Abstract
In this paper, we consider a novel cache-enabled heterogeneous network (HetNet), where macro base stations (BSs) with traditional sub-6 GHz are overlaid by dense millimeter wave (mmWave) pico BSs. These two-tier BSs, which are modeled as two independent homogeneous Poisson Point Processes, cache multimedia contents following the popularity rank. High-capacity backhauls are utilized between macro BSs and the core server. In contrast to the simplified flat-top antenna pattern analyzed in previous articles, we employ an actual antenna model with the uniform linear array at all mmWave BSs. To evaluate the performance of our system, we introduce two distinctive user association strategies: 1) maximum received power (Max-RP) scheme; and 2) maximum rate (Max-Rate) scheme. With the aid of these two schemes, we deduce new theoretical equations for success probabilities and area spectral efficiencies (ASEs). Considering a special case with practical path loss laws, several closed-form expressions for coverage probabilities are derived to gain several insights. Monte Carlo simulations are presented to verify the analytical conclusions. We show that: 1) the proposed HetNet is an interference-limited system and it outperforms the traditional HetNets in terms of the success probability; 2) there exists an optimal pre-decided rate threshold that contributes to the maximum ASE; and 3) Max-Rate achieves higher success probability and ASE than Max-RP but it needs the extra information of the interference effect.
Highlights
W ITH the rapid development of the traditional cellular networks and novel Internet-enabled applications, such as multimedia sensors [2] and electric vehicles [3], [4], the total throughput of mobile networks in 2020 is expected to become 1000-fold larger than that in 2010 [5]
We organize the rest of our treatise as follows: In Section II, we present the system model where two-tier base stations (BSs) and users in the proposed cache-enabled hybrid heterogeneous networks (HetNets) are modeled as three independent homogeneous Poisson Point Process (HPPP)
As discussed in the previous sections, we conclude that the considered system has two different processes in sending multimedia contents: 1) Association Mode, when the requested f -th file obeys (1 ≤ f ≤ Hc), the typical user equipments (UEs) chooses the suitable BS as the corresponding BS depending on two association strategies; and 2) Server Mode, when the demanded f -th content only exists in the server due to limited storage capacity at BSs, which means (Hc < f ≤ Nc), the typical UE requests such content from the server via the nearest macro BS
Summary
W ITH the rapid development of the traditional cellular networks and novel Internet-enabled applications, such as multimedia sensors [2] and electric vehicles [3], [4], the total throughput of mobile networks in 2020 is expected to become 1000-fold larger than that in 2010 [5]. Liu and Yang [15] analyzed the energy efficiency and throughput of cellular networks with caches, but they only considered the small cell networks (SCNs) and BSs were modeled following a regular hexagonal grid. Since stochastic geometry is a useful tool to acquire the networks’ randomness [16], modeling a tier of BSs in SCNs or HetNets with a homogeneous Poisson Point Process (HPPP) is more accurate than the traditional hexagonal scenario [17]–[19] Under this condition, the throughput of multi-tier cache-enabled HetNets was discussed in [20], where BSs were modeled as mutually independent PPPs. the high-capacity backhauls were employed at all nodes including the macro BSs and relays, which is uneconomical in reality. Recent works [24], [32] presented a realistic channel model with Nakagami fading to improve the theoretical accuracy
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