CN102869026B

CN102869026B - Based on the Distributed fusion method and system of collaboration communication

Info

Publication number: CN102869026B
Application number: CN201210198973.1A
Authority: CN
Inventors: 韩宇; 费礼; 高强
Original assignee: Beihang University
Current assignee: Beihang University
Priority date: 2012-06-14
Filing date: 2012-06-14
Publication date: 2015-08-26
Anticipated expiration: 2032-06-14
Also published as: CN102869026A

Abstract

The invention discloses a kind of Distributed fusion method and system based on collaboration communication.Wherein method comprises: fusion center is according to the observation quality determination cooperative node pair of each sensor node to information source, and cooperative node is to by mutually a good node of observation quality of cooperative partner and the poor node of observation quality form each other; Fusion center carries out transmit power allocation according to current channel conditions and observation quality to each sensor node; Each sensor node judges whether self has cooperative partner, if have, then good for observation quality node carries out observing the observation information obtained transfer to fusion center to information source by the two sensors node of cooperative partner respectively each other mutually, otherwise does not have the sensor node of cooperative partner self to be carried out observing the observation information obtained directly transfer to fusion center to information source; Fusion center merges the observation information received, and obtains the estimated value of information source.The present invention is conducive to the estimated accuracy improving Distributed fusion system.

Description

Distributed estimation method and system based on cooperative communication

Technical Field

The present invention relates to wireless network technologies, and in particular, to a distributed estimation method and system based on cooperative communication.

Background

Distributed estimation is one of important applications of a wireless sensor network, and a distributed estimation system observes sensor node information sources in the network through a plurality of sensor nodes in the system and estimates the information sources according to observation information obtained by the nodes.

In the existing distributed estimation system, a plurality of sensor nodes independently observe an information source, each sensor node directly transmits observation information acquired by the sensor node to a fusion center through a wireless channel, and the fusion center performs information fusion on the observation information of the plurality of sensor nodes to acquire an estimation result of the information source. In the process that the sensor nodes transmit the observation information to the fusion center, the sensor nodes transmit the information in a broadcasting mode, and due to the fact that transmission signals are influenced by factors such as multipath fading and noise, the observation information of some sensor nodes cannot be effectively transmitted to the fusion center, even if the observation information transmitted to the fusion center is possibly not information with high observation quality, the estimation accuracy of the fusion center on the information source is low. Therefore, a distributed estimation method with high estimation accuracy is needed.

Disclosure of Invention

The invention provides a distributed estimation method and a distributed estimation system based on cooperative communication, which can effectively transmit observation information of a sensor node with higher observation quality, thereby providing a distributed estimation method with high estimation precision.

The first aspect of the present invention provides a distributed estimation method based on cooperative communication, including:

step 1, a fusion center determines a cooperative node pair according to the observation quality of each node pair information source, wherein the cooperative node pair consists of a node with better observation quality and a node with poorer observation quality which are mutually cooperative partners, and the determination result of the cooperative node pair is sent to the corresponding node;

step 2, the fusion center distributes transmission power to each node according to the current channel condition and the observation quality;

step 3, each node judges whether the node has a cooperation partner according to the received determination result of the cooperation node pair, if so, the step 4 is executed, otherwise, the step 5 is executed;

step 4, determining a node with better observation quality and a node with poorer observation quality by two nodes which are mutually cooperative partners in the cooperative node pair according to the determination result, and respectively transmitting observation information obtained by observing the information source by the node with better observation quality to the fusion center according to the transmission power distributed by the fusion center;

step 5, the nodes without the cooperation partners directly transmit observation information obtained by observing the information source by the nodes without the cooperation partners to the fusion center according to the transmission power distributed by the fusion center;

and 6, fusing the received observation information by the fusion center to obtain an estimated value of the information source.

Another aspect of the present invention is to provide a distributed estimation system based on cooperative communication, including: the information source, the nodes and the fusion center are used for determining a cooperative node pair according to the observation quality of each node in the nodes to the information source, the cooperative node pair is composed of a node with better observation quality and a node with poorer observation quality which are mutually cooperative partners, and the determination result of the cooperative node pair is sent to the corresponding node; the system is also used for carrying out channel estimation on the transmission channel of each node, acquiring the channel condition and carrying out transmission power distribution on each node according to the current channel condition and the observation quality; the device is used for fusing the received observation information to obtain an estimated value of the information source; the plurality of nodes are used for observing the information source to obtain observation information, the two nodes which are positioned in the cooperative node pair and are mutually cooperative partners determine a node with better observation quality and a node with poorer observation quality according to the received determination result of the cooperative node pair, and the observation information obtained by observing the information source by the node with better observation quality is transmitted to the fusion center according to the transmission power distributed by the fusion center; and the nodes without the cooperation partners directly transmit the observation information obtained by observing the information source by the nodes without the cooperation partners to the fusion center according to the transmission power distributed by the fusion center.

