Abstract:
A repeater system for extending cell coverage, including a frequency band translation repeater for transmitting radio frequency (RF) signals to and receiving RF signals from a base station and translating between the frequency band of THE RF signals and a different frequency band for RF transmission directly between the repeater and user equipment.

Description:
FIELD 
     The present invention relates to a repeater system that can be used to extend cell coverage of a public land mobile telecommunications system. 
     BACKGROUND 
     The base stations of public land mobile telecommunications networks each have a radio range determined by the characteristics of their transmitting and receiving equipment and their location. The range determines the coverage area of the cell of the base station in which user equipment (LIE), such as a telephone handset, is able to establish a communications channel with the base station. Accordingly, the coverage of the network is determined by both the selection and position of the base station of the network. Coverage in remote areas is always problematic, as it is generally cost prohibitive to install a base station in an area where usage of the network is very low. Accordingly, alternatives need to be adopted in order to extend network service to users in remote locations. 
     One alternative for remote locations is the use of satellite telecommunications infrastructure. Satellite telephones and access charges to satellite networks are however costly. Another alternative which has been used in Australia is to place mobile handset equipment at the edge of a mobile network&#39;s coverage, and then run a fixed copper line from the handset to terminal equipment at the remote location, e.g. the user&#39;s home. This gives rise to disadvantages associated with installation and maintenance of the copper lines for users, together with the cost of having the dedicated phones placed at the edge of the network. 
     Two other alternatives involve the use of radio frequency (RF) repeater systems. These are:
         (i) a RF repeater at the edge of the coverage of the network so as to directly retransmit or relay the RF signals to and from the donor base station of the cell and the UE at a remote location outside of the coverage area. This, however, introduces the problem of feedback between the receiving and transmitting antennas of the repeater. Attempts have been made to reduce this feedback by introducing echo cancellers to remove the original signal at the repeater from the retransmitted signal, but this has proved expensive and feedback still occurs, such as from reflections from transport vehicles moving within the area.   (ii) a two stage RF translation system including a RF translator located at the donor base station of the cell to translate the RF signals from the donor base station to a different carrier frequency to that of the network for transmission to a RF repeater located on the edge of the coverage area. The repeater in turn then translates the received RF signals from the RF translator back to the original carrier frequency for transmission to the UE. RF transmission from the UE is similarly translated at the repeater site to communicate with the RF translator and hence to the donor base station. This however is a more expensive solution than (i) and suffers the disadvantage of having to install and maintain additional equipment at the base station as well infrastructure at the repeater site.       

     Accordingly, it is desired to address the above, or at least provide a useful alternative. 
     SUMMARY 
     In accordance with the present invention there is provided a repeater system for extending cell coverage, including a frequency band translation repeater for transmitting radio frequency (RF) signals to and receiving RF signals from a base station and translating between the frequency band of said RF signals and a different frequency band for RF transmission directly between the repeater and user equipment. 
     The present invention also provides a repeater system, including:
         a donor port for a frequency band of a base station of a mobile telecommunications network;   a service port for a different frequency band, the different frequency band including a carrier frequency for communication with user equipment of the network; and   a repeater circuit for converting signals on the donor port and the service port between the bands.       

     The present invention also provides a method of extending cell coverage for a Universal Mobile Telecommunications System (UMTS) network, including:
         retransmitting signals on the UMTS operating band of the network as signals on one or more different UMTS operating bands; and   retransmitting signals of the one or more different UMTS operating bands as signals on the operating band of the network.       

    
    
     
       DESCRIPTION OF DRAWINGS 
       Preferred embodiments of the present invention are hereinafter described, by way of example only, with reference to the accompanying drawings, wherein: 
         FIG. 1  is a diagram of a preferred embodiment of a repeater system in accordance with the present invention; 
         FIG. 2  is a block circuit diagram of a repeater of the system; 
         FIG. 3  is a flow diagram of a cell selection process performed by user equipment when using the system; 
         FIG. 4  is a schematic illustration showing use of the system to extend cell coverage; and 
         FIG. 5  is a schematic diagram illustrating use of two embodiments of the system to extend cell coverage. 
     
    
    
     DETAILED DESCRIPTION 
     A repeater system  100 , as shown in  FIG. 1 , can be placed within the area of coverage of an existing telecommunications network to extend the coverage of that network without requiring any modification to be made to the standard user equipment (UE) that is normally used for that network. Cell coverage can be considerably extended outside of and beyond the existing range of the network by placing the system  100  at the edge of coverage of a cell of the network. The system  100  includes a first antenna  102  for the carrier frequency of the network, a second antenna  104  for a different carrier frequency on which the user equipment can also operate, and a repeater  106  connected to the antennas  102  and  104  so as to translate between the frequency bands of the two carrier frequencies. 
     The repeater system  100  is a single stage translation system and is particularly applicable to Universal Mobile Telecommunications System (UMTS) networks, i.e. 3G Networks, which operate according to the standards of the 3 rd  Generation Partnership Project (3GPP). The 3GPP has established standard operating bands for all user equipment, i.e. mobile terminals. The operating bands are set out in the table below. 
     
