U.S. patent application number 11/342868 was filed with the patent office on 2006-08-31 for system and method for generating shaped ultrawide bandwidth wavelets.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to John W. McCorkle, James E. Thompson.
Application Number | 20060193372 11/342868 |
Document ID | / |
Family ID | 24751171 |
Filed Date | 2006-08-31 |
United States Patent
Application |
20060193372 |
Kind Code |
A1 |
McCorkle; John W. ; et
al. |
August 31, 2006 |
System and method for generating shaped ultrawide bandwidth
wavelets
Abstract
An ultra-wide band (UWB) waveform generator and encoder for use
in a UWB digital communication system. The UWB waveform is made up
of a sequence of shaped wavelets. The waveform generator produces
multi-amplitude, multi-phase wavelets that are time-constrained,
zero mean, and can be orthogonal in phase, yet still have a -10 dB
power spectral bandwidth that is larger than the frequency of the
peak of the power spectrum In one embodiment, the wavelets are
bi-phase wavelets. The encoder multiplies each data bit by an n-bit
identifying code, (e.g., a user code), resulting in a group of
wavelets corresponding to each data bit. The identifying codeword
is passed onto the UWB waveform generator for generation of a UWB
waveform that can be transmitted via an antenna.
Inventors: |
McCorkle; John W.; (Laurel,
MD) ; Thompson; James E.; (Phoenix, AZ) |
Correspondence
Address: |
POSZ LAW GROUP, PLC
12040 SOUTH LAKES DRIVE, SUITE 101
RESTON
VA
20191
US
|
Assignee: |
FUJITSU LIMITED
Kawasaki
JP
|
Family ID: |
24751171 |
Appl. No.: |
11/342868 |
Filed: |
January 31, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09685205 |
Oct 10, 2000 |
7010056 |
|
|
11342868 |
Jan 31, 2006 |
|
|
|
Current U.S.
Class: |
375/130 ;
375/295 |
Current CPC
Class: |
H04B 1/7172 20130101;
H04L 27/0004 20130101; H04B 1/7174 20130101; H04B 1/7183
20130101 |
Class at
Publication: |
375/130 ;
375/295 |
International
Class: |
H04B 1/69 20060101
H04B001/69; H04L 27/20 20060101 H04L027/20 |
Claims
1-30. (canceled)
31. A circuit for generating shaped ultrawide bandwidth wavelets,
comprising: a data encoder for receiving an input data stream and
encoding the input data stream into N parallel bit streams; and an
encoded wavelet generator for generating an encoded M-ary wavelet
encoded with N bit values received from the N parallel bit streams,
respectively, wherein N is an integer greater than 1.
32. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 31, wherein the encoded wavelet generator
further comprises a digital-to-analog converter for receiving one
or more of the N parallel bit streams and generating an M-ary
wavelet generation signal.
33. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 32, wherein the encoded wavelet generator
further comprises a modulator for modulating the M-ary wavelet
generation signal with a base wavelet shape to generate the encoded
M-ary wavelet.
34. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 33, wherein the encoded wavelet generator
further comprises a switching circuit for selecting the base
wavelet shape from one or more possible wavelet shapes based on one
or more of the N parallel bit streams.
35. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 31, wherein the encoded wavelet generator
further comprises: N modulators for modulating the N parallel bit
streams with N possible wavelet shapes, respectively, to generate N
intermediate encoded wavelets; and a summer for adding together the
N intermediate encoded wavelets to generate the encoded M-ary
wavelet.
36. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 35, wherein the encoded wavelet generator
further comprises N digital-to-analog converter located between the
N parallel bit streams and the N modulators, respectively.
37. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 31, wherein one of the N parallel bit streams
sets the polarity of the encoded M-ary wavelet.
38. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 37, wherein at least one of the N parallel bit
streams comprises non-return-to-zero data.
39. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 31, wherein at least one of the N parallel bit
streams sets the amplitude of the encoded M-ary wavelet.
40. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 31, wherein the encoder further comprises a
look-up table.
41. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 31, wherein the base wavelet shape is one of a
Gaussian shape, a derivative of a Gaussian shape, and a weighted
sinusoidal shape.
42. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 41, wherein the weighted sinusoidal shape is
one of a Gaussian weighted sinusoidal shape and an
inverse-exponentially weighted sinusoidal shape.
43. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 31, wherein the circuit is formed on as an
integrated circuit.
44. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 31, further comprising a filter for filtering
the encoded M-ary wavelet to generate a filtered M-ary wavelet.
45. A method for generating shaped ultrawide bandwidth wavelets,
comprising: receiving an input data stream including multiple data
bits; encoding the input data stream into N parallel bit streams;
generating an encoded M-ary wavelet based on the N parallel bit
streams, wherein N is an integer greater than 1.
46. A method for generating shaped ultrawide bandwidth wavelets, as
recited in claim 45, wherein the generating of an encoded M-ary
wavelet further comprises generating an intermediate wavelet
generation signal in response to at least one of the N parallel bit
streams, and wherein the M-ary wavelet is generated based on the
intermediate wavelet generation signal.
47. A method for generating shaped ultrawide bandwidth wavelets, as
recited in claim 46, wherein the generating of an encoded M-ary
wavelet further comprises modulating the intermediate wavelet
generation signal with a base wavelet shape to generate the encoded
M-ary wavelet.
48. A method for generating shaped ultrawide bandwidth wavelets, as
recited in claim 47, further comprising selecting the base wavelet
shape from a plurality of possible wavelet shapes based on at least
one of the N parallel bit streams.
49. A method for generating shaped ultrawide bandwidth wavelets, as
recited in claim 47, wherein the base wavelet shape is one of a
Gaussian shape, a derivative of a Gaussian shape, and a weighted
sinusoidal shape.
