Bit Error Rate Simulations Research Articles

Phase compensation communication technique against time reversal for ultra‐wideband channels

Phase compensation (PC) prefiltering is experimentally investigated for multipath channels over the frequency band spanning 2–12 GHz, a topic which to the best of the authors knowledge has not been studied in the literature on ultra-wideband (UWB) communications. The authors emphasis is to assess the capabilities of PC compared to time reversal (TR) prefilters over indoor UWB channels regarding multipath suppression, channel hardening, noise sensitivity and high-speed data transmission. Experiments were carried out for PC and TR prefilters in both line-of-sight (LOS) and non-LOS (NLOS) environments. The multipath compression effectiveness is characterised by computing the root-mean-square delay spread and peak-to-average power ratio for actual measured channels and for the IEEE 802.15.4(a) UWB model. The authors study suggests PC outperforms TR considerably in mitigating the multipath channel dispersion. Bit-error-rate (BER) curves have been simulated for data rates in the range of 125–4000 Mbps based on the measured channel responses. The BER simulations suggest that while the TR performance is prohibitively saturated by its residual intersymbol interference for data rates of 500 Mbps and above (especially in NLOS), PC can be used for high-speed data transmissions as fast as 2 Gbps in both LOS and NLOS environments.

Modelling of free space optical link for ground‐to‐train communications using a Gaussian source

The demand for access to broadband data services in high-speed trains is increasing as more people are travelling to and from work, which is not met by the existing radio frequency technology. Therefore an alternative technology known as free space optics (FSO) could be readily adopted that could overcome the bandwidth bottleneck problem. The study presents a mathematical model of an FSO link for ground-to-train communications link and analyses the system performance in terms of the signal-to-noise ratio and the bit error rate (BER). The authors show that the simulated BER is in good agreement with the predicted results for bit rates up to 50 Mbps. The link budget analysis for the proposed system is also presented showing a link margin of 17.75 dB.

On performance of analog network coding in the presence of phase noise

Analog network coding (ANC) as a simple implementation of physical layer network coding based on orthogonal frequency division multiplexing (OFDM) has been proposed to increase the network capacity and reliability of bi-directional link between a pair of users. In ANC protocol, an information between a pair of users is exchanged through two orthogonal time phases (i.e., multiple-access and broadcast phases). On the other hand, the phase noise (PN) introduces phase offset and inter carrier interference (ICI) to the useful signal. Thus, in ANC scheme PN will affect the useful signal during both multiple-access and broadcast phases. In this article, we present a performance analysis of ANC scheme using OFDM in the presence of PN in frequency-selective fading channel. We derive the total composite variance of ANC scheme in the presence of PN to obtain the signal-to-interference-plus-noise ratio (SINR) expression. Then, we evaluate the system’s performance in terms of bit error rate (BER), SINR degradation, and ergodic capacity through both numerical and computer simulations. Computer simulated average BER has been consistent with the numerical results, validating the presented analysis. Our results have shown that the ANC scheme is more sensitive to the PN introduced during the broadcast phase (i.e., at destination) than during the multiple-access phase (i.e., at relay). This is because of the higher ICI to the useful signal and enhanced noise due to the imperfect self-information removal at the destination. In addition, the performance degradation of ANC scheme based on OFDM in the presence of PN is highly expressed for the PN linewidth values up to 20 Hz.

Paired Bernoulli Circular Spreading: Attaining the BER Lower Bound in a CSK Setting

This paper is concerned with the Paired Bernoulli Circular Spreading (PBCS), a way of generating optimal spreading for the single-user coherent chaos shift-keying (CSK) system. PBCS is optimal spreading in the sense that it attains the Bit Error Rate (BER) lower bound of the system, therefore it has a potential engineering impact on the choice of signal carrier in CSK communications. PBCS optimality is justified theoretically and is further demonstrated through BER simulations. The statistical properties of PBCS are of interest too, as it is an invariant stochastic process with a mixed joint density which allows to sample infinitely many points from a circle.

