KR101038079B1 - Data transmission method and apparatus for wireless sensor network, using M-1-1 cooperative communication and OSOC-SS - Google Patents

Abstract

The present invention is to improve the existing transmit diversity technology using a cooperative protocol and spread spectrum (SS) technology in the high-speed wireless transmission USN. The present invention provides a problem in the existing cooperative communication system, that is, the number of frequency bandwidths, power consumption, and the number of relay nodes during data transmission by helping data transmission of M sensor nodes having the same number of M relay nodes. It is designed to solve a vast problem. According to the present invention, M sensor nodes multiply their M OSOCs with their data and transmit them to one relay node and a destination node. The relay node performs a sum operation on the data received from the M nodes, multiplies by an orthogonal code (OC), and transmits the result to the destination node. Since OSOCs are orthogonal to the OC, the destination node can recover the data of M users delivered by one relay node. The relay node R (relay) and the destination node D (destination) receive the information of several sensor nodes S (source) that transmit information in the process of transmitting and receiving signals. send. D, the final destination node, receives data of S and R through independent channels using MRC (Maximum Ratio Combining), thereby receiving more reliable data.

Description

Data transmission method and apparatus for wireless sensor network, using M-1-1 cooperative communication and OSOC-SS}

The present invention relates to a high capacity data transmission method and apparatus in a wireless sensor network using M-1-1 cooperative protocol using OSOC-SS for supporting high capacity data transmission using limited power and frequency.

USN collects information related to control from sensors installed. Future USNs are expected to meet the enormous demand for communication using a variety of data such as voice, data, images and video that can be accessed anytime and anywhere. Environmental information is collected to realize various functions through numerous wireless nodes located everywhere.

In limited bandwidth USNs, high speed transmission systems are needed for the development of multimedia sensors. In wireless communication, signal fading due to multipath propagation is a major problem. This problem can be solved by placing multiple antennas in the transmitter to diversity transmission. However, in the multi-antenna arrangement, it is difficult to install the multi-antenna because the node size required for each sensor node to be installed in the single antenna is reduced.

As a solution to this problem, there is a method of relaying an original signal to a destination node by using an idle sensor node (in other words, a relay node) around the transmitting node. In this case, nodes can effectively use mutual antennas in the form of spatial diversity without physically arranging antennas. In addition, since the node size required for each sensor node to be installed in a single antenna is reduced, it may be a solution suitable for a wireless USN scenario. A processing method for receiving a signal from a desired node via an idle sensor node is known as a cooperative protocol.

On the other hand, OSOC stands for orthogonal subset of orthogonal code, which has been proposed as a new classification orthogonal code for multicode modulation, and SS (spread spectrum) communication uses channel bandwidth and multipath. Due to their relative insensitivity to interference and the potential for enhanced privacy, they are currently being developed for wireless mobile communication devices. OSOC-SS modulation is also used flexibly for multi-rate transmission. The OSOC multicode system can increase the data rate and the number of users in the CDMA system.

The present invention is to improve the existing transmission diversity technology using a cooperative protocol and spread spectrum (SS) technology in the high-speed wireless transmission USN. The present invention provides a problem in the existing cooperative communication system, that is, the number of frequency bandwidths, power consumption, and the number of relay nodes during data transmission by helping data transmission of M sensor nodes having the same number of M relay nodes. It is designed to solve a vast problem.

According to the present invention for solving the above problems, since each sensor node has its own OSOC that can access a destination node, only one relay node can cooperate with the sensor node group at the same time.

M sensor nodes multiply M OSOCs with their data and transmit them to one relay node and a destination node. The relay node performs a sum operation on the data received from the M nodes, multiplies by an orthogonal code (OC), and transmits the result to the destination node. Since OSOCs are orthogonal to the OC, the destination node can recover the data of M users delivered by one relay node. The relay node R (relay) and the destination node D (destination) receive the information of several sensor nodes S (source) that transmit information in the process of transmitting and receiving signals. send. D, the final destination node, receives data of S and R through independent channels using MRC (Maximum Ratio Combining), thereby receiving more reliable data.

