internet of things (iot): wide-area iot protocols* · internet of things (iot): wide-area iot...
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Department of Electronics and Communications Engineering
Internet of Things (IoT): Wide-area IoT protocols*
*Long-range IoT radio access technologies (RATs)
Department of Electronics and Communications Engineering
Tampere University of Technology, Tampere, Finland
Vitaly Petrov: [email protected]
Department of Electronics and Communications Engineering
People-centric IoT applications and services
Department of Electronics and Communications Engineering
Features of long-range IoT radio access technologies (RATs)
q Massive amount of connected devices (we currently
talk about ~0.01-10 devices per square meter) q Specific traffic characteristics q Stringent requirements of the end devices
§ Energy consumption / battery lifetime § Communication range § Simplicity of the solution / low cost
q Therefore, we end up designing dedicated RATs for IoT, preferably, long-range.
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Historical insights..
q Originally, there was no common understanding that
dedicated technologies are needed. q Approach 1: Let machines talk “conventional” Wi-Fi q Approach 2: Let machines talk “conventional” LTE
q Below, we discuss, why this idea is not nice at all☺
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Approach 1 motivation (Conventional Wi-Fi for IoT)
App App App App
IoT optimized fixed/wireless connectivity
Interoperability, connectivity, access control, service
discovery, privacy
q Mitigate technology fragmentation by reusing existing deployments
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Problem statement
q Wi-Fi – de-facto technology for WLANs q Expected to minimize time-to-market for various MTC applications q Assessing their performance is important
*N. Hunn, “Using 802.11 for M2M”, http://www.m2mforum.com/2006/eng/images/stories/hunnezurio.pdf
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q Application challenges ― Small burst transmissions ― Large number of devices ― Tight battery budget
q Technology challenges ― Contention-based access ― High signaling overhead
Challenges
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Measurement of PER 1. MTC aware use case 2. State-of-the-art technology 3. Saturated queues 4. Two signaling schemes
Open-source driver: ath9k ― Manual rate control ― No retries (genuine statistics)
IEEE 802.11 test bench
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PER measurements
q Realistic levels of PER estimated
RTS/CTS scheme
Basic scheme
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Optimistic scenario: ― Full-buffer traffic ― Single link ― Fixed data rate ― Maximum power
Goodput prediction
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Goodput estimation
Semi-analytical model verified
*G. Martorell, F. Riera-Palou, and G. Femenias, ”Closed-Loop Adaptive IEEE 802.11n with PHY/MAC Cross-Layer Constraints”, MACOM 2011
Basic scheme
RTS/CTS scheme
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Reference MTC device
A typical MTC device Traffic rate 100 Kbps Message size ~20 bytes
*N. Himayat, S. Talwar, K. Johnsson, S. Andreev, O. Galinina, A. Turlikov, ”Proposed IEEE 802.16p Performance Requirements for Network Entry by Large Number of Devices”, IEEE 802.16 Broadband Wireless Access Working Group C80216p-10-0006, 2010.
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Deployment requirements
q Wi-Fi coverage area ~50 meters q ~200 MTC devices per cluster
*A. Maeder, P. Rost, D. Staehle, ”The Challenge of M2M Communications for the Cellular Radio Access Network”, 11th Wurzburg Workshop on IP EuroView2011, 2011
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Conventional system
Conventional system works bad
q Scales poorly q Too much overhead
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Aggregation techniques
*defined by IEEE 802.11-2007
*defined by IEEE 802.11n-2009
q MAC layer aggregation
q PHY layer aggregation
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Aggregation results (asymptotic)
q Potential for some improvement
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Numerical results (optimistic)
q Scalable MTC support is challenging
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Approach 1. Major conclusions
q Main results ― Conventional IEEE 802.11-2007 scales poorly for MTC ― IEEE 802.11n-2009 aggregation looks promising, but still
non-sufficient
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• Aggregated traffic (M2M applications) • Traffic analysis (numerous devices)
• Performance metrics analysis (closed-form approximation)
• Throughput • Mean delay • Energy efficiency
• Target: • Performance evaluation
• Challenges • Overload protection • Energy efficiency • Small data transmission
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Approach 2. Use “conventional” LTE for IoT. System topology
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Approach 2. Initial network entry
Msg1: Preamble
Msg2: Random access response (RAR)
Msg3: Layer 3 message
Msg4: Contention resolution identity
Msg1: Preamble retransmission
Collision
Ramping failureRamping failure
UE eNodeB
Traffic arrival
Del
ayRAR Rx
+ proces-
sing
Scheduling opportunity
Scheduling grant (SG)
Data transmission
Scheduling request
UE eNodeB
Del
ay
Scheduling opportunity
Per
iodi
city
Traffic arrival
SG Rx +
proces-sing
Response window + backoff window
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LTE RACH model
Specialty: • dependant queues • ~30000 sources • 54 preambles
Metrics (closed-form approximation) • throughput • energy expenditure • energy efficiency
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Approach 2 numerical results (1)
q Delay is too high for all the schemes...
0
0.2
0.4
0.6
0.8
1
0 20 40 60 80 100
Prob
abili
ty
Delay, ms
COBALTPRACHPUCCH
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Approach 2 numerical results (2)
q Energy efficiency is too low for all the schemes...
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
1000 5000 10000Indi
vidu
al p
ower
con
sum
ptio
n, m
W
Number of MTC devices
PUCCHPRACHCOBALTTheory
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Approach 2. Major conclusions
q Main results ― Conventional LTE scales poorly for MTC ― LTE-Advanced with certain channel access
enhancements scales better, but still not sufficient
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Therefore, novel IoT-specific radio access technologies are proposed
q Due to the abovementioned limitations of
“conventional” RATs for IoT, novel IoT-specific radio access technologies were proposed
q These are, including but not limited to:
§ SIGFOX § LoRaWAN § IEEE 802.11ah (branded as Wi-Fi HaLow) § NB-IoT (roughly, IoT version of LTE)
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Motivation to go lower in carrier and bandwidth
q Why do we move from 2.4GHz to 900MHz?
q Why do we move from 5MHz channel bandwidth in LTE to 180kHz channel bandwidth in NB-IoT?
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Motivation to go lower in carrier and bandwidth
q Why do we move from 2.4GHz to 900MHz?
Answer: lower path loss -> greater comm. range
q Why do we move from 5MHz channel bandwidth in LTE to 180kHz channel bandwidth in NB-IoT?
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Motivation to go lower in carrier and bandwidth
q Why do we move from ~2GHz to ~900MHz?
Answer: lower path loss -> greater comm. range
q Why do we move from 5MHz channel bandwidth in LTE to 180kHz channel bandwidth in NB-IoT?
Answer: higher Tx power spectral density -> greater comm. range
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Long-range IoT RATs vs short-range IoT RATs
q Long-range strengths:
§ More devices connected to a single access point -> economical gains
§ Greater communication range -> more applications/services supported
§ ... q Short-range strengths:
§ Ability to control/modify internal parameters and the topology -> Greater level of flexibility
§ Shorter communication range -> higher security § ...