50. A method for generating shaped ultrawide bandwidth wavelets, as
recited in claim 49, wherein the weighted sinusoidal shape is one
of: a Gaussian weighted sinusoidal shape and an
inverse-exponentially weighted sinusoidal shape.
51. A method for generating shaped ultrawide bandwidth wavelets, as
recited in claim 45, wherein one of the N parallel bit streams sets
the polarity of the encoded M-ary wavelet.
52. A circuit for generating shaped ultrawide bandwidth wavelets,
as recited in claim 45, wherein the one of the N parallel bit
streams comprises non-return-to-zero data.
53. A method for generating shaped ultrawide bandwidth wavelets, as
recited in claim 45, wherein at least one of the N parallel bit
streams sets the amplitude of the encoded M-ary wavelet.
54. A method for generating shaped ultrawide bandwidth wavelets, as
recited in claim 45, wherein the method is implemented in an
integrated circuit.
55. A method for generating shaped ultrawide bandwidth wavelets, as
recited in claim 45, further comprising filtering the encoded M-ary
wavelet to generate a filtered M-ary wavelet.
56. A ultrawide bandwidth radio, comprising: a data encoder for
receiving an input data stream and encoding the input data stream
into N parallel bit streams; an encoded wavelet generator for
generating an encoded M-ary ultrawide bandwidth wavelet encoded
with N bit values received from the N parallel bit streams,
respectively; and a timing generator for providing timing signals
to the encoded wavelet generator, wherein N is an integer greater
than 1.
Description
CROSS REFERENCE TO RELATED PATENT DOCUMENTS
[0001] The present application is a continuation application of
U.S. patent application Ser. No. 09/685,205, filed Oct. 10, 2000,
entitled SYSTEM AND METHOD FOR GENERATING ULTRA WIDEBAND
PULSES.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to ultra wideband radio
communication systems, and in particular to methods, systems and
devices for generating waveforms that include wavelets that are
shaped and modulated to convey digital data over a wireless radio
communication channel using ultra wideband signaling
techniques.
[0004] 2. Description of the Background
[0005] 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.
[0006] Ultra wideband (UWB) communications systems transmit
carrierless high data rate, low power signals. Since a carrier is
not used, it is necessary that the transmitted waveforms themselves
contain the information being communicated. Accordingly,
conventional UWB systems transmit pulses, the information to be
communicated being contained in the pulses themselves, and not on a
carrier.
[0007] Conventional UWB communication systems send a sequence of
identical pulses, the timing of which contains 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 to mean a `1` has been sent,
whereas if the pulse is received at the end of that same time
window, the receiver will decode that to mean that a `0` has been
received.
[0008] Several problems arise with this technique, however. 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.
[0009] 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, now issued as U.S. Pat. No. 6,700,939, the
entire contents of which being incorporated herein by reference,
information is carried by the shape of the pulse, or the shape in
combination with its position in the pulse-sequence.
[0010] 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 ULTRA WIDE BANDWIDTH SPREAD
SPECTRUM COMMUNICATIONS SYSTEM, now issued as U.S. Pat. No.
6,700,939. 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.
[0011] 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. Accordingly, 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.
[0012] 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 data transmitted 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.
[0013] Furthermore, UWB receivers often suffer from leakage of the
UWB signal driving the mixer. These UWB drive signals can radiate
into space and be received by the antenna where it can jam the
desired UWB signal due to its very close proximity and large
amplitude. 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.
[0014] 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.
[0015] 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.
[0016] 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
[0017] 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. Another object of
the present invention is to provide a novel approach to encoding
data onto UWB wavelets by controlling the shape of the wavelets,
rather than the time position of the wavelets.
[0018] The inventors of the present invention have recognized that
a highly integratable UWB wavelet generator may be designed that
uses an analog mixer and a pulse generator to create various shapes
of UWB wavelets. The inventors of the present invention have also
recognized that a single UWB wavelet can carry more than one bit of
information by varying the shape of the wavelet (including
magnitude), the position of the wavelet, or both, according to an
encoding scheme.
[0019] These and other objects are achieved according to the
present invention by providing a novel approach for generating
wavelets that is highly integratable, and an approach to encoding
data onto a UWB wavelet by controlling the shape of the wavelet,
rather than the time position of the wavelet.
[0020] The wavelet generator is a circuit which is highly
integratable and in one embodiment uses two pulse streams that
provide an early pulse and late pulse respectively, from a pulse
generation circuit, that when mixed with a positive or a negative
voltage (from a non-return-to-zero (NRZ) data stream, for example)
in a conventional differential mixer, creates a wavelet that is
either positive or negative (i.e., non-inverted or inverted),
accordingly. In other embodiments, the data to be encoded and the
pulse streams generated by the pulse generator are manipulated so
as to further change the shape of the resultant UWB wavelets. By
mixing the pulse streams generated by the pulse generator with a
stream of NRZ data (positive voltage for a `1`, negative voltage
for a `0`), a waveform having a sequence wavelets can be created
that can be transmitted as a UWB signal. In a preferred embodiment,
the conventional 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 bulk
semiconductor device, or a micro-machine device.
[0021] 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."
