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In Vehicular Ad Hoc Networks (VANETs), TDMA-based MAC protocol has received extensive attention because of its ability to overcome the unbounded access delay and low reliability of 802.11p in safety-related message broadcasting. However, the performance of existing TDMA-based MAC protocols for VANETs is still limited by the congestion of the control channel. To solve this problem, based on VeMAC, we propose a multichannel TDMA-based protocol with auxiliary reservation on a service channel, called VeMAC-R. In VeMAC-R, the node attempting to access the control channel makes a reservation on a specific service channel after its selection of target time slot, then the result of its reservation is determined cooperatively by surrounding nodes. A successful reservation ensures that the access node has ownership of the time slot, while a failed one makes the access node actively abandon to avoid interference. In this way, collisions in channel access process of VeMAC has been greatly reduced when the node density is high, thus higher access efficiency and packet delivery ratio can also be achieved. The performance gain of the proposed VeMAC-R over VeMAC has been verified by extensive simulations. It is shown that, compared with VeMAC, VeMAC-R can reduce the access collision rate by up to 95%, and increase the packet delivery ratio by up to 50.9%.

LoRa is a well-known Low-Power Wide-Area Network (LPWAN) specification that often uses a star topology to directly connect IoT devices to the gateway, which sends data to the network server. In practical deployment, determination of the number of gateways and their locations is the key problem in LoRa network planning. In this paper, we model LoRa network planning as a constrained clustering problem and propose an improved ISODATA algorithm to solve it. Simulation results show that, the packet reception rate and the average throughput can be improved by 23.30% and 23.51% compared with the basic ISODATA algorithm.

For typical monitoring and control applications in industrial wireless sensor network (IWSN), multiple sensor nodes periodically sample analog signals and send the digitalized data to the control center for remote estimation and further control. When the channel capacity is limited, the resource should be scheduled to minimize the time-average Mean Square Error (MSE) of the estimated signal. In this paper, we first formulate it as an MSE-minimized optimal scheduling problem with capacity constraint. Then we propose an optimized slot allocation strategy based on Lyapunov Optimization, which minimizes the drift-plus-penalty function considering the variance of the estimated signal and the Age of Information (AoI) from sensor nodes. Numerical results show that the proposed time slot allocation method can effectively reduce MSE compared to simple sequential allocation strategy.

With the amazing development of mobile internet, the traditional client/server architecture is facing problems such as centralization and scalability. Therefore, many researchers have been focusing on applying P2P networks to dynamic mobile systems. However, mobile nodes tend to join/leave the network frequently, which makes the P2P system unstable and inefficient. To solve this problem, this paper proposes a reliable and efficient semantic discovery model for mobile P2P networks. It is consisted of two layers, with the cluster administrators in the upper layer and data nodes in the lower layer. The data nodes of each cluster provide the storage of files with similar semantics. The heartbeat and recovery mechanism inside each cluster contributes to reducing the impact of churn and preventing data loss. The simulation results show that under heavy level of churn, the proposed mechanism can achieve better performance than other implementations of Kademlia in terms of lookup success rate, average lookup hops and average lookup delay.

Since local sensing system is inherently limited, it is a trend to combine Cooperative Vehicle Infrastructure System (CVIS) and autonomous driving technologies to address the limitations of the vehicle-centric perception. However, problems such as high vehicle cost and perception limitations still exist. In this paper, from the perspective of distributed cooperative processing, a scalable 5G multi-access edge computing (MEC) driven vehicle infrastructure cooperative system is proposed. Based on the edge offload capability of 5G MEC, this system supports mapping sensor observations into a semantic description of the vehicle's environment. Through interactive perception fusion, it provides environment awareness of high-precision maps for autonomous driving. The experiment confirms that the cooperative sensing network can achieve 33 fps and improve the detection precision by around 10% as opposed to the typical detection method. In addition, compared with single viewpoint perception, the accuracy of the fusion scheme is further improved. In particular, over the 5G telecommunication network, the cooperative system can be more scalable to connect distributed sensors and is expected to lead to efficient autonomous driving.

