Application Research of Multi-Mode Relay in Future Heterogeneous Networks

Literature [12] indicated the system performance of equal relay power, because the serving nodes are considered in same layer of wireless network. But in heterogeneous networks, especially in HHWN system, the powers of relay to UE nodes are usually different, since UE nodes are in different layer of HHWN, as mentioned above. So the main contribution of this paper is that we propose the unequal transmitting power structure in HHWN system and derive the expression of outage probability in this structure. We also apply our expression to the system level simulation to research system performance of future heterogeneous networks with unequal relay powers to each UE nodes.

With the fast growing of mobile terminals, the traffic of the mobile data communication is growing extremely fast, which is becoming one of the challenges of the network capacity and transport rate of the community network. The traditional cellular network will be incapable to address these problems effectively. Massive MIMO is believed to be a significant approach of meeting the massive growth in data traffic. However, the growing number of antennas brings hardware cost dramatically, especially the overhead of radio frequency (RF) links. There are many researchers focus on the analog beamforming technique to decrease the RF resources [1–3]. These techniques need extra computational cost at both transceiver sides. Heterogeneous Hierarchical wireless Networks is also considered as an important architecture candidate to meet demands of wireless networks in the future due to the scarcity of RF resources [1].

Figure 8. Spectral efficiency of HHWN with MMR as different relay power pr2 equals

9/10,1/2,1/3,1/4,1/5 times pr1

Fig.8 depicts the system spectral efficiency (SE) with different power ratios. The solid, dashed, triangle, rhombus, square and star lines indicate SE of pr2 = l ∗ pr1, l = 1, 9/10, 1/2, 1/3, 1/4, 1/5, respectively. As is shown in figure, the base line is pr2 = pr1 and the other SEs of HHWN system decreases when the power gap grows. When SE is more than 4bits/s/Hz, the gap between pr2 = pr1 and pr2 = 0.25 ∗ pr1 reaches 3dB. Consequently, in order to avoid 3dB loss of SE, the power ratio should be higher than 0.25.

The increase of the low power base stations may result in the inconvenience since a lot of base stations are equipped in a certain area. There may even appear the complex situation that multi-BSs (picocell, femtocell) and multi-HotPoints (wireless router, WiFi relay) coexist, especially at the edge of macrocell. To solve the aforementioned problems, we unify two or more kinds of BSs to one single equipment. It makes us consider that the emission powers of different kinds of BSs are different. Accordingly, we provide an equipment that can produce different powers to cater to different level of HHWN. Multi-Mode Relay: MMR, in brief, has different mode of emission powers, which is out of ordinary relay in present. We may consider that the base station in picocell and femtocell, which locates at the edge of macrocell, could be represented as relays, as is shown in Fig. 1. Because of the different transmission power in the base stations of different layers, the relay must use more than two modes if it wants to integrate the picocell station and the femtocell station. In other words, the relay is not only picocell BS, but also femtocell BS. Consequently, the different coverage area of the cell served by MMR leads to the different transmitting power required. Then unequal relay power problems extremely need to be studied.

Literature [12] indicated the system performance of equal relay power, because the serving nodes are considered in same layer of wireless network. But in heterogeneous networks, especially in HHWN system, the powers of relay to UE nodes are usually different, since UE nodes are in different layer of HHWN, as mentioned above. So the main contribution of this paper is that we propose the unequal transmitting power structure in HHWN system and derive the expression of outage probability in this structure. We also apply our expression to the system level simulation to research system performance of future heterogeneous networks with unequal relay powers to each UE nodes.

5G Network architecture is a perfect example of future heterogeneous hierarchical wireless networks to guarantee the users’ reliability and integrity [5]. Usually 5G heterogeneous network manages all sorts of networks by using Software Defined Virtual Intelligent Network System. Network function visualization (NFV) represents a significant transformation for telecommunications/service provider networks, driven by the goals of reducing cost, increasing flexibility, and providing personalized services. Software-defined network(SDN) is suggested to control, initialize, manage, and change network behaviour automatically by open interfaces and abstraction of lower-level functionality pro grammatically.

Figure 8. Spectral efficiency of HHWN with MMR as different relay power pr2 equals

9/10,1/2,1/3,1/4,1/5 times pr1

Fig.8 depicts the system spectral efficiency (SE) with different power ratios. The solid, dashed, triangle, rhombus, square and star lines indicate SE of pr2 = l ∗ pr1, l = 1, 9/10, 1/2, 1/3, 1/4, 1/5, respectively. As is shown in figure, the base line is pr2 = pr1 and the other SEs of HHWN system decreases when the power gap grows. When SE is more than 4bits/s/Hz, the gap between pr2 = pr1 and pr2 = 0.25 ∗ pr1 reaches 3dB. Consequently, in order to avoid 3dB loss of SE, the power ratio should be higher than 0.25.

In order to improve the ability of the HHWN, amounts of studies have been done. In [2] the Hybrid Grid Routing Protocol (HGRP) is used to take on the lower cost advantages of routing and energy consumption. To cope with the handover management and co-channel interference, by combining cloud ratio access network with small cells, a novel network architecture is proposed in [3]. Applying an effective CoMP clustering scheme to mitigate cell edge users0 interference. To save system energy, literature [4] showed an energy-efficient approach, and the utilization of heterogeneous aware enhanced hierarchical clustered (HEHC) can obtain better energy availability. To handle the problem of cross-tier interference in the spectrum-sharing deployment, Zhang et al. gave a resource allocation scheme[5], set up a model for the sub-channel and power allocation , and presented an iterative sub-channel and power allocation algorithm. In order to cope with the problem of severe inter-cell interference when we increase the wireless network capacity, literature [6] investigated the coexistence problems of sharing the unlicensed spectrum between WiFi and 4G cellular networks and proposed an new scheme to avoid interference based on estimating the density of WiFi access points nearby small cells. To improve the system reliability, literature [7] indicated that resource management unit can be introduced into HHWN to implement the distributed grids, then proposed a semi centralized hierarchical architecture to balance the load of HHWN.