Abstract:
Received data is filtered to produce pre-noise suppression data. Noise is removed from the pre-noise suppression data to provide noise-suppressed data. At least one weighted filter coefficient is dynamically determined using at least the pre-noise suppression data and not the noise suppressed data. The determination occurs independently from and is not affected by removing the noise from the pre-noise suppression data. Removing the noise from the pre-noise suppression data occurs independently from and is not affected by dynamically determining the at least one weighted coefficient.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of prior U.S. patent application Ser. No. 10/735,270 filed Dec. 12, 2003 entitled “Echo Canceler Circuit and Method,” naming James Piket, Kyle Iwai, and Daniel Rokusek as inventors, the content of which is hereby incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to communication systems and more particularly to echo cancelers and echo cancellation methods. 
       BACKGROUND OF THE INVENTION 
       [0003]    Communications systems may employ echo cancelers to compensate for the effects of echo. These systems may also employ noise suppressors to compensate for the effects of noise in a communication environment. 
         [0004]    Echo in a communication system is commonly characterized as the return of a part of the transmitted uplink signal from an end user back to the originator of the transmitted signal after a delay period. The reflection of the transmitted signal may occur due to a number of reasons, such as an impedance mismatch in a four/two wire hybrid, or feedback from acoustic coupling in a telephone, wireless device or hands free speaker phone at the far end. An echo signal corresponding to the delayed transmitted uplink signal is perceived as annoying to the near end user and in some cases can result in an unstable condition known as “howling”. 
         [0005]    Echo cancelers may be employed in wireless devices including a hands free speaker phone, such as cellular phones, car phones, two-way radios, car kits for cellular telephones and other suitable devices that can move throughout a geographic area. Additionally, echo cancelers may be employed in wireline devices such as hands free speaker phones, video and audio conference phones and telephones otherwise commonly referred to in the telecommunications industry as plain old telephone system (POTS) devices. Hands free speaker phones typically include a microphone to produce the uplink signal, a speaker to acoustically produce the downlink signal, the echo canceler to cancel the echo signal and a telephone circuit. 
         [0006]    Hands free speaker phones may be integrated into an in-vehicle audio system. The vehicle may be an automobile, a boat, an airplane, or any suitable vehicle. The in-vehicle audio system may include an amplifier, speakers and an audio source, such as a tuner module, CD/DVD player, tape player, satellite radio, etc. The in-vehicle audio system may be integrated with a communication apparatus, such as a telematics communication module. For example, the telematics communication module may be a component of a General Motors&#39; OnStar system. The telematics communication module typically collects and disseminates data, such as location information and audio, such as speech. 
         [0007]    Echo cancelers are known to attempt to cancel the echo signals produced at the near end when the far end is transmitting by generating echo estimation data corresponding to a portion of an amplified downlink audio signal traveling through the acoustic coupling channel. The echo canceler generates the echo estimation data through the use of an echo canceler adaptive filter. The echo canceler adaptive filter typically employs a finite impulse response (FIR) filter having a set of weighting coefficients to model the acoustic coupling channel between the speaker and the microphone. During the downlink talking mode, the echo canceler adaptive filter attempts to model the acoustic coupling channel by dynamically adapting the weighting coefficients of the finite impulse response filter. Additionally, attenuators in the uplink path and in the downlink path may also be used to mitigate the effects of the echo signal in response to changes in the acoustic coupling channel. 
         [0008]    When the near end user is not talking, then the echo canceler adaptive filter coefficient update procedure is typically idle since no downlink signal is present, however the filtering operation may still be active. When both the near end and far end are talking (i.e., double talk mode), the pre-echo canceler uplink microphone signal includes both interfering signals and the echo signal. Again the echo canceler adaptive filter coefficient update procedure is typically idle or significantly slower due to the interference of the noise end signal sources. The interfering signal includes near end speech, various noise components, and distortion. The various noise components may include elements such as non-linearities of the audio system, speaker distortion, and background noise. During double talk, the coefficient update procedure may be idle or altered, but the filtering operation will be active in an attempt to remove the echo component. One problem, however, is that real world effects including limitations in algorithm echo modeling convergence rates and steady state performance, variability in the echo path, mathematical precision limitations of a particular device employed, and non-linear audio system components, among others, all effect the ability of the adaptive echo canceller to remove or reduce the echo component from the transmit signal. As such, advanced modeling techniques, such as multiple cascaded adaptive filters have been explored to further improve the ability of an echo canceller system to minimize modeling errors and the corresponding residual echo. 
