Rajarajan Senguttuvan

Pro-VIZOR: process tunable virtually zero margin low power adaptive RF for wireless systems

In this paper, a process tunable, continuously adaptive wireless front end architecture and related adaptation algorithms are presented that allow an RF transceiver to function at minimum power irrespective of channel conditions and process variability induced performance loss in the RF front end and baseband interface. Current wireless transceiver front ends are designed for worst case channel conditions and a limited degree of post manufacture tuning is performed to compensate for process variations. It is shown how the proposed architecture can result in significant power savings over current practice without compromising system-level bit error rate. The adaptation methodology is applied to a WLAN transceiver design and hardware measurement data for an adaptive receiver is presented.

Environment-Adaptive Concurrent Companding and Bias Control for Efficient Power-Amplifier Operation

The design of power-efficient orthogonal frequency division multiplexing (OFDM) transmitters suffers from a major bottleneck due to the high peak-to-average ratio (PAR) of OFDM signals as the efficiency of a linear RF power amplifier (PA) reduces drastically due to backoff requirements. In this paper, we propose a system-level approach for dynamic power reduction in OFDM transmitters with varying channels. The proposed methodology uses adaptive baseband companding/expanding of the OFDM signal along with concurrent PA rebiasing to save power. Using channel quality information for dynamic PAR adaptation, the proposed approach achieves a PAR reduction of as high as 7.25 dB, under favorable channels. This translates to a power savings of 5.5× compared with static PAs and 3.6× compared with adaptive PAs with only output-power adaptation.

Production test technique for measuring BER of ultra-wideband (UWB) devices

Ultra-wideband is an emerging standard for short-range high data-rate wireless communication. In a production test environment, ultra-wideband devices are tested for bit error rate (BER) in the presence of an external interferer. As the target BER values are small at low interference levels, it requires a long test sequence for measuring BER, incurring a long test time. This paper describes a novel production test technique for BER testing of orthogonal frequency-division multiplexing transceivers. By adjusting the phase values of the baseband signal, the proposed manufacturing test methodology reduces the overall test time considerably (up to 20/spl times/), while keeping the error vector magnitude and peak-to-average ratio of the transmitted signal unchanged. This method can be extended to any phase modulation scheme to reduce the test time for BER.

Multidimensional Adaptive Power Management for Low-Power Operation of Wireless Devices

Currently, wireless circuits are designed to meet minimum quality-of-service requirements under worst case wireless link conditions (interference, noise, multipath effects), leading to high power consumption when the channel is not worst case. In this work, we develop a multidimensional adaptive power management approach that optimally trades-off power versus performance across temporally changing operating conditions by concurrently tuning control parameters in the RF and digital baseband components of the wireless receiver. Simulation and hardware results indicate significant power savings in the receiver using the proposed approach while maintaining the system bit error rate specification.

Concurrent PAR and power amplifier adaptation for power efficient operation of WiMAX OFDM transmitters

High peak-to-average ratio (PAR) of OFDM signals is a major bottleneck in the implementation of power efficient transmitters since the efficiency of a linear RF power amplifier reduce drastically due to backoff requirements. In this paper, a concurrent approach that uses adaptive baseband companding/ expanding of the OFDM signal along with dynamic PA biasing to achieve significant power savings in the transmitters is proposed. While using existing channel estimation techniques to drive the dynamic PAR adaptation, the proposed approach achieves a PAR reduction as high as 7.25 dB and power savings of 5.27X when channel conditions are good.

Alternate Diagnostic Testing and Compensation of RF Transmitter Performance Using Response Detection

Digital predistortion is used as a compensation technique in communication systems to minimize the effect of power amplifier non-linearity while increasing its operational efficiency. Prior linearization schemes use the receiver chain to feed data to the baseband processor that adaptively adjusts the predistortion coefficients. The procedure is iterative, requires many test applications, is sensitive to receiver quality, and is not suitable for RF communication front ends in which the mixer, LNA and PA are dynamically reconfigured to adapt to changing operating conditions. In the proposed scheme, a single multi-sine diagnostic test is applied from the baseband, and the response of the transmitter is captured via a response envelope detector. A novel unified methodology for co-tuning predistortion coefficients along with the PA bias voltage based on response diagnosis is proposed, thereby, enabling the transmitter to operate at high efficiency and linearity.

VIZOR: Virtually zero margin adaptive RF for ultra low power wireless communication

Modern wireless transceiver systems are often overdesigned to meet the requirements of low bit error rate values at high data rates under worst-case channel operating conditions (interference, noise, multi-path effects). This results in circuits being designed with ldquosufficientrdquo margins leading to lower efficiency and high power consumption. In this paper, we develop an adaptive power management strategy for RF systems that optimally trades-off power vs. performance for the RF front-end to maintain operation at or below a specified maximum bit error rate (BER) across temporally changing operating conditions. As the communication channel degrades, more power is consumed by the RF front end and vice versa. Since the maximum bit-error rate specification is not violated, minimum voice or video quality through the wireless channel is always guaranteed.

EVM Testing of Wireless OFDM Transceivers Using Intelligent Back-End Digital Signal Processing Algorithms

In production testing of wireless systems, measurement of EVM (a critical spec that is directly related to bit error rate) incurs significant test time due to the large numbers of symbols that need to be transmitted for reasons of accuracy. In our approach, EVM is modeled as a function of the system static non-idealities (IQ mismatch, gain, IIP3 parameters) and dynamic non-idealities (system noise, VCO phase noise). Using a selected subset of the OFDM tones, the static parameters are calculated first. These are then used to facilitate noise estimation using a back-end constellation compensation and noise amplification procedure. The data generated is used to predict EVM using machine learning methods. Significant reduction in test time is achieved with little loss in test accuracy.

Efficient testing of wireless polar transmitters

Polar radio architectures are gaining in popularity due to the promise of an all digital implementations in future CMOS systems-on-chip (SoCs) solutions. Test cost is an important consideration for manufacturers developing these complex devices. Phase noise is an important specification in all digital polar radios as it affects the signal modulation quality. In this paper, a low cost test technique for predicting gain, IIP3, phase noise, and EVM with good accuracy is proposed. The method uses a single down-conversion module and a low pass filter on the load board. Although this test setup has been proposed in the past for other specifications, it has not used to test for phase noise and EVM specifications.

Fast Accurate Tests for Multi-Carrier Transceiver Specifications: EVM and Noise

Production testing of digitally modulated transceivers such as those based on orthogonal frequency division multiplexing (OFDM) has become challenging, particularly in the context of measuring specifications such as error-vector-magnitude (EVM) which require the use of precision test equipment with digital modulation capability and low noise floor. Moreover, test time is an issue due to the need to transmit and receive a large number of data bits for accurate test measurement. In this paper, a multi-tone based test method is presented for accurately measuring the EVM and noise specifications of a wireless device. We present the theory behind the proposed approach along with simulation results. The proposed test method is low-cost, and has the potential to significantly reduce EVM test time under production test conditions.