A Millimeter-Wave Quasi-Optical Circuit for Compact Triple-Band Receiving System

A novel receiver optical system designed for Korean VLBI Network (KVN) has been used for conducting simultaneous millimeter-wave very long baseline interferometry (VLBI) observations at frequencies of 22, 43, 86, and 129 GHz. This multi-frequency band receiver system has been effective in compensation of atmospheric phase fluctuation by unique phase referencing technique in mm-VLBI observations. However, because the original optics system incorporated individual cryogenic receivers in separate cryostats, a rather bulky optical bench of size about 2600 mm x 2300 mm x 60 mm was required. To circumvent difficulties in installation and beam alignment, an integrated quasi-optical circuit incorporating a more compact triple-band receiver in single cryostat is proposed in this paper. The recommended frequency bands of the improved triple-band receiver are K(18–26 GHz) band, Q(35–50 GHz) band, and W(85–115 GHz) band. A frequency-independent quasi-optical circuit for triple band is adopted to obtain constant aperture efficiency as a function of the observed frequencies. The simulation results show that total aperture efficiency of each recommended frequency band is maintained almost constant within 1%. We present the design details of the compact wideband quasi-optical circuit and the triple-band receiver optimized for simultaneous multi-frequency observations.     

A computationally efficient selected mapping technique for reducing PAPR of OFDM

In orthogonal frequency division multiplexing (OFDM) system, high value of peak-to-average power ratio (PAPR) is an operational problem that may cause non-linear distortion resulting in high bit error rate. Selected mapping (SLM) is a well known technique that shows good PAPR reduction capability but inflicts added computational overhead. In this paper, using Riemann sequence based SLM method, we applied reverse searching technique to find out low PAPR yielding phase sequences with significant reduction in computational complexity. Additionally, we explored side-information free transmission that achieves higher throughput but sacrifices PAPR reduction. Finally, to overcome this loss in PAPR reduction, we proposed application of Square-rooting companding technique over the output OFDM transmitted signal. Simulation results show that the proposed method is able to compensate the sacrifice in PAPR and achieved PAPR reduction of 8.9 dB with very low computational overhead.     

DFC++ Processing Framework Concept

Development of modern Software Defined Radio (SDR) based communication systems can be accelerated significantly by the use of processing frameworks. The evolution of SDR and the involved departure from digital representations of classical radio architecture towards more abstract software systems raises new requirements of increased flexibility and versatility. The proposed Data Flow Control for C++ (DFC++) processing framework concept addresses those requirements by employing modern programming techniques and flow control mechanisms to allow for variable data rates, dynamic paths, and flexible component designs. Another important trend is the integration of various embedded platforms in the software radio domain. The rapidly increasing performance and efficiency of embedded processors enables the deployment of SDR systems in more space and power constrained environments. Therefore covering a heterogeneous hardware selection becomes increasingly important for processing frameworks. By relying exclusively on C++ and minimizing external dependencies, DFC++ is specifically aiming for excellent portability and adaptability to support a wide range of current and future software radio projects while maintaining high performance and ease of use. This paper introduces the key aspects of the DFC++ concept and implementation with focus on the reference pointer based data transport mechanisms responsible for the propagation of user data between different processing components.     

Congestion detection technique for multipath routing and load balancing in WSN

In WSN, nodes collect the information from the surrounding environment and transferring to base station. Multiple data transmission in a WSN causes the nodes near the base station to get congested. Here we propose to develop a congestion avoidance and mitigation technique. For that, we select routes based on the distance between sender and receiver, relative success rate (RSR) value of node and buffer occupancy of a node. Based on these three parameters, we define a utility function to be applied to each neighbor of a transmitter node. Hence the transmitter node chooses the highest U-valued node as its next hop node among its neighbors in packet forwarding. Thus we avoid congestion by choosing non-congested nodes as its next hop node and then we mitigate congestion based on RSR values.     

Energy-efficient stable multipath routing in MANET

In MANET, node’s battery energy and stability of the links are often affecting the communication activities in the network. These two factors are one of the main reasons which are responsible for the loss of data packets and occurrence of congestion issue that networks are facing today. In order to overcome these issues, we propose an approach known as efficient and stable multipath routing in MANETs with congestion awareness. This approach is an extension work to our previous work where bandwidth and delay are considered during the routing. Here, in this approach, network estimates the residual energy and stability of the links in the network. While estimating the residual energy, it also considers the receiving energy and transmitting energy of the node. Then, stability of the link LET is estimated; this LET is obtained by using motion parameters (i.e. velocity, direction of the nodes). Based on these parameters, the network selects the path to transmit the data packets between the nodes.     

