Ultra-wideband high data-rate communication apparatus and methods Number:7,394,846 from the United States Patent and Trademark Office (PTO) owispatent An RF transmitter includes a reference signal generator, a signal generator, and a mixer. The reference signal generator provides a reference signal that has a prescribed or desired frequency. The signal generator provides an operating signal in response to a selection signal. The operating signal has a frequency that equals the frequency of the reference signal multiplied by a number. The mixer mixes the operating signal with another signal to generate a transmission signal. An RF receiver includes a first mixer, a second mixer, an integrator/sampler, and a signal generator. The first mixer receives as its inputs an input RF signal and a second input signal, and mixes its input signals to generate a mixed signal. The integrator/sampler receives the mixed signal and processes it to provide an output signal. The signal generator provides an operating signal in response to a selection signal. The operating signal has a frequency equal to the frequency of a reference signal, multiplied by a number. The second mixer mixes the operating signal with a template signal to generate the second input signal of the first mixer.<H communication, apparatus, Ultra, wideband, , 7394846.html, Patent, pto, 7394846

Title: Ultra-wideband high data-rate communication apparatus and methods

Abstract: An RF transmitter includes a reference signal generator, a signal generator, and a mixer. The reference signal generator provides a reference signal that has a prescribed or desired frequency. The signal generator provides an operating signal in response to a selection signal. The operating signal has a frequency that equals the frequency of the reference signal multiplied by a number. The mixer mixes the operating signal with another signal to generate a transmission signal. An RF receiver includes a first mixer, a second mixer, an integrator/sampler, and a signal generator. The first mixer receives as its inputs an input RF signal and a second input signal, and mixes its input signals to generate a mixed signal. The integrator/sampler receives the mixed signal and processes it to provide an output signal. The signal generator provides an operating signal in response to a selection signal. The operating signal has a frequency equal to the frequency of a reference signal, multiplied by a number. The second mixer mixes the operating signal with a template signal to generate the second input signal of the first mixer.

Patent Number: 7,394,846 Issued on 07/01/2008 to Siwiak

Inventors: Siwiak; Kazimierz (Coral Springs, FL)
Assignee: Alereon, Inc. (Austin, TX)

Appl. No.: 11/712,099

Filed: February 28, 2007

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
10436646	May., 2003	7206334
10206648	Jul., 2002
60451538	Mar., 2003
60402677	Aug., 2002
60401711	Aug., 2002

Current U.S. Class: 375/146 ; 375/295

Current International Class: H04B 1/00 (20060101)

Field of Search: 375/146,295

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Primary Examiner: Payne; David C.
Assistant Examiner: Bolourchi; Nader
Attorney, Agent or Firm: Sprinkle IP Law Group

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of, and claims a benefit of priority under 35 U.S.C. 120 to U.S. patent application Ser. No. 10/436,646, filed on May 13, 2003 now U.S. Pat. No. 7,026,334, by inventor Kazimierz Siwiak, entitled "Ultra-Wideband High Data-Rate Communication Apparatus and Associated Methods" which is a continuation-in-part of U.S. patent application Ser. No. 10/206,648, filed on Jul. 26, 2002 now abandoned, by inventor Kazimierz Siwiak entitled "High Data-Rate Transmitter Apparatus And Associated Methods", and claims priority under 35 U.S.C. .sctn.119 to U.S. Provisional Patent Application Ser. No. 60/451,538, filed on Mar. 3, 2003, by inventor Kasimierz Siwiak, entitled "Ultra-Wideband High Data-Rate Communication Apparatus And Associated Methods", and claims priority to under 35 U.S.C. .sctn.119 to U.S. Provisional Patent Application Ser. No. 60/401,711, filed on Aug. 7, 2002, by inventor Kasimierz Siwiak, entitled "High Data-Rate Communication Apparatus And Associated Methods," and claims priority to under 35 U.S.C. .sctn. 119 to U.S. Provisional Patent Application Ser. No. 60/402,677 filed on Aug. 12, 2002, by inventor Kasimierz Siwiak, entitled "High Data Rate Communication Apparatus And Associated Methods," the entire contents of all above references are hereby expressly incorporated by reference for all purposes.

Furthermore, one may selectively enable or turn ON each harmonic signal, as desired. Put another way, one may configure the harmonic signals independently. In one configuration, the harmonic signals are not ON or enabled simultaneously. In effect, one may hop from one harmonic signal or frequency to another harmonic signal or frequency as a function of time, as desired.

Claims

I claim:

1. A method for transmitting, comprising: generating a reference signal having a first frequency; generating a first operating signal from the reference signal, wherein the first operating signal has a second frequency which is a multiple of the first frequency and the second frequency is based on a selection signal; generating a first transmission signal from the first operating signal and a first signal comprising data; detecting interference; and based upon the detection of the interference, varying the selection signal to vary the second frequency to allow the first transmission signal to avoid the detected interference, wherein the selection signal is varied according to a predetermined PSD mask, the PSD mask corresponding to a channel frequency and a timing plan configured to generate the transmission signal on a plurality of harmonic frequencies in a predetermined order such that a transmission time on any one of the plurality of harmonic frequencies lasts for a predetermined time.

2. The method of claim 1, further comprising; generating a second operating signal from the reference signal wherein the operating signal has a third frequency distinct from the second frequency, the third frequency is a multiple of the first frequency and the third frequency is based on the selection signal; and generating a second transmission signal from the second operating signal and the first signal.

3. The method of claim 1, wherein the selection signal is varied to allow the frequency of the first operating signal to vary in accordance with a channel frequency and timing plan.

