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Full-Duplex Revolution
4/17/2014 1 Proprietary and Confidential
Kumu Networks Challenging the basic assumptions of wireless networking
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Executive Team and Investors • Two Stanford EE & CS faculty and four Stanford EE PhDs
• Augmented with industry veterans
• Top-tier investors:
Invented In-Band Full Duplex Radios • Full Duplex Breaks a Fundamental Assumption in Wireless
• Best Paper & Demo Awards at SIGCOMM 2012 and MOBICOM 2010
• Rich Patent Portfolio
• Candidate for Next Generation Wireless Standards
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Radios today cannot transmit and receive at the
same time on the same channel
Why Are Radios Today Half Duplex?
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TX
RX
RX
TX
Radio 1 Radio 2
Self-Interference is billions of times stronger
than the received signal
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Kumu Radios can transmit and receive on the
same channel!
Kumu In-Band Full Duplex Radios
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Kumu has developed a patented self-interference cancellation
technology which isolates the receiver from the transmitter
TX
RX
RX
TX
Radio 1 Radio 2
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isolator
Σ
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PA LNA
Cancellation Front-End
ANT
Modem
Transceiver
Simple addition to any radio
Existing Radio
Full Duplex Boosts Spectral Efficiency in face of slowing gains due to coding technology limits
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
HSPA Rel-61x2
HSPA Rel-71x2
HSPA Rel-72x2
LTE 1x2 LTE 2x2
Bit
s/Se
c/H
ert
z
Spectral Efficency Gains
1.42 1.36
1.29
1.08
0.72
Source: NGMN
The next major jump in spectral efficiency
Before getting to the handset, Full-Duplex can and
should be introduced on the infrastructure side only
• Full-Duplex is key to CoMP
interference coordination and
management
• Self-Interference Cancellation
allow LTE and WiFi to coexist
in unlicensed spectrum
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Kumu technology on infrastructure-side
Kumu’s Self Interference Cancellation is
fundamental, applies broadly beyond full duplex
Tunable RF Front End – Cure for Global Roaming
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Transmitted Self-Interference
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Channel 1 Channel 2
In-Band Full
Duplex
Double capacity
Received Signal
Adaptive
Frequency Division
Full Duplex (FDD)
Flexibly decide which
channels to transmit &
receive on
Transmitted Self-Interference
Received Signal
Channel 1 Channel 2
WiFi AP leaks significant adjacent channel noise into its
receiver, thus unable to simultaneously receive, even
on a different channel
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WiFi channels interfere with each other
Adjacent Channel Noise Buries Received Signal 60dB increase
in noise
Self-Interference Cancellation allows WiFi AP to
leverage all channels simultaneously
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Kumu cancells self-interference noise, in and out of band
Cancellation Enables the AP to Utilize All Channels
Simultaneously
LTE in unlicensed spectrum (LTE-u) would occupy one
or more channels in same frequency as WiFi
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LTE and WiFi coexistance
e.g., 1800MHz e.g., 5GHz
Kumu allows LTE-u and WiFi to be collocated in
the same access point
• Likely to be very attractive
indoors, particularly in the
enterprise where RF
environment is better
controlled
• Collocated deployment with
WiFi would be desirable to
reduce equipment cost,
installation, and wiring
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Self-Intereference Cancellation betwen WiFi and LTE-u
LTE-u
Use side-band Self-Interference Cancellation in
unlicensed spectrum as a step toward Universal Radio
• Build Access Points that simultaneously use
multiple channels in the same frequency band
– WiFi and LTE-u
– Dynamic selection of ‘quiet’ channel
• Define standards to remotely configure RF front-
end of such flexible APs, ensuring interoperability
• Direct industry toward Universal RF Front-End
vision, maximizing flexibility and utilization
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Spectrum Policy Evolution
Densification is inevitable. The issue is managing
RF resources and interference.
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Organizing the airwaves
Macrocell
Picocell
Microcell
Femtocell
Interference is local. Macro coverage area natural
locality to manage interference.
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Think globally. Act locally.
