Effects of Doppler spread on adaptive orthogonal frequency division multiplexing channel capacity employing diversity in multipath environments

This paper derives the capacity of a fading channel with orthogonal frequency division multiplexing transmission employing diversity techniques and adaptive policies in Rayleigh fading environments. The effects of Doppler shift f_d on channel capacity are analysed. The main contribution of this work is to model intercarrier interference as a function of f_d and symbol duration T_s. Two diversity techniques are considered (i) maximal ratio combining (MRC) and (ii) selective combining (SC). Three adaptive policies are combined with MRC and SC to estimate the following channel capacity: (i) optimal rate adaptive; (ii) optimal power and rate adaptive; and (iii) channel inversion with fixed rate adaptive. Closed‐form expressions and bounds on channel capacity employing different diversity techniques are derived. Simulation results are given. Copyright © 2011 John Wiley & Sons, Ltd.     

Channel capacity of OFDM systems employing diversity in fading environments

This paper derives capacity of a fading channel with orthogonal frequency division multiplexing (OFDM) transmission employing diversity techniques and adaptive policies involving (i) power and rate, (ii) optimal rate and (iii) channel inversion with fixed rate. Two major diversity techniques are considered (i) maximal ratio combining (MRC) and (ii) selective combining (SC). Closed‐form expressions and/or bounds on various channel capacity with OFDM transmission under different scenarios are derived. Simulation results are given. Copyright © 2011 John Wiley & Sons, Ltd.     

On geometric statistics with diversity in multipath scattering channels

This paper studies four aspects of multipath propagation with randomly distributed scatterers: (i) Gaussian and hyperbolic time‐of‐arrival (ToA) probability density functions (pdfs); (ii) theoretical bounds on the ToA pdfs; (iii) geometric pdfs in multipath propagation via Gaussian and hyperbolic scattering channels; and (iv) implementation of selective combining diversity as a method to decrease propagation delay, thus improving transmission performance. The Gaussian and hyperbolic scattering channels are employed to model random scatterers between a base station and a user equipment. One‐dimensional and three‐dimensional results of Gaussian and hyperbolic ToA pdfs are reported. Detailed discussions are given. Copyright © 2012 John Wiley & Sons, Ltd.     

Two base station location techniques with adjusted measurements in circular scattering environments

In circular scattering environments, novel location techniques with only two base stations (BSs) are proposed in this paper. The proposed techniques estimate the true or line‐of‐sight ranges and angle based on non‐line‐of‐sight range and angle measurements. Three new variables are introduced when range measurements and angle measurement are available from two BSs and the serving BS, respectively. Bounds and relationships between the three variables are extracted from the geometry of the cell layout with the unknown and known scattering radius conditions, respectively. Our aim is to obtain the estimation of three new variables and then the hybrid line of position technique with the adjusted ranges, and angle is utilized to obtain the position estimation of a mobile station. In order to obtain the estimation of three new variables, a new nonlinear objective function is built to form the constrained nonlinear optimization and solved by the existing optimization algorithms. However, because of the nonconvex objective function, the optimization algorithm may converge to the local optimum and lead to bad performance. Thus, a heuristic search algorithm is proposed by averaging all the potential point. Simulation results show that the proposed techniques outperform conventional hybrid techniques. Copyright © 2015 John Wiley & Sons, Ltd.