Rudi de Buda

Bio: Rudi de Buda is an academic researcher from McMaster University. The author has contributed to research in topics: Amplitude and phase-shift keying & Square (algebra). The author has an hindex of 2, co-authored 2 publications receiving 22 citations.

Fast FSK signals and their demodulation

Abstract: The Fast FSK is a particular kind of FSK (Frequency Shift Keying) which is useful for the transmission of digital data over an r.f. channel which is limited in both bandwidth and power. This paper describes the performance of the Fast FSK, and outlines the practical circuits which demodulate it.

Frequency Synthesis Using Walsh Functions

Abstract: A new scheme for the programmable generation of either square or sine waves of a required frequency is proposed. It uses neither feedback, nor table lookup of stored values, but it derives the desired square wave from a Walsh function, fairly simple to select and to generate with digital circuits. For this purpose, the Walsh function is counted down in a binary counter, at whose output a function with clean spectrum results, whose spurious components can be bounded by a simple formula. This approach becomes the design principle for a programmable frequency synthesizer with phase-continuous output, practically instantaneous switching between frequencies, and no limit on the number of closely and evenly spaced frequencies that can be selected.

Minimum shift keying: A spectrally efficient modulation

Abstract: The ever increasing demand for digital transmission channels, in the radio frequency (RF) band presents a potentially serious problem of spectral congestion and is likely to cause severe adjacent and cochannel interference problems. This has, in recent years, led to the investigation of a wide variety of techniques for solving the problem of spectral congestion. Some solutions to this problem include: 1) new allocations at high frequencies; 2) better management of existing allocations; 3) the use of frequency-reuse techniques such as the use of narrow-beam antennas and dual polarizing systems; 4) the use of efficient source encoding techniques; and 5) the use of spectrally efficient modulation techniques [l]. This article will consider the last approach and analyze, in particular, a modulation scheme known as minimum shift keying (MSK). The MSK signal format will be explained and its relation to other schemes such as quadrature phase shift keying (QPSK), offset QPSK (OQPSK), and frequency shift keying (FSK) pointed out. The main attributes of MSK, such as constant envelope, spectral efficiency, error rate performance of binary PSK, and self-synchronizing capability will all be explained on the basis of the modulation format.

Quadrature-quadrature phase-shift keying

Abstract: Quadrature-quadrature phase-shift keying (Q/sup 2/PSK) is a spectrally efficient modulation scheme which utilizes available signal space dimensions in a more efficient way than two-dimensional schemes such as QPSK and MSK (minimum-shift keying) It uses two date shaping pulses and two carriers, which are pairwise quadrature in phase, to create a four-dimensional signal space and increases the transmission rate by a factor of two over QPSK and MSK However, the bit error rate performance depends on the choice of pulse pair With simple sinusoidal and cosinusoidal data pulses, the E/sub b//N/sub 0/ requirement for P/sub b/(E)=10/sup -5/ is approximately 16 dB higher than that of MSK Without additional constraints, Q/sup 2/PSK does not maintain a constant envelope, however, a simple block coding can provide a constant envelope This coded signal substantially outperforms MSK and TFM (time-frequency multiplexing) in bandwidth efficiency Like MSK, Q/sup 2/PSK also has self-clocking and self-synchronizing ability An optimum class of pulse shapes for use in Q/sup 2/PSK format is presented One suboptimum realization achieves the Nyquist rate of 2 b/s/Hz using binary detection >

A bandwidth-efficient class of signal-space codes

Abstract: A new class of codes in signal space is presented, and their error and spectral properties are investigated. A constant-amplitude continuous-phase signal carries a coded sequence of linear-phase changes; the possible signal phases form a cylindrical trellis in phase and time. Simple codes using 4-16 phases, together with a Viterbi algorithm decoder, allow transmitter power savings of 2-4 dB over binary phase-shift keying in a narrower bandwidth. A method is given to compute the free distance, and the error rates of all the useful codes are given. A software-instrumented decoder is tested on a simulated Gaussian channel to determine multiple error patterns. The error parameter R_{o} is computed for a somewhat more general class of codes and is shown to increase rapidly when mere phases are employed. Finally, power spectral density curves are presented for several codes, which show that this type of coding does not increase the transmitted signal bandwidth.

Linear Receivers for Correlatively Coded MSK

Abstract: In this paper we show that many spectrally efficient modified MSK schemes, termed generalized MSK, although not representable as OQPSK, may nevertheless be (suboptimally) demodulated using an I-Q receiver with a proper choice of carrier-phase offset. Correlatively coded MSK schemes with I-Q receivers are studied, and it is concluded that duobinary MSK and (1 + 2D + D^{2})/4 MSK represent good performance-bandwidth tradeoffs among first- and second-order correlative coding polynomial schemes. The optimal design of these receivers are considered subject to the constraint of a finite duration impulse response, especially for asymptotic cases of arbitrarily small and large SNR. Filter design based on a zero-intersymbol interference constraint for PAM-based approximations of the signals is also considered. The optimized linear I-Q receivers for (1 + D)/2 MSK and (1 + D)^{2}/4 MSK are presented. These receivers are only 0.28 and 1.24 dB poorer than the optimal (Viterbi) receivers at high SNR.

Optimal Alphabets and Binary Labelings for BICM at Low SNR

Abstract: Optimal binary labelings, input distributions, and input alphabets are analyzed for the so-called bit-interleaved coded modulation (BICM) capacity, paying special attention to the low signal-to-noise ratio (SNR) regime. For 8-ary pulse amplitude modulation (PAM) and for 0.75 bit/symbol, the folded binary code results in a higher capacity than the binary reflected Gray code (BRGC) and the natural binary code (NBC). The 1 dB gap between the additive white Gaussian noise (AWGN) capacity and the BICM capacity with the BRGC can be almost completely removed if the input symbol distribution is properly selected. First-order asymptotics of the BICM capacity for arbitrary input alphabets and distributions, dimensions, mean, variance, and binary labeling are developed. These asymptotics are used to define first-order optimal (FOO) constellations for BICM, i.e., constellations that make BICM achieve the Shannon limit -1.59 dB. It is shown that the Eb/N0 required for reliable transmission at asymptotically low rates in BICM can be as high as infinity, that for uniform input distributions and 8-PAM there are only 72 classes of binary labelings with a different first-order asymptotic behavior, and that this number is reduced to only 26 for 8-ary phase shift keying (PSK). A general answer to the question of FOO constellations for BICM is also given: using the Hadamard transform, it is found that for uniform input distributions, a constellation for BICM is FOO if and only if it is a linear projection of a hypercube. A constellation based on PAM or quadrature amplitude modulation input alphabets is FOO if and only if they are labeled by the NBC; if the constellation is based on PSK input alphabets instead, it can never be FOO if the input alphabet has more than four points, regardless of the labeling.