According to the present invention, signal interference, which can only occur between adjacent sensor nodes, is reduced through OSOC-SS technology using orthogonality, thereby improving performance. In addition, throughput of the sensor node may increase due to the addition of OSOCs at the relay node. In addition, the cooperative transmission by the OSOC of the present invention will provide a very high flexibility in controlling the data rate with the parameters related to QoS. As such, the present invention will be a key technology in future WSN application technologies by more effectively utilizing limited power and frequency in wireless sensor networks that require high capacity data transmission.

1. Cooperative Protocol

The cooperative transport protocol is a multi-hop protocol in that the receiver combines data from the desired source node and data from the relay node of all nodes (not from the last relay node as in the multi-hop protocol). It can be seen as an extension of. Many kinds of collaborative transmission protocols have been proposed, and have brought many advantages such as diversity gain, coverage expansion, and energy saving. In this protocol, a user transmits information, and wireless transmissions can be broadcast, so that destination node and relay node groups receive this transmission. The relay node then transfers the received information to achieve spatial diversity at the destination node. Depending on the propagation method in the relay node, collaborative communication protocols are classified into three categories: amplify-forward (AF), decode-forward (DF), and coded cooperation (CC). . In the WSN, DF is considered to be a suitable collaboration. This is because in this case, each receiver only needs the CSI of the channel being listened to and has the lowest complexity. In conventional DF, direct transmission time slots are divided into two stages. The sensor node sends the data to the destination node and the relay node using the first step. After decoding the received signal, the relay node delivers the resulting signal to the destination node. The destination node combines the received signals in two steps based on MRC (maximum ratio combining) to make a final decision on the initial data.

In the present invention, when information is transmitted from M sensor nodes to one destination node, it is assisted by one relay node as shown in FIG. Accordingly, the present invention becomes an M-1-1 cooperative transmission protocol (in the existing cooperative communication system, since M relay nodes help data transmission of M sensor nodes having the same number, it is called a 1-1-1 cooperative protocol. Called).

In FIG. 1, the M sensor nodes 51 transmit data using OSOC codes having orthogonality to each other, the partner node transmits data to the relay node 52 and the destination node 53, and the relay node ( 52 sends data back to the destination node using OSOC-SS technology. Here, the partner node means a source node that forms a partner with the relay node. In the present invention, M sensor nodes, one relay node, and one destination node each have one relay node, thereby obtaining the same diversity effect as the existing system, and reducing frequency bandwidth, power, and the number of relay nodes. To be.

The protocol according to the present invention provides diversity performance similar to that of conventional DF, resulting in much less bandwidth at the same power. M sensor nodes transmit their data to the destination node and the relay node simultaneously using their OSOCs.

In the protocol of the present invention, time slots are divided into two stages. The first step is to transmit information from the M sensor nodes to both the destination node and the relay node using OSOC. The destination node multiplies the corresponding OSOC, detects each user information, and stores it for combining after the second step. The relay node collects signals transmitted from M sensor nodes. After the sum of these data, the second step multiplies the OC and transmits the data to the destination node. Since the OSOC is orthogonal to the OC, as described above, the destination node can detect each user data. Therefore, the destination node receives two signals from each node and combines the two signals using MRC (maximum ratio combining).

According to the data transmission method (protocol) of the present invention, similar degree of diversity is possible with the same power and a much smaller bandwidth as compared with the conventional cooperative transmission. Since one relay node assists M sensor nodes by using the OSOC method, information of M nodes can be simultaneously transmitted.

2. Methods and OSOCs to Reduce PAPR

An orthogonal subset (OSOC) of an orthogonal code for multicode modulation is well known and can be simply designed as shown in FIG. 2.

