Beanair WSN Deployment
Contents
1. 2483 5MHz z Key Channel does not overlap with WLAN in USA Channel does not overiap with WLAN in Europe Figure 12 ISM Band Sharing Any fixed channel system such as WLAN that uses the same radio channel as an IEEE 802 15 4 network can seriously disrupt the network when handling large amounts of data However in most applications it is possible to arrange that the WLAN and IEEE 802 15 4 systems use different channels As can be seen in Figure 12 it is usually possible to find channels that are not used by WLAN systems To avoid interference the channel scanning algorithm in IEEE 802 15 4 can be used to ensure that the best channel is chosen Another widely used system that shares the ISM band at 2 4 GHz is Bluetooth Used mainly for headsets and some peripheral connections the Bluetooth system rapidly hops across most of the Please consider the environnement before printing this document Page 33 37 A Rethinking sensing technology Document version 1 2 f D ea nAi r WSN Deployment Guideline Document Type Application Note 2 4 GHz band This may disrupt an IEEE 802 15 4 Network but degradation in performance would be gradual Microwave ovens are present in many IEEE 802 15 4 operating areas and do exhibit low levels of leakage that can disrupt IEEE 802 15 4 or any ISM 2 4 GHz equipment However the duty cycle of microwave cavity ovens is such that there is plenty of time between cooking cycles for IEEE2. these situations are line of sight with little or no obstructions and therefore do not suffer largely from multipath effects In these situations it is acceptable to neglect the traditional fade margin Please consider the environnement before printing this document Page 28 37 a Rethinking sensing technology Document version 1 2 e n ea nAi r WSN Deployment Guideline Document Type Application Note Using a free space approximation is a good starting point for such situations a range of 500meters to 1km should be achievable if each node is 2 3 meters or higher above the local ground word of caution here the height at which a node is installed is crucial to using free space rules In short if the free space approximation is applied the nodes at transmit and receive ends must be elevated above local obstructions This is especially important as the required range increases 11 4 INDOOR ENVIRONMENT GUIDELINES Following on from Chapter 10 it is certain that when a link is set up inside a building it will exhibit a shorter range than suggested by the free space guidelines even when a line of sight is present In cluttered environments the range reduction can be very significant There are many different types of environment for any model that is created to cover indoor radio propagation However this document has used a generalized and modified version of the models For a guide to node spacings at diff
3. it is convenient to use a logarithmic scale to express signal levels This method involves a calculation based on the ratio of two signal levels the result expressed in the unit of the decibel dB the calculation is given by the expression 10log Po Pr where Po is the power level of interest and Pr is a reference power level Therefore the reference power level must be stated and is normally incorporated into the unit dBm means dB referred to 1 mW while dBw means dB referred to 1 W Hence 0 dBm is 1 mW while 20 dBm is 100 mW and corresponds to 10 dBw An important concept in radio networks is line of sight LOS As an example consider a radio signal broadcast in Space from one satellite to another satellite If the two satellites can visually see each other they have a line of sight In a wireless network a LOS link means that the two nodes can see each other but a non LOS link is also possible where the two nodes cannot physically see each other but can still communicate Cf Chapter 10 for further informations Taking the ideal case of the two satellites once again assuming they both have antenna that radiate equally in all directions with no losses the range between them is determined by Equation 1 below Please consider the environnement before printing this document Page 13 37 A Rethinking sensing technology Document version 1 2 d D ea nAi r WSN Deployment Guideline Document Type Application Not
4. loss dipole types As a general rule this type of antenna is about 2 to 4 times more efficient than the integral ceramic type achieving up to double the free space range of the latter The dipole antenna is much bigger than the tiny ceramic antenna There are many situations in which small size is important particularly in hand held equipment but generally speaking good performance does not come with small antenna size It is possible to attach an antenna directly to the module connector but this is not recommended for situations where there could be mechanical stress on the antenna which could potentially damage the module As with the ceramic antenna it is important to mount the connectable antenna away from other metallic structures obeying the same 6 cm clearance rule It is also unlikely that the larger antennae would be placed inside the equipment case Please consider the environnement before printing this document Page 17 37 fo Rethinking sensing technology Document version 1 2 Bea WSN Deployment Guideline Document Type Application Note Beanair provides any type antennas amp coaxial cable as an option accessory Don t hesitate to ask our accessories catalog Please consider the environnement before printing this document Page 18 37 a Rethinking sensing technology Document version 1 2 e n ea nAi r WSN Deployment Guideline Document Type Application Note 9 ANTENNA P
