Patent Publication Number: US-6661342-B2

Title: System and method for using impulse radio technology to track the movement of athletes and to enable secure communications between the athletes and their teammates, fans or coaches

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to a system, electronic device and method capable of using impulse radio technology to track the movement of athletes and/or to enable secure communications to take place between the athletes and their teammates, fans or coaches. 
     2. Description of Related Art 
     In a sports environment, it would be desirable to have a system that can track the positions of athletes (e.g., football players, baseball players, soccer players, hockey players and the like) as they move on a field (e.g., football field, baseball diamond, soccer field, hockey rink and the like) and at the same time with the same type of technology enable secure communications to take place between these athletes and their teammates, fans or coaches. Unfortunately, to date there does not appear to be any tracking system that can effectively track the movement of one or more athletes on a field. In addition, to date there does not appear to be any communications system that can effectively enable one or more athletes to communicate in a secure manner with their teammates, fans or coaches. As such, there does not appear to be any conventional system that can track athletes and at the same time enable the athletes to communicate in a secure manner with their teammates, fans or coaches. Accordingly, there is a need for a system, electronic device and method that tracks a moving athlete and/or enables secure communications to occur between an athlete and their teammates, fans or coaches. These needs and other needs are satisfied by the present invention. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention includes a system, electronic device and method that utilizes the positioning capabilities of impulse radio technology to track one or more moving athletes. The movement of these athletes can be displayed on a television, a handheld unit or an Internet site. In addition, the present invention can utilize the communication capabilities of impulse radio technology to enable secure communications to take place between an athlete and their teammates, fans or coaches. The athletes can include, for example, track and field athletes, baseball players, football players, basketball players, soccer players or hockey players. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the present invention may be had by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein: 
     FIG. 1A illustrates a representative Gaussian Monocycle waveform in the time domain; 
     FIG. 1B illustrates the frequency domain amplitude of the Gaussian Monocycle of FIG. 1A; 
     FIG. 1C represents the second derivative of the Gaussian Monocycle of FIG. 1A; 
     FIG. 1D represents the third derivative of the Gaussian Monocycle of FIG. 1A; 
     FIG. 1E represents the Correlator Output vs. the Relative Delay in a real data pulse; 
     FIG. 1F graphically depicts the frequency plot of the Gaussian family of the Gaussian Pulse and the first, second, and third derivative. 
     FIG. 2A illustrates a pulse train comprising pulses as in FIG. 1A; 
     FIG. 2B illustrates the frequency domain amplitude of the waveform of FIG. 2A; 
     FIG. 2C illustrates the pulse train spectrum; 
     FIG. 2D is a plot of the Frequency vs. Energy Plot and points out the coded signal energy spikes; 
     FIG. 3 illustrates the cross-correlation of two codes graphically as Coincidences vs. Time Offset; 
     FIGS. 4A-4E graphically illustrate five modulation techniques to include: Early-Late Modulation; One of Many Modulation; Flip Modulation; Quad Flip Modulation; and Vector Modulation; 
     FIG. 5A illustrates representative signals of an interfering signal, a coded received pulse train and a coded reference pulse train; 
     FIG. 5B depicts a typical geometrical configuration giving rise to multipath received signals; 
     FIG. 5C illustrates exemplary multipath signals in the time domain; 
     FIGS. 5D-5F illustrate a signal plot of various multipath environments. 
     FIG. 5G illustrates the Rayleigh fading curve associated with non-impulse radio transmissions in a multipath environment. 
     FIG. 5H illustrates a plurality of multipaths with a plurality of reflectors from a transmitter to a receiver. 
     FIG. 5I graphically represents signal strength as volts vs. time in a direct path and multipath environment. 
     FIG. 6 illustrates a representative impulse radio transmitter functional diagram; 
     FIG. 7 illustrates a representative impulse radio receiver functional diagram; 
     FIG. 8A illustrates a representative received pulse signal at the input to the correlator; 
     FIG. 8B illustrates a sequence of representative impulse signals in the correlation process; 
     FIG. 8C illustrates the output of the correlator for each of the time offsets of FIG.  8 B. 
     FIG. 9 is a diagram illustrating the basic components of a system in accordance with the present invention. 
     FIG. 10 is a diagram illustrating in greater detail an electronic device of the system shown in FIG.  9 . 
     FIG. 11 is a diagram illustrating the system of FIG. 9 used on a football field. 
     FIG. 12 is a flowchart illustrating the basic steps of a preferred method for tracking an athlete and/or for enabling communications between the athlete and their teammates, fans or coaches in accordance with the present invention. 
     FIG. 13 is a block diagram of an impulse radio positioning network utilizing a synchronized transceiver tracking architecture that can be used in the present invention. 
     FIG. 14 is a block diagram of an impulse radio positioning network utilizing an unsynchronized transceiver tracking architecture that can be used in the present invention. 
     FIG. 15 is a block diagram of an impulse radio positioning network utilizing a synchronized transmitter tracking architecture that can be used in the present invention. 
     FIG. 16 is a block diagram of an impulse radio positioning network utilizing an unsynchronized transmitter tracking architecture that can be used in the present invention. 
     FIG. 17 is a block diagram of an impulse radio positioning network utilizing a synchronized receiver tracking architecture that can be used in the present invention. 
     FIG. 18 is a block diagram of an impulse radio positioning network utilizing an unsynchronized receiver tracking architecture that can be used in the present invention. 
     FIG. 19 is a diagram of an impulse radio positioning network utilizing a mixed mode reference radio tracking architecture that can be used in the present invention. 
     FIG. 20 is a diagram of an impulse radio positioning network utilizing a mixed mode mobile electronic device tracking architecture that can be used in the present invention. 
     FIG. 21 is a diagram of a steerable null antennae architecture capable of being used in an impulse radio positioning network in accordance the present invention. 
     FIG. 22 is a diagram of a specialized difference antennae architecture capable of being used in an impulse radio positioning network in accordance the present invention. 
     FIG. 23 is a diagram of a specialized directional antennae architecture capable of being used in an impulse radio positioning network in accordance with the present invention. 
     FIG. 24 is a diagram of an amplitude sensing architecture capable of being used in an impulse radio positioning network in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention includes a system, electronic device and method capable using impulse radio technology to track a moving athlete and/or enable secure communications to occur between an athlete and their teammates, fans or coaches. This ability to track an athlete as they move around a field and/or enable secure communications to occur between an athlete and their teammates, fans or coaches are significant improvements over the state-of-art. These significant improvements over the state-of-art are attributable, in part, to the use of the emerging and revolutionary ultra wideband technology (UWB) called impulse radio communication technology (also known as impulse radio). 
     Impulse radio has been described in a series of patents, including U.S. Pat. Nos. 4,641,317 (issued Feb. 3, 1987), 4,813,057 (issued Mar. 14, 1989), 4,979,186 (issued Dec. 18, 1990) and 5,363,108 (issued Nov. 8, 1994) to Larry W. Fullerton. A second generation of impulse radio patents includes U.S. Pat. Nos. 5,677,927 (issued Oct. 14, 1997), 5,687,169 (issued Nov. 11, 1997), 5,764,696 (issued Jun. 9, 1998), and 5,832,035 (issued Nov. 3, 1998) to Fullerton et al. 
     Uses of impulse radio systems are described in U.S. patent application Ser. No. 09/332,502, titled, “System and Method for Intrusion Detection using a Time Domain Radar Array” and U.S. patent application Ser. No. 09/332,503, titled, “Wide Area Time Domain Radar Array” both filed on Jun. 14, 1999 both of which are assigned to the assignee of the present invention. The above patent documents are incorporated herein by reference. 
     This section provides an overview of impulse radio technology and relevant aspects of communications theory. It is provided to assist the reader with understanding the present invention and should not be used to limit the scope of the present invention. It should be understood that the terminology ‘impulse radio’ is used primarily for historical convenience and that the terminology can be generally interchanged with the terminology ‘impulse communications system, ultra-wideband system, or ultra-wideband communication systems’. Furthermore, it should be understood that the described impulse radio technology is generally applicable to various other impulse system applications including but not limited to impulse radar systems and impulse positioning systems. Accordingly, the terminology ‘impulse radio’ can be generally interchanged with the terminology ‘impulse transmission system and impulse reception system.’ 
     Impulse radio refers to a radio system based on short, low duty-cycle pulses. An ideal impulse radio waveform is a short Gaussian monocycle. As the name suggests, this waveform attempts to approach one cycle of radio frequency (RF) energy at a desired center frequency. Due to implementation and other spectral limitations, this waveform may be altered significantly in practice for a given application. Many waveforms having very broad, or wide, spectral bandwidth approximate a Gaussian shape to a useful degree. 
     Impulse radio can use many types of modulation, including amplitude modulation, phase modulation, frequency modulation, time-shift modulation (also referred to as pulse-position modulation or pulse-interval modulation) and M-ary versions of these. In this document, the time-shift modulation method is often used as an illustrative example. However, someone skilled in the art will recognize that alternative modulation approaches may, in some instances, be used instead of or in combination with the time-shift modulation approach. 
     In impulse radio communications, inter-pulse spacing may be held constant or may be varied on a pulse-by-pulse basis by information, a code, or both. Generally, conventional spread spectrum systems employ codes to spread the normally narrow band information signal over a relatively wide band of frequencies. A conventional spread spectrum receiver correlates these signals to retrieve the original information signal. In impulse radio communications, codes are not typically used for energy spreading because the monocycle pulses themselves have an inherently wide bandwidth. Codes are more commonly used for channelization, energy smoothing in the frequency domain, resistance to interference, and reducing the interference potential to nearby receivers. Such codes are commonly referred to as time-hopping codes or pseudo-noise (PN) codes since their use typically causes inter-pulse spacing to have a seemingly random nature. PN codes may be generated by techniques other than pseudorandom code generation. Additionally, pulse trains having constant, or uniform, pulse spacing are commonly referred to as uncoded pulse trains. A pulse train with uniform pulse spacing, however, may be described by a code that specifies non-temporal, i.e., non-time related, pulse characteristics. 
     In impulse radio communications utilizing time-shift modulation, information comprising one or more bits of data typically time-position modulates a sequence of pulses. This yields a modulated, coded timing signal that comprises a train of pulses from which a typical impulse radio receiver employing the same code may demodulate and, if necessary, coherently integrate pulses to recover the transmitted information. 
     The impulse radio receiver is typically a direct conversion receiver with a cross correlator front-end that coherently converts an electromagnetic pulse train of monocycle pulses to a baseband signal in a single stage. The baseband signal is the basic information signal for the impulse radio communications system. A subcarrier may also be included with the baseband signal to reduce the effects of amplifier drift and low frequency noise. Typically, the subcarrier alternately reverses modulation according to a known pattern at a rate faster than the data rate. This same pattern is used to reverse the process and restore the original data pattern just before detection. This method permits alternating current (AC) coupling of stages, or equivalent signal processing, to eliminate direct current (DC) drift and errors from the detection process. This method is described in more detail in U.S. Pat. No. 5,677,927 to Fullerton et al. 
     Waveforms 
     Impulse transmission systems are based on short, low duty-cycle pulses. Different pulse waveforms, or pulse types, may be employed to accommodate requirements of various applications. Typical pulse types include a Gaussian pulse, pulse doublet (also referred to as a Gaussian monocycle), pulse triplet, and pulse quadlet as depicted in FIGS. 1A through 1D, respectively. An actual received waveform that closely resembles the theoretical pulse quadlet is shown in FIG. 1E. A pulse type may also be a wavelet set produced by combining two or more pulse waveforms (e.g., a doublet/triplet wavelet set). These different pulse types may be produced by methods described in the patent documents referenced above or by other methods, as persons skilled in the art would understand. 
     For analysis purposes, it is convenient to model pulse waveforms in an ideal manner. For example, the transmitted waveform produced by supplying a step function into an ultra-wideband antenna may be modeled as a Gaussian monocycle. A Gaussian monocycle (normalized to a peak value of 1) may be described by:            f   mono          (   t   )       =       e          (     t   σ     )          e       -     t   2         2        σ   2                             
     where σ is a time scaling parameter, t is time, and e is the natural logarithm base. 
     The power special density of the Gaussian monocycle is shown in FIG. 1F, along with spectrums for the Gaussian pulse, triplet, and quadlet. The corresponding equation for the Gaussian monocycle is:            F   mono          (   f   )       =         (     2      π     )       3   2          σ                 f                   e       -   2            (     πσ                 f     )     2                           
     The center frequency (f c ), or frequency of peak spectral density, of the Gaussian monocycle is:          f   c     =     1     2      πσ                       
     It should be noted that the output of an ultra-wideband antenna is essentially equal to the derivative of its input. Accordingly, since the pulse doublet, pulse triplet, and pulse quadlet are the first, second, and third derivatives of the Gaussian pulse, in an ideal model, an antenna receiving a Gaussian pulse will transmit a Gaussian monocycle and an antenna receiving a Gaussian monocycle will provide a pulse triplet. 
