Patent Publication Number: US-2007123290-A1

Title: Low power transmission mode

Description:
RELATED APPLICATIONS  
      This application claims priority under 35 U.S.C. § 119 based on U.S. Provisional Application Ser. No. 60/739,961, filed Nov. 28, 2005, the disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD OF THE INVENTION  
      The present invention relates to a mobile terminal for use in power sensitive environments. The mobile terminal uses a reduced or low power transmission mode when operating in power sensitive environment, e.g. inside an airplane. The invention also relates to a method for operating a mobile terminal using a low power transmission mode.  
     DESCRIPTION OF RELATED ART  
      The popularity and use of mobile terminals or mobile telephones has skyrocketed through the past 20 years. People now take their mobile telephones with them everywhere, even when they travel. One place where the use of mobile telephones is, however, restricted is on airplanes and in other power sensitive environment, such as hospitals. The use of mobile telephones in airplanes is restricted because the high power transmissions from the mobile telephone may interfere with the systems of the airplane used during flight.  
      The airlines have used various airphone systems to provide their passengers with the ability to make telephone calls during a flight. These systems however require the passenger to use one of the telephones provided in the airplane by the airlines. Typically, these systems utilize corded telephones which are wired into the seatbacks of some of the seats in the cabin of the aircraft. Since the telephones are wired into the telephone system high transmission power levels are not a concern. Unfortunately, there are several problems with these telephone systems. Other passengers may be using the telephones when a passenger wishes to make a call or the nearest telephone may be broken or out of service. Furthermore, these telephone systems are very expensive to install and maintain. Finally, passengers, if given the option, would rather use their own mobile telephones.  
      As mentioned above, the problem with using mobile telephones on an airplane is the possibility of interfering with the flight systems of the airplane. For example, in a communication system, such as GSM (Global System for Mobile Communication), UMTS (Universal Mobile Telecommunications System), Enhanced Data for GSM Evolution), GPRS (General Packet Radio Service) systems, a random access burst is transmitted by the mobile telephone on the random access channel (RACH) at initial setup. The random access burst is always transmitted at full power. These full power transmissions, of course, may interfere with the systems of the aircraft. Another problem with these communication systems is that when a first base station has been found, the mobile telephone continues to search for other (better) base stations. So even if a base station were located in an aircraft, the mobile telephone will continue to search for other base stations which are external to the airplane. For example, a mobile telephone connected to a base station in an airplane might find a base station on the ground and attempt to switch to that base station. All of this searching results in high power transmissions by the mobile telephone that may interfere with flight systems of the airplane.  
      Thus, there is a need for a method and apparatus for allowing mobile telephones to operate in power sensitive environments by controlling the power level of transmissions from the mobile telephone.  
     SUMMARY OF THE INVENTION  
      According to an embodiment, a method for operating a mobile terminal using a low power transmission mode, comprises transmitting an access request to a base station; receiving, in response to the access request, from the base station a request to transmit using a low power transmission mode; and communicating with the base station using a reduced transmit power level.  
      The receiving may comprise receiving at least an identification code, which is a request to transmit using the low power transmission mode and which identifies the base station as a special base station.  
      The receiving may comprise receiving a request to disable a base station search function.  
      The transmitting may comprise using a predetermined reduced transmit power setting, which is less than the maximum possible transmit power setting, to transmit the access request.  
      The method may comprise receiving an assigned reduced transmit power level from the base station for subsequent transmission while in the low power transmission mode.  
      The method may comprise receiving the request to transmit from a special base station, which is a base station in an aircraft.  
      The method may comprise receiving the request to transmit from a special base station, which is operating in a power sensitive environment.  
      The method may comprise transmitting the access request using maximum transmit power when said mobile terminal is not in the low power transmission mode. The receiving may comprise receiving a request from the base station to switch to the low power transmission mode when the maximum power is above a predetermined level.  
