In-phase Channels Research Articles

I/Q multiplexed code assignment for fast cell search in asynchronous DS/CDMA cellular systems

For flexible system deployment, we consider asynchronous cell site operation which requires much longer cell search time than in synchronous operation. A new code assignment scheme is proposed to minimize the cell search time in which a group code is assigned to the in-phase pilot channel and a cell-specific code assigned to the quadrature pilot channel. Simulation results show that cell search can be accomplished in less than about 200 ms at 90% of the locations when the pilot code of length 1024 and eight group codes (64 cell-specific codes/group) are used.

A 200-MHz complex number multiplier using redundant binary arithmetic

Modern digital communication systems rely heavily on baseband signal processing for in-phase and quadrature (I-Q) channels, and complex number processing in low-voltage CMOS has become a necessity for channel equalization, timing recovery, modulation, and demodulation. In this work, redundant binary (RB) arithmetic is applied to complex number multiplication for the first time so that an N-bit parallel complex number multiplier can be reduced to two RE multiplications (i.e., an addition of N RB partial products) corresponding to real and imaginary parts, respectively. This efficient RE encoding scheme proposed can generate RB partial products with no additional hardware and delay overheads. A prototype 8-bit complex number multiplier containing 11.5 K transistors is integrated on 1.05/spl times/1.33 mm/sup 2/ using 0.8 /spl mu/m CMOS. The chip consumes 90 mW with 2.5 V supply when clocked at 200 MHz.

Sources of calibration errors in helicopter EM data

The procedures used to calibrate helicopter electromagnetic systems are analysed to determine the errors produced both by mispositioning the Q-coil and by the effects of conducting ground at the calibration site. In general, errors produced by mispositioning the Q-coil can be greater than 2 percent/cm of displacement for movement in-line with the bird axis. Displacement in other directions produces smaller errors. The use of calibration jigs to stabilise Q-coil position is strongly recommended. The effect of conductive ground at the calibration site depends upon the conductivity of the ground, the transmitter frequency, and the coil geometry. As transmitter frequency increases, conductivity effects appear at higher resistivities for typical five-coil-pair birds with frequencies ranging from 900 Hz to 56 kHz. In general, these effects start to appear in the quadrature channels as resistivities drop below 100 ohm-m. Inphase channels are not affected until resistivities are less than 10 ohm-m. The horizontal coplanar coil geometry is more susceptible to conductivity effects than the vertical coaxial coil geometry, which is relatively immune to these effects at resistivities greater than 10 ohm-m for frequencies up to at least 7200 Hz.

BER expressions for differentially detected π/4 DQPSK modulation

Closed form bit-error rate (BER) expressions for differentially detected /spl pi//4-shifted differentially encoded quadrature phase-shift keying (QPSK) modulation (/spl pi//4 DQPSK) are derived for both additive white Gaussian noise (AWGN) and Rayleigh-fading channels. The derivations are carried out in an exact and most general manner in that in-phase (I) and quadrature (Q) channel bit-error probabilities P/sub cl/ and P/sub cQ/ are separately obtained in terms of the same-quadrature and cross-quadrature noise Correlation functions, including a measure of noise nonstationarity. We then specialize the general expressions for uncorrelated noise and equal noise powers in successive symbol periods to obtain a useful bit-error probability expression for the AWGN channel in the form P/sub e//spl ap/Q(/spl radic/(1.1716/spl middot/E/sub b//N/sub 0/)) where Q(/spl middot/) is the Gaussian distribution Q-function and E/sub b//N/sub 0/ is the bit energy-to-noise density ratio. Exact BER expressions for the Rayleigh-fading channel that involve the noise parameters are also given and are extended to the case of L-fold diversity combining.

