System BER Research Articles

Analytical EVM, BER, and TD performances of the OFDM systems in the presence of jointly nonlinear distortion and IQ imbalance

The orthogonal frequency-division multiplexing (OFDM) systems are highly sensitive to the nonlinear distortions introduced by the high-power amplifier at the transmitter and to the in-phase and quadrature (IQ) imbalance of the down converter at the receiver. In this paper, the joint effects of these impairments on the performance of the OFDM systems with M signal points quadrature amplitude modulation (M-QAM) are investigated. Moreover, the analytical formulations for the error vector magnitude, the bit error rate, and the total degradation performances of the M-QAM-OFDM systems in additive white Gaussian noise channels as a function of the output back off and IQ imbalance parameters are derived. The computer simulation results confirm the accuracy and validity of our proposed analytical approach.

Simulative investigation of the impact of EDFA and SOA over BER of a single-tone RoF system

In this paper, we investigate the impact of EDFA and SOA amplifiers over BER and Q-parameter of a Radio-over-Fiber (Rof) system consisting of two different system set-ups using direct- and external-laser modulation techniques. In this work, we also measured and compared the electric Rf power at receiver at different modulating Rf frequencies up to 20 GHz using two different optical amplifiers, i.e. EDFA and SOA. Further, we also compared the received electric Rf power at different optical powers without and with different optical amplifiers. An improvement of −11 dB (approx.) of received Rf power was observed using EDFA with the external modulation technique, on comparing with direct modulation.

Precoding Technique for Minimizing BER of MIMO-OFDM System Employing MLD under Multicell Co-channel Interference

This paper proposes a MIMO-OFDM precoder that can minimize a BER upper bound of the maximum likelihood detector (MLD) under a non-cooperative downlink multicell co-channel interference (CCI) environment. Since there is no cooperation among base stations (BSs), it is assumed that information on the interference can be estimated at a mobile station (MS) and then fed back to the desired BS for the precoder. The proposed scheme controls its precoding parameters under a transmit power constraint so as to minimize the BER upper bound, which is derived from the pairwise error probability (PEP) averaged with respect to CCI plus noise. Computer simulations demonstrate that the proposed precoder can effectively improve BER performance of cell edge users and is superior in terms of BER to the eigenmode and the minimum mean squared error (MMSE) precoded transmissions which aim to maximize the channel capacity and to minimize MSE, respectively.

Adaptive code allocation for interference management on the downlink of DS-CDMA systems

A new technique based on adaptive code-to-user allocation for interference management on the downlink of BPSK based TDD DS-CDMA systems is presented. The principle of the proposed technique is to exploit the dependency of multiple access interference on the instantaneous symbol values of the active users. The objective is to adaptively allocate the available spreading sequences to users on a symbol-by-symbol basis to optimize the decision variables at the downlink receivers. The presented simulations show an overall system BER performance improvement of more than an order of a magnitude with the proposed technique while the adaptation overhead is kept less than 10% of the available bandwidth.

An Efficient Adaptive Channel Estimation Algorithm for MIMO OFDM Systems—Study of Doppler Spread Tolerance

In this paper we develop an adaptive MIMO channel estimation algorithm for space---time block coded OFDM systems. The presented algorithm is based on Expectation Maximization (EM) technique by decomposing the superimposed received signals into their signal components, and estimating the channel parameters of each signal component separately. We also study and compare our proposed EM-based algorithm with a previously introduced recursive-least-squares based algorithm for MIMO OFDM systems. At each iteration the EM algorithm decomposes the problem of multi-channel estimation into channel estimation for each transmit---receive link. In this paper we also study the Doppler spread tolerance of our proposed algorithm in a fast fading environment, and investigate how it affects the system BER performance.

Fast-processing statistical methods for measurement of BER in optical fiber communication systems

We propose two fast-processing statistical methods for the determination of transmission performance, in particular the eye diagram and BER in optical fiber communication systems. Detailed guidelines for optimizing the accuracies of the statistical techniques are given. These methods provide BERs within one decade, hence more superior than those offered by Monte-Carlo and semi-analytical techniques.

Mechanisms for Stormwater Surges in Vertical Shafts

A num ber of large scale combined sewer systems have experienced events in which surges have resulted in the return of poor quality stormwater to grade in what are referred to as geysers. In spite of current concerns that these events be avoided by the proper design of new systems, there have been limited investigations to understand the conditions that lead to these surges or how to avoid them. In the course of an ongoing investigation into the dynamics of rapidly filling pipelines, two phenomena have been identified that may result in geyser-like phenomena. Both of these are associated with the movement of a large pocket of entrapped air along the crown of a nearly horizontal pipe. One case occurs when the leading edge of the air cavity arrives at a vertical riser at a location along the pipeline that is already in a surcharged state. A second case occurs as the trailing edge of the same air pocket arrives at the riser and the pipe is not in a surcharged condition. Experiments have been performed to reproduce both of these situations in a simplified fashion where several of the key variables can be controlled. The features of these experiments are described as well as some of the results obtained to date. These results are interpreted to identify aspects of a storage tunnel system that are under design control and how these affect the magnitude of the observed surges. Finally, since the experiments are performed in a relatively small-scale apparatus, speculation is presented on

