Abstract:
The invention proposes a repeater designed for indoor transmissions. The useful frequency band is split into two frequency bands and the repeater amplifies the signals from one of the bands and translates them to the other band. The transposition of frequency bands results in preventing creating significant interference effects on the signal to be amplified. A management circuit is used to address, at lower cost, interference problems between the bands.

Description:
This application claims the benefit, under 35 U.S.C. § 365 of International Application PCT/EP03/50270, filed Jun. 26, 2003, which was published in accordance with PCT Article 21(2) on Jan. 22, 2004 in English and which claims the benefit of France patent application No. 0209094, filed Jul. 10, 2002. 
   FIELD OF THE INVENTION 
   The invention relates to a radio communication repeater and more specifically for indoor communication. 
   BACKGROUND OF THE INVENTION 
   Radio communication repeaters are used to amplify the signal to increase the range of a transmitter. The use of repeaters for broadcast signals is known. A receive antenna directed at a transmitter receives the signal which is amplified and then transmitted via another antenna the radiation of which does not cover the receive antenna. In some cases the broadcast signal comes from a satellite and is translated to another frequency band in order to be broadcast in a more restricted frequency band. 
   For indoor communications, the use of frequency bands situated at around 2.4 GHz and at around 5 GHz and intended for wireless domestic networks is known. However, these radio frequencies do not propagate easily, even not at all, through walls and ceilings. Such systems struggle to cover large houses which have several floors and a large number of internal walls. 
   One idea is to use one or more repeaters to overcome the propagation problems associated with the indoor environment and with the frequencies used. However, domestic networks are bidirectional networks which must make provision to repeat signals from various positions in multiple directions. Furthermore, these signals are strongly reflected by obstacles, creating interference with the transmitted signals. 
   Presently, there is no repeater designed for indoor transmissions and adapted to overcome echoes. 
   SUMMARY OF THE INVENTION 
   The invention proposes a repeater designed for indoor transmissions. To address the multi-directional aspect of antennas, the useful frequency band is split into two frequency bands and the repeater amplifies the signals from one of the bands and translates them to the other band. The transposition of frequency bands helps avoid creating significant interference effects on the signal to be amplified. 
   Thus, the invention is a radio communication repeater which includes a first path to receive signals in a first frequency band, to translate the received signals into a second frequency band and to transmit in the second frequency band, and a second path to receive signals in the second frequency band, to translate the received signals into the first frequency band and to transmit in the first frequency band. 
   According to a preferred embodiment, the repeater includes a management circuit to disable transmission from the first path if the second path receives signals first, and to disable transmission from the second path if the first path receives signals first. The management circuit disables the transmission means of the first and second paths when no signal is received by the first and second paths. The disabling of the transmission means of the first and second paths is carried out by cutting the power to amplifiers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood, and other features and advantages will become apparent from reading the description that follows, with reference to the accompanying drawings in which: 
       FIG. 1  represents the paths of the signals translated and amplified by the repeater according to the invention, and 
       FIG. 2  represents a circuit for managing the paths of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following description, the transmission band is assumed to lie between 5.15 and 5.825 GHz and is split into a first frequency band, for example between 5.15 and 5.35 GHz for Europe and the USA, and a second frequency band, for example between 5.5 and 5.7 GHz. 
     FIG. 1  represents a repeater with two signal paths. The first signal path includes a first receive antenna ARx 1  connected to a first filter  10  to receive and convert signals located in the first frequency band to electrical signals, the first filter  10  being a bandpass filter with a passband corresponding to the first frequency band. A first amplifier  11  amplifies the signal from the first filter  10  and delivers it to a first mixer  12 . The first mixer  12  mixes the signal from the first amplifier  11  with a signal, for example of frequency 4.15 GHz, from a first local oscillator OSC 1 . A second filter  13  selects, from the output of the first mixer  12 , the translated signals corresponding to an intermediate band for example between 1 and 1.2 GHz, the second filter  13  being a bandpass filter with a passband corresponding to the intermediate frequency. A second mixer  14  mixes the signals from the second filter  13  with a signal, for example of frequency 4.5 GHz, from a second local oscillator OSC 2 . A third filter  15  selects, from the output of the second mixer  14 , the signals corresponding to the second frequency band, the third filter  15  being a bandpass filter with a passband corresponding to the second frequency band. A second amplifier  16  amplifies the signals from the third filter  15  and delivers them to a first transmission antenna ATx 2 . 