Pyroelectric Thermal-Wave Resonant Cavity: A Precision Thermal Diffusivity Sensor for Gases and Vapors

A novel thermal-wave resonant cavity (TWRC) was constructed and used for thermophysical measurements of gases and vapors, with an AC current-heated thin-film resistive element acting as a thermal-wave source. A thin-film pyroelectric element was used both as a cavity wall and as a signal transducer. A theoretical model of the cavity length-scanned thermal-wave field was developed to quantify the standing-wave resonance antinode patterns in the demodulated lock-in signal output in-phase and quadrature channels. These resonance extrema were used to measure precisely the thermal diffusivity of the intracavity gas or vapor. Seven high-purity gases (nitrogen, dry air, oxygen, methane, hydrogen in nitrogen, pure hydrogen, and helium) were measured using the cavity. Fourth-significant-figure precision was obtained for this parameter, with standard deviations less than 0.32% for the five measurements performed with each gas. Furthermore, three grades of gasoline vapors from Imperial Oil were studied with the cavity. The measured thermal diffusivities showed that the TWRC can monitor fundamental evaporation kinetics as an analytical quality-control instrument. These results, together with the simplicity of TWRC sensor fabrication, are indicative of its potential to become a new standard measurement instrument for the determination of gas thermal diffusivity with improved precision, and a new in situ monitor of chemical evaporation kinetics over conventional methodologies, such as gas chromatography and mass spectrometry.

Impacts of I/Q imbalance on QPSK-OFDM-QAM detection

The impacts of the I/Q imbalance in the quadrature down-converter on the performance of a QPSK-OFDM-QAM system are studied. Either amplitude or phase imbalance introduces inter-channel interference (ICI). In addition to the ICI, there is a cross-talk between in-phase and quadrature channels in each and every sub-carrier when both amplitude and phase imbalances are present. The BER (bit error ratio) performance of QPSK sub-carriers are also calculated to illustrate the impacts of the I/Q imbalance. It is observed that with the amplitude imbalance less than 1 dB and phase imbalance less than 5 degrees, the degradation of BER performance is less than 0.5 dB for a BER>10/sup -6/.

New time-domain clutter-lock algorithm

The authors present a new clutter-lock algorithm to estimate the Doppler spectrum centre frequency. The algorithm is based on the fact that the number of zero crossings in the in-phase and quadrature channels is minimum when the azimuth received signal is base-band converted by using the correct Doppler centroid. Although the problem of estimating the Doppler centre frequency is of interest in many fields, the authors investigated the performance of the proposed algorithm when used in the context of SAR data focussing. First, the authors briefly recall the problem of SAR signal processing, then they introduce the proposed algorithm. Its validity is demonstrated by applying it both to simulated and real data. Finally, the algorithm is compared to existing clutter-lock techniques in terms of both estimation accuracy and processing time.

3 V, 28 mW Si-bipolar front-end IC for900 MHz homodyne wireless receivers

A 900 MHz homodyne receiver front-end bipolar chip is presented. The circuit consists of a low-noise amplifier and two double-balanced mixers for in-phase and quadrature channels. The power supply voltage is 3 V and power dissipation is 28 mW. The measured performance includes 33.5 dB voltage gain, a 3.1 dB noise figure, –13 dBm input referred IP3, –95 dB LO leakage into the RF port on wafer probing, and less than 0.1 dB I/Q magnitude imbalance.

False alarm analysis of the envelope detection GO-CFAR processor

The greatest of constant false alarm rate processor (GO CFAR) is a useful architecture for adaptively setting a radar detection threshold in the presence of clutter edges. The GO CFAR input is often the envelope detected in-phase (I) and quadrature (Q) channels of the baseband signal (x/sub e/=/spl radic/(I/sup 2/+Q/sup 2/)). This envelope detection can also be approximated using x=a max{|I|,|Q|}+b min{|I|,|Q|} which requires less complex hardware (a and b are simple multiplying coefficients). The envelope GO CFAR processor and several envelope approximation GO CFAR processors are compared in terms of the probability of false alarm (PFA) performance. Closed-form expressions which describe the PFA performance are given and their accuracy evaluated. It is shown that for all cases, the PFA is proportional to the number of reference cells n for small threshold multiplier T and inversely proportional to n for large T. A region of intersection occurs where the PFA is the same for two different values of n. For example, at T'=1.68 in the |I|+|Q| GO CFAR (a=1, b=1) the PFA for n=1 is equal to the optimal n=/spl infin/ fixed-threshold PFA (PFA=0.112).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Random Wave Method for Detecting Phase Imbalance in a Coherent Radar Receiver

The question of monitoring the angle between the in-phase (I) and quadrature (Q) channels of a coherent radar receiver is considered in this paper. Random interference-type scattering (e.g., rain echo) is assumed so that the received signal is a random phasor sum. It is also assumed that I and Q voltages have a (90 + ϕ0) phase difference. The effects of nonzero phase imbalance ϕ0 on the I and Q statistics are examined. Joint I and Q as well as amplitude and phase probability distributions are derived. It is shown that the cross-correlation coefficient at zero lag between I and Q time series is proportional to ϕ0, which provides a simple algorithm to detect the phase imbalance. This is verified by Monte Carlo simulations.

