Multi-band mobile telecommunications station

Abstract: A mobile telecommunications station for use in a multiple network environment is disclosed. The mobile telecommunications station includes a radio receiver capable of operating in a plurality of different frequency bands used by different networks. The mobile telecommunications station further includes a network preference data storage for storing data which identifies a level of priority for each network. At least one of the networks is a preferred network, and a search controller determines the search frequency at which each network is searched in accordance with the preference data.

Description: This invention relates to a multi-band mobile telecommunications station for use in a multiple network environment, for example an environment in which there is a network of terrestrial base stations and another network of orbiting satellite stations. Description of the Related Art: The mobile station needs to be able to establish a connection when it is in the coverage zone of any terrestrial base station or orbiting satellite station, but the operations required to enable the mobile station to search for such stations are power consuming. EP-A-0 283 955 relates to an apparatus for selecting control channels in a mobile communication system. In a mobile communication system having two operating systems co-existing in one area, and a mobile station having a transmitting and receiving circuit and a control unit subscribing to one of the two mobile communication systems for selecting a control channel thereof, a normal scan of the control channel of the subscribed-to system is activated, and then an extra scan of the control channel is activated when the control channel is not available during the normal scan, thereby reducing the possibility of an involuntary use of a non-subscribed-to system when the mobile station is temporarily in a blind section of the subscribed-to system for a while. WO 98/10617 A discloses methods and apparatus for performing automatic mode selection in a multi-mode mobile terminal. A wireless terminal, such as a multimode cellular telephone, includes at least three master control systems, specifically a primary system controller, a secondary system controller, and a multimode controller. The multimode controller is capable of bidirectionally exchanging control messages and status messages with the primary and secondary system controllers for automatically switching the state of the terminal bidirectionally between the primary and secondary systems. US-A-5,517,677 relates to adaptive weighting of a scanning sequence. A programmable queue is written with a communication channel identity code based on a predefined criterion, such as each time the channel is actually used. The preferential queue is scanned in association with all the remaining communication channel identity codes, thereby providing a weighting factor that is skewed toward the selection of channels that have experienced actual use. System identification codes utilized in a mobile radio complex are stored in the queue in accordance with a roaming function, and group identity codes are stored in the queue when scanning home channels of mobile radio systems to determine incoming calls. It is accordingly an object of the present invention to provide a mobile telecommunications station which overcomes this problem. The object is achieved by the features of the claims. A mobile telecommunications station in accordance with the invention includes a radio receiver capable of operating in a plurality of different frequency bands used by different networks, network preference data storage means for storing data which identifies a level of priority for each network, at least one of the networks being a preferred network, and a search control means determining the search frequency at which each network is searched in accordance with the preference data. The search control means preferably varies the search strategy according to the network stations found in a previous search. For example, in GSM/Satellite dual mode mobile station, the search control means would normally reduce the frequency of satellite searches to a minimum. When the mobile station was not in the coverage zone of any GSM or Satellite base station, the frequency of both satellite and GSM scans would be increased. When the mobile station was not in the coverage zone of any GSM base station, but still in the coverage zone of a satellite network, the frequency of GSM scans would not be reduced. The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention. Fig. 1 is a block diagram of a multi-band multi-mode mobile telecommunications station; and Fig. 2 is a flowchart of software used in the mobile station to control scanning operations. Fig. 1 shows the basic blocks of the mobile phone, namely an RF stage 10 for receiving and transmitting, an interface stage 11 which includes frequency translation components and filtering, calibration, DAC and ADC functions, a DSP 12 which implements speech coding and decoding and various frequency control and synchronisation algorithms, and a CPU 13 which exercises control over the functioning of the phone in accordance with data stored in ROM 14 and in a SIM module (personal ID card) 15. The CPU is, in particular, responsible for the timing of scans for nearby terrestrial base stations and for satellite stations. During scanning operations, the CPU commands the DSP to scan up to three frequency values during one TDMA frame. The CPU provides the DSP with the three frequency values to check, and progressively scans through the whole terrestrial band. This cycling normally continues until there is a detected signal sufficiently strong for AGC to be established within the RF stage and then RSSI levels are received. The CPU orders the frequencies in increasing levels of RSSI. If any is above a threshold value, the CPU commands the DSP to synchronise to the channel. The DSP attempts to decode broadcast messages by first synchronising its operation to the exact timing and frequency of the transmission and then attempts to decode a synchronisation burst. If this is successful this is registered by the CPU and the mobile station leaves out-of-zone (OOZ) operation and "camps" on the channel found. Operations in the terrestrial and satellite bands involve different RF tuning procedures and different protocols for channel recognition and signal decoding. Thus, when searching terrestrial channels the DSP, interface and RF stages must operate in one mode and when searching for satellite channels, the same blocks must operate in a different mode. Fig. 1 shows each of the blocks 10, 11, 12 with a mode control switch 10 a , 11 a and 12 a controlled by the CPU for switching the blocks between modes when necessary. The CPU is programmed to give priority to terrestrial operation. Network preference data is stored in the CPU ROM (preferably EEPROM) or in the SIM as a list of networks at successive addresses in the memory. The list could contain names for the networks, such as GSM 900 MHz, GSM 1800 MHz, satellite, or tokens for the network names, the networks being listed in order of preference. In the example described herein GSM 900 MHz is the most preferred network and satellite the least preferred. Such prioritisation is illustrated in Fig. 2. As shown, based on decisions as to whether the mobile station is currently in OOZ operation or is camped on a satellite or terrestrial channel, the CPU instructs the DSP to search at different intervals. If the mobile stations is in OOZ operation, then terrestrial searches are carried out every thirty seconds and satellite searches every two minutes. If the mobile station is camped on a satellite network channel, the terrestrial band is searched every two minutes. If the mobile station is camped on a terrestrial channel, the satellite band is searched every five minutes. It will be clear to those skilled in this art that the principle described above can be extended to mobile stations capable of operating in three or more bands and in three or more different modes. While a preferred embodiment of the present invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be mode without departing from the scope of the following claims.