The invention has the technical effects that: determining a cooperative node pair by a fusion center according to the observation quality of each sensor node to the information source, wherein the cooperative node pair consists of a node with better observation quality and a node with poorer observation quality which are mutually cooperative partners, and the node with poorer observation quality assists the node with better observation quality to transmit data so as to improve the signal transmission quality of the node and further improve the estimation precision; and the sensor nodes which do not form the cooperative node pair also transmit observation information obtained by observation to the fusion center in a direct transmission mode, so that the fusion center is ensured to fully utilize the observation information of the nodes in the network, and a more accurate estimation value of the information source is obtained.

Drawings

FIG. 1 is a schematic structural diagram of an embodiment of a distributed estimation system based on cooperative communication according to the present invention;

FIG. 2 is a flow chart of an embodiment of a distributed estimation method based on cooperative communication according to the present invention;

FIG. 3 is a flow chart of the assignment of cooperative node pairs in an embodiment of the present invention;

FIG. 4 is a flow chart illustrating operation of transmission power allocation in an embodiment of the present invention;

fig. 5 is a flowchart of a transmission power allocation method according to an embodiment of the present invention;

FIG. 6 is a comparison graph of the estimation accuracy simulation result test of the present invention and the prior art;

FIG. 7 is a comparison graph of the interrupt probability simulation results of the present invention and the prior art.

Detailed Description

The following detailed description of the present invention is provided with reference to the accompanying drawings, and the nodes in the following embodiments are exemplified by sensor nodes, but are not limited to sensor nodes.

Fig. 1 is a schematic structural diagram of an embodiment of a distributed estimation system based on cooperative communication according to the present invention, and as shown in fig. 1, the system of the embodiment includes: information source theta, a plurality of sensor nodes i₁₁，i₁₂......i_K1，i_K2，j₁......j_L-2KThe fusion center FC is used for determining a cooperative node pair according to the observation quality of each sensor node in the sensor nodes to the information source, the cooperative node pair consists of a node with better observation quality and a node with poorer observation quality which are mutually cooperative partners, and the determination result of the cooperative node pair is sent to the corresponding sensor node;the system is also used for carrying out channel estimation on the transmission channel of each sensor node, acquiring the channel condition and carrying out transmission power distribution on each sensor node according to the current channel condition and the observation quality; the device is used for fusing the received observation information to obtain an estimated value of the information source; the sensor nodes are used for observing the information source to acquire observation information, the two sensor nodes which are cooperative partners with each other in the cooperative node pair determine a node with better observation quality and a node with poorer observation quality according to the received determination result of the cooperative node pair, and the observation information acquired by observing the information source by the node with better observation quality is transmitted to the fusion center according to the transmission power distributed by the fusion center; and the sensor nodes without the cooperation partners directly transmit the observation information obtained by observing the information source by the sensor nodes according to the transmission power distributed by the fusion center to the fusion center. Node i in FIG. 1₁₁，i₁₂......i_K1，i_K2Two nodes forming a cooperative node pair, e.g. node i₁₁And i₁₂，i_K1And i_K2Respectively observing nodes i with better quality₁₁The observation information obtained by observing the information source theta is transmitted to the fusion center without the node j forming the cooperative node pair₁......j_L-2KAnd directly transmitting the observation information obtained by observing the information source theta to the fusion center, so that the fusion center can perform information fusion on all the observation information received by the fusion center to obtain an estimated value of the information source.

Fig. 2 is a flowchart of an embodiment of a distributed estimation method based on cooperative communication according to the present invention, where the method of the present embodiment may be executed by the system shown in fig. 1, and the method of the present embodiment includes:

step 1, the fusion center determines the cooperative node pairs according to the observation quality of each sensor node to the information source, and sends the determination results of the cooperative node pairs to the corresponding sensor nodes.

