1. Week #05 Heterogeneous Networks
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Week #05 Heterogeneous 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
Operators have 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 capacity in 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 Network with Large and Small Cells
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
Large cell
High-power eNB
Macro-eNB site can be difficult to find
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 Uu interface
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)
To increase the area served by the small cell, through the use of a positive cell selection offset to the SSDL of 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 Strategy Analytics

15. Challenges to Operators
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 through increasing network density by deploying an overlay network of small cells over 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 (accessed November 2013)

17. Towards Heterogeneous Networks
A small cell could be
An indoor femtocell or an outdoor picocell
A compact base station or a 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 as Heterogeneous Networks or 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:

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 macrocell network
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 nodes that are connected via fiber to a central processing unit
Public Access Picocells/Metrocells
Open to all members of the public
Covering a smaller area and are specific to a particular wireless access technology
Consumer-Grade Femtocells
Small stand-alone low-power nodes that are 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 UE traffic 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 UE load across all base stations uniformly
Interference Management
The dense deployment of small cells increases interference
System performance will degrade if intercell interference 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 macrocell and 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 / 3GPP LTE R8)
4G: OFDMA and flat all-IP
IMT-Advanced
3GPP2 LTE-Advanced (LTE-A) R10
IEEE m 5G
IMT-2020
3GPP LTE-Advanced Pro
LTE Release 11 introduced coordination among different base stations of a HetNet

24. Performance Requirements of Various 3GPP Releases
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
3GPP TS , E-UTRA; UE radio access capabilities

26. 3GPP Standardization Process

27. 3GPP UMTS/LTE Specification Releases
Date Frozen
New Features
R99
Mar 2000
WCDMA air interface R4
Mar 2001
TD-SCDMA air interface R5
Jun 2002
HSDPA, IP multimedia subsystem R6
Mar 2005
HSUPA R7
Dec 2007
Enhancements to HSPA R8
Dec 2008
LTE, SAE R9
Dec 2009
Enhancements to LTE and SAE
R10
Jun 2011
LTE-Advanced (4G)
R11
Jun 2013
Enhancements to LTE-Advanced
R12
Mar 2015
R13
Mar 2016
R14
(Sep 2014-Jun 2017)
R15
(Jun 2016-Sep 2018)
Pre-5G (LTE-Advanced Pro)

28. 3GPP UMTS/LTE Specification Series
Scope 21
High-level requirements 22
Stage 1 service specifications (user’s point of view) 23
Stage 2 service and architecture specifications (system’s high-level operation) 24
Signaling protocols - Non-access stratum protocols (UE to network) 25
WCDMA and TD-SCDMA air interfaces and radio access network 26
Codecs 27
Data terminal equipment 28
Signaling protocols - Tandem free operation of speech codecs 29
Signaling protocols - Core network protocols 30
Programme management 31
UICC and USIM 32
Operations, administration, maintenance, provisioning and charging 33
Security 34
UE test specifications 35
Security algorithms 36
LTE air interface and radio access network 37
Multiple radio access technologies 38
Radio technology beyond LTE
The most useful TSs: TS (EPC) and TS (Air Interface)

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 due to 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 in a distributed and dynamic fashion to take decisions
C-RAN systems are implemented, a huge amount of signal processing and storage is 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 v 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 v Third Generation Partnership Project, Technical Report, September 2012.
[4] 3GPP (2012) Evolved Universal Terrestrial Radio Access (E-UTRA), Multiplexing and channel coding 3GPP TS v Third Generation Partnership Project, Technical Report, September 2012.
[5] 3GPP (2012) Evolved Universal Terrestrial Radio Access (E-UTRA), Physical layer procedures 3GPP TS v Third Generation Partnership Project, Technical Report, September 2012.
[6] Ericsson (2012) Rp , New Carrier Type for LTE. Ericsson, Technical Report, December 2012.
[7] Huawei, HiSilicon (2013) R , Performance Evaluations of S-NCT vs. BCT. Huawei, Technical Report, August 2013.