Communication method in ad-hoc network

COMMUNICATION METHOD IN AD-HOC NETWORK

1 is a diagram illustrating an embodiment of a node arrangement in an ad-hoc network communication;

2 is a diagram illustrating an embodiment of a channel divided according to multi-carrier communication;

3 is a diagram showing an embodiment of a communication protocol according to the present invention.

4 is a flowchart illustrating a data bit allocation process according to the present invention.

5 is a diagram illustrating a signal-to-noise ratio (SNR) for each subchannel.

FIG. 6 is a diagram illustrating an operation result of an initially allocated number of data bits for each sub-channel; FIG.

7 is a diagram illustrating the number of data bits corrected to an integer type according to a modulation method for each subchannel;

8 is a diagram illustrating an energy increase when one data bit is further allocated to each subchannel;

9 is a diagram showing data bits finally allocated to each subchannel;

10 is a diagram comparing energy per packet between the case where the transmission method using the communication method according to the present invention is used and the case where the single carrier transmission method is used.

<backgroundart><p>The present invention relates to a communication method, and more particularly, to a communication method in an ad-hoc network.</p><p>The ad-hoc network refers to a network without an infrastructure configured autonomously by nodes. A base network device such as a base station or an access point is not required for network configuration and maintenance. Ad-hoc nodes communicate with each other using the air interface, overcome the communication distance limitation of the air interface by the multi-hop routing function, and the network topology changes dynamically because nodes are free to move. There is a characteristic to be The ad hoc network may be completely standalone, or may be linked with an underlying network such as the Internet through an Internet gateway. Applications include emergency rescue, emergency conferences, and military networks on the battlefield.</p><p> Since the basic configuration of an ad-hoc network is to utilize a mobile node or terminal operating with a limited storage battery capacity, a protocol or algorithm that can reduce energy consumed in the data transmission/reception process is one of the fields studied a lot in the ad-hoc network field.</p><p>As a prior art, there are largely two methods that have been introduced as a method for reducing energy consumption of an ad hoc network. These are a method of transitioning nodes to a doze state and a method of utilizing power control.</p><p>First, looking at a method for transitioning nodes to a doze state, this method uses different amounts of This method is proposed based on the consumption of energy. However, this method requires a complicated time schedule and has a problem in that the actual data transmission capacity is reduced due to the control signals communicated in the network in order to reduce energy consumption.</p><p>Another method of using power control to reduce energy consumption is a method of reducing energy consumption by minimizing transmission power capable of maintaining a connection of a radio link between nodes or terminals. This method has an advantage over the method of transitioning to the dormant state described above in that there is no additional time schedule and the decrease in the communication capacity in the network does not occur significantly. However, since the principle of 'minimizing transmission power' in the power control utilization method is a broadly defined vague concept, there may be various specific methods.</p><p>In addition, since the conventionally introduced power minimization technology focuses on reducing transmission/reception power while using a single carrier, there is a possibility that an unused frequency band may occur among the frequency bands allocated for ad hoc network communication. There was a problem in that the efficiency was lowered and it was greatly affected by the channel state. In addition, even if multi-carriers are used, problems such as crosstalk or radio wave attenuation may occur between nodes when there is one or more nodes within the radius of radio waves transmitted by one node. In addition, if the required transmission speed for data to be transmitted is not satisfied due to a cause such as a poor channel state, inefficient energy consumption occurs as data bits are unreasonably allocated to satisfy the QoS (Quality of Service) of the sender. there was</p></backgroundart><abstractproblem><p>Accordingly, an object of the present invention is to maximize the utilization of bandwidth by performing multi-carrier communication on a channel secured through channel negotiation in communication using an ad-hoc network, and to allocate data bits to be transmitted to the secured channel. It is to provide a method for minimizing the energy consumed in the present invention.</p><p>In order to achieve the above object, a communication method using an ad hoc network according to the present invention provides a negotiation channel and at least one between a specific node (hereinafter referred to as a first node) and a neighboring node (hereinafter referred to as a second node) to transmit/receive data. establishing more than one data transmission channel; detecting a common unused channel between the first node and the second node among the set data transmission channels; and transmitting data through the detected channel.</p><p>Preferably, the step of detecting the channel comprises: providing information about a channel not being used by itself through the negotiation channel to a neighboring node to transmit/receive data; and receiving information on a channel not used by the neighbor node from among the provided channel information, and detecting a channel that is not commonly used.</p><p>In addition, when a commonly unused channel is secured through channel negotiation, a process of allocating data bits to one or more secured channels is required. The method includes: initially allocating data bits to each channel based on a signal to noise ratio (SNR) value calculated for each detected common channel; calculating an energy that increases when one more data bit is allocated than the value of the initially allocated data bit and an energy that decreases when one less data bit is allocated; A process of adjusting increase/decrease of data bits allocated to each detected channel according to a result of comparing the total amount of data to be transmitted with the sum of the data bits initially allocated to each detected channel It is characterized in that it is composed of;</p></abstractproblem>