Wherein the cooperative node pair consists of a node with better observation quality and a node with poorer observation quality which are mutually cooperative partners,

step 2, the fusion center distributes transmission power to each sensor node according to the current channel condition and the observation quality;

step 3, each sensor node judges whether the sensor node has a cooperation partner according to the received determination result of the cooperation node pair, if so, the step 4 is executed, otherwise, the step 5 is executed;

step 4, determining a node with better observation quality and a node with poorer observation quality by two sensor nodes which are cooperative partners in the cooperative node pair according to the determination result, and respectively transmitting observation information obtained by observing the information source by the node with better observation quality to the fusion center according to the transmission power distributed by the fusion center;

step 5, the sensor node without the cooperation partner directly transmits observation information obtained by observing the information source by the sensor node according to the transmission power distributed by the fusion center to the fusion center;

In this embodiment, the fusion center first determines, according to the observation quality of each sensor node to the information source in the network, that a cooperative node pair is composed of a node with better observation quality and a node with poorer observation quality, and sends the determination result to the corresponding node, so that the corresponding node can know whether the node has a cooperative partner and is determined as a node with better observation quality or a node with poorer observation quality when receiving the result, and the node with poorer observation quality assists the node with better observation quality to perform data transmission, so as to improve the information transmission quality of the node with better observation quality, thereby improving the estimation accuracy. Multiple cooperative node pairs are allowed to exist in the network, and the specific number of the cooperative node pairs is determined by calculation of the fusion center. Specifically, when each sensor node in the network observes the same information source, the observation quality of each sensor node is different, the channel condition of each node transmitting data to the fusion center is also different, and when the sensor node transmits observation data to the fusion center, people hope to transmit the observation information of the node with better observation quality to the fusion center as effectively as possible. In order to improve the utilization rate of observation information in the network, the sensor nodes which do not form the cooperative node pairs also transmit observation information obtained by observation to the fusion center in a direct transmission mode, so that the fusion center is ensured to fully utilize the observation information of the nodes in the network, and information fusion is carried out according to more observation information, thereby obtaining an estimated value of a more accurate information source.

In the embodiment, the fusion center determines the cooperative node pairs according to the observation quality of each sensor node to the information source, the cooperative node pairs are composed of a node with better observation quality and a node with poorer observation quality which are mutually cooperative partners, and the node with poorer observation quality assists the node with better observation quality to transmit data so as to improve the signal transmission quality of the node and improve the estimation precision; and the sensor nodes which do not form the cooperative node pair also transmit observation information obtained by observation to the fusion center in a direct transmission mode, so that the fusion center is ensured to fully utilize the observation information of the nodes in the network, and a more accurate estimation value of the information source is obtained.

In the above embodiment, the channel condition of the transmission channel of each sensor node may be obtained by the fusion center performing channel estimation in real time, or may be obtained by obtaining a pre-stored channel condition of the node. When obtaining the updated channel condition, before performing step 2, the fusion center further includes: and 7, the fusion center performs channel estimation on the transmission channels of the sensor nodes to acquire the current channel condition. Of course, the fusion center may also perform channel estimation of the node after each time the information source estimation value is calculated, acquire a channel condition, and use the channel condition as a basis for next transmission power allocation of the fusion center.

Fig. 3 is a flow chart of allocation of a cooperative node pair in the embodiment of the present invention, and as shown in fig. 3, the allocation operation of the cooperative node pair in step 1 in the embodiment shown in fig. 2 may specifically include:

and 11, arranging the sensor nodes from small to large according to the observation noise by the fusion center, and correspondingly dividing the sensor nodes into a node set with better observation quality and a node set with poorer observation quality by taking the mean value of the minimum observation noise and the maximum observation noise as a boundary.

Specifically, the observation noise variance of the sensor node can reflect the quality of the node to the observation quality of the information source, and in the step, the observation noise variances of the nodes are arranged in an ascending order, and the method comprises the following steps:and are provided withAs a boundary for distinguishing the good and bad observation performance of the nodes, i is used₁，i₂...，i_K(variance arranged from low to high) node numbers j with better observation quality₁，...，j_L-K(variance is arranged from low to high) indicates the node sequence number with poor observed quality (assuming there are L nodes in the network).

And step 12, the fusion center obtains the functional relation between the observation noise of each node with better observation quality and the observation noise threshold of the cooperative partner node under a certain observation quality condition in a linear fitting mode.

The specific method comprises the following steps: taking two nodes as an example for explanation, a network scene with only two nodes is constructed, wherein node 1 is an information source node, observation noise is known, and node 2 is a relay node with unknown observation noise. The observation noise threshold (lower bound) of the relay node (node 2) which enables the system performance after cooperation to be better is obtained by comparing the two transmission modes, namely, the fusion center obtains the requirement of the observation noise of the cooperation partner node under the set condition that the observation performance is better than that of the two nodes in independent transmission through calculation.

In the method A, the node 1 transmits observation information, the node 2 serves as a relay node, and the two transmit the observation information of the node 1 in a cooperative communication mode.

