Efficiency and linearity of the microwave power amplifier are critical elements for mobile communication systems. This paper discusses improvements in system efficiency that are obtainable when a DC-DC converter is used to convert available battery voltage to an optimal supply voltage for the output RF amplifier. A boost DC-DC converter with an operating frequency of 10 MHz is demonstrated using GaAs heterojunction bipolar transistors. Advantages of 10 MHz switching frequency and associated loss mechanisms are described. For modulation formats with a time-varying envelope, such as CDMA, the probability of power usage is described. Gains in power efficiency and battery lifetime are calculated. An envelope detector circuit with a fast feedback loop regulator is discussed. Effects of varying supply voltage with respect to distortion are examined along with methods to increase system linearity.

High-efficiency power amplifier using dynamic power-supply voltage for CDMA applications

Single- and Multi-carrier Quadrature Amplitude Modulation Principles and Applications for Personal Communications, WLANs and Broadcasting L. Hanzo Department of Electronics and Computer Science, University of Southampton, UK W. Webb Motorola, Arlington Heights, USA formerly at Multiple Access Communications Ltd, Southampton, UK T. Keller Ubinetics, Cambridge Technology Centre, Melbourn, UK formerly at Department of Electronics and Computer Science, University of Southampton, UK Motivated by the rapid evolution of wireless communication systems, this expanded second edition provides an overview of most major single- and multi-carrier Quadrature Amplitude Modulation (QAM) techniques commencing with simple QAM schemes for the uninitiated through to complex, rapidly-evolving areas, such as arrangements for wide-band mobile channels. Targeted at the more advanced reader, the multi-carrier modulation based second half of the book presents a research-orientated outlook using a variety of novel QAM-based arrangements. * Features six new chapters dealing with the complexities of multi-carrier modulation which has found applications ranging from Wireless Local Area Networks (WLAN) to Digital Video Broadcasting (DVB) * Provides a rudimentary introduction for readers requiring a background in the field of modulation and radio wave propagation * Discusses classic QAM transmission issues relevant to Gaussian channels * Examines QAM-based transmissions over mobile radio channels * Incorporates QAM-related orthogonal techniques, considers the spectral efficiency of QAM in cellular frequency re-use structures and presents a QAM-based speech communications system design study * Introduces Orthogonal Frequency Division Multiplexing (OFDM) over both Gaussian and wideband fading channels By providing an all-encompassing self-contained treatment of single- and multi- carrier QAM based communications, a wide range of readers including senior undergraduate and postgraduate students, practising engineers and researchers alike will all find the coverage of this book attractive.

Single- and Multi-carrier Quadrature Amplitude Modulation : Principles and Applications for Personal Communications, WLANs and Broadcasting

An efficiency-enhanced power-amplifier system design is presented based on wide-bandwidth envelope tracking (WBET) with application to orthogonal frequency-division multiplexing wireless local area network systems. Envelope elimination and restoration (EER) and WBET are compared in terms of the time mismatch sensitivity between the base-band amplitude path and the RF path, and it is demonstrated that WBET is much less sensitive than EER to these effects. An adaptive time-alignment algorithm for the WBET system is developed and demonstrated. The analysis and algorithm are verified by experimental results. The measurement shows that the peak drain efficiency of the complete system was 30% at a 2.4-GHz orthogonal frequency-division multiplexing output power of 20 dBm.

Design of wide-bandwidth envelope-tracking power amplifiers for OFDM applications

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Quadrature Amplitude Modulation: From Basics to Adaptive Trellis-Coded, Turbo-Equalised and Space-Time Coded OFDM, CDMA and MC-CDMA Systems

In a mobile cellular communication system, a base station is wired to a Local Area Network (LAN), and has wireless communication with a plurality of mobile stations. Multipath fading is substantially reduced in the system by utilizing antenna diversity techniques at the base station and each of the plurality of mobile stations. The combination of the independent operation of antenna selection diversity at both a base station and a mobile station results in the selection of the best propagation path between the two stations.

