Ultra Electronics (Canada)

The exponential growth of traffic in mobile networks is leading to an increased pressure on the infrastructure of mobile networks and in particular on their backhaul networks. It is more critical than ever to carefully plan backhaul networks. In this paper, we formulate and solve the problem of hierarchical wireless backhaul network design. In our problem, we cover different requirements, namely: topology simplicity, network resiliency and link reliability. We formulate the problem as an Integer Linear Programming (ILP) problem, allowing us to solve the problem to optimality. Furthermore, we provide a graph theory based algorithm that allows to solve the problem overlarge scale. The proposed algorithm exploits the properties of the graph representing the network. The results of our evaluations in various network scenarios demonstrate the efficiency of our ILP formulation and the provided algorithm in keeping the backhaul network simple, resilient and reliable. Using a practical channel propagation model and different node densities that are representative of small-scale and large-scale urban environments, our results also show that even with high resiliency requirements, the network traffic can be backhauled with only5−10%of the nodes for the considered densities. Our results also demonstrate that our algorithm leads to near-optimal solutions in different scenarios.

Based on analyzing two-day ship-to-shore propagation measurements performed simultaneously at two frequency bands (1.39 GHz and 4.5 GHz), we extract the small-scale fading (SSF) and show that the higher the frequency, the larger the amplitudes of the SSF. Consequently, we introduce a modification to the 2-ray model so that the behavior of the SSF at different frequency bands is captured. We model the effect of the randomness and the unknown dynamic details of the propagation environment as a zero-mean Gaussian random variable which is then superimposed on the length of the rays in the traditional 2-ray model. For the measured environment, it is found that a standard deviation in the sub-centimeter range is able to characterize these unknown details and almost replicate the behavior of the observed SSF at these two bands.

One main disadvantage of the multiple-input-multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system is that the signals transmitted on each antenna may experience high peak-to-average-power ratio (PAPR). We will present a new hybrid PAPR reduction technique that combines and optimizes three methods, namely convolutional code, successive suboptimal cross-antenna rotation and inversion (SS-CARI), and iterative modified companding and filtering. The results for the hybrid PAPR reduction technique show that this scheme significantly reduces the PAPR compared with SS-CARI alone; it can improve the bit error rate to levels better than what obtains with the space–time block coding MIMO-OFDM system, and the spectral splatter due to companding is also controlled by the use of frequency-domain filtering. In addition, it is a flexible technique in which the net gain can be optimized based on the requirements of scheme parameters, such as the code rate, the constraint length of the convolutional code, the number of subblocks for SS-CARI, and the companding parameters.

The development of a piezoelectric hydrophone based on lead magnesium niobate-lead titanate [PbMg1/3Nb2/3O3-PbTiO3 (PMN-PT)] single-crystal piezoelectric as the hydrophone substrate is reported. Although PMN-PT can possess much higher piezoelectric sensitivity than traditional lead zirconate titanate (PZT) piezoelectrics, it is highly anisotropic and therefore there is a large gain in sensitivity only when the crystal structure is oriented in a specific direction. Because of this, simply replacing the PZT substrate with a PMN-PT cylinder is not an optimal solution because the crystal orientation does not uniformly align with the circumferential axis of the hydrophone. Therefore, a composite hydrophone that maintains the optimal crystal axis around the hydrophone circumference has been developed. An 11.3 mm diameter composite hydrophone cylinder was fabricated from a single <110> cut PMN-PT rectangular plate. Solid end caps were applied to the cylinder and the sensitivity was directly compared with a solid PZT-5A cylindrical hydrophone of equal dimensions in a hydrophone test tank. The charge sensitivity showed a 9.1 dB improvement over the PZT hydrophone and the voltage sensitivity showed a 3.5 dB improvement. This was in good agreement with the expected theoretical improvements of 10.1 and 4.5 dB, respectively.