Effects Of Bandlimiting Research Articles

Generalized Theory of BOC Signal Unambiguous Tracking With Two-Dimensional Loops

The multipeaked correlation functions of binary offset carrier (BOC) modulated signals introduce an ambiguity threat into the code tracking. Several techniques have been proposed to solve this problem, such as a class of two-dimensional (2-D) tracking techniques, in which the spreading code and the subcarrier are tracked separately. In this paper, the key properties of correlation functions and the theoretical tracking performance analysis considering noise and multipath environments of the general 2-D tracking loop are studied. Exact explicit expressions, taking into account the effects of local subcarrier waveform mismatching and the front-end bandlimiting, are provided for the correlation function employed in 2-D tracking. From these expressions, the key characteristics of 2-D correlation functions such as the shape, coupling relation between dimensions, and the effects of bandlimiting can be clearly seen. Moreover, general theoretical methods to predict the performance of the 2-D tracking techniques under the multipath and noise environments are provided. The results obtained in this paper can facilitate investigations in the area of 2-D tracking technique parameter optimization and performance assessment.

Double phase estimator: new unambiguous binary offset carrier tracking algorithm

Several new global navigation satellite system modulations adopt a binary offset carrier (BOC) subcarrier to shape the signal spectrum, increase the frequency separation and improve the tracking performance. BOC modulated signals are, however, characterised by ambiguous multi-peaked correlation functions and several techniques have been proposed in the literature to solve the problem of locking into secondary peaks. In this study, a novel unambiguous BOC tracking technique, the double phase estimator (DPE), is designed to account for the effect of signal bandlimiting. The DPE is an effective alternative to the double estimator (DE) tracking technique where the subcarrier lock loop is replaced by a subcarrier phase lock loop. In the presence of signal bandlimiting, the DPE is able to generate local signal replicas matched in a better manner to the input components, outperforming the DE. The performance of the DPE is thoroughly characterised and the processing of real wideband BOC signals is used to demonstrate the effectiveness of the algorithm proposed. In addition to this, the DPE requires a lower computational load than the DE and thus should be adopted for the processing of wideband BOC signals.

Unambiguous Double Delta Discriminator for sine-phased BOC(n,n) receiver

A new unambiguous discriminator similar to a conventional Double Delta correlator is tailored for sinephased BOC(1,1) signal tracking. It is shown in this paper that it has efficient multipath mitigation at the cost of degraded noise resistance due to correlation loss of using waveform subtraction. Its multipath performances is evaluated in both coherent and dot-product type noncoherent structures. The advantage of dot-product type discriminator structure for multipath resistance is shown. Tracking code jitters are examined theoretically and empirically. A new simplified jitter expression is provided to facilitate the comparison of relative noise performance for various Strobe Correlators with the proposed discriminator, without considering the effect of bandlimiting.

Marine broadband case study offshore China

Dual tow-depth acquisition configurations are used to mitigate the band-limiting effect of the sea-surface ghost in marine streamer surveys. Here we report on the analysis of a 2D broadband marine seismic project acquired offshore China. The deployment configuration included over/under sources and three streamers towed at different depths (5, 17, and 23 m). This configuration allowed not only for analysis of dual tow depth as a method for increasing bandwidth, but also for evaluation of two distinct dual tow-depth combinations, over/under and sparse-under. The project provided the first opportunity to make this comparison. Evaluation of reflection images, filter panels, amplitude spectra, and signal/noise separations demonstrates that both techniques are effective at compensating for the filtering effect of the ghost response, but also suggest that the improved results from each dual tow-depth technique are very comparable. Given the operational advantages of the sparse-under technique, due to the reduced streamer requirements, we conclude that the sparse-under technique is an attractive option for 3D deployments.

