Abstract:
A receiver for ultra-wideband communications is provided. One feature of the receiver architecture is that includes only a single correlator. The receiver may be used in wireless and wire communication mediums. The single correlator may be used to update a locally generated signal based on an incoming signal and detect data. This Abstract is provided for the sole purpose of complying with the Abstract requirement rules that allow a reader to quickly ascertain the subject matter of the disclosure contained herein. This Abstract is submitted with the explicit understanding that it will not be used to interpret or to limit the scope or the meaning of the claims.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to ultra-wideband communications. More particularly, the invention concerns an apparatus for receiving and demodulating ultra-wideband electromagnetic pulses for wire and wireless communications. 
     BACKGROUND OF THE INVENTION 
     The Information Age is upon us. Access to vast quantities of information through a variety of different communication systems are changing the way people work, entertain themselves, and communicate with each other. For example, as a result of increased telecommunications competition mapped out by Congress in the 1996 Telecommunications Reform Act, traditional cable television program providers have evolved into full-service providers of advanced video, voice and data services for homes and businesses. A number of competing cable companies now offer cable systems that deliver all of the just-described services via a single broadband network. 
     These services have increased the need for bandwidth, which is the amount of data transmitted or received per unit time. More bandwidth has become increasingly important, as the size of data transmissions has continually grown. Applications such as movies-on-demand and video teleconferencing demand high data transmission rates. Another example is interactive video in homes and offices. Moreover, traffic across the Internet continues to increase, and with the introduction of new applications, such as the convergence of voice and Internet data, traffic will only increase at a faster rate. Consequently, carriers and service providers are overhauling the entire network infrastructure—including switches, routers, backbone, and the last mile (i.e., the local loop)—in an effort to provide more bandwidth. 
     Other industries are also placing bandwidth demands on Internet service providers, and other data providers. For example, hospitals transmit images of X-rays and CAT scans to remotely located physicians. Such transmissions require significant bandwidth to transmit the large data files in a reasonable amount of time. The need for more bandwidth is evidenced by user complaints of slow Internet access and dropped data links that are symptomatic of network overload. 
     Therefore, there exists a need for a method to increase the bandwidth of wired network or communication system, as well as a wireless network or communication system. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for receiving and demodulating an ultra-wideband signal. The receiver may be configured to work in conjunction with wireless or wire communications mediums, whether the medium is twisted-pair wire, coaxial cable, fiber optic cable, or other types of wire media. 
     One feature of the present invention is it provides a receiver with demodulation capability of amplitude-, phase-, and timing-based modulation schemes. Another feature of the present invention is that it uses only a single correlator to detect and demodulate ultra-wideband pulses. 
     These and other features and advantages of the present invention will be appreciated from review of the following detailed description of the invention, along with the accompanying figures in which like reference numerals refer to like parts throughout. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of different communication methods; 
         FIG. 2  is an illustration of two ultra-wideband pulses; 
         FIG. 3 . is an illustration of a conventional non-coherent receiver architecture; 
         FIG. 4 . is an illustration of two conventional coherent receiver architectures; 
         FIG. 5 . is an illustration of the functional blocks of the present invention according to one embodiment of the invention; 
         FIG. 6 . is an illustration of an RF front end and correlator according to one embodiment of the invention; 
         FIG. 7 . is an illustration of the pulse detector and energy estimator according to one embodiment of the invention; 
         FIG. 8 . is an illustration of the microprocessor and template generator according to one embodiment of the invention; 
         FIG. 9  is an illustration of an overall ultra-wideband receiver according to one embodiment of the invention; 
         FIG. 10  is a schematic block diagram of a method for receiving ultra-wideband signals according to one embodiment of the invention; and 
         FIG. 11  is a schematic block diagram of a system for receiving ultra-wideband signals according to one embodiment of the invention. 
