Abstract:
A repeater system for wireless communication system is disclosed forthwith. The repeater system uses an analog frequency converter and digital down and up converter in order to allow the processing of the repeated signal in a relatively low frequency (in the 30 MHz range) and in a digital form (rather than in analog form). The repeater system also provides a programmable multi-band filter which can identify and suppress out of band noises to increase the signal-to-noise ratio of the system.

Description:
REFERENCE TO CROSS-RELATED APPLICATION 
       [0001]    This application claims priority from US provisional patent application No. 61/251,376, filed on Oct. 14, 2009 and US provisional patent application No. 61/251,744, filed on Oct. 15, 2009, both herein incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to wireless communication systems, more particularly, to repeater systems for wireless communication systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    Wireless technologies such as cellular, Personal Communication Systems (PCS), Multiuser Multipath Distribution Systems (MMDS), Wireless Local Loop (WLL) etc. have inherently limited ranges dependent upon transmitting power, antennas gain, path loss, noise, data rate, etc. In locations where wireless connectivity is required, yet the reception signal power is low, the use of repeaters is prevalent. 
         [0004]    Repeaters are bi-directional amplifier devices that receive a low power signal using the receiving (Rx) antenna (first antenna), amplify it and then re-transmit the signal using a higher power signal via a transmitting (Tx) antenna (second antenna). Many repeaters also filter out the noise from the received signal in order to get a clean transmission signal. 
         [0005]    Every repeater employs at least two antennas: a receiving antenna (also known as “donor” antenna) which communicates with the networks base stations and a transmitting antenna (also known as “service” antenna) which communicates with the remote stations and subscribers. Having these two antennas in proximity to each other may create a feedback loop when the signal that is transmitted from the “service” is received by the “donor” antenna, filtered, amplified and then transmitted again by the “service” antenna. This creates a positive feedback loop, which causes interferences and disruptions to the regular transmissions, in some cases this can jam nearby cellular base station receivers (BTS&#39;s). 
         [0006]    In order to avoid a feedback loop, it is required to have a margin of about 10-15 dB between the isolation between the antennas and the repeater gain. For example, if the isolation between the antennas is 65 dB, the maximum gain of the repeater needs to be less than 50-55 dB. 
         [0007]    Isolation between the antennas is usually achieved by physically separating the antennas. The “donor” antenna is sometimes installed outside of the area where the repeater is located, which may lead to problems due to wall penetrations and zoning issues. Even when no external antennas are used, separating the antennas may require physical separation of at least 2 meters. 
         [0008]    Another option used to overcome the feedback loops is by using echo cancellation algorithms which estimate the feedback signal received by the “donor” antenna and subtracting it from the signal transmitted by the “service” antenna. 
         [0009]      FIG. 1  of the prior art is a schematic block diagram of a first typical prior are repeater system (PARS)  10  which uses echo cancellation to overcome the feedback loop. 
         [0010]    Prior to operation (and possibly periodically during operation) the prior art repeater system (PARS)  10  moves to a training mode in which a switch  116  connects a training signal generator  106  to a transmit (Tx) filter  108  instead of connecting an adder  114  to the Tx filter  108  (which is the normal, operational connection) and the training signal generator  106  transmits a training signal through the switch  116 , the transmit (Tx) filter  108  and a digital-to-analog converter (DAC)  110  to a second antenna  216 . 
         [0011]    The training signal and a cancellation filter control  112  are also supplied to a cancellation filter  124  for use in the cancellation of the feedback signal. 
         [0012]    Prior art repeater systems (PARS)  10  use white noise as the training signal. The PARS  10  sends out a White Noise signal, which essentially blocks out any communications in the vicinity of the PARS  10  until the estimation algorithm (usually located within the cancellation filter  124 ) converges. 
         [0013]    The second antenna  216  transmits the training signal via the feedback channel  118  (which is normally the air). Some of the transmitted signals&#39; power is received by a first antenna  214  and is supplied to an analog-to-digital converter (ADC)  102  and to a receive (Rx) filter  104 . The filtered signal is then goes to an adder  114  which subtracts a cancellation signal coming from the cancellation filter  124 . The result of the subtraction is fed back to the cancellation filter  124  to determine if adjustments to the cancellation signal are required. 
