CN101557607A - Method for controlling transmission of sink nodes in wireless sensor network - Google Patents

Abstract

The invention provides a method for controlling the transmission of sink nodes in a wireless sensor network. The method comprises the following steps: firstly, averaging the confirmed time intervals of ack packets, then, measuring the available bandwidth and further filtering the acquired available bandwidth with a filter to eliminate errors, thereby acquiring the more accurate value of the available bandwidth; dividing the congestion avoidance stage into two linear-growth stages by measuring the buffer length of the bottleneck link and combining the estimated value of the available bandwidth, particularly, increasing the sending rate of data packets towards the maximal network capacity rapidly and then reducing the rate of reaching the maximal network capacity, so that the sending process can remain stable at a higher sending rate for a long time; and distinguishing congestion packet loss from wireless error code packet loss by the buffer length of the bottleneck link when the packet loss occurs, and rapidly restoring the sending window to the normal size in the wireless sensor network environment with a higher bit error rate, so that the ssthresh (slow start threshold) and the sending window can be adjusted to a proper value according to the network status, and the stability and the throughput rate of the transmission can be effectively improved.

Description

The transfer control method of aggregation node in the wireless sensor network

Technical field

The present invention relates to field of wireless, particularly wireless sensor network protocols design field specifically provides the transfer control method of aggregation node in the wireless sensor network, although can be with the feature application that provides in other network designs.

Background technology

The system configuration of wireless sensor network generally includes sensor node (SensorNode), aggregation node (Sink Node) and management node (Manager Node) as shown in Figure 1.A large amount of sensor nodes are arranged in the monitored area, and node constitutes network by the mode of self-organizing.The information that sensor node self collects sends it to aggregation node in the multi-hop mode after this locality carries out tentatively handling.Aggregation node also claims gateway (gateway), and near the report data of sensor node can converging is picked out some wrong or unusual data, carries out data fusion and incident and judges, is sent to management node by networks such as the Internet, Cellular Networks at last.The terminal use also can manage wireless sensor network by management node, configuration, issue monitoring task or collection passback data.

In wireless sensor network system, sensor node has different characteristics with aggregation node, the common disposal ability of sensor node, storage capacity a little less than, its communication distance is also less, and the common relatively sensor node of aggregation node, its data-handling capacity is stronger, memory space and communication distance etc. are all bigger, sensor network is usually by aggregation node and external network such as Internet, satellite network, 3G networks etc. link to each other, realize communicating by letter between task management node and the transducer, aggregation node is used for receiving control command that management node sends and the ordinary node that is distributed to sensor network.Because it is relatively big to be pooled to the data flow of aggregation node, the transmission control ability that improves aggregation node is very big to strengthening the influence of wireless sensor network overall performance.

Traditional transfer control method such as cable network Transmission Control Protocol adopt the congestion window growth pattern of the additivity increase property taken advantage of minimizing (AIMD), and be low in the error rate, and congested be that the performance performance is well in the cable network environment of packet loss main cause.Yet aggregation node wireless network environment of living in has higher bit error rate (Bit Error Rate, BER), characteristics such as link bandwidth is asymmetric, and bigger bandwidth time-delay is long-pending make that performance was low when traditional transmission control algolithm directly applied to the wireless sensor network aggregation node.

Summary of the invention

Technical problem: the present invention provides the transfer control method of aggregation node in a kind of wireless sensor network for solving above-mentioned problems of the prior art, transmits control to improve the aggregation node transmission performance at the wireless sensor network characteristics.

Technical scheme: the transfer control method of aggregation node in the wireless sensor network may further comprise the steps:

1. based on the available bandwidth measurement that wraps the arrival interval, calculate available bandwidth again by measure to confirm time interval that bag arrives and the time interval averaged, with filter the available bandwidth that measures is carried out filtering then and eliminate error, obtain available bandwidth measurement value comparatively accurately with this;

2. the congestion avoidance phase control mode that increases of piecewise linearity, in conjunction with available bandwidth measurement value and current bottleneck link buffer length measured value, the stage that congestion avoidance phase is divided into two linear growths, data package transmission velocity is comparatively fast increased near the network heap(ed) capacity, slow down the speed that arrives the network heap(ed) capacity again, make the process of transmitting long period be stabilized in higher transmission rate;

3. distinguish in the wireless environment congested and error code packet loss reason and take reasonable measure, when taking place, packet loss distinguishes congestion packet loss or wireless error code packet loss according to the bottleneck link buffer length, make under the higher wireless network environment of the error rate fast quick-recovery congestion window size, and wait a moment actuation threshold value and send window can be adjusted to a suitable value according to network condition.

