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Reengineering GSM/GPRS Towards a Dedicated Network for Massive Smart Metering
Germán Corrales MadueñoČedomir Stefanović Petar Popovski
Index
• Motivation
• Traffic Modeling
• Protocol Limitations in GSM
• Reengineering GSM to Support Large Number of Devices
• Results: The Potential of GSM for Machine-Type-Communications (MTC)
• Conclusions
Why is machine-to-machine different?
3
Thousands of devices sending short messages.
It is not the same to send
100 byte from 10,000 users10,000 bytes from 100 users VS
Motivation
• The clear dominance of 2G based solutions in M2M motivates us to investigate if and how GSM networks can be evolved into efficient smart metering networks.
• But its capacity may be not sufficient and the spectral efficiency is very low compared to LTE. Operators want GSM’s spectrum for LTE.
• Our findings shows that, with a suitable reengineering, GSM networks can support a surprisingly massive M2M devices at even a single frequency channel.
What if GSM is reengineered to support large number of M2M devices?
4
Traffic modeling
• Before we optimize GSM/GPRS for M2M, we need to characterize the traffic it shall support.
Appliances/+Devices+ Arrival+Rate+[report/s]+
+
Average+Message+Size+
[bytes]+
Number+of+Devices+
Distribu>on+
Smart+Meters!–!Periodic!Repor,ng! 1/60,!1/120,!1/180,!etc…!
<!1000! 13941! Poisson!
Smart+Meters+–!Alarm!Repor,ng! /! <!1000! 13941! Beta(3,4)!
Home!Security!System! 1/600! 20! 3098! Poisson!
Elderly!Sensor! 1/60! 128! 310! Poisson!
Credit!Machines! 1/120! 24! 1172! Poisson!
Roadway!Signs! 1/30! 24! 2963! Uniform!
Traffic!Lights! 1/60! 1! 360! Uniform!
Traffic!Sensors! 1/60! 1! 360! Poisson!
Alarm reporting is event-triggered, where the allowed reception delay is up to 1 minute and loss of reports is not tolerated.
Periodic reporting: if a report is not successfully received, the metering application waits for the next scheduled reception.
A
P
Suburban cell, radius of 1000m, three sectorsIEEE 802.16p Machine to Machine (M2M) Evaluation Methodology Document, 2011
Sketch of the problem & the solution: Resource granularity allocation
• Ideally, a TDMA system should be able to allocate as many as possible devices as long as the quality of service is guaranteed.
• However, in practice, systems are typically not able to operate in this manner.
What about GSM/GPRS Protocol Limitations?6
1 2 3 4
Time
Multiframe I Multiframe IIa)
b)
LegendDevice #1Device #2
Multiframe III
Applica'on*limit*
Number*of*Devices*
Data*rate*
1*Mbps*
250*kbps*
125*kbps*
protocol*limit*
1** 4* 8*
500*kbps*
2* Achievable*Capacity*
1 2 3 4
1 2 3 4
1 2 3 4
1 2 3 4
1 2 3 4
Protocol Limit
Application Limit
Number of Devices
Quick introduction to GPRS link time organization
1 2 3 4 5 6 70 1 2 3 4 5 6 70 1 2 3 4 5 6 70
Frame 1 Frame 2 Frame 3
time
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34
56
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70TN 0
TN 1
TN 2
TN 3
TN 4
TN 5
TN 6
TN 7
FN 1
FN 2
FN 3
FN 4
FN 5
FN 6
FN 7
FN 8
FN 9
FN 10
FN 11
FN 12
FN 13
FN 14
FN 15
FN 16
FN 17
FN 18
FN 19
FN 20 ··· 52
·····
Each Mobile Station transmits in one Time Slot (TS)
Multiframe structure
TN 0 RACH RACH RACH RACH RACH RACH RACH RACH RACH RACH RACH RACH
TN 1 Data Data Data Data Data Data Data Data Data Data Data Data
TN 2 Data Data Data Data Data Data Data Data Data Data Data Data
TN 3 Data Data Data Data Data Data Data Data Data Data Data Data
TN 4 Data Data Data Data Data Data Data Data Data Data Data Data
TN 5 Data Data Data Data Data Data Data Data Data Data Data Data
TN 6 Data Data Data Data Data Data Data Data Data Data Data Data
TN 7 Data Data Data Data Data Data Data Data Data Data Data Data
Block 0 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11
UPLINK
RACHRandom Access Channel
(4 RACHs opportunities per block)
Control Channels
Data Packet Data Traffic Channel
Data Channels (PACCH/PDTCH)
Multiframe structure
TN 0 PBCCH PPCH PPCH PPCH PAGCH PAGCH PAGCH PAGCH PAGCH PAGCH PAGCH PAGCH
TN 1 Data Data Data Data Data Data Data Data Data Data Data Data
TN 2 Data Data Data Data Data Data Data Data Data Data Data Data
TN 3 Data Data Data Data Data Data Data Data Data Data Data Data
TN 4 Data Data Data Data Data Data Data Data Data Data Data Data
TN 5 Data Data Data Data Data Data Data Data Data Data Data Data
TN 6 Data Data Data Data Data Data Data Data Data Data Data Data
TN 7 Data Data Data Data Data Data Data Data Data Data Data Data
Block 0 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11
DOWNLINK
PBCCH Packet Broadcast Channel
PPCH Packet Paging Channel
PAGCH Packet Access Granted Channel
Control Channels
Data Packet Data Traffic Channel
Data Channels (PACCH/PDTCH)
*Idle and PTCH frames not show
Connection establishment
GPRS Bottlenecks:
• Random access: Slotted ALOHA based. Number of RACH opportunities limited. Collisions might occur.
