Claims:5. CLAIMS
I/We Claim
1. An FPGA based high precision time-frequency-phase synchronization system (100) for beamforming and spectrum sensing, comprises:
an FPGA (10 & 20) based server node (2) and multiple client nodes (4) wirelessly configured; wherein the said server (2) and client nodes, includes:
an application signal frequency F2 (17) that generates a beamforming output with no phase error;
a synchronization signal frequency F1 (16) that is transmitted from wireless server node (2) and received at client nodes (4);
the said server node (2) poses by transmitting said synchronization signal F1 (16) and trans-receive application signal F2 (17);
the said plurality of client nodes (4) poses by receiving said synchronization signal F1 (16) and trans-receive application signal F2 (17);
an ADC(A) (18), DAC(D) (13) and both ADC & DAC(M) converters for converting analog signal into a binary and the binary signal to an analog value;
an OCXO (15) ensures minimum drift during the window of application execution;
Characterized in that:
the said system (100) allows the server node (2) to generate the synchronization signal F1 (16) initially for some time without any modulated command data, the client node (4) carrier locks the signal F1 (16);
the mapping function in FPGA (20) generates signal F2 (17) with direct transformation function in function translator (25);
the said direct transformation function ensures phase lock on F1 (16) that lead to automatically phase lock on F2 (17);
the synchronization signal F1 (16) from server (2) starts sending commands to client (4) synchronization signal F1 after a predefined period;
the application signal F2 (17) without any phase shift from client node (4) is transmitted and received by the server node (2) application signal F2;
the application signal F2 at server node (2) estimates the phase shift between local copy of application signal and received signal from respective node;
the said phase shift value along with desired beamforming weight is loaded to client (4), when all the client nodes (4) are loaded with desired beamforming coefficients (19) the application starts; and
after a pre-defined time, the system (100) recalibrates itself and generates the beamforming coefficients (19) for the received signal from respective nodes.

2. The system (100) as claimed in claim 1, wherein the FPGA (10) based server node (2) majorly comprises of a modulation block (27), a function translator (25), and a phase detector block (24).

3. The system (100) as claimed in claim 1, wherein the FPGA (20) based client nodes (4) majorly comprise of a Digital Down Convertor (DDC) (22), a carrier lock loop (32), a function translator (25), and a bit decoder (34).

4. The system (100) as claimed in 1, wherein the function translator (25) implements the frequency mapping based on the received F1 frequency and generates the F2.

5. The system (100) as claimed in claim 1, wherein the phase detector block (24) in the server node (2) estimates the phase difference in the received signal and internally generated signal, based on the phase difference server sends CAL command client.

6. The system (100) as claimed in claim 1, wherein the process of synchronizing, locking to F1 and calibrating the value for all the available client nodes (4) is done when the power is ON.

7. The system (100) as claimed in claim 1, wherein when the beamforming application (19) is running the synchronization phase is switched off for some time where high sensitive measurement on application signal takes place.

8. The system (100) as claimed in claim 1, wherein over the time there is a chance of losing synchronization between server (2) and client (4) nodes, to ensure synchronization continuity server (2) initiates synchronization among the clients (4) periodically.

9. The system (100) as claimed in claim 1, wherein generates highly accurate time stamp in conjunction with self position accuracy and decides the overall time stamp accuracy for moving nodes.

10. The system (100) as claimed in claim 1, wherein the time stamp generate highly accurate time stamp is presented which can give accuracy order of few tens of pico seconds and corresponds to spatial distance of few centimeters.

6. DATE AND SIGNATURE

Dated this June 11, 2021
Signature

(Mr. Srinivas Maddipati)
IN/PA 3124
Agent for Applicant
Unistring Tech Solutions Pvt. Ltd.
, Description:4. DESCRIPTION

Technical Field of the Invention

Present invention relates to Multi channel synchronized signal processing for beamforming, direction finding and several other spatial diversity applications. More particularly, the invention relates to Field Programmable Gate Array (FPGA) based high precision time-frequency-phase synchronization system for beamforming and spectrum sensing.

Background of the Invention

The advancements in wireless technologies are enabling realization of novel applications covering civilian and military applications. In cellular applications and sensor networks the wireless synchronization between nodes is widely researched to achieve beamforming advantages. However, there are not many solutions evolved to meet the spectrum surveillance or Spectrum Sensing using this concept. The invention described here is an architecture and scheme, which provides practical solution for this.

