Method and system for controlling a robot Number:7,069,111 from the United States Patent and Trademark Office (PTO) owispatent

Title: Method and system for controlling a robot

Abstract: A system and method are described that use impulse radio technology to enhance the capabilities of a robot. In one embodiment, a system, a robot and a method are provided that use the communication capabilities of impulse radio technology to help a control station better control the actions of the robot. In another embodiment, a system, a robot and a method are provided that use the communication, position and/or radar capabilities of impulse radio technology to help a control station better control the actions of a robot in order to, for example, monitor and control the environment within a building.

Patent Number: 7,069,111 Issued on 06/27/2006 to Glenn,   et al.

---

Inventors:	Glenn; Susan J. (Huntsville, AL); Shreve; Gregory A. (Huntsville, AL)
Assignee:	Time Domain Corp. (Huntsville, AL)
Appl. No.:	097838
Filed:	April 1, 2005

---

Related U.S. Patent Documents

---

	Application Number	Filing Date	Patent Number	Issue Date
	10826440	Apr., 2004	6879878
	09873639	Jun., 2001	6763282

---

Current U.S. Class:	700/245 ; 318/568.11; 342/353; 342/89; 375/295; 375/316; 700/247; 700/248; 700/249; 700/250; 700/259; 701/207; 701/209; 701/213; 701/23
Current International Class:	G06F 19/00 (20060101)
Field of Search:	700/245 318/568.11 701/213

---

References Cited [Referenced By]

---

U.S. Patent Documents

	4641317		February 1987		Fullerton
	4813057		March 1989		Fullerton
	4979186		December 1990		Fullerton
	5285209		February 1994		Sharpin et al.
	5363108		November 1994		Fullerton
	5677927		October 1997		Fullerton et al.
	5687169		November 1997		Fullerton
	5764696		June 1998		Barnes et al.
	5832035		November 1998		Fullerton
	6111536		August 2000		Richards et al.
	6133876		October 2000		Fullerton et al.
	6177903		January 2001		Fullerton et al.
	6218979		April 2001		Barnes et al.
	6300903		October 2001		Richards et al.
	6300914		October 2001		Yang
	6304623		October 2001		Richards et al.
	6421389		July 2002		Jett et al.
	6763282		July 2004		Glenn et al.
	2005/0018762		January 2005		Aiello et al.
	2005/0131922		June 2005		Kennedy et al.
	2005/0237966		October 2005		Aiello et al.

Other References

Patwari et al., Locating the nodes, 2005, Internet, p. 1-16. cited by exam- iner . R.J. Fontana et al. "An Ultra Wideband Communication Link for Unmanned Vehicle Applications", Association for Unmanned Vehicle Systems International 1997 Conference (AUVSI'97), Baltimore, Jun. 3-6, 1997. cite- d by other . Multispectral Solutions Press Release Multispectral Solutions Develops First Ultra Wideband Radio to Exploit Ground Wave Propagation for Non Line-Of-Sight Applications, Dec. 2, 1997. cited by other . A. Valejo et al. "Short-Range DGPS for Mobile Robots with Wireless Ethernet Links", 1998 5th International Workshop on Advance Motion Control, pp. 334-339, 1998. cited by other . "Intelligent Taskable System Colonies for Small Unit Operations", USA Robotics Research Laboratory Report to DARPA, May 10-13, 1999. cited by other . G.S. Sukhatme et al. "Heterogeneous Tobot Group Control and Applications", Proceedings of the AUVS 99 Conference, 1999. cited by other . G.S. Sukhatme et al. "Design and Implementation of a Mechanically Heterogeneous Robot Group", Proceedings of SPIE: Sens Fusion and Decentralized Control in Robotic Systems II, vol. 3839, pp. 122-133, Sep. 1999. cited by other . C.H. Spenny et al. "Closely Supervised Control of a Target-Steered UAV", Proceedings of SPIE, Telemanipulator and Telepresence Technologies VI, v 3840, pp. 179-190, 1999. cited by other . R.J. Fontana "Recent Applications of Ultra Wideband Radar and Communications Systems, in Ultra-Wideband Short-Pulse Electromagnetics" Kluwer Academic/Plenum Publishers, 2000. cited by other . Time Domain Corporation Press Release, "Time Domain Demonstrates Revolutionary Ultra Wideband (UWB) Technology at Roving Sands 2000", June 20, 2000. cited by other . R.T. Vaughan et al. "Fly Spy: Lightweight Localization and Target Tracking for Cooperating Air and Ground Robots", Proc. Int. Symp. Distributed Autonomous Robot Systems, 2000. cited by other . G.S. Sukhatme et al. "Experiments with Cooperative Aerial-Ground Robots", in Robot Teams: From Diversity to Polymorphism, Eds. T. Balch and L.E. Parker, AK Peters, 2001(possible prior art since not known exactly when published in 2001). cited by other . U.S. Appl. No. 09/591,690, filed Jun. 12, 2000. cited by other . U.S. Appl. No. 09/875,290, filed Jun. 7, 2001. cited by other . U.S. Appl. No. 09/537,692, filed Mar. 29, 2000. cited by other . U.S. Appl. No. 09/538,519 filed Mar. 29, 2000. cited by other . U.S. Appl. No. 09/332,501, filed Jun. 14, 1999. cited by other . U.S. Appl. No. 09/587,033, filed Jun. 2, 1999. cited by other . U.S. Appl. No. 09/586,163, filed Jun. 2, 1999. cited by other . U.S. Appl. No. 09/537,264, filed Mar. 29, 2000. cited by other . U.S. Appl. No. 09/538,292, filed Mar. 29, 2000. cited by other . U.S. Appl. No. 09/592,249, filed Jun. 12, 2000. cited by other . U.S. Appl. No. 09/592,250, filed Jun. 12, 2000. cited by other . U.S. Appl. No. 09/592,290, filed Jun. 12, 2000. cited by other . U.S. Appl. No. 09/591,691, filed Jun. 12, 2000. cited by other . U.S. Appl. No. 09/592,289, filed Jun. 12, 2000. cited by other . U.S. Appl. No. 09/592,248, filed Jun. 12, 2000. cited by other . U.S. Appl. No. 09/592,288, filed Jun. 12, 2000. cited by other . Business Editors & High Tech Writers "Automated Identification Technologies Long Range Wireless ID Tags Add Powerful New Capabilities to Cybermotion's Automated Patrol Systems", Business Wire dated 12/14/00, 3 pages. cited by other . "Cybermotion CyberGuard Robotic Security System . . . ", downloaded Dec. 14, 2000 from http://www.cybermotion.com, 18 pages. cited by other.

