Tutorials

TU06: Advanced Wireless Networking and Cross-Layer Optimization Using Adaptive MIMO-aided Transceivers
Instructor: Lajos Hanzo, University of Southampton, United Kingdom

Wednesday 5 April 2006
9:00 - 12:30

Objectives

This research-oriented presentation is based on theWiley/IEEE Press monographs [1] - [11] and considers the joint benefits of both adaptive physical and adaptive network-layer performance enhancement techniques, with special emphasis on the latter. More specifically, conventional systems would drop a call in progress, if the communications quality falls below the target quality of service and it cannot be improved by handing over to another physical channel. By contrast, the adaptive transceivers of the near future are expected to simply ’instantaneously drop the throughput, rather than dropping the call’ by reconfiguring themselves in a more robust mode of operation. It is demonstrated that the proposed beam-forming and adaptive transmission techniques may double the expected teletraffic capacity of the system, whilst maintaining the same AVERAGE performance as their conventional fixed-mode counterparts.

Tutorial Theme and Key Topics

1. FDD VERSUS TDD AIDED NETWORKS

The network performance of a Frequency Division Duplex (FDD) and Time Division Duplex (TDD) Code Division Multiple Access (CDMA) based system is investigated using system parameters similar to those of the Universal Mobile Telecommunication System (UMTS) . The new call blocking and call dropping probabilities, the probability of low-quality access as well as the required average transmit power are quantified both with and without adaptive antenna arrays as well as when subjected to shadow fading. In the scenarios investigated the system’s user capacity is doubled with the advent of adaptive antennas. The employment of adaptive modulation techniques in conjunction with adaptive antenna arrays resulted in further significant network capacity gains. This is particularly so in the context of TDD CDMA, where the system’s capacity becomes poor without adaptive antennas and adaptive modulation owing to the high BS to BS interference inflicted as a consequence of potentially using all time-slots in both the uplink and downlink.

2. THE NETWORK-LAYER BENEFITS OF LOOSELY SYNCHRINIZED SPREADING CODES

The capacity of a UTRA-like Frquency Division Duplex (FDD) Code Division Multiple Access (CDMA) system employing Loosely Synchronized (LS) spreading codes is also discussed. Current CDMA systems are interference limited, suffering from Inter-Symbol-Interference (ISI), since the orthogonality of the spreading sequences is destroyed by the channel. They also suffer from Multiple-Access- Interference (MAI) owing to the non-zero cross- correlations of the spreading codes. LS codes exhibit a so-called Interference Free Window (IFW) , where both the autocorrelation and cross-correlation of the codes become zero. Therefore LS codes have the promise of mitigating the effects of both ISI and MAI in time dispersive channels. Hence, LS codes have the potential of increasing the capacity of CDMA networks. This contribution studies the achievable network performance by simulation and compares it to that of a UTRA-like FDD/CDMA system using Orthogonal Variable Rate Spreading Factor (OVSF) codes.

3. GENETICALLY ENHANCED PERFORMANCE OF A UTRA-LIKE TDD CDMA NETWORK

In this part of the overview a Dynamic Channel Allocation (DCA) algorithm is developed, which minimizes the amount of Multi-User Interference (MUI) experienced at the Base Stations (BSs) by employing Genetic Algorithms (GAs). A GA is utilized for finding a suboptimum, but highly beneficial Uplink (UL) or Downlink (DL) Timeslot (TS) allocation for improving the achievable performance of the third generation UTRA system’s Time Division Duplex (TDD) mode. It is demonstrated that a GA-assisted UL/DL timeslot scheduling scheme may avoid the severe BS to BS inter-cell interference potentially inflicted by the UTRA TDD CDMA air interface owing to allowing all TSs to be used both in the UL and DL.

Lajos Hanzo received his first-class Master degree in electronics in 1976, his PhD in 1983 and his Doctor of Sciences (DSc) degree in 2004. He is a Fellow of the Royal Academy of Engineering (FREng). During his career in telecommunications he has held various research and academic posts in Hungary, Germany and the UK. Since 1986 he has been with the School of ECS, University of Southampton, UK, where holds the Chair in Telecommunications. He co-authored 11 books [1]-[11] totalling 8000 pages on mobile radio communications, published in excess of 500 research papers, organised and chaired conference sessions, presented overview lectures and has been awarded a number of distinctions. Currently he heads an academic research team, working on a range of research projects in the field of wireless multimedia communications sponsored by industry, the Engineering and Physical Sciences Research Council (EPSRC) UK, the European IST Programme and the Mobile Virtual Centre of Excellence (VCE), UK. He is an enthusiastic supporter of industrial and academic liaison and he offers a range of industrial courses. Lajos is also an IEEE Distinguished Lecturer of both the Communications as well as the Vehicular Technology Society and a Fellow of both the IEE and IEEE. For further information on research in progress and associated publications please refer to http://wwwmobile. ecs.soton.ac.uk;