Low Complexity Time-Concatenated Turbo Equalization for Block Transmission Without Guard Interval: Part 1—The Concept

This paper proposes a novel time-concatenated turbo equalization technique, chained turbo equalization (CHATUE), that allows block transmission systems to eliminate the guard interval (GI), while achieving excellent performance. The proposed CHATUE algo- rithm connects turbo equalizers neighboring in time, so that they exchange information about their inter-block-interference components in the form of a posteriori log-likelihood ratio. The latest version of the low complexity sub-optimal turbo equalization technique for block-wise single carrier transmission, frequency domain soft cancellation and minimum mean squared error, is fully exploited in developing the CHATUE algorithm. Results of extrinsic informa- tion transfer chart analysis as well as a series of bit-error rate (BER) simulations show that excellent performances can be achieved without imposing heavy computational burden in multipath-rich (quasi-static) block Rayleigh fading channels. It is shown that, if the informa- tion bit-rate is kept identical (because it may be unpreferable for the industry to change the frame structure), the CHATUE algorithm achieves lower BER than that with block transmis- sion with GI, because lower rate (strong) code for error protection can be used by utilizing the time-duration made available by eliminating the GI. In addition, by combining the proposed structure with a simple rate-1 doped accumulator, further BER improvement exhibiting clear turbo cliff can be achieved. A sister paper (a Part-2 paper) applies the proposed CHATUE algorithm to single carrier frequency division multiple access systems Hui et al. (Wirel Pers Commun, 2011).

BER Analysis of Uplink OFDMA in the Presence of Carrier Frequency and Timing Offsets on Rician Fading Channels

In orthogonal frequency-division multiple access (OFDMA) on the uplink, the carrier frequency offsets (CFOs) and/or timing offsets (TOs) of other users with respect to a desired user can cause multiuser interference (MUI). Analytically evaluating the effect of these CFO/TO-induced MUI on the bit error rate (BER) performance is of interest. In this paper, we analyze the BER performance of uplink OFDMA in the presence of CFOs and TOs on Rician fading channels. A multicluster multipath channel model that is typical in indoor/ultrawideband and underwater acoustic channels is considered. Analytical BER expressions that quantify the degradation in BER due to the combined effect of both CFOs and TOs in uplink OFDMA with M-state quadrature amplitude modulation (QAM) are derived. Analytical and simulation BER results are shown to match very well. The derived BER expressions are shown to accurately quantify the performance degradation due to nonzero CFOs and TOs, which can serve as a useful tool in OFDMA system design.

Multi-tone CDMA design for arbitrary frequency offsets using orthogonal code multiplexing at the transmitter and a tunable receiver

The authors propose a new multi-tone (MT) code division multiple access (CDMA) design which has a superior bit error rate (BER) performance than conventional MT CDMA in the presence of frequency offset. The design involves multiplexing of Walsh codes onto the sub-carriers in conjunction with double differential modulation. To exploit the full potential of the design a partial correlation receiver has been proposed. Depending on the signal-to-noise ratio (SNR) and frequency offset it is possible to tune this receiver for the best possible performance. The simulated BER performance of the proposed system has been found to be better than MT CDMA for small as well as large frequency offsets for both single and multi-user systems in additive white Gaussian noise (AWGN) and Rayleigh fading channels.

Performance Analysis of a Concatenated LDPC Coded Alamouti-Based STBC-OFDM System on Text Message Transmission

This paper investigates the impact of concatenation of an interleaved low density parity check (LDPC) code with convolutional channel coding on the performance of the space time block coded (STBC) orthogonal frequency-division multiplexing (OFDM) wireless communication system on text message transmission. The concatenated channel encoded OFDM system deploys various digital modulations (BPSK, QPSK and QAM) over an additative white gaussian noise (AWGN) and other fading (Raleigh and Rician) channels. Computer simulation results on bit error rate (BER) demonstrate that the 1/2-rated convolutional and LDPC channel encoded OFDM system outperforms with BPSK modulation technique as compared to other digital modulation schemes and the system is highly effective to combat inherent interferences under AWGN, Rayleigh and Rician fading channels. The BER performance of the concatenated channel encoded OFDM system with 1/2-rated channel coding is better as compared to 3/4rated channel coding. The transmitted text message is found to have retrieved effectively under noisy and fading situations. It is anticipated from the BER simulations that the performance of the communication system degrades with the increase of noise power.

