Claims:
1. A continuous wave ranging system with in-band self-interference cancellation, said system comprising:
a direct sequence spread spectrum (DSSS) transmitter (101) configured to transmit a spread modulated signal to a transmit and receive chain through a digital to analog converter (DAC) (102), said transmit and receive chain is configured to convert a baseband signal to a pass band signal and to amplify the pass band signal for wireless transmission over a first antenna;
a plurality of RF receiving chains, wherein one of the RF receiving chains is configured to utilize the transmitted signal for calibration after down conversion and the other RF receiving chain is configured to provide digital samples of the passband signal from a second antenna;
a Phase-Locked Loop (PLL) (113) configured to provide a common clock to the transmit and receive chain;
an interference canceller (114) that operates on a calibration signal from one of the RF receiving chains and on a composite signal from the other RF receiving chain, said interference canceller (114) is configured to:
modify the calibration signal, and
formulate a cancelling signal, wherein the cancelling signal is subtracted from the composite signal to cancel the in-band self-interference, and
a ranging module (115) configured to measure the range by computing a code phase difference between the calibration signal and the output signal of the interference canceller (114).

2. The system as claimed in claim 1, wherein the interference canceller (114) comprises:
a correlation based sample selector (301) configured to select a sample from the modulated signal, and
a channel estimator (302) configured to estimate the characteristics of a wireless channel by comparing the calibration signal and the composite signal.

3. The system as claimed in claim 1, wherein the ranging module (115) is configured to measure the range is based on two DSSS receiver chain approach, wherein the first chain is configured to independently track the calibration signal and the second chain is configured to track the output signal of the interference canceller (114).

4. The system as claimed in claim 3, wherein the two DSSS receiver chain approach has a plurality of parallel chains of acquisition and a plurality of tracking loops with non-integer sampling block.

5. The system as claimed in claim 1, wherein the composite signal is sum of a coupled signal from the first antenna and a reflected signal from a target (116).

6. A method with in-band self-interference cancellation, said method comprising:
transmitting, by a direct sequence spread spectrum (DSSS) transmitter (101), a spread modulated signal to a transmit and receive chain through a digital to analog converter (DAC) (102), wherein the transmit and receive chain includes:
converting a baseband signal to a pass band signal; and
amplifying the pass band signal for wireless transmission over a first antenna;
utilizing, by one of a plurality of RF receiving chains, the transmitted signal for calibration after down conversion;
providing, by the other RF receiving chain, digital samples of the passband signal from a second antenna;
providing, by a Phase-Locked Loop (PLL) (113), a common clock to the transmit and receive chain;
operating, by an interference canceller (114), on a calibration signal from one of the plurality of RF receiving chains and on a composite signal from the other RF receiving chain, said interference canceller (114) includes:
modifying the calibration signal, and
formulating a cancelling signal, wherein the cancelling signal is subtracted from the composite signal to cancel the in-band self-interference, and
measuring, by a ranging module (115), the range by computing a code phase difference between the calibration signal and the output signal of the interference canceller (114).

7. The method as claimed in claim 6, wherein the method further comprises:
selecting, by a correlation based sample selector (301), a sample from the modulated signal, and
estimating, by a channel estimator (302), the characteristics of a wireless channel by comparing the calibration signal and the composite signal.
, Description:FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
[SEE SECTION 10, RULE 13]

A CONTINUOUS WAVE RANGING SYSTEM WITH IN-BAND SELF-INTERFERENCE CANCELLATION AND METHOD THEREOF

BHARAT ELECTRONICS LIMITED
WITH ADDRESS:
OUTER RING ROAD, NAGAVARA, BANGALORE 560045,INDIA

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
FIELD OF INVENTION
[0001] The present disclosure relates generally to continuous wave ranging systems. The disclosure, more particularly, relates to a continuous wave ranging system with in-band self-interference cancellation and a method thereof.

