Measurement and model-based characterization of indoor wireless channels.

摘要

In wireless communication systems, the transmitted signal is distorted by various phenomena that are intrinsic to the structure and contents of the wireless channel. Among these, multipath fading is a dominant source of distortion in indoor wireless communications. The effects of multipath can be determined from the channel impulse response (CIR). The structure of the CIR is a function of the channel geometry and its contents as well as the transmission frequency and bandwidth. The multipath effect can be pronounced with increase in transmission bandwidth. The transition of existing narrow band cellular systems to wideband communication will require a deeper fundamental understanding of the wireless channel and its impact on the performance of wireless systems.; In this work, the measurement and modeling of narrow and wideband channel impulse responses is undertaken. The channels considered are of the indoor type, with a focus on classroom and laboratory environments in the University. The measurements are made using a frequency sweep method. From the channel measurement and frequency selective fading features caused by multipath components are identified. The wideband characteristics of indoor wireless channel are investigated through delay parameters and the pole-zero characteristics of the channel transfer function. The narrow band characteristics are examined using the band limited CIR and its intersymbol interference (ISI) power and performance in orthogonal frequency division multiplexing (OFDM) systems. The dynamics of poles and zeros in the case of ideal 1-D lossless medium are discussed and time varying characteristics are studied using a 3-D empty room CIR which calculated by method of image.; The reverberation part of the CIR is classified into two regions, the coherent and the diffuse part. The coherent region is composed of line of sight (LOS), if it exists, and a number of first and second reflections and is highly affected by geometrical configulation of transmitter and receiver. The diffuse region is formed by multiple reflections and depends more on overall structure of the channel such as size of the room and material properties of boundary surfaces. The communication performance is affected by the high energy coherent region.