Mode B, node 1, 2 independently transmit their own observation information

The cooperation mode in A comprises the following steps:

in the first time slot, node 1 transmits its observation information to the fusion center, and node 2 listens for this information.

In the second time slot, the node 2 transmits the observation information of the node 1 acquired by monitoring to the fusion center.

If the node 2 is a relay node of the node 1 (with better observation performance), according to the amplify-and-forward cooperation mode (see the step 4) and the information fusion mode (see the step 6) adopted by the invention, under the condition that only the two nodes are considered in the network, the signal received by the fusion center FC is y of the following formula (1)₁And y₂

Wherein P represents the sum of the power consumed by the nodes, α₁Representing the amplification factor, alpha, of the node 1 to the observed information₂Representing the amplification factor of node 2 to the received information of node 1. g₁，g₂Representing the channel gain from the node to the fusion center, g_1，2Representing the channel gain, α, between nodes 1, 2_cRepresenting the forward amplification factor, n, of the node 2 in cooperation with the node 1_1，2Representing channel interference between nodes 1, 2, n₁Representing the observed noise at node 1 and,reference to corresponding noise n_xSecond order moment of (a). If two nodes are specified to consume the same power, then for the calculation of the amplification factor, there are:

wherein, P_cPower for transmitting its own observation information to node 2 on behalf of node 1

In the system described in the present invention, the following assumptions are adopted:

1. the communication noise between the nodes and the fusion center FC are independently and equally distributed.

2. The communication noise in the network follows a gaussian distribution with the same statistical properties.

3. The nodes are far from the fusion center and the distances between the nodes are close, so the distances from the nodes to the fusion center can be regarded as approximately the same.

4. The node-to-fusion center channel is subject to a rayleigh model.

The present invention takes the following simplified approach to obtain an approximation of the estimation error: the sensor nodes are densely distributed, and the channel path loss between the nodes is ignored (namely, g is considered)_1，21); considering that for practical scenarios of distributed applications, the amplification power is typically significantly larger than the channel noise, and thus is approximated by a₂1, when it is assumed that the communication noise between the nodes and the communication noise returned by the nodes to the fusion center FC are independent from each other, it can be obtained:

in the assumed model, the sensor nodes are densely distributed, ignoring channel fading between nodes (i.e., consider g as_1，21), there are:

considering that for practical scenarios of distributed applications, the amplification power is typically significantly larger than the channel noise, and thus is approximated by a₂1 is approximately distributed; the Additive White gaussian Noise (AWGN Noise) encountered by the node-to-FC transmission is considered to be co-distributed, i.e.:after the above equation (3) is simplified and approximated, we get:

under the above process, the estimation error can be expressed as

Then, the average estimation error of the system under a certain channel condition can be obtained through a Monte Carlo simulation mode, and the system performance after cooperation is better than the observation noise threshold of the uncooperative relay node under a certain observation quality (if the system performance after cooperation is higher than the threshold, the system performance after cooperation is better). Furthermore, by adopting a linear fitting mode, the relationship between the node observation noise and the relay observation noise threshold can be obtained, which includes:

y＝kx+b (7)

x represents the node observation noise, y represents the observation noise threshold corresponding to the node observation noise, and the formula is the function relation of the calculated threshold.

And step 13, the fusion center searches the nodes of the sets with better observation quality for the cooperative partner nodes in the sets with poorer observation quality one by one according to the observation quality from good to bad.

If the observation noise of the candidate node in the set with poor observation quality is greater than the corresponding observation noise threshold, and the candidate node is not marked as a cooperative partner node of other nodes.

In a specific embodiment, let i_rAnd the K nodes search own cooperative partners one by one according to the good to bad observation quality, and for each node, the nodes are sequentially arranged at j according to the sequence of s 1 to K_sIf a node meeting the threshold requirement and not marked as a relay of another node is found (if the observed noise of the cooperative node is greater than the observed noise threshold obtained by the function in the previous step 14), or j is found_sAnd ending the middle traversal. I.e. if a certain i_qNode in the remaining node set j that has not been selected_w1，...j_weE ∈ {1, 2.,. L-K } cannot find its own collaboration partner, then i_qLater nodes are less likely to find their own collaboration partners because they have higher requirements on the variance of the observed noise of the collaboration nodes。

Step 14, the fusion center marks the found candidate nodes meeting the search condition as cooperative partner nodes corresponding to the nodes with better observation quality, determines the nodes with better observation quality and the candidate nodes as cooperative node pairs, and respectively sends the determination results to the two corresponding nodes;

step 15, observing all nodes in the set with better quality to find whether the nodes of the cooperation partner are traversed completely, if so, executing step 16, otherwise, repeatedly executing step 13;

and step 16, the fusion center takes the nodes in the set with better observation quality and not meeting the searching condition and the nodes in the set with worse observation quality and not meeting the searching condition as the sensor nodes without the cooperation partners.

The invention can ensure i through the steps_rEach node of K can find a node which just meets the requirement of the node, and the node which is sequenced in the past and observed can preferentially search a cooperation partner, so that the node has better probability of finding the cooperation node; meanwhile, the node which preferentially searches the cooperation partner has low requirement on observation noise, so that the node with higher observation noise is preferentially selected, the possibility of finding the own cooperation partner as high as possible is provided for the following nodes, more nodes participate in cooperative communication, and the estimation precision is improved.

Fig. 4 is a flowchart of an operation of allocating transmission power in the embodiment of the present invention, as shown in fig. 4, in the embodiment shown in fig. 2, the allocating of transmission power in step 2 may specifically include:

step 21, the fusion center calculates and determines the opening states of the cooperative node pairs and the sensor nodes without cooperative partners according to the division of the cooperative node pairs;

step 22, carrying out transmission power distribution on the opened cooperative node pair and the sensor node without the cooperative partner;

step 23, performing internal transmission power redistribution on the two sensor nodes by the open cooperative node pair according to the channel conditions of the two sensor nodes in the cooperative node pair;

and 24, correspondingly sending the opening state of each node and the distributed transmission power to each sensor node so that each node determines whether to transmit observation information according to the opening state and transmits the observation information according to the distributed transmission power.

In the operation steps, the fusion center equivalently converts the cooperative node pairs into one node in calculation, after the fusion center performs initial transmission power distribution on the opened nodes (including the nodes without cooperative partners and the cooperative node pairs), the transmission power distribution is performed on the two nodes in the cooperative node pairs, finally, the opening state and the transmission power of each node are sent to each sensor node, and each node determines whether to participate in observation information transmission according to the received opening state and correspondingly transmits the observation information to the fusion center according to the distributed transmission power.

The above power allocation process and solution principle are analyzed in detail below.

Firstly, analyzing system performance, wherein the number of cooperative node pairs in the system is represented by K, and all nodes participating in cooperation can use i₁₁，i₁₂，...，i_K1，i_K2Is indicated in which i_r1Indicates the node with better observation performance, i, in the r-th cooperative node pair_r2Represents i_r1The partner node of (1); the rest nodes adopt the working mode of self observation and forward transmission fusion center FC, and j is used₁，j₂，...，j_L-2KAnd (4) showing. The observation information received by the fusion center can be expressed as:

. . . .

(8)

. . . .

wherein the subscript i_m，nRepresenting the nth node, j, of m cooperating node pairs in the i sequence (cooperating node pair sequence)_kRepresenting the kth node in the j sequence (the sequence of non-cooperative nodes).Indicating the channel gain between two nodes for the r-th cooperative node,representing the channel noise of the r-th cooperative node for information transmission between two nodes,denotes the channel gain between the r-th cooperative node pair, index i_r1，i_r2Respectively representing nodes with good observation quality and nodes with poor observation quality in the r-th cooperation node pair.

Then, the observed covariance can be expressed as:

C = [\begin{matrix} C_{i_{11}} & R_{i_{1}} & 0 \\ R_{i_{1}} & C_{i_{12}} \\ . . . \\ C_{i_{K 1}} & R_{i_{K}} \\ R_{i_{K}} & C_{i_{K 2}} \\ C_{j_{1}} \\ . . . \\ 0 & C_{j_{L - 2 K}} \end{matrix}] - - - (9)

a variance representing channel noise between the Kth node pair;

representing the observation noise variance of the node with better observation quality in the Kth node pair;

representing the channel gain between the kth node pair.

The above equation (9) can be simplified to:

C = [\begin{matrix} B_{i_{1}} & 0 \\ . . . \\ B_{i_{K}} \\ C_{j_{1}} \\ . . . \\ 0 & C_{j_{L - 2 K}} \end{matrix}]

B_{i_{r}} = [\begin{matrix} C_{i_{r 1}} & R_{ir} \\ R_{ir} & C_{i_{r 2}} \end{matrix}] - - - (10)

further obtaining:

C^{- 1} = {[\begin{matrix} B_{i_{1}}^{- 1} & 0 \\ . . . \\ B_{i_{K}}^{- 1} \\ C_{j_{1}}^{- 1} \\ . . . \\ 0 & C_{j_{L - 2 K}}^{- 1} \end{matrix}]}_{L - K, L - K}

considering the assumption that the channel gain between nodes is considered to be 1, there are:

g_{i_{p}} = 1, p = 1, . . ., K

so that there are

We assume that the noise is independently and equally distributed, and in the forwarding environment, the channel noise between nodes is the same as the node-to-FC channel noise, so that there is:

a，b＝1，......，K；d＝1，......L-2K

assuming and considering that the channel gain between the nodes is approximately 1, and the communication noise in the system is represented by sigma²To express, then, the estimation error can be expressed as:

in the power distribution solution, firstly, power is distributed to each node without a cooperation partner and a cooperation node pair, and then, power obtained by the cooperation node pair is distributed to two nodes participating in cooperation, considering that the cooperation node pair is only divided according to the quality of a channel, under the previous assumption, the channel between the nodes can be considered as an independent and identically distributed variable, so that, although the internal power distribution of the node pair can be different under one-time channel realization, in the long term, the power obtained by the two nodes is completely the same, and therefore, when the power distribution is carried out on the node pair, the power obtained by the two cooperation partners can be considered to be the same for the convenience of problem analysis; further, since the inter-node channel fading is neglected, and the communication noise energy is much smaller than the signal energy of the inter-node information transmission in practice, there may be:later considered in practical systemsThen the following simplification occurs:

r＝1，...，K

the original equation (11) is simplified approximately as follows:

the optimization problem can be described as follows:

<math> <mrow> <msub> <msup> <mi>α</mi> <mo>′</mo> </msup> <msub> <mi>i</mi> <mrow> <mi>i</mi> <mn>1</mn> </mrow> </msub> </msub> <mo>&GreaterEqual;</mo> <mn>0</mn> <mo>,</mo> <msub> <msup> <mi>α</mi> <mo>′</mo> </msup> <msub> <mi>j</mi> <mi>s</mi> </msub> </msub> <mo>&GreaterEqual;</mo> <mn>0</mn> <mo>,</mo> <mi>r</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mi>K</mi> <mo>;</mo> <mi>s</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mi>L</mi> <mo>-</mo> <mn>2</mn> <mi>K</mi> </mrow> </math>

wherein:

(14)

from the previous assumptions, it is easy to have:the optimization problem can be transformed into:

<math> <mrow> <msub> <msup> <mi>α</mi> <mo>′</mo> </msup> <msub> <mi>i</mi> <mrow> <mi>r</mi> <mn>1</mn> </mrow> </msub> </msub> <mo>&GreaterEqual;</mo> <mn>0</mn> <mo>,</mo> <msub> <msup> <mi>α</mi> <mo>′</mo> </msup> <msub> <mi>j</mi> <mi>s</mi> </msub> </msub> <mo>&GreaterEqual;</mo> <mn>0</mn> <mo>,</mo> <mi>r</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mi>K</mi> <mo>;</mo> <mi>s</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mi>L</mi> <mo>-</mo> <mn>2</mn> <mi>K</mi> </mrow> </math>

wherein P is_totThe total power transmitted by the nodes in the network.

Further, this optimization problem can be converted into the following equivalent form:

in order to further simplify the solution, an equivalent idea is adopted, and the method comprises the following steps:

for equivalent nodes, there are:

construction of α'_mv，v＝1，...，L-K，

Order:

so that there is a need for,

wherein,

s_{mv} = \{\begin{matrix} s_{z_{v}} / 2, v = 1, . . ., K \\ s_{j_{v - K}}, v = K + 1, . . ., L - K \end{matrix};

and defines: eta_mv＝s_mv/(1+γ_mv) v＝1，...，L-K

The optimization problem at this time can be expressed as:

α′_mv≥0，v＝1，...，L-K

a lagrange multiplier is constructed, having:

the constraints can be expressed as:

α′_mv≥0 v＝1，...，L-K

μ_mvα′_mv＝0 v＝1，...，L-K

μ_mv≥0 v＝1，...，L-K

<math> <mrow> <mo>-</mo> <mfrac> <msubsup> <mi>s</mi> <mi>mv</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msubsup> <msup> <mrow> <mo>(</mo> <msubsup> <mi>γ</mi> <mi>mv</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msubsup> <msub> <msup> <mi>α</mi> <mo>′</mo> </msup> <mi>mv</mi> </msub> <mo>+</mo> <msubsup> <mi>s</mi> <mi>mv</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msubsup> <mo>)</mo> </mrow> <mn>2</mn> </msup> </mfrac> <mo>+</mo> <msub> <mi>λ</mi> <mn>0</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <msubsup> <mi>γ</mi> <mi>mv</mi> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msubsup> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>μ</mi> <mi>mv</mi> </msub> <mo>=</mo> <mn>0</mn> <mo>,</mo> <mo>&ForAll;</mo> <mi>v</mi> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>19</mn> <mo>)</mo> </mrow> </mrow> </math>

according to the above system analysis, simplification and approximation, the practical application of step 2 may include the following specific solving steps, fig. 5 is a flow chart of a transmission power allocation method according to an embodiment of the present invention, as shown in fig. 5, the operations of which include:

step 201, in the fusionThe center is determined according to the division of the node pairAnd is_mvSorting according to the size, and representing the newly-sorted sequence by a, namely satisfying the condition:

