| Wireless CommunicationChapter: Wireless Propagation Channels |
Contributed by Peter E. Leuthold and
Pascal Truffer
Efficient wireless transmission over the indoor channel represents a key technology to pave the way toward the realization of universal personal telecommunications (UPT). Cordless telephony and data services on wireless local area networks (WLAN) are already well established. Today, indoor communications without wiring evolve from voice and low data rate services toward high bit rate services, e.g. videophony and even multi-media, causing an increasing demand of mobile ISDN and B-ISDN terminals (Broadband-Integrated Services Digital Network) as well as the need of larger interconnection capacity between movable personal computers or workstations, respectively, and their servers. In order to achieve compatibility with wirebounded networks, e.g. Ethernet (10 Mbit/s), FDDI (Fiber Distributed Data Interface, 100 Mbit/s) and B-ISDN (155 Mbit/s), radio transmission of bit rates higher than 1 Mbit/s up to the range of 100 Mbit/s is required. Correspondingly, the large bandwidths increase the interference effects which entail the development of transceiver structures using complex modulation schemes, e.g. subband transmission or spread spectrum techniques combined with interference cancellation methods and multi user detection. Moreover, the need of wider bandwidths up to a few 100 MHz leads to a gradual displacement of the exploited frequency bands toward the millimeter-wave range.
During the forthcoming decade the development of new powerful wireless indoor communication systems can be expected according to already introduced standards, i.e. IEEE 802.11 (1...2 Mbit/s) and HIPERLAN (20 Mbit/s) or taking account of specific normalization activities performed within the frame of European UMTS (Universal Mobile Telecommunication Systems) or MBS programs (Mobile Broadband Systems). Indoor RLAN have to cope with the frequency and time selective channel characteristics mainly because of multipath propagation and movements of the terminals and reflectors or scatterers, respectively. Hence, the detailed knowledge of the radiowave propagation effects within buildings is inevitable for the development, performance assessment and design of such wireless transmission systems. Global channel parameters like delay spread, coherence bandwidth, coherence time, number of dominant paths, path loss etc. are needed to achieve a first approach of optimum parameters. In the design phase a simulation of the whole system including a channel model which accurately imitate the transmission constellation by means of synthesized channel impulse responses (CIR) in accordance with the real environment allows the necessary performance evaluation. The model parameters have to be either calculated or extracted from measurements.
Three principal solutions have been proposed to simulate the radio channel:
The SRCM approach seems to be advantageous compared to the two others due to the following properties:
