 1030 and 1040.

The biggest difference between the embodiment presented through FIG. 10 and the above-described embodiment of FIGS. 2 and 7 is also the number of the best relay nodes. It is best to use two best relay nodes to improve transmission speed and ensure reliability, but the best relay can be found based on relay response and no best relay can be found at all given conditions. . 10 proposes a method of effectively transmitting data in this case. In summary, the number of best relay nodes utilized by the embodiments of FIGS. 2, 7 and 10 are 2, 1 and 0, respectively.

In step 1030, the source node searches for the best relay node having better transmission performance than the direct transmission between the source and target nodes from the relay response transmitted in step 1020. If the best relay node is not found as a result of the search, one alternative relay node having the best transmission performance is selected based on the relay response. Here, the alternative relay node is not the best relay node introduced above, and does not satisfy the condition of Equations 1 and 2 above. Therefore, the transmission rate of data transmission through the alternate relay node is lower than that of the data transmission using the direct path between the source and target nodes.

In step 1040, the source node cooperatively transmits the data to the target node using one alternate relay node selected in step 1030. At this time, the source node directly transmits the data to the target node, and the one alternate relay node is used as a backup node for auxiliary transmission of the data. That is, data transmission is performed through the direct path between the source and target nodes, which has relatively high transmission performance, and backup data transmission is performed by using one alternative relay node to cope with a problem situation considering fading or network failure. .

FIG. 11 is a flowchart illustrating in more detail a process of cooperatively transmitting data to a target node using one alternate relay node in the communication method of FIG. 10 according to another embodiment of the present invention. FIG. 5 and FIG. There is a difference between the paths for data transmission.

인 경우, 소스 노드는 최대 결합 전송률을 갖는 릴레이 노드를 최선 릴레이 노드의 대체자로서 선택하고, 자신은 목표 노드에 직접 패킷을 전송한다.In step 1041, the source node sends data directly to the target node. If no best relay is found with a combined transmission rate that is better than that of the direct path between the source and target nodes, i.e. for ∀i (where relay node identifier i is a positive integer)

If, the source node selects the relay node with the maximum combined transmission rate as the substitute for the best relay node, and sends itself a packet directly to the target node.

After the transmission of the data in step 1041, in step 1042, the source node checks whether or not to receive a confirmation message indicating the normal reception of the data. If a confirmation message is received, the process proceeds to step 1043, otherwise, the method proceeds to step 1044.

In step 1043, the source node completes the data transfer and the best relay nodes clear their buffer. On the other hand, in step 1044 where the confirmation message is not received, the source node auxiliaryly transmits the data through the alternate relay node. That is, the alternate relay node jumps after a preset relay timeout and transmits data received from the source node to the target node. If the acknowledgment message is not received, the data packet is transmitted according to the same message sequence as shown in FIG. 9.

FIG. 12 is an exemplary diagram for describing a data transmission process when a relay response is not received in the embodiments of the present invention, and assumes a situation where no relay node is available.

First, when the source node sends the RTS packet to the target node, the target node returns the CTS packet to the target node. Then, it can be seen that each relay node is sending a relay response (RR) message to the source node. However, if relay feedback is not received during the relay response frame due to collision or absence of relay, the source node sends data directly to the target node without utilizing any relay node as shown in FIG.

According to the embodiments of the present invention described above, by selecting the best relay node having better transmission performance than the direct transmission between the source and target nodes and adaptively performing cooperative communication according to the detected network state, Maximize the throughput and improve the reliability of data transmission by utilizing the relay node that performs backup communication. Fading condition by using the direct transmission between the source and target nodes and the indirect transmission method using the best relay node. It is possible to simultaneously provide higher throughput with higher success rates of data transfer.

Meanwhile, embodiments of the present invention can be implemented by computer readable codes on a computer readable recording medium. A computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored.

Examples of the computer-readable recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device and the like, and also a carrier wave (for example, transmission via the Internet) . In addition, the computer-readable recording medium may be distributed over network-connected computer systems so that computer readable codes can be stored and executed in a distributed manner. In addition, functional programs, codes, and code segments for implementing the present invention can be easily deduced by programmers skilled in the art to which the present invention belongs.

