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The Fourth International Conference on Access Networks ACCESS 2013 July 21 - 26, 2013 - Nice, France |
| Tutorials |
T1. Methods for System Performance Improvement of Shadowed Fading Channels
Prof. Dr. Dragana Krstić, University of Nis, Serbia
T2. EARS: Easy Approach to Requirements Syntax
John Terzakis, Intel Corporation, USA
DETAILED DESCRIPTION
T1. Methods for System Performance Improvement of Shadowed Fading Channels
Prof. Dr. Dragana Krstić, University of Nis, Serbia
The wireless channels are simultaneously affected by short-term fading (fast fading) and long-term fading (shadowing). Fast fading is caused by multiple signal propagation paths. Due to the shadowing from various objects in the propagation paths, in addition to multipath fading, the quality of the received signal is also affected by slow variations of the mean signal level. In wireless communication systems, various techniques for reducing fading effect and influence of shadow effect are used: diversity reception, dynamic channel allocation and power control. Upgrading transmission reliability and increasing channel capacity without increasing transmission power and bandwidth is the main goal of diversity techniques.
Well-known way to mitigate the effects of fading and shadowing is diversity reception. The wireless communication system following microdiversity to mitigate the effects of fast fading and macrodiversity processing to reduce shadowing effects will be studied. Fast signal variations are described by several distributions such as Rayleigh, Rice, Nakagami-m, α-μ, Weibull and Hoyt. Diversity reception, based on using multiple antennas at the receiver is a very efficient method used for improving system’s quality of service. Multiple received copies of signal could be combined on various ways. Usually L-branch maximal-ratio combining (MRC) or selection combining (SC) is implemented at the micro level (single base station) and selection combining (SC) with two base stations (dual diversity) is implemented at the macro level. Complex mathematical calculations are used to obtain telecommunication system performances.
The level crossing rate (LCR) and the average fading duration (AFD) are second-order statistical quantities, which complement the static probabilistic description of the fading signal (the first-order statistics), and have found several applications in the modelling and design of practical systems and designing of wireless communication systems.
Also, it will be shown that system performances are better if sampling is done in two time instants. First, the expressions for probability density function (PDF) and joint probability density function (PDF) of combiner output signal at two time instants in the presence of different distributed fading is determinated. Then, these expressions are used for calculation of the system performance. It will be highlighted the improvement that is achieved by sampling in two time instants by using these formulae in some complex systems consisting of switch and stay (SSC) and MRC or SC combiners.
T2. EARS: Easy Approach to Requirements Syntax
John Terzakis, Intel Corporation, USA
Properly wording functional requirements is essential for eliminating ambiguity and minimizing misinterpretation amongst stakeholders. One technique to improve readability and understanding is using a consistent syntax. However, functional requirements can take many different forms. Some are ubiquitous--they state a fundamental property of the software and always occur. Others are not--they depend on an event, error condition, state or option (i.e., a trigger) to occur. Correctly identifying these categories and then selecting the appropriate syntax to express them can improve quality and reduce defects. For example, "The software shall warn of low battery" is written as a ubiquitous requirement but is actually not since it lacks a trigger. The developer is left to guess when to display a warning, which introduces defects.
This tutorial will provide examples of functional requirements, demonstrate how to identify ubiquitous requirements versus those that are not and explain how to rewrite them using the Easy Approach to Requirements Syntax (EARS), developed at Rolls-Royce. EARS provides a simple yet powerful method of capturing the nuances of functional requirements.