     
    
    
     It will be recognized that some or all of the Figures are schematic representations for purposes of illustration and do not necessarily depict the actual relative sizes or locations of the elements shown. The Figures are provided for the purpose of illustrating one or more embodiments of the invention with the explicit understanding that they will not be used to limit the scope or the meaning of the claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following paragraphs, the present invention will be described in detail by way of example with reference to the attached drawings. Throughout this description, the preferred embodiment and examples shown should be considered as exemplars, rather than as limitations on the present invention. As used herein, the “present invention” refers to any one of the embodiments of the invention described herein, and any equivalents. Furthermore, reference to various feature(s) of the present invention throughout this document does not mean that all claimed embodiments or methods must include the referenced feature(s). 
     The present invention provides a method of receiving and demodulating a plurality of electromagnetic ultra-wideband (UWB) pulses. The pulses can be transmitted and received wirelessly, or through any wire medium, whether the medium is twisted-pair wire, coaxial cable, fiber optic cable, hybrid fiber-coax, or other type of wire media. 
     The UWB pulse reception and demodulation method of the present invention enables the simultaneous coexistence of the ultra-wideband pulses with conventional carrier-wave signals. Thus, the methods of the present invention enable an increase in the bandwidth, or data rates of a communication system. 
     Referring to  FIGS. 1 and 2 , ultra-wideband (UWB) communication technology employs pulses of electromagnetic energy that are emitted at, for example, nanosecond or picosecond intervals (generally tens of picoseconds to a few nanoseconds in duration). For this reason, ultra-wideband is often called “impulse radio.” That is, the UWB pulses are transmitted without modulation onto a sine wave carrier frequency, in contrast with conventional radio frequency technology as described above. A UWB pulse is a single electromagnetic burst of energy. That is, a UWB pulse may be a single positive burst of electromagnetic energy, a single negative burst of electromagnetic energy or a single burst of electromagnetic energy with a predefined phase. 
     Alternate implementations of UWB can be achieved by mixing baseband pulses with a carrier wave that controls a center frequency of a resulting UWB signal. Ultra-wideband generally requires neither an assigned frequency nor a power amplifier. 
     An example of a conventional radio frequency technology is illustrated in  FIG. 1 . IEEE 802.11a, a wireless local area network (LAN) protocol, transmits radio frequency signals at a 5 GHz center frequency, with a radio frequency spread of about 5 MHz. A UWB pulse may have a 2.0 GHz center frequency, with a frequency spread of approximately 4 GHz, as shown in  FIG. 2 , which illustrates two typical UWB pulses.  FIG. 2  illustrates that the shorter the UWB pulse in time, the broader the spread of its frequency spectrum. This is because bandwidth is inversely proportional to the time duration of the pulse. A 600-picosecond UWB pulse can have about a 1.8 GHz center frequency, with a frequency spread of approximately 1.6 GHz and a 300-picosecond UWB pulse can have about a 3 GHz center frequency, with a frequency spread of approximately 3.2 GHz. Thus, UWB pulses generally do not operate within a specific frequency, as shown in  FIG. 1 . Because UWB pulses are spread across an extremely wide frequency range, UWB communication systems allow communications at very high data rates, such as 100 megabits per second or greater. According to one embodiment of the invention, the transmitter may be configured to transmit both carrier-wave signals and UWB signals. The carrier-wave signals and the UWB signals may be transmitted substantially simultaneously. The transmitter may include a carrier-wave transmitter portion that enables carrier-wave signals to be transmitted. A single antenna may be used for transmitting both the carrier-wave signals and the UWB signals. 
     Further details of UWB technology are disclosed in U.S. Pat. No. 3,728,632 (in the name of Gerald F. Ross, and titled: Transmission and Reception System for Generating and Receiving Base-Band Duration Pulse Signals without Distortion for Short Base-Band Pulse Communication System), which is referred to and incorporated herein in its entirety by reference. 