       
         
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 Operating 
                 UL Frequencies 
                 DL frequencies 
               
               
                 Band 
                 UE transmit, Node B receive 
                 UE receive, Node B transmit 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 I 
                 1920-1980 
                 MHz 
                 2110-2170 
                 MHz 
               
               
                 II 
                 1850-1910 
                 MHz 
                 1930-1990 
                 MHz 
               
               
                 III 
                 1710-1785 
                 MHz 
                 1805-1880 
                 MHz 
               
               
                 IV 
                 1710-1755 
                 MHz 
                 2110-2155 
                 MHz 
               
               
                 V 
                 824-849 
                 MHz 
                 869-894 
                 MHz 
               
               
                 VI 
                 830-840 
                 MHz 
                 875-885 
                 MHz 
               
               
                 VII 
                 2500-2570 
                 MHz 
                 2620-2690 
                 MHz 
               
               
                 VIII 
                 880-915 
                 MHz 
                 925-960 
                 MHz 
               
               
                 IX 
                 1749.9-1784.9 
                 MHz 
                 1844.9-1879.9 
                 MHz 
               
               
                 X 
                 1710-1770 
                 MHz 
                 2110-2170 
                 MHz 
               
               
                   
               
             
          
         
       
     
     The radio access networks (RANs) provided by the base stations of UMTS mobile networks accordingly use a selected one of the operating bands that is normally determined by the telecommunications provider. For example, in Australia two networks provided by different service providers, e.g. carriers, are UMTS networks that operate using Band I. For these networks the carrier frequencies are referred to as being 2100 MHz. Another network provided in Australia, however, is a UMTS network that operates using Band V and is referred to as using a carrier frequency of 850 MHz. Operating on the 850 MHz band provides greater reach and penetration thereby extending the range for each base station on the network. For simplicity of description, the repeater system  100  is hereinafter described as operating between Bands I and V, although the repeater system could be used to translate between any two or more of the operating bands, provided the bands on one side (i.e. port  202 ) of the repeater  106  are different to those on the other side (i.e. port  204 ) of the repeater. 
     To shift between Band V and Band I, the first antenna  102  is configured to receive and transmit from a first band at 850 MHz, and is a standard base station antenna of the existing 850 MHz network. The first antenna  102  is placed within the range of coverage of a cell  404  of the 850 MHz network provided by an 850 MHz base station  402 , as shown in  FIG. 4 . The repeater  106  has one port  202  connected to the antenna  102  and is placed in a shelter at the base of the antenna structure. A second port  204  of the repeater  106  is connected to a 2100 MHz antenna  104  which is configured and positioned to establish a new and extended cell  406  operating on the 2100 MHz band. The second antenna  104  may be a Yagi or Omnidirectional antenna. 
     The repeater  106 , as shown in  FIG. 2 , has a donor port  202  that provides an 835 MHz uplink signal and an 880 MHz downlink signal for the first antenna  102 . A service port  204  of the repeater  106  provides a 1950 MHz uplink signal and a 2140 MHz downlink signal for the second antenna  104 . 
     The circuitry for the downlink part of the repeater  106  includes a duplexer for the donor port  202  that includes a downlink part  206  with an 880 MHz band pass filter. This is connected to a downlink low noise amplifier  208 . The output of the amplifier  208  is connected to a variable gain amplifier  210  that can be adjusted by a gain control circuit  230 . The gain control may be automatic based on the power level of the common pilot channel (CPICH) of the RAN signals. A first superheterodyne mixer  212  receives the output of the amplifier  210  and produces an intermediate frequency (IF). The intermediate frequency is selected by a first voltage controlled oscillator (VCO)  224 , that in turn is controlled by a phase locked loop (PLL) circuit  226 . The PLL circuit  226  is driven by a high stability reference oscillator  228 . The PLL circuit  226  also includes a control microprocessor for controlling other circuit components of the repeater  106 . 
     An intermediate frequency terminal filter  214  receives the output of the first mixer  212 . The filter  214  is a SAW filter that is configured to provide filtering at the intermediate frequency to achieve single channel filtering, i.e. for a UMTS channel of 5 MHz. The bandwidth of the SAW filter  214  can be expanded by multiples of 5 MHz so as to allow additional channels to be retransmitted by the repeater  106 , if desired. A second mixer  216  converts the filtered intermediate frequency signal to the downlink service port frequency of 2140 MHz. The output of the mixer  216  is connected to a power amplifier  218  which drives a duplexer for the service port  204  that includes a downlink part  220  with a 2140 MHz band pass filter. The second mixer  216  is driven by a second voltage controlled oscillator (VCO)  230  that is also controlled by the PLL  226 . The output of the power amplifier  218  provides a feedback signal to the variable gain amplifier  210  for control purposes. 
