Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
1998-07-20
2001-09-04
Chang, Vivian (Department: 2682)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S071000, C455S502000
Reexamination Certificate
active
06285864
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns a method for adjusting or setting a transmitter carrier frequency in a subscriber station of a point-to-multipoint radio transmission system, in which a base station is provided with as many modems as the maximum number of subscriber stations that can be connected with it and similarly each subscriber station has a modem.
This sort of point-to-multipoint radio transmission system is described in the unpublished German Patent Application 196 355 33.8. In this radio transmission system communication between the base station and the individual subscriber stations occurs by frequency division multiple access (FDMA). Thus the flexible transmission capacity is designed for the needs and number of the subscribers, since the bandwidth of the individual transmitter channels is adjusted to the data transmission rate required by the respective individual subscribers stations. Flexible assignment and adjustment of the transmission capacity is possible in the connected subscriber stations without interference and interruption. Also every modem in the base station and in the individual subscriber stations has at least two transmitter and at least two receiver channels, and the signal transmission between the base station and one of the subscriber stations occurs first only over one transmitter and receiver channel. When the transmitter channel is changed, a control device sets the new transmission parameters (channel carrier frequencies, data rate, modulation, coding and transmitter signal level) in the at least one transmitter or receiver channel not found in operation, while the signal transmission in the other transmitter or receiver channel is continued. After finishing acquisition of the channel with the new transmission parameters switching to the transmitter or receiver channel not previously in operation occurs.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process of the above-described kind for synchronization of the transmitter and receiver carrier frequencies of the base station and the subscriber stations with minimal hardware expense.
This object, and others which will be made more apparent hereinafter, is attained in a method for adjusting or setting a transmitter carrier frequency in a subscriber station of a point-to-multipoint radio transmission system, in which a base station is equipped with as many modems as the maximum number of subscriber stations that can be connected with it by radio transmissions and similarly each subscriber station has a modem.
According to the invention, all receiver carrier frequencies and all transmitter carrier frequencies of the base station are derived from a common reference frequency; a transmitter carrier frequency of a transmitter carrier propagated from a respective subscriber station is compared with the corresponding receiver carrier frequency in the base station; an average frequency deviation between the transmitter carrier frequency of the subscriber station and the receiver carrier frequency of the base station is transmitted to the subscriber station and the transmitter carrier frequency of the subscriber station is adjusted so that the frequency deviation is minimized.
In preferred embodiments also the receiver carrier frequency of the subscriber station is changed according to the frequency deviation so that the frequency deviation is minimized.
Because all transmitter and receiver carrier frequencies are derived from a single reference in the base station, the relative positions of all carrier frequencies with respect to each other are comparatively very stable. The position of the carrier frequencies of the individual subscriber stations adjusts itself to the relative position of the carrier frequency in the base station. One can thus use free-running local oscillators in the base station and in the subscriber stations, which do not need to be synchronized with each other with expensive circuitry.
In other embodiments each modem in the base station and in the subscriber stations has two transmitter channels and two receiver channels. Switching from one transmitter/receiver channel to the other transmitter/receiver channel occurs, when data should be transmitted with another pair of transmitter and receiver frequencies. Prior to the switching of the transmitter and receiver channels the new transmitter and receiver carrier frequencies for the concerned subscriber station are derived from the frequency deviation between the previous transmitter carrier frequency of the subscriber and the previous receiver carrier frequency of the base station and from the new transmitter carrier frequency and the new receiver carrier frequency of the base station.
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Bollmann Andreas
Ruemmer Wolfgang
Appiah Charles N.
Chang Vivian
Robert & Bosch GmbH
Striker Michael J.
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