Abstract:
Various embodiments relate to a device for reducing noise in a received signal, the device including a memory; a processor configured to: receive a signal containing narrow band noise which was transmitted over a channel and received at an analog front end; add two separate delays to the signal to generate a first delayed signal and a second delayed signal; apply an adaptive noise cancellation using the first delayed signal and the second delayed signal to estimate the narrow band noise; and remove the narrow band noise based upon the estimated narrow band noise.

Description:
TECHNICAL FIELD 
     Various embodiments disclosed herein relate generally to noise reduction. 
     BACKGROUND 
     Electronic communications oftentimes use cables and other wires to send data across either long or short distances. The wiring may take place on the Open Systems Interconnection (OSI) model layer 1 or the physical layer often called PHY. For example, Ethernet uses a serial communications PHY as well Universal Serial Bus (USB). Machine to machine communications may thus transfer data from one end to another using these wires, for example using copper. The cables may receive some Radio Frequency (RF) noise. The noise may enter the PHY layer. 
     SUMMARY 
     A brief summary of various embodiments is presented below. Some simplifications and omissions may be made in the following summary, which is intended to highlight and introduce some aspects of the various embodiments, but not to limit the scope of the invention. Detailed descriptions of a preferred embodiment adequate to allow those of ordinary skill in the art to make and use the inventive concepts will follow in later sections. 
     Various embodiments described herein relate to a device for reducing noise in a received signal, the device including a memory; a processor configured to: receive a signal containing narrow band noise which was transmitted over a channel and received at an analog front end; add two separate delays to the signal to generate a first delayed signal and a second delayed signal; apply an adaptive noise cancellation using the first delayed signal and the second delayed signal to estimate the narrow band noise; and remove the narrow band noise based upon the estimated narrow band noise. 
     Various embodiments described herein relate to a method for reducing noise in a received signal, the method including receiving a signal containing narrow band noise which was transmitted over a channel and received at an analog front end; adding two separate delays to the signal to generate a first delayed signal and a second delayed signal; applying an adaptive noise cancellation using the first delayed signal and the second delayed signal to estimate the narrow band noise; and removing the narrow band noise based upon the estimated narrow band noise. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to better understand various embodiments, reference is made to the accompanying drawings, wherein: 
         FIG. 1  illustrates an example of a system for implementing the noise elimination scheme; 
         FIG. 1A  illustrates an exemplary test setup; 
         FIG. 1B  illustrates noise due to BLW effect; 
         FIG. 2  illustrates an example of related art adaptive noise cancellation; 
         FIG. 3  illustrates an example an embodiment of adaptive noise cancellation using delays; 
         FIG. 4  illustrates an embodiment of adaptive noise cancellation; 
         FIG. 5  illustrates an embodiment of adaptive noise cancellation; 
         FIG. 6  illustrates an embodiment of adaptive noise cancellation; and 
         FIG. 7  illustrates an embodiment of adaptive algorithm. 
     
    
    
