Radio system

Details Radio system Radio system

1995-05-25

1997-10-14

Pham, Chi H.

Telecommunications

Transmitter and receiver at separate stations

455 541, 455 70, H04B 726

Patent

active

056781920

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a radio system, comprising a fixed radio network having base stations and mobile radio stations, each mobile station with no ongoing call normally monitoring messages transmitted by a base station on a control channel in order to enable a fast call set-up.
Subscriber units used in mobile telephone systems are often hand-portable battery-powered telephones. Because the intention is to make portable subscriber units as small-sized and light as possible, very contradictory demands are made on the batteries to be used in them, viz. small size and as long operation time as possible by one charge. To achieve these properties, a portable subscriber unit is usually implemented by means of a technology consuming as little energy as possible, and the purpose is to minimize unnecessary power consumption in different ways. It is difficult to reduce the power consumption during a call. Also in an idle state, a subscriber unit without an ongoing call monitors the control channel of its base station for possible incoming messages, which implies that at least a receiver, a corresponding synthesizer circuitry as well as a control logic are in operation. It is not directly possible to entirely switch off the subscriber unit between calls, because possible messages from the fixed network may then be lost. For this reason, some cellular radio networks, such as NMT900 and GSM, use continuously a specific sleeping facility for energy saving, by means of which facility the system informs the subscriber unit by signalling on a control channel how long it may "sleep" safely, i.e. be in a state consuming little energy (with the receiver and the synthesizer switched off, for instance), without losing messages. The subscriber unit contains a timer function, which "awakens" the subscriber unit after a predetermined time. The system again attends to that the messages which have come to the subscriber unit during "sleeping" are not transmitted until the subscriber unit is "awake". However, the sleeping facility as per described above is problematic, if a fast call set-up time is required in the system simultaneously. Such systems are, e.g., private trunking radio networks used for transmitting commands, etc., from one subscriber to another. A call may come at any moment, and therefore, the subscriber unit has to be always "awake", so that a command may be passed through immediately. The wake-up facility as described above, in which the system controls the subscriber unit "to sleep", might delay a call set-up even by tens of seconds, which is not always acceptable for all users. For this reason, such a sleeping facility has not been applied to systems requiring fast call set-up, even though a reduction of power consumption of hand-portable subscriber units would be very desirable also in these systems.
U.S. Pat. No. 5,150,361 discloses a TDMA or TDMA/FDMA device having two operating modes: energy saving mode and normal operating mode. In the system described in the prior art document, time frames are transmitted, each of them comprising at least two control time slots. In the energy saving mode, all main parts of the device are shut down during the entire frame, except for one control time slot. In the normal operating mode, the device monitors both control time slots of each frame. In the example presented in the document, the length of a frame is 180 msec and a frame contains four time slots of 45 msec each. So the device is shut down for 135 msec in each frame and active for 45 msec. The shut down periods are thus very short and depend on the length of the time slot, which means only minor savings in energy.


SUMMARY OF THE INVENTION

An object of the present invention is to provide a radio system, which may implement a fast call set-up as well as a significant reduction in power consumption of a subscriber unit by causing the subscriber unit to "sleep" intermittently.
According to one aspect of the invention, the radio system described in the preamble is characterized in that the

REFERENCES:
patent: 4794649 (1988-12-01), Fujiwara
patent: 5146214 (1992-09-01), Yamada et al.
patent: 5150361 (1992-09-01), Wieczorek et al.
patent: 5257406 (1993-10-01), Ito
patent: 5517679 (1996-05-01), Yahagi

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