ANT (network)

ANT is a proprietary wireless sensor network technology featuring a wireless communications protocol stack that enables semiconductor radios operating in the 2.4GHz Industrial, Scientific and Medical allocation of the RF spectrum ("ISM band") to communicate by establishing standard rules for co-existence, data representation, signalling, authentication and error detection. ANT is characterized by a low computational overhead, and high efficiency that results in low power consumption by the radios supporting the protocol. ANT is ported to a semiconductor transceiver from a specialist manufacturer (typically Nordic Semiconductor of Oslo, Norway) for practical implementations.

ANT has been targeted at the sports sector, particularly fitness and cycling performance monitoring. The transceivers are embedded in equipment such as heart rate belts, watches, cycle power and cadence meters, and distance and speed monitors to form wireless Personal Area Networks (PANs) monitoring a user's performance.

Manufacturers such as Garmin,cite web|title=Garmin Forerunner 50 press release|publisher=Garmin|date=2007-3-16|url = http://www8.garmin.com/pressroom/outdoor/100407.html|accessdate=2007-12-11] Nike, and Suunto have used ANT technology in their performance monitoring products. Recently, ANT (the company) has attempted to diversify, claiming ANT wireless sensor networking technology's low overhead, low power, interference free characteristics and operation in the 2.4 GHz ISM band suit applications the health, home automation and industrial sectors.

Overview

The applications for which ANT is targeted are characterized by periodic transfer of small amounts of sensor information between several, scores or hundreds of interconnected devices in point-to-point, star, tree or mesh network topologies. These applications are often constrained by strict power, footprint and cost requirements. Typical applications measure parameters that don't change rapidly (for example, temperature or humidity) so updates every few seconds are satisfactory.

Commercial wireless sensor networks must be reliable, feature low power consumption (to extend battery life and minimize maintenance), and be low cost to purchase, install and maintain.cite web|title=The Economist Special Report "A world of connections"|publisher=The Economist|date=2007-4-26|url = http://www.economist.com/specialreports/displaystory.cfm?story_id=9032026|accessdate=2007-12-11] In addition, transceivers in close proximity need to co-exist in harmony by being able to transmit and receive without interference from their neighbors and other wireless devices operating in the 2.4 GHz band.

ANT-powered nodes are claimed to be capable of acting as slaves or masters within a wireless sensor network. This means the nodes can act as transmitters, receivers or transceivers to route traffic to other nodes. In addition, every node is capable of determining when to transmit based on the activity of its neighbors.

The ANT protocol is designed and marketed by Dynastream Innovations, a Cochrane, Canada based company, which in turn is a wholly owned subsidiary of GPS equipment manufacturer Garmin.

Technical information

The ANT protocol has an efficiency (determined by the ratio of overhead to data) of 47 percent. ANT can be configured to spend long periods in a low power “sleep” mode (consuming of the order of microamps of current), wake up to briefly to communicate (when consumption rises to around 22mA (at -5dB) when receiving and 13.5mA (at -5dB) when transmitting)cite web|title=Nordic Semiconductor figures for nRF24AP1|publisher=Nordic Semiconductor|url = http://www.nordicsemi.com/index.cfm?obj=product&act=display&pro=88|accessdate=2007-12-11] and return to sleep mode. Each ANT channel consists of one or more transmitting nodes and one or more receiving nodes depending on the network topology. Any node can transmit or receive so the channels are bi-directional.

ANT accommodates three types of messaging: broadcast, acknowledged and burst. Broadcast is a one-way communication from one node to another. The receiving node transmits no acknowledgment. This technique is suited to sensor applications and is the most economical method of operation.

Acknowledged messaging confirms receipt of data packets. The transmitter is informed of success or failure, although there are no retransmissions. This technique is suited to control applications. ANT can also be used for burst messaging; this is a multi-message transmission technique using the full data bandwidth and running to completion. The receiving node acknowledges receipt and informs of corrupted packets that the transmitter then resends. The packets are sequence numbered for traceability. This technique is suited to data block transfer where the integrity of the data is paramount.

Comparison with Bluetooth and ZigBee

The Bluetooth protocol is designed for rapid file transfer between devices in a PAN such as a PDA, cell-phone and portable computer. It is not designed for large wireless sensor networks, but is capable of forming star networks of up to eight devices (one master and seven slaves). [citeweb|title=How Bluetooth Technology Works|url=http://www.bluetooth.com/Bluetooth/Technology/Works/|publisher=bluetooth.com|accessdate=2008-02-08] A more direct comparison can be drawn with ZigBee. ZigBee is based on the IEEE 802.15.4 standard PHY and Media Access Control (MAC) layers, and supports the ZigBee Alliance's own Network (NWK) and Application (APL) layers (refer to the OSI model). ZigBee's IEEE802.15.4 PHY has a raw data rate of 250kbit/s,cite web|title=Ember figures for e250|publisher=Ember|url = http://www.ember.com/products_zigbee_chips_e250.html|accessdate=2007-12-11] compared to ANT's 1 Mbit/s,cite web|title=Nordic Semiconductor figures for nRF24AP1|publisher=Nordic Semiconductor|url = http://www.nordicsemi.com/index.cfm?obj=product&act=display&pro=88|accessdate=2007-12-11] requiring ZigBee to stay on air longer than ANT to transmit a given volume of data.

ANT transceivers using coin cell-type batteries can operate up to three years in low use applications.cite web|title=ANT figures|publisher=ANT|url=http://www.thisisant.com/index.php?section=24|accessdate=2007-12-11]

Interference immunity

ANT, ZigBee, Bluetooth, Wi-Fi and some cordless phones all use the 2.4 GHz band (as well as 868- and 915 MHz for regional variants in the latter's case), along with proprietary forms of wireless Ethernet and USB.

Wi-Fi/ZigBee and Bluetooth employ Direct Sequence Spread Spectrum (DSSS) and Frequency-Hopping Spread Spectrum (FHSS) schemes respectively to maintain the integrity of the wireless link.

ANT uses an adaptive isochronous network technology to ensure co-existence. This scheme provides the ability for each transmission to occur in an interference free time slot within the defined frequency band. The radio transmits for less than 150µs per message, allowing a single channel to be divided into hundreds of timeslots. The ANT messaging period (the time between each node transmitting its data) determines how many time slots are available.

ANT's adaptive isochronous scheme doesn't require a master clock. Transmitters start broadcasting at regular intervals but then modify the transmission timing if interference from a neighbor is detected on a particular timeslot. This flexibility allows ANT to adapt to hostile conditions but ensures there is no overhead when interference is not present. If the radio environment is very crowded, ANT can use frequency agility to allow an application microcontroller-controlled "hop" to an alternative 1 MHz channel in the 2.4 GHz band which can then be subdivided into timeslots.

References

External links

* [http://www.thisisant.com ANT]
* [http://www.dynastream.com Dynastream Innovations]
* [http://www.nordicsemi.com Nordic Semiconductor]
* [http://www.ieee.org IEEE]
* [http://www.bluetooth.org Bluetooth SIG]
* [http://www.zigbee.org Zigbee Alliance]
* [http://www.wi-fi.org Wi-Fi Alliance]