Online fountain code with Unequal Error Protection (UEP) has been proposed to provide better protection for the More Important Symbols (MISs) than that of the Less Important Symbols (LISs). However, the greater priority for MISs is accomplished substantially through choosing MISs with higher probability than that of LISs in encoding. Compared with normal online fountain code, this requires more code symbols to recover all symbols, which leads to high overhead. To reduce the overhead without affecting UEP performance, we propose a novel UEP online fountain codes scheme with sequential window strategy to provide best protection for LISs after decoding MISs in the completion phase. We have theoretically analyzed the upper bound on the overhead of the proposed UEP scheme and evaluated the performance by simulation. Both results show that the proposed scheme has lower overhead than the UEP online fountain codes scheme in [1].

This paper proposes a novel three-phase rectifier which combines the benefits of diode bridge and PWM rectifier with high efficiency and low THD, making it suitable for high power DC fast charging applications. It targets at achieving high efficiency and control simplicity compared to conventional PWM type rectifier. The operation principle, current compensation method at voltage zero-crossing point and power loss analysis are presented and analyzed. Besides, simulations were performed in Matlab/Simulink and a 60kW prototype using IGBT modules and fast recovery diode bridge rectifier was built and tested. The experiment results manifest the merits of proposed three-phase rectifier with 99.5% peak efficiency and 9.2% THD.

In this paper a novel phase-shift autotransformer is proposed to reduce the required kVA capacity in multi-pulse rectifier applications with utility interface. The structure and operation principle of proposed autotransformer are presented and analyzed in detail. Design criteria of turn ratio, phase-shift angle and equivalent capacity for the proposed autotransformer is illustrated. It can be shown that the proposed method can significantly lower the kVA rating of transformer to 9.38% of output power. Simulations in Matlab/Simulink and experimental results of a 40kW prototype further validate the proposed concept.

Industrial Wireless Sensor Networks (IWSNs) are mainly used for critical monitoring and control applications in industrial automation systems. The applications require realtime data delivery within strict delay constraints. Exceeding the required delay bound for emergency traffic could result in economic losses or even safety incidents. In this paper, we propose a Priority-enhanced slot Allocation Medium Access Control protocol (PriAlloc-MAC), which can guarantee the transmission of different traffic categories of IWSNs in given time constraints. In this protocol, the nodes with emergency traffic are allowed to preempt slots to reduce the channel access delay. Multiple nodes with emergency traffic access the channel without conflicts according to their access sequence numbers (ASNs). In addition, the protocol utilizes a short time slot design and allocates a different number of time slots to each node according to the length of the data packet to be transmitted to improve channel utilization. In this paper, the performance of PriAlloc-MAC is evaluated and compared with WirelessHART. Results show that PriAlloc-MAC is significantly better than WirelessHART in terms of traffic delay and channel utilization.

Despite the substantial progress of communication with Shannon theory in recent years, there are still many development opportunities in the transmission process. In this paper, we focus on the convergence of communication and computing to reduce transfer bandwidth, which transfers feature instead of information. Specifically, we propose a framework based on the Generative Adversarial Networks (GANs) for the first time to transfer feature. The simulation test and result analysis show that the joint process of communication and the computing relied on knowledge architecture opens up new possibilities for improving communication capability and surpass the Shannon limit under certain circumstances.

In Aeronautical Ad Hoc Network (AANET), attacks are often diverse, and a lack of preventive measures may cause serious losses. Therefore, compared with traditional MANET, AANET has higher security requirements. In this paper, we propose a trust-based partially distributed key management scheme to consider both capability and integrity trust of network. Capability trust reflects the link state of the routing path and the metric is used to choose reliable intermediate nodes for transmission. The integrity trust distinguishes compromised nodes from well-behaving nodes. The key management scheme only issues certificates to the well-behaving nodes to verify their legitimacy. We perform simulations and compare the proposed scheme with a composite trust-based public key management scheme (CTPKM). The simulation results demonstrate the performance advantages of our scheme in terms of overhead, packet delivery ratio and evaluation accuracy.

The broadcast scheme is a basic and important data dissemination mechanism in FANET. In this paper, we propose an efficient neighbor quality based mMultil- Ppoint Rrelay (MPR) broadcast scheme based on local neighbor status. The local neighbor status includes two aspects, i.e., the physical link status and the congestion status. The physical link status is indicated by the expected successful packet delivery ratio and link expiration time calculated from the Received Signal Strength Indication (RSSI). The congestion status is determined by the queue length of each neighboring nodes. Then an efficient MPR set can be selected from one-hop neighbors by local neighbor status. Each node uses its MPR set to rebroadcast messages. We use RSSI to calculate the packet successful expectation and link expiration time, and MAC layer queue length to indicate how busy the node is. Simulation result shows that our method performs better in terms of end-to-end delay and packet delivery rate than probability methods and other deterministic methods.