BACKGROUND
[0002] Radar based ranging has been extensively used for finding the distance of terrestrial objects. Traditionally, radar ranging systems were primarily dominated by continuous wave (CW) systems. In continuous wave (CW) systems, the phase difference is measured between the synchronized clocks. However, CW tone based systems have drawbacks such as range ambiguity in the presence of multi path, susceptible to jamming, requires high peak power to be transmitted.
[0003] Further, determining distance or range using radio waves has many applications in navigation, positioning and situational awareness. The most widespread GPS technology is a one-way ranging technology. This system determines distance by measuring the time it takes for the radio signal to travel from the transmitter to the receiver’s antenna and then, using the speed of light in vacuum (which is also the speed of radio wave). Radars are another common two-way ranging system, which relies on reflections (passive ranging) or transponders (active ranging) to return a signal to the point of transmission.
[0004] The mono-pulse radars can eliminate range ambiguity by transmitting very short pulses in time can achieve centimeter level-accuracies. However, their measuring range capability is limited. For long distance ranging, long pulses with very high power are transmitted by trading off the range accuracy. However, this technique increases the bandwidth up to multi-GHz levels. The drawbacks of these systems are required bandwidth is more. Range resolution will be traded off when ultra-wide band (UWB) systems when constrained to operate under FCC regulations. The UWB systems also require complex RF electronics which can drive up system cost.
[0005] Spread spectrum technologies have several advantages over UWB systems that include low probability of intercept, low susceptibility to jamming, increased range over UWB systems when radios are required to confirm to FCC regulations. Many commercial spread spectrum systems operate in ISM bands. The range is calculated in these systems based on angle of arrival, and received signal strength (RSSI) with accuracies of several meters.
[0006] Cellular networks also estimate radio locations and find range with accuracies of tens of meters. In addition, in dense signal environments where GPS signals are not reachable, certain infrastructure radio signals such as Wi-Fi hotspots can be used to estimate location within several meters, depending on the availability of signals.
[0007] Moreover, the available spread spectrum based two way ranging systems can be broadly classified into two: one type of systems are using customized preambles, synchronization words and only based on acquisition coarse time delay, fine time delay by peak error measurements. Other type of systems involve both acquisition and tracking loops for considering code as well as carrier phase offsets after receiving. However, when applied to missile seeker applications, first kind of systems has a limitation of less range resolution and cannot operate at negative SNRs. In the second kind of systems, range accuracy is less. In addition, these mission critical applications need continuous range/velocity measurements are required to produce based on targets position.
[0008] Infrastructure less applications such as surface to air missiles, radars are used in seekers in last mile. These applications require high precision ranging systems. Furthermore, the main challenge in these systems is cancellation of self-interference signal, while parallel tracking the code phase and carrier phase variations of reflected signal from target.
[0009] EP1253437A2 describes the two way round trip ranging using spread spectrum based communication system, which embeds/interleaves the pulses in such a manner that voice and data communication will not be disturbed. DSSS based Wi-Fi frame structure along with CSMA/CA protocol is used to exchange the messages. Further, leading edge curve fitting for improving range accuracy and frequency diversity technique to improve on multi path effect.
[0010] US8199047 describes the method for full duplex and half duplex communication systems, where in the originator and transponder present. Full duplex case, the transponder without any signal processing, retransmits to the originator. Half duplex case, the transponder with some signal processing, retransmits to the originator. Coarse time measurement from acquisition and fine time measurement from plurality of peak error measurements.
[0011] In another conventional technology, a spread ranging system analysis and simulation is described The DSSS based ranging system is used for range measurement. It has acquisition and tracking loops where the reference is taken from transmitter. Here, the drawback is range accuracy/resolution will be less as the transmitter and receiver works with integer multiple of chip rate. Increasing the resolution of a DSSS system requires increasing the chip rate or increasing synchronization accuracy of the system or both. These both approaches increase system complexity.
[0012] US9602157B2 describes a full duplex communication system with self-interference cancellation using auxiliary chain. The channel between two antennas is estimated using Least Squares (LS) method. The same is applied on auxiliary signal and resultant signal is subtracted from received signal to cancel the self-interference. Cancellation efficiency depends on the channel characterization. As mentioned, employed channel estimation method, is more prone to front end chain imperfections.
