Ruiqin Zhao

Broadcasting with Least Redundancy in Wireless Sensor Networks

In wireless sensor networks (WSN), broadcasting could allow the nodes to share their data efficiently. Due to the limited energy supply of each sensor node, it has become a crucial issue to minimize energy consumption and maximize the network lifetime in the design of broadcast protocols. In this paper, we propose a Broadcast Algorithm with Least Redundancy (BALR) for WSN. By identifying the optimized number of induced forwarders as 2, BALR establishes a weighted sum model, taking both rebroadcast efficiency and residual energy into consideration, as a new metric to compute the self-delay of the nodes before rebroadcasting. BALR further incorporates both strategies based on distance and coverage degree which means the number of neighbors that have not yet received the broadcast packet, to optimize the rebroadcast node selections. To reveal the performance bounds, rebroadcast ratios in the ideal and worst case are theoretically analyzed, indicating that the rebroadcast ratio of BALR decreases with the increase of node density. BALR can significantly prolong the network lifetime of WSN and is scalable with respect to network size and node density, as demonstrated by simulations.

Link Scheduling Method for Underwater Acoustic Sensor Networks Based on Correlation Matrix

The unique characteristic of the underwater acoustic communication channel force development of new protocols for underwater acoustic sensor networks. Especially, the pretty slower propagation speed of acoustic signals in underwater should be taken into consideration. This paper constructs a link scheduling model on medium access control (MAC) layer for multihop underwater acoustic sensor networks. The proposed model employs correlation matrix to describe the conflicts relationship among links and uses propagation delay to generate conflict matrix for collision detection. In order to minimum the frame length, a power control strategy is introduced and aimed to reduce the effect of link interference. Then, a heuristic algorithm is presented to solve the conflict-free problem based on the model. Simulation results show that the link scheduling method and the power control strategy can effectively improve network performance with respect to throughput and end-to-end delay.

Minimum delay multipath routing based on TDMA for underwater acoustic sensor network

Multipath routing is an alternative routing technique, which uses redundant paths to deliver data from source to destination. Compared to single path routing protocols, it can address reliability, delay, and energy consumption issues. Thus, multipath routing is a potential technique to overcome the long propagation delay and adverse link condition in underwater environment. However, there are still some problems in multipath routing. For example, the multiple paths may interfere with each other and arouse large end-to-end delay difference amongst multiple paths. This paper proposes a novel multipath routing structure and a conflict-free algorithm based on TDMA scheme. The forwarding nodes are selected based on the propagation delay and location information. This special multiple routing structure not only can ensure parallel multiple transmission without collision, but also can get a small end-to-end delay difference amongst multiple paths. Simulation results show that the multipath routing scheme proposed in this paper outperforms the traditional strategy.

Joint time-frequency synchronization and channel estimation in two-way relay networks

Abstract This work investigates joint time-frequency synchronization and channel estimation in two-way relay networks (TWRN) that utilize amplify-and-forward (AF) relay strategy. A two-way transmission model for joint time-frequency synchronization and channel estimation in TWRN is provided. Due to the high dimension and complexity of the model, the maximum likelihood (ML) algorithm is over complex and a standard Markov chain Monte Carlo (MCMC) algorithm is ineffective. We instead develop a hybrid Metropolis–Hastings–Gibbs algorithm in order to facilitate joint time-frequency recovery and effective channel estimation. In particular, we present a reparameterized model to facilitate Gibbs sampling with respect to the self-interference channel. Then the second order truncated Taylor series approximation is adopted for carrier frequency offsets (CFOs) estimation. Furthermore, a heuristic way of determining update order of parameters is proposed and initial value of the Markov chain is discussed as well. To test the robustness and objectivity of our proposed algorithm, two MCMC estimators, each with its own prior distribution, are compared against each other. Numerical results are provided to verify the effectiveness and robustness of proposed algorithm in terms of both mean-square errors (MSE) and estimation bias. The bit error rate (BER) performance results are further offered for comparison.

An heuristic link scheduling model for underwater acoustic sensor networks

The significantly slower propagation speed of acoustic signals, in contrast to RF signals, make the protocol design differ from RF wireless networks. This paper presents an efficient link scheduling method applied to underwater acoustic networks based on TDMA by analyzing the four conflict model in wireless network, and puts forward a conflict description method based on correlation matrix. The proposed conflict matrix can describe the conflict relationships among links completely. It can simplify the designing of channel access controlling. The solution dealing with the conflict matrix proposed in the paper which is not only taking spatial reuse in consider, but also has a low complexity. It can find a conflict-free scheduling and the approximate minimum frame under the conflict-free scheduling in finite iteration. Simulation results show that the proposed method can get a approximate minimum frame length under different slot length. It also improves network throughput and reduces the average end to end delay performances of the networks.

