In this paper, a reliable small-signal model parameter extraction method for GaN high electron mobility transistor (HEMT) on Si substrate has been developed and validated with respect to different gate width devices. The main advantage of this approach is its accuracy and dependency on only pinched-off and unbiased S-parameter measurements. The developed procedure shows reliable and physically relevant results for the investigated devices and scaled with the gate width. A very good agreement is obtained between small-and large-signal simulations and measurements of the considered GaN HEMTs.

This paper presents experimental results of overwater radio path loss in the 4.4 to 5.0 GHz band. These measurements involve horizontal and vertical polarizations. Based on electromagnetic theory, a deterministic two ray model that mimics measurements is developed. The model can predict the received power level for all distances lower and higher than the critical distance. The model is consistent with measurements in MIMO modes using any kind of linear polarized antennas.

The channel capacity and the channel statistics are both important performance metrics to consider for appropriate design of wireless systems. In tactical mobile ad hoc networks environment, the capacity and the second order statistics are investigated based on an optimized physical layer simulation tool which includes tactical scenarios generator and propagation modeler. The possible link data rate is stemmed from the average channel capacity analysis between all pair of nodes. And based on the minimum data rate requirement for typical services (web, audio and video streaming, VoIP, videoconference), connectivity graphs are constructed. Moreover, level cross rate (ICR) and average duration of fade (ADF) are simulated as function of double mobility degree and the results show how the double mobility affects the second order channel statistics and the error probability.

Constant-amplitude transmitter architectures offer high amplification efficiencies by using one or more nonlinear amplifiers. In this article, we propose one new such architecture, dubbed DbPSK, for efficient MQAM transmission. The proposed architecture decomposes the MQAM constellation into two pseudo-MPSK constellations that are independently amplified, with high efficiency nonlinear amplifiers, then combined to generate the original MQAM signal amplified. We show that the proposed architecture provides interesting performance in terms of power, efficiency and linearity for any MQAM signal transmission and we discuss its implementation aspects. This architecture can be considered as an improvement of the NLA-QAM architecture used in satellite applications.

It has been demonstrated that zero correlation of a random multiple-input multiple-output channel is not a guarantee of its high capacity. Degenerate channels exist, which have zero correlation and still low capacity. We provide a statistical analysis of this phenomenon, formulate the general condition for a channel to be degenerate, and propose a method to estimate its capacity.

A universal upper bound on the MIMO architecture capacity, which is not limited to a particular scenario, is derived using the correlation matrix approach and the Jensen's inequality. This bound accounts for both transmit and receive branch correlation in such a way that the impact of these branches can be estimated separately, which simplifies the procedure substantially and also allows one to decide which site is responsible for capacity reduction, which is not easy to do using traditional approaches. Further, using the results above and the Salz-Winters (1994) model of fading spatial correlation, it is demonstrated that the correlation has no impact on the MIMO capacity provided that the two-element antenna array beamwidth is smaller than the angle spread of the incoming multipath signals. A fundamental tradeoff between MIMO capacity and diversity order is also pointed out.

Fade depth prediction on airborne line-of-sight communication links is considered. There is no specific model for this scenario at the moment. The two ray multipath model, adapted to a realistic scenario of hilly or mountainous terrain, was used to account for flight and terrain geometry and for antenna parameters. Surprisingly, it was found that (i) in many practically important cases the fade depth depends on the path clearance angle only and (ii) the two-ray model predicts roughly the same fade depth dependence on the path clearance angle as the well-known Olsen-Segal model. This may be considered as a theoretical justification, to the best of our knowledge for the first time, of the path elevation angle factor in that model.