Comparison of adaptive beamforming and orthogonal STBC with outdated feedback

We compare the achievable performance of adaptive beamforming (A-BF) and adaptive orthogonal space time block coding (A-OSTBC) with outdated channel feedback. We extend our single user setup to multiuser diversity systems employing adaptive modulation, and illustrate the impact of feedback delay on the multiuser diversity gain with either A-OSTBC or A-BF. Using closed-form expressions for spectral efficiency and average BER of a multiuser diversity system derived in this paper, we prove that the A-BF scheme outperforms the A-OSTBC scheme with no feedback delay. However, when the feedback delay is large, the A-OSTBC scheme achieves better performance due to the reduced diversity advantage of A-BF. We observe that more transmit antennas bring higher spectral efficiency for BF. With small feedback delay, this becomes inverted using OSTBC, due to the effect of channel-hardening. Interestingly, however, we show that A-OSTBC with multiple users enjoys improved spectral efficiency when the number of transmit antennas is increased and the feedback delay is significant

CPLD-PGPS scheduler in wireless OFDM systems

In this paper, we propose a new scheduler for orthogonal frequency-division multiplexing (OFDM) wireless communication systems, called channel-condition and packet-length dependent packet generalized processor sharing (CPLD-PGPS) scheduler. Based on PGPS, the CPLD scheduler considers both the physical channel condition and the length of packets, and optimally allocates the sub-carriers to different users. The total transmit power is adoptively allocated to each subcarrier. With this scheduler, the system can achieve better system BER performance, and correspondingly superior PER performance. The system throughput is improved, the required bandwidth is guaranteed, and long term fairness for all traffic in the system is provided. In order to reduce the complexity, a simplified algorithm is proposed, which maintains the system throughput as in the original scheduler, and guarantees the system performance with properly set system parameters. The superior performance of the proposed schedulers is demonstrated by simulation with multimedia traffic

Reverse link average BER of DS-CDMA system with fast and slow power controlled users

Analytical expressions for the average bit error rate in the reverse link of a DS-CDMA system with coexisting fast and slow power controlled users are presented. The combined effects of a frequency selective Nakagami fading channel with an arbitrary multipath intensity profile, the power control error and the use of a cell selection process based on a minimum attenuation criterion are considered.

Hybrid DFE with variable length feedback filter

In the paper, a hybrid decision feedback equaliser (DFE) with a feedback filter (FBF) whose length can be dynamically adjusted is presented and investigated. The equaliser is an adaptive DFE with a feedforward filter (FFF) implemented in the frequency domain with its length fixed by the FFT/IFFT size and a feedback filter (FBF) in the time domain. The FBF length is adjusted according to the achieved mean squared error (MSE). In addition, the impact of small FBF coefficients on system BER performance is taken into account so that a shorter filter length can be considered. Computer simulations show that the proposed approach is capable of adjusting the feedback filter length to a satisfactory level in terms of MSE and system BER performance and is able to track channel changes successfully.

Performance analysis of spectral-phase-encoded optical code-division multiple-access system regarding the incorrectly decoded signal as a nonstationary random process

The performance of a spectral-phase-encoded SPE optical code-division multiple-access OCDMA system is analyzed. Regarding the incorrectly decoded signal IDS as a nonstationary random process, we derive a novel probability distribution for it. The probability distribution of the IDS is considered a chi-squared distribution with degrees of free- dom r=1, which is more reasonable and accurate than in previous work. The bit error rate BER of an SPE OCDMA system under multiple- access interference is evaluated. Numerical results show that the system can sustain very low BER even when there are multiple simultaneous users, and as the code length becomes longer or the initial pulse be- comes shorter, the system performs better. © 2005 Society of Photo-Optical

MIMO Systems in Random Uncorrelated, Correlated and Deterministic Radio Channels

The paper discusses the BER and spectral efficiency of different MIMO systems in random uncorrelated, correlated and deterministic environments, and more specifically uncorrelated and correlated Rayleigh and Ricean fading channels. It is known that the so-called MIMO eigenmode transmission assumes channel knowledge at the transmitter for pre-coding, whereas V-BLAST and STC do not assume the channel knowledge at the transmitter, instead they use it at the receiver for recovering the transmitted information. It is shown that for the same spectral efficiency, the BER performance of the MIMO eigenmode transmission outperforms MIMO systems like V-BLAST and STBC. In fully correlated random environment, transmitting through the largest eigenmode exploits the full transmitter-receiver array gain and diversity order, giving the maximal possible performance in terms of reducing the BER. In any of the scenarios, transmitting through the largest eigenmode gives better performance in terms of reducing the BER compared with STBC systems. Spatial multiplexing through the so-called eigensets (sets which consist of transmission modes with significant channel gain) outperforms systems like V-BLAST. In this context, adaptive modulation has been used to minimize the overall BER for a given spectral efficiency.

