CN105490755A - Underwater acoustic sensor network time synchronization method adapting to mobility - Google Patents

Abstract

The invention discloses an underwater acoustic sensor network time synchronization method adapting to mobility, and belongs to the field of time synchronization algorithms of underwater acoustic sensor networks. The method is characterized in that the method can well adapt to the inherent mobility of nodes, namely, the mobility of the nodes and the influence of clock skew are considered when relative movement speeds among the nodes are established through Doppler frequency shift, and relationships among a combined Doppler scaling factor, a node mobility Doppler scaling factor and a clock skew Doppler scaling factor are acquired in a way of building a mathematical model in order to acquire accurate relative movement speeds among the nodes. Thus, relative movement distances and transmission time delays among the nodes are obtained, and the accuracy of time synchronization among the nodes is increased.

Description

The ambulant water sound sensor network method for synchronizing time of a kind of adaptation

Technical field

The invention belongs to the Time synchronization algorithm field of water sound sensor network, it is characterized in that adapting to the intrinsic mobility of node preferably, when namely adopting the internodal relative moving speed of Doppler frequency estimation, consider the impact of node mobility and skewed clock, and obtain the relation between associating Doppler zoom factor and node mobility Doppler zoom factor and skewed clock Doppler zoom factor by founding mathematical models, to obtain internodal accurate relative moving speed, thus obtain internodal relative movement distance and propagation delay, improve the precision of time synchronization between nodes.

Background technology

Water sound sensor network is the underwater monitoring network system be made up of the sensor node with acoustic communication and computing capability, it is deployed in the underwater environments such as ocean, realizing the contamination monitoring of underwater environment, aquatic organism sample collection, natural calamity is prevented, and the aspects such as assisting navigation possess wide application prospect.Time synchronized is as the important foundation of water sound sensor network and support technology, most important to the design and devdlop of water sound sensor network.

In water sound sensor network, the basis of Time synchronization algorithm is internodal synchronizing process, and to calculate and compensate internodal propagation delay be of paramount importance link in synchronizing process.Current existing Time synchronization algorithm have ignored the intrinsic mobility of water sound sensor network node (as shown in Figure 1), symmetry (the i.e. τ of its hypothesis propagation delay ₁[i]=τ ₂[i]), use the half of round-trip delay to represent propagation delay (as shown in Figure 2).This hypothesis keeps geo-stationary scene at node, not only simple but also effectively, but in the water sound sensor network of reality, the symmetry of propagation delay can destroy by the intrinsic mobility of node.

Due to water sound sensor network sensor node between distant and propagation delay is larger, consider to reply time of message, MAC layer is waited for and turn-on time again, physical layer transceiver change-over time, node receives the processing time, (the i.e. T such as internodal message interaction time ₄[i]-t ₂[i], as shown in Figure 2), the relative distance alterable several meters at this moment between section interior nodes even tens meters, cause result of calculation to occur several milliseconds even error of tens milliseconds, it must be compensated.

Internodal relative movement will produce Doppler frequency shift, and Doppler frequency shift measures acquisition by physical layer, then can adopt the relative moving speed that Doppler frequency shift comes between computing node, and then calculate relative movement distance and propagation delay, improve the precision of time synchronized.

Summary of the invention

Object of the present invention:

In water sound sensor network, internodal relative movement can produce Doppler frequency shift, and it can measure acquisition by physical layer.Adopt the relative moving speed between Doppler frequency shift computing node, and then calculate relative movement distance and propagation delay, effectively can improve the precision of time synchronized.

The present invention, by analyzing the relation between Doppler frequency shift, internodal relative moving speed and skewed clock, optimizes the method for calculating propagation delay to improve the precision of time synchronized.

Technical scheme of the present invention:

Internodal time synchronized obtains by calculating propagation delay, as long as can obtain the change of propagated between nodes time delay, just can realize accurate time synchronization.The change of propagated between nodes time delay has come from reference to the relative movement of message interaction process interior joint certain distance, this distance calculates by relative moving speed, relative moving speed is then estimated by measuring Doppler frequency shift, as long as therefore can obtain Doppler frequency shift accurately can calculate propagation delay, and then it is synchronous to realize precise time.In fact the Doppler frequency shift of receiving node place estimation is relative movement and the coefficient result of skewed clock between node, in order to accurately obtain internodal relative moving speed, need extract due to the Doppler frequency shift (as shown in Figure 3) caused mobile between node.

The present invention proposes internodal Doppler frequency shift is jointly caused by internodal relative movement and skewed clock, adopt during the internodal relative moving speed of Doppler frequency estimation and need consider the design philosophy that clock jitter affects, and provide and a kind ofly obtain relation between associating Doppler effect zoom factor and node mobility Doppler zoom factor and skewed clock Doppler zoom factor by founding mathematical models, and then estimate the scheme of internodal relative moving speed.

Beneficial effect of the present invention:

1) skewed clock and the internodal Doppler frequency shift of internodal relative movement joint effect.The present invention proposes Doppler frequency shift is design philosophy by internodal relative movement and skewed clock joint effect, rejects skewed clock impact, can accurately calculate relative moving speed between node, and then effectively improve the precision of time synchronized.

