Saeed Farsi

Mutual Coupling Reduction Between Planar Antennas by Using a Simple Microstrip U-Section

Mutual coupling is an inevitable phenomenon in multiantenna systems, usually reducing the system performance. Numerous works have focused on the reduction of this effect. The aim is maintaining the mutual coupling suppressing structure as simple as possible while having a high amount of mutual coupling reduction. This letter presents a novel structure suppressing the mutual coupling between nearby patches. It is composed of only a simple U-shaped microstrip, which reduces the mutual coupling considerably. The structure has been constructed and tested. The measurement results prove the high efficiency of this configuration.

A smart wearable textile array system for biomedical telemetry applications

A smart wearable textile array system (SWTAS) with direction of arrival (DoA) estimation and beamforming is proposed and developed for biomedical telemetry applications. This conformal system enables effective and continuous patient monitoring when combined with one or more health sensors, as information about the subjects health condition is received adaptively to guarantee link reliability. This operation is facilitated by a receiver front-end and a digital baseband beamforming network, which enables scalability and flexibility. The proposed SWTAS also features flexible antenna arrays made using textiles, which are arbitrarily located on a cylindrically shaped body phantom to ensure wide spatial DoA estimation capability. Besides being designed to suit on-body placement, the system performance is also characterized for on-body usage using a commercial body-emulating liquid, and placed at a realistic distance from the body, considering user clothing. Investigation indicated a good performance in the systems ±80° forward plane with a DoA accuracy of 3° . Finally, a practical evaluation is presented using two transmitters placed at distinct locations and distances. The system successfully estimated both DoAs and received the telemetry signals using beamforming.

All-Digital Cancellation Technique to Mitigate Receiver Desensitization in Uplink Carrier Aggregation in Cellular Handsets

Future handsets will employ uplink carrier aggregation to increase transmit data rates. This can lead to significant receiver desensitization for a number of LTE band combinations, because of the cross-modulation products created by the nonlinearity of antenna switches and duplexers in the RF front end. To mitigate this effect, an all-digital cancellation algorithm is proposed that relies solely on the digital representation of the signals, a peak covariance search for time alignment, and an adaptive distortion canceller. The recursive least squares (RLS) algorithm is used to find the optimal coefficients for the adaptive filter. Employing the distortion canceller improved the signal-to-interference-plus-noise ratio (SINR) and error-vector-magnitude (EVM) of the desired received signal by up to 20 dB.

Characterization of Intermodulation and Memory Effects Using Offset Multisine Excitation

This paper proposes a new class of multisine excitations that allows efficient characterization of nonlinear circuits. By offsetting the frequency of tones, one can distinguish between different intermodulation products in a multisine response. This property leads to many applications for nonlinear circuit characterization, such as in-band distortion measurements, memory effects characterization, and model performance assessment. Some applications are highlighted in this paper, focusing especially on the characterization of memory effects. The effectiveness of the approach is demonstrated with a series of measurement results.

Implementation of a Project-Based Telecommunications Engineering Design Course

This paper describes and discusses the implementation of a project-based graduate design course in telecommunications engineering. This course, which requires a combination of technical and soft skills for its completion, enables guided independent learning (GIL) and application of technical knowledge acquired from classroom learning. Its main implementation challenge is the need for instructors to define graduate-level GIL activities that are unique for the project objectives and scope. This process is required at both the system and subsystem levels. These activities must also satisfy the program learning outcomes and course outcomes (PLOs and COs). The course initiation, implementation, and management are first described from the instructors perspective. Technical specifications and outcomes from a recently implemented project titled “A Human-Inspired Telecommunication System” is taken as a case study. Besides explaining the methodology used to evaluate both the course and the students, an empirical assessment of PLOs and COs against the associated educational activities is also presented. Results of a student exit survey, in which each instrument was mapped to specific COs, indicated that the intended course objectives had been accomplished and that there was a good level of student satisfaction.

Modeling of Deterministic Output Emissions of Power Amplifiers Into Adjacent Receive Bands

This paper discusses the measurement and modeling of the deterministic components of power amplifier (PA) emissions into neighboring receive (Rx) bands caused by PA nonlinearity, and proposes ways to distinguish these components from stochastic components. A method is presented to determine the orders of nonlinearity that are the principal contributors to the Rx band emissions. A Volterra-based model for their estimation is proposed, along with considerations for estimation accuracy. A criterion based on the matrix condition number for efficient pruning of the Volterra-based models is also presented. The proposed techniques are verified with measurements. The proposed model can be used to gain a deeper understanding of the nonlinearity mechanisms responsible for PA spurious emissions, and offers the possibility of canceling the deterministic components to improve receiver sensitivity.

Design of efficient rectifier for low-power wireless energy harvesting at 2.45 GHz

This paper reports an efficient rectifier operating at 2.45 GHz for wireless energy harvesting applications with low input power levels. Single diode shunt-mounted topology is adopted for operation with low input power level. The efficiency is measured as 27.7% at -20 dBm of input power, 39.2% at -15 dBm, and 51.2% at -10 dBm. The maximum efficiency of 61.7% is measured at -0.4 dBm input power.

An FPGA-based digital predistorter for RF power amplifier linearization using cross-memory polynomial model

A cost-effective and flexible FPGA-based system architecture for digital predistortion (DPD) based linearization of power amplifiers (PAs) is proposed. The system is used to show the effectiveness of the cross-memory polynomial model (CMPM) for DPD. Two commercial amplifiers are linearized using single and two-carrier Wideband Code Division Multiple Access (WCDMA) signals as excitation and the performance of CMPM for DPD is compared to those of the memory polynomial (MPM) and memoryless models (MLM).

Efficient Dithering Technique With Periodic Waveforms for RF Test and Characterization

A dithering technique based on ensemble averaging of waveforms is proposed. In the proposed method, we perform a single measurement of multiple periods of a sine-dithered periodic waveform, whereas in the existing ensemble averaging methods several different measurements with dithering additive noise are performed. The measured waveform is then segmented and the segments are averaged to obtain a noise-reduced post-processed waveform. This technique provides improved efficiency in test and characterization applications where accuracy higher than that of the built-in data converters of the measurement equipment is required. Moreover, we show that by using large dithering signals in the proposed technique, we can reduce the nonideal effects found in real applications. As an example, we show in a simulated example that by using the approach with an ensemble size of five in an ideal quantizer, we are able to reduce the mean-square error and adjacent channel distortion by 11 dB. A reduction of 6 dB is achieved when we use the same ensemble size in a nonideal quantizer. An experiment is then conducted to evaluate the reduction in the adjacent channel power of a modulated signal emanating from an arbitrary waveform, by using the proposed technique. The experimental results show that even for a modulated signal with 160-MHz bandwidth at 4.5 GHz, by using an ensemble size of four, we are able to reduce the adjacent channel distortion by 5 dB.

Behavioral modeling approach for array of amplifiers in active antenna array system

Memory polynomial behavioral models are widely used to model nonlinear distortion mechanisms in a single RF power amplifier. However, when a number of power amplifiers are used in parallel, as in the case of active antenna arrays, the total number of parameters will increase significantly. Hence, new strategies are required to model and linearize these systems efficiently. In this paper a novel efficient modeling approach for these array systems is presented and experimentally verified by applying the method to the measured data of an array of amplifiers. The experimental results prove the efficiency of the approach.