enabling technologies: bluetooth, homerf and ... · elt-53306d.moltchanov, tut 1. ieee 802.15 wg...

WPAN/WBANs: ZigBee

Dmitri A. Moltchanov

E-mail: [email protected]

http://www.cs.tut.fi/˜kurssit/ELT-53306/

ELT-53306 D.Moltchanov, TUT

• IEEE 802.15 WG breakdown;

• ZigBee

– Comparison with other technologies;

– PHY and MAC;

– Network topologies;

– Message forwarding: unicast/broadcast;

– Networking and routing;

Lecture: WPAN/WBANs: ZigBee 2


1. IEEE 802.15 WG802.15: specifies WPANs:

• TG 1: 802.15.1: WPAN/Bluetooth

– defines PHY and MAC of Bluetooth;

– standard issued in 2002 and 2005.

• TG 2: 802.15.2: coexistence

– coexistence of WPANs with other networks in unlicensed band;

– IEEE 802.15.2-2003 published in 2003 and then ”hibernated”.

• TG 3: high rate WPAN

– 802.15.3-2003 is a MAC and PHY standard for high-rate (11 to 55 Mbit/s) WPANs;

– 802.15.3a: UWB PHY... no agreement when choosing PHY (MB-OFDM vs. DS-UWB);

– 802.15.3b-2005: improve implementation and interoperability of the MAC;

– 802.15.3b-2009: mm-wave-based PHY, 57-64Ghz unlicensed band, >2Gbps.

UWB: see UWB forum (2002-2006), WiMedia Alliance (2002-2009).



• TG 4: Low Rate WPANs

– long battery life, low data rate, low complexity;

– 802.15.4 standard released in May 2003;

– many networks runs on top of 802.15.4: ZigBee, 6LoWPAN, WirelessHART, etc.

• Enhancements of 802.15.4

– 802.15.4a-2007: additional PHYs, e.g. UWB pulsed radio;

– 802.15.4-2006: clarification of the original standard;

– IEEE 802.15.4c: adaptation to unlicensed bands in China;

– IEEE 802.15.4d: adaptation to unlicensed bands in China;

– IEEE 802.15.4e: enhancements for industrial apps, e.g. channel hopping;

– IEEE 802.15.4f: active RFID systems;

– IEEE 802.15.4g: smart utility networks: large networks with a lot of end systems.



• TG 5: Mesh networking

– two parts: low rate and high rate mesh networks;

– low rate: IEEE 802.15.4-2006 MAC; high rate: IEEE 802.15.3/3b MAC;

– common features: network initialization, addressing, multihop unicasting;

– low rate: multicasting, broadcasting, portability, trace route and energy saving.

• TG 6: Body Area Networks

– low-power short range standard, draft in 2011.

• TG 7: visible light communication

– draft in 2011, work in progress.



2. ZigBeeCommon facts:

• developed by ZigBee Alliance;

• developed on top of IEEE 802.15.4;

• particular implementation of those features specified in IEEE standard.

Potential topologies very flexible:

• centralized star;

• cluster-tree-based;

• full mesh (requires additional routing protocol).

Specifics:

• low-rate (even compared to Bluetooth);

• extremely low power consumption;

• example of applicability: sensors networks.



2.1. Comparison with other technologies

Zigbee general characteristics:

• was formally adopted in December 2004;

• targets industry: low rates, but low power, cost and simple usage;

• apps: remote control, home automation, industrial sensor networks;

• range: 10-100 meters;

• offered data rates:

– 250 Kbits at 2.4 GHz;

– 40 Kpbs at 915 Mhz and 20Kbps at 868MHz.

• currently offers three levels of security;

• costs around half that of Bluetooth;

• can network up to 256 devices;

• has power requirements much less than Bluetooth;

• uses star, tree or mesh topology.



Bluetooth:

• is designed for voice and higher data-rate applications;

• also operates in the 2.4 GHz spectrum;

• operates typically over a distance of 10 metres;

• has a range of around 10 metres;

• has power requirements of 40 to 100mW per device;

• can network up to 8 devices;

• cost 3e per chip.