      The method may comprise comparing the identification code to at least one identification code stored in the mobile terminal to determine if the received identification code is for a special base station.  
      The method may comprise disabling search for a base station when a base station is not located using the low power transmission mode.  
      According to another embodiment, a mobile terminal capable of operating in a low power transmission mode comprises a processor; a transmitter adapted to transmit an access request to a base station; and a receiver adapted to receive, in response to a transmitted access request, from the base station a request to transmit using a low power transmission mode. The transmitter is adapted to communicate with the base station using a reduced power level in the low power transmission mode.  
      The processor may be adapted to determine whether an identification code, which is received in the request to transmit, identifies a special base station and disable a base station search function when the base station is a special base station.  
      The transmitter may be adapted to transmit the access request using a predetermined reduced power setting when the mobile terminal is in the low power transmission mode.  
      The receiver may be adapted to receive an assigned reduced power level from the base station for subsequent transmission while in the low power transmission mode.  
      The mobile terminal may be a portable or handheld mobile radio communication equipment, a mobile radio terminal, a mobile telephone, a smartphone, or a communicator.  
      According to another embodiment, a method for operating a base station in a power sensitive environment comprises receiving an access request from a mobile terminal; determining the power level of the access request; and sending a request for the mobile terminal to enter a low power transmission mode when the power level of the access request is above a predetermined level.  
      The sending may comprise sending to the mobile terminal an identification code, which identifies the base station as a special base station, which is a request to enter a low power transmission mode.  
      According to another embodiment, a base station for operating in a power sensitive environment comprises a receiver operative to receive an access request from a mobile terminal; a processor operative to determine the power level of the access request; and a transmitter operative to send a request for the mobile terminal to enter a low power transmission mode when the power level of the access request is above a predetermined level.  
      The transmitter may be operative to send to the mobile terminal an identification code, which identifies the base station as a special base station, which is a request to enter a low power transmission mode.  
      According to another embodiment, a computer program product comprises computer program code portions for executing the method for operating a mobile terminal when said computer program code portions are run by an electronic device having computer capabilities.  
      The computer program product comprising computer program code portions for executing the method for operating a mobile terminal may be comprised on computer readable medium, a record medium, or in a signal.  
      According to another embodiment, a computer program product comprises computer program code portions for executing the method for operating a base station when said computer program code portions are run by an electronic device having computer capabilities.  
      The computer program product comprising computer program code portions for executing the method for operating a base station may be comprised on computer readable medium, a record medium, or in a signal.  
      Further embodiments of the invention are defined in the dependent claims.  
      The mobile terminal may be a portable or handheld mobile radio communication equipment, a mobile radio terminal, a mobile telephone, a smartphone, a communicator, or any other electronic device with wireless voice communication capabilities.  
      Some embodiments of the invention provide for low power transmission mode for mobile terminals when they are in a flight mode.  
      It is an advantage of embodiments of the invention that the mobile terminal operates without affecting the flight systems of an aircraft while saving power by operating at lower power transmission levels.  
      It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Further objects, features and advantages of embodiments of the invention will appear from the following detailed description, reference being made to the accompanying drawings, in which:  
       FIG. 1  is a block diagram of a mobile terminal according to one embodiment of the invention;  
       FIG. 2  is schematic view of a communication system according to one embodiment of the invention;  
       FIG. 3  is a block diagram of a communications system in an aircraft according to one embodiment of the invention;  
       FIG. 4  is a flow chart of one embodiment of the method for operating a mobile terminal using a low power transmission mode according to one embodiment of the invention;  
       FIG. 5  is a block diagram of a base station according to one embodiment of the invention; and  
       FIG. 6  is a flow chart of one embodiment of the method for operating a base station in a power sensitive environment according to one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       FIG. 1  illustrates a mobile terminal  1 . The mobile terminal  1  may comprise a man-machine interface, such as a keypad  2 , a display  3 , a joystick  4 , a microphone  5  and a loudspeaker  6 , though which a user may interact with the mobile terminal  1 . The mobile terminal  1  may be a portable or handheld mobile radio communication equipment, a mobile radio terminal, a mobile telephone, a communicator, a smartphone or any other electronic device with wireless voice or data communications capabilities. Thus, the mobile terminal  1  may be connected to a network  10 .  
