Abstract:
A method of processing a signal including the steps of: (a) modulating the signal using a modulator corresponding to a modulation, (b) sending the modulated signal over multiple frequencies where the signal is offset in time in each frequency, (c) receiving the signal over the multiple frequencies, (d) reconstructing the sent signal by reversing the time delay and combining the received signal from each frequency, and (e) demodulating the received combined signal using a demodulator corresponding to the modulation used in (a).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of application Ser. No. 14/160,473, filed on Jan. 21, 2014, which patent application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/754,286, filed Jan. 18, 2013, which applications are incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The invention broadly relates to signal processing in wired, optical, and wireless communication. 
     BACKGROUND OF THE INVENTION 
     Current techniques for signal processing in wired and wireless communication require sub-dividing the available bandwidth along one or more dimensions (i.e., frequencies, time, signal shape, signal phase, etc.), with the consequence that supporting a larger number of logical channels either requires increasing the available bandwidth (e.g., number of frequencies), or reducing the share of total bandwidth used for each logical channel. This results in bandwidth becoming a limited shared resource, subject to congestion and even exhaustion. 
     This method provides an exceptionally large number of logical channels over a set of shared signal frequencies without interleaving or subdividing the available bandwidth. It uses the statistical properties of signals coupled with a simple multiplexing technique to enable each channel to fully employ all standard signal properties (dimensions) concurrently. It is compatible with many existing signal encoding modulation/demodulation) techniques, and can leverage existing signal processing technologies. 
     BRIEF SUMMARY OF THE INVENTION 
     A method of processing a signal including the steps of: (a) modulating the signal using a modulator corresponding to a modulation, (b) sending the modulated signal over multiple frequencies where the signal is offset in time in each frequency, (c) receiving the signal over the multiple frequencies, (d) reconstructing the sent signal by reversing the time delay and combining the received signal from each frequency, and (e) demodulating the received combined signal using a demodulator corresponding to the modulation used in (a). 
     A method of processing a signal, including the steps of (a) modulating the message to be sent to form a baseband signal using a specified modulation and baseband frequency, (b) converting the baseband signal to multiple transmission frequencies, (c) applying a time delay offset to the signal in each transmission frequency, (d) combining the multiple transmission frequencies into a single combined signal, (e) transmitting the combined signal, followed by (f) receiving the combined signal, (g) separating the combined signal into components corresponding to each transmission frequency, (h) reversing the time delay offset used in (c) for the signal in each transmission frequency, (i) converting the signal for each transmission frequency to the frequency of the baseband signal, (j) reconstructing an estimate of the original baseband signal by combining the baseband signal from each transmission frequency, and (k) demodulating the combined baseband signal to recover the original message using a demodulator corresponding to modulation utilized in (a). 
     The present invention provides a method for multiplexing a large number of logical communications channels (data streams) over a set of shared signal frequencies, and does so without interleaving or subdividing the available bandwidth by employing offset time delays applied to each frequency that are unique to each logical communications channel. This allows the individual channels to fully employ all standard signal properties (dimensions) concurrently. Consequently, the bandwidth can be used more effectively by (1) allowing a larger number of communications channels to share the same set of frequencies, and/or (2) enabling each communications channel to achieve a higher data rate, and/or (3) achieve a lower error rate for each communication channel. 
     The invention can be utilized with any transmission medium capable of carrying multiple, nearly-continuous real or complex valued signals, including wired and wireless radio-frequency and fiber-optic systems. Further, it is compatible with many existing modulation, demodulation, decoding and other signal processing techniques. As a consequence it possible to develop systems based on this new invention while leverage existing signal processing equipment, techniques, and technologies. 
     Multiple independent communications streams over a shared (wired or wireless) resource can be accomplished using multiplexing. Multiplexing combines one or more logical signals into a single signal by assigning each logical signal some unique combination of the properties of the signal. Current multiplexing approaches utilize a particular signal property, including: 
     1. Location (wireless) or Connectedness (wired): Space-division multiplexing 
     2. Carrier Frequency: Frequency-division multiplexing 
     3. Time: Time-division multiplexing 
     4. Signal shape: Code-division multiplexing 
     5. Polarization: Polarization-division multiplexing 
     6. Orbital angular momentum (experimental) 
     The key concept for this invention is to send the same signal over multiple frequencies with a different time offset (delay) in each frequency, using the same modulation technique in each frequency. The original signal is then reconstructed by reversing this process. 
     The additive nature of signals, and the statistical properties of sums of values with the same mean (signal value) and differing noise (or interference) [cf. the central limit theorem], means that a message broadcast over multiple frequencies can be recovered with high fidelity even from very noisy samples. 
