Paul A. Goud

An adaptive digital technique for compensating for analog quadrature modulator/demodulator impairments

Analog quadrature modulators and demodulators have three major impairments: gain imbalance, phase imbalance, and dc-offset. A digital technique is presented for compensation of these modulator and demodulator impairments. Part of the RF signal is fed to an envelope detector. The detector output, along with the baseband quadrature components, is used to estimate the impairment values. The estimated impairment values are then used to compensate for the impairments. Simulation results show that spurious signals can be suppressed by more than 30 dB using this technique. The effect of modulator/demodulator impairments on RF power amplifier linearization techniques is also discussed. The quadrature modulator and demodulator impairment compensator can decrease intermodulation distortion products by 12 dB for the complex gain predistorter and by about 5 dB for the Cartesian coordinate negative feedback method of RF power amplifier linearization.<<ETX>>

Power amplifier linearization using cubic spline interpolation

An adaptive RF power amplifier linearization technique is presented. The demodulated amplifier output is compared with the baseband input signal to estimate the amplifiers AM-AM and AM-PM characteristics, using cubic spline interpolation. The input signal is predistorted using these estimated characteristics to compensate for the amplifiers nonlinearity. The proposed technique has nearly 14 dB better suppression of the intermodulation products than the complex gain predistortion technique. The out-of-band power emission is about 12 dB lower in the first two adjacent RF channels than is obtained using the Cartesian coordinate negative feedback technique.

A scalable LDPC decoder ASIC architecture with bit-serial message exchange

We present a scalable bit-serial architecture for ASIC realizations of low-density parity check (LDPC) decoders. Supporting the architectures potential, we describe a decoder implementation for a (256,128) regular-(3,6) LDPC code that has a decoded information throughput of 250Mbps, a core area of 6.96mm^2 in 180-nm 6-metal CMOS, and an energy efficiency of 7.56nJ per uncoded bit at low signal-to-noise ratios. The decoder is fully block-parallel, with all bits of each 256-bit codeword being processed by 256 variable nodes and 128 parity check nodes that together form an 8-stage iteration pipeline. Extrinsic messages are exchanged bit-serially between the variable and parity check nodes to significantly reduce the interleaver wiring. Parity check node processing is also bit-serial. The silicon implementation performs 32 iterations of the min-sum decoding algorithm on two staggered codewords in the same pipeline. The results of a supplementary layout study show that the reduced wiring congestion makes the decoder readily scaleable up to the longer kilobit-size LDPC codewords that appear in important emerging communication standards.

A portable MIMO testbed and selected channel measurements

A portable multiple-input multiple-output (MIMO) testbed that is based on field programmable gate arrays (FPGAs) and which operates in the 902–928 MHz industrial, scientific, and medical (ISM) band has been developed by the High Capacity Digital Communications (HCDC) Laboratory at the University of Alberta. We present a description of the HCDC testbed along with MIMO channel capacities that were derived from measurements taken with the HCDC testbed for three special locations: a narrow corridor, an athletics field that is surrounded by a metal fence, and a parkade. These locations are special because the channel capacities are different from what is expected for a typical indoor or outdoor channel. For two of the cases, a ray-tracing analysis has been performed and the simulated channel capacity values closely match the values calculated from the measured data. A ray-tracing analysis, however, requires accurate geometrical measurements and sophisticated modeling for each specific location. A MIMO testbed is ideal for quickly obtaining accurate channel capacity information.

Electrical measurement of the junction temperature of an RF power transistor

An enhanced electrical method is presented for measuring the average junction temperature of an RF bipolar transistor. A two-step procedure, previously developed for DC operation, is extended to include the junction temperature measurement for an RF power transistor in a tuned amplifier circuit. The measurement technique is convenient, since it can be used with normal, packaged devices, and does not require a complex heat flow model or ambient temperature measurements. >

Indoor MIMO channel measurements using dual polarized patch antennas

A mobile 4/spl times/4 multiple input multiple output (MIMO) system containing dual polarized patch antennas is used to perform wireless measurement campaigns on nonline of sight (NLOS) channels in an indoor office setting. The MIMO system uses orthogonal 500 kchips/s Walsh coded signals that are filtered and simultaneously transmitted at 916 MHz. The patch antennas have high isolation between their two ports and are used at both transmitter and receiver stations. The complex MIMO channel matrices obtained in the campaigns were used to calculate the theoretical capacity for a 4/spl times/4 system. Our mean measured capacity for the campaign is 21.3 bits/use and the 90/sup th/ percentile channel capacity is 19.5 bits/use. These values are slightly higher than those (mean of 21.1 bits/use and 90/sup th/ percentile channel capacity of 18.9 bits/use) obtained for an identical campaign which used single polarized whip antennas.

