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5 - Dense networks of small cells
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- By Jialing Liu, Huawei R&D, Weimin Xiao, Huawei R&D, Anthony C. K. Soong, Huawei R&D
- Edited by Alagan Anpalagan, Ryerson Polytechnic University, Toronto, Mehdi Bennis, University of Oulu, Finland, Rath Vannithamby
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- Book:
- Design and Deployment of Small Cell Networks
- Published online:
- 05 December 2015
- Print publication:
- 17 December 2015, pp 96-121
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- Chapter
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Summary
Introduction
During the last few years, wireless data traffic has skyrocketed, driven mainly by a large penetration of smart phones and devices. In 2013, an exabyte of data traveled across the global mobile network monthly [1]. By 2020, data traffic served by such networks is expected to increase by up to a factor of 100, including traffic generated by the widespread adoption of device–device (D2D) and the Internet of Things (IoT) connected via machine–machine (M2M) communications. It is widely recognized that this general trend toward more explosive growth may accelerate even further in future, and how to meet such a demand has been one of the most active and rapidly growing areas in the wireless communication community in the past decade in terms of both academic and industrial research and development [2].
Facing the unprecedented challenge, the wireless communication community has considered many candidate solutions. A significant portion of these are focused on increasing the communication resources, e.g., deploying more network nodes, which leads to densification of existing networks, utilizing wider bandwidth, increasing antenna numbers, and employing additional resources to offload. Among them, the dense network approach stands out for its high scalability of providing magnitudes of capacity increase. Extensive research has been devoted to dense networks (see e.g., [3–8] and references therein).
Indeed, commercial wireless networks are already becoming denser and dense-network deployment will be a critical factor (together with other solutions) to meet the ever-increasing traffic demand. The trends for traffic and network-density growth over a 20-year span are illustrated in Figure 5.1.
In Figure 5.1, the network densities for the years 2000 to 2015 were estimated from 3GPP publications (e.g., [3, 9], etc.), whereas the network density for year 2020 is a projection based on historic data and recent trends. In more detail, around year 2000, sparse 3G network deployments of macro base stations covered wide areas with typical cell radii of several kilometers. Starting from around 2005, the network density increased to about 10 to 20 nodes/km2 and cell radii shrunk to between one kilometer and several hundreds of meters, according to the study in 3GPP LTE Rel-8/9; however, macro eNBs (evolved NodeB, also known as base stations, BS, BTS, etc.) were still the main focus.
4 - 3GPP RAN standards for small cells
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- By Weimin Xiao, Huawei R&D, Jialing Liu, Huawei R&D, Anthony C. K. Soong, Huawei R&D
- Edited by Alagan Anpalagan, Ryerson Polytechnic University, Toronto, Mehdi Bennis, University of Oulu, Finland, Rath Vannithamby
-
- Book:
- Design and Deployment of Small Cell Networks
- Published online:
- 05 December 2015
- Print publication:
- 17 December 2015, pp 75-95
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- Chapter
- Export citation
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Summary
Introduction
The so-called Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) and its evolved version, LTE-Advanced, is currently the most prominent and advanced mobile communication system. When it was designed and standardized, starting in 2004 and first released in 2008 as Release 8, it was targeted mainly for macro base station networks with uniform, well-planned and deployed high-power nodes where coverage, mobility, and the provision of high throughput across large areas are at the heart of its requirements. As a consequence, small cell (or low-power node) deployments together with high-power macro base stations were not considered for the original designs. The specific issues with the introduction of small cells in the system therefore cannot be addressed sufficiently without additional features to deal with interference, mobility, traffic load management, etc., related to such deployments.
The major problems from deploying small cells, especially together with macro base stations, include:
More severe interference conditions. Although interference is always a key issue for cellular communication and handling interference is built into the core of LTE designs, coexistence of network nodes of different power levels, especially in the co-channel scenario where the same frequency channel (known as the component carrier) is used for both macro base station cells and small cells, results in much worse interference condition than before. The LTE system generally has a very robust physical layer design to ensure that each physical channel can be reliably received at fairly low signal to interference-plus-noise ratio (SINR) range. However, in order to fully utilize the potential of small cells to offload traffic, small cells sometimes need to serve users at even lower SINR, which requires a mechanism to either avoid or cope with strong interference.
Mobility management and traffic load balancing. The introduction of small cells with low transmission power basically creates cells with a small footprint within the system, which increases the frequency of handovers between cells due to user mobility. This then results in dramatically larger handover failure as well as associated backhaul signaling. Furthermore, also because of much smaller coverage area, the traffic loads between the cells are more likely to be unbalanced and time-varying, and a more efficient load-balancing and shifting mechanism is needed.