Presence Of Adjacent Channel Interference Research Articles

Modulation classification in the presence of adjacent channel interference using convolutional neural networks

SummaryThis paper investigates a vital issue in wireless communication systems, which is the modulation classification. A proposed framework for modulation classification based on deep learning (DL) is presented in the presence of adjacent channel interference (ACI). This framework begins with the generation of constellation diagrams from the received data. These constellation diagrams are fed to convolutional neural networks (CNNs) for modulation classification. The objective of this process is to eliminate the manual feature extraction from the received data and make feature extraction process as a built‐in step with CNNs. Three types of CNNs are considered in this paper and compared for this objective. These types are AlexNet, VGG‐16, and VGG‐19. The proposed classifier is applied on Rayliegh and Rician fading channels.

A Windowing Technique for Optimal Time-Frequency Concentration and ACI Rejection in OFDM-Based Systems

In this paper, we introduce a windowing technique, which provides optimal time-frequency containment and maximal adjacent channel interference (ACI) rejection for orthogonal frequency-division multiplexing (OFDM)-based systems. Instead of using a single pulse shape function for all subcarriers, multiple functions are considered in order to maximize the time-frequency containment of the OFDM waveform. The main strategy is to concentrate the spectrum of windowing functions into a given bandwidth while achieving maximum suppression in the out-of-band region. This is achieved by employing prolate-based windowing functions which give optimal spectral concentration for time-limited pulse shapes. The windowing functions are designed per-subcarrier basis in order to exploit available concentration band for each subcarrier. In addition, the proposed concept is considered for the receive filtering in the presence of ACI. It is shown that the optimal spectral concentration property also maximizes ACI rejection for OFDM receivers.

Performance improvement techniques for the DVB‐RCS2 return link air interface

SummaryThis paper presents performance improvement techniques for the second‐generation digital video broadcast return channel via satellite air interface, which can be used for supporting future demands for Tbit/s traffic requirements. In particular, we have investigated minimum‐shift keying (MSK) type of continuous phase modulation (CPM) waveforms by considering both single‐carrier and multi‐carrier transmission and single‐amplitude and multi‐amplitude signals, which improve the spectral efficiency. In addition, we consider frame timing and synchronization techniques, which make synchronization more accurate and robust. Our research has shown that the MSK single‐carrier frequency‐division multiple access (SC‐FDMA) outperforms the quadrature phase‐shift keying SC‐FDMA in terms of resilience to distortion with the performance gap increasing when the amplifier shows a milder distortion. The performance of a multi‐amplitude CPM scheme, based upon the superposition of two single‐amplitude MSK signals at the radio frequencies level, is also investigated. In comparison with other equivalent linear modulation schemes, performance evaluation results have been shown that the proposed multi‐amplitude CPM scheme significantly improves the spectral efficiency in the presence of adjacent channel interference. Finally, we have proposed a viable and efficient methodology, which enables reliable and accurate timing and frequency synchronization for the SC‐FDMA satellite return link. This involves a combination of global positioning system (GPS)‐based pre‐compensation of differential timing between user terminals, preamble detection in an integrated random access channel, and user channel frequency estimation based on repetitive symbols in the time domain. Copyright © 2015 John Wiley & Sons, Ltd.

System performance of Rayleigh fading channel in the presence of adjacent channel interference

In this paper, the authors study the system performance of adaptive transmission techniques in the presence of adjacent channel interference (ACI). The authors obtain closed-form expressions for system capacity when employing different adaptive transmission policies with and without diversity schemes. The simulation results of spectrum efficiency in a WiMAX network employing 256 orthogonal frequency division multiplexing subcarriers are obtained for the analytical expressions derived for selection combining diversity under various adaptation policies. Analytical results show that the optimal power and rate adaptation policy provides the highest spectrum efficiency. Both analytical and simulation results are found to be in close agreement with each other, which shows that the obtained analytical results works well with the scenario of ACI. Also, maximal ratio combining scheme yields the highest spectrum efficiency when subjected to ACI.

