Ultra wideband communication system, method, and device with low noise pulse formation Number:7,394,866 from the United States Patent and Trademark Office (PTO) owispatent An ultra-wide band (UWB) waveform generator and encoder are provided. The encoder multiplies each data bit by an n-bit identifying code to create a stream of bits corresponding to each data bit, i.e., an original codeword. The original codeword is passed to the UWB waveform generator for generation of a UWB waveform comprised of shaped wavelets that can be transmitted via an antenna. The UWB waveform generator may use a two-stage differential mixer. A first stage combines pulses from a pulse generator with a first derivative codeword derived from the original codeword. The wavelet output from the first stage is input to a second differential mixer along with a second derivative codeword also derived from the original codeword and orthogonal to the first derivative codeword. The wavelet output from the second mixer represents an inversion of the original codeword, and is passed to an inverting amplifier before being transmitted.<H communication, formation, Ultra, wideband, , 7394866.html, Patent, pto, 7394866

Title: Ultra wideband communication system, method, and device with low noise pulse formation

Abstract: An ultra-wide band (UWB) waveform generator and encoder are provided. The encoder multiplies each data bit by an n-bit identifying code to create a stream of bits corresponding to each data bit, i.e., an original codeword. The original codeword is passed to the UWB waveform generator for generation of a UWB waveform comprised of shaped wavelets that can be transmitted via an antenna. The UWB waveform generator may use a two-stage differential mixer. A first stage combines pulses from a pulse generator with a first derivative codeword derived from the original codeword. The wavelet output from the first stage is input to a second differential mixer along with a second derivative codeword also derived from the original codeword and orthogonal to the first derivative codeword. The wavelet output from the second mixer represents an inversion of the original codeword, and is passed to an inverting amplifier before being transmitted.

Patent Number: 7,394,866 Issued on 07/01/2008 to McCorkle

Inventors: McCorkle; John W. (Laurel, MD)
Assignee: Freescale Semiconductor, Inc. (Austin, TX)

Appl. No.: 10/705,120

Filed: November 12, 2003

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
09684400	Oct., 2000	6735238

Current U.S. Class: 375/295 ; 375/130

Current International Class: H04L 27/04 (20060101); H04B 1/69 (20060101)

Field of Search: 375/130,295,146,346,286,289 398/183 329/313

References Cited [Referenced By]

U.S. Patent Documents


3921171	November 1975	Strother, Jr. et al.
4145568	March 1979	Ehrat
5519400	May 1996	McEwan
5583892	December 1996	Drakul et al.
5677927	October 1997	Fullerton et al.
6026125	February 2000	Larrick, Jr. et al.
6735238	May 2004	McCorkle
7010056	March 2006	McCorkle et al.

Other References

Richard Comerford, "Handhelds Duke It Out For The Internet", pp. 35-41, Aug. 2000. cited by other.

Primary Examiner: Ghebretinsae; Temesghen

Parent Case Text

CROSS REFERENCE TO RELATED PATENT DOCUMENTS

The present application is a continuation application of application Ser. No. 09/684,400, filed Oct. 10, 2000 now U.S. Pat. No. 6,735,238, entitled ULTRA WIDEBAND COMMUNICATION SYSTEM, METHOD, AND DEVICE WITH LOW NOISE PULSE FORMATION, the contents of which are incorporated by reference in their entirety.

Claims

The invention claimed is:

1. A system for suppressing self-noise in an ultra wideband wavelet transmitter, comprising: an exclusive OR circuit having a first input configured to receive data, a second input configured to receive a whitening sequence from a noise source, and an output; a first differential mixer having a first port, a second port and an output, said second port being a differential input port having a first differential input and a second differential input, said first port being coupled to the output of the exclusive OR circuit; a second mixer having a first input, a second input and an output, said output of said first differential mixer being coupled to the first input of said second mixer; a pulse generator configured to generate at least two pulse streams; wherein: one of said at least two pulse streams is input to the first differential input of said first differential mixer, and a different one of said at least two pulse streams is input to the second differential input of said first differential mixer, said whitening sequence is input to the second input of said second mixer, and said output of said second mixer provides an ultra wideband sequence of wavelets modulated in accord with the data, for transmission.

2. A system for suppressing self-noise in an ultra wideband wavelet transmitter, comprising: an encoder configured to encode data, received from a source at a chipping rate, into a first derivative codeword at one half of the chipping rate and a second derivative codeword at one half of the chipping rate and 90.degree. out of phase with respect to said first derivative codeword; a first differential mixer having a first port coupled to receive the first derivative codeword from the encoder, a second port and an output, said second port being a differential input port having a first differential input and a second differential input; a second mixer having a first input coupled to said output of said first differential mixer, a second input coupled to receive the second derivative codeword from the encoder, and an output; and a pulse generator configured to generate at least two pulse streams; wherein: one of said at least two pulse streams is input to the first differential input of said first differential mixer, and another of said at least two streams is input to the second input of said first differential mixer, and said output of said second mixer provides an ultra wideband sequence of wavelets having the data encoded therein at the chipping rate, for transmission.

3. A system for suppressing self-noise in an ultra wideband wavelet transmitter, comprising: a code generator having an input configured to receive a data stream, and configured to encode the data stream so as to generate a first output stream and a second output stream such that mixing the first output stream with the second output stream would produce an encoded representation of the data stream; a pulse generator configured to generate at least two pulse streams; a first mixer having a first port, a second port and an output, said second port being a differential input port having a first differential input and a second differential input, the first port being configured to receive the first output stream from the code generator, the first differential input being configured to receive one of the at least two pulse streams, and the second differential input being configured to receive another one of the at least two pulse streams; and a second mixer having a first input, a second input and an output, the first input being coupled to the output of the first mixer, and the second input being configured to receive the second output stream from the code generator, wherein the output of the second mixer is a sequence of ultra wideband wavelets having the data stream encoded therein, for transmission.

4. An encoder system for an ultra wideband transmitter, the encoder system comprising: an encoder responsive to a data stream, for generating a first signal output and a second signal output such that if the first and second signal outputs of the encoder were mixed, the mixing would return a representation of the data stream; a pulse generator configured to generate a sequence of pulses; a first mixer coupled to the encoder and the pulse generator, for mixing the first signal output from the encoder with at least a portion of the sequence of pulses, to product a mixing result; and a second mixer coupled to the encoder and the first mixer, for mixing the second signal output from the encoder with the mixing result, to produce a sequence of ultra wideband wavelets shape encoded in accord with the data stream.