     Also, because a UWB pulse is spread across an extremely wide frequency range, the power sampled at a single, or specific frequency is very low. For example, a UWB one-watt pulse of one nano-second duration spreads the one-watt over the entire frequency occupied by the UWB pulse. At any single frequency, such as at the carrier frequency of a CATV provider, the UWB pulse power present is one nano-watt (for a frequency band of 1 GHz). This is calculated by dividing the power of the pulse (i.e., 1 watt) by the frequency band (i.e., 1 billion Hertz). This is well within the noise floor of any communications system and therefore does not interfere with the demodulation and recovery of the signals transmitted by the CATV provider. Generally, a multiplicity of UWB pulses are transmitted at relatively low power (when sampled at a single, or specific frequency), for example, at less than −30 power decibels to −60 power decibels, which reduces interference with conventional radio frequencies. UWB pulses, however, transmitted through many wire media typically do not interfere with wireless radio frequency transmissions. Therefore, the power (sampled at a single frequency) of UWB pulses transmitted though wire media may range from about +30 dBm to about −140 dBm. 
     The present invention may be employed in any type of network, be it wireless, wire, or a mix of wire media and wireless components. That is, a network may use both wire media, such as coaxial cable, and wireless devices, such as satellites, or cellular antennas. As defined herein, a network is a group of points or nodes connected by communication paths. The communication paths may be use wires or be wireless. A network as defined herein may interconnect with other networks and contain sub-networks. A network as defined herein may be characterized in terms of a spatial distance, for example, such as a local area network (LAN), a personal area network (PAN), a metropolitan area network (MAN), a wide area network (WAN), and a wireless personal area network (WPAN), among others. A network as defined herein may also be characterized by the type of data transmission technology in use on it, for example, a Transmission Control Protocol/Internet Protocol (TCP/IP) network, and a Systems Network Architecture network, among others. A network as defined herein may also be characterized by whether it carries voice signals, data signals, or both. A network as defined herein may also be characterized by users of the network, such as, for example, users of a public switched telephone network (PSTN) other type of public networks, and private networks (such as within a single room or home), among others. A network as defined herein may also be characterized by the usual nature of its connections, for example, a dial-up network, a switched network, a dedicated network, and a non-switched network, among others. A network as defined herein may also be characterized by the types of physical links that it employs, for example, optical fiber, coaxial cable, a mix of both, unshielded twisted pair, and shielded twisted pair, among others. 
     The present invention may also be employed in any type of wireless network, such as a wireless PAN, LAN, MAN, or WAN. The present invention may be implemented in a “carrier free” architecture, which does not require the use of high frequency carrier generation hardware, carrier modulation hardware, stabilizers, frequency and phase discrimination hardware or other devices employed in conventional frequency domain communication systems. The present invention dramatically increases the bandwidth of conventional networks that employ wire media, but can be inexpensively deployed without extensive modification to the existing wire media network. 
     In one embodiment, the present invention may provide increased bandwidth by injecting, or otherwise super-imposing an ultra-wideband (UWB) signal into an existing data signal and subsequently recovering the UWB signal at an end node, set-top box, subscriber gateway, or other suitable location. 
     One method practiced by the present invention involves recovery of phase-modulated data for an ultra-wideband receiver. An incoming signal may be a plurality of ultra-wideband (UWB) pulses wherein each of the pulses includes data encoded within a phase of the pulse. One method herein described initially estimates timing of the incoming signal with the use of a correlator and an energy estimator. In one embodiment of the present invention, the correlator may include a filter whose transfer function is matched to an output filter of a UWB transmitter. The matched filter shapes a locally generated pulse to closely represent an expected incoming signal. Additional components of the correlator may include a mixer, amplifier, and low-pass filter. The incoming signal may be correlated with a local template signal then sent to the energy estimator. 
     The energy estimator may include an absolute value detector such as a rectifier or a square law detector that outputs the square of the incoming signal. The function of the absolute value detector is to provide an energy pulse to an integrator. The integrator sums the signal across a finite time period and provides its output as a coarse timing signal to a local signal generator. This summed signal gives the receiver a coarse timing estimate of the incoming signal. This coarse signal is appropriate for detection and demodulation of position based signal modulation schemes such as Pulse Position Modulation. 