Primary Examiner: Black; Thomas G.
Assistant Examiner: Marc; McDieunel
Attorney, Agent or Firm: Tucker; William J.

---

Parent Case Text

---

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patent application Ser. No. 10/826,440, filed Apr. 17, 2004, now U.S. Pat. No. 6,879,878, which is a continuation application of Ser. No. 09/873,639 filed Jun. 4, 2001 now U.S. Pat. No. 6,763,282 B2.

---

Claims

---

What is claimed is:

1. A method for identifying and locating a physical asset, said method comprising the steps of: associating a first ultra wideband radio with said physical asset; associating a second ultra wideband radio with a robot; obtaining, at said robot, information that identifies said physical asset based upon the interaction of said first ultra wideband radio and said second ultra wideband radio; and locating a position of said physical asset based upon the interaction of said first ultra wideband radio and at least two of a plurality of reference ultra wideband radios.

2. The method of claim 1, wherein said physical asset is at least one of a commercial asset, a military asset, a work of art, a computer, and a cash drawer.

3. The method of claim 1, wherein said physical asset is located inside a building.

4. The method of claim 1, further comprising the step of: interfacing said robot with a control station.

5. The method of claim 4, wherein said control station is used to control said robot.

6. The method of claim 4, further comprising the steps of: determining a position of said robot based upon the interaction of said second ultra wideband radio and at least two of a plurality of reference ultra wideband radios; and controlling the actions of said robot based upon said position of said robot.

7. The method of claim 4, further comprising the step of: conveying said information that identifies said physical asset from said robot to said control station, wherein said control station uses said information that identifies said physical asset to monitor said physical asset.

8. The method of claim 4, wherein said control station is located remotely to said robot.

9. The method of claim 4, wherein said second ultra wideband radio communicates with a third ultra wideband radio associated with said control station.

10. The method of claim 4, further comprising the step of: interfacing said robot with one or more sensors, wherein said control station uses information obtained from said one or more sensors to monitor said physical asset.

11. The method of claim 1, wherein the second ultra wideband radio has radar capabilities which are used to detect a person in the vicinity of the robot.

12. The method of claim 1, wherein said first ultra wideband radio periodically wakes-up from a sleep mode to transmit at predetermined intervals the information that identifies the physical asset.

13. The method of claim 12, wherein said first ultra wideband radio listens for a transmission from said second ultra wideband radio for a period of time following the transmission of the information that identifies the physical asset.

14. The method of claim 13, wherein said transmissions comprise at least one of a range request and a status request.

15. The method of claim 1, further comprising the step of: determining a range between said first ultra wideband radio and said second ultra wideband radio.

16. A physical asset location system, comprising: a first ultra wideband radio associated with a physical asset; a robot associated with a second ultra wideband radio that interacts with said first ultra wideband radio to determine information that identifies said physical asset; and a plurality of reference ultra wideband radios, at least two of which interact with said first ultra wideband radio to enable a position of said physical asset to be determined.

17. The physical asset location system of claim 16, further comprising: a control station having an interface with said robot.

18. The physical asset location system of claim 17, wherein said control station is associated with a third ultra wideband radio that interacts with said second ultra wideband radio.

19. The physical asset location system of claim 16, wherein at least two of said plurality of reference ultra wideband radios interact with said second ultra wideband radio to enable a position of said robot to be determined, wherein said determined position is used to control one or more actions of said robot.

20. The physical asset location system of claim 16, further comprising: at least one sensor associated with said robot.

---

Description

---

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to robots and, in particular, to a system and method capable of using impulse radio technology to enhance the capabilities of a robot.

2. Description of Related Art

In the robotics field, one of the most significant design challenges involves the development of new ways to improve the way a control station can interact with and control the actions of a robot. To date many control stations have a standard radio transceiver, which transmits and receives radio signals to and from another standard radio transceiver attached to the robot in order to interact with and control the actions of that robot. Unfortunately, problems have arisen in the past with the use of standard radio equipment because there are often problematical "dead zones" within a building that may interfere with the communications between the control station and a moving robot. Dead zones are caused by the closed structure of the building, which can make it difficult for a moving robot using a standard radio transceiver to maintain contact with a control station using a standard radio transceiver. For instance, the standard radio signals sent from the standard radio transceiver attached to the control station may not be able to penetrate a certain wall or floor within the building and as such may not reach the standard radio transceiver attached to the moving robot.

The closed structure of the building may also cause "multipath interference" which can interfere with standard radio transmissions between the control station and the robot. Multipath interference is an error caused by the interference of a standard radio signal that has reached a standard radio receiver by two or more paths. For instance, the standard radio receiver attached to the robot may not be able to demodulate a received radio signal because the originally transmitted radio signal effectively cancels itself out by bouncing of walls and floors of the building before reaching the robot. Accordingly, there has been a need to provide a system, robot and method that can overcome the traditional shortcomings associated with communications between the control station and robot. This need and other needs are addressed by the system, robot and method of the present invention.