Localization in underwater acoustic networks based on double rates

Localization is a major issue and a challenging task for underwater acoustic networks. The characteristics of underwater acoustic networks are fundamentally different from that of terrestrial networks. For example, it is not easy to get GPS into water and underwater acoustic networks often just have few anchors. Thus many of the localization schemes for terrestrial networks cannot be used directly in underwater acoustic networks. In this paper, we present a localization scheme based on double rates which competes node localization with only one anchor. It is a range-based localization scheme which separates data transmission into two modes by changing the symbol durations at physical layer. Based on the double rates schemes, our method completes acoustic ranging among the whole network with only one hop, which eliminates the accumulated inaccuracy caused by multi-hop ranging in localization schemes based on single rate. Simulation results show that our method has the highest positioning accuracy compared with MSL and DV-Hop.

A Double Rate Localization Algorithm with One Anchor for Multi-Hop Underwater Acoustic Networks

Localization is a basic issue for underwater acoustic networks (UANs). Currently, most localization algorithms only perform well in one-hop networks or need more anchors which are not suitable for the underwater environment. In this paper, we proposed a double rate localization algorithm with one anchor for multi-hop underwater acoustic networks (DRL). The algorithm firstly presents a double rate scheme which separates the localization procedure into two modes to increase the ranging accuracy in multi-hop UANs while maintaining the transmission rate. Then an optimal selection scheme of reference nodes was proposed to reduce the influence of references’ topology on localization performance. The proposed DRL algorithm can be used in the multi-hop UANs to increase the localization accuracy and reduce the usage of anchor nodes. The simulation and experimental results demonstrated that the proposed DRL algorithm has a better localization performance than the previous algorithms in many aspects such as accuracy and communication cost, and is more suitable to the underwater environment.

Energy-aware channel model for Underwater Acoustic Networks

Interest in Underwater Acoustic Networks (UAN) has grown rapidly with the desire to monitor the ocean, depending on the potential capability of UAN to support a large variety of applications, such as monitoring of equipment and natural events. Moreover, these applications may have requirement for saving energy at each node adaptively in the underwater power limited system. In this paper, we establish an energy-aware underwater channel model based on passive sonar equation, with some specific characteristics included, such as Source Level, Transmission Loss, Ambient-Noise Level and Detection Threshold, which have not been extensively considered in the UAN environment before. Moreover, Our proposed model is not only simple enough to be easily operated, but also useful in guiding higher layer protocol design. Finally, we implement the proposed channel model in MATLAB.

Path Diversity Improved Opportunistic Routing for Underwater Sensor Networks

The packets carried along a pre-defined route in underwater sensor networks are very vulnerble. Node mobility or intermittent channel availability easily leads to unreachable routing. Opportunistic routing has been proven to be a promising paradigm to design routing protocols for underwater sensor networks. It takes advantage of the broadcast nature of the wireless medium to combat packet losses and selects potential paths on the fly. Finding an appropriate forwarding candidate set is a key issue in opportunistic routing. Many existing solutions ignore the impact of candidates location distribution on packet forwarding. In this paper, a path diversity improved candidate selection strategy is applied in opportunistic routing to improve packet forwarding efficiency. It not only maximizes the packet forwarding advancements but also takes the candidate’s location distribution into account. Based on this strategy, we propose two effective routing protocols: position improved candidates selection (PICS) and position random candidates selection (PRCS). PICS employs two-hop neighbor information to make routing decisions. PRCS only uses one-hop neighbor information. Simulation results show that both PICS and PRCS can significantly improve network performance when compared with the previous solutions, in terms of packet delivery ratio, average energy consumption and end-to-end delay.

Underwater acoustic network node design and anechoic pool network experimentation with five nodes

In this paper, an underwater acoustic network system is presented and produced, which consists of five underwater acoustic node devices with a networking capability. The underwater acoustic network system adopts the high speed hardware architecture of DSP plus FPGA, and utilizes a Time Division Multiple Access (TDMA) mechanism when networking. The system could not only supply quick and reliable underwater acoustic communication at a physical layer, but also complete stable networking at higher layer based on TDMA. At the physical layer, a one-hop underwater acoustic communication rate of 500 bit/s at the range of 2000m is achieved. And the system could complete node localization of the network through a ranging method between neighbouring nodes. At the upper layer, a TDMA medium access control mechanism is produced in the presented underwater acoustic network system. Finally an anechoic pool experiment has proved the stability and validity of the proposed underwater acoustic network system.