Multiplex communications – Wide area network – Packet switching
Patent
1995-04-11
1996-10-22
Marcelo, Melvin
Multiplex communications
Wide area network
Packet switching
455 341, 455 342, 4552262, H04B 712, H04J 102
Patent
active
055684807
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to a method of classifying incoming signals in frequency-division multiplex radiocommunication systems comprising a transmitter search device which scans the associated radiocommunication channels, and wherein a radiocommunication channel is recognized as being free (open for communication) if the measured electrical field strength in the radiocommunication channel is below a threshold value.
EP-A2-299 515 discloses a method of linking together a base station and a mobile section of a cordless telephone via a radiocommunication channel. In this method, the electrical field strength is first determined on priority channels. If the field strength on a priority channel is below a threshold value for a certain time, said priority channel is recognized as free and the transmission and reception frequency in the base station and mobile section are tuned to said priority channel.
A disadvantage of said method is that the sideband noise of a nearby transmitter in the adjacent channels may produce an electrical field strength which is large enough for the radio transmission channels to be incorrectly recognized as occupied.
DE-C2-35 08 900 relates to an arrangement for deriving a switching criterion for radio equipment from a field-strength measurement. This arrangement contains a comparator which compares the electrical field strength periodically measured in a communication channel with a threshold value. If the measured field strength is above the threshold value, a first number is added to a counter reading in an accumulator; if the measured field strength is below the threshold value, a second number is subtracted from the counter reading in the accumulator. If the counter reading in the accumulator falls below a certain value, the switching criterion is fulfilled and a change is made to another communication channel.
In the event of interference due to adjacent channels, however, this relatively expensive circuit arrangement achieves no improvement compared with methods in which only the field strength in the communication channel is measured.
EP-A2-298 750 discloses a cordless telephone in which the field strength is evaluated in a test channel in order to establish whether it is occupied. For this purpose, a comparison is made with a threshold value. In addition, the field strength in a communication channel is used to determine the transmission quality. As soon as the field strength in the communication channel is below a threshold value, a warning signal sounds. The user then has the option of inputting a lower threshold value so that the measured field strength is again above the threshold value. If the user does not select a lower threshold value for the field strength, the link is disconnected after a certain time.
In the case of this procedure, too, it is not possible to recognize interference due to adjacent channels. Furthermore, it is a disadvantage that a distinction cannot be made between noise and information on the communication channel.
EP-A2-359 231 discloses a cordless telephone in which it is ascertained whether the mobile section is situated inside or outside the radio service area. This decision is reached on the basis of a comparison of the incoming field strength with a threshold value. If the incoming field strength drops below the threshold value, the amplification of the incoming signal is reduced.
In the case of this cordless telephone, it is a disadvantage that a distinction cannot be made between a communication channel with interference and one without interference and, consequently, a signal without interference having low field strength can no longer be adequately amplified. The recognition of interference due to an adjacent channel is also not possible.
EP-A2-283 401 discloses a circuit arrangement which prevents an interference of two frequency-modulated signals. In this case, the incoming signal is amplified by a logarithmic amplifier and then fed to a comparator which compares the amplitude with a reference signal. If it is found that the
REFERENCES:
patent: 4166927 (1979-09-01), Hamaoki
Hulbert et al., "The Relationship Between Adjacent Channel Rejection and Spectral Efficiency for Advanced Cordless Telephones," IEEE/IEICE Global Telecommunications Conference, Bd. 3, Nov. 15, 1987, Tokyo.
Carman Melissa Kay
Grundig E.M.V. Elektro-Mechanische Versuchsanstalt Max Grundig
Marcelo Melvin
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