     By selecting unique offsets, multiple independent communication channels can utilize the same set of frequencies without the need to subdivide by other properties of the signal (e.g., time-division multiplexing). Provided that the number of frequencies and offsets is large enough, the number of concurrent channels can be exceptionally large. For instance, utilizing ten (10) non-overlapping frequencies, and sixteen (16) possible offsets, over one trillion logical channels are possible, 16 10 =1.10e+12, and the signal to noise ratio of the individual logical channels can be up to √{square root over ((10))}=3.2 times higher than the per-channel signal to noise ratio. 
     The process described herein provides a mechanism for multiplexing multiple data streams for transmission over a common medium and then for recovering the original data streams from the received transmission. It can be utilized in a variety of contexts by one or multiple senders and for one or multiple receivers. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which: 
         FIGS. 1 a , 1 b , and 1 c    illustrate an example of Binary Amplitude Shift Keying (ASK) modulation for a channel 1 message; 
         FIG. 2  illustrates encoding for the channel 1 message depicted in  FIGS. 1 a , 1 b   , and  1   c;    
         FIGS. 3 a , 3 b , and 3 c    illustrate an example of Binary Amplitude Shift Keying (ASK) modulation for a channel 2 message; 
         FIG. 4  illustrates encoding for the channel 2 message depicted in  FIGS. 3 a , 3 b   , and  3   c;    
         FIG. 5  depicts the combined signals for channel 1 and channel 2; 
         FIGS. 6 a , 6 b , and 6 c    illustrate the decoding of the combined signals into messages 1 and 2; 
         FIG. 7  is a diagram of an example encoder for a single data stream; and, 
         FIG. 8  is a diagram of an example decoder for a single data stream. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the invention. While the present invention is described with respect to what is presently considered to be the preferred aspects, it is to be understood that the invention as claimed is not limited to the disclosed aspect. The present invention is intended to include various modifications and equivalent arrangements within the spirit and scope of the appended claims. 
     Furthermore, it is understood that this invention is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present invention, which is limited only by the appended claims. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods, devices, and materials are now described. 
     The invention provides for sending multiple signals over a set of common transmission frequencies. Each signal of interest (logical channel) is frequency multiplied onto a set of shared transmission frequencies. Next, set of offset delays unique to the logical channel is applied to each of the transmission frequencies. This results in multiple copies of the signal of interest carried on different frequencies and with different offset in time. The individual transmission frequencies are then combined and transmitted over the shared transmission medium, which may also carry transmissions of other logical channels. 
     Upon reception, the process is reversed, with individual transmission frequencies being separated (e.g., by filtering and frequency division), followed by reversal of the offset delays corresponding to the logical channel of interest. This yields multiple time-aligned copies of the original signal of interest (plus noise and/or interference). 
     The use of a unique set of delay offsets for each logical channel allows the corresponding baseband modulated signal to be recovered, while the use of multiple copies of the signal of interest (one in each frequency) yields a substantial processing gain and corresponding improvement in effective signal to noise ratio. 
     The multiple logical channels provided may be used for multiple-access (e.g., for a cell-phone system), or for multiplexing (e.g., to provide a higher data throughput for a single data stream), or for a combination of both multiple access and multiplexing. 
     An individual device may include one or more transmitters, receivers, or both, and such transmitters and receivers may share physical or logical components. 
     The frequencies utilized by a specific logical channel are either all of or only a subset of the frequencies used by all logical channels. 
     A separate physical medium for each time-offset copy of the original signal instead of separate carrier frequencies over a shared transmission medium may be implemented. 
     Logical communications channel c is a data stream, for example, consisting of a single logical transmitter and one or more logical receivers intended to receive and decode the data stream originating from the transmitter. For clarity of exposition, we further assume the absence of frequency-specific fading, multi-path interference, and the near-far problem. 
     The process will be illustrated using binary (on-off) amplitude shift keying (ASK) modulation for two logical channels, each consisting of a single transmitter and receiver. In one example, two 8-bit messages are sent, encoded using simple binary amplitude modulation, a code length of 1/100 sec=0.01 sec, and a guard period of ¼ of the code length. Single modulation will occur on 10 carrier frequencies, ranging from 1000 Hz to 1100 Hz. The waveform will be modeled with resolution 1100*50 Hz=55,000 Hz. 
     Setup 
       FIG. 1 a    represents carrier wave CW 1 .  FIG. 1 b    represents mask: (0, 1, 0, 1, 1, 0, 0, 1).  FIG. 1 c    represents a signal. Together,  FIGS. 1 a , 1 b , and 1 c    illustrate an example of Binary Amplitude Shift Keying (ASK) modulation for a channel 1 message.  FIG. 2  is a signal encoding for bits (0, 1, 0, 1, 1, 0, 0, 1) and offsets (11, 10, 10, 11, 14, 14, 3, 14, 4, 7). 
