Bit Error Rate Performance Loss Research Articles

A New Frequency-Bin-Index LoRa System for High-Data-Rate Transmission: Design and Performance Analysis

As an attempt to tackle the low-data-rate issue of the conventional LoRa systems, we propose two novel frequency-bin-index (FBI) LoRa schemes. In scheme I, the indices of starting frequency bins (SFBs) are utilized to carry the information bits. To facilitate the actual implementation, the SFBs of each LoRa signal are divided into several groups prior to the modulation process in the proposed FBI-LoRa system. To further improve the system flexibility, we formulate a generalized modulation scheme and propose scheme II by treating the SFB groups as an additional type of transmission entity. In scheme II, the combination of SFB indices and that of SFB group indices are both exploited to carry the information bits. We derive the theoretical expressions for bit error rate (BER) and throughput of the proposed FBI-LoRa system with two modulation schemes over AWGN and Rayleigh fading channels. Simulation results not only verify the accuracy of theoretical BER and throughput analyses but also show that the proposed FBI-LoRa schemes can significantly increase the transmission throughput compared with the existing LoRa systems at the expense of a slight loss in BER performance. The proposed FBI-LoRa system is a promising alternative for high-data-rate Internet of Things (IoT) applications.

Efficient Timing Offset Estimation Method Tailored for ACO-OFDM VLC Systems

The asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM)-based visible light communication (VLC) system has received widespread attention due to its capability to support high spectrum efficiency as well as high power efficiency. The accuracy of symbol timing offset estimation is a critical factor limiting the performance of ACO-OFDM. In order to cope with this challenge, a training symbol-aided symbol timing synchronization method tailored for ACO-OFDM is put forward. The influence of the design of training symbol structure and timing metric on the synchronization accuracy is investigated, and three timing metrics are presented to supply simple and efficient timing offset estimation by utilizing the structure of odd-even mirror-symmetric and complementary symmetric of the newly designed training symbol. In addition, the system bit error rate (BER) penalty induced by timing synchronization error is analyzed, and the approximate relationship between BER performance loss and timing estimation error probability and ideal BER performance is presented. Simulation is used to assess the performance of the three proposed timing metric methods in different channel environments, and they are compared with the two existing timing synchronization algorithms in ACO-OFDM, namely the modified Park method and the Tian method. The results show that the new synchronization method is superior to the comparison methods concerning achievable synchronization accuracy and system BER penalty.

Peak-to-Average Power Ratio Reduction in Pilot-Embedded OTFS Modulation Through Iterative Clipping and Filtering

In this letter, the method to reduce peak-to-average power ratio (PAPR) is studied in the pilot-embedded orthogonal time frequency space modulation where guard symbols with zero padding are introduced to avoid the interference between data and pilot symbols. By permitting the guard symbols to be padded with signals of small magnitudes, an efficient PAPR reduction method based on the iterative clipping and filtering (ICF) framework is proposed. In the proposed method, first, the clipping noise other than the clipped signal is filtered; second, the filtering coefficients for the clipping noises in the data-plus-pilot region and guard region are set to be different values to achieve good tradeoff between PAPR and bit error rate (BER) performance. Simulation results show that the proposed method can reduce the PAPR efficiently with mild BER performance loss.

A Low-Complexity Receiver for Multicarrier Faster-Than-Nyquist Signaling Over Frequency Selective Channels

In this letter, we propose a low-complexity receiver for multicarrier faster-than-Nyquist (MFTN) signaling over frequency selective channels. By introducing a time-frequency trellis state, we are able to reformulate the MFTN detection problem into a linear state-space model. Building on this, a vector-form Forney style cycle-free factor graph is constructed. Then, Gaussian message passing technique is employed to derive the parametric message updating expressions. Accordingly, only the mean vectors and covariance matrices have to be calculated, which significantly reduces the computational complexity of MFTN detection. Simulation results demonstrate that the proposed receiver outperforms the symbol-by-symbol receiver by about 1 dB in terms of bit error rate (BER) and approaches the BER performance of the maximum a posteriori probability detector. Meanwhile, 39% more spectral efficiency can be obtained at a BER performance loss of less than 0.3 dB.

Simple metric to enhance multiple signaling techniques for nonlinear OFDM transmission

This paper proposes a simple and effective metric to choose the best orthogonal frequency division multiplexing (OFDM) signal within multiple signaling (MS) techniques such as PTS (Partial Transmit Sequence) or SLM (Selective Mapping), in order to reduce the deleterious effects of nonlinear amplification on the bit error rate (BER). The proposed metric is derived on the basis of a simplified mathematical analysis of the distortion produced by the nonlinear amplification and is calculated without the use of any mathematical model of the amplifier. This gives rise to lower computational cost in comparison to other metrics recently proposed with the same aim, besides reducing sensitivity to model mismatch. A simulation-based BER comparison over contiguous and non-contiguous OFDM shows that the advantages of the metrics here proposed are obtained without significant BER performance loss.