An Accurate Transient Analysis of High-Speed Package Interconnects Using Convolution Technique

An accurate transient analysis of a package interconnect requires the modeling and analysis of conductor and dielectric losses, as well as other high-frequency effects of 3D structures. The skin effect and dispersion of interconnects are more accurately modeled in frequency domain. Consequently, an accurate time-domain simulation of such a system is only possible using convolution techniques. Although the convolution method is well understood, the application of windowing for frequency-dependent interconnect analysis is less so. In this paper, we present the practical considerations of window selection and its application to improve the accuracy of convolution simulators. We introduce the Tukey window and study the tradeoff between how smoothly data can be set to zero to avoid aliasing and suppress ripples and how much information tapering will discount at the edge of the window in order to obtain meaningful results. The bandlimiting effects of the Tukey window and other well-known windows are also compared. Finally, to verify the validity and accuracy of the proposed method, a wirebond PBGA package and a PCB-connector system are analyzed using the scattering parameters obtained from simulation and measurement, respectively.

Information-theoretic comparisons of cellular multiple-access systems with bandwidth-dependent fading considerations

The coding performances of generic DS-CDMA, FDMA and hybrid F/TDMA systems with equivalent operating conditions are analysed and compared based on two information-theoretic performance measures, namely, channel capacity and probability of codeword decoding error. Statistical signal models for the different systems are developed, which, among other practical considerations, incorporate the effects of multicell operation, raised-cosine bandlimiting and multipath fading statistics which vary with the signalling bandwidth used. The results obtained provide insights into some fundamental mechanisms which contribute to the relative spectral efficiency among different multiple-access systems.

Half-sine and triangular despreading chip waveforms for coherent delay-locked tracking in DS/SS systems

The performance of a coherent delay-locked tracking scheme for direct-sequence/spread-spectrum systems using half-sine or triangular chip waveforms for early and late despreading sequences is analyzed. The effect of band-limiting on the received signals is considered. Mean time to lose lock (MTLL) and root mean square (rms) tracking error of the delay-locked loop (DLL) are compared with that of a conventional DLL which uses rectangular chip despreading waveforms. Linear and nonlinear (based on the renewal process approach) analyses are employed to evaluate the performance of the DLL. Results show that the use of either the half-sine or triangular chip waveform reduces the rms tracking error and increases the MTLL considerably when the early-late spacing is approximately between 0.7-1.3 chip times. The results apply in particular to the commonly used DLL using one chip early-late spacing. Computer simulation for band-limited signals confirms the analytical results. The use of these despreading chip waveforms also reduces tracking offset in multipath environments.

Performance evaluation of pragmatic TCM codes through band-limited nonlinear satellite channel. a computer simulation approach

Most early communication satellite systems are power-limited; as improvements are made on launch vehicles and satellites become larger, the tendency has shifted from powerlimited to bandwidth-limited systems. In bandlimited nonlinear satellite applications, various papers have shown that respectable coding gains can be achieved by Ungerboeck TCM (trellis code modulation) codes, making them popular in this application owing to the advantage of performance improvement without bandwidth increase or transmitter power increase, and with the codes displaying their robustness to the nonlinearity and band-limiting that prevail in satellite channels. A recent paper by Viterbi proposed pragmatic codes which have a single coder and decoder for various bandwidth efficiencies and achieve a performance comparable to that of Ungerboeck codes on a linear Gaussian channel. These codes are punctured versions of the basic 1/2 rate convolutional code mapped into MPSK signal phase constellation. In this paper, the performance on band-limited nonlinear satellite channel of pragmatic 8PSK codes is studied with respect to equivalent Ungerboeck 8PSK codes. Computer simulation is used to estimate the coding gains achieved on these various codes, and lower bounds for bit error probability are estimated through formulas approximated by Forney. Signal space diagrams are also plotted to show the band-limiting effect, giving a better picture of the signal point dispersion phenomenon caused by severe band-limitation of the satellite channel.

