Research Report - Communications
The Communications group is engaged in research topics that generally span the hardware areas of communications engineering. Accordingly, most of the focus is on microwave, wireless and photonic engineering (see §G.2.6) but at the system level, research is now being influenced by a strong combination of these hardware technologies with techniques from the field of signal processing. Much of the research of the group is therefore involved with the development of novel communications hardware incorporating these two disciplines. What follows is a sampling of research that illustrates these trends.
In the wireless area the groups’ emphasis is on antennas such as antennas for mobile base stations, handsets, vehicular and other specialised applications. Stringent telecommunications requirements and 3G mobile standards now dictate that base station antenna arrays should have a certain amount of built in intelligence to adapt to various dynamic scenarios. The so-called ‘smart antenna’ concept borrows heavily from the signal processing areas where estimation theory and beam forming processing are closely linked to CDMA processing. The main benefit accruing from this approach is that the cellular system capacity is substantially increased with fewer base stations.
A second instance involving multidisciplinary research is where the feeding system (which forms the beams of the antenna) is optoelectronically controlled. This arrangement results in a very light weight compact feed system that avoids the electromagnetic coupling problems that normally occur in regular microwave feed networks. Furthermore, wideband arrayed operation can be achieved with true time delay using fibre and optoelectronic links. This avoids problems of conventional phase shifters that are essentially narrow band in operation. The challenge is now to develop circuits that carry out optical to microwave and vice versa much more efficiently than is possible at present.
Another instance that involves the combination of signal processing algorithms and electromagnetics is in the area of radar target recognition by passive interrogation. In this research a very short (sub-nanosecond) pulse is incident on a target and the transient back scatter is measured. Once the signature signal is acquired, signal processing techniques are used to determine the aspect-independent parameters that help identify the target from a library of signatures. Current research is focussing on obtaining better library signatures in the time domain directly (rather than the frequency domain) and examining how to better store the salient features of the signature that are generally aspect dependent.
In the photonics area research is concerned with the design and modelling of novel semiconductor laser diode structures, more specifically the Vertical-Cavity Surface-Emitting Laser (VCSEL), including their applications to 2D optical signal processing. These devices are of particular importance to optical high speed access networks, 10-gigabit Local Area Networks (LANs) and optical interconnects. A project is underway to design VCSEL (single devices and arrays) for operation at 850 nm. They will be fabricated using MOCVD facilities at ANU.
At a more fundamental level, work is being carried out on the modelling of optical properties of semiconductor materials that are used for optoelectronic device manufacturing. The major task of this project is accurate and comprehensive modelling of semiconductor materials for optoelectronic devices: semiconductor lasers, photodiodes and modulators for applications in communication systems. The composition changes in group III-V and group II-VI semiconductor ternary and quaternary alloys allow for engineering of material properties in order to produce semiconductors with the desired optical and electrical characteristics. Accurate models for the optical properties of semiconductors are needed for optoelectronic device design purposes and also for real-time monitoring and control during the growth of these materials. Currently, there are two advanced methods that allow engineering of optoelectronic materials, namely Molecular Beam Epitaxy (MBE) and Metal-Organic Chemical Vapour-Deposition (MOCVD), both requiring growth monitoring. In this project comprehensive models have been developed that can be readily used for this purpose.
Lastly, the area of interconnects at the optical level is being considered in a project that examines optical interconnects using optoelectronic arrays. The advantage of optical interconnects investigated in this project is that they will allow higher operational speed (GBps), better Bit-Error-Rate (BER), and reduced power consumption compared to the electrical interconnects in current computer systems. The outcome of this project is to develop design oriented models for optical interconnects using Vertical-Cavity Surface-Emitting Laser (VCSEL) arrays, microlenses and photodetector arrays.
Associated Staff
A/Prof Marek Bialkowski
Dr John Homer
A/Prof Jaga Indulska
A/Prof Marian Majewski
Dr Aleksandar Rakic
A/Prof Nicholas Shuley