The Data Link Layer for Pico Radio Networks

1
The Data Link Layer for Pico Radio Networks

• Charlie Zhong
• Winter Retreat, 2002

2
Outline

• Introduction (Charlie)
• System level description
• Component view
• Operation
• Power control and MAC algorithms (Chunlong)
• Error control algorithms (Enyi)
• Implementation (Johnathan)

3
Data Link Layer Functions

• Transfers data between network and physical
  layers
• Maintains identification and neighborhood info
• Power control, error control and access control
• Computes location

4
A Robust Design

• Our data link layer (DLL) needs to
• Adapt to network changes
• Be survivable over catastrophic events
• Be insensitive to small environmental changes
• Have no single point of failure
• But This may cost us extra energy!

5
A Low Energy Design

• We are saving energy in one or several of the
  following ways
• Power management
• Power control
• Collision control
• Overhead reduction
• Problem One way to reduce energy may increase
  energy in other ways

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A Design for Ad-hoc Network

• We must design DLL such that
• Nodes can organize themselves onto a network with
  no or little human intervention
• Nodes dont rely on a master or central base
  station
• No global synchronization is necessary
• Problem This costs us extra energy as well

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What We have Seen So Far
Low energy
Robust
Bang!!
Conflicting requirements
Ad-hoc

• Even for energy requirement alone,
• Conflicting ways of power reduction

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Our Design Problem
A constrained optimization problem
Robust
Ad-hoc
DLL
Constraints
Optimization goal
Low Energy

• To focus on DLL,
• We assume certain network and physical layer
  implementations
• The energy includes transmit energy for every
  message and computation energy of DLL

9
A Manageable Version

• We want to find a combination of algorithms
  with lower energy under these constraints.

10
Power
RX
Idle
TX
Init EI
t
Sleep
0
T

• TN is the number of data packets per period from
  network layer LN is the size of the packets.
• LOH is the size of overhead added by DLL and
  PHY, which includes ACK and session setup
  messages.
• NR is the number of retransmissions ET is the
  energy needed to transmit a bit EM is the
  transmit energy for maintenance per period.

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Average Energy Per bit

• Modeling of the other components is crucial to
  the design tradeoffs of any component

12
Component View
Error control
Power control
MAC
Local address
Location

• Design of components are interrelated

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Major Components
SNIR
For every component, tradeoff is between OH and
output.
Error Control
Bit Error Rate
Ones output has impact on others inputs through
channel. It changes other components OH as well.
14
Local Address
Locally unique address has higher scalability.
(2) NBs IDs must be different
(1) Nodes ID
NBs ID
Address list
 
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Operation

• Three phases
• Discovery/Initialization
• To discover neighborhood
• To assign identification
• To set initial power level
• To compute location
• Maintenance
• To respond to network changes
• Data transfer

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Initialization Scenario
Start sequence
Random ID
Power control
Location
Local Address
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Initialization Messages
1. Power control messages
2. Local address messages
 
 
Assume 128 synchronization bits and 16 bits
start frame delimiter
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Maintenance Scenarios
Reactive
A combination of reactive and proactive
approaches
Proactive
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Maintenance Messages
 
1. Power control messages
2. Local address messages
Assume 128 synchronization bits and 16 bits
start frame delimiter
 
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Data Transfer Scenario
21
Energy for Data Transfer
The more accurate model
Energy of the transmitted signal
Session setup packet format