Browsing by Subject "Beamforming"
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Item CMOS circuits for multi-antenna communication systems.(2010-09) Patnaik, SatwikMulti-antenna systems allow for higher communication rates without substantial increase in hardware and power. This has led to significant interest in incorporating multi-antenna communication into upcoming wireless standards, like the 802.11n. This thesis focuses on CMOS circuits and architectures for multi-antenna wireless communication systems. Specifically, we will propose solutions for a special class of multi-antenna systems called phased-array systems. The most important circuit block in a phased-array system is the phase-shifter. Traditional phased-array systems, mostly military radars, used external ferrite phase-shifters for microwave applications, which were wide-band, almost noiseless, highly linear and had high power-handling capability, but were bulky. Commercial wireless systems rely on portability and low-power, with the result that CMOS is the technology of choice and most products are fully integrated on a single-chip. On-chip CMOS phase-shifters have not been able to match the performance of ferrite phase-shifters. Consequently, CMOS-based phased-array systems have relied on a modified architecture known as the LO-phase shifting architecture to deliver comparable performance. In this work, we first present two novel schemes for the phase-generation network for the LO-phase-shifting architecture, based on a phenomenon called injection-locking. The injection-locked oscillator (ILO) is used as a phase-shifter. The two schemes are integrated into a dual-mode architecture for a phased-array receiver providing us with the advantages of both. The prototype, operating at 2.4-GHz, is fabricated in a 0.13-μm CMOS technology. It requires lower power and area compared to previous state-of-the-art designs. Measurement results from this prototype show excellent agreement with the theoretical performance predicted for the phased-array receiver. Both architectures have also been extended to two-dimensional phased-array systems. A majority of the commercial phased-array applications are focused on the mm-wave regime. We have verified that our architecture can operate at these frequencies as well. A 24-GHz two-channel CMOS phased-array receiver has been designed and fabricated in 0.13-μm BiCMOS technology. In this architecture, the injection-locked oscillator not only acts as a phase-shifter and buffer, but also as a frequency tripler. Because of this multi-functionality of the ILO, the overall area and power of this receiver are better than other state-of-the-art designs. Since the LO distribution network now operates at one-third the LO frequency, it allows for further power savings in the distribution network. Finally, a beam-forming receiver based on the Fast-Fourier Transform (FFT) is presented. In this architecture, the beam-forming operations are performed in the baseband processing section. Owing to a low-power FFT architecture and the inherent properties of the FFT, multiple beams can be created at closely-spaced frequencies. This allows the use of narrow-band transmitter and receiver architectures for the RF section. A two-channel receiver based on this architecture has been designed in a 65-nm CMOS process. In addition, to these different receiver architectures, a novel 24-GHz UWB-LNA is presented. The LNA, which has been integrated as part of a UWB receiver, is presented in this thesis. However, the overall UWB receiver design is not presented here.Item Fast Unit-modulus Least Squares with Applications in Beamforming and Phase Retrieval(2016-05) Tranter, JohnUnit-modulus Least Squares (ULS) problems arise in many applications, including phase-only beamforming, phase retrieval and radar code design. These problems are NP-hard, so there exist problem instances that we cannot solve efficiently, and whether such solution exists remains elusive. ULS formulations can always be recast as Unit-modulus Quadratic Programs (UQPs), to which Semi-Definite Relaxation (SDR) can be applied, and is often the state-of-the-art approach (e.g., PhaseCut). SDR lifts the problem dimension and requires solving a much larger-scale convex problem, which makes it ill-suited for large-scale ULS/UQP. In this paper, we propose several first-order algorithms that meet or exceed SDR performance in terms of minimizing the cost function, and compare favorably to SDR in terms of runtime complexity. We establish convergence of the proposed first-order algorithms to a KKT point, and we demonstrate their superiority in two applications: beamforming using only phase-shifts, and phase retrieval.Item Frugal sensing and estimation over wireless networks(2014-04) Mehanna, OmarSpectrum sensing and channel estimation are two important examples of background tasks needed for efficient wireless network operations. Channel and spectrum state communication overheads can become a serious burden, unless appropriate sensing and estimation strategies are designed that can do the job well with very limited, judicious feedback. This thesis considers two `frugal' sensing and estimation problems in this regime: crowdsourced power spectrum sensing using a network of low-end sensors broadcasting few bits; and channel estimation and tracking for transmit beamforming in frequency-division duplex (FDD) mode.In the case of spectrum sensing, each sensor is assumed to pass the received signal through a random wideband filter, measure the average power at the output of the filter, and send out a single bit to a fusion center (FC) depending on its measurement. Exploiting linearity with respect to the autocorrelation as well as important non negativity properties in a novel linear programming (LP) formulation, it is shown that adequate power spectrum sensing is possible from few bits, even for dense spectra. The formulation can be viewed as generalizing classical nonparametric spectrum estimation to the case where the data is in the form of inequalities, rather than equalities. Taking into account fading and insufficient sample averaging considerations, a different convex maximum likelihood (ML) formulation is developed, outperforming the LP formulation when the power estimates prior to thresholding are noisy. Assuming availability of a downlink channel that the FC can use to send threshold information, active sensing strategies are developed which quickly narrow down the power spectrum estimate.For the downlink channel tracking problem, the receiver is assumed to send back to the transmitter a coarsely quantized version of the received transmitter-beamformed pilot signal, instead of sending quantized channel information as in codebook-based beamforming. A novel channel tracking approach is proposed that exploits the quantization bits in a maximum a posteriori (MAP) estimation formulation, and closed-form expressions for the channel estimation mean-squared error and the corresponding signal-to-noise ratio are derived under certain conditions.