      The mobile terminal  1  may comprise various applications for carrying out functions within the mobile terminal  1 . The applications may be provided within an operational platform. Alternatively or additionally, the applications may be provided within a communication platform. The operational platform may comprise systems software run by an application processor, such as a CPU (Central Processing Unit)  7 , which may also be referred to as the ACPU (Application CPU). Similarly, the communication platform may comprise both hardware and software for carrying out e.g. communication with the network  10 . Thus, also the communication platform may comprise a CPU, which may be referred to as a CCPU, (Communication CPU), for providing various applications. The ACPU and the CCPU may run different operational systems. Also, the communication platform and the operational platform may interact to exchange information.  
      The mobile terminal  1  further comprises a transmitter  11  and a receiver  12  (or a transceiver) for sending and receiving signals to and from the network  10 . The mobile terminal may also comprise a transmit power controller  13  for controlling the transmit power used by the mobile terminal  1 . The transmit power controller  13  may form part of the transmitter.  
       FIG. 2  illustrates a communication system  100 , which includes a power sensitive environment, according to one embodiment of the invention. In this illustrative example, the power sensitive environment is inside an aircraft  102 , such as an airplane. The invention also pertains to any other power sensitive environment such as an airport, airport terminal, nuclear power plant, a hospital etc., and the invention is not limited thereto.  
      The communications network  100  may be a cellular communications system, which may be comprised of a plurality of mobile terminals communicating through a plurality of earth-based base stations  108   a - c . The base stations may be connected to the public switched telephone network (PSTN)  110  in a known manner. Furthermore, the communications network  100  may also comprise a satellite  112  for further facilitating communication between the mobile terminals.  
      The aircraft  102  is flying through a plurality of cells (not illustrated), which may be serviced by the earth-based base stations  108   a - c . The aircraft  102  comprises an aircraft base station (ABS)  104  and at least one mobile terminal  106 . As will be explained below in more detail, the mobile terminal  106  may communicate with devices both inside and external to the aircraft  102  using the communications network  100 . The mobile terminals  106  communicate with the aircraft base station  104  using reduced power transmission so as to not interfere with the systems of the aircraft  102 . The passenger air-to-ground communications between the aircraft  102  and ground based devices e.g. telephones may be achieved by transmission from the aircraft base station  104  and the ground based base stations  108   a - c  via a radio communication link  116 . Alternatively, the aircraft base station  104  may use a radio communication link  118  to the satellite  112  to facilitate the communications between the mobile terminals  106  and the ground based telephones.  
      The earth based base stations  108   a - c  may be base stations that are dedicated for communication with aircrafts. The earth based base stations may be co-located with or operatively connected to base stations for other communications networks, such as a GSM, a UMTS, a GPRS and/or an EDGE communication network. Thus  
      Reduced transmit power or power level when used herein means a transmit power or power level, which is less than the maximum transmit power or power level, which the mobile terminal  106  is capable of using. The reduced transmit power may be within a certain lower range of the transmit power range useable by the mobile terminal  106 . The certain range may e.g. be below 100 mW and above 1 mW. The maximum allowable transmit power of the reduced transmit power may e.g. be set dependent on the maximum expected attenuation of signals communicated in the environment of the base station.  
      For a base stations search in a low power transmission mode, the transmit power level may e.g. be 5 mW output power, which is the minimum output power for GSM. Alternatively, the transmit power level for a base station search in the low power transmission mode may be 5 mW output power. These levels are only examples. Other example may apply, which has to be tested and evaluated in each particular case.  