         [0014]    In order to achieve the correct cancellation signal, the energy of the signal coming from the adder  114  must be minimized, this means that the estimated cancellation filter  124  is similar to the feedback path  118 , when in full training mode since there is no real data signal being transmitted, the only signal received by the first antenna  214  should be the signal transmitted by the second antenna  216  which is the training signal. In cases where the incoming signals are sufficient, the incoming signals can be used for training. 
         [0015]    Due to changes in the feedback channel  118 , such as small movements of the antennas, changes in reflection elements such as moving trees or cars, it is required to perform the procedure described above periodically according to the physical requirements to maintain stability. Adaptive algorithms can be used to correct the transfer function in a continuous manner using the incoming signals. 
         [0016]    A typical repeater includes transmissions in both directions, but for simplicity, only one direction was described herein and below. 
         [0017]    Normally, the filters in the repeater systems (such as the Rx filter  104  and Tx filter  108 ) are designed to comply with telecommunication standards in a way which will minimize their impact on adjacent frequency bands and also have minimal impact on signal integrity, (minimal propagation delay and amplitude ripple). Such filters are typically band pass filters and the compliance requirements cause the filters to be very close to ideal filters. As most of the filters are implemented as Finite Impulse Response (FIR) filters, the resultant filters become very long and complex filters. As the cancellation filter  124  estimates the signal path from the splitting point  126 , it needs to estimate these complex filters (Rx filter  104  and Tx filter  108 ) therefore, requiring it to be a very long and complex filter itself. 
         [0018]      FIG. 2  of the prior art is an example of a first typical band-pass filter magnitude response graph, whose pass-band is 10 MHz, and which attenuates 40 dB in 200 KHz, and 60 dB in 300 KHz. 
         [0019]    Such a filter may require 400 taps at a processing frequency of 50 MHz. 
         [0020]      FIG. 3  of the prior art is an example of a second typical band-pass filter magnitude response graph, whose transition band is widened to 1 MHz, and may be implemented with 100 taps. 
         [0021]    It is possible to see that this band-pass filter is further away from an ideal band-pass filter than the filter described in  FIG. 2 . 
         [0022]      FIG. 4  of the prior art is an example of a second prior are repeater system (PARS)  10  which uses echo cancellation to overcome the feedback loop. 
         [0023]    In this second example, the Tx filter  108  is placed after the digital-to-analog converter (DAC)  110  and is therefore an analog filter; typically, a Surface Acoustic Wave (SAW) filter. 
         [0024]    The main advantage of SAW filters is that they are easy and relatively inexpensive to manufacture. Yet, since SAW filters are hard-wired by nature, it is impossible to change their profiles once they are built. 
         [0025]    From the perspective of the cancellation filter  124 , there is little difference (if any) between the two repeater systems depicted in  FIG. 1  and  FIG. 4 , as the complexity of the Tx filter  108  remains high and requires that the cancellation filter  124  to be long and complex. 
         [0026]    All of the prior art repeater systems operate at the native radio-frequency (RF) bands which are at the 0.7-5 GHz range. These high frequencies generally yield highly complex designs which can be difficult to implement. 
         [0027]    None of the prior art repeater systems include a solution for a simple, inexpensive and programmable cancellation filter which can operate at relatively low frequencies. 
         [0028]    There is therefore a need for a repeater system, which comprises a combination of all of the above characteristics and functions. 
       SUMMARY OF THE INVENTION 
       [0029]    The background art does not teach or suggest a repeater system which includes a solution for a simple, inexpensive and programmable feedback cancellation filter, in addition to an adaptive algorithm that can use incoming signals for estimation and adaptation of the filter. 
         [0030]    The present invention overcomes these deficiencies of the background art by providing a solution which splits the Tx filter into two separate Tx filters that are digital and can be programmed according to the user&#39;s needs as well as operating in a relatively low frequency range. 
