Radar waveform design for spectral coexistence

We consider the problem of waveform design for Multiple-Input Multiple-Output (MIMO) radar in the presence of signal-dependent interference embedded in white Gaussian disturbance. We present two sequential optimization procedures to maximize the Signal to Interference plus Noise Ratio (SINR), accounting for a constant modulus constraint as well as a similarity constraint involving a known radar waveform with some desired properties (e.g., in terms of pulse compression and ambiguity). The presented sequential optimization algorithms, based on a relaxation method, yield solutions with good accuracy. Their computational complexity is linear in the number of iterations and trials in the randomized procedure and polynomial in the receive filter length. Finally, we evaluate the proposed techniques, by considering their SINR performance, beam pattern as well as pulse compression property, via numerical simulations.

In an asynchronous DS-CDMA system using random signature sequences and correlation receivers, the signal-to-interference-plus-noise ratio (SINR) at the output of each correlation receiver depends on the shape of the chip waveform employed. The use of double chip waveforms instead of a single chip waveform is investigated, in order to increase the SINR performance. An analytical expression for the SINR when double chip waveforms are used is obtained. To evaluate the performance of the proposed technique, an extension to Holtzman's approximation of the error probability for the case of double chip waveforms and signalling over an additive white Gausian noise channel is derived. Numerous numerical examples are given to demonstrate the advantage of using double chip waveforms over the single chip waveform. Moreover, the advantage of using double chip waveforms for improving the SINR performance over a multipath Rayleigh fading channel is also demonstrated.

Massive multiple-input multiple-output (MIMO) is an emerging technology, which enables future broadband wireless connections. In this paper we investigate the optimization problem of signal-to- interference-plus-noise ratio (SINR) balancing for users in a typical massive MIMO network. We present a fast converging robust beamforming solution for the case of imperfect channel state information at the transmitter. The proposed method applies the Smith form reformulation to transform the original non-convex optimization problem into a standard second-order cone program. The matrix stuffing technique and the alternative direction method of multipliers are then used to provide an efficient solution to the problem. Simulation results show that the proposed solution gives SINR performance with lower accuracy averaging 97%, while it converges to a solution more than twice faster than the optimal solution, which uses CVX and the SeDuMi solver.

In this paper, a two stage hybrid interference cancellation and equalization framework is proposed for interference cancellation in the uplink of multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. The first stage uses time domain equalization to suppress cochannel interference, mitigate asynchronism, and shorten the postequalization channel response to be no longer than the length of the cyclic prefix. The second stage performs low-complexity single tap equalization and detection in the frequency domain. The framework is developed specifically for spatial multiplexing and is applied to multiuser MIMO-OFDM systems with asynchronism between users as well as to single-user MIMO-OFDM systems. Various equalizer design methods are proposed that determine the coefficients directly from the training data and are compared with methods based on channel estimates. The equalizer coefficients and postequalization channel response are found by solving a joint optimization that maximizes the signal to interference-plus-noise ratio (SINR) in the frequency domain. Simulations compare various training-based methods and show the proposed methods provide good bit error rate (BER) and SINR performance in a variety of interference scenarios.

Aiming at the characteristics that the performance of millimeter wave fuze is easily affected by the natural environment, this paper studies the performance of millimeter wave fuze under rainfall conditions. By analyzing the theory of rain attenuation effect and backscattering effect, it is concluded that the rain attenuation effect reduces the received power of the signal, and the backscattering effect reduces the signal to interference plus noise ratio (SINR) of the receiving end. Based on this, the signal propagation path model under rainfall conditions is established. Finally, the variation of the maximum reliable detection range with signal wavelength and rainfall rate is simulated under different SINR requirements, and the variation of signal to noise ratio (SNR) and SINR with rainfall rate is compared under different distances. The simulation results show that both the rain attenuation effect and the backscattering effect lead to the decrease of the maximum reliable detection distance of millimeter wave fuze. With the increase of rainfall rate, the detection performance of millimeter wave fuze decreases, and the detection distance decreases by about 23.2 % under extreme conditions. The rain backscattering effect on millimeter wave fuze is higher than its attenuation effect, and the influence of rain backscattering effect on millimeter wave fuze increases with the increase of detection distance. When the detection distance increases from 15 m to 30 m, the difference between SNR and SINR at the receiving end of millimeter wave fuze increases by about 3 times. This study has important reference significance for the application of millimeter wave fuze in precision guided weapons.

In this letter, we focus on the signal-to-interference-plus-noise ratio (SINR) enhancement using transmitting waveform covariance matrix optimization in colocated MIMO radars. In our proposed algorithm, transmitted waveform covariance matrix has been optimized to focus the transmit beampattern into the target direction and in the receiver, we try to reject maximum number of interfering objects. In the proposed algorithm, transmitted waveform covariance matrix is able to be synthesized with binary phase shift keying waveforms in closed form. Simulation results show that our proposed method has better SINR performance in comparison with methods in which transmitted covariance matrix is designed independently from the interferences locations.

