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In cellular networks, balancing the throughput among users is important to achieve a uniform Quality-of-Service (QoS). This can be accomplished using a variety of cross-layer techniques. In this paper, the authors investigate how the downtilt of basestation (BS) antennas can be adjusted to maximize the user throughput fairness in a heterogeneous network, considering the impact of both a dynamic user distribution and capacity saturation of different transmission techniques.Finding the optimal down-tilt in a multi-cell interferencelimited network is a complex problem, where stochastic channel effects and irregular antenna patterns has yielded no explicit solutions and is computationally expensive.The investigation first demonstrates that a fixed tilt strategy yields good performances for homogeneous networks, but the introduction of HetNet elements adds a high level of sensitivity to the tilt dependent performance. This means that a HetNet must have network-wide knowledge of where BSs, access-points and users are. The paper also demonstrates that transmission techniques that can achieve a higher level of capacity saturation increases the optimal down-tilt angle.A distributed reinforcement learning algorithm is proposed, where BSs do not need knowledge of location data. The algorithm can achieve convergence to a near-optimal solution rapidly (6-15 iterations) and improve the throughput fairness by 45-56% and the energy efficiency by 21-47%, as compared to fixed strategies. Furthermore, the paper shows that a tradeoff between the optimal solution convergence rate and asymptotic performance exists for the self-learning algorithm.

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The concept of a secure electromagnetic building (SEB) which can successfully prohibit wireless communications is presented. Wireless security is achieved using a slow phaseswitching technique and can be realized by time-varying the transmission properties of a frequency-selective surface (FSS) to increase the bit error rate (BER) of the unwanted signal. Results are presented which demonstrate that a technique of phase switching at rates much lower than the baseband data rate can be used successfully. The system has been implemented using a reconfigurable dual-polarized dual layer FSS incorporating varactor diodes where over 100 • of phase change can be achieved for voltage changes of ±0 − 3V . A vector signal analyzer was used to evaluate the BER performance of the system for a GSM signal operating at 2 GHz. BERs are shown to be as high as 36% which are sufficient to successfully prohibit wireless communication. The solution is also shown to be robust over a wide range of incidence angles, which is important for real-world applications where the location of the prohibited wireless source may be unknown or mobile. Furthermore, as the system is reconfigurable, the building can be switched between secure and nonsecure modes.

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