         [0031]    It should be noted that any measurements, values, frequencies and frequency ranges mentioned in the current patent application are indicative and exemplary only and are not used by any means to limit the use and scope of the current invention. 
         [0032]    In the present invention, the incoming signal which is in the RF range of 700-2400 MHz is down-converted twice: first in an analog frequency converter in order to reduce the frequency to a range suitable for conversion to digital (in the intermediate frequency range IF of approximately 120 MHz), and then in a digital down-converter (after being digitized with an analog-to-digital converter (ADC)) to a frequency of approximately 30 MHz. Once the signal is digitized and down-converted, it is filtered to remove any noises and an echo cancellation signal is subtracted from the signal in order to remove any feedback echoes coming from the transmitting antenna. The resultant signal is then filtered by a configurable multi-band filter suitable for any multiple band-pass filter combination (according to the specific wireless communication bands and sub-band used) and then it goes through another transmit filter, a digital up-converter, and a digital-to-analog converter. Once in the up-converted frequency and back in analog form, the signal is converted back to its radio frequency range, amplified and transmitted by the transmitting antenna. 
         [0033]    An estimation algorithm is used to estimate the optimal cancellation signal to be used in the subtraction phase and to control the training signal generator in order to have more flexibility in changing environmental conditions and wireless communication protocols. 
         [0034]    The training signal, which can be either internal signal or the communication signals passing through the system, can be used for training and adaptation. 
         [0035]    According to a first embodiment of the present invention there is provided a repeater system including: at least first antenna, an analog-to-digital converter (ADC), wherein the analog-to-digital converter (ADC) is operatively connected to the at least one first antenna, a receive (Rx) filter, wherein the receive (Rx) filter is operatively connected to the analog-to-digital converter (ADC), a first transmit (Tx) filter, wherein the first transmit (Tx) filter is operatively connected to the receive (Rx) filter, a digital-to-analog converter (DAC), wherein the digital-to-analog converter (DAC) is operatively connected to the first transmit (Tx) filter, at least one second antenna, wherein the at least one second antenna is operatively connected to the first transmit (Tx) filter, and a feedback channel, wherein the feedback channel is wirelessly connected to both the at least one second antenna and the at least one first antenna. According to further features of the described embodiment of the present invention the repeater system, includes a digital signal processor that contains: a cancellation filter, an adder, wherein the adder is operatively connected between the receive (Rx) filter and the at least one transmit (Tx) filter and is further operatively connected to the cancellation filter, a cancellation filter control, wherein the cancellation filter control is operatively connected to the adder and the cancellation filter, a training signal generator, a splitting point, wherein the splitting point is operatively connected to the cancellation filter, a switch, wherein the switch is operatively connected to the training signal generator, the first one transmit (Tx) filter and to the splitting point; and a second transmit (Tx) filter, wherein the second transmit (Tx) filter is operatively connected to the splitting point and to the digital-to-analog converter (DAC). 
         [0036]    According to a second embodiment of the present invention there is provided a repeater system including: a first antenna, a first duplexer, wherein the first duplexer is operatively connected to the first antenna, an uplink block, wherein the uplink block is operatively connected to the first duplexer, a downlink block, wherein the downlink block is operatively connected to the first duplexer, a second duplexer, wherein the second duplexer is operatively connected to the uplink block and to the downlink block and a second antenna, wherein the second antenna is operatively connected to the second duplexer. 
         [0037]    According to further features of the described embodiment of the present invention the repeater system further includes: a mixed-signal processor (MSP), wherein the mixed-signal processor (MSP) is operatively connected to the uplink block and to the downlink block. 
         [0038]    According to further features of the described embodiment of the present invention the repeater system further includes: a first mixed-signal processors (MSP), wherein the first mixed-signal processor (MSP) is operatively connected to the uplink block; and a second mixed-signal processor (MSP), wherein the second mixed-signal processor (MSP) is operatively connected to the downlink block. 