<p>Hereinafter, preferred embodiments of the present invention will be described.</p><p>1 is a diagram illustrating an embodiment of a node arrangement in an ad-hoc network communication.</p><p>As shown in FIG. 1, four nodes, A, B, C, and D, which function as a mobile base station or an access point in ad hoc network communication are indicated. For communication between the A node point and the D node point, data transmission may be performed sequentially like ABCD, or data transmission may be performed like ACD. In addition, individual communication can be made between nodes within the communication radius of each node (eg, between AB, BC, CD). In addition, since each of the nodes shown in FIG. 1 has mobility, if there is a node within the communication radius range of a specific node due to the movement of the node, communication can be made between nodes within the radius range.</p><p>In FIG. 1, the communication radius of node A is indicated by a circular dotted line, which indicates the communication radius in a circle because radio waves radiate radially during wireless communication. The communication radius of each node is variable, and if the power of radio waves emitted from node A is increased, the communication radius of node A may be widened. However, since more energy is consumed when the power of the emitted radio waves is increased, increasing the transmission power in a mobile node operating with limited power resources, such as a rechargeable battery, will accelerate the discharge of the rechargeable battery.</p><p>As shown in Fig. 1, since both node B and node C are included within the communication radius of node A, node C may be affected by communication between node A and node B, and vice versa. It may affect communication between nodes. A method for removing such inter-node interference will be described in the next section.</p><p>2 is a diagram illustrating an embodiment of a channel divided according to multi-carrier communication.</p><p>As shown in FIG. 2 , one negotiation channel and five separate channels are indicated for each node (node A and node B). In FIG. 2 , the bandwidth used by each node is indicated as 2.4 Ghz to 2.5 Ghz, but this is only an example, and the bandwidth used may vary according to each network, communication device, communication protocol, and the like. Although FIG. 2 shows the negotiation channel in the low frequency part of the bandwidth used by each node, this is also only an example, and the part occupied by the negotiation channel in the bandwidth is also variable. However, it is preferable that the range of the bandwidth occupied by the negotiation channel is set to be the same in each node.</p><p>In FIG. 2 , the bandwidth of a portion excluding the negotiation channel is divided into five, which is only an example, and the number of channels used by dividing the bandwidth is a variable number that can be adjusted according to a communication environment or protocol.</p><p>As shown in FIG. 2 , when a bandwidth used for data communication is divided into at least one or more bandwidths, and then parallel communication is performed through each divided bandwidth, the determined bandwidth is set using one carrier wave. Compared to data transmission (single carrier communication), it is possible to increase the efficiency of data transmission. However, if the number of divided bandwidths is too large, the bandwidth of each divided channel becomes narrow, which may increase the probability of inter-channel interference or errors.</p><p>In FIG. 2, a negotiation channel means a channel for identifying a channel that is not commonly used between nodes. In FIG. 2, the channels in use are shaded and displayed. The A node is using the channel, and the B node is using the and channels. Therefore, common unused channels that can be identified through the negotiation channel between the A node and the B node are channels , , and .</p><p>3 is a diagram illustrating an embodiment of a communication protocol according to the present invention.</p><p>3 shows nodes A, B, and C. The diagrams are based on a case in which there are nodes B and C within a communication radius of node A and communication between nodes AB is attempted. This will be applicable even when nodes A, B, and C are arranged as shown in FIG. 1 . The term 'subchannel' shown in FIG. 3 is used to refer to a channel of a partial bandwidth divided for multi-carrier communication. In FIG. 3, subchannels 1 to 4 are indicated, because the division of the bandwidth into four bandwidths is exemplified as an example, and the number of divisions of the bandwidth can be arbitrarily changed. In FIG. 3, a case in which the bandwidth is divided into five bandwidths (one for the negotiation channel and four for the subchannel) including the negotiation channel is illustrated as an example.</p><p>The protocol shown in FIG. 3 will be described as follows.