     A number of receiver architectures are known in the art of ultra-wideband communications. These conventional architectures can be classified into two basic groups: coherent and non-coherent. One usual approach, as illustrated in  FIG. 3 , to non-coherent detection and demodulation involves the use of envelope detectors  12  to provide an output signal  40  that is representative of an incoming signal  10 . The incoming signal  10  arrives at an envelope detector  12  that includes a resistor R 1  and a Diode D 1 . A negative part of the incoming signal  10  is suppressed by the diode D 1  and a half wave rectified signal  20  is developed across the resistor R 1 . The half-wave rectified signal  20  contains high frequency components that are attenuated by a low-pass filter  14 . A resultant low frequency signal  30  is representative of the input signal but has a direct current (DC) offset. A capacitor C 1  blocks the DC component of the signal  30  and the output signal  40  is developed across a resistor R 2 . 
     Non-coherent architectures have been used in the field of communications to receive and demodulate both amplitude-related signal modulation schemes, such as Amplitude Modulation (AM), dual sideband modulation, single sideband modulation, vestigial sideband modulation, as well as angle-related modulation schemes such as Frequency Modulation (FM) and Phase Modulation (PM). 
     Conventional UWB receivers, as described above, typically use two correlating chains. A correlating chain is a process for performing one or more functions. For example, a continuous time correlating chain includes an analog correlator that includes a product (or mixer) followed by an integrator. An incoming signal is multiplied by a locally generated signal and transmitted to an integrator that integrates and dumps the signal over a period of time. 
     One correlating chain is used to provide a coarse timing estimate of a pulse. The coarse timing estimate is used to dither the frequency and phase of a locally generated signal. A second correlating chain is used as a data detector to lock-in on a precise timing of the signal and a peak of the pulse. 
     According to one embodiment of the invention, a UWB receiver uses only a single correlator to estimate the coarse timing and also updates a locally generated signal for data detection. In another embodiment, the correlator may include an absolute value detector that receives output from a mixer and delivers inputs into an integrator. By using an absolute value detector in such a manner, this allows the integrator to integrate and dump over a wider range of time. In addition, the absolute value detector provides twice as much energy as typically transmitted to the integrator by adding a negative portion of the correlated signal (i.e., taking the absolute value of the signal) to the positive portion of the correlated signal. This is because conventional UWB receivers use a diode which prevents the negative portion of a correlated signal from being transmitted to the integrator. Thus, only half of a signal is used to obtain the coarse timing signal. 
     In communication systems having a transmitter that uses a signal modulation technique that does not include a carrier in a resultant spectrum, such as Dual Sideband Suppressed Carrier (DSBSC), a coherent detector is commonly used. A conventional coherent receiver architecture  60  is illustrated in  FIG. 4 . An incoming signal is multiplied by a locally generated signal cos(ω c t) using a mixer  50 ( a ). The locally generated signal is at the same frequency ω c  as a carrier of the incoming signal. The product of the incoming signal and the locally generated signal will have two components. Because the locally generated signal is at a carrier frequency, the first signal component will be low frequency or close to DC. The second signal component is at twice the carrier frequency. A low-pass filter  52  may be used to attenuate a high frequency component of the output signal. 
     Other coherent receiver architectures exist, such as a “Costas loop” architecture  70 , illustrated in  FIG. 4 . In this architecture, a voltage controlled oscillator (VCO)  62  generates a local signal which is mixed with an incoming signal by a mixer  50 ( b ) to produce a first mixed signal. A copy of the local signal may be phase delayed by π/2 and mixed with the incoming signal by mixer  50 ( c ) to produce a second mixed signal. The mixed signals are then mixed to produce an error signal, which may then be transmitted through a low-pass filter  64 ( a ),  64 ( b ),  64 ( c ) to control the VCO  62 . In this configuration, the first mixed signal is taken as an output. 
