The global caching gain of multi-antenna coded caching techniques can be also mostly achieved in dynamic network setups, where the cache contents of users are dictated by a central server, and each user can freely join or leave the network at any moment. In the dynamic setup, users are assigned to a limited set of caching profiles and the nonuniformness in the number of users assigned to each profile is compensated during the delivery phase by either adding phantom users for multicasting or serving a subset of users with unicast transmissions. In this paper, we perform a thorough analysis and provide closed-form representations of the achievable degrees of freedom (DoF) in such hybrid schemes, and assess the inherent trade-off between the global caching and spatial multiplexing gains caused by either adding phantom users or serving parts of the data through unicasting.

Enabling cooperation in a NOMA system is a promising approach to improve its performance. In this paper, we study the cooperation in a secure NOMA system, where the legitimate users are distributed uniformly in the network and the eavesdroppers are distributed according to a homogeneous Poisson point process. We consider a cooperative NOMA scheme (two users are paired as strong and weak users) in two phases: 1) Direct transmission phase, in which the base station broadcasts a superposition of the messages, 2) Cooperation phase, in which the strong user acts as a relay to help in forwarding the messages of the weak user. We study the secrecy outage performance in two cases: (i) security of the strong user, (ii) security of both users, are guaranteed. In the first case, we derive the exact secrecy outage probability of the system for some regions of power allocation coefficients and a lower bound on the secrecy outage probability is derived for the other regions. In the second case, the strong user is a relay or a friendly jammer (as well as a relay), where an upper bound on the secrecy outage probability is derived at high signal-to-noise-ratio regimes. For both cases, the cooperation in a two-user paired NOMA system necessitate to utilize the joint distribution of the distance between two random users. Numerical results shows the superiority of the secure cooperative NOMA for a range of the cooperation power compared to secure noncooperative NOMA systems.

In this contribution, a thorough investigation of the performance of rate splitting is conducted in terms of outage and secrecy outage for the simultaneous service to a near user and far user, where the latter attempts to overhear the message of the former. The source transmits a linear combination of the users' common stream and private streams. Once the common stream is retrieved, two decoding strategies can be adopted by each user. In the first strategy, the nodes (near or far) treat the far user's private stream as noise to retrieve the private stream of the near user, then the far user decodes its own stream. In the second strategy, the nodes decode the far user's private stream by treating the one of the near user as noise, then the near user retrieves its private stream while the far user decodes the stream of the near user in its attempt to overhear it. Considering the four decoding combinations, we obtain exact closed-form expressions for the outage probability, and provide tight approximations for the secrecy outage probability. Comparative results are also provided. In particular, it is shown that to achieve better outage probability, with no concern about secrecy, once the decoding of the common stream is completed, each user should first retrieve the private stream with lower target data rate by treating the other private stream as noise. To improve the secrecy outage probability, once the common stream is decoded, the near user must first decode the far user's private stream, and the far user should first retrieve the private stream with lower target data rate.

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