The present invention has been described above with reference to various embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

Claims (18)

In a communication method for transmitting data from a source node to a target node in a network including a source node, a destination node, and a relay node,
The source node detecting whether a channel of the network is idle and reserving the channel;
After the reservation of the channel, the relay node transmits a relay response including its presence and rate capacity to the source node with a single bit feedback within a relay response frame configured for a predetermined time interval. Transmitting;
Selecting, by the source node, two best relay nodes having better transmission performance than direct transmission between source and target nodes from the transmitted relay response; And
The source node cooperatively transmitting the data to the target node using the selected two best relay nodes;
The relay response frame is composed of a plurality of slots and uses one collision-free bit for each relay node in one slot, thereby allowing the source node to avoid collisions and relay contentions caused by the presence of multiple relay nodes. To identify each relay node,
The first best relay node of the two best relay nodes is a primary node that transmits the data preferentially and provides a higher data rate than the direct transmission between the source and target nodes, and the second best relay node of the two best relay nodes. Is a back-up node for assisting in transmitting the data, and improves data transmission reliability under a fading state according to relay path utilization. The method of claim 1,
Selecting the best relay node,
Selecting a first best relay node having a combined transfer rate value representing a transfer rate when passing through a relay node based on the transmitted relay response having a value greater than a source-target transfer rate;
Dividing the combined rate value by the source-target rate value; And
Selecting a second best relay node having a relay-target rate value greater than a predetermined multiplier of the source-target rate based on the divided value and having a source-relay rate value greater than that of the first best relay node; ;, Including. The method of claim 1,
The two best relay nodes,
The sum of the transmission time between the source node and the first best relay node, the transmission time between the first best relay node and the target node, and the transmission time between the second best relay node and the target node is equal to the source node and the target node. And selected to be less than a direct transfer time between target nodes. The method of claim 1,
Cooperatively transmitting the data to the target node,
The source node sending the data to the target node via the first best relay node; And
If the source node receives a confirmation message indicating the normal reception of the data after the data is transmitted, the source node completes the data transmission, and the best relay nodes clear the buffer. ;, Including. The method of claim 1,
Cooperatively transmitting the data to the target node,
The source node sending the data to the target node via the first best relay node; And
If the source node does not receive an acknowledgment message indicating the normal reception of the data after the transmission of the data, the source node auxiliaryly transmitting the data through the second best relay node. The method of claim 5, wherein
If the source node does not receive a confirmation message indicating the normal reception of the data after the transmission of the data, the second best relay node jumps after a preset relay timeout, and the source Transmitting data received from the node to the target node. The method of claim 1,
Cooperatively transmitting the data to the target node,
The source node sequentially transmitting the data to the target node via the first best relay node and the second best relay node; And
If the source node has not received any acknowledgment message indicating the normal reception of the data after the transmission of the data, the best relay nodes clear the buffer and the source node has exponential back-off. Retrying the data transfer using a procedure. The method of claim 1,
Reserving the channel,
Sending, by the source node, a request-to-send packet for the channel reservation to the target node; And
After the target node receives the RTS packet, the target node responding to the source node with a clear-to-send packet. The method of claim 1,
Monitoring, by the relay node, data transmission of neighboring nodes, and updating a network allocation vector (NAV) table for identifying a transmission interval through the network;
And the network allocation vector table includes data rates estimated using average path loss. The method of claim 1,
And wherein said network operates in accordance with IEEE 802.11 distributed coordination function (DCF) protocol. In a communication method for transmitting data from a source node to a target node in a network including a source node, a target node and a relay node,
The source node detecting whether a channel of the network is idle and reserving the channel;
After the reservation of the channel, the relay node transmitting a relay response including its presence and a rate capacity to the source node in a single bit feedback within a relay response frame set in a predetermined time interval;
The source node searching for at least two best relay nodes having better transmission performance than direct transmission between source and target nodes from the transmitted relay response;
Selecting the one best relay node by finding only one best relay node as a result of the search; And
The source node cooperatively transmitting the data to the target node using the selected one best relay node;
The relay response frame consists of a plurality of slots and uses one collision-free bit for each relay node in one slot, thereby causing the source node to relay each relay from collision and relay contention caused by the presence of multiple relay nodes. To identify the node,
Wherein said source node preferentially transmits said data directly to said target node, and said one best relay node improves data transmission reliability as a backup node for auxiliary transmission of said data. The method of claim 11,
Selecting the best relay node,
And selecting a relay node having a combined transfer rate value representing a transfer rate in a case of passing through the relay node based on the transmitted relay response as a best relay node. The method of claim 11,
Cooperatively transmitting the data to the target node,
The source node sending the data directly to the target node; And
If the source node does not receive an acknowledgment message indicating the normal reception of the data after the transmission of the data, the source node auxiliaryly transmitting the data through the best relay node. The method of claim 13,
If the source node does not receive a confirmation message indicating the normal reception of the data after the transmission of the data, the best relay node jumps after a preset relay timeout, and the data received from the source node is the target node. Transmitting to. delete delete delete A computer-readable recording medium storing a program for causing a computer to execute the method according to any one of claims 1 to 14.

Images