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1a is a block diagram of an ultra-wide band (UWB)
transceiver, according to the present invention;
[0023] FIG. 1b is a diagram for illustrating the operation of the
transceiver of FIG. 1a, according to the present invention;
[0024] FIG. 2 is a block diagram of the transceiver of FIG. 1a,
that manipulates a shape of UWB pulses, according to the present
invention;
[0025] FIG. 3 is a schematic diagram of a general-purpose
microprocessor-based or digital signal processor-based system,
which can be programmed according to the teachings of the present
invention;
[0026] FIG. 4A illustrates a non-return-to-zero data stream bit
representing a `1` being mixed with an early and a late pulse from
a pulse generator according to one embodiment of the present
invention;
[0027] FIG. 4B illustrates a non-return-to-zero data stream bit
representing a `0` being mixed with an early and a late pulse from
a pulse generator according to one embodiment of the present
invention;
[0028] FIG. 5A illustrates a single wavelet encoded with a `1`
generated by the circuit FIG. 4A;
[0029] FIG. 5B illustrates a single wavelet encoded with a `0`
generated by the circuit FIG. 4B;
[0030] FIG. 6 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;
[0031] FIG. 6A is a schematic diagram of an AND gate used in the
circuit of FIG. 6 according to one embodiment of the present
invention;
[0032] FIG. 7A is a schematic diagram of a Gilbert cell
differential mixer;
[0033] FIG. 7B is an illustration of the early and late pulses
generated by the pulse generating circuit of FIG. 6;
[0034] FIG. 7C illustrates a bi-phase wavelet generated by the
pulse generating circuit of FIG. 6 when the incoming data bit is
high;
[0035] FIG. 7D illustrates a bi-phase wavelet generated by the
pulse generating circuit of FIG. 6 when the incoming data bit is
low;
[0036] FIG. 7E is a schematic diagram of a FET bridge differential
mixer;
[0037] FIG. 7F is a schematic diagram of a diode bridge
differential mixer;
[0038] FIG. 8A illustrates a non-return-to-zero data stream bit
representing a `1` being mixed with a mid pulse from a pulse
generator on a first input of a differential port of a mixer and an
early and a late pulse from the pulse generator on a second input
of a differential port of a mixer according to one embodiment of
the present invention;
[0039] FIG. 8B illustrates a non-return-to-zero data stream bit
representing a `0` being mixed with a mid pulse from a pulse
generator on a first input of a differential port of a mixer and an
early and a late pulse from the pulse generator on a second input
of a differential port of a mixer according to one embodiment of
the present invention;
[0040] FIG. 9A illustrates a single wavelet encoded with a `1`
generated by the circuit FIG. 8A;
[0041] FIG. 9B illustrates a single wavelet encoded with a `0`
generated by the circuit FIG. 8B;
[0042] FIG. 10 illustrates a circuit for creating a constellation
of shapes of UWB wavelets according to one embodiment of the
present invention;
[0043] FIG. 10A illustrates a circuit for creating a constellation
of shapes of UWB wavelets using a look-up table and D/A converters
according to one embodiment of the present invention;
[0044] FIG. 11 illustrates two exemplary waveforms that are summed
at the summer of FIG. 10 according to one embodiment of the present
invention;
[0045] FIG. 12 illustrates an exemplary constellation of UWB
wavelet shapes produced by the circuit of FIG. 10 according to one
embodiment of the present invention;
[0046] FIGS. 13A-13D illustrate exemplary UWB wavelet shapes
wherein data has been further encoded into the amplitude of the
wavelets according to one embodiment of the present invention;
[0047] FIGS. 14A-14D illustrate further exemplary UWB wavelet
shapes wherein data has been further encoded into the amplitude of
the wavelets according to one embodiment of the present
invention;
[0048] FIG. 15 is a schematic of an exemplary digital to analog
device for adding amplitude to a waveform according to one
embodiment of the present invention;
[0049] FIG. 16 is a schematic of a UWB wavelet generator for
generating wavelets that include encoding in their amplitude with a
digital to analog device according to one embodiment of the present
invention;
[0050] FIG. 17 is a schematic of a UWB wavelet generator that
generates wavelets having a constellation of shapes according to
one embodiment of the present invention;
[0051] FIG. 18 illustrates an encoding of data with a multi-bit
user code according to one embodiment of the present invention;
and
[0052] FIG. 19 is a schematic of a circuit for encoding
non-return-to-zero data with a user code according to one
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.i.di-elect cons.{1, a1,
a2, . . . , aK}, .beta..di-elect cons.{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 .di-elect cons. {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).
[0057] 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 T i = j = 0 i .times. t j .
##EQU1## 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.i corresponds to the zero-crossings of
a chirp, i.e., the sequence of T.sub.i's, and where T i = i - a k
##EQU2## 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.
[0058] 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).
x .function. ( t ) = i = 0 .infin. .times. g B i .function. ( t - T
i ) ( 1 ) ##EQU3##
[0059] 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.
[0060] 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)
[0061] 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.
[0062] 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. f B i .function. ( t ) =
.PSI. .function. ( B i , 2 , B i , 3 ) .times. ( d B i , 3 d t B i
, 3 .times. e - [ B i , 2 .times. t ] 2 ) ( 3 ) ##EQU4##
[0063] 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.
[0064] 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.2sin
(.omega..sub.it+k.sub.it.sup.2). (4)
[0065] 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.
[0066] 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. g
B i .function. ( t ) = ( 1 e - ( t - t .times. .times. 1 f .3 * t r
i + 1 - 1 e - ( t - t .times. .times. 2 i ) .3 * tf i + 1 ) sin
.function. ( .theta. i + .omega. i .times. t + k i .times. t 2 )
.times. .times. where .times. .times. { B i , 2 , B i , 3 , B i , 4
, B i , 5 , B i , 6 , B i , 7 , B i , 8 } = { t 1 i , t 2 i , t r i
, t f i , .theta. i , .omega. i , k i } ( 5 ) ##EQU5##
[0067] In the above equation, the leading edge turn on time is
controlled by t1, and the turn-on rate is controlled by tr. The
trailing edge turn-off time is controlled by t2, and the turn-off
rate is controlled by tf. 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 .omega.+kT.sub.D. An example assignment of parameter values is
.omega.=1, tr=tf=0.25, t1=tr/0.51, and t2=T.sub.D-tr/9.
[0068] 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.
[0069] 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.
[0070] 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).
[0071] 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)} (6)
[0072] where p.sup.H(t) is the Hilbert transform of p(t).
[0073] 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.
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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).
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.).
[0084] 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.
[0085] 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.
[0086] 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.
[0087] 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.
[0088] 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.