   The second signal path includes a second receive antenna ARx 2  connected to a fourth filter  20  to receive and convert signals located in the second frequency band to electrical signals, the fourth filter  20  being a bandpass filter with a passband corresponding to the second frequency band. A third amplifier  21  amplifies the signal from the fourth filter  20  and delivers it to a third mixer  22 . The third mixer  22  mixes the signal from the third amplifier  21  with the signal from the second local oscillator OSC 2 . A fifth filter  23  selects from the output of the third mixer  22  the signals corresponding to the intermediate band, the fifth filter  23  being a bandpass filter with a passband corresponding to the intermediate band. A fourth mixer  24  mixes the signals from the fifth filter  23  with the signal from the first local oscillator OSC 1 . A sixth filter  25  selects from the output of the fourth mixer  24  the signals corresponding to the first frequency band, the fifth filter  25  being a bandpass filter with a passband corresponding to the first frequency band. A fourth amplifier  26  amplifies the signals from the sixth filter  25  and delivers them to a second transmission antenna ATx 1 . 
   Various embodiments of the signal paths are possible, the important aspect being that the first frequency band is translated to the second frequency band while amplifying the signals, and that the second frequency band is translated to the first frequency band while amplifying the signals. 
   Using an intermediate frequency band relaxes the constraints that would exist if a single translation were carried out to pass from the first frequency band to the second frequency band and vice versa. By using a single intermediate band for both paths, the same oscillators can be used for both paths, thus reducing costs. 
   Using two amplifiers per signal path means that lower cost amplifiers can be used and the amplification process can be distributed in order to reduce the noise factor at the receive end (amplifiers  11  and  21 ) while benefiting from sufficient transmit power (amplifiers  16  and  26 ). Nevertheless it is possible to use a single amplifier. 
   Moreover, although the example describes a system using four antennas, two for reception ARx 1  and ARx 2  and two for transmission ATx 1  and ATx 2 , this number of antennas can be reduced to two, one transmitting and receiving in the first frequency band and the other transmitting and receiving in the second frequency band. It is even possible to use a single antenna, but this increases the filtering constraints on the first and fourth filters  10  and  20  for separating out the first and second frequency bands. 
   As represented in  FIG. 1 , there is a coupling between the antennas operating in the same frequency bands (a coupling that is very pronounced when the same antenna is used for both transmission and reception). One solution is to use an adaptive filter on each path, for example in place of filters  10  and  20 , to suppress not only the signal amplified by the other path but also all the echoes resulting from the signals transmitted by the other path. Such a solution is relatively complex to implement. 
   In the context of an indoor transmission system operating according to the HiperLAN2 or IEEE 802.11a standard, a full-duplex type system is not necessary. Thus, as a preference, it is proposed to disable one signal path as soon as a signal is detected on the other signal path. 
   To this end, a management circuit retrieves the signals M 1  from the output of the second filter  13  and the signals M 2  from the output of the fifth filter  23 . Based on signals M 1  and M 2 , the management circuit generates control signals C 1  and C 2  which control the power supply to the fourth amplifier  26  and the second amplifier  16  respectively. As soon as a signal is detected on one of the paths, the amplifier of the other path is powered down. 
   To prevent unstable states, associated with the response time of the management circuit or the amplification of noise, the management circuit should preferably cut off the power supply to the second and fourth amplifiers  16  and  26  when no input signal is detected. 
     FIG. 2  shows an example embodiment of a management circuit according to the invention. 
   The management circuit includes a first and second thresholding means  30  and  31  receiving respectively signals M 1  and M 2  and outputting respectively binary signals M 1 ′ and M 2 ′ representing the state of signals M 1  and M 2  with respect to a threshold. Each thresholding means  30  or  31  is for example formed by a circuit measuring the average power of signals M 1  or M 2  in the intermediate band and by a Schmitt trigger which outputs a logic signal M 1 ′ or M 2 ′ representing the average power with respect to a predetermined threshold. The logic signal M 1 ′ (respectively M 2 ′) is at a logic level “0” when the signals M 1  (respectively M 2 ) are below the threshold and at a logic level “1” when the signals M 1  (respectively M 2 ) are above the threshold. 
   Logic gates  32  to  35  implement an asynchronous flip-flop reflected by the following truth table: 
   
