Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-04-27
2001-10-23
Hunter, Daniel (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S466000, C455S515000, C455S553100
Reexamination Certificate
active
06308068
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates to a method and an arrangement in a communication network. More precisely the invention relates to a method and an arrangement for controlling scanning of radio channels by a mobile station operating in standby mode in a radio communication network.
DESCRIPTION OF RELATED ART
A mobile station in standby mode (idle mode), i.e. when neither originating or receiving a call, is monitoring a control channel in a serving cell of a first cellular network for the purpose of receiving system information and paging messages.
While in standby mode and thus monitoring the control channel of the serving cell, there is often also a need for the mobile station to scan for other radio channels. There may be several different reasons for performing channel scanning e.g. finding a control channel in the first network having superior signal quality or finding a control channel of a second preferred network.
In networks using time division multiple access (TDMA) technology, e.g. networks according to the GSM or PDC standards, each control channel is only allocated certain time slots. Some of the remaining time slots may be used by the mobile station for channel scanning. As an example, a GSM mobile station operating in a visited network uses some of the remaining time slots to scan for both control channels of the visited network having superior signal quality as well as control channels of a home network.
In many other networks using other technologies than TDMA, e.g. Frequency Division Multiple Access (FDMA) or Code Division Multiple Access (CDMA), the control channel information is transmitted continuously without any time gaps. Examples of such networks are networks according to the AMPS, TACS or NMT standards. Since the control channel information is transmitted continuously the mobile station is at all times busy monitoring the control channel of the serving cell and hence there is no free time available to scan for other radio channels. The basic problem is that if the mobile station were to scan for other radio channels during certain time intervals, the mobile station runs the risk of missing paging messages indicating incoming calls to the mobile station.
U.S. Pat. No. 5,260,988 describes a dual mode cellular cordless portable radiotelephone. The radiotelephone preferentially selects to operate in a cordless system over a cellular network. When the radiotelephone is operating in the cellular network, the radiotelephone scans for a radio channel associated with the cordless system. When said radio channel is detected, the radiotelephone changes its mode of operation and starts operating in the cordless system. When operating in the cellular network, the radiotelephone must monitor a control channel for page messages indicating an incoming call. Each page message is repeated. The radiotelephone schedules the scanning for radio channels in a way that ensures the radiotelephone never misses an incoming call because it was scanning for radio channels during both page messages transmission times. The scheduling is done by determining two fixed time periods, one for monitoring the control channel and one for channel scanning, having a special relationship derived from the time between the two page messages and the time needed to transmit one page message.
A disadvantage of the described way of scheduling channel scanning is that there is an increased risk that an incoming call will not be detected by the radiotelephone since the radiotelephone only monitors the control channel when one of the two page messages are transmitted.
The international patent application WO 95/34178 describes a channel scanning method for use in a cellular network. The method involves transmitting from a base station a control signal to at least one mobile station for informing them that no pages will be issued for a predetermined time period. Upon receipt of said control signal the mobile station scans for radio channels in the network having superior characteristics during said time period. If such a channel is found, the channel number is stored in the mobile station for later use.
This channel scanning method requires that there is a special control signal (message), e.g. the battery saving order message in networks of the NMT type, indicating the time during which no pages will be issued and the method can thus only be used in networks where such a special message is transmitted.
The international patent application WO 94/27377 describes a method for reducing standby power consumption of a mobile station. The method involves receiving messages in a mobile station from a base station. The messages comprises repeated blocks of information bits, each block having a number of data bits and check bits whose value depends on the data bits. Check indication is generated when the data bits and check bits are consistent with each other. When a check indication is generated, portions of the mobile station are turned off until receipt of a next block of non redundant information is expected.
The described method is solely directed to the problem of reducing standby power consumption in the mobile station.
SUMMARY OF THE INVENTION
The problem dealt with by the present invention is enabling a mobile station, operating in standby mode and monitoring a control channel in a first radio communication network, to scan for other radio channels without missing information on the control channel intended for the mobile station.
The problem is solved essentially by a method implemented in the mobile station in which upon receipt of a message on the monitored control channel, the mobile station dynamically determines a time period during which no new information intended for the mobile station will be transmitted. At least part of said time period is then used for scanning of other radio channels. The problem solution includes the necessary means for implementing the method in the mobile station.
More specifically, the problem is solved in the following manner. Each message comprises at least one block of information bits. The information bits comprises a number of data bits and a number of check bits whose value depend on said data bits. When the data bits are considered as correctly received, a first indication is generated. Upon generation of said first indication, a time period is determined during which the blocks of information conveying the message contains no new information for the mobile station. At least part of said time period is then used for scanning of other radio channels.
According to one embodiment of the invention, applicable when the information blocks are repeated a number of times, once the mobile station has correctly received an information block, said time period is determined as lasting until receipt of a next block of non redundant information is expected.
According to a second embodiment of the invention, applicable when said message comprises at least two information blocks and the mobile station can determine from the received subset of information blocks that the message is not intended for the mobile station, said time period is determined as lasting until receipt of a next message is expected.
A general intention of the invention is to provide the mobile station with a method and an arrangement for scanning for other radio channels without increasing the risk for missing information intended for the mobile station transmitted on the monitored control channel.
Another intention is to provide a method and an arrangement for channel scanning that further does not require the transmission of a special message to the mobile station with an explicit indication of a time period during which no page messages will be transmitted to the mobile station.
One advantage afforded by the invention is that the mobile station may scan for other radio channels without an increased risk for missing information intended for the mobile station transmitted on the monitored control channel.
Another advantage is that the invention does not require the transmission of a sp
Hunter Daniel
Jenkens & Gilchrist A Professional Corporation
Telefonaktiebolaget LM Ericsson (publ)
Tran Pablo
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