Synchronization among wireless nodes is studied well in context of wireless communication as part of carrier and timing synchronization. Most of the existing papers and patents discuss the problem of wireless synchronization as an extended problem of typical carrier synchronization and symbol time synchronization seen in digital demodulators. The noise analysis and its effect on phase noise also discussed in multiple papers and patents. The present work in comparison with existing papers and patents can be seen with few major differences.

The present work describes solution beyond carrier synchronization in terms of building spectrum sensing application. The solution for real time calibration and reducing phase noise effects are clearly indicated here. The key contributions by other related papers and patents and their commonalities and differences with the current work are given below.

Prior art
[1] O. Simeone, U. Spagnolini, Y. Bar-Ness and S. H. Strogatz, "Distributed synchronization in wireless networks," in IEEE Signal Processing Magazine, vol. 25, no. 5, pp. 81-97, September 2008, doi: 10.1109/MSP.2008.926661.

[2] R. Mudumbai, J. Hespanha, U. Madhow and G. Barriac, "Scalable feedback control for distributed beamforming in sensor networks," Proceedings. International Symposium on Information Theory, 2005. ISIT 2005., Adelaide, SA, Australia, 2005, pp. 137-141, doi: 10.1109/ISIT.2005.1523309.

[3] European Patent EP3195672A1 titled “Beam synchronization methods for beamforming wireless networks”.

[4] Simeone, O., Spagnolini, U. Distributed Time Synchronization in Wireless Sensor Networks with Coupled Discrete-Time Oscillators. J Wireless Com Network 2007, 057054 (2007).

[5] M. A. Alvarez and U. Spagnolini, "Distributed Time and Carrier Frequency Synchronization for Dense Wireless Networks," in IEEE Transactions on Signal and Information Processing over Networks, vol. 4, no. 4, pp. 683-696, Dec. 2018, doi: 10.1109/TSIPN.2018.2812039.

[6] Mudumbai, R.; Barriac, G.; Madhow, U. (2007). On the Feasibility of Distributed Beamforming in Wireless Networks., 6(5), 1754–1763. doi:10.1109/twc.2007.360377

[7] F. Quitin, M. M. Ur Rahman, R. Mudumbai and U. Madhow, "Distributed beamforming with software-defined radios: Frequency synchronization and digital feedback," 2012 IEEE Global Communications Conference (GLOBECOM), Anaheim, CA, USA, 2012, pp. 4787-4792, doi: 10.1109/GLOCOM.2012.6503876.

[8] L. Li, B. Li and H. Wang, "Clock Synchronization of Wireless Distributed System Based on IEEE 1588," 2010 International Conference on Cyber-Enabled Distributed Computing and Knowledge Discovery, Huangshan, China, 2010, pp. 205-209, doi: 10.1109/CyberC.2010.45.

[9] F. Quitin, U. Madhow, M. M. U. Rahman and R. Mudumbai, "Demonstrating distributed transmit beamforming with software-defined radios," 2012 IEEE International Symposium on a World of Wireless, Mobile and Multimedia Networks (WoWMoM), San Francisco, CA, USA, 2012, pp. 1-3, doi: 10.1109/WoWMoM.2012.6263729.

[10] Raghu Mudumbai, Upamanyu Madhow, Rick Brown, Patrick Bidigare, "DSP-centric algorithms for distributed transmit beamforming", Signals Systems and Computers (ASILOMAR) 2011 Conference Record of the Forty Fifth Asilomar Conference on, pp. 93-98, 2011.

[11] Sairam Goguri, Dennis Ogbe, Soura Dasgupta, Raghuraman Mudumbai, D. Richard Brown, David J. Love, Upamanyu Madhow, "Optimal Precoder Design for Distributed Transmit Beamforming Over Frequency-Selective Channels", IEEE Transactions on Wireless Communications 17, no. 11, pp. 7759-7773, (2018)

[12] F. Quitin, U. Madhow, M.M.U. Rahman and R. Mudumbai, "Demonstrating distributed transmit beamforming with software-defined radios", Proc. WoWMoM 2012, San Francisco, CA, June 2012

[13] R. Mudumbai, B. Wild, U. Madhow and K. Ramchandran, "Distributed Beamforming using 1 Bit Feedback: from Concept to Realization", Proc. of 44'th Allerton Conference on Communication Control and Computing, Sept 2006

[14] US. Pat. No. US4843397A titled “Distributed-array radar system comprising an array of interconnected elementary satellites”.

