1. AD-HOC Networks and Wireless Sensors Networks
Course Assignment
An Enhanced Routing Protocol for ZigBee/IEEE Wireless Networks
Guy Mishol
Assaf Matalon
DR. Omer Gorewitz

2. Layout Introduction to ZigBee ZigBee IEEE Standards Development
What is ZigBee?
Motivation to ZigBee
Typical ZigBee Applications
Landmarks of ZigBee
ZigBee IEEE Standards Development
ZigBee Features
ZigBee Architecture
PHY Layer
MAC Layer
Article
Motivation
Preliminaries
Tree-based hierarchical routing (THR)
AODV routing
Performance evaluation
Conclusion

3. What is ZigBee?
ZigBee is a communication protocol using small, low-power digital radios based on the IEEE standard for wireless Personal Area Networks.
ZigBee is intended to be simpler and less expensive than other WPANs, such as Bluetooth. ZigBee is targeted at radio-frequency (RF) applications that require a low data rate, long battery life, and secure networking.

4. Origin of the Name
An urban myth perpetuated by the ZigBee Alliance is that the term “ZigBee” originates from the silent, but powerful method of communication used by honeybees to report information about food sources.

5. Motivation for ZigBee low cost ultra-low power consumption
use of unlicensed radio bands
cheap and easy installation
flexible and extendable networks
integrated intelligence for network set-up and message routing

6. Typical ZigBee Applications
Home Entertainment and Control - Smart lighting, advanced temperature control, safety and security, movies and music.
Home Awareness - Water and power sensors, smoke and fire detectors.
Mobile Services - m-payment, m-monitoring, m-security and access control, m-healthcare.
Commercial Building - Energy monitoring, lighting, access control.
Industrial Plant - Process control, environmental management, energy management, industrial device control.

7. Landmarks of ZigBee
ZigBee-style networks began to be conceived about 1998, when many installers realized that both Wi-Fi and Bluetooth were going to be unsuitable for many applications. In particular, many engineers saw a need for self-organizing ad-hoc digital radio networks.
IEEE is the 15th working group of the IEEE 802 which specializes in Wireless PAN (Personal Area Network) standards. It was founded on 2002.

8. Landmarks of ZigBee
The ZigBee Alliance Founded on October 21, The ZigBee Alliance is an association of companies working together to create a very low-cost, very low-power consumption, two-way wireless communications global standard.

9. ZigBee Alliance Members

10. ZigBee Features
Range: Meters, depending on the RF environment and the power output consumption required for a given application. 
Frequencies: 2.4GHz global, 915MHz Americas or 868 MHz Europe 
Data Rate: The data rate is 250kbps at 2.4GHz, 40kbps at 915MHz and 20kbps at 868MHz. 
Optimized for low duty-cycle applications (<0.1%)
CSMA-CA channel access Yields high throughput and low latency
Low power (battery life multi-month to years)
Addressing space of up to:
18,450,000,000,000,000,000 devices (64 bit IEEE address)
65,535 networks
Optional guaranteed time slot for applications requiring low latency
Fully hand-shacked protocol for transfer reliability

11. ZigBee Features (Cont.)

12. ZigBee Architecture Network Entities
There only three general entities:
Coordinator (ZC): All ZigBee networks must have one (and only one) Coordinator. Mainly needed at system initialization. It selects the frequency channel to be used by the network and allows other devices to connect to it (that is, to join the network).
Router (ZR): The main tasks of a Router are relays messages from one node to another and allows child nodes to connect to it.
End Device (ZED): End Devices are always located at the extremities of a network. The main tasks of an End Device at the network level are sending and receiving messages.

13. ZigBee Architecture Network Entities
All devices are divided into two categories:
Full Function Devices (FFDs)
Refined Function Devices (RFDs)
Coordinator and router are FFDs, and End device is a RFD.

14. ZigBee Architecture Network Topologies
ZigBee network has three kinds of topologies: Star, Tree and Mesh.
The Star topology is the simplest and most limited of the possible ZigBee topologies. A Star network consists of a Coordinator and a set of End Devices. Each End Device can communicate only with the Coordinator.

15. ZigBee Architecture
A Tree topology consists of a Coordinator, to which other nodes are connected as follows:
The Coordinator is linked to a set of Routers and End Devices - its children.
A Router may then be linked to more Routers and End Devices - its children. This can continue to a number of levels.

16. ZigBee Architecture
The structure of the Mesh topology is similar to that of the Tree topology, with the Coordinator at the top of a tree-like structure.
However, the communication rules are more flexible in that Router nodes within range of each other can communicate directly.

