Yoke Leen Sit

A Compact Double-Layer On-Body Matched Bowtie Antenna for Medical Diagnosis

A compact double-layer Bowtie antenna optimized for medical diagnosis is presented in this paper. This on-body antenna is matched to the human body to allow more energy to be radiated into the human body to obtain stronger reflections for image processing. By using a Bowtie antenna with double layers as well as a folded structure and meandered microstrip lines at the bottom of the antenna, a small size of 30 × 30 mm2 with a size reduction of 40% is achieved, compared to the reference antenna of 50 × 50 mm2 within the same operational frequency range. After the optimization of the antenna parameters, the antenna is characterized from 0.5 to 2 GHz, where the low frequencies enable a high penetration into human body and the large frequency range contributes to a high bandwidth and hence a fine range resolution. The simulated and measured results are shown with respect to the impedance matching, near-field pattern, gain and SAR distributions. With features such as a very small size, very low operational frequency, high front-to-back ratio, this design shows a high potential for use in medical diagnosis of stroke, breast cancer and water accumulation detection in the human body.

Extension of the OFDM joint radar-communication system for a multipath, multiuser scenario

In this paper an extension of the OFDM joint radar and communication system concept to cope in a multipath and multiuser environment is explored. A realistic multipath propagation channel model is built with an established ray-tracing algorithm and incorporated into the radar system simulation and one additional user/interferer is then introduced into the scenario for the observation of the radars performance. From a theoretical point of view as well as from measurement results, the interferer causes a severe degradation of the radars dynamic range, thus requiring an interference cancellation scheme to remove the traces of the interferer. Inherent to the interference cancellation scheme is the phase and frequency offset estimation algorithm for the high fidelity reconstruction of the interferer signal for subtraction from the radar signal which are explored in this paper. The result of the end-system and the improvement to the radars dynamic range are then presented.

MIMO OFDM radar with communication and interference cancellation features

This paper presents a system concept of a MIMO OFDM Radar with sensing and communication abilities. With the proposed spectrally-interleaved OFDM signal model, multi-user access and object position estimation based on spatial diversity can be accomplished within the same system. Since the OFDM signals are sensitive and susceptible to inter-carrier misalignment, an interference handling technique must be incorporated into the system. This paper presents the signal model used to accomplish the multi-user access capability and analyzes the inter-carrier interference due to 1) the non-synchronized local oscillators between two MIMO OFDM Radar systems, and 2) the phase rotations caused by radar channel, and proposes an interference cancellation algorithm to overcome the problem.

Direction of arrival estimation using the MUSIC algorithm for a MIMO OFDM radar

In this paper, the OFDM Radar and Communication System, which is equipped with a range and Doppler estimation algorithm, is extended to a MIMO configuration for target localization in the azimuth. This is done by exploiting the phase difference between multiple transmit-receive antenna pairs, along with utilizing orthogonal transmit signals. This paper presents a simulation-based investigation of achievable performance in terms of angular resolution with MUSIC. The MIMO-OFDM Radar adopts an interleaving frame structure for transmitting orthogonal waveforms in order to null the signal-to-interference ratio in the respective subchannels used and to avoid directivity of the transmit radiation pattern. The accuracy increases as more transmit and receive antenna pairs are used, as demonstrated in the paper where the simulation results of the 4×4 MIMO system outperforms the 2×2 system tremendously in terms of object separability at the separation angle of 5°.

Maximum capacity antenna design for an indoor MIMO-UWB communication system

In this paper, the synthesis of scenario-based capacity maximizing/optimal antennas for an indoor MIMO-UWB system is presented. Since the wavelength changes significantly across the whole spectrum, a solution must be found in order to utilize the same optimal antenna configuration for the whole UWB band. A systematic framework is presented here whereby the optimal outcome with orthogonal channels is guaranteed. The synthesis also aids in reducing the number of antenna elements needed contrary to the traditional antenna array used in MIMO systems. The resulting optimal radiation pattern and its capacity analysis are also shown.

Verification of an OFDM-based range and Doppler estimation algorithm with ray-tracing

In this paper, a simulation and validation method using ray-tracing for an OFDM joint radar and communication system is presented. The motivation is to verify the range and Doppler estimation algorithm and to observe the behaviour of the OFDM radar system in a real scenario where there are multipath and multiusers in its environment. The OFDM radar system has only been performance verified for a single user and since Doppler measurement is not easily repeatable, it is thus unreliable to use measurement verification for performance observation purposes of a real scenario. Hence a ray-tracing technique based on geometrical-optics is used where the wave propagation, material parameters and traffic are modeled according to realistic environments. The ray-tracing results are then exported into the OFDM radar systems model on MATLAB and the result is observed from the radar image where the set distance and velocity are compared to those processed with the novel range and Doppler estimation algorithm.

3D Radar imaging with a MIMO OFDM-based radar

This paper presents a 3-dimensional radar imaging concept using a MIMO OFDM-based radar. The transmit OFDM signal is designed in such a way that the multiple transmitters will only radiate at the subcarriers unique to itself while preserving the total bandwidth and the range resolution. The virtual antenna array concept is utilized to widen the basis of the antenna array with the least possible transmit-receive elements. Using beamforming techniques at the receiver together with novel radar processing techniques, the range, azimuth and elevation information for an arbitrary number of objects (relative to the number of antenna elements used in the antenna array) can be estimated through a simultaneous transmission.

Demonstration of interference cancellation in a multiple-user access OFDM MIMO Radar-Communication network using USRPs

It is well known that OFDM-based systems are susceptible and weak towards subcarrier misalignment, which can lead to erroneous demodulation of the receive signal. In the usage of OFDM Radar-Communication systems, whether within cooperative or non-cooperative networks, non-overlapping subcarriers are assigned to all RadCom nodes in the vicinity. Even so OFDM subcarrier misalignment can still arise from Doppler and hardware carrier frequency offset, which lead to inter-system interference. Particularly for radar applications, the goal of interference cancellation is not only to recover the payload data correctly, but also to enable a reliable radar estimation. This paper presents a measurement verification of an inter-system OFDM-based MIMO RadCom system interference cancellation concept for use in a multiple-user access environment at a scaled-down carrier frequency using universal software radio peripherals (USRPs).

On Mutual Interference Cancellation in a MIMO OFDM Multiuser Radar-Communication Network

This paper presents a multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) joint radar-communication (RadCom) system and explores its tolerance toward mutual interference. Since OFDM signals are weak toward subcarrier misalignment caused by frequency offsets, some form of interference cancellation will definitely be required for operation in real scenarios. A simple and flexible system level interference cancellation algorithm is proposed, which is to be employed when the radar estimation is no longer reliable. For the proof-of-concept verification, the MIMO RadCom node is implemented on universal software radio peripherals to take hardware imperfections and propagation losses into account. Real-time measurements are also presented to prove the 2D+velocity estimation capability as well as the effectiveness of the interference cancellation algorithm. With this system concept, the dual functions of the RadCom node will be possible in a realistic automotive scenario for vehicle-to-vehicle and vehicle-to-infrastructure communication with the aim of enhancing overall road safety by making driving a collaborative effort instead of an individual one.

A planar dual-mode UWB antenna design for an indoor MIMO communication system

This paper presents the design of a planar UWB dual-mode antenna, which can radiate two orthogonal modes for data transmission through two subchannels simultaneously. An optimized theoretical radiation pattern has been synthesized for a typical indoor office scenario, and this is used as a basis to design a corresponding real world antenna. Since the antenna is expected to be used on a handheld device such as a cellphone or laptop, the antenna is required to be flat and sufficiently small.