Diversity transmission strategy in mobile/indoor cellular radio communications

A technique is proposed for improving the power-added efficiency of linear, class-A FET power amplifiers operating with varying-envelope signafs. It involves dynamically controlling the gate "dc" bias voltage with the envelope of the input RF signal. It is shown theoretically that this technique, which is referred to as "class A," results in a significant improvement in the power-added efficiency over standard class A, independently of the FET power gain. The efficiency is also better than that of standard class B if the FET gain is less than about 10 dB, which is the case normally encountered at higher microwave frequencies. The practical implementation of class /sup /spl equiv//A requires FET's with essentially linear drain-current-versus-gate-voltage transfer characteristics.

Improving the Power-Added Efficiency of FET Amplifiers Operating with Varying-Envelope Signals

The present invention relates to a portable transceiver and a remote terminal station each using at least two antennas with different polarization transmission capabilities for an adaptive retransmission technique. In the present adaptive retransmission technique, the terminal station transmits the same preamble signal in at least two time slots of a frame period of a time division sequence using the antenna receiving the strongest signal from the transceiver in the immediately prior frame period followed by a binary message signal using the same antenna. The transceiver receives each of the preamble transmissions from the terminal station via a separate one of differently oriented antennas and determines which antenna received the strongest signal. The message signal from the terminal station is then received via the antenna of the transceiver having received the strongest signal and also sends its response message signal on that antenna during a separate time slot of a frame period.

Time division adaptive retransmission technique for portable radio telephones

To determine a channel which may be advantageously assigned to a mobile user via a preferred one of a plurality of spacially remote base stations, a central control computer considers the status of use of all communication channels utilized by the system. All of these channels constitute but a single set, so any of them may be assigned to a mobile user by way of any base station. Thus, the allocation procedures utilized by the computer feature optimization tests which insure minimal station-to-station interference with optimal "packing" and re-use of the channels over the entire system.

Dynamic program control for channel assignment in mobile communication systems

Available devices including quadrature detectors, delta coders and nonlinear amplifying devices are used to produce linear amplification of a bandpass analog input signal having amplitude variations. This linear amplification technique is primarily useful at high frequencies. The analog input signal is resolved into two variable amplitude quadrature components, the envelopes of which together contain the total information content of the input. The envelopes are applied to separate delta coders which each produce a delta bitstream whose weighted time average approximates the respective envelope. The constant amplitude delta bitstreams phase reverse (phase shift key) modulate two quadrature reference signals. In one embodiment, nonlinear high level phase reverse modulators are used to produce two high level output signals, which are then summed and bandpass filtered to produce a linearly amplified replica of the original analog input signal. In another embodiment, two output signals from low level phase reverse modulators are each amplified by separate nonlinear amplifiers. The amplified resultants are then summed and bandpass filtered to produce a linearly amplified replica of the original analog input signal. In all embodiments, a decoder feedback loop is required. This loop may be either internal to the delta coder or external and coupled to the linearly amplified replica.

Linear amplification using quantized envelope components to phase reverse modulate quadrature reference signals

The present invention relates to a linear, class A FET amplifier circuit capable of providing linear amplifier of input signals with a time-varying envelope function. An envelope detector (12) is responsive to an input signal (vi (t)) for extracting the envelope signal (Vi (t)) therefrom. A gate controller (16) subsequently adds the envelope signal to a predetermined gate bias voltage (EG) and applies the sum (EG (t)) as the "d-c" gate input to the FET amplifier (14). Therefore, the gate bias voltage is dynamically controlled by the envelope of the input signal, resulting in a significant improvement in the power-added efficiency (ηadded) over prior art class A FET amplifiers.

Donald Clyde Cox

Papers

Improving the Power-Added Efficiency of FET Amplifiers Operating with Varying-Envelope Signals

Time division adaptive retransmission technique for portable radio telephones

Dynamic program control for channel assignment in mobile communication systems

Linear amplification using quantized envelope components to phase reverse modulate quadrature reference signals

Dynamic class-4 FET amplifier