5. The system as in claim 4, wherein the system substantially suppresses self-noise.

6. The system as in claim 4, wherein the system receives the data stream at a chipping rate, and the encoder comprises a splitter for splitting the data stream into a first derivative encoded stream at half the chipping rate as the first signal output and a second derivative encoded stream at half the chipping rate as the second signal output.

7. The system as in claim 6, wherein the second derivative encoded stream is 90.degree. out of phase relative to the first derivative encoded stream.

8. The system as in claim 4, wherein the encoder comprises a de-spur code generator for producing the first output signal and the second output signal in response to the data stream.

9. The system as in claim 4, wherein at least one of the first and second mixers is a differential mixer.

10. The system as in claim 4, wherein: the sequence of pulses generated by the pulse generator comprises a first pulse stream, and a second pulse stream delayed with respect to the first pulse stream by a period corresponding to width of a pulse of the first pulse stream; and the first mixer comprises a differential mixer having a differential input for receiving the first and second pulse streams from the pulse generator.

11. The system as in claim 4, wherein the data stream as received by the encoder comprises high rate non-return-to-zero data.

12. An encoder system for an ultra wideband transmitter, the encoder system comprising: a pulse generator for generating a first pulse stream, and a second pulse stream delayed with respect to the first pulse stream by a period corresponding to width of a pulse of the first pulse stream; a differential mixer having a data port for receiving a stream of data and a differential port, the differential port receiving the first pulse stream on a first differential input and receiving the second pulse stream on a second differential input, wherein the differential mixer is responsive to the stream of data and the first and second pulse streams to produce an ultra wideband sequence of wavelets modulated in accord with the stream of data.

13. The system as in claim 12, wherein the wavelets of the ultra wideband sequence are shape modulated in accord with the stream of data.

14. The system as in claim 12, wherein the pulse generator comprises: a logic gate responsive to a clock pulse signal and a delayed version of the clock pulse signal, for producing an intermediate stream of pulses, each pulse of the intermediate stream having a width corresponding to the width of the pulse of the first pulse stream; and differential delay means, responsive to the intermediate stream of pulses, for producing the first pulse stream and the second pulse stream.

15. The system as in claim 14, wherein the logic gate comprises an exclusive OR gate.

16. The system as in claim 14, wherein the logic gate comprises an AND gate.

17. The system as in claim 12, wherein the pulse generator further comprises a differential delay means, responsive to a clock, for supplying the clock pulse signal and the delayed version of the clock pulse signal to inputs of the logic gate.

Description

The present document contains subject matter related to that disclosed in commonly owned, co-pending application Ser. No. 09/209,460 filed Dec. 11, 1998, entitled ULTRA WIDE BANDWIDTH SPREAD-SPECTRUM COMMUNICATIONS SYSTEM; Ser. No. 09/633,815 filed Aug. 7, 2000, entitled ELECTRICALLY SMALL PLANAR UWB ANTENNA; application Ser. No. 09/563,292 filed May 3, 2000, entitled PLANAR ULTRAWIDE BAND ANTENNA WITH INTEGRATED ELECTRONICS; Application Ser. No. 60/207,225 filed May 26, 2000, entitled ULTRAWIDEBAND COMMUNICATION SYSTEM AND METHOD; application Ser. No. 09/685,198 filed Oct. 10, 2000, entitled ANALOG SIGNAL SEPARATOR FOR UWB VERSUS NARROWBAND SIGNALS; Application Ser. No. 60/238,466 filed Oct. 10, 2000, entitled ULTRA WIDE BANDWIDTH NOISE CANCELLATION MECHANISM AND METHOD; Application Ser. No. 60/217,099 filed Jul. 10, 2000, entitled MULTIMEDIA WIRELESS PERSONAL AREA NETWORK (WPAN) PHYSICAL LAYER SYSTEM AND METHOD; application Ser. No. 09/685,203 filed Oct. 10, 2000, entitled SYSTEM AND METHOD FOR BASEBAND REMOVAL OF NARROWBAND INTERFERENCE IN ULTRA WIDEBAND SIGNALS; application Ser. No. 09/685,197 filed Oct. 10, 2000, entitled MODE CONTROLLER FOR SIGNAL ACQUISITION AND TRACKING IN AN ULTRAWIDEBAND COMMUNICATION SYSTEM; application Ser. No. 09/685,195 filed Oct. 10, 2000, entitled ULTRAWIDE BANDWIDTH SYSTEM AND METHOD FOR FAST SYNCHRONIZATION; application Ser. No. 09/684,401 filed Oct. 10, 2000, entitled ULTRAWIDE BANDWIDTH SYSTEM AND METHOD FOR FAST SYNCHRONIZATION USING SUB CODE SPINS; application Ser. No. 09/685,196 filed Oct. 10, 2000, entitled ULTRA WIDE BANDWIDTH SYSTEM AND METHOD FOR FAST SYNCHRONIZATION USING MULTIPLE DETECTION ARMS; application Ser. No. 09/685,199 filed Oct. 10, 2000, entitled A LOW POWER, HIGH RESOLUTION TIMING GENERATOR FOR ULTRA-WIDE BANDWIDTH COMMUNICATION SYSTEMS; application Ser. No. 09/685,202 filed Oct. 10, 2000, entitled METHOD AND SYSTEM FOR ENABLING DEVICE FUNCTIONS BASED ON DISTANCE INFORMATION; application Ser. No. 09/685,201 filed Oct. 10, 2000, entitled CARRIERLESS ULTRA WIDEBAND WIRELESS SIGNALS FOR CONVEYING APPLICATION DATA; application Ser. No. 09/685,205 filed Oct. 10, 2000, entitled SYSTEM AND METHOD FOR GENERATING ULTRAWIDEBAND PULSES; application Ser. No. 09/684,782 filed Oct. 10, 2000, entitled ULTRA WIDEBAND COMMUNICATION SYSTEM, METHOD, AND DEVICE WITH LOW NOISE RECEPTION; and application Ser. No. 09/685,200 filed Oct. 10, 2000, entitled LEAKAGE NULLING RECEIVER CORRELATOR STRUCTURE AND METHOD FOR ULTRA WIDE BANDWIDTH COMMUNICATION SYSTEM, the entire contents of each of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to ultra wideband (UWB) radio communication systems, methods and devices used in the system for generating UWB waveforms that include wavelets that are modulated to convey digital data over a wireless radio communication channel using ultra wideband signaling techniques.

