Dhammika Jayalath

Microstrip to Parallel Strip Balun as Spiral Antenna Feed

This paper presents the design and implementation of a microstrip to parallel strip balun which are frequently used as balanced antennas feed. This wideband balun transition is composed of a parallel strip which is connected to the spiral antenna and a microstrip line where the width of the ground plane is gradually reduced to eventually resemble the parallel strip. The taper accomplishes the mode and impedance transformation. This balun has significantly improved bandwidth characteristics. The entire circuit was fabricated on RT Duriod 5880 substrate. The circuit designs were simulated and optimised using CST Microwave Studio and the simulated results are compared with the measured results. The back-to-back microstrip to parallel strip has a return loss of better than 10 dB over a wide bandwidth from 1.75 to 15 GHz. The performance of the proposed balun was validated with the spiral antenna. The measured results were compared with the simulated results and it shows that the antenna operates well in wideband frequency range from 2.5 to 15 GHz.

Cross layer optimization of VANET routing with Multi-objective decision making

Vehicular Ad-hoc Networks (VANET) have different characteristics compared to other mobile ad-hoc networks. The dynamic nature of the vehicles which act as routers and clients are connected with unreliable radio links and Routing becomes a complex problem. First we propose CO-GPSR (Cooperative GPSR), an extension of the traditional GPSR (Greedy Perimeter Stateless Routing) which uses relay nodes which exploit radio path diversity in a vehicular network to increase routing performance. Next we formulate a Multi-objective decision making problem to select optimum packet relaying nodes to increase the routing performance further. We use cross layer information for the optimization process. We evaluate the routing performance more comprehensively using realistic vehicular traces and a Nakagami fading propagation model optimized for highway scenarios in VANETs. Our results show that when Multi-objective decision making is used for cross layer optimization of routing a 70% performance increment can be obtained for low vehicle densities on average, which is a two fold increase compared to the single criteria maximization approach.

Efficient route update and maintenance processes for multipath routing in large-scale industrial wireless sensor networks

Communication reliability is one of the major concerns in wireless sensor networks (WSNs). Multipath routing is an effective way to improve communication reliability in WSNs. However, most of existing multipath routing protocols for sensor networks are reactive and require dynamic route discovery. If there are many sensor nodes from a source to a destination, the route discovery process will create a long end-to-end transmission delay, which causes difficulties in some time-critical applications. To overcome this difficulty, efficient route update and maintenance processes are proposed in this paper. They limit the amount of routing overhead with a two-tier routing architecture, and use combined piggyback and trigger updates instead of periodic update, which is the main source of unnecessary routing overhead. Simulations are carried out to demonstrate the effectiveness of the proposed processes in reducing routing overhead over existing popular routing protocols.

Empirical vehicle-to-vehicle pathloss modeling in highway, suburban and urban environments at 5.8 GHz

In this paper, we present a pathloss characterization for vehicle-to-vehicle (V2V) communications based on empirical data collected from extensive measurement campaign performed under line-of-sight (LOS), non-line-of-sight (NLOS) and varying traffic densities. The experiment was conducted in three different V2V propagation environments: highway, suburban and urban at 5.8GHz. We developed pathloss models for each of the three different V2V environments considered. Based on a log-distance power law model, the values for the pathloss exponent and the standard deviation of shadowing were reported. The average pathloss exponent ranges from 1.77 for highway, 1.68 for the urban to 1.53 for the suburban environment. The reported results can contribute to vehicular network (VANET) simulators and can be used by system designers to develop, evaluate and validate new protocols and system designs under realistic propagation conditions.

Deterministic diffraction loss modelling for novel broadband communication in rural environments

This paper presents a deterministic modelling approach to predict diffraction loss for an innovative Multi-User-Single-Antenna (MUSA) MIMO technology, proposed for rural Australian environments. In order to calculate diffraction loss, six receivers have been considered around an access point in a selected rural environment. Generated terrain profiles for six receivers are presented in this paper. Simulation results using classical diffraction models and diffraction theory are also presented by accounting the rural Australian terrain data. Results show that in an area of 900 m by 900 m surrounding the receivers, path loss due to diffraction can range between 5 dB and 35 dB. Diffraction loss maps can contribute to determine the optimal location for receivers of MUSA-MIMO systems in rural areas.

