Abstract: A method of switching a call to a multipoint conference call includes sending a message (201) from a first terminal (105-T1) to a gatekeeper (102) which provides address translation and control access to a shared network medium (101). The call is initially established as a point to point communication between first terminal (101) and a second terminal (105-TN) over shared network medium (101) while complying with H.323 standard. Message (201) contains a request for the multipoint conference call. The method furthermore includes selecting a multipoint control unit (104) connected to shared network medium (101) to allocate resources for the multipoint conference call, and then switching the call to the multipoint conference call via the allocated resources. Thereby, the initial call is switched to a multipoint conference call without interrupting the initial call.
Abstract: Hook- and-loop-type tapes are selectively attached to a video display unit and to flexible elongated strips of magnetic material so that the strips of magnetic material may be removably mounted around the video display unit in orthogonally intersecting planes to absorb magnetic radiation from the source. Each strip of magnetic material has a grain orientation parallel to its longitudinal axis and may be formed from grain-oriented ferromagnetic material in the range from M3 to M7. A multiple-layer magnetic shielding material is provided by securing first and second layers of such grain-oriented ferromagnetic material together with the grain orientation of the first layer orthogonal to the grain orientation of the second layer. Each strip of magnetic material may also be formed from this multiple-layer magnetic shielding material.
Abstract: Coded modulation schemes based on codes for QPSK modulation are directly incorporated into QAM based modulation systems, forming trellis coded QAM for communicating information. Concatenated coding with QPSK based trellis coding and symbol error correcting coding is used. In an encoder, an N-bit QAM constellation pattern is divided into four subsets, each including N/4 symbol points of the constellation pattern. A two-bit QPSK codeword is assigned to each of the four subsets. A symbol to be transmitted is first encoded using an outer error correcting encoding algorithm. Part of the symbol is then encoded with an inner code that comprises a rate 1/2 trellis encoding algorithm to provide a QPSK codeword, which is mapped with the remaining bits of the symbol to provide a modulation function. The remaining bits correlate the symbol with one of the symbol points included in the subset defined by the QPSK codeword. A receiver is provided to recover information from the modulation function.
July 26, 1991
Date of Patent:
August 3, 1993
General Instrument Corporation
Woo H. Paik, Scott A. Lery, Chris Heegard
Abstract: A radio data transmission system wherein signals received via a plurality of diversity antennas are switched at a cycle of subtime slot so that, when the reception level of at least one antenna is sufficiently high to receive the required signal in the relevant time slot, the digital signal in that time slot can be detected properly even if the reception level of any other antenna is not sufficiently high. Accordingly, the code error rate can be minimized by constituting the system in such a manner that the correlation of variations in the reception levels of the diversity antennas becomes extremely low.