Sum Channel Research Articles

Main lobe deceptive jamming suppression based on blind source separation and energy detection for monopulse radar

AbstractMain lobe deceptive jamming always causes the serious degradation of signal detection ability and angle measurement precision of monopulse radar. In recent years, the Blind Source Separation (BSS) method has been adopted to suppress the main lobe jamming. However, the separation results of BSS have the problem of amplitude ambiguity, which will cause the radar using monopulse angle measurement fail to measure the angle parameters after jamming suppression. To tackle this problem, a novel main lobe jamming suppression method is proposed based on BSS and energy detection. Firstly, the models of target echoes and jamming in the sum and difference beam receiving channels are derived. Secondly, the target echoes and interferences are separated by the Joint Approximate Diagonalisation of Eigenmatrices (JADE) algorithm, and then the unperturbed signal segments in the mixed signal are extracted by energy detection, thereby obtaining the precise ratio of the sum and difference channels to complete the angle measurement. Performance of the method was verified by numerical simulation. The results show that the proposed method can achieve interference suppression while accurately estimating the angle parameter of the target.

Hybrid Sidelobe Recognition Method Using Boresight Error and Quadrant Signal Difference for Monopulse Array

In this paper, a sidelobe recognition method using boresight error and quadrant signal difference for a monopulse array is proposed. A conventional sidelobe recognition method compares the difference between the sum and delta channels. This method works well for the azimuth and elevation planes. However, the method is prone to many errors in the diagonal region of the two-dimensional plane. To overcome this problem, a method to calculate the deviation of the boresight error difference with different frequency combinations and a threshold to identify the sidelobe is proposed, and the method is validated to significantly reduce the error region. If a four-quadrant signal can be extracted separately, the signal deviation can be calculated and compared with the threshold, and the error region can be further reduced. The effects of each margin and bandwidth on the recognition performance are analyzed, and a slot array antenna is simulated to assess the method’s effectiveness.

Bandwidth Enhancement of Comparator Applied in W-Band Circularly Polarized Monopulse Antenna

In this letter, a novel wideband comparator for W-band circularly polarized (CP) monopulse antenna is proposed and analyzed. The comparator mainly consists of four 3 dB waveguide couplers and a novel wideband phase shifter (PS). The bandwidth of the comparator is greatly enhanced by combining the sequential rotation feeding technique with the wideband PS technique for the first time. To verify its wideband performance, the CP monopulse antenna consisting of the comparator and a 2×2 CP horn array is fabricated and measured. The experimental results are in good agreement with the simulation. For the measured sum (Σ) channel, the reflection coefficient lower than -10 dB, the realized gain not less than 11.5 dBi, and the axial ratio (AR) better than 0.45 dB are realized in the whole W-band (75-110 GHz). For the measured azimuth (AZ) and elevation (EL) difference (Δ) channels, the null depths of the difference patterns are less than -25.8 dB at 80, 92.5, and 105 GHz, and the difference patterns are symmetrical and stable.

Experimental demonstration of an optics-based 4-PSK half-adder using nonlinear wave mixing.

We experimentally demonstrate an optics-based half-adder of two 4-phase-shift-keying (4-PSK) data channels using nonlinear wave mixing. The optics-based half-adder has two 4-ary phase-encoded inputs (i.e., SA and SB) and two phase-encoded outputs (i.e., Sum and Carry). The input quaternary base numbers {0,1,2,3} are represented by 4-PSK signals A and B with four phase levels. Along with the original signals A and B, the phase-conjugate signal copies A* and B*and phase-doubled signal copies A2 and B2 are also generated to form two signal groups SA(A, A*, A2) and SB(B, B*, B2). All of the above signals in the same signal group are (a) prepared in the electrical domain with a frequency spacing of Δf and (b) generated optically in the same IQ modulator. When combined with a pump laser, group SA mixes with group SB in a periodically poled lithium niobate nonlinear (PPLN) device. At the output of the PPLN device, both the Sum (A2B2) and the Carry (AB + A*B*) are simultaneously generated with four phase levels and two phase levels, respectively. In our experiment, the symbol rates can be varied between 5 Gbaud and 10 Gbaud. The experimental results show that (i) the measured conversion efficiency of two 5-Gbaud outputs is approximately -24 dB for Sum and approximately -20 dB for Carry, and (ii) the measured optical signal-to-noise ratio (OSNR) penalty of the 10-Gbaud Sum and Carry channels is <10 dB and <5 dB, compared with that of the 5-Gbaud channels at the BER of 3.8 × 10-3.