2. Description of the Background

There are numerous radio communication techniques to transmit digital data over a wireless channel. These techniques include those used in mobile telephone systems, pagers, remote data collection systems, and wireless networks for computers, among others. Most conventional wireless communication techniques modulate the digital data onto a high-frequency carrier that is then transmitted via an antenna into space.

Ultra wideband (UWB) communications systems transmit carrierless high data rate, low power signals. Since a carrier is not used, the transmitted waveforms themselves contain the information being communicated. Accordingly, conventional UWB systems transmit pulses, the information to be communicated is contained in the pulses themselves, and not on a carrier.

Conventional UWB communication systems send a sequence of identical pulses, the timing of which carries the information being communicated, for example, as described by Fullerton and Cowie (U.S. Pat. No. 5,677,927). This technique is known as pulse position modulation (PPM). In a PPM scheme, the information in a pulse is obtained by determining an arrival time of the pulse at a receiver relative to other pulses. For example, given an exemplary time window, if a pulse is received at the beginning of that time window, the receiver will decode that pulse as a `1,` whereas if the pulse is received at the end of that same time window, the receiver will decode that pulse as a `0.`

Several problems arise with this technique, however, as recognized by the present inventors. First, it is not as efficient as other techniques, for example, sending non-inverted and inverted pulses where 3 dB less radiated power is required to communicate in the same memory-less Gaussian white noise channel. Second, reflections from objects in the vicinity of the transmitter and receiver can cause a pulse that was supposed to be at the beginning of the time window, to appear in at the end of time window, or even in the time window of a subsequent pulse.

As a result, it would be advantageous if the data stream to be transmitted could be encoded by changing a shape of the UWB pulse rather than a position of the UWB pulse as with conventional systems. For example, if the UWB pulses had two possible shapes, a single time frame could be used encode a single bit of data, rather than the two time frames (i.e., early and late) that would be required by a PPM system. In the present UWB communications system, and related co-pending application Ser. No. 09/209,460 filed May 14, 1998, entitled ULTRA WIDE BANDWIDTH SPREAD SPECTRUM COMMUNICATIONS SYSTEM, information is carried by the shape of the pulse, or the shape in combination with its position in the pulse-sequence.

Conventional techniques for generating pulses include a variety of techniques, for example, networks of transmission lines such as those described in co-pending application Ser. No. 09/209,460 filed May 14, 1998, entitled ULTRAWIDE BANDWIDTH SPREAD SPECTRUM COMMUNICATIONS SYSTEM. One of the problems associated with this technique is that the transmission lines take up sizeable space and accordingly, are not amenable to integration on a monolithic integrated circuit. Given that a key targeted use of UWB systems is for small, handheld mobile devices such as personal digital assistants (PDAs) and mobile telephones, space is at a premium when designing UWB systems. Furthermore, it is highly desirable to integrate the entire radio onto a single monolithic integrated circuit in order to meet the cost, performance, and volume-production requirements of consumer electronics devices.

A key attribute that must be maintained, however, regardless of how the information is carried, is that no tones can be present. In other words, the average power spectrum must be smooth and void of any spikes. In generating these UWB pulse streams, however, non-ideal device performance can cause tones to pass through to the antenna and to be radiated. In particular, switches, gates, and analog mixers that are used to generate pulses are well known to be non-ideal devices. For example, leakage is a problem. A signal that is supposed to be blocked at certain times, for example, can continue to leak through. Similarly, non-ideal symmetry in positive and negative voltages or current directions can allow tones be generated or leak through. In another example, the output of a mixer can include not only the desired UWB pulse stream, but also spikes in the frequency domain at the clock frequency and its harmonics, as well as other noise, due to leakage between the RF, LO, and IF ports. This is problematic since one of the design objectives is to generate a pulse stream that will not interfere with other communications systems.

Similar problems to those discussed above regarding transmitters are also encountered in UWB receivers. Mixers are used in UWB receivers to mix the received signal with known waveforms so that the transmitted data may be decoded. As discussed above, the spectral spikes (DC and otherwise) introduced by the non-ideal analog mixers can make decoding of only moderately weak signals difficult or impossible.

Furthermore, UWB receivers often suffer from leakage of the UWB signal driving the mixer due to the large amplitude of the drive signal and its very close proximity to the antenna as well as adjacent components. These UWB drive signals can radiate into space and be received by the antenna where it can jam the desired UWB signal, or be coupled via the substrate. This reception of the drive signal being used to decode the received signal can therefore cause a self-jamming condition wherein the desired signal becomes unintelligible.

The challenge, then, as presently recognized, is to develop a highly integratable approach for generating shape-modulated wavelet sequences that can be used in a UWB communications system to encode, broadcast, receive, and decode a data stream. It would be advantageous if the data stream to be transmitted could be encoded by changing a shape of the UWB pulse rather than a position of the UWB pulse as with conventional systems.

Furthermore, the challenge is to build such a wavelet generator where the smooth power spectrum calculated by using ideal components, is realized using non-ideal components. In other words, an approach to generating and receiving UWB waveforms that does not generate unwanted frequency domain spikes as a by-product, spikes that are prone to interfere with other communications devices or cause self-jamming, would be advantageous.

It would also be advantageous if the UWB waveform generation approach were to minimize the power consumption because many of the targeted applications for UWB communications are in handheld battery-operated mobile devices.

SUMMARY OF THE INVENTION

Accordingly, one object of this invention is to provide a novel programmable wavelet generator for generating a variety of wavelets for use in a UWB communication system that addresses the above-identified and other problems with conventional devices.

The inventors of the present invention have recognized that by implementing a two-mixer approach to generating UWB waveforms, that the noise leakage from the non-ideal analog mixers can be whitened, thereby avoiding the interference problems caused by conventional single-mixer approaches. The present inventors have provided a contrarian approach of suppressing mixer-created interference by using a second mixer.

The inventors of the present invention have also recognized that by creating a UWB waveform by mixing two derivative data streams running at one-half a chipping rate of the original data stream, that power consumption can be reduced within the UWB device.

These and other objects are achieved according to the present invention by providing a novel circuit for generating wavelets that is highly integratable, and a two-mixer approach for using the wavelets for encoding a data stream while canceling the leakage introduced by non-ideal analog mixers.