LOW FREQUENCY FALSE-LOCK PHENOMENON IN SAMPLED COSTAS-LOOPS

The effect of the low frequency false-lock phenomenon has been considered in sampled decision feedback Costas-loops used in BPSK direct sequence spread spectrum (DS SS) systems. This new physical phenomenon can occur in each arm-filtered nonlinear sampled PLL applying digital signal processing algorithms for phase detector implementations. This contribution provides details of calculation of false-locking phase detector characteristics of the sampled Costas-loops without and with hard-limited in-phase channel (the latter system will be referred to as sampled decision feedback loop) and analyzes different methods of filterless subharmonic false-lock detection. Besides in the case of white Gaussian noisy environment the phase detector characteristics at the false-lock frequencies, and the false alarm and false detection probabilities of the filterless subharmonic false-lock detectors are derived based on the new circuit models. The theoretical results have been checked by experimental implementations.

New multigate pulsed Doppler system using second-order sampling

A new multigate Doppler system using second-order sampling is proposed. To reduce the hardware complexity and to eliminate the balancing problem between in-phase and quadrature signal channels in conventional systems, the proposed system uses a single signal processing channel. This system can be used in a multigate Doppler system and implemented in a full digital fashion.

XPSK: A New Cross-Correlated Phase-Shift Keying Modulation Technique

A new modulation technique, cross-correlated phase-shift keying ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">XPSK</tex> ), is introduced. XPSK is a band-limited offset QPSK modulation technique which has an almost constant envelope. In XPSK modulators, a controlled amount of cross correlation between the in-phase ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</tex> ) and quadrature ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> ) channels is introduced. <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> cross correlation reduce the envelope fluctuation Of the intersymbol-interference and jitter-free OQPSK (IJF-OQPSK) modulation scheme, introduced by Feher et al. [1], [2], from 3 dB to approximately 0 dB, thus further improving the performance of IJF-OQPSK systems in nonlinear radio systems [7], [14]. It is shown that the baseband signal of the modulator, the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_{e} = f(E_{b}/N_{0})</tex> performance, and the spectral characteristics of nonlinearly amplified (hard-limited or saturated) radio systems of XPSK and tamed frequency modems (TFM) are practically the same. The XPSK demodulator is a conventional OQPSK demodulator, the TFM demodulator requires a somewhat more complex signal processor. For this reason, the XPSK approach may lead to significant demodulator hardware cost savings, particularly in point-to-multipoint distribution systems such as broadcast systems. Simulation results for linear and nonlinear (saturated amplifier) systems operated in an adjacent-channel interference environment (in addition to thermal noise) are presented. Measurement results performed on a 128 kbit/s rate hardware-prototype modem are also reported. Experimental eye diagram and power spectrum density measurement results are in close agreement with the computer simulation results.

Probability of error in CPSK systems with intersymbol interference and additive noise

A simple lower bound, an upper bound and a simple approximation to the upper bound on the probability of error for coherent phase-shift-keyed (CPSK) systems operating in the presence of intersymbol interference and additive noise are obtained. The additive noises in the in-phase channel and the quadrature channel are assumed to be independent, and are independent of the signal, but not restricted to be Gaussian. The approximation to the upper bound is four times the lower bound, hence the tightness of these bounds is uniform for all cases. This fact and the simplicity of the bounds make these bounds a useful system design tool. Numerical examples for quaternary and octonary systems are presented and compared to known results.

The Correction of I and Q Errors in a Coherent Processor

A method is presented for correcting the gain and phase imbalances and the bias errors of the in-phase and quadrature channels of a coherent signal processor [1] by means of coefficients which are derived from measurements of a test signal. The residual errors after correction depend upon the signal-to-noise ratio (S/N) of the test signal and the degree of filtering used in deriving the correction coefficients.