[0089] 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).
[0090] 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.
[0091] 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.
[0092] 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.
[0093] 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.
[0094] 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.
[0095] 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.
[0096] 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.
[0097] 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.
[0098] 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.
[0099] The UWB transceiver of FIGS. 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.
[0100] 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.
[0101] 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.
[0102] 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.
[0103] 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.
[0104] 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 computer readable media further includes the computer program
product of the present invention for performing all or a portion
(if processing is distributed) of the processing performed in
implementing the invention.
[0105] The computer code devices of the present invention may be
any interpreted or executable code mechanism, including but not
limited to scripts, interpretable programs, dynamic link libraries,
Java or other object oriented classes, and complete executable
programs. Moreover, parts of the processing of the present
invention may be distributed for better performance, reliability,
and/or cost.
[0106] The term "computer readable medium" as used herein refers to
any medium that participates in providing instructions to the
processor 305 for execution. A computer readable medium may take
many forms, including but not limited to, non-volatile media,
volatile media, and transmission media. Non-volatile media
includes, for example, optical, magnetic disks, and magneto-optical
disks, such as the storage device 311. Volatile media includes
dynamic memory, such as the main memory 307. Transmission media
includes coaxial cables, copper wire and fiber optics, including
the wires that comprise the bus 303. Transmission media may also
take the form of acoustic or light waves, such as those generated
during radio wave and infrared data communications.
[0107] Common forms of computer readable media include, for
example, hard disks, floppy disks, tape, magneto-optical disks,
PROMs (EPROM, EEPROM, Flash EPROM), DRAM, SRAM, SDRAM, or any other
magnetic medium, compact disks (e.g., CD-ROM), or any other optical
medium, punch cards, paper tape, or other physical medium with
patterns of holes, a carrier wave, carrierless transmissions, or
any other medium from which a system can read.
[0108] Various forms of computer readable media may be involved in
providing one or more sequences of one or more instructions to the
processor 305 for execution. For example, the instructions may
initially be carried on a magnetic disk of a remote computer. The
remote computer can load the instructions for implementing all or a
portion of the present invention remotely into a dynamic memory and
send the instructions over a telephone line using a modem. A modem
local to system 301 may receive the data on the telephone line and
use an infrared transmitter to convert the data to an infrared
signal. An infrared detector coupled to the bus 303 can receive the
data carried in the infrared signal and place the data on the bus
303. The bus 303 carries the data to the main memory 307, from
which the processor 305 retrieves and executes the instructions.
The instructions received by the main memory 307 may optionally be
stored on a storage device 311 either before or after execution by
the processor 305.
[0109] The processor system 301 also includes a communication
interface 319 coupled to the bus 303. The communications interface
319 provides a two-way UWB data communication coupling to a network
link 321 that is connected to a communications network 323 such as
a local network (LAN) or personal area network (PAN) 323. For
example, the communication interface 319 may be a network interface
card to attach to any packet switched UWB-enabled personal area
network (PAN) 323. As another example, the communication interface
319 may be a UWB accessible asymmetrical digital subscriber line
(ADSL) card, an integrated services digital network (ISDN) card, or
a modem to provide a data communication connection to a
corresponding type of communications line. The communications
interface 319 may also include the hardware to provide a two-way
wireless communications coupling other than a UWB coupling, or a
hardwired coupling to the network link 321. Thus, the
communications interface 319 may incorporate the UWB transceiver of
FIG. 2 as part of a universal interface that includes hardwired and
non-UWB wireless communications coupling to the network link
321.
[0110] The network link 321 typically provides data communication
through one or more networks to other data devices. For example,
the network link 321 may provide a connection through a LAN to a
host computer 325 or to data equipment operated by a service
provider, which provides data communication services through an IP
(Internet Protocol) network 327. Moreover, the network link 321 may
provide a connection through a PAN 323 to a mobile device 329 such
as a personal digital assistant (PDA) laptop computer, or cellular
telephone. The LAN/PAN communications network 323 and IP network
327 both use electrical, electromagnetic or optical signals that
carry digital data streams. The signals through the various
networks and the signals on the network link 321 and through the
communication interface 319, which carry the digital data to and
from the system 301, are exemplary forms of carrier waves
transporting the information. The processor system 301 can transmit
notifications and receive data, including program code, through the
network(s), the network link 321 and the communication interface
319.
[0111] The encoder 21 and waveform generator 17 of the transceiver
of the present invention function together to create a UWB waveform
from a digital data stream by first multiplying each bit of data in
the data stream by an identifying code (e.g., an n-bit user code),
thereby expanding each bit of data into a codeword of data bits
equal in length to the length of the identifying code. In one
embodiment, the codeword is then further processed to create two
derivative codewords that are that are sent to the UWB waveform
generator 17 where they are mixed with a pulse generator and
recombined through a two-stage mixing process prior to being
transmitted via the antenna 15.
[0112] As stated above, the encoder 21 receives a digital data
stream from an external source via the radio and controller
interface 9. The encoder 21 multiplies each bit of the digital data
stream by a user code, which in one embodiment is a unique sequence
of bits corresponding to a particular user. For example,
multiplying a user code of `1101 0110` by a data bit of `1` results
in an 8-chip representation of the `1` that is identical to the
user code, or `1101 0110.` On the other hand, multiplying that same
user code by a data bit of `0` results in an 8-bit representation
of the `0` that is the 8 chip user code inverted, or `0010
1001.`
[0113] Continuing with the above example, the encoder 21 multiplies
the user code by each bit of the digital data stream to create a
sequence of n-chip codewords, where n is the length of the user
code. Once the digital data stream has been encoded, the UWB
waveform generator 17 further processes the sequence of codewords
in creating an UWB waveform that can be transmitted.