[15] Li Zhang, Ning Xie, Li Zhang, Hui Wang, "Time-slotted interactive multiple-input multiple-output radar for phase synchronization at target with low overhead", Radar Sonar & Navigation IET, vol. 11, no. 9, pp. 1435-1443, 2017.

[16] G. Sklivanitis and A. Bletsas, "Testing zero-feedback distributed beamforming with a low-cost SDR testbed," 2011 Conference Record of the Forty Fifth Asilomar Conference on Signals, Systems and Computers (ASILOMAR), Pacific Grove, CA, USA, 2011, pp. 104-108, doi: 10.1109/ACSSC.2011.6189964.

[17] P. Bidigare et al., "Implementation and demonstration of receiver-coordinated distributed transmit beamforming across an ad-hoc radio network," 2012 Conference Record of the Forty Sixth Asilomar Conference on Signals, Systems and Computers (ASILOMAR), Pacific Grove, CA, USA, 2012, pp. 222-226, doi: 10.1109/ACSSC.2012.6488994.

The prior art document [1] provides survey of research on distributed synchronization for decentralized wireless networks and illustrates the role of signal processing therein, with emphasis on physical layer-based synchronization schemes. The paper describes the synchronization is a straight extension of Phase locked loop. The paper doesn’t provide any means of how to utilize the same frequency for the required application. Phase noise analysis also given in paper. But methods to overcome the phase noise effect are not given. The emphasized applications and hence their demanded technological requirements are different in the work presented here in comparison with what is given at [1].

The scheme proposed in prior art document [2] provides distributed beamforming scheme based on feedback of received SNR. The iterative approach given discusses the convergence of phase shifts over multiple iterations. This method is applicable for only few classes of sensor networks and has same limitations as described above in the application context of spectrum sensing.

The solution proposed in prior art document [3] relies on method of beacon signal transmission information by a base station in a beamforming mobile communication network, wherein a plurality of beacon signals are transmitted over a plurality of control beams from neighboring base stations. Only to the extent of carrier transmission for synchronization is common between this and the presented scheme here. The total solution and methodology proposed is completely different.

The work as per prior art document [4] aims at scalability and complexity reduction in physical-layer based synchronization using Phase Locked Loop (PLL) compared with conventional packet-based synchronization, where only time synchronization is possible. This work also focuses on the convergence properties by modeling the network as a set of discrete-time coupled oscillators and relying on the analytical framework of algebraic graph theory. The work only focuses on comparing the conventional PLLs performance when compared to their extension to distributed systems.

The work as per prior art document [5] presents method for Time Offset (TO) and Carrier Frequency Offset (CFO) estimation and correction algorithm in dense sensor networks application. The work also studies effects of propagation delays in such network.

The work published by authors in papers [6][10][11][12][13] discusses challenges in distributed beamforming with phase noise, low SNR of synchronization signal and SDR based architectures. The paper [6] discusses using different frequency for application f2 = (m/n) f1, where m and n are integers. However, the work only highlights problem of phase drift with it and doesn’t provide solution for that. The solution provided here address the problem and also associated challenges arise due to phase noise.
.
The prior art document [14] describes a satellite based scheme for distributed beamforming, which performs accurate measurement of the position and altitude of elementary satellites and real-time adaptive waveform for RADAR. This method is completely different when compared with what is proposed here.

The prior art document referred as [15], proposes a time-slotted interactive MIMO radar system in which the separated antenna arrays operate in a time-division way. The current work differs from this as the aim here is form beam using distributed sensor nodes, where as in the paper [15] the goal for achieving synchronization for MIMO RADAR configuration.

The work as per prior art document [16] describes Zero-feedback collaborative beamforming method with a low-cost testbed. However, this doesn’t explain how challenges of calibration which are common in any transmit or receive type beamforming systems are handled.

The work as per prior art document [17] implements receiver-coordinated transmit beamforming technique. This scheme is useful for distributed coherent communications from a wireless network of radios to a distant receiver. This scheme doesn’t become reality in spectrum sensing applications. When high speed electronic scanning is required in application the possibility of positioning receiver doesn’t become feasible.

Brief Summary of the Invention

Synchronization among different channels of processing is widely used in several fields covering acoustics in air, Electromagnetic waves and under water acoustics. Multi channel synchronized signal processing is used for beamforming, direction finding and several other spatial diversity applications.