• Feedback channel limited: Typical configuration foresees 24 AGCH/s! It can be improved by granting multiple smart meters per AGCH.
• Uplink State Flag (USF):Lack of multiplexing identifiers for the uplink. Maximum 49 per carrier. Most limiting factor once AGCH is solved.
10
MS BS
Packet Channel Request
- Establishment Cause- Random Reference
Packet Uplink Assignment- Packet request reference- TA information- TBF Starting time- Uplink TFI- Medium Access Parameters
Packet Resource Request- Access Type- TLLI -Channel request description-MS capability
Packet Uplink Assignment
- TLLI-TBF Starting time- Uplink TFI-Medium Access Parameters
AGCH
RACH
USF
Access Granted Channel in GPRS
TN 0 PBCCHPAGCH PAGCH PAGCH PAGCH PAGCH PAGCH
Block 0 B1 B2 B3 B4 ··· B10 B11
DOWNLINK
TN 0 R1 R2 R3 R4 · · · · R52
Block 0
UPLINK
24 AGCH/s 217 RACH/s
R1 R2 R3 R4
Access Granted USF = 6 in TN = 5R1 Access Granted
USF = 2 in TN = 5R4
Uplink data transmission
• GPRS use dynamic allocation to coordinate uplink transmissions. The USF indicates who is to transmit.
MS BS
USF TFI RLC Control Block
TFI Uplink Data Block
···
Block K-1 (Downlink)
Block K (Uplink)
• The USF indicates who is to transmit, but it is only 3 bits. Therefore, only 7 devices can be active at the same time in the same slot.
• If all time slots are used for data: A maximum of 49 devices per frequency channel!!
12
Reengineering GPRS for massive smart metering: Expanded USF
Legend: Device #3 with USF 2Device #2 with USF 2Device #1 with USF 1 Device #4 with USF 1Legend: Device #3 with USF 2Device #1 with USF 1 Device #1 with USF 2 Device #4 with USF 1
Uplink PDCH #0
Uplink PDCH #0
Uplink PDCH #0
Multiframe 1 Multiframe 2 Multiframe 3 Multiframe 4
Uplink PDCH #0
B11B1B0
···B11B1B0 B11B1B0 B11B1B0
Active Period (X = 2 Multiframes) Wait Period (M = 2 Multiframes)
+
The main conception behind it is that the validity range of USF is reinterpreted, allowing for accommodation of a substantially increased number of active connections.
UplinkTN 1
Reengineering GPRS for massive smart metering: Expanded USF
Legend: Device #3 with USF 2Device #2 with USF 2Device #1 with USF 1 Device #4 with USF 1Legend: Device #3 with USF 2Device #1 with USF 1 Device #1 with USF 2 Device #4 with USF 1
Uplink PDCH #0
Uplink PDCH #0
Uplink PDCH #0
Multiframe 1 Multiframe 2 Multiframe 3 Multiframe 4
Uplink PDCH #0
B11B1B0
···B11B1B0 B11B1B0 B11B1B0
Active Period (X = 2 Multiframes) Wait Period (M = 2 Multiframes)
The main conception behind it is that the validity range of USF is reinterpreted, allowing for accommodation of a substantially increased number of active connections.
UplinkTN 1
Capacity analysis
• 3GPP Capacity analysis for M2M considers each stage individually, where λRACH= λAGCH = λUSF ??
�RACH
�AGCH
�USF
s
�RACH
�AGCH
�USF
s
RACH AGCH DATA+
Collisions
No AGCH Resources Available!
No USFs Available!