In the IEEE 802.11e MAC protocol, the Enhanced Distributed Channel Access (EDCA) was issued to support the quality of service (QoS) for the different categories of traffic. However, the performance will deteriorate rapidly when the network is overloaded, and the QoS required by real-time services cannot be guaranteed. In this paper, we first derive a Markov chain model to analyze the performance of the EDCA at different transmission distances. Then, we propose a dynamic access threshold-based MAC protocol that supports working at different transmission distances, called DAT-EDCA, with the goal of improving access performance when the network is overloaded. The ns3 simulation results show that the DAT-EDCA can significantly improve throughput and reduce access delay when the network is overloaded, while QoS is also guaranteed. The protocol can be seamlessly integrable with the EDCA and works without APs which has guiding significance for the design of the Ad Hoc network MAC protocol.

In this paper, we firstly establish the model of inductive power transfer (IPT) through metal barriers by using the electromagnetic model. Then we theoretically analyze the operating frequency range of IPT through metal barriers, which includes the optimal operating frequency. After that, the theoretical results are proved by simulation in MAXWELL and SIMPLORER.

In this paper, a new hierarchical protocol has been proposed for the emerging wireless powered sensor network (WPSN) in which a centralized hybrid sink node (HSN) firstly supplies the sensor nodes (SN) with stable power wirelessly, and then it aggregates packets of sensed data through multiple hops for energy saving. In WPSN, the performance of packet aggregation will be dramatically influenced by severe Doubly Near-Far Effect, thus some SNs located far from HSN require much more energy to send packets but only can harvest little energy. So in our model, from the perspective of energy saving, the network is proposed to be divided into several layers. In order to obtain the exact border of each layer, the energy broadcasted by HSN and the radius of each layer are optimized. Numerical results are provided to demonstrate the proposed solutions. Our proposed protocol outperforms the typical protocols of WSN and the star network topology in the same condition.

In this paper, we study the model design for realizing simultaneous wireless information and power transmission (SWIPT) in multi-user universal filtered multi-carrier (UFMC) downlink system, which can transfer energy as well as information at the same time. Different from orthogonal frequency division multiplexing (OFDM) which filters the whole band, UFMC filters a serial of subcarriers and does not need cyclic prefix (CP), thus it can enhance the spectrum efficiency. So combining UFMC and SWIPT technology can improve information rate as well as harvested energy. To achieve the rate-energy region, we jointly optimize the power allocation strategy as well as the subcarrier allocation scheme in a multiuser UFMC downlink system by Lagrange duality method. At the receiver, the power splitting (PS) method is used to coordinate the energy harvesting (EH) with information decoding (ID) process. The simulation results show that UFMC-based SWIPT system outperforms OFDM-based SWIPT system under the same channel condition.

In the next generation network, Low Earth Orbit (LEO) satellite networks are indispensable due to global seamless coverage and lower orbit altitude to maintain low- latency communication. However, the time-variant topologies of satellite networks bring great challenges to network management and robust routing algorithms design. Furthermore, non-uniform distribution of users will cause load unbalance among intersatellite links (ISL). In this paper, we embrace the idea of software-defined networking (SDN) to divide the satellite network into control and data plane. The satellites as switches only forward the data so that the on-board processing capacity is minimized. To realize flexible centralized management of the satellite network, we design a master controller and several slave controllers around the earth. Based on this, we propose a software defined routing algorithm (SDRA) which can obtain the optimal routing path by centralized routing strategy. With collecting congestion status of the satellites in real time, the controllers can bypass the congested ISLs when calculating routing paths. Compared with other routing algorithms, the proposed SDRA reduces the queueing delay by a nearly half, achieves a better traffic distribution and has better performance in terms of end-to- end delay, packet dropping probability and network throughput.

Recently, 802.11ah with restricted access window for collision attenuation has been proposed for Internet of Things (IoT) applications. Random grouping of nodes in different access window is utilized to reduce the hidden node collision probability. However, when the coverage area of the sink node is large, the occurrence probability of hidden node problem is still high and severely impacts the system energy efficiency. Hence, in this paper, we propose a Signal Strength Assistant (SSA) grouping scheme to further alleviate this problem. In the proposed SSA grouping, several Reference Nodes (RN) with known locations are installed in the application scenario evenly. RNs sequentially transmit beacon signals, while the normal nodes monitor the signal strength from different RNs and join the group identified by the RN with the strongest average signal strength. We formulate the analytical model of the hidden node collision probability in SSA and analyze the optimal number of RN nodes to satisfy specific hidden node collision probability requirement. Furthermore, the performance of SSA is evaluated through extensive simulation. It is shown that mathematical and simulation results of SSA match well and the proposed SSA grouping can significantly reduce the hidden node collision probability in 802.11ah.

