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In a transistorized push-pull amplifier, third order intermodulation distortion was effectively reduced at VHF frequencies with an output power of two watt. The non-linear distortion of the amplifier is modeled using a power series. The resulting expression is used as the basis for choosing the push-pull configuration to reduce the third order intermodulation distortion. The amplifier was built and tested, and the experimental results compare favorably with the theoretical results. The level of the third order intermodulation distortion is found to be at least 30 dB below the interfering signal level.

This report summarizes the design of a 25kW peak power pulse modulator for an airborne medium--range weather radar. It is the purpose of the modulator to collect and store energy over a certain time period and to form this energy into a short, high-power pulse. The modulator is required to drive a coaxial magnetron with a pulse of 5kV at 5A. System considerations make a pulse width of 3.5us and repetition rate of 99Hz necessary. The pulse is generated in a line-type pulse circuit which utilizes an SCR as a switching device. It is shown that a solid-state modulator can use a commercial grade SCR for the pulse generation. Although currents of 100A are switched, the instantaneous power dissipation in the SCR is reduced significantly through the use of a saturable delay reactor. A pulse transformer is used to achieve maximum power transfer from the modulator to the magnetron. The pulse transformer is insulated with semi-rigid epoxy. Corona generation is avoided by limited the voltage gradients in the insulation to 80V/mil.

Third generation wireless mobile communication networks are characterized by the increasing utilization of data services — e-mail, web browsing, video streaming, etc. Such services allow the transition of the network from circuit switched to packet switched operation (circuit switched operation will still be supported), resulting in increased overall network performance. These new data services require increased bandwidth and data throughput, due to their intrinsic nature. Examples are graphics-intensive web browsing and video streaming, the latter being delay sensitive and requiring priority over less sensitive services such as e-mail. This increasing demand for bandwidth and throughput has driven the work of third generation standardization committees, resulting in the specification of improved modulation and coding schemes, besides the introduction of more advanced link quality control mechanisms. Among the several proposals for the evolution from 2G to 3G, GPRS (General Packet Radio Services) and EDGE (Enhanced Data Rates for GSM Evolution) stand out as transitional solutions for existing TDMA IS-136 and GSM networks (they are also referred to as 2.5G systems). In the CDMA arena, WCDMA (Wideband CDMA) has emerged as the most widely adopted solution, with CDMA 2000, an evolution from IS-95, also being considered. This thesis compiles and analyzes the results of the work by the standardization committees involved in the specification of 3G standards, focusing on the receiver performance in the presence of additive noise, fading and interference. Such performance results will ultimately determine design and optimization conditions for 3G networks. This document concerns the description of the TDMA-based 2.5G solutions that allow the introduction of multimedia and enhanced data services to existing 2G networks. It focuses on GPRS and EDGE. It also addresses WCDMA — a 3G spread spectrum solution. Such proposals permit the utilization of existing spectrum with increased efficiency, yielding extended network capacity and laying the ground for full support of wireless multimedia applications. The study is focused on the link implementation aspect of these solutions, showing the impact of the modulation schemes and link quality control mechanisms on the performance of the radio link. / Master of Science

Previous attempts to adapt MIMO systems in the presence of varying channel conditions typically focus on characterizing the performance of a limited and predefined set of joint MoDem/CoDec and MIMO configurations over a representative set of channel realizations. Other work has attempted to adapt only the MIMO scheme to varying channel conditions without considering modulation format or the channel code used. Finally, attempts to configure the system through direct BER calculation based on channel conditions were also proposed. These methods suffer the problems of dependence on a limited set of simulated curves which may not account for all channel conditions that a real system might see, not configuring all parameters jointly or implicitly requiring channel state information to be fed back to the transmitter. None of these previous attempts have handled both cases where CSIT is available or not while jointly configuring the MoDem, CoDec and multi-antenna scheme. This work consists of two parts, focusing on energy efficiency in the presence of unoccupied frequency bands and on spectrally efficient operation under static frequency assignment. Utilizing minimum Euclidean distances of MoDem constellations and the minimum free Hamming distance metrics for channel codes, we develop distance metrics to describe the MIMO schemes which are considered. A minimum required distance is then determined as a function of desired BER and constellation. Based on the unified set of distance metrics, adaptive algorithms can evaluate the total distance of a signaling scheme, including MoDem, CoDec and MIMO scheme, and then calculate a decision metric based on the total distance and the required distance to meet the desired BER. The proposed system which aims to maximize energy efficiency is able to choose, based on spatial correlation, available channels, CSIT availability, and power amplifier configuration, the appropriate multi-antenna configuration, MoDem and Codec to meet a fixed throughput requirement while maximizing the energy efficiency or robustness of the link. The proposed work assumes that the open channels of a network can be accessed through individually tunable RF chains of the multi-antenna systems. This assumption permits the use of a multi-antenna, multi-channel scheme which sacrifices spatial diversity for frequency diversity. In addition to traditional, single-channel transmit diversity schemes, the adaptive system is also able choose, when more energy efficient, this novel, multi-channel configuration. When focusing on the maximization of spectral efficiency, a more conventional, single-channel model is assumed. In addition to the distance metrics for single-channel diversity schemes, distance metrics are then developed for spatial multiplexing schemes which take into account the interaction of spatial correlation, number of antennas and the rate of the channel code. The adaptive system uses the total distance of the joint configuration of MoDem, CoDec and MIMO scheme to calculate a decision metric which indicates whether the configuration will meet the desired BER. From a list of joint configurations which will meet the desired BER, the adaptive system then chooses the one which maximizes the spectral efficiency. / Master of Science