[0114] FIGS. 4A and 4B illustrate an exemplary circuit using a
differential mixer 401 for generating UWB wavelets encoded with
data according to one embodiment of the present invention. As shown
in FIGS. 4A and 4B, a binary non-return-to-zero (NRZ) data source
is connected to an input of a differential mixer 400. Connected to
the two differential inputs of the LO port 407, 408 of the
differential mixer 401 are two outputs of a pulse generator that
generates a pair of pulse streams configured to apply an early
pulse 403 at the first differential input 407 and immediately
thereafter, a late pulse 404 at the second differential input 408
of the LO port. The wavelet generator is configured such that the
NRZ data source is at a rate such that each bit of data will be as
long or longer than the combined duration of an early pulse and a
late pulse generated by the pulse generator. Accordingly, each bit
of NRZ data will be mixed with both the early pulse 403 and the
late pulse 404.
[0115] FIG. 4A illustrates the example where the incoming bit from
the NRZ data source is a `1` (i.e., positive voltage), whereas FIG.
4B illustrates the example where the incoming data bit is a `0`
(i.e., negative voltage). The output of the differential mixer 402
for both examples is a UWB wavelet that occupies the same time
frame and has the data encoded in the shape of the wavelet, not in
the time position of the wavelet.
[0116] FIGS. 5A and 5B illustrate the shapes of the UWB wavelets
produced by the differential mixer 401 in the two examples
described in FIGS. 4A and 4B respectively. As shown in FIG. 5A, a
UWB wavelet 500 is produced by mixing a NRZ data `1` with the early
pulse input to the first differential input of the mixer 407 and
the late pulse input to the second differential input of the mixer
408 as illustrated by FIG. 4A. As will be described below, the
early and late pulses generated by a pulse generator cause the
mixer to produce a `high` then `low` output that, when mixed with a
NRZ data `1,` will produce the wavelet shown in FIG. 5A. As would
be well understood by one of ordinary skill in the communications
art, the shape of the resultant UWB wavelet is such that the
integral of the wavelet is 0.
[0117] FIG. 5B illustrates a UWB wavelet 501 produced by mixing a
NRZ data `0` (e.g., a negative voltage) with the early pulse input
to the first differential input of the mixer 407 and the late pulse
input to the second differential input of the mixer 408 as
illustrated by FIG. 4B. As shown in FIGS. 5A and 5B, the two
different UWB wavelets are inverted representations of one another.
By encoding the data (i.e., the `0` and the `1`) onto the shape of
the UWB wavelet, the single bit of information may be encoded as
one of the two shapes corresponding to a `0` or a `1` accordingly.
Comparing this novel UWB modulation technique with that of a
conventional PPM UWB systems, it can be seen that by using this
technique, a bit of information may be transmitted in the time
taken to transmit a single wavelet (i.e., a `1` being a positive
then negative wavelet and a `0` being a negative then positive
wavelet), as compared to the necessarily longer time required to
transmit a time-positioned encoded bit of information (i.e., a `1`
being represented by a wavelet occurring early in a larger time
window, and a `0` being represented by a wavelet occurring late in
a larger time window).
[0118] FIG. 6 is a schematic diagram of a circuit for generating a
UWB waveform in one embodiment of the present invention. As shown
in FIG. 6, data 416 is mixed at a first mixer 701 with the outputs
of an early/late pulse generator 200. The early/late pulse streams
run at the chipping rate. The chipping rate can be the same as the
data rate of derived input data 416, in which case a single
wavelet, or chip, is transmitted for each bit. The chipping rate
may also be an integer multiple of the data rate of the derived
input data 416. In such a case, each bit is made up of a
predetermined number of bits. For example, if the data stream 416
is at 50 Mb/s and there are 16 chips per bit, then the early/late
pulse streams 286, 288 are at 800 MHz.
[0119] As shown in FIG. 6, the pulse generator 200 receives its
input from a differential clock 210 which generates a pulse 203,
which is differentially transmitted on lines 202 and 204. Input
lines 202, 204 feed into the first of a set of seven buffers 212,
214, 216, 218, 220, 222, and 224 connected in series. While seven
buffers are shown in this first series-connected set of buffers, it
would be understood by one of ordinary skill in the art that other
numbers of buffers could be used to provide a different time delay
through the set. Buffers 214 and 216 are connected in series via
lines 224, 226. In the preferred embodiment disclosed in FIG. 6,
data lines 228 and 230 branch off from lines 224 and 226
respectively and serve as inputs to buffer 244. The output of
buffers 242 and 244 serve as inputs via lines 246, 248 to an
exclusive OR gate 250, which generates a pulse 205. In another
embodiment, an AND gate could be used in place of the exclusive OR
gate 250, where the inverting output of one of either buffer 242 or
buffer 244 is used to feed the AND gate 600 instead of the
non-inverting output, as shown in FIG. 6A. An AND gate 600 provides
some advantages since the AND gate 600 generates a pulse only on
the rise of the pulse, whereas an exclusive OR gate 250 gives a
pulse both on the rise and the fall of the pulse. Therefore, timing
of the circuit is less difficult to implement with an AND gate. The
output of the exclusive OR gate 250 is a differential pulse 205
which feeds into another series-connected set of buffers, in this
example, seven buffers 260, 262, 264, 266, 268, 270, and 282 via
lines 252, 254. Buffers 262 and 264 are connected in series via
lines 253 and 255. In the preferred embodiment disclosed in FIG. 6,
data lines 276 and 278 branch off from lines 253 and 255
respectively and serve as inputs to buffer 280. The output from
buffers 280 and 282 feed into differential mixer 701 via lines 286
and 288. The differential mixer 701 receives the data stream from
encoder 21 over lines 292, 294.
