Error rate analysis of MDPSK/CPSK with diversity reception undervery slow Rayleigh fading and cochannel interference

The distribution of the phase noise due to additive white Gaussian noise (AWGN) and cochannel interference (CCI) is analyzed for differential phase detection (DPD) and coherent phase detection (CPD) in a very slow nonfrequency selective Rayleigh fading environment. The effects of modulation timing offset between the desired signal and the CCI and of the overall channel filter response are considered. Simple closed-form expressions are derived for ideal selection diversity reception. The derived phase noise distributions are used for evaluating the bit error rate (BER) performance of 2-16DPSK/CPSK assuming square-root raised cosine Nyquist transmit/receive filters. It is found that the BER performance of CPSK is less sensitive to CCI modulation timing offset than DPSK, and that increasing the filter rolloff factor can improve the BER performance due to CCI. Finally, the accuracy of the BER approximation that uses the symbol error rate is discussed     

Turbo equalisation in non-Gaussian impulsive noise

Turbo equalisation is a state-of-the-art receiving scheme for coded data transmission over channels introducing intersymbol interference (ISI). The author investigates turbo equalisation performance in the presence of ISI and impulsive noise. The design imperfections contributing to the non-robustness of the standard turbo equaliser to outliers are identified, and a novel turbo equaliser, at almost no additional increase in complexity, is proposed for joint mitigation of ISI and impulsive noise. The proposed turbo equaliser incorporates a Talwar penalty function into the maximum a posteriori (MAP) component equaliser to serve two purposes. First, it improves the estimation of the transition probabilities for all transitions through the trellis and for subsequent determination of the a posteriori log-likelihood ratio. Secondly, it absorbs the outliers and prevents them from spreading into the MAP constituent decoder. Simulation results based on Proakis's channel models show that the proposed turbo equaliser achieves a dramatic improvement over the standard turbo equaliser in impulsive noise. At a bit error rate (BER) of 10/sup -2/, the performance gain is as large as 3.5 to 5 dB, and as large as 7 to 8 dB at a BER of 10/sup -3/.     

水声通信系统中基于迭代自适应的脉冲噪声抑制方法

针对水声通信系统中脉冲噪声抑制问题,提出了一种迭代自适应的脉冲噪声抑制方法。基于 OFDM子载波之间的正交性,该方法首先利用空子载波矩阵从接收信号中提取出背景噪声和脉冲噪声。然后,利用空子载波矩阵构造导频矩阵,得到脉冲噪声的干扰协方差矩阵,并在加权最小二乘准则下通过对代价函数的求解得到脉冲噪声的闭式解。最后,在接收信号中减去脉冲噪声的估计值,完成对脉冲噪声的抑制。仿真结果表明,本文方法有效降低了水声通信系统的误码率,且在高信干噪比下性能提升更加明显。     

Theoretical and experimental analysis of clipping-induced impulsivenoise in AM-VSB subcarrier multiplexed lightwave systems

A new theoretical and experimental analysis of clipping-induced impulsive noise in directly modulated AM-VSB/digital hybrid lightwave systems is presented. The theoretical model is based on asymptotic clipping and shot noise theories, and the probability density of combined Gaussian and impulsive noise is obtained by performing a numerical inverse Fourier transform on the closed-form characteristic function. Similar analyzes in previously published work have resulted in closed-form expressions for the BER in hybrid AM-VSB/QAM systems, but these models, which do not use the numerical inverse Fourier transform, have either required the use of an experimentally measured clipping rate using a spectrum analyzer or have had limited BER prediction accuracy. Application of our theory to experimental results for the BER in a hybrid AM-VSB/64 QAM system demonstrates that the performance of the model if better than the models of previously published works. Theoretical analysis of a similar hybrid system employing the N-VSB HDTV digital modulation format rather than QAM indicates that an improvement in BER is achieved if 8-VSB at double the symbol rate is used instead of 64 QAM. We also present the first experimental characterization of the amplitude and time distribution of (1) low-frequency bandpass and (2) down-converted impulsive noise and we show that the time interval between clipping events has a high probability of being 167 μs, 1.5 μs, or 4 ms in an NTSC system with unmodulated carriers. These results have potential impact on forward error correcting codes used to ameliorate the degrading effects of clipping     

An improved subspace tracking algorithm for blind adaptive multiuser detection

As the Projection Approximation Subspace Tracking with deflation(PASTd) algorithm is sensitive to impulsive noise, an improved subspace tracking algorithm is proposed and applied to blind adaptive multi-user detection. Simulation results show that the improved PASTd algorithm not only remains the properties of the conventional PASTd algorithm, but also has good Bit Error Rate(BER) performance in impulsive noise environment, thus it can effectively improve the system performance.     

