Diversity-combining Techniques Research Articles

Identity-based attack detection using received signal strength in MIMO systems

This paper proposes RSS-based multiple-input multiple-output (MIMO) receiver diversity-combining techniques for identity-based attack detection. The diversity-combining techniques considered for identity-based attack detection using MIMO systems include selection combining (SLC), equal gain combining (EGC), and maximal ratio combining (MRC). First, we exploit the spatial correlation of the RSS hereditary from wireless nodes to detect identity-based attacks. Analytical expressions of the proposed method for the spatial correlation of the RSS hereditary using MIMO-combining diversities are provided and validated through simulation results. Second, we propose unsupervised machine learning (ML) algorithms such as k-means and k-medoids for the detection of identity-based attacks using RSS with different MIMO-combining diversities. Complete statistical derivations for the detection of identity-based attacks using k-means and k-medoids algorithms were performed. The simulation results confirm that the proposed techniques exploiting MIMO diversity-combining techniques for identity-based attack detection using unsupervised ML algorithms outperform the previously proposed techniques in terms of the false positive rate (FPR) and detection rate (DR). Furthermore, the simulation showed that the EGC-combining diversity with k-means and k-medoids outperformed the SLC- and MRC-combining techniques.

On the Performance of Decode-and-Forward Equal-Gain-Combining Relay Systems over Weibull Fading Channels

Relay-assisted wireless communications, where both the relay and the final destiny employ diversity-combining techniques, represent a compelling strategy for improving the signal-to-noise ratio (SNR) for mobile terminals, mainly at millimeter-wave (mmWave) frequency bands. In this sense, this work considers a wireless network that employs a dual-hop decode-and-forward (DF) relaying protocol, in which the receivers at the relay and at the base station (BS) use an antenna array. Moreover, it is considered that the received signals are combined at reception using equal-gain-combining (EGC). Recent works have enthusiastically employed the Weibull distribution so as to emulate the small-scale fading behavior in mmWave frequencies, which also motivates its use in the present work. For this scenario, exact and asymptotic expressions for the system's outage probability (OP) and average bit error probability (ABEP) are derived in closed form. Useful insights are gained from these expressions. More precisely, they illustrate how the system and fading parameters affect the performance of the DF-EGC system. Monte Carlo simulations corroborate the accuracy and validity of the derived expressions. Furthermore, the mean achievable rate of the considered system is also evaluated via simulations. Useful insights regarding the system performance are obtained from these numerical results.

A Novel Diversity Receiver Design for Cooperative Transmission System

In this paper, we consider the performance of an amplify-and-forward relaying-based multiple-input multiple-output space–time-block-coded cooperative communication system. We propose an efficient two-stage receiver design for a relay-assisted transmission scenario over frequency-selective channels. It is also demonstrated that the receiver is able to achieve the full diversity order of the system by incorporating linear processing techniques. With this method, the potential spatial diversity and multipath diversity can be obtained by using the diversity-combining technique, which frequency-selective fading channels can be equivalently transformed. Simulation results show that the proposed scheme significantly outperforms the minimum mean square error and ZF receivers, while maintaining nearly linear complexity.

Survey on diversity‐combining techniques for interference suppression in fast frequency hopping systems

Over the past few decades, frequency hopping (FH) techniques have attracted considerable interest in both military and commercial communications. However, fading and interference can significantly degrade the performance of an FH system. One method commonly employed to overcome the degradation in performance because of the fading is the use of diversity. Furthermore, fast FH (FFH) systems can enjoy both time and frequency diversity and hence FFH systems employed in conjunction with diversity-combining techniques are effective for combating fading and interference effects. In this study, the authors provide a comprehensive survey on the past and current research work on diversity-combining techniques for suppressing different types of interference in FFH M-ary frequency-shift-keying systems over various fading channels. Some commonly used theoretical approaches for analysing performance of FFH systems are also presented. In addition to the survey, they will also discuss some interesting areas of future work in this research topic.

Diversity-combining technique for discreet Hartley transform-based asymmetrical clipping optical orthogonal frequency-division multiplexing

In this Letter, we propose a scheme that integrates a diversity-combining technique with asymmetrical clipping optical orthogonal frequency-division multiplexing (ACO-OFDM) based on a discreet Hartley transform (DHT). Simulations are demonstrated for the DHT-based ACO-OFDM system with a diversity-combining technique. The simulation results indicate that when the optimal weighting factor is chosen, the bit error rate (BER) performance is improved by about 2 dB when the binary phase-shift keying (BPSK) is modulated and about 3 dB when the 16 pulse-amplitude modulation is modulated. Additionally, experiments are presented to verify the feasibility of diversity-combining DHT-based ACO-OFDM. In the transmission experiments, a BPSK-modulated DHT-based ACO-OFDM with a diversity-combining receiver is realized, which improves the BER performance by 1.5 and 1.3 dB for a span length of back-to-back and a 50 km standard single-mode fiber, respectively.

