Abstract:
A method is provided of transmitting information from a mobile terminal in a wireless telecommunications network. The method involves sending a radio signal from a first base station to a second base station. The mobile terminal modulates the radio signal so as to include the information into the radio signal. The second base station receives the radio signal and decodes the information.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to telecommunications, in particular to wireless telecommunications. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    In known wireless telecommunications networks, the shift towards higher data rates causes mobile terminals to require relatively more radio frequency (RF) transmission power. Higher transmission power enables greater accuracy of reception, thereby permitting higher data rates. 
         [0003]    A mobile terminal gets connected to a wireless telecommunications network when the mobile terminal is within range of an antenna of a base station of the network. To ensure good uplink connectivity, i.e. good coverage in the direction of transmissions from the mobile terminal to the base station, either the transmission power of the RF transmitter in the mobile terminal has to be high, or a large number of base stations are required per unit area, so that the mobile terminals are practically always within range of a base station. 
       SUMMARY OF THE INVENTION 
       [0004]    The inventor found a method of transmitting information that could, in many circumstances, lower the transmission power of the radio signals transmitted from mobile terminals whilst maintaining appropriately accurate reception by a base station. 
         [0005]    An example of the present invention is a method of transmitting information from a mobile terminal in a wireless telecommunications network. The method involves sending a radio signal from a first base station to a second base station. The mobile terminal modulates the radio signal so as to include the information into the radio signal. The second base station receives the radio signal and decodes the information. 
         [0006]    Signals can advantageously be sent from mobile terminals with lower power than otherwise, in some embodiments, yet still be accurately received. In consequence, a mobile terminal can be built with a less powerful transmitter than otherwise. As there is less demand on batteries, smaller and lighter batteries can be provided in the mobile terminals. Also, the batteries will have longer use-times between recharges. 
         [0007]    Incidentally, the radio signal, which is transmitted directly between base stations can be used to carry data from one base station to another, for example through the network, or so as to allow multiple transmissions of the same data to a mobile terminal from different base stations. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    An embodiment of the present invention will now be described by way of example and with reference to the drawings, in which: 
           [0009]      FIG. 1  is a diagram illustrating a known wireless telecommunications network (PRIOR ART), 
           [0010]      FIG. 2  is a diagram illustrating a wireless telecommunications network according to a first embodiment of the present invention, 
           [0011]      FIG. 3  is a diagram illustrating in greater detail the mobile terminal shown in  FIG. 2 , 
           [0012]      FIG. 4  is a message sequence diagram illustrating messaging in setting up a connection from the mobile terminal to a base station shown in  FIG. 2 , and 
           [0013]      FIG. 5  is a message sequence diagram illustrating possible further messaging in setting up a connection from the mobile terminal to a base station shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION  
       [0014]    A known network will first be described for purposes of comparison. Then the example network according to the first embodiment of the invention will be described in detail. 
       Known Approach 
       [0015]    As shown in  FIG. 1 , a known wireless telecommunications network, includes a first base station  11  and a second base station  12 . A mobile station can be connected to a base station when radio frequency (RF) signals are received sufficiently strongly by both the mobile terminal and base station that data can be transferred in both directions. For example, as shown in  FIG. 1 , a mobile terminal  13  then becomes connected to the first base station  12  via an uplink transmission path  15  and a downlink transmission path  15 ′. 
         [0016]    The acceptable distance between a transmitter and a receiver is limited by the strength of the transmitted signal. For example, in  FIG. 1 , the mobile terminal  13  is within the range of the first base station  1 , as the distance of the uplink path  15  is such that the base station  11  correctly receives a signal that is transmitted from the mobile station  3 . On the other hand, the distance  16 , 16 ′ between a second mobile terminal  14  and the base station  11  is greater, such that a signal transmitted by the second mobile terminal  14  is not correctly received by the first base station. The distance  17 , 17 ′ between the second mobile terminal  14  and its closest base station  12  is also so large that signals from the second mobile terminal  14  to that second base station  12  are also not received correctly. 
         [0017]    A known way to have uplink connectivity between one of the base stations  11 ,  12  and the second mobile terminal  14  is simply to increase the transmission power of the second mobile terminal  14 . However, as mobile terminals are powered by batteries, this means that the strength of the battery would need to be higher, and, assuming they are of the rechargeable type, they would need to be recharged more often There are severe practical limits to the extent that transmission signal power can be increased, for example, due to limits on battery size and the need to avoid possible ill effects on user&#39;s health. 
         [0018]    Another known way to ensure connectivity is to increase the density of base stations, i.e. the number per unit area. Unfortunately, this would require more investment in base stations, and base station use would be less efficient as the ratio of terminals to base stations would be reduced. 
         [0019]    Down-stream connectivity is less of a concern because the base station is supplied with mains electricity. Accordingly, increasing transmission power to ensure more accurate signal reception is straight-forward and causes less problems than it does at the mobile terminals. 
       Example Embodiment 
       [0020]    When considering the known system, the inventor realised that the mobile could send its signal to a base station using less transmission power by modulating a radio signal being sent from one base station to another. 
       Modulating Mode 
       [0021]    A network according to an embodiment of the invention is shown in  FIG. 2 . For simplicity, only two base stations and two mobile terminals are shown. The network shown in  FIG. 2  is broadly similar to that shown in  FIG. 1 ; however, (a) a continuous radio frequency (RF) signal  28 ,  28 ′ is transmitted between a first base station  21  and (b) a second base station  22  and a mobile terminal  24 , instead of transmitting an RF signal directly to a base station, modulates the RF signal  28  (and/or  28 ′) transmitted between base stations  21 , 22 . The mobile terminal can thus be considered to be in a “modulating mode” of uplink connection. 