[0013] Therefore, there is still a need of an invention which mitigates one or more of the shortcomings of previous techniques and provide an effective system and method that is capable of cancelling the self-interference while also improving range accuracy.
SUMMARY
[0014] This summary is provided to introduce concepts related to a continuous wave ranging system with in-band self-interference cancellation and a method thereof. This summary is neither intended to identify essential features of the present invention nor is it intended for use in determining or limiting the scope of the present invention.
[0015] In an embodiment of the present invention a continuous wave ranging system with in-band self-interference cancellation is disclosed. The system comprises a direct sequence spread spectrum (DSSS) transmitter that transmits a spread modulated signal to a transmit and receive chain through a digital to analog converter. The transmit and receive chain converts a baseband signal to a pass band signal and amplifies the pass band signal for wireless transmission over a first antenna. The system further includes a plurality of RF receiving chains. One of the RF receiving chains utilizes the transmitted signal for calibration after down conversion and the other RF receiving chain provides digital samples of the passband signal from a second antenna. Further, the system includes a Phase-Locked Loop (PLL) that provides a common clock to the transmit and receive chain. Further, it includes an interference canceller that operates on a calibration signal from one of the RF receiving chains and a composite signal from the other RF receiving chain. This interference canceller modifies the calibration signal and formulates a cancelling signal, wherein the cancelling signal is subtracted from the composite signal to cancel the in-band self-interference. The system further includes a ranging module that measures the range by computing a code phase difference between the calibration signal and the output signal of the interference canceller.
[0016] In another embodiment of the present invention a method with in-band self-interference cancellation is provided. The method includes transmitting a spread modulated signal to a transmit and receive chain through a digital to analog converter (DAC). The transmit and receive chain further includes converting a baseband signal to a pass band signal and amplifying the pass band signal for wireless transmission over a first antenna. The method further includes utilizing the transmitted signal for calibration after down conversion and providing digital samples of the passband signal from a second antenna. Further, the method includes providing a common clock to the transmit and receive chain and operating on a calibration signal from one of the plurality of RF receiving chains and a composite signal from the other RF receiving chain. The interference canceller further includes modifying the calibration signal and formulating a cancelling signal. The cancelling signal is subtracted from the composite signal to cancel the in-band self-interference. Further, the method includes measuring the range by computing a code phase difference between the calibration signal and the output signal of the interference canceller.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0017] The detailed description is described with reference to the accompanying figures.
[0018] Figure 1 illustrates an exemplary block diagram demonstrating transmit and receive chain separation with different antennas, in accordance with an embodiment of the present invention.
[0019] Figure 2 illustrates an exemplary block diagram demonstrating transmit and receive chain separation with circulator, in accordance with an embodiment of the present invention.
[0020] Figure 3 illustrates an exemplary block diagram of the self-interference canceller module of the system, in accordance with an embodiment of the present invention.
[0021] Figure 4 illustrates an exemplary block diagram of the correlation based sample selector of the system, in accordance with an embodiment of the present invention.
[0022] Figure 5 illustrates an exemplary block diagram of the ranging system architecture with two DSSS receiver approach, in accordance with an embodiment of the present invention.
[0023] Figure 6 illustrates an exemplary block diagram of the major blocks in one DSSS Rx-chain include fractional sampling and filtering, acquisition, and code and carrier tracking loops, in accordance with an embodiment of the present invention.
[0024] Figure 7 illustrates a flowchart of a transmit chain in digital signal processing, in accordance with an embodiment of the present invention.
[0025] Figure 8 illustrates a flowchart of a receiver chain that includes the interference cancellation module and the ranging module in the digital signal processing, in accordance with an embodiment of the present invention.
[0026] Figure 9 illustrates a flowchart of a method with in-band self-interference cancellation, in accordance with an embodiment of the present invention.
[0027] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present invention. Similarly, it will be appreciated that any flow chart, flow diagram, and the like represent various processes which may be substantially represented in computer readable medium and so executed by a computer or processor, whether or not such computer or processor is explicitly shown.