BRIEF DESCRIPTION OF THE INVENTION

The present invention includes a system and method capable of using impulse radio technology to enhance the capabilities of a robot. In one embodiment of the present invention, a system, a robot and a method are provided that use the communication capabilities of impulse radio technology to help a control station better control the actions of the robot. In another embodiment of the present invention, a system, a robot and a method are provided that use the communication, position and/or radar capabilities of impulse radio technology to help a control station better control the actions of a robot in order to, for example, monitor and control the environment within a building.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein:

FIG. 1A illustrates a representative Gaussian Monocycle waveform in the time domain;

FIG. 1B illustrates the frequency domain amplitude of the Gaussian Monocycle of FIG. 1A;

FIG. 1C represents the second derivative of the Gaussian Monocycle of FIG. 1A;

FIG. 1D represents the third derivative of the Gaussian Monocycle of FIG. 1A;

FIG. 1E represents the Correlator Output vs. the Relative Delay in a real data pulse;

FIG. 1F graphically depicts the frequency plot of the Gaussian family of the Gaussian Pulse and the first, second, and third derivative.

FIG. 2A illustrates a pulse train comprising pulses as in FIG. 1A;

FIG. 2B illustrates the frequency domain amplitude of the waveform of FIG. 2A;

FIG. 2C illustrates the pulse train spectrum;

FIG. 2D is a plot of the Frequency vs. Energy Plot and points out the coded signal energy spikes;

FIG. 3 illustrates the cross-correlation of two codes graphically as Coincidences vs. Time Offset;

FIGS. 4A 4E graphically illustrate five modulation techniques to include: Early-Late Modulation; One of Many Modulation; Flip Modulation; Quad Flip Modulation; and Vector Modulation;

FIG. 5A illustrates representative signals of an interfering signal, a coded received pulse train and a coded reference pulse train;

FIG. 5B depicts a typical geometrical configuration giving rise to multipath received signals;

FIG. 5C illustrates exemplary multipath signals in the time domain;

FIGS. 5D 5F illustrate a signal plot of various multipath environments.

FIG. 5G illustrates the Rayleigh fading curve associated with non-impulse radio transmissions in a multipath environment.

FIG. 5H illustrates a plurality of multipaths with a plurality of reflectors from a transmitter to a receiver.

FIG. 5I graphically represents signal strength as volts vs. time in a direct path and multipath environment.

FIG. 6 illustrates a representative impulse radio transmitter functional diagram;

FIG. 7 illustrates a representative impulse radio receiver functional diagram;

FIG. 8A illustrates a representative received pulse signal at the input to the correlator;

FIG. 8B illustrates a sequence of representative impulse signals in the correlation process;

FIG. 8C illustrates the output of the correlator for each of the time offsets of FIG. 8B.

FIG. 9 is a diagram illustrating the basic components of a system in accordance with the present invention.

FIG. 10 is a diagram illustrating in greater detail the components of a robot and control station of the system shown in FIG. 9.

FIG. 11 is a diagram illustrating the robot and control station of FIG. 10 used in a manner to monitor and control, if needed, the environment within a building.

FIG. 12 is a diagram illustrating in greater detail the robot and control station of FIG. 10 used in a manner to monitor and track physical assets within the building.

FIG. 13 is a flowchart illustrating the basic steps of a preferred method for controlling the actions of a robot in accordance with the present invention.

FIG. 14 is a block diagram of an impulse radio positioning network utilizing a synchronized transceiver tracking architecture that can be used in the present invention.

FIG. 15 is a block diagram of an impulse radio positioning network utilizing an unsynchronized transceiver tracking architecture that can be used in the present invention.

FIG. 16 is a block diagram of an impulse radio positioning network utilizing a synchronized transmitter tracking architecture that can be used in the present invention.

FIG. 17 is a block diagram of an impulse radio positioning network utilizing an unsynchronized transmitter tracking architecture that can be used in the present invention.

FIG. 18 is a block diagram of an impulse radio positioning network utilizing a synchronized receiver tracking architecture that can be used in the present invention.

FIG. 19 is a block diagram of an impulse radio positioning network utilizing an unsynchronized receiver tracking architecture that can be used in the present invention.

FIG. 20 is a diagram of an impulse radio positioning network utilizing a mixed mode reference radio tracking architecture that can be used in the present invention.

FIG. 21 is a diagram of an impulse radio positioning network utilizing a mixed mode mobile apparatus tracking architecture that can be used in the present invention.

FIG. 22 is a diagram of a steerable null antennae architecture capable of being used in an impulse radio positioning network in accordance the present invention.

FIG. 23 is a diagram of a specialized difference antennae architecture capable of being used in an impulse radio positioning network in accordance the present invention.

FIG. 24 is a diagram of a specialized directional antennae architecture capable of being used in an impulse radio positioning network in accordance with the present invention.

FIG. 25 is a diagram of an amplitude sensing architecture capable of being used in an impulse radio positioning network in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes a system and method capable of using impulse radio technology to enhance the capabilities of a robot. The use of impulse radio technology to enhance the capabilities of a robot is a significant improvement over the state-of-art. This significant improvement over the state-of-art is attributable, in part, to the use of an emerging, revolutionary ultra wideband technology (UWB) called impulse radio communication technology (also known as impulse radio).

Impulse radio, which is not a continuous wave carrier-based system, has been described in a series of patents, including U.S. Pat. No. 4,641,317 (issued Feb. 3, 1987), U.S. Pat. No. 4,813,057 (issued Mar. 14, 1989), U.S. Pat. No. 4,979,186 (issued Dec. 18, 1990) and U.S. Pat. No. 5,363,108 (issued Nov. 8, 1994) to Larry W. Fullerton. A second generation of impulse radio patents includes U.S. Pat. No. 5,677,927 (issued Oct. 14, 1997), U.S. Pat. No. 5,687,169 (issued Nov. 11, 1997), U.S. Pat. No. 5,764,696 (issued Jun. 9, 1998), and U.S. Pat. No. 5,832,035 (issued Nov. 3, 1998) to Fullerton et al.