Existing systems can be categorized into two types:
(1) Multichannel processing systems with frequency and phase coherency, achieve desired processing gain by coherently summing or subtracting channel data. The beamforming systems which derive advantage of high array gain are examples of coherent summing. Whereas the monopulse is best example of system when coherent signal difference allows precise tracking.
(2) The second type of wireless networks only use time synchronization. The IEEE 1588 is example for this type of synchronization.

The invention described here address both the above category of the requirements. The proposed architecture gives FPGA realizable practical solution to achieve this.

The invention given here addresses the challenges and proposes an FPGA implementable architecture for distributed wireless nodes synchronization in terms of realizing the spectrum surveillance related beamforming applications.

In accordance with the aspect of the present invention, the time-frequency-phase synchronization system for beamforming and spectrum sensing comprises an FPGA based server node and multiple client nodes that are wirelessly configured.

In accordance with the aspect of the present invention, the server and client node include an application signal frequency F2 that generates beamforming output with no phase error and a synchronization signal frequency F1 that is transmitted from wireless server node and received at client nodes.

In accordance with the aspect of the present invention, wherein the server node poses in transmitting the synchronization signal F1 and trans-receive application signal F2 and the client node(s) poses in receiving synchronization signal F1 and trans-receive application signal F2.

In accordance with the aspect of the present invention, wherein the server node and client node(s) include an ADC(A), DAC(D) and both ADC & DAC(M) converters for converting analog signal into a binary and the binary signal to an analog value and an OCXO ensures minimum drift during the window of application execution.

In accordance with the aspect of the present invention, wherein the FPGA based server node majorly comprises of a modulation block, a function translator, and a phase detector block.

In accordance with the aspect of the present invention, wherein the FPGA based client nodes majorly comprise of a Digital Down Convertor (DDC), a carrier lock loop, a function translator, and a bit decoder.

In accordance with the aspect of the present invention, wherein the system implemented provides a wireless synchronisation mechanism with real time implementation of FPGA based algorithm. The proposed system not only synchronises the carrier but uses other frequency which is application-specific. This is very crucial in sensing application such as spectrum surveillance.

In accordance with the aspect of the present invention, wherein the process of synchronizing, locking to F1 and calibrating the value for all the available nodes is done when the power is ON.

In accordance with the aspect of the present invention, wherein the when the beamforming application is running the synchronization phase is switched off for some time where highly sensitive measurement on application signal takes place.

In accordance with the aspect of the present invention, wherein the system generates highly accurate time stamp in conjunction with self-position accuracy and decides the overall time stamp accuracy for moving nodes.

In accordance with the aspect of the present invention, the implemented architecture uses same wireless channel for command communication. Hence, synchronization and data control are achieved through same mechanism.

In accordance with the aspect of the present invention, wherein the implemented architecture provides synchronization solution even when the nodes are on non-static platforms such as ground or air vehicles.

In accordance with the aspect of the present invention, wherein the implemented architecture generates highly accurate time stamp which can give accuracy order of few tens of pico seconds and corresponds to spatial distance of few centimeters.

Brief Description of the Drawings

Various objects and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments, in conjunction with the accompanying drawings, wherein like reference numerals have been used to designate like elements, and wherein:

The present invention is illustrated by accompanying drawing, wherein:

Fig.1 illustrates the block diagram depicting the set of wireless synchronization among FPGA based server and client(s) wireless nodes according to the present invention;

Fig.2 illustrates the architecture of wireless server node depicting the components and working involved in the FPGA processing system in the server node according to the present invention;

Fig.3 illustrates the architecture of wireless client node depicting the components and working involved in the FPGA processing system in the client node according to the present invention;

Fig.4 illustrates the block diagram depicting the calibration sequence processed at the server and client wireless nodes according to the present invention;

Fig.5 shows the time slot pulse for synchronization and application signal frequencies at steady state transitions between calibration and synchronization in each node according to the present invention;

Fig.6 shows the precise time stamp generation using the phase of synchronous tone carrier according to the present invention;

Fig.7 shows the beamforming output with no phase error according to the present invention;

Fig.8 shows the array gain degradation with phase synchronization error according to the present invention;

Fig.9A and 9B shows the array gain degradation with respective node positioning error by considering the cumulative positional error and non-cumulative positional error according to the present invention;

Fig.10A and 10B shows the practical setup of server and client hardware modules for verifying time, frequency and phase synchronization through wireless means according to the present invention.