     Pulse Trains 
     Impulse transmission systems may communicate one or more data bits with a single pulse; however, typically each data bit is communicated using a sequence of pulses, known as a pulse train. As described in detail in the following example system, the impulse radio transmitter produces and outputs a train of pulses for each bit of information. FIGS. 2A and 2B are illustrations of the output of a typical 10 megapulses per second (Mpps) system with uncoded, unmodulated pulses, each having a width of 0.5 nanoseconds (ns). FIG. 2A shows a time domain representation of the pulse train output. FIG. 2B illustrates that the result of the pulse train in the frequency domain is to produce a spectrum comprising a set of comb lines spaced at the frequency of the 10 Mpps pulse repetition rate. When the full spectrum is shown, as in FIG. 2C, the envelope of the comb line spectrum corresponds to the curve of the single Gaussian monocycle spectrum in FIG.  1 F. For this simple uncoded case, the power of the pulse train is spread among roughly two hundred comb lines. Each comb line thus has a small fraction of the total power and presents much less of an interference problem to a receiver sharing the band. It can also be observed from FIG. 2A that impulse transmission systems typically have very low average duty cycles, resulting in average power lower than peak power. The duty cycle of the signal in FIG. 2A is if 0.5%, based on a 0.5 ns pulse duration in a 100 ns interval. 
     The signal of an uncoded, unmodulated pulse train may be expressed:          s        (   t   )       =         (     -   1     )     f        a          ∑   j          ω        (       ct   -     jT   f       ,   b     )                           
     where j is the index of a pulse within a pulse train, (−1) f  is polarity (+/−), a is pulse amplitude, b is pulse type, c is pulse width, ω(t,b) is the normalized pulse waveform, and T f  is pulse repetition time. 
     The energy spectrum of a pulse train signal over a frequency bandwidth of interest may be determined by summing the phasors of the pulses at each frequency, using the following equation:          A        (   ω   )       =            ∑     i   =   1     n            e     j                 Δ                 t       n                            
     where A(ω) is the amplitude of the spectral response at a given frequency□□ω□ is the frequency being analyzed (2πf), Δt is the relative time delay of each pulse from the start of time period, and n is the total number of pulses in the pulse train. 
     A pulse train can also be characterized by its autocorrelation and cross-correlation properties. Autocorrelation properties pertain to the number of pulse coincidences (i.e., simultaneous arrival of pulses) that occur when a pulse train is correlated against an instance of itself that is offset in time. Of primary importance is the ratio of the number of pulses in the pulse train to the maximum number of coincidences that occur for any time offset across the period of the pulse train. This ratio is commonly referred to as the main-lobe-to-side-lobe ratio, where the greater the ratio, the easier it is to acquire and field a signal. 
     Cross-correlation properties involve the potential for pulses from two different signals simultaneously arriving, or coinciding, at a receiver. Of primary importance are the maximum and average numbers of pulse coincidences that may occur between two pulse trains. As the number of coincidences increases, the propensity for data errors increases. Accordingly, pulse train cross-correlation properties are used in determining channelization capabilities of impulse transmission systems (i.e., the ability to simultaneously operate within close proximity). 
     Coding 
     Specialized coding techniques can be employed to specify temporal and/or non-temporal pulse characteristics to produce a pulse train having certain spectral and/or correlation properties. For example, by employing a PN code to vary inter-pulse spacing, the energy in the comb lines presented in FIG. 2B can be distributed to other frequencies as depicted in FIG. 2D, thereby decreasing the peak spectral density within a bandwidth of interest. Note that the spectrum retains certain properties that depend on the specific (temporal) PN code used. Spectral properties can be similarly affected by using non-temporal coding (e.g., inverting certain pulses). 
     Coding provides a method of establishing independent communication channels. Specifically, families of codes can be designed such that the number of pulse coincidences between pulse trains produced by any two codes will be minimal. For example, FIG. 3 depicts cross-correlation properties of two codes that have no more than four coincidences for any time offset. Generally, keeping the number of pulse collisions minimal represents a substantial attenuation of the unwanted signal. 
     Coding can also be used to facilitate signal acquisition. For example, coding techniques can be used to produce pulse trains with a desirable main-lobe-to-side-lobe ratio. In addition, coding can be used to reduce acquisition algorithm search space. 
     Coding methods for specifying temporal and non-temporal pulse characteristics are described in commonly owned, co-pending applications titled “A Method and Apparatus for Positioning Pulses in Time,” application Ser. No. 09/592,249, and “A Method for Specifying Non-Temporal Pulse Characteristics,” application Ser. No. 09/592,250, both filed Jun. 12, 2000, and both of which are incorporated herein by reference. 
     Typically, a code consists of a number of code elements having integer or floating-point values. A code element value may specify a single pulse characteristic or may be subdivided into multiple components, each specifying a different pulse characteristic. Code element or code component values typically map to a pulse characteristic value layout that may be fixed or non-fixed and may involve value ranges, discrete values, or a combination of value ranges and discrete values. A value range layout specifies a range of values that is divided into components that are each subdivided into subcomponents, which can be further subdivided, as desired. In contrast, a discrete value layout involves uniformly or non-uniformly distributed discrete values. A non-fixed layout (also referred to as a delta layout) involves delta values relative to some reference value. Fixed and non-fixed layouts, and approaches for mapping code element/component values, are described in co-owned, co-pending applications, titled “Method for Specifying Pulse Characteristics using Codes,” application Ser. No. 09/592,290 and “A Method and Apparatus for Mapping Pulses to a Non-Fixed Layout,” application Ser. No. 09/591,691, both filed on Jun. 12, 2000, both of which are incorporated herein by reference. 
     A fixed or non-fixed characteristic value layout may include a non-allowable region within which a pulse characteristic value is disallowed. A method for specifying non-allowable regions is described in co-owned, co-pending application titled “A Method for Specifying Non-Allowable Pulse Characteristics,” application Ser. No. 09/592,289, filed Jun. 12, 2000, and incorporated herein by reference. A related method that conditionally positions pulses depending on whether code elements map to non-allowable regions is described in co-owned, co-pending application, titled “A Method and Apparatus for Positioning Pulses Using a Layout having Non-Allowable Regions,” application Ser. No. 09/592,248 filed Jun. 12, 2000, and incorporated herein by reference. 
     The signal of a coded pulse train can be generally expressed by:            s   tr     (   k   )       *     (   t   )       =       ∑   j              (     -   1     )       f   j     (   k   )              a   j     (   k   )            ω        (           c   j     (   k   )          t     -     T   j     (   k   )         ,     b   j     (   k   )         )                           
     where k is the index of a transmitter, j is the index of a pulse within its pulse train, (−1)f j   (k) , a j   (k) , b j   (k) , c j    (k) , and ω(t,b j   (k) ) are the coded polarity, pulse amplitude, pulse type, pulse width, and normalized pulse waveform of the jth pulse of the kth transmitter, and T j   (k)  is the coded time shift of the jth pulse of the kth transmitter. Note: When a given non-temporal characteristic does not vary (i.e., remains constant for all pulses), it becomes a constant in front of the summation sign. 
     Various numerical code generation methods can be employed to produce codes having certain correlation and spectral properties. Such codes typically fall into one of two categories: designed codes and pseudorandom codes. A designed code may be generated using a quadratic congruential, hyperbolic congruential, linear congruential, Costas array, or other such numerical code generation technique designed to generate codes having certain correlation properties. A pseudorandom code may be generated using a computer&#39;s random number generator, binary shift-register(s) mapped to binary words, a chaotic code generation scheme, or the like. Such ‘random-like’ codes are attractive for certain applications since they tend to spread spectral energy over multiple frequencies while having ‘good enough’ correlation properties, whereas designed codes may have superior correlation properties but possess less suitable spectral properties. Detailed descriptions of numerical code generation techniques are included in a co-owned, co-pending patent application titled “A Method and Apparatus for Positioning Pulses in Time,” application Ser. No. 09/592,248, filed Jun. 12, 2000, and incorporated herein by reference. 
     It may be necessary to apply predefined criteria to determine whether a generated code, code family, or a subset of a code is acceptable for use with a given UWB application. Criteria may include correlation properties, spectral properties, code length, non-allowable regions, number of code family members, or other pulse characteristics. A method for applying predefined criteria to codes is described in co-owned, co-pending application, titled “A Method and Apparatus for Specifying Pulse Characteristics using a Code that Satisfies Predefined Criteria,” application Ser. No. 09/592,288, filed Jun. 12, 2000, and incorporated herein by reference. 
     In some applications, it may be desirable to employ a combination of codes. Codes may be combined sequentially, nested, or sequentially nested, and code combinations may be repeated. Sequential code combinations typically involve switching from one code to the next after the occurrence of some event and may also be used to support multicast communications. Nested code combinations may be employed to produce pulse trains having desirable correlation and spectral properties. For example, a designed code may be used to specify value range components within a layout and a nested pseudorandom code may be used to randomly position pulses within the value range components. With this approach, correlation properties of the designed code are maintained since the pulse positions specified by the nested code reside within the value range components specified by the designed code, while the random positioning of the pulses within the components results in particular spectral properties. A method for applying code combinations is described in co-owned, co-pending application, titled “Method and Apparatus for Applying Codes Having Pre-Defined Properties,” application Ser. No. 09/591,690, filed Jun. 12, 2000, and incorporated herein by reference. 
     Modulation 
     Various aspects of a pulse waveform may be modulated to convey information and to further minimize structure in the resulting spectrum. Amplitude modulation, phase modulation, frequency modulation, time-shift modulation and M-ary versions of these were proposed in U.S. Pat. No. 5,677,927 to Fullerton et al., previously incorporated by reference. Time-shift modulation can be described as shifting the position of a pulse either forward or backward in time relative to a nominal coded (or uncoded) time position in response to an information signal. Thus, each pulse in a train of pulses is typically delayed a different amount from its respective time base clock position by an individual code delay amount plus a modulation time shift. This modulation time shift is normally very small relative to the code shift. In a 10 Mpps system with a center frequency of 2 GHz, for example, the code may command pulse position variations over a range of 100 ns, whereas, the information modulation may shift the pulse position by 150 ps. This two-state ‘early-late’ form of time shift modulation is depicted in FIG.  4 A. 
     A pulse train with conventional ‘early-late’ time-shift modulation can be expressed:            s   tr     (   k   )            (   t   )       =       ∑   j              (     -   1     )       f   j     (   k   )              a   j     (   k   )            ω        (           c   j     (   k   )          t     -     T   j     (   k   )       -     δ                   d     [     j   /     N   s       ]       (   k   )           ,     b   j     (   k   )         )                           
     where k is the index of a transmitter, j is the index of a pulse within its pulse train, (−1)f j   (k) , a j   (k) , b j   (k) , c j   (k) , and ω(t,b j   (k) ) are the coded polarity, pulse amplitude, pulse type, pulse width, and normalized pulse waveform of the jth pulse of the kth transmitter, T j   (k)  is the coded time shift of the jth pulse of the kth transmitter, d is the time shift added when the transmitted symbol is 1 (instead of 0), d (k)  is the data (i.e., 0 or 1) transmitted by the kth transmitter, and N s  is the number of pulses per symbol (e.g., bit). Similar expressions can be derived to accommodate other proposed forms of modulation. 
     An alternative form of time-shift modulation can be described as One-of-Many Position Modulation (OMPM). The OMPM approach, shown in FIG. 4B, involves shifting a pulse to one of N possible modulation positions about a nominal coded (or uncoded) time position in response to an information signal, where N represents the number of possible states. For example, if N were four (4), two data bits of information could be conveyed. For further details regarding OMPM, see “Apparatus, System and Method for One-of-Many Position Modulation in an Impulse Radio Communication System,” U.S. patent application Ser. No. 09/875,290, filed Jun. 7, 2001, assigned to the assignee of the present invention, and incorporated herein by reference. 
     An impulse radio communications system can employ flip modulation techniques to convey information. The simplest flip modulation technique involves transmission of a pulse or an inverted (or flipped) pulse to represent a data bit of information, as depicted in FIG.  4 C. Flip modulation techniques may also be combined with time-shift modulation techniques to create two, four, or more different data states. One such flip with shift modulation technique is referred to as Quadrature Flip Time Modulation (QFTM). The QFTM approach is illustrated in FIG.  4 D. Flip modulation techniques are further described in patent application titled “Apparatus, System and Method for Flip Modulation in an Impulse Radio Communication System,” application Ser. No. 09/537,692, filed Mar. 29, 2000, assigned to the assignee of the present invention, and incorporated herein by reference. 
     Vector modulation techniques may also be used to convey information. Vector modulation includes the steps of generating and transmitting a series of time-modulated pulses, each pulse delayed by one of at least four pre-determined time delay periods and representative of at least two data bits of information, and receiving and demodulating the series of time-modulated pulses to estimate the data bits associated with each pulse. Vector modulation is shown in FIG.  4 E. Vector modulation techniques are further described in patent application titled “Vector Modulation System and Method for Wideband Impulse Radio Communications,” application Ser. No. 09/169,765, filed Dec. 9, 1999, assigned to the assignee of the present invention, and incorporated herein by reference. 