         [0022]    The modulating signal  29  is relatively weak compared to the uplink signal that would otherwise be required if no carrier signal was modulated so the uplink signal was solely direct from the mobile station. 
         [0023]    The modulating signal is based on one or more modulating signal characteristics of known type such as a frequency modulation, code modulation (e.g. as in code division multiple access systems), or time modulation. Multiple mobile terminals can modulate a single continuous RF signal  28 , 28 ′, for example using different codes or different time slots. Either the mobile terminal can use pre-set signal characteristics to effect its modulation, or one or more of the base stations  21 , 22  can, from time to time, inform the mobile terminal of signal characteristics to be used for subsequent uplink transmissions. 
         [0024]    In the downlink direction, a direct RF link  27 ′ (or  26 ′) is used from a base station  22  (or  21 ) to the mobile terminal  24 . 
         [0025]    It will be noted that as there are RF signals  28 , 28 ′ between base stations  21 , 22 , these signals  28 ,  28 ′ can be usefully used for direct data transfer from base station to base station. One example is to transmit data across the network as an alternative to the wired network route. Another example is so as to enable the sending of the same data from two base stations to a mobile terminal, i.e. using so-called “redundant” connections, to increase accurate reliability of reception at the mobile station. 
         [0026]    The network shown in  FIG. 2  may, of course, include further base stations (not shown). 
       Direct Mode 
       [0027]    For completeness, we would add that the wireless telecommunications network shown in  FIG. 2  includes a further mobile terminal  23  within the range of the first base station  21 , as the distance of the uplink path  25  is such that the base station  21  correctly receives a signal that is transmitted from the mobile station  23  with reasonable, rather than high, power. Accordingly, the further mobile terminal  23  is directly connected to the first base station  22  via an uplink transmission path  25  and a downlink transmission path  25 ′. This can be considered as a “direct mode” of uplink connection. 
         [0028]    The network shown in  FIG. 2 , may, of course, include further mobile terminals (not shown). 
       Mobile Terminal 
       [0029]    Each mobile terminal is configured so that either of the direct mode or the modulating mode is selectable for an uplink connection. 
         [0030]    As shown in  FIG. 3 , a mobile terminal  23 ,  24  includes a transmitter  30  and a receiver  32 . The transmitter  30  is connected to a modulating signal generator  34  and a direct signal generator  36 . The modulating signal generator  34  is operative to produce signals for transmission when the mobile terminal is in the modulating mode. The direct signal generator  36  is operative to produce signals for transmission when the mobile terminal is in the direct mode. The generators are selectable for use by a control circuit  38  connected to the two generators  34 , 36 . The control circuit  38  is connected to the receiver  32 , which receives decoded paging and handshake signals as discussed below. 
         [0031]    The control circuit  38  includes a timer  39  for use as explained below. 
       Selection of Connection Mode 
       [0032]    The network is configured to have base stations  21 , 22  spaced sufficiently closely that any mobile terminal  23 , 24  within the overall coverage area of the network would likely be able to connect to a base station at any time. The base stations  21 , 22  each periodically transmit paging messages. As shown in  FIG. 4 , a mobile terminal  24  receives ( FIG. 4 : steps a, b) one or more paging messages, each from a different base station  22 , 21  around the current location of the mobile terminal  24 . 
         [0033]    The mobile terminal then selects (step c) a paging message to respond to and sends back an acknowledgement message to the selected base station. The criterion for the selection is, for example, which of the paging messages from different base stations is received most strongly. The mobile terminal then selects which mode to use for uplink connection, namely direct mode or modulating mode, then sends (step e) a corresponding initialisation message to the base station. Assuming it successfully receives the initialisation message, the base station sends (step f) a signal, often known as a handshake message, which confirms to the mobile terminal that the selected mode is acceptable for use. 
         [0034]    As shown in  FIG. 5 , on the other hand, if no handshake message is received by the mobile station from the base station within a predetermined time-out period (step f′) as measured by the timer  39  of the mobile terminal, (in other words, step f as shown in  FIG. 4  does not then occur), then the mobile terminal instead sends (step g) an acknowledgment signal followed by an initialisation signal (step h) to another base station. This second base station might be selected on the basis that it is the base station from which the second strongest paging message was received. If no handshake message is received from that other base station within a further time out period (step i), then the mobile terminal selects the other one of the two modes of uplink connection, namely direct mode and modulating mode, and sends (step j) a fresh acknowledgement message to the first base station. 
         [0035]    This process continues (indicated by k in  FIG. 5 ) with different base stations and modes being selected in a repeating sequence until the mobile terminal successfully receives (step l) a handshake message. 
       Signal Degradation in Modulating Mode 
       [0036]    Referring again to  FIG. 2 , should there be a signal degradation, for example due to poor weather conditions attenuating radio signals, then this degradation will be detected by the base station  28  receiving the modulated signal  28  modulated by mobile terminal  24 . The base station  22  then communicates with neighbouring base stations  23  to check that the other neighbouring base stations also received lower signal strength. If signal degradation is identified, the base station instructs the mobile terminal  24  to switch from modulating mode to direct mode, to ensure better reception accuracy at the base station. This is despite the disadvantage of increased radio transmission power required at the mobile terminal. 
       General 
       [0037]    In some other embodiments, the mobile terminal can be uplink connected using both direct mode and modulating mode at the same time. This is so as to increase the chances of accurate reception by at least one base station of the data the mobile terminal transmits. This is sometimes known as increased “redundancy”. 
         [0038]    The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.