2) founding mathematical models distinguishes internodal relative movement and skewed clock to the impact of Doppler frequency shift.The present invention obtains the relation between associating Doppler effect zoom factor and node mobility Doppler zoom factor and skewed clock Doppler zoom factor by founding mathematical models, and then estimate internodal relative moving speed, effectively can improve the precision of time synchronized.

Accompanying drawing explanation

Relative movement orbit schematic diagram between Fig. 1 node

Fig. 2 time data gathers schematic diagram

The internodal relative movement of Fig. 3 and clock deflection influence time synchronized flow chart

In Fig. 1,101 is general node running orbit, and 102 is reference node running orbit, and 103 is with reference to message.

In Fig. 2,201 is general node, and 202 is reference node, and 203 is time shaft.

Embodiment

Provide below and a kind ofly obtain relation between associating Doppler effect zoom factor and node mobility Doppler zoom factor and skewed clock Doppler zoom factor by founding mathematical models, and then estimate the scheme of internodal relative moving speed.

The present invention is not limited only to this Mathematical Modeling scheme; every when the time synchronized research carrying out water sound sensor network; utilize design philosophy of the present invention; namely skewed clock is considered on the impact adopting the internodal relative moving speed of Doppler frequency estimation, all within protection scope of the present invention.

Embodiment is described below:

Definition v is the relative moving speed of node A to Node B, and in Underwater Acoustic Environment, between node, Signal transmissions is generally multipath transmisstion, supposes for m paths, and the Doppler's zoom factor caused due to internodal relative movement is,

a _m＝v/c(1-1)

Wherein, c is the propagation velocity of sound.

Consider that the signal received at receiving node B place is that the signal waveform expression formula that then can obtain receiving node B place is by the signal sum arrived along many physical pathways,

$y_{\mathrm{AB}}\left(t\right)={\mathrm{\Σ}}_{p=1}^{N_p}{A}_p{x}_{\mathrm{AB}}((1+{\mathrm{\α}}_m)t-{\mathrm{\τ}}_p)---(1-2)$

Wherein N _prepresent the quantity of physical pathway, A _prepresent signal amplitude, τ _prepresent the time delay in path.

Suppose sample frequency f _sfixing, then input waveform can be turned to formula (1-3) by discrete,

$x_{\mathrm{AB}}\left[n\right]=x_{\mathrm{AB}}\left(t\right){|}_{\mathrm{\τ}=n/f_s}---(1-3)$

For from node A to the reference message at Node B place, suppose that skewed clock is θ, then the sample frequency at acceptance point B place is θ f _s, waveform can discrete representation be,

$y_{\mathrm{AB}}\left[n\right]=y_{\mathrm{AB}}\left(t\right){|}_{t=n/\mathrm{\θ}{f}_s}={\mathrm{\Σ}}_{p=1}^{N_p}{A}_p{x}_{\mathrm{AB}}(\frac{1+a_m}{\mathrm{\θ}}n-{\mathrm{\τ}}_p)---(1-4)$

Order then α _m=(1+ α _aB) θ-1.

The associating Doppler zoom factor that receiving node A place measures is internodal mobility and the coefficient result of skewed clock, for from Node B to the reference message of node A, at the waveform at node A place is

$y_{\mathrm{AB}}\left[n\right]=y_{\mathrm{BA}}\left(t\right){|}_{t=\mathrm{n\θ}{/f}_s}={\mathrm{\Σ}}_{p=1}^{N_p}{A}_p{x}_{\mathrm{BA}}((1+{\mathrm{\α}}_m)\mathrm{\θn}-{\mathrm{\τ}}_p)---(1-5)$

Make (1+ α _m) θ=1+ α _bA, then α _m=(1+ α _bA)/θ-1.

Can calculate internodal relative moving speed from formula (1-4) and formula (1-5) is,

$v={\mathrm{\α}}_{m}c=\left\{\begin{array}{cc}((1+{\mathrm{\α}}_{\mathrm{AB}})\mathrm{\θ}-1)c,& A\→B\\ ((1+{\mathrm{\α}}_{\mathrm{BA}})/\mathrm{\θ}-1)c,& B\→A\end{array}\right.---(1-6)$

Internodal relative movement distance and propagation delay can be calculated according to the relative moving speed that above-mentioned Doppler frequency shift provided by the invention is estimated, and then realize internodal exact time synchronization.

Claims (2)

1. one kind adapts to ambulant water sound sensor network method for synchronizing time, it is characterized in that: based between Doppler frequency estimation node during relative moving speed, distinguish the impact of node relative mobility and skewed clock, to obtain internodal accurate translational speed, and then obtain internodal relative movement distance and propagation delay, realize internodal exact time synchronization.

2. the ambulant water sound sensor network method for synchronizing time of adaptation as claimed in claim 1, the present invention obtains the relation between associating Doppler zoom factor and individual node mobility Doppler's zoom factor and skewed clock Doppler zoom factor by founding mathematical models, to distinguish node relative mobility and skewed clock, and then obtain internodal accurate translational speed, internodal relative movement distance and propagation time, realize internodal exact time synchronization.