     Reception and Demodulation 
     Impulse radio systems operating within close proximity to each other may cause mutual interference. While coding minimizes mutual interference, the probability of pulse collisions increases as the number of coexisting impulse radio systems rises. Additionally, various other signals may be present that cause interference. Impulse radios can operate in the presence of mutual interference and other interfering signals, in part because they do not depend on receiving every transmitted pulse. Impulse radio receivers perform a correlating, synchronous receiving function (at the RF level) that uses statistical sampling and combining, or integration, of many pulses to recover transmitted information. Typically, 1 to 1000 or more pulses are integrated to yield a single data bit thus diminishing the impact of individual pulse collisions, where the number of pulses that must be integrated to successfully recover transmitted information depends on a number of variables including pulse rate, bit rate, range and interference levels. 
     Interference Resistance 
     Besides providing channelization and energy smoothing, coding makes impulse radios highly resistant to interference by enabling discrimination between intended impulse transmissions and interfering transmissions. This property is desirable since impulse radio systems must share the energy spectrum with conventional radio systems and with other impulse radio systems. FIG. 5A illustrates the result of a narrow band sinusoidal interference signal  502  overlaying an impulse radio signal  504 . At the impulse radio receiver, the input to the cross correlation would include the narrow band signal  502  and the received ultrawide-band impulse radio signal  504 . The input is sampled by the cross correlator using a template signal  506  positioned in accordance with a code. Without coding, the cross correlation would sample the interfering signal  502  with such regularity that the interfering signals could cause interference to the impulse radio receiver. However, when the transmitted impulse signal is coded and the impulse radio receiver template signal  506  is synchronized using the identical code, the receiver samples the interfering signals non-uniformly. The samples from the interfering signal add incoherently, increasing roughly according to the square root of the number of samples integrated. The impulse radio signal samples, however, add coherently, increasing directly according to the number of samples integrated. Thus, integrating over many pulses overcomes the impact of interference. 
     Processing Gain 
     Impulse radio systems have exceptional processing gain due to their wide spreading bandwidth. For typical spread spectrum systems, the definition of processing gain, which quantifies the decrease in channel interference when wide-band communications are used, is the ratio of the bandwidth of the channel to the bit rate of the information signal. For example, a direct sequence spread spectrum system with a 10 KHz information bandwidth and a 10 MHz channel bandwidth yields a processing gain of 1000, or 30 dB. However, far greater processing gains are achieved by impulse radio systems, where the same 10 KHz information bandwidth is spread across a much greater 2 GHz channel bandwidth, resulting in a theoretical processing gain of 200,000, or 53 dB. 
     Capacity 
     It can be shown theoretically, using signal-to-noise arguments, that thousands of simultaneous channels are available to an impulse radio system as a result of its exceptional processing gain. 
     The average output signal-to-noise ratio of the impulse radio may be calculated for randomly selected time-hopping codes as a function of the number of active users, N u , as:            SNR   out          (     N   u     )       =         (       N   s          A   1          m   p       )     2         σ   rec   2     +       N   s          σ   a   2            ∑     k   =   2       N   u            A   k   2                             
     where N s  is the number of pulses integrated per bit of information, A k  models the attenuation of transmitter k&#39;s signal over the propagation path to the receiver, and σ rec   2  is the variance of the receiver noise component at the pulse train integrator output. The monocycle waveform-dependent parameters m p  and σ a   2  are given by          m   p     =       ∫     -   ∞     ∞              ω        (   t   )            [       ω        (   t   )       -     ω        (     t   -   δ     )         ]               t                         
     and            σ   a   2     =       T   f     -   1              ∫     -   ∞     ∞              [       ∫     -   ∞     ∞            ω        (     t   -   s     )            υ        (   t   )               t         ]     2             s             ,                   
     where ?(t) is the monocycle waveform, ?(t)=?(t)−?(t−d) is the template signal waveform, d is the time shift between the monocycle waveform and the template signal waveform, T f  is the pulse repetition time, and s is signal. 
     Multipath and Propagation 
     One of the advantages of impulse radio is its resistance to multipath fading effects. Conventional narrow band systems are subject to multipath through the Rayleigh fading process, where the signals from many delayed reflections combine at the receiver antenna according to their seemingly random relative phases resulting in possible summation or possible cancellation, depending on the specific propagation to a given location. Multipath fading effects are most adverse where a direct path signal is weak relative to multipath signals, which represents the majority of the potential coverage area of a radio system. In a mobile system, received signal strength fluctuates due to the changing mix of multipath signals that vary as its position varies relative to fixed transmitters, mobile transmitters and signal-reflecting surfaces in the environment. 
     Impulse radios, however, can be substantially resistant to multipath effects. Impulses arriving from delayed multipath reflections typically arrive outside of the correlation time and, thus, may be ignored. This process is described in detail with reference to FIGS. 5B and 5C. FIG. 5B illustrates a typical multipath situation, such as in a building, where there are many reflectors  504 B,  505 B. In this figure, a transmitter  506 B transmits a signal that propagates along three paths, the direct path  501 B, path  1   502 B, and path 2   503 B, to a receiver  508 B, where the multiple reflected signals are combined at the antenna. The direct path  501 B, representing the straight-line distance between the transmitter and receiver, is the shortest. Path  1   502 B represents a multipath reflection with a distance very close to that of the direct path. Path  2   503 B represents a multipath reflection with a much longer distance. Also shown are elliptical (or, in space, ellipsoidal) traces that represent other possible locations for reflectors that would produce paths having the same distance and thus the same time delay. 
     FIG. 5C illustrates the received composite pulse waveform resulting from the three propagation paths  501 B,  502 B, and  503 B shown in FIG.  5 B. In this figure, the direct path signal  501 B is shown as the first pulse signal received. The path  1  and path  2  signals  502 B,  503 B comprise the remaining multipath signals, or multipath response, as illustrated. The direct path signal is the reference signal and represents the shortest propagation time. The path  1  signal is delayed slightly and overlaps and enhances the signal strength at this delay value. The path  2  signal is delayed sufficiently that the waveform is completely separated from the direct path signal. Note that the reflected waves are reversed in polarity. If the correlator template signal is positioned such that it will sample the direct path signal, the path  2  signal will not be sampled and thus will produce no response. However, it can be seen that the path  1  signal has an effect on the reception of the direct path signal since a portion of it would also be sampled by the template signal. Generally, multipath signals delayed less than one quarter wave (one quarter wave is about 1.5 inches, or 3.5 cm at 2 GHz center frequency) may attenuate the direct path signal. This region is equivalent to the first Fresnel zone in narrow band systems. Impulse radio, however, has no further nulls in the higher Fresnel zones. This ability to avoid the highly variable attenuation from multipath gives impulse radio significant performance advantages. 
     FIGS. 5D,  5 E, and  5 F represent the received signal from a TM-UWB transmitter in three different multipath environments. These figures are approximations of typical signal plots. FIG. 5D illustrates the received signal in a very low multipath environment. This may occur in a building where the receiver antenna is in the middle of a room and is a relatively short, distance, for example, one meter, from the transmitter. This may also represent signals received from a larger distance, such as 100 meters, in an open field where there are no objects to produce reflections. In this situation, the predominant pulse is the first received pulse and the multipath reflections are too weak to be significant. FIG. 5E illustrates an intermediate multipath environment. This approximates the response from one room to the next in a building. The amplitude of the direct path signal is less than in FIG.  5 D and several reflected signals are of significant amplitude. FIG. 5F approximates the response in a severe multipath environment such as propagation through many rooms, from corner to corner in a building, within a metal cargo hold of a ship, within a metal truck trailer, or within an intermodal shipping container. In this scenario, the main path signal is weaker than in FIG.  5 E. In this situation, the direct path signal power is small relative to the total signal power from the reflections. 
     An impulse radio receiver can receive the signal and demodulate the information using either the direct path signal or any multipath signal peak having sufficient signal-to-noise ratio. Thus, the impulse radio receiver can select the strongest response from among the many arriving signals. In order for the multipath signals to cancel and produce a null at a given location, dozens of reflections would have to be cancelled simultaneously and precisely while blocking the direct path, which is a highly unlikely scenario. This time separation of mulitipath signals together with time resolution and selection by the receiver permit a type of time diversity that virtually eliminates cancellation of the signal. In a multiple correlator rake receiver, performance is further improved by collecting the signal power from multiple signal peaks for additional signal-to-noise performance. 
     Where the system of FIG. 5B is a narrow band system and the delays are small relative to the data bit time, the received signal is a sum of a large number of sine waves of random amplitude and phase. In the idealized limit, the resulting envelope amplitude has been shown to follow a Rayleigh probability distribution as follows:          p        (   r   )       =       r     σ   2            exp        (       -     r   2         2        σ   2         )                         
     where r is the envelope amplitude of the combined multipath signals, and s(2)½is the RMS power of the combined multipath signals. The Rayleigh distribution curve in FIG. 5G shows that 10% of the time, the signal is more than 10 dB attenuated. This suggests that 10 dB fade margin is needed to provide 90% link availability. Values of fade margin from 10 to 40 dB have been suggested for various narrow band systems, depending on the required reliability. This characteristic has been the subject of much research and can be partially improved by such techniques as antenna and frequency diversity, but these techniques result in additional complexity and cost. 
     In a high multipath environment such as inside homes, offices, warehouses, automobiles, trailers, shipping containers, or outside in an urban canyon or other situations where the propagation is such that the received signal is primarily scattered energy, impulse radio systems can avoid the Rayleigh fading mechanism that limits performance of narrow band systems, as illustrated in FIGS. 5H and 5I. FIG. 5H depicts an impulse radio system in a high multipath environment  500 H consisting of a transmitter  506 H and a receiver  508 H. A transmitted signal follows a direct path  501 H and reflects off reflectors  503 H via multiple paths  502 H. FIG. 5I illustrates the combined signal received by the receiver  508 H over time with the vertical axis being signal strength in volts and the horizontal axis representing time in nanoseconds. The direct path  501 H results in the direct path signal  502 I while the multiple paths  502 H result in multipath signals  504 I. In the same manner described earlier for FIGS. 5B and 5C, the direct path signal  502 I is sampled, while the multipath signals  504 I are not, resulting in Rayleigh fading avoidance. 
     Distance Measurement and Positioning 
     Impulse systems can measure distances to relatively fine resolution because of the absence of ambiguous cycles in the received waveform. Narrow band systems, on the other hand, are limited to the modulation envelope and cannot easily distinguish precisely which RF cycle is associated with each data bit because the cycle-to-cycle amplitude differences are so small they are masked by link or system noise. Since an impulse radio waveform has no multi-cycle ambiguity, it is possible to determine waveform position to less than a wavelength, potentially down to the noise floor of the system. This time position measurement can be used to measure propagation delay to determine link distance to a high degree of precision. For example, 30 ps of time transfer resolution corresponds to approximately centimeter distance resolution. See, for example, U.S. Pat. No. 6,133,876, issued Oct. 17, 2000, titled “System and Method for Position Determination by Impulse Radio,” and U.S. Pat. No. 6,111,536, issued Aug. 29, 2000, titled “System and Method for Distance Measurement by Inphase and Quadrature Signals in a Radio System,” both of which are incorporated herein by reference. 
     In addition to the methods articulated above, impulse radio technology along with Time Division Multiple Access algorithms and Time Domain packet radios can achieve geo-positioning capabilities in a radio network. This geo-positioning method is described in co-owned, co-pending application titled “System and Method for Person or Object Position Location Utilizing Impulse Radio,” application Ser. No. 09/456,409, filed Dec. 8, 1999, and incorporated herein by reference. 
     Power Control 
     Power control systems comprise a first transceiver that transmits an impulse radio signal to a second transceiver. A power control update is calculated according to a performance measurement of the signal received at the second transceiver. The transmitter power of either transceiver, depending on the particular setup, is adjusted according to the power control update. Various performance measurements are employed to calculate a power control update, including bit error rate, signal-to-noise ratio, and received signal strength, used alone or in combination. Interference is thereby reduced, which may improve performance where multiple impulse radios are operating in close proximity and their transmissions interfere with one another. Reducing the transmitter power of each radio to a level that produces satisfactory reception increases the total number of radios that can operate in an area without saturation. Reducing transmitter power also increases transceiver efficiency. 
     For greater elaboration of impulse radio power control, see patent application titled “System and Method for Impulse Radio Power Control,” application Ser. No. 09/332,501, filed Jun. 14, 1999, assigned to the assignee of the present invention, and incorporated herein by reference. 