4. The method of claim 2, wherein the interference is multipath interference.

5. A method for transmitting, comprising: generating a reference signal having a first frequency; generating a plurality of operating signals from the reference signal, wherein each operating signal has a distinct operating frequency which is a multiple of the first frequency, and the operating frequencies are based on a selection signal; generating transmission signals from the operating signals and a first signal comprising data; detecting interference; and based upon the detection of the interference, varying the selection signal and the operating signals generated to allow a power spectral density (PSD) of the transmission signals to conform to a PSD profile to avoid the detected interference, wherein the selection signal is varied according to a predetermined PSD mask, the PSD mask corresponding to a channel frequency and a timing plan configured to generate the transmission signal on the one or more of the operating frequencies in a predetermined order such that a transmission time on the one or more of the operating frequencies lasts for a predetermined time.

6. The method of claim 5, wherein the PSD profile can vary over time.

7. A method for transmitting, comprising: generating a reference signal having a first frequency; generating a first operating signal from the reference signal, wherein the first operating signal has a second frequency which is a multiple of the first frequency and the second frequency is based on a selection signal; generating a first transmission signal from the operating signal and a first signal comprising data; detecting interference; and based upon the detection of the interference, varying selection signal according to a predetermined PSD mask to vary the second frequency in accordance with a modifiable channel frequency and timing plan, said channel frequency and timing plan configured to generate the first transmission signal on one or more of a plurality of harmonic frequencies in a predetermined order such that a transmission time on any one of the plurality of harmonic frequencies lasts for a predetermined time.

8. The method of claim 7, wherein the frequencies used in conjunction with the channel frequency and timing plan can be modified.

9. The method of claim 7, wherein the channel frequency and timing plan can be modified to allow the first transmission signal to avoid interference.

10. The method of claim 9, wherein the modification of the channel frequency and timing plan occurs automatically.

Description

TECHNICAL FIELD

This patent application relates generally to communication apparatus and, more particularly, to ultra-wideband (UWB) high data-rate (HDR) communication apparatus.

BACKGROUND

The proliferation of wireless communication devices in unlicensed spectrum and the ever increasing consumer demands for higher data bandwidths has placed a severe strain on those frequency spectrum bands. Examples of the unlicensed bands include the 915 MHz, the 2.4 GHz Industrial, Scientific and Medical (ISM) band, and the 5 GHz Unlicensed National Information Infrastructure (UNII) bands. New devices and new standards emerge continually, for example, the IEEE 802.11b, IEEE 802.11a, IEEE 802.15.3, HiperLAN/2 standards. The emergence and acceptance of the standards has placed, and continues to place, a further burden on those frequency bands. Coexistence among the many systems competing for radio-frequency (RF) spectrum is taking on an increasing level of importance as consumer devices proliferate.

Persons skilled in the art know that the available bandwidth of the license-free bands (and the RF spectrum available generally) constrains the available data bandwidth of wireless systems. Furthermore, data-rate throughput capability varies proportionally with available bandwidth, but only logarithmically with the available signal-to-noise ratio. Hence, to transmit increasingly higher data rates within a constrained bandwidth requires the use of complex communication systems with sophisticated signal modulation schemes.

The complex communication systems typically need significantly increased signal-to-noise ratios, thus making the higher data rate systems more fragile and more easily susceptible to interference from other users of the spectrum and from multipath interference. The increased susceptibility to interference aggravates the coexistence concerns noted above. Furthermore, regulatory limitations within given RF bands constrain the maximum available signal-to-noise ratio and therefore place a limit on the data-rate throughput of the communication system. A need therefore exists for a high data-rate communication apparatus and system that can readily coexist with other existing wireless communication systems, and yet can robustly support relatively high data-rates in a multipath environment.

SUMMARY

One aspect of the invention relates to communication apparatus, such as communication transmission apparatus and communication receiver apparatus. In one exemplary embodiment, an RF transmitter according to the invention includes a reference signal generator, a signal generator, and a mixer.

The reference signal generator provides a reference signal that has a prescribed or desired frequency. The signal generator provides an operating signal in response to a selection signal. The operating signal has a frequency that equals the frequency of the reference signal multiplied by a number. More particularly, in some embodiments, the number may constitute an integer number, whereas in other embodiments, the number may constitute a non-integer number, as desired. The mixer mixes the operating signal with another signal to generate a transmission signal.

In another exemplary embodiment, an RF receiver according to the invention includes two mixers, a first mixer and a second mixer. The receiver further includes an integrator/sampler and a signal generator.

The first mixer receives as its inputs an input RF signal and a second input signal. The first mixer mixes its input signals to generate a mixed signal. The integrator/sampler receives the mixed signal and processes it to provide an output signal. The signal generator provides an operating signal in response to a selection signal. The operating signal has a frequency equal to the frequency of a reference signal, multiplied by a number. More particularly, in some embodiments, the number may constitute an integer number, whereas in other embodiments, the number may constitute a non-integer number, as desired. The second mixer mixes the operating signal with a template signal to generate the second input signal of the first mixer.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings illustrate only exemplary embodiments of the invention and therefore should not be considered as limiting its scope. The disclosed inventive concepts lend themselves to other equally effective embodiments. In the drawings, the same numeral designators used in more than one drawing denote the same, similar, or equivalent functionality, components, or blocks.

FIG. 1 shows several power spectral density (PSD) profiles in various embodiments according to the invention.

FIG. 2 illustrates exemplary signal waveforms corresponding to a high data-rate UWB apparatus.

FIG. 3 depicts an exemplary embodiment of a high data-rate UWB transmitter according to the invention.

FIG. 4 shows exemplary waveforms corresponding to a high data-rate UWB transmitter according to the invention.

FIG. 5 illustrates an exemplary embodiment of high data-rate UWB receiver according to the invention.

FIG. 6 depicts exemplary waveforms corresponding to a high data-rate UWB receiver according to the invention.