Detailed Description of the Invention

The following description is merely exemplary in nature and is not intended to limit the present invention, applications, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

The key difference in spectrum surveillance related beamforming applications is the signal of interest is very low in energy and require to be present at different frequency F2 in comparison with the synchronization signal’s frequency F1.

In spectrum surveillance, while the synchronization frequency F1 is continuously present among wireless nodes the beamforming needs to happen on frequency F2. The target signal is very low power and only possible to process when the synchronization tone is at different frequency. In EW applications such as surveillance and jamming also similar requirement exists. The proposed scheme achieves this configuration of dual frequency topology.

Another challenge is to measure the low power signal with its doppler information the phase noise of the Tx and Rx processing must be under control. When the wireless synchronization loop is running the jitter present on phase due to the noise in synchronization tone F1 will result very high phase noise. Similarly in surveillance application to measure closely spaced frequencies which are with high amplitude difference the phase noise must be in control. The present implemented architecture controls the SYNC and application time slots. However, in such application when coarse measurements are required in which we shall continue to use application frequency F2 even when synchronization signal frequency F1 is ON.

The invention offers an implementable solution to realize application of Spectrum surveillance using multiple platforms which are connected wirelessly. Synchronization among wireless nodes which are distant apart is of interest in several emerging modern applications. The challenges increase in case where the nodes are on moving platform and has random positional errors.

The proposed architecture is illustrated through figures (1), (2) and (3) that shows the real time synchronization implementation using FPGAs. The figures (4) and (5) shows the power ON initial synchronization and further steady state transitions.

Referring to the figures,
Figure.1 illustrates the block diagram (100) depicting the set of wireless synchronization among FPGA based server and client(s) wireless nodes according to the present invention. As shown in figure.1, the system includes one server node (2) and multiple client nodes (4). The server node (2) poses hardware for transmission (11) only on synchronization signal F1 (16) and trans-receive hardware (12) for application signal F2 (17). The client node (4) poses hardware for receiving (14) only synchronization signal F1 (16) and trans-receive hardware (12) for application signal F2 (17). The trans-receive hardware (12) on application signal F2 (17) is selected to ensure the usability of proposed solution to applications where transmission and reception both are required.

The server node (2) generates the synchronization signal F1 (16) for initially sometime without any modulated command data on it. This allows the client (4) to carrier lock the signal F1 (16). The mapping function implemented with lookup table (ROM) in FPGA (20) generates signal F2 (17) with direct transformation function. This transformation ensures the phase lock on F1 (16) which lead to automatically phase lock on F2 (17). The decision directed phase locked loop (DDPLL) ensures the carrier lock even when commands are transmitted on synchronization carrier using binary phase shift keying (BPSK).

After a predefined time, the synchronization signal from server (2) starts sending commands. The first command is to set the application tone F2 addressing to a specific node address. Once the command is received at client (4) the application signal F2 (17) without any phase shift is transmitted. The signal is then received by the server (2) and the server (2) estimates the phase shift between local copy of application signal and received signal from respective node. This phase shift value along with desired beamforming weight is loaded to client (4).

Computation of desired weights is given in equation (1). When all client nodes (4) are loaded with desired beamforming coefficients the application starts. A command will be issued by server (2) to start application.
A(n)=exp?(-1i*2*p*(n-1)*dx*cos?(az)*cos?(el)/?)* exp?(1i*2*p*(n-1)*dy*sin?(az)*cos??(el)/?? ) * exp?(1i*2*p*(n-1)*dz*sin(el)/?) (1)

where n= 1,2,3,..., N ( total number of nodes)
? is wavelength here we use F2 frequency to compute the wavelength
az,el is the orientation of the desired beam in azimuth and in elevation direction
dx, dy,dz are the spacing between server node and client node in x, y, z direction in meters.
Beamformed data is given in equation 2
Y= correlation matrix * steeringvector (2)
where correlation matrix R is given by
R=(X*X^H)/(k ) (3)
where k is no of snapshots, X is the received signal, X^H is conjugate transpose of X. Steering vector for a given azimuth and elevation can be computed from equation (1) by taking the conjugate. Here X is phase synchronized.

If beamforming application (19) is running the synchronization phase is switched off (optionally) for some time where high sensitive (fine) measurement on application signal takes place. The OCXO (15) used in nodes ensures minimum drift during the window of application execution. Further the drifted phase is synchronized in the SYNC time slot.