BER for optical heterodyne DPSK receivers using delay demodulationand integration detection

Previous work on the bit error rate (BER) performance of differential phase-shift keying (DPSK) including the effects of additive white Gaussian noise (AWGN) and phase noise has concentrated on the delay demodulator with narrow-band intermediate frequency (IF) bandpass filtering (BPF) and sampling detection. No similar analysis has yet been performed for the delay demodulator with wideband IF bandpass filtering and integration detection. Phase noise is an important consideration in coherent optical communication systems and the most widely accepted model is a Brownian motion process. A closed-form BER expression along with detailed Monte Carlo simulation results are presented for the DPSK delay demodulator with wideband IF bandpass filtering and integration detection filtering including phase noise effects using the Brownian motion model. Analytic expressions are also obtained for the moments of the phase noise component of the decision variable. Using these moments, estimates of the phase noise BER floor are produced. It is found that this receiver has noise performance comparable to receivers with narrowband IF bandpass filtering and sampling detectors for signal-to-noise ratio (SNR) and phase noise in the range of practical interest, but with potentially less degradation due to intersymbol interference (ISI)     

Effect of noisy phase reference on coherent detection ofband-limited offset-QPSK signals

The performance of bandlimited offset-quaternary-phase-shift-keying (OQPSK) systems in the presence of noisy phase reference and additive Gaussian noise is analyzed. Expressions for error probability calculation are obtained. A new search method for computing the detection loss and the required SNR of the phase reference is proposed. It is shown that when the rolloff factor for the Nyquist filtering is large, OQPSK surpasses QPSK, but when the rolloff factor is small, QPSK surpasses OQPSK     

冲击噪声干扰下SC分集接收的系统性能分析

现实的无线通信环境不仅存在着高斯白噪声干扰,而且存在着随机冲击干扰。采用高斯混合噪声的模型,对存在冲击噪声干扰的Rayleigh信道应用选择式合并分集接收,并对MPSK系统的误码率性能做了研究和分析。仿真结果显示了系统性能与随机冲击干扰的关系,同时也证明了SC分集接收是改善无线通信系统的性能的一项有效技术。     

NCFSK bit-error rate with unsynchronized slowly fading interferers

An expression for the bit-error rate (BER) of noncoherent frequency-shift keying with a nonfaded desired signal in the presence of N Rayleigh-faded unsynchronized cochannel interferers (UCCIs) and additive white Gaussian noise is first derived. This result can be used to obtain the BER for a faded desired signal. For a large number of UCCIs, numerical evaluation of this expression can be quite time-consuming. An approximate method that yields fairly accurate results is thus described. Numerical results show that for a Rician-faded desired signal with a strong specular component in an interference-limited environment, the BER decreases slightly with N whereas for a Rayleigh-faded desired signal, the BER varies very little with N. A comparison to the BER performance with synchronized cochannel interferers is also provided     

Neural networks applications for CDMA systems in non-Gaussian multi-path channels

Non-Gaussian noise is one of the most common noise models observed in wireless channels. This type of noise has severe impact on wireless systems with multiuser detection devices. In this paper, the issue of multiuser detection in non-Gaussian noise multipath channel is addressed. We also pay a close attention to the neural network applications, and propose a new robust neural network detector for multipath impulsive channels. The maximal ratio combining (MRC) technique is adopted to combine the multipath signals. Moreover, we discuss the performance of the proposed multiuser neural network decorrelating detector (NNDD), under class A Middleton model. Furthermore, the performance of the system under power imbalance scenario is shown. We show that the proposed NNDD has magnificent effect on the system performance. The system performance is measured through the bit error rate (BER). It is shown that the proposed robust receiver reduces the impact of the impulsive noise by processing the received signal and clipping the extreme amplitudes.     