Complementary sequence inverse keying for indoor wireless infrared channels

Complementary sequence inverse keying is proposed to ameliorate multipath ISI effects in an indoor wireless infrared communication system. The method involves the transmission of a pair of complementary binary sequences. The system BER performance is presented in comparison with OOK and the results demonstrate that CSIK, unlike OOK, does not incur a power penalty due to ISI.

Q factor: the wrong answer for service providers and equipment manufacturers

This article discusses a particular alternative to the long-term BER test and is an attempt to stimulate debate about the value of this alternative method until an accurate universally acceptable option is developed. Understandably, telecommunications industry players want an acceptable method that can determine error ratios faster than the traditional BER test can. One alternative to emerge thus far is quality factor, or "Q factor," testing, which basically can be used to calculate the theoretical BER of a transmission system. This "quick and dirty" test in fact provides a small incremental benefit in that it saves time. However, some network operators and network equipment manufacturer (NEM) installers are discovering that Q factor, for a variety of technical reasons discussed, can be an inconclusive measurement of BER. Consequently, some who use Q factor testing may base their operational decisions and hence their competitive position in the market on misleading assumptions.

Relative Performance of BPSK and QPSK in the Presence of Complex Multiuser CDMA Interference

In a typical mobile communications channel, the multiple access interference (MAI) experienced by any user in a multiuser CDMA system will be complex-valued due to independent phase offsets between signals received from different users. In addition, complex spreading codes may also be employed, in which case MAI is complex-valued even without phase offsets. This paper shows that complex MAI substantially alters the single-user relationship between BPSK and QPSK modulation, in which QPSK offers twice the bandwidth efficiency of BPSK without sacrificing BER versus Eb/N0 performance. It is shown both analytically and through simulations that it is possible to adjust system parameters to achieve identical system bandwidth efficiency and BER performance in BPSK and QPSK systems using the conventional detector. The performance of the well-known successive interference canceller and decorrelating detector are also examined.

Evaluation of bit error rate and optimization of error correcting capability assignment for a diversity system with multilevel coding over a fading channel

In a fading channel without ISI, the approximate theoretical BER for a diversity reception system where multilevel coding is applied has been determined. The result obtained from the approximate theoretical BER method matches the simulation result, and thus this method can be used as an alternative for evaluating a coding system through simulation. Using the approximate theoretical BER method with a BCH code of length 31 and a rate of 63/93, the optimum error correcting capability assignments at BER = 10−6 for two and three branches have been determined. The error capability assignments (3, 2, 1), (5, 1, 1) have been found to be optimum for levels 1, 2, 3 of the block code, respectively. In the case of a channel with M intersymbol interference, it has been shown that the BER for a given SNR = η [dB] of an interleaving, adaptive equalization, multilevel coding combination system can be estimated using the approximate theoretical BER of an (M + 1) branch diversity whose SNR is η − 10 log10( M + 1) [dB] . © 1999 Scripta Technica, Electron Comm Jpn Pt 3, 82(6): 26–35, 1999

The monitoring of analog and digital program signals in DBS system

The purpose of monitoring the broadcast transmission system is to provide a means of determining how the transmission system is performing and where a fault or abnormal condition exists in the transmission chain. The discussion in this paper focuses on the monitoring requirements in relation to which signals need to be monitored, where to monitor in the transmission chain, and how often each signal needs to be monitored. This paper discusses the equipment required to observe the parameters of essential signals and their attributes such as the NTSC video signal, analogue audio signal, transmitted signal spectrum, power levels, frequency accuracy, received signal spectrum, and BER of a digital broadcasting system. This paper also emphasises the monitoring schemes relating to effective, fast, repeatable, and reliable monitoring of the DBS transmission system and describes implementation issues such as routing, switching, converting, and interfacing. Finally an evaluation and assessment relating to the trouble shooting and the monitoring results affecting the present transmitter station operation and picture quality are addressed.

Signal self-restoration characteristic and bit error rate performance of terrestrial cascaded erbium doped fibre amplifier systems

A normalised gain formula of perturbed erbium doped fibre amplifier (EDFA) is derived. For terrestrial systems where EDFAs work under low saturation, it is shown that optical power can regain 90% of its original value within three stages when the system suffers a 3 dB dip of EDFA output power. On the other hand, the corresponding system BER will be deteriorated by more than two orders of magnitude and the later the perturbation starts the more degradation in BER. Less saturated EDFAs would result in worse BER under the same perturbation.

BER performance of QDPSK with postdetection diversity reception in mobile radio channels

The bit-error-rate performance of Nyquist raised-cosine-filtered quaternary differential phase shift keying (RC-QDPSK) and pi /4-shift RC-QDPSK with postdetection diversity reception is theoretically analyzed for Rayleigh fading channels. A selection combiner, equal-gain combiner, and maximal-ratio combiner are considered for postdetection diversity reception. Diversity improvements on the average BER due to additive white Gaussian noise, cochannel interference, random FM noise, and delay spread of the multipath channel are calculated. Also analyzed is the combined effect of diversity reception and error control. The required E/sub b//N/sub 0/ and allowable RMS delay spread for achieving a certain BER and spectrum efficiency in cellular mobile systems are calculated when short BCH forward error correcting codes are used. The performance of automatic repeat request combined with time diversity reception is investigated. >