Macrocell
Picocell
Microcell
Femtocell
Internet
• Tools to handle
interference have been
defined by 3GPP
– ICIC
– eICIC
– CoMP CB/CS
– CoMP JT
Macrocell
Picocell
Microcell
Femtocell
Core
Distributed MIMO (CoMP-JT) is critical for
network densification
• Coordinated Multipoint –
Joint Transmission (CoMP-
JT) tries to exploit the
interfering links to provide
capacity gains
• ICIC, eICIC, and
Coordinated Scheduling/
Beamforming (CS/CB) try
to avoid interference
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3GPP Coordinated Multipoint
Macrocell
Picocell
Microcell
Femtocell
Latency significantly reduces CoMP performance.
CoMP ideally requires 1 millisecond latency.
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3GPP Coordinated Multipoint
Thro
ugh
pu
t Lo
ss
(re
lati
ve t
o la
ten
cy =
0m
s)
Source: Qualcomm
Achieving 1 millisecond latency is difficult due to
buffers in the data path, even in a fiber network
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3GPP Coordinated Multipoint
Average Latency vs. Advertised Speed - 2012
Source: FCC
Lack of uniform approach to backhauling makes it
impossible to ensure end-to-end latency
• Haphazard technology
selection
• “Direct” logical connectivity
may include switches and
routers in the physical path
• Buffers contribute to latency
– not the physical medium
• Too expense to engineer
the network for small cells
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Access is standardized. Backhaul is not.
Interference management calls for new approach
to RAN control plane
• Truly DIRECT exchange between
small cells and macro cell of
Channel State Information (CSI)
from each cell to each UE
• Uniform approach to control plane
infrastructure to ensure 1ms latency
and sufficient bandwidth for CSI
• Separate high-bandwidth data plane
that continue to use any and all
available backhaul technologies
• Not another “small cell backhaul”
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Separate Control and Data Plane for the RAN
Wireless link is ideal for control plane due to low latency
and direct communication between relevant entities
• Lowest possible LTE latency (1ms)
• Lowest possible UE modem cost
• Sufficient bandwidth for control (~Mbps)
• Addition to existing data plane
• Scheduler to scheduler communication
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RAN Control Plan should be... WIRELESS
Self-Interference prevents devices from simultaneously
operating both as eNB and UE on same frequencies
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Why hasn’t it been implemented before?
Macrocell
Picocell
Microcell
Femtocell
eNB
eNB UE
eNB UE
UE eNB
Self-Interference
Self-Interference Cancellation key to cost-
effective low-latency RAN control plane
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Small Cell
LTE Modem
DL
UL
Self - Interference
UL DL
Data Backhaul
Kumu Networks Self-Interference Cancellation
Cost-effective
Low cost UE
modem,
straightforward
networking
Low-latency
Direct connectivity
between radios
operating on same
frequency (~1ms)
Full-Duplex Relay / Self-Backhauled Small Cell
for situations where wired backhaul is unavailable
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Full-Duplex Relay
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Full Duplex Self-Backhauled
Small Cell
FDD Macro
Free Backhaul
In-Band NLOS LTE
Same channel for access and
backhaul at the same time Capacity
On-Par with a Small
Cell with Fiber
Simple to Deploy
Only Requires
Power
FDD UE No Changes
DL
UL
Self - Interference
Leverage Full-Duplex Technology on Network
side while Planning for Handset Introduction
• Decouple backhaul infrastructure of control and data planes, optimizing each for its unique purpose
• Allow backhaul of the control plane (X2) to be transported directly over low-latency LTE link
• Use full-duplex relay functionality for control channel and optionally for data channel
• Design MAC and Link layers to operate over full-duplex channel
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Network Architecture Recommendations
Summary
• Full-duplex technology is the future of wireless
– Eliminate duplexing, double spectral efficiency
• Cancellation enables tunable RF front-end
– Realizing the vision of Universal Radio
• Plenty of immediate network-side applications
– Handset penetration not initially required
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Full-Duplex Revolution
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