Uses of impulse radio systems are described in U.S. Pat. No. 6,177,903 entitled, "System and Method for Intrusion Detection using a Time Domain Radar Array" and U.S. Pat. No. 6,218,979 entitled, "Wide Area Time Domain Radar Array" both of which are assigned to the assignee of the present invention. These patents are incorporated herein by reference.

This section provides an overview of impulse radio technology and relevant aspects of communications theory. It is provided to assist the reader with understanding the present invention and should not be used to limit the scope of the present invention. It should be understood that the terminology `impulse radio` is used primarily for historical convenience and that the terminology can be generally interchanged with the terminology `impulse communications system, ultra-wideband system, or ultra-wideband communication systems`. Furthermore, it should be understood that the described impulse radio technology is generally applicable to various other impulse system applications including but not limited to impulse radar systems and impulse positioning systems. Accordingly, the terminology `impulse radio` can be generally interchanged with the terminology `impulse transmission system and impulse reception system.`

Impulse radio refers to a radio system based on short, low duty-cycle pulses. An ideal impulse radio waveform is a short Gaussian monocycle. As the name suggests, this waveform attempts to approach one cycle of radio frequency (RF) energy at a desired center frequency. Due to implementation and other spectral limitations, this waveform may be altered significantly in practice for a given application. Many waveforms having very broad, or wide, spectral bandwidth approximate a Gaussian shape to a useful degree.

Impulse radio can use many types of modulation, including amplitude modulation, phase modulation, frequency modulation, time-shift modulation (also referred to as pulse-position modulation or pulse-interval modulation) and M-ary versions of these. In this document, the time-shift modulation method is often used as an illustrative example. However, someone skilled in the art will recognize that alternative modulation approaches may, in some instances, be used instead of or in combination with the time-shift modulation approach.

In impulse radio communications, inter-pulse spacing may be held constant or may be varied on a pulse-by-pulse basis by information, a code, or both. Generally, conventional spread spectrum systems employ codes to spread the normally narrow band information signal over a relatively wide band of frequencies. A conventional spread spectrum receiver correlates these signals to retrieve the original information signal. In impulse radio communications, codes are not typically used for energy spreading because the monocycle pulses themselves have an inherently wide bandwidth. Codes are more commonly used for channelization, energy smoothing in the frequency domain, resistance to interference, and reducing the interference potential to nearby receivers. Such codes are commonly referred to as time-hopping codes or pseudo-noise (PN) codes since their use typically causes inter-pulse spacing to have a seemingly random nature. PN codes may be generated by techniques other than pseudorandom code generation. Additionally, pulse trains having constant, or uniform, pulse spacing are commonly referred to as uncoded pulse trains. A pulse train with uniform pulse spacing, however, may be described by a code that specifies non-temporal, i.e., non-time related, pulse characteristics.

In impulse radio communications utilizing time-shift modulation, information comprising one or more bits of data typically time-position modulates a sequence of pulses. This yields a modulated, coded timing signal that comprises a train of pulses from which a typical impulse radio receiver employing the same code may demodulate and, if necessary, coherently integrate pulses to recover the transmitted information.

The impulse radio receiver is typically a direct conversion receiver with a cross correlator front-end that coherently converts an electromagnetic pulse train of monocycle pulses to a baseband signal in a single stage. The baseband signal is the basic information signal for the impulse radio communications system. A subcarrier may also be included with the baseband signal to reduce the effects of amplifier drift and low frequency noise. Typically, the subcarrier alternately reverses modulation according to a known pattern at a rate faster than the data rate. This same pattern is used to reverse the process and restore the original data pattern just before detection. This method permits alternating current (AC) coupling of stages, or equivalent signal processing, to eliminate direct current (DC) drift and errors from the detection process. This method is described in more detail in U.S. Pat. No. 5,677,927 to Fullerton et al.

Waveforms

Impulse transmission systems are based on short, low duty-cycle pulses. Different pulse waveforms, or pulse types, may be employed to accommodate requirements of various applications. Typical pulse types include a Gaussian pulse, pulse doublet (also referred to as a Gaussian monocycle), pulse triplet, and pulse quadlet as depicted in FIGS. 1A through 1D, respectively. An actual received waveform that closely resembles the theoretical pulse quadlet is shown in FIG. 1E. A pulse type may also be a wavelet set produced by combining two or more pulse waveforms (e.g., a doublet/triplet wavelet set). These different pulse types may be produced by methods described in the patent documents referenced above or by other methods, as persons skilled in the art would understand.

For analysis purposes, it is convenient to model pulse waveforms in an ideal manner. For example, the transmitted waveform produced by supplying a step function into an ultra-wideband antenna may be modeled as a Gaussian monocycle. A Gaussian monocycle (normalized to a peak value of 1) may be described by:

.function..times..sigma..times.e.times..sigma. ##EQU00001## where .sigma. is a time scaling parameter, t is time, and e is the natural logarithm base.

The power special density of the Gaussian monocycle is shown in FIG. 1F, along with spectrums for the Gaussian pulse, triplet, and quadlet. The corresponding equation for the Gaussian monocycle is:

.function..times..pi..times..sigma..times..times..times..times..times..pi.- .times..times..sigma..times..times. ##EQU00002##

The center frequency (f.sub.c), or frequency of peak spectral density, of the Gaussian monocycle is:

.times..pi..sigma. ##EQU00003##

It should be noted that the output of an ultra-wideband antenna is essentially equal to the derivative of its input. Accordingly, since the pulse doublet, pulse triplet, and pulse quadlet are the first, second, and third derivatives of the Gaussian pulse, in an ideal model, an antenna receiving a Gaussian pulse will transmit a Gaussian monocycle and an antenna receiving a Gaussian monocycle will provide a pulse triplet.

