1. Yao Liang (IUPUI, Indianapolis USA)
The IEEE standard
Credits to:
Yao Liang (IUPUI, Indianapolis USA)

2. Wireless Simplified Stack

3. Principal options and difficulties
Medium access in wireless networks is difficult mainly because of
Impossible (or very difficult) to send and receive at the same time
Interference situation at receiver is what counts for transmission success, but can be very different from what sender can observe
High error rates compound the issues
Requirement
As usual: high throughput, low overhead, low error rates, …
Additionally: energy-efficient, handle switched off devices!

4. Requirements for energy-efficient MAC protocols
Recall
Transmissions are costly
Receiving about as expensive as transmitting
Idling can be cheaper but is still expensive
Energy problems
Collisions and high BERs – wasted effort when two packets collide or corrupted packet
Overhearing – waste effort in receiving a packet destined for another node
Idle listening – sitting idly and trying to receive when nobody is sending
Protocol overhead
Always nice: Low complexity solution

5. Schedule- vs. contention-based MACs
Schedule-based MAC
A schedule exists, regulating which participant may use which resource at which time (TDMA component)
Schedule can be fixed or computed on demand
Usually: mixed – difference fixed/on demand is one of time scales
Usually, collisions, overhearing, idle listening no issues
Needed: time synchronization!
Contention-based MAC
Risk of colliding packets is deliberately taken
Hope: coordination overhead can be saved, resulting in overall improved efficiency
Mechanisms to handle/reduce probability/impact of collisions required
Usually, randomization used somehow

6.
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [IEEE Tutorial]
Date Submitted: [4 January, 2003]
Source: [Jose Gutierrez] Company: [Eaton Corporation]
Address: [4201 North 27th Street, Milwaukee WI ]
Voice:[(414) ], FAX: [(414) ],
Re: [IEEE Overview; Doc. IEEE /358r0, TG4-Overview; Doc IEEE /509r0]
Abstract: [This presentation provides a tutorial on the draft standard.]
Purpose: []
Notice: This document has been prepared to assist the IEEE P It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P

7. 802.15.4 Applications Space Home Networking Automotive Networks
Industrial Networks
Interactive Toys
Remote Metering

8. 802.15.4 Applications Topology
Cable replacement - Last meter connectivity
Virtual Wire
Wireless Hub
Stick-On Sensor
Mobility
Ease of installation

9. Some needs in the sensor networks
Thousands of sensors in a small space  Wireless
but wireless implies Low Power!
and low power implies Limited Range.
Of course all of these is viable if a Low Cost transceiver is required

10. Solution:
LR-WPAN Technology!
By means of
IEEE

11. 802.15.4 General Characteristics
Data rates of 250 kb/s, 40 kb/s and 20 kb/s.
Star or Peer-to-Peer operation.
Support for low latency devices.
CSMA-CA/TDMA channel access.
Dynamic device addressing.
Fully handshaked protocol for transfer reliability.
Low power consumption.
Frequency Bands of Operation
16 channels in the 2.4GHz ISM band
10 channels in the 915MHz ISM band
1 channel in the European 868MHz band.

12. 802.15.4 Architecture Upper Layers IEEE 802.2 LLC Other LLC
IEEE MAC
IEEE
IEEE
868/915 MHz
2400 MHz
PHY
PHY

13. Operating Frequency Bands
IEEE PHY Overview
Operating Frequency Bands
Channel 0
Channels 1-10
868MHz / 915MHz
PHY
2 MHz
868.3 MHz
902 MHz
928 MHz
2.4 GHz
PHY
Channels 11-26
5 MHz
2.4 GHz
GHz

14. IEEE 802.15.4 PHY Packet Structure
PHY Packet Fields
Preamble (32 bits) – synchronization
Start of Packet Delimiter (8 bits)
PHY Header (8 bits) – PSDU length
PSDU (0 to 1016 bits) – Data field
Start of
Packet
Delimiter
PHY
Header
PHY Service
Data Unit (PSDU)
Preamble
6 Octets
0-127 Octets

15. Mappatura bit a simbolo
IEEE : PHY Layer
Input Bit
Output signal
Symbol to chip
Bit to symbol
Modulation
PHY
Frequency
Channel numbering
Spreading
Data parameters
Chip rate
Modulation
Bit rate
Symbol rate
Mappatura bit a simbolo
800/915 MHz
MHz
300 kchip/s
BPSK
20 kb/s
20 kbaud
Binary
MHz
Da 1 a 10
600 kchip/s
40 kb/s
40 kbaud
2.4 GHz
GHz
Da 11 a 26
2.0 Mchip/s
O-QPSK
250 kb/s
62.5 kbaud
16-ary Orthogonal
16 channels, 5 MHz each

16. IEEE 802.15.4 PHY Primitives PHY Data Service PHY Management Service
PD-DATA – exchange data packets between MAC and PHY
PHY Management Service
PLME-CCA – clear channel assessment
PLME-ED - energy detection
PLME-GET / -SET– retrieve/set PHY PIB parameters
PLME-TRX-ENABLE – enable/disable transceiver

17. Simple but flexible protocol
IEEE MAC Overview
Design Drivers
Extremely low cost
Ease of implementation
Reliable data transfer
Short range operation
Very low power consumption
Simple but flexible protocol

18. Typical Network Topologies
IEEE MAC Overview
Typical Network Topologies
An example network topology in the area of home (living room) control. A set-top-box is acting as the master with a remote, TV, DVD, lamp and curtains enumerated on the network. This has no functionality since the slaves can only talk to the master. What the consumer actually wants is to be able to control the TV, DVD, lamp and curtains using the remote. In this case there needs to be some virtual peer-to-peer links between the remote and the other devices on the network. The mechanism of creating these links is known as pairing.