FIG. 7 shows the timing relationship among various signals in a high data-rate UWB transmitter according to the invention.

FIG. 8 illustrates exemplary desired or prescribed PSD profiles that correspond to the two modes of operation in illustrative embodiments according to the invention.

FIG. 9 shows a PSD profile for an exemplary embodiment of the invention that uses higher-order harmonics.

FIG. 10 illustrates an illustrative PSD profile in an exemplary embodiment according to the invention.

FIG. 11A shows one cycle of an exemplary output signal of a transmitter in a UWB communication apparatus according to the invention.

FIG. 11B illustrates one cycle of another exemplary output signal of a transmitter in a UWB communication apparatus according to the invention.

FIG. 12 depicts a timing relationship between several signals in an exemplary embodiment according to the invention.

FIG. 13 shows several PSD profiles for an illustrative embodiment according to the invention.

FIG. 14 illustrates several PSD profiles for other exemplary embodiments according to the invention.

FIG. 15 depicts PSD profiles for other illustrative embodiments according to the invention.

FIG. 16 shows PSD profiles for other exemplary embodiments of communication systems or apparatus according to the invention.

FIG. 17 illustrates an exemplary embodiment according to the invention of a communication system that incorporates mode switching.

FIG. 18 depicts illustrative chipping sequences for use in communication systems and apparatus according to the invention.

FIG. 19 shows an exemplary embodiment 19 of a differential receiver according to the invention.

FIG. 20 illustrates a set of offset quadrature phase shift keyed (OQPSK) UWB signals in an exemplary embodiment according to the invention.

FIG. 21 depicts a set of chipping signal waveforms in an exemplary embodiment according to the invention.

FIG. 22 shows an exemplary embodiment of a transmitter according to the invention that uses independently modulated harmonic signals.

FIG. 23 illustrates an exemplary embodiment of a receiver according to the invention for receiving independently modulated harmonic signals.

FIG. 24 depicts a sample waveform in an illustrative embodiment according to the invention.

FIG. 25 shows a Fourier transform of the signal in FIG. 24.

FIG. 26 illustrates sample waveforms in an exemplary embodiment of a transmitter according to the invention.

FIG. 27 depicts an exemplary in-phase channel pulse as a function of time in an illustrative embodiment according to the invention.

FIG. 28 shows the magnitude of the spectrum of the signal in FIG. 27.

FIG. 29 illustrates an exemplary quadrature channel pulse as a function of time in an illustrative embodiment according to the invention.

FIG. 30 depicts the magnitude of the spectrum of the signal in FIG. 29.

FIG. 31 shows two signals as a function of time in illustrative embodiments according to the invention.

FIG. 32 illustrates the spectra resulting from using the signal shaping shown in FIG. 31.

FIG. 33 depicts two signals as a function of time in other illustrative embodiments according to the invention.

FIG. 34 shows the spectra resulting from using the signal shaping shown in FIG. 33.

DETAILED DESCRIPTION

This invention contemplates high data-rate communication apparatus and associated methods. Communication apparatus according to the invention provide a solution to the problems of coexisting communication systems, and yet providing relatively high data-rates. Note that wireless or radio communication systems according to the invention provide relatively high data-rates in "hostile" propagation environments, such as multipath environments. Furthermore, as described below, one may apply the inventive concepts described here to land-line communication systems, for example, communication systems using coaxial cables, or the like.

In one exemplary embodiment according to the invention, a high data-rate UWB data transmission system uses a binary phase shift keying (BPSK) modulation of a carrier frequency, known to persons of ordinary skill in the art with the benefit of the description of the invention. One obtains the power spectral density (PSD) at frequency f of such a system as:

.times..times..times..pi..function..pi..times..times. ##EQU00001## where f.sub.c denotes the reference clock frequency, and n represents the number of carrier cycles per chip. In other words,

.times..times..times..times..times..times..times..times. ##EQU00002## A chip refers to a signal element, such as depicted in FIG. 11A or FIG. 11B. Put another way, a chip refers to a single element in a sequence of elements used to generate the transmitted signal. The transmitted signal results from multiplying the sequence of chips (the chip sequence) by a spreading code, i.e., the code that spreads the transmitted signal spread over a relatively wide band. Multiple chips in proportion to a desired energy level per bit encode each data bit.

In this embodiment, the modulation chipping rate is commensurate with the carrier frequency. Put another way, n is a relatively small number. In illustrative embodiments, for example, n has a value of less than ten, such as 3 or 4. In other illustrative embodiments, one may use n in the range of 1 to 500, or 1 to 42. Using the latter range of values of n, one may achieve a UWB bandwidth of 500 MHz or greater, up to a frequency limit of approximately 10.6 GHz, as prescribed in the Federal Communications Commission's (FCC) Part 15 rules.

As persons of ordinary skill in the art with the benefit of the description of the invention understand, one may use other positive integer values of n, as desired. Generally speaking, the choice of the values of n depend on one's definition of ultra-wideband. Depending on a desired bandwidth, one may select appropriate values of n, as desired.

The value of n (rounded up to an integer value) corresponds to approximately the desired center operating frequency divided by one half the desired bandwidth. In other words,

.DELTA..times..times..times. ##EQU00003## .times..DELTA..times..times. ##EQU00003.2## where f.sub.0 and .DELTA.f denote, respectively, the center operating frequency and the desired bandwidth. For instance, the above example of the FCC's definition of UWB results in values of n in the range of 1 to 42. More specifically, a 500-MHz-wide UWB system operating below (by half the bandwidth) the current FCC Part 15 limit frequency of 10.6 GHz results in:

.times. ##EQU00004## ##EQU00004.2##

The FCC has also allowed UWB signals of at least a 500-MHz bandwidth in the frequency range of 22-29 GHz, which corresponds to an upper value of n=116,000. Thus, persons skilled in the art with the benefit of the description of the invention may choose virtually any appropriate ranges of values for n, depending on the performance and design specifications and requirements for a given application. Note that generally the signal bandwidth varies inversely with the value of n.

