Much research has been done to support remote collaboration on physical tasks. However, the focus of the research has been mainly on system and interface design and their impact on collaboration. Relatively less attention has been paid to investigating how network performance can affect user experience and task performance. In this paper, we present a preliminary user study on this issue in which participants were asked to work collaboratively in pair using a remote mobile tele-assistance system we developed. In this study, five network scenarios were examined and network performance (QoS) was measured using four metrics including delay, jitter, bandwidth and packet loss. User experience (QoE) was measured using both objective and subjective metrics. The formal included time taken and number of instructions repeated for task performance while the latter included user ratings of quality of audio experience, quality of video experience and overall quality of experience. The results indicated that the packet loss rate in QoS is the biggest contributor to loss in QoE. We also discuss implications of the study and possible directions of future work.
In order to alleviate the node mobility problem which cause frequent link ruptures between source and destination nodes and data packets loss during transmission in Mobile Ad hoc Networks, we propose a new routing protocol called AD-AODV based on the famous AODV protocol. By introducing a novel metric M whose value depends on the hop number and average mobility of a given route, we improve the routing mechanism of AODV and enable AD-AODV to select the most stable route.A lot of simulations are operated based on the variation of node number and node speed to evaluate the performance of AD-AODV protocol. Simulation results compared with AODV protocol indicate our protocol's superiority in terms of packet delivery ratio therefore AD-AODV's enhancement of routing reliability is proved.
To achieve security in distributed wireless sensor networks, one of the most promising approaches is the so-called random pre-distribution of key seeds. Pair-wise secure communication channels between nodes were established or discovered by using key information that were constructed and pre-distribution to each node in distributed wireless sensor networks. Combining DNA model with the idea of multiple key pool, an extended DNA model based pair-wise key establishment scheme is proposed. The nodes select multi-DNA strands as its key ring and use the code of some oligonucleotide in some DNA strand as their actual pair-wise key. The key connectivity, security and overhead of the scheme are discussed. The analysis shows that the overhead of computation and communication of the new scheme is little and the security is greatly improved than the original DNA model scheme.
We propose a novel position-based routing protocol Anchor-based Connectivity Aware Routing (ACAR) for Vehicular Ad-hoc Networks (VANETs), which considers both buses and cars as vehicular nodes running in both clockwise and anti-clockwise directions. ACAR is a hybrid protocol, uses both the greedy forwarding approach and the carry-store-and-forward approach to ensure the connectivity of the routes. Our solution to situations, when the network is sparse and when any (source or intermediate) node left its initial position, makes this protocol better in city scenarios. We only consider Vehicleto-Vehicle (V2V) communication in which both the source and destination nodes are moving vehicles. Finally, we compare our protocol with A-STAR (one of the plausible connectivity aware routing protocol for city environment) and, the simulation results in NS-2 show that the packet delivery ratio of ACAR is better than A-STAR in all cases: either when the network is fully connected or when the network is sparse.
Error concealment at the decoder side is an economical approach to ensuring an acceptable and stable video quality in case of packet erasure or loss, and thus attracts lots of interest. Current techniques mainly employ the spatial or temporal correlation to predict the motion vectors of the missing blocks, and interpolation, extrapolation or boundary matching schemes are usually effective. However, for heavily corrupted sequences, e.g., with macroblock loss rate beyond 50%, most methods might perform less satisfactorily. Inspired by the tracking efficiency of Kalman filter, in the present work, we adopted it to predict the missing MVs, and the unpredicted ones (minority) were recovered complementarily by using the bilinear motion field interpolation (MFI) method. The experimental results on typical sequences reveal that the proposed algorithm outperforms the boundary matching algorithm and the MFI technique by up to about 4.77 dB and 3.66 dB respectively for heavily corrupted videos.
Mobility of terminals would bring changes of network topology. In dense VANET multi-hop communication with nodes of high speed, a problem how to choose a next hop relay rapidly made a significant sense. In this paper, a slot assignment for voice access named Black-burst scheme based TDMA was proposed for channel access contention. The problem of relay selection could be solved as a method of voice access control with priority. Numerical results show that in scenarios of movement with different nodes distribution, a shorter access delay and a lower cost could be obtained in MAC protocols based on Black-burst mechanism comparing with the traditional TDMA random channel access method.
