Next Generation Mobile Networks - awcc.uec.ac.jp€¦ · Cellular System: New Paradigm • Spectrum (licensed, unlicensed, other) • Infrastructure (cell site locations, access point

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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The Highly Ambitious: Article from NGMN Site


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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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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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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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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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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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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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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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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)


`

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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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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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

28Tokyo Wireless Summit 2014 - Waseda University, Japan, Mar 7, 2014

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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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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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Related Concepts since Then• 2007: Femtocells• Self-organizing networks (SON)• Heterogeneous networks• Mixed 3G & WiFi in terminals• Small cells


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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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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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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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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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Antenna Off-Loading


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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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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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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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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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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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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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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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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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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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

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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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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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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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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)


Documents

Next Generation Mobile Networks - awcc.uec.ac.jp€¦ · Cellular System: New Paradigm • Spectrum (licensed, unlicensed, other) • Infrastructure (cell site locations, access point