Journal of China Universities of Posts and Telecommunications最新文献

A kind of high-power pulse driver is designed to drive semiconductor laser. The circuit consists of three parts: generator of pulse signal, power amplifier of pulse signal and storage circuit controlled by metal-Oxide-semiconductor field-effect transistor (MOSFET). According to the experimental results, this kind of high-power pulse driver well restrained the pulse spike and overshoot by proper design, better choice of components and improvement of electro magnetic compatibility (EMC). The circuit can output pulse signal with better quality, which provides qualified driving signal to laser diode. The pulse width is under 50 ns and the output ranges from 10 A to 50 A.

This paper investigates the performance of an underlay cognitive relay system where secondary users (SUs) suffer from a primary outage probability constraint and spectrum-sharing interference imposed by a primary user (PU). In particular, we consider a secondary multi-relay network operating in the selection decode-and-forward (SDF) mode and propose a best-relay selection criterion which takes into account the spectrum-sharing constraint and interference. Based on these assumptions, the closed-form expression of the outage probability of secondary transmissions is derived. We find that a floor of the outage probability occurs in high signal-to-noise ratio (SNR) regions due to the joint effect of the constraint and the interference from the PU. In addition, we propose a generalized definition of the diversity gain for such systems and show that a full diversity order is achieved. Simulation results verify our theoretical solutions.

Because of its potential applications in agriculture, environment monitoring and so on, wireless underground sensor network (WUSN) has been researched more and more extensively in recent years. The main and most important difference of WUSN to terrestrial wireless sensor network (WSN) is the channel characteristics, which determines the design methodology of it. In this paper, the propagation character of electromagnetic (EM) wave in the near surface WUSN is analyzed, as well as the path loss model of it is given. In addition, the influence of human's ankle to the channel characteristics of near surface WUSN is investigated by electromagnetic theory analysis, simulation and experiment. A novel path loss model of near surface WUSN which takes the interference of human's ankle into consideration is proposed. It is verified that the existing of human above the WUSN system may cause additional attenuation to the signal of near surface WUSN which propagates as lateral wave along the ground. Moreover, the relation of the attenuation and operating frequency is deduced, which gives a reference to extend the frequency band applied in WUSN.

In this paper, we present a new lightweight block cipher named eight-sided fortress (ESF), which is suitable for resource-constrained environments such as sensor networks and low-cost radio rrequency identification (RFID) tags. Meanwhile, we present the specification, design rationale and evaluation results in terms of the hardware implementation. For realizing both efficiency and security in embedded systems, similar to the other lightweight block ciphers, ESF is 64 bits block length and key size is 80 bits. It is inspired from existing block cipher, PRESENT and LBlock. The encryption algorithm of ESF is based on variant Feistel structure with SPN round function, used Feistel network as an overall structure with the purpose of minimizing computational resources.

Community-based question answer (CQA) makes a figure network in development of social network. Similar question retrieval is one of the most important tasks in CQA. Most of the previous works on similar question retrieval were given with the underlying assumption that answers are similar if their questions are similar, but no work was done by modeling similarity measure with the constraint of the assumption. A new method of modeling similarity measure is proposed by constraining the measure with the assumption, and employing ensemble learning to get a comprehensive measure which integrates different context features for similarity measuring, including lexical, syntactic, semantic and latent semantic. Experiments indicate that the integrated model could get a relatively high performance consistence between question set and answer set. Models with better consistency tend to get a better precision according to answers.

In this paper, a walking robot is established. The zero-moment point (ZMP) is used to stabilize the working robot. The kinematic model of the robot based on denavit-hartenberg (D-H) method is presented in this thesis. And then the dynamic model, based on Lagrange method, is built by simplifying the kinematic model of robot body. A kinematic simulation to the robotic system is achieved based on Adams. Driving torque of left ankle is calculated according to joint angle, angular velocity and angular acceleration. The validity of the dynamic model is testified by comparing with the result of simulation.

The transmission antennas of cooperative systems are spatially distributed on multiple nodes, so the received signal can be asynchronous due to propagation delays. A receiving scheme for cooperative relay networks is proposed, multiple asynchronous signals are reconstructed at the receiver by forward and backward interference cancellation, which can obtain gains of cooperative transmission diversity with obvious delay and with no requiring timing synchronization or orthogonal channelization between relays. Analysis and simulation show that the bit error rate (BER) of the proposed scheme is similar to Alamouti code, and the scheme has the diversity order of orthogonal transmission scheme accompanied by minimal BER losses. It is demonstrated that the performance can be further improved by adding an error correcting code (ECC).

In downlink coordinated multi-point (CoMP) system, full cooperation is always not applicable in real world because of its high request in the backhaul. To deal with this problem, clustering decision is made to process transmission. In this paper clustering methods based on the metric signal-to-leakage-plus-noise (SLNR) is proposed. In addition, user scheduling schemes based on SLNR is also put up to make the scheduling set as large as possible. Simulation results show that the proposed clustering methods not only reduce the data sharing among the cooperating base stations (BSs), but also improve the system throughput compared with the traditional clustering methods based on channel strength.

This article introduces the classic locating method based on the receiving signal strength in the cognitive radio and puts forward a cognitive radio-receiving signal strength (CR-RSS) localization algorithm which solves the problem of secondary users locating the primary user and succeeds in estimating the primary user's location and transmission power. Through the establishment of cognitive radio network, evaluating the number of secondary users, sampling and the environmental factors to the results in CR-RSS approach. The consequence shows that this approach can effectively locate the primary user and the technology of localization in cognitive radio can assist network optimization.

Opportunistic networks are derived from delay tolerant networks, where mobile nodes have no end-to-end connections. Nodes are represented by people, which means that opportunistic networks can be regarded as social networks. Human mobility plays an important role in affecting the performance of forwarding protocols in social networks, furthermore, the trajectory of people's movements are driven by social characteristics. However, current routing protocols rely on simple mobility models, and rarely consider social characteristics. Considering two heterogeneous network models, an social opportunistic networks routing (SONR) was proposed which brings an adapted discrete Markov chain into nodes' mobility model and calculates the transition probability between successive status. Comparison was made between Spray, Wait and Epidemic protocol. Simulation show that SONR can improve performance on delivery ratio, delivery latency and network overhead, meanwhile. SONR approaches the performance of Epidemic routing.