     Mitigating Effects of Interference 
     A method for mitigating interference in impulse radio systems comprises the steps of conveying the message in packets, repeating conveyance of selected packets to make up a repeat package, and conveying the repeat package a plurality of times at a repeat period greater than twice the period of occurrence of the interference. The communication may convey a message from a proximate transmitter to a distal receiver, and receive a message by a proximate receiver from a distal transmitter. In such a system, the method comprises the steps of providing interference indications by the distal receiver to the proximate transmitter, using the interference indications to determine predicted noise periods, and operating the proximate transmitter to convey the message according to at least one of the following: (1) avoiding conveying the message during noise periods, (2) conveying the message at a higher power during noise periods, (3) increasing error detection coding in the message during noise periods, (4) re-transmitting the message following noise periods, (5) avoiding conveying the message when interference is greater than a first strength, (6) conveying the message at a higher power when the interference is greater than a second strength, (7) increasing error detection coding in the message when the interference is greater than a third strength, and (8) re-transmitting a portion of the message after interference has subsided to less than a predetermined strength. 
     For greater elaboration of mitigating interference in impulse radio systems, see the patent application titled “Method for Mitigating Effects of Interference in Impulse Radio Communication,” application Ser. No. 09/587,033, filed Jun. 02, 1999, assigned to the assignee of the present invention, and if incorporated herein by reference. 
     Moderating Interference in Equipment Control Applications 
     Yet another improvement to impulse radio includes moderating interference with impulse radio wireless control of an appliance. The control is affected by a controller remote from the appliance which transmits impulse radio digital control signals to the appliance. The control signals have a transmission power and a data rate. The method comprises the steps of establishing a maximum acceptable noise value for a parameter relating to interfering signals and a frequency range for measuring the interfering signals, measuring the parameter for the interference signals within the frequency range, and effecting an alteration of transmission of the control signals when the parameter exceeds the maximum acceptable noise value. 
     For greater elaboration of moderating interference while effecting impulse radio wireless control of equipment, see patent application titled “Method and Apparatus for Moderating Interference While Effecting Impulse Radio Wireless Control of Equipment,” application Ser. No. 09/586,163, filed Jun. 2, 1999, and assigned to the assignee of the present invention, and incorporated herein by reference. 
     Exemplary Transceiver Implementation 
     Transmitter 
     An exemplary embodiment of an impulse radio transmitter  602  of an impulse radio communication system having an optional subcarrier channel will now be described with reference to FIG.  6 . 
     The transmitter  602  comprises a time base  604  that generates a periodic timing signal  606 . The time base  604  typically comprises a voltage controlled oscillator (VCO), or the like, having a high timing accuracy and low jitter, on the order of picoseconds (ps). The control voltage to adjust the VCO center frequency is set at calibration to the desired center frequency used to define the transmitter&#39;s nominal pulse repetition rate. The periodic timing signal  606  is supplied to a precision timing generator  608 . 
     The precision timing generator  608  supplies synchronizing signals  610  to the code source  612  and utilizes the code source output  614 , together with an optional, internally generated subcarrier signal, and an information signal  616 , to generate a modulated, coded timing signal  618 . 
     An information source  620  supplies the information signal  616  to the precision timing generator  608 . The information signal  616  can be any type of intelligence, including digital bits representing voice, data, imagery, or the like, analog signals, or complex signals. 
     A pulse generator  622  uses the modulated, coded timing signal  618  as a trigger signal to generate output pulses. The output pulses are provided to a transmit antenna  624  via a transmission line  626  coupled thereto. The output pulses are converted into propagating electromagnetic pulses by the transmit antenna  624 . The electromagnetic pulses are called the emitted signal, and propagate to an impulse radio receiver  702 , such as shown in FIG. 7, through a propagation medium. In a preferred embodiment, the emitted signal is wide-band or ultrawide-band, approaching a monocycle pulse as in FIG.  1 B. However, the emitted signal may be spectrally modified by filtering of the pulses, which may cause them to have more zero crossings (more cycles) in the time domain, requiring the radio receiver to use a similar waveform as the template signal for efficient conversion. 
     Receiver 
     An exemplary embodiment of an impulse radio receiver (hereinafter called the receiver) for the impulse radio communication system is now described with reference to FIG.  7 . 
     The receiver  702  comprises a receive antenna  704  for receiving a propagated impulse radio signal  706 . A received signal  708  is input to a cross correlator or sampler  710 , via a receiver transmission line, coupled to the receive antenna  704 . The cross correlation  710  produces a baseband output  712 . 
     The receiver  702  also includes a precision timing generator  714 , which receives a periodic timing signal  716  from a receiver time base  718 . This time base  718  may be adjustable and controllable in time, frequency, or phase, as required by the lock loop in order to lock on the received signal  708 . The precision timing generator  714  provides synchronizing signals  720  to the code source  722  and receives a code control signal  724  from the code source  722 . The precision timing generator  714  utilizes the periodic timing signal  716  and code control signal  724  to produce a coded timing signal  726 . The template generator  728  is triggered by this coded timing signal  726  and produces a train of template signal pulses  730  ideally having waveforms substantially equivalent to each pulse of the received signal  708 . The code for receiving a given signal is the same code utilized by the originating transmitter to generate the propagated signal. Thus, the timing of the template pulse train matches the timing of the received signal pulse train, allowing the received signal  708  to be synchronously sampled in the correlator  710 . The correlator  710  preferably comprises a multiplier followed by a short term integrator to sum the multiplier product over the pulse interval. 
     The output of the correlator  710  is coupled to a subcarrier demodulator  732 , which demodulates the subcarrier information signal from the optional subcarrier. The purpose of the optional subcarrier process, when used, is to move the information signal away from DC (zero frequency) to improve immunity to low frequency noise and offsets. The output of the subcarrier demodulator is then filtered or integrated in the pulse summation stage  734 . A digital system embodiment is shown in FIG.  7 . In this digital system, a sample and hold  736  samples the output  735  of the pulse summation stage  734  synchronously with the completion of the summation of a digital bit or symbol. The output of sample and hold  736  is then compared with a nominal zero (or reference) signal output in a detector stage  738  to provide an output signal  739  representing the digital state of the output voltage of sample and hold  736 . 
     The baseband signal  712  is also input to a lowpass filter  742  (also referred to as lock loop filter  742 ). A control loop comprising the lowpass filter  742 , time base  718 , precision timing generator  714 , template generator  728 , and correlator  710  is used to generate an error signal  744 . The error signal  744  provides adjustments to the adjustable time base  718  to position in time the periodic timing signal  726  in relation to the position of the received signal  708 . 
     In a transceiver embodiment, substantial economy can be achieved by sharing part or all of several of the functions of the transmitter  602  and receiver  702 . Some of these include the time base  718 , precision timing generator  714 , code source  722 , antenna  704 , and the like. 
     FIGS. 8A-8C illustrate the cross correlation process and the correlation function. FIG. 8A shows the waveform of a template signal. FIG. 8B shows the waveform of a received impulse radio signal at a set of several possible time offsets. FIG. 8C represents the output of the cross correlator for each of the time offsets of FIG.  8 B. For any given pulse received, there is a corresponding point that is applicable on this graph. This is the point corresponding to the time offset of the template signal used to receive that pulse. Further examples and details of precision timing can be found described in U.S. Pat. No. 5,677,927, and commonly owned co-pending application application Ser. No. 09/146,524, filed Sep. 3, 1998, titled “Precision Timing Generator System and Method,” both of which are incorporated herein by reference. 
     Because of the unique nature of impulse radio receivers, several modifications have been recently made to enhance system capabilities. Modifications include the utilization of multiple correlators to measure the impulse response of a channel to the maximum communications range of the system and to capture information on data symbol statistics. Further, multiple correlators enable rake pulse correlation techniques, more efficient acquisition and tracking implementations, various modulation schemes, and collection of time-calibrated pictures of received waveforms. For greater elaboration of multiple correlator techniques, see patent application titled “System and Method of using Multiple Correlator Receivers in an Impulse Radio System”, application Ser. No. 09/537,264, filed Mar. 29, 2000, assigned to the assignee of the present invention, and incorporated herein by reference. 
     Methods to improve the speed at which a receiver can acquire and lock onto an incoming impulse radio signal have been developed. In one approach, a receiver includes an adjustable time base to output a sliding periodic timing signal having an adjustable repetition rate and a decode timing modulator to output a decode signal in response to the periodic timing signal. The impulse radio signal is cross-correlated with the decode signal to output a baseband signal. The receiver integrates T samples of the baseband signal and a threshold detector uses the integration results to detect channel coincidence. A receiver controller stops sliding the time base when channel coincidence is detected. A counter and extra count logic, coupled to the controller, are configured to increment or decrement the address counter by one or more extra counts after each T pulses is reached in order to shift the code modulo for proper phase alignment of the periodic timing signal and the received impulse radio signal. This method is described in more detail in U.S. Pat. No. 5,832,035 to Fullerton, incorporated herein by reference. 
     In another approach, a receiver obtains a template pulse train and a received impulse radio signal. The receiver compares the template pulse train and the received impulse radio signal. The system performs a threshold check on the comparison result. If the comparison result passes the threshold check, the system locks on the received impulse radio signal. The system may also perform a quick check, a synchronization check, and/or a command check of the impulse radio signal. For greater elaboration of this approach, see the patent application titled “Method and System for Fast Acquisition of Ultra Wideband Signals,” application Ser. No. 09/538,292, filed Mar. 29, 2000, assigned to the assignee of the present invention, and incorporated herein by reference. 
     A receiver has been developed that includes a baseband signal converter device and combines multiple converter circuits and an RF amplifier in a single integrated circuit package. For greater elaboration of this receiver, see the patent application titled “Baseband Signal Converter for a Wideband Impulse Radio Receiver,” application Ser. No. 09/356,384, filed Jul. 16, 1999, assigned to the assignee of the present invention, and incorporated herein by reference. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 9-24, there are disclosed a system  900 , an electronic device  910  and a method  1200  in accordance with the present invention. Although the present invention is described as being used on a football field, it should be understood that the present invention can be used in many different sporting venues including, for example, a baseball field, soccer field, hockey rink, basketball court or any sports environment in which people train and compete. Accordingly, the system  900 , electronic device  910  and method  1200  should not be construed in a limited manner. 
     Referring to FIG. 9, there is a diagram illustrating the basic components of the system  900  in accordance with the present invention. Essentially, the system  900  includes an electronic device  910  (only one shown) and a central station  930 . The electronic device  910  is attached to any desired location on an athlete  920  which can be one of many such athletes playing on a field  1100  (see FIG.  11 ). The electronic device  910  is capable of transmitting and receiving impulse radio signals  915  to and from the central station  930 . In particular, the impulse radio signals  915  convey information using a known pseudorandom sequence of pulses that look like a series of Gaussian waveforms (see FIGS.  1 - 3 ). The information conveyed in the impulse radio signals enables people (e.g., coaches  940   a,  broadcasters  940   b,  fans  940   c ) to track the position of the athlete  920  as he/she moves around the field  1100  and/or enables secure communications to occur between the athlete  920  and their teammates, fans or coaches. For clarity, only the broadcaster  940   b  and one athlete  920  are shown in FIG.  9 . To accomplish these tasks, both the electronic device  910  and central station  930  can incorporate one chip that enables the revolutionary and highly scalable communication capabilities and position capabilities of impulse radio technology. Essentially, the electronic device  910 , other electronic devices  910  and the central station  930  can use impulse radio signals  915  to transmit and receive information to and from one another in places and situations not possible with traditional tracking and communication systems. 
     Traditional tracking systems generally use the well known Global Positioning System (GPS) based technology to determine the position of a person or object. Unfortunately, GPS based technology is not suitable for tracking athletes  920  within an enclosed arena because of the difficulty a GPS unit has in communicating with GPS satellites through the roof, outer walls and inner walls of the arena. Even if the arena is not enclosed, GPS based technology is not able to meet the needs of the present invention due to the physical constraints and power requirements of a GPS unit that must be carried by the athletes  920 . For instance, the use of GPS based technology would require that each athlete  920  carry a relatively large GPS unit that is made up of GPS electronics, memory, logic, a R/F transceiver and a battery. As such, the GPS unit is not small enough to be conveniently carried by the athlete  920 . 