DETAILED DESCRIPTION
[0028] The various embodiments of the present invention describes a continuous wave ranging system with in-band self-interference cancellation and a method thereof.
[0029] In the following description, for purpose of explanation, specific details are set forth in order to provide an understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these details.
[0030] One skilled in the art will recognize that embodiments of the present invention, some of which are described below, may be incorporated into a number of systems.
[0031] However, the system is not limited to the specific embodiments described herein. Further, structures and devices shown in the figures are illustrative of exemplary embodiments of the present invention and are meant to avoid obscuring of the present invention.
[0032] Furthermore, connections between components and/or modules within the figures are not intended to be limited to direct connections. Rather, these components and modules may be modified, re-formatted or otherwise changed by intermediary components and modules.
[0033] The appearances of the phrase “in an embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
[0034] The present invention describes a novel self-interference cancellation improvement method that distinguishes the wireless channel between the transmit and receive antennas by comparing the calibration signal with the coupled signal. The characterized channel is applied on the calibration signal to generate a cancellation signal and then subtract the same from the composite signal. Further, a ranging system is disclosed that is based on two DSSS receiver chain approach, which has two parallel acquisition and tracking loops along with non-integer sampling (or) fractional sampling between the transmitters and the receivers. The first chain independently tracks the reference or the calibration signal, and the second chain tracks the self-interference cancelled signal. The code phase difference between them with the receiver channel as reference will improve the range resolution.
[0035] Further, the present invention provides a continuous wave ranging system with in-band self-interference cancellation. The system comprises a direct sequence spread spectrum (DSSS) transmitter that transmits a spread modulated signal to a transmit and receive chain through a digital to analog converter. The transmit and receive chain converts a baseband signal to a pass band signal and amplifies the pass band signal for wireless transmission over a first antenna. The system further includes a plurality of RF receiving chains. One of the RF receiving chains utilizes the transmitted signal for calibration after down conversion and the other RF receiving chain provides digital samples of the passband signal from a second antenna. Further, the system includes a Phase-Locked Loop (PLL) that provides a common clock to the transmit and receive chain. Further, it includes an interference canceller that operates on a calibration signal from one of the RF receiving chains and a composite signal from the other RF receiving chain. This interference canceller modifies the calibration signal and formulates a cancelling signal, wherein the cancelling signal is subtracted from the composite signal to cancel the in-band self-interference. The system further includes a ranging module that measures the range by computing a code phase difference between the calibration signal and the output signal of the interference canceller.
[0036] In another embodiment, a method with in-band self-interference cancellation is provided. The method includes transmitting a spread modulated signal to a transmit and receive chain through a digital to analog converter (DAC). The transmit and receive chain further includes converting a baseband signal to a pass band signal and amplifying the pass band signal for wireless transmission over a first antenna. The method further includes utilizing the transmitted signal for calibration after down conversion and providing digital samples of the passband signal from a second antenna. Further, the method includes providing a common clock to the transmit and receive chain and operating on a calibration signal from one of the plurality of RF receiving chains and a composite signal from the other RF receiving chain. The interference canceller further includes modifying the calibration signal and formulating a cancelling signal. The cancelling signal is subtracted from the composite signal to cancel the in-band self-interference. Further, the method includes measuring the range by computing a code phase difference between the calibration signal and the output signal of the interference canceller.
[0037] In another embodiment, the interference canceller includes a correlation based sample selector that selects a sample from the modulated signal and a channel estimator that estimates the characteristics of a wireless channel by comparing the calibration signal and the composite signal.
[0038] In another embodiment, the ranging module measuring the range of the target is based on two DSSS receiver chain approach, wherein the first chain independently tracks the calibration signal and the second chain tracks the output signal of the interference canceller.
[0039] In another embodiment, the two DSSS receiver chain approach has a plurality of parallel chains of acquisition and a plurality of tracking loops with non-integer sampling block.
[0040] In another embodiment, the composite signal is sum of a coupled signal from the first antenna and a reflected signal from a target.
[0041] Figure 1 illustrates an exemplary block diagram demonstrating transmit and receive chain separation with different antennas, in accordance with an embodiment of the present invention. The direct sequence spread spectrum (DSSS) based ranging system has one transmitting chain, where the PN sequence is modulated with binary phase shift keying (BPSK) modulation and the digital samples are sent through a transmit and receive chain through digital to analog converter (DAC) 102. The transmit and receive chain is configured to convert a baseband signal to a pass band signal and to amplify the pass band signal for wireless transmission over a first antenna. The system has a plurality of two RF receiving chains, one of the receiving chains is configured to utilize the copy of the transmitted signal for calibration purpose and the other RF receiving chain is configured to provide digital samples of the passband signal from a second antenna. Further, a Phase-Locked Loop (PLL) 113 is configured to provide a common clock to the transmit and receive chain. Further, after analog to digital conversion (ADC) by the analog to digital converters (108, 109), an interference canceller 114 is configured to operate on a calibration signal from one of the RF receiving chains and a composite signal from the other RF receiving chain. This interference canceller 114 is configured to modify the calibration signal and to formulate a cancelling signal. This cancelling signal is subtracted from the composite signal to cancel the in-band self-interference. The system further includes a ranging module 115 is configured to measure the range by computing a code phase difference between the calibration signal and the output signal of the interference canceller.