Empirical prediction of BER in ESK data communication systemssubjected to impulsive noise

A method is proposed for predicting the degradation in performance of FSK data communication systems subjected to impulsive noise. It involves overlaying a representation of the incoming noise, expressed in terms of the noise amplitude distribution (NAD), on a family of isodegradation curves drawn with BER as the parameter. A direct prediction of the BER to be expected in the presence of the noise can be obtained by reading off the value of BER corresponding to the point of tangency between the two sets of curves (termed the tangential BER), and multiplying this by a factor F, characteristic of the radio location. The value of F can be found either experimentally or analytically. The usefulness of the method has been demonstrated, using vehicle-born equipment, by a series of experiments designed to be representative of typical mobile radio reception conditions. The method is very powerful experimental assessment technique. It is simple in concept, easy to apply, and has the advantage of being readily generalized for applications with different modulation techniques     

Adaptive equalization for high-speed indoor wireless data communication

The performance of a 4-QAM indoor wireless data communication system with adaptive equalizer is investigated. The effectiveness of using linear and decision-feedback equalizer for Rayleigh and Rician frequency-selective indoor channels is evaluated, and contrasted to the performance of a 4-QAM modem without equalizer. The effects of some important channel and system parameters (multipath spreads up to 200 ns, data rates up to 25 Mbit/s, signaling pulse rolloff factor between 0.5 and 1.0, and additive, white Gaussian noise) on the indoor communication system performance are examined and presented in the paper. The indoor propagation measurements, carried out in a research laboratory, provided data to be used for BER performance assessments of the system with and without equalizer. The performance results based on computer generated channels are then compared with those obtained for measured channel impulse responses.     

A Novel Solution for OFDM Based Relay Systems

In this paper we propose a novel solution for performance enhancement of dual-hop orthogonal frequency division multiplexing (OFDM) based decode-and-forward (DF) relay system, which assumes that relay station uses more than one antenna for downlink communications and implements transmit antenna selection (TAS) on subcarrier basis jointly with ordered subcarrier mapping (SCM). Ordered SCM is technique where subcarriers from the first hop are mapped to corresponding subcarriers on the second hop in accordance to their instantaneous signal-to-noise ratios (SNRs). It is proven to be a mapping scheme that maximizes the achievable ergodic capacity in OFDM based relay systems, while enabling bit error rate (BER) improvement at the same time. In order to assess the level of BER performance improvement in the system proposed in this paper, we analytically derive closed form BER expression of binary phase shift keying modulated OFDM DF relay system with TAS and SCM, assuming a scenario with Rayleigh fading statistics on both hops. Additionally, for further BER reduction, we analyze the combination of TAS with a modified SCM scheme, in which the subcarriers having the lowest SNRs on both hops are omitted. All derived analytical results are completely verified through simulations, showing that significant BER performance improvements are achieved with the novel proposed OFDM relay system, compared to the systems implementing only SCM, or only TAS, which approves that it can be considered as an interesting solution for the next generation of mobile cellular systems.     

New concept in long-reach PON Planning: BER-aware wavelength allocation

With the use of arrayed-waveguide grating (AWG) and erbium-doped-fiber amplifier (EDFA), the long-reach passive optical network (LR-PON) can provide enormous bandwidth over large distances. However, these new technologies can also deteriorate the receivers' bit-error rate (BER) performance. By bringing the concept of BER-awareness into network planning, we can alleviate the performance deterioration, which could in turn lead to simpler design of receiver and thus lower the total cost of LR-PON.The effects of AWG and EDFA on BER are studied in this paper. An analytical model of BER performance is developed as a function of the output port location in the AWG and the distance of the receiver from the AWG. Not only does the proposed model capture the power loss caused by AWG, but it also accounts for several transmission impairments, including the beat noise due to inter-channel crosstalk in the AWG, the amplified spontaneous emission (ASE) noise related to EDFA, and the thermal noise related to the receiver. Based on this model, we propose both short-term and long-term distance-aware wavelength allocation schemes, which balance the BER among the optical network units (ONUs) at different distance. Simulation results show that average BER improves and the relative standard deviation decreases.     

An Analytical Approach for Performance Evaluation of Bit-Patterned Media Channels

In this work, a new analytical approach is used to evaluate the error performance of bit-patterned media (BPM) magnetic recording channels that employ one-dimensional (1D) and two-dimensional (2D) generalized partial response (GPR) equalizers to combat the significant inter-track interference (ITI) expected in BPM magnetic recording systems. The probability density function of ITI is obtained analytically and is used to estimate the bit error rate (BER) from the Viterbi detector. The proposed method takes into account most of the important factors affecting the BER such as ITI, un-equalized intersymbol interference (ISI), colored noise and the distance and the multiplicity of error events. In this work, it is shown that for 1D channels, modeling ITI and un-equalized ISI by Gaussian PDFs leads to inaccurate BERs and that the non-Gaussian distribution of the ITI and un-equalized ISI must be taken into account for more accurate BER estimates. This method provides fast and accurate estimates of BERs for moderate to high signal-to-noise ratios (SNRs). By using this analytical method, time-consuming numerical simulations for error performance evaluation can be avoided.     

