Multiplex communications – Communication over free space – Signaling for performing battery saving
Reexamination Certificate
2000-01-31
2002-10-22
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Communication over free space
Signaling for performing battery saving
C370S349000, C370S410000
Reexamination Certificate
active
06469990
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates, in general, to a method for controlling the reception of data packets in a receiving unit of a mobile station such that power consumption of the mobile station can be conserved, and to such a mobile station.
Such methods for controlling reception of data packets in a receiving unit of a mobile station in a mobile radio system, and such mobile stations having control apparatus for controlling reception of data packets in a receiving unit in the mobile station are known from the prior art. During a call, that is to say when connected to a present base station, and during readiness to receive, that is to say when in the idle state, a mobile station in a mobile radio system has to regularly search predetermined frequencies for data packets from adjacent base stations and has to recognize their identity while it is connected to the present base station. As a rule, the identity is recognized by decoding the so-called BSIC (Base Station Identity Code) in the synchronization data packet. To do this, each base station regularly transmits synchronization data packets. In the GSM Standard, the base stations transmit a synchronization data packet with a duration of one time slot every ten or eleven time frames, with eight time slots forming one time frame.
In the GSM Standard, during a call, a mobile station can monitor an adjacent channel every 26 frames, for a period of somewhat more than one time frame. This one time frame is the so-called idle frame, in which the mobile station does not interchange data with the present base station. The idle frame is used to monitor adjacent channels and, if necessary, to find and to decode synchronization data packets from adjacent base stations. In the GSM Standard, the base stations transmit five synchronization data packets, with a duration of one time slot, within each multiple frame, which comprises 51 time frames. These synchronization data packets are transmitted by the base stations four times every ten frames, and then once after eleven frames. Since the mobile stations have an idle frame for monitoring the adjacent channels once in each 26 time frames, a mobile station can receive a synchronization data packet from an adjacent base station at the latest after eleven idle frames, irrespective of the relative timing of the synchronization data packets. Rather than monitoring a specific adjacent channel in two successive idle frames, another known option is to switch the mobile station to receive data packets from the adjacent base station in every other idle frame. This method is somewhat more elegant, but doubles the mean time that passes before reception of a synchronization data packet from an adjacent base station.
If a mobile station is ready to receive, that is to say in the idle state, more time is available for monitoring adjacent channels, since there is no need to interchange data continuously with the present base station. The mobile station can then continuously be switched to receive data packets from in each case one adjacent base station, and thus recognizes a synchronization data packet from an adjacent base station at the latest after eleven time frames. If it is not possible to receive data packets from one adjacent base station since, for example, the distance between the mobile station and the base station is too great or there is excessive interference on the transmission path, then this is confirmed after eleven time frames when the mobile station is ready to receive and after 26×11 time frames during a call.
In the method known from the prior art and the apparatus for controlling reception of data packets in a mobile station, the receiving unit of the mobile station is switched to receive synchronization data packets. That is to say a search is carried out for synchronization data packets from the respective adjacent base stations. The mobile station uses the synchronization data packets to synchronize itself to the adjacent base stations, in order to allow a handover from a present base station to an adjacent base station. In the GSM Standard, the base stations always transmit a frequency correction data packet one time frame before the synchronization data packets. This frequency correction data packet is used to match the frequency of the crystal oscillator in the mobile station to the base station when a link is set up (or set up again) from a mobile station to an adjacent base station. Since the crystal oscillator in the mobile stations is not generally sufficiently frequency-stable, the mobile station uses the frequency correction data packet to determine the frequency of the base station relative to the frequency of the crystal oscillator when it synchronizes itself to a base station for the first time.
A disadvantage of the methods and apparatus known from the prior art for controlling reception of data packets in a receiving unit of a mobile station in a mobile radio system is that the receiving unit in the mobile station is switched on in each time frame associated with a specific adjacent base station (for example the idle frames during a call), in order to attempt to receive synchronization data packets from the respective base station. This means that the receiving unit is switched to receive synchronization data packets even if there is no chance whatsoever of being able to receive synchronization data packets from the respective base station. However, switching on the receiving unit in the mobile station costs energy and reduces the call time and the time during which the mobile station is ready to receive.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a method and an apparatus to ensure that power consumption in the mobile station is reduced.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for controlling reception of data packets in a receiving unit of a mobile station in a mobile radio system. The receiving unit can in each case be switched during predetermined time frames to receive data packets to be detected from base stations, in which case a plurality of predetermined time frames are each assigned to receive data packets from a specific base station. The base station transmits characteristic data packets at a predetermined time interval before the data packets to be detected. The receiving unit is also switched to receive characteristic data packets from the respective base station during the predetermined time frames in which it is switched to receive data packets to be detected. If it does not receive either a data packet to be detected or a characteristic data packet from the respective base station in a predetermined time frame, the receiving unit is not switched to receive data packets from this base station during the next predetermined time frame which is assigned to this base station because no data packet to be detected from this base station can occur.
In accordance with the invention, a mobile station in a mobile radio system is correspondingly provided with a control apparatus for controlling reception of data packets in a receiving unit in the mobile station. The control apparatus can in each case switch the receiving unit during predetermined time frames to receive data packets to be detected from base stations. A plurality of predetermined time frames are in each case assigned to receive data packets from a specific base station, and the base stations transmit characteristic data packets at a predetermined time interval before the data packets to be detected. The control apparatus also switches the receiving unit to receive characteristic data packets from the respective base station during the predetermined time frames in which it switches this receiving unit to receive data packets to be detected. If it does not receive either a data packet to be detected or a characteristic data packet from the respective base station in a predetermined time frame, the receiving unit does not switch to recei
Hsu Alpus H.
Qureshi Afsar M.
LandOfFree
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