</p><p>First, the transmitting node (node A) uses a channel negotiation request message (Negotiation ReQuest: NRQ) to provide the status of a subchannel not used by itself to the receiving node (node B) through the negotiation channel. The receiving node (node B) receives the channel negotiation request message, and for the subchannels (subchannels 1, 3, and 4) not used by itself (node B) among the unused subchannels of the transmitting node (node A) Channel negotiation is performed in such a way that information is provided to the transmitting node (node A). In FIG. 3 , the channel negotiation response message (Negotiation RePly) provided by the receiving node (node B) to the transmitting node (node A) for the channel negotiation request message (NRQ) is denoted as NRP.</p><p>As shown in FIG. 3, as node B transmits an NRP message in response to node A's NPQ message, node C within the communication radius of node A can perform NAV ( Network Allocation Vector) state. When the NAV state is reached, the corresponding sub-channel becomes in a state in which data transmission or the like cannot be performed. Since multi-carrier communication is made through subchannels 1, 3, and 4 between node A and node B, only subchannels 1, 3, and 4 that are in NAV state in node C are not used as communication channels between node A and node B. Subchannel 2 does not go into NAV state. The subchannel 2 may be used by node C to communicate with nodes other than the nodes A and B.</p><p>In the conventional ad hoc network, when setting the NAV state period, the focus is on preventing interference with other channels, so the time taken to transmit data between the transmitting and receiving nodes at the minimum transmission rate is set as a reference. . However, in setting the NAV period in the present invention, since the requested transmission rate between the transmitting and receiving nodes is taken into consideration, the NAV period can be accurately adjusted to the point at which the transmission between the transmitting and receiving nodes is completed. Accordingly, it is possible to improve the problem that the node within the communication radius of the transmission/reception node remains in the NAV state even though all data transmission between the transmission/reception nodes is performed, and the efficiency of node utilization is decreased.</p><p>As shown in FIG. 3 , when channel negotiation is performed between the transmitting node and the receiving node through the NRQ NRP process, data transmission is performed through the negotiated subchannel, and the process is as follows. First, the sending node (node A) transmits an RTS (Request to Send) message. The RTS message corresponds to a message asking the receiving node whether to transmit data. The receiving node (node B) responds to the RTS message with a CTS (Clear to Send) message, which serves as a permission message for the transmission permission request signal (RTS message) of the transmitting node. Accordingly, when the transmitting node receives the CTS message, it transmits data, and when it does not receive the CTS message, it does not transmit data.</p><p>As shown in FIG. 3 , the transmitting node (node A) transmits an RTS message through the subchannels (subchannels 1, 3, and 4) secured through channel negotiation, and the receiving node (node B) transmits the RTS message. Since CTS messages are received for all subchannels (subchannels 1, 3, and 4), data transmission is performed through subchannels 1, 3, and 4. When the receiving node (node B) receives data, it sends an ACK (Acknowledge) message to the sending node (node A) indicating that the data has been received.</p><p>In the process of transmitting the RTS CTS message, the maximum transmission power is allocated when the transmitting node transmits the RTS message. Since the range that can receive the RTS message transmitted with the maximum transmission power becomes the communication radius of the transmitting node, other nodes (within the communication radius of the transmitting and receiving nodes) that are likely to be affected by the communication between the transmitting and receiving nodes through the above process other nodes that exist) can be transitioned to the NAV state. Nodes in the area where the signal of the maximum transmission power can reach may cause the problem of exposed/hidden terminals (Exposed/Hidden Terminal problem), so that the NAV state is made.</p><p>In addition, information on the maximum transmission rate can be obtained through the RTS CTS message transmission process. The method of providing channel state information and receiving feedback again through the RTS CTS message transmission process is Basic Power Control (BPC). ) is called When trying to transmit data bits by allocating them to multiple channels, since the status of each channel is not the same, it is necessary to know information about the channels in advance.