         [0009]    Noise suppressors may be employed at both the near end and the far end to reduce the noise content of a transmitted voice signal. Noise suppression can be particularly useful when the wireless device is a mobile handset or hands-free telephone operating in the presence of background noise, such as when operating a vehicle. In vehicular environments, background noise may be generated as a result of driving at high speeds or on bumpy roads, operating a blower fan resulting in air turbulence over the microphone, lowering or raising a window resulting in wind rumble, operating windshield wipers, operating turn signals or performing other activities resulting in other sources of noise within the vehicle. While noise suppression techniques may reduce background noise in a static or slowly changing noise environment, both noise suppression and echo cancellation performance can be significantly degraded by the combined generation of noise and echo signals. 
         [0010]      FIG. 1  illustrates a prior art cascade echo cancellation and noise suppression module  10  employing noise suppression logic  20 , an echo canceler circuit  30 , a digital-to-analog converter  40 , a speaker  50 , an analog-to-digital converter  60 , and a microphone  70 . The digital-to-analog converter  40  receives downlink data  52 , and in response produces a downlink signal  54 . The microphone  70  is coupled to the echo canceler circuit  30  via the analog-to-digital converter  60 . The analog-to-digital converter  60  receives a pre-echo canceler uplink signal  62  and produces pre-echo canceler uplink data  64 . Microphone  70  receives a portion of the downlink signal  54  produced by speaker  50  over an acoustic coupling channel  72  and in response produces the pre-echo canceler uplink signal  62 . 
         [0011]    Echo canceler circuit  30  includes a first echo canceler adaptive filter  80 , first adder logic  82 , a second echo canceler adaptive filter  84 , and second adder logic  86 . The first adder logic  82  receives the pre-echo canceler uplink data  64  and first echo estimation data  88  from the first echo canceler adaptive filter  80  and in response produces first post-echo canceler uplink data  90 . The second adder logic  86  receives the first post-echo canceler uplink data  90  and second echo estimation data  92  from the second echo canceler adaptive filter  84  to produce second post-echo canceler uplink data  94 . The noise suppression logic  20  receives final post-echo canceler uplink data  96  from the second echo canceler adaptive filter  84  and in response produces final uplink data  98 . 
         [0012]    Background noise is a persistent and common issue when echo cancellers are operating is harsh environments such as in an automobile environment. Due to the highly linear properties of the first echo canceler adaptive filter  80 , background noise present in the pre-echo canceler uplink data  64  will be passed relatively unaffected as part of the first echo canceller uplink data  90  to the second echo canceler adaptive filter  84 . However, due to the known suppression (non-linear) characteristics of the second stage cascaded adaptive filter  84 , the background noise level or amplitude will be modulated roughly based on the far end voice signal receive activity and due to some subsequent degree of linear echo cancellation in the first echo canceler adaptive filter  80 . Consequently, the noise suppression logic  20  receives, as part of the final post-echo canceler uplink data  96 , the noise modulation of the background noise primarily due to the second echo canceler adaptive filter  84 . 
         [0013]    As known in the art, noise suppression algorithms typically employed such as Non-Linear Spectral Subtraction (NLSS) are most effective when the background noise power remains relatively constant or varies slowly (such as with the increase and decrease of vehicle velocity). The noise modulation effect introduced primarily due to the second echo canceler adaptive filter  84  can be quite rapid, and results in poor performance of the noise suppression module  20  such as reduced signal to noise ratio (SNR) as well as annoying noise artifacts introduced by the noise suppression module  20  itself. Therefore, while the multiple filter topology improves echo cancellation in the presence of noise, the far end user will receive the final uplink data  98  containing annoying background noise artifacts. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present invention is illustrated, by way of example and not limitation, in the accompanying figures, in which like reference numerals indicate similar elements, and in which: 
           [0015]      FIG. 1  is a block diagram of a prior art echo cancellation and noise suppression module; 
           [0016]      FIG. 2  is a block diagram illustrating one example of an echo canceler circuit according to one embodiment of the invention; 
           [0017]      FIG. 3  is a flowchart illustrating one example of a method for echo cancellation and noise suppression according to one embodiment of the invention; 
           [0018]      FIG. 4  is a block diagram illustrating another example of an echo canceler circuit according to one embodiment of the invention; 
           [0019]      FIG. 5  is a block diagram illustrating an example of a communication system according to one exemplary embodiment of the invention; and 
           [0020]      FIG. 6  is a block diagram of an in-vehicle communication system according to one exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    An echo canceler circuit and method performs echo cancellation and noise suppression in a non-interfering manner. The echo canceler circuit includes pre-noise suppression logic, echo canceler coefficient logic, noise suppression logic and an echo canceler filter. The pre-noise suppression logic receives pre-echo canceler uplink data and downlink data, and in response produces pre-noise suppression uplink data. The echo canceler coefficient logic receives the pre-noise suppression uplink data and the pre-echo canceler uplink data, and in response produces filter coefficient data. The noise suppression logic receives the pre-noise suppression uplink data, and in response produces noise suppressed uplink data. The echo canceler filter receives the noise suppressed uplink data and the filter coefficient data and in response produces final uplink data. The invention described herein presents a unique cascaded echo canceller filter and noise suppression topology that allows for increased echo cancellation as well as a fully effective noise suppression module with compromising the performance of either. 