This paper presents a transmitting scheme and corresponding user selection algorithms for simultaneous unicast and multicast services. On the subcarriers assigned to multicast services, BS transmits the superposition of unicast and multicast signals. Block diagonalization (BD) and power control are applied to unicast signal, to make sure interference from unicast not reduce the rate of multicast signal. We propose the optimal and a suboptimal user selection scheme to make the unicast rate as much as possible. Theoretical analysis and simulation results show that, the performance of the suboptimal scheme is close to that of the optimal approach, while the complexity is effectively decreased. Besides that, both the optimal and suboptimal schemes can get better unicast rate than random selection while the multicast rate is the same as the one before superposition.
Based on NGN present security current situation, set up the security frame of NGN. Open the characteristic of network business to NGN, put forward NGN safe demand model. This model and UML technology combine together, constructs the security mechanism of NGN in terms of different business effectively.
Push-to-Talk over Cellular (PoC) system in mobile communication network, such as TD-SCDMA, is considered to have more wide coverage and more flexibility than traditional trunk communication systems. It is ideal for group communication in many cooperative work environments. But the foremost block for wider application of PoC system is the longer session setup latency comparing to other trunk communication systems. This paper analyzes the main cause of the longer call latency and the main research activities about this. A scheme for reducing the session setup latency is provided, which emphasized on the SIP signaling compressed with an improved dictionary-based compression method (IDCM). The prototype of PoC system adopting the scheme is also described and the performance estimation is given. Simulation results show the reduction of session setup latency is achieved.
This paper presented an FPGA implementation of high- throughout adaptive equalizer for QAM receiver. The system was designed based on the architecture for adaptive decision feedback equalizer. Constant modulus algorithm was considered for the blind equalization mode which was followed by direct- decision (DD) mode. The feed forwards filter and feedback filter were designed based on FIR filter in the transpose-form which can achieve shorter critical path for hardware design. The whole design, which can achieve the channel equalization for 16-, 32- 64-, 128- and 256-QAM, was implemented under Xilinx Vertex 4 XC4VSX55 FPGA. The maximum clock frequency after routed reached to 128.6MHz. Simulations showed the good performance of this design. By FPGA implementation, the efficiency was proved.
In this paper, we provides a simple and accurate analysis by Markov chain modeling to evaluate the IEEE 802.11 DCF performance in the presence of capture effect. We extend the Bianchi's multidimensional Markov chain analytical model of IEE 802.11 DCF to characterize the behavior of DCF considering capture effect and packet retransmission limits. We compare the NS-2 simulation results with the derived analysis. Numerical results and simulations are provided to validate the accuracy of our model.
The single message ferry routing scheme works well in the small scale clustered DTNs (Delay/Disruption Tolerant Networks). However, as the increasing of the network scale, this scheme will lead to high delay. To solve this problem, a hierachical multiple ferries routing scheme (HMFRS) was proposed in this paper. In this scheme, a message ferry and a ferry access point are deployed in each DTN cluster, in which the ferry access point is utilized to orchestrate the message ferry and the global message ferry which connected the clusters. The theoretical analysis and the simulation results show that the proposed scheme can greatly reduce the average delay.
This paper proposes a novel distance matrix reconstruction (DMR) algorithm from incomplete and inaccurate distance information for nodes localization in wireless sensor networks. By using DMR algorithm, we address an improvement for self-organizing isometric embedding (SIEMAP) based localization in which DMR is used instead of the original distance matrix. The core of DMR is finding an Euclidean distance matrix to approximate the incomplete and inaccurate original distance matrix, and DMR based SIEMAP algorithm will be more robust for node localization when distance measurements are incomplete and inaccurate. Simulation results demonstrate that DMR can improve the location estimation effectively when the original distance matrices are incomplete and inaccurate. The results can be also applicable to many localization methods, such as dwMDS, SDP, Steep-SDP and so forth. In conjunction with proposed SIEMAP algorithm, we illustrate that the DMR based localization is robust and accurate for incomplete and inaccurate distance measurements.
