A tight upper bound on the BER of linear systematic block codes

We present in this letter new upper bounds for linear and systematic block codes. Both perfect and quasi-perfect codes are considered. Numerical results show that our new bounds give much tighter results compared to the classical union-Chernoff bound. In addition, these bounds are more accurate than the leading term approximations especially at low signal-to-noise ratio.     

Optimal power allocation for relayed transmissions over Rayleigh-fading channels

Relayed transmission is a way to attain broader coverage by splitting the communication link from the source to the destination into several shorter links/hops. One of the main advantages of this communication technique is that it distributes the use of power throughout the hops. This implies longer battery life and lower interference introduced to the rest of the network. In this context, this paper investigates the optimal allocation of power over these links/hops for a given power budget. All hops are assumed to be subject to independent Rayleigh fading. Outage probability which is the probability that the link quality from source to destination falls below a certain threshold is used as the optimization criterion. Numerical results show that optimizing the allocation of power enhances the system performance, especially if the links are highly unbalanced in terms of their average fading power or if the number of hops is large. Interestingly, they also show that nonregenerative systems with optimum power allocation can outperform regenerative systems with no power optimization.     

Impact of the gain saturation dynamics in semiconductor optical amplifiers on the characteristics of an analog optical link

We evaluate both theoretically and experimentally the gain saturation dynamics of semiconductor optical amplifiers when inserted into an analog optical link. Its impact in terms of radio frequency response, nonlinearity, and noise is investigated. In particular, the frequency response is shown to be a peculiar high-pass filter exhibiting two characteristic frequencies.     

Average outage duration of multihop communication systems with regenerative relays

Closed-form expressions for the average outage duration (AOD) of multihop regenerative communication systems over generalized fading channels are presented. Both noise-limited and interference-limited systems are studied. To show the usefulness of the presented expressions, some specific fading scenarios are considered. In addition, some numerical examples of interest comparing direct versus relayed transmission and studying the effect of increasing the number of hops and/or cochannel interferers are plotted and discussed.     

Outage probability of mimo optimum combining in presence of unbalanced co-channel interferers and noise

This paper studies the performance of multiple-input-multiple-output (MIMO) systems with optimum combining in the presence of both co-channel interference (CCI) and noise. We assume that both desired and CCI users are subject to Rayleigh fading and allow the number of CCI users to be arbitrary and their short-term average powers to be non-identical. Given these assumptions, we derive exact results on the cumulative distribution function (CDF) of the output signal-to-interference-plus-noise ratio (SINR), or equivalently, the outage probability of this MIMO optimum combining scheme. Finally, we present and discuss some numerical examples to validate our analytical expressions and to show the effect of CCI on the performance of MIMO optimum combining systems     

Dual tunable wavelength Er,Yb:glass laser for terahertz beatfrequency generation

Dual tunable wavelength operation of Er,Yb:phosphate glass laser is reported. The spatial separation of the laser eigenstates and the use of two properly designed intracavity etalons permit one to tune the two wavelengths independently from 1540.5 to 1562.7 nm. The generated beat note, monitored using a Michelson interferometer, is experimentally shown to be adjustable from dc to 2.7 THz. The linewidth of this beat note is found to be less than 10 kHz. Several applications are discussed     

Outage probability and spectrum efficiency of cellular mobile radio systems with smart antennas

Relying on the distribution of noncentral multivariate F variates, we investigate the outage probability and spectrum efficiency performance of cellular systems with smart antennas. We consider interference-limited systems in which the number of interferers exceeds or is equal to the number of antenna elements, and we present closed-form expressions when the desired signal is subject to Rician-type fading and interfering signals exhibit Rayleigh-, or, more general Nakagami-type fading. When applicable, these new expressions are compared to those previously reported in the literature dealing with the performance of cellular systems without smart antenna capabilities and the performance of cellular systems with optimum combining when both the desired and interfering signals are subject to Rayleigh-type fading. Corresponding numerical results and plots are also provided and discussed.     

Effect of channel estimation error on M-QAM BER performance inRayleigh fading

We determine the bit-error rate (BER) of multilevel quadrature amplitude modulation (M-QAM) in flat Rayleigh fading with imperfect channel estimates, Despite its high spectral efficiency, M-QAM is not commonly used over fading channels because of the channel amplitude and phase variation. Since the decision regions of the demodulator depend on the channel fading, estimation error of the channel variation can severely degrade the demodulator performance. Among the various fading estimation techniques, pilot symbol assisted modulation (PSAM) proves to be an effective choice. We first characterize the distribution of the amplitude and phase estimates using PSAM. We then use this distribution to obtain the BER of M-QAM as a function of the PSAM and channel parameters. By using a change of variables, our exact BER expression has a particularly simple form that involves just a few finite-range integrals. This approach can be used to compute the BER for any value of M. We compute the BER for 16-QAM and 64-QAM numerically and verify our analytical results by computer simulation. We show that for these modulations, amplitude estimation error leads to a 1-dB degradation in average signal-to-noise ratio and combined amplitude-phase estimation error leads to 2.5-dB degradation for the parameters we consider     

A Threshold-Based Channel State Feedback Algorithm for Modern Cellular Systems

In this paper we propose a channel state feedback algorithm that uses multiple feedback thresholds to reduce the number of users transmitting feedback to a minimum. The users are polled with lower and lower threshold values and only the users that are above a threshold value transmit feedback to the base station. We show how this feedback algorithm can be used for any scheduling algorithm and show how closed-form expressions for the optimal threshold values can be obtained for two well-known scheduling algorithms. Finally, we propose a two-step optimization procedure for optimizing the feedback algorithm for real-life cellular standards.     

Minimum estimation and combining generalized selection combining (MEC-GSC)

This paper introduces and analyzes a new adaptive minimum-estimation minimum-combining switched-combining based scheme that reduces considerably the average receiver channel estimation complexity and the power drain from the battery while satisfying a certain desired performance requirement. The mathematical formalism is supported by some selected numerical examples that show that the newly proposed combining scheme can essentially achieve the same performance as competing schemes such as generalized selection combining (GSC) while offering 50 % channel estimation and 75 % processing power savings for some system parameters of interest