         [0022]    Among other advantages, the present invention performs both cascaded echo cancellation and noise suppression in a non-interfering manner. The noise suppression logic does not interfere with the generation of the filter coefficient data because the echo canceler coefficient logic receives pre-noise suppression uplink data without having been first processed in the noise suppression logic. Accordingly, the echo canceler coefficient logic models the changing acoustic coupling channel and produces the filter coefficient data without any interference from the noise suppression logic. As a result, the echo canceler coefficient logic functions independently from the noise suppression logic. 
         [0023]    Although the echo canceler filter receives the noise suppressed uplink data from the noise suppression logic, the generation of filter coefficient data is unaffected by the noise suppression logic. Therefore, the echo canceler filter may perform the adaptive echo cancellation function on the noise suppressed uplink data based on the independently generated filter coefficient data. As a result, the echo canceler filter produces final uplink data that has both been processed for echo cancellation and noise suppression, such that these functions are performed in a non-interfering manner. Since the noise suppression function is not introduced until after the modeling of the acoustic coupling channel and the generation of filter coefficient data, the generation of the filter coefficient data is independent of the noise suppressed uplink data. Additionally, the noise suppression logic does not encounter any artificial variations in a noise floor due to known suppression characteristics associated with cascaded echo cancellers. Consequently, the adaptation function of the filter coefficient data generator is able to achieve maximum echo cancellation performance since the noise suppression function does not affect the echo cancellation function and the maximum noise suppression performance available since the noise modulation caused by cascaded echo cancellation adaptive filtering and is eliminated. 
         [0024]      FIG. 2  is a block diagram of an echo canceler circuit  200  for performing both cascaded echo cancellation and noise suppression in a non-interfering manner. The echo canceler circuit  200  may be one or more suitably programmed processors, such as a microprocessor and a microcontroller, or a digital signal processor, and therefore includes associated memory, which contains executable instructions that when executed cause the echo canceler circuit  200  to carry out the operations described herein. In addition, the echo canceler circuit  200 , as used herein, may include discrete logic, state machines or any other suitable combination of hardware, software, middleware, and/or firmware. The echo canceler circuit  200  may also be employed in an analog or digital modem in a telecommunications system. 
         [0025]    The echo canceler circuit  200  includes pre-noise suppression logic  210 , noise suppression logic  212 , and echo canceler logic  214 . As discussed later, the pre-noise suppression logic  210  effectively performs at least some of the functions of the first stage of the overall cascaded echo canceller. The echo canceler logic  214  effectively performs at least some of the functions of the second stage of the overall cascaded echo canceller and includes an echo canceler filter  216 , and echo canceler coefficient logic  218 . The echo canceler coefficient logic  218  includes a filter coefficient data generator  220  and adder logic  222 . 
         [0026]    The pre-noise suppression logic  210  receives the pre-echo canceler uplink data  64  and the downlink data  52 , and in response produces pre-noise suppression uplink data  224 . The echo canceler coefficient logic  218  receives the pre-noise suppression uplink data  224  and the pre-echo canceller uplink data  64  and in response produces filter coefficient data  226 . The noise suppression logic  212  receives the pre-noise suppression uplink data  224 , and in response produces noise suppressed uplink data  228 . The echo canceler filter  216  receives the noise suppressed uplink data  228  and the filter coefficient data  226 , and in response produces final uplink data  230 . 