Main-Lobe Recognition for Sum-Delta Monopulse of Single-Ring Circular Array Antenna

The target must be located within the main-lobe of the antenna in order to measure the direction of the target by using sum-delta monopulse technique. The most common way if the target is located within the main-lobe is to compare the amplitude of the sum channel received signal with the delta channel received signal. However, in the case of the single-ring circular array antenna, it is difficult to apply the conventional method due to its structural limitation where antenna elements do not exist in the center of the array. In this paper, we proposed a novel method to identify whether a target is located within the main-lobe by appropriately adjusting the feeding amplitude of each element constituting the single-ring circular array antenna through the particle swarm optimization method. Simulation results showed that the proposed method can determine whether the target is located within the main-lobe of the single-ring circular array antenna.

A time‐varying angle extraction method for refined proximity group targets tracking

AbstractIn order to improve the detection probability of weak targets, tracking radar using sum and difference beams often adopt the method of long‐time coherent integration. However, the multidimensional migration of time‐varying targets will lead to the decline of parameter estimation accuracy. To solve this problem, this article proposes a refined angle estimation method for time‐varying targets with the traditional sum and difference beam echo model, this method compensates and searches the angle parameters of the targets based on subarray rotation invariant and focus process. In addition, this article also studies the masking problem of highly dynamic proximity group targets detection, and proposes an adaptive weighted LMS‐CLEAN based on Least Mean Square criterion, which effectively reduces the influence of masking effect on the parameter estimation accuracy of weak targets. Firstly, the proposed algorithm performs angle search and phase compensation on the pulse compression echo of sum and difference channels based on subarray rotation invariant. Secondly, focus the search matrix, reconstruct the strong target echo, and stripe it from both channels by adaptive weighting. Lastly, repeat the above steps until parameters of all targets are achieved precisely. The proposed two algorithms maintain a very low computational effort while effectively reducing the parameter estimation error, and are highly promising for engineering applications. In order to verify the effectiveness of the proposed algorithm, this article also provides some numerical experiments to compares with two existing algorithms in error performance, anti‐noise performance, and computational complexity.

Millimeter-Wave Monopulse Filtenna Array with Directive Dielectric Resonators

This paper presents a new millimeter-wave monopulse dielectric resonator (DR) filtering antenna (filtenna) array based on substrate-integrated waveguide (SIW) technology. The monopulse comparator realized by a square dual-mode (&lt;i&gt;TE&lt;/i&gt;&lt;sub&gt;102&lt;/sub&gt; and &lt;i&gt;TE&lt;/i&gt;&lt;sub&gt;201&lt;/sub&gt;) SIW feed cavity uses diagonal irises, of which couplings between the feed and next-stage cavities lead to almost identical filter responses for the sum and difference channels with compact size and a planar single-substrate structure. Both dielectric resonator antennas (DRAs) adopting &lt;i&gt;HEM&lt;/i&gt;&lt;sub&gt;133&lt;/sub&gt; mode for enhanced directivity are implemented with two filters based on SIW. The DR acts as the last resonator and the radiator in the filtenna. The prototype is designed at the Ka-band with a center frequency of 27.65 GHz and an operation bandwidth of 700 MHz. The measurement shows a 15-dB fractional bandwidth of 2.36%, a gain of 10.84 dBi for the sum channel, and a null depth of -15.6 dB for the difference channel.