     To facilitate understanding, identical reference numerals have been used to designate elements having substantially the same or similar structure or substantially the same or similar function. 
     DETAILED DESCRIPTION 
     The description and drawings presented herein illustrate various principles. It will be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody these principles and are included within the scope of this disclosure. As used herein, the term, “or” refers to a non-exclusive or (i.e., and/or), unless otherwise indicated (e.g., “or else” or “or in the alternative”). Additionally, the various embodiments described herein are not necessarily mutually exclusive and may be combined to produce additional embodiments that incorporate the principles described herein. 
     When a received signal is noisy as a result of narrow band RF noise, the receiver performance may be poor. The narrow band RF noise may affect performance of adaptive filters such as an equalizer, echo canceller, and timing recovery. 
     Low frequency components such as Direct Current (DC), for example, may be present in wired communications interfaces, while low frequency component free signaling may be desired. Long sequences of received symbols when averaged for a long period (such as infinite) may be low frequency component free. But if one observes a sequence of data for a short time interval, it may not be low frequency component free. The low frequency component must be compensated for which may occur typically using a high pass coupling filter, for example, a transformer or a coupling capacitor. 
     A coupling capacitor may charge and discharge symbols on a line. For example, symbols such +1, 0, or −1 may be affected as the receiver integrates the long run length. Main sources of narrow band RF noise in a serial communication system may include 1) Bulk Current Injection (BCI)/Direct Power Injection (DPI) and 2) Residual Baseline Wander (BLW) due to the coupling networks. The presence of narrow band RF noise in data may degrade the Signal to Noise Ratio (SNR) and results in longer startup time, partial cancellation due to Inter-Symbol Interference (ISI), and/or near-end/far-end echo or crosstalk. When a system&#39;s SNR becomes poor, the performance of timing recovery may also degrade and not be able to meet the worst case channel requirements. 
     Some embodiments may include techniques to cancel not only a single tone, but may cancel multi-tone narrow band RF noise. This noise may originate from BCI, DPI, BLW or combinations of these or other types of noise. Low frequency components may be eliminated through adaptive algorithms at the receiver. Complete removal of residual low frequency RF noise may increase Analog to Digital Converter (ADC) dynamic range. Similarly one may want to make sure that adaptive algorithms are tolerant to low frequency noise. Efficiency in terms of area, power, and complexity is also a goal. 
       FIG. 1  illustrates an exemplary environment for implementing noise reduction algorithms  100 . Environment  100  may include system  105 , connector  110 , and system  115 . Systems  105  and  115  may be any kind of system such as a computer, laptop, server, receiver, multimedia receiver, amplifier, etc. Connector  110  may be any kind of connection such as a wired connection comprising copper twisted wire. Connector  110  may be an Ethernet connection such as 4-pair copper structured cabling, category 5 cable. Similarly, connector  110  may be avionics full-duplex switched Ethernet and time triggered Ethernet. 
       FIG. 1A  illustrates an exemplary test setup  120 . Exemplary test setup may be an Immunity test setup including parameters;
         RF power=36 dBm   Freq.→1 Hz to 1 GHz   RF noise power injected through a coupling network with capacitors and resistors       

     After common-mode to differential mode conversion, differential RF noise may not be seen at the receiver. 
       FIG. 1B  illustrates noise due to BLW effect  130 . Noise  130  may be Residual RF noise due to BLW effect. Noise  130  may include types of noise which are to be compensated for in different embodiments. 
       FIG. 2  illustrates an example of related art basic adaptive noise cancellation  200 . Basic adaptive noise cancellation typically uses a reference signal to eliminate the added noise. In basic noise cancellation, one may only cancel the single tone narrow band RF noise. Basic noise cancellation typically does not cancel multi-tone narrow band RF noise. In exemplary basic adaptive noise cancellation  200 , reference signal Ref n  is used as an input to an adaptive algorithm. The input signal x n  is modified with Noise n  from the environment and the modified signal is combined with the output of the adaptive algorithm to produce an estimate e n  of input signal x n . 
       FIG. 3  illustrates an example embodiment of adaptive noise cancellation using delays  300 . Embodiment  300  may include channel  305 , narrow band RF noise input  310 , which is added to the signal on the channel  305 , analog front end  320 , narrow band RF noise  350  which is added  325  to the output of the analog front end  320 , Adaptive multi-tone Narrow Band RF Noise canceller  328 , filter  330 , omega delay  335 , delta delay  340 , and adaptive algorithm  345 . 
     There are two delay blocks that are added so that you do not need a reference signal, but rather fact that the data symbols are not correlated, but that the noise is somewhat correlated may be used to estimate and cancel the narrow band noise. 
     A clean signal may enter channel  305  from, for example, system  105 . Channel  305  may be connector  110 , for example. On the channel, any type of noise such as narrow band RF noise  310  may be added  315  to the clean signal in step  315  and then input into the analog front end  320  as a distorted signal or the noise may be added before the channel. Analog front end  320  may be on system  115 , for example. The distorted signal may further be distorted  325  by narrow band RF noise  350  inside the receiver and input to Adaptive multi-tone Narrow Band RF Noise canceller  328 . 
     Adaptive multi-tone Narrow Band RF Noise canceller  328  may include filter  330 , omega delay  335 , delta delay  340 , and adaptive algorithm  345 . Adaptive algorithm  345  may be any adaptive known noise reduction algorithm such as Least Mean Square (LMS), Recursive Least Squares Filter (RLS), sign LMS, sign-sign LMS. Filter  330  may be a 1-tap filter using a LMS algorithm, for example. 
     Two delay blocks, omega delay  335  and delta delay  340  may be added so that one does not require a reference signal to reduce multi-tones narrow band RF noise. Correlation may be achieved by tuning the values of Ω≧1 and Δ≧1. The two delays may be added to the signal containing transmitted symbols and the added noise. This signal may be a transverse signal with noise added on top of it. 
     The signal, after adding the delays may be cross correlated. When two signals have full orthogonality, then their cross correlations will be zero. The sampled signal along with the multiple delays may be fed into any adaptive noise reduction algorithm. One may find the cross correlation between the two signals. For example, the run length may be very far from one symbol to the next on a distorted signal. One may then find the correlation between the two signals in order to estimate the narrow band noise. 
     In one example, the adaptive algorithm may be a LMS algorithm where:
 