FIG. 1 illustrates several PSD profiles for various values of n (the number of carrier cycles per chip). PSD profile 11 corresponds to n=1, whereas PSD profile 12 and PSD profile 13 correspond, respectively, to n=2 and n=3. Note that as the value of n increases, the bandwidth of the modulated signal decreases. Note further that, in a UWB system that one wishes to constrain to a predetermined maximum PSD (e.g., PSD characteristics prescribed by a regulatory authority), one seeks to achieve as flat a spectrum as possible in order to maximize the total transmitted power in a predetermined bandwidth.

In such a system, one likewise seeks to choose a transmission bandwidth independent of the modulation rate in order to maximize the total transmitted power. As persons of ordinary skill in the art appreciate, in conventional BPSK systems, the PSD profile is not flat even in the highest bandwidth case, where n=1. Furthermore, the bandwidth depends on the chip rate, as manifested by the parameter n. The dependence of the bandwidth on the parameter n may be undesirable for a variety of reasons, such as difficulty or failure to meet prescribed regulatory or design specifications.

For illustrative purposes, FIG. 2 depicts various signals corresponding to a BPSK transmission system. Carrier signal 21 may include only a fundamental frequency. Alternatively, rather than a continuous sine-wave signal, carrier signal 21 may include other waveforms, as described below. FIG. 2 also shows a pseudo-random noise (PN) sequence 22. Note that the waveforms in FIG. 2 correspond to a communication system with one chip per RF cycle (i.e., n=1), and 4 chips per data bit.

The third waveform in FIG. 2 corresponds to data bits 23. Beginning at time 27 and ending at time 28, PN sequence 22 codes data bits 23. The coding of data bits 23 results in signal 24. Signal 24 modulates carrier 21 to generate modulated signal 25. Signal 26 acts a gating signal. Put another way, the communication system transmits modulated signal 25 while the gating signal 26 is active (during the active portion of signal 26). Modulated signal 25 has a spectrum substantially the same as spectrum 11 in FIG. 1 (i.e., the case where the parameter n has a value of unity).

One may determine the data-rate or data throughput of the communication system from various system parameters. For example, assume that the carrier signal has a frequency of 4 GHz, and that the system operates with one chip per RF cycle (i.e., n=1) and 4 chips per data bit. Given those parameters, persons of ordinary skill in the art who have the benefit of the description of the invention readily appreciate that the system provides a 1-gigabit-per-second (Gb/s) data rate.

One exemplary embodiment of a high data-rate UWB system according to the invention includes a high data-rate UWB transmitter and a high data-rate UWB receiver. FIG. 3 shows an exemplary embodiment of high data-rate UWB transmitter 4 according to the invention.

Transmitter 4 includes reference clock 41 (a reference clock generator), timing controller 42, data buffer 43, PN generator 45 (a pseudo-random noise sequence generator), data/PN combiner 46, mixer 47, antenna 48, and harmonic generator 49. Reference clock 41 generates a signal with a desired frequency. The frequency of reference clock 41 corresponds to a carrier frequency for transmitter 4. Thus, the frequency of reference clock 41 corresponds to the desired carrier frequency. One may implement reference clock 41 in a number of way and by using various techniques that fall within the knowledge of persons skilled in the art with the benefit of the description of the invention.

Reference clock 41 couples to harmonic generator 49. Based a clock signal it receives from reference clock 41, harmonic generator 49 generates one or more harmonics of the carrier frequency (the frequency of clock reference 41). For example, given a clock frequency f.sub.c, a second harmonic signal at the output of harmonic generator 49 has a frequency 2f.sub.c, and so on, as persons skilled in the art with the benefit of the description of the invention understand. Harmonic generator 49 generates the one or more of harmonics synchronously with respect to the reference clock (i.e., the one or more harmonics are synchronized to the reference clock).

Note that one may realize harmonic generator 49 in a number of ways, for example, comb line generators, as persons of ordinary skill with the benefit of the description of the invention understand. As another example, one may use phase-locked loops, as desired. As other examples, one may employ an oscillator followed by digital divider circuitry. By dividing a signal of a given frequency by various integers, one may obtain the one or more harmonics. In connection with such an implementation, one may use fractional-N synthesizers, as desired.

Furthermore, one may use a variety of circuitry and techniques to synchronize the one or more harmonics to the reference clock. Such circuitry and techniques fall within the knowledge of persons of ordinary skill in the art who have the benefit of the description of the invention. As an example, a comb line generator may provide synchronization of the one or more harmonics to the reference clock.

Mixer 47 receives the one or more harmonics from harmonic generator 49. Mixer 47 mixes the one or more harmonics of the carrier frequency with a signal (described further below) that it receives from data/PN combiner 46. Mixer 47 provides the resulting signals to antenna 48. Antenna 48 propagates those signals into the transmission medium. In illustrative embodiments, antenna 48 may constitute a wide-band antenna.

Examples of wide-band antennas include those described in the following patent documents: U.S. Pat. No. 6,091,374; U.S. patent application Ser. No. 09/670,792, filed on Sep. 27, 2000; U.S. patent application Ser. No. 09/753,244, filed on Jan. 2, 2001; U.S. patent application Ser. No. 09/753,243, filed on Jan. 2, 2001; and U.S. patent application Ser. No. 09/077,340, filed on Feb. 15, 2002; and U.S. patent application Ser. No. 09/419,806, all assigned to the assignee of the present application. Furthermore, one may use wide-band horn antennas and ridged horn antennas, as desired. As yet another alternative, one may employ a differentially driven wire segment as a simple, effective, wide-band radiator. In addition, one may use other suitable wide-band antennas, as persons of ordinary skill in the art who have the benefit of the description of the invention understand.

