Week #05 Heterogeneous Networks

1. 教育部行動寬頻尖端技術人才培育計畫-小細胞基站聯盟中心教育部行動寬頻尖端技術人才培育計畫-小細胞基站聯盟中心 示範課程：行動寬頻網路之異質性存取 Week #05Heterogeneous Networks 助理教授：吳俊興 助教：王瑞元 國立高雄大學 資訊工程學系

2. Outline • Motivation • Introduction to Heterogeneous Networks - Heterogeneous Network Deployments - Features of Heterogeneous Networks - Evolution of Cellular Technology and Standards - Future Trends in Heterogeneous Networks • Future Trends in Heterogeneous Networks - Small Cells and Cloud RAN - Small Cells, Millimeter Wave Communications and Massive MIMO - Small Cells and Big Data Reference: Joydeep Acharya, Long Gao, and Sudhanshu Gaur, Heterogeneous Networks in LTE-Advanced, John Wiley & Sons, Ltd, 2014

3. Motivation • Challenge: increasing number of • Mobile broadband data subscribers, and • Bandwidth-intensive services Competing for limited radio resources • Operatorshave met this challenge by • Increasing capacity with new radio spectrum • Adding multi-antenna techniques • Implementing more efficient modulation and coding schemes

4. Expand a Homogeneous Network • These measures alone are insufficient in the most crowded environments and at cell edges • Adding small cells and tightly-integrating these with their macro networks to spread traffic loads • Widely maintain performance and service quality while reusing spectrum most efficiently • Add more sectors per eNB or deploying more macro-eNBs • Maintaining it as a homogeneous network

5. Toward a Heterogeneous Network Finding new macro-sites becomes increasingly difficult and can be expensive • Introduce small cells through the addition of low-power base stations (eNBs, HeNBs or Relay Nodes (RNs)) or Remote Radio Heads (RRH) to existing macro-eNBs • Added to increase capacityin hot spots with high user demand and to fill in areas not covered by the macro network – both outdoors and indoors • They also improve network performance and service quality by offloading from the large macro-cells • The result is a heterogeneous network with large macro-cells in combination with small cells providing increased bitrates per unit area

6. A Heterogeneous Networkwith Large and Small Cells Large cell • High-power eNB • Macro-eNB site can be difficult to find Small cell • Low-power base station or RRH • Off load for large cell • Small site size • Indoor coverage • Hot-spot coverage • Coverage at cell edge of large cell • Coverage in area not covered by the macro-network In heterogeneous networks the cells of different sizes are referred to as macro-, micro-, pico- and femto-cells; listed in order of decreasing base station power

7. History of Heterogeneous Network Planning • Already used in GSM • Separated through the use of different frequencies • LTE networks mainly use a frequency reuse of one to maximize utilization of the licensed bandwidth • The actual cell size depends not only on the eNB power but also on antenna position, as well as the location environment; e.g. rural or city, indoor or outdoor • LTE Standardization • HeNB (Home eNB) introduced in LTE Release 9 (R9) (March 2010) • Introduces the complete integration of the Femtocell concept (Home eNodeB) • eICIC and Relay Node (RN) in LTE R10 (LTE-Advanced, June 2011) • feICIC, LTE-CA, CoMP in LTE R11 (March 2013) • LTE-CA/Small cell enhancements in LTE R12 (March 2015) • Small cell dual-connectivity and architecture in LTE R13 (March 2016)

8. HeNB (Home eNB) in LTE Release 9 • The HeNB (Home eNB) was introduced in LTE R9 • It is a low power eNB which is mainly used to provide indoor coverage, femto-cells, for Closed Subscriber Groups (CSG), for example, in office premises • They are privately owned and deployed without coordination with the macro-network • There is a risk of interference between the femto-cell and the surrounding network if • The frequency used in the femto-cell is the same as the frequency used in the macro-cells • And the femto-cell is only used for CSG

9. Relay Node (RN) in LTE Rlease 10 • Roles or a Relay Node (RN) • From the UE perspective the RN will act as an eNB, and • from the DeNB’s view the RN will be seen as a UE. • The RN is connected to a Donor eNB (DeNB) via the Un radio interface, which is based on the LTE Uuinterface • RRHs connected to an eNB via fibre can be used to provide small cell coverage • When the frequencies used on Uu and Un for the RN are the same, there is a risk of self interference in the RN

10. HeNB (R9) and RN (R10)

11. Cell Selection Under Mixed Cells • In a network with a frequency reuse of one, the UE normally camps on the cell with the strongest received DL signal (SSDL) • Hence the border between two cells is located at the point where SSDL is the same in both cells (SSDLsmall < SSDLmacro in the grey area) • In a heterogeneous network, with high-power nodes in the large cells and low-power nodes in the small cells, the point of equal SSDL will not necessarily be the same as that of equal path loss for the UL (PLUL)

12. Cell Range Extension (CRE) • Cell Range Extension (CRE) • To increase the area served by the small cell, through the use of a positive cell selection offset to the SSDLof the small cell • To ensure that the small cells actually serve enough users • Negative effect: increased interference on the DL experienced by the UE located in the CRE region and served by the base station in the small cell • Especially the reception of the DL control channels in particular

