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M.I. Schöpe

2 records found

Authored

Improvement of Hybrid Codes for MIMO radar using multi-pulse waveforms and signal processing

Theoretical analysis and experimental evaluation

Master thesis (2017) - M.I. Schöpe, J.N. Driessen, Alexander Yarovoy , Marc Lesturgie

According to literature, MIMO radars often use orthogonal waveforms on their different channels to achieve a wide angular beam and so-called colored transmission. The generation of orthogonal signals is very difficult and true orthogonality cannot be achieved in practice. The Circulating Codes provide a simplified alternative to orthogonal signals, by transmitting the same waveform, but slightly shifted in time from channel to channel. By applying digital beamforming on transmit through signal processing on receive, a performance similar to orthogonal signals can be achieved. The Circulating Codes can also be used with a spatial code along the antenna elements, to improve the auto-correlation properties of the signal and thus the range resolution of the radar. These codes are called Hybrid or Delft Codes.

In this thesis, the Circulating Codes, as well as Hybrid Codes are revisited and analyzed again. An implementation for simulations has been created in Matlab to examine their behavior in more detail. To improve the range resolution of the Hybrid Codes, this thesis proposes the use of so-called Golay pairs as spatial codes. Each Golay pair consists of two codes, which have the property that the sum of their auto-correlation functions produces one strong peak and zero sidelobes. Since the application of these codes requires the transmission of two pulses, the phase shift due to the displacement of a moving target in between of the pulses has an impact on the result. This thesis focuses on the mitigation or correction of this phase shift, by the use of different methods and presents two possible solutions which perform well in simulations.

Finally, some of the techniques are applied in practical measurements with an available radar system. The results of these measurements show that the single-pulse techniques of the Circulating and Hybrid Codes perform well with the system, while the multi-pulse techniques with Golay pairs suffer from much higher sidelobes than expected from the simulations. First of all, this shows that the system has certain issues that need to be improved. Secondly, it shows that Hybrid Codes with Golay pairs are sensitive to disturbances and phase shifts. Therefore, very clean signals are required that might be difficult to generate in practice.

Contributed

Approximately Optimal Radar Resource Management for Multi-Sensor Multi-Target Tracking

A First Step Towards a Distributed Solution for Radar Resource Management in a Sensor Network

Master thesis (2021) - H.B. van der Werk, M.I. Schöpe, J.N. Driessen

The Radar Resource Management (RRM) problem in a multi-sensor multi-target scenario is considered. The problem is defined as a constrained optimization problem in which the predicted error covariance is minimized subject to resource budget constraints. By applying Lagrangian Relaxation (LR) the problem is decoupled into multiple sub-optimization problems. The problem is modeled according to a Partially Observable Markov Decision Process (POMDP). Using a stochastic optimization framework called policy rollout, the POMDP is solved non-myopically by looking ahead into the expected future. Two novel implementations, namely a centralized and distributed implementation are presented as viable approaches for solving this problem for a multi-sensor case. The centralized implementation, defined as the approximately optimal solution, utilizes a global policy per task. As such, the policy rollout for a single target needs to explore the actions of multiple sensors. The distributed implementation is considered as a practical alternative to improve on the computational complexity of the policy rollout of the centralized implementation. Now per sensor and per task a policy rollout is computed. To maintain a similar performance as the centralized implementation, at the beginning of each policy rollout the last known actions of the other sensors are shared. An additional third independent implementation is considered. The independent implementation uses no communication during the optimization process and is considered to be the implementation with the lowest performance with respect to the cost. All implementations have been applied to multiple two-dimensional simulated radar tracking scenarios. A comparison is made between the centralized, distributed and independent implementation based on the average cost and runtime. Results indicate that both the centralized and distributed implementation outperform the independent implementation with respect to the cost by a factor two. Subsequently, the distributed solution converges to similar results as the centralized implementation while requiring significantly less computational resources.