Note that some antennas are of the "constant gain with frequency" types, and result in systems that have frequency dependent propagation characteristics. Other antennas, for example, horn antennas, are of the "constant aperture" variety, and produce frequency-independent propagation behavior. To use harmonics with relatively high frequencies, exemplary embodiments according to the invention use "constant aperture with frequency" antennas, although one may employ other types of antenna, as persons of ordinary skill in the art who have the benefit of the description of the invention understand.

Reference clock 41 also couples to timing controller 42. Timing controller 42 clocks the data in data buffer 43. Note that timing signals from timing controller 42 also clock PN generator 45. Data buffer 43 receives its input data from data port 44. A PN sequence from PN generator 45 modulates the data from data buffer 43 by using data/PN combiner 46, in a manner that persons of ordinary skill in the art with the benefit of the description of the invention understand. PN encoded data from data/PN combiner 46 modulates the one or more harmonics in mixer 47. In illustrative embodiments according to the invention, data/PN combiner 46 constitutes an exclusive-OR (XOR) gate, although one may use other suitable circuitry, as persons of ordinary skill in the art with the benefit of the description of the invention understand.

In illustrative embodiments, one may use filters at the output of harmonic generator 49 to adjust the amplitudes of the one or more harmonics so that have substantially the same value. Note, however, that in other embodiments according to the invention, one may use unequal amplitudes, as desired. By using unequal amplitudes, one may control the amount of energy in the transmitted signals at particular frequencies or bands of frequencies.

Unequal amplitudes affect the amount of energy in various parts of the corresponding PSD profile. For example, reduced (or eliminated) amplitudes result in reduced energy in corresponding frequency bands. (FIG. 16 shows an example of such a system, where one desires to radiate less energy in band 267 so as to improve coexistence with radio systems operating within that band.)

FIG. 4 illustrates exemplary waveforms corresponding to high data-rate UWB transmitter 4. Signal 421 corresponds to the output of harmonic generator 49. Signal 422 corresponds to a relatively short PN sequence of 4 chips per data bit. Signal 423 illustrates a relatively short data sequence. Signal 429, shown to provide more timing detail for transmitter 4, constitutes the output signal of reference clock 41.

Persons of ordinary skill in the art who have the benefit of the description of the invention appreciate that, depending on the application, chip sequences longer than 4 chips per bit may be desirable. For example, one may use such chip sequences when the transmission medium constitutes an RF channel with substantial multipath, or when one desires more energy per data bit (at the cost of the data throughput rate).

Generally, one may use as few as one chip per bit to obtain the maximum data rate, as desired. Furthermore, one may employ as many as tens of thousands of chips per bit in order to obtain "integration" gain at the cost of data rate. Thus, the range for the number of chips per bit may be very broad, as desired, depending on the design and performance specifications for a particular application, as persons skilled in the art understand. For example, in illustrative embodiments according to the invention, one may generally use 1 to 200 chips per bit, as desired. As another example, in embodiments that comply with IEEE 802.15, one typically desires data rates as high as 480 Mb/s, corresponding to a few chips per bit, and as low as 11 Mb/s, implying approximately several hundred chips per bit.

Persons of ordinary skill in the art who have the benefit of the description of the invention appreciate that the number of the PN chips per data bit is a measure of coding gain useful in mitigating against interference and against multipath impairments. Thus, using a larger number of chips per data bit provides one mechanism for reducing the effects of interference and multipath.

As noted above, one may implement data/PN combiner 46 using an exclusive-OR gate. Signal 424 depicts the result of an exclusive-OR operation on signals 422 and 423. Modulated RF signal 425 results from combining signal 421 and signal 424 in mixer 47. Timing signal 426 depicts the transmission time for the sequence of data bits 423.

FIG. 5 illustrates an exemplary embodiment of high data-rate UWB receiver 5 according to the invention. Receiver 5 includes reference clock 53, tracking loop 52, integrator/sampler 51, PN generator 55, data/PN combiner 56, mixer 57, antenna 58, and harmonic generator 59. Similarly named blocks and components in receiver 5 may have similar structure and operation as the corresponding blocks and components in transmitter 4 depicted in FIG. 3.

Referring to FIG. 5, in high data-rate UWB receiver 5, receiving antenna 58 couples received modulated signal 425 (shown as the signal coupled to the transmission medium in FIG. 3, with an exemplary waveform depicted in FIG. 4) to mixer 57. Mixer 57 supplies its output signal to integrator/sampler 51. Integrator/sampler 51 integrates the output signal of mixer 57 to deliver recovered data bit signal 563 as data output 54.

Mixer 57 also receives template signal 567. Data/PN combiner 56 generates template signal 567 from an output of PN generator 55 and harmonic generator 59. In illustrative embodiments according to the invention, data/PN combiner 56 constitutes an exclusive-OR (XOR) gate, although one may use other suitable circuitry, as persons of ordinary skill in the art with the benefit of the description of the invention understand. Harmonic generator 59 operates in a similar manner as harmonic generator 49 in FIG. 3, and may have a similar structure or circuitry.

A tracking loop 52, well known in the art, controls reference clock 53 and PN generator 55. Tracking loop 52 controls the timing of PN generator 55 for proper signal acquisition and tracking, as persons of ordinary skill in the art with the benefit of the description of the invention understand. Reference clock 53 provides reference clock signal 569 to PN generator 55 and harmonic generator 59.

