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UofT Wireless Lab
Evolution of Public Wireless System Infrastructure: What Follows 4G?
Elvino S. SousaJeffrey Skoll Professor in
Computer Networks and InnovationUniversity of Toronto
Wireless Lab
Tokyo Wireless Summit 2014 - Waseda University, Japan, Mar 7, 2014 1
UofT Wireless Lab
Next Generation Mobile Networks
• Currently there is world-wide interest in defining 5G?• NGMN (operators group) will come up with white
paper by summer (operators vision in announcement in MWC - Barcelona.
• 3GPP – 5G will follow on LTE-Advanced• Typical with setting requirements for next generation
(“need 10x capacity of the previous generation”).• Qualcomm: pushing vision of 1000x capacity (small
cells)
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UofT Wireless Lab
The Highly Ambitious: Article from NGMN Site
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UofT Wireless Lab
Average Data Rates• 4G Americas white paper (Feb, 2014)
– 2011: 248 Kbps– 2012: 526 Kbps– 2017: 3.9 Mbps
• Smartphones & Tablets• 2012: 2 Mbps (smartphones), 3.7 Mbps
(tablets)• These are a lot more conservative
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Total Network Data CarriedAnother measure of network Capacity
4G Americas:“ ... Research firm Strategy Analytics predicts strong
growth in mobile phone data traffic, over 300 percent growth by 2017 to 21 exabytes up from 5 exabytes of data per year in 2012. Video and web traffic will drive this rise, with compound annual growth of 42 percent and 30 percent respectively”
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UofT Wireless Lab
Wireless Network Performance Metrics
• Peak data rates: They are too unrealistic, place all the emphasis on the modulation scheme.
• Total data carried by the network. Sum capacity is not a good metric for wireless, (reason for proportional-fair scheduling). A few links very close to BS can greatly skew results.
• Average Data Rate: Difficult to define. Too many cases
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UofT Wireless Lab
Cellular System Performance Goals
• Current Data Plans - A few GBytes per month – e.g. 2 GBytes
• Current Plans for fixed network access (Home) – A few 10s of Gbytes, e.g. 60 Gbytes
• Ratio = 30: 1 1 month : 1 day• Technologies have evolved but this ratio has remained
somewhat constant• Goal: User expects web access experience to be equal
for wireless and wireline. Make these two rates equal!
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UofT Wireless Lab
Past Emphasis on Peak Dates! (LTE -Advanced)
• With the assumption of 8x8 MIMO in DL peak spectral efficiencies can even be calculated at over 30 b/s/Hz, with corresponding data rate in 20 MHz = 600 Mbps!
• The main problem however is the existence of wireless channels with enough propagation modes and terminals of reasonable size to model credibly as 8x8 MIMO
• We can concoct a specialized set-up with 8x8 MIMO but then if it is a rare case why not use an optical link?
• There seems to be an impression that as technology improves we can go to higher orders of point to point MIMO, but this is of course not true. We are limited by physics!
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UofT Wireless Lab
Squeezing out more bits/s/Hz/cell
• Much higher order MIMO does not seem to be the answer with regular network architecture.
• Coordinated multi-point transmission will offer some improvement but not by large factor – may depend on cell positions.
• Most references to the capability of LTE-Advanced to meet future rate requirements refer to the peak data rate!
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UofT Wireless Lab
The currency for wireless system evaluation
• Peak rates (emphasized with LTE) => hyper-inflation!
• In the past it was common to set a target of 10x capacity for next generation systems
• Have seen at least one case where this goal is mentioned for Beyond 4G. But if LTE with carrier aggregation is 4x300 MBps = 1.2 Gbps, then 10x is 12 GBps! Is this realistic?
• We need a new currency for wireless system evaluation!
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Generations of Cellular System Technology
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Cellular Networks vs. Computing
Computers• Computer technology evolution was initially classified
according to generations• First four generations were clear and centered on
building a computer (1953 – 1982), i.e about 8 years per generation (vacuum tubes, transistors, LSI, VLSI)
• Fifth generation was introduced in 1982 (Japan) with great fanfare. Then it seems interest in this classification was lost. World changed in a major way with the introduction of PC and Internet.