      The transmit power may e.g. be reduced by controlling the transmit power applied by a power amplifier of the transmitter. After set up of a communication link, the transmit power may be controlled by the base station.  
      The radio communication links  116 ,  118 , and the communication links between the base station  104  and the mobile terminal  106  typically comprise at least one pilot signal and a plurality of radio frequency voice channels, but the invention is not limited thereto. Each base station  108   a - c  broadcasts a pilot signal for the benefit of the aircraft  102 . The pilot signal informs the aircraft  102  of various types of information, e.g., voice channel availability, frequencies, etc.  
       FIG. 3  illustrates a communication system for use in the aircraft  102 . As mentioned above, the aircraft communications system comprises an aircraft base station  104  and at least one mobile terminal  106   a - f . It will be understood that the aircraft communications system may comprise any number of aircraft base stations  104 .  
      The operation of the mobile terminals  106  in the aircraft  102  will now be described with reference to  FIG. 4 . The mobile terminal  106 , according to one embodiment of the invention, is equipped with a reduced or low power transmission mode or a “flight mode”. When the mobile terminal  106  is in the low power transmission mode, the mobile terminal  106  uses a predetermined power setting for transmission, wherein the predetermined power setting is less than the maximum transmit power setting for the individual mobile terminal  106 . Thus, when communicating with the base station in the aircraft  102 , a reduced transmit power level will be used when the mobile terminal  106  has entered the low power transmission mode. The mobile terminal  106  can be manually put into the low power transmission mode by the user, for example on entry into the aircraft  102 . Alternatively, the mobile terminal  106  may be automatically switched to the low power transmission mode when requested to do so by the communications network  100 .  
      A communication link is initially requested, the mobile terminal  106  first determined if it is in the flight mode in step  401 . If the mobile terminal  106  is in the flight mode, the mobile terminal  106  will transmit an access request, such as a random access burst, on an access channel, such as random access channel (RACH), using a predetermined power level which is below the maximum power in step  403 . Some maximum and minimum power levels for various communication systems are described below.  
      The maximum transmit power level for a GSM antenna is 2 W (33 dBm over 1 mW). The Minimum level is 1 mW. A maximum distance between BS at ground level is 35 km.  
      The maximum transmit power level for DCS/PCS is 1 W (30 dBm over 1 mW). The level is controlled via a power control loop in the mobile terminal.  
      The maximum transmit power level for Bluetooth is 0.1 W (20 dBm over 1 mW).  
      The maximum transmit power level for WCDMA is in power class III 0.25 W (24 dBm over 1 mW). Or in power class IV 0.125 W (21 dBm over 1 mW). The minimum transmit power level for WCDMA is as low as 10 nW.  
      The maximum transmit power level for GPRS is split into classes between 8 W (39 dBm) and 0.8 W (29 dBm). The minimum transmit power level for GPRS is 3.16 mW.  
      If it is determined that the mobile terminal is not in flight mode, the mobile terminal  106  will transmit a random access burst at full or maximum power in step  405 . In one embodiment, the mobile terminal  106  will then receive a request from the aircraft base station  104  to switch to the flight mode in step  407 . The request may be displayed on the display  3  so that the user will be informed of the request and the user can manually switch the mobile terminal  106  into the flight mode. Thus, the request may be a text message. Alternatively, the mobile terminal  106  may automatically switch to the flight mode in response to the request in step  409 .  
      The aircraft base station  104  may also transmit on the broadcast channel a new transmission power level for the mobile terminal  106  to use for further transmissions to the aircraft base station  104  in step  411 .  
      In some embodiments, the aircraft base station may transmit an identification code, such as ID: 001 01, which identifies the base station. The Base station may be identified as a special base station. Special base stations may be base stations provided in power sensitive environments and with which the low power transmission mode should be used for communications. The identification code may be a request to transmit using the low power transmission mode. Thus, the access request may be transmitted using the maximum transmit power level, and the identification code is received in response thereto. Then, mobile terminal may communicate using a reduced transmit power level in further transmission.  