+
�RACH
�AGCH
�USF
s
�RACH
�AGCH
�USF
s
�RACH
�AGCH
�USF
s
�RACH
�AGCH
�USF
s
0 20 40 60 80 100 120 140 160 1800
0.01
0.02
0.03
0.04
0.05
0.06
0.07
k − Number of Arrivals
P(X=
k)
Ideal Poisson Distribution h = 40AGCH Arrival Rate DistributionRACH Arrival Rate Distribution
0 5 10 15 20 25 30 35 400
0.1
0.2
0.3
0.4
0.5
0.6
k − Number of Arrivals
P(X=
k)
USF Arrival Rate DistributionTruncated Poisson Distribution (h = 61)
a)
b)
0 20 40 60 80 100 120 140 160 1800
0.01
0.02
0.03
0.04
0.05
0.06
0.07
k − Number of Arrivals
P(X=
k)
Ideal Poisson Distribution h = 40AGCH Arrival Rate DistributionRACH Arrival Rate Distribution
0 5 10 15 20 25 30 35 400
0.1
0.2
0.3
0.4
0.5
0.6
k − Number of Arrivals
P(X=
k)
USF Arrival Rate DistributionTruncated Poisson Distribution (h = 61)
a)
b)
Results - Comparison with 3GPP Studies
• Blocking Probabilities for AGCH and DATA stages, obtained by 3GPP model and simulations for asynchronous traffic.
GPRS PARAMETERSMaximum Transmissions (M) 4Coding Scheme (CS) 1 (Most robust)RACH Integer (T) 20 framesNumber of AGCH/s (Legacy) 24Number of AGCH/s (Improv.) 3*24AGCH Response Timer (S) 105 framesPayload Size 152 bytesAlarm Distribution Beta (3,4)
0 20 40 60 80 1000
2
4
6
8
10
h (Arrival/s)
P B [%]
AGCH (Legacy 3GPP)USF (Legacy 3GPP)AGCH (Legacy Simulations)USF (AGCH Improvement.)USF (eUSF Improvement.)
0 20 40 60 80 1000
5
10
15
20
25
30
h (Arrival/s)O
utag
e [%
]
Legacy SystemAGCH ImprovementeUSF Improvement
0 1000 2000 3000 4000 47000
10
20
30
40
50
60
70
Devices Activated within 120 seconds
Out
age
[%]
Legacy System (Alarms)AGCH Improvement (Alarms)Expanded USF Improvement (Alarms)Legacy SystemAGCH ImprovementExpanded USF Improvement
c)b)a)
Blocking Probability: probability of not getting through in one shot.
• Outage: fraction of the accessing devices that have reached the maximum number of connection attempts (M=4) without success.
The Potential of GSM for MTC
0 20 40 60 80 1000
2
4
6
8
10
h (Arrival/s)
P B [%]
AGCH (Legacy 3GPP)USF (Legacy 3GPP)AGCH (Legacy Simulations)USF (AGCH Improvement.)USF (eUSF Improvement.)
0 20 40 60 80 1000
5
10
15
20
25
30
h (Arrival/s)
Out
age
[%]
Legacy SystemAGCH ImprovementeUSF Improvement
0 1000 2000 3000 4000 47000
10
20
30
40
50
60
70
Devices Activated within 120 seconds
Out
age
[%]
Legacy System (Alarms)AGCH Improvement (Alarms)Expanded USF Improvement (Alarms)Legacy SystemAGCH ImprovementExpanded USF Improvement
c)b)a)
0 20 40 60 80 1000
2
4
6
8
10
h (Arrival/s)
P B [%]
AGCH (Legacy 3GPP)USF (Legacy 3GPP)AGCH (Legacy Simulations)USF (AGCH Improvement.)USF (eUSF Improvement.)
0 20 40 60 80 1000
5
10
15
20
25
30
h (Arrival/s)
Out
age
[%]
Legacy SystemAGCH ImprovementeUSF Improvement
0 1000 2000 3000 4000 47000
10
20
30
40
50
60
70
Devices Activated within 120 seconds
Out
age
[%]
Legacy System (Alarms)AGCH Improvement (Alarms)Expanded USF Improvement (Alarms)Legacy SystemAGCH ImprovementExpanded USF Improvement
c)b)a)
P Periodic reporting: Alarm reporting:A
AGCH/eUSF solution can roughly support up to 1500 synchronously reporting devices with an outage that is below rather demanding 0.1%, as required for massively deployed sensors.
The total expected arrival rate of the asynchronous traffic, modeled by uniform and Poisson distributions, is 42 arrival/s.
Conclusions
• We have presented a concept to transform GSM into a dedicated network for massive smart metering.
• Boosted performance in comparison to the legacy system. Up to 13000 smart meters reporting every 5 minutes in addition to the expected M2M traffic per cell.
• Also, up to 1500 synchronously reporting meters can be supported for rather demanding outage levels of 0.1%.
• The proposed changes are incurred only at the access control layer, leaving the physical interfaces intact - a highly desirable feature in practice.
• 3GPP modeling methodology of the GSM access is not valid.