RADIO SYSTEM.
O. Langewellpott - 7 (Revision) I 46148 lO i" i RADIO SYSTEM Background of the Invention The present invention relates to a radio system such as the type C radio telephone network of the German Bundespost ("Frequenz" 36, 1982, 4/5, pp. 90-99).
For reasons of economy, it is desirable to use the same radio channels simultaneously in several areas which follow one another at the shortest possible intervals. To avoid cochannel interference, the transmitting power is usually varied according to the field strength measured at the receiver. However, such a measurement has the disadvantage that it is not possible to distinguish between useful and interfering signals, so that in the presence of a weak useful signal and a strong interfering signal, for example, no transmitting-power increase will be effected.
The object of the invention is to effectively suppress cochannel interference.
The advantage offered by the invention lies in the fact that signals which interfere with the communication but do not change the contents of the transmitted messages will not cause the receiver to increase the transmitting power. Accordingly, a change in transmitting power will be effected only if the useful signals cannot be reliably detected or processed.
i0 l 5175-71 The invention can be summarized, according to a broad aspect, as a radio system comprising mobile and base stations wherein digital signals are transmitted, and wherein the base stations vary the transmitting power of the mobile stations according to the transmission quality, characterized in that the digital signals are encoded by means of a code word such that, in addition, the mobile stations vary the transmitting power of the base stations according to the transmission quality, that the received signals are correlated with said code word, and that the ratio between the average values of the highest and second-highest correlation peaks is regarded as the transmission quality criterion.
The invention will now be explained in more detail with the aid of examples. Only two stations of the radio system will be considered. Each of the two stations varies the transmitting power of the respective other station. This also applies if a station communicates with a plurality of stations using timedivision multiplexing, for example. In that case, the transmitting power of this station may vary from channel to channel.
Advantageously, the transmitting power is variable in several steps, e.g., 0 dB (maximum power), 6 dB, 16 dB, 26 dB (minimum power).
In a first example, the message to be transmitted is encoded with an error-detecting or -correcting code. In a simple case, this can be done by adding parity bits. The transmission quality is judged in the receiver from the rate of the errors detected or corrected by a decoder. If the number of errors i0 i 46ï48 5175-71 exceeds an upper limit within a few seconds, the receiver will cause an increase in transmitting power. To this end, a corresponding signal is transmitted from the transmitter of the receiving station to the transmitting station. If the number of errors falls below a lower limit, the transmitting power will be reduced. Otherwise, the transmitting power remains unchanged.
Both limits are chosen so that a character error probability of 10-4 is not exceeded, receiving conditions permitting.
Reference should now be made to the English translation of German Patent Document DE-OS 31 18 018 published on November 25, 1982 in the name of Standard Elektrik Lorenz Aktiengesellschaf This document, attached hereto as an appendix, discloses a radio system in which the signals to be transmitted are encoded by means of a code word. The receiver contains a correlator which correlates the received signals with this code word. More particularly, referring to Fig. Il of the Appendix, which shows the unit for recovering the transmitted signal which is provided behind the receiver 8, it will be seen the signal is applied to 17 correlators 31 which are controlled by a code generator 37. One of the correlators 341 serves to synchronize the time slots. The other 16 correlators 31 are followed by 16 detectors 33, which detect maxima in the autocorrelation function. A subsequent decision stage 34 selects the greatest from all detected maxima.
Thus, it recognizes the correct signal by the height of the correlation peaks. In such a system, the transmission-quality criterion may be the ratio of the largest to the second largest cori0 ÆZ46148 5175-71 relation peak. During a low-noise transmission, this magnitude relation will be large, particularly if averaged over several successively received signals, while in case of strong interference, the two values will differ only little. Analogously to the first example, the transmitter power will be changed if the magnitude ratio exceeds an upper limit or falls below a lower limit. It is adjusted by a corresponding signal in a preamble preceding the message (Fig. 5 of DE-OS 3i 18 018).
In a third example, the two above-described possibilities of judging the transmission quality are combined. An increase in transmitting power will be initiated even if only one judgment indicates a poor transmission quality. The transmitting power will be reduced if both judgments are "good".
In addition, the decision to reduce the transmitting power can be influenced in all examples by measuring the received field strength or the phase jitter. Should the field strength fall below a predetermined minimum value, the transmitting power will not be further reduced despite good transmission quality.
îZ461 8 5175-71 THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
i. A radio system comprising mobile and base stations wherein digital signals are transmitted, and wherein the base stations vary the transmitting power of the mobile stations according to the transmission quality, characterized in that the digital signals are encoded by means of a code word such that, in addition, the mobile stations vary the transmitting power of the base stations according to the transmission quality, that the received signals are correlated with said code word, and that the ratio between the average values of the highest and second-highest correlation peaks is regarded as the transmission quality criterion.
2. A radio system as claimed in claim i, characterized in that, in addition, the received field strength or the phase jitter is taken into account in varying the transmitting power.
SMART & BIGGAR OTTAWA, CANADA PATENT AGENTS A radio system with mobile and stationary radio stations is described, in which the radio stations communicating with one another set the transmitting power of the respective other radio station depending on the transmission quality. Criteria for assessing the transmission quality are specified. A digital mobile-radio system comprising means in each station involved in a radio communication in said system for exchanging signals, in a time-division multiplex channel, with the respective other station involved in the same radio communication, means for transmitting the signals in an error-detecting or error-correcting code, for determining the transmission quality by measuring the bit error rate, for deriving a control signal characteristic of the transmission quality, and for transmitting said control signal to the other station involved in the radio communication, means for adjusting the transmitting power in one of the two stations in response to a control signal received from the other station involved in the radio communication, and means for encoding the signals to be transmitted with a code word, characterized in that one station is a base station which comprises means for communicating with several mobile stations on a time-division multiplex basis, that means are provided at the receiving end for correlating the encoded signals with the code word in a correlator and at the same time determining the ratio between the largest and second-largest correlation peaks, and that the means for deriving the control signal characteristic of the transmission quality also take into account the determined ratio between the largest and second-largest correlation peaks, such that an increase in transmitting power will be initiated if either the bit error rate or the ratio between the largest and second-largest correlation peaks points to an insufficient transmission quality, and that a decrease in transmitting power will be initiated if both values point to a sufficient transmission quality. A mobile-radio system as claimed in claim 1, characterized in that the means for adjusting the transmitting power are also influenced by the received field strength or by phase jitter.