MMSE Turbo Equalization and Detection for Multicarrier Faster-Than-Nyquist Signaling

In this paper, two minimum mean-squared error (MMSE) turbo equalization and detection schemes for spectral efficient multicarrier faster-than-Nyquist (MFTN) signaling system are presented. First, the two-dimensional (2-D) soft input and soft output (SISO) MMSE equalization intended for magnetic recording channels, i.e., 2-D intersymbol interference (ISI), is extended to the detection of MFTN signals. Although the 2-D MMSE turbo equalization exhibits an attractive bit-error-rate (BER) performance under certain time-frequency spacing packing between adjacent symbols/subcarriers, the BER performance will be degraded when introducing serious intercarrier interference. Second, a 1-D SISO MMSE equalization combined with soft successive interference cancellation (SIC) is further proposed for the detection of MFTN signals, and it shows that the MMSE equalization combined with SIC could asymptotically approach the maximum a posterior equalization combined with SIC with negligible BER performance loss. Our computational complexity analysis and numerous simulation results demonstrate that the proposed MMSE turbo equalization schemes may be more preferred choice in the practical detection of MFTN signals.

Viterbi equalization for long-distance, high-speed underwater laser communication

In long-distance, high-speed underwater laser communication, because of the strong absorption and scattering processes, the laser pulse is stretched with the increase in communication distance and the decrease in water clarity. The maximum communication bandwidth is limited by laser-pulse stretching. Improving the communication rate increases the intersymbol interference (ISI). To reduce the effect of ISI, the Viterbi equalization (VE) algorithm is used to estimate the maximum-likelihood receiving sequence. The Monte Carlo method is used to simulate the stretching of the received laser pulse and the maximum communication rate at a wavelength of 532 nm in Jerlov IB and Jerlov II water channels with communication distances of 80, 100, and 130 m, respectively. The high-data rate communication performance for the VE and hard-decision algorithms is compared. The simulation results show that the VE algorithm can be used to reduce the ISI by selecting the minimum error path. The trade-off between the high-data rate communication performance and minor bit-error rate performance loss makes VE a promising option for applications in long-distance, high-speed underwater laser communication systems.

Power imbalance induced BER performance loss under limited-feedback CoMP techniques

Coordinated multipoint (CoMP) technology utilizes simultaneous transmission/reception from/to different access points, and it is considered as an important feature to exploit and/or mitigate intercell interference in fourth-generation mobile networks. Yet, channel power imbalance at the receiver is experienced in CoMP systems due to, e.g., spatially distributed transmissions. Traditional co-located multi-antenna systems may also experience power imbalance among antenna branches due to inaccurate antenna calibration. This paper presents a bit error rate (BER) analysis and derives asymptotic and approximate BER expressions for some practical CoMP transmission techniques under channel power imbalance. Besides the analytical results, numerical analysis is made to thoroughly capture the performance impact of channel power imbalance on the performance gain of the CoMP methods. The results demonstrate that power imbalance considerably affects BER performance and applying long-term amplitude information with fast phase feedback has insignificant benefit to effectively compensate the detrimental effect of large channel power imbalance when base stations use a single antenna. In this case, exploiting both short-term amplitude and phase information is a very good choice. On the contrary, for a large number of diversity antennas in base stations, using long-term amplitude information with a sparsely quantized phase shows BER performance close to the case where full channel state information is applied.

Asymptotic BER Comparison of MPSK and MDPSK in Lognormal Fading Channels

The bit error rate (BER) performance loss of $M$ -ary differential phase-shift keying (MDPSK) with respect to $M$ -ary phase-shift keying (MPSK) in wireless fading channels has been extensively studied, but the understanding of this problem in lognormal fading channels has been limited. The most recent work has shown the asymptotic BER performance losses of BDPSK and QDPSK with respect to BPSK and QPSK, respectively, in the lognormal fading channels. However, it is not known how the modulation order increases. In this paper, we derive the general expression of the relative BER performance loss of MDPSK with respect to MPSK for arbitrary $M$ over the lognormal fading channels in high signal-to-noise ratio regimes. We start our analysis by investigating the asymptotic BER performance losses of MDPSK with respect to MPSK for $M=\mbox{4}, \mbox{8}, \mbox{and} \mbox{16}$ . Using the regularity of these results, we obtain the general closed-form expression of the relative BER performance loss in the lognormal fading channels.