     A number of correlator designs, or architectures are used in ultra-wideband communications. In one architecture, two correlators are used. Each correlator includes a mixer and an integrator. A local template signal is generated and delayed with a delay element to produce a second template signal. The first template signal is correlated with an incoming signal. The incoming signal is additionally correlated with the delayed template signal. Either the first or second correlator provides a feedback signal to the template generator. 
       FIGS. 5–8  illustrate an ultra-wideband correlating receiver constructed according to one embodiment of the present invention. An incoming signal is received at an RF front end  80 . As shown in  FIG. 6 , the RF front end  80  may include an antenna  80 ( a ), a Transmit/Receive (TX/RX) switch  80 ( b ), at least one filter  80 ( c ), and at least one amplifier (AMP)  80 ( d ). The filter  80 ( c ) may be a band-pass filter (BPF) or a low-pass filter. The amplifier  80 ( d ) may be a low noise amplifier or an automatic gain control (AGC) amplifier. 
     As shown in  FIGS. 5 and 6 , the correlator  90  may include a mixer  50 ( d ), matched filter  90 ( a ), and low-pass filter (LPF)  90 ( b ). Additionally, there may be an optional amplifier in the correlator (not shown). The optional amplifier may be an AGC or low noise amplifier. The mixer  50 ( d ) multiplies the incoming signal by a locally generated template signal. The product of these signals has a high frequency component and a low frequency component. The high frequency component is attenuated by the low-pass filter  90 ( b ). 
     The matched filter  90 ( a ) is optional. When used, the matched filter  90 ( a ) may have a similar transfer function as an output filter in the transmitter sending the incoming signal. The matched filter  90 ( a ) shapes a locally generated coarse template signal to approximate an expected incoming signal. By approximating the incoming signal with the template signal, the correlator  90  outputs a better approximation of time of receipt and produces a better estimate of frequency, polarity or phase of the incoming signal, when compared to conventional devices. 
     Referring to  FIGS. 5 and 7 , an energy estimator  110  may be used to generate a coarse timing signal. The coarse timing signal may be transmitted to a template generator  120  through a computer microprocessor  130  to improve the time resolution of the template. Additionally, the energy estimator  110  produces a window signal that is transmitted to the microprocessor  130 . The energy estimator  110  may include an absolute value detector  110 ( a ) that converts a negative portion of a correlated signal into a positive portion. The absolute value detector  110 ( a ) may include a square law detector. The energy detector  110  may additionally include an integrate and dump function  110 ( b ). The integrate and dump function  110 ( b ) sums energy over a fixed time period and outputs a signal corresponding to the amount of energy summed over that time period. In one embodiment of the present invention, the integrate and dump function  110 ( b ) may integrate energy sums over a fixed time period that ranges from about 100 picoseconds to about 1 millisecond. According to one embodiment, the fixed time period for the integrate and dump function  110 ( b ) is 1 microsecond. 
     The energy estimator  110  may further include a sample-and-hold function  110 ( c ) and an analog-to-digital (A/D) converter  110 ( d ). In this embodiment, the sample-and-hold (S&amp;H) function  110 ( c ) and A/D converter  110 ( d ) may provide a window signal to the microprocessor  130 . One purpose of the window signal is to provide a timing reference related to the presence of the incoming signal to the microprocessor  130 . 
     As shown in  FIGS. 5 and 7 , the pulse detector  100  may include a sample-and-hold function  100 ( a ) and an A/D function  100 ( b ). The correlated signal may be sampled by the sample-and-hold function  100 ( a ) and converted to a digital signal by the A/D function  100 ( b ). The correlated signal may carry data that represents the phase, amplitude or time of arrival of the incoming signal. The A/D function  100 ( b ) may be multi-level wherein it is capable of producing 2 or more bit resolution from a sample. In a preferred embodiment, the A/D function  100 ( b ) is 8-bit per sample. Alternatively, the A/D function  100 ( b ) may be 2-bit, 3-bit, 4-bit, 5-bit, 6-bit or 7-bit per sample. 