Benchmarking Iterative Receivers for BICM Multi-Carrier Systems Against Capacity Bounds

In this paper, we analyze iterative receivers for bit-interleaved coded modulation (BICM) multi-carrier systems and compare them against theoretical capacity bounds for the channel, coded modulation, and BICM. We map the theoretical capacity bounds into bit-error rate (BER) versus average signal-to-noise ratio per bit plots to simplify the comparison between the theoretical capacity bounds and simulated BER curves. As BER simulations show, iterative receivers with code doping or spreading reach the turbo-cliff within 1 or 0.3dB of the independent Rayleigh fading channel capacity. While the iterative receiver with spreading is closer to the channel capacity than the one with code doping, the later one can eliminate the residual bit-errors after the turbo-cliff. We further present a combinatorial analysis of the distribution of the spread symbol constellation for Walsh-Hadamard spreading codes used in a BICM multi-carrier system to explain the above results.

Partial Multiuser Detection for CS-CDMA/CP over Multipath Channels

Convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) enables multiuser interference-free (MUI-free) transmission over multipath downlink channels with the use of zero correlation zone (ZCZ) codes. However, MUI-free transmission is guaranteed only when the data length D, channel delay L, and ZCZ length Z satisfy Z+1 ≥ D + L. In this paper, we consider the situation that MUI-free transmission is not realized inevitably because of excessive multipath delays or deliberately because of the necessity to get a higher bandwidth efficiency, clarify the structure of MUI in the CS-CDMA/CP system employing M-ZCZ codes, and propose iterative partial multiuser detection (IPMUD). The detection is implemented at symbol-level (after despreading) and the number of users jointly considered can be adjusted flexibly to offer a tradeoff between system performance and receiver complexity. The performance of the proposed scheme is verified numerically by density evolution approach and BER simulations. The CS-CDMA/CP system with IPMUD is shown to be much less complex than the DS-CDMA system with Wang and Poor's turbo MUD receiver and to be less complex and better, in terms of bit error rate (BER) performance, than the DS-CDMA system with iterative chip-wise equalization receivers.

Cooperative Networks: Bit-Interleaved Coded Modulation with Iterative Decoding

In this paper the performance of bit-interleaved coded modulation-iterative decoding (BICM-ID) based cooperative network is analyzed over Rayleigh, Nakagami-m and Rician fading channels. In this system coding diversity is obtained through BICM and spatial diversity through cooperative relaying network. The analysis is performed for the relays operating in both amplify-and-forward (AF) and decode-and-forward (DF) modes. The bit error rate (BER) bound of multiple-relay cooperative system with the serial concatenated BICM-ID using the set partitioning (SP) and Gray mapped (GM) labeling for M-ary Phase Shift Keying (M-PSK) modulations over Nakagami-m fading channels is obtained. For the numerical results of union bound on BER, moment generating function (MGF) based approach is used. The expression of MGF derived for Nakagami distribution is then extended to Rayleigh and Rician fading channels. The comparisons of BER theoretical and simulation results are also shown. The performance of bit-interleaved low-density parity-check coded modulation with iterative decoding (BILDPCM-ID) based cooperative system, using low-density parity-check (LDPC) code instead of convolutional code, is also analyzed in term of bit-error rate (BER). The performance comparisons of BICM-ID and BILDPCM-ID based systems are shown using the set partitioning (SP) labeling for 8-PSK modulation scheme by performing Monte Carlo simulation.

Improving bit-error-rate performance of the free-space optical communications system with channel estimation based on radiative transfer theory

In order to improve the performance of terrestrial free-space optical communication systems in adverse visibility conditions, we present a method for estimation of the atmospheric channel impulse response function which governs the optical intensity propagation. This method reduces run-time computational demands and system complexity in comparison to our previously proposed dual-wavelength channel estimation technique. We consider propagation of optical wavelengths in fog, where the droplet diameters are close to the wavelength and thus scattering and absorption effects are significant. A method for rapid calculation of a channel response function based on estimating the effective optical depth of the channel and curve-fitting is described. The channel response estimate can then be used to design a receiver-side equalizer (minimum mean-squared error linear equalizer) to correct the signal distortion due to propagation through the dispersive channel. The channel estimates are based on parametric curve-fitting functions which have been developed using the modified-vector radiative transfer theory to model the channel response. The optimal fit parameters are found using particle-swarm optimization to minimize the simulated bit-error rate of the received signal.