         [0027]    The filter coefficient data generator  220  receives the pre-echo canceler uplink data  64  and post echo canceler data  234  and in response produces echo estimation data  232  and the filter coefficient data  226 . The adder logic  222  receives the pre-noise suppression uplink data  224  and the echo estimation data  232  and in response provides the post-echo canceler data  234  to the filter coefficient data generator  220 . 
         [0028]      FIG. 3  illustrates a method  300  for performing echo cancellation and noise suppression according to one embodiment of the invention. The method  300  may be carried out by the echo canceler circuit  200  of  FIG. 2 . However, any other suitable structure may also be used. It will be recognized that the method  300  beginning with Step  310  will be described as a series of operations, but the operations may be performed in any suitable order and may be repeated in any suitable combination. As shown in Step  320 , the pre-noise suppression logic  210  produces the pre-noise suppression uplink data  224  in response to the downlink data  52  and the pre-echo canceler uplink data  64 . 
         [0029]    As shown in Step  330 , the echo canceler coefficient logic  218  produces the filter coefficient data  226  in response to the pre-noise suppression uplink data  224  and the pre-echo canceler uplink data  64 . As previously described, the echo canceler coefficient logic  218  produces the filter coefficient data  226  by adapting to changes in the pre-echo canceler uplink data  64  and pre-noise suppression uplink data. 
         [0030]    As shown in Step  340 , the noise suppression logic  212  produces the noise suppressed uplink data  228  in response to the pre-noise suppression uplink data  224 . Since the pre-noise suppression uplink data  224  is not processed by the echo canceler logic  214 , the pre-noise suppression uplink data  224  is not affected by the adapting function of echo canceler logic  214 . 
         [0031]    As shown in Step  350 , the echo canceler filter  216  produces the final uplink data  230  in response to the noise suppressed uplink data  228  and the filter coefficient data  226 . Since the echo canceler filter  216  receives the noise suppressed uplink data  228  from the noise suppression logic  212 , the echo canceler filter  216  may perform the adaptive filter function on the noise suppressed uplink data  228  by applying the filter coefficient data  226  previously produced. 
         [0032]    According one example, the pre-echo canceller uplink data  64  includes echo component data  240  and noise component data  242 , such that the echo canceler filter  216  produces the final uplink data with reduced echo component data  240 . As previously stated, the noise suppression logic  212  produces the noise suppressed uplink data  228  with reduced noise component data  242  without being affected by the generation of the filter coefficient data  226  produced by the echo canceler coefficient logic  218 . Accordingly, the noise suppression logic  212  produces the noise suppressed uplink data  228  with reduced noise component data  242  without being affected by the generation of the final uplink data  230  produced by the echo canceler filter  216 . 
         [0033]      FIG. 4  is a block diagram of a communication apparatus  400  in accordance with one embodiment of the invention. The communication apparatus  400  includes the echo canceler circuit  200 , a transceiver  410 , an audio system  420 , and the microphone  70 . The audio system  420  includes an amplifier  430 , at least one speaker  432 , a tuner module  434 , a tape player  436  and a CD/DVD player  438 . According to one embodiment, the echo canceller circuit  200  further includes a digital-to-analog converter  440 , and an analog-to-digital converter  442 . 
         [0034]    The pre-noise suppression logic  210  includes a pre-noise suppression coefficient data generator  460 , a pre-noise suppression filter  462 , and pre-noise suppression adder logic  464 , which when combined effectively perform the first stage of the cascaded adaptive filter. The pre-noise suppression coefficient data generator  460  receives the downlink data  52 , and in response produces pre-noise suppression coefficient data  466 . The pre-noise suppression filter  462  receives the pre-noise suppression coefficient data  466  and in response produces the pre-noise suppression echo estimation data  468 . The pre-noise suppression adder logic  464  receives the pre-noise suppression echo estimation data  468  and the pre-echo canceler uplink data  82  and in response produces the pre-noise suppression uplink data  224 . 