Design of a discrete cosine transform based speech scrambler

A discrete cosine transform based speech-encryption system, suitable for communication over band-limited telephone channels, is described. An energy modification technique is presented which dramatically reduces the residual intelligibiltiy of the scrambled speech. In addition, a method used to reduce the undesirable effects of band limitation is described. Simulation results are included which demonstrate the improved performance of the scheme.

A method of a spread-spectrum radar polyphase code design

A new method of pulse compression polyphase code synthesis based on the aperiodic autocorrelation function properties and the assumption of coherent processing in the radar receiver is presented. Properties of the proposed code, including spectrum, ambiguity function, precompression bandlimiting effects, and the noise/clutter influence are analyzed. The main features of the synthesized code are the absence of sidelobes in the compressed pulse and its tolerance of precompression bandlimiting limitations. A comparison to the known classes of pulse compression does is made. >

Multipath distortion of differentially encoded GMSK with 2-b differential detection in bandlimited frequency-selective mobile radio channel

Error performance of Gaussian minimum-shift keying (GMSK) with 2-b differential detection in a frequency-selective mobile radio channel is analyzed. The two-wave model using two Rayleigh waves with constant group time-delay is adopted to describe a frequency-selective mobile radio channel. The Gaussian-type bandpass filter is introduced as a receiving filter to demonstrate the effects of band limitation at the receiver. A preferable receiving bandwidth in the frequency-selective mobile channel is also discussed. It is shown that the preferable receiving bandwidth is almost that obtained in an additive Gaussian noise channel since the magnitude of the interfering (or delayed) wave is relatively small. It is hardly affected by the maximum Doppler frequency and remains almost constant for the various parameters, e.g. average carrier-to-noise power ratio. >

Performance of a rate-3/4 coded signal, incorporated with a circular signal set for regenerative satellite transmissions

The paper studies a digital modem that transmits a rate-3/4 convolutionally encoded 16-ary amplitude and phase modulated (CE16APM) signal, over a regenerative satellite link. The signal uses a (4, 12) circular signal constellation set and has a coding gain of about 4 dB at a bit error rate of 10-4, over an uncoded eight-phase-shift keyed (8PSK) signal. Several different earth stations are assumed to have simultaneous access to a given regenerative satellite using frequency division multiple access. Thus, the CE16APM signals that occupy the immediately adjacent frequency bands can introduce adjacent-channel interference (ACI) into the transmitted CE16APM signal. The high-power amplifier (HPA) at each of the earth-station transmitters or on board the satellite transmitter may introduce nonlinear AM-AM and AM-PM conversion effects into the CE16APM signal. Results of a series of computer-simulation tests are presented. These evaluate the effects of bandlimiting, nonlinear distortion and ACI on the performance of the modem. The HPA are tested with different values of output backoff (OBO). The performances of the preferred system arrangements are compared with those of a rate-3/4 convolutionally encoded 16-ary quadrature-amplitude-modulated (CE16Q AM) signal, using a rectangular signal constellation set, and of an uncoded 8PSK signal. It has shown that the CE16APM signal performs better than the CE16QAM and 8PSK signals over nonlinear channels.

Performance of a CE16QAM modem in a regenerative satellite system

AbstractThis paper studies a digital modem for use over a regenerative satellite link. The modem transmits a convolutionally encoded 16‐ary quadrature‐amplitude‐modulated (CE16QAM) signal. The convolutional code has a three‐bit constraint length and a coding rate of 3/4. The high power amplifier (HPA) on board the satellite transmitter and at each station may introduce non‐linear distortion into the CE16QAM signal, but only a single‐link transmission is considered. Several different earth‐stations are assumed to be used in an arrangement of frequency division multiple access. Thus adjacent‐channel interference (ACI) can be introduced into the signal by the signals that occupy the immediately adjacent frequency bands.Extensive computer‐simulation tests have been carried out to determine the effects of bandlimiting, non‐linear distortion and ACI, on the tolerance to additive white Gaussian noise of the modem, using an equivalent baseband model of the transmission system. The results are used to select the preferred system arrangement. It has been shown that, with 4 dB output back‐off (OBO) in the HPA, a bandwidth efficiency of 2·4 b/s Hz can be achieved, with an improvement in perforamnce of 2·5 dB, relative to that of an ideal uncoded eight‐phase‐shift keyed (8PSK) signal, at a bit‐error rate of 10·4.