</p><p>As shown in FIG. 3 , the transmitting node (node A) receives the CTS message from the receiving node (node B) through channels (subchannels 1, 3, and 4) secured through channel negotiation and then transmits DATA. At this time, the transmitting node (node A) transmits the DATA message with the minimum transmit power capable of successful transmission using the receive power information included in the CTS message received from the receiving node (node B). Here, the minimum transmission power capable of successful transmission is based on information such as the power size of the maximum output transmitted by the transmitting node, the distance between the transmitting/receiving nodes, the size of the receiving power, and the BER required for communication between the transmitting/receiving nodes. Calculate.</p><p>When the receiving node (node B) successfully receives the DATA, it transmits an ACK (acknowledge) message to the sending node (node A). In addition, if the receiving node (B node) has data to transmit to another node (C node) within the communication radius, a channel other than the commonly used channel ( When the NAV state of subchannel 2) ends, a Negotiation ReQuest (NRQ) message is transmitted to the C node. Thereafter, in the data transmission process between the B node and the C node, the channel is negotiated using the NRQ NRP message in the same order as in the A node and the B node, and the channel (subchannel 2) secured through the channel negotiation is Data transmission/reception is performed according to the RTS CTS DATA ACK message sequence.</p><p>As described above, when multi-carrier communication is performed through channel negotiation between transmitting/receiving nodes, a process of allocating data to be transmitted to a plurality of secured channels is required. For this, first, the speed required for data transmission is calculated at the transmitting node. The required speed is variably determined by various factors such as the amount of data to be transmitted, the communication standard, the degree to which the user feels call delay, the channel state, and the amount of power consumed.</p><p>If the requested transmission rate is greater than the maximum transmission rate in the current channel state secured through channel negotiation, since the QoS (Quality of Service) of the sender is not satisfied, it is necessary to allocate additional data bits to each channel. On the other hand, when the requested transmission rate is smaller than the maximum transmission rate in the current channel state, it is possible to increase the power consumption efficiency according to the data transmission by reducing the previously allocated data bits.</p><p>In multi-carrier communication using each channel secured through channel negotiation, since the communication environment of each channel is not the same, when more or less data bits allocated to each channel are allocated, the communication environment of each channel is adjusted. need to be considered. In addition, in an ad-hoc network that communicates using a mobile base station, each mobile base station is located in a different place and the location may change frequently due to movement, so the channel environment is also different for each mobile base station in many cases. Even if the same amount of data bits are transmitted, energy consumption may vary depending on how many data bits are allocated to which channel. Therefore, the same data transmission can be performed with minimum energy only when bits are appropriately allocated to each channel environment.</p><p>Accordingly, in the present invention, a bit allocation algorithm capable of minimizing energy consumption during data transmission has been proposed, which will be described with reference to FIG. 4 as follows.</p><p>4 is a flowchart illustrating a data bit allocation process according to the present invention.</p><p>As shown in FIG. 4, first, SNR is calculated for each channel in order to understand the characteristics of each channel for data transmission. (S10) In order to obtain a transmission power value of data bits, an SNR value is required, and the SNR is signal to noise. It is an abbreviation of ratio, and is defined as follows.</p><p><maths num="1"><df><img file="KR20080098263A_D0001.tif" /></df></maths></p><p>where σ<sp>2</sp>: noise variance of AWGN (Additive White Gaussian Noise) , H : channel gain, S : transmit power per symbol, n : sub-channel index respectively. The SNR Gap can be calculated using the SNR value. The SNR Gap is the ratio of the current SNR value to the SNR value when the BER (bit error rate) required by the modulation scheme is satisfied. Assuming that the transmission rate by Shannon Capacity is the practical bit rate and the data rate when the BER required by the modulation scheme is satisfied is the Maximum bit rate of system, the SNR Gap is defined as follows.</p><p><maths num="2"><df><img file="KR20080098263A_D0002.tif" /></df></maths></p><p>Here, a: dimension for M-QAM modulation scheme, Γ: SNR Gap, C: practical bit rate, R: means the maximum bit rate of system. </p><p>When the SNR value and the SNR Gap value are calculated for each subchannel according to the above equation, the number of initially allocated data bits for each subchannel is calculated. (S11) The number of data bits allocated for each subchannel can be calculated as follows .