의 관계가 성립한다(여기서 TC와 TOSOC는 각각 OC와 OSOC의 듀레이션 시간을 나타냄).FIG. 2 is an exemplary diagram of a WH matrix for an orthogonal code (OC) and an orthogonal subset of orthogonal code (OSOC), where [] shows the OSOCG for any WH matrix of size N × N. In FIG. 2, an OSOC can be obtained from an OSOCG (OSOC group) having a size LxL (L is the length of an OSOC). For example, in the case of an 8x8 Walsh-Hadamard (WH) matrix in Figure 2, two OSOCGs of size 2x2 and 4x4 are possible. In addition, OC is constructed by N × N WH matrix techniques used in mobile communication systems such as CDMA. Apply this system to the sensor network field. The duration of OC and OSOC

Relationship is established, where TC and TOSOC represent duration time of OC and OSOC, respectively.

Sensor nodes cannot transmit and receive signals simultaneously in order to reduce implementation complexity. This is because a significant amount of attenuation over the radio channel and insufficient electrical separation between the transmitting and receiving circuits causes the sensor node's transmit signal to eat at the receiver input.

In order to solve this problem, the present invention applies code division multiplexing (CDM) for channel access. The M sensor nodes multiply the data of each sensor node by their OSOC sequences. By the OSOC sequence, M data may be transmitted from M sensor nodes to a relay node and a destination node at the same time. The output signal of the Mth sensor node is given by the following equation. In the following equation, a _m is a BPSK modulated data symbol, and OSOC _m represents the OSOC for the Mth sensor node.

The signal received from the relay node through the independent carrier is as follows.

The combined data at the relay node is as follows.

The maximum power of the signal S _RD1 may go up to M ² (M is the number of sensor nodes, that is, the number of OSOCs).

Meanwhile, the peak-to-average power ratio (PAPR) also increases in proportion to the number of OSOCs. The present invention applies a mapping technique on the relay node side to reduce the PAPR, which is a serious problem in hardware design. In the present invention, the PAPR is only high after summation in OSOC. Therefore, the (M + 1) PSK mapping unit 20 is additionally inserted next to the OSOCG in the relay node shown in FIG. 3, and as shown in FIG. 4, the (M + 1) PSK demapping unit between the OC and OSOC in the destination node. Insert (30).

The mapping unit 20 serves to map the PAM signal S _RD1 (t) of the output terminal of the OSOC spreading part to the signal CONSTELLATION S _RD2 (t) of (M + 1) PSK as follows.

와

는 듀레이션 T_C를 갖는 단위 진폭의 사각형파를 나타낸다.Next, the signal S _RD2 is continuously spread (spreaded) by the OC to generate a waveform as shown below. In the expression below

Wow

Denotes a square wave of unit amplitude with a duration T _C.

가 된다. 매핑 후에, 각 중계노드 신호를 구별하기 위해 승산부(30)에서 OC 부호를 곱하여준 뒤 신호를 전송한다. When sending data from the source to the relay node, M sensor nodes multiply their OSOC sequence by their data and send it to the relay node and the destination node. 3 shows the configuration of the relay node. In FIG. 3, the signal input to the relay node is represented as y _SRm . First, the adder 10 of the relay node adds up the M y _SRm signals received from the source. Here, when the data passed through the adder 10 is generated, high PAPR and average power are generated in the system due to continuous generation of '0' data. To solve this problem, the mapping unit 20 was added to allow the summed signals to go through the mapping process. If the signal after passing through the mapping unit 20 is _expressed as S _RD2 ,

Becomes After mapping, the multiplier 30 multiplies the OC code in order to distinguish each relay node signal and then transmits the signal.

As described above, an OSOC code is used to distinguish a source, an OC code is used to distinguish a relay node, and a mapping process is performed to solve a high PAPR problem.

는 복조기의 입력신호이고,

는

의 복원된 심볼을 나타낸다.Demodulation can be easily processed by the configuration as shown in FIG. In the expression below

Is the input signal of the demodulator,

Is

Reconstructed symbol of.

4 shows a configuration of a destination node for restoring a signal sent from the relay node of FIG. The multiplication unit 40 multiplies the signal y _RD (t) received from the relay node of FIG. 3 by the multiplier 40 to distinguish the relay node, and is modified by the mapping unit 20 in the signal transmission process. Demapping (demapping) is performed through the demapping unit 50 to restore the state of the signal to its original state. Each source data is restored using an OSOC code. The recovered symbols can be expressed as Equation (6).