     The circuitry is effectively repeated for the uplink part of the repeater  106 . An uplink part  256  of the service port duplexer includes a band pass filter for 1950 MHz. The output of this filter is fed to a second low noise amplifier  258 , which in turn is connected to a second variable gain amplifier  260 . The output of the amplifier  260  is connected to a third mixer  262  which down converts the up link frequency of the service port  204  to the intermediate frequency. The mixer  262  is driven by a third VCO  280 . The down converted signal is fed to a second intermediate frequency filter  264  that is the same as the first IF filter  214 . 
     The output of the second filter  264  is passed to a fourth mixer  266  that is driven by a fourth VCO  274 . The mixer  266  produces a signal at the 835 MHz uplink frequency. The signal is amplified by a second power amplifier  268 , the output of which is fed to the uplink part  270  of the duplexer of the donor port  202 . The gain control circuit  230  is also able to control the gain of the second variable gain amplifier  260  based on the level obtained from the CIPCH (the common pilot channel). 
     The user equipment  410  for a UMTS network is able to move between a cell  404  of the network, and the extended cell  406  by using the frequency and channel selection control logic that is built into the user equipment  410 . For example, when a user terminal  410  of the network is switched on within the extended cell  406  ( 302 ), as shown in  FIG. 3 , the UE  410  first searches for the common pilot channel (CIPCH) on the last stored carried frequency, i.e. a frequency of Band V of the network ( 304 ). If no suitable signal is found on that carrier frequency, the UE starts to search for other public land mobile networks at frequencies stored in the terminal&#39;s UMTS subscribed identity module (SIM) ( 306 ). If no suitable signal is found on other SIM frequencies, the UE begins to scan all of the UMTS operating bands ( 308 ). The UE locks onto the strongest carrier frequency found and reads information available from a broadcast control channel (BCCH) ( 310 ) of the UMTS network location. Accordingly, it will locate the repeated signal of the 850 MHz network on the 2100 MHz band and then using data available on the BCCH will seek to register with the network ( 312 ). The process looks for a match between the Mobile Network Code (MNC) and Mobile Country Code (MCC) of the PLMN received and that stored in the USIM. It also looks to determine if the Signal Quality Level (Squal) and Signal Receive Level (Srslev) received are sufficient before successfully registering with the PLMN. If registration is successful then the UE  410  will camp on the extended cell  406  at the 2100 MHz band which effectively means it is camping on the cell  404  ( 314 ). If registration is unsuccessful, then the UE  410  will record the LA (Location Area) of the rejected cell and simply move to the next strongest carrier frequency and attempt the registration process again. 
     A UE  410  can also move between the cells  404  and  406  by relying on the measurements the UE takes regarding the signals from neighbouring cells, notwithstanding that they are of different bands. Neighbouring cells are ranked on quality by the UE  410  based on data obtained from the CIPCH and the ranking can trigger re-selection to a different cell. When this occurs the UE  410  will move to the different cell. 
     In addition to extending cell coverage to one area, the repeater system  100  can also be used to extend the extended cell  406  to a further extended cell  502  at a different band. This can be done using another repeater system  504  that is essentially the same as the first repeater system  100  but which translates between the extended band of the cell  406  to another band for the further extended cell  502 . This other band may be the same as the band of the network of the first cell  404 . 
     In addition to extending cell coverage to a new location, the repeater system  100  can also be used to provide extended coverage within an existing cell  404  at different frequencies or a different operating band. For example, the repeater system  100  could be used at an airport to translate between the band of a network that covers the airport to the band of a visitor&#39;s UE that they use at home. The repeater system  100  could also be used to improve coverage in poor coverage areas, such as within a building. This can be done by mounting the system  100  within windows or specific areas to reduce black spots. Also, with interference that might be created by adjacent cells of a UMTS network, the repeater system  100  could be used to improve access to or performance of the High Speed Downlink Packet Access (HSDPA) system. The repeater system  100  could also be used to provide selective repeating for the bands of selected carriers (i.e. service providers) to certain locations in circumstances where a carrier only operates on one band. UEs could also be locked to a single band or a repeated band only and then coverage provided in an area by the repeater system  100  specifically for those UEs. This can be particularly useful for emergency services where quick and high reliability local coverage may be required and network capacity controlled. Coverage enhancement and signal quality enhancement can also be provided for particular hot spot areas with small coverage by installing the repeater system  100  at the hot spot. 
     Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention herein described with reference to the accompanying drawings. For example, one antenna for two or more bands can be connected to both the donor port  202  and the service port  204  rather than having dedicated antennas for each port.