Mansour Rachid

Filtering by Aliasing

In this manuscript we describe a fundamentally novel approach to the design of anti-aliasing filters. The approach, termed Filtering by Aliasing, incorporates the frequency-domain aliasing operation itself into the filtering task. The spectral content is spread with a periodic mixer and weighted with a simple analog filter before it aliases at the sampler. By designing the system according to the formulations presented in this manuscript, the sampled output will have been subjected to sharp, highly programmable anti-alias filtering. This manuscript describes the proposed Filtering by Aliasing idea, the effective programmable anti-aliasing filter, its design, and its range of frequency responses. The manuscript also addresses the implementation sensitivities of the proposed Filtering by Aliasing approach and provides a performance comparison against existing techniques in the context of reconfigurable anti-alias filtering.

Iterative MIMO sphere decoding throughput guarantees under realistic channel conditions

Block-based early termination has been proposed for depth-first based MIMO sphere decoders (SD) in order to provide throughput guarantees. We show in this letter that such termination incurs, even under simple tree and norm choices, significant overhead in the required number of iterations under realistic channel conditions due to the depth-first searchs highly variable complexity (number of iterations to achieve a target performance). We propose the use of a constrained version of Dijkstras metric-first search which exhibits indistinguishable performance while avoiding the impractical memory requirements of Dijkstras search. We show that for a 4×4 64-subcarrier OFDM system, the proposed alternative achieves ~2x decrease in complexity as compared to the depth-first SD with block early termination for the same throughput guarantee.

Frequency-Domain Analysis of

N-path filters are finding increased prominence in recent architectures for tunable transceivers. The clock-programmable center frequency together with programmable baseband bandwidth makes it a natural fit for wide programmability required in software-defined radios and cognitive radios. However, the analysis of such filters remains difficult due to their linear periodically time-varying (LPTV) nature. This brief presents an analysis of N-path filters using conversion matrices. Conversion matrices allow for the analysis of an LPTV circuit with equivalent frequency-domain circuits that can, in turn, be analyzed similar to a linear time-invariant circuit. On applying this method to N-path filters, results already established in prior art are accurately reproduced. Furthermore, the effects of a few important nonidealities, such as clock overlaps, nonideal clock duty cycles, and parasitic elements, are also calculated and verified.

N

This paper presents the 1st integrated circuit demonstration of Filtering by Aliasing (FA). FA is a recent technique that uses linear periodically time varying (LPTV) analog circuitry prior to a sampler to provide a desired CT-to-DT transfer function. Such LPTV signal processing offers far superior programmability and performance relative to LTI design. The presented IC applies FA to a single-pole passive RC filter. The resistor, realized as a switched resistor ladder, is continuously varied using on-chip digital control while the output is sampled at a baseband rate. Measured CT-to-DT responses show tunable-bandwidth filter roll-off better than 60 dB/dec, stop-band suppression up to 60 dB, tunable carrier up to 800 MHz, up to 31 dBm out-of-band IIP3, and harmonic rejection.

-Path Filters Using Conversion Matrices

MIMO technology has been widely applied in terrestrial wireless communications due to its high spectral efficiency in the presence of rich multi-paths. The benefits of MIMO in airborne communications, however, have not been fully recognized. The lack of scattering in the airborne environment may lead one to incorrectly believe that the spectral efficiency gain of an airborne MIMO is rather limited. In this article, we describe how spatial multiplexing gain can be obtained in airborne environments by antenna system design rather than natural scattering. In particular, we will focus on two techniques: the use of dual polarized antennas and the choice of antenna separation relative to the carrier wavelength. We present both field test results and computer simulations demonstrating the benefits of MIMO in airborne environments.

A sharp programmable passive filter based on filtering by Aliasing

A 65nm CMOS, 8mW spectrum scanner using simple but linear periodically time-varying (LPTV) circuits is presented. The scanner spans a 1GHz spectrum by providing sharp filters at programmable centre frequencies. Its passive structure gives it a measured out-of-band IIP3 of > +31dBm and a sensitivity of <; -142dBm/Hz across the 1GHz band leading to an SFDR of 75dB in a 1MHz resolution bandwidth.

MIMO for airborne communications [Industry Perspectives]

We propose a novel technique for the controlled suppression of aliasing interferers during analog-to-digital conversion. The technique exploits the aliasing inherent in the sampling operation to perform interference cancellation. This is achieved by optimally spreading and weighting the aliasing bands in the frequency domain prior to the analog-to-digital converter (ADC). The resulting filtering response scales automatically with the ADC bandwidth and can be digitally reconfigured to target specific interference profiles to maximize the signal-to-interference-and-noise ratio (SINR). The proposed technique eliminates the need for complex reconfigurable filters in a varying spectral content scenario while maintaining minimal ADC bandwidth and resolution requirements.

An 8mW, 1GHz span, passive spectrum scanner with > +31dBm out-of-band IIP3

This paper presents a low power and highly linear passive spectrum scanner based on the filtering by aliasing principle. The scanner utilizes a linear periodically time-varying circuit followed by a sampler to achieve sharp apparent filters from a continuous-time input to a discrete-time output. This paper describes the design of the scanner and provides an analysis of the expected and measured performance in the presence of circuit non-idealities. The scanner enables a DC −1 GHz spectrum scan while consuming 8 mW of power, with an out-of-band IIP3 that is better than +31 dBm across the band.

A novel reconfigurable alias interference cancellation technique for A-to-D conversion

Recent work on highly selective reconfigurable radios has focused on techniques such as DT analog signal processing [1], N-path filtering [2], and mixer-first approaches [3,4]. Mixer-first receivers have been able to achieve excellent out-of-band (OOB) linearity even with noise cancellation [3], but only for far-out blockers due to only first-order baseband filtering. Higher-order baseband filters give sharper filtering, but are not as linear [4], while high-order active N-path filters have poor S11 [2]. DT approaches are also limited by the linearity of the front-end LNTA [1]. Hence, new approaches are needed to handle large blockers that are close to the signal band.

Design and Analysis of an 8 mW, 1 GHz Span, Passive Spectrum Scanner With >+31 dBm Out-of-Band IIP3 Using Periodically Time-Varying Circuit Components

The analysis of a mixer-first receiver using conversion matrices is presented. Conversion matrices provide a systematic approach to analyze linear periodically time-varying (LPTV) circuits. Using conversion matrices of LPTV components in a frequency domain equivalent circuit allows analysis similar to a linear time invariant (LTI) circuit. For example, Ohms law, Kirchhoffs voltage and current laws, impedance combination rules, etc., can all be used in such equivalent circuits. On applying this method to a mixer-first receiver, a common LPTV circuit, results already established in prior art are reproduced accurately. Further, effects of a few important non-idealities, such as clock overlaps, imperfect clock edges and parasitic components that were not considered previously, are also calculated and verified.