Chen Canfeng

Adaptive Copy and Spread data dissemination in vehicular ad-hoc networks

Vehicular ad-hoc networks (VANETs) are promising for more and more intelligent transportation applications, where information is disseminated over a group of vehicles. VANETs are characterized for its unstable framework, in which the isolated vehicles communicate with others only when the unexpected meetings occur. As a result, some available data dissemination schemes do not work well in VANETs. In this paper, we propose an opportunistic auto-adaptive dissemination scheme - Adaptive Copy and Spread (ACS) Algorithm - for VANETs, which makes use of the moving patterns of vehicles like direction and velocity, and dynamically adjusts the dissemination strategies. This scheme dynamically increases or decreases the number of message copies inside the broadcast area, and vehicles can intelligently decide when to start or stop broadcast a message. ACS is designed to keep the message at the effective areas boundary to inform the entering vehicles as soon as possible. The simulation results show that ACS enhance the data dissemination performance significantly with a smaller network load compared with random choice algorithm and Epidemic dissemination algorithm over a series of scenarios.

A 122Mb/s Turbo decoder using a mid-range GPU

Parallel implementations of Turbo decoding has been studied extensively. Traditionally, the number of parallel sub-decoders is limited to maintain acceptable code block error rate performance loss caused by the edge effect of code block division. In addition, the sub-decoders require synchronization to exchange information in the iterative process. In this paper, we propose loosening the synchronization between the sub-decoders to achieve higher utilization of parallel processor resources. Our method allows high degree of parallel processor utilization in decoding of a single code block providing a scalable software-based implementation. The proposed implementation is demonstrated using a graphics processing unit. We achieve 122.8Mbps decoding throughput using a medium range GPU, the Nvidia GTX480. This is, to the best of our knowledge, the fastest Turbo decoding throughput achieved with a GPU-based implementation.

Mobile Wireless Sensor Networks: Architects for Pervasive Computing

A mobile wireless sensor network owes its name to the presence of mobile sink or sensor nodes within the network. The advantages of mobile wireless sensor network over static wireless sensor network are better energy efficiency, improved coverage, enhanced target tracking and superior channel capacity. In this chapter we will present and discuss different classifications of mobile wireless sensor network as well as hierarchical multi-tiered architectures for such networks. This architecture makes basis for the future pervasive computing age. The importance of mobility in traditional wireless sensor network (WSN) is highlighted in this chapter along with the impact of mobility on different performance metrics in mobile WSN. A study of some of the possible application scenarios for pervasive computing involving mobile WSN is also presented. These application scenarios will be discussed in their implementation context. While discussing the possible applications, we will also study related technologies that appear promising to be integrated with mobile WSN in the ubiquitous computing. With an enormous growth in number of cellular subscribers, we therefore place the mobile phone as the key element in future ubiquitous wireless networks. With the powerful computing, communicating and storage capacities of these mobile devices, the network performance can benefit from the architecture in terms of scalability, energy efficiency and packet delay, etc. For mobile wireless sensor networks, there are basically two sensing modes, local sensing and remote sensing. By allowing and leveraging sink mobility and sink coordination, mobile WSN can achieve the goal of lower and balanced energy consumption with the following features:  Single-hop clustering. By allowing only single hop transmission between sensor and sink node, most previous multi hop relaying sensor nodes may become unnecessary. In fact, sensor nodes can enter sleep mode until the sink approaches. Therefore, the original energy budget for multi hop relaying can be saved.  Sink mobility and coordination. For a delay tolerant application, single mobile sink in fact equals virtually multiple static sinks at different positions. Multi-sink deployment can bring more uniform energy dissipation, therefore the possibility of energy hole will be reduced and network coverage will be improved. 1

A high throughput LDPC decoder using a mid-range GPU

A standard-throughput-approaching LDPC decoder has been implemented on a mid-range GPU in this paper. Turbo-Decoding Message-Passing algorithm is applied to achieve high throughput. Different from traditional host managed multi-streams to hide host-device transfer delay, we use kernel maintained data transfer scheme to achieve implicit data transfer between host memory and device shared memory, which eliminates an intermediate stage of global memory. Data type optimization, memory accessing optimization, and low complexity Soft-In Soft-Out algorithm are also used to improve efficiency. Through these optimization methods, the 802.11n LDPC decoder on NVIDIA GTX480 GPU, which is released in 2010 with Fermi architecture, has achieved a high throughput of 295Mb/s when decoding 512 codewords simultaneously, which is close to highest bit rate 300Mb/s with 20MHz bandwidth in 802.11n standard. Decoding 1024 and 4096 codewords achieve 330 and 365Mb/s. A 802.16e LDPC decoder is also implemented, 374Mb/s (512 codewords), 435Mb/s (1024 codewords) and 507Mb/s (4096 codewords) throughputs have been achieved.