         [0035]    The digital-to-analog converter  440  receives the downlink data  52 , and in response produces a downlink audio signal  470 . The amplifier  430  receives the downlink audio signal  470  and in response produces an amplified downlink audio signal  472 . The at least one speaker  432  receives the amplified downlink audio signal  472  and in response produces a downlink acoustic signal  474 . The microphone  70  receives at least a portion of the downlink acoustic signal  474  produced as a result of the at least one speaker  432  acoustically producing the amplified downlink audio signal  472 , and in response produces a pre-echo canceler uplink signal  478 . The analog-to-digital converter  442  receives the pre-echo canceler uplink signal  478  and in response produces the pre-echo canceler uplink data  82 . The transceiver  410  receives the final uplink data  230  from the echo canceler filter  216  and also provides the downlink data  52  to the pre-noise suppression coefficient data generator  460  and the digital-to-analog converter  440 . 
         [0036]      FIG. 5  is a block diagram of a communication system  500  according to one exemplary embodiment of the invention. The communications system  500  includes the communication apparatus  400 , the audio system  420 , the at least one speaker  432 , the microphone  70 , a wireless wide area network (WWAN) transceiver  510 , WWAN antennas  520 ,  530 ,  550 ,  552 , wireless devices  540 ,  542 , and wireless local area network (WLAN) antennas  560 ,  570 . 
         [0037]    The communication apparatus  400  includes the processor  594 , the memory  320 , a WWAN transceiver  580 , a WLAN transceiver  590 , and a location information generator module  592 , such as a global positioning system (GPS) receiver. The processor  594  receives location information  595  from the location information generator  592  and in response relays the location information  595  to the WWAN transceiver  510 ,  580  or to the wireless device  540 ,  542 . 
         [0038]    According to one alternative embodiment, the echo canceler circuit  200  is coupled to either one or any combination of the WWAN transceiver  580 , the WWAN transceiver  510  or the WLAN transceiver  590 . For example, the WWAN transceiver  580 ,  510  may represent any one of a number of wireless devices, such as, for example, a portable cellular phone, an in-vehicle mobile phone, a wireless personal digital system (PDA), a wireless fidelity device (WiFi, i.e., a device based on the IEEE 802.11 specification) or any suitable communication device. According to another embodiment, the WWAN transceiver  510  may be external to the communication apparatus  400  and, therefore, the echo canceler circuit  200  may be coupled to the WWAN transceiver  510  via an appropriate link, such as a wired cable. 
         [0039]    According to one embodiment, the WLAN transceiver  590  may be integrated into the communication apparatus  400 . The WLAN transceiver  590  may be a Bluetooth compliance device or a wireless fidelity device (WiFi, i.e., a device based on the IEEE 802.11 specification, or any suitable communication device). 
         [0040]    The WLAN transceiver  590  may interface with the wireless device  540  via a WLAN interface  594 , the WLAN  560  antenna, and the WLAN antenna  570 . The wireless device  540 ,  542  may be a cellular phone, a personal digital assistant equipped with a wireless interface, a portable computer also equipped with a WWAN and WLAN interface or any suitable wireless device. The wireless device  540 ,  542  may communicate with a WWAN, such as a cellular telephone system suitable for communicating with a public switching telephone network (PSTN). Accordingly, the wireless device  540 ,  542  may communicate with the cellular telephone system using any wireless communication protocol, such as, for example, code division multiple access (CDMA), time division multiple access (TDMA), advance mobile phone standard (AMPS), group special mobile (GSM), or any other suitable wireless communication protocols available now or in the future. 
         [0041]    The communication apparatus  400  according to one embodiment includes a housing containing the processor  594 , the wireless wide area transceiver  580 , the WLAN transceiver  590  and the location information generator  592 . Additional or fewer components may be included in the communication apparatus  400  other than those described above. As is known in the art, the processor  594 , the WWAN transceiver  580 , the WLAN transceiver  590  and the location information generator  592  may each be manufactured as separate circuit boards or integrated circuit chips from one or more manufacturers. The circuit boards may be interconnected as required through the use of a mother board, a flat or non-flat flexible multi-conductor cable, a multi-conductor wired cable or any suitable type of interconnection device. Each circuit board may be attached or coupled either directly or indirectly to the housing or to other circuit boards via a suitable fastening device as is known in the art, such as a connector, a clamp, a clip, a screw, a nut and a bolt. The integrated circuit chips may be interconnected as required via a circuit board, a multi-circuit chip carrier, a flat flexible multiconductor cable, a multiconductor wired cable or any suitable type of interconnection device. The circuit boards and integrated circuit chips may be mounted using chemical bonding such as an adhesive or any suitable fastening device. 