19. IEEE 802.15.4 MAC Overview Device Classes Full function device (FFD)
Any topology
Network coordinator capable
Talks to any other device
Reduced function device (RFD)
Limited to star topology
Cannot become a network coordinator
Talks only to a network coordinator
Very simple implementation

20. IEEE 802.15.4 MAC Overview Star Topology PAN Coordinator Master/slave
Full function device
Communications flow
Reduced function device

21. IEEE 802.15.4 MAC Overview Peer-Peer Topology Point to point
Cluster tree
Full function device
Communications flow

22. IEEE 802.15.4 MAC Overview Combined Topology
Clustered stars - for example,
cluster nodes exist between rooms
of a hotel and each room has a
star network for control.
Communications flow
Full function device
Reduced function device

23. IEEE 802.15.4 MAC Overview Addressing All devices have IEEE addresses
Short addresses can be allocated
Addressing modes:
Network + device identifier (star)
Source/destination identifier (peer-peer)

24. General Frame Structure
IEEE MAC Overview
General Frame Structure
4 Types of MAC Frames:
Data Frame
Beacon Frame
Acknowledgment Frame
MAC Command Frame

25. Optional Superframe Structure
IEEE MAC Overview
Optional Superframe Structure
GTS 2
GTS 1
Contention Access Period
Contention Free Period
15ms * 2n
where 0  n  14
Network beacon
Transmitted by network coordinator. Contains network information,
frame structure and notification of pending node messages.
Beacon extension
period
Space reserved for beacon growth due to pending node messages
Contention period
Access by any node using CSMA-CA
Guaranteed
Time Slot
Reserved for nodes requiring guaranteed bandwidth [n = 0].

26. IEEE 802.15.4 MAC Overview Traffic Types Periodic data
Application defined rate (e.g. sensors)
Intermittent data
Application/external stimulus defined rate (e.g. light switch)
Repetitive low latency data
Allocation of time slots (e.g. mouse)

27. IEEE 802.15.4 MAC Overview Originator Recipient MAC Data Service
MCPS-DATA.request
Channel
access
Data frame
Originator
Recipient
Acknowledgement
(if requested)
MCPS-DATA.indication
MCPS-DATA.confirm

28. IEEE 802.15.4 PHY Overview MAC Primitives MAC Data Service
MCPS-DATA – exchange data packets between MAC and PHY
MAC Management Service
MLME-ASSOCIATE/DISASSOCIATE – network association
MLME-SYNC / SYNC-LOSS - device synchronization
MLME-SCAN - scan radio channels
MLME-GET / -SET– retrieve/set MAC PIB parameters
MLME-START / BEACON-NOTIFY – beacon management
MLME-POLL - beaconless synchronization
MLME-GTS - GTS management
MLME-ORPHAN - orphan device management
MLME-RX-ENABLE - enabling/disabling of radio system

29. A numerical example Adopting beacon-enabled networks;
Data transfer protocols (e.g. towards PANC);
Maximum bandwidth 250 kb/s = 62.5 ksym/s (16-ary coding, 1sym = 4 bits);
Maximum number of GTS (Guaranteed Time Slots) = 7.
Only part of the MAC superframe can be allocated to real-time services;
the Superframe Order (SO) enlarges or reduces the distance between two
consecutive beacons.
AP= 16 (slots) * 960 (baseslotduration) * 2SO цs
17/04/2017

30. Transfer of large data sets (1)
Suppose you want to transmit 1 picture (P2P), use the lowest resolution (80 * 64 pel):
is 1.6 kBytes
Maximum MAC MSDU (payload) is 102 bytes, i.e. 16 MAC frames each resulting in 132 bytes = 264 sym at the PHY layer;
The average amount of time to transmit the data in CSMA is (BE=2, default) w/o taking into account traffic and different sources of overheads:
16 * [(1.5 (avg BT) * BP) + 2 * SP (CCA) ] sym/ 62.5 Ksym/s = 80 ms (optimistic);
In free access:
16 * 264 sym / 62.5 Ksym/s = 68 ms (but pay attention at the reservation cost).
The optimistic time to send the picture in CSMA is not bad but no guarantees are given to operate at 12 fps.
Accurate performance studies on the medium must be done in order to estimate the traffic volume (and the caused delay) as a function of the time.
In the CFP you pay the reservation cost which is dependent on the Superframe Order.

31. Transfer of large data sets (2)
To fit the transmission into 6 slots of CAP we have to use SO = 4:
960 цs * 24 * 6 > 80 ms;
If we want to use the GTSs:
we have an overhead of 1 superframe + minimum CAP (440 symbols) = 16 * 960 * 24 цs + 7 ms = 100 ms (maximum) !!!!!
2 examples show how to set the Superframe Order so to fit the transaction into the CAP or the CFP.
Reminder: the longer the superframe period, the more distant the beacons approaching several minutes.
From a networking point of view, distant beacons generate problems concerning time synchronization and bandwidth dynamically allocated to different stations.