Note that one may implement tracking loop 52 in a variety of ways, as desired. The choice of implementation depends on a number of factors, such as design and performance specifications and characteristics, as persons skilled in the art understand. Tracking loop 52 operates in conjunction with template signal 567 to provide a locking mechanism for receiving a transmitted signal (template receiver or matched template receiver), as persons skilled in the art who have the benefit of the description of the invention understand.

Mixer 57 mixes the signal received from antenna 58 with template signal 567 to generate signal 568. Integrator/sampler 51 integrates signal 568 to generate recovered data signal 563. Integrator/sampler 51 drives tracking loop 52, which controls signal acquisition and tracking in high data-rate UWB receiver 5.

FIG. 6 illustrates exemplary waveforms corresponding to high data-rate UWB receiver 5. Signal 562 constitutes the output of PN generator 55. Signal 561 corresponds to the output of harmonic generator 59, whereas signal 567 is the output signal of data/PN combiner. Signal 568 constitutes the output signal of mixer 57, which feeds integrator/sampler 51. Signal 563 is the output signal of integrator/sampler 51. Finally, signal 569, shown to provide more timing detail for receiver 5, constitutes the output signal of reference clock 53.

FIG. 7 shows further details of the timing relationship among various signals in the high data-rate UWB transmitter 4. Waveform 75 corresponds to the signals in the transmission medium (i.e., propagated from antenna 48). Waveform 76 shows the transmission periods, i.e., periods of time during which transmitter 4 transmits. Finally, waveform 73 illustrates data bit stream 73 during transmission periods 76. Waveform 79 depicts the clock tick marks for timing reference with respect to the other waveforms in FIG. 7.

In other embodiments according to the invention, one may operate high data-rate UWB transmitter 4 in either of two modes, depending on a selected or prescribed parameter. Each mode may generate a particular or prescribed PSD profile by using particular or prescribed harmonic orders (i.e., the choice of the harmonics of the carrier to use for each mode). By selecting a particular mode, one may operate transmitter 4 such that it produced output signals that conform to a particular PSD profile or meet prescribed conditions (as set forth, for example, by a regulatory authority, such as the FCC).

FIG. 8 depicts two exemplary desired or prescribed PSD profiles that correspond to the two modes of operation in such embodiments. A transmitter according to the invention may produce outputs that conform to a selected one of predetermined PSD amplitude profile mask 80 and predetermined PSD amplitude profile mask 81. In an embodiment of such a transmitter, the frequency of the reference clock (i.e., the frequency of reference clock 41 in FIG. 3) is approximately 1.8 GHz. Accordingly, the second and third harmonics appear at approximately 3.6 GHz and 5.4 GHz, respectively.

In a first mode of operation conforming to PSD amplitude profile mask 80, one modulates the 3.6 GHz carrier (the second harmonic of the reference clock frequency) with one chip per two RF carrier cycles. Furthermore, one modulates the 5.4 GHz carrier (the third harmonic of the reference clock frequency) with one chip per three RF cycles. In this mode of operation, the transmitter has a chipping rate of 1.8 giga-chips per second. The transmitter produces a transmitted PSD profile 83. Note that transmitted PSD profile 83 has a substantially flat shape, and conforms to PSD mask 80 (i.e., it remains under PSD mask 80).

In a second operating mode, one suppresses the second harmonic while modulating the third harmonic 1.80-GHz clock (i.e., the harmonic appearing at 5.6 GHz) at a rate of one chip per four RF cycles. As a result, the transmitter has a chipping rate of 1.35 giga-chips per second.

Note that one may implement embodiments according to the invention that include more than two operating modes, as desired. For example, one may provide a UWB apparatus that includes m operating modes, where m denotes an integer larger than unity. One may implement such a system in a variety of ways, as persons of ordinary skill in the art with the benefit of the description of the invention understand. For example, one may use a bank of selectable harmonic filters (i.e., selectable choice of which harmonic orders to use) to select any combination of one or more harmonics. Such a UWB radio apparatus may selectively avoid interference from or with other radio systems operating in the same band or bands. Note that in illustrative embodiments according to the invention, one may consider "one or more of m harmonics" as a form of modulation in addition to the polarity modulation (i.e., BPSK modulation).

Although the description above refers to the second and third harmonic, persons of ordinary skill in the art who have the benefit of the description of the invention appreciate that one may use other harmonics, as desired. Put another way, in each operating mode, one may employ additional harmonics beyond the third harmonic. Using additional harmonics increases the total transmitted power, while simultaneously conforming to the prescribed respective masks (i.e., remaining under the PSD masks).

FIG. 9 shows a PSD profile for an exemplary embodiment of the invention that uses higher-order harmonics. Transmitted PSD profile 91 corresponds to modulated third and fourth harmonics of a 1.1-GHz reference clock. PSD profile 91 assumes modulation at the rate of 1.1 giga-chips per second.

If one desired more transmitted power, one may employ the third through seventh harmonics. Doing so results in transmitted PSD profile 93. Note that both PSD profile 92 and PSD profile 93 have substantially flat shapes. Note further that both PSD profile 92 and PSD profile 93 conform to a prescribed or desired PSD amplitude profile mask 90. Thus, by using a number of harmonics of the reference clock frequency that have an appropriate order, one may implement communication systems with particular output power profiles that conform to prescribed PSD profiles, as desired.

Note that one may use an appropriate clock reference frequency and associated harmonics to provide co-existence with other devices that use a particular RF band or spectrum. For example, in other embodiments according to the invention, the clock reference parameters and the harmonic carriers are selected so that the PSD of the high data rate UWB transmissions coexist with wireless devices operating in the 2.4 GHz ISM band and in the 5 GHz UNII bands.

More specifically, in such embodiments, the reference clock has a frequency of approximately 1.1 GHz. Furthermore, the transmitter uses as carrier frequencies modulated at the reference clock rate of approximately 1.1 GHz both the third and fourth harmonics of the reference clock frequency (i.e., 3.3 GHz and 4.4 GHz, respectively).