The current coordinates (x, y, z) of the client node (4) are used to estimate the drift (in case of moving platforms) and compensate for the beamforming coefficient. The system assumes high precision positioning technology when the desired beamforming (19) is above VHF frequency range or so. The wavelength itself when order of meters, the positioning system must have accuracy order of few centimeter level.

Figure.2 illustrates the architecture (200) of wireless server node depicting the components and working involved in the FPGA processing system in the server node according to the present invention. The FPGA (10) based server node (10) majorly comprises of a modulation block (27), a function translator (25), and a phase detector block (24). The server node (2) initially generates the synchronization signal F1 (16) and the client (4) carrier locks to the signal F1 (16) for the client node (4) to synchronize. Based on the application signal F2 received by the server node (2) from the client (4), the server node (2) issues the calibration command.

After synchronization is established between server node (2) and client node (4), the server node (2) receives application signal F2 (17) from the client node (4). Upon receiving the application signal F2 from the client node (4) is then passed to Digital Down Convertor (DDC) (22). The application signal F2 from the Digital down Convertor (22) is sent to phase detector (24) to estimate the phase difference of the received signal and internally generated signal with frequency F2. Frequency mapping is implemented in functional translator (25) that generates F2 frequency based on the F1 frequency.

Based on the phase difference CAL command (26) is dispatched through a modulation block (27), the CAL command (26) is modulated with F1 frequency and transmitted through DAC (13).

Figure.3 illustrates the architecture (300) of wireless client node depicting the components and working involved in the FPGA processing system in the client node according to the present invention. The FPGA (20) based client nodes (4) majorly comprise of a Digital Down Convertor (DDC) (22), a carrier lock loop (32), a function translator (25), and a bit decoder (34). The client node (4) receives the synchronization signal F1 (16) from server node (2), this received signal is passed through Digital Down Convertor (DDC) (22).

The signal from DDC (22) is given to carrier recovery loop (32) for the carrier lock. Upon carrier recovery signal is passed through bit decoder (34), where demodulation and bits decoding will happen. Based on the carrier frequency F1 the received signal is sent to bit decoder (34), the bit decoder (34) demodulates and decodes the command sent by the server node (2). Based on the locked carrier frequency F1, F2 frequency will be generated using the frequency mapping implemented in function translator (25). This F2 frequency is the application frequency used for the beamforming.

Figure.4 illustrates the block diagram (400) depicting the calibration sequence processed at the server and client wireless nodes according to the present invention. The server (2) first sends F1 (16) signal for synchronization, upon client receiving, locks the F1 (16), client sets application tone F2 (17). Next server (2) will send the command for calibration value, client (4) loads the calibration and starts the application. This process will be done for all the available client nodes (4) during power ON.

Figure.5 shows the time slot pulse (500) for synchronization and application signal frequencies according to the present invention. The time slot pulse shows the power ON at initial synchronization and further steady state transitions when the beamforming application is running. The time slot pulse shows the steady state transitions between calibration and synchronization in each node.

Figure.6 shows the precise time stamp generation (600) using the phase of synchronous tone carrier according to the present invention. The applications where the event time stamping is required to an accuracy of the order of sub nano seconds, the proposed method can be used. The figure 6 shows the concept of the proposed time stamp. The coarse time stamp is derived with common clock shared between nodes. This will be accurate upto cycle rate.

For example, when 100 MHz OCXO is used the cycle level accuracy will be of the order of 10 nsec. Further the quantized phase can be used to derive fine time stamp information. Considering that up to 4 degree phase lock possible under practical SNR conditions. The resolution of 1/90 can be achieved, to produce time stamp resolution of 0.11 nsec. This corresponds to spatial resolution of 3 centimeters (approximately). By increasing the synchronization clock rate to higher value even fine resolutions can be achieved. However, considering the self-position accuracies achievable and other SNR effects on spectrum sensing event considered for time stamping, this resolution is optimal for most of the applications. It is to be noted that the time stamp accuracy in conjunction with self-position accuracy decides the overall time stamp accuracy for moving nodes.

Figure.7 shows the beamforming output with no phase error (700) according to the present invention. The desired beam formation without any phase error is generated in a graph by plotting beam direction and gain.