Modeling and performance evaluation of the IEEE 802.15.4e LLDN mechanism designed for industrial applications in WSNs

The IEEE 802.15.4 standard has been introduced for low latency and low energy consumption in wireless sensor networks. To better support the requirements of industrial applications, where the use of this standard is limited, the low latency deterministic network (LLDN) mechanism of the IEEE 802.15.4e amendment has been proposed. In this paper, we develop a three dimensional Markov chain model for the IEEE 802.15.4e LLDN mechanism. Then, we estimate the stationary probability distribution of this chain in order to derive theoretical expressions of some performance metrics, as the reliability, energy consumption, throughput, delay and jitter. After that, we conduct a comparative study between the IEEE 802.15.4e LLDN and the IEEE 802.15.4 slotted carrier sense multiple access with collision avoidance (CSMA/CA). Numerical results show that the deterministic behavior of the LLDN mechanism significantly reduces the collision probability providing best performances in terms of reliability, energy consumption, throughput and delay compared to the IEEE 802.15.4 slotted CSMA/CA. Finally, the accuracy of our theoretical analysis is validated by Monte Carlo simulations.     

Cooperation-enabled energy efficient base station management for dense small cell networks

Dense small cell networks are deployed for future wireless communication to meet the ever-increasing mobile traffic demand. However, network densification will significantly increase the energy budget and lead to energy inefficiency due to the constant operation of network hardware. In this paper, we consider cooperation-enabled dynamic base station (BS) management for downlink dense small cell networks. By introducing two traffic-aware sleep modes, i.e., deep sleep mode and opportunistic sleep mode which are operating in different time and energy consumption scales, the network hardwares are turned to be the resources that can be occupied and released dynamically. Small cell BSs (SBSs) with zero or low load are completely switched off and reside in deep sleep mode during a predefined time interval. At each time slot, SBS dynamically turn some antennas and associated physical components into opportunistic sleep mode according to the short term traffic distribution, and the users are jointly served by the remaining antennas via cooperative transmission. The corresponding sleep mode decision making are presented respectively to find the optimal number of SBS and antennas that should be switched off. Numerical results are then presented to illustrate the superior performance in terms of energy efficiency gain. In summary, the proposed cooperation-aided sleep strategies for dense small cell networks take both traffic features and optimal cooperative transmission into account, and can achieve great energy saving while maintaining required quality of service.     

A stable energy efficient clustering protocol for wireless sensor networks

Sensor networks comprise of sensor nodes with limited battery power that are deployed at different geographical locations to monitor physical events. Information gathering is a typical but an important operation in many applications of wireless sensor networks (WSNs). It is necessary to operate the sensor network for longer period of time in an energy efficient manner for gathering information. One of the popular WSN protocol, named low energy adaptive clustering hierarchy (LEACH) and its variants, aim to prolong the network lifetime using energy efficient clustering approach. These protocols increase the network lifetime at the expense of reduced stability period (the time span before the first node dies). The reduction in stability period is because of the high energy variance of nodes. Stability period is an essential aspect to preserve coverage properties of the network. Higher is the stability period, more reliable is the network. Higher energy variance of nodes leads to load unbalancing among nodes and therefore lowers the stability period. Hence, it is perpetually attractive to design clustering algorithms that provides higher stability, lower energy variance and are energy efficient. In this paper to overcome the shortcomings of existing clustering protocols, a protocol named stable energy efficient clustering protocol is proposed. It balances the load among nodes using energy-aware heuristics and hence ensures higher stability period. The results demonstrate that the proposed protocol significantly outperforms LEACH and its variants in terms of energy variance and stability period.     

SR3: secure resilient reputation-based routing

In this paper, we propose SR3 (which means secure resilient reputation-based routing), a secure and resilient algorithm for convergecast routing in wireless sensor networks. SR3 uses lightweight cryptographic primitives to achieve data confidentiality and unforgeability. Security of SR3 has been proven formally using two verification tools: CryptoVerif and Scyther. We made simulations to show the resiliency of SR3 against various scenarios, where we mixed selective forwarding, blackhole, wormhole, and Sybil attacks. We compared our solution to several routing algorithms of the literature. Our results show that the resiliency accomplished by SR3 is drastically better than the one achieved by those protocols, especially when the network is sparse. Moreover, unlike previous solutions, SR3 self-adapts after compromised nodes suddenly change their behavior.     

Certificateless Signcryption in the Standard Model

Signcryption can realize encryption and signature simultaneously with lower computational costs and communicational overheads than those of the traditional sign-then-encrypt approach. Certificateless cryptosystem solves the key escrow problem in the identity-based cryptosystem and simplifies the public key management in the traditional public key cryptosystem. There have been some certificateless signcryption schemes proposed in the standard model up to now, but all of them are just proposed in a weaker Type I security model, which is weaker than the original security model of Barbosa and Farshim, who proposed the first certificateless signcryption scheme. In this paper, we propose a certificateless signcryption scheme in the standard model by using bilinear pairings, which is Type I secure in the original security model of Barbosa and Farshim and can resist the malicious-but-passive key generation center Type II attack. The proposed scheme is proved confidential assuming the modified decisional bilinear Diffie–Hellman (M-DBDH) problem is hard, and unforgeable assuming the square computational Diffie–Hellman (Squ-CDH) problem is hard. At last, we evaluate its efficiency which shows it is of high efficiency.