• Can still refer to generations of technologies in computing, but not centered on one thing – the computer.
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UofT Wireless Lab
Cellular Systems• 1G, 2G, 3G, 4G, clear. 1 – Analog, 2 - digital
voice, 3 - voice plus variable data, 4 LTE-Advanced (Internet access). 1978 – 2012, or about 8 years per generation
• 5th generation? ... Not clear and we could also loose interest in calling it a generation.
• One difference: Terminology here is dictated by industry group.
• Currently we see the term “Beyond 4G”.
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UofT Wireless Lab
Current Cellular System Paradigm
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First Four Generations• Construct one product – the network.• Product components
– Licensed spectrum– Cell Sites for base stations– BS equipment– Cluster controllers (deleted with 4G)– Switches
• The network interacts with standard terminals.
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Regular Cellular Structure
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Re-use partitioning
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Coordinated Multi-Point
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MIMO
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Beamforming
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Relays (for Coverage)
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Receive Transmit
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Cooperative Relaying (Extensive Research)
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Path to the Future
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Cellular System: New Paradigm• Spectrum (licensed, unlicensed, other)• Infrastructure (cell site locations, access point
positions, right-of-way for fibre, existing cable/fibre, future deployments)
• Operator sharing framework (spectrum/infrastructure)
• Front-Haul/Back-Haul Framework• Base Stations/Access points/Remote Radio
Heads/Could Processors• Core Network
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UofT Wireless Lab
Country/Region Dependency• Solutions based on new paradigm may be country dependent
– Existing infrastructure: Cables, fibre, right-of-way– City characteristics– Construction characteristics– Rural characteristics– Regulatory environment (central/local governments)– Cultural aspects– Ease of organic growth
• North America, Central and South America, Africa, Japan/Korea, China, Southeast Asia, Middle East ..
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UofT Wireless Lab
Current Initiatives of NGMN• Cloud Ran (C-RAN)• Coordinated Multi-Point (CoMP)
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Cloud Ran (C-RAN)• Centralized/Cloud/Coordinated/Cooperative RAN• Proposed by China Mobile in 2009• Alternative implementation to RAN
– Conventional RAN referred to as Distributed RAN (D-RAN)
• China Mobile Research Institute, “C-RAN: The Road towards Green RAN (ver. 2.5)”, Oct., 2011.
• NGMN, “Suggestions on Potential Solutions to C-RAN”, 2012.
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C-RAN Implementation (one aspect) – China Mobile
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C-RAN Issues• Ultimately it provides the highest capacity
per BS/AP/RRH• High bandwidth transmission links in the
Front-Haul (FH), e.g. 10 Gbps for 20 MHz LTE
• Lower Cost of BS/AP installation• Higher cost of the FH Infrastructure?• Growth Flexibility?
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UofT Wireless Lab
Coordinated Multipoint (CoMP)• Minimize interference at cell edge• Old ideas
– Multi-user/multi-sensor detection– Soft-handoff in CDMA
• Approach to extract more capacity from a fixed set of base stations
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CoMP: Architecture• CSI: Channel State Information, CRI: Coordinated Resource
Information
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CoMP: Architecture• Distributed
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CoMP: Architecture• Centralized
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Autonomous Infrastructure Wireless Systems
• University of Toronto• White Paper: 2003!
• “Autonomous Infrastructure Wireless Networks: 4G is Here!”– Unified air interface based on cellular– Mixture of large/small cells handled in a unified manner– Flat IP architecture
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UofT Wireless Lab
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UofT Wireless Lab
Related Concepts since Then• 2007: Femtocells• Self-organizing networks (SON)• Heterogeneous networks• Mixed 3G & WiFi in terminals• Small cells
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UofT Wireless Lab
Future Cellular Systems• Spectrum: Hybrid of private, public, and private-public in one
terminal• Different Infrastructure Solutions• Fuzzy concept of cells, small/large, randomly placed, self-
configurable• Switch for connection to backbone• Wireless to wireless• Relays• Remote RF (Front-Haul)• Self-Organizing/Autonomous Deployment• Two-Tier networks: L1 - Order, L2 – Disorder
– L1: Smart antennas, high level MIMO, virtual MIMO, high power– L2: Organic, omni, self-organizing, low power
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UofT Wireless Lab
Life is a game!• Analogy with American football
– Zone defense versus man-to-man• 1-4G, design for zone, • Future, more-like man-to-man => target specific
scenarios• Instead of wide area (zone): Target Homes, offices,
vehicles, pedestrians, events, large open distances, highways, city streets, moving platforms, underground transportation
• Specialized consideration to each of the above scenarios
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UofT Wireless Lab
Two-Tier Wireless Networks:Our take on Relays
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Two -Tier Cellular Networks• Variability of antenna efficiency is a big issue =>
coverage• Use a relay (possibly fixed), or intermediate node (IN)• Two-hop per link
– Base to Relay (IN)– Relay (IN) to Terminal
• Base to Relay: well behaved channel (order), smart antenna techniques, possibly higher power, MIMO, virtual MIMO, massive MIMO, very high spectral efficiency.