Visible light communications (VLC) is an emerging wireless communication technology that can serve high speed data rates by using existing lighting infrastructure without congesting the radio spectrum. This paper studies the effect of various multi-element VLC transmitter and receiver configurations on the link quality. With this purpose, the signal-to-interference-plus-noise-ratio (SINR) distribution is investigated via extensive simulations considering a multipath environment with different transceiver configurations and diversity combining techniques. Additionally, we propose a beam steering technique using the piezo-electric based tilting of LEDs to improve the SINR, which tilts the LEDs with piezo-electric actuators towards the location of the receiver. Simulation results show that significant gains can be obtained on SINR performance by using optimized transceiver configurations and diversity combining at the receiver. Moreover, even with small titling angles at the transmitter, up to 12 dB SINR gain is obtained using beam steering.

In the first part of the thesis we investigate bandwidth allocation in next generation cellular systems employing relays similar to LTE advanced systems with type-I relays. We jointly optimize the bandwidth and power usage under constraints on required rate, bandwidth and transmit power. We study scenarios wherein, the relay acts as a forwarder for multiple User Equipments (UEs/users) in both uplink and/or downlink. This includes scenarios when the relay has its own data to send along with forwarding the data of other users. We examine the weighted power minimization problem for relaying with multiple users. We also show specifi c results with N user scenario and also single user case in order to understand how the bandwidth and power are allocated. Numerical evaluations with N users on a three sector LTE-A cell employing Fractional Frequency Reuse (FFR) indicate that power savings of at least 3 dB can be achieved by optimizing over both bandwidth and power. Base stations with a large number of transmit antennas have the potential to serve a large number of users simultaneously at higher rates. They also promise a lower power consumption due to coherent combining at the receiver. However, the receiver processing in the uplink relies on the channel stimates which are known to su ffer from pilot contamination. In the second part of the thesis, we perform an uplink large system analysis of multi-cell multi-antenna system when the receiver employs a matched fi ltering and MMSE fi ltering with a pilot contaminated estimate. We find the asymptotic Signal to Interference plus Noise Ratio (SINR) as the number of antennas and number of users per base station grow large while maintaining a fixed ratio. To do this, we make use of the similarity of the uplink received signal in a multi-antenna system to the representation of the received signal in CDMA systems. The asymptotic SINR expression for both matched fi lter and the MMSE fi lter explicitly captures the e ffect of pilot contamination and that of interference averaging. This also explains the SINR performance of receiver processing schemes at di fferent regimes such as instances when the number of antennas are comparable to number of users as well as when antennas exceed greatly the number of users. Specifi cally, we explore the scenario where the number of users being served are comparable to the number of antennas at the base station. It is seen that MMSE fi lter is capable of suppressing the in-cell interference and that the interference power due to pilot contamination is the same as in a matched fi lter with a pilot contaminated estimate. We find the expression for the amount of interference suppression obtained using an MMSE filter which is an important factor when there are signi ficant number of users in the system as compared to the number of antennas. We validate the asymptotic expression through simulations and compare with an MMSE fi lter with a perfect estimate. Simulation results for achievable rate is close to theory for even a 10-antenna base station with 3 or more users per cell. In a typical set up, in terms of the five percentile SIR, the MMSE fi lter is shown to provide signifi cant gains over matched fi ltering and is within 5 dB of MMSE fi lter with perfect channel estimate. We also show that the achievable rates are within a 1 bit/symbol of the MMSE with perfect estimate when the number of users is comparable to the number of antennas.

This paper considers the finite-order filter design problem for the source and multiple full-duplex (FD) relays in a cooperative communication system under frequency-selective fading channels. The goal is to optimize the source and relay filters such that the end-to-end signal-to-interference-plus-noise ratio (SINR) of minimum mean-squared error decision-feedback equalizer (MMSE-DFE) can be maximized. The resultant design problem is very difficult since we need to deal with self interference (SI), inter-relay interference (IRI), and inter-symbol interference (ISI) at the same time. Novel designs are then proposed to overcome the difficulty in this work. Transforming the signals into the frequency domain and using some optimization techniques, we first theoretically derive the power spectrum of the source filter and the spectrums of the relay filters. Then, the finite-order design is developed to approach the derived spectrums. Based on the weighted least-square (WLS) criterion, the Steiglitz-McBride method is exploited to obtain the filter coefficients in finite lengths. Numerical results demonstrated that complete removal of SI may not be a good strategy; preserving a certain amount of SI at each relay instead provides better SINR performance.