     Another problem with the GPS unit is that it provides a rough approximation of the position of the athlete  920  on a field  1100 . The approximation of the position is usually rough due to selective authority (now disabled) and atmospheric alterations. Selective authority was a government-controlled way of making GPS based technology inaccurate for defense purposes. GPS units can attempt to mitigate selective authority inaccuracies and other inaccuracies by utilizing a correction signal received from a base station on or near the field  1100  or from another satellite. However, GPS units that receive this correction signal still generate an inaccurate measurement that may be off five or more meters. To date there is nothing that can compensate for atmospheric alterations which are an inherent problem with GPS based technology. Moreover, GPS based technology suffers from a highly unreliable infrastructure because the GPS unit requires that at least two separate signals from two separate satellites be received at all times to remain operable. However, impulse radio technology enables very precise position calculations having an accuracy of less than +/−2 centimeters to occur in less than a second, which is a marked improvement over the traditional GPS based technology. 
     Traditional communication systems used to transmit and receive radio signals between a traditional central station and traditional electronic devices within a sports arena often suffer from the adverse affects of “dead zones” and “multipath interference”. Dead zones in a sports arena make it difficult for a central station to enable communications with an electronic device attached to an athlete using standard radio signals. For instance, the standard radio signals sent from the standard radio transceiver attached to the central station may not be able to penetrate a certain wall or floor within the building and as such may not reach the standard radio transceiver attached to the athlete. This is especially true when the athlete moves to different locations within the sports arena. Fortunately in the present invention, the impulse radio signals  915  transmitted between the electronic device  910  and central station  930  are located very close to DC which makes the attenuation due to walls, stands and roof minimal when compared to standard radio signals. 
     In addition, “multipath interference” which is very problematic within the closed structure of a sports arena can be caused by the interference of a standard radio signal that has reached either the traditional electronic device or traditional central station by two or more paths. Essentially, a standard radio receiver attached to a athlete may not be able to demodulate a radio signal because the originally transmitted radio signal effectively cancels itself out by bouncing of the walls, roof (if any) and stands of the sports arena before reaching the athlete and vice versa. The present invention is not affected by “multipath interference” because the impulses of the impulse radio signals  915  delayed by multipath reflections typically arrive outside a correlation (or demodulation) period of the receiving impulse radio unit. 
     Moreover, traditional central stations use either standard radio or infrared electromagnetic waves to transfer data to and from a traditional electronic device. However, these traditional communication means impose undesirable limits on range, data rate and communication quality. For instance, traditional wireless communication technologies suffer from the following undesirable characteristics: 
     Have limited spectral bandwidth. 
     Have shared broadcast medium. 
     Are unprotected from outside signals. 
     In contrast, the use of impulse radio technology in the present invention provides many advantages over traditional wireless communication technologies including, for example, the following: 
     Ultra-short duration pulses which yield ultrawide bandwidth signals. 
     Extremely low power spectral densities. 
     Excellent immunity to interference from other radio systems. 
     Consumes substantially less power than conventional radios. 
     Capable of high bandwidth and multi-channel performance. 
     Referring to FIG. 10, there is a diagram illustrating in greater detail the electronic device  910  in accordance with the present invention. As illustrated in FIG. 10, the electronic device  910  incorporates a first impulse radio unit  1002 . And, as illustrated in FIG. 9, the central station  930  incorporates a second impulse radio unit  1004 . Each impulse radio unit  1002  and  1004  can be configured as a transceiver and include a receiving impulse radio unit  602  and a transmitting impulse radio unit  702  (see FIGS.  6  and  7 ). In the alternative, the impulse radio units  1002  and  1004  can be configured as either a receiver or transmitter depending on the functional requirements of the central station  930  and electronic device  910 . For instance, the central station may only need to download information and, as such, the first impulse radio unit  1002  could be a transmitting impulse radio unit and the second impulse radio unit  1004  would be a receiving impulse radio unit. Again, the central station  930  and electronic device  910  use impulse radio signals  915  to transmit and receive information to and from one another in places and situations not possible with standard radio signals. 
     The electronic device  910  may also include an interface unit  1008  (e.g., speaker, microphone) that enables two-way impulse radio secured voice communications between the athlete  920  and other people including coaches  940   a,  broadcasters  940   b,  fans  940   c  and other athletes  920  (see FIG.  11 ). In addition to enabling secure communications, impulse radio technology can also enable the central station  930  to track the position of the electronic device  910  attached to the athlete  920 . To determine the current position of the electronic device  910 , the first impulse radio unit  1002  associated with the electronic device  910  interacts with one or more reference impulse radio units  1102  (see FIG. 11) such that either the electronic device  910 , the central station  930 , or one of the reference impulse radio units  1102  can calculate the current position of the electronic device  910 . How the impulse radio units  1002  and  1004  interact with one another to determine the position of the electronic device  910  can best be understood by referring to the description associated with FIGS.  11  and  13 - 24 . 
     The electronic device  910  may also incorporate or interact with one or more sensors  1006 . For instance, the sensor  1006  can be attached in any manner to the athlete  920  and is capable of functioning as a heart rate monitor, blood pressure monitor, blood monitor, temperature monitor and/or perspiration monitor. In particular, the sensor  1006  can monitor one or more vital signs of the athlete  920  and forward that information to the first impulse radio unit  1002  which, in turn, modulates and forwards the information using high bandwidth impulse radio signals  915  to the central station  930 . The sensor  1006  can have a hardwire connection or wireless connection (as shown) to the electronic device  910 . 
     A variety of monitoring techniques that can be used in the present invention have been disclosed in U.S. patent application Ser. No. 09/407,106. For instance, the central station  930  can remotely activate the sensor(s)  1006  to monitor any one of the vital signs of the athlete  920 . Each sensor  1006  can also be designed to compare a sensed vital sign to a predetermined range of acceptable conditions. And, in the event the sensor  1006  monitors a vital sign that falls outside of a predetermined range of acceptable conditions, then the electronic device  910  can send an alert to the central station  930 . For instance, the sensor  1006  can send an alert whenever one of the at least one monitored vital signs indicates that an illegal substance has detected on the athlete  920 . 
     Referring to FIG. 11, there is a diagram illustrating a system  900  that can be used on a football field  1100 . As illustrated, the football field  1100  includes the playing field  1104 , side lines  1105  and a grandstand  1106 . The grandstand  1106  is where broadcasters  940   b  can use the central station  930  and fans  940   c  can use handheld units  1108   a  which operate in a similar manner as the central station  930 . And, the side lines  1105  are where one or more coaches  940   a  or other athletes  920  can use handheld units  1108   b  which operate in a similar manner as the central station  930 . Of course, the athletes  920  (shown as Xs and Os) on the playing field  1104  and the athletes  920  on the side lines  1105  can also carry an electronic device  910 . It should be understood that the illustrated layout of football field  1100  is for purposes of discussion only and is not intended as a limitation to the present invention which can operate in a wide variety of sporting venues. 
     The reference impulse radio units  1102  (only 8 shown) have known positions and are located to provide maximum coverage on the football field  1100 . The central station  930  typically has a wireless connection or hardwire connection to the reference impulse radio units  1102 , and the electronic device  910  typically has a wireless connection to the reference impulse radio units  1102 . Each athlete  920  can carry an electronic device  910  that is capable of interacting with one or more of the reference impulse radio units  1102  such that either the electronic device  910 , the central station  930 , or one of the reference impulse radio units  1102  can calculate the current position and track the movement of the athlete  920 . Moreover, a football  1107  (or any other piece of sports equipment such as a soccer ball, baseball, hockey puck or the like) can carry an electronic device  910  or an impulse radio unit that is capable of interacting with one or more of the reference impulse radio units  1102  such that either the electronic device  910 , the central station  930 , or one of the reference impulse radio units  1102  can calculate the current position and track the movement of the football  1107 . A variety of impulse radio positioning networks (e.g., two or more reference impulse radio units  1102  and one or more electronic devices  910 ) that enable the present invention to perform the positioning and tracking functions are described in greater detail below with respect to FIGS. 13-24. 
     For instance, the positioning and tracking functions can be accomplished by stepping through several steps. The first step is for the reference impulse radio units  1102  to synchronize together and begin passing information. Then, when an electronic device  910  enters or is powered-up on the football field  1100 , it synchronizes itself to the previously synchronized reference impulse radio units  1102 . Once the electronic device  910  is synchronized, it begins collecting and time-tagging range measurements from any available reference impulse radio units  1102 . The electronic device  910  then takes these time-tagged ranges and, using a least squares-based or similar estimator, calculates its position on the football field  1100 . Alternatively, one of the reference impulse radio units  1102  can calculate the position of the electronic device  910  which is attached to a known athlete  920 . 
     Thereafter, the electronic device  910  or one of the reference impulse radio units  1102  forwards its position calculation to the central station  930  for storage and/or real-time display. The central station  930  could then calculate the time it takes the athlete  920  or football  1107  to travel from one position on the football field  1100  to another position on the football field  1100 . In addition, the central station  930  can forward these position and time calculations to the handheld units  1108   a  and  1108   b  for storage and/or real-time display. 
     It should be understood that the central station  930  and each handheld unit  1108   a  and  1108   b  can be programmed to track only the athletes(s)  920  that the broadcasters  940   b  and other people  920 ,  940   a  and  940   c  want to watch at one time. Moreover, the central station  930 , electronic device  910  and handheld units  1108   a  and  1108   b  can each be programmed to sound an alarm whenever one of the monitored vital signs (e.g., blood pressure, heart rate) of one of the athletes  920  falls outside a predetermined range of acceptable conditions. As such, the coaches  940   a  can use the monitored vital signs of the athlete  920  to help assist them in the physical conditioning and training of that athlete  920 . 
     The central station  930  may also provide a variety of sports related information to the users of the handheld units  1108   a  and  1108   b.  The sports related information can include the same type of information that is often found in the program guides and various statistic books. For instance, the sports related information may also include real-time scores of other games and/or details about the history of a particular athlete  920  including that athlete&#39;s past statistics, previous teams etc . . . Each user may have to pay a predetermined fee to rent a handheld unit  1108   a  or  1108   b  where the fee is based on the type and amount of sports related information that can be assessed by the handheld unit and the other capabilities of the handheld unit. 
     The central station  930  may also provide an Internet site  1110  and other football fields, gambling halls, television stations with the current positions of the athletes  920  on the football field  1100 , the monitored vital signs of each athlete  920  and/or other sports related information. Thus, fans (not shown) can watch the game on their computer (or television) and at the same time obtain all the details they would want to know about a specific athlete  920 . The game (or play) shown on the computer or television may just show moving numbers or similar indicia of the moving athletes  920  and not the athletes  920  themselves. 
     In particular, the central station  930  can use Kalman filtering, spline curve fitting and other techniques to perform multilateration on the received positioning data to determine the position and/or velocity of one or more athletes  920 . The position and/or velocity data can be used to represent the path of each athlete  920  during a play, which can be viewed instantaneously. In other words, accurate positions of all athletes  920  could be reflected on a screen (e.g., computer, television). And, the varying velocities of the athletes  920  could also be reflected on the screen. 
     Referring to FIG. 12, there is a flowchart illustrating the basic steps of a preferred method  1200  for tracking an athlete and/or for enabling communications between the athlete and their teammates, fans or coaches in accordance with the present invention. Beginning at step  1202 , the electronic device  910  (including the impulse radio unit  1002 ) is attached to an athlete  920 . 
     At step  1204 , the electronic device  910  includes a sensor  1006  that is coupled to the athlete  920  which enables the monitoring of at least one vital sign of the athlete  920 . As described above, the sensor  1006  is capable of functioning as a heart rate monitor, blood pressure monitor, blood monitor and/or perspiration monitor (for example). The central station  930  and handheld units  1108   a  and  1108   b  can display and/or monitor the one or more vital signs of the athlete  920 , and can sound an alert upon detecting any health related problems or detecting the presence of any illegal substance(s) on the athlete  920 . 
     As mentioned earlier, the sensor  1006  can be remotely activated by the central station  930  to monitor any one of the vital signs of the athlete  920 . The sensor  1006  can also be programmed to compare a monitored vital sign to a predetermined range of acceptable conditions. And, in the event the sensor  1006  monitors a vital sign that falls outside of a predetermined range of acceptable conditions, then the electronic device  910  can send an alert to the central station  930 . 