• Relay to Terminal: badly behaved, omni antenna, disorder, low spectral efficiency, low power.
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UofT Wireless Lab
Two -Tier Networks: Issues• Single relay networks (strictly 2-hops, not standard
relays)• Relaying technique: active versus passive• One to one (terminal to relay), or many terminals to one
relay• Spectrum used for the two links? (equal/unequal)• Seamless operation of terminal with or without relay• Strategies for relay location
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UofT Wireless Lab
Antenna Off-Loading
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SMART ANTENNA
Tier I Tier II
RelayIN
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How to do Indoors?• Indoor cells vs. Coverage from the outside.• Two systems (macro/femto) or continuum?• Isolate indoors?• Could even modify construction:• Advantage of isolating indoors vs. Flexibility of capturing
external signals
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UofT Wireless Lab
An Approach: Fixed Relays
• Small, low powered and cost effective relays present near the edge of the building (in a window)
• Relays receive the signals reliably and retransmit it on different band with just enough power to overcome the building insertion losses without causing too much interference in the network.
• These relays will employ directional antennas for both uplink and downlink
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UofT Wireless Lab
Proposed Relay• Our Proposed relay operates in decode and forward mode.• Relay receives the user data on backhaul link and retransmits it on
the access link (or front-haul)• The backhaul link and relay link operate in orthogonal frequency
bands.• If frequency reuse of N is used, the 1 band will be used for backhaul
and rest, N-1 bands, will be available for relaying• Since reuse bands are only used indoors with low power the effect
of interference on adjacent cells will be minimal
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Tokyo Wireless Summit 2014 - Waseda University, Japan, Mar 7, 2014 46Backhaul links
Access links
User 1
User 2
User 3
User 4
Indoor
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Proposed Relay• In multi-user scenario, a user will have more
resources available in the access link than the backhaul link.
• Relay can employ 2x2 or 4x4 MIMO on the backhaul link and because of more resources, SISO link would be sufficient in the access link.
• Hence more complicated antenna technology has been offloaded from the Mobile station.
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UofT Wireless Lab
Proposed Relay• The relay appears as femto base station to the users
and they select the relay with the highest received power.
• One relay can handle more than one users and the relays allocate the recourses to their users on the access link independently, to avoid signalling overhead.
• Relays allocate the resources on the access link to achieve the data rate for each user that it is receiving on the backhaul link.
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UofT Wireless Lab
Interference Considerations• Co-tier interference:• Interference on the access link of co-channel relays.• Adjacent Channel Interference/ Receiver blocking:• Imperfect filters mean that even transmission in adjacent
band will cause interference for the receiver.• Hence the backhaul and access link of a relay cannot
operate simultaneously on adjacent bands• More over nearby relays should also avoid transmitting
when a relay is receiving• Emerging possibilities: Transmit/Receive on same band
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UofT Wireless Lab
Solution• The Backhaul and Access links operate on alternative
frames for a relay.• Nearby relays should synchronize there Backhaul and
Access frames• Relays should choose a band for access link so that
there is maximum separation between co-channel relays.
• If a co-channel relay is too close both relays should reduce their transmit power.
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UofT Wireless Lab
Self-Organizing Relays• First time when the relay is turned on, it goes into
initialization mode.• In the initialization mode the relay senses the spectrum
and chooses a band with minimum interference and if necessary it communicates with nearby co-channel relays to adjust their transmit powers.