Error rate analysis of differentially encoded and detected 16APSKunder Rician fading

Mobile radio systems require highly bandwidth efficient digital modulation schemes because of the limited resources of the available radio spectrum. A theoretical analysis of bit error rate (BER) is presented for the differential detection of differentially encoded 16-level amplitude/phase shift keying (16DAPSK) under Rician fading in the presence of Rayleigh faded co-channel interference (CCI) and additive white Gaussian noise (AWGN). Differential detection comprises eight-level differential phase detection (DPD) and two-level amplitude ratio detection (ARD). Exact expressions for probability distributions of differential phase noise and amplitude ratio are derived for the BER calculation. The calculated BER performance of 16DAPSK is presented for various values of Rician fading K factor, Doppler spread of diffused component, and Doppler shift of the specular component, and is compared with that of 4-16DPSK. It is shown that 16DAPSK is superior to 16DPSK and requires 1.7 (1.6) dB less E_b/N₀ (SIR) at BER=10^-3 in Rician channels with K=5 dB     

Urban wide-band measurement of the UMTS electromagnetic environment

Measurements of impulsive noise in the universal mobile telecommunications system (UMTS) electromagnetic environment in urban areas have been conducted and its effect on the UMTS system is analyzed. An impulsive noise-measurement system for the UMTS frequency band has been designed and built, which meets and improves the main features of classical equipments used to measure noise, offering inphase and quadrature outputs simultaneously. This measurement system was carefully calibrated before a measurement campaign was conducted in an urban environment to get impulsive noise statistics. Results show that noise pulses may have high power, long duration, and high repetition rate, so the performance of UMTS could be significantly reduced.     

A VLSI Architecture for Novel Decision Feedback Differential Phase Detection with an Accumulator

This paper proposes a novel decision feedback differential phase detection (DF‐DPD) for M‐ary DPSK. A conventional differential phase detection method for M‐ary Differential Phase Shift Keying (DPSK) can simplify the receiver architecture. However, it possesses a poorer bit error rate (BER) performance than coherent detection because of the prior noisy phase sample. Multiple‐symbol differential detection methods, such as maximum likelihood differential phase detection, Viterbi‐DPD, and DF‐DPD using L‐1 previous detected symbols, have attempted to improve BER performance. As the detection length, L, increases, the BER performance of the DF‐DPD improves but the complexity of the architecture increases dramatically. This paper proposes a simplified DF‐DPD architecture replacing the conventional delay and additional architecture with an accumulator. The proposed architecture also improves BER performance by minimizing the current differential phase noise through the accumulation of previous differential phase noise samples. The simulation results show that the BER performance of the proposed architecture approaches that of a coherent detection with differential decoding.     

OFDM performance in amplifier nonlinearity

The activities of the current European RACE and ACTS projects have led to an increasing interest in OFDM (orthogonal frequency division multiplexing) as a means of combating impulsive noise and multipath effects and making fuller use of the available bandwidth of the system. This paper analyses the performance of OFDM signals in amplifier nonlinearity. In particular, bit error rate (BER) degradation as a result of amplitude limiting or clipping are analysed. In the presence of both nonlinear distortion and additive Gaussian noise, optimized output power back off is provided to balance the requirements of minimum BER and power amplifier efficiency. For this purpose, an OFDM system has been built using the SPW (Signal Processing Worksystem) simulator     

Performance of block Markov superposition transmission over non-Gaussian impulsive channels

Block Markov superposition transmission scheme was used over channels with symmetric alpha-stable (SαS) impulsive noise.Based on the equivalent genie-aided system,the lower bound of the block Markov superposition transmission system was analyzed.Numerical simulations over non-Gaussian impulsive channels with different characteristic exponents show that,in the low bit-error rate region,performance of the block Markov superposition transmission system matches well with the lower bound.Block Markov superposition transmission scheme performs well (with 0.85 dB away from Shannon limits at the BER of 10^-5) over non-Gaussian impulsive channels.