     At step  1206 , the electronic device  910  can determine the current location of an athlete  920  on the football field  1100  by interacting with a predetermined number of reference impulse radio units  1102 . After completing or during the progress of each step  1204  and  1206 , the electronic device  910  operates to forward to the central station  930  a series of impulse radio signals  915  containing information including, for example, the monitored vital signs of the athlete  920  and/or the current position of the athlete  920  on the football field  1100 . It should be noted that one or more of the reference impulse radio units  1102  and the central station  930  are also capable of determining the current position of the athlete  920  on the football field  1100 . 
     At step  1208 , the central station  930  is operable to display all or a selected portion of the information received from the electronic device  910 . Again, the information that can be displayed includes the monitored vital sign(s) of the athlete  920  and/or the current position of the athlete  920  (and other athletes  920 ) on the football field  1100 . The central station  930  can also display an alarm whenever one of the monitored vital signs of the athlete  920  exceeds a predetermined threshold. Moreover, the central station  930  is capable of distributing this information to the handheld units  1108   a  and  1108   b  and/or the Internet site  1110 . Like, the central station  930  each of the handheld units  1108   a  and  1108   b,  the Internet site  1110  can all display an overlay of the football field  1100  that indicates the position of each moving athlete  920  and/or the monitored vital signs of each athlete  920  along with other sports related information. 
     At step  1210 , the electronic device  912  can enable two-way secure communications between the athlete  920  and other people such as coaches  940   a,  broadcasters  940   b,  fans  940   c  and other athletes. For instance, one athlete  920  (e.g., quarterback) can communicate in a secure manner with the coaches  940   a.  Or, the coaches  940   a  on one team can talk to one another in a secure manner using impulse radio technology. 
     At step  1212 , the central station  930  may also provide a variety of sports related information to the users of the handheld units  1108   a  and  1108   b,  the Internet site  1110 . The sports related information can include the same type of information that is often found in the program guides and various statistic books. For instance, the sports related information may include real time scores of other games and/or details about the history of a particular athlete  920  including that athlete&#39;s past statistics, previous teams etc . . . Each user may have to pay a predetermined fee to rent a handheld unit  1108   a  or  1108   b  where the fee is based on the type and amount of sports related information that can be assessed by the handheld unit and the other capabilities of the handheld unit. 
     Impulse Radio Positioning Networks 
     A variety of impulse radio positioning networks capable of performing the positioning and tracking functions of the present invention are described in this Section (see also U.S. patent application Ser. No. 09/456,409). An impulse radio positioning network includes a set of reference impulse radio units  1102  (shown below as reference impulse radio units R 1 -R 6 ), one or more electronic devices  910  (shown below as electronic devices M 1 -M 3 ) and a central station  930 . 
     Synchronized Transceiver Tracking Architecture 
     Referring to FIG. 13, there is illustrated a block diagram of an impulse radio positioning network  1300  utilizing a synchronized transceiver tracking architecture. This architecture is perhaps the most generic of the impulse radio positioning networks since both electronic devices M 1  and M 2  and it reference impulse radio units R 1 -R 4  are full two-way transceivers. The network  1300  is designed to be scalable, allowing from very few electronic devices M 1  and M 2  and reference impulse radio units R 1 -R 4  to a very large number. 
     This particular example of the synchronized transceiver tracking architecture shows a network  1300  of four reference impulse radio units R 1 -R 4  and two electronic devices M 1  and M 2 . The arrows between the radios represent two-way data and/or voice links. A fully inter-connected network would have every radio continually communicating with every other radio, but this is not required and can be dependent upon the needs of the particular application. 
     Each radio is a two-way transceiver; thus each link between radios is two-way (duplex). Precise ranging information (the distance between two radios) is distributed around the network  1300  in such a way as to allow the electronic devices M 1  and M 2  to determine their precise three-dimensional position within a local coordinate system. This position, along with other data or voice traffic, can then be relayed from the electronic devices M 1  and M 2  back to the reference master impulse radio unit R 1 , one of the other reference relay impulse radio units R 2 -R 4  or the central station  930 . 
     The radios used in this architecture are impulse radio two-way transceivers. The hardware of the reference impulse radio units R 1 -R 4  and electronic devices M 1  and M 2  is essentially the same. The firmware, however, varies slightly based on the functions each radio must perform. For example, the reference master impulse radio unit RP directs the passing of information and is typically responsible for collecting all the data for external graphical display at the central station  930 . The remaining reference relay impulse radio units R 2 -R 4  contain a separate version of the firmware, the primary difference being the different parameters or information that each reference relay impulse radio unit R 2 -R 4  must provide the network. Finally, the electronic devices M 1  and M 2  have their own firmware version that calculates their position. 
     In FIG. 13, each radio link is a two-way link that allows for the passing of information, both data and/or voice. The data-rates between each radio link is a function of several variables including the number of pulses integrated to get a single bit, the number of bits per data parameter, the length of any headers required in the messages, the range bin size, and the number of radios in the network. 
     By transmitting in assigned time slots and by carefully listening to the other radios transmit in their assigned transmit time slots, the entire group of radios within the network, both electronic devices M 1  and M 2  and reference impulse radio units R 1 -R 4 , are able to synchronize themselves. The oscillators used on the impulse radio boards drift slowly in time, thus they may require continual monitoring and adjustment of synchronization. The accuracy of this synchronization process (timing) is dependent upon several factors including, for example, how often and how long each radio transmits. 
     The purpose of this impulse radio positioning network  1300  is to enable the tracking of the electronic devices M 1  and M 2 . Tracking is accomplished by stepping through several well-defined defined steps. The first step is for the reference impulse radio units R 1 -R 4  to synchronize together and begin passing information. Then, when an electronic device M 1  or M 2  enters the network area, it synchronizes itself to the previously synchronized reference impulse radio units R 1 -R 4 . Once the electronic device M 1  or M 2  is synchronized, it begins collecting and time-tagging range measurements from any available reference impulse radio units R 1 -R 4  (or other electronic device M 1  or M 2 ). The electronic device M 1  or M 2  then takes these time-tagged ranges and, using a least squares-based or similar estimator, calculates the position of the electronic device M 1  or M 2  in local coordinates. If the situation warrants and the conversion possible, the local coordinates can be converted to any one of the worldwide coordinates such as Earth Centered Inertial (ECI), Earth Centered Earth Fixed (ECEF), or J2000 (inertial coordinates fixed to year 2000). Finally, the electronic device M 1  or M 2  forwards its position calculation to the central station  930  for storage and real-time display. 
     Unsynchronized Transceiver Tracking Architecture 
     Referring to FIG. 14, there is illustrated a block diagram of an impulse radio positioning network  1400  utilizing an unsynchronized transceiver tracking architecture. This architecture is similar to synchronized transceiver tracking of FIG. 14, except that the reference impulse, radio units R 1 -R 4  are not time-synchronized. Both the electronic devices M 1  and M 2  and reference impulse radio units R 1 -R 4  for this architecture are full two-way transceivers. The network is designed to be scalable, allowing from very few electronic devices M 1  and M 2  and reference impulse radio units R 1 -R 4  and to a very large number. 
     This particular example of the unsynchronized transceiver tracking architecture shows a network  1400  of four reference impulse radio units R 1 -R 4  and two electronic devices M 1  and M 2 . The arrows between the radios represent two-way data and/or voice links. A fully inter-connected network would have every radio continually communicating with every other radio, but this is not required and can be defined as to the needs of the particular application. 
     Each radio is a two-way transceiver; thus each link between radios is two-way (duplex). Precise ranging information (the distance between two radios) is distributed around the network in such a way as to allow the electronic devices M 1  and M 2  to determine their precise three-dimensional position within a local coordinate system. This position, along with other data or voice traffic, can then be relayed from the electronic devices M 1  and M 2  back to the reference master impulse radio unit R 1 , one of the other reference relay impulse radio units R 2 -R 3  or the central station  930 . 
     The radios used in the architecture of FIG. 14 are impulse radio two-way transceivers. The hardware of the reference impulse radio units R 1 -R 4  and electronic devices M 1  and M 2  is essentially the same. The firmware, however, varies slightly based on the functions each radio must perform. For example, the reference master impulse radio unit R 1  directs the passing of information, and typically is responsible for collecting all the data for external graphical display at the central station  930 . The remaining reference relay impulse radio units R 2 -R 4  contain a separate version of the firmware, the primary difference being the different parameters or information that each reference relay radio must provide the network. Finally, the electronic devices M 1  and M 2  have their own firmware version that calculates their position and displays it locally if desired. 
     In FIG. 14, each radio link is a two-way link that allows for the passing of information, data and/or voice. The data-rates between each radio link is a function of several variables including the number of pulses integrated to get a single bit, the number of bits per data parameter, the length of any headers required in the messages, the range bin size, and the number of radios in the network. 
     Unlike the radios in the synchronized transceiver tracking architecture, the reference impulse radio units R 1 -R 4  in this architecture are not time-synchronized as a network. These reference impulse radio units R 1 -R 4  operate independently (free-running) and provide ranges to the electronic devices M 1  and M 2  either periodically, randomly, or when tasked. Depending upon the application and situation, the reference impulse radio units R 1 -R 4  may or may not talk to other reference radios in the network. 
     As with the architecture of FIG. 13, the purpose of this impulse radio positioning network  1400  is to enable the tracking of electronic devices M 1  and M 2 . Tracking is accomplished by stepping through several steps. These steps are dependent upon the way in which the reference impulse radio units R 1 -R 4  range with the electronic devices M 1  and M 2  (periodically, randomly, or when tasked). When a electronic device M 1  or M 2  enters the network area, it either listens for reference impulse radio units R 1 -R 4  to broadcast, then responds, or it queries (tasks) the desired reference impulse radio units R 1 -R 4  to respond. The electronic device M 1  or M 2  begins collecting and time-tagging range measurements from reference (or other mobile) radios. The electronic device M 1  or M 2  then takes these time-tagged ranges and, using a least squares-based or similar estimator, calculates the position of the electronic device M 1  or M 2  in local coordinates. If the situation warrants and the conversion possible, the local coordinates can be converted to any one of the worldwide coordinates such as Earth Centered Inertial (ECI), Earth Centered Earth Fixed (ECEF), or J2000 (inertial coordinates fixed to year 2000). Finally, the electronic device M 1  or M 2  forwards its position calculation to the central station  930  for storage and real-time display. 
     Synchronized Transmitter Tracking Architecture 
     Referring to FIG. 15, there is illustrated a block diagram of an impulse radio positioning network  1500  utilizing a synchronized transmitter tracking architecture. This architecture is perhaps the simplest of the impulse radio positioning architectures, from the point-of-view of the electronic devices M 1  and M 2 , since the electronic devices M 1  and M 2  simply transmit in a free-running sense. The network is designed to be scalable, allowing from very few electronic devices M 1  and M 2  and reference impulse radio units R 1 -R 4  to a very large number. This architecture is especially applicable to an “RF tag” (radio frequency tag) type of application. 
     This particular example of synchronized transmitter tracking architecture shows a network  1500  of four reference impulse radio units radios R 1 -R 4  and two electronic devices M 1  and M 2 . The arrows between the radios represent two-way and one-way data and/or voice links. Notice that the electronic devices M 1  and M 2  only transmit, thus they do not receive the transmissions from the other radios. 
     Each reference impulse radio unit R 1 -R 4  is a two-way transceiver; thus each link between reference impulse radio units R 1 -R 4  is two-way (duplex). Precise ranging information (the distance between two radios) is distributed around the network in such a way as to allow the synchronized reference impulse radio units R 1 -R 4  to receive transmissions from the electronic devices M 1  and M 2  and then determine the three-dimensional position of the electronic devices M 1  and M 2 . This position, along with other data or voice traffic, can then be relayed from reference relay impulse radio units R 2 -R 4  back to the reference master impulse radio unit R 1  or the central station  930 . 
     The reference impulse radio units R 1 -R 4  used in this architecture are impulse radio two-way transceivers, the electronic devices M 1  and M 2  are one-way transmitters. The firmware in the radios varies slightly based on the functions each radio must perform. For example, the reference master impulse radio unit R 1  is designated to direct the passing of information, and typically is responsible for collecting all the data for external graphical display at the central station  930 . The remaining reference relay impulse radio units R 2 -R 4  contain a separate version of the firmware, the primary difference being the different parameters or information that each reference relay impulse radio unit R 2 -R 4  must provide the network. Finally, the electronic devices M 1  and M 2  have their own firmware version that transmits pulses in predetermined sequences. 