</p><p><maths num="3"><df><img file="KR20080098263A_D0003.tif" /></df></maths></p><p>And, the data rate of the entire carrier is as follows. </p><p><maths num="4"><df><img file="KR20080098263A_D0004.tif" /></df></maths></p><p>where, T<sb>sym</sb> : means symbol duration.</p><p>From Equation 3, the number of bits allocated per sub-carrier of each subchannel is R<sb>n</sb>Then, the transmission power value at that time is defined as follows.</p><p><maths num="5"><df><img file="KR20080098263A_D0005.tif" /></df></maths></p><p>When the operation on the number of initially allocated data bits for each subchannel is performed (S11), the calculated number of bits is an integer value (hereinafter, the number of integer data bits allocated to the i-th subchannel is denoted as b(i)) (S12) Since a modulation process is usually performed on a signal to be transmitted, b(i) is modified to 0, 1, 2, 4, 6 to match the modulation order. process may be added. It is not necessary to limit the modulation order value to 0, 1, 2, 4, 6, but in case of matching with commonly used modulation methods such as BPSK, QPSK, 4-QAM, 16-QAM, 64-QAM, the modulation It is necessary to adjust the b(i) value to fit the order.</p><p>After correcting the number of bits (S12), the transmission power gap (power gap: e) when one more or fewer data bits are allocated to each channel using the channel gain, noise dispersion value, and transmission power value<sb>up</sb>(i), e<sb>down</sb>(i)) is obtained. (S13)</p><p>The sum of the number of data bits (b(i)) modified with an integer value and the total amount of data to be transmitted (hereinafter referred to as B<sb>total</sb>by comparing (S14), the sum of b(i) is<sb>total</sb>If greater than , it means that the current total bit allocation is greater than the total amount of bits to be transmitted. Therefore, it is necessary to reduce the bit allocation in order to optimize energy consumption. At this time, when less bits are allocated, the power gain that can be obtained the most, that is, e<sb>down</sb>(i) reduces the bit allocation of the largest subchannel. (S16) Conversely, the sum of b(i) is<sb>total</sb>If it is less than, it means that the current total bit allocation is smaller than the total amount of bits to be transmitted, so it is necessary to increase the bit allocation. Therefore, when allocating more bits, the additional power that will be burdened is the least, that is, e<sb>up</sb>(i) increases the bit allocation of the smallest subchannel. (S15) This process is repeated until the current total bit allocation equals the total amount of bits to be transmitted. (S17)</p><p>The simulation results to which the data bit allocation algorithm according to the present invention is applied are shown in FIGS. 5 to 9 . Since conditions such as bandwidth used between nodes, the number of nodes, the distance between nodes, the number of subchannels secured by channel negotiation, and the level of noise during simulation are variable, the simulation results shown in Figs. only to In the above simulation, it is assumed that the channel state has a characteristic of a Rayleigh distribution, and the data bit allocation algorithm according to the present invention is applied when the number of subchannels secured by channel negotiation is 16.</p><p>5 is a diagram illustrating a signal-to-noise ratio (SNR) for each subchannel.</p><p>As described above, the subchannel referred to herein refers to a channel secured through channel negotiation between nodes. That is, when subchannels 1 to 16 are shown in FIG. 5, it means that 16 channels are secured through channel negotiation. Since the communication environment is different for each subchannel, the SNR value is also different.</p><p>6 is a view showing the results of calculation of the initially allocated number of data bits for each subchannel.</p><p>As shown in FIG. 6 , the calculated number of data bits for each subchannel is a floating point value, not an integer value. Since a bit is the smallest unit of information, it is necessary to modify it to an integer value.</p><p>7 is a diagram illustrating the number of data bits corrected to an integer type according to a modulation method for each channel.</p><p>As shown in FIG. 7 , the number of data bits for each subchannel has an integer value and is expressed as one of 1, 2, 4, and 6 values. The integer value shown in FIG. 7 is a value adjusted according to the modulation order after the floating point value shown in FIG. 6 is corrected to an integer type. There may be various methods for modifying a floating-point value to an integer value, such as rounding off, rounding off, and rounding up.</p><p>8 is a diagram illustrating energy increased when one more data bit is allocated to each subchannel.