Fritz Gfeller

Wireless in-house data communication via diffuse infrared radiation

A novel wireless broadcast/multi-access channel is described for flexibly interconnecting a cluster of data terminals located within the same room. The transmission medium is diffusively scattered infrared radiation at 950-nm wavelength. Transmission is low-to-medium speed and the range up to 50 m. Theoretical analysis indicates that the time dispersion limits the transmission bandwidth of the system to 260 Mbit ċ m/s, but background noise produced by ambient daylight reduces the transmission speed below 1 Mbit/s. The transmission properties of the diffuse optical channel are analyzed, and experimental digital links for baseband PCM at 125 kbit/s and PSK 64 kbit/s are demonstrated.

Dynamic Cell Planning for Wireless Infrared In-House Data Transmission

A simulation model for characterizing the geometry of infrared communication cells representing full connectivity has been developed. Measured spatial daylight distributions in a large open-plan office have been incorporated into the model. With a 1 Mbps transmission system based on 16-slot pulse-position modulation and a non-directed infrared source of 250 mW average optical power, cell sizes of up to 10 m and 20 m diameter can be achieved for peer-to-peer and client/server topologies, respectively. Daylight variations cause severe distortions and size reductions of the cells. A transmission system with adaptive data rate control (10 kbps to 10 Mbps) maintains full network connectivity within the cells at the expense of a graceful throughput degradation for terminals exposed to high levels of ambient light.

Advanced infrared (AIr): physical layer for reliable transmission and medium access

Advanced infrared (AIR) is a new standard of the Infrared Data Association (IRDA) to create wireless ad-hoc networks using a time division multiple access protocol (TDMA). The use of TDMA requires a physical layer providing approximate infrared channel symmetry and extended access-signaling range to reach all potentially interfering stations. We describe the underlying physical layer for AIR and derive transceiver parity conditions for achieving channel symmetry. In addition, we investigate the effects of channel asymmetry on the effectiveness of the access protocol.