13. Outline • Motivation • Introduction to Heterogeneous Networks - Heterogeneous Network Deployments - Features of Heterogeneous Networks - Evolution of Cellular Technology and Standards - Future Trends in Heterogeneous Networks • Future Trends in Heterogeneous Networks - Small Cells and Cloud RAN - Small Cells, Millimeter Wave Communications and Massive MIMO - Small Cells and Big Data

14. Introduction • Rapid proliferation in mobile broadband data • Strategy Analytics* estimates that • Mobile data traffic grew by 100% in 2012 • The data traffic is expected to increase by about 400% by 2017 • The major contributors to the traffic are bandwidth-intensive real-time applications such as mobile gaming and video Growth forecast in annual mobile data traffic *Reference: Strategy Analytics (2013) Handset data traffic (2001–2017), June 2013. Strategy Analytics

15. Challenges to Operators • Challenges • Increasing data traffic: network capability using traditional macrocell-based deployments is growing at about 30% less than the demand for data • Decreasing profit margins: the profit margins of most operators have also been decreasing globally • The flat rate pricing policies prevent the mobile data revenues of an operator to scale proportionately with the increased usage of mobile broadband data • The cost incurred as a result of setting up more base stations to provide increased capacity and coverage • Rethink methods of operating their networks • Key principle: deliver higher capacity at a reduced cost

16. Ways to Increase Capacity • A 1000× increase in capacity is required to support rising demand in 2020* • High capacity can be achieved by • Improving spectral efficiency • Employing more spectrum • Increasing network density • The major gains are expected throughincreasing network density by deployingan overlay network of small cellsover the macro coverage area Related to link level enhancements(but already at near optimal) *Reference: Mallinson, K. (2012) The 2020 vision for LTE. Available at http://www.3gpp.org/2020-vision-for-LTE (accessed November 2013)

17. Towards Heterogeneous Networks • A small cell could be • An indoor femtocell or an outdoor picocell • A compact base station ora distributed antenna system (DAS)controlled by a central controller • The different types of small cells • have low transmit power and coverage • and together with the macro cells are referred to asHeterogeneous Networksor simply HetNets small cell Macro cell HetNet: a wireless network comprised of different types of base stations and wireless technologies, including macro base stations, small cells, distributed antenna systems (DAS), and even Wi-Fi access points

18. Licensed Small Cells Source: http://electronicdesign.com/engineering-essentials/understanding-small-cell-and-hetnet-movement

19. Benefits of Heterogeneous Networks • Improve capacity • Mobile broadband data is highly localized as the majority of current traffic is generated indoors and in hotspots such as malls and convention centers • Add capacity where it is needed by deploying an overlay of small cells in those regions of the macro coverage area which generates heavy data demand • Small cells offload data from the macro coverage area and improve frequency reuse • They can offer higher capacity than the macro as they can better adapt to the spatio-temporal variations in traffic by dynamic interference management techniques • Reduce cost • A small cell-based heterogeneous network is much more energy efficient than a macrocellnetwork • A macrocell needs high transmit power which requires a cooling unit • A low transmit power of the small cell reduces power consumption (by 25–30%*) • Incorporating small cells into the network can save service providers 12–53% in CAPEX and 5–10% in OPEX, depending on traffic loading (Bell Labs study)

20. Heterogeneous Network Deployments There are many different kinds of small cells which results in different kinds of heterogeneous networks: each has unique deployment, coverage, and capacity characteristics • Distributed Antenna Systems (DAS) • Consisting of a network of DAS nodesthat are connected via fiber toa central processing unit • Public Access Picocells/Metrocells • Open to all members of the public • Covering a smaller area and are specificto a particular wireless access technology • Consumer-Grade Femtocells • Small stand-alone low-power nodes thatare typically installed indoors • WiFi Systems • Operated in the unlicensed band • Integrated with an existing cellular network by offloading some of its load Single Antenna Distributed Antenna Systems

21. Features of Heterogeneous Networks • Association and Load Balancing • One of the main functions is to offload UEtraffic from the macro • Downlink reference signal received power (RSRP) is the most basic criterion but this does not lead to much offloading • Since the transmit power of a macrocell is much greater than that of the small cell • The macrocell and the picocell can operate at different carrier frequencies • Reference signal received quality (RSRQ) leads to better load balancing • Load balancing will distribute UEload across all base stations uniformly • Interference Management • The dense deployment of small cells increases interference • System performance will degrade if intercellinterference is not managed properly • Various techniques proposed • Frequency-domain (R8): two neighboring cells can coordinate their data transmission and interference in frequency domain • Time-domain (R10, R11): a cell can mute some subframes to reduce its interference to its neighboring cell • R12 • Dynamic activation/deactivation • Full-dimension (FD) MIMO • CoMP: a macrocelland a small cell can cooperate to simultaneously serve a UE