FIG. 5 illustrates the mapping for 8x8 (M = 8, L = 8) and 6x8 (M = 6, L = 8) OSOCGs, adopted from a 16x16 size WH matrix. By this mapping method, the PAPR at the output of the OSOC-SS mapping modulator at the relay node can be guaranteed to be '1' regardless of the number of OSOCs. 5 is a constellation diagram in a system without a conventional mapping process, and the right diagram is a new constellation diagram according to the (M + 1) PSK method, and is a constellation diagram of a signal represented by mapping. This change in constellation is based on the orthogonality of the I and Q channels. When the transmitter maps the signal according to the I, Q channel mapping method, the threshold that is initially set with the received data with noise is set. This is determined in the reverse mapping process based on the threshold. In other words, if you map as above and then display the PAPR in decibels, all of them will be displayed as 0dB, which shows excellent performance in the system.

3. Signal Analysis

The protocol of the present invention utilizes the M-1-1 scheme (i.e., M transmitting nodes, one relay node, and one destination node). For convenience of explanation, the transmission source node will be abbreviated as SN, the relay node as R, and the destination node as D.

은 식(1)에서와 같고,

은

의 평균 송신전력을 나타낸다. In the first step, signals received at R and D through independent carriers are represented by Equation (2) and Equation (7) below. here

Is the same as in equation (1),

silver

Represents the average transmit power.

R is shown in FIG. 3. After summing the signals received from the M SNs, the signals are mapped and then multiplied by OC. R then sends this signal to D in the second time slot.

는 식(4)에서 나타낸 것과 같은 것이다. D receives the signal transmitted in R. In the expression below

Is the same as shown in equation (4).

는 OC와 곱하는 블록을 이용한 역확산(de-spreading) 신호이고,

는 노드 i (S 및 R)에서의 AWGN의 분산치이다. Now, the destination node combines the signal received from S (see equation (7)) and the signal received from its partner (see equation (8)) to recover the original data bits. In this case, by applying a simple maximum ratio coupling method (MRC) to combine as shown in equation (9) below. In equation (9),

Is a de-spreading signal using a block multiplied by OC,

Is the variance of AWGN at node i (S and R).

By this combination technique, the spatial diversity gain can be obtained. This is because the partner carries data from M sources under good inter-SR channel conditions. After de-mapping of a series of r _m and de-spreading by OSOC, it is possible to recover the received signal a ' _m which is a copy of a _m .

Through this process, it is possible to overcome the high complexity and size of the system, which is a disadvantage of multiple antennas, by achieving the diversity effect that occurs when using multiple antennas with a single antenna, and to reduce the high transmission power and save the battery consumption of the sensor. can do. In R (relay), the path loss can be reduced by receiving and modifying the information of the sensors and retransmitting them to D.

Therefore, the conventional cooperative transmission and the protocol according to the present invention can perform the same degree of diversity. In addition, the protocol of the present invention can reduce the bandwidth.

Since there are M transmitting nodes, the total power of the system must be MP _T. If the SNs transmit the same power, the following equations must be satisfied between the protocols of the present invention. Therefore, this energy saving is as follows. P _T represents the average transmission power of S in the case of direct transmission.

4. Simulation Results

는 제로평균(zero-mean)을 갖는 독립적 복소수 가우시안 랜덤변수의 샘플로 모델링되며 two-chip 듀레이션 동안에 일정한, 대부분의 공간다이버시티 시스템에 대해서는 통상, FLAT FADING 채널인 것으로 가정한다. Compare the performance of the direct transmission (DT) and the cooperative transmission (CT) protocol according to the present invention. Path gain from transmitting antenna i to receiving antenna j

Is modeled as a sample of an independent complex Gaussian random variable with zero-mean and is assumed to be a FLAT FADING channel, for most spatial diversity systems, which are constant during two-chip durations.

By the mapping technique, it is possible to reduce the PAPR, which can improve the stability of the system. The table below shows the PAPR values before and after the mapping method is applied depending on the number of sensor nodes.