Alias Lock Behavior of Sampled-Data Costas Loops

The potential false problem associated with the sampled data type of Costas loop implementation is addressed in this paper. The term lock is used here to differentiate this type of false behavior from the data sideband false behavior of analog Costas loops [1]-[8]. It is shown that the sampled-data version of the conventional Costas loop, sampled at a rate 1/T_{s} , can alias at frequencies that are multiples of 1/2T_{s} away from the carrier frequency. It is also shown that the alias problem of the sampled data version of the Costas loop with hard-limited in-phase channel is further Compounded by the potential occurrence of false frequencies at rational multiples of 1/2T_{s} , away from the carrier. The false S -curves of I-Q loops and decision-directed I-Q loops are investigated in detail, with and without additive noise. Close agreement between theory and earlier experimental results is also demonstrated.

Detection Performance of Hard-Limited Phase-Coded Signals

The performance of a complex phase-coded waveform digital processor with hard-limiting constant false-alarm rate (CFAR) is presented. Processing losses relative to ideal matched-filter performance are computed and verified by hardware measurement. The losses considered include the consequences of hard limiting, envelope algorithm implementation, range cusping, and the associated effects of code length, IF filter bandwidth, and in-phase and quadrature channel phase offset. The range resolution properties of two closely spaced targets are also considered.

Tracking Performance of Costas Loops with Hard-Limited In-Phase Channel

It is becoming increasingly popular in the design of suppressed carrier receivers, which employ Costas loops for earrier reconstruction, to hard-limit the output of the in-phase channel. Doing so allows replacement of the analog multiplier, which forms the loop error signal, with a chopper-type device which typically exhibits much less dc offset. The false lock behavior of such a hard-limited loop was recently investigated and shown to be quite different from that of the conventional Costas loop without the hard limiter. This paper presents the companion, analysis of the tracking performance of the hard-limited loop and assesses the penalty, if indeed it is a penalty rather than an improvement, in this performance relative to the conventional Costas loop with an analog third multiplier. In particular, for the case of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</tex> arm filters and NRZ data, the squaring loss (or equivalently the linear loop tracking jitter) is evaluated and illustrated as a function of the ratio of arm filter bandwidth to data rate and data signal-to-noise ratio. Superimposed on these numerical results will be the corresponding ones for the conventional Costas loop. As a finale, the equivalence in operation of the Costas loop with hard-limited in-phase channel and a baseband modulation carrier reconstruction loop referred to as a demod/ remod loop is discussed.

The False Lock Performance of Costas Loops with Hard-Limited In-Phase Channel

The ability of a Costas loop to false lock on a data sideband is a problem which must be dealt with in the design of suppressedcarrier receivers which employ such loops for carrier reconstruction. For conventional Costas loops wherein the error signal is formed from the product of two analog signals, the false lock problem has recently been investigated by the author and others and is now well understood. For implementation reasons associated with the reduction of dc offsets, it is often desirable to hard limit the output of the in-phase channel and replace the analog multiplier which forms the above product with a chopper-type device. The false lock behavior of such a Costas loop with hard-limited in-phase channel is quite different from that of the conventional Costas loop and is the subject of investigation in this paper. Results are also presented for a modified version of the Costas loop wherein the quadrature arm filter is removed. This configuration has recently been suggested as a means of improving the false lock performance of the Costas loop with hard-limited in-phase channel.

Fluctuation Loss and Diversity Gain for In - Phase Systems with Post - Detection Integration

This paper presents a simple method for determining the losses resulting from detecting only the in-phase component of the complex signal vector returned from a Rayleigh-distributed target. A simple rule is given in terms of the fluctuation loss and integration gain of square-law-detected pulses. The integration improvement for the in-phase channel is given for both slow and fast fluctuating Rayleigh targets. The loss associated with failure to use the quadrature signal component is basic in that it accounts for only one Gaussian sample and, therefore, one degree of freedom. The loss incurred with one square-law-detected return as normally implemented in radar receivers represents two degrees of freedom. It is well known that the system performance improves, approaching that for the constant target, with increasing degrees of freedom of the received data. This paper is an extension of earlier work in that it relates previously computed data to a simple rule.