Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 77-79). Also available via the Internet.

The ever-increasing demand for wireless throughput requires modern handset receivers to aggregate signals from multiple non-contiguously allocated RF carriers. This poses significant receiver design challenges, including concurrent signal reception, RF input interface, out-of-band (OB) linearity, and suppression of spurious responses. Commercial solutions use external antenna switches and off-chip RF multiplexers to provide non-tunable, narrowband filtering and impedance matching. The RF signal is then divided into separate signal chains, each with a dedicated receiver for signal reception. Although this solution allows the selection of any carrier combinations supported by the available RF filters, as the number of aggregation band combinations increases, the scale of the passive front-end module grows rapidly, leading to increased system complexity, extra signal loss, and degraded performance. This thesis presents the design and implementation of two receiver architectures that support reconfigurable operations and flexible, concurrent reception from two inter-band carriers with a tuned RF interface. We first present a multi-branch receiver with modulated mixer clocks (MMC). It unifies the functions of single-carrier and dual-carrier reception, as well as compressive-sampling spectrum scanning into a single architecture. With continuous-wave-modulated mixer clocks, the receiver supports concurrent reception from two distinct bands and realizes tuned impedance matching that greatly improves the OB linearity. With pseudo-noise-modulated mixer clocks, the receiver supports spectrum scanning. Disabling modulation reverts the receiver into a single-carrier receiver with good OB linearity. The 65nm CMOS prototype is developed that operates from 300 to 1300MHz and offers 2.7dB minimum NF, -1.3dBm B1dB, and +8.0dBm IIP3 for single-carrier reception. Concurrent dual-carrier reception is demonstrated that offers -8.4dBm B1dB and sub-6dB NF with the two carriers separated from 200 to 600MHz apart. For spectrum scanning, the receiver achieves a 66dB dynamic range with -75dBm sensitivity over a 630MHz RF span. In addition, a discussion of the higher-order MMC technique is included to improve the receiver’s spurious and noise performance by suppressing the higher-order responses and mitigating the noise-folding effect. Next, we present an IF-filterless, double-conversion receiver. The concurrent, narrowband RF interface is realized with two layers of passive mixing in its mixer-first branches, which translate the low-pass, baseband impedance twice to two distinct bands and improve the OB linearity. Branches with DDS-modulated LNTAs for multi-phase, switched-Gm mixing offer rejection of spurious responses and improved noise performance. The 65nm CMOS prototype is developed that operates from 100 to 1200MHz. For single-carrier reception, the receiver delivers 4.8dB minimum NF, +7.9dBm B1dB, and +22.8dBm IIP3. For concurrent signal reception, two arbitrarily-allocated RF carriers, separated from 200 to 600MHz apart, can be received concurrently. The receiver delivers a +1.9dBm B1dB and supports 8-/16-phase DDS modulation with a 30dB spurious rejection across its operating range. In addition, a theoretical study of a modified, mixer-first branch is included. By re-arranging the connections of the baseband termination resistors, the baseband noise can be fully cancelled, thus improving the receiver’s noise performance.

Receiver sensitivity is an important parameter in the design of optical communication systems. Prior results on receiver sensitivity for on-off keying modulated direct detection systems with an optical preamplifier are generalized for the cases of frequency-shift keying and subcarrier modulation. Our results, obtained by using the Gaussian approximation, are compared to those obtained by an 'exact' analysis. The results are also generalized for N-ary modulation schemes and systems having optical amplifiers as linear repeaters. Simple analytic formulae are derived for the maximum system gain of optical amplifiers systems for the following two cases: 1) Constant signal power at each amplifier. 2) Equal amplifier spacing, which ensures constant total power at each amplifier. The functional dependence of system gain on various system parameters, and the effects of optical filtering at the receiver as well as at the intermediate amplifiers, is studied. The analysis is extended to include the effects of random power variations at the output of each amplifier. / Master of Science

Monte Carlo algorithms can be used to estimate the state of a system given relative observations. In this dissertation, these algorithms are applied to physical layer communications system models to estimate channel state information, to obtain soft information about transmitted symbols or multiple access interference, or to obtain estimates of all of these by joint estimation. Initially, we develop and analyze a multiple access technique utilizing mutually orthogonal complementary sets (MOCS) of sequences. These codes deliberately introduce inter-chip interference, which is naturally eliminated during processing at the receiver. However, channel impairments can destroy their orthogonality properties and additional processing becomes necessary. We utilize Monte Carlo algorithms to perform joint channel and symbol estimation for systems utilizing MOCS sequences as spreading codes. We apply Rao-Blackwellization to reduce the required number of particles. However, dense signaling constellations, multiuser environments, and the interchannel interference introduced by the spreading codes all increase the dimensionality of the symbol state space significantly. A full maximum likelihood solution is computationally expensive and generally not practical. However, obtaining the optimum solution is critical, and looking at only a part of the symbol space is generally not a good solution. We have sought algorithms that would guarantee that the correct transmitted symbol is considered, while only sampling a portion of the full symbol space. The performance of the proposed method is comparable to the Maximum Likelihood (ML) algorithm. While the computational complexity of ML increases exponentially with the dimensionality of the problem, the complexity of our approach increases only quadratically. Markovian structures such as the one imposed by MOCS spreading sequences can be seen in other physical layer structures as well. We have applied this partitioning approach with some modification to blind equalization of frequency selective fading channel and to multiple-input multiple output receivers that track channel changes. Additionally, we develop a method that obtains a metric for quantifying the convergence rate of Monte Carlo algorithms. Our approach yields an eigenvalue based method that is useful in identifying sources of slow convergence and estimation inaccuracy.