     
       
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
           
         
             
                 
             
             
               line N° 
               M1′ 
               M2′ 
               C1(t) 
               C2(t) 
               C1(t + δt) 
               C2(t + δt) 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               1 
               0 
               0 
               X 
               X 
               0 
               0 
             
             
               2 
               0 
               1 
               0 
               X 
               1 
               0 
             
             
               3 
               0 
               1 
               X 
               0 
               1 
               0 
             
             
               4 
               0 
               1 
               1 
               1 
               0 
               0 
             
             
               5 
               1 
               0 
               0 
               X 
               0 
               1 
             
             
               6 
               1 
               0 
               X 
               0 
               0 
               1 
             
             
               7 
               1 
               0 
               1 
               1 
               0 
               0 
             
             
               8 
               1 
               1 
               0 
               0 
               1 
               1 
             
             
               9 
               1 
               1 
               0 
               1 
               0 
               1 
             
             
               10 
               1 
               1 
               1 
               0 
               1 
               0 
             
             
               11 
               1 
               1 
               1 
               1 
               0 
               0 
             
             
                 
             
           
        
       
     
   
   In this table, C 1 (t) and C 2 (t) correspond to the states of the control signals C 1  and C 2  respectively before a switching action of logic gates  32  to  35 ; C 1 (t+δt) and C 2 (t+δt) correspond to the states of control signals C 1  and C 2  respectively resulting from the switching of logic gates  32  to  35 . Level “0” of a control signal C 1  or C 2  corresponds to cutting off the power to the amplifier  26  or  16  that the signal controls. Level “1” of a control signal C 1  or C 2  corresponds to powering up the amplifier  26  or  16  controlled by the said signal. 
   Line 1 corresponds to the case in which none of the paths receives. Lines 2, 3, 5 and 6 correspond to the case in which only one path receives signals. Lines 9 and 10 correspond to both paths receiving signals while an amplifier was already activated, which happens when the signal is amplified after it has been translated to the other band. 
   Lines 8 and 11 correspond to abnormal operation having a low probability of occurrence. Line 8 corresponds to unlikely cases in which both paths stimultaneously receive signals at the input from two different sources, resulting in the simultaneous activation of the amplifiers of both paths. Line 11 corresponds to a state following the state of line 8, which cuts off both amplifiers. The states of lines 8 and 11 then oscillate between each other as long as signals are received simultaneously by both paths. 
   Lines 4 and 7 correspond to states that can occur only if the previous state was that of line 8 and if one of the external sources stops transmitting. The next state then corresponds to the state of one of lines 2, 3, 5 or 6. 
   Assuming that the probability of attaining the state of line 8 is not negligible, it is preferable to suppress the abnormal operation. To avoid the scenario in which the state of line 8 starts to oscillate with the state of line 11, one of the gates  32  to  35  simply need be dimensioned such that it has a slower switching time than the other gates so as to pass either to the state of line 9 or to the state of line 10. 
   Another solution is to introduce at the output of a gate a delay circuit  40  the delay period δt of which is at least equal to the switching time of logic gates  32  to  35 . If positioned as shown in  FIG. 2 , the delay circuit  40  introduces an additional line in the truth table: 
   
     
       
             
             
             
             
             
             
             
           
         
             
                 
             
             
               line N° 
               M1′ 
               M2′ 
               C1(t) 
               C2(t) 
               C1(t + δt) 
               C2(t + δt) 
             
             
                 
             
           
           
             
               8′ 
               1 
               1 
               0 
               0 
               1 
               0 
             
             
                 
             
           
        
       
     
   
   Since line 8′ occurs before line 8 and the delay δt is at least equal to the switching time of gates  32  to  35 , the next state corresponds to that of line 10. Line 8 can no longer disturb the system, the states corresponding to lines 4, 7 and 11 no longer occurring. 
   The management circuit of  FIG. 2  is given only as a guide and can be replaced by any other circuit that can provide management of both signal paths as indicated previously. 
   Other embodiments of the invention are possible. In particular, the first and second frequency bands can be much more restricted in size than indicated previously. The frequency band allocated in Europe includes a first band between 5.15 and 5.35 GHz and a second band between 5.47 and 5.725 GHz, corresponding to a 200 MHz band and a 255 MHz band that include, respectively, 9 and 11 channels of 20 MHz. The frequency band allocated to the USA includes a first band between 5.15 and 5.35 GHz and a second band between 5.725 and 5.825 GHz, corresponding to a 200 MHz band and a 100 MHz band that include, respectively, 9 and 4 channels of 20 MHz. For a domestic installation, a single channel is sufficient for the most part and the intermediate band can be reduced to a single channel. Channels are selected during the installation of the various devices according to the location in the premises. The repeater must be equipped with means for selecting the channel used as first frequency band and the channel used as second frequency band. The said selection means will then directly affect the frequencies of the local oscillators OSC 1  and OSC 2 .