      When the identification code is received by the mobile terminal  106 , the mobile terminal identifies the base station as a special base station, e.g., an aircraft base station. For example, the identification code may be compared to identification codes stored in the mobile terminal  106  to see if the identification code is for a special base station. Different identification codes may e.g. be used for base stations in different environments, such as aircrafts, hospitals etc. When the base station is identified as a special base station, the mobile terminal may disable it&#39;s base station search function so that the mobile terminal  106  will not search for other base stations in step  413 . Instead, the mobile terminal  106  will stay connected to the aircraft base station  104  in step  415  until the flight mode is switched off. Furthermore, if the mobile terminal  106  is in the flight mode and does not find a special base station, the mobile terminal  106  does not attempt to find other base stations.  
       FIG. 5  illustrates one embodiment of a base station  420  according to the invention. The base station comprises a receiver  421 , a transmitter  422  and a processor  423 . The receiver  421  and the transmitter  422  are operative to communicate with the mobile terminal  106 . The processor  423  is operative to perform functions of the base stations, to e.g. determine whether the mobile terminal  106  is transmitting using the low power transmission mode. Also, the processor may be adapted to prepare requests to be transmitted to the mobile terminal  106 .  
      The operation of the aircraft base station will now be described with reference to  FIG. 6 . When the aircraft base station receives an access request from a mobile terminal  106  in step  501 , the aircraft base station  104  first determines, e.g. by measuring or estimating, the transmit power of the received signal in step  503 . If the transmission power is above a predetermined level, the aircraft base station sends a request to the mobile terminal  106  to switch to or enter the low power transmission mode in step  505 . The aircraft base station  104  may also transmit on the broadcast channel a new transmission power level for the mobile terminal  106  to use for further transmissions to the aircraft base station  104  in step  507 . As the request or in addition, the aircraft base station may transmit the identification code, which identifies the base station as a special base station. The aircraft base station then communicates with the mobile terminal  106  and land-based base stations  108   a - c  or satellite  112  as needed in step  509 .  
      Each of the mobile terminal and the special base station may comprise a processor for performing the determinations described above. For example, the processor of the mobile terminal  106  may be adapted to determine whether the request to transmit using the low power transmission mode comprises any identification code, determining whether the base station is a special base station, etc. Similarly, the processor of the base station may be adapted to determine whether the power level of received signal are above a predetermined level. The predetermined level may be a level corresponding the maximum allowable transmit power level in the low power transmission mode.  
      When in the low power transmission mode, not only the transmit power for communications with the base station may be restricted. The transmit power for communications with other electronic devices may also be reduced, such as communication using short-range communication capabilities, e.g. Bluetooth and/or WLAN (Wireless Local Area Network) communication capabilities.  
      The invention may be embedded in a computer program product, which enables implementation of the method and functions described herein. The invention may be carried out when the computer program product is loaded and run in a system having computing capabilities, such as a processor. Computer program, software program, program product, or software, in the present context mean any expression, in any programming language, code or notation, of a set of instructions intended to cause a system having a processing capability to perform a particular function directly or after conversion to another language, code or notation. The computer program product may be stored on a computer readable medium.  
      A computer program product may comprise computer program code portions for executing the method, as described in the description and the claims, for operating a mobile terminal or the base station when said computer program code portions are run by an electronic device having computer capabilities.  
      A computer readable medium having stored thereon a computer program product may comprise computer program code portions for executing the method, as described in the description and the claims, for operating a mobile terminal or the base station when said computer program code portions are run by an electronic device having computer capabilities.  
      The present invention has been described above with reference to specific embodiments. However, other embodiments than the above described are equally possible within the scope of the invention. Different method steps than those described above, performing the method by hardware or software, may be provided within the scope of the invention. The different features and steps of the invention may be combined in other combinations than those described. The scope of the invention is only limited by the appended patent claims.