Ever since the FCC allocated 7.5 GHz (from 3.1 GHz to 10.6 GHz) for ultra wideband (UWB) technology, interest has been renewed in both academic and industrial circles to exploit this vast spectrum for short range, high data rate wireless applications. The great potential of UWB lies in the fact that it can co-exist with the already licensed spectrum users and can still pave the way for a wide range of applications. However, this wide bandwidth complicates the circuit level implementation of key RF blocks like the power amplifier (PA), transmit/receive switch, low noise amplifier (LNA) and mixers in an UWB transceiver. Though expensive technologies like SiGe or GaAs have been used for transceiver realizations, the ultimate goal is to have a single-chip, low-cost solution which can only be achieved by using CMOS technology. Nevertheless, some of the inherent limitations of CMOS like lower fT of transistors make the design of UWB circuits in CMOS an extremely challenging task. Two proposals- Multi-Band OFDM and Direct-Sequence CDMA have been put before the IEEE 802.15.3a task group to decide on the industry standard for the commercial deployment of this technology. Though the debate on which standard is better has not been resolved, proponents of both the groups have already begun to develop prototypes of their respective proposals. This thesis describes the design of a key RF block in the UWB transceiver - the Power Amplifier. For the first part of this work, a PA suitable for MB-OFDM specifications was designed and fabricated in TSMC 0.18um CMOS technology. The class-AB PA is able to cover the lower UWB frequency band from 3.1 GHz to 4.75 GHz and delivers an output power of -2 dBm at 4 GHz. Simulated results show a gain of 19±2 dB achieved over the entire band and the PA consumes 36.54 mW from a 1.8V supply. In the second part of this work, a PA that meets the DS-CDMA specifications was designed and fabricated. This PA operates in the class-AB regime, delivering an output power of -4.2 dBm with input-1dB compression point at -22 dBm. Complete design and implementation was done using TSMC 0.18um CMOS technology and it consumes a very low power of 25 mW, while realizing a flat gain of 19±1 dB across the whole band of operation. All the above mentioned results are from simulations in SpectreRF and measurements are yet to be taken. Additional features like power ON/OFF scheme and output impedance control has also been incorporated in the design. / Master of Science

This dissertation addresses physical layer security concerns, resiliency of the Orthogonal Frequency Division Multiplexing (OFDM) and the Multiple Input Multiple Output (MIMO) systems; the `de-facto' air-interface of most wireless broadband standards including LTE and WiMAX. The major contributions of this dissertation are: 1) developing jamming taxonomy, 2) proposing OFDM and MIMO equalization jamming attacks and countermeasures, 3) developing antijam (AJ) MIMO systems, and 4) designing null space projected overlapped-MIMO radar waveform for spectrum sharing between radar and communications system. First, we consider OFDM systems under various jamming attacks. Previous research is focused on jamming OFDM data transmissions. We focus on energy efficient attacks that can disrupt communication severely by exploiting the knowledge of target waveform. Specifically, these attacks seek to manipulate information used by the equalization algorithm to cause errors to a significant number of symbols, i.e., pilot tones jamming and nulling. Potential countermeasures are presented in an attempt to make OFDM waveform robust and resilient. The threats were mitigated by randomizing the location and value of pilot tones, causing the optimal attack to devolve into barrage jamming. We also address the security aspects of MIMO systems in this dissertation. All MIMO systems need a method to estimate and equalize channel, whether through channel reciprocity or sounding. Most OFDM-based MIMO systems use sounding via pilot tones. Like OFDM attacks, this research introduces MIMO channel sounding attack, which attempts to manipulate pilot tones to skew the channel state information (CSI) at the receiver. We describe methods of designing AJ MIMO system. The key insight is that many of the theoretical concepts learned from transmit beamforming and interference alignment (IA) in MIMO systems can be applied to the field of AJ and robust communications in the presence of jammers. We consider a realistic jamming scenario and provide a `receiver-only' and a transmitter `precoding' technique that allow a pair of two-antenna transceivers to communicate while being jammed by a malicious non-cooperative single-antenna adversary. Finally, we consider designing a collocated MIMO radar waveform, which employs a new MIMO architecture where antenna arrays are allowed to overlap. This overlapped-MIMO radar poses many advantages including superior beampattern and improvement in SNR gain. We combine this radar architecture with a projection-based algorithm that allows the radar waveform to project onto the null space of the interference channel of MIMO communications system, thus enabling the coexistence of radar and communications system. / Ph. D.

Ultra-Wideband has recently gained great interest for high-speed short-range communications (e.g. home networking applications) as well as low-speed long-range communications (e.g. sensor network applications). Two flavors of UWB have recently emerged as strong contenders for the technology. One is based on Impulse Radio techniques extended to direct sequence spread spectrum. The other technique is based on Orthogonal Frequency Division Multiplexing. Both schemes are analyzed in this thesis and modifications are proposed to increase the performance of each system. For both schemes, the issue of simultaneously operating users has been investigated. Current MAC design for UWB has relied heavily on existing MAC architectures in order to maintain backward compatibility. It remains to be seen if the existing MACs adequately support the UWB PHY (Physical) layer for the applications envisioned for UWB. Thus, in this work we propose a new MAC scheme for an Impulse Radio based UWB PHY, which is based on a CDMA approach using a code-broker in a piconet architecture. The performance of the proposed scheme is compared with the traditional CSMA scheme as well as the receiver-based code assignment scheme. A new scheme is proposed to increase the overall performance of the Multiband-OFDM system. Two schemes proposed to increase the performance of the system in the presence of simultaneously operating piconets (namely Half Pulse Repetition Frequency and Time spreading) are studied. The advantages/disadvantages of both of the schemes are discussed. / Master of Science

