Pulse or digital communications – Repeaters – Testing
Patent
1995-05-10
1998-04-07
Chin, Stephen
Pulse or digital communications
Repeaters
Testing
375227, 370321, 370333, 455 673, 4552261, 455424, H04Q 738
Patent
active
057373590
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a method for supervising base station radio channels by means of interference measurement. The invention relates further to a method for supervising base station radio channels by measuring the quality of a received signal.
One of the most critical factors in radio systems, for example in cellular mobile telephone systems, is the quality of the radio connection between the base station and a mobile station. The quality of this radio connection is influenced substantially by the condition of the radio parts, i.e. the antennas and the transceivers, of the base station. Therefore, the condition of the radio parts of the base station is supervised by means of various measurements and tests. Another factor influencing the quality of the radio connection is radio-frequency interference occurring in radio channels, resulting from, for example, other radio devices or base stations.
Therefore, the specifications of the PanEuropean GSM mobile radio system, for instance, require a base station to supervise the quality of received signals during normal traffic operation, for example by calculating the bit error rate (BER) on the basis of a signal obtained from the output of the receiver of the base station. Moreover, the base station is required to measure continuously the interference level of a radio channel in all non-active dedicated channels, i.e. both in signalling and traffic channels. At the moment, the interference level of the radio path is measured at the base station separately for each connection, whereupon the base station transmits information of the interference level of each free signalling or traffic connection to other parts of the system, for example to the base station controller (BSC), at predetermined intervals. The problem with the present measuring technique is that even though disturbances in the radio path usually vary greatly as a function of frequency, a measuring method of the present type cannot give any information about this "interference distribution" between different radio channels, especially if the base station uses frequency hopping. Frequency hopping refers to operation where the transmitting frequency and correspondingly the receiving frequency at the receiving end are continuously changed during a connection by using a suitable number of frequencies and a predetermined frequency hopping sequence. The use of frequency hopping yields two different advantages, namely frequency diversity and interference diversity. Frequency diversity improves the quality of a radio connection mainly when a transmitter and a receiver move slowly in relation to each other. If the frequency of a radio connection in a time division multiple access (TDMA) system is changed enough from one channel time slot to another, the fading situations imposed on different time slots do not correlate. The interference diversity effect is based on the fact that the frequency hopping sequences of base stations using the same or adjacent frequencies are different or at least are phased in relation to each other, and therefore the frequencies interfering with each other also change on transition from one time slot to another, and the effect of strong sources of interference is distributed among several connections, whereupon the effect of the interference on a single connection decreases. However, this only accentuates further the aforementioned problem that the present techniques of interference measurement do not provide information about the distribution of interference between different radio channels.
SUMMARY OF THE INVENTION
One aim of the present invention is to eliminate the above problem. This aim is achieved by means of a method according to the invention which is characterized in that the interference level of a control or traffic channel hopping from one radio channel to another during a connection is measured separately for each used radio channel, and the measured interference levels are stored separately for each radio channel, that the interfere
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Patent Abstracts of Japan, vol. 12, No. 397, E-672, abstract of JP,A,63-138824, Jun. 10, 1988.
Chin Stephen
Le Amanda T.
Nokia Telecommunications Oy
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