FIG. 10 shows an exemplary PSD profile for such an embodiment of the invention. Transmission PSD profile 101 fits between the 2.4 GHz ISM band 102 and the 5 GHz UNII bands 103, satisfying a desired level of coexistence. Note that the communication system can still support a relatively high data-rate. For example, if one uses 10 PN chips to comprise one data bit, the resulting data rate is 110 megabits per second (Mb/s).

Signal harmonics may be added with a selectable, desired, or designed degree of freedom regarding relative phase of the carriers. For example, in a communication system according to the invention that uses the third and fourth harmonics, one may generally represent the time signals x(t), the sum of the carrier harmonics, by: x(t)=sin(2.pi.3f.sub.rt)+sin(2.pi.4f.sub.rt+.phi.), where f.sub.r represents the reference clock frequency and .phi. denotes a selectable or prescribed phase angle between 0 and 2.pi. cradians. Note that in exemplary embodiments according to the invention, one may realize the phase angle by using a filter, as persons of ordinary skill in the art with the benefit of the description of the invention understand.

Note that in exemplary embodiments according to the invention, one may use various values of .phi., as desired, where 0.ltoreq..phi..ltoreq.2.pi.. FIG. 11A illustrates one cycle of an exemplary output signal 121A of a transmitter in a UWB communication system according to the invention. Signal 121A corresponds to .phi.=.pi.. Starting point 122 and ending point 123 coincide with the chip boundaries, as illustrated, for example, by signal 421 and chip signal 422 (output signal of PN generator) in FIG. 4.

Furthermore, note that one may represent output signal x(t) by using cosines, as desired. In other words, x.sub.i(t)=cos(2.pi.3f.sub.rt)+cos(2.pi.4f.sub.rt+.phi.), where f.sub.r represents the reference clock frequency and .phi. denotes a selectable or prescribed phase angle between 0 and 2.pi. radians (inclusive of the end points). FIG. 11B shows one cycle of another exemplary output signal 121B of a transmitter in a UWB communication system according to the invention. Output signal 121B has starting point 122B and ending point 123B.

Persons skilled in the art with the benefit of the description of the invention appreciate that It will be appreciated that signals x(t) and x.sub.i(t) constitute orthogonal signals. One may therefore use signals x(t) and x.sub.i(t) to implement quadrature phase shift keying (QPSK) modulation, as described below.

Note that signals 121A and 121B have relatively small signal levels at both their starting points (i.e., 122A and 122B, respectively) and their ending points (i.e., 123A and 123B). Exemplary embodiments according to the invention switch signals ON and OFF at those relatively small signal levels. Doing so tends to avoid switching transients that with imperfect switching might alter the resulting spectrum undesirably.

In illustrative embodiments according to the invention, one may represent the harmonic carriers by a composite signal S that constitutes a summation of sinusoidal and/or cosinusoidal signals, i.e., S(t)=.SIGMA. sin{2.pi.nf.sub.r(t-s)}, where the summation extends over the range of harmonics n desired (i.e., it spans the order of the desired harmonics, from the lowest to the highest). Put another way, the composite signal S constitutes a sum of harmonic carriers over a selected range, n. Note that one may also add cosine harmonics to implement a quadrature UWB communication apparatus.

As noted above, in some embodiments, n may range from 3 to 4 (corresponding to a UWB communication apparatus operating in a desired 3.1 GHz to 5.2 GHz frequency range). FIG. 12 shows the timing relationship between several signals in such an embodiment according to the invention, with n=3. Signal 139 depicts a reference clock signal, included to facilitate presentation of the timing relationship between the various signals. Signal 131 corresponds to composite signal S, described above. Signal 132 denotes the sinusoidal signal the harmonics of which result in composite signal 131. Reference clock signal 139 corresponds to the positive-going zero-crossings of sinusoidal signal 132.

Note that time displacement s offsets the chipping signal from the carrier signal. More specifically, time displacement s appears as an offset between reference clock signal 139 (or sinusoidal signal 132) and the chipping signals.

FIG. 12 shows signals corresponding to several values of time displacement s. Each time displacement s signifies the offset between reference clock signal 139 (or sinusoidal signal 132) and one of chipping signal 133, chipping signal 134, and chipping signal 135, respectively. Specifically, chipping signal 133 corresponds to a time displacement s of zero. Chipping signal 134 and chipping signal 135 denote, respectively, time displacements of 0.25 and 0.5, respectively.

Persons of ordinary skill in the art who have the benefit of the description of the invention appreciate that, because of symmetry, negative values of s give the same results as positive values of s. Hence, the description of the invention refers to the magnitude of s, or |s|. Also, note that, although FIG. 12 illustrates the chipping sequence "101" as an example for the sake of illustration, persons skilled in the art with the benefit of the description of the invention understand that one may generally use a desired PN sequence.

FIG. 13 illustrates several PSD profiles for an illustrative embodiment according to the invention. PSD profile 143 depicts the power spectral density of signal 131 multiplied by PN chipping sequence 133. Similarly, PSD profile 144 corresponds to the power spectral density of signal 131 multiplied by PN chipping sequence 134. Finally, PSD profile 145 illustrates the power spectral density of signal 131 multiplied by PN chipping sequence 135.

FIG. 13 also illustrates boundary 146 of the 2.4 GHz ISM band and boundary 147 of the UNII band. For two harmonics, a time displacement value |s|=0.25 provides a substantially flat PSD profile 144. Persons of ordinary skill in the art who have the benefit of the description of the invention understand, however, that one may use time displacement values (s) in a range of approximately 0.1 and approximately 0.9 to provide substantially similar PSD profiles for the third and fourth harmonics, as desired. In a similar manner, one may use other values of time displacement s and appropriate numbers of harmonics to implement communication systems having desired or prescribed PSD profiles, as desired.