In one embodiment, the wavelet generator uses two pulses, an early pulse and a late pulse, from a pulse generation circuit, that when mixed with a positive or a negative voltage in a conventional differential mixer, creates a wavelet that is either positive or negative (i.e., non-inverted or inverted). By mixing the pulse generator output with a stream of data (positive voltage for a `1`, negative voltage for a `0`), a waveform having a sequence of wavelets is created are transmitted as a UWB signal. In a preferred embodiment, the mixer is a Gilbert cell mixer. In other embodiments, the mixer is, for example, a diode bridge mixer, or any electrically, optically, or mechanically-driven configuration of switching devices including, for example, an FET, a heterojunction, a bulk semiconductor device, or a micro-machine device.

In one embodiment of the two-mixer configuration for creating the UWB waveform, the noise introduced by the analog devices is canceled by whitening the output of the first mixer by mixing it with a white signal at the second mixer. In this embodiment, the data stream is divided into two derivative data streams, one of which is mixed with the pulse generator at the first analog mixer, and the other is mixed with the wavelets created by the first mixer. Since the derivative data streams are sufficiently white, mixing the result of the first mixer with the second derivative data stream will spread the unwanted spikes introduced by the first mixer. Moreover, in this embodiment, the two derivative data streams are at one-half the chipping rate of the original data stream, thereby reducing the power consumption by running at a lower clock rate.

In a second embodiment of the two-mixer configuration, a noisy signal is applied through an exclusive OR (XOR) to a single data stream. The result is then mixed with the pulse generator to create the wavelets at a first mixer. The result of the first mixer is then mixed with the noisy signal at the second mixer, again, to spread the unwanted spikes introduced by the first mixer.

Consistent with the title of this section, the above summary is not intended to be an exhaustive discussion of all the features or embodiments of the present invention. A more complete, although not necessarily exhaustive description of the features and embodiments of the invention is found in the section entitled "DESCRIPTION OF THE PREFERRED EMBODIMENTS" as well as the entire document generally.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of an ultra-wide band (UWB) transceiver, according to the present invention;

FIG. 1B is a diagram for illustrating the operation of the transceiver of FIG. 1a, according to the present invention;

FIG. 2 is a block diagram of the transceiver of FIG. 1A, that manipulates a shape of UWB pulses, according to the present invention;

FIG. 3 is a schematic diagram of a general-purpose microprocessor-based or digital signal processor-based system, which can be programmed by a skilled programmer to implement the features of the present invention;

FIGS. 4A and 4B are a flow chart of a process implementing an algorithm used as a startup procedure for generating two derived codewords from an original codeword according to the present invention;

FIG. 5 illustrates a process flow for splitting a single original data stream into 2 data streams including even bits and odd bits of the original data stream, respectively, at one-half the chipping rate of the original data stream according to the present invention;

FIG. 6 is a schematic diagram of a logic circuit for creating two derived codewords from an even-bit data stream and an odd-bit data stream produced by the splitter illustrated in FIG. 5;

FIG. 7 is a schematic diagram of a two-stage differential mixer for generating low-noise wavelets according to one embodiment of the present invention;

FIG. 8 is a schematic diagram of a circuit used to generate an early pulse and a late pulse according to one embodiment of the present invention;

FIG. 9A is a schematic of a Gilbert cell differential mixer;

FIG. 9B is an illustration of the early and late pulses generated by the pulse generating circuit of FIG. 8;

FIG. 9C illustrates a bi-phase wavelet generated by the pulse generating circuit of FIG. 8 when the incoming data bit is high;

FIG. 9D illustrates a bi-phase wavelet generated, by the pulse generating circuit of FIG. 8 when the incoming data bit is low;

FIG. 9E is a schematic diagram of a FET bridge differential mixer;

FIG. 9F is a schematic diagram of a diode bridge differential mixer;

FIG. 10 is an exemplary timing chart illustrating the inputs and outputs of the first differential mixer of the two-stage mixer according to one embodiment of the present invention;

FIGS. 11A and 11B are graphs that illustrate the spectral spikes produced by non-ideal analog devices and the whitening of those spikes;

FIG. 12 is an exemplary timing chart illustrating the inputs and outputs of the second differential mixer of the two-stage mixer according to one embodiment of the present invention;

FIG. 13 is a schematic diagram of a two-stage differential mixer for generating low-noise wavelets by mixing the data stream with noise according to one embodiment of the present invention; and

FIG. 14 is a schematic diagram of a generalized two-stage mixing circuit for achieving noise cancellation in an ultra wideband transmitter according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A is a block diagram of an ultra-wide band (UWB) transceiver. In FIG. 1A, the transceiver includes three major components, namely, receiver 11, radio controller and interface 9, and transmitter 13. Alternatively, the system may be implemented as a separate receiver 11 and radio controller and interface 9, and a separate transmitter 13 and radio controller and interface 9. The radio controller and interface 9 serves as a media access control (MAC) interface between the UWB wireless communication functions implemented by the receiver 11 and transmitter 13 and applications that use the UWB communications channel for exchanging data with remote devices.

The receiver 11 includes an antenna 1 that converts a UWB electromagnetic waveform into an electrical signal (or optical signal) for subsequent processing. The UWB signal is generated with a sequence of shape-modulated wavelets, where the occurrence times of the shape-modulated wavelets may also be modulated. For analog modulation, at least one of the shape control parameters is modulated with the analog signal. More typically, the wavelets take on M possible shapes. Digital information is encoded to use one or a combination of the M wavelet shapes and occurrence times to communicate information.

In one embodiment of the present invention, each wavelet communicates one bit, for example, using two shapes such as bi-phase. In other embodiments of the present invention, each wavelet may be configured to communicate nn bits, where M.gtoreq.2.sup.nn. For example, four shapes may be configured to communicate two bits, such as with quadrature phase or four-level amplitude modulation. In another embodiment of the present invention, each wavelet is a "chip" in a code sequence, where the sequence, as a group, communicates one or more bits. The code can be M-ary at the chip level, choosing from M possible shapes for each chip.