BER of Subcarrier MPSK and MDPSK Systems in Atmospheric Turbulence

Bit-error rate (BER) performance of subcarrier $M$ -ary phase-shift keying (MPSK) and $M$ -ary differential PSK (MDPSK) is analyzed for optical wireless communications over Gamma–Gamma and lognormal turbulence channels. We study the relation between the exact BER and the approximate BER, which is obtained by dividing the symbol-error rate by the number of bits per symbol, for subcarrier MPSK and MDPSK modulations. The asymptotic BER performance gap between the exact and the approximate BERs is quantified analytically through our asymptotic analyses. The accuracy of the approximate BER of both MPSK and MDPSK depends on the channel conditions. Under weak turbulence conditions, the approximate BER expression can be used to predict the system performance with high accuracy, while under strong turbulence conditions the approximate BER becomes inaccurate and can only serve as a loose lower bound of the exact BER. The asymptotic BER performance loss of MDPSK with respect to MPSK is also quantified analytically.

New Computational Complexity Reducing IDD Scheme Designed with Optimum Parameters

An Iterative Detection and Decoding (IDD) scheme in a high-order Multiple-Input Multiple-Output (MIMO) wireless communication system requires a heavy computational complexity for an outstanding Bit Error Rate (BER) performance in a given Signal-to-Noise Ratio (SNR) environment. A new computational complexity reducing IDD scheme designed with optimum parameters is proposed in this paper to guarantee Quality of Service (QoS) without the loss of BER performance. There are three parameters to control the trade-off between computational complexity and BER performance of an IDD scheme: a candidate list size of Dynamic List Sphere Detector (D-LSD), a number of intra-iteration of Turbo decoder, and a number of IDD iteration. A complexity reduction of about 70 % is demonstrated in this study, when the target BER is around 1.0×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(-4)</sup> at E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> /N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> =7dB in the case of a 4 x 4 MIMO system with 16-ary Quadrature Amplitude Modulation (QAM).

MIMO-OFDM equaliser for spatial multiplexing transmission modes

Abstract. In search for faster and more reliable communication, multiple-input multiple-output (MIMO) in conjuction with Orthogonal Frequency Division Multiplexing (OFDM) are subject of extensive research. In spatial multiplexing transmission an instantaneous rise of data rates governed by the number of transmit antennas can be realised. The system performance depends highly on signal-to-interference-plus-noise ratios (SINR) at the receiver. The receiver's equaliser is supposed to maximize the SINR by mitigating the spatial interference and thus separating the transmitted signals. For this problem several solutions exist such as linear and nonlinear, per subcarrier or OFDM symbol-based. An overview of common algorithms is given and complexity is discussed. Bit error rate (BER) performance evaluations are presented. Another aspect is the impact of the equalisation strategy on the performance of bit-interleaved soft information-based channel coding schemes. As a representative, LDPC codes are chosen. Simulation results show a significant BER performance loss for symbol decision-based equalisers compared to the uncoded performance. To overcome this problem a modification of the Maximum Likelihood algorithm is proposed which yields good performance for low SNR applications.

Thresholding-Based Optimal Detection of Wireless Optical Signals

The receiver design for a high-speed free-space (wireless) optics (FSO) signal is necessarily highly complex when channel state information (CSI) is not available. Currently, although most approaches provide high detection performance in terms of bit error, receiver design is difficult to implement. This paper proposes two practical thresholding-based detection schemes, which offer significant improvement to receiver throughput on a computational load basis when CSI is not available. The first is based on a simple maximum likelihood (ML) function where the bit error rate (BER) is the same as conventional symbol-by-symbol detection. This method, however, causes a loss of BER performance. The second uses the aid of pilot-symbol-assisted modulation (PSAM) to modify the ML function when channel coefficients are temporally correlated. While numerical analysis based on this method shows that the BER performance in a log-normally distributed fading channel is very close to detection achieved with perfect CSI, the receiver suffers from increased complexity. If random processes for fading and noise are assumed as stationary and given that the detection threshold is quickly calculated and applied during a given period, such complexity of PSAM-based and symbol-by-symbol detection methods can be reduced.

Quasi-chaotic coding over GF(q)

In this paper, we present quasi-chaotic (QC) schemes for secure digital communication systems, designed over Galois fields (GFs) with optimal randomness properties. Schemes with the maximum-output sequence length (all-zero input response) are presented for different GFs. Two coefficients are used to quantitatively measure the proximity of the behavior of these schemes with respect to the ideal white noise behavior. The proposed schemes outperform those presented by Frey in his paper, and achieve the optimal QC properties available for a given chaotic digital scheme. The proposed schemes have also a very little loss in bit-error rate performance so that they are a good alternative to the design of systems for which encryption and error correction are important joint goals. They can be implemented with time-variant coefficients in order to highly improve the cryptographic properties of the transmission.