[0120] The function of the pulse generator 200 shown in FIG. 6 will
now be described. The clock 210 generates a differential
semi-square wave clock signal 203, which are transmitted over lines
202, 204 to buffer 212. Buffer 212 serves to amplify, saturate, and
generally square up the incoming signal, and then buffer 214
squares it up some more. The transmission of the clock signal 203
through two paths, one through buffers 216, 218, 220, 222, and 242,
and the other through buffer 244, causes the clock signal to reach
the output of buffer 244 before it reaches the output of buffer
242. In other words, the output of buffer 244 leads the output of
buffer 242 by the delay accumulated in buffers 216, 218, 220, and
222. Since the inputs to the exclusive OR gate 250 are matched
except at the clock transitions, pulse 205 is generated at the
output of exclusive OR gate 250 at each transition of the clock.
The pulse stream, therefore, is at twice the clock frequency
because an exclusive OR gate 250 generates a pulse on both leading
and trailing clock transitions.
[0121] In another embodiment, an AND gate 600 could be used in
place of the exclusive OR gate 250, where the inverting output of
either buffer 242 or buffer 244 is used to feed the AND gate 600
instead of the non-inverting output, as shown in FIG. 6A. Since the
inputs to the AND gate 600 are mismatched except at the leading
clock edge transition (if the inverting output of buffer 242 is
used), or the trailing clock edge transition (if the inverting
output of buffer 244 is used) the output of the AND gate 600 is a
pulse stream that equals the clock frequency. An AND gate 600
provides some advantages since the AND gate 600 generates a pulse
only on the rise or fall of the pulse, whereas an exclusive OR gate
250 gives a pulse both on the rise and the fall of the pulse.
Therefore, the duty-cycle of the clock does not have to be exactly
50% in order to have an equal time period between all pulses.
Instead, the duty cycle can be anything, making the circuit is less
difficult to implement.
[0122] The pulse 205 is transmitted over differential lines 252 and
254 to buffer 260. Buffer 260 serves to amplify, saturate, and
generally square up the pulse and then buffer 262 squares it up
some more. The transmission of the pulse 205 through two paths, one
path via differential lines 253 and 255 through buffers 264, 266,
268, 270, and 282, and the other path via differential lines 246
and 248 through buffer 280 causes the pulse 205 to reach the output
of buffer 280 before it reaches the output of buffer 282. In other
words, output 286 of buffer 280 leads output 288 of buffer 282 by
the delay accumulated in buffers 264, 266, 268, and 270.
Accordingly, line 286 has an early pulse and line 288 has a late
pulse, making pulse streams 203a and 203b respectively.
[0123] The early pulse on line 286 feeds the non-inverting
differential LO input of multiplier 701. The late pulse on line 288
feeds the inverting differential LO input of multiplier 701. The
differential data-source 416 generates data, which is
differentially transmitted on lines 292 and 294. Input lines 292
and 294 feed into the first of a set of two series-connected
buffers 296 and 298. The differential output data from buffer 298
drives the differential RF-input port of multiplier 701. Given the
data on the RF-port of multiplier 701, and the early and late pulse
on the non-inverting and inverting input lines of the differential
LO-port of multiplier 701, the output of the multiplier is the
desired wavelet shape. When the data is a `1,` the output wavelet
has a ground-positive-negative-ground shape, and when the data is a
`0,` the output wavelet has a ground-negative-positive-ground
shape.
[0124] FIG. 7A is a schematic diagram of a transistor-based Gilbert
cell differential mixer used in one embodiment of the present
invention. In this embodiment, it is shown that mixing the
resultant early/late pulse streams 286, 288 generated by the pulse
generator 200 shown in FIG. 6, the result is a sequence of bi-phase
wavelets corresponding to the input data 416. In other embodiments
of the present invention, the wavelets generated may have different
shapes, such as, but not limited to multilevel and/or quad-phase
wavelets. Accordingly, if different encoding schemes are used,
different amounts of information may be encoded in any single
wavelet, thereby affecting the data rates achievable at a given
chip rate.
[0125] As would be understood by one of ordinary skill in the art,
FIG. 7A is a schematic diagram of a bipolar transistor-based
Gilbert cell differential multiplier. It is capable of multiplying
the differential signal across 330 and 332, by the differential
signal across 286 and 288, the product appearing across the
differential output 340 and 342. It includes a current mirror 704,
which provides a current that will be steered between the
differential output nodes 340 and 342. Differential pair 706 steers
the current between two paths, the first path to differential pair
710, and the second path to differential pair 708. Differential
pair 710 and differential pair 708 are connected to differential
input lines 330 and 332, and to the differential output nodes 340
and 342 so as to oppose one another, (i.e., if the differential
input 330 is high, then differential pair 710 steers its current to
pull 342 low but differential pair 708 steers its current to pull
342 high). The pair that dominates is determined by which has the
most current available to it, which is determined by differential
pair 706. Differential pair 706 accepts differential inputs 286 and
288. When 286 is higher than 288, the current is steered to
differential pair 710 and the output 340 is inverted from input 330
(i.e., multiplying by -1). When 288 is higher than 286, the current
is steered to differential pair 708 and the output 340 is not
inverted from input 330 (i.e., multiplying by +1). When 286 is
equal to 288, the current is steered identically to the output
nodes 340 and 342 so that the output is independent of the input
330 and 332 (i.e., multiplying by zero). Accordingly, by mixing the
early/late pulses shown in FIG. 7B with a high input to A 330, the
output waveform will be of the form shown in FIG. 7C. On the other
hand, by mixing the early/late pulses shown in FIG. 7B with a low
input to A 330, the output waveform will be of the form shown in
FIG. 7D.
[0126] In other embodiments, the wavelet generating function of the
differential mixer 701 is accomplished using, for example, bridge
circuits using switches. The can be electronically controlled
switches such as an FET-bridge mixer 702 of FIG. 7E or a
diode-bridge mixer 703 of FIG. 7F. In other embodiments, the
switches are mechanical, using, for example, MEM (micro
electromechanical machine) technology, or optically driven switches
such as a bulk semiconductor material. In various embodiments of
the present invention, all of the ports of the mixer are
differential or all of the ports of the mixer accept digital
inputs, or both.