Error Rate Analysis of Band-Limited BPSK With Nakagami/Nakagami ACI Considering Nonlinear Amplifier and Diversity

An exact expression of the average error rate is developed for a band-limited binary phase-shift keying (BPSK) system in the presence of adjacent channel interference (ACI) considering a Nakagami fading channel. The system employs a root-raised cosine (RRC) filter both in the transmitter and receiver sides and a transmitter power amplifier (PA) that may have nonlinear input/output characteristics. These practical considerations are accurately taken into account. By utilizing the characteristic function (CF) method of error-rate analysis, we interestingly blend the concepts of time and frequency domains and develop an error-rate expression that is simple and general for several system parameters, including adjacent channel separation, RRC filter roll-off factor, and PA output back-off (OBO). Hence, the error rate in the presence of cochannel interference (CCI) is obtained as a special case. The developed results for a single-branch receiver are then extended for diversity receivers, and several interesting observations are made.

Joint Channel Synchronization under Interference Limited Conditions

Spectral efficiency is of great concern in the return channel of satellite based broadband systems. In (Beidas, 2002) the feasibility of increased efficiency by reducing channel spacing below the symbol rate was demonstrated using joint detection and decoding for a synchronized system. We extend this work by addressing the critical synchronization problem in the presence of adjacent channel interference (ACI) which limits performance as carrier spacing is reduced. A pilot sequence aided joint synchronization scheme for a multi-frequency time division multiple access (MF-TDMA) system is proposed. Based on a maximum likelihood (ML) criterion, the channel parameters, including frequency, time and phase are jointly estimated for the channel of interest and the adjacent channels. The impact of ACI on the synchronization and detection performance is investigated. It is shown that joint channel parameter estimation outperforms single carrier synchronization with reasonable additional computational complexity in the receiver. Based on the proposed synchronization scheme in conjunction with an appropriate joint detection mechanism, see (Beidas, 2002), carrier spacing can be reduced significantly compared to current systems providing a substantial increase in spectral efficiency.

Low complexity multi-channel synchronization for satellite systems with adjacent channel interference

In satellite communications, the space segment is a large slice of the operating costs. Therefore every effort should be made to increase the spectral efficiency, thereby reducing the space segment costs. In order to optimize spectral efficiency, channel spacing (CS) should be reduced. Unfortunately, this introduces spectrally overlapping transmissions, thereby creating adjacent channel interference (ACI), which impairs the performance of satellite communication systems. To overcome this problem, intelligent interference mitigation schemes should be considered. This paper considers the problem of multi-channel synchronization of several spectrally overlapping transmissions in a satellite TDMA/frequency division multiple access burst system. The synchronization aims to estimate carrier frequency, carrier phase and symbol timing in the presence of ACI. The potential performance gain of multi-channel processing over conventional single channel processing is shown. Two types of low-complexity algorithms are proposed: ‘channelized’ expectation maximization and ‘channelized’ interference cancellation. Both of these algorithms attain this performance gain. Computer simulations show a 78% improvement in spectral efficiency for a wide range of carrier-imbalance values. This translates into a large potential saving in space segment costs compared to conventional CS. Copyright © 2006 John Wiley & Sons, Ltd.

Television Receiver Optimization in the Presence of Adjacent Channel Interference

Improved DTTV reception in a crowded spectrum can be attained by automatically shifting the front-end filter and by automatically steering the pattern of the receive antenna. This paper shows how 3rd order intermodulation distortion (IM/sub 3/) and other interference due to strong adjacent channels can be minimized and the signal to noise ratio maximized for optimally robust reception.

Effects of ACI and nonlinearities on the performance of differentially detected GMSK signals

The effects on the performance of differentially detected Gaussian minimum shift keying (GMSK) signals operated in the presence of adjacent channel interference (ACI), modulator impairments, amplifier nonlinearities and additive white Gaussian noise is investigated. By means of computer simulation, the bit error rate (BER) performance of 1- and 2-bit conventional and decision feedback differentially detected (C-DD and DF-DD) GMSK systems in the presence of static and Rayleigh faded ACI is obtained. It is found that the best performance is achieved by the 2-bit DF-DD receiver and has resulted in BER performance improvements for the static ACI channel and error floor reductions for the Rayleigh faded ACI channel. The effects on the BER performance of a cascade of imperfect GMSK quadrature modulators and a nonlinear amplifier in conjunction with the resulting ACI are also investigated. The combination of 'typical' and 'extreme' operating conditions for the modulator are considered. For all combinations, it was found that the DF-DD receivers perform better than the C-DD receivers. However, for systems operating under 'typical' operating conditions, the 2-bit DF-DD receiver exhibits the best performance.

