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Dr Doug Pulley
Co-founder and Chief Technical Officer
LTE and the death of the macrocellLTE and the death of the macrocell……
The Ascent of RAN?The Ascent of RAN?The Ascent of RAN?The Ascent of RAN?
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Agenda
Brief Introductions
The Problem Statement
The Solution Statement
The Challenge Statement
Femtocell “Re-use”
Self-organising for an easier life
Making a cheap base station
Network interference simulation
Conclusions
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Who are we?
a fabless semiconductor business founded in 2000,making multicore DSP chips, and reference designsfor HSPA, TDSCDMA, WiMAX and LTE base stations
funded by >$75M of venture capitalinvestors include Intel, AT&T and Samsung and isthe leading supplier of chips for femtocells
Bath, UKBath, UKBath, UKBath, UK Beijing, ChinaBeijing, ChinaBeijing, ChinaBeijing, China
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Traffic trends: where and why
Outside
Work Home
Outside
Work Home
FutureNow
29% of calls placed at home: JD Power 200657% of mobile minutes at home or at work: Northstream 200775% of 3G traffic to originate in-building by 2011: VisionGain 2006
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Macrocells “don’t do” in-building coverageO
ve
rvie
w
Come inside…
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64QAM
16QAM
QPSK
But we have new air interfaces…?
HSPA, LTE and WiMAX focus
on high speed packet data
World is converging on OFDMA-
MIMO variants with higher
bandwidth etc
For max throughput:
� Largest constellation
� higher SNIR
� well-equalised channel
� All packets successfully
scheduled/received
� MIMO channel decorrelation
Look at the distance scale on
typical LSTI result plots!signal
distancewall
Indoor penetration significantly increases the likelihood of poor SNR
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The problem statement
Wide area macrocell coverage will only deliver a small
proportion of the theoretical aggregate throughput
This reduced throughput is smeared over a large
geographical area, and hence many users, resulting in a
double reduction in per user throughput – a poor utilisation
of spectrum and electronics
In addition, indoor penetration will be poor resulting in
poor user experience
� To solve using macro network:
For a small network of 5,000 initial sites and €225,000 net present
value per site, achieving a metre of extra coverage depth in-
building via an increased macrocell deployment would cost €290
million - Prof. Simon Saunders, Femtoforum
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Shannon, Isenberg & Cooper
Shannon’s Law
There is a limit to link capacity… and we are getting close to it.Higher C/I means shorter range.
“The rise of the stupid network”Push intelligence out to the edge
Isenberg
Wireless capacity doubled every 30 months for 105 years.Most significant gain is the reuse of frequencies in smaller and smaller cells.
Cooper’s Law
A route to scalability?
Capacity gain since 1950
2700
15
5 5
1
10
100
1000
10000
100000
1000000
Total
Smaller cells
More spectrum
Channelisation
Modulation
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The solution statement
Much smaller cell radius with indoor deployment as required to ensure
higher SNRs
� hence higher aggregate throughputs per carrier than the macrocell shared
by a smaller population of users – a double win
Use a two part deployment model:
� For public access
� A deployment of contiguous small cells to create “hot zones” (driven first by HSPA/LTE USB modems)
� An overlay network of macrocells for predominantly for rural, sparse or low traffic density areas
� For private access and hence public RAN traffic offload
� residential femtocell (driven later by traditional form-factor handsets)
If you are an HSPA operator – you already have the overlay network
as terminals will be dual mode
� LTE can be a very incremental roll-out and hence incremental capex
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The challenge statement
Basic small cell base stations requirements:
� very cheap (if the cell radius has shrunk ten times then there need
to be 100 times more cells)
� easy and cheap to operate and manage
� coexist with each other and the macro network in an efficient
amount of spectrum
If you are an operator of HSPA and LTE
� for public access – you want to light up spectrum with both from the
same box
� for residential access – you want to provide access to all the
devices in the property (not just the LTE user)
� you need dual mode…
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“status quo ante bellum”
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Failing to achieve escape velocity
Real mass deployment of picocells has always been “just
around the corner”
Capacity by some cell radius shrink
� but still macrocell/microcell units
Indoor coverage by Distributed Antenna Systems (DAS)
Why?
� held back by cost
� held back by deployability
� held back to avoid revenue cannibalisation
why sell a cheap one when an expensive one will do?
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A what-o-cell? The traditional definition
femtocell - noun
a low-power domestic access point…
…using conventional mobile technology
…in licensed spectrum
…generating coverageand capacity
…over internet-grade backhaul
…at prices comparable with Wi-Fi access points
…with full operator management
Generic Femto Network Architecture
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Topical News Quiz
A. Residential
B. Enterprise
C. Metro
D. Rural
E. All of the above
femto cut my capex!
