Enabling Relaying Over Heterogeneous Backhauls in the Uplink of Femtocell Networks

Cellular NetworksInternational audienceIn this paper, we develop novel two-tier interference management strategies that enable macrocell users (MUEs) to improve their performance, with the help of open-access femtocells. To this end, we propose a rate-splitting technique using which the MUEs optimize their uplink transmissions by dividing their signals into two types: a coarse message that is intended for direct transmission to the macrocell base station and a fine message that is decoded by a neighboring femtocell and subsequently relayed over a heterogeneous (wireless/wired) backhaul. For deploying the proposed technique, we formulate a non-cooperative game between the MUEs in which each MUE can decide on its relaying femtocell while maximizing a utility function that captures both the achieved throughput and the expected backhaul delay. Simulation results show that the proposed approach yields up to 125% rate improvement and up to 2 times delay reduction with wired backhaul and, 150% rate improvement and up to 10 times delay reduction with wireless backhaul, relative to classical interference management approaches, with no cross-tier cooperation

Exploiting Diversity by Opportunistic Scheduling in Energy Harvesting Wireless Networks

It is in recent years that harvesting energy from ambient energy sources (e.g., solar, wind, or vibration) has been commercialized, which is a promising technique to fulfil sustainable operations for many kinds of electrical systems. To advocate reducing the emission of greenhouse gases, people in communication society are seeking to accommodate and take advantage of this new technology for wireless systems, such as sensor networks, Internet of Things, and heterogeneous networks. In this dissertation, we focus on energy harvesting (EH) based wireless networks, where multiple users are powered by energy harvesters and share limited spectrum resources. In this system, the design of efficient access schemes plays a crucial role in optimizing the system performance. Moreover, different from the conventional wireless systems, there are two random processes that must be jointly counted in the transmission design: the channel fading and the dynamics of the EH powered battery. Specifically, we narrow down the design onto two typical network setups. First, in a single channel access scenario, an ad hoc network with multiple transmitter-receiver pairs is considered, where all EH-based transmitters share one channel by random access. Two EH rate models are applied: Constant and i.i.d. (i.e., independent and identically distributed) EH rate models. To quantify the roles of both the energy and channel state information, a distributed opportunistic scheduling framework is proposed such that the average throughput of the network is maximized. Second, in a multi-channel access scenario, we study an uplink transmission under a heterogeneous network hierarchy, where each EH-based mobile user (MU) is capable of both deterministically accessing to a large network via one private channel, and dynamically accessing a small network with a certain probability via one common channel shared by multiple MUs. Considering a time-correlated EH model, we study an opportunistic transmission scheme to maximize the average throughput for each MU by jointly exploiting the statistics of the system states. Finally, back to the single channel access setup, we investigate the multiuser energy diversity by analyzing the fundamental scaling law of the throughput over the number of EH-based users under both centralized and distributed access schemes. We reveal the throughput gain coming from both the increase of total available energy harvested over time/space and the combined dynamics of batteries