As the transition from 5G to 6 G unfolds, a substantial increase in Internet of Things (IoT) devices is expected, enabling seamless and pervasive connectivity across various applications. Accommodating this surge and meeting the high capacity demands will necessitate the integration of NonTerrestrial Networks (NTNs). However, the extensive coverage area of satellites, relative to terrestrial receivers, will lead to a high density of users attempting to access the channel at the same time, increasing the collision probability. In turn, the deployment of mega constellations make it possible for ground users to be in visibility of more than one satellite at the same time, enabling receiver diversity. Therefore, in this paper, we evaluate the impact of multi-receivers in scenarios where IoT nodes share the channel following a non-orthogonal multiple access (NOMA)irregular repetition slotted ALOHA (IRSA) protocol. Considering the impairments of satellite channels, we derive a lower bound of system performance, serving as a fast tool for initial evaluation of network behavior. Additionally, we identify the trade-offs inherent to the network design parameters, with a focus on packet loss rate and energy efficiency. Notably, in the visibility of only one extra satellite as receiver yields significant gains in overall system performance.

We evaluate a modification of irregular repetition slotted ALOHA (IRSA) involving intermediate decoding and early transmission termination by some nodes, upon their decoding success. This is meant to avoid unnecessary transmissions, thereby reducing energy consumption. We expect this to be particularly useful at low loads, where most transmissions can be avoided as they do not often result in a collision and are therefore redundant. To validate this proposal, we observe that most of the literature related to IRSA considers an asymptotic heavily loaded regime; thus, we also present a model of energy consumption and success probability for frames of limited length and low offered loads. Thanks to our analysis, also confirmed by simulation, we are able to show that the proposed technique is able to reduce IRSA energy consumption by minimizing transmissions, while preserving performance gains over standard ALOHA. For example, we are able to get a 33% energy saving at offered loads around 10% without affecting throughput.

We study the performance of caching schemes based on two different coding techniques. A heterogeneous network is assumed, in which cache-aided relays are connected through a backhaul link to a primary node while no connection exits between users and the primary node. The first caching scheme considers to fill the cache with encoded content while the second scheme considers to encode the content during the delivery phase. We compare the schemes by characterizing the average transmission load when users ask for downloading content to the network. We provide an approximation of the expression of the average load which allows a fast evaluation of the network behavior for each scheme considered. We further assume a constraint on the capacity of the backhaul link and derive the expression of the outage probability, i.e. the probability that the system is not able to serve the entire set of users demands. Finally, we examine and discuss how the derived analysis of a two relays scenario can be scaled to study the performance of a network with a generic number of relays.

Caching multimedia contents at the network edge is a key solution to decongest the amount of traffic in the backhaul link. In this paper, we extend and analyze the coded caching technique [1] in an unexplored scenario, i.e. at the edge of two-tier heterogeneous networks with an arbitrary number of users. We characterize the performance of such scheme by deriving a closed-form expression of the average backhaul load and reveal a significant gain compared to other benchmark caching schemes proposed in the literature.

Caching at the edge of wireless networks is a key technology to reduce traffic in the backhaul link. However, a concentrated amount of requests during peak-periods may cause the outage of the system, meaning that the network is not able to serve the whole set of demands. The outage probability is a fundamental metric to take into account during the network design. In this paper, we derive the analytical expression of the outage probability as a function of the total amount of users requests, library size, requests distribution, cache size and capacity constraints on the backhaul resources. In particular, we focus on a scenario where end-users have no direct connection to the master node which holds the complete library of content that can be requested. A general formulation of the outage is derived and studied for two relevant caching schemes, i.e. the random caching scheme and the most popular caching schemes. The exact closed form expressions presented in this paper provide useful insights on how requests, memory and resources can be balanced when the parameters of a cache-enabled network have to designed.

We study the problem of caching optimization in heterogeneous networks with mutual interference and per-file rate constraints from an energy efficiency perspective. A setup is considered in which two cache-enabled transmitter nodes and a coordinator node serve two users. We analyze and compare two approaches: 1) a cooperative approach where each of the transmitters might serve either of the users and 2) a non-cooperative approach in which each transmitter serves only the respective user. We formulate the cache allocation optimization problem so that the overall system power consumption is minimized while the use of the link from the master node to the end users is spared whenever possible. We also propose a low-complexity optimization algorithm and show that it outperforms the considered benchmark strategies. Our results indicate that significant gains both in terms of power saving and sparing of master node's resources can be obtained when full cooperation between the transmitters is in place. Interestingly, we show that in some cases storing the most popular files is not the best solution from a power efficiency perspective.

Small cells will play an important role in the fifth generation mobile networks. As recent works pointed out, a significant improvement in energy efficiency can be obtained if small base stations (SBSs) are provided with storage capabilities. In this paper, we study the problem of caching optimization in the presence of interference with and without cooperation between the SBSs. We consider a setup in which two SBSs and one macro base station (MBS) are connected through a wireless backhaul link. Cooperation is applied following the Han-Kobayashi rate splitting approach and its variation including common information. Our results show that applying cooperation to caching systems yields significant gains in terms of power and provide indications on how much interference can be tolerated which, in turn, has impact on the network design both in terms of frequency reuse planning and SBS deployment.