Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Patent
1996-01-16
1998-03-31
Eisenzopf, Reinhard J.
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
455 132, H04B 700
Patent
active
057349851
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to mobile communications, and in particular to cases where there are a plurality of base stations which provide radio communication channels to mobile stations, and where these plurality of base stations transmit identical paging signals simultaneously and at the same frequencies. This invention specifically relates to phase synchronization technology for the signals transmitted by this plurality of base stations.
BACKGROUND TECHNOLOGY
A prior art example will be explained with reference to FIG. 10, which is a block diagram serving to explain phase synchronization according to the prior art example. The explanation given here will deal with the case of a radio paging system in which the mobile stations comprise receivers and do not have transmitting devices. In a radio paging system, paging signals are transmitted from a plurality of base stations 30-37 at the same frequencies, and it is therefore necessary for the transmission timing of the radio signals at each base station 30-37 to be synchronized. The paging signals are transmitted to base stations 30-37 from central station 1 by means of links 20-27 (as a rule, these are wire circuits). By adding a fixed delay to the aforementioned paging signals at base stations 30-37, they will be transmitted as radio waves at the same frequencies in such manner that the transmission timing at base stations 30-37 becomes synchronized.
A widely used method to synchronize base stations 30-37 is to have base stations 30-37 receive (i) the paging signals transmitted via links 20-27 and (ii) paging signals from a reference base station, these latter paging signals being transmitted as radio waves. The respective reception timings of these paging signals are extracted and any time differences corrected by means of delay circuits, thereby keeping the radio signal transmission timing of any given base station in step with the radio signal transmission timing of the reference base station.
However, in a conventional phase synchronization system of this sort, because reception timing measurement errors in respect of links 20-27 and reception timing measurement errors in respect of radio waves received through the air accumulate, synchronization accuracy deteriorates, and, especially when transmission speed is high, the synchronization timing may no longer come within the required range.
In Japanese Unexamined Patent No. 61-62244 there is disclosed a system wherein a time signal generator, i.e., a reference clock, is provided in central station 1 and in each base station 30-37. This system is constituted so that the phase of the radio signals transmitted from central station 1 and base stations 30-37 is transmitted in accordance with time information generated by these references clocks. In addition, time correction of these reference clocks is performed in accordance with correction information transmitted from central station 1. In this case, however, because the delay time of the correction information will differ according to the length of the link between central station 1 and a given base station 30-37, time correction cannot be carried out with more than a certain limiting accuracy. One solution considered as regards this problem is to compensate for delay time differences in accordance with distance information for each link. This would be possible if the communication links connecting base stations 30-37 with central station 1 were invariably fixed-length links. However, in many cases the routes of the communication links connecting central station 1 and base stations 30-37 will vary in accordance with traffic conditions at any given time, and under such circumstances accurate correction of the reference clocks will be impossible.
Even if the reference clock provided at each base station in a system of the sort described above could be accurately corrected so that transmission could be carried out in synchronization with the reference clocks, the following sorts of problems would remain. Namely, the paging signals transmitted
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Ito Shogo
Murata Mitsuru
Nishikawa Nobuhiro
Nozawa Toshihiro
Eisenzopf Reinhard J.
Kincaid Lester G.
NTT Mobile Communications Network Inc.
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