At the chip, or wavelet level, embodiments of the present invention produce UWB waveforms. The UWB waveforms are modulated by a variety of techniques including but not limited to: (i) bi-phase modulated signals (+1, -1), (ii) multilevel bi-phase signals (+1, -1, +a1, -a1, +a2, -a2, . . . , +aN, -aN), (iii) quadrature phase signals (+1, -1, +j, -j), (iv) multi-phase signals (1, -1, exp(+j.pi./N), exp(j.pi./N), exp(+j.pi.2/N), exp(-j.pi.2/N), . . . , exp(+j(N-1)/N), exp(-j.pi.(N-1)/N)), (v) multilevel multi-phase signals (a.sub.i exp(j2.pi..beta./N)|a.sub.1.epsilon.{1, a1, a2, . . . , aK}, .epsilon..epsilon.{0, 1, . . . , N-1}), (vi) frequency modulated pulses, (vii) pulse position modulation (PPM) signals (possibly same shape pulse transmitted in different candidate time slots), (viii) M-ary modulated waveforms g.sub.B.sub.i (t) with B.sub.i.epsilon.{1, . . . , M}, and (ix) any combination of the above waveforms, such as multi-phase channel symbols transmitted according to a chirping signaling scheme. The present invention, however, is applicable to variations of the above modulation schemes and other modulation schemes (e.g., as described in Lathi, "Modern Digital and Analog Communications Systems," Holt, Rinehart and Winston, 1998, the entire contents of which is incorporated by reference herein), as will be appreciated by those skilled in the relevant art(s).

Some exemplary waveforms and characteristic equations thereof will now be described. The time modulation component, for example, can be defined as follows. Let t.sub.i be the time spacing between the (i-1).sup.th pulse and the i.sup.th pulse. Accordingly, the total time to the i.sup.th pulse is

.times..times. ##EQU00001## The signal T.sub.i could be encoded for data, part of a spreading code or user code, or some combination thereof. For example, the signal T.sub.i could be equally spaced, or part of a spreading code, where T.sub.1 corresponds to the zero-crossings of a chirp, i.e., the sequence of T.sub.i's, and where

##EQU00002## for a predetermined set of a and k. Here, a and k may also be chosen from a finite set based on the user code or encoded data.

An embodiment of the present invention can be described using M-ary modulation. Equation 1 below can be used to represent a sequence of exemplary transmitted or received pulses, where each pulse is a shape modulated UWB wavelet, g.sub.B.sub.i(t-T.sub.i).

.function..infin..times..times..function. ##EQU00003##

In the above equation, the subscript i refers to the i.sup.th pulse in the sequence of UWB pulses transmitted or received. The wavelet function g has M possible shapes, and therefore B.sub.i represents a mapping from the data, to one of the M-ary modulation shapes at the i.sup.th pulse in the sequence. The wavelet generator hardware (e.g., the UWB waveform generator 17) has several control lines (e.g., coming from the radio controller and interface 9) that govern the shape of the wavelet. Therefore, B.sub.i can be thought of as including a lookup-table for the M combinations of control signals that produce the M desired wavelet shapes. The encoder 21 combines the data stream and codes to generate the M-ary states. Demodulation occurs in the waveform correlator 5 and the radio controller and interface 9 to recover to the original data stream. Time position and wavelet shape are combined into the pulse sequence to convey information, implement user codes, etc.

In the above case, the signal is comprised of wavelets from i=1 to infinity. As i is incremented, a wavelet is produced. Equation 2 below can be used to represent a generic wavelet pulse function, whose shape can be changed from pulse to pulse to convey information or implement user codes, etc. g.sub.B.sub.i(t)=Re(B.sub.i,1)f.sub.B.sub.i,2.sub., B.sub.i,3.sub., . . . (t)+Im(B.sub.i,1)h.sub.B.sub.i,2.sub., B.sub.i,3.sub., . . . (t) (2)

In the above equation, function f defines a basic wavelet shape, and function h is simply the Hilbert transform of the function f. The parameter B.sub.i,1 is a complex number allowing the magnitude and phase of each wavelet pulse to be adjusted, i.e., B.sub.i,1=a.sub.i.angle..theta..sub.i, where a.sub.i is selected from a finite set of amplitudes and .theta..sub.i is selected from a finite set of phases. The parameters {B.sub.i,2, B.sub.i,3, . . . } represent a generic group of parameters that control the wavelet shape.

An exemplary waveform sequence x(t) can be based on a family of wavelet pulse shapes f that are derivatives of a Guassian waveform as defined by Equation 3 below.

.function..PSI..function..times.dd.times.e.times. ##EQU00004##

In the above equation, the function .PSI.( ) normalizes the peak absolute value of f.sub.B.sub.i(t) to 1. The parameter B.sub.i,2 controls the pulse duration and center frequency. The parameter B.sub.i,3 is the number of derivatives and controls the bandwidth and center frequency.

Another exemplary waveform sequence x(t) can be based on a family of wavelet pulse shapes f that are Gaussian weighted sinusoidal functions, as described by Equation 4 below. f.sub.B.sub.i,2.sub.,B.sub.i,3.sub.,B.sub.i,4=f.sub..omega..sub.i.sub.,k.- sub.i.sub.,b.sub.i(t)=e.sup.-[b.sup.i.sup.t].sup.2 sin(.omega..sub.it+k.sub.it.sup.2). (4)

In the above equation, b.sub.i controls the pulse duration, .omega..sub.i controls the center frequency, and k.sub.i controls a chirp rate. Other exemplary weighting functions, beside Gaussian, that are also applicable to the present invention include, for example, Rectangular, Hanning, Hamming, Blackman-Harris, Nutall, Taylor, Kaiser, Chebychev, etc.

Another exemplary waveform sequence x(t) can be based on a family of wavelet pulse shapes f that are inverse-exponentially weighted sinusoidal functions, as described by Equation 5 below.

.function.ee.function..theta..omega..times..times..times..times..times..ti- mes..times..theta..omega. ##EQU00005##

In the above equation, the leading edge turn on time is controlled by t.sub.1, and the turn-on rate is controlled by t.sub.r. The trailing edge turn-off time is controlled by t.sub.2, and the turn-off rate is controlled by t.sub.f. Assuming the chirp starts at t=0 and T.sub.D is the pulse duration, the starting phase is controlled by .theta., the starting frequency is controlled by .omega., the chirp rate is controlled by k, and the stopping frequency is controlled by w+kT.sub.D. An example assignment of parameter values is .omega.=1, t.sub.r=t.sub.f=0.25, t.sub.1=t.sub.r/0.51, and t.sub.2=T.sub.D-t.sub.r/9 .