Performance of convolutional codes in asynchronous CDMA communications under imperfect phase-tracking conditions

In this paper, the performance of short constraint length convolutional codes in imperfect phase tracking conditions is discussed. Convolutional codes are used to provide error protection to a particular user in an Asynchronous CDMA (A- CDMA) system undergoing slow Rician fading. Maximum likelihood decoding with a Viterbi algorithm recovers the information symbols. A Phase Locked Loop (PLL) depicting the variations in the phase error for abrupt phase changes in the input signal is considered. Analytical bounds, which are useful in predicting the performance of the A-CDMA system are derived and plotted for the cases of infinite and finite channel memory. The upper bounds on the unconditional Bit Error Rate (BER) with Viterbi decoding are derived and plotted for the various convolutional codes considered. The simulated BERs are found to agree well with their upper bounds.

Linear Predictive Detection for Power Line Communications Impaired by Colored Noise

Robust detection algorithms capable of mitigating the effects of colored noise are of primary interest in communication systems operating on power line channels. In this paper, we present a sequence detection scheme based on linear prediction to be applied in single-carrier power line communications impaired by colored noise. The presence of colored noise and the need for statistical sufficiency requires the design of an optimal front-end stage, whereas the need for a low-complexity solution suggests a more practical suboptimal front-end. The performance of receivers employing both optimal and suboptimal front-ends has been assessed by means of minimum mean square prediction error (MMSPE) analysis and bit-error rate (BER) simulations. We show that the proposed optimal solution improves the BER performance with respect to conventional systems and makes the receiver more robust against colored noise. As case studies, we investigate the performance of the proposed receivers in a low-voltage (LV) power line channel limited by colored background noise and in a high-voltage (HV) power line channel limited by corona noise.

Frame/Training Sequence Synchronization and DC-Offset Removal for (Data-Dependent) Superimposed Training Based Channel Estimation

Over the last few years there has been growing interest in performing channel estimation via superimposed training (ST), where a training sequence is added to the information-bearing data, as opposed to being time-division multiplexed with it. Recent enhancements of ST are data-dependent ST (DDST), where an additional data-dependent training sequence is also added to the information-bearing signal, and semiblind approaches based on ST. In this paper, along with the channel estimation, we consider new algorithms for training sequence synchronization for both ST and DDST and block (or frame) synchronization (BS) for DDST (BS is not needed for ST). The synchronization algorithms are based on the structural properties of the vector containing the cyclic means of the channel output. In addition, we also consider removal of the unknown dc offset that can occur due to using first-order statistics with a non-ideal radio-frequency receiver. The subsequent bit error rate (BER) simulations (after equalization) show a performance not far removed from the ideal case of exact synchronization. While this is the first synchronization algorithm for DDST, our new approach for ST gives identical results to an existing ST synchronization method but with a reduced computational burden. In addition, we also present analysis of BER simulations for time-varying channels, different modulation schemes, and traditional time-division multiplexed training. Finally, the advantage of DDST over (conventional, non semi-blind) ST will reduce as the constellation size increases, and we also show that even without a BS algorithm, DDST is still superior to conventional ST. However, iterative semiblind schemes based upon ST outperform DDST but at the expense of greater complexity

Design, Simulation, and Testing of a CMOS Analog Decoder for the Block Length-40 UMTS Turbo Code

In this paper, we present an all-analog implementation of the rate-1/3, block length 40, universal mobile telecommunications system (UMTS) turbo decoder. The prototype was designed and fabricated in 0.35 μm complementary metal-oxide-semiconductor technology and operates at 3.3 V. We also introduce a discrete-time first-order model for analog decoders which allows fast bit-error rate simulations, while taking into account circuit transient behavior and component mismatch. The model is applied to the rate-1/3 analog turbo decoder for UMTS defined in the Third Generation Partnership Project standard, and the discrete-time model predictions are compared with the decoder experimental performance and the transistor-level simulations. These results demonstrated that this model can be successfully used as a tool to both predict analog decoder performance and give design guidelines for complex decoders, for which circuit-level simulations are impractical.