New approaches to adjacent channel interference suppression in FDMA/TDMA mobile radio systems

The capacity and signal quality of wireless communication systems can be improved by enhancing receiver performance in the presence of adjacent channel interference (ACI), In this paper, maximum-likelihood sequence estimation (MLSE) receivers based on joint demodulation and successive cancellation of adjacent channel signals are developed. The proposed receivers provide significant improvement in performance over a wide range of carrier-to-interference ratios. To provide coherent reception, novel channel estimation techniques are used, exploiting knowledge of the transmit and receive filter responses. Performance is evaluated and compared via simulation for the Global System for Mobile communications (GSM) digital cellular system.

MSK-type signals in the presence of adjacent channel interference and white noise

In this letter, the problem of adjacent channel interference (ACI) caused by the close packing of constant envelope MSK-type users in a given frequency band is considered. An optimal receiver filter, based on the theory of matched filtering, is found, and it serves as an upper bound on the signal-to-interference ratio. The intersymbol interference (ISI) caused by the time response of the matched filter is eliminated by a decision feedback equalizer (DFE) which, however, degrades performance. It was found that the matched-filter upper bound allows about 3-15 dB more ACI than the performance of a classical correlation detector (for additive white Gaussian noise only), depending on the frequency separation between channels. The DFE performance is only a little bit worse than that of the matched filter.

Performance of 1REC-MHPM in the presence of adjacent channel interference

The effect of adjacent channel interference (ACI) on the error probability of the rectangular frequency pulse multi-h phase-coded modulation (1REC-MHPM) is studied. Evaluations through simulation were done for different values of the absolute adjacent channel frequency spacing |/spl Delta/f|, different time delay /spl tau/ between the main channel and the interfering channel, and schemes with different number of modulation indexes. It is found that ACI effects can only be eliminated when |/spl Delta/f| approaches 2.0. Comparison with minimum shift keying (MSK) is also made through simulation.

An Optical Heterodyne PSK Receiver using an Improved Decision Directed PLL in Presence of Adjacent Channel Interference

An optical phase-shift-keying (PSK) heterodyne receiver using synchronous detection by means of a decision directed phase locked loop (PLL) has been investigated taking the effect of shot noise, phase noise, adjacent channel interference and loop propagation delay. The evaluation of phase-error variance and error probability calculations are performed without affecting the loop stability. The plots of error probability with PNB are presented as a function of normalised optical domain channel spacing for several linewidth-to-bit-rate ratios. A relative improvement in error probability of 4 dB has been obtained with normalised control parameter of 0.4, D = 10Rb & δf = 0.001Rb.

Performance evaluation of linear equalizers in the presence of adjacent channel interference

Abstract An analytical technique is developed to evaluate the error rate and the minimum mean-square-error (MMSE) performance of linearly equalized Atf-ary quadrature amplitude modulation and quadrature partial response signalling in the presence of adjacent channel interference. Both symbol- and fractionally-spaced linear equalizers (SSE and FSE) are considered. The tap gains of these equalizers are evaluated in the MMSE sense. The transfer function and MMSE of the infinite tap SSE are derived in the presence of interfering channels. The underlying structure of the infinite-tap SSE is used to develop an infinitely long FSE. Numerical results indicate that the proposed structure does not yield the same MMSE as obtained by a sufficiently long FSE. A frequency domain analysis in conjunction with singular value decomposition reveals that the case for the failure of the proposed structure is due to a built-in rank reduced property.

Nonlinear continuous phase modulation

A class of nonlinear CPM signals is introduced by extending nonlinear CPFSK signals to other forms of frequency pulses. The distance results and spectral properties of nonlinear CPM signals are reported. Bit error probabilities of nonlinear CPM signals are simulated in presence of adjacent channel interference.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance of a satellite modem transmitting convolutionally and differentially encoded 8PSK signals

AbstractThe paper studies a digital satellite modem for mobile systems. The modem transmits a convolutionally and differentially encoded eight‐phase‐shift‐keyed (CDE8PSK) signal over a satellite link and employs a near‐maximum‐likelihood decoder at the receiver. The signal can tolerate phase ambiguities that are multiples of 4 radians, which normally result from the carrier recovery loop at the receiver. However, the carrier recovery loop is not considered here. The high‐power amplifier (HPA) at the earth‐station transmitter may introduce non‐linear distortion to the CDE8PSK signal, and predistortion may or may not be used. Several different earth‐stations are assumed to have simultaneous access to a given transponder on the satellite, in an arrangement of frequency division multiple access, but the satellite transponder is assumed to be linear. Thus the CDE8PSK signals that occupy the immediately adjacent frequency bands can introduce adjacent‐channel interference (ACI) to the desired CDE8PSK signal. Extensive computer‐simulation tests have been carried out to evaluate the effects of non‐linear distortion with predistortion, in the presence of ACI, on the tolerance of the modem to additive white Gaussian noise. Four different bandwidths of the transmitted signal are considered, together with 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. In all simulation tests, an equivalent baseband model of the transmission system is used, and the results are used to determine the preferred modem design.