</p><p>In FIG. 8 , five subchannels having a small increase in transmission energy when one more data bit is allocated are separately indicated. When there are 5 data bits to be additionally allocated, data bits will be additionally allocated to subchannels 4, 7, 8, 13, and 15 as shown in FIG. 8 . In FIG. 8 , the fact that the number of subchannels with low transmission energy is 5 is not significant in itself. However, it is shown in the drawing on the assumption that the number of bits to be additionally allocated to satisfy the required transmission rate is 5. . That is, the number of additionally allocated data bits is variable depending on the case.</p><p>In FIG. 8, subchannels 6, 14, and 16 did not correspond to five channels with a small increase in transmission energy even though the increased energy was displayed as 0 [mJ], which limits data bit allocation according to the modulation order. because it did 7, subchannels 6, 14, and 16 have 6 integer data bits allocated. Additional data bits are not allocated to the subchannels 6, 14, and 16 to which 6 data bits are allocated, and thus the increase energy is displayed as 0 [mJ]. That is, when one more data bit is allocated to the subchannels 6, 14, and 16, there is no increased energy, but because the maximum number of data bits to be allocated is already allocated, the increasing energy is not indicated.</p><p>9 is a diagram illustrating finally allocated data bits for each subchannel.</p><p>As shown in FIG. 9 , the initial number of integer data bits allocated to each subchannel is indicated on the left side of the drawing, and the final number of data bits allocated as a result of additional data bits allocated on the right side of the drawing is indicated. Compared with the initially allocated number of bits, some subchannels have one additionally allocated data bit number, and some have two subchannels. This is because the simulation was performed in consideration of the modulation order. That is, when actually assigning the number of data bits to transmit, considering the modulation order, the number of data bits is limited to one of 0, 1, 2, 4, and 6 The number is shown as six.</p><p>10 is a diagram comparing energy per packet between the case where the transmission method using the communication method according to the present invention is used and the case where the single carrier transmission method is used.</p><p>It is simulated assuming that 4 nodes arranged at intervals of 50m from 50m to 200m transmit data in the order of Node 1 Node 2 Node 3 Node 4 Node 1, and calculated based on the result. One value is shown in FIG. 10 . In the simulation, the data to be transmitted was set to generate 2020 bytes every 90 ms (millisecond), and the required bit rate was fixed at 24 Mbps. The number of subchannels is 48, and the symbol period is 4 μs. According to the IEEE 802.11a standard, when 16-QAM with a code rate of 1/2 is used to achieve a required bit rate of 24 Mbps, 192 bits should be allocated per symbol. SNR GAP is QAM BER=10<sp>-6</sp>A value of 8.8 dB was used.</p><p>As shown in FIG. 10 , when the multi-carrier transmission and bit allocation algorithm according to the present invention is used, energy consumption per packet is reduced to less than half as compared to data transmission using a single carrier. This is equivalent to an increase in energy efficiency of more than 100%. That is, when the communication method proposed by the present invention is used, energy consumption can be reduced by half or less when transmitting the same amount of data, so energy utilization can be increased in an ad hoc network using a mobile base station equipped with a battery. will be.</p><p>Above, preferred embodiments of the present invention and simulation results have been described with reference. Here, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.</p><p>Accordingly, the configuration shown in the embodiments and drawings described in the present specification is the most preferred embodiment of the present invention, or merely a simulation result under specific conditions, and does not represent all of the technical spirit of the present invention. It should be understood that there may be various equivalents and variations that can be substituted for them.</p>

<p>As described above, the communication method through the ad hoc network according to the present invention has an effect of minimizing energy consumption in transmitting the same amount of data. Minimizing the energy consumed for data transmission can also extend the usage time of the mobile base station, which is powered by the battery.</p><p>In addition, in using a frequency band allocated to be used for ad hoc communication, since multi-carrier communication is performed by dividing the frequency band into a plurality of sub-channels, channel diversity is increased and the utilization rate of the allocated frequency bandwidth is also increased.</p><p>In addition, there is an effect of preventing crosstalk or interference between nodes by transitioning other nodes within the communication radius of a specific node to the NAV state.</p>