17. ZigBee Components Example

18. ZigBee Power States
An important aim of ZigBee and the IEEE standard is low-powered devices. These devices are powered from an internal source, such as a battery pack or solar cells, and therefore need no external power supply or power cabling.
Low duty cycle: Most of the power consumption of a wireless network device corresponds to the times when the device is active. The active time as a proportion of the time interval between activities is called the duty cycle.
Sleep mode: When not transmitting or receiving, the device should revert to a sleep mode during which the power consumption is minimal.

19. Layer stack

20. PHY frame structure PHY packet fields
Preamble (32 bits) – synchronization
Start of packet delimiter (8 bits) – shall be formatted as “ ”
PHY header (8 bits) – PSDU length
PSDU (0 to 127 bytes) – data field
Sync Header
PHY Header
PHY Payload
Start of
Packet
Delimiter
Frame
Length
(7 bit)
Reserve
(1 bit)
PHY Service
Data Unit (PSDU)
Preamble
4 Octets
1 Octets
1 Octets
0-127 Bytes

21. ZigBee PHY overview Operating frequency bands 868MHz/ 915MHz PHY
2.4 GHz
868.3 MHz
Channel 0
Channels 1-10
Channels 11-26
GHz
928 MHz
902 MHz
5 MHz
2 MHz

22. Frequency bands and data rates
The standard specifies two PHYs :
868 MHz/915 MHz Direct Sequence Spread Spectrum (DSSS) PHY (11 channels)
1 channel (20Kb/s) in European 868MHz band
10 channels (40Kb/s) in 915 ( )MHz ISM band
2450 MHz direct sequence spread spectrum (DSSS) PHY (16 channels)
16 channels (250Kb/s) in 2.4GHz band

23. ZigBee MAC Overview frame structure
MAC Header - Comprises frame control (Data, Ack, Command, Network Management), sequence number, and address information
MAC Payload - variable length, contains information specific to the frame type
MAC Footer - Contains FCS (using CRC)

24. MAC's Communication Differences
Beacon Enabled - The coordinator synchronizes the transmissions in the network
Non Beacon Enabled – Based on a-synchronic transmissions

25. Superframe Structure A superframe is divided into two parts
Inactive: all devices sleep (especially coordinator and routers)
Active:
Active period will be divided into 16 slots
16 slots can further divided into two parts
CAP - Contention Access Period
CFP - Contention Free Period

26. Superframe
The structure of superframes is controlled by two parameters: beacon order (BO) and superframe order (SO)
BO decides the length of a superframe
SO decides the length of the active potion in a superframe
For a beacon-enabled network, the setting of BO and SO should satisfy the relationship 0≦SO≦BO≦14
For channels 11 to 26, the length of a superframe can range from msec to sec.
which means very low duty cycle

27. Superframe (cont.)
Each device will be active for at most 2-(BO-SO) portion of the time, and sleep for 1-2-(BO-SO) portion of the time
In IEEE , devices’ duty cycle follow the specification
BO-SO 1 2 3 4 5 6 7 8 9
≧10
Duty cycle (%)
100 50 25 12
6.25
3.125
1.56
0.78
0.39
0.195
< 0.1

28. QoS In 802.15.4 GTS – Guaranteed Time Slots
A Device asks from the PAN Coordinator allocation of time slots
PAN Coordinator can assign up to 7 time slots
GTS Request frame includes the following:
Number of time slots, sending / receiving, allocation / deallocation.

29. Data Transfer Model (device to coordinator)
Data transferred from device to coordinator
In a beacon-enable network, device finds the beacon to synchronize to the superframe structure. Then using slotted CSMA/CA to transmit its data.
In a non beacon-enable network, device simply transmits its data using unslotted CSMA/CA
Communication to a coordinator
In a non beacon-enabled network
Communication to a coordinator
In a beacon-enabled network

30. Slotted CSMA

31. UnSlotted CSMA

32. An Enhanced Routing Protocol for ZigBee/IEEE 802. 15
An Enhanced Routing Protocol for ZigBee/IEEE Wireless Networks Xianghua Xu, Daomin Yuan, Jian Wan Grid and Services Computing Lab, School of Computer Science Hangzhou Dianzi University , Hangzhou, China

33. Motivation
ZigBee networks have the limited resources such as computation complexity and storage space
It is especially important to design an efficient and effective routing protocol to save the consuming energy and extend the lifetime for ZigBee networks
This paper survey two kinds of routing methods of the existing ZigBee routing protocol and then propose two improved algorithms respectively

34. Preliminaries
In ZigBee networks, the network addresses are assigned using a distributed address allocated mechanism
Every potential parent is provided with a finite sub-block of the address space which its size at depth d is decided by several appointed parameters:
Cm - the maximum number of children a parent may have
Lm – the maximum depth in the spanning-tree network
Rm – the maximum number of routers a parent may have as children

35. Preliminaries (cont.)
A node with a Cskip(d) value greater than 1 shall permit other nodes to associate and be capable of allocate addresses.
Where: k is for router’s address and n is for end-device’s address

36. Tree-based hierarchical routing (THR)
ZigBee Tree-based routing algorithm
Firstly checks whether source address S and destination address D meet the following equation:
If the equation is satisfied (destination node is the descendant of source) directly sends to children by:
Otherwise, it transmits the data to its parent node.
Shortage: Considers only parent-child relationship to transmit. The destination node can be just the source node’s 1-hop neighbor node but has to be routed through many hops.

37. Tree-based hierarchical routing (THR)
An enhanced tree-based routing algorithm
In ZigBee, every device maintains a neighbor table which has all the neighbor information in the 1-hop transmission range.
Step 1: If the destination node is in its neighbor table, directly transmit to corresponding node
Step 2: If the destination node is its descendant node, choose one of its children node as next hop node just as the way of ZigBee
Step 3: If the above conditions are not satisfied, then choose the node with minimum hop to destination node among neighbor table except its descent node as next hop node
Improvement: Based on Greedy algorithm, so will get a whole shortest path at last.

38. AODV routing ZigBee AODV routing
Checks whether there is an entry in the route table for the destination
If it is there, it gets the next hop address from the routing table
Otherwise, it has to perform routing discovery process by broadcasting RREQ in order to build a routing path
When receiving the RREQ, the destination node responds by unicasting RREP along the reverse path
The routing discovery process is finished when RREP reaches the source node
Then the built path is added into the routing table and the source node starts to transmit data along the path
Shortage: Broadcast is blind flooding which brings to excessive redundancy and contention collision

39. AODV (Ad-hoc On-Demand) routing
RREQ Message B? B? B? B?
Make sure you explain how an intermediate node distinguishes between copies of the same RREQ. In your graph, the node in the middle receives two copies of the RREQ. In this case, the hop count from the source (A) is the same, so it doesn’t matter how its own routing back to A is updated.
If you look at the example graph I included in the overview, you see that node B and the destination node F both receive multiple copies of the RREQ. In both cases, each copy followed a different route to get to the respective node. Therefore, B and F must choose the correct version of the message to use for updating their own routing tables and also for forwarding. The hop count field is the key that allows them to decide which message to keep and which message to throw away. B? B? B? B

40. AODV (Ad-hoc On-Demand) routing
RREP Message A A A A A A B

41. An enhanced AODV algorithm
AODV routing
An enhanced AODV algorithm
Partition the whole network into clusters according to following rules:
FFD nodes with even depth are assigned to be cluster heads.
FFD nodes with odd depth and RFD nodes are assigned to be cluster members and the cluster heads are their respective father nodes
improvement: It forms a 1-hop non-overlapping cluster structure with two hops between neighboring cluster-heads. Now we can route data in a clustering manner and do not need any extra computation and memory to store cluster information.

42. AODV routing
Example

43. Performance evaluation
Packet delivery ratio vs. Number of Nodes
Average end-to-end delay vs. Number of Nodes

44. Conclusion
When the number of network nodes is increased, the average of end-to-end delays of ZigBee routing protocol and enhanced routing protocol are both increased corresponsively but the latter achieves higher performance.
The packet delivery ratio of the enhanced algorithm is decreased less rapidly as the number of nodes increased. This is due to an increase in probability of packet collisions as the network traffic increased.
Both enhanced algorithms significantly reduce routing hops and therefore energy consumption.

45. Credits
Yuan Yuxiang, ZigBee IEEE , Department of Electrical Engineering Keio University
Joe Hoffert, Kevin Klues, Obi Orjih, Configuring the IEEE MAC Layer for Single-sink Wireless Sensor Network Applications, Washington University
Ed Callaway, Low Power Consumption Features of the IEEE /ZigBee LR - WPAN Standard, Florida Communication Research Lab
Sinem Coleri Ergen, ZigBee/IEEE Summary, Berkeley University
Johan Lönn and Jonas Olsson, ZigBee for wireless networking, Linköping University