Influence of design on performance of a satellite modem transmitting coded PSK signals

The paper studies a digital modem that transmits a convolutionally encoded eight-phaseshift- keyed (CE8PSK) signal over a satellite link. Several different earth stations are assumed to have simultaneous access to a given transponder in the satellite, in an arrangement of frequency division multiple access. Thus, adjacent channel interference (ACI) can be introduced into the CE8PSK signal by the corresponding CE8PSK signals that occupy the immediately adjacent frequency bands. The high power amplifier (HPA) at the earth station transmitter, within the satellite link, may introduce nonlinear distortion into the CE8PSK signal, but the satellite transponder is assumed to be linear. Predistortion may or may not be used. Results are presented of an extensive series of computer-simulation tests. These measure the effects of bandlimiting, nonlinear distortion with and without predistortion, ACI and the demodulation process at the receiver, on the tolerance of the modem to additive white Gaussian noise. Four different bandwidths of the transmitted signal are considered, together with three different levels of output back-off in the HPA at the transmitter, and three different arrangements of the demodulator. The predistorter operates on the baseband signal at the input to the modulator and assumes a prior knowledge of the HPA characteristics. An equivalent baseband model of the transmission system is used to determine the performance of the modem at each of a number of different combinations of the various conditions studied, and the results are used to determine the preferred modem designs. It has been shown that a transmission rate of 16/9 bit/s per hertz of bandwidth can be achieved, with a loss in tolerance to additive white Gaussian noise of less than 1/2 dB relative to the ideal undistorted CE8PSK system.

Performance of a 16-ARY DEQAM modem employing a baseband or RF predistorter over a regenerative satellite link

The paper presents the results of a series of computer-simulation tests that determine the effects of bandlimiting (nonlinear distortion with and without predistortion) on the tolerance to additive white Gaussian noise of a digital modem. The modem transmits a 16-ary differentially encoded quadrature amplitude modulation (16-ary DEQAM) signal over a regenerative satellite link, where the high power amplifier (HPA) on board the satellite transmitter may introduce AM-AM and AM-PM conversion effects into the 16-ary DEQAM signal. Four different bandwidths of the transmitted signal are tested, together with different levels of output back-off in the HPA at the transmitter. The arrangements achieving the most efficient use of the power are selected. There sults show that a surprisingly good improvement in performance can be achieved by using predistortion of the 16-ary DEQAM signal to reduce the nonlinear distortion of the high power amplifier.

Effects of baseband predistortion at the transmitter on the performance of a DEQPSK satellite modem

AbstractThe paper presents the results of an extensive series of computer‐simulation tests to determine the effects of bandlimiting, nonlinear distortion with and without predistortion, and adjacent channel interference (ACI), on the tolerance to additive white Gaussian noise of a digital satellite modem. The modem transmits a differentially encoded quaternary phase‐shift keyed (DEQPSK) signal over a satellite link, where the high‐power amplifier (HPA) at the earth‐station transmitter may introduce AM—AM and AM—PM conversion effects into the DEQPSK signal, but the satellite transponder is linear. Four different bandwidths of the transmitted signal are tested, together with three different levels of output back‐off in the HPA at the transmitter. The predistorter operates on the baseband signal at the input to the modulator in the transmitter and assumes a prior knowledge of the HPA characteristics. ACI can be introduced into the transmitted DEQPSK signal by the corresponding DEQPSK signals, which occupy the two immediately adjacent frequency bands. The latter signals are assumed to have the same transmission rate and bandwidths as the first signal.Various combinations of the different distortion and interference effects are studied, using an equivalent baseband model of the transmission system, and the arrangements selected are those achieving the most efficient use of bandwidth together with the best tolerance to additive white Gaussian noise. A surprisingly good performance is achieved.