Analytical BER and PER Performance of Frequency-Domain Diversity Combining, Multipacket Detection and Hybrid Schemes

Diversity Combining (DC) and Multipacket Detection (MPD) are efficient techniques that cope with packet errors due to severe propagation conditions and/or collisions. To evaluate their network performance on a network simulator, an accurate characterization of the Bit Error Rate (BER) and Packet Error Rate (PER) can successfully replace the behavior of the PHY layer. This choice is better in terms of computational time than implementing a full PHY layer to be jointly simulated with the upper layers. In this paper, an analytical model is proposed to compute the BER and PER of DC, MPD and hybrid techniques, considering a Single-Carrier with Frequency-Domain Equalization (SC-FDE) scenario. The paper also considers two frequency-domain detection methods: a simple linear receiver and a powerful iterative receiver. The proposed model is simple and versatile, since it can support nonhomogeneous transmitting powers, and different channel conditions concerning retransmissions and channel randomization techniques. Several simulations show that the proposed model provides accurate BER and PER results for a wide range of scenarios.

Performance Analysis for Optical OFDM Transmission in Short-Range IM/DD Systems

This paper investigates the performance of some recently proposed optical orthogonal frequency-division multiplexing (OFDM) transmission techniques in a short-range intensity-modulated, direct-detected (IM/DD) optical channel. Due to the unipolarity of the IM/DD channel, asymmetric clipping and associated nonlinear distortion is inevitable, resulting in an unfavorable dc power and a significant performance penalty. Using a detailed analysis of the clipped signal, our recent work focused on reducing this clipping-resulted dc via both power optimization and frequency planning. In this paper, a set of effective receiver signal-to-noise ratio formulas is proposed, which helps in accurately and efficiently evaluating the system performance across various optical OFDM systems. We conduct a power efficiency analysis to reveal tradeoffs between power and spectral efficiencies among different systems. Our results show that with a cost of additional complexity, a diversity-combining technique offers significant benefits in all cases.

Capacity of coherent free-space optical links using diversity-combining techniques: errata

Capacity of coherent free-space optical links using diversity-combining techniques: errata

Capacity of coherent free-space optical links using diversity-combining techniques

We study the performance of diversity combining techniques applied to synchronous laser communication through the turbulent atmosphere. We assume that a single information-bearing signal is transmitted over two or more statistically independent fading channels, and that the multiple replicas are combined at the receiver to improve detection efficiency. We consider the effects of log-normal amplitude fluctuations and Gaussian phase fluctuations, in addition to local oscillator shot noise. We study the effect of various parameters, including the ratio of receiver aperture diameter to wavefront coherence diameter, the scintillation index, and the number of independent diversity branches combined at the receiver. We consider both maximal-ratio combining (MRC) and selective combining (SC) diversity schemes. We derive expressions for the outage Shannon capacity, thus placing upper bounds on the spectral efficiency achievable using these techniques.

Simple Tight Upper Bounds for Average SEP and BEP of Coherent Diversity $M$-ary Biorthogonal Signals Over Fading Channels

This paper presents simple tight upper bound expressions for the average symbol error probability and bit error probability of coherent M-ary biorthogonal signals over fading channels with diversity reception. The upper bounds, which do not involve numerical integration and are expressed with only elementary functions, can be efficiently evaluated. In addition, they are valid for different diversity-combining techniques, as well as for arbitrarily correlated and/or nonidentically distributed channels. The tightness of the derived upper bounds is clarified under various channel conditions. Numerical results are also provided to demonstrate the impact of nonidentical channels on the system average error performance.

Robust Diversity-Combing Receivers for LDPC Coded FFH-SS with Partial-Band Interference

Diversity-combining followed by min-sum decoding is proposed for mitigating partial-band interference in low-density parity-check (LDPC) coded frequency-hopping systems with diversity transmission. A new robust diversity-combining technique is derived based on the generalized maximum-likelihood ratio test (GMLRT). Simulations show that, among various diversity-combining techniques, the GMLRT, envelope self-normalizing and clipped-linear combining schemes are appealing for use in practice.

Performance study of linear and nonlinear diversity-combining techniques in synchronous FFH∕MA communication systems over fading channels

Based on the Fourier-Bessel series and exponential characteristic function approach, the paper presents analytical bit-error-rate expressions for synchronous fast frequency-hopped spread-spectrum multiple-access systems over Rician fading channels with M-ary frequency-shift-keying modulation. Linear-combining, product-combining and clipper receivers are studied. Numerical results show that both the clipper and product-combining receivers perform significantly better than the linear-combining receiver. The clipper receiver with an optimum threshold level slightly outperforms the product-combining receiver. However, the product-combining receiver is the preferred diversity-combining method because it is completely nonparametric. In addition, the optimum diversity levels for various diversity-combining receivers over Rayleigh fading channels are higher than that of the Rician fading channels.