UWB:

• transmits over a wide frequency band using very low power;

• very high rates over distances of up to 10m;

• offering data rates around 500 Mbps at a range of 2 metres;

• has power demands typically twice that of Bluetooth;

• typically twice as expensive as Bluetooth implementations.



IEEE 802.11x technologies:

• three times more expensive than Bluetooth implementations;

• around five times the power consumption of Bluetooth devices;

• 802.11a uses OFDM, in the 5GHz band with data rates up to 54Mbps;

• 802.11b uses DSSS, in the 2.4GHz band with data rates up to 11 Mbps;

• 802.11g uses OFDM, in the 2.4GHz band with data rates up to 54Mbps;

• 802.11n is likely to operate in the 5GHz band with data rates over 100Mbps.



Reasons for choosing ZigBee:

• low cost;

• high reliability;

• very long battery life;

• high security;

• self-healing properties;

• large number of nodes supported;

• ease of deployment;

• guaranteed delivery;

• route optimization.

Not choosing:

• very specific apps;

• BLE...



2.2. ZigBee applications

Examples of applications:

• smart buildings;

• smart industry;

• automatic control of lighting spaces;

• control of heating and ventilation;

• security systems;

• environmental control (forests, gardens, etc.).

• various detectors e.g. smoke.

In general: wireless sensor networks.



2.3. ZigBee protocol overview

Three layers architecture.



2.4. IEEE 802.15.4 PHY

Three low power unlicensed radios:

• 2.4GHz: 250Kbps (EU) 16 channels (ch11-ch26);

• 915MHz: 40Kbps (US) 10 channels (ch1-ch10);

• 868MHz: 20Kbps (Europe and Japan) 1 channel (ch0).

Channels and modulation in 2.4GHz:

• 16 channels, each 5MHz wide: ch11-ch26;

• actual throughput: half of 250Kbps due to overheads;

• overheads: addressing, security, error control;

• direct sequence spread spectrum (DSSS) channel access;

• O-QPSK (Offset Quadrature Phase Shift Keying ) modulation.

Other responsibilities of PHY:

• detecting transmissions from new nodes;

• assessing quality of links with other nodes.



2.5. IEEE 802.15.4 MAC

Functionality:

• CSMA/CA;

• Max length of a packet is 127bytes;

• 2 bytes are used for CRC;

• guarantees? retransmissions...

Two modes of operation:

• acknowledged;

• unacknowledged;

How ACK mode is implemented:

• setting ACK bit in a forward packet;

• if set: receiver ACKs correct reception;

• if no ACK is received with some time: retransmission.

Note: positive ACKs just like in IEEE 802.11! Think why?



2.6. Device types

There could be one of:

• full function device (FFD);

• reduced function device (RFD).

FFD:

• capable of all the features and always ”on”;

• routing/coordination/network formation;

• can talk to other FFDs and RFDs;

• FFDs require more power!

RFD:

• sometimes called leaf nodes;

• simple networking functions;

• end-systems in a sensor networks;

• can talk to FFD only.



2.7. Logical entities

Consists of FFDs and RFDs.

Three logical entities;

• ZigBee network coordinator;

• ZigBee router;

• ZigBee end device.



Network coordinator:

• FFD device, one per network;

• creates a networks, assign a channel/addresses;

• adds new devices to a network;

• has constant power supply;

• sometimes serves as a gateway;

• a node may join if the coordinator is up;

• if down no new nodes may join;

• if down, already existing node may continue to network.



Router functionality:

• FFD devices serving as a relay node;

• used to extend the range of a network;

• has constant power supply;

• sores packets sent to sleeping nodes;

• can be used to access the network.

End device:

• FFD or RFD devices;

• low power consumption;

• sleeping modes are defined;

• communicate through routers.