     As shown in  FIG. 5 , the microprocessor  130  receives the data signal from a pulse detector  100  and the window signal from the energy estimator  110 . The microprocessor  130  may comprise one or more of: a Digital Signal Processor (DSP); a general-purpose computer processor; or a finite state machine. The microprocessor  130  may further demodulate the data signal to recover the data received. 
     Additionally, as shown in  FIGS. 5 and 8 , the microprocessor  130  may generate two output signals to the template generator  120 . The first output may be based on an input window signal and the coarse timing signal. The coarse timing signal and the window signal inform the microprocessor  130  when an incoming signal has been detected and sets a timeframe for the microprocessor  130  to activate the template generator  120 . The second output of the microprocessor  130  may include a clock signal that approximates the phase and frequency of the incoming signal. These signals may be transmitted to the template generator  120 . 
     Referring to  FIGS. 5 and 8 , the template generator  120  may include a signal generator  122  such as a phase locked loop (PLL), a gating function  120 ( b ), and an optional amplifier  124 . The signal generator  122  may include components normally present in a PLL such as a Voltage Controlled Oscillator (VCO), filters, and amplifiers to name a few. The signal generator  122  receives the first signal from the microprocessor  130  and generates a signal whose phase and frequency is a function of the signal received from the microprocessor  130 . The gating function  120 ( b ) allows a time limited template signal to pass when the microprocessor  130  sends the second signal. When the microprocessor  130  determines the coarse timing of an incoming signal it begins to dither the first and second signals to achieve the optimum correlation from the correlator  90 . Optimum correlation values are achieved when the frequency of the template signal best matches the frequency of the incoming signal. Minimum correlation values then indicate a phase shift in the data relative to the template, and maximum values indicate no phase shift between template signal and the incoming signal. 
       FIG. 9  illustrates an ultra-wideband correlator receiver  200  that uses binary phase shift keying according to one embodiment of the invention. The receiver  200  may include an RF front end  202 . The RF front end  202  may include an antenna  204 , band-pass filter  206 , and amplifier  208 . According to one embodiment, the band-pass filter  206  filters signals having a frequency in a range of 3–5 GHz and the amplifier  208  is an automatic gain control (AGC) amplifier. 
     The RF front end  202  may be in communication with a correlator  210 . The correlator  210  may include a mixer  212 , a first low-pass filter  214 , amplifier  216 , and a second low-pass filter  218 . According to one embodiment, the amplifier  216  is an AGC amplifier. The correlator  210  receives an incoming signal from the RF front end  202 . A template generator  220  generates a local signal that is transmitted to the correlator  210 . The template generator  220  may include a mixer amplifier  222 , gate  224 , and clock generator  226 . According to one embodiment, the clock generator  226  may be a phase-locked loop (PLL) synthesizer. It will be appreciated that other components may be added, or substituted for any of the above described components. 
     The local signal from the template generator  220  is multiplied with the incoming signal from the RF front end  202  by the mixer  212  of the correlator  210 . A high frequency component of the resulting signal is attenuated by the first low-pass filter  214 . The low frequency component of the resulting signal may be transmitted to the amplifier  216  and subsequently pass through the second low-pass filter  218 , yielding a correlated signal. The correlated signal may be transmitted to an energy estimator  228 . The energy estimator  228  may include an absolute value detector  230 , an integrate-and-dump function  232 , a sample-and-hold function  234 , and an analog-to-digital function  236 . The absolute value detector  230  converts a negative portion of the correlated signal into a positive portion. The absolute value detector  230  may include a square law detector that outputs the square of the incoming signal. 
     An integrate-and-dump function  232  may be used to sum energy over a fixed period of time and output a signal corresponding to an amount of energy summed over that period. The fixed time period may be, for example, 100 picoseconds to 1 millisecond. 
     The correlated signal may also be passed to a pulse detector  238 . The pulse detector  238  may include a sample-and-hold function  240  and also an analog-to-digital function  242 , which may provide a window signal to a microprocessor  244 . The correlated signal may be sampled by the sample-and-hold function  240  and converted to a digital signal by analog-to-digital function  242 . According to one embodiment, the analog-to-digital converter  242  is a 2, 3, 4, 5, 6, 7, or 8 bit per sample. 