Diversity Combining With Imperfect Channel Estimation

The optimal diversity-combining technique is investigated for a multipath Rayleigh fading channel with imperfect channel state information at the receiver. Applying minimum mean-square error channel estimation, the channel state can be decomposed into the channel estimator spanned by channel observation, and the estimation error orthogonal to channel observation. The optimal combining weight is obtained from the first principle of maximum a posteriori detection, taking into consideration the imperfect channel estimation. The bit-error performance using the optimal diversity combining is derived and compared with that of the suboptimal application of maximal ratio combining. Numerical results are presented for specific channel models and estimation methods to illustrate the combined effect of channel estimation and detection on bit-error rate performance.

Diversity Combining With Imperfect Channel Estimation

We propose an iterative extension of the Bell Laboratory Layered Space-Time (BLAST) algorithm and its variant VBLAST. A characteristic feature of the BLAST-type algorithm is that symbol de- cisions with low reliability are fed back to decode other symbols. Both performance analysis based on Gaussian approximation of residual inter- ference and simulation results demonstrate that error propagation due to unreliable decision feedback can severely limit system performance. The extended algorithm exploits inherent signal diversity in BLAST to mitigate residual interference, thus overcoming the performance bottleneck due to error propagation. It yields an impressive performance gain over BLAST. In particular, the extension of BLAST with zero-forcing interference nulling (EXT-ZF-BLAST) admits a simple QR implementation and exhibits excellent performance with low complexity. Abstract—An optimal diversity-combining technique is investigated for a multipath Rayleigh fading channel with imperfect channel state informa- tion at the receiver. Applying minimum mean-square error channel esti- mation, the channel state can be decomposed into the channel estimator spanned by channel observation and the estimation error orthogonal to channel observation. The optimal combining weight is obtained from first principle of maximum a posteriori detection, taking into consideration the imperfect channel estimation. The bit-error performance using the optimal diversity combining is derived and compared with that of the suboptimal application of maximal ratio combining. Numerical results are presented for specific channel models and estimation methods to illustrate the com- bined effect of channel estimation and detection on bit-error rate perfor- mance.

Second-order statistics for diversity-combining techniques in Nakagami-fading channels

Exact and closed-form expressions for the level crossing rate and average fade duration are presented for the M branch pure selection combining (PSC), equal gain combining (EGC), and maximal ratio combining (MRC), techniques, assuming independent branches in a Nakagami (1960) environment. The analytical results are thoroughly validated by reducing the general case to some special cases, for which the solutions are known, and by means of simulation for the more general case. The model developed here is general and can be easily applied to other fading statistics (e.g., Rice).

Capacity of Rayleigh fading channels under different adaptive transmission and diversity-combining techniques

We study the Shannon capacity of adaptive transmission techniques in conjunction with diversity-combining. This capacity provides an upper bound on spectral efficiency using these techniques. We obtain closed-form solutions for the Rayleigh fading channel capacity under three adaptive policies: optimal power and rate adaptation, constant power with optimal rate adaptation, and channel inversion with fixed rate. Optimal power and rate adaptation yields a small increase in capacity over just rate adaptation, and this increase diminishes as the average received carrier-to-noise ratio (CNR) or the number of diversity branches increases. Channel inversion suffers the largest capacity penalty relative to the optimal technique, however, the penalty diminishes with increased diversity. Although diversity yields large capacity gains for all the techniques, the gain is most pronounced with channel inversion. For example, the capacity using channel inversion with two-branch diversity exceeds that of a single-branch system using optimal rate and power adaptation. Since channel inversion is the least complex scheme to implement, there is a tradeoff between complexity and capacity for the various adaptation methods and diversity-combining techniques.

A mode-averaging diversity combiner

A diversity-combining technique is described which reduces frequency distortion caused by multipath propagation in high-frequency single- or double-sideband voice radio transmission. By repetitively sweeping a null through the vertical polar pattern of the receiving antenna, the relative amplitude of signal components arriving by the various propagation modes is varied at a rate which is high compared with the highest audio modulating frequency. A running average of the time-varying resultant of the various mode voltages is diode-rectified to extract the audio intelligence. Transmission nulls caused by mode interference at particular frequencies in the radio spectrum are filled in by this averaging process. The technique requires no more equipment than conventional combining and would appear to offer superior performance. A test of a three-channel version of a combiner using this principle has now been made. To demonstrate the most distinctive feature of the combiner, its ability to fill in mode-interference nulls or minima in a radio channel, special frequency-modulated transmissions were used. It was found that substantial null filling occurred and that, as expected, the filling in is more effective when a pair of antennas is spaced along the line to the distant station than when the same pair is spaced transversely with respect to that line. It is concluded that the theory of this combining operation, as described in this paper, is correct to a first order of accuracy.