         [0039]    According to further features of the described embodiment of the present invention the uplink block of the repeater system includes: a low noise amplifier (LNA), an analog frequency converter (AFC), wherein the analog frequency converter (AFC) is operatively connected to the low noise amplifier (LNA) and a power amplifier (PA), wherein the power amplifier (PA) is operatively connected to the analog frequency converter (AFC). 
         [0040]    According to further features of the described embodiment of the present invention the uplink block of the repeater further includes: a mixed-signal processor (MSP), wherein the mixed-signal processor (MSP) is operatively connected to the analog frequency converter (AFC). 
         [0041]    According to further features of the described embodiment of the present invention the downlink block of the repeater system includes: a low noise amplifier (LNA), an analog frequency converter (AFC), wherein the analog frequency converter is operatively connected to the low noise amplifier (LNA) and a power amplifier (PA), wherein the power amplifier (PA) is operatively connected to the analog frequency converter (AFC). 
         [0042]    According to further features of the described embodiment of the present invention the downlink block of the repeater system further includes: a mixed-signal processor (MSP), wherein the mixed-signal processor (MSP) is operatively connected to the analog frequency converter (AFC). 
         [0043]    According to further features of the described embodiment of the present invention the mixed-signal processor (MSP) of the repeater system further includes: an analog-to-digital converter (ADC), a digital down-converter (DDC), wherein the digital down-converter (DDC) is operatively connected to the analog-to-digital converter (ADC), a receive (Rx) filter, wherein the receive (Rx) filter is operatively connected to the digital down-converter (DDC), an adder, wherein the adder is operatively connected to the receive (Rx) filter, a configurable multi-band filter, wherein the configurable multi-band filter is operatively connected to the adder, a control central processing unit, wherein the control central processing unit is operatively connected to the configurable multi-band filter, a training signal generator, a splitting point, a switch, wherein the switch is operatively connected to the training signal generator, the configurable multi-band filter and to the splitting point, a transmit (Tx) filter, wherein the transmit (Tx) filter is operatively connected to the splitting point, a digital up-converter (DUC), wherein the digital up-converter (DUC) is operatively connected to the transmit (Tx) filter, a digital-to-analog converter (DAC), wherein the digital-to-analog converter (DAC) is operatively connected to the digital up-converter (DUC), a cancellation filter, wherein the cancellation filter is operatively connected to the adder and to the splitting point and an estimation algorithm execution unit, wherein the estimation algorithm execution unit is operatively connected to the adder, the cancellation filter and the training signal generator. 
         [0044]    According to further features of the described embodiment of the present invention the repeater system further includes: a first mixed-signal processor (MSP), wherein the first mixed-signal processor (MSP) is operatively connected to the uplink block, and a second mixed-signal processor (MSP), wherein the second mixed-signal processor (MSP) is operatively connected to the downlink block. 
         [0045]    According to further features of the described embodiment of the present invention the first mixed-signal processor (MSP) of the repeater system includes: an analog-to-digital converter (ADC) a digital down-converter (DDC), wherein the digital down-converter (DDC) is operatively connected to the analog-to-digital converter (ADC), a receive (Rx) filter, wherein the receive (Rx) filter is operatively connected to the digital down-converter (DDC), an adder, wherein the adder is operatively connected to the receive (Rx) filter, a configurable multi-band filter, wherein the configurable multi-band filter is operatively connected to the adder, a control central processing unit, wherein the control central processing unit is operatively connected to the configurable multi-band filter, a training signal generator, a splitting point, a switch, wherein the switch is operatively connected to the training signal generator, the configurable multi-band filter and to the splitting point, a transmit (Tx) filter, wherein the transmit (Tx) filter is operatively connected to the splitting point, a digital up-converter (DUC), wherein the digital up-converter (DUC) is operatively connected to the transmit (Tx) filter, a digital-to-analog converter (DAC), wherein the digital-to-analog converter (DAC) is operatively connected to the digital up-converter (DUC), a cancellation filter, wherein the cancellation filter is operatively connected to the adder and to the splitting point and an