As an example, FIG. 14 depicts several PSD profiles that correspond to exemplary embodiments of the invention that use increasing numbers of harmonics. FIG. 14 includes PSD profile 151, PSD profile 152, and PSD profile 153. A substantially flat PSD profile 151 corresponds to a signal that includes the fundamental frequency through the seventh harmonic, using a time displacement value of |s|=0.375. Similarly, PSD profile 152 pertains to a signal that includes the second through the seventh harmonics, using a time displacement value of |s|=0.375. Finally, PSD profile 153 corresponds to a signal that includes the third through the seventh harmonics and uses a time displacement value of |s|=0.375.

Note that values of time displacement s between approximately 0.1 and approximately 0.9 provide substantially flat PSD profiles, similar to the PSD profiles that FIG. 14 illustrates. As noted above, using larger numbers of harmonics while conforming to PSD profiles (i.e., constrained to a maximum PSD value) results in an increase in the total transmitted or radiated power.

One may generate and implement the time displacement s in variety of ways, as persons of ordinary skill in the art who have the benefit of the description of the invention understand. For example, one may implement s as digitally derived clock shift in timing controller 42 of transmitter 4 and PN generator 55 in receiver 4. As another example, one may implement the desired time shift by using a physical delay line in the path of the digital input of mixer 47 in transmitter 4 and mixer 57 in receiver 5.

One may obtain the spectra shown in the figures by computing the Fourier Transform of the composite signal S. More specifically, where the data pulses have a generally rectangular shape and have not been filtered (e.g., chipping signal 422 in FIG. 4), one may obtain the PSD as:

.times..times..intg..times..times..function..times..pi..function..times.e.- pi..times..times..times..times..times.d ##EQU00005## where f.sub.r denotes the chipping clock frequency, and n.sub.1 and n.sub.2 correspond to the order of the harmonics used (i.e., the lower and upper boundaries of the range of harmonics used). Note that one may omit selected harmonics within the range n.sub.1 to n.sub.2 to further shape the spectrum, as desired. FIG. 15 shows an example of applying this technique.

Referring to FIG. 15, PSD profile 161 shows the power spectral density for an embodiment of a communication system according to the invention that uses the third through seventh harmonics of a 1.1-GHz clock. In contrast, PSD profile 162 corresponds to a system that employs the fifth through the seventh harmonics. As a result, the PSD energy in the latter system lies mostly above 5 GHz.

As a third example, PSD profile 163 corresponds to a system that uses the third, fourth, sixth, and seventh harmonics. Omitting the fifth harmonic in this system results in a gap in the vicinity of 5 GHz to 6 GHz. As a result, the system may effectively coexist with systems that operate in the 5-GHz UNII band. Note that one may use filtering to readily remove energy in the side lobes shown in FIG. 15.

The PSD profiles shown in FIG. 15 correspond to illustrative embodiments of communication systems according to the invention. By judiciously employing selected harmonics together with a chosen clock frequency, one may design and implement a wide variety of communication systems with prescribed PSD profiles in a flexible manner. The choice of design parameters (e.g., clock frequency and the number and order of harmonics) depend on desired design and performance specifications and fall within the knowledge of persons of ordinary skill in the art who have the benefit of the description of the invention.

FIG. 16 shows PSD profiles for other exemplary embodiments of communication systems or apparatus according to the invention. These embodiment conform with a PSD mask in which the emissions at 3.1 GHz are at least -10 dB from the peak (marker labeled as 265 in FIG. 16). Furthermore, the mask specifies emissions at 10.6 GHz of at least -10 dB from the peak (marker denoted as 266 in FIG. 16).

UNII band 267 extends from 5.15 GHz to approximately 5.9 GHz. FIG. 16 illustrates four PSD profiles (denoted as profiles 261, 262, 263, and 264, respectively) that correspond to different choices of the order of harmonics used. All four PSD profiles correspond to a baseband chipping reference clock frequency of 1.4 GHz. Furthermore, the PSD profiles assume time displacement s of approximately 0.375 between the reference clock signal and the chipping sequences (see FIG. 13 and accompanying description for an explanation of time displacement s and its effect on PSD profiles).

As noted above, PSD profiles 261, 262, 263, and 264 denote various choices of the order of harmonics used. PSD profile 261 corresponds to a communication system that uses the 3rd through the 7th harmonics of the chipping reference clock. Thus, such a system effectively occupies the allowed bandwidth between 3.1 GHz and 10.6 GHz.

PSD profile 262 corresponds to a system that employs the 3rd, the 5th, the 6th, and the 7th harmonics of the chipping reference clock. In other words, unlike the system corresponding to PSD profile 261, it omits the fourth harmonic, which overlaps UNII band 267.

The system corresponding to PSD profile 263 uses the 3rd through the 6th harmonics of the chipping reference clock. Thus, this system omits the relatively higher frequencies by not using higher-order harmonics.

PSD profile 264 pertains to a communication system that uses the 3rd, the 5th, and the 6th harmonics of the chipping reference clock. This system omits the fourth harmonic, which overlaps UNII band 267. The system may switch its operation modes between PSD profile 261 and PSD profile 262 or, alternatively, between PSD profile 263 and PSD profile 264, as described below in detail.

Table 1 below summarizes the harmonics used in the systems corresponding to PSD profiles 261, 262, 263, and 264:

TABLE-US-00001 TABLE 1 PSD Profile Harmonic Orders Used 261 3, 4, 5, 6, and 7 262 3, 5, 6, and 7 263 3, 4, 5, and 6 264 3, 5, and 6

As noted above, communication systems according to exemplary embodiments of the invention may include multi-mode op