Pulse Trains

Impulse transmission systems may communicate one or more data bits with a single pulse; however, typically each data bit is communicated using a sequence of pulses, known as a pulse train. As described in detail in the following example system, the impulse radio transmitter produces and outputs a train of pulses for each bit of information. FIGS. 2A and 2B are illustrations of the output of a typical 10 megapulses per second (Mpps) system with uncoded, unmodulated pulses, each having a width of 0.5 nanoseconds (ns). FIG. 2A shows a time domain representation of the pulse train output. FIG. 2B illustrates that the result of the pulse train in the frequency domain is to produce a spectrum comprising a set of comb lines spaced at the frequency of the 10 Mpps pulse repetition rate. When the full spectrum is shown, as in FIG. 2C, the envelope of the comb line spectrum corresponds to the curve of the single Gaussian monocycle spectrum in FIG. 1F. For this simple uncoded case, the power of the pulse train is spread among roughly two hundred comb lines. Each comb line thus has a small fraction of the total power and presents much less of an interference problem to a receiver sharing the band. It can also be observed from FIG. 2A that impulse transmission systems typically have very low average duty cycles, resulting in average power lower than peak power. The duty cycle of the signal in FIG. 2A is 0.5%, based on a 0.5 ns pulse duration in a 100 ns interval.

The signal of an uncoded, unmodulated pulse train may be expressed:

.function..times..times..times..omega..function. ##EQU00004## where j is the index of a pulse within a pulse train, (-1).sup.f is polarity (+/-), a is pulse amplitude, b is pulse type, c is pulse width, .omega.(t,b) is the normalized pulse waveform, and T.sub.f is pulse repetition time.

The energy spectrum of a pulse train signal over a frequency bandwidth of interest may be determined by summing the phasors of the pulses at each frequency, using the following equation:

.function..omega..times..times..times..DELTA..times..times. ##EQU00005## where A(.omega.) is the amplitude of the spectral response at a given frequency . . . .omega.. is the frequency being analyzed (2.pi.f), .DELTA.t is the relative time delay of each pulse from the start of time period, and n is the total number of pulses in the pulse train.

A pulse train can also be characterized by its autocorrelation and cross-correlation properties. Autocorrelation properties pertain to the number of pulse coincidences (i.e., simultaneous arrival of pulses) that occur when a pulse train is correlated against an instance of itself that is offset in time. Of primary importance is the ratio of the number of pulses in the pulse train to the maximum number of coincidences that occur for any time offset across the period of the pulse train. This ratio is commonly referred to as the main-lobe-to-side-lobe ratio, where the greater the ratio, the easier it is to acquire and track a signal.

Cross-correlation properties involve the potential for pulses from two different signals simultaneously arriving, or coinciding, at a receiver. Of primary importance are the maximum and average numbers of pulse coincidences that may occur between two pulse trains. As the number of coincidences increases, the propensity for data errors increases. Accordingly, pulse train cross-correlation properties are used in determining channelization capabilities of impulse transmission systems (i.e., the ability to simultaneously operate within close proximity).

Coding

Specialized coding techniques can be employed to specify temporal and/or non-temporal pulse characteristics to produce a pulse train having certain spectral and/or correlation properties. For example, by employing a PN code to vary inter-pulse spacing, the energy in the comb lines presented in FIG. 2B can be distributed to other frequencies as depicted in FIG. 2D, thereby decreasing the peak spectral density within a bandwidth of interest. Note that the spectrum retains certain properties that depend on the specific (temporal) PN code used. Spectral properties can be similarly affected by using non-temporal coding (e.g., inverting certain pulses).

Coding provides a method of establishing independent communication channels. Specifically, families of codes can be designed such that the number of pulse coincidences between pulse trains produced by any two codes will be minimal. For example, FIG. 3 depicts cross-correlation properties of two codes that have no more than four coincidences for any time offset. Generally, keeping the number of pulse collisions minimal represents a substantial attenuation of the unwanted signal.

Coding can also be used to facilitate signal acquisition. For example, coding techniques can be used to produce pulse trains with a desirable main-lobe-to-side-lobe ratio. In addition, coding can be used to reduce acquisition algorithm search space.

Coding methods for specifying temporal and non-temporal pulse characteristics are described in commonly owned, co-pending applications titled "A Method and Apparatus for Positioning Pulses in Time," application Ser. No. 09/592,249, and "A Method for Specifying Non-Temporal Pulse Characteristics," application Ser. No. 09/592,250, both filed Jun. 12, 2000, and both of which are incorporated herein by reference.

Typically, a code consists of a number of code elements having integer or floating-point values. A code element value may specify a single pulse characteristic or may be subdivided into multiple components, each specifying a different pulse characteristic. Code element or code component values typically map to a pulse characteristic value layout that may be fixed or non-fixed and may involve value ranges, discrete values, or a combination of value ranges and discrete values. A value range layout specifies a range of values that is divided into components that are each subdivided into subcomponents, which can be further subdivided, as desired. In contrast, a discrete value layout involves uniformly or non-uniformly distributed discrete values. A non-fixed layout (also referred to as a delta layout) involves delta values relative to some reference value. Fixed and non-fixed layouts, and approaches for mapping code element/component values, are described in co-owned, co-pending applications, titled "Method for Specifying Pulse Characteristics using Codes," application Ser. No. 09/592,290 and "A Method and Apparatus for Mapping Pulses to a Non-Fixed Layout," application Ser. No. 09/591,691, both filed on Jun. 12, 2000, both of which are incorporated herein by reference.