     Each reference radio link is a two-way link that allows for the passing of information, data and/or voice. The data-rates between each radio link is a function of several variables including the number of pulses integrated to get a single bit, the number of bits per data parameter, the length of any headers required in the messages, the range bin size, and the number of radios in the network. 
     By transmitting in assigned time slots and by carefully listening to the other radios transmit in their assigned transmit time slots, the entire group of reference impulse radio units R 1 -R 4  within the network are able to synchronize themselves. The oscillators used on the impulse radio boards drift slowly in time, thus they may require monitoring and adjustment to maintain synchronization. The accuracy of this synchronization process (timing) is dependent upon several factors including, for example, how often and how long each radio transmits along with other factors. The electronic devices M 1  and M 2 , since they are transmit-only transmitters, are not time-synchronized to the synchronized reference impulse radio units R 1 -R 4 . 
     The purpose of the impulse radio positioning network is to enable the tracking of electronic devices M 1  and M 2 . Tracking is accomplished by stepping through several well-defined steps. The first step is for the reference impulse radio units R 1 -R 4  to synchronize together and begin passing information. Then, when a electronic device M 1  or M 2  enters the network area and begins to transmit pulses, the reference impulse radio units R 1 -R 4  pick up these pulses as time-of-arrivals (TOAs). Multiple TOAs collected by different synchronized reference impulse radio units R 1 -R 4  are then converted to ranges, which are then used to calculate the XYZ position of the electronic device M 1  or M 2  in local coordinates. If the situation warrants and the conversion possible, the local coordinates can be converted to any one of the worldwide coordinates such as Earth Centered Inertial (ECI), Earth Centered Earth Fixed (ECEF), or J2000 (inertial coordinates fixed to year 2000). Finally, the reference impulse radio units R 1 -R 4  forward their position calculation to the central station  930  for storage and real-time display. 
     Unsynchronized Transmitter Tracking Architecture 
     Referring to FIG. 16, there is illustrated a block diagram of an impulse radio positioning network  1600  utilizing an unsynchronized transmitter tracking architecture. This architecture is very similar to the synchronized transmitter tracking architecture except that the reference impulse radio units R 1 -R 4  are not synchronized in time. In other words, both the reference impulse radio units R 1 -R 4  and the electronic devices M 1  and M 2  are free-running. The network is designed to be scalable, allowing from very few electronic devices M 1  and M 2  and reference impulse radio units R 1 -R 4  to a very large number. This architecture is especially applicable to an “RF tag” (radio frequency tag) type of application. 
     This particular example of the unsynchronized transmitter tracking architecture shows a network  1900  of four reference impulse radio units R 1 -R 4  and two electronic devices M 1  and M 2 . The arrows between the radios represent two-way and one-way data and/or voice links. Notice that the electronic devices M 1  and M 2  only transmit, thus they do not receive the transmissions from the other radios. Unlike the synchronous transmitter tracking architecture, the reference impulse radio units R 1 -R 4  in this architecture are free-running (unsynchronized). There are several ways to implement this design, the most common involves relaying the time-of-arrival (TOA) pulses from the electronic devices M 1  and M 2  and reference impulse radio units R 1 -R 4 , as received at the reference impulse radio units R 1 -R 4 , back to the reference master impulse radio unit R 1  which communicates with the central station  930 . 
     Each reference impulse radio unit R 1 -R 4  in this architecture is a two-way impulse radio transceiver; thus each link between reference impulse radio unit R 1 -R 4  can be either two-way (duplex) or one-way (simplex). TOA information is typically transmitted from the reference impulse radio units R 1 -R 4  back to the reference master impulse radio unit R 1  where the TOAs are converted to ranges and then an XYZ position of the electronic device M 1  or M 2 , which can then be forwarded and displayed at the central station  930 . 
     The reference impulse radio units R 1 -R 4  used in this architecture are impulse radio two-way transceivers, the electronic devices M 1  and M 2  are one-way impulse radio transmitters. The firmware in the radios varies slightly based on the functions each radio must perform. For example, the reference master impulse radio R 1  collects the TOA information, and is typically responsible for forwarding this tracking data to the central station  930 . The remaining reference relay impulse radio units R 2 -R 4  contain a separate version of the firmware, the primary difference being the different parameters or information that each reference relay impulse radio units R 2 -R 4  must provide the network. Finally, the electronic devices M 1  and M 2  have their own firmware version that transmits pulses in predetermined sequences. 
     Each reference radio link is a two-way link that allows for the passing of information, data and/or voice. The data-rates between each radio link is a function of several variables including the number of pulses integrated to get a single bit, the number of bits per data parameter, the length of any headers required in the messages, the range bin size, and the number of radios in the network. 
     Since the reference impulse radio units R 1 -R 4  and electronic devices M 1  and M 2  are free-running, synchronization is actually done by the reference master impulse radio unit R 1 . The oscillators used in the impulse radios drift slowly in time, thus they may require monitoring and adjustment to maintain synchronization at the reference master impulse radio unit R 1 . The accuracy of this synchronization (timing) is dependent upon several factors including, for example, how often and how long each radio transmits along with other factors. 
     The purpose of the impulse radio positioning network is to enable the tracking of electronic devices M 1  and M 2 . Tracking is accomplished by stepping through several steps. The most likely method is to have each reference impulse radio unit R 1 -R 4  periodically (randomly) transmit a pulse sequence. Then, when a electronic device M 1  or M 2  enters the network area and begins to transmit pulses, the reference impulse radio units R 1 -R 4  pick up these pulses as time-of-arrivals (TOAs) as well as the pulses (TOAs) transmitted by the other reference radios. TOAs can then either be relayed back to the reference master impulse radio unit R 1  or just collected directly (assuming it can pick up all the transmissions). The reference master impulse radio unit R 1  then converts these TOAs to ranges, which are then used to calculate the XYZ position of the electronic device M 1  or M 2 . If the situation warrants and the conversion possible, the XYZ position can be converted to any one of the worldwide coordinates such as Earth Centered Inertial (ECI), Earth Centered Earth Fixed (ECEF), or J2000 (inertial coordinates fixed to year 2000). Finally, the reference master impulse radio unit R 1  forwards its position calculation to the central station  930  for storage and real-time display. 
     Synchronized Receiver Tracking Architecture 
     Referring to FIG. 17, there is illustrated a block diagram of an impulse radio positioning network  1700  utilizing a synchronized receiver tracking architecture. This architecture is different from the synchronized transmitter tracking architecture in that in this design the electronic devices M 1  and M 2  determine their positions but are not able to broadcast it to anyone since they are receive-only radios. The network is designed to be scalable, allowing from very few electronic devices M 1  and M 2  and reference impulse radio units R 1 -R 4  to a very large number. 
     This particular example of the synchronized receiver tracking architecture shows a network  2000  of four reference impulse radio units R 1 -R 4  and two electronic devices M 1  and M 2 . The arrows between the radios represent two-way and one-way data and/or voice links. Notice that the electronic devices M 1  and M 2  receive transmissions from other radios, and do not transmit. 
     Each reference impulse radio unit R 1 -R 4  is a two-way transceiver, and each electronic device M 1  and M 2  is a receive-only radio. Precise, synchronized pulses are transmitted by the reference network and received by the reference impulse radio units R 1 -R 4  and the electronic devices M 1  and M 2 . The electronic devices M 1  and M 2  take these times-of-arrival (TOA) pulses, convert them to ranges, then determine their XYZ positions. Since the electronic devices M 1  and M 2  do not transmit, only they themselves know their XYZ positions. 
     The reference impulse radio units R 1 -R 4  used in this architecture are impulse radio two-way transceivers, the electronic devices M 1  and M 2  are receive-only radios. The firmware for the radios varies slightly based on the functions each radio must perform. For example, the reference master impulse radio unit R 1  is designated to direct the synchronization of the reference radio network. The remaining reference relay impulse radio units R 2 -R 4  contain a separate version of the firmware, the primary difference being the different parameters or information that each reference relay impulse radio unit R 2 -R 4  must provide the network. Finally, the electronic devices M 1  and M 2  have their own firmware version that calculates their position and displays it locally if desired. 
     Each reference radio link is a two-way link that allows for the passing of information, data and/or voice. The electronic devices M 1  and M 2  are receive-only. The data-rates between each radio link is a function of several variables including the number of pulses integrated to get a single bit, the number of bits per data parameter, the length of any headers required in the messages, the range bin size, and the number of radios in the network. 
     By transmitting in assigned time slots and by carefully listening to the other reference impulse radio units R 1 -R 4  transmit in their assigned transmit time slots, the entire group of reference impulse radio units R 1 -R 4  within the network are able to synchronize themselves. The oscillators used on the impulse radio boards may drift slowly in time, thus they may require monitoring and adjustment to maintain synchronization. The accuracy of this synchronization (timing) is dependent upon several factors including, for example, how often and how long each radio transmits along with other factors. 
     The purpose of the impulse radio positioning network is to enable the tracking of electronic devices M 1  and M 2 . Tracking is accomplished by stepping through several well-defined steps. The first step is for the reference impulse radio units R 1 -R 4  to synchronize together and begin passing information. Then, when an electronic device M 1  or M 2  enters the network area, it begins receiving the time-of-arrival (TOA) pulses from the reference radio network. These TOA pulses are converted to ranges, then the ranges are used to determine the XYZ position of the electronic device M 1  or M 2  in local coordinates using a least squares-based estimator. If the situation warrants and the conversion possible, the local coordinates can be converted to any one of the worldwide coordinates such as Earth Centered Inertial (ECI), Earth Centered Earth Fixed (ECEF), or J2000 (inertial coordinates fixed to year 2000). 
     Unsynchronized Receiver Tracking Architecture 
     Referring to FIG. 18, there is illustrated a block diagram of an impulse radio positioning network  1800  utilizing an unsynchronized receiver tracking architecture. This architecture is different from the synchronized receiver tracking architecture in that in this design the reference impulse radio units R 1 -R 4  are not time-synchronized. Similar to the synchronized receiver tracking architecture, electronic devices M 1  and M 2  determine their positions but cannot broadcast them to anyone since they are receive-only radios. The network is designed to be scalable, allowing from very few electronic devices M 1  and M 2  and reference impulse radio units R 1 -R 4  to a very large number. 
     This particular example of the unsynchronized receiver tracking architecture shows a network  1800  of four reference impulse radio units R 1 -R 4  and two electronic devices M 1  and M 2 . The arrows between the radios represent two-way and one-way data and/or voice links. Notice that the electronic devices M 1  and M 2  only receive transmissions from other radios, and do not transmit. 
     Each reference impulse radio unit R 1 -R 4  is an impulse radio two-way transceiver, each electronic device M 1  and M 2  is a receive-only impulse radio. Precise, unsynchronized pulses are transmitted by the reference network and received by the other reference impulse radio units R 1 -R 4  and the electronic devices M 1  and M 2 . The electronic devices M 1  and M 2  take these times-of-arrival (TOA) pulses, convert them to ranges, and then determine their XYZ positions. Since the electronic devices M 1  and M 2  do not transmit, only they themselves know their XYZ positions. 
     The reference impulse radio units R 1 -R 4  used in this architecture are impulse radio two-way transceivers, the electronic devices M 1  and M 2  are receive-only radios. The firmware for the radios varies slightly based on the functions each radio must perform. For this design, the reference master impulse radio unit R 1  may be used to provide some synchronization information to the electronic devices M 1  and M 2 . The electronic devices M 1  and M 2  know the XYZ position for each reference impulse radio unit R 1 -R 4  and as such they may do all of the synchronization internally. 
     The data-rates between each radio link is a function of several variables including the number of pulses integrated to get a single bit, the number of bits per data parameter, the length of any headers required in the messages, the range bin size, and the number of impulse radios in the network. 
     For this architecture, the reference impulse radio units R 1 -R 4  transmit in a free-running (unsynchronized) manner. The oscillators used on the impulse radio boards often drift slowly in time, thus requiring monitoring and adjustment of synchronization by the reference master impulse radio unit R 1  or the electronic devices M 1  and M 2  (whomever is doing the synchronization). The accuracy of this synchronization (timing) is dependent upon several factors including, for example, how often and how long each radio transmits. 
     The purpose of the impulse radio positioning network is to enable the tracking electronic devices M 1  and M 2 . Tracking is accomplished by stepping through several steps. The first step is for the reference impulse radio units R 1 -R 4  to begin transmitting pulses in a free-running (random) manner. Then, when an electronic device M 1  or M 2  enters the network area, it begins receiving the time-of-arrival (TOA) pulses from the reference radio network. These TOA pulses are converted to ranges, then the ranges are used to determine the XYZ position of the electronic device M 1  or M 2  in local coordinates using a least squares-based estimator. If the situation warrants and the conversion possible, the local coordinates can be converted to any one of the worldwide coordinates such as Earth Centered Inertial (ECI), Earth Centered Earth Fixed (ECEF), or J2000 (inertial coordinates fixed to year 2000). 
     Mixed Mode Tracking Architecture 
     For ease of reference, in FIGS. 19-24 the below legend applies. 
     