Claims: A mobile telecommunications station, comprising: a radio receiving means for operating in a plurality of different frequency bands used by different networks; coverage zone determination means for establishing a time-based search interval; network preference data storage means for storing data which identifies a level of priority for each network, wherein at least one of the networks is a preferred network; and search control means for determining the number of times each network is to be searched in a predetermined interval, in accordance with the preference data received from said network preference data storage means, wherein the search control means is for varying a search strategy for the networks based on the networks found in a previous search and is for searching the other networks less frequently than it searches its preferred network when the mobile telecommunications station is camped on a communications channel of its preferred network. The mobile telecommunications station as claimed in claim 1 wherein said coverage zone determination means is for varying the time-based search interval for searching each network according to whether said mobile telecommunications station is camped on the communications channel or is operating in an out-of-zone mode. The mobile telecommunications station as claimed in claim 2 wherein the search control means is for searching the preferred network more frequently than the other networks when said mobile telecommunications station is operating in an out-of-zone mode. The mobile telecommunications station according to any of claims 1 to 3 being for communicating with a terrestrial base station and an orbiting satellite station. The mobile telecommunications station according to any of claims 1 to 4 wherein said coverage zone determination means is for determining whether said mobile telecommunications station is camped on a communications channel or is operating in an out-of-zone mode. The mobile telecommunications station according to any of claims 1 to 5 wherein the communications channel is either a satellite or terrestrial channel. A mobile telecommunications station according to any of claims 1 to 6 wherein said radio receiving means comprises: a radio receiver/transmitter (10), an interface (11) for receiving an input from said radio receiver and performing frequency translation, and a digital signal processor (12) for receiving an input from said interface to implement speech coding/decoding by synchronizing its operation to a timing and frequency of the input from said interface; said network preference data storage means is a memory, and said search control means is a central processing unit (13) for receiving inputs from said digital signal processor and said memory to execute time-based search intervals for detecting one of said different networks being nearby terrestrial stations and satellite stations from the network preference data, and commanding said digital signal processor to scan a plurality of frequency bands until a signal is detected which exceeds a predetermined threshold value. The mobile telecommunications station according to claim 7 wherein said memory is a read only memory (14). The mobile telecommunications station according to claim 7 wherein said memory is a personal ID card (15). The mobile telecommunications station according to any of claims 7 to 9 wherein said memory is for storing the network preference data in order of preference. The mobile telecommunications station according to any of claims 7 to 10 wherein the central processing unit is programmed to give priority to terrestrial operation.

Inventors: GRAYSON MARK, JOUIN CHRISTOPHE, GRAYSON, MARK, JOUIN, CHRISTOPHE, Grayson, Mark, c/o NEC Techn. (UK) Ltd., Jouin, Christophe, c/o NEC Techn. (UK) Ltd.
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1998
Main classification: H04Q7
IPC codes: H04B7, H04W88, H04W52, H04W48