estimation algorithm execution unit, wherein the estimation algorithm execution unit is operatively connected to the adder, the cancellation filter and the training signal generator and wherein the second mixed-signal processor (MSP) includes: an analog-to-digital converter (ADC), a digital down-converter (DDC), wherein the digital down-converter (DDC) is operatively connected to the analog-to-digital converter (ADC), a receive (Rx) filter, wherein the receive (Rx) filter is operatively connected to the digital down-converter (DDC), an adder, wherein the adder is operatively connected to the receive (Rx) filter, a configurable multi-band filter, wherein the configurable multi-band filter is operatively connected to the adder, a control central processing unit, wherein the control central processing unit is operatively connected to the configurable multi-band filter, a training signal generator, a splitting point, a switch, wherein the switch is operatively connected to the training signal generator, the configurable multi-band filter and to the splitting point, a transmit (Tx) filter, wherein the transmit (Tx) filter is operatively connected to the splitting point, a digital up-converter (DUC), wherein the digital up-converter (DUC) is operatively connected to the transmit (Tx) filter, a digital-to-analog converter (DAC), wherein the digital-to-analog converter (DAC) is operatively connected to the digital up-converter (DUC), a cancellation filter, wherein the cancellation filter is operatively connected to the adder and to the splitting point and an estimation algorithm execution unit, wherein the estimation algorithm execution unit is operatively connected to the adder, the cancellation filter and the training signal generator. 
         [0046]    Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0047]    The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: 
           [0048]      FIG. 1  of the prior art is a schematic block diagram of a first typical prior art repeater system (PARS) which uses echo cancellation to overcome the feedback loop. 
           [0049]      FIG. 2  of the prior art is an example of a first typical band-pass filter magnitude response graph. 
           [0050]      FIG. 3  of the prior art is an example of a second typical band-pass filter magnitude response graph. 
           [0051]      FIG. 4  of the prior art is an example of a second prior art repeater system (PARS) which uses echo cancellation to overcome the feedback loop. 
           [0052]      FIG. 5  is a schematic block diagram of a first embodiment of a repeater system which uses echo cancellation to overcome the feedback loop, including two Tx filters, according to the present invention. 
           [0053]      FIG. 6  is a schematic block diagram of a second embodiment of repeater system which uses echo cancellation to overcome the feedback loop, according to the present invention. 
           [0054]      FIG. 7  is a schematic block diagram of a mixed-signal processor (MSP), according to the present invention. 
           [0055]      FIG. 8  is a schematic block diagram of a third embodiment of repeater system (MSP) which uses echo cancellation to overcome the feedback loop, according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0056]    The present invention is of a repeater system. 
         [0057]    The principles and operation of a repeater system according to the present invention may be better understood with reference to the drawings and the accompanying description. 
         [0058]    Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. 
         [0059]    Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, dimensions, methods, and examples provided herein are illustrative only and are not intended to be limiting. 
         [0060]    The following list is a legend of the numbering of the application illustrations:
     10  prior art repeater system (PARS)     20  repeater system     102  analog-to-digital converter (ADC)     104  receive (Rx) filter     106  training signal generator     108  transmit (Tx) filter     108   a  first transmit (Tx) filter     108   b  second transmit (Tx) filter     110  digital-to-analog converter (DAC)     112  cancellation filter control     114  adder     116  switch     118  feedback channel     124  cancellation filter     126  splitting point     200  duplexer     202  low noise amplifier (LNA)     204  analog frequency converter (AFC)     206  power amplifier (PA)     208  mixed-signal processor (MSP)     210  uplink block     212  downlink block     214  first antenna     216  second antenna     300  digital down-converter (DDC)     302  control central processing unit (CPU)     304  configurable multi-band filter     306  digital up-converter (DUC)     308  estimation algorithm execution unit   
 
         [0090]    Referring now to the drawings,  FIG. 5  is a schematic block diagram of a first embodiment of a repeater system  20  which uses echo cancellation to overcome the feedback loop, including two Tx filters, according to the present invention. 