Number of sensor nodes
(Number of OSOCs) PAPR value Before mapping After mapping 4 3.0 0 6 3.5 0 8 3.8 0

Figure 6 compares the performance while changing the number of sensor nodes cooperated by one relay node. M is the order of SN and the number of OSOCs, and L represents the length of OSOC. At a target BER of 10 ⁻¹ , the 4-1-1 protocol outperforms the conventional protocol. The time required to transfer data from four SNs can be reduced, and OSOC can be used to increase bandwidth utilization. All items of the present protocol are superior to direct transmission. If the SNRs are the same, the BER of the system will decrease as the order of M increases from 4 to 8. This is because the bandwidth of each node decreases when the number of nodes M is increased at a fixed total bandwidth.

5. Conclusion

The cooperative transmission protocol of the present invention enables idle nodes to help other sensor nodes transmit data to the destination node. According to the present invention, a novel modulation scheme using mapped OSOCs results in lower PAPR, improved performance, flexibility in changing modulation levels, and very low implementation complexity. In addition, by using a spread spectrum technique using OSOC and OC, various interference problems, which are major problems of the USN in which many nodes are scattered in a large area, can be solved. According to the simulation result, according to the protocol of the present invention, the channel utilization efficiency and the output efficiency can be greatly improved without additional complicated implementation of the sensor node. The present invention can also effectively cope with narrowband and wideband jamming by increasing the size of the spreading code.

1 is a conceptual diagram illustrating a method (protocol) according to the present invention.

2: Exemplary WH matrix for OC and OSOC.

3; Block diagram of relay node.

4 is a block diagram of a destination node.

5 is a diagram illustrating mapping schemes for OSOCG 8X8 and OSOCG 6X8.

6: BER performance graph of the protocol using direct transmission and OSOC-SS of the present invention.

Claims (10)

A method of transmitting data from a sensor node of a wireless sensor network to a destination node through a relay node, Transmitting the information acquired from each sensor to one relay node and one destination node, The relay node receives the signals transmitted from the sensor node and summing these data to transmit to the destination node, The destination node includes the step of restoring M data received from the sensor node and the relay node, The relay node After summing the data received from the sensor nodes, in order to reduce the PAPR, the summed signal is mapped according to the (M + 1) PSK method, and the mapped signal is multiplied by an orthogonal code (OC) to the destination node. Data transmission method in a wireless sensor network, characterized in that for transmitting a signal. The method of claim 1, wherein the M sensor nodes include multiplying OSOC times data of each sensor node by a respective orthogonal subset of orthogonal code (OSOC) sequence. M data is transmitted from the M sensor nodes to the relay node and the destination node at the same time, the data transmission method in a wireless sensor network. delete delete The method of claim 1, wherein the destination node In order to recover the signal received from the relay node has been transformed by the mapping in the relay node to the original state, and the data transmission in the wireless sensor network, characterized in that to restore the signal by despreading by OSOC Way. A device for transmitting data from a sensor node of a wireless sensor network to a destination node through a relay node, M sensor nodes for transmitting the information acquired from each sensor to the relay node and the destination node, One relay node for receiving the signals transmitted from the sensor node and summing these data to transmit to the destination node, And one destination node for restoring M data received from the sensor node and the relay node, The relay node Means for summing data received from the sensor node, Means for performing mapping according to the (M + 1) PSK method on the summed signal to reduce the PAPR, And a means for transmitting a signal to the destination node by multiplying a mapped signal by an orthogonal code (OC). The method of claim 6, wherein the M sensor nodes include means for multiplying OSOC times data of each sensor node by a respective orthogonal subset of orthogonal code (OSOC) sequence. M data is transmitted from the M sensor nodes to the relay node and the destination node at the same time, the data transmission device in a wireless sensor network. delete delete The method of claim 6, wherein the destination node De-mapping means for restoring the signal received from the relay node to the original state that the signal is transformed by the mapping at the relay node; And means for restoring a signal by despreading by the OSOC.

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