By exchanging soft information between the detector and the channel decoder, an iterative receiver can significantly improve the performance compared to the non-iterative receiver. In this paper, a low complexity soft-input soft-output (SISO) fixed-complexity sphere decoding (FSD) algorithm is proposed for iterative MIMO receiver. The algorithm introduces a simplified parallel candidate adding (SPCA) scheme to provide more accurate soft information. Furthermore, by employing our proposed improved hybrid-enumeration method, the SISO-FSD can reduce the computational complexity substantially. Simulation results show that the algorithm can achieve a near Max-Log optimal maximum a posteriori (MAP) detection performance under flat fading Rayleigh channels. Compared to the SISO K-Best algorithm (K=50), the proposed algorithm saves about 60% computations and provides almost the same performance for detecting 4×4 64-QAM MIMO signal, making it a promising scheme for real-life hardware implementation.
IEEE 802.1x and EAP in a WLAN to the laptop as a terminal is widely used. However, with the WLAN terminal more and more miniaturized, portable, such as WIFI phone, PDA, tablet PCs, which have limited bandwidth and computing power, it is difficult to perform the complex operations of EAP authentication. This paper proposes a new EAP authentication methods based on the hash function, designs a specific certification process. Analysis result shows that the method is suitable for portable terminals, and better safety performance.
CDMA2000 is a family of 3G mobile technology standards, which use CDMA channel access, to send voice, data, and signaling data between mobile phones and cell sites. In this paper, we present some observations of a CDMA mobile network of some city by analyzing the characteristics of the data, such as login time, logout time, delay of transmission, and user attributes. The author provided a basis analysis of regular user behaviors using user attribute pattern clustering. From this observation, the time-of-day behavior gives better indication of mobile user behaviors in CDMA network.
Modulation level classification (MLC) is a process which detects the transmitter's digital modulation level from a received signal, using a priori knowledge of the modulation class and signal characteristics needed for down conversion and sampling. In this paper, we compared three different modulation classification methods: a cumulant (Cm) based classification, a goodness-of-fit (GoF) test using Kolmogorov-Smirnov (KS) statistic and a modified method using KS statistic (rcKS) to achieve low computational complexity. Simulation results show that rcKS method has the best performance.
The AAL2 of ATM switching system uses the cyclic redundancy check code(CRC) to correct one bit error of the Common Part Sub-layer payload head(CPS-PH). Heavily based on CRC principle, in this paper analyses the process of one bit error correction of the CPS-PH is explored in detail.
Aiming at the shortages of positioning technology in Wireless Sensor Networks (WSNs), a fuzzy positioning algorithm based on WSNs is proposed. Line segments connecting anchor nodes intersect and the algorithm regards intersection points as sample points which should assist with the positioning and improve positioning precision when there are fewer anchor nodes. The positional relationship of the sample point and unknown node is described using grade of membership functions of fuzzy theory, and then the sample nodes whose grade of membership are larger will be chosen to calculate the position coordinates by weighted average. The algorithm reduces the influences to a certain extent which are caused by errors of Received Signal Strength Indication (RSSI) measure. Therefore the algorithm improves the accuracy of positioning and avoids high computational complexity and the requirement of more anchor nodes. Simulation results indicate that the algorithm has better performance and practicability.
This paper presents a performance analysis of a spectrum sharing model which based on dynamic spreading spectrum approach for cognitive radio networks. This model consists of two phases: In the first, if the sensing results show that the primary user (PU) is inactive, the secondary user (SU) can transmit data based on its own benefit. In the other hand, if the PU is active, the SU can coexist with the PU and maintain its communication by adopting dynamic spreading spectrum method. Here, we analyzed performance of this model under both interference constraints for PU and quality of service (QoS) constraints for SU. We also compared the performance of this model to the opportunistic spectrum access model to show the performance superiority. Simulation results are presented to verify our analyses, and the results also show that the spectrum sharing scheme can achieve much better performance compared to the previously opportunistic spectrum access model.
