Presenting a new method for joint positioning and synchronization in underwater wireless sensor networks

Master's thesis

In the field of information technology engineering, computer networks

Abstract

Location and synchronization are key elements in many underwater communication applications that, despite being highly dependent, usually operate separately. But since the synchronization services are the prerequisite of the positioning algorithms and the information about the location of the sensors is used to estimate the propagation delay, the positioning and synchronization can be done together. One of the advantages of this method is the significant saving in energy consumption, which is caused by reducing the number of message exchanges.

In this thesis, a new sequential method including five phases of determining the initial position, gradualizing the movement of the sensor, estimating the deviation of the clock and timing bias, compensating the effect of layering and positioning along with repetition refinement, is presented to perform simultaneous synchronization and positioning in underwater wireless sensor networks. In this method, in addition to considering the movement of sensors, the non-movement of underwater sound waves in a straight path and the change in the propagation speed of these waves at different depths are considered. The proposed method in this thesis has been simulated with the material software and the results have been compared with a suitable standard method and also the Kramer-Rao lower bound. The results show that the presented method has an efficiency close to the lower limit of Kramer-Rao and performs better than the standard method. It should be noted that the proposed method applies more computational load to the network than the previous methods and is suitable for applications where obtaining accurate information is more important than energy consumption.

Key words: underwater wireless sensor networks, positioning, synchronization.

Chapter 1: General

1-1-

With the ever-increasing expansion of smart tools With the miniaturization and convergence of wireless communications with small devices, it is possible to create low-cost networks in different dimensions, networks that can collect environmental information for humans, networks that are quickly established without infrastructure and can organize themselves and do not need external energy. The most important of these networks are wireless sensor networks, and every day new applications and uses in the field of military and civilian affairs are presented and used for this type of networks.

Underwater wireless sensor networks are a type of sensor networks that are placed in the underwater environment and communicate with each other by sound waves. Underwater wireless sensor networks are used for purposes such as water bottom data collection, water pollution monitoring, coastal environment monitoring, navigation and environmental monitoring military applications[1]. Since in underwater wireless sensor networks, water is the transmission medium, it has its own challenges and problems that affect the design of the network, among these challenges can be the change of sound speed according to the depth, temperature and salinity of the water, constant movement of sensors, propagation delay. called long and multi-path [1]. Therefore, the protocols and algorithms of ground sensor network layers are unsuitable for underwater sensor networks. So far, there are many protocols and algorithms, especially in the field of routing and in the field of media access control, including Slotted FAMA, UWAN-MAC and so on. It has been proposed [2] [3] [4], in all of which the problem of locating and synchronizing sensors is of particular importance, for example, time division multiple access (TDMA) [2] is one of the things commonly used in media access protocols (MAC) [3], which requires accurate synchronization between sensors. As another example of the importance of synchronization and positioning, it can be pointed out that a large number of routing algorithms depend on the location information of sensors [5] and [6].

Although synchronization and positioning services are interdependent, they have usually been studied independently, and this is because positioning has been studied from the point of view of radio networks and signal processing [7] and synchronization has been studied from the point of view of protocol design [8]. In underwater wireless sensor networks, positioning is mostly done through time of reception (TOA) [4] and time of difference of reception (TDOA) [5] which are dependent on synchronization services and in fact these services are a prerequisite.In underwater wireless sensor networks, positioning is mostly done through time of reception (TOA) [4] and time of difference of reception (TDOA) [5], which are dependent on synchronization services, and in fact, these services are a prerequisite for positioning algorithms. On the other hand, the information related to the location of the sensors, as it is used to estimate the propagation delay [9], helps a lot to synchronize the sensors. According to these communications, positioning and synchronization can be done together, which has two very important advantages:

In a joint strategy, fewer message exchanges are required, and we will have a significant saving in energy consumption, which is one of the most important things in underwater sensor networks.

A joint solution can help increase accuracy[6] in both services. Synchronization, which is a prerequisite for most protocols and algorithms and is one of the basic requirements in underwater wireless sensor networks, requires that these two issues be addressed, but since these two services are interdependent, it is of particular importance to provide a solution that combines these two services, taking into account the specific challenges of the underwater environment. Ocean and sea monitoring, searching for submarine mines, detecting harmful chemical and biological substances, autonomous submarine defense systems, gathering environmental data to guide ships, etc. All these applications need to know the location of sensor nodes, but due to the mobile nature of submarine nodes, existing positioning techniques cannot be used for terrestrial sensor networks. Therefore, there is a need for techniques that can develop techniques for locating terrestrial sensor networks for underwater sensor networks.

Synchronization is also one of the main requirements for services provided by distributed networks, a large number of synchronization protocols have been proposed for wireless sensor networks, but none of them can be used directly for underwater networks. Consider sensors as well. These challenges make the accuracy of the synchronization procedure more critical for submarine wireless sensor networks, so synchronization solutions are needed that are specifically designed for submarine wireless networks in order to meet these requirements.

Considering the issues raised above and the need to consider them in submarine wireless sensor networks and considering the underwater environment, which has its own challenges, the purpose of this thesis is to study the aspects various features and challenges of the underwater environment and underwater wireless sensor networks and finally, presenting a method that performs the location and synchronization of underwater sensors together and at the same time takes into account the limitations in the underwater environment.

To show the effectiveness of the presented method, the simulator will be used and the presented technique will be compared with the techniques that have been presented before.

1-3- Thesis design implementation methods and techniques

In this thesis, firstly, the topics related to underwater wireless sensor networks will be presented and the protocols presented in it will be collected. Then, positioning and synchronization techniques in sensor networks will be studied and investigated, and taking into account the challenges in the underwater environment, the most important of which are the mobility of nodes and the long propagation delay caused by voice communication, a method is presented that performs the synchronization of nodes in addition to positioning.

The proposed method is that in the first stage, a sequential procedure includes five phases of primary positioning using the TOA technique, gradually [7] the movement of sensors, estimation Timing bias [8] and deviation [9], layering effect compensation [10] and positioning along with repetition refinement are used. The purpose of the first four phases is to obtain the propagation delay, and then using the least squares technique in the fifth phase, the location of the sensor is estimated, and finally, the position error variance calculation is used in different iterations so that the error variance reaches an acceptable value and the results of positioning are reliable.