         [0091]    In the present embodiment, the Tx filter  108  of the prior are is divided into two Tx filters; a first transmit (Tx) filter  108   a  and a second transmit (Tx) filter  108   b . Putting the splitting point  126  after the first transmit (Tx) filter  108   a  allows for the cancellation filter  124  to estimate only the second transmit (Tx) filter  108   b . With the first transmit (Tx) filter  108   a  designed as a very sharp band-pass filter, the second transmit (Tx) filter  108   b  can be a very soft band-pass filter and therefore a very simple filter. Therefore, the cancellation filter  124  can now be designed as a soft band-pass filter as well. 
         [0092]    The term “sharp” is used here to infer that the filter has a high rejection ratio (usually more than 20 dBc at 1 MHz from the corner frequency, up to 40 dBc at 600 KHz from the corner frequency), and “soft” is used here to infer that the filter has a lower rejection ratio (usually 10 dBc at 5 MHz from the corner frequency up to 20 dBc at 6 MHz from corner frequency). 
         [0093]    When the second transmit (Tx) filter  108   b  is placed before the digital-to-analog converter (DAC)  110  as described in the present illustration, it is a digital filter (typically, a FIR filter). In case the second transmit (Tx) filter  108   b  is placed after the digital-to-analog converter (DAC)  110  it is an analog filter (typically a SAW filter). 
         [0094]    If the input signal level is sufficient the training can be performed, in wide band modulations (i.e. code division multiple access (CDMA), wideband code division multiple access (WCDMA), orthogonal frequency-division multiplexing (OFDM) etc.) without using white noise as a training signal namely the incoming transmissions can be used as a training signal and perform estimation or adaptation without stopping the system operation and without interrupting nearby communications. 
         [0095]    Even though the present embodiment (as well as the following embodiments) are described using separate functional blocks, it is possible to implement all of the blocks within a single device such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). 
         [0096]      FIG. 6  is a schematic block diagram of a second embodiment of repeater system  20  which uses echo cancellation to overcome the feedback loop, according to the present invention. 
         [0097]    In the present embodiment, a signal is received by one of the two antennas (either the first antenna  214  or the second antenna  216 , depending on the transmission direction—upstream or downstream) and using a duplexer  200 , the signal is transferred to the appropriate block (an uplink block  210  or a downlink block  212 ) for processing and using another duplexer  200 , the signal is transferred to the other antenna for transmitting. 
         [0098]    The operational principles of the uplink block  210  and the downlink block  212  are alike and thus only a single block is described, as follows. 
         [0099]    Once the signal arrives from the duplexer  200 , it is amplified by the low noise amplifier (LNA)  202  in order to have a higher gain signal with better signal-to-noise ratio (SNR) which is easier to work with. The amplified signal is converted into a lower frequency, using the analog frequency converter (AFC)  204 , to a frequency range which is easier to convert into a digital signal later on in the process. The signal is then input into the mixed-signal processor (MSP)  208 , for processing (e.g., echo cancellation, filtration etc.). From the mixed-signal processor (MSP)  208  the processed signal is converted back into a high frequency (RF) signal using the analog frequency converter (AFC)  204  so that it can be amplified by the power amplifier (PA)  206  and transmitted through the other antenna (by way of the other duplexer  200 ). 
         [0100]    The mixed-signal processor (MSP)  208  in the present embodiment is a single block, shared by both the uplink block  210  and the downlink block  212 . 
         [0101]      FIG. 7  is a schematic block diagram of a mixed-signal processor (MSP)  208 , according to the present invention. 
         [0102]    The present illustration describes a mixed-signal processor (MSP)  208  for a single uplink block  210  or downlink block  212  (both not shown in the present figure, shown in  FIG. 6 ). Other embodiments may have a dual block mixed-signal processor (MSP)  208  in which there are two identical structures as the single structure depicted herein. 