A fixed or non-fixed characteristic value layout may include a non-allowable region within which a pulse characteristic value is disallowed. A method for specifying non-allowable regions is described in co-owned U.S. Pat. No. 6,636,567 which is entitled "A Method for Specifying Non-Allowable Pulse Characteristics," and is incorporated herein by reference. A related method that conditionally positions pulses depending on whether code elements map to non-allowable regions is described in co-owned, co-pending application, titled "A Method and Apparatus for Positioning Pulses Using a Layout having Non-Allowable Regions," application Ser. No. 09/592,248 filed Jun. 12, 2000, and incorporated herein by reference.

The signal of a coded pulse train can be generally expressed by:

.function..times..times..times..omega..function..times. ##EQU00006## where k is the index of a transmitter, j is the index of a pulse within its pulse train, (-1)f.sub.j.sup.(k), a.sub.j.sup.(k), b.sub.j.sup.(k), c.sub.j.sup.(k), and .omega.(t,b.sub.j.sup.(k)) are the coded polarity, pulse amplitude, pulse type, pulse width, and normalized pulse waveform of the jth pulse of the kth transmitter, and T.sub.j.sup.(k) is the coded time shift of the jth pulse of the kth transmitter. Note: When a given non-temporal characteristic does not vary (i.e., remains constant for all pulses), it becomes a constant in front of the summation sign.

Various numerical code generation methods can be employed to produce codes having certain correlation and spectral properties. Such codes typically fall into one of two categories: designed codes and pseudorandom codes. A designed code may be generated using a quadratic congruential, hyperbolic congruential, linear congruential, Costas array, or other such numerical code generation technique designed to generate codes having certain correlation properties. A pseudorandom code may be generated using a computer's random number generator, binary shift-register(s) mapped to binary words, a chaotic code generation scheme, or the like. Such `random-like` codes are attractive for certain applications since they tend to spread spectral energy over multiple frequencies while having `good enough` correlation properties, whereas designed codes may have superior correlation properties but possess less suitable spectral properties. Detailed descriptions of numerical code generation techniques are included in a co-owned, co-pending patent application titled "A Method and Apparatus for Positioning Pulses in Time," application Ser. No. 09/592,248, filed Jun. 12, 2000, and incorporated herein by reference.

It may be necessary to apply predefined criteria to determine whether a generated code, code family, or a subset of a code is acceptable for use with a given UWB application. Criteria may include correlation properties, spectral properties, code length, non-allowable regions, number of code family members, or other pulse characteristics. A method for applying predefined criteria to codes is described in co-owned U.S. Pat. No. 6,636,566 which is entitled "A Method and Apparatus for Specifying Pulse Characteristics using a Code that Satisfies Predefined Criteria," and is incorporated herein by reference.

In some applications, it may be desirable to employ a combination of codes. Codes may be combined sequentially, nested, or sequentially nested, and code combinations may be repeated. Sequential code combinations typically involve switching from one code to the next after the occurrence of some event and may also be used to support multicast communications. Nested code combinations may be employed to produce pulse trains having desirable correlation and spectral properties. For example, a designed code may be used to specify value range components within a layout and a nested pseudorandom code may be used to randomly position pulses within the value range components. With this approach, correlation properties of the designed code are maintained since the pulse positions specified by the nested code reside within the value range components specified by the designed code, while the random positioning of the pulses within the components results in particular spectral properties. A method for applying code combinations is described in co-owned U.S. Pat. No. 6,671,310 which is entitled "A Method and Apparatus for Applying Codes Having Pre-Defined Properties," and is incorporated herein by reference.

Modulation

Various aspects of a pulse waveform may be modulated to convey information and to further minimize structure in the resulting spectrum. Amplitude modulation, phase modulation, frequency modulation, time-shift modulation and M-ary versions of these were proposed in U.S. Pat. No. 5,677,927 to Fullerton et al., previously incorporated by reference. Time-shift modulation can be described as shifting the position of a pulse either forward or backward in time relative to a nominal coded (or uncoded) time position in response to an information signal. Thus, each pulse in a train of pulses is typically delayed a different amount from its respective time base clock position by an individual code delay amount plus a modulation time shift. This modulation time shift is normally very small relative to the code shift. In a 10 Mpps system with a center frequency of 2 GHz, for example, the code may command pulse position variations over a range of 100 ns, whereas, the information modulation may shift the pulse position by 150 ps. This two-state `early-late` form of time shift modulation is depicted in FIG. 4A.

A pulse train with conventional `early-late` time-shift modulation can be expressed:

.function..times..times..times..omega..function..times..delta..times..time- s. ##EQU00007## where k is the index of a transmitter, j is the index of a pulse within its pulse train, (-1) f.sub.j.sup.(k), a.sub.j.sup.(k), b.sub.j.sup.(k), c.sub.j.sup.(k), and .omega.(t,b.sub.j.sup.(k)) are the coded polarity, pulse amplitude, pulse type, pulse width, and normalized pulse waveform of the jth pulse of the kth transmitter, T.sub.j.sup.(k) is the coded time shift of the jth pulse of the kth transmitter, .delta. is the time shift added when the transmitted symbol is 1 (instead of 0), d.sup.(k) is the data (i.e., 0 or 1) transmitted by the kth transmitter, and N.sub.s is the number of pulses per symbol (e.g., bit). Similar expressions can be derived to accommodate other proposed forms of modulation.

An alternative form of time-shift modulation can be described as One-of-Many Position Modulation (OMPM). The OMPM approach, shown in FIG. 4B, involves shifting a pulse to one of N possible modulation positions about a nominal coded (or uncoded) time position in response to an information signal, where N represents the number of possible states. For example, if N were four (4), two data bits of information could be conveyed. For further details regarding OMPM, see "Apparatus, System and Method for One-of-Many Position Modulation in an Impulse Radio Communication System," U.S. patent application Ser. No. 09/875,290, filed Jun. 7, 2001, assigned to the assignee of the present invention, and incorporated herein by reference.

