Reengineering GSM/GPRS Towards a Dedicated Network for ... · -TBF Starting time-Uplink TFI-Medium Access Parameters AGCH RACH USF. Access Granted Channel in GPRS TN 0 PBCCH PAGCH

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







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








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


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


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


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

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10

h (Arrival/s)

P B [%]


0 20 40 60 80 1000

5

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h (Arrival/s)

Out

age

[%]


0 1000 2000 3000 4000 47000

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Out

age

[%]


c)b)a)

0 20 40 60 80 1000

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h (Arrival/s)

P B [%]


0 20 40 60 80 1000

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h (Arrival/s)

Out

age

[%]


0 1000 2000 3000 4000 47000

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Out

age

[%]


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.

Documents

Reengineering GSM/GPRS Towards a Dedicated Network for ... · -TBF Starting time-Uplink TFI-Medium Access Parameters AGCH RACH USF. Access Granted Channel in GPRS TN 0 PBCCH PAGCH