• The relay then synchronizes the access and backhaul frames with the nearby relays. If there are no nearby relays, the relay asks the base station for the backhaul and access frame
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UofT Wireless Lab
How to do the car?• Car movement is regular. • Room for better smart antennas.• GM (Barcelona 2013): WiFi hot spot inside the car.• Many possibilities here for a new system architecture.• This is very promising, but details need to be worked out.• Initial benefits: (hot spot at night?, one wireless
account?). Other better benefits.
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UofT Wireless Lab
Car Scenarios• Car in the city – high level MIMO link• Car at home – user at home, evening and
night• Car in the country side – link range
extension• Car in the highway (remote area) – reduce
density of base stations required to cover countries highways.
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Assessing Networks
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Assessing The Wireless Network Solution Benefit/Cost (Performance)
• 1 – 4G, performance is typically throughput per base station.
• Future: Need to consider the overall infrastructure, including large/small cells, interconnection network, adaptability of infrastructure to changing scenarios of population, user behavior, and application, rather than just design for generic bps/Hz/location (base).
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UofT Wireless Lab
Evolution of Standards• Standards are too complex (usually fully specify
transmitted signal)• Increasingly written in pseudo code for the most part• Will be a nightmare for inter-operability• Becoming obsolete too soon!• Should Revisit:
– Standard specifies the transmitter: Make the standard simpler.– E.g. The standard should specify the spectral format of the
system (for purposes of co-existence and interference management)
– Allow for transmitter to do a configuration dump on the receiver.– Result is more innovation for the transmitted signal and higher
degree of proprietary solution.Tokyo Wireless Summit 2014 - Waseda University, Japan, Mar 7, 2014 56
UofT Wireless Lab
Autonomous: Our Current Focus• Resource allocation and interference management in
environment of randomly placed cells.Different Cases:• Equal AP powers, variable rates, proportional fair
scheduling, simulation models similar to 3GPP, full buffer traffic assumption.
• Include our own models on Log-Normal fading: Correlated fading links
• Non-equal AP powers• Algorithms for adaptation of configuration versus small
changes in “topology”. Configuration frames.• Self-healing (e.g. react to an AP outage)
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UofT Wireless Lab
Generalized Frequency Re-Use • Consider network with n APs (random locations and powers)• Form a set of clusters of AP’s where coordinated transmission is to
be performed. Think of these as Meta Cells. Two APs are in the same cluster if they have strong mutual interference.
• Consider all the terminals in a cluster and partition into 2 sets: 1) those with low interference from other AP’s (e.g. close to their base and) and 2) those with strong interference on more than one AP –sort of on cell edges. Orthogonal set & Re-use set (e.g. fractional re-use)
• Split the frequency resources (spectrum) into two parts: Orthogonal part and re-use part. The re-use part is assigned to terminals in 1) above. The orthogonal part is assigned to terminals in 2) above.
• Run scheduling algorithms (TDMA) for all the terminals in the re-use sets using standard PF algorithms.
• Run scheduling algorithms for the terminals in the orthogonal sets, using a modified PF algorithm.
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UofT Wireless Lab
Generations of Generic Wireless System Complexity
• 1C: No cooperation in transmission, no cooperation in configuration/scheduling. (1G to 4G)
• 2C: No cooperation in transmission but cooperation in configuration/scheduling. (autonomous/SON)
• 3C: Cooperation in transmission and configuration/scheduling. (long term)
Application for 3C: Massive capacity data networks in controlled environments such as for stadiums.
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UofT Wireless Lab
Summary• Development of Public Wireless Network Infrastructure (past and
future)• Getting away from focus on peak data rates (movie: 800 MB in 1s
=> 6.4 Gbps)• New Paradigm: Resources: Spectrum, FH infrastructure, Equipment• Zone coverage vs. adaptation to scenario (indoors, car, events, etc).• Autonomous Infrastructure Wireless• The car? Interest in auto industry.• The home? Should we isolate? Solutions?• Two-tier networks• Evolution of wireless system complexity: 1C – 3C• U of T - WSL focus
– Autonomous/SON/small cells– spectrum management, – Two-Tier (idea is not standard relays)
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