[0042] Figure 2 illustrates an exemplary block diagram demonstrating transmit and receive chain separation with circulator, in accordance with an embodiment of the present invention. As shown in figure 2, the system is similar to the system explained in the figure 1. The only difference a circulator is used for separating the transmit and the receive chain. Here, the circulator 117 is used to route the passband signal from the transmitter to the antenna and from the antenna to the receiver.
[0043] Figure 3 illustrates an exemplary block diagram of the self-interference cancellation module of the system, in accordance with an embodiment of the present invention. The self-interference cancellation module comprises of a channel estimator 302, an interference canceller 114 and a correlation based sample selector (CBSS) 301. The correlation based sample selector 301 is configured to select a sample from the modulated signal, and the channel estimator 302 is configured to estimate the characteristics of a wireless channel by comparing the calibration signal and the composite signal. The interference canceller 114 is configured to operate on two input signals which are the calibration signal from one of the RF receiving chain and composite signal from the other RF receiving chain. The calibration signal is a transmitted signal along with the transmit front end noise, PA non-linearity and receive chain front end noise. The composite signal is a sum of the coupled signal from the first antenna and the reflected signal from a target 116. The coupled signal is a transmitted signal that passed through the wireless channel between the first antenna and the second antenna. The reflected signal is a signal which travelled over the air to intercept the target 116 and reflected back to the system.
[0044] Further, the system operates on two modes which are the calibration mode and the operation mode. In the calibration mode, the wireless channel between the first antenna and the second antenna will be computed. In the operation mode, by using the estimated channel response, the coupled signal is cancelled from the composite signal. Thus, the self-interference cancellation module does the cancellation of the coupled signal with the help of the calibration signal. This helps in achieving the goal of estimating target distance.
[0045] Figure 4 illustrates an exemplary block diagram of the correlation based sample selector of the system, in accordance with an embodiment of the present invention. The correlation based sample selector 301 is the first block of the self-interference cancellation module which operates directly on the digital samples of input oversampled signal. The self-interference cancellation module can characterize for the channel transfer function (h) in calibration mode without the CBSS. But with this estimate, the interference cancellation will be inferior in the operation mode. This is because of improper characterization of channel (h). One of the reasons can be sample timing errors while digitizing the signal. At this point, either timing error can be corrected using conventional timing error detectors (TED) or correlation based proper sample can be chosen from available over samples. For the proposed system, the correlation based sample selector is opted because of its implementation simplicity.
[0046] The CBSS 301 is configured to select the sample based on the spread code correlation. The CBSS 301 consists of correlator, delay element, PN Sequence memory, decimator and maximum finder. The PN sequence memory element transmits the PN Sequence code and it will be used to correlate the input samples. The delay element provides one sample delay to the input and number of delay elements required depends on input oversampling factor.
[0047] In an exemplary embodiment, the input is oversampled by factor of 4, so four parallel processing paths are considered. Every path is delayed by one sample with respect to its next path. The CBSS 301 has a decimator block that is configured to decimate the input signal by a factor of 4 and passes to the correlator. The correlator is configured to correlate the input signal with the stored PN sequence memory. This correlator is further configured to process the input at sample rate and to provide the correlation value, once in a code interval time. These correlation values from all 4 parallel chains are compared at max finder block for maximum value. The chain which gives the highest correlation value among all parallel chains is considered, and respective chain samples are processed.
[0048] In FIG.4, in the calibration mode of the self-interference cancellation module, based on the CBSS output samples are passed to channel estimator block. While estimating the wireless channel between the first antenna and the second antenna, it is assumed that there is no reflected signal. The channel is estimated using Least Square (LS) method that is by dividing the frequency domain copy of the composite signal with frequency domain copy of the calibration signal. The estimated channel coefficients are stored and utilized for cancelling the coupled signal during the operation mode of the self-interference cancellation module.
[0049] Further, the interference canceller 114 is configured to modify the calibration signal using the estimated channel coefficients and to formulate a cancelling signal. This cancelling signal is subtracted from the composite signal to cancel the in band self-interference.
[0050] Figure 5 illustrates an exemplary block diagram of the ranging system architecture with two DSSS receiver approach, in accordance with an embodiment of the present invention. Figure 6 illustrates an exemplary block diagram of the major blocks in one DSSS Rx-chain include fractional sampling and filtering, acquisition, and code and carrier tracking loops, in accordance with an embodiment of the present invention.
