Download Heterogeneous Networks - 教育部行動寬頻尖端技術跨校教學聯盟

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 #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
Outline
1. Motivation
2. Introduction to Heterogeneous Networks
- Heterogeneous Network Deployments
- Features of Heterogeneous Networks
- Evolution of Cellular Technology and Standards
- Future Trends in Heterogeneous Networks
3. 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
2
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
3
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
4
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
5
A Heterogeneous Network
with Large and Small Cells
Small cell
• Low-power base station or RRH
• Off load for large cell
• Small site size
• Indoor coverage
• Hot-spot coverage
Large cell
• High-power eNB
• Macro-eNB site can
be difficult to find
• 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
6
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)
7
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
8
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
9
HeNB (R9) and RN (R10)
10
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)
11
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 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
12
Outline
1. Motivation
2. Introduction to Heterogeneous Networks
- Heterogeneous Network Deployments
- Features of Heterogeneous Networks
- Evolution of Cellular Technology and Standards
- Future Trends in Heterogeneous Networks
3. Future Trends in Heterogeneous Networks
- Small Cells and Cloud RAN
- Small Cells, Millimeter Wave Communications and Massive MIMO
- Small Cells and Big Data
13
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
14
Challenges to Operators
• Challenges
– Increasing data traffic: network capability using traditional macrocellbased 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
15
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
Related to link level enhancements
(but already at near optimal)
• The major gains are expected through
increasing network density by deploying
an overlay network of small cells
over the macro coverage area
*Reference:
Mallinson, K. (2012) The 2020 vision for LTE. Available at
http://www.3gpp.org/2020-vision-for-LTE (accessed November 2013)
16
Towards Heterogeneous Networks
• A small cell could be
– An indoor femtocell or an outdoor picocell
– A compact base station or
small cell
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
Macro cell
or simply HetNets
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 17
Licensed Small Cells
Source: http://electronicdesign.com/engineering-essentials/understanding-small-cell-and-hetnet-movement
18
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 spatiotemporal 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)
19
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
Single Antenna
• 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
Distributed Antenna Systems
• WiFi Systems
– Operated in the unlicensed band
– Integrated with an existing cellular network by offloading some of its load
20
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
21
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
22
Evolution of Cellular Technology and
Standards
• 1G: Analog systems
• 2G: Hybrid FDMA
and TDMA
• 3G: CDMA
(IMT-2000
/ 3GPP LTE R8)
• 4G: OFDMA and flat all-IP
– IMT-Advanced
– 3GPP2 LTE-Advanced (LTE-A) R10
– IEEE 802.16m
• 5G
– IMT-2020
– 3GPP LTE-Advanced Pro
LTE Release 11 introduced coordination among different base stations of a HetNet
23
Performance Requirements of
Various 3GPP Releases
• Influenced by guidelines of International Telecommunications Union (ITU)
– International Mobile Telecommunication (IMT) requirements
24
UE Categories
• http://www.3gpp.org/keywords-acronyms/1612-ue-category
• 3GPP TS 36.306, E-UTRA; UE radio access capabilities
http://www.3gpp.org/DynaReport/36306.htm
25
3GPP Standardization Process
26
3GPP UMTS/LTE Specification Releases
Release
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
Enhancements to LTE-Advanced
R13
Mar 2016
R14
(Sep 2014-Jun 2017)
R15
(Jun 2016-Sep 2018)
Pre-5G (LTE-Advanced Pro)
27
3GPP UMTS/LTE Specification Series
Series
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
Scope
High-level requirements
Stage 1 service specifications (user’s point of view)
Stage 2 service and architecture specifications (system’s high-level operation)
Signaling protocols - Non-access stratum protocols (UE to network)
WCDMA and TD-SCDMA air interfaces and radio access network
Codecs
Data terminal equipment
Signaling protocols - Tandem free operation of speech codecs
Signaling protocols - Core network protocols
Programme management
UICC and USIM
Operations, administration, maintenance, provisioning and charging
Security
UE test specifications
Security algorithms
The most useful TSs:
TS 23.401 (EPC) and
LTE air interface and radio access network
TS 36.300 (Air Interface)
Multiple radio access technologies
Radio technology beyond LTE
http://www.3gpp.org/specifications/specification-numbering
28
Outline
1. Motivation
2. Introduction to Heterogeneous Networks
- Heterogeneous Network Deployments
- Features of Heterogeneous Networks
- Evolution of Cellular Technology and Standards
- Future Trends in Heterogeneous Networks
3. Future Trends in Heterogeneous Networks
- Small Cells and Cloud RAN
- Small Cells, Millimeter Wave Communications and Massive MIMO
- Small Cells and Big Data
29
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
30
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
31
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
32
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
33
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.
34