Conceptual Design of a Semi-Dual Polarized Monopulse Antenna by Computer Simulation

Presented in this paper is a conceptual design by computer simulation of a monopulse reflector antenna with dual-circularly polarized sum patterns and linearly polarized azimuth and elevation difference patterns, which can be called a semi-dual polarized antenna. The proposed antenna consists of a five-element monopulse feed and a prime-focus parabolic reflector. The novelty of the proposed antenna is a monopulse feed consisting of a dual-circularly polarized square waveguide sum channel radiator and linearly polarized rectangular waveguide azimuth and elevation difference channel radiators. The separation of dual circular polarization is realized by a septum polarizer. The difference pattern is obtained by feeding two rectangular waveguides in opposite directions using a coaxial probe. The proposed monopulse feed geometry requires only two power combiners for a monopulse comparator network while providing dual-polarized performance comparable to the full dual-polarized sum and difference channel monopulse scheme. The concept of the proposed antenna is shown in a conceptual design by computer simulation. The monopulse feed is designed first, and then combined with a parabolic reflector. The designed monopulse reflector antenna operates at 14.5–16.0 GHz, and shows excellent sum and difference pattern characteristics: 36.1–36.7 dBc sum channel directivity with 0.65 dB boresight axial ratio and 32.6–32.9 dBi difference channel directivity with 1.56–1.66° crossover angle.

Design of a Ku-Band Monopulse Antenna with a Truncated Reflector and an Open-Ended Waveguide Feed

This paper presents a design for a monopulse reflector antenna with asymmetric beamwidths for radar applications at the Ku band. The proposed design features a rectangular waveguide monopulse feed and a truncated parabolic reflector. An array of four open-ended rectangular waveguides were employed to realize a compact monopulse feed. The reflector is cut in the H plane of the feed producing a wider beam in the azimuth plane. This type of pattern is useful in applications such as projectile tracking and airport surveillance. The design parameters for optimum performances are chosen at all stages of the design. The design and analysis have been carried out using the commercial simulation tool CST Studio Suite 2022. The directivity of the sum, elevation difference and azimuth difference channels of the reflector antenna are 32.1, 28.1, and 26.4 dB at 14 GHz; 30.9, 29, and 27.3 dB at 15 GHz; 31.7, 29.6, and 27.6 dB at 16 GHz; 31.6, 29.9, and 27.8 dB at 17 GHz.

Performance of Outage Probability and Ergodic Sum Rate for Two-User Paired NOMA Downlink System

Non-Orthogonal Multiple Access (NOMA) is a technique to support a massive number of users to access the radio resources simultaneously and frequently. Existing conventional multiple access has been exhausting and insufficient for providing physical layer services in fifth Generation (5G) cellular systems. The user-pairing principle is adapted to resolve this issue that fulfils the maximum sum rate and channel utility. But it is lacking when a user with a near gain enters a user pair. Therefore, this paper considers a single pair occupying two different gain users who understand practical circumstances by evaluating outage probability using the stochastic geometry method. The paired users will calculate the ergodic sum rate and calculates the closed-loop solution for the outrage probability. The outage probability performance is obtained between NOMA paired users and the traditional multiple access approaches.

Deep Reinforcement Learning Based Optical and Acoustic Dual Channel Multiple Access in Heterogeneous Underwater Sensor Networks.

In this paper, we investigate how to efficiently utilize channel bandwidth in heterogeneous hybrid optical and acoustic underwater sensor networks, where sensor nodes adopt different Media Access Control (MAC) protocols to transmit data packets to a common relay node on optical or acoustic channels. We propose a new MAC protocol based on deep reinforcement learning (DRL), referred to as optical and acoustic dual-channel deep-reinforcement learning multiple access (OA-DLMA), in which the sensor nodes utilizing the OA-DLMA protocol are called agents, and the remainder are non-agents. The agents can learn the transmission patterns of coexisting non-agents and find an optimal channel access strategy without any prior information. Moreover, in order to further enhance network performance, we develop a differentiated reward policy that rewards specific actions over optical and acoustic channels differently, with priority compensation being given to the optical channel to achieve greater data transmission. Furthermore, we have derived the optimal short-term sum throughput and channel utilization analytically and conducted extensive simulations to evaluate the OA-DLMA protocol. Simulation results show that our protocol performs with near-optimal performance and significantly outperforms other existing protocols in terms of short-term sum throughput and channel utilization.