[0051] The ranging block has two parallel DSSS receiver chains. Each DSSS receiver chain has a non-integer sampler block or a fractional sampling block followed by a filtering block, an acquisition block and a tracking block. The fractional block maintains the non-integer multiple of chip rate as the sampling frequency, between the transmitter and the receiver. The fractional sampler output is filtered and sent to the acquisition block and the tracking block.
[0052] The acquisition block has reference PN code generator that is configured to generate the early (one sample ahead), late (one sample delayed), and prompt copies of the reference PN code samples as outputs. These outputs along with incoming received samples are sent to time domain correlation block. The correlation block has one carrier numerically controlled oscillator (NCO), where the received samples are first shifted by one of the frequency bins from the group and then correlated with output of reference PN code generator is, and provide the start of the PN code in the incoming samples. The tracking block uses traditional delay locked loop (DLL), frequency locked loop (FLL) and a Coastas phase locked loop (PLL) to track the code phase and carrier phase shift in the received signal with respective to the reference PN code. For this tracking purpose, code discriminator and code loop filter are used to track the changes in code phase. The carrier discriminator and the carrier loop filter are used for tracking carrier phase shift changes with respective to reference known PN code carrier phase. The code phase difference between these two receiver chains will be taken for range computation block.
[0053] Figure 7 illustrates a flowchart of a transmit chain in digital signal processing, in accordance with an embodiment of the present invention.
[0054] At step 701, the PN sequence generator generates continuously pseudo random code and forwards it to the IQ separation step 702.
[0055] At step 702, the in phase and the quadrature phase are separated and sent to interpolation filters.
[0056] At step 703, the baseband sampling rate ("N") are converted to the RF front end sampling rates ("Z").
[0057] At step 704, the IQ samples are transmitted through RF front end.
[0058] Figure 8 illustrates a flowchart of a receiver chain that includes the interference cancellation module and the ranging module in the digital signal processing, in accordance with an embodiment of the present invention.
[0059] At step 801, the one of the RF receiving chains will take the samples from the transmitter output and the other RF receiving chain will take the received samples at the receive antenna.
[0060] At step 802, in power ON condition, the samples tapped directly from transmitter output are sent to interference cancellation step through RF front end at sampling rate of (Z).
[0061] At step 803, the down conversion module will down convert the samples to make sure at least four samples will enter to correlation based best sample selector (CBSS).
[0062] At step 804, the CBSS will compute the correlation for all the four samples and stored PN code in frequency domain and chooses the best sample.
[0063] At step 805, the channel estimator will estimate the channel between the transmit antenna and the receive antenna using the knowledge of reference samples and leaked signal samples through wireless.
[0064] At step 806, the estimated channel coefficients will be stored.
[0065] At step 807, once the system is moved from power ON state to operation mode, the estimated channel coefficient will be applied on the composite signal (leaked and reflected signal) and through equalization step. Then, the output of interference cancellation block is only the reflected signal with suppressed leaked signal.
[0066] At step 808, the reference signal samples and output of the interference cancellation block are sent to ranging module. Here, the non-integer sampling will be applied (4.16 times the baseband sampling rate "N"). This method of non-integer sampling or fractional sampling at receiver will improve the range accuracy. This difference of transmitter sampling to receiver sampling creates more precise code phases and from simulations 4.16 times the transmit sampling is giving the accuracy of ± 1 meter round trip distance.
[0067] At step 809, the output of the non-integer sampling will be sent to PN sequence receiver chains.
[0068] At step 810, the receiver chains continuously acquire and track the reference signal and reflected signal and give the code phase differences between the signals through code phase comparator. The acquisition and tracking of PN sequence are based on conventional Coastas loop receiver methods.
[0069] At step 811, the range value will be computed next in range calculation step and reported as output.
[0070] Figure 9 illustrates a flowchart of a method with in-band self-interference cancellation, in accordance with an embodiment of the present invention.
[0071] At step 902, transmitting, by a direct sequence spread spectrum (DSSS) transmitter (101), a spread modulated signal to a transmit and receive chain through a digital to analog converter (DAC) (102). The transmit and receive chain includes converting a baseband signal to a pass band signal and amplifying the pass band signal for wireless transmission over a first antenna.
[0072] At step 904, utilizing, by one of a plurality of RF receiving chains, the transmitted signal for calibration after down conversion.
[0073] At step 906, providing, by the other RF receiving chain, digital samples of the passband signal from a second antenna.
[0074] At step 908, providing, by a Phase-Locked Loop (PLL) (113), a common clock to the transmit and receive chain.
[0075] At step 910, operating, by an interference canceller (114), on a calibration signal from one of the plurality of RF receiving chains and on a composite signal from the other RF receiving chain. The interference canceller (114) includes modifying the calibration signal, and formulating a cancelling signal. This cancelling signal is subtracted from the composite signal to cancel the in-band self-interference.
[0076] At step 912, measuring, by a ranging module (115), the range by computing a code phase difference between the calibration signal and the output signal of the interference canceller (114).
[0077] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the invention.