Jabran Akhtar

An ECCM Scheme for Orthogonal Independent Range-Focusing of Real and False Targets

This article develops a radar signaling scheme providing full immunity against a repeat jammer. Resistance against the jammer is achieved by employing the concept of pulse diversity where the radar continuously emits either modified version of previous waveforms or new pulses following a specific orthogonal structure. This structure enables the radar to successfully separate the signals being reflected off the real targets and the false reflectors being emulated by the jammer, resulting in full independent range-focusing. The method permits combination of various types of pulses and also offers waveform diversity.

Cancellation of range ambiguities with block coding techniques

This paper presents radar signaling schemes for cancellation of late time arriving echos. Signal reflections arriving delayed at the radar when the radar has already emitted a next pulse result in range ambiguities and materialize as potential false targets. In this work we propose pulse block coding techniques to distinguish echo reflections originating through the recently emitted pulse and those impending from subsequent pulses. The methods introduced require only simple matched filtering operations at the receiver and permit usage of arbitrary waveforms with potential for waveform diversity gains.

Formation of Range-Doppler Maps Based on Sparse Reconstruction

This paper presents an application of compressed sensing in a pulsed system, such as a radar or sonar to form range-Doppler maps. Instead of transmitting a train of pulses, we portrait a system where the pulse emission itself takes place in a sparse manner. We show that any empty data segments can effectively be filled in by sparse reconstruction, which can also be used to extrapolate supplementary values. Simulations covering various conditions are used to demonstrate the effectiveness of the proposed setup.

Antenna selection for MIMO radar transmitters

Radar systems with widely separated transmitters and receivers offer advantages of spatial diversity as incoming echos can be observed originating through diverse aspect angles. This can be utilized to improve the overall sensitivity and performance of radar systems. This work introduces low-complexity antenna selection for MIMO radar systems where only a few of the available transmit antennas are selected. The antenna selection is carried out by making use of statistical radar information such as transmit antenna correlation and line-of-sight (LOS) reflectivity levels. The scheme is designed to ensure that the total available energy is only spread across the most viable antennas with independent diversity branches and strong LOS reflectors. Simulations are used to demonstrate that the use of statistical information and antenna selection can yield good performance compared to an all antenna system in many scenarios.

A power distribution scheme for correlated MIMO radar transmitters

MIMO (multiple-input multiple-output) radar systems with distributed transmitters and receivers have potential to significantly improve the performance of radar systems. MIMO systems benefit by utilizing the notion of spatial diversity as the receivers have the ability to observe incoming echos originating off various aspect angles. This capability is however dependent upon the fact that the antennas are not correlated with each others which can diminish the diversity gain. This article attempts to improve correlated MIMO system performance by proposing a power distribution algorithm which weights the antennas taking account of any correlation present at the emitters. Antennas who show strong correlations transmit pulses with less power so that the total available energy is spread across diversity branches more befittingly. Simulations are used to validate the results.

Compressed sensing with interleaving slow-time pulses and hybrid sparse image reconstruction

This paper explores a type of hybrid sparse reconstruction technique for modern multifunction task scheduling radars and on following range-Doppler plots. A compressed sensing (CS) framework is devised to emit and then receive interleaved radar pulses in a scarce manner within a coherent processing interval. Sparse reconstruction methods are subsequently employed to regenerate full resolution range-Doppler images. Hybrid reconstructed solutions are finally formed by merging acquired data with sparsely recovered solutions. We show that this is essential for obtaining robust results in the presence of noisy environments and to measure outcomes on equal terms. Real data obtained from an experimental radar observing a Boeing 737 aircraft is employed to demonstrate the practical effectiveness of CS and hybrid sparse reconstruction.

Sparse phase estimation and processing of independent coherent processing intervals

Radars employing electronically steering arrays are capable of instantaneously altering the direction of the beam along with other parameters. This flexibility offers great opportunities to a radar as it may e.g. divide its time between several directions or frequently modify the waveforms being emit. These kinds of techniques can often result in several sequences of coherent processing intervals illuminating the same area, however, the data may not necessarily be coherent across the acquired sections. In this paper we propose a technique based on sparse reconstruction to transform such groups of blocks into a single continuous coherent entity. Data obtained from an experimental radar is used to validate the techniques.

A compressed sensing based design for formation of range-Doppler maps

Compressed sensing (CS) based reconstruction methods have been in much focus over the last years as they provide a mean to work with limited amount of data. In this article we present an application of CS and sparse reconstruction in a radar setup to form range-Doppler maps. We characterize a radar system where instead of transmitting a train of pulses the pulse transmission occurs in a sparse manner. An array based radar may thus for example alternate beams between two or more angles within the same processing interval applying the entire array. We show that gaps in data can very adequately be filled in by sparse reconstruction which can also be used to extrapolate additional values. Comprehensive simulations covering various scenarios, including sea clutter conditions, are used to demonstrate the effectiveness of the scheme.

Compressed Sensing for Multistatic Radar Systems with Arbitrary Block Codes

Multistatic radar systems with multiple elements at transmitting and/or receiving side permit multiple target observations from different viewpoints providing various advantageous. In an environment with multiple transmitters the emitters may transmit independent waveform or use a coding structure to emit pulses across antennas over a predetermined coherent time-interval. In this work we extend the principles of employing orthogonal block codes for this purpose and emphasize on arbitrary or randomly designed block codes with a compressed sensing based detection at receiver. By employing a compressed sensing approach only a subset of incoming data needs to be stored and processed thus significantly reducing the sampling and integration requirement at the receivers. We show that the use of more general type of block codes allows for greater flexibility and better performance in target detection and are hence more suitable for compressed sensing methods than orthogonal, or quasi-orthogonal, block codes. Through simulations it is validated that such a system can operate well and compressed sensing techniques allow for data reduction and improved detection with a shorter dwell period.

Doppler compensated space-time block coding for multistatic radar systems

Space-time block coding techniques are useful for multistatic / MIMO radar systems as they allow for the use of non-orthogonal waveforms while providing waveform diversity with full signal separation. Block coding, however, necessitates the assumption of no or negligible target motion. This paper attempts to alleviate the issue of target Doppler shifts by introducing an adaptive block coding scheme. The modified block code is appropriately tailored to make certain that the detection degradation caused by Doppler shift remains tolerable at the expense of lower emit antenna power. This work can be seen as bridging the gap between the usage of a full block code in the existence of no target Doppler and the emission of a single, but Doppler resilient, waveform with extensive object motion. Simulations are used to demonstrate how adaptation of a block code significantly reduces some of the issues caused by target motion providing detectional benefits.