[0127] Using a differential mixer to generate the UWB wavelets
according to the present invention provides advantages over
conventional methods. For example, using a conventional method of
passing a pulse through one or more transmission line stubs to
create a waveform includes using components (i.e., the stubs) that
are not integratable. Accordingly, the conventional approach uses
up more space, which is of a premium when designing UWB wireless
devices. Accordingly, by using highly integratable components, such
as transistor-based differential components in combination with the
pulse generator 200 described above, the present invention provides
a highly integratable solution for creating UWB wavelets, even into
the microwave regime.
[0128] FIGS. 8A and 8B illustrate an exemplary circuit for using a
mixer 401 to generate UWB wavelets encoded with data according to
another embodiment of the present invention. As shown in FIGS. 8A
and 8B, a binary NRZ data source is connected to an input of a
differential mixer 400. Connected to the two differential inputs of
the LO port 407, 408 of the differential mixer 401 are two outputs
of a pulse generator 200 providing a pair of pulse streams
configured to apply an early pulse and a late pulse 410 at the
second differential input 408 and a mid-pulse 409, occurring
between the early pulse and late pulse, at the first differential
input 407 of the LO port. The wavelet generator is configured such
that the NRZ data source is at a rate such that each bit of the
data will be as long or longer than the combined duration of an
early pulse, a mid-pulse, and late pulse generated by the pulse
generator. Accordingly, each bit of NRZ data will be mixed with an
early pulse, a mid-pule, and a late pulse.
[0129] FIG. 8A illustrates the example where the incoming bit from
the NRZ data source is a `one,` whereas FIG. 8B illustrates the
example where the incoming data bit is a `zero.` The output of the
differential mixer 402 for both examples is a UWB wavelet that
occupies the same time frame and has the data encoded in the shape
of the wavelet, not in the time position of the wavelet.
[0130] FIGS. 9A and 9B illustrate the shapes of the UWB wavelets
produced by the two examples described in FIGS. 8A and 8B
respectively. As shown in FIG. 9A, a UWB wavelet 900 is produced by
mixing a NRZ data `1` (i.e., a positive voltage) with the early
pulse and late pulse 410 input to the second differential input of
the mixer 408, and the mid pulse input to the first differential
input of the mixer 407 as illustrated by FIG. 8A. In this
embodiment, the early and late pulses generated by the pulse
generator are at one-half the amplitude of the mid-pulse generated
by the pulse generator. Accordingly, the areas of the two negative
portions of the waveform 902, 903, as shown in FIG. 9A, are each
one-half the area of the positive portion of the waveform 904.
Again, as with the positive-negative UWB wavelet described in FIGS.
5A and 5B, the shape of the UWB wavelet is such that the integral
of the wavelet is 0.
[0131] FIG. 9B illustrates the UWB wavelet 901 produced by mixing a
NRZ data `0` (i.e., a negative voltage) with the early pulse and
late pulse input to the second differential input of the mixer 408,
and the mid pulse input to the first differential input of the
mixer 407 as illustrated by FIG. 8B. As shown in FIGS. 9A and 9B,
the two different UWB wavelets are inverted representations of one
another. As discussed above, by encoding the data onto the shape of
the UWB wavelet, a single bit of information may be encoded as one
of the two shapes corresponding to a `0` or a `1` accordingly.
[0132] FIG. 10 illustrates an exemplary UWB wavelet generator for
generating UWB wavelets that encode more than one bit of data. As
shown in FIG. 10, the UWB wavelet generator uses two mixers 1003,
1004, and a summer 1005 to encode two bits of NRZ data. In this
embodiment, the odd bits 1001 of the NRZ data stream are input to a
first differential mixer 1003, and the even bits 1002 of the NRZ
data stream are input to a second differential mixer 1004. The
first differential mixer 1003 has an early pulse and a late pulse
input to the first and second differential inputs of the LO port,
respectively, as described above in FIGS. 4A and 4B. The second
differential mixer 1004, on the other hand, has an early pulse, a
mid pulse, and a late pulse 1007 input to the two differential
inputs of the LO port, as described above in FIGS. 8A and 8B. The
output of the first differential mixer 1003 and the output of the
second differential mixer 1004 are input to the summer 1005.
Accordingly, since each of the two inputs to the summer 1005 can be
one of two different shapes, as discussed above in FIGS. 5A, 5B,
9A, and 9B, the output of the summer 1005 can take on one of four
distinct shapes. The four distinct shapes output by the summer 1005
correspond to the four unique values that can be encoded in the two
bits of NRZ data (i.e., `00,` `01,` `10,` and `11`).
[0133] FIG. 10A illustrates an exemplary UWB wavelet generator for
generating UWB wavelets in another embodiment of the present
invention. As shown in FIG. 10A, the input data stream is input to
a look-up table (LUT) 1014, where the shape of the UWB wavelets is
determined. Based on the value in the look-up table 1014
corresponding to the input data stream, the two digital to analog
converters (D/A) 1010, 1012 apply amplitude information onto the
incoming data. The varying amplitude signals are then mixed with
the outputs of the pulse generator at the two mixers 1003, 1004, as
discussed in FIG. 10. Using this circuit, the incoming data stream
may be encoded into UWB wavelets having a constellation of shapes
and magnitudes which correspond to various data values according to
the encoding scheme provided by the look-up table 1014 values.
[0134] FIG. 11 shows the two exemplary intermediate UWB wavelets
generated by the circuit of FIG. 10. As shown in FIG. 11, a first
wavelet 1102 results from mixing an early pulse and a late pulse
1006 with a NRZ data bit of `1` at mixer 1003. A second UWB wavelet
1101 results from mixing an early pulse, a mid pulse, and a late
pulse 1007 with a NRZ data bit of `1` at mixer 1004. Accordingly,
the output of the summer 1005 will be the addition of these two UWB
wavelets which will create a UWB wavelet that corresponds to a
two-bit value of `11.`
[0135] FIG. 12 shows four uniquely-shaped waveforms, all occurring
within the same time frame, that correspond, for example, to the
four possible values of the two bits encoded in the circuit of FIG.