     The microprocessor  244  may include a digital signal processor  246  and analog-to-digital converter  248 . The microprocessor  244  receives a data signal from the pulse detector  238  and the window signal from the energy estimator  228 . The data and window signals may be received by the digital signal processor  246  of the microprocessor  244 . The microprocessor  244  may demodulate the data signal to recover the data received. The analog-to-digital converter  248  may be used to convert an analog signal to a digital signal. 
     An output of the microprocessor  244  may be used as input to the template generator  220 . The output may include a first output and a second output. The first output may be an input window signal and a coarse timing signal. The coarse timing signal and the window signal may be used to inform the microprocessor  244  when an incoming signal has been detected and set a timeframe for the microprocessor  244  to activate the template generator  220 . The second output may be a clock signal that approximates the phase and frequency of the incoming signal. The input window, coarse timing, and clock signals may be transmitted to the template generator  220 . It will be appreciated that the correlator receiver  200  may have components added to, removed from, or substituted for any of the above described components to achieve the same, or similar function(s). 
       FIG. 10  illustrates a method for receiving ultra-wideband signals according to one embodiment of the invention. In step  302 , an incoming signal from a transmitting device may be received. In step  304 , a template signal may be generated locally by, for example, a voltage controlled oscillator. Preferably, the template signal is at the same frequency as the incoming signal. In step  306 , the incoming signal and the template signal may then be correlated. Correlating may include multiplying the incoming signal and the template signal using, for example, a mixer. The product of the incoming and template signals typically results in a signal having a high frequency component and a low frequency component. Correlation may also include attenuating the high frequency component using, for example, a low-pass filter. 
     In step  308 , a coarse timing reference may be estimated. The coarse timing reference is preferably a signal that may be used to improve the time resolution of the template signal. In step  310 , the template signal may be updated using the coarse timing reference. In step  312 , the updated template signal and the incoming signal may be correlated. In step  314 , an ultra-wideband pulse from the correlated incoming signal and the updated template signal may then be detected. 
       FIG. 11  illustrates a system  320  for receiving ultra-wideband signals according to one embodiment of the invention. The system  320  may include an incoming signal receiver  322 , template signal generator  324 , incoming signal and template signal correlator  326 , coarse timing reference estimator  328 , template signal updater  330 , incoming and updated template signal correlator  332 , and pulse detector  334 . The incoming signal receiver  322  may receive one or more transmitted signals using, for example, an antenna. A template signal may be generated using the template signal generator  324 . The template signal generated is preferably of the same frequency as the incoming signal. The incoming signal and the template signal may be transmitted to the incoming and template signal correlator  326 . The incoming and template signal correlator  326  may be used to correlate the incoming signal with the template signal. The incoming and template signal correlator  326  may multiply the incoming signal and the template signal and attenuate a high frequency component of a resulting signal. 
     The coarse timing reference estimator  328  may be used to estimate a coarse timing reference that may be used to improve the time resolution of the template signal. The template signal updater  330  may then update the template signal using the coarse timing reference estimated. The updated template signal and the incoming signal may be correlated using the incoming and updated template signal correlator  332 . A pulse from the correlated incoming signal and updated template signal may then be detected using pulse detector  334 . 
     One feature of the present invention is to provide a receiver device, or architecture for ultra-wideband (UWB) communications which is capable of receiving and demodulating data that is transmitted using a variety of signal modulation techniques or methods. For example, some of the modulation methods may be: Pulse Amplitude Modulation, On-Off keying, Ternary Modulation, Pulse Position Modulation, and Binary Phase Shift Keying (BPSK). One feature of the present invention is that the multi-level A/D function  100 ( b ), shown in  FIG. 7 , allows for the detection of pulse amplitudes. On-Off keying may be demodulated in the present invention by the presence or absence of energy at a specific time. Ternary modulation carries data in unique data groups that always contain a polarity of a pulse and also the absence of a pulse within each data group. Because the present invention can determine the difference between polarities and the time of arrival of the pulse, the microprocessor  130  may demodulate ternary modulation. BPSK carries data in one of two distinct phases and the correlating receiver architecture herein described is capable of demodulating incoming signals with two (2) distinct polarities or phases. 