In order to solve the severe issues of current TCP/IP Internet architecture, Named Data Networking(NDN) recently attracts lots of researchers, deemed to be one of the most futuristic Internet paradigms among numerous Information-Centric Networking(ICN) proposals. Although the forwarding strategy is the key feature of NDN, it is still at a preliminary stage. Current forwarding strategies either base on the flooding strategy trying to reduce the side effect of Interest flooding or base on the route-driven strategy paying attention to decrease the extra cost in maintaining the routing information. They are both deficient because of the storm issues or too much extra overhead. In this paper, we present the feasibility of using reinforcement learning algorithm such as Q-Learning in NDN. By modifying Q-Learning algorithm to solve the inherent issues, we design and implement IQ-Learning(Interest Q-Learning) strategy and DQ-Learning(Data Q-Learning) strategy, which learn from the past experience and make the best forwarding choice. The simulation results on NDNSim show that our forwarding strategies achieve higher Interest satisfaction ratio, shorter Interest satisfaction delay and are more sensitive to the changes of network than Flooding strategy and the state-of-the-art BestRoute strategy.

Coded caching in a broadcast link proposed by Maddah-Ali and Niesen can significantly reduce peak-hour traffic by exploiting coded multicasting opportunities. In this paper, we develop a testbed to validate the performance of decentralized coded caching for video transmission in a real wireless environment. Our testbed is built upon USRP (hardware platform) and GNU Radio (software development tool) and contains one server and three clients. The system operates in two phases, a cache placement phase and a content delivery phase. In the cache placement phase, the server selects at random some packets of each video file to transmit and cache in each client subject to the cache size limit. In the content delivery phase, each client requests a distinct video file and the sever delivers the uncached packets of each requested file using coded multicasting. We propose and implement a novel packet structure so that multicast transmission is realized at the physical layer. Experimental results of the actual delivery time and traffic load at the content delivery phase are generated. It indicates that coded caching indeed outperforms uncoded caching. The performance of coded caching compared to uncoded caching becomes better as the normalized cache size increases.

Real-time computing system attracts more and more attention in both academic researches and industrial applications. One of the real-time computing systems, Apache Storm, because of its characteristics of stream processing and high fault tolerance, is widely used for machine learning and distributed remote process call (RPC), etc. However, the existing approaches to decompose topology for Storm cannot ensure an optimized performance. In this paper, we propose an adaptive topology decomposition algorithm for Storm where topology decomposition based on cluster status and components of topology can be performed at run time. We have evaluated the processing performance and the load balancing of the algorithm. The evaluation results indicate that the proposed algorithm has better performances on task processing and load-balancing than the existing algorithms.

Video streaming over networks has grown rapidly in recent years. Increasing focus has gradually turned from Quality of Service (QoS) awareness to user Quality of Experience (QoE) awareness. In this paper, we propose a unified QoE prediction framework for HEVC encoded video streaming. Firstly, the impact of network impairment on QoE is modelled by packet loss rate. Secondly, features of HEVC encoding process are analyzed and the most relevant one is selected to formulate the impact of HEVC encoder. Thirdly, the impact of video content is incorporated by analyzing the average number of bits for one coding unit (CU). Finally, the impacts of network impairment, HEVC encoder and video content are taken into account as multiplicative factors to develop a QoE metric. Experiments has been done for typical video sequences in terms of Pearson correlation coefficient, Spearman correlation coefficient and outlier ratio. Results show that the proposed QoE framework not only provides good correlation (93.4%) with subjective ratings, but also outperforms the existing results.