A patrol grid protocol for mobile wireless sensor network

Nowadays more requirements for wireless sensor networks are utilized to military, science and our daily life gradually, however the sink mobility is still bottleneck problem in a number of WSN application scenarios. In some fields like environmental monitoring, the solution is an especially urgent request. In this paper we propose Patrol Grid Protocol (PGP), a sink mobility supported route protocol for environmental monitoring which builds on a previously developed routing protocol called TWO-Tier Data Dissemination (TTDD). We prove that PGP can be more suitable for urgent events and query-driven mode than TTDD. The description of mechanisms and simulation are presented firstly, then we evaluate the performance of the new protocol and analyze the overhead and delay. PGP is a more applicable protocol for environmental monitoring.

Efficient data collection in wireless sensor networks by applying network coding

Considering a wireless sensor network with optimal mobile sink track along which data are transmitted to the nodes, a fraction of nodes in the area of interest generate data packets and send them to the sink. Usually the single path routing is adopted in such scenarios which may cause unnecessary transmissions. We address the problem of how to collect these packets efficiently by using network coding technique. Network coding is a kind of innetwork computation which has many advantages over traditional routing, such as providing higher network throughput, using bandwidth efficiently and balancing the traffic. In this paper, we propose a data collection strategy by using network coding for efficient data collection in event driven WSNs and explore its performance through theoretical analysis. We present a strategy for network coding algorithm which can guarantee the successful decoding for all the encoded packets. Specifically, our numerical results show the decrease in the total number of transmissions by applying network coding than that by using the single path routing. Also numerical results indicate that the delivery packets rate is significantly improved as the increase of the link loss rate comparing network coding we adopt with single path routing

3-D ambiguity analysis method of arbitrary antenna array for direction finding

In this paper we propose an approach to 3-D ambiguity (type I ambiguity [l]) analysis of arbitrary antenna arrays. Ambiguity characterization is very important in designing antenna array for direction finding in mobile communications/indoor positioning/radar, which greatly influences practical capability of Direction of Arrival (DOA) estimation. Conventional 2-D ambiguity analysis loses most of ambiguity information in 3-D space and cannot indicate ambiguity from 3-D space out of the selected 2-D plane; Cramér-Rao bound (CRB) analysis outputs unidentified pattern when real measured data exhibits less regular behavior than ideal data, moreover it only provides variance low bound instead of exact value or upper bound. We defined and proposed the 3-D ambiguity analysis with full 3-D ambiguity information of antenna array, and shows (by real measured data) that proposed method is a plain and utility tool for ambiguity characterization suitable for practically designing arbitrary antenna arrays.

THTA: Triangle-Shaped Hierarchy Aggregation Time Allocation Algorithm for Wireless Sensor Network

Aiming at the periodical data gathering application of Wireless Sensor Network, this paper first analyzed the network traffic flow and transmission delay in typical aggregation model. Then it investigated how to properly allocate aggregation time to minimize total network traffic within certain delay bound. An optimization problem was deduced and numerical solutions for regular network are calculated. Inspired by the numerical results, this paper introduced the concept of the critical aggregation level and presented an algorithm called Triangle-shaped Hierarchy aggregation Time Allocation (THTA). In our simulation experiments, THTA can lead the network to the maximum aggregation performance and fine adaptability compared with other existing algorithms.

Dynamic Prediction of Data Validity for Mobile Databases

Optimistic replication which does not lock resources and can tolerate disconnections appears to be the natural choice for mobile computing environment. The replication approach allows updates to be performed independently at any replica, so the fundamental problem in this scheme is that data at any replica has the probability of invalidation. To resolve this problem, this paper presents a new dynamic prediction of data validity algorithm (DPDVA), which predicts the validity of data replica stored in mobile nodes by local history information. Experimental results show that DPDVA is an effective prediction algorithm to maintain database consistency. The more local information mobile nodes store, the better the prediction effects will be.