A feature of the present invention is that the M-ary parameter set used to control the wavelet shape is chosen so as to make a UWB signal, wherein the center frequency f.sub.c and the bandwidth B of the power spectrum of g(t) satisfies 2f.sub.c>B>0.25f.sub.c. It should be noted that conventional equations define in-phase and quadrature signals (e.g., often referred to as I and Q) as sine and cosine terms. An important observation, however, is that this conventional definition is inadequate for UWB signals. The present invention recognizes that use of such conventional definition may lead to DC offset problems and inferior performance.

Furthermore, such inadequacies get progressively worse as the bandwidth moves away from 0.25f.sub.c and toward 2f.sub.c. A key attribute of the exemplary wavelets (or e.g., those described in co-pending U.S. patent application Ser. No. 09/209,460) is that the parameters are chosen such that neither f nor h in Equation 2 above has a DC component, yet f and h exhibit the required wide relative bandwidth for UWB systems.

Similarly, as a result of B>0.25f.sub.c, it should be noted that the matched filter output of the UWB signal is typically only a few cycles, or even a single cycle. For example, the parameter n in Equation 3 above may only take on low values (e.g., such as those described in co-pending U.S. patent application Ser. No. 09/209,460).

The compressed (i.e., coherent matched filtered) pulse width of a UWB wavelet will now be defined with reference to FIG. 1B. In FIG. 1B, the time domain version of the wavelet thus represents g(t) and the Fourier transform (FT) version is represented by G(.omega.). Accordingly, the matched filter is represented as G*(.omega.), the complex conjugate, so that the output of the matched filter is P(.omega.)=G(.omega.)G*(.omega.). The output of the matched filter in the time domain is seen by performing an inverse Fourier transform (IFT) on P(.omega.) so as to obtain p(t), the compressed or matched filtered pulse. The width of the compressed pulse p(t) is defined by T.sub.C, which is the time between the points on the envelope of the compressed pulse E(t) that are 6 dB below the peak thereof, as shown in FIG. 1B. The envelope waveform E(t) may be determined by Equation 6 below. E(t)= {square root over ((p(t)).sup.2+(p.sup.H(t)).sup.2)}{square root over ((p(t)).sup.2+(p.sup.H(t)).sup.2)} (6)

where p.sup.H(t) is the Hilbert transform of p(t).

Accordingly, the above-noted parameterized waveforms are examples of UWB wavelet functions that can be controlled to communicate information with a large parameter space for making codes with good resulting autocorrelation and cross-correlation functions. For digital modulation, each of the parameters is chosen from a predetermined list according to an encoder that receives the digital data to be communicated. For analog modulation, at least one parameter is changed dynamically according to some function (e.g., proportionally) of the analog signal that is to be communicated.

Referring back to FIG. 1A, the electrical signals coupled in through the antenna 1 are passed to a radio front end 3. Depending on the type of waveform, the radio front end 3 processes the electric signals so that the level of the signal and spectral components of the signal are suitable for processing in the UWB waveform correlator 5. The UWB waveform correlator 5 correlates the incoming signal (e.g., as modified by any spectral shaping, such as a matched filtering, partially matched filtering, simply roll-off, etc., accomplished in front end 3) with different candidate signals generated by the receiver 11, so as to determine when the receiver 11 is synchronized with the received signal and to determine the data that was transmitted.

The timing generator 7 of the receiver 11 operates under control of the radio controller and interface 9 to provide a clock signal that is used in the correlation process performed in the UWB waveform correlator 5. Moreover, in the receiver 11, the UWB waveform correlator 5 correlates in time a particular pulse sequence produced at the receiver 11 with the receive pulse sequence that was coupled in through antenna 1 and modified by front end 3. When the two such sequences are aligned with one another, the UWB waveform correlator 5 provides high signal to noise ratio (SNR) data to the radio controller and interface 9 for subsequent processing. In some circumstances, the output of the UWB waveform correlator 5 is the data itself. In other circumstances, the UWB waveform correlator 5 simply provides an intermediate correlation result, which the radio controller and interface 9 uses to determine the data and determine when the receiver 11 is synchronized with the incoming signal.

In some embodiments of the present invention, when synchronization is not achieved (e.g., during a signal acquisition mode of operation), the radio controller and interface 9 provides a control signal to the receiver 11 to acquire synchronization. In this way, a sliding of a correlation window within the UWB waveform correlator 5 is possible by adjustment of the phase and frequency of the output of the timing generator 7 of the receiver 11 via a control signal from the radio controller and interface 9. The control signal causes the correlation window to slide until lock is achieved. The radio controller and interface 9 is a processor-based unit that is implemented either with hard wired logic, such as in one or more application specific integrated circuits (ASICs) or in one or more programmable processors.

Once synchronized, the receiver 11 provides data to an input port ("RX Data In") of the radio controller and interface 9. An external process, via an output port ("RX Data Out") of the radio controller and interface 9, may then use this data. The external process may be any one of a number of processes performed with data that is either received via the receiver 11 or is to be transmitted via the transmitter 13 to a remote receiver.

During a transmit mode of operation, the radio controller and interface 9 receives source data at an input port ("TX Data In") from an external source. The radio controller and interface 9 then applies the data to an encoder 21 of the transmitter 13 via an output port ("TX Data Out"). In addition, the radio controller and interface 9 provides control signals to the transmitter 13 for use in identifying the signaling sequence of UWB pulses. In some embodiments of the present invention, the receiver 11 and the transmitter 13 functions may use joint resources, such as a common timing generator and/or a common antenna, for example. The encoder 21 receives user coding information and data from the radio controller and interface 9 and preprocesses the data and coding so as to provide a timing input for the UWB waveform generator 17, which produces UWB pulses encoded in shape and/or time to convey the data to a remote location.

The encoder 21 produces the control signals necessary to generate the required modulation. For example, the encoder 21 may take a serial bit stream and encode it with a forward error correction (FEC) algorithm (e.g., such as a Reed Solomon code, a Golay code, a Hamming code, a Convolutional code, etc.). The encoder 21 may also interleave the data to guard against burst errors. The encoder 21 may also apply a whitening function to prevent long strings of "ones" or "zeros." The encoder 21 may also apply a user specific spectrum spreading function, such as generating a predetermined length chipping code that is sent as a group to represent a bit (e.g., inverted for a "one" bit and non-inverted for a "zero" bit, etc.). The encoder 21 may divide the serial bit stream into subsets in order to send multiple bits per wavelet or per chipping code, and generate a plurality of control signals in order to affect any combination of the modulation schemes as described above (and/or as described in Lathi).