The advent of software radio technology has enabled radio developers to design and implement radios with great ease and flexibility. Software radios are effective in experimentation and development of radio designs. However, they have limitations when it comes to high-speed, high-throughput designs. This limitation can be overcome by introducing a hardware element to the software radio platform. Enhancing GNU Radio for Hardware Accelerated Radio Design project implements such a scheme by augmenting an FPGA co-processor to a conventional GNU Radio flow. In this thesis, this novel platform is evaluated in terms of performance of a radio design, as well as hardware and software system requirements. A simple and efficient Zigbee receiver design is presented. Implementation of this receiver is used as a proof-of-concept for the effectiveness and design methodology of the modified GNU Radio. This work also proposes a scheme to extend this idea for design of ultra-wideband radio systems based on multiband-OFDM. / Master of Science

Yes / Fourth generation systems require the use of both amplitude and phase modulation to efficiently utilize the available spectrum and to obtain high data rates, hence imposing stringent requirements on the power amplifier in terms of efficiency and linearity and requires the power amplifier to operate linearly and efficiently. The B3G base station transceiver Doherty power amplifier was designed to operate over the frequency range of 3.47GHz to 3.53GHz mobile WiMAX band using Freescale¿s N-Channel Enhancement-Mode Lateral MOSFET Transistor, MRF7S38010HR3; The performances of the Doherty amplifier are compared with that of the conventional Class AB amplifier. The results of 43 dBm output power and 66% power added efficiency are achieved.

No / Wavelets are alternative building kernels of the multicarrier systems, such as the orthogonal frequency division multiplexing (OFDM). The wavelets can be designed by changing the parent basis functions or constructing new filters. Some two new wavelets are considered for multicarrier design; one is designed using raised-cosine functions while the other was constructed using ideal filters. The spectrums of raisedcosine wavelet filters are controlled by a roll-off factor which leads to many distorting sidelobes. The second family of wavelet, which the raised-cosine wavelet is compared to, have no distorting sidelobes. It will be shown that raised-cosine wavelets are less suitable for multicarrier design in multicarrier environment, in terms of BER when compared to the wavelet constructed from the ideal filter.

No / Orthogonal frequency division multiplexing (OFDM) is pronounced in wireless communication systems. Methods for improving the performance of the OFDM-based systems are mostly sought. A method of doing this involves error correction coding and another, a better multicarrier modulation kernel. In this work, convolutional error correction coding with interleaving is introduced in wavelet multicarrier modulation OFDM system (wavelet-OFDM) to improve the performance of multicarrier systems as the signal traverses the multipath and noisy transmission channels. This is compared with FFT-based multicarrier modulation (FFT-OFDM). Results show that coded wavelet-OFDM saves more than a half of the transmit power than the uncoded wavelet. Also it will be shown that, the interleaved and non-interleaved coded wavelet-OFDM well outperform interleaved coded and non-interleaved coded FFT-OFDM systems respectively.

Yes / The MIMO technology towards achieving future generation broadband networks design criteria is presented. Typical next generation scenarios are investigated. The MIMO technology is integrated with the OFDM technology for effective space, time and frequency diversity exploitations for high speed outdoor environment. Two different OFDM design kernels (fast Fourier transform (FFT) and wavelet packet transform (WPT)) are used at the baseband for OFDM system travelling at terrestrial high speed for 800MHz and 2.6GHz operating frequencies. Results show that the wavelet kernel for designing OFDM systems can withstand doubly selective channel fading for mobiles speeds up to 280Km/hr at the expense of the traditional OFDM design kernel, the fast Fourier transform.

Yes / High Peak-to-Average-Power Ratio (PAPR) of transmitted signals is a common problem in broadband telecommunication systems using an orthogonal frequency division multiplexing (OFDM) modulation scheme, as it increases transmitter power consumption. In consumer applications where it impacts mobile terminal battery life and infrastructure running costs, this is a major factor in customer satisfaction. Companding techniques have been recently used to alleviate this high PAPR. In this paper, a companding scheme with an offset, amidst two nonlinear companding levels, is proposed to achieve better PAPR reduction while maintaining an acceptable bit error rate (BER) level, resulting in electronic products of higher power efficiency. Study cases have included the effect of companding on the OFDM signal with and without an offset. A novel closed-form approximation for the BER of the proposed companding scheme is also presented, and its accuracy is compared against simulation results. A method for choosing best companding parameters is presented based on contour plots. Practical emulation of a real time OFDM-based system has been implemented and evaluated using a Field Programmable Gate Array (FPGA).

Approved for public release, distribution is unlimited / Synchronization of orthogonal frequency-division multiplexed (OFDM) signals is significantly more difficult than synchronization of a single-carrier system. The recently approved IEEE Standard 802.11g specifies a packet-based OFDM system that provides a basis for the discussion of OFDM synchronization in a packet-based environment. Algorithms that synchronize the receiver carrier demodulation frequency and phase, the data frame, the OFDM symbol timing, and the data symbol timing are discussed and analyzed in an AWGN channel. System View simulation is used to implement the frame and carrier frequency synchronization algorithms, where the performance of these algorithms is analyzed and they are shown to be useful detection algorithms for Standard 802.11g signal reception. / Lieutenant Commander, United States Navy