2.8. Network topologies

Topologies: star

Shortcomings and advantages:

• +: single hop, thus, small delay;

• −−: single point of failure;

• −−: end devices cannot communicate directly.



Topologies: cluster-tree

• two levels of hierarchy;

• more nodes can be added via routers;

• larger coverage areas;

• several pathes in-between end nodes.



Topologies: mesh

• extension of cluster-tree topology;

• connections to devices at different layers feasible;

• RFD are still unable to communicate directly;

• +: delay can be reduced but complexity of routing is high.



2.9. Access methods

Two methods for all topologies:

• non-beacon access;

• beacon-based access.

Non-beacon access:

• transmit at anytime when channel is idle;

• ”free-for-all” environment.

Beacon-based access:

• coordinator generates a superframe identified at beacon time;

• all nodes are synchronized;

• nodes transmit only in its designated time slot;

• superframe may contain common slot when stations compete.

• in-between: could go to sleeping.



2.10. Creating a network

Initialization for coordinator:

• a node searches for coordinators on all channels;

• if no coordinators, starts its own one using unique 16-bits PAN ID;

Initialization for end nodes:

• scanning all available channels;

• can detect router and coordinator with the same PAN ID;

• if yes, device with strongest SNR is chosen;

• end device sends ”Can I join?”;

• address is allocated if there is place for a new node.

Parameters set by a coordinator:

• max number of child devices allowed per router;

• max number of hops from the co-ordinator to the most distant device.



2.11. Network example

Measuring temperature, pressure, alarming, etc.



2.12. Addressing

Three types of IDs:

• MAC address: used when joining a network;

• network address: used for routing/unicating/broadcasting;

• name of device: used for scanning nodes with common letters.

MAC address (called extended address):

• unique 64-bits ID assigned by IEEE;

• link-level ID for communication;

• coordinator may specify which ranges of MAC are allowed.

Network address (called short address):

• 16-bits ID identifying a node in a network, not unique;

• may change, not used when registering in the network;

• allocated by a parent node (router or coordinator);

• coordinator 0x0000, 216 = 65536 max nodes in a network.



2.13. Unicasting and broadcasting

Usage of addresses:

• while joining: extended MAC address;

• while connected: short network address.

Unicast:

• network address is used as destination address in MAC header;

• message is routed in the network;

• destination accepts the message, others drop;

• destination answers with ACK;

• the process is a bit more complex: local ACKs.



Broadcasting is used when:

• joining or rejoining a network;

• discovering routes in the network;

• note: should be minimized.

Broadcasting:

• MAC address is 0xFFFF;

• all active devices receive and analyze the message;

• all active FFD devices retransmit it.

ACKing broadcast message:

• no explicit active ACKs;

• passive ACKing: listening whether all neighbors retransmitted;

• if not: repeat the retransmission!



2.14. Routing and route discovery

General considerations:

• no routing needed for star topology;

• routing is needed for cluster-tree and mesh topologies;

• more than one approach available.

Cluster-tree topology:

• tree-routing: works fine for small networks;

• route discovery: work when network is unstable or large.

Mesh: route discovery is only possible. AODV.



Tree routing:

• uses tree hierarchial structure to route;

• first decision: whether to go up or down in hierarchy;

• examining address structure:

– destination is a descendant, the device sends the packet to a child;

– otherwise: send it to a parent.

• upon reception by a node:

– accepts if the destination is a directly connected child;

– otherwise: sends to a parent.

Shortcomings and advantages:

• ”–”: path could be longer than needed;

• ”+”: quite stable as tree structure is guaranteed;



2.15. Sleeping modes

General facts?

• reducing power consumption of end devices;

• still retain network address while sleeping;

• parent devise buffers packets while child is asleep.

• upon wake up it checks whether there are some in store.

Two types of sleeping modes:

• cyclic sleep: classic;

• additional modes: can be controlled, e.g. pin sleep.


enabling technologies: bluetooth, homerf and ... · elt-53306d.moltchanov, tut 1. ieee 802.15 wg...

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