Abstract
It is well established that the performance of communication systems is improved when deploying multiple antennas at one or both of the transmit/receive sides; and the amount of the gained improvement depends on the level of multipath richness of the propagation channel. In ship-to-ship overwater channels, quantifying such an improvement is not an easy task due to the effect of evaporation duct on imposing complex rangeand height-dependent patterns of the received signal level. In this study, based on the parabolic equations (PE) method and using realistic evaporation duct distributions, we conduct extensive simulations in order to quantify the link-level improvement achieved when using 2 × 2 vertically-spaced Multiple-Input Multiple-Output (MIMO) systems against 1 × 2 Single-Input Multiple-Output (SIMO) and Single-Input Single-Output (SISO) systems. Then, we analyze the implication of such link improvement on the performance of a system comprised of a network of randomly distributed ships. When evaluating the outage throughput at the 2 nd percentile using realistic system parameters, it was found that 2 × 2 MIMO-MRC (maximum ratio combining) systems with 1 m antenna spacing are able to improve the outage throughput by three-fold compared to SISO systems. This improvement increases to one order of magnitude when the antenna spacing increases to 10 m. It was also found that, in all cases, assuming using the same vertical spacing, 1 × 2 SIMO-MRC systems capture about 60% of the improvement achieved by 2 × 2 MIMO-MRC systems. On the other hand, 1 × 2 SIMO-DIV (diversity combining) systems are very sensitive to antenna spacing, and when assuming using the same vertical spacing, they can capture from 20% and up to 55% of the improvement achieved by 2 × 2 MIMO-MRC systems if the antenna spacing increases from 1 m to 10 m, respectively.
Highlights
There is a continuous increase in demand for reliable and high throughput maritime wireless communication systems
Besides the reference Single-Input Single-Output (SISO) case, three diversity combining schemes are studied: 1) Single-Input Multiple-Output (SIMO)-DIV: the strongest received signal is selected for detection [19], 2) SIMO-MRC: the received signals are co-phased and phase-coherently added [19], and 3) Multiple-Input Multiple-Output (MIMO)-MRC: the beamforming vector is chosen to be the eigenvector corresponding to the maximum eigenvalue λmax of H †H, where H is the 2 × 2 MIMO channel and (.)† is the Hermitian conjugate operator, for more details on the way of applying the beamforming vector of MIMO-MRC we refer the readers to [20]
Since we evaluate the performance based on instantaneous realizations of the channel which are assumed to be known at the transmitter/receiver, the distribution of the imposed phase x doesn’t affect the performance of the SISO, SIMO-DIV, nor SIMO-MRC combining schemes
Summary
There is a continuous increase in demand for reliable and high throughput maritime wireless communication systems. Ray-tracing [4], [5] and the parabolic equations [6] are two main methods used to estimate the path loss in maritime channels They both consider the effects of the tropospheric height-dependent refractivity profile on the characteristics of the received signal. The main contribution of this work is to evaluate the improvement that can be gained from using multipleantenna systems in maritime communications, where: 1) we use realistic evaporation duct distributions, and 2) we assume realistic system parameters supporting two possible diversity combining schemes. The propagation environment is fully characterized by the height-dependent refractivity profile, where the tropospheric radio refractive index (n) is a function of the atmospheric parameters: pressure, wind, temperature, and humidity [16], [17]. Where M0 is the value of the modified refractivity at the surface which is taken as 300 M-units, z is the vertical height in m, z0 is the aerodynamic roughness which is assumed as 1.5 × 10−4 m, δ is the duct height in m, which signifies the height at which M (z) reaches its minimum value [18]
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