The radio controller and interface 9 may provide some identification, such as user ID, etc., of the source from which the data on the input port ("TX Data In") is received. In one embodiment of the present invention, this user ID may be inserted in the transmission sequence, as if it were a header of an information packet. In other embodiments of the present invention, the user ID itself may be employed to encode the data, such that a receiver receiving the transmission would need to postulate or have a priori knowledge of the user ID in order to make sense of the data. For example, the ID may be used to apply a different amplitude signal (e.g., of amplitude "f") to a fast modulation control signal to be discussed with respect to FIG. 2, as a way of impressing the encoding onto the signal.

The output from the encoder 21 is applied to a UWB waveform generator 17. The UWB waveform generator 17 produces a UWB pulse sequence of pulse shapes at pulse times according to the command signals it receives, which may be one of any number of different schemes. The output from the UWB generator 17 is then provided to an antenna 15, which then transmits the UWB energy to a receiver.

In one UWB modulation scheme, the data may be encoded by using the relative spacing of transmission pulses (e.g., PPM, chirp, etc.). In other UWB modulation schemes, the data may be encoded by exploiting the shape of the pulses as described above (and/or as described in Lathi). It should be noted that the present invention is able to combine time modulation (e.g., such as pulse position modulation, chirp, etc.) with other modulation schemes that manipulate the shape of the pulses.

There are numerous advantages to the above capability, such as communicating more than one data bit per symbol transmitted from the transmitter 13, etc. An often even more important quality, however, is the application of such technique to implement spread-spectrum, multi-user systems, which require multiple spreading codes (e.g., such as each with spike autocorrelation functions, and jointly with low peak cross-correlation functions, etc.).

In addition, combining timing, phase, frequency, and amplitude modulation adds extra degrees of freedom to the spreading code functions, allowing greater optimization of the cross-correlation and autocorrelation characteristics. As a result of the improved autocorrelation and cross-correlation characteristics, the system according to the present invention has improved capability, allowing many transceiver units to operate in close proximity without suffering from interference from one another.

FIG. 2 is a block diagram of a transceiver embodiment of the present invention in which the modulation scheme employed is able to manipulate the shape and time of the UWB pulses. In FIG. 2, when receiving energy through the antenna 1, 15 (e.g., corresponding antennas 1 and 15 of FIG. 1A) the energy is coupled in to a transmit/receive (T/R) switch 27, which passes the energy to a radio front end 3. The radio front end 3 filters, extracts noise, and adjusts the amplitude of the signal before providing the same to a splitter 29. The splitter 29 divides the signal up into one of N different signals and applies the N different signals to different tracking correlators 31.sub.1-31.sub.N. Each of the tracking correlators 31.sub.1-31.sub.N receives a clock input signal from a respective timing generator 7.sub.1-7.sub.N of a timing generator module 7, 19, as shown in FIG. 2.

The timing generators 7.sub.1-7.sub.N, for example, receive a phase and frequency adjustment signal, as shown in FIG. 2, but may also receive a fast modulation signal or other control signal(s) as well. The radio controller and interface 9 provides the control signals, such as phase, frequency and fast modulation signals, etc., to the timing generator module 7, 19, for time synchronization and modulation control. The fast modulation control signal may be used to implement, for example, chirp waveforms, PPM waveforms, such as fast time scale PPM waveforms, etc.

The radio controller and interface 9 also provides control signals to, for example, the encoder 21, the waveform generator 17, the filters 23, the amplifier 25, the T/R switch 27, the front end 3, the tracking correlators 31.sub.1-31.sub.N (corresponding to the UWB waveform correlator 5 of FIG. 1A), etc., for controlling, for example, amplifier gains, signal waveforms, filter passbands and notch functions, alternative demodulation and detecting processes, user codes, spreading codes, cover codes, etc.

During signal acquisition, the radio controller and interface 9 adjusts the phase input of, for example, the timing generator 7.sub.1, in an attempt for the tracking correlator 31.sub.1 to identify and the match the timing of the signal produced at the receiver with the timing of the arriving signal. When the received signal and the locally generated signal coincide in time with one another, the radio controller and interface 9 senses the high signal strength or high SNR and begins to track, so that the receiver is synchronized with the received signal.

Once synchronized, the receiver will operate in a tracking mode, where the timing generator 7.sub.1 is adjusted by way of a continuing series of phase adjustments to counteract any differences in timing of the timing generator 7.sub.1 and the incoming signal. However, a feature of the present invention is that by sensing the mean of the phase adjustments over a known period of time, the radio controller and interface 9 adjusts the frequency of the timing generator 7.sub.1 so that the mean of the phase adjustments becomes zero. The frequency is adjusted in this instance because it is clear from the pattern of phase adjustments that there is a frequency offset between the timing generator 7.sub.1 and the clocking of the received signal. Similar operations may be performed on timing generators 7.sub.2-7.sub.N, so that each receiver can recover the signal delayed by different amounts, such as the delays caused by multipath (i.e., scattering along different paths via reflecting off of local objects).

A feature of the transceiver in FIG. 2 is that it includes a plurality of tracking correlators 31.sub.1-31.sub.N. By providing a plurality of tracking correlators, several advantages are obtained. First, it is possible to achieve synchronization more quickly (i.e., by operating parallel sets of correlation arms to find strong SNR points over different code-wheel segments). Second, during a receive mode of operation, the multiple arms can resolve and lock onto different multipath components of a signal. Through coherent addition, the UWB communication system uses the energy from the different multipath signal components to reinforce the received signal, thereby improving signal to noise ratio. Third, by providing a plurality of tracking correlator arms, it is also possible to use one arm to continuously scan the channel for a better signal than is being received on other arms.

In one embodiment of the present invention, if and when the scanning arm finds a multipath term with higher SNR than another arm that is being used to demodulate data, the role of the arms is switched (i.e., the arm with the higher SNR is used to demodulate data, while the arm with the lower SNR begins searching). In this way, the communications system dynamically adapts to changing channel conditions.

The radio controller and interface 9 receives the information from the different tracking correlators 31.sub.1-31.sub.N and decodes the data. The radio controller and interface 9 also provides control signals for controlling the front end 3, e.g., such as gain, filter selection, filter adaptation, etc., and adjusting the synchronization and tracking operations by way of the timing generator module 7, 19.

