QoS-Assured In-Network Processing in Wireless Cyber-Physical Systems: A Survey

Qiao Xiang

Advisor: Hongwei Zhang

Outlines

Introduction

In-Network Processing Methods

QoS-Assured INP in WCPS

Open Issues

Conclusion

Outlines

Introduction

In-Network Processing Methods

QoS-Assured INP in WCPS

Open Issues

Conclusion

Introduction

Wireless Sensor Networks:

Highly Resource- (Energy-) and Environment- Constrained

In-Network Processing:

Reduce Traffic Flow → Resource (Energy) Efficient

Category:

Application Independent Application Dependent

Data AggregationPacket PackingNetwork Coding

Data FusionQuery Processing

From WSN to WCPS

Wireless Cyber-Physical Systems:

Close-Loop vs. Open-Loop

INP in WCPS:

More emphasis on Quality of Service

e.g., latency and reliability

Outlines

Introduction

In-Network Processing Methods

QoS-Assured INP in WCPS

Open Issues

Conclusion

In-Network Processing Methods

Data Aggregation

Packet Packing

Network Coding

Data Fusion

Query Processing

Data Aggregation

Aggregate/Compress Correlated Data

Most common INP mechanism

Different Design Goals:

Energy Efficiency

Collision Reduction

Scalability

Network Lifetime

Data Aggregation

Current Research:

How to build efficient aggregation structure

Representative approaches: Chain structure Cluster structure Tree structure Structure free

Packet Packing

Assemble small packets into larger ones (No aggregation)

Data correlation is not important

Current Research:

Schedule small packets to transmit or wait.

Approaches: Opportunistic,

Pre-defined waiting time

Greedy

Drawbacks: No hard latency guarantee

Network Coding

Make use of the broadcast nature of wireless communication

Main Goal: improve throughput

Current Research:

Cooperation of random linear

network coding and routing

Network Coding

Inter-flow coding: COPE

Only packets with different destinations can be coded together

Intra-flow coding: MORE, Pacifier

Only packets with the same destination get coded together

Hybrid coding:

First do inter-flow coding, then do intra-flow coding

Examples of Inter and Intra Flow Coding

D

C

A

B

P1, P3

P1, P4

P3, P4

P1, P2, P3, P4

DC

A

B

P1, P2 P2, P3 P3, P4

P1, P2, P3, P4

Data Fusion

Main Goal: Assure data accuracy

More complex than aggregation/compression

Data is processed by sensors before the transmission

Data can be further processed at intermediate sensors during the transmission

Sensors’ roles are more flexible.

Representative works: DFuse

Query Processing

Main Goal: Data Accuracy and energy efficient

Data is only collected when there is a query request.

Requests are optimized before being sent to sensors.

Depending on different query requests, data is processed during the transmission.

Not every sensor need to response to a query request.

Representative works: TAG, CAG, TinyDB

Outlines

Introduction

In-Network Processing Methods

QoS-Assured INP in WCPS

Open Issues

Conclusion

QoS-Assured INP in WCPS

Mission-Critical Real-Time WCPS

Latency-Guaranteed INP

Reliability-Guaranteed INP

Latency-Guaranteed INP

Data Aggregation:

Only Soft-Latency guarantee is provided

End-to-End Latency One-hop Latency

Feedback control Define rewards function

Evenly divide the spare time Semi-Markov chain

Define new metric

Latency-Guaranteed INP

Packet Packing

Only Soft-Latency guarantee is provided

End-to-End Latency One-hop Latency

Grouping packets Pre-defined packet size

Opportunistic

Feedback control

Latency-Guaranteed INP

Network Coding

Network Coding can improve average end-to-end delay

Individual delay of each packet is still an unexplored area

Data Fusion

Latency constraints can be achieved by adjusting network density

Reliability-Guaranteed INP

Data Aggregation, Data Fusion, and Query Processing

Traffic load reduced → Collision and Interferences reduced → Reliability is assured

Packet Packing

Packet size is controlled to ensure the reliability

Network Coding

Similar to packet packing, coding degree can be controlled to ensure the reliability

Outlines

Introduction

In-Network Processing Methods

QoS-Assured INP in WCPS

Open Issues

Conclusion

Open Issues

Systematic Modeling and Complexity Analysis

Joint Optimization of QoS and WCPS-specific INP

Cooperation of Different INP Methods in WCPS

Theoretical Foundations of Algorithm

Outlines

Introduction

In-Network Processing Methods

QoS-Assured INP in WCPS

Open Issues

Conclusion