     The addition of a second correlator channel may allow for detection and demodulation of signals where four phases are used to carry information. In that situation, amplitude and timing information may be extracted in a similar manner making this alternative architecture suitable for Quadrature Phase Shift Keying (QPSK) and multi-amplitude QPSK both with and without additional PPM. 
     Thus, many different signal modulation methods may be received and demodulated by the present invention. Ultra-wideband pulse modulation techniques enable a single representative data symbol to represent a plurality of binary digits, or bits. This has an advantage of increasing the data rate in a communications system. A few examples of modulation include Pulse Width Modulation (PWM), Pulse Amplitude Modulation (PAM), and Pulse Position Modulation (PPM). In PWM, a series of predefined UWB pulse widths are used to represent different sets of bits. For example, in a system employing 8 different UWB pulse widths, each symbol could represent one of 8 combinations. This symbol would carry 3 bits of information. In PAM, predefined UWB pulse amplitudes are used to represent different sets of bits. A system employing PAM 16  would have 16 predefined UWB pulse amplitudes. This system would be able to carry 4 bits of information per symbol. In a PPM system, predefined positions within a UWB pulse timeslot are used to carry a set of bits. A system employing PPM 16  would be capable of carrying 4 bits of information per symbol. 
     Additional UWB pulse modulation techniques may include: Coded Recurrence Modulation (CRM); Sloped Amplitude Modulation (SLAM); ternary modulation; 1-pulse modulation; and other UWB pulse modulation methods. 
     For example, in some conventional ultra-wideband (UWB) modulation techniques, a doublet or wavelet “chip” is modulated by a data signal. The data signal imparts a phase to the chip. A “doublet” or “wavelet” in some instances is a positive UWB pulse followed by a negative UWB pulse, or vice-versa. The two UWB pulses include a single chip, which is the smallest element of data in a modulated signal. In this case, the chip, comprising the two UWB pulses, represents a single bit of data (a 1 or a 0). If the data bit being sent is a 0, the chip may start with a positive UWB pulse and end with a negative UWB pulse, and if the data bit being sent is a 1, the chip may start with a negative UWB pulse and end with a positive UWB pulse. For example, in a bi-phasic or antipodal system, the two-pulse “wavelet” or “doublet” or its inverse (180° phase shift) represents a 1 or a 0. Other phase shifts may also be used such as 0°, 90°, 180°, and 270° shifts to develop quad-phasic systems. One element common to these modulation techniques, however, is that a 0 or 1 is represented by at least a positive and a negative pulse of energy. In the bi-phasic or antipodal system described above, a 0 is represented by two pulses of energy—a positive pulse and a negative pulse (or vice-versa). Thus, conventional modulation techniques use energy in the form of at least two UWB pulses having a specific phase (positive or negative) to send each data bit. This type of modulation may be received and demodulated by the present invention. 
     Another signal modulation method that may be demodulated by the present invention includes transmitting at least one data symbol with every UWB pulse. The data symbol may represent one or more binary digits, or bits. 
     Thus, it is seen that an apparatus for receiving ultra-wideband signals is provided. The present invention is suitable for both wireless and wire communications media. One skilled in the art will appreciate that the present invention can be practiced by other than the above-described embodiments, which are presented in this description for purposes of illustration and not of limitation. The description and examples set forth in this specification and associated drawings only set forth preferred embodiment(s) of the present invention. The specification and drawings are not intended to limit the exclusionary scope of this patent. Many designs other than the above-described embodiments will fall within the literal and/or legal scope of the instant disclosure, and the present invention is limited only by the instant disclosure. It is noted that various equivalents for the particular embodiments discussed in this description may practice the invention as well.