Array of subarrays using adaptive element patterns

This paper explores the use of subarrays as array elements. Benefits of such a concept include improved gain in any direction without significantly increasing the overall size of the array and enhanced pattern control. The architecture for an array of subarrays will be discussed via a systems approach. Individual system designs are explored in further details and proof of principle is illustrated through a manufactured examples.

Distributed orthogonal space-time block codes with adaptive diversity gain

In this paper we present a novel distributed coding protocol for multi-user cooperative networks. The proposed distributed coding protocol exploits the existing orthogonal space-time block codes to achieve higher diversity gain by repeating the code across time and space (available relay nodes). The achievable diversity gain depends on the number of relay nodes that can fully decode the signal from the source. These relay nodes then form space-time codes to cooperatively relay to the destination using number of time slots. However, the improved diversity gain is archived at the expense of the transmission rate. The design principles of the proposed space-time distributed code and the issues related to transmission rate and diversity trade off is discussed in detail. We show that the proposed distributed space-time coding protocol out performs existing distributed codes with a variable transmission rate.

Spectral-efficient resource allocation for mixed services in OFDMA-based 5G heterogeneous networks: Spectral-efficient resource allocation for mixed services in OFDMA-based 5G heterogeneous networks

One of the principal thrusts of proposed 5G networks is the provisioning of mixed services or heterogeneous Quality-of-Service (QoS) which includes delay-sensitive (DS) and delay tolerant (DT) services. Guaranteeing the fairness in data rate among end-users in such a complex network brings many challenges. In this paper, we consider heterogeneous QoS and fairness in the problem of spectrally efficient resource allocation in OFDMA based 5G heterogeneous networks (HetNets) with femtocells. We aim to maximize the total capacity of all femtocells while satisfying the following: fairness constraint for DT users, minimum throughput for DS users, cross-tier interference threshold of femtocell HetNets and exclusive property of OFDMA subchannels. The formulated problem is combinatorial and non-convex due to the integer constraint of OFDMA subchannels and non-affine equality constraint of the fairness. To make the problem more tractable, we propose to maximise the overall throughput over instantaneous data rate instead of power and subchannel. By doing this, the fairness equality becomes affine on instantaneous data rate. The feasible domain of the problem is redefined with the constraints of subchannels readily included. The transformed problem takes the standard convex form which is much simpler and is easily solved using the Lagrangian dual method. The proposed algorithm has a low complexity and provides a higher spectral efficiency compared to existing algorithms.

Low Complexity Throughput Optimisation in OFDMA HetNets with Heterogeneous Services

In this work, we study a practical resource allocation (RA) scheme that considers heterogeneous services in OFDMA femtocell networks. Heterogeneous services include guarantees of the minimum data-rate for delay-sensitive (DS) users and the fairness for delay-tolerant (DT) users. The RA problem is formulated to maximize the total throughput of all femtocells while satisfying the constraints of cross-tier interference and heterogeneous services. To tackle this issue, we solve the problem in three steps. First, we relax the fairness constraint of DT users by introducing a new relaxation coefficient. Then, the relaxed problem is addressed by using the Lagrangian dual method. Finally, we develop an iterative algorithm for joint power and resource block (RB) allocation. The proposed scheme outperforms existing methods in terms of the complexity and the total achievable throughput.

Dual-Level Sensing Based Multiple Access Protocol for Cognitive Radio Networks

In this paper, we improve throughput performance of a cognitive radio network through a proposed dual-level sensing strategy. Throughput performance of secondary users cannot be enhanced while providing higher priority to protect primary users from secondary user interference. Therefore, we propose a novel multiple access scheme based on dual-level sensing strategy by which both the interference protection and the throughput enhancement can be accomplished. We propose a dual-level sensing regime within the short sensing period to explore higher transmission opportunities and then utilize the sensing outcome to reduce the collision during the multiple access phase. Performance evaluation shows that the proposed scheme improves the throughput of the secondary users and guarantees the primary user protection during multiple access.