GB2144309A - Method of linear radio transmission of communications - Google Patents

Abstract

Fixed stations (A, B, C) arranged linearly are keyed in groups one after the other in time and the radio ranges of the fixed stations of one group do not overlap. An exchange sends a superordinate activation signal for time- staggered keying through a modulation line to the fixed stations, the group identification of which is transmitted to a mobile station (BS) to be called. The mobile station on correct reception transmits a fixed number of call confirmations in time slots, which it determines from the received group identifications, while stating the respective time slot. <IMAGE>

Description

SPECIFICATION Method of the linear radio transmission of communications The present invention relates to a method of radio transmission between a mobile station and a plurality of linearly arranged fixed stations transmitting on a common frequency and combined into n groups to operate within each group in nonoverlapping ranges, such a method being disclosed in DE-OS 27 39 561.

In order to transmit in a radio channel free of interference, three radio frequencies are usually required in alternation. In the case of a keying of the fixed stations in groups, a single frequency can be utilised for transmission staggered in time. In that case, the duration of occupation of the channel is multiplied by the number n of the groups.

There is thus scope for improvement in the utilisation of the duration of ocuppation of the channel and to increase the call probability.

According to the present invention there is provided a method of radio transmission between a mobile station and a plurality of linearly arranged fixed stations transmitting on a common frequency and combined into n groups to operate within each group in mutually exclusive ranges, the method comprising the steps of transmitting a superordinate keying signal from an exchange through a modulation line to all the fixed stations for keying of transmitters thereof to effect transmission by the groups in succession of both data and an identification of each group, and transmitting from the mobile station to the fixed stations, on fault-free reception of the group transmissions by the mobile station, both a call confirmation in n time slots determined in accordance with the received group identifications and an identification of the time slot, the step of transmitting from the mobile station comprising transmitting n call confirmations in the time slots 1 to non reception of the transmission from the first group, transmitting n-m+1 call confirmations in the time slots m to n on reception of the transmission from the mth group and transmitting a single call confirmation in the time slot n on reception of the transmission from the nth group.

An example of the present invention will now be more particularly described with reference to the accompanying drawings, in which: Fig. 1A is a schematic illustration of a radio transmission system in which a method exemplifying the present invention can be carried out; Fig. 1 B is a diagram illustrating transmission and reception by fixed stations of the system under the control of an exchange of the system; Fig. 2 is a diagram showing transmission from the exchange to a mobile station of the system by way of the fixed stations; and Fig. 3 is a diagram showing transmission from the mobile station to the exchange by way of the fixed stations.

Referring now to the drawings, there is shown in Fig. 1A a linear radio connection with a mobile station BS (hereinafter referred to as "vehicle") and fixed stations A1, B,, C (i = running index), which are each arranged in alternation along a path and connected through a modulation line with an exchange. In the illustrated example, the fixed stations are thus combined in a number n of groups, the number n thus being 3.

The same transmitting frequency is used by all fixed stations in the transmitter keying. The vehicle receives on only one frequency and transmits on only one frequency, which is the same for further such vehicles.

In order to be able to transmit free of interference, three frequencies (A, B, C) would usually be required in alternation. This division into three is also applied to the keying in groups, but in time range. A temporally staggered transmission of the fixed transmitters is effected at tA, tB and tc, wherein all fixed stations with the index Ai transmit simultaneously at the instant tA, all fixed stations will B, at tB and so forth, as indicated in Fig. 1 B.

The response of the vehicle is taken up by not only one fixed station, but by several (A, B, C). If the reception is faultless, then the fixed station switches to the line to the exchange at an instant t'A, t's, t'c.

This procedure enables use of a receiver with utilisation of all receiving channels and not only the "next best", which leads to an appreciable increase in the call probability in the exchange and in the vehicles.

Preferably, the reception conditions in transmission from the fixed stations A, B and C to the vehicle and from the vehicle to the fixed stations A, B and C are detected, which is of advantage for a positional determination and for an optimum switching of the connection for speech transmission.

Since a fixed station occupies the line to the exchange only when the reception from the vehicle is fault-free, superimpositions on the modulaton line through fragmentary reception are avoided.

For preference, the fixed stations acknowledge the call of a vehicle automatically and subsequently ensure that the received information is passed to the exchange, i.e. not the vehicle, but the intelligent fixed station is (in receiving direction) a partner of the exchange.

In transmission direction from the exchange to the vehicle, the call transmission is performed without testing and intermediate storage because of the high quality of the feeder (modulation line) in comparison with the radio transmission.

This method thus makes possible an appreciable improvement in the call probability compared with a line radio transmission, for example train line radio transmission, of conventional construction. This is based on the gain in station diversity, because the vehicle receives from up to three fixed stations and the exchange receives its information from up to three fixed stations. In conventional train radio transmission, due to the channel diversity the vehicle receives only one fixed station and the exchange also receives its information from only one fixed station.

Fig. 2 shows a flow diagram for a command transmission from the exchange to a vehicle. The diagram is to be read from bottom to top. The time axis is always plotted towards the right.

The transmission presupposes no positional information about the vehicle to be addressed. The exchange transmits the information three times to the fixed stations and the stations A1, B1 and C, are keyed, staggered in time, through the presupposed, superordinate activation signal X, wherein the time element ST bridges over the reaction time for the switching on and off of the transmitter. The communications in direction of the vehicie are generally not intermediately stored in the fixed station, but a regeneration can take place.

On reception of the information to the vehicle, a call acknowledgement RB1 . . . 3 is triggered. The information can in this case be received from several fixed stations A, B and C. The information transmitted by way of the stations A, B and C has already been identified differently by the exchange and the group identification was also transmitted each time to the vehicle.

If the vehicle receives only from the fixed station C, then only one call confirmation RB3 (in time slot 3) is transmitted from the vehicle to the fixed stations and it is also identified by a time slot statement. When the vehicle receives from the station B, then two call confirmations RB2 and RB3 (time slot 2 and 3) are transmitted. Correspondingly, three call confirmations take place on reception from station A. The suppression of informaton transmission in station B or C, in case a call confirmation has already been received through the respective station, is possible, but confers no advantage, since reception from the station A in any case initiates three call confirmations (or, in the case of B, two call confirmations).On the other hand, the radio channel should be occupied, if possible, for as long as the transmission to the exchange lasts in order to avoid interference through simultaneous occupations.

The recognition of the state of occupation is improved through the keying of one A group, B group and C group in place of a discrete station.

The fixed stations evaluate the call confirmations and switch to the line to the exchange at a certain instant only in the case of faultfree reception. In this case, the fixed stations carry out evaluations as follows: Station A evaluates call confirmations by time slot 1, Station B evaluates call confirmations by time slots 1 and 2, and Station C evaluates call confirmations by time slots 1,2 and 3.

For call confirmation, the fixed station group, the fixed station number within the group and the receiving data of the fixed station as well as status information are advantageously transmitted to the exchange. Because of the non-synchronous switching-on of the line, synchronisation symbols are inserted before each transmission.

If the modulation lines so permit, the modulation line for the fixed stations more remote from the exchange can be interrupted for the duration time of their own switching to the exchange in order to avoid overlapping of signal in the case of propagation beyond the horizon.

Fig. 3 is a flow diagram for a call transmission from vehicle to exchange in an advantageous form.

The vehicle tests the channel occupation and by reference to received time slot information occupies the channel becoming free at the suitable time. The transmission M1, M2 and M3 takes place three times. A single transmission brings no advantage except in special cases, since the fixed stations in any case occupy the channel longer for their acknowledgement transmission QA, 0, and Qc- Moreover, the channel should preferably be occupied for as long as the transmission to the exchange lasts, in order to reduce interference through simultaneous occupation of the channel and thereby of the line to the exchange.

Each information M (call) contains a time slot statement so that a correct, temporally staggered acknowledgement is possible. The station A evaluates M1, station B evaluates M, and M2 and station C evaluates M1, M2 and M3.

The information is tested for freedom from error and intermediately stored until the temporally staggered acknowledgement through the locally fixed station. Each fixed station acknowledges only once and this only in the case of fault-free reception of the (one) call corresponding to the predetermined time slot. A vehicle thus receives up to three acknowledgements. Connected therewith is a transfer of the call to the exchange. This operation is identical with thetransmisson of the call confirmations to the exchange as reaction to a command transmission. The fixed stations transmit the calls MA, Ms and MC recognised by them on the modulation line in corresponding time slots.In the case of call transmission from the vehicle, however, the individual fixed station awaits a reaction of the exchange ("clear" as reaction for the call transmission to the exchange). The cancellation command LQA, LB and LC is triggered automatically and can be selective or superordinate, corresponding to the reception by way of the stations A, B and C. Stations of which the transfer of calls has not been cancelled (acknowledged) repeat the transfer automatically.

If the fixed station receives a call which is not identical with the previous one, then the automatic acknowledgement Q and the switching to the line is omitted, i.e. the further call is ignored, until the first call is cancelled by the exchange. In the case of identical calls, the acknowledgement is of course transmitted automatically to the vehicle at the provided time. The repeated transfer to the exchange is at first omitted.

As already explained by reference to Fig. 2, calls from the exchange are acknowledged from the vehicle by a call confirmation. For example, the call confirmations RB1, RB2 and RB3 can advantageously contain statements on the quality of reception in the vehicle, since the threefold call of the exchange according to the ABC-time slot can also be associated with a certain fixed station.

Correspondingly, the vehicle can state the associated quality of reception in each call confirmation on the transmission of the temporally staggered call confirmations, for example: RB1 contains quality of reception from Fst A, RB2 contains quality of reception from Fst B, and RB3 contains quality of reception from Fst C.

If the call confirmation RB8 and RBC is passed on by the fixed stations to the exchange without reception from RB2 or RB3, then no quality statement is made through the fixed station.

On each telegram exchange with a vehicle, the reception values in the fixed stations, and the receiving conditions in the vehicle in the communication content of the call confirmation, are advantageously communicated to the exchange by means of telegram prefix. With these data in conjunction with the fixed station identification, a reliable positional determination can be brought about by telegram transmission, particularly since the data from three neighbouring fixed stations is present.

Claims (13)

1. A method of radio transmission between a mobile station and a plurality of linearly arranged fixed stations transmitting on a common frequency and combined into n groups to operate within each group in mutually exclusive ranges, the method comprising the steps of transmitting a superordinate keying signal from an exchange through a modulation line to all the fixed stations for keying of transmitters thereof to effect transmission by the groups in succession of both data and an identification of each group, and transmitting from the mobile station to the fixed stations, on fault-free reception of the group transmissions by the mobile station, both a call confirmation in n time slots determined in accordance with the received group identifications and an identification of the time slot, the step of transmitting from the mobile station comprising transmitting n call confirmations in the time slots 1 to non reception of the transmission from the first group, transmitting n-m+1 call confirmations in the time slots m to n on reception of the transmission from the mth group and transmitting a single call confirmation in the time slot n on reception of the transmission from the nth group.

2. A method as claimed in claim 1, comprising the step of effecting intermediate storage of the call confirmations in the fixed stations receiving the confirmations.

3. A method as claimed in either claim 1 or claim 2, comprising the step of testing, by the mobile station, of the radio channel for occupation before transmission and then transmitting a call at least once at a given time together with an identification of the time slot.

4. A method as claimed in claim 3, comprising the steps of effecting intermediate storage of such call in the fixed stations, transmitting from each fixed station to the mobile station, on fault-free reception of such call by that fixed station, a respective acknowledgement in a time slot corresponding to the group to which that fixed station belongs, and transmitting the received call from the fixed stations to the exchange by way of the modulation line in a predetermined sequence.

5. A method as claimed in either claim 2 or claim 4, comprising the step of evaluating received call confirmations or calls in the time slot 1 by the fixed stations of the first group, in the time slots 1 to m by the stations of the mth group and in the time slots 1 ton by the stations of the nth group.

6. A method as claimed in claim 5, comprising the step of transmitting the last call confirmation or call received by each fixed station to the exchange in a time slot corresponding to the group to which that fixed station belongs.

7. A method as claimed in claim 6, comprising the step of causing, after transmission of a call by the mobile station, the exchange to send a cancellation command to the fixed stations for cancellation of calls intermediately stored therein, and causing those fixed stations of which call transmission to the exchange has not been cancelled to repeat such call transmission in a later time slot.

8. A method as claimed in claim 6, comprising the step of transmitting to the exchange with said last call confirmation or call an identification of the group to which said fixed station belongs.

9. A method as claimed in claim 8, comprising the step of transmitting to the exchange with said identification of the group an identification of the station number within that group.

10. A method as claimed in claim 6, comprising the step of transmitting from the fixed stations to the exchange an indication of the reception quality of call confirmations and calls received by the fixed stations.

11. A method as claimed in claim 6, comprising the step of interrupting the modulation line for the fixed stations more distant from the exchange during switching of those stations to the exchange.

12. A method as claimed in claim 1, comprising the step of transmitting from the mobile station together with the call confirmation an indication of the reception quality of transmission from the individual fixed stations.

13. A method of radio transmission substantially as hereinbefore described with reference to the accompanying drawings.