Telefonaktiebolaget Lm Ericsson (Publ)

Svenska Utvecklingsaktiebolaget

Stefan E Kallander

Philippe Charas

Radio coverage in closed environments

A repeater system in a communication system including a base station and a mobile unit provides a communications link between the base station and the mobile unit when the mobile unit is located in an environment that is substantially closed off to high radio frequency communication between the base station and the mobile unit. The repeater system has a first linear two-way frequency converter including a high frequency port for two-way coupling to the base station and a low frequency port for two-way coupling to a low frequency signal that is capable of distributing radio frequency power through the closed environment. The low frequency port is connected to a cable which propagates and receives low radio frequency power within the closed environment. The repeater system also includes a first antenna for wireless coupling to the cable, and a second linear two-way frequency converter having a low frequency port connected to the first antenna for two-way coupling to a low frequency signal and a high frequency port for two-way coupling to a signal that is compatible with the high radio frequency signal used by the communications system. A second antenna is connected to the high frequency port of the second linear two-way frequency converter for wireless coupling of the second linear two-way frequency converter to a nearby mobile unit.

A method of reducing in a digital time multiplex mobile telephony system the risk of poor reception as a result of the occurrence of points of low signal strength, so-called zero points. Transmission from fixed stations is performed with a polarization direction which is changed stepwise between different parts of the transmitted information. This causes the fading patterns around receiving stations to change in time, and also causes any zero points to be moved in the geography, therewith making it improbable that more than a small part of an information frame will be lost. In the case of a GSM-type system, the polarization direction is changed for each new TDMA-frame.

Method for reducing the risk of poor reception in a mobile telephony

The invention relates to a dust indicator for detecting the presence of suspended particles, either solid or liquid, in a gas. A concentrated, substantially parallel light beam (1) of suitable wavelength is directed through a measuring chamber (2) containing the gas to be examined. The light beam is surrounded by an internally reflecting elliptical cylindrical reflector (4) in a manner such that the beam (1) coincides with one focal axis (B.sub.1) of the reflector. Arranged in the other focal axis (B.sub.2) of the reflector (4) is at least one light detector (6) with its active surface facing the reflector and the center axis of its field of view directed, preferably perpendicularly, towards the first said focal axis (B.sub.1) along which the beam (1) is directed.

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Lidingo, Sweden

Stefan E Kallander