5. m D D 4 5 Q S al s D a 2 6 6 8 10 12 14 16 18 20 Elapsed Time s Figure 8 Multipath Fading Over Time Depending on the strength of the direct signal compared with the reflected signal this variation can be serious In a non LOS situation at 2 45 GHz it is possible to move the receive antenna only 3 to 4 cm and see signal levels vary from 6 dB to 20 dB when compared with the local average This can be characterized by using a statistical multipath model although this is rarely used in practical situations Instead a fade margin can be applied This works by ensuring that the average signal level is well above the sensitivity of the system allowing a margin of error when fades occur The required size of this margin depends on the desired level of confidence When the network is sparser the confidence level should be increased perhaps to 75 or even 90 A word of caution here a law of diminishing returns applies to confidence levels with any wireless system to achieve a confidence level of 99 9 would probably require extremely low node spacing a typical guide when nodes are installed there should be about 20 dB path loss margin allowed to take fades into account and to give an acceptable level of confidence 11 3 OPEN SPACE GUIDELINES For an open space a typical installation would be the provision of nodes along a perimeter fence or across a car park In radio propagation terms
6. to work well beyond 40 GHz This connector is particularly suitable for product evaluation and measurement as it is widely available on antennae and test equipment N Type antennas are more adapted for industrial environment these antennas are robust and waterproof IP66 IP67 For embedded applications Radome antenna will be more suitable Radome antennas are used on Smartsensor products lines v Antenna frequency range There are an increasing number of connectable antennae available for all kinds of wireless systems It is very important that an antenna is selected that is designed to operate in the 2400 2500 MHz ISM band The antenna is a tuned component and antennae designed to work in other systems such as mobile phones at 900 MHz will not function correctly and cause severe range problems V Cables There are a number of cables available that are designed for 2 4 GHz operation They are co axial cables designed with low loss dielectric insulation plated inner conductor and high density or double braided outer shielding If cable must be used to relocate an antenna as is beneficial in some situations then it is important to use suitable cable In addition the cable must use the correct co axial connector In order to avoid installation and later reliability issues Beanair recommends that cables are bought as completed and tested sub assemblies designed for use at the relevant frequency The recommended antenna are typically low
7. 6 separate channels that allow the system to choose a channel that is not being used by either other IEEE 802 15 4 networks or other 2 4 GHz deployed systems More information on sharing the frequency band is provided in Chapter 13 Once set up to use one of these channels the IEEE 802 15 4 protocol provides a reliable radio link The protocol employs a robust modulation scheme that is not easily disturbed by other 2 4 GHz band users Furthermore the radio modem uses Direct Sequence Spread Spectrum DSSS coding that improves transmitter to receiver range and offers some protection against interference We have already raised the issue that the radio link can be interrupted by a variety of factors Received data is checked for corruption i e errors using instantaneous handshaking message checking the receiving device can acknowledge a correct or incorrect message by transmitting a short return message With this feature enabled any unsuccessful messages can be re sent until they eventually reach their recipient Please consider the environnement before printing this document Page 12 37 a Rethinking sensing technology Document version 1 2 ee ea n Ai r WSN Deployment Guideline Document Type Application Note 7 2 TRANSMIT POWER RECEIVE SENSITIVITY AND RANGE The concepts of transmit power receive sensitivity and range are very familiar to radio engineers and are fundamental to the operation of a radio li
8. 802 15 4 packets to be transmitted successfully As a general rule for any installation it is always worth assessing the other systems that may be installed nearby When transmitter and receiver are close together they couple energy very well indeed The same rule also applies to any interfering systems Therefore if the situation allows it is worth locating nodes as far away as possible from items such as Wi Fi routers and microwave ovens A distance of several meters may suffice but ten meters is preferable Note that international radio regulations which govern radio equipment ensure that cellphones use their allocated bands only It is therefore highly unlikely that cellphones will interfere with IEEE 802 15 4 equipment The BeanScape software integrates a wireless sensor networks diagnostic tool allowing the user to track in real time the PER Packet Error Rate and LQI Link Quality Indicator on each wireless sensor For further information don t hesitate to read our Technical Note on Wifi IEEE 802 15 4 Cohabitation Please consider the environnement before printing this document Page 34 37 a Rethinking sensing technology Document version 1 2 Ge ea n Ai r WSN Deployment Guideline Document Type Application Note 14 DEPLOYMENT CHECKLIST The following checklist provides a summary of factors from an RF view point that you need to consider when designing installing a wireless network v Choos