The transfer control method of aggregation node in the wireless sensor network, step in 1. to the time interval method of averaging is: sending node record a period of time, each confirmed the moment of bag-ACK arrival, and calculate the time interval and the time interval total number of confirming between the bag, then to these time interval summations and except that the mean value that obtains the time interval in time interval total number.

The transfer control method of aggregation node in the wireless sensor network, step is divided into the method in the stage of two linear growths with congestion avoidance phase in 2. and is specially: preestablish threshold value λ, if bottleneck link buffer length measured value is smaller or equal to threshold value λ, then increase send window fast, the send window growth pattern is cwnd=cwnd+ β ₁/ cwnd.Wherein cwnd is a send window, β ₁Be regulatory factor, be used to control the send window growth rate; If bottleneck link buffer length measured value then slows down the send window growth rate greater than threshold value λ, the send window growth pattern is cwnd=cwncd+1/ (β ₂* cwnd).Here β ₂Be regulatory factor, be used to control the send window growth rate.

The transfer control method of aggregation node in the wireless sensor network, 3. step distinguishes that congested and error code packet loss reason method is specially in the wireless environment: threshold value δ is set, when receiving 3 repeat ACK bags,, show that packet loss is former because channel error code if record bottleneck link buffer length L＜δ; As L＜δ, show that packet loss is former because network is tending towards congested.

The transfer control method of aggregation node in the wireless sensor network, step are provided with the suitable threshold method of startup slowly according to the packet loss reason in 3. and are specially: the channel error code if packet loss is former is provided with then that to start threshold value slowly be ssthresh=bwe * (RTT _Cur+ RTT _Min)/2 are if the former because network congestion of packet loss is provided with then that to start threshold value slowly be ssthresh=bwe * RTT _MinSsthresh wherein is for starting threshold value slowly, and bwe is the bandwidth of current measurement, RTT _CurBe the ACK bag two-way time of current measurement, RTT _MinFor the minimum ACK that measures wraps two-way time.

Beneficial effect: bandwidth estimation method that adopts among the present invention and the sectional-regulated method of congestion avoidance phase, when making aggregation node transmission data, its process of transmitting can be stabilized in higher transmission rate state the long period.Adopt the correct mechanism of distinguishing packet loss reason and differentiated treatment simultaneously, make and send window takes place behind the packet loss and start threshold value slowly to be arranged on rational state, thereby the stability when effectively having improved aggregation node transmission data, send window fluctuation is less in the data transmission procedure, and the throughput of transmission data obviously gets a promotion.

Description of drawings

Fig. 1 has the wireless sensor network structure chart now,

Fig. 2 congestion avoidance phase segment transmissions of the present invention window variation diagram,

Fig. 3 congestion avoidance phase segment transmissions of the present invention control method flow chart,

Fig. 4 is of the present invention to be provided with the suitable threshold value flow chart that starts slowly.

Embodiment

Below in conjunction with accompanying drawing and concrete embodiment technical scheme of the present invention is further specified.

Wrap the availability bandwidth measurement method of arrival interval among the present invention based on ACK, calculate available bandwidth again by measure to confirm time interval that bag arrives and the time interval averaged, with filter the available bandwidth that measures is carried out filtering then and eliminate error, obtain available bandwidth measurement value comparatively accurately with this.Concrete grammar is: tentation data bag size is P, and through behind the bottleneck link, packet forms certain interval, and the time interval that arrives the ACK bag formation of replying after the destination node is Δ t ₁, Δ t ₂, Δ t ₃..., Δ t _N-1, Δ t _n, then the available bandwidth measurement value is:

$B=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{P}_i/\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{\mathrm{\Δt}}_i=n\×P/\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{\mathrm{\Δt}}_i=P/(\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{\mathrm{\Δt}}_i/n)---\left(1\right)$

Availablely from formula (1) find out that the bandwidth that measures is that the packet size is removed in Mean Time Between Replacement.

Be that sending node record a period of time, each ACK confirmed the moment that bag arrives, and calculated the time interval and time interval number between the ACK bag, then these time intervals was asked mathematic expectaion to the time interval method of averaging.

After obtaining current bandwidth measurement value, adopt discrete time filter to eliminate measure error, suppose at time t _kThe time, the bandwidth value that measures is b _k, the bandwidth value that obtains through filter sample is

Then according to list of references " TCP westwood:congestion window control using bandwidth estimation " (Gerla M, Sanadidi M Y, Wang R, IEEE Globecom, San Antonio, pp.1698-1702,2001) the bandwidth measurement method in obtains:

${\hat{b}}_k={\mathrm{\α}}_k{\hat{b}}_{k-1}+(1-{\mathrm{\α}}_k)\left(\frac{b_k+b_{k-1}}{2}\right)=\frac{2\mathrm{\τ}-{\mathrm{\Δt}}_k}{2\mathrm{\τ}+{\mathrm{\Δt}}_k}\×{\hat{b}}_{k-1}+(1-\frac{2\mathrm{\τ}-{\mathrm{\Δt}}_k}{2\mathrm{\τ}+{\mathrm{\Δt}}_k})\×\left(\frac{b_k+b_{k-1}}{2}\right)---\left(2\right)$

α wherein _kFor the time varying index filter factor, 1/ τ is the switch cut-off frequency of filter, b _K-1With

Be respectively the bandwidth measurement value of last time and the bandwidth value that last process filter sample obtains.

Estimated value to bottleneck link length adopts and list of references " TCP Vegas:end to end congestionavoidance on a global internet " (Brakmo L S, Perterson L L., IEEE Journal onSelected Areas in Communications, 13 (8): 1465-1480,1995) similar method, if current packet transmission rate is cur_rate=cwnd/RTT, and the benchmark transmission rate is base_rate=cwnd/BaseRTT, wherein BaseRTT is minimum data bag value two-way time that records, RTT is for eliminating data after interference bag value two-way time through filter, cwnd is the current congestion window size, make that the bottleneck link buffer length is L, then bottleneck link buffer length computational methods are L=cur_rate * (RTT-BaseRTT).

The send window growth pattern that congestion avoidance phase control adopts piecewise linearity to increase, in conjunction with available bandwidth measurement value and current bottleneck link buffer length measured value, the stage that congestion avoidance phase is divided into two linear growths, data package transmission velocity is comparatively fast increased near the network heap(ed) capacity, slow down the speed that arrives the network heap(ed) capacity again, make the process of transmitting long period be stabilized in higher transmission rate.Fig. 2 is that congestion avoidance phase segment transmissions window changes schematic diagram, and Fig. 3 is a congestion avoidance phase transfer control method flow chart, and establishing and measuring the bottleneck link buffer length is L, threshold value λ is set, if L＜λ; The expression network also is not tending towards congested, and can increase congestion window size fast this moment, and process of transmitting is increased to rapidly near the network heap(ed) capacity, and the congestion window variation pattern is cwnd=cwnd+ β ₁/ cwnd corresponds to that slope is k among Fig. 2 ₁Propagation process.If L＞λ, expression network this moment is near congested, and the window added value that need slow down as far as possible is stabilized near the network capacity maximum process of transmitting long period, and its send window increase mode is cwnd=cwncd+1/ (β ₂* cwnd), correspond to that slope is k among Fig. 2 ₂Propagation process.β wherein ₁And β ₂Be regulatory factor, β ₁Be used to control congestion avoidance phase send window growth rate, work as β ₁Congestion window increases too fastly when excessive, causes congestion packet loss to influence transmission performance easily, otherwise then can't make full use of network capacity; β ₂Influence the time that process of transmitting stops at network heap(ed) capacity place.The send window size of each congestion avoidance phase is at minimum value W ₀With maximum W _MaxBetween change.

In having the wireless sensor network of error code, by distinguishing in the wireless environment congested and error code packet loss reason and taking reasonable measure, when taking place, packet loss distinguishes congestion packet loss or wireless error code packet loss according to the bottleneck link buffer length, make under the higher wireless network environment of the error rate fast quick-recovery congestion window size, and wait a moment actuation threshold value and send window can be adjusted to a suitable value according to network condition.Threshold value δ is set, when receiving 3 repeat ACK bags, if record bottleneck link buffer length L＜δ, it is congested to show that present network does not take place, need not too much to reduce ssthresh and cwnd, so the time start threshold value slowly and can be set to ssthresh=bwe * (RTT _Cur+ RTT _Min)/2 as L＞δ, show that current network is tending towards congested, are provided with that to start threshold value slowly be ssthresh=bwe * RTT this moment _Min, repeatedly to show that the δ value is set to 5 o'clock effects better in experiment.Specific algorithm is as shown in Figure 4 following.When sending the timer expired packet loss, can be judged as substantially and send data volume and exceed the bottleneck link heap(ed) capacity and cause network congestion, so the bandwidth value that will measure this moment starts threshold value slowly and is set to ssthresh=bwe * RTT as the foundation that starts the threshold value setting slowly _Min

Claims (5)

1. the transfer control method of aggregation node in the wireless sensor network is characterized in that this method may further comprise the steps:

1. based on the available bandwidth measurement of bag arrival interval: calculate available bandwidth again by measure to confirm time interval that bag arrives and the time interval averaged, with filter the available bandwidth that measures is carried out filtering then and eliminate error, obtain available bandwidth measurement value comparatively accurately with this;

2. the congestion avoidance phase control mode that increases of piecewise linearity, in conjunction with available bandwidth measurement value and current bottleneck link buffer length measured value, the stage that congestion avoidance phase is divided into two linear growths, data package transmission velocity is comparatively fast increased near the network heap(ed) capacity, slow down the speed that arrives the network heap(ed) capacity again, make process of transmitting be stabilized in higher transmission rate:

3. distinguish in the wireless environment congested and error code packet loss reason and take reasonable measure, when taking place, packet loss distinguishes congestion packet loss or wireless error code packet loss according to the bottleneck link buffer length, making under the higher wireless network environment of the error rate can fast quick-recovery congestion window size, and wait a moment actuation threshold value and send window can be adjusted to a suitable value according to network condition.

2, the transfer control method of aggregation node in the wireless sensor network according to claim 1, it is characterized in that during described step 1. to the time interval method of averaging being: sending node record a period of time, each confirmed the moment that bag-ACK arrives, and calculate to confirm the time interval and time interval total number between the bag, then to these time intervals summations and obtain the mean value in the time interval divided by time interval total number.

3, the transfer control method of aggregation node in the wireless sensor network according to claim 1 is characterized in that congestion avoidance phase being divided into the method in the stage of two linear growths during described step 2. is specially: preestablish threshold value λ

If 1. bottleneck link buffer length measured value is smaller or equal to threshold value λ, then increase send window fast, the send window growth pattern is cwnd=cwnd+ β ₁/ cwnd; Wherein cwnd is a send window, β ₁Be regulatory factor, be used to control the send window growth rate;

If 2. bottleneck link buffer length measured value is greater than threshold value λ, then slow down the send window growth rate, the send window growth pattern is cwnd=cwncd+1/ (β ₂* cwnd).Here β ₂Be regulatory factor, be used to control the send window growth rate.

4, the transfer control method of aggregation node in the wireless sensor network according to claim 1, it is characterized in that 3. described step distinguish that congested and error code packet loss reason method is specially in the wireless environment: threshold value δ is set, when receiving 3 repeat ACK bags, if record bottleneck link buffer length L＜δ, show that packet loss is former because channel error code; As L＞δ, show that packet loss is former because network is tending towards congested.

5, the transfer control method of aggregation node in the wireless sensor network according to claim 1, it is characterized in that according to the packet loss reason the suitable threshold method of startup slowly being set during described step 3. is specially: if the former because channel error code of packet loss is provided with then that to start threshold value slowly be ssthresh=bwe * (RTT _Cur+ RTT _Min)/2 are if the former because network congestion of packet loss is provided with then that to start threshold value slowly be ssthresh=bwe * RTT _Min, ssthresh wherein is for starting threshold value slowly, and bwe is the bandwidth of current measurement, RTT _CurBe the ACK bag two-way time of current measurement, RTT _MinFor the minimum ACK that measures wraps two-way time.

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