An impulse radio communications system can employ flip modulation techniques to convey information. The simplest flip modulation technique involves transmission of a pulse or an inverted (or flipped) pulse to represent a data bit of information, as depicted in FIG. 4C. Flip modulation techniques may also be combined with time-shift modulation techniques to create two, four, or more different data states. One such flip with shift modulation technique is referred to as Quadrature Flip Time Modulation (QFTM). The QFTM approach is illustrated in FIG. 4D. Flip modulation techniques are further described in patent application titled "Apparatus, System and Method for Flip Modulation in an Impulse Radio Communication System," application Ser. No. 09/537,692, filed Mar. 29, 2000, assigned to the assignee of the present invention, and incorporated herein by reference.

Vector modulation techniques may also be used to convey information. Vector modulation includes the steps of generating and transmitting a series of time-modulated pulses, each pulse delayed by one of at least four pre-determined time delay periods and representative of at least two data bits of information, and receiving and demodulating the series of time-modulated pulses to estimate the data bits associated with each pulse. Vector modulation is shown in FIG. 4E. Vector modulation techniques are further described in patent application titled "Vector Modulation System and Method for Wideband Impulse Radio Communications," application Ser. No. 09/169,765, filed Dec. 9, 1999, assigned to the assignee of the present invention, and incorporated herein by reference.

Reception and Demodulation

Impulse radio systems operating within close proximity to each other may cause mutual interference. While coding minimizes mutual interference, the probability of pulse collisions increases as the number of coexisting impulse radio systems rises. Additionally, various other signals may be present that cause interference. Impulse radios can operate in the presence of mutual interference and other interfering signals, in part because they do not depend on receiving every transmitted pulse. Impulse radio receivers perform a correlating, synchronous receiving function (at the RF level) that uses statistical sampling and combining, or integration, of many pulses to recover transmitted information. Typically, 1 to 1000 or more pulses are integrated to yield a single data bit thus diminishing the impact of individual pulse collisions, where the number of pulses that must be integrated to successfully recover transmitted information depends on a number of variables including pulse rate, bit rate, range and interference levels.

Interference Resistance

Besides providing channelization and energy smoothing, coding makes impulse radios highly resistant to interference by enabling discrimination between intended impulse transmissions and interfering transmissions. This property is desirable since impulse radio systems must share the energy spectrum with conventional radio systems and with other impulse radio systems.

FIG. 5A illustrates the result of a narrow band sinusoidal interference signal 502 overlaying an impulse radio signal 504. At the impulse radio receiver, the input to the cross correlation would include the narrow band signal 502 and the received ultrawide-band impulse radio signal 504. The input is sampled by the cross correlator using a template signal 506 positioned in accordance with a code. Without coding, the cross correlation would sample the interfering signal 502 with such regularity that the interfering signals could cause interference to the impulse radio receiver. However, when the transmitted impulse signal is coded and the impulse radio receiver template signal 506 is synchronized using the identical code, the receiver samples the interfering signals non-uniformly. The samples from the interfering signal add incoherently, increasing roughly according to the square root of the number of samples integrated. The impulse radio signal samples, however, add coherently, increasing directly according to the number of samples integrated. Thus, integrating over many pulses overcomes the impact of interference.

Processing Gain

Impulse radio systems have exceptional processing gain due to their wide spreading bandwidth. For typical spread spectrum systems, the definition of processing gain, which quantifies the decrease in channel interference when wide-band communications are used, is the ratio of the bandwidth of the channel to the bit rate of the information signal. For example, a direct sequence spread spectrum system with a 10 KHz information bandwidth and a 10 MHz channel bandwidth yields a processing gain of 1000, or 30 dB. However, far greater processing gains are achieved by impulse radio systems, where the same 10 KHz information bandwidth is spread across a much greater 2 GHz channel bandwidth, resulting in a theoretical processing gain of 200,000, or 53 dB.

Capacity

It can be shown theoretically, using signal-to-noise arguments, that thousands of simultaneous channels are available to an impulse radio system as a result of its exceptional processing gain.

The average output signal-to-noise ratio of the impulse radio may be calculated for randomly selected time-hopping codes as a function of the number of active users, N.sub.u, as:

.function..times..times..sigma..times..sigma..times..times. ##EQU00008## where N.sub.s is the number of pulses integrated per bit of information, A.sub.k models the attenuation of transmitter k's signal over the propagation path to the receiver, and .sigma..sub.rec.sup.2 is the variance of the receiver noise component at the pulse train integrator output. The monocycle waveform-dependent parameters m.sub.p and .sigma..sub.a.sup.2 are given by

.intg..infin..infin..times..omega..function..function..omega..function..om- ega..function..delta..times.d ##EQU00009## ##EQU00009.2## .sigma..times..intg..infin..infin..times..intg..infin..infin..times..omeg- a..function..times..upsilon..function..times.d.times.d ##EQU00009.3##

where .omega.(t) is the monocycle waveform, .upsilon.(t)=.omega.(t)-.omega.(t-.delta.) is the template signal waveform, .delta. is the time shift between the monocycle waveform and the template signal waveform, T.sub.f is the pulse repetition time, and s is signal.

Multipath and Propagation

One of the advantages of impulse radio is its resistance to multipath fading effects. Conventional narrow band systems are subject to multipath through the Rayleigh fading process, where the signals from many delayed reflections combine at the receiver antenna according to their seemingly random relative phases resulting in possible summation or possible cancellation, depending on the specific propagation to a given location. Multipath fading effects are most adverse where a direct path signal is weak relative to multipath signals, which represents the majority of the potential coverage area of a radio system. In a mobile system, received signal strength fluctuates due to the changing mix of multipath signals that vary as its position varies relative to fixed transmitters, mobile transmitters and signal-reflecting surfaces in the environment.