<math> <mrow> <msub> <mi>η</mi> <msub> <mi>a</mi> <mn>1</mn> </msub> </msub> <mo>&GreaterEqual;</mo> <msub> <mi>η</mi> <msub> <mi>a</mi> <mn>2</mn> </msub> </msub> <mo>&GreaterEqual;</mo> <mo>.</mo> <mo>.</mo> <mo>.</mo> <mo>&GreaterEqual;</mo> <msub> <mi>η</mi> <msub> <mi>a</mi> <mrow> <mi>L</mi> <mo>-</mo> <mi>K</mi> </mrow> </msub> </msub> <mo>;</mo> </mrow> </math>

step 202, introducing a function f (k):

traverse from 1 to L-K, solve for the f (K) value.

Step 203, determine if there is a K₁Satisfy f (K)₁) > 0 and f (K)₁+1) is less than or equal to 0, if yes, the step is switched to the step 204, otherwise, the step 205 is executed;

step 204, according to K₁Determining whether the node is on or off: when K is less than or equal to K₁When K is larger than K, the corresponding node is opened₁When yes, the corresponding node is turned off, and the step 206 is carried out;

step 205, enabling all nodes to be opened;

step 206, the transmission power of the node or the cooperative node pair is distributed according to the following formula (21)

<math> <mrow> <msub> <msup> <mi>α</mi> <mo>′</mo> </msup> <mi>mv</mi> </msub> <mo>=</mo> <mfrac> <msub> <mi>γ</mi> <mi>mv</mi> </msub> <msub> <mi>s</mi> <mi>mv</mi> </msub> </mfrac> <msup> <mrow> <mo>(</mo> <msqrt> <mfrac> <msub> <mi>η</mi> <mi>mv</mi> </msub> <msub> <mi>λ</mi> <mn>0</mn> </msub> </mfrac> </msqrt> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>+</mo> </msup> <mo>&ForAll;</mo> <mi>v</mi> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>21</mn> <mo>)</mo> </mrow> </mrow> </math>

And step 207, the cooperative node redistributes the internal power.

Based on the above step 201 and 206, the internal power of the cooperative node is determined according to the principle

P_{i_{r 1}} : P_{i_{r 2}} = s_{i_{r 1}}^{2} : s_{i_{r 2}}^{2}

The redistribution is performed.

And step 208, the fusion center transmits the opening state and the transmission power to each sensor node.

In the above embodiment of the present invention, the step 4 may specifically include:

step 41, two nodes which are mutually cooperative partners in the cooperative node pair judge whether the node is a node with better observation quality or a node with poorer observation quality according to the determination result, if the node with better observation quality is present, the step 42 is executed, and if the node with better observation quality is not present, the step 43 is executed;

step 42, amplifying observation information obtained by observing the information source according to the transmission power distributed by the fusion center and transmitting the information to the fusion center;

and 43, monitoring the observation information amplified by the node with better observation quality in the cooperative node pair, acquiring a noise-containing copy of the amplified observation information, and transmitting the noise-containing copy to the fusion center after amplifying the noise-containing copy according to the transmission power distributed by the fusion center.

The step 6 may specifically be: and the fusion center performs information fusion on all the received observation information by adopting a linear optimal unbiased estimation method to obtain an estimation value of the information source.

In a specific implementation, the estimate may be calculated as follows:

y＝hθ+v

wherein the first equation expresses the received observation information in a linear relationship with the source, and R in the second equation represents a covariance matrix of errors.

The estimation precision and the interruption probability are two important technical indexes of the distributed estimation system, the estimation precision is obtained by adopting a Monte Carlo mode, and a calculation method in one-time implementation refers to a formula (22). The outage probability refers to the probability that the system satisfies a certain estimation error index, which is expressed by the following equation (23):

wherein D₀Refers to an estimation error indicator.

By adopting the cooperative estimation mechanism in the invention, higher estimation precision and lower interruption probability can be obtained compared with the existing general distributed estimation and the adoption of a node direct transmission and power distribution optimization mechanism.

FIG. 6 is a comparison graph of the estimation accuracy simulation result test of the present invention and the prior art; FIG. 7 is a comparison graph of the interrupt probability simulation results of the present invention and the prior art. The invention has the advantages that the estimation error is lower and the interruption probability is lower under the condition of the same total transmission power, namely the estimation precision is higher, thereby improving the performance of the estimation system.

Those of ordinary skill in the art will understand that: all or part of the steps for implementing the method embodiments may be implemented by hardware related to program instructions, and the program may be stored in a computer readable storage medium, and when executed, the program performs the steps including the method embodiments; and the aforementioned storage medium includes: various media that can store program codes, such as ROM, RAM, magnetic or optical disks.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the invention without departing from the spirit and scope of the invention.

Claims

1. A distributed estimation method based on cooperative communication, comprising:

step 6, the fusion center fuses the received observation information to obtain an estimated value of the information source;

the step 1 specifically comprises:

step 11, the fusion center arranges all nodes from small to large according to observation noise, and correspondingly divides the nodes into a node set with better observation quality and a node set with poorer observation quality by taking the mean value of the minimum observation noise and the maximum observation noise as a boundary;

step 12, the fusion center obtains the functional relation between the observation noise of each node with better observation quality and the observation noise threshold of the cooperative partner node under a certain observation quality condition in a linear fitting mode;

step 13, the fusion center searches the nodes in the set with better observation quality for the cooperation partners in the set with poorer observation quality one by one according to the observation quality from good to bad, wherein the searching condition is that if the observation noise of the candidate node in the set with poorer observation quality is greater than the corresponding observation noise threshold value, the candidate node is not marked as the cooperation partner of other nodes;

step 14, the fusion center marks the found candidate nodes meeting the search condition as cooperative partners corresponding to the nodes with better observation quality, determines the nodes with better observation quality and the candidate nodes as cooperative node pairs, and respectively sends the determination results to the two corresponding nodes;

step 15, if all nodes in the set with better observation quality find the cooperation partner and are not traversed, executing step 13;

the step 4 specifically includes:

43, monitoring the observation information amplified by the node with better observation quality in the cooperative node pair, acquiring a noise-containing copy of the amplified observation information, and transmitting the noise-containing copy to the fusion center after amplifying the noise-containing copy according to the transmission power distributed by the fusion center;

the step 2 specifically comprises:

step 22, carrying out transmission power distribution on the opened cooperative node pair and the nodes without cooperative partners;

step 23, performing internal transmission power redistribution on the two nodes by the open cooperative node pair according to the channel conditions of the two nodes in the cooperative node pair;

and 24, correspondingly sending the opening state of each node and the distributed transmission power to each node so that each node determines whether to transmit observation information according to the opening state and transmits the observation information according to the distributed transmission power.

2. The method of claim 1, wherein step 2 is preceded by:

and 7, the fusion center performs channel estimation on the transmission channel of each node to acquire the channel condition.

3. The method of claim 1, wherein step 15 is further followed by:

and step 16, if all nodes in the set with better observation quality search the cooperative partner nodes and traverse, the fusion center takes the nodes in the set with better observation quality which do not find the search condition and the nodes in the set with poorer observation quality which do not accord with the search condition as the nodes without the cooperative partners.

4. The method according to claim 1 or 2, characterized in that said step 6 is in particular: and the fusion center performs information fusion on all the received observation information by adopting a linear optimal unbiased estimation method to obtain an estimation value of the information source.

5. A cooperative communication based distributed estimation system, comprising: a source, a plurality of nodes, and a fusion center,

the fusion center is used for determining a cooperative node pair according to the observation quality of each node in the plurality of nodes to the information source, the cooperative node pair consists of a node with better observation quality and a node with poorer observation quality which are mutually cooperative partners, and the determination result of the cooperative node pair is sent to the corresponding node; the system is also used for carrying out channel estimation on the transmission channel of each node, acquiring the channel condition and carrying out transmission power distribution on each node according to the current channel condition and the observation quality; the device is used for fusing the received observation information to obtain an estimated value of the information source;

the plurality of nodes are used for observing the information source to obtain observation information, the two nodes which are positioned in the cooperative node pair and are mutually cooperative partners determine a node with better observation quality and a node with poorer observation quality according to the received determination result of the cooperative node pair, and the observation information obtained by observing the information source by the node with better observation quality is transmitted to the fusion center according to the transmission power distributed by the fusion center; and the nodes without the cooperation partners directly transmit the observation information obtained by observing the information source by the nodes without the cooperation partners to the fusion center according to the transmission power distributed by the fusion center.