FEMTOCELL WITH RELAYS TO ENHANCE THE MACROCELL BACKHAUL BANDWIDTH

Transcription

1 FEMTOCELL WITH RELAYS TO ENHANCE THE MACROCELL BACKHAUL BANDWIDTH, Abstract In the future of Mobile networks it is important to implement a Femtocell at homes and to improve the domestic network. Even though a lot of work has been done in studying the optimization of domestic Femtocell, much more problems needs to be studied. With a huge growth in the mobile phone market and the increase in the wireless network technology, it has become very important to provide a reliable connection to the mobile smart phones. With the increase in the number of users of smart phones consumer have started downsizing the number of personal computers at home. But this is not possible due to various factors. Consumers want great voice quality, reliable service, and low prices. But today s networks provide poor indoor coverage and High pricing. In fact, with the continuous development in the internet offerings such as Skype and Imo, wireless operators are at a serious disadvantage in the home. Hence, the mobile operators are trying to enhance their coverage by deploying Femtocell base stations. These miniature base stations are the size of a DSL router or cable modem and provide indoor wireless coverage to mobile phones using existing broadband Internet connections. Keywords: Backhaul, Femtocell, Femto-relay, Interference, Macrocell I. INTRODUCTION Recent studies show that 50 percent of all voice calls and 70 percent of all data traffic originates indoors and this ratio is likely to only increase [1]. For this reason the research on the Femtocell has increased. The Femtocell is a low-power, low-cost data access point capable of providing high quality, high-speed voice and data services with coverage of tens of meters, and is mainly used for indoor environment. It communicates with the cellular network over a broadband connection such as a digital consumer line (DSL) or a cable modem. Fig 1 Basic Femtocell operation 382 P a g e

2 The Femtocell has numerous advantages like Low cost and low power consumption. The Femtocells are small in size and are compatible with standards such as EVDO, UMB and LTE standards. The Femtocell is connected via the internet protocol (IP) and flat base station architecture and is connected to the operator network via a broadband network. The Femtocell provides an increased indoor coverage with coverage of 40m-600m. unlike Macrocells which support hundreds of users the Femtocell will provide coverage to 5-7 users delivering higher data rates per user because of which there would be better voice quality and better Data and Multimedia experience. II.FEMTOCELL ARCHITECTURE As shown in the Figure 2 the Femtocell network architecture consists of three network elements a) Femtocell Access points (FAP), b) Security Gateway (SeGW), c) Femtocell Device Management System (FMS). The two other elements help in the connectivity to the mobile operator core. According t the Architecture there can be a Femtocell Convergence Server (FCS) or a Femtocell Network Gateway (FNG) Fig 2 Femtocell Network Architecture The Femtocell Access Point (FAP) is present in the home or office. The FAP acts as the base station and base station controller and connects to the operator network over a secure tunnel via the internet. A FAP can be introduced in home in several ways, One way is the standalone method in which it is directly connected to the home router in some cases the FAP s are a complete package consisting of built-in WI-FI and a broadband modem. The Security Gateway (SeGW) is a network node and secures the internet connection between the Femtocell user and the Mobile operator core network. The SeGW uses standard internet protocols for its operation. The SeGW connects a large number of Femtocells to the Mobile Operator Core network. The Femtocell Device Management System is present in the Operator core network; it plays an important role in the operational management and activation of Femtocells using industrial standards. This is a very important node in ensuring the scalability of a Femtocell network to hundreds of devices. The FSM consists of two important elements. The Device Manager Application and the Automatic Network Planner Application. 383 P a g e