         [0103]    A signal comes into the mixed-signal processor (MSP)  208  from the analog frequency converter (AFC)  204  (not shown in the present figure, shown in  FIG. 6 ) and is converted to a digital signal using an analog-to-digital converter (ADC)  102  and is then down-converted to a lower frequency using a digital down-converter (DDC)  300 . The signal is filtered with the Rx filter  104  to remove any noises it may have picked up and is moved to the adder  114  where the cancellation signal from the cancellation filter  124  is subtracted from it. The subtracted signal is filtered by the configurable multi band filter  304  (which functions like the first transmit (Tx) filter  108   a  of the repeater system  20  depicted in  FIG. 6 . In normal operation mode, the switch  116  transfers the filtered signal to the Tx filter  108  which is then up-converted using a digital up-converter (DUC)  306 , converted to an analog signal using the digital to analog (DAC)  110  and transmitted back to the analog frequency converter (AFC)  204  (not shown in the present figure, shown in  FIG. 6 ). 
         [0104]    In the training mode the switch  116  connects the training signal generator  106  to the transmit path (from the Tx filter  108  onwards) in order to train the repeater system  20  in echo cancellation as described before in  FIG. 5 . 
         [0105]    An estimation algorithm execution unit  308  receives the subtracted signal coming out of the adder  114  and can improve on the existing manner of controlling the cancellation filter  124  by providing optional computation possibilities to the repeater system  20 . 
         [0106]    The estimation algorithm execution unit  308  can also control the training signal generator  106  in order to use different types of training signals for use in different types of wireless communication protocols and frequency bands. In cases in which the incoming communication signals that pass through the system are sufficiently high and consist of wide-bands modulations (such as CDMA, WCDMA etc.), the estimation algorithm can use these signals to perform estimation and adaptation of the cancellation filter. 
         [0107]    The estimation algorithm execution unit  308  may also analyze the incoming signal for out-of-band noises in order to adjust the cancellation filter so that it would filter out any out-of-band noises. This estimation can be done continuously even in normal operation mode and not just in the training mode. 
         [0108]    One possible algorithm that can be used as the estimation algorithm execution unit  308  is the well known Least-Mean-Square (LMS) algorithm to find the transfer function H(t) that minimizes Σ[Noise′(t)-H(Noise(t))] 2  where Noise(t) is the transmit noise through from the output and Noise′(t) is the receive noise from the input. The Noise (t) can be either an internal wide-band noise, or (in cases of wide-band modulations), the communication signal itself. 
         [0109]    The configurable multi band filter  304  may include more than one band-pass filter for applications which use multiple frequency bands. The band-pass filters within the configurable multi band filter  304  are controlled and programmed by a control central processing unit (CPU)  302 . 
         [0110]      FIG. 8  is a schematic block diagram of a third embodiment of repeater system  20  which uses echo cancellation to overcome the feedback loop, according to the present invention. 
         [0111]    In the present embodiment, a signal is received by one of the two antennas (either the first antenna  214  or the second antenna  216 , depending on the transmission direction—upstream or downstream) and using a duplexer  200 , the signal is transferred to the appropriate block (an uplink block  210  or a downlink block  212 ) for processing and using another duplexer  200 , the signal is transferred to the other antenna for transmitting. 
         [0112]    The operational principles of the uplink block  210  and the downlink block  212  are alike and thus only a single block is described, as follows. 
         [0113]    Once the signal arrives from the duplexer  200 , it is amplified by the low noise amplifier (LNA)  202  in order to have a higher gain signal with better signal-to-noise ratio (SNR) which is easier to work with. The amplified signal is converted into a lower frequency, using the analog frequency converter (AFC)  204 , to a frequency range which is easier to convert into a digital signal later on in the process. The signal is then input into the mixed-signal processor (MSP)  208 , for processing (e.g., echo cancellation, filtration etc.). From the mixed-signal processor (MSP)  208  the processed signal is converted back into a high frequency (RF) signal using the analog frequency converter (AFC)  204  so that it can be amplified by the power amplifier (PA)  206  and transmitted through the other antenna (by way of the other duplexer  200 ). 
         [0114]    The present embodiment includes two separate mixed-signal processor (MSP)  208  units; one for the uplink block  210  and one for the downlink block  212 . 
         [0115]    While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made.