Doppler Properties of Polyphase Coded Pulse Compression Waveforms

Doppler properties of the Frank polyphase code and the recently derived P1, P2, P3, and P4 polyphase codes are investigated and compared. An approximate 4 dB cyclic variation of the peak compressed signal is shown to occur as the Doppler frequency increases. The troughs in the peak-signal response occur whenever the total phase shift across the uncompressed pulse, due to Doppler, is an odd multiple of ? radians. It is shown that while the P3 and P4 codes have larger zero-Doppler peak sidelobes than the other codes, the P3 and P4 codes degrade less as the Doppler frequency increases. Also, the effects of amplitude weighting and receiver bandlimiting for both zero and nonzero Doppler are investigated.

A Survey of Modem Design and Performance in Digital Satellite Communications

This paper summarizes the important aspects of digital modem (modulator-demodulator) design for linear and nonlinear satellite channels using time-division multiple access (TDMA). The modem performance degradations caused by transmission anomalies, such as amplitude and delay distortions, effects of single and cascaded nonlinearities, and band-limiting effects in nonlinear channels, have been examined using the test data gathered from various field test programs using INTELSAT IV satellites and laboratory simulations using both INTELSAT IV and INTELSAT V parameters. A systematic methodology has been prescribed to reduce the effect of transmission anomalies on the performance of the modems. This paper consists of three main sections; essential features of TDMA modem design, transmission anomalies and their effects on modem performance, and optimization of modem performance in the presence of transmission deviations. The latter includes a brief description of an advanced maximum-likelihood sequence detection (MLSD) technique for application to the nonlinear channel.

A Modified PN Code Tracking Loop: Its Performance Analysis and Comparative Evaluation

A modified noncoherent PN code tracking loop (MCTL) has been previously presented by the authors [3]. The loop was shown to have the hardware simplicity of the tau-dither loop and a tracking performance superior to the traditional delay-locked code tracking loop (TCTL). Further work conducted herein expands on these previous results by considering the band-limiting effects of the bandpass arm filters on the performance of the MCTL. It will be shown that an even greater improvement in tracking performance is experienced by the MCTL over the TCTL when such effects are included. Furthermore, it was mentioned in [3] that a specific <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S/N</tex> existed below which the MCTL acquisition behavior was superior to the TCTL and above which its behavior was inferior. The bandlimiting effects will be shown to have a more deleterious effect on the TCTL and, as such, the crossover <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S/N</tex> will increase, thus enhancing the comparable capabilities in favor of the MCTL. This paper also discusses the implementation sensitivities to hardware gain and phase imbalance by expanding on the noise-free work in [3] to include the noisy case.

Spectral Properties and Band-Limiting Effects of Time-Compressed TV Signals in a Time-Compression Multiplexing System

Time-compression multiplexing (TCM) has recently been proposed for application in multiple TV transmissions through satellites. It is advantageous over frequency-division multiplexing because of its relative immunity to nonlinear transponder effects. Here we study two important and fundamental aspects of TCM — the spectral properties and band-limiting effects on the time-compressed signal. We derive the output spectrum of a time-compressed signal and show that if the original input signal is assumed to be: (i) band-limited to B Hz, (ii) segmented into T-second intervals before time compression by a factor of α(α ≥ 1), and (iii) 1/T ≪ B, then essentially all the spectral power in the output time-compressed signal is contained in the bandwidth |f| ≥ αB Hz. This result is applicable to the TV case. Numerical examples on various types of spectra are also presented. Using the TV example, we further demonstrate that the ripples created by low-pass filtering the time-compressed signal up to αB Hz are small, and interburst interference due to these ripples can be kept negligible with a small guard time (about 2 percent of the burst duration) between different signal bursts. We also provide a brief discussion on some interesting spectral properties of time-compressed signals in spectrum-expansion applications.