10. As shown in FIG. 12, a data value of `11` may be represented by
the UWB wavelet 1201 resulting from the addition of the two
waveforms shown in FIG. 11. The four uniquely-shaped UWB wavelets
1201, 1202, 1203, and 1204 shown in FIG. 12, therefore, correspond
to the four potential values of two bits of data (i.e., `00, `
`01,` `10,` and `11`).
[0136] FIGS. 13A-13D and 14A-14D further illustrate how UWB
wavelets may be shaped so as to allow the encoding of further
information thereon. By adding amplitude information to the wavelet
shapes already discussed, additional information may be encoded on
the wavelets while still requiring only a single time frame to
transmit the information. As shown in FIGS. 13A-13D, the wavelets
produced by the circuit described in FIGS. 4A and 4B can be used to
convey two bits of information if the wavelets are transmitted with
one of two different amplitudes. For example, the wavelet
illustrated in FIG. 13A may correspond to an encoded data value of
`11,` whereas the wavelet illustrated in FIG. 13B, having a smaller
amplitude than that wavelet shown in FIG. 13A, may correspond to an
encoded data value of `10.` Accordingly, the wavelets shown in
FIGS. 13C and 13D may correspond to encoded data values of `00,`
and `01,` respectively.
[0137] FIGS. 14A-14D similarly show how UWB wavelets having other
shapes may also be further encoded with amplitude data. As would be
well understood by one of ordinary skill in the art, multiple
amplitude values could be used to further encode additional bits of
information, and if used in a circuit such as that described in
FIG. 10, for example, an entire constellation of values could be
represented by the various shapes of UWB wavelets generated.
[0138] FIG. 15 is a schematic of a simple, yet very fast, digital
to analog device 1601 that can be used to apply amplitude data to
either a NRZ data source or pulse streams generated by a pulse
generator. As shown in FIG. 15, the simple digital to analog device
1601 uses a current mirror circuit 1501 to generate two current
sinks, 1505 and 1507, and it uses two differential pairs, 1520 and
1522 to steer the two currents to differential output nodes
V.sub.out1 1524 and V.sub.out2 1526. As a result, the circuit
generates an output voltage according to table 1503. As would be
understood by one of ordinary skill in the art, the simple digital
to analog device 1601 shown in FIG. 15 is a simple and fast device
for generating various output voltage levels that could be used to
further encode either the NRZ data stream, or the pulse streams
generated by the pulse generator.
[0139] FIG. 16 is a schematic showing an exemplary circuit for
using a digital to analog converter (D/A) 1601 and a differential
mixer 1602 to generate UWB wavelets having encoded thereon two bits
of data. As shown in FIG. 16, multiple bits (e.g., odd and even, or
some other interleaved or encoding method output by an encoder
1603) are connected to the D/A 1601, for example, in accordance
with table 1503 in FIG. 16. Accordingly, multiple bits are encoded
onto individual wavelets as amplitude and phase (0.degree. or
180.degree.) information.
[0140] The number of distinct amplitude values is determined by the
number of bits in the D/A and is not limited to two bits as shown
in the exemplary circuit in FIG. 16.
[0141] FIG. 17 is a schematic illustrating a circuit through which
a constellation of shapes of UWB wavelets may be generated to
encode three bits of data. As shown in FIG. 17, a lookup table 1712
receives the NRZ data stream and encodes a group of data bits to
drive the D/A 1601 and switch 1705 combination. The switch 1705 is
configured to select one of two orthogonal drive waveforms 1708,
1710 to couple to one input port of the mixer 1706. D/A 1601 is
configured to drive various amplitudes into another input port of
the mixer 1706. The output of the mixer 1706 is a constellation of
multi-amplitude, quadrature-phase, zero mean, UWB wavelets that are
generated at extremely high rates. As would be understood by one of
ordinary skill in the art, many variations of the circuit shown in
FIG. 17 are possible. For example, by applying a D/A to both NRZ
inputs shown in FIG. 10, more than the four phases described could
be added to the multi-amplitude modulation to encode more bits of
information. Furthermore, other variations could be made to the
shapes and amplitudes of the data being encoded.
[0142] FIG. 18 illustrates an approach whereby a single bit of
information is encoded as a group of several wavelets (or chips),
where the group corresponds to a unique user code 1901 (e.g., `0100
1010`). As shown in FIG. 18, the encoder 1900 multiplies the unique
user code 1901 with each bit of data 1902 to be transmitted. A data
value of `0` will be encoded as an inverted representation of the
user code 1901 (e.g., `1011 0101`), whereas a data value of `1`
will be encoded as the sequence of chips that make up the user code
1901 (e.g., `0100 1010`).
[0143] FIG. 19 is a schematic of a circuit implementing the
encoding scheme discussed in FIG. 18. As shown in FIG. 19, each bit
of data 2001 will be input to an exclusive OR (XOR) gate 2002 along
with each bit of the N-bit user code. The output of the XOR 2002
will be the exclusive OR of the data (i.e., `0,` or `1`) and the
N-bit user code. Accordingly, as described in FIG. 18, a data bit
of `0` will cause the output of the XOR gate 2002 to be an inverted
representation of the N-bit user code, whereas a data bit of `1`
will cause the output of the XOR gate 2002 to be the same bit
sequence as the N-bit user code. As would be well understood by one
of ordinary skill in the art, many variations of this encoding
scheme may be employed. For example, in another embodiment of the
present invention, the N-bit user code is encoded M times for each
bit of data to be transmitted.
[0144] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *