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Caching at network edges has attracted more and more research interests recently for the purpose of alleviating the network traffic pressure especially in backhaul links and improving user experience. We study Heterogeneous Cellular Caching Networks (HCCNs) consisting of macro cells in which $N$ small cell base stations (SBSs) equipped with cache memory operate in conjunction with the macro cell base station (MBS). We provide closed-form expressions of the MBS and SBSs utilization factors and average user-experienced-delay in HCCNs with overlapping coverage regions, considering general traffic models for the request arrivals based on the Independent Reference Model (IRM) and renewal traffic models. Moreover, we propose a novel caching scheme in HCCNs, namely Cooperative Most Popular Caching (CMPC), which outperforms the existing schemes in terms of delay. Subsequently, we present the bandwidth assignment problem aiming to minimize the average user-experienced-delay under stability and cache size constraints in HCCNs with overlapping coverage regions and stochastic request arrivals. Finally, the analytic results are validated through numerical results and real trace-driven experiments. [ABSTRACT FROM AUTHOR]

Although the hybrid of cell-free (CF) massive multiple-input multiple-output (MIMO) and non-orthogonal multiple access (NOMA) promises massive spectral efficiency gains, the type of precoders employed at the access points (APs) impacts the gains. In this paper, we thus comprehensively evaluate the system performance with maximum ratio transmission (MRT), full-pilot zero-forcing (fpZF) and modified regularized ZF (mRZF) precoders. We derive their closed-form sum rate expressions by considering Rayleigh fading channels, the effects of intra-cluster pilot contamination, inter-cluster interference, and imperfect successive interference cancellation (SIC). Our results reveal that this system supports significantly more users simultaneously at the same coherence interval compared to its OMA equivalent. However, intra-cluster pilot contamination and imperfect SIC degrade the system performance when the number of users is low. Moreover, with perfect SIC, mRZF and fpZF significantly outperform MRT. Also, we show that this system with either mRZF or fpZF precoding outperforms OMA systems with MRT. The analytical findings are verified by numerical results. [ABSTRACT FROM AUTHOR]

We investigate the achievable rate of a hybrid cell-free (CF) massive multiple-input multiple-output (MIMO) non-orthogonal multiple-access (NOMA) underlaid below a primary massive MIMO. We propose a low complexity sub-optimal user-clustering method and derive the closed-form sum rate expression for Rayleigh fading channels by considering the effects of intra-cluster pilot contamination, inter-cluster interference, imperfect successive interference cancellation (SIC) and statistical downlink channel state information (CSI) at secondary users (SUs). Our results reveal that NOMA based underlay CF massive MIMO-NOMA can exploit the scarce spectrum bands more efficiently than its counterpart orthogonal multiple-access (OMA). [ABSTRACT FROM AUTHOR]

We develop an analytical framework for queueing and delay analysis in the case of a number of distinct flows arriving at a network node, where asynchronous partial network coding is applied for an efficient packet transmission. In order to perfectly model and analyze the practical communication networks, the arriving flows are assumed to be general Markovian arrival processes. As a key example, we apply the proposed model to the problem of coded caching in single bottleneck caching networks. In addition, we verify the accuracy of the proposed model through simulations and real trace-driven experiments. [ABSTRACT FROM AUTHOR]

In this paper, we propose an interference alignment (IA) scheme in which the performance of the secondary users (SUs) transmitting their information on the same frequency band of the preexisting primary links is improved in terms of achievable sum rate without generating interference on the primary network. In our scenario, in which the primary users (PUs) are cooperating through IA and a set of SUs joins the network, we propose an efficient approach to find the values of the preprocessing and postprocessing filters of these SUs. Moreover, the SUs must not receive/generate any interference from/to the PUs. To preserve the primary network from the interference caused by the SUs, we also employ a method in which the distance between the subspace of the received signal from each secondary transmitter at the PUs and the set of interference subspaces at the primary links is minimized. In result, we would tackle with a computationally hard optimization problem with the sum rate of the secondary links as the objective function. We present the solutions in the cases where one or two SUs join the network. In situations where more SUs join the network simultaneously, we may apply other levels of IA between the secondary links after suppressing the mutual interference between the primary and secondary networks. The analytical results are confirmed through simulations. [ABSTRACT FROM PUBLISHER]

Caching has been widely considered an efficient way of reducing and balancing the growing traffic in communications networks in recent years. The cache network of interest consists of one content server connected via a shared link to a number of caching nodes, also known as a single bottleneck caching network. In this paper, for the first time, the stochastic requests traffic model in such networks is considered and a performance analysis is provided based on such a realistic assumption. In addition, we introduce new comprehensive performance metrics, which simultaneously take into account, the cache hit probability, load on the bottleneck link, and requests arrival rates. The main contribution of this paper is to present a system model based on queuing theory and provide an analysis of the stability, maximum stable throughput, load on the bottleneck link, and average response delay for various coded and uncoded caching schemes. Moreover, we propose a novel hybrid scheme that improves the shared link utilization factor, maximum stable throughput, and delay of single bottleneck caching networks compared to existing methods. Our results, validated against simulations and real trace-driven experiments, provide interesting insights into the performance of single bottleneck caching networks. [ABSTRACT FROM AUTHOR]