Impulse radios, however, can be substantially resistant to multipath effects. Impulses arriving from delayed multipath reflections typically arrive outside of the correlation time and, thus, may be ignored. This process is described in detail with reference to FIGS. 5B and 5C. FIG. 5B illustrates a typical multipath situation, such as in a building, where there are many reflectors 504B, 505B. In this figure, a transmitter 506B transmits a signal that propagates along three paths, the direct path 501B, path 1 502B, and path 2 503B, to a receiver 508B, where the multiple reflected signals are combined at the antenna. The direct path 501B, representing the straight-line distance between the transmitter and receiver, is the shortest. Path 1 502B represents a multipath reflection with a distance very close to that of the direct path. Path 2 503B represents a multipath reflection with a much longer distance. Also shown are elliptical (or, in space, ellipsoidal) traces that represent other possible locations for reflectors that would produce paths having the same distance and thus the same time delay.

FIG. 5C illustrates the received composite pulse waveform resulting from the three propagation paths 501B, 502B, and 503B shown in FIG. 5B. In this figure, the direct path signal 501B is shown as the first pulse signal received. The path 1 and path 2 signals 502B, 503B comprise the remaining multipath signals, or multipath response, as illustrated. The direct path signal is the reference signal and represents the shortest propagation time. The path 1 signal is delayed slightly and overlaps and enhances the signal strength at this delay value. The path 2 signal is delayed sufficiently that the waveform is completely separated from the direct path signal. Note that the reflected waves are reversed in polarity. If the correlator template signal is positioned such that it will sample the direct path signal, the path 2 signal will not be sampled and thus will produce no response. However, it can be seen that the path 1 signal has an effect on the reception of the direct path signal since a portion of it would also be sampled by the template signal. Generally, multipath signals delayed less than one quarter wave (one quarter wave is about 1.5 inches, or 3.5 cm at 2 GHz center frequency) may attenuate the direct path signal. This region is equivalent to the first Fresnel zone in narrow band systems. Impulse radio, however, has no further nulls in the higher Fresnel zones. This ability to avoid the highly variable attenuation from multipath gives impulse radio significant performance advantages.

FIGS. 5D, 5E, and 5F represent the received signal from a TM-UWB transmitter in three different multipath environments. These figures are approximations of typical signal plots. FIG. 5D illustrates the received signal in a very low multipath environment. This may occur in a building where the receiver antenna is in the middle of a room and is a relatively short, distance, for example, one meter, from the transmitter. This may also represent signals received from a larger distance, such as 100 meters, in an open field where there are no objects to produce reflections. In this situation, the predominant pulse is the first received pulse and the multipath reflections are too weak to be significant. FIG. 5E illustrates an intermediate multipath environment. This approximates the response from one room to the next in a building. The amplitude of the direct path signal is less than in FIG. 5D and several reflected signals are of significant amplitude. FIG. 5F approximates the response in a severe multipath environment such as propagation through many rooms, from corner to corner in a building, within a metal cargo hold of a ship, within a metal truck trailer, or within an intermodal shipping container. In this scenario, the main path signal is weaker than in FIG. 5E. In this situation, the direct path signal power is small relative to the total signal power from the reflections.

An impulse radio receiver can receive the signal and demodulate the information using either the direct path signal or any multipath signal peak having sufficient signal-to-noise ratio. Thus, the impulse radio receiver can select the strongest response from among the many arriving signals. In order for the multipath signals to cancel and produce a null at a given location, dozens of reflections would have to be cancelled simultaneously and precisely while blocking the direct path, which is a highly unlikely scenario. This time separation of mulitipath signals together with time resolution and selection by the receiver permit a type of time diversity that virtually eliminates cancellation of the signal. In a multiple correlator rake receiver, performance is further improved by collecting the signal power from multiple signal peaks for additional signal-to-noise performance.

Where the system of FIG. 5B is a narrow band system and the delays are small relative to the data bit time, the received signal is a sum of a large number of sine waves of random amplitude and phase. In the idealized limit, the resulting envelope amplitude has been shown to follow a Rayleigh probability distribution as follows:

.function..sigma..times..times..sigma. ##EQU00010## where r is the envelope amplitude of the combined multipath signals, and .sigma.(2).sup.1/2 is the RMS power of the combined multipath signals. The Rayleigh distribution curve in FIG. 5G shows that 10% of the time, the signal is more than 10 dB attenuated. This suggests that 10 dB fade margin is needed to provide 90% link availability. Values of fade margin from 10 to 40 dB have been suggested for various narrow band systems, depending on the required reliability. This characteristic has been the subject of much research and can be partially improved by such techniques as antenna and frequency diversity, but these techniques result in additional complexity and cost.

In a high multipath environment such as inside homes, offices, warehouses, automobiles, trailers, shipping containers, or outside in an urban canyon or other situations where the propagation is such that the received signal is primarily scattered energy, impulse radio systems can avoid the Rayleigh fading mechanism that limits performance of narrow band systems, as illustrated in FIGS. 5H and 5I. FIG. 5H depicts an impulse radio system in a high multipath environment 500H consisting of a transmitter 506H and a receiver 508H. A transmitted signal follows a direct path 501H and reflects off reflectors 503H via multiple paths 502H. FIG. 5I illustrates the combined signal received by the receiver 508H over time with the vertical axis being signal strength in volts and the horizontal axis representing time in nanoseconds. The direct path 501H results in the direct path signal 502I while the multiple paths 502H result in multipath signals 504I. In the same manner described earlier for FIGS. 5B and 5C, the direct path signal 502I is sampled, while the multipath signals 504I are not, resulting in Rayleigh fading avoidance.

Distance Measurement and Positioning

Impulse systems can measure distances to relatively fine resolution because of the absence of ambiguous cycles in the received waveform. Narrow band systems, on the other hand, are limited to the modulation envelope and cannot easily distinguish precisely which RF cycle is associated with each data bit because the cycle-to-cycle amplitude differences are so small they are masked by link or system noise. Since an impulse radio waveform has no multi-cycle ambiguity, it is possible to determine waveform posit