In addition, the radio controller and interface 9 serves as an interface between the communication link feature of the present invention and other higher level applications that will use the wireless UWB communication link for performing other functions. Some of these functions would include, for example, performing range-finding operations, wireless telephony, file sharing, personal digital assistant (PDA) functions, embedded control functions, location-finding operations, etc.

On the transmit portion of the transceiver shown in FIG. 2, a timing generator 7.sub.0 also receives phase, frequency and/or fast modulation adjustment signals for use in encoding a UWB waveform from the radio controller and interface 9. Data and user codes (via a control signal) are provided to the encoder 21, which in the case of an embodiment of the present invention utilizing time-modulation, passes command signals (e.g., .DELTA.t) to the timing generator 7.sub.0 for providing the time at which to send a pulse. In this way, encoding of the data into the transmitted waveform may be performed.

When the shape of the different pulses are modulated according to the data and/or codes, the encoder 21 produces the command signals as a way to select different shapes for generating particular waveforms in the waveform generator 17. For example, the data may be grouped in multiple data bits per channel symbol. The waveform generator 17 then produces the requested waveform at a particular time as indicated by the timing generator 7.sub.0. The output of the waveform generator is then filtered in filter 23 and amplified in amplifier 25 before being transmitted via antenna 1, 15 by way of the T/R switch 27.

In another embodiment of the present invention, the transmit power is set low enough that the transmitter and receiver are simply alternately powered down without need for the T/R switch 27. Also, in some embodiments of the present invention, neither the filter 23 nor the amplifier 25 is needed, because the desired power level and spectrum is directly useable from the waveform generator 17. In addition, the filters 23 and the amplifier 25 may be included in the waveform generator 17 depending on the implementation of the present invention.

A feature of the UWB communications system disclosed, is that the transmitted waveform x(t) can be made to have a nearly continuous power flow, for example, by using a high chipping rate, where the wavelets g(t) are placed nearly back-to-back. This configuration allows the system to operate at low peak voltages, yet produce ample average transmit power to operate effectively. As a result, sub-micron geometry CMOS switches, for example, running at one-volt levels, can be used to directly drive antenna 1, 15, such that the amplifier 25 is not required. In this way, the entire radio can be integrated on a single monolithic integrated circuit.

Under certain operating conditions, the system can be operated without the filters 23. If, however, the system is to be operated, for example, with another radio system, the filters 23 can be used to provide a notch function to limit interference with other radio systems. In this way, the system can operate simultaneously with other radio systems, providing advantages over conventional devices that use avalanching type devices connected straight to an antenna, such that it is difficult to include filters therein.

The UWB transceiver of FIG. 1A or 2 may be used to perform a radio transport function for interfacing with different applications as part of a stacked protocol architecture. In such a configuration, the UWB transceiver performs signal creation, transmission and reception functions as a communications service to applications that send data to the transceiver and receive data from the transceiver much like a wired I/O port. Moreover, the UWB transceiver may be used to provide a wireless communications function to any one of a variety of devices that may include interconnection to other devices either by way of wired technology or wireless technology. Thus, the UWB transceiver of FIG. 1A or 2 may be used as part of a local area network (LAN) connecting fixed structures or as part of a wireless personal area network (WPAN) connecting mobile devices, for example. In any such implementation, all or a portion of the present invention may be conveniently implemented in a microprocessor system using conventional general purpose microprocessors programmed according to the teachings of the present invention, as will be apparent to those skilled in the microprocessor systems art. Appropriate software can be readily prepared by programmers of ordinary skill based on the teachings of the present disclosure, as will be apparent to those skilled in the software art.

FIG. 3 illustrates a processor system 301 upon which an embodiment according to the present invention may be implemented. The system 301 includes a bus 303 or other communication mechanism for communicating information, and a processor 305 coupled with the bus 303 for processing the information. The processor system 301 also includes a main memory 307, such as a random access memory (RAM) or other dynamic storage device (e.g., dynamic RAM (DRAM), static RAM (SRAM), synchronous DRAM (SDRAM), flash RAM), coupled to the bus 303 for storing information and instructions to be executed by the processor 305. In addition, a main memory 307 may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor 305. The system 301 further includes a read only memory (ROM) 309 or other static storage device (e.g., programmable ROM (PROM), erasable PROM (EPROM), and electrically erasable PROM (EEPROM)) coupled to the bus 303 for storing static information and instructions for the processor 305. A storage device 311, such as a magnetic disk or optical disc, is provided and coupled to the bus 303 for storing information and instructions.

The processor system 301 may also include special purpose logic devices (e.g., application specific integrated circuits (ASICs)) or configurable logic devices (e.g, simple programmable logic devices (SPLDs), complex programmable logic devices (CPLDs), or re-programmable field programmable gate arrays (FPGAs)). Other removable media devices (e.g., a compact disc, a tape, and a removable magneto-optical media) or fixed, high density media drives, may be added to the system 301 using an appropriate device bus (e.g., a small system interface (SCSI) bus, an enhanced integrated device electronics (IDE) bus, or an ultra-direct memory access (DMA) bus). The system 301 may additionally include a compact disc reader, a compact disc reader-writer unit, or a compact disc juke box, each of which may be connected to the same device bus or another device bus.

The processor system 301 may be coupled via the bus 303 to a display 313, such as a cathode ray tube (CRT) or liquid crystal display (LCD) or the like, for displaying information to a system user. The display 313 may be controlled by a display or graphics card. The processor system 301 includes input devices, such as a keyboard or keypad 315 and a cursor control 317, for communicating information and command selections to the processor 305. The cursor control 317, for example, is a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to the processor 305 and for controlling cursor movement on the display 313. In addition, a printer may provide printed listings of the data structures or any other data stored and/or generated by the processor system 301.

The processor system 301 performs a portion or all of the processing steps of the invention in response to the processor 305 executing one or more sequences of one or more instructions contained in a memory, such as the main memory 307. Such instructions may be read into the main memory 307 from another computer-readable medium, such as a storage device 311. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in the main memory 307. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, embodiments are not limited to any specific combination of hardware circuitry and software.

As stated above, the processor system 301 includes at least one computer readable medium or memory programmed according to the teachings of the invention and for containing data structures, tables, records, or other data described herein. Stored on any one or on a combination of computer readable media, the present invention includes software for controlling the system 301, for driving a device or devices for implementing the invention, and for enabling the system 301 to interact with a human user. Such software may include, but is not limited to, device drivers, operating systems, development tools, and applications software. Such comp