       
         
           
               
             
               
                   
               
               
                 Symbols and Definitions 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                   
                 Receiver Radio (receive only) 
               
               
                   
                 X 
                 Transmitter Radio (transmit only) 
               
               
                   
                   
                 Transceiver Radio (receive and transmit) 
               
               
                   
                 R i   
                 Reference Radio (fixed location) 
               
               
                   
                 M i   
                 Mobile Radio (radio being tracked) 
               
               
                   
                   
                 Duplex Radio Link 
               
               
                   
                   
                 Simplex Radio Link 
               
               
                   
                   
               
            
           
         
       
     
     T O A, D T O A Time of Arrival, Differenced T O A 
     Referring to FIG. 19, there is illustrated a diagram of an impulse radio positioning network  1900  utilizing a mixed mode reference radio tracking architecture. This architecture defines a network of reference impulse radio units R 1 -R 6  comprised of any combination of transceivers (R 1 , R 2 , R 4 , R 5 ), transmitters (R 3 ), and receivers (R 6 ). Electronic devices (none shown) entering this mixed-mode reference network use whatever reference radios are appropriate to determine their positions. 
     Referring to FIG. 20, there is a diagram of an impulse radio positioning network  2000  utilizing a mixed mode mobile electronic device tracking architecture. Herein, the electronic devices M 1 -M 3  are mixed mode and reference impulse radio units R 1 -R 4  are likely time-synched. In this illustrative example, the electronic device M 1  is a transceiver, electronic device M 2  is a transmitter, and electronic device M 3  is a receiver. The reference impulse radio units R 1 -R 4  can interact with different types of electronic devices M 1 -M 3  to help in the determination of the positions of the mobile electronic devices. 
     Antennae Architectures 
     Referring to FIG. 21, there is illustrated a diagram of a steerable null antennae architecture capable of being used in an impulse radio positioning network. The aforementioned impulse radio positioning networks can implement and use steerable null antennae to help improve the impulse radio distance calculations. For instance, all of the reference impulse radio units R 1 -R 4  or some of them can utilize steerable null antenna designs to direct the impulse propagation; with one important advantage being the possibility of using fewer reference impulse radio units or improving range and power requirements. The electronic device M 1  can also incorporate and use a steerable null antenna. 
     Referring to FIG. 22, there is illustrated a diagram of a specialized difference antennae architecture capable of being used in an impulse radio positioning network. The reference impulse radio units R 1 -R 4  of this architecture may use a difference antenna analogous to the phase difference antenna used in GPS carrier phase surveying. The reference impulse radio units R 1 -R 4  should be time synched and the electronic device M 1  should be able to transmit and receive. 
     Referring to FIG. 23, there is illustrated a diagram of a specialized directional antennae architecture capable of being used in an impulse radio positioning network. As with the steerable null antennae design, the implementation of this architecture is often driven by design requirements. The reference impulse radio units R 1 -R 4  and the mobile electronic device A 1  can incorporate a directional antennae. In addition, the reference impulse radio units R 1 -R 4  are likely time-synched. 
     Referring to FIG. 24, there is illustrated a diagram of an amplitude sensing architecture capable of being used in an impulse radio positioning network. Herein, the reference impulse radio units R 1 -R 4  are likely time-synched. Instead of the electronic device M 1  and reference impulse radio units R 1 -R 2  measuring range using TOA methods (round-trip pulse intervals), signal amplitude is used to determine range. Several implementations can be used such as measuring the “absolute” amplitude and using a pre-defined look up table that relates range to “amplitude” amplitude, or “relative” amplitude where pulse amplitudes from separate radios are differenced. Again, it should be noted that in this, as all architectures, the number of radios is for illustrative purposes only and more than one mobile impulse radio can be implemented in the present architecture. 
     Although various embodiments of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it should be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.