This paper focuses on the radar waveform design in a spectrally crowded environment. A spectral constraint is forced on the radar waveform to ensure spectral compatibility with the overlayed licensed electromagnetic radiators. The waveform design problem is formulated by maximizing the output signal-to-interference-plus-noise ratio (SINR) under the energy, similarity and spectral constraints. Inspired by the feasibility and high-quality solution properties of feasible point pursuit successive convex approximation (FPP-SCA), we develop an efficient al-gorithm framework based on FPP-SCA to solve the waveform design problem. Numerical results demonstrate the effectiveness of the proposed algorithm.

Due to cell planning in a cellular communication network, it is difficult for a mobile user in a cell to get ranging measurements from other neighboring cells. Consequently, it is necessary to enhance signal sensitivity using long integration techniques so that the user position is obtained by trilateration. In order to maximize integration gain in coherent/noncoherent hybrid long integration, it is desirable to make SNR (signal to noise ratio) after coherent integration become as large as possible. Because SIR (signal to interference ratio) is not improved by the long integration, however, it is needed to mitigate CCI (Co-Channel Interference) so that the resultant hearability can be enhanced for weak signals. This paper presents a hybrid long integration scheme in presence of CCI. SNIR (signal to noise plus interference ratio) is employed to explain the loss induced by interference as well as noise. Together with interference cancellation and residual frequency estimation technique, design procedure of hybrid long integration is proposed to maximize SNIR. Simulation results show that hearability is greatly improved at most of cell coverage when the proposed method is used.

In this paper, a novel radar waveform phase function design is presented that constructs a radar waveform that spectrally manuevers around in-band co-channel interference (CCI) from active communications users that are co-channel with the radar system. The design approach treats the CCI problem as the physical interpretable problem of optical refraction where the time-frequency (TF) signature of the radar waveform is made to be analogous to a light ray propagating from a start time and position (frequency) to an end time and position (frequency) and will naturally accelerate through the CCI as if the equivalent light ray accelerated in through different mediums (with an index of refraction related to CCI power spectral density (PSD)). Using the Euler-Lagrange equations, we design the radar phase function that is used to modulate a constant modulus (CM) waveform. The radar waveform design will generally result in a nonlinear-frequency modulated (NLFM) waveform that provides improved signal-to-interference-plus-noise-ratio (SINR) on a potential target in the presence of CCI leading to improved probability of detection performance. We provide theoretical analysis and simulation results for the proposed waveform design.

This paper deals with the problem of waveform design for through-the-wall radar with the presence of signal-dependent interference embedded in white Gaussian noise. Based on the target matched illumination theory, we present a linear combination method (LCM) to design the transmitted waveform for target detection. The LCM divides the waveform design problem into two independent optimization problems, and combines the solutions of them linearly. Simulation results depict that the LCM has better convergence performance and computational efficiency comparing with the alterative algorithm, while getting a signal to interference plus noise ratio (SINR) improvement.

Joint radar communication systems have been recently proposed for radar and communication sharing spectrum and hardware, to reduce the resource cost of platforms. In this paper, we consider the waveform design problem for a joint multiuser MIMO communication and MIMO radar system. We propose an optimization problem for waveform design, in which the signal-to-interference-plus-noise ratio (SINR) at users and the transmit beam pattern of radar are jointly optimized. To guarantee the efficiency of power amplifiers, the transmit waveform is constrained to be constant modulus. To deal with the non-convex constant modulus constraint, we propose an alternating descend method to solve the problem. The simulation results indicate that under high transmit signal-to-noise ratio (SNR), the communication quality can be guaranteed, along with a reasonable performance loss of radar. Moreover, the performance gap between the constant modulus constraint and the more relaxed per-antenna power constraint, is not significant.

The paper proposes a new set of normalization techniques for precoding/beamforming matrices applicable to broadband multiuser multiple-input multiple-output (MIMO) satellite systems. The proposed techniques adapt known normalization methods to account for the signal attenuation experienced by users due to the degradation of antenna gain and free space losses towards the edge of the coverage. We use, as an example, an array-fed reflector (AFR) antenna onboard a satellite in geosynchronous orbit (GEO), which provides a favorable trade-off between high-directivity, reconfigurability, and the requirement for digital processing, but suffers from high scan losses away from broadside due to optical aberrations when considered for global coverage applications. Three different precoding/beamforming techniques are employed, namely zero forcing (ZF), minimum mean squared error (MMSE), and matched filtering (MF). Low-complexity power normalization techniques digitally applied after the beamformer are introduced that, in the absence of any atmospheric effects, lead to iso-flux-like characteristics whilst satisfying the power constraint per feed. In comparison with other methods reported in the literature, mainly based on iterative algorithms, the proposed techniques consist in closed-form expressions to provide uniform signal-to-noise ratio (SNR) and signal-to-noise plus interference ratio (SNIR) across the users without significant impact on the payload sum rate. Numerical results are presented to comparatively demonstrate the achieved performance in terms of total capacity and distribution of SNR and SNIR at various noise and interference scenarios.