From “Cash-strapped Spectrum Owners Gazette”:
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Dual Mode HSPA/LTE Femto Network
Uu (LTE)
Uu (HSPA+)
Uu (LTE)
Iu-h
Gn
Femtocell (HNB and eHNB)
MSC SGSN GGSN
Iu-CS Iu-PS
Femto (HNB) Gateway (3G)
MME Femto (eHNB) Gateway (LTE)
S1
S1 X2
S1/X2 to/from other eHNBs
Home: DSL connection, ISP network Enterprise: Ethernet LAN connection & through gateway to internet
Iu-h to/from other HNBs
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Residential
Dual mode HSPA+/LTE xFemtocell
RF
feynman SoC
HSPA+
PHY
LTE
PHYRF
HSPA+
Stack
LTE
Stack
O A & MSync
DDR
Flash
OSC
WiFi
RFIC
4 port
Ethernet
Home Network
Router
ADSL
TCVR + AFE
Flash
EnterpriseEthernet PHY
Public Access
Backhaul i/f
Iuh, S1, X2
Deployment Scenario I/F
DDR
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Dual mode HSPA+/LTE xFemto
Feature
TechnologiesLTE rel8 FDD/TDD
HSPA+ rel8 FDD (including 64QAM+MIMO on the downlink)
BandwidthsLTE: <=20 MHz
HSPA+: 5 MHz
ThroughputsLTE max throughput 90 Mb/s with 2x2 MIMO for both UL and DL
HSPA+ 42 Mb/s DL (2x2 MIMO DL+64QAM), 11.5 Mb/s UL
Capacity
Residential:
8 users LTE plus 8 simultaneous users HSPA+
Enterprise:
16 users LTE plus 16 simultaneous users HSPA+
BackhaulResidential: DSL
Enterprise: Ethernet
MIMOLTE: 2x2 SU-MIMO DL, 2x2 MU-MIMO UL
HSPA+: 2x2 SU-MIMO DL, 1x2 SIMO UL
Max cell range/mobility 500m / 30km/h @ 2.5GHz
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LTE and SON
A key part of the deployment of LTE eNodeBs is the use of Self Organising Networks (SON)� eNBs take responsibility for some of their own:
� Self-configuration
� Self-optimisation
� A formalisation of the “plug-and-play” concept being used in WCDMA Femtocell deployments
SON relies on measurements made by eNBs and by connected UEs� Some eNB measurements may require the use of a Network
Monitor mode; aka “DL Receiver” or “UE sniffer”
� For LTE Femtocells, a multi-mode UE sniffer may also be required where there is no overlaying LTE macro coverage
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LTE SON Stages
HSPA Femtocell has
already cracked this!
LTE is easier as
femtocells are
comprehended from
the outset
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Interference Scenarios
Aggressor Victim
1 UE attached to Home Node B Macro Node B Uplink
2 Home Node B Macro Node B Downlink
3 UE attached to Macro Node B Home Node B Uplink
4 Macro Node B Home Node B Downlink
5 UE attached to Home Node B Home Node B Uplink
6 Home Node B Home Node B Downlink
[From 3GPP TR25.820 V1.0.0 (2007-11) – other system scenarios not shown]
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Its all about the statistics!
house
Max UE area
Max femto BS area
Two levels of analysis to perform:
� In-building propagation:
� Residential
� Enterprise
� Network layer: All forms (includes metro, rural)
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Macro/Femto Network Coexistence
Worst case scenario:
� All eNBs and HeNBs are co-channel (“re-use=1”)
� Operation of LTE femto under LTE macro layer with closed access
� No mitigation techniques
Femtos only increase aggregate network throughput
� Open case and interference mitigation only improve the situation
Femtos per Macro Sector
Thro
ug
hp
ut
(kb/s
)
Macro Layer Downlink
Av. sector throughput
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Indoor Environment Modelling
Apartment block
Semi-detached
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LTE In-building Environment Simulation
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Scenario analysis: Uplink Noise Rise
3GPP LTE Power Control Algorithm
(3GPP TR 36.942)
With cross correlated shadowing
But no special mitigation techniques
Femto
d
d
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Comparison between HSPA and LTE?
WCDMA femtocell has paved the way:
� established the concept
� driven innovation in network, system and component technologies
� and is hence ahead time-wise in market maturity etc
LTE has life a little easier:
� WCDMA has paved the way - femtocells have to be retro-fitted into
established networks with some operator apprehension
� LTE can introduce femtocells far earlier
� LTE has a more amenable network architecture
� BUT interference management needs careful attention
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Fast track to wireless endgame.
Theoretical air interface throughputs are not delivered in
wide area coverage
Residential femtocells have generated the innovation and
acceptance required to liberate small base stations for
mass deployment in public access networks
LTE provides formalised approaches to the intelligent
base stations required but you still have to insert the
intelligence
ENDGAME:
� Reliance on centrally-managed macrocells for delivery of any
significant proportion of network capacity can be consigned to the
past
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