         [0042]    According to one embodiment, the communication apparatus  400  housing may include: a circuit board comprising the processor  594  and memory  320 , a circuit board comprising the WWAN transceiver  580 , and a circuit board comprising the WLAN transceiver  590 . The circuit boards may be interconnected and attached or coupled to the housing either directly or indirectly as previously discussed. Additionally, the communication apparatus  400  housing may include connectors for coupling to external components such as the audio system  420 , the microphone,  70 , WWAN antenna  530 , WLAN antenna  570 , WWAN transceiver  510  or any other suitable device. For example, the communication apparatus  400  may interface with other suitable components not described herein. The connectors may be any suitable device for interconnecting the communication apparatus  400  to any external components such as via a wired cable, a fiber optic link, or a radio frequency interface. 
         [0043]    According to one embodiment, the communication apparatus  400  is a telematics communication module supporting the collection and dissemination of data, including audio speech. For example, the telematics communication module may be based on General Motors&#39; OnStar System, which automatically calls for emergency assistance if the vehicle is in an accident. According to another embodiment, the communication apparatus  400  also can perform such functions as remote engine diagnostics, tracking stolen vehicles and providing roadside assistance, as well as other functions. 
         [0044]      FIG. 6  is a block diagram of an in-vehicle communication system  600  according to at least one embodiment of the invention. The in-vehicle communication system  600  includes the communication apparatus  400  coupled to the wireless device  540  via the wireless local area network antenna  570 . For example, the communication interface between the wireless device  540  and the communication apparatus  400  may be a Bluetooth interface, as previously discussed. However, the in-vehicle communication system  600  may include a wireless wide area network transceiver  580 , as shown previously with respect to  FIG. 5 . Alternatively, the communication apparatus  400  may interface with the WWAN transceiver  510 ,  580  either external or internal to the communication apparatus  400  and coupled to WWAN antenna  520 ,  530  and may be mounted in any suitable location. 
         [0045]    The communication apparatus  400  is also shown to interface with the vehicle&#39;s audio system  420 . Although the audio system  420  and the communication apparatus  400  are shown in the trunk area of the vehicle, the communication apparatus  400  and the audio system  420  may be located in any suitable location, including in the dashboard or under the dashboard. According to one embodiment, the audio system  420  may include the communication apparatus  400  and any necessary transceiver, such as the wireless wide area network transceiver  510 ,  580  and the wireless local area network transceiver  590 . 
         [0046]    Among other advantages, the present invention performs both cascaded echo cancellation and noise suppression in a non-interfering manner. The noise suppression logic  212  does not interfere with the generation of the filter coefficient data  226  because the echo canceler coefficient logic  218  receives pre-noise suppression uplink data  224  without having been first processed in the noise suppression logic  212 . Accordingly, the echo canceler coefficient logic  218  produces the filter coefficient data  226  without any interference from the noise suppression logic  212 . As a result, the echo canceler coefficient logic  218  functions independently from the noise suppression logic  212 . 
         [0047]    Although the echo canceler filter  216  receives the noise suppressed uplink data  228  from the noise suppression logic  212 , the generation of filter coefficient data  226  is unaffected by the noise suppression logic  212 . Therefore, the echo canceler filter  216  may perform the adaptive echo cancellation function on the noise suppressed uplink data  228  based on the independently generated filter coefficient data  226 . As a result, the echo canceler filter  216  produces final uplink data  230  that has both been processed for echo cancellation and noise suppression, such that these functions are performed in a non-interfering manner. Since the noise suppression function is not introduced until after the modeling of the acoustic coupling channel  72  and the generation of filter coefficient data  226 , the generation of the filter coefficient data  226  is independent of the generation of the noise suppressed uplink data. As a result, the noise suppression logic  212  does not encounter or at least encounters reduced artificial variations in a noise floor due to know suppression characteristics of cascaded echo cancellers. Consequently, the adaptation function of the filter coefficient data generator  220  is able to achieve both maximum echo cancellation performance and maximum noise suppression performance available since the noise suppression function has a minimal effect the echo cancellation function. 
         [0048]    It is understood that the implementation of other variations and modifications of the present invention and its various aspects will be apparent to those of ordinary skill in the art and that the present invention is not limited by the specific embodiments described. It is therefore contemplated to cover by the present invention any modifications, variations or equivalents that fall within the spirit and scope of the basic underlying principles disclosed and claimed herein.