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Thesis (M.App.Sc.) - Carleton University, 2005. / Includes bibliographical references (p. 146-148). Also available in electronic format on the Internet.

In order to meet the ever-growing demand for mobile data, a number of different technologies have been adopted by the fourth generation standardization bodies. These include multiple access schemes such as spatial division multiple access (SDMA), and efficient modulation techniques such as orthogonal frequency division multiplexing (OFDM)-based modulation. The specific objectives of this theses are to develop an effective feedback method for interference management in smart antenna SDMA systems and to design an efficient OFDM-based modulation technique, where an additional dimension is added to the conventional two-dimensional modulation techniques such as quadrature amplitude modulation (QAM). In SDMA time division duplex (TDD) systems, where channel reciprocity is maintained, uplink (UL) channel sounding method is considered as one of the most promising feedback methods due to its bandwidth and delay efficiency. Conventional channel sounding (CCS) only conveys the channel state information (CSI) of each active user to the base station (BS). Due to the limitation in system performance because of co-channel interference (CCI) from adjacent cells in interference-limited scenarios, CSI is only a suboptimal metric for multiuser spatial multiplexing optimization. The first major contribution of this theses is a novel interference feedback method proposed to provide the BS with implicit knowledge about the interference level received by each mobile station (MS). More specifically, it is proposed to weight the conventional channel sounding pilots by the level of the experienced interference at the user’s side. Interference-weighted channel sounding (IWCS) acts as a spectrally efficient feedback technique that provides the BS with implicit knowledge about CCI experienced by each MS, and significantly improves the downlink (DL) sum capacity for both greedy and fair scheduling policies. For the sake of completeness, a novel procedure is developed to make the IWCS pilots usable for UL optimization. It is proposed to divide the optimization metric obtained from the IWCS pilots by the interference experienced at the BS’s antennas. The resultant new metric, the channel gain divided by the multiplication of DL and UL interference, provides link-protection awareness and is used to optimize both UL and DL. Using maximum capacity scheduling criterion, the link-protection aware metric results in a gain in the median system sum capacity of 26.7% and 12.5% in DL and UL respectively compared to the case when conventional channel sounding techniques are used. Moreover, heuristic algorithm has been proposed in order to facilitate a practical optimization and to reduce the computational complexity. The second major contribution of this theses is an innovative transmission approach, referred to as subcarrier-index modulation (SIM), which is proposed to be integrated with OFDM. The key idea of SIM is to employ the subcarrier-index to convey information to the receiver. Furthermore, a closed-form analytical bit error ratio (BER) of SIM OFDM in Rayleigh channel is derived. Simulation results show BER performance gain of 4 dB over 4-QAM OFDM for both coded and uncoded data without power saving policy. Alternatively, power saving policy maintains an average gain of 1 dB while only using half OFDM symbol transmit power.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / Digital modulation schemes that are power and bandwidth efficient are highly desirable. After non-linear amplification has been done, signal modulation schemes having constant or quasi-constant envelopes are not as susceptible to spectral regrowth as those with non-constant envelopes. Since such distortion generates interference in the adjacent channels, the power operation of the amplifier in non-constant envelope modulations is typically backed off, resulting in systems with reduced power efficiency. On the other hand, constant envelope modulation may have different bandwidth spectra. This paper examines the statistical characteristics of N-GMSK and N-FQPSK [1] signals to assess the bandwidth efficiency in the presence of amplifier nonlinearities.