1 INTRODUCTION - By Author
At the start of the new millennium, an exciting perspective is emerging in the field of wireless channel modeling. In the past, the wireless multi path channel was thought to be a harsh, unavoidable consequence of wireless communications. In recent years, new technology in hardware and channel coding have not just overcome the difficulties of communicating in a multipath channel – algorithms such as space-time coding actually use the unpredictable nature of the multipath channel to enhance the communications link [1].
One fact is inescapable: the development of new wireless systems requires that the channel be measured and modeled to an increasingly higher degree of detail. It no longer suffices to make oversimplifying assumptions about the spatial channel, such as omni directional multi path propagation and Rayleigh fading. Multiple antenna receivers cannot function properly if designed with-out an understanding of the spatiotemporal characteristics of the multipath channel.
Multipath propagation leads to two unpredictable types of behavior in the wireless channel. The first is frequency selectivity caused by multipath components arriving with different delays. The second is spatial selectivity caused by multipath components arriving from different directions in space. While frequency selectivity is a well-understood phenomenon, the problem of describ-ing spatial selectivity, which results in small-scale fading, has traditionally been difficult for wireless engineers to model for emerging space-time applications. There is a need to relate basic small-scale fading characteristics to the spatial geometry of arriving multi path.
This chapter presents a theoretical framework for characterizing the angle-of-arrival of multipath power in a way that produces simple-but-powerful in-sight into the nature of small-scale fading. By emphasizing the parallel mathematical analysis used for frequency selectivity and spatial selectivity, we show that small-scale fading behavior may be described with only three geometrical angle-of-arrival parameters: angular spread, angular constriction, and azimuthal angle of maximum fading. These three shape factors relate to spatial selectivity much like RMS delay spread relates to frequency selectivity.
The rest of the chapter is broken into the following sections: Section 2 dis-cusses basic concepts in modeling stochastic wireless channels. Section 3 de-fines the three basic shape factors – geometrical parameters that describe multi path angles-of-arrival. Several examples illustrating the shape factor concept are found in Section 4. Section 5 then presents practical problems in wireless channel modeling which are solved easily by using multi path shape factors. The chapter concludes with a final perspective on the work presented.
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At the start of the new millennium, an exciting perspective is emerging in the field of wireless channel modeling. In the past, the wireless multi path channel was thought to be a harsh, unavoidable consequence of wireless communications. In recent years, new technology in hardware and channel coding have not just overcome the difficulties of communicating in a multipath channel – algorithms such as space-time coding actually use the unpredictable nature of the multipath channel to enhance the communications link [1].
One fact is inescapable: the development of new wireless systems requires that the channel be measured and modeled to an increasingly higher degree of detail. It no longer suffices to make oversimplifying assumptions about the spatial channel, such as omni directional multi path propagation and Rayleigh fading. Multiple antenna receivers cannot function properly if designed with-out an understanding of the spatiotemporal characteristics of the multipath channel.
Multipath propagation leads to two unpredictable types of behavior in the wireless channel. The first is frequency selectivity caused by multipath components arriving with different delays. The second is spatial selectivity caused by multipath components arriving from different directions in space. While frequency selectivity is a well-understood phenomenon, the problem of describ-ing spatial selectivity, which results in small-scale fading, has traditionally been difficult for wireless engineers to model for emerging space-time applications. There is a need to relate basic small-scale fading characteristics to the spatial geometry of arriving multi path.
This chapter presents a theoretical framework for characterizing the angle-of-arrival of multipath power in a way that produces simple-but-powerful in-sight into the nature of small-scale fading. By emphasizing the parallel mathematical analysis used for frequency selectivity and spatial selectivity, we show that small-scale fading behavior may be described with only three geometrical angle-of-arrival parameters: angular spread, angular constriction, and azimuthal angle of maximum fading. These three shape factors relate to spatial selectivity much like RMS delay spread relates to frequency selectivity.
The rest of the chapter is broken into the following sections: Section 2 dis-cusses basic concepts in modeling stochastic wireless channels. Section 3 de-fines the three basic shape factors – geometrical parameters that describe multi path angles-of-arrival. Several examples illustrating the shape factor concept are found in Section 4. Section 5 then presents practical problems in wireless channel modeling which are solved easily by using multi path shape factors. The chapter concludes with a final perspective on the work presented.
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