Diversity Analysis for Frequency-Selective MlMO-OFDM Systems With General Spatial and Temporal Correlation Model

In the low signal-to-noise ratio regime, the performance of concatenated coding schemes is limited by the convergence properties of the iterative decoder. Idealizing the model of iterative decoding by an indepen- dence assumption, which represents the case in which the codeword length is infinitely large, leads to analyzable structures from which this perfor- mance limit can be predicted. Mutual information-transfer characteristics of the constituent coding schemes comprising convolutional encoders and soft-in/soft-out decoders have been shown to be sufficient to characterize the components within this model. Analyzing serial and parallel concate- nations is possible just by these characteristics. In this paper, we extend the method of extrinsic information transfer charts that is limited to the case of a concatenation of two component codes, to the case of multiple turbo codes. Multiple turbo codes are parallel concatenations of three or more constituent codes, which, in general, may not be identical and may not have identical code rates. For the construction of low-rate codes, this concept seems to be very favorable, as power efficiencies close to the Shannon limit can be achieved with reasonable complexity. Abstract—In this paper, we present quasi-chaotic schemes for secure digital communication systems, designed over Galois fields with optimal randomness properties. Schemes with the maximum output sequence length (all-zero input response) are presented for different Galois fields. Two coefficients are used to quantitatively measure the proximity of the behavior of these schemes with respect to the ideal white-noise behavior. The proposed schemes outperform those presented by Frey in his paper, and achieve the optimal quasi-chaotic properties available for a given chaotic digital scheme. The proposed schemes have also a very little loss in bit-error rate performance, so that they are a good alternative to the design of systems for which encryption and error correction are important joint goals. They can be implemented with time-variant coefficients in order to highly improve the cryptographic properties of the transmission. Abstract—In this paper, the effect of a general spatial and tem- poral fading correlation structure on the performance of coded mul- tiple-input multiple-output-orthogonal frequency-division multiplexing (MIMO-OFDM) systems is studied. The analysis handles an arbitrary joint transmit-receive spatial correlation model, including the non-Kronecker model. An upper bound on the maximum achievable diversity order for frequency-selective MIMO-OFDM systems with general temporal and spatial correlation is derived. Furthermore, a space-time-frequency code design that can achieve the upper bound for any arbitrarily cor- related channel scenario is provided. The general framework of the analysis includes space-frequency-coded systems as a special case. For the space-frequency-coded MIMO-OFDM system, it is shown that any space-frequency code designed to achieve full diversity in the indepen- dent fading channel can achieve full diversity in an arbitrary spatially correlated channel. The derived analytical results are consistent with those in the existing literature for special correlation structures. Extensive simulation results are provided to confirm the theoretical analysis. Abstract—A new modulation method for linear space-time codes is pro- posed, based on using constellations of different sizes for different symbols. It is shown that the proposed method significantly reduces the complexity of the sphere-decoding algorithm. The complexity reduction is more pro- nounced in high-rate codes, where each code matrix carries a large number of symbols. We also show that the choice of constellation size provides a tradeoff between performance and complexity. Using this, some guidelines for choosing constellation size are presented. As one introduces more con- stellation disparity in the code, the complexity is further reduced, while the performance loss grows. Typically, a complexity reduction of one to two or- ders of magnitude can be achieved at the expense of about 3 dB coding gain. We suggest modification in our design to reduce this loss to about 2 dB.

DC-Free Error-Control Block Codes

DC-free codes and error-control (EC) codes are widely used in digital transmission and storage systems. To improve system performance in terms of code rate, bit-error rate (BER), and low-frequency suppression, and to provide a flexible tradeoff between these parameters, this paper introduces a new class of codes with both dc-control and EC capability. The new codes integrate dc-free encoding and EC encoding, and are decoded by first applying standard EC decoding techniques prior to dc-free decoding, thereby avoiding the drawbacks that arise when dc-free decoding precedes EC decoding. The dc-free code property is introduced into standard EC codes through multimode coding techniques, at the cost of minor loss in BER performance on the additive white Gaussian noise channel, and some increase in implementation complexity, particularly at the encoder. This paper demonstrates that a wide variety of EC block codes can be integrated into this dc-free coding structure, including binary cyclic codes, binary primitive BCH codes, Reed-Solomon codes, Reed-Muller codes, and some capacity-approaching EC block codes, such as low-density parity-check codes and product codes with iterative decoding. Performance of the new dc-free EC block codes is presented.

Combined space–time block coding and eigen-space tracking in MIMO systems

A combined space–time block coding (STBC) and eigen-space tracking (EST) scheme in multiple-input-multiple-output systems is proposed. It is proved that the STBC-EST is capable of shifting hardware complexity from the receiver to the transmitter without any bit error rate (BER) performance loss. A computation efficient EST algorithm is also proposed, which makes the STBC-EST affordable. Simulation results show that the STBC-EST with a modest feedback requirement results in a negligible BER performance loss compared with a dual system configuration.