9. EMS 33 14 DEPLOYMENT CHECKLIST LU a aaa aa a aE a aE AA aan aoaaa aa aaa aaa aatia 35 Please consider the environnement before printing this document Page 3 37 a Rethinking sensing technology Document version 1 2 e n ea nAi r WSN Deployment Guideline Document Type Application Note Disclaimer The information contained in this document is the proprietary information of BeanAir The contents are confidential and any disclosure to persons other than the officers employees agents or subcontractors of the owner or licensee of this document without the prior written consent of BeanAir Ltd is strictly prohibited BeanAir makes every effort to ensure the quality of the information it makes available Notwithstanding the foregoing BeanAir does not make any warranty as to the information contained herein and does not accept any liability for any injury loss or damage of any kind incurred by use of or reliance upon the information BeanAir disclaims any and all responsibility for the application of the devices characterized in this document and notes that the application of the device must comply with the safety standards of the applicable country and where applicable with the relevant wiring rules BeanAir reserves the right to make modifications additions and deletions to this document due to typographical errors inaccurate information or improvements to programs and or equipment at any time and without not
10. EedEE es gedEeEREAE eege SEAN Zeen ia 11 7 RADIO CHANNEL BASIGS U UL Un pqveeeshasecevabqestevisse enins paver a eng rede a nas 12 7 1 2 4 GHz ISM Band Living with Your Neighbours 12 7 2 Transmit Power Receive Sensitivity and Range U L 13 8 ANTENNAOPIIONS u u u u L Su u Egide gebeten ege ebe gd stat TAER 15 8 1 Products with External antenna sise 15 9 ANTENNA PROPERTIES AND TYPES iii sense saeeesaaeeseaeeseeeeescaeeseaeeseneeees 19 91 Antena Dire lr EE 19 9 2 Antenna Issues and Types sienne 20 9 2 1 tee et AMENNA E 20 9 2 2 Half Wave Dipole Antenna iii 20 9 23 Yagil AMENNA osd u Sua aym iee aani aaae tante ler tasse ddr hate une tds 21 9 3 Antenna ET DEE 22 94 Antenna Polaris e EE 23 9 5 Ant nna COMMISSIONING gedet ESA 23 10 REFLECTIONS OBSTRUCTIONS AND MULTIPATH I n aa 25 11 DEPLOYMENT GUIDELINES uuu uu uu enraciner aea qhaquna a aaas eiaa daaa 27 11 1 General Guidelines sise 27 Please consider the environnement before printing this document Page 2 37 le Le a Rethinking sensing technology Document version 1 2 e WSN Deployment Guideline Document Type Application Note 11 2 Multipath and Fade Margins UI iien EEA A 27 BCRel EE ET 28 11 4 Indoor Environment Guidelines sise 29 12 POINT TO POINT LINK GUIDELINES uuu u ua ulus ua aaa awa nest ne tienne 31 13 SHARING CHANNELS WITH OTHER RADIO SYST
11. ROPERTIES AND TYPES This section introduces certain key antenna properties and the main types of antenna 9 1 ANTENNA DIRECTIVITY A consequence of a highly directive antenna is that it has very poor sensitivity in other directions The sensitivity or directivity of an antenna can be mapped as a function of the angle of arrival of radio waves the result is referred to as the radiation pattern or polar diagram of the antenna An antenna with equal sensitivity in all directions will result in a spherical radiation pattern while a highly directional antenna will have a significant main beam or major lobe as well as a number of smaller side lobes these are illustrated in Figure 4 below Isotropic Antenna Directive Antenna Figure 4 Radiation Patterns for Isotropic and Directive Antennae The directivity of an antenna in a certain direction can be thought of as its sensitivity as a receiver in that direction However it is easier to think of directivity in terms of the relative power of the antenna in the given direction when used as a transmitter As a numerical quantity the directivity is expressed relative to that of an isotropic antenna that is an antenna which is equally sensitive as a receiver or radiates equally as a transmitter in all directions The directivity of an isotropic antenna in any direction is defined as 1 The directivity of another antenna in a certain direction is then stated relative
12. Ref RF_AN_007 V1 2 www beanair com Rethinking sensing technology Document version 1 2 WSN Deployment Guideline Document Type Application Note DOCUMENT V1 1 RF_AN_007 10 01 2014 Christophe DONTEGREUIL N A WSN Deployment guideline VALIDATION e Goen For For Function Recipients Validation information X X MAILING LIST Function Recipients For action For Info Staffer 1 Christophe DONTEGREUIL X Staffer 2 Mohamed Yosri Jaouadi X Updates Version Date Author Evolution amp Status 1 1 07 05 2011 Christophe Appendices added Dontegreuil 1 2 10 04 2013 Christophe BeanDevice pictures changed Dontegreuil Please consider the environnement before printing this document Page 1 37 Rethinking sensing technology Document version 1 2 f e ea nAi r WSN Deployment Guideline Document Type Application Note Ty TE CANIGAL SUPPORT L aun u anaa maa AAE aaa EEEa E a a A ns 5 2 VISUAL SYMBOLS DEEINITTION aka 6 3 ACRONYMS AND ABBREVIA IONS snssseeeseesseessnssressrnsrