The document provides an introduction to IEEE 802.15.4 and low-rate wireless personal area networks (LR-WPANs). It describes the network topologies, physical and MAC sublayers, and superframe structure. It also outlines the operating bands and data rates of IEEE 802.15.4 networks.

1. Introduction to IEEE 802.15.4
LR-WPANs/ZigBee

2. Outline
Introduction
General Description
Network topologies
PHY Sublayer
MAC Sublayer
Superframe Structure
Frame Structure
PHY Specification
2450 MHz Mode
868/915 MHz Mode
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3. Introduction

4. The IEEE 802 Family
802.1 => Spanning Tree Bridge
802.2 => Logical Link Control (LLC) Protocol
802.3 => CSMA/CD Networks (Ethernet) MAC Protocol
802.4 => Token Bus Networks MAC Protocol LAN
802.5 => Token Ring Networks MAC Protocol
802.6 => Metropolitan Area Networks (MAN)
802.11 => WLAN (wireless local area network)
802.11b => 2.4GHz Band; 11 Mbps; direct-sequence
802.11a => 5.0GHz Band; 54 Mbps; OFDM
802.11g => 2.4GHz Band; 54 Mbps; OFDM
802.15 => WPAN (wireless personal area network)
802.15.3 UWB (Ultra Wide Band)
802.15.4 LR-WPAN (low rate wireless PAN)
802.16 => WLL (wireless local loop)
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5. Overview
LR-WPANs stands for low-rate wireless personal area
networks.
Wireless personal area networks (WPANs) are used to
convey information over relatively short distance.
Unlike wireless local area networks (WLANs),
connections effected via WPANs involve little or no
infrastructure. This feature allows small, power-efficient,
inexpensive solutions to be implemented for a wide
range of devices.
Typically operating in the personal operating space
(POS) of 10m.
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6. ZigBee & IEEE 802.15.4
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7. ZigBee Membership
ZigBee Alliance grows to over 90 members (August 16,
2004)
Promoter
Ember
Honeywell
Invensys
Mitsubishi Electric
Motorola
Philips
Samsung
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8. Traffic Types
Periodic data
Sensors
Intermittent data
Light switch
Repetitive, low-latency data
Mouse
The raw data rate will be high enough (maximum of 250
kb/s) to satisfy a set of simple needs such as interactive
toys, but scalable down to the needs of sensor and
automation needs (20 kb/s or below) for wireless
communications.
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9. General Description

10. General Description
A LR-WPAN is a simple, low-cost communication
network that allows wireless connectivity in applications
with limited power and relaxed throughput requirements.
Some of the characteristics of an LR-WPAN are:
Over-the-air data rates of 250 kb/s, 40 kb/s, and 20 kb/s.
Star or peer-to-peer operation
Allocated 16 bit short or 64 bit extended addresses
Allocation of guaranteed time slots (GTSs)
Carrier sense multiple access with collision avoidance
(CSMA-CA) channel access
Fully acknowledged protocol for transfer reliability
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11. General Description
Low power consumption
Energy detection (ED)
Link quality indication (LQI)
16 channels in the 2450 MHz band, 10 channels in the 915
MHz band, and 1 channel in the 868 MHz band
Two different device types can participate in an LR-
WPAN network:
Full-function device (FFD)
Can talk to RFDs or other FFDs.
Reduced-function device (RFD)
Can only talk to an FFD.
Intended for applications that are extremely simple.
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12. Components of the IEEE 802.15.4 WPAN
The most basic component in the IEEE 802.15.4 WPAN
is the device.
A device can be an RFD or an FFD.
Two or more devices within a POS communicating on
the same physical channel constitute a WPAN.
A network shall include at least one FFD, operating as
the PAN coordinator.
An IEEE 802.15.4 network is part of the WPAN family
of standards.
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13. Network Topologies
Depending on the application requirements, the LR-
WPAN may operate in either of two topologies: the star
topology or the peer-to-peer topology.
Each independent PAN will select a unique identifier.
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14. Star Topology
The communication is established between devices and
a single central controller, called the PAN coordinator.
A PAN coordinator is the primary controller of the PAN.
The PAN coordinator may be mains powered, while the
devices will most likely be battery powered.
Applications that benefit from a star topology include
home automation, personal computer (PC) peripherals,
toys and games, and personal health care.
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15. Star Network Formation
After an FFD is activated for the first time, it may
establish its own network and become the PAN
coordinator.
All star networks operate independently from all other
star networks currently in operation. This is achieved by
choosing a PAN identifier, which is not currently used
by other network within the radio sphere of influence.
Once the PAN identifier is chosen, the PAN coordinator
can allow other devices to join its network; both FFDs
and RFDs may join the network.
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16. Peer-to-Peer Topology
The peer-to-peer topology also has a PAN coordinator.
Any device can communicate with any other device as
long as they are in range of one another.
Allows more complex network formations to be
implemented, such as mesh networking topology.
Applications such as industrial control and monitoring,
wireless sensor networks, asset and inventory tracking,
intelligent agriculture, and security would benefit from
such a network topology.
Can be ad hoc, self-organizing and self-healing.
Allow multiple hops to route messages from any device
to any other device on the network.
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17. Peer-to-peer Network Formation
Each device is capable of communicating with any other
device within its radio sphere of influence.
One device will be nominated as the PAN coordinator,
for instance, by virtue of being the first device to
communicate on the channel.
An example of the use of the peer-to-peer
communications topology is the cluster-tree.
The cluster-tree network is a special case of a peer-to-peer
network in which most devices are FFDs.
An RFD may connect to a cluster tree network as a leave node
at the end of a branch, because it may only associate with one
FFD at a time.
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18. Topology Models
Star Mesh Cluster tree
PAN Coordinator
Full function device
Reduced function device
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19. LR-WPAN Device Architecture
The upper layers consist of
a network layer, which
provides network
configuration,
manipulation, and
message routing.
an application layer
provides the intended
function of the device.
LLC: logical link control.
SSCS: service specific
convergence sublayer.
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20. PHY Sublayer
The PHY provides two services
The PHY data service
The PHY management service interfacing to the physical layer
management entity (PLME).
The PHY data service enables the transmission and
reception of PHY protocol data units (PPDUs) across
the physical radio channel.
The features of the PHY are activation and deactivation
of the radio transceiver, ED, LQI, channel selection,
clear channel assessment (CCA), and transmitting as
well as receiving packets across the physical medium.
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21. ZigBee Operating Bands
2.4 GHz
PHY Channels 11-26 5 MHz
2.4 GHz 2.4835 GHz
Channel 0 Channels 1-10 2 MHz
868MHz / 915MHz
PHY
868.3 MHz 902 MHz 928 MHz
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22. Frequency Band and Data Rate
# of Rx
Frequency Band Coverage Data Modulation
Channels Sensitivity
2.4 GHz ISM Worldwide 250 kbps 16 -85 dbm O_QPSK
868 MHz Europe 20 kbps 1 -92 dbm BPSK
915 MHz ISM Americas 40 kbps 10 -92 dbm BPSK
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23. MAC Sublayer
The MAC sublayer provides two services:
The MAC data service
The MAC management service interfacing to the MAC
sublayer management entity (MLME) service access point
(SAP).
The MAC data service enables the transmission and
reception of MAC protocol data units (MPDUs) across
the PHY data service.
The features of the MAC sublayer are beacon
management, channel access, GTS management, frame
validation, acknowledged frame delivery, association,
and disassociation.
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24. Superframe Structure
The LR-WPAN standard allows the optional use of a superframe
structure.
The format of the superframe is defined by the coordinator.
The superframe is bounded by network beacons, is sent by the
coordinator, and is divided into 16 equally sized slots.
The beacon frame is transmitted in the first slot of each
superframe.
If a coordinator does not wish to use a superframe structure, it
may turn off the beacon transmissions.
The beacons are used to synchronize the attached devices, to
identify the PAN, and to describe the structure of the superframes.
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25. Superframe Structure without GTSs
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26. Superframe Structure with GTSs
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27. Frame Structure
The LR-WPAN defines four frame structures
A beacon frame, used by a coordinator to transmit beacons
A data frame, used for all transfers of data
An acknowledgement frame, used for confirming successful
frame reception
A MAC command frame, used for handling all MAC peer
entity control transfers
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28. Schematic View of the Beacon Frame
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29. Schematic View of the Data Frame
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30. Schematic View of the Acknowledgement
Frame
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31. Schematic View of the MAC Command
Frame
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32. Concept of Primitives
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33. PHY Specification

34. Introduction
The PHY is responsible for the following tasks:
Activation and deactivation of the radio transceiver
Energy detection (ED) within the current channel
LQI for received packets
CCA for CSMA-CA
Channel frequency selection
Data transmission and reception
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35. Operating Frequency Range
Frequency bands and data rates
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36. Channel Assignments and Numbering
A total of 27 channels, numbered 0 to 26, are available
across the three frequency bands.
Sixteen channels in the 2450 MHz band.
Ten channels in the 915 MHz band.
One channels in the 868 MHz band.
The center frequency of these channels is defined as
follows:
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37. Receiver Sensitivity Definition
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38. General Packet Format
Each PPDU packet consists of the following basic
components:
A SHR (synchronization header), which allows a receiving
device to synchronize and lock onto the bit stream.
A PHR (PHY header), which contains frame length information.
A variable length payload, which carriers the MAC sublayer
frame.
General packet format
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39. Packet Fields
Preamble field
Used by the transceiver to obtain chip and symbol
synchronization with an incoming message.
Composed of 32 binary zeros.
SFD (start-of-frame delimiter) field
An 8 bit field indicating the end of the synchronization
(preamble) field and the start of the packet data.
Format of the SFD field
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40. Packet Fields
Frame length field
7 bits in length and specifies the total number of octets
contained in the PSDU.
PSDU field
Has a variable length and carries the data of the PHY packet.
For all packet types of length five octets or greater than seven
octets, the PSDU contains the MAC sublayer frame (i.e.,
MPDU).
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41. PHY Constants
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42. PHY PIB Attributes
PIB: PAN information base.
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43. 2450 MHz PHY Specifications
Data rate: 250 kb/s.
Modulation and spreading
Employs a 16-ary quasi-orthogonal modulation technique.
During each data symbol period, four information bits are used
to select one of 16 nearly orthogonal pseudo-random noise
(PN) sequences to be transmitted.
The PN sequences for successive data symbols are
concatenated.
The aggregate chip sequence is modulated onto the carrier
using offset quadrature phase-shift keying (O-QPSK)
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44. 2450 MHz PHY Specifications
Reference modulator diagram
Reference transmitter diagram
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45. Symbol to Chip Mapping
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46. 2450 MHz PHY Specifications
O-QPSK modulation
The chip sequences representing each data symbol are
modulated onto the carrier using O-QPSK with half-sine
pulse shaping.
Pulse shape
⎧ ⎛ t ⎞
⎪sin ⎜ π ⎟ 0 ≤ t ≤ 2Tc
p ( t ) = ⎨ ⎝ 2Tc ⎠
⎪
⎩ 0 otherwise
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47. 2450 MHz PHY Specifications
Sample baseband chip sequences with pulse shaping
Symbol rate
The 2450 MHz PHY symbol rate shall be 62.5 ksymbol/s.
Receiver sensitivity
A compliant device shall be capable of achieving a sensitivity
of -85 dBm or better.
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48. 868/915 MHz PHY Specifications
868/915 MHz band data rates
868 MHz: 20 kb/s.
915 MHz: 40 kb/s.
Modulation and Spreading
The 868/915 MHz PHY shall employ direct sequence spread
spectrum (DSSS).
The binary phase-shift keying (BPSK) is used for chip
modulation.
Differential encoding is used for data symbol encoding.
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49. 868/915 MHz PHY Specifications
Reference modulator diagram
Differential encoding
Differential encoding is the modulo-2 addition (exclusive or)
of a raw data bit.
En = Rn ⊕ En −1
Rn is the raw data bit being encoded,
En is the corresponding differentially encoded bit,
En −1 is the previous differentially encoded bit.
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50. 868/915 MHz PHY Specifications
For each packet transmitted, R1 is the first raw bit to be
encoded and E0 is assumed to be zero.
Conversely, the decoding process, as performed at the
receiver, can be described by:
Rn = En ⊕ En −1
For each packet received, E1 is the first bit to be decoded,
and E0 is assumed to be zero.
Bit-to-chip mapping
Each input bit shall be mapped into a 15-chip PN sequence
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51. 868/915 MHz PHY Specifications
BPSK modulation
The chip sequences are modulated onto the carrier using
BPSK with raised cosine pulse shaping (roll-off factor = 1).
The chip rate is 300 kchip/s for the 868 MHz band and 600
kchip/s in the 915 MHz band.
Pulse shape
The raised cosine pulse shape (roll-off factor = 1) used to
represent each baseband chip is described by
sin (π t / Tc ) cos (π t / T )
p (t ) =
π t / T 1 − ( 4t 2 / Tc2 )
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52. 868/915 MHz PHY Specifications
Symbol rate
868 MHz: 20 ksymbol/s
915 MHz: 40 ksymbol/s
Receiver sensitivity
A compliant device shall be capable of achieving a sensitivity
of -92 dBm or better.
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53. Receiver Architecture
Over-Sampling
Rate (n‧chip rate)
RF A/D
Coarse
Synchronization
Half-sine Packet Fine Syn. Down
and/or Sampling
Matched Filter Detection Start of Data to Chip Rate
Detection OQPSK Despreading
Data Stream Demodulation to
(Sym. Rate) (Sym. Rate) (Sym. Rate)
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54. Despreading and Demodulation
F
+ i
n
- d
CI1 CI2 CI3 CI4 CI5 CI6 CI16
M
a
x
i
+
m
+ u
m
CQ1 CQ2 CQ3 CQ4 CQ5 CQ6 CQ16
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55. CSMA/CA Algorithm
The CSMA/CA algorithm shall be used before the
transmission of data or MAC command frames
transmitted within the CAP, and shall not be used for
the transmission of beacon frames, acknowledgment
frames or data frames transmitted in the CFP.
NB is the number of times the CSMA/CA algorithm
was required to backoff.
CW defines the number of backoff periods that need
to be clear of channel activity.
BE is related to how many backoff periods a device
shall wait before assess a channel.
＊backoff = 20 symbols
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56. CSMA-CA
NB=0,CW=2
Battery life Y
BE=lesser of (2,macMinBE)
extension?
N
Slotted
BE=macMinBE
Locate backoff
period boundary
Delay for random (2
BE
− 1)
unit backoff periods
Performance CCA on
backoff period boundary
Channel Y
idle?
N
CW=2,NB=NB+1, CW=CW-1
BE=min(BE+1,aMaxBE)
N
N NB>macMaxCS
MABackoff? CW=O?
Y Y
Failure 56 Success
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57. CSMA-CA
NB=0,
BE=macMinBE
Unslotted
Delay for random (2
BE
− 1)
unit backoff periods
Perform CCA
Channel Y
idle?
N
NB=NB+1,
BE=min(BE+1,aMaxBE)
N NB>macMaxCS
MABackoffs?
Y
57
Failure
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Success