3 The FCS or FNG enables the Femtocells to connect to the Operator Core Network. This is important as it allows the Femtocells to communicate with the core elements in the operator s Network and ensures continuous connectivity for the Mobile Phones. The PDSN/xGSN allows Femtocell users to receive packet data services over the operator s core, these are usually the same used by the operator s macro Network. III.INTERFERENCE PROBLEMS IN FEMTOCELL The Femtocell has the potential to make the mobile phones even more popular with improved connectivity, but there are still problems with the interferences between the Femtocell and the Macrocell and similar devices. The Femtocells are present independently of the cellular network. One of the suggested methods to tackle the interference in Femtocell is discussed in [2]. To find an answer to this problem the Small Cell Forum [3] has been used in conducting research for mitigating the problem of interference in Femtocells. As per the Small Cell Forum [3], the different types of interferences found in Femtocells are: 1) Femtocells Interfering with the Base Stations; 2) Base Stations Interfering with the Femtocells; 3) Interference between Femtocells; 4) Cell phone signals received by both Femtocell and Macrocell. The problems listed above all can cause for the degradation of the network and hence reducing the QoS. 3.1 Interference Mitigation Because the Femtocells are present independently and not connected to the network the interference suppression techniques will not prove to be reliable. One technique for Interference Mitigation has been suggested in [4]. This method helps in increasing the uplink capacity for a shared network in the same spectrum. A few more solutions are given in [3] and these are as follows. Directional Antennas which are present inside the Femtocell avoid interference by restricting radio interferences within an antenna sector. In Adaptive Power Control the Femtocell detects the signals from the other devices and then it adjusts its own transmission signal power while still maintain its coverage area. In Dynamic Receiver gain management an adaptive attenuation level is integrated in the Femtocell receiver to reduce its gain. For the maximum efficiency of the Femtocell in the presence of high-power mobile phones the Femtocell receiver must have a very high dynamic range. VI. BACKHAUL As shown in Figure 1, the Femtocell uses the Internet as a Backhaul to connect to the Femtocell Gateway and the core network. This Backhaul has many problems like limited Bandwidth. In the usual scenario the Internet Service Providers (ISPs) provide uneven bandwidth to the broadband users, with more Bandwidth available for downlink and less bandwidth for the uplink because of which the number of users of the Femtocell might be limited by the Uplink bandwidth. Therefore, to solve this issue the Femto-Relays can be used to Increase the Macrocell Backhaul bandwidth. 4.1 Femto-Relays The need to improve the indoor coverage has led to the development of the heterogeneous technologies. The wireless relaying has been introduced in the LTE networks so as to maintain fair QoS and uniform QoS because 384 P a g e

4 of the multi-hop transmissions. Femtocells and wireless relays seem to have various distinctiveness due to their different beginning but they target similar goals from a heterogeneous networks perspective. The grouping of the Femtocell and the Relay can be used to get the optimal solution. The Femto-Relay backhaul consist of both the Wired and the Wireless links and thus a combination of both of these is used and because of this no change in the equipments is required. The Femto-relays from the mobile terminal side appear to be a standard base station whereas the donor base station sees it as a mobile terminal. Fig 3 Femto-Relay 4.2 Femto-Relay to increase Macrocell Backhaul Bandwidth In a Base Station all the requests of the registered user are forwarded to the Femtocell whereas those of the Non- Registered users go to the Base station. The voice Packets travel in both directions. When a Base Station receives a request it makes the decision to use its own backhaul or the Backhaul of the Femtocell using the associated user as a relay. This decision is made based on the average utilization in the past α and the given utilization threshold. When α>, the Base station chooses a user who is related with a Femtocell as the relay and forwards the data request through it to the Femtocell and when α< the Base Station uses its own backhaul to serve any demand. The Base station maintains a list of users in a top to bottom manner of fairness index and is given as = (1) Where is the uplink rate to the Base Station and is the uplink data rate usage in recent past and i denotes the number of users [5]. Hence, the node with the highest fairness sits at the top of the list. The Base station chooses the relay from the list. V. CONCLUSION The Femtocell is a device which can help to solve the network problems and would help in increasing the QoS and Reliability of the network. In this paper we first discussed the Femtocell and the architecture of the Femtocell and also discussed the Interference problems and the interference mitigation techniques associated 385 P a g e

5 with the Femtocell. We then discussed the problems with the Femtocell Backhaul and solved it with the help of the Femto-Relay model to increase Macrocell Backhaul Bandwidth. VI.REFERENCES [1] Yizhe Li, Zhiyong Feng, Ding Xu, Qixun Zhang, Hui Tian.; Automated Optimal Configuring of Femtocell Base Stations' Parameters in Enterprise Femtocell Network in Proc IEEE Global Telecommunication Conference, 2011, pp [2]K. Han, Y. Choi, D. Kim, M. Na, S. Choi and K. Han, "Optimization of femtocell network configuration under interference constraints," th International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks, Seoul, 2009, pp [3] Small Cell Forum; Interference Management in UMTS Femtocells; 2008, available online at [4]Chandrasekhar V. and Andrews J.; Uplink Capacity & Interference Avoidance for Two-Tier Networks; Proceedings of IEEE Global Telecommunications Conference, Washington DC, USA; Pages [5] E. Dahlman, S. Parkvall, J. Skold, and P. Beming, 3G Evolution: HSPA and LTE for Mobile Broadband. AcademicPress, P a g e