Impact of frequency offsets and IQ imbalance on MC-CDMA reception based on channel tracking

New air interfaces are currently being developed to meet the high spectral efficiency requirements of the emerging wireless communication systems. Multicarrier code-division multiple access (MC-CDMA) is seen as a promising candidate for the fourth-generation (4G) cellular communication systems because it can interestingly deal with the multipath propagation at a low processing complexity. Besides spectral efficiency and power consumption, the production cost of the transceiver should also be optimized. Direct conversion radio frequency (RF) receivers are appealing because they avoid costly intermediate frequency (IF) filters. However, they imply RF IQ separation, introducing a phase and amplitude mismatch between the I and Q branches. A communication system based on MC-CDMA is sensitive to synchronization errors and front-end non-idealities because it uses a long symbol duration. The goal of this paper is to evaluate the impact of the carrier frequency offset, the sampling clock offset, and the IQ imbalance on the MC-CDMA downlink system performance, considering a receiver based on channel tracking designed to cope with high mobility conditions. It is demonstrated that part of the effects is compensated by the channel estimation and an expression of the variance of the remaining symbol estimation error is provided. For the cellular system and the target performance considered in this paper, specifications are defined on the non-idealities. The results are validated with bit-error rate simulations

PSK communications systems using fully saturated power amplifiers

Quasiconstant envelope phase-shift keying (PSK) is analyzed to assess its ability to overcome nonlinearities caused by fully saturated RF power amplifiers in communications systems. These modulations can achieve bit error rate (BER) performance comparable to linear BPSK in additive white Gaussian noise (AWGN) channel. Quasiconstant envelope offset quadrature PSK (OQPSK) is presented as a design example. At a BER = 10/sup -5/, the SNR degradation caused by fully saturated power amplifiers is 0.1 dB. The simulated BER matches analytically derived results. For a communications system employing the quasiconstant envelope OQPSK and a rate 1/2 convolutional code with K = 7, the demodulation performance is degraded by 0.25 dB at a BER = 10/sup -5/ when a fully saturated power amplifier is employed.

Decoding for magnetic recording media with overlapping tracks

Increasing recording track density by allowing overlap of adjacent tracks can lead to a substantial increase in storage density for magnetic recording. However, track overlap may cause severe intertrack interference (ITI) and result in loss of performance. Sophisticated signal processing techniques must then be used to recover this loss. We study the use of joint equalization and decoding for magnetic recording with overlapping tracks. We present results for a scheme that uses minimum mean-squared-error (MMSE) equalization in conjunction with error-correction coding using low-density parity-check (LDPC) codes. The recording process is simulated using a micromagnetic model for longitudinal magnetic recording. We use a three-track system to study the track overlap. The outer two tracks are allowed to overlap on the middle track to simulate ITI. Bit-error rate simulations show that the MMSE-LDPC decoding scheme incurs negligible loss when each of the outer tracks overlaps 10% on the middle track. By varying the recording parameters, the tradeoff between storage density and performance is also studied. We show that by a judicious choice of LDPC codes, a recording with track overlap can have better performance than when there is no overlap. Hence, a higher storage density can be obtained without loss in performance.

A new performance evaluation technique for iteratively decoded magnetic recording systems

This paper proposes a performance evaluation technique for iteratively (turbo) equalized magnetic recoding systems. The technique decomposes the bit-error rate (BER) function into an integral of two functions. The first function has a closed form expression and is determined by the characteristics of the noise. The second function depends on the parameters of the concatenated system and can be approximated using an interpolation between sample points that rely on a small number of simulations. We present numerical and simulated BER results for coded PR4 and EPR4 channels with turbo equalization. In the "waterfall region" of the BER curves, the calculated and simulated results are within about 0.1 dB.