22. Features of Heterogeneous Networks (cont.) • Self-Organizing Networks • Base stations (notably the small cells) can sense their environment, coordinate with other base stations and automatically configure their parameters such as cell ID, automatic power control gains, and so on • SONs are therefore critical to small cell deployments • A SON optimizes network parameters for controlling interference • Manages the traffic load among different cells and different radio access networks • Provides the user with the best possible service • Mobility Management • Using the same set of handover parameters for all cells/UEs may degrade the mobility performance in a heterogeneous network • Desirable to have a cell-specific handover offset for different classes of small cells • For high-mobility UEs passing through a dense heterogeneous network, the normal handover process between small cells will lead to very frequent changes in the serving cell • solved by associating this UE to the macrocell at all times, leading to UE-specific handover parameter optimization

23. Evolution of Cellular Technology and Standards • 1G: Analog systems • 2G: Hybrid FDMA and TDMA • 3G: CDMA (IMT-2000 / 3GPP LTE R8) • 4G: OFDMAand flat all-IP • IMT-Advanced • 3GPP2 LTE-Advanced (LTE-A) R10 • IEEE 802.16m • 5G • IMT-2020 • 3GPPLTE-Advanced Pro LTE Release 11 introduced coordination among different base stations of a HetNet

24. Performance Requirements ofVarious 3GPPReleases • Influenced by guidelines of International Telecommunications Union (ITU) • International Mobile Telecommunication (IMT) requirements

25. UE Categories • http://www.3gpp.org/keywords-acronyms/1612-ue-category • 3GPPTS36.306, E-UTRA; UE radio access capabilitieshttp://www.3gpp.org/DynaReport/36306.htm

26. 3GPP Standardization Process

27. 3GPP UMTS/LTE Specification Releases

28. 3GPP UMTS/LTE Specification Series The most useful TSs:TS 23.401 (EPC) andTS 36.300 (Air Interface) http://www.3gpp.org/specifications/specification-numbering

29. Outline • Motivation • Introduction to Heterogeneous Networks - Heterogeneous Network Deployments - Features of Heterogeneous Networks - Evolution of Cellular Technology and Standards - Future Trends in Heterogeneous Networks • Future Trends in Heterogeneous Networks - Small Cells and Cloud RAN - Small Cells, Millimeter Wave Communications and Massive MIMO - Small Cells and Big Data

30. Small Cells and Cloud RAN • A distributed deployment has the following limitations • The cost of deploying an eNodeB is high mainly due to its support facilities • The interference between two neighboring eNodeBs in the same frequency is difficult to coordinate in the case of non-ideal backhaul • The average utilization of the signal processing unit at each eNodeB is low due to the spatio-temporal variations in traffic • The eNodeB is designed to satisfy the peak rate requirements and is therefore under-utilized most of the times

31. Small Cells, Millimeter Wave Communications and Massive MIMO • The International Telecommunication Union (ITU) • Allocate new spectra for cellular networks in 2015 • At least 1000MHz will be assigned by 2020 in the frequency bands 1.5 GHz, 3.3–3.6 GHz, and above 5 GHz • Transmission over high frequencies • millimeter wave communications dueto the resulting smallwavelengths

32. Small Cells and Big Data • Big Data analytics is one of the new and challenging topics in information technology • Incomplete, noisy, and data mining has to be performed ina distributed and dynamic fashion to take decisions • C-RAN systems are implemented, a huge amount of signal processing and storageis required at the multiple nodes that virtualize the RAN

33. Summary • Background to heterogeneous networks • Trends of mobile broadband data • Challenges to operators and ways to increase capacity • Deployments and features of heterogeneous networks • Evolution of Cellular Technology and Standards • 3GPP Standardization Process • Heterogeneous networks have led to massive improvements in the quality of service offered to the customers of a wireless network • a continuous stream of innovations have taken place that encompass fundamental technological research with new business models • The future holds the key to more exciting technological developments, some of which will be adopted in practical systems with relative ease and improve network performance

34. References • [1] 3GPP (2010) Evolved Universal Terrestrial Radio Access (E-UTRA); Carrier-Based HetNet ICIC Use Cases and Solutions 3GPP TR 03.024 v0.3.0. Third Generation Partnership Project, Technical Report, May 2010. • [2] Ye, S., Wong, S.H., and Worrall, C. (2013) Enhanced physical downlink control channel in LTE Advanced Release 11. IEEE Communications Magazine, 51(2), 82–89. • [3] 3GPP (2012) Evolved Universal Terrestrial Radio Access (E-UTRA), Physical channels and modulation • 3GPP TS 36.211 v11.0.0. Third Generation Partnership Project, Technical Report, September 2012. • [4] 3GPP (2012) Evolved Universal Terrestrial Radio Access (E-UTRA), Multiplexing and channel coding 3GPP TS 36.212 v11.0.0. Third Generation Partnership Project, Technical Report, September 2012. • [5] 3GPP (2012) Evolved Universal Terrestrial Radio Access (E-UTRA), Physical layer procedures 3GPP TS 36.213 v11.0.0. Third Generation Partnership Project, Technical Report, September 2012. • [6] Ericsson (2012) Rp-122028, New Carrier Type for LTE. Ericsson, Technical Report, December 2012. • [7] Huawei, HiSilicon (2013) R1-133817, Performance Evaluations of S-NCT vs. BCT. Huawei, Technical Report, August 2013.