Recent studies have preliminarily investigated and proven the feasibility and effectiveness of applying Content Centric Networking (CCN) principles to Mobile Ad-hoc Networks (MANETs) for content-oriented wireless communications in infrastructure-less mobile environments. However, existing designs may not achieve the full potential of CCN-MANETs. In this paper, we develop a content-centric communication system, named CC-OffGrid, for efficient content delivery (over possibly long distances) in infrastructure-less mobile environments, by deploying a CCN layer directly on top of the media access control (MAC) and physical (PHY) layers. In CC-OffGrid, each user is equipped with a mobile installing a designed APP and an integrated chip with Bluetooth4.0, MSP430 and Lora'™ module. We propose a MAC frame structure to achieve unicast, broadcast as well as multi-hop transmissions. We also design an interface protocol for the communication between the APP and the MAC layer. In addition, to effectively alleviate the broadcast storm of Interest Packets, we propose two optimization-based next-hop broadcasting node selection algorithms for Interest Packet broadcasting, based on one-hop and two-hop neighbor information, respectively, obtained using global positioning system (GPS). By adding a hop counter in Interest Packets and a data dissemination limit (DDL) counter in Data Packets, we can obtain node speed-based DDL and use it for alleviating the broadcast storm of Data Packets in mobile environments. We also propose an efficient caching algorithm for data caching by effectively exploiting content popularity information. Finally, we evaluate the performance of CC-OffGrid in ns-3 and test CC-OffGrid on hardware testbeds.

In this paper, by first analyzing the circuit model of series-parallel compensated inductive power transfer (IPT) system, the relation among voltage gain, transfer efficiency, operation frequency and load resistance is obtained. According to the analysis, a novel design of series-parallel compensated IPT system realizing optimized transfer efficiency and voltage gain regardless of load resistance is then proposed. Simulation and experiment verification are carried out with various load resistances. An almost load-independent voltage gain and efficiency up to 96.8% are achieved when the air gap between coupled coils is 17.91mm.

Space-based Automatic Identification System (AIS) uses Gaussian minimum shift keying modulation (GMSK) as the modulation scheme. Thus, Viterbi Algorithm (VA) is commonly implemented considering the tradeoff between performance and complexity. For the further improvement of the performance of Viterbi decoding, we propose a Soft-Output Viterbi Algorithm for AIS receiver (SOVA-AIS) in this paper. The proposed SOVA-AIS introduces soft values to quantify the error probability of demodulated bits and use them to update the survivor path in VA to get more precise estimation of the signal phase. Simulation results show that, compared with VA, SOVA-AIS can provide 0.5–1.5dB gain in the case with only one AIS signal and 1–3dB gain in the case with two collided AIS signals.

Detection probability is one of the most important criteria in the satellite-based automatic identification system. It represents how many vessels can be detected in the monitoring area of the system. However, existing research often neglects practical factors in S-AIS (satellite-based AIS) and cannot assess the performance of a practical system. In this paper, we propose a much detailed collision model by considering both the effects of SINR (Signal to Interference plus Noise Ratio) caused by antenna patterns and the demodulation performance. Through this model, we can construct much more accurate and reasonable detection probability calculation method. Simulation results show that the detection probability from the proposed practical model is much larger than that from the legacy model.

Video streaming over networks has grown rapidly in recent years. Increasing focus has gradually turned from Quality of Service (QoS) awareness to user Quality of Experience (QoE) awareness. In this paper, we propose a subjective QoE model based HEVC encoder adaptation scheme for multi-user video streaming. Firstly, the impact of HEVC encoder on video streams is investigated with different configurations to generate an encoder parameter model. Secondly, considering loss-prone channels, the effect of network impairment factor together with HEVC encoder is taken into account to derive a subjective QoE prediction model. Thirdly, an encoder parameter adaptation scheme is modeled as an optimization problem based on the subjective QoE model and encoder parameter model, aiming at maximizing user satisfaction with constraint bandwidth. To validate the performance of our proposed scheme, a set of simulations are carried out. Compared with fixed encoder parameter method, our proposal achieves maximal end user's MOS and supports the weighted encoder adaptation according to the user priority.

Because of the wide field of view (FOV) to monitor vessel movements, satellite-based automatic identification system (S-AIS) has been promoted in recent years. However, synchronization is a tough work in S-AIS receiver because of the large Doppler shift and serious signal collision resulting from simultaneous transmission in the FOV of a satellite. In this paper, we propose a pipelined synchronization approach with good performance and low complexity. It consists of three parts, i.e., packet detection, windowing and timing recovery, and frequency and timing offset estimation, which can be implemented in feedforward structure with low complexity. Simulation results show that the proposed synchronization approach has significant performance gain compared with existing algorithms and provides an acceptable estimation range to cope with large Doppler shift and message collision.

As the technology scales into deep sub-micron regime, leakage power has become comparable to dynamic power, playing an important role in total power consumption of modern processors. Power gating is a well-known technique to reduce leakage power by switching off the power supply of idle logic blocks. This paper proposes a novel Double-Control Power Gating (DCPG) which can lower the IR drop and enable more power savings. We applied the proposed technique to the embedded ARM® Cortex™-A9 MPCore Quad-core processor in 28 nm technology. Experimental results show that DCPG achieves 99.8% leakage power reduction when the CPU is powered off.

Broadband communication is demanded to satisfy a much wider variety of multimedia services. Among the multi-carrier schemes proposed in recent years, Orthogonal Frequency Division Multiplexing Access (OFDMA) and Single-carrier Frequency Division Multiple Access (SC-FDMA) are the most appealing candidates for broadband systems. However, traditional sampling scheme with a single high-rate Analog Digital Converters (ADC) are no longer applicable due to the limited sampling speed and extreme large-scale Fast Fourier Transform (FFT). Hence, we propose a parallel sampling scheme with multiple interleaved low-speed ADCs for multi-carrier system. Nevertheless, system performance is sensitive to synchronization precision, as well as the local radio frequency oscillators. Therefore, we investigate the interference caused by timing offset jitter, residual carrier frequency offset and sampling clock jitter in the proposed receiver. Simulation results show that SC-FDMA based system achieve better interference suppression performance over OFDMA based system.

Time synchronization is important for many distributed applications in Underwater Acoustic Networks (UANs) with large propagation delay, such as precise scheduling, target tracking and energy conservation. In this paper, we prove that the accuracy of time skew estimation increases as the number of overheard packet exchange from other neighboring nodes increases, and propose a light-weighted synchronization algorithm for multi-hop UANS, named as Improved Multi-hop time Synchronization for Underwater Acoustic Networks(IMSUAN). IMSUAN consists of three parts. The first one is to establish a time synchronization tree with the reference node as the root, and assign each node a tree level as low as possible. The second one is to synchronize with the parent node by dedicated three-time handshake and overhear exchange packets from parent and neighboring nodes. The third is to filter the inaccurate time-stamps of the overheard synchronization packets. In the paper, we establish a simulation platform in OPNET to evaluate the performance of IMSUAN. Simulation results show that the performance of extended Tri-message, MSUAN and IMSUAN are the same when no overhearing exists. However, when overhearing is possible in a random topology, the performance of IMSUAN can be 60% better than extended Tri-Message and 40% better than MSUAN.

Due to the harsh Quality of Service (QoS) requirements of video streaming, it is a great challenge to provide multimedia service over wireless networks. In this paper, we consider video transmission in IEEE 802.11e networks, and propose a Load Adaptive Dynamic Mapping (LADM) scheme to improve the video transmission quality. In LADM, the enqueue rate of different kinds of packets and the dequeue rate of the queues are used as detailed indication of traffic load. Then the video packets are dynamically mapped into appropriate access categories according to both the significance of the video data and the network traffic load. To further improve the video transmission performance, the active packet discarding method is adopted to protect more important packets in case of heavy traffic load. The simulation results show that the LADM scheme improves the Peak Signal to Noise Ratio (PSNR) of the received video.

In this paper, we propose an Iterative Collision Recovery (ICR) method to significantly alleviate the hidden terminal problem in OFDM based Wireless Local Area Networks (WLAN). We prove that when hidden terminal exists, more than half of the overall collisions are repeated because of the retransmission and binary exponential backoff mechanisms in IEEE 802.11. ICR is designed to recover the repeatedly collided packets by iterative cancellation. ICR first reconstructs the collided packets and gets an interference suppressed estimation of the transmitted signal. Then the estimation is iteratively updated by Successive Interference Cancellation (SIC) technique to fully decode the whole packets. Mathematical analysis of a network with two hidden nodes shows that the system throughput can be improved by 80% when ICR is utilized. Simulation results illustrate that the Bit Error Rate (BER) of ICR is much lower than that of Zigzag, and ICR is more suitable for OFDM based WLAN system.

In this paper, we propose a Differential Overlap Decoding (DOD) algorithm to solve the hidden-terminal problems in OFDM based WLAN systems. DOD exploits the retransmission and random-jitter features of WLAN to decode the collided packets as a whole. DOD provides with new methods and views to jointly separate and decode collided packets in OFDM based system. In DOD, we formulate IFFT/FFT, channel influence and packet collision as linear processes. Thus we can express the received collided packets as linear equations, and simplify this problem into solving linear equations. We evaluate the performance of DOD through simulation, and results show that when DOD is applied, hidden-terminal problems can be viewed as a 3-5 dB BER performance degradation rather than network contention.

Wireless signal RSSI (Received Signal Strength Indication) is widely used in indoor localization. However, due to severe multipath effect in indoor environment, RSSI measured by the user equipment varies in a large range. Inaccurate RSSI measurement yields large localization error and decreases the performance of indoor localization and navigation. Through extensive tests, we prove that the variance of RSSI in indoor environment does not keep the same all the time, while varies with the mean of RSSI. In this paper, we analyze the relationship between the mean value and variance of RSSI, and propose a novel Weighted Distance Fingerprint (WDF) algorithm, which assigns different weights to different RSSI measurements based on its variance. We apply the proposed WDF algorithm in our indoor localization testbed, and evaluation result shows that WDF reach a 0.8m to 2m improvement on the average localization error.

Time synchronization plays an important role in UANs, which need fine-grained coordination among nodes. Precise time synchronization is also needed for a variety of other coordinate tasks in UANs such as data fusion, TDMA scheduling, localization, power-saving and so on. Recently, time synchronization protocol for point-to-point with high propagation delay has been proposed, while time synchronization for multi-hop UANs is still an open issue. In this paper, we propose a multi-hop time synchronization scheme for Underwater Acoustic Networks (MSUAN). MSUAN includes three stages. In the first stage, we assign each node a level by establishing a path to the reference node. During the second phase, nodes realize synchronization by receiving synchronization packets both from it's parent node and neighboring nodes. The third stage re-synchronizes nodes because the clock may drift away without synchronization for long time. Mathematical analysis of MSUAN's synchronization error shows that the more time-stamps we get, the more accurate skew we will get. At the end, we use OPNET to simulate MSUAN, and the simulation result under pyramid topology shows that even the hop accumulates to 8, for MSUAN, the average offset error is maintained at about 58us and the average skew error is below 2ppm.

Most of the widely used Automatic Incident Detection (AID) methods are based on the basic principle of the California Algorithms which detects incidents by comparing the difference of macro traffic parameters between upstream and downstream. However, these AID algorithms cannot perform well under low-volume condition due to many incidents under low-volume don't cause significant changes on traffic conditions. To improve the incident detection under low-volume condition, the paper proposes a new detection method based on Automatic Vehicle Identification (AVI) technique by using high-resolution cameras. First, the paper introduces the basic theory and characteristics of Low-volume Incidents (LVIs) detection by using high-resolution cameras, analyzes the time-space relationship of vehicles passing different detection sections, designs a elimination method for the false plate identification, and proposes a new AID method for LVIs. Second, the paper studies how the main influence factors, including the detection devices density, accuracy rate of AVI and flow level impact the new AID model's performance. Finally, simulation cases are studied to examine the performance of the new AID model. The case study shows that the new AID model can produce satisfied detection results even with very low detection devices density.

This paper addresses the transmissions of a multi-antenna Base Station (BS), when communicating simultaneously with groups of radios in a multi-hop network of single-antenna radios. Each group is supposed to receive a distinct data stream, such that all members of the group receive the same packet at the same time. The intention is that each group will perform cooperative transmission in the next time slot or slots. We focus on just the first hop, in which the BS chooses the group members and beamforms to them, so that their individual signal to interference and noise ratios all exceed a minimum threshold. The problem we address, therefore, is a combination of spatial multiplexing and multicasting. Our approach does zero forcing on selected nodes and then checks that an adequate number of nodes in each group have at least the minimum signal-to-noise-and-interference ratio (SINR). Using simulation, we compare our approach to others and we consider the effects of errors in transmit-side channel state information.

There are lots of devices with different power in the network. This phenomenon may be nothing in the wired network, but in the wireless network that would be a serious problem. Most of the traditional routing protocols assume that the link is symmetric. We found that heterogeneity network performance will be severely affected. We give new routing protocol that employs adaptive technique to the MANET routing protocols. In this routing protocol, nodes can sense the power to determine whether to forward packets or not. By avoiding dependence on periodic beaconing, this method requires low overhead and delay. Performance results show that technique improve performance in heterogeneous environments.