       FIG. 3 a    represents carrier wave CW 2 .  FIG. 3 b    represents mask: (0, 0, 1, 1, 1, 1, 0, 1).  FIG. 3 c    represents a signal. Together,  FIGS. 3 a , 3 b , and 3 c    illustrate an example of Binary Amplitude Shift Keying (ASK) modulation for a channel 2 message.  FIG. 4  is a signal encoding for bits (0, 0, 1, 1, 1, 1, 0, 1) and offsets (0, 13, 8, 2, 7, 4, 1, 0, 14, 11). 
       FIG. 5  is the combined signals for channel 1 and channel 2.  FIGS. 6 a , 6 b , and 6 c    illustrate the decoding of the combined signals into messages 1 and 2.  FIG. 7  is a diagram of an example encoder for a single data stream.  FIG. 8  is a diagram of an example decoder for a single data stream. 
     The following should be viewed in light of  FIGS. 1 a    through  8 . Transmission occurs on a set of F&gt;1 frequencies, f 1 , f 2 , . . . , f F , each of which is the center of a frequency interval with the same bandwidth B. For each communications channel, select a set of F offset delays: d c,1 , d c,2 , . . . , d c,F , such that no two channels share the same set of offsets. Modulation M (along with corresponding demodulation/decoding method M′) and data rate R that are compatible with bandwidth B and the selected frequencies are selected. In other words, M and R must be compatible with each pair (f i , B). Common modulation examples include binary amplitude shift keying (ASK), binary phase shift keying (BPSK), gaussian-mean shift keying (GMSK), quadrature amplitude modulation (n-QAM), etc. 
     Encoding the Data Stream for a Single Logical Channel 
     As shown in  FIG. 7 , encoding a data stream I c  for channel c proceeds as follows: 
     1. Modulate the input data stream I c  using modulation M at data rate R to generate symbol stream S c (t) at baseband frequency f b . 
     2. For each transmission frequency f i , i=1, 2, . . . F (note that the order of the following two steps may be reversed):
         a. Use a frequency multiplier to convert symbol stream S c (t) from baseband frequency f b  to transmission frequency f i  to form transmission symbol stream S *   c,i (t).   b. Apply a time delay of d c,i  to transmission symbol stream S* c,i (t) to yield delayed transmission symbol stream O c,i (t).       

     3. Combine the delayed transmission symbol streams O c,i (t) by component-wise addition to yield the combined signal O +   c (t). 
     4. Amplify A the combined signal O +   c (t) (if necessary) and send to transmitter T. 
     Decoding the Data Stream for a Single Logical Channel 
     As shown in  FIG. 8 , decoding data stream I* c  for channel c proceeds as follows: 
     1. Receive signal from receiver R and amplify A (if necessary) to yield combined signal N(t), which may include noise and interference, including signals from other communications channels. 
     2. For each transmission frequency f i , i=1, 2, . . . F (note that order of the following two steps may be reversed):
         a. Use filter  30  and frequency-divider pair (or frequency-divide and then filter  30 ) to convert the combined N(t) from transmission frequency f i  to baseband frequency f b  to yield O* i (t).   b. Reverse the offset delay, e.g., by applying delay d of the form d c,max −d c,i  where d c,max =max(d c,i ) over i=1, 2, . . . , F to form O −   c,i (t).       

     3. Combine the now-aligned baseband signal streams O −   c,i (t) (via addition) to form the estimated symbol stream E c (t). 
     4. Apply the demodulation/decoder method M′ to estimated symbol stream E c (t) yielding the output data stream I* c . 
     When the receiver(s) have access to offsets for multiple channels {d c,i }, multi-channel decoders can be constructed that reduce the error rate in I* c  by performing joint estimation of the symbol streams {E c,i (t)}. 
     One example embodiment includes: 
     A single physical transmitter sending C=2 logical channels 
     Two physical receivers, each decoding a single logical channel c 
     Amplitude-shift keying (ASK), with amplitude of ±1 Volt for the modulation M 
     F=10 frequency bands each of width B=10 hz, spanning 1000 hz to 1100 hz, centered at f 1 =1005 hz, f 2 =1015 hz, . . . f 12 =1095 hz 
     Data rate of R=10 samples/sec 
     Offsets for each channel c selected by sampling the d c,i  with replacement from the set {0.0 sec, 0.10 sec, . . . , 2.00 sec}, i.e. 0 through 20 cycle lengths. 
     Receivers amplify the received signals to amplitude of ±1 Volt. 
     Thus, it is seen that the objects of the present invention are efficiently obtained, although modifications and changes to the invention should be readily apparent to those having ordinary skill in the art, which modifications are intended to be within the spirit and scope of the invention as claimed. It also is understood that the foregoing description is illustrative of the present invention and should not be considered as limiting. Therefore, other embodiments of the present invention are possible without departing from the spirit and scope of the present invention.