 h ( n+ 1)= h ( n )+ uX ( n ) e *( n );
         h(n+1) represents a new coefficient;   h(n) represents a previous coefficient;   u represents a gain factor;   x(n) represents signal samples; and   e*(n) represents error.       

     The previous coefficient h(n) may be multiplied with the omega delay and subtracted from the delta delay to produce the error e*(n). X(n) may be time delayed by omega delay. e*(n) and X(n) may be multiplied and then amplified by gain factor u. This output signal may be input into the adaptive filter along with a new coefficient. 
       FIG. 4  illustrates an embodiment of adaptive noise cancellation  400 . Embodiment  400  may include channel  405 , narrow band RF noise  410 , analog front end  415 , low frequency narrow band RF noise  420 , adaptive narrow band RF noise canceller  425 , echo canceller  430 , subtractor  435 , adaptive equalizer  440 , and timing recovery  445 . 
     In embodiment  400 , noise may be removed before echo canceller  430 , adaptive equalizer  440 , and timing recovery  445  steps are performed. The noise canceller  425  may include the elements discussed in  FIG. 3 . A signal may enter channel  405 , which may be connector  110 . The signal may be distorted by narrow band RF noise  410  before entering analog front end  415 . Narrow band RF noise  410  may be BCI or DPI, for example. A signal with noise may then enter analog front end  415 , which may be part of system  115 , for example. The modified signal may have multi-tone narrow band RF noise suppressed or eliminated when leaving noise canceller  425 . At step  435 , the noise suppressed signal may then be modified by echo cancellation from echo canceller  430 . Echo canceller  430  may use any acoustic echo suppression (AES), acoustic echo cancellation (AEC), and line echo cancellation (LEC) techniques. 
     The signal may then be modified by adaptive equalizer  440 . Adaptive equalizer  440  may be any type of equalizer as described above such as a linear equalizer or a decision feedback equalizer. The adaptive equalizer  440  may update the equalizer parameters, for example, filter coefficients. The adaptive equalizer  440  may use, for example, cost functions such as Mean Squared Error (MSE). Next, carrier recovery may be performed in timing recovery  445 . In timing recovery  445 , frequency and phase differences between a carrier wave and the receiver&#39;s oscillator may be estimated and compensated for in order to complete demodulation. 
       FIG. 5  illustrates another embodiment of adaptive noise cancellation  500 . Embodiment  500  may include channel  505 , narrow band RF noise  510 , analog front end  515 , low frequency narrow band RF noise  520 , echo canceller  525 , subtractor  530 , adaptive narrow band RF noise canceller  535 , adaptive equalizer  540 , and timing recovery  545 . 
     In embodiment  500 , noise may be removed by the noise canceller  535  after echo canceller  525 , and before adaptive equalizer  540  and timing recovery  545 . Noise canceller  535  may include the elements discussed in  FIG. 3 . A signal may enter channel  505 , which may be connector  110 . The signal may be distorted by narrow band RF noise  510  before entering analog front end  515 . Narrow band RF noise  510  may similarly be BCI or DPI, for example. Analog front end  515  may be part of system  115 . The signal may then be modified by echo canceller  525  before entering noise canceller  535 . 
     After exiting the noise canceller  535 , the signal may have multi-tone narrow band RF noise suppressed. The signal may then be modified by adaptive equalizer  540 . Adaptive equalizer  540  may be any type of equalizer as described above such as a linear equalizer or a decision feedback equalizer. The adaptive equalizer  540  may update the equalizer parameters, for example, filter coefficients. The adaptive equalizer  540  may use, for example, cost functions such as Mean Squared Error (MSE). Next, carrier recovery may be performed in timing recovery  545 . In timing recovery  545 , frequency and phase differences between a carrier wave and the receiver&#39;s oscillator may be estimated and compensated for in order to complete demodulation. 
       FIG. 6  illustrates an embodiment of adaptive noise cancellation  600 . Embodiment  600  may include channel  605 , narrow band RF noise  610 , analog front end  615 , low frequency narrow band RF noise  620 , echo canceller  625 , subtractor  630 , adaptive narrow band RF noise canceller  640 , and timing recovery  645 . 
     RF noise may be cancelled after the echo cancellation  625  and adaptive equalization  635  takes place in embodiment  600 . Noise cancellation may be more effective after echo and ISI are removed. The tradeoff is that echo and equalizer convergence may be longer. 
     A simulation was performed with plot eye diagrams attached to the echo canceller both before and after the noise canceller. Narrow band noise with the following characteristics were used:
         RF Noise-1: 500 kHz-200 mVpp before the analog front end input.   RF Noise-2: 800 kHz-100 mVpp after the analog front end output.   Total 300 mVpp of RF Noise       

