无线通信信道ECSE 6961 The Wireless Channel【国外优秀研究报告】.ppt

ECSE 6961The Wireless Channel Shiv Kalyanaraman shivkuma@ecse.rpi.edu Google: “Shiv RPI” Wireless Channel is Very Different! Wireless channel “feels” very different from a wired channel. Not a point-to-point link Variable capacity, errors, delays Capacity is shared with interferers Characteristics of the channel appear to change randomly with time, which makes it difficult to design reliable systems with guaranteed performance. Cellular model vs reality: Basic Ideas: Path Loss, Shadowing, Fading Variable decay of signal due to environment, multipaths, mobility Attenuation, Dispersion Effects: ISI! Wireless Multipath Channel MultiPath Interference: Constructive Destructive Mobile Wireless Channel w/ Multipath Game plan We wish to understand how physical parameters such as carrier frequency mobile speed bandwidth delay spread angular spread impact how a wireless channel behaves from the cell planning and communication system point of view. We start with deterministic physical model and progress towards statistical models, which are more useful for design and performance evaluation. Large-scale Fading: Path Loss, Shadowing Large-scale fading: Cell-Site Planning In free space, received power attenuates like 1/r2. With reflections and obstructions, can attenuate even more rapidly with distance. Detailed modelling complicated. Time constants associated with variations are very long as the mobile moves, many seconds or minutes. More important for cell site planning, less for communication system design. Path Loss Modeling Maxwell’s equations Complex and impractical Free space path loss model Too simple Ray tracing models Requires site-specific information Empirical Models Don’t always generalize to other environments Simplified power falloff models Main characteristics: good for high-level analysis Free-Space-Propagation If oscillating field at transmitter, it produces three components: The electrostatic and inductive fields that decay as 1/d2 or 1/d3 The EM