Stationary charge transport in metal‐semiconductor‐metal (MSM) structures

Important physical processes affecting charge transport in the metal‐semiconductor‐metal (MSM) structure have been studied from the diffusion theory point of view, in combination with boundary conditions based on thermionic emission theory. At current densities exceeding about 0.1 A cm−2, the stationary unipolar charge transport of injected charge carriers, to which the problem reduces if thermal and avalanche generation of electron‐hole pairs can be neglected, is described by the conduction current equation and Poissons equation. Charge conduction through a semiconductor with nonuniform electric field and mobile‐charge distribution is described using the low‐field diffusion constant and field‐dependent mobility. The current‐dependent concentration of mobile charges at the M‐S interfaces represent the boundary conditions. Physical processes in four MSM structures (PtSi‐n Si–PtSi), differing in doping concentration (ND = 4.4 and 12 × 1014 cm−3) and semiconductor width (L = 4 and 10 μm), have been investig...

Trellis-Coded CPFSK and Soft-Decision Feedback Equalization for Micro-Cellular Wireless Applications

In this paper, trellis-codedM-ary CPFSK with noncoherent envelope detection and adaptive channel equalization are investigated to improve the bit error rate (BER) performance of microcellular digital wireless communications systems. For the same spectral efficiency, the trellis-coded modulation (TCM) schemes studied outperform minimum shift keying (MSK) with noncoherent or differentially coherent detection in Rayleigh fading channels. For the case of frequency-selective fading channels, adaptive channel equalization is applied to mitigate the time-variant intersymbol interference (ISI). A new equalizer structure is proposed which, in its feedback path, makes use of fractionally spaced signal samples instead of symbol-spaced hard decisions on transmitted symbols. Computer simulation results indicate that the soft-decision feedback equalizer (SDFE) can significantly improve the systems performance.

The Direct-Detection Noise-Measuring System and Its Threshold

This paper describes a typical direct-detection noise-measuring system, with particular attention given to the use of Schottky-barrier diodes as envelope detectors. The rise of threshold at low modulation frequencies encountered in these systems has been found to be mainly attributable to FM-to-AM conversion occurring in comparatively narrow-band detectors rather than to diode-flicker noise and thus is largely removable. A sensitivity improvement of 10-20 dB may result at low frequencies, yielding a noise-to-carrier ratio threshold range of about -150 to -155 dB/100 Hz at modulation frequencies from 100 Hz to 50 kHz for measurements of AM noise, and below 0.01 Hz/100 Hz for FM noise, of microwave oscillators at C band.

Multiple-antenna communication systems: an emerging technology

A recent development in wireless communications is the application of multiple-input multiple-output (MIMO) systems to radio communications via use of multiple antennas. In order to investigate the technologys potential, an experimental MIMO system containing two four-element antenna arrays (4x4) has been developed at the University of Alberta. The system is used to obtain MIMO channel measurements in a typical indoor office environment in the ISM band (902-928 MHz). Measurement campaigns have been performed using different antenna spacings and two different types of antenna: half-wavelength (lambda/2) centre-fed dipoles and dual-polarized patches. The measurements are used to calculate channel capacities for an indoor 4x4 MIMO system. The measurements confirm the high capacity potential of a MIMO channel, with ergodic capacity of approximately 21 bits per channel use available with either antenna type at a signal-to-noise ratio of 20 dB if the antenna element separation is lambda/2 or larger. An introduction to basic MIMO theory, a discussion of the University of Alberta wireless MIMO testbed, and observations regarding the measured indoor MIMO channel are presented in the paper.