     The results of the simulation illustrated the following benefits:
         Better echo cancellation where less residual will be left;   Better ISI cancellation where less ISI residual will be left;   Improved SNR margins;   Convergence of adaptive echo and equalizer with increased speed; and   Quicker start-up time.       

       FIG. 7  illustrates an embodiment of adaptive algorithm  700 . The received symbol x(k) may be delayed by delayer Ω and Δ. x(n) may be multiplied with e(n) and later multiplied with a step size (gain) u. Each new value of coefficient h(n+1) may be stored in a register. Current coefficient h(n) may be multiplied with x(n) and results in p(n). Delayed received symbol x(k), using delayer Δ, may be subtracted from p(n) and result in error e(n). These same steps above may repeat for each clock cycle. 
     It should be apparent from the foregoing description that various embodiments of the invention may be implemented in hardware. Furthermore, various embodiments may be implemented as instructions stored on a non-transitory machine-readable storage medium, such as a volatile or non-volatile memory, which may be read and executed by at least one processor to perform the operations described in detail herein. A machine-readable storage medium may include any mechanism for storing information in a form readable by a machine, such as a personal or laptop computer, a server, or other computing device. Thus, a non-transitory machine-readable storage medium excludes transitory signals but may include both volatile and non-volatile memories, including but not limited to read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, and similar storage media. 
     It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the invention. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in machine readable media and so executed by a computer or processor, whether or not such computer or processor is explicitly shown. 
     Although the various embodiments have been described in detail with particular reference to certain aspects thereof, it should be understood that the invention is capable of other embodiments and its details are capable of modifications in various obvious respects. As is readily apparent to those skilled in the art, variations and modifications can be effected while remaining within the spirit and scope of the invention. Accordingly, the foregoing disclosure, description, and figures are for illustrative purposes only and do not in any way limit the invention, which is defined only by the claims.