Tunable absolute-frequency laser at 1.5 μm

Frequency stabilisation of a two-frequency diode-pumped Er,Yb:glass laser is demonstrated using Doppler-broadened or saturated-absorption lines of ¹³C₂H₂. Continuous tunability in the 1530-1550 nm range is obtained. Beat note measurements lead to a frequency accuracy better than 10 kHz for a 10s response time     

Level crossing rate over multiple independent random processes: an extension of the applicability of the rice formula

This paper presents general expressions for the calculation of the level crossing rate of various combinations of multiple independent random processes. These new formulas are then applied to obtain the outage rate and average outage duration of several communication systems and networks of current interest. Applications include for example multi-hop communication systems with and without selection combining as well as communication networks with routing diversity.     

Generalized switch-and-examine combining (GSEC) over fading paths with unequal average SNR

A generalized switch-and-examine combining (GSEC) scheme was previously proposed by the authors as a low-complexity diversity technique for diversity-rich environments. In this letter, we extend the study of GSEC to independent and nonidentically distributed (i.n.d.) fading environments. In particular, after presenting the mode of operation of the GSEC scheme over i.n.d. fading paths, we analyze its error performance based on the moment generating function of combined signal-to-noise ratios. We then study its complexity in terms of the average number of path estimations. We finally investigate the effect of path examination order on the performance and complexity of GSEC over i.n.d. paths.     

Improving the performance of switched diversity with post-examining selection

Switched diversity offers one of the lowest complexity solution for fading mitigation. The receiver employing switched combining schemes. seeks and uses an acceptable diversity path for data reception. However, when no acceptable path is found after all paths have been examined, the receiver ends up randomly choosing an unacceptable path. In this paper, we consider the performance improvement of switched combining schemes. In particular, we modify conventional multi-branch switch and examine combining (SEC) schemes in a way that the best path is selected when no acceptable path is found after all paths have been examined. We carry out a thorough performance versus complexity tradeoff study on the resulting scheme: SEC with post-examining selection and illustrate the study with some selected numerical examples.     

Capacity of correlated MIMO Rayleigh channels

Abstract-This paper presents some exact results on the capacity of multiple-input-multiple-output (MIMO) channels subject to correlated Rayleigh fading when perfect channel state information (CSI) is known at the receiver. The authors focus on the semicorrelated scenario in which correlation exists either at the transmitter or at the receiver., They consider two cases: 1) the transmitter does not have any CSI and as such allocates power equally among transmitter antennas and 2) the transmitter only knows the statistical distribution of the channel. The first case derives the moment generating function (MGF) of the mutual information (MI) and then deduces from this MGF the mean MI. The authors also study the cumulative distribution function (CDF) of the MI, which can serve as an upper bound to the outage probability under the capacity versus outage formulation when the channel is nonergodic. The second case studies the capacity achieved by optimum power-loading and beamforming schemes based on covariance feedback. Numerical results illustrate that the full capacity of MIMO systems can be preserved even for relatively high values of correlation coefficients.     

Average SNR of dual selection combining over correlated Nakagami-mfading channels

We investigate the effect of fading correlation and branch gain imbalance on the average output signal-to-noise ratio (SNR) in conjunction with dual selection combining (SC). In particular, starting with the moment generating function of the dual SC output SNR, we derive a closed-form expression for the average output SNR in the general case of correlated unbalanced Nakagami-m fading channels. We then show that the generic result can be further simplified for the special cases of Rayleigh fading, uncorrelated branches, and/or equal average SNRs. Because of their simple form, the given expressions readily allow numerical evaluation for cases of practical interest     

A comparative study on the performance of MIMO MRC systems with and without cochannel interference

This paper presents exact closed-form expressions for the performance of multiple-input/multiple-output systems employing maximal ratio combining in the absence and presence of cochannel interference. The results are applicable to systems operating over Rayleigh fading channels, and in which the minimum number of antenna elements at the transmitter and receiver is two. The mathematical formalism is illustrated by some numerical examples which study the effects of various parameters on the system performance.     

A new simple model for land mobile satellite channels: first- and second-order statistics

We propose a new shadowed Rice (1948) model for land mobile satellite channels. In this model, the amplitude of the line-of-sight is characterized by the Nakagami distribution. The major advantage of the model is that it leads to closed-form and mathematically-tractable expressions for the fundamental channel statistics such as the envelope probability density function, moment generating function of the instantaneous power, and the level crossing rate. The model is very convenient for analytical and numerical performance prediction of complicated narrowband and wideband land mobile satellite systems, with different types of uncoded/coded modulations, with or without diversity. Comparison of the first- and the second-order statistics of the proposed model with different sets of published channel data demonstrates the flexibility of the new model in characterizing a variety of channel conditions and propagation mechanisms over satellite links. Interestingly, the proposed model provides a similar fit to the experimental data as the well-accepted Loo's (1985) model but with significantly less computational burden.     

Outage probability of dual-branch diversity systems in presence of co-channel interference

Outage probability of two low-complexity dual-branch diversity schemes with the consideration of both minimum carrier-to-interference ratio and the carrier-to-noise ratio constraints is investigated. More specifically, closed-form expressions for this outage probability for selection combining and switch and stay combining in single-interferer Rayleigh fading environment are derived, first under the assumption of perfectly estimated independent diversity paths, then by taking into account the effect of branch correlation and outdated/imperfect channel estimates. When applicable, the results obtained as special cases of the offered generic closed-form expressions are compared with those previously reported in the literature. In addition, some numerical examples are provided and discussed.     

Closed-form analysis of dual-diversity equal-gain combining over Rayleigh fading channels

Starting with a new expression for the probability density function of the signal-to-noise ratio at the output of dual-diversity equal-gain combining (EGC) over Rayleigh channels, we provide closed-form expressions for the average bit and symbol error rate of M-ary phase-shift keying signals. Numerical examples indicate that EGC maintains a good diversity gain as long as the degree of unbalance is not very low but suffers a sharp and significant degradation when the degree of unbalance approaches zero.