Synchronization error budgeting in distributed beamforming
In distributed beamforming total error is contributed by all the resources as shown in the below equation (4).
total sync error =sync error due to PLL jitter +drift in PLL off time due to OCXO stability+ position wise error between nodes (4)

Figure.8 shows the array gain degradation with phase synchronization error (800) according to the present invention. It shows the array gain degradation with phase synchronization error. The phase error for all nodes with respect to server node is same considered here. Here one reference node and 63 client nodes are considered. We can conclude that even with phase synchronization error of 10 deg among the node very negligible degradation of array gain is observed.

Figure 9A and 9B shows the array gain degradation with respective node positioning error by considering the cumulative (900A) and non-cumulative (900B) positional error according to the present invention. This figure shows the array gain degradation with respective the node positioning error in for different VHF and UHF frequencies, considering 8 element linear array. The beamforming problem for nodes which are on moving platform is considered. Two types of positioning technologies are considered for simulation of positional errors. The adjacent node reference based scheme results in incremental positional error growth. The channel one reference based positioning scheme results in positional error which is offset from its expected position and it doesn’t lead to growing positional error.

In figure 9A, shows maximum position error considered between two adjacent nodes is considered on X axis. The position error with respective to reference server node to last node will be increasing assuming the positioning technology takes adjacent node as reference. Whereas figure 9B shows positional error offset by maximum value considering its original position for all nodes equally and its effect on array gain. It is to be noted that the simulation shown here in both figure 9a and 9b considering maximum positional error. In practical considering random error values less than this maximum value, results in less compromise on array gain.

Figure 10A and 10B shows the practical setup of server (1000A) and client hardware modules (1000B) for verifying time, frequency and phase synchronization through wireless means according to the present invention. The proposed solution for time, frequency and phase synchronization through wireless means is experimentally verified with hardware setup as shown in figure 10. The setup shows server node and client node with associated antennas. The server node and client nodes has wireless synchronization hardware in addition to 4 channel beamforming hardware. The master node with 4 wireless channels for beamforming and one wireless transmitter for synchronization to client is shown in figure. The client node has 4 channel beam forming hardware and one synchronization channel. There are additional observer antennas shown in setup which are used to verify the beam formation after synchronization.

The setup of two hardware modules is shown in figure 10B. Each node is based on ZYNQ FPGA hardware boards. Practical verification of beamforming and spatial power combining for all channels is verified. The effect of synchronization errors are verified.

Compromise in doppler analysis in radar signal processing due to distributed beamforming:
In radar system detection of target highly dependent on fact that moving targets create doppler distribution where as stationary clutter will not create doppler shift. Capability of any radar system to distinguish slow moving target i.e., minimum doppler frequency is decided by its system inside phase noise. Phase noise of the system is due to instability of OCXO, degradation in RF stages and degradation in digital stages. In the proposed configuration with OCXO stability during the offtime of synchronization link, the stability is achieved. The effect of PLL loop bandwidth resulting phase noise will not effect the performance of RADAR.

The architecture presented here achieves the solution of synchronization and provides two crucial advantages which are key requirements in beamforming applications. The first advantage is removed phase noise effects due to wireless synchronization, in pulse or frame processing type of applications such as Spectrum sensing. Second advantage is the scheme permits application frequency to maintain differently than the frequency of signal used for synchronization, which is must for electronic surveillance and jamming type of applications.

In the foregoing description, certain terms have been used for brevity, clearness and understanding; but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such terms are used for descriptive purposes and are intended to be broadly construed. Moreover, the description and illustration of the inventions is by way of example, and the scope of the inventions is not limited to the exact details shown or described.

Although the foregoing detailed description of the present invention has been described by reference to an exemplary embodiment, and the best mode contemplated for carrying out the present invention has been shown and described, it will be understood that certain changes, modification or variations may be made in embodying the above invention, and in the construction thereof, other than those specifically set forth herein, may be achieved by those skilled in the art without departing from the spirit and scope of the invention, and that such changes, modification or variations are to be considered as being within the overall scope of the present invention. Therefore, it is contemplated to cover the present invention and any and all changes, modifications, variations, or equivalents that fall within the scope of the underlying principles disclosed and claimed herein. Consequently, the scope of the present invention is intended to be limited only by the attached claims, all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having now described the features, discoveries and principles of the invention, the manner in which the invention is constructed and used, the characteristics of the construction, and advantageous, new and useful results obtained; the new and useful structures, devices, elements, arrangements, parts and combinations, are set forth in the appended claims.