Simulation study of 8psk and ce16psk signals for satellite transmissions

The paper presents the results of an extensive series of computer-simulation tests to determine the effects of nonlinear distortion and adjacent channel interference (ACI) on the tolerances to noise of an uncoded eight-phase-shiftkeyed (8PSK) signal and a rate−3/4 convolutionally encoded 16-ary phase-shift-keyed (CE16PSK) signal for transmitting over satellite channels. Both signals have the same theoretical spectral efficiency of 3 bit/s/Hz, but the CE16PSK signal has an asymptotic coding gain of 4 dB over the uncoded 8PSK signal. Several different earth stations are assumed to have simultaneous access to a given transponder in a satellite by frequency division multiple access, so that ACI can be introduced into the wanted channel by the channels in the immediately frequency bands. It is assumed in the study that the high-power amplifier (HPA) of each earth station may or may not introduce nonlinear distortion into the transmitted signal, but the satellite transponder is linear. The optimum performances of the systems are compared with these using a rate-3/4 convolutionally encoded 16-ary quadrature-amplitude-modulated (CE16QAM) signal and a rate-3/4 convolutionally encoded 16-ary amplitude-phase-modulated (CE16APM) signal. It has been shown that, in the absence of ACI, the CE16PSK system has advantages of 1.3 dB, 2.6 dB and 2.8 dB over the CE16APM, CE16QAM and 8PSK signals, respectively, at a bit-error rate of 10−4; and, in the presence of ACI, the advantages are 0.6 dB, 1.3 dB and 3.5 dB, respectively.

Adjacent channel and cochannel interferences in CPFSK systems with nonlinear transmitters and limiter-discriminator detection

The performance of continuous-phase FSK (frequency-shift keying) systems with rectangular modulation pulse shaping and limiter-discriminator detection is analytically evaluated in the presence of transmission nonlinearities as well as adjacent channel and cochannel interference. Consideration of modulation pulses with length tau , shorter than symbol time, T, is investigated. The algorithm developed to evaluate bit-error probability shows that the choice tau /T=1, and even more so in the presence of adjacent channel interference. Moreover, for tau /T=0.5, numerical results are reported that describe system performance under different working conditions and can be used to develop design criteria. >

Performance of Partial Response CPM in the Presence of Adjacent Channel Interference and Gaussian Noise

Partial response continuous phase modulation (CPM) schemes have found wide acceptance because of their compact spectra and comparable performance with other traditional modulation schemes. Although optimum receivers are complex, simple suboptimum receivers are found to yield very good performance in special cases. Performance of such modulation schemes is of interest in a multiple user environment where adjacent channels are spaced closely to improve the system capacity. This paper presents the performance of partial response CPM in the presence of adjacent channel interference and Gaussian noise. The meansquare crosstalk in CPM systems employing MSK-type receivers is formulated. Based on this formulation, a number of modulation schemes employing different receiver filters are analyzed for their ACI rejection. Comparison of results proves that receiver filters, in addition to the spectral occupancy of the signal, play an important role in deciding the crosstalk. The error performance of various schemes evaluated using simulation technique is compared, and it is found that in the presence of adjacent channel interference, certain schemes perform better than minimum shift keying (MSK). The results of the simulation further prove the inadequacy of Gaussian assumption for the adjacent channel interference. It is seen that judicious choice of modulation scheme and receiver filter can result in better spectrum utilization.

Comparison of Performance of Digital Modulation Techniques in the Presence of Adjacent Channel Interference

The performance of four digital modulation techniques are compared to one another when each is received in the presence of adjacent channel interference. The interfering waveforms that each modulation format sees are identical to the modulation format under consideration. The four types of modulation are QPSK, 8-PSK, 16QASK, and QPR. Upper bounds to the probability of error are derived and used to evaluate the relative merits of the different schemes.