Sub-CPI STAP based clutter suppression and target refocusing with airborne radar system

Under the interference of airborne radar clutter, it is a challenge for fast maneuvering target detection, because of the nonstationary echo signal involved within the long coherent processing interval (CPI). To tackle this issue, a robust clutter suppression and small maneuvering target detection method is proposed in airborne radar system, which is referred to as the sub-CPI space-time adaptive processing (STAP) based refocusing. For robust clutter suppression, the whole CPI is divided into a series of equal-length and overlapped sub-CPIs with the sliding window technique. In each sub-CPI, the STAP algorithm is adopted for robust clutter suppression, in which the consistent covariance matrix estimation is derived to guarantee the linear phase response within the whole CPI. However, as endo-clutter weak target is considered, the signal-to-clutter-plus-noise ratio (SCNR) after sub-CPI STAP still cannot meet the performance requirement. Thus, the target refocusing is applied for further SCNR improvement based on the semi-searching mechanism. However, the range walking (RW) and Doppler frequency migration problems defocus the energy of fast maneuvering target over range and Doppler frequency dimensions, respectively. To circumvent such problems, Keystone transform is utilized to correct the RW, followed by the Lv's distribution to achieve target refocusing. Numerical simulations and measured results with sum and difference channels validate the effectiveness of the proposed method.

Performance Analysis of Multiple Antennas Synthetic False Target Jamming

The radar jamming technology has been studied in this paper mainly, which uses the antenna synthetic wave to generate phase distortion at the signal reception to carry out angle measuring jamming, such as traditional cross-eye jamming. However, cross-eye jamming has strict parameter tolerance. To improve the tolerance range of the phase parameters, a multiple antennas synthetic false target electromagnetic jamming technique is proposed in this paper, which has a wider phase parameter tolerance and jamming range. The jamming method can be regarded as an improved cross eye jamming method. We can conclude that this method can generate a “false target” in space and far away from the carrier which has jamming system, which mislead the radar to point to “false target” rather than to real targets. A jamming system with three jamming antennas was considered as the research object. The position of “false target” can be controlled casually by adjusting the feed amplitude and phase of the three antennas simultaneously. The jamming mathematical model of synthetic false target with three antenna emitters is constructed under the sum and difference channel transceiver mechanism of radar in this paper. The error angle and synthetic gain of the three jamming antennas were derived. The phase parameter tolerance of the proposed method was obtained- and compared with cross-eye jamming. A rigorous mathematical derivation is proposed in this paper, and the superiority of the multiple antennas synthetic false target jamming method is verified.

Joint source-channel coding via model predictive control

We propose a joint source-channel coding (JSCC) scheme based on model-predictive control (MPC) for encoding an analog discrete-time source over a memoryless communication channel. The decoder is assumed to be fixed and given, and the MPC encoder is set to minimize the frequency-weighted mean-squared error (FWMSE) while satisfying a channel input constraint. We derive analytic expressions for the associated finite-horizon optimization MPC problem for an asymptotic (in time) average or sum channel input constraint. For the case of complex additive white Gaussian noise channel and an M-quadrature-amplitude modulation (M-QAM) decoder, these expressions can be written explicitly, which allows for an efficient numerical solution. For the case M=4 and considering a frequency weighting criterion that models the sensitivity of the human hearing, we show by simulations that our proposed scheme yields an FWMSE significantly smaller than that yielded by the corresponding non-JSCC scheme (a 2-bit uniform quantizer in tandem with a 4-QAM channel encoder and decoder).

Partially Coherent Direct Sum Channels

We introduce Partially Coherent Direct Sum (PCDS) quantum channels, as a generalization of the already known Direct Sum quantum channels. We derive necessary and sufficient conditions to identify the subset of those maps which are degradable, and provide a simplified expression for their quantum capacities. Interestingly, the special structure of PCDS allows us to extend the computation of the quantum capacity formula also for quantum channels which are explicitly not degradable (nor antidegradable). We show instances of applications of the results to dephasing channels, amplitude damping channels and combinations of the two.

Capacity Enhancement of NOMA-MIMO With OAM-IM

In this letter, non-orthogonal multiple access (NOMA) is integrated with orbital angular momentum (OAM)-based multiple-input multiple-output (MIMO), denoted as OAM-MIMO, and OAM with index modulation, denoted as OAM-IM, to improve its downlink channel capacities for multiple users. The user and sum channel capacities are evaluated and compared with those of existing schemes such as NOMA with OAM-MIMO, conventional NOMA with MIMO, and conventional orthogonal multiple access with OAM-IM. The simulation results show that the proposed scheme outperforms the conventional schemes in terms of both individual user and sum channel capacities.

Capacity Analysis of Cooperative NOMA-OAM-MIMO Based Full-Duplex Relaying for 6G

A cooperative non-orthogonal multiple access (CNOMA) system and an orbital angular momentum (OAM) -based multiple-input multiple-output multiplexing system is proposed as full-duplex relaying (referred to as CNOMF) by the cell center user to the cell edge user in this letter. The proposed CNOMF scheme can significantly improve the capacity of cell edge user and sum channel capacity via user-assisted decode and forward based full-duplex relaying by utilizing different ranges of OAM modes for a 6G (Sixth generation) wireless communication system, compared to other existing schemes (For example, CNOMA-MIMO with FDR, and orthogonal multiple access with OAM-MIMO and half duplex relaying); this was demonstrated via numerical result analysis.

Forward-looking Imaging via Doppler Estimates of Sum-difference Measurements in Scanning Monopulse Radar

Monopulse technique is used in scanning radar systems to improve image quality in the forward-looking area. However, monopulse measurements fail to resolve multiple targets in the same resolution cell because of angular glint which often results to image blurring. In response to this, we propose a monopulse forward-looking imaging method utilizing Doppler estimates of sum-difference measurements. First, target multiplicity is resolved by exploiting the different Doppler shifts caused by the relative motion between the platform and the targets at different directions. High azimuthal angle measurement accuracy of the Doppler estimates is then obtained using the Sum-Difference Amplitude-Comparison (SDAC) monopulse technique. Subsequently, the intensity of the sum channel estimates is projected onto the image plane according to the range and angle measurements. To further improve the precision of angle measurements, a Chirp-Z Transform (CZT)-based algorithm is proposed for the reconstruction of the Doppler estimates of the sum-difference channels. Simulation results demonstrate the capability of the proposed methods in resolving multiple targets at high squint angles in a large scanning field. Real data experiments show significant improvement of image profiles using the CZT-based algorithm compared to that of the conventional monopulse imaging method.

A 1-D Electronic Beam-Scanning Monopulse Antenna Array Based on a Compact Stripline Phase-Shifter

A completely passive method of enabling 1-D beam-scanning for a monopulse antenna array with controllable sidelobe levels (SLLs) is presented in this letter. To achieve this unique function, a compact frequency-dependent phase-shifter composed of stripline resonators is proposed. This proposed phase-shifter provides similar sensitivity as conventional meander striplines, while its size is much smaller, enabling a successful implementation into a highly integrated feeding network with monopulse functions. The validation is provided by a 4 × 16 monopulse antenna array operated at X-band. A good correspondence is achieved between simulation and measurement for both S-parameter and far-field results. Measurement results of the prototype indicate a scanning range from -54° (10.5 GHz) to 48° (11.5 GHz) can be covered. Within the entire operational frequency range, the sidelobe levels are smaller than -15 dB for the sum channel, while a null depth better than -20 dB is observed in the difference channel. The proposed method is characterized by control simplification and very suitable to be deployed in cost-effective tracking systems.

Channel Capacity Analysis of Non-Orthogonal Multiple Access With OAM-MIMO System

In this letter, an orbital angular momentum-based multiple-input multiple-output (OAM-MIMO) multiplexing system is integrated with non-orthogonal multiple access (NOMA) to enhance the user and sum channel capacities of the downlink NOMA for multiple users. The user and sum capacities of the proposed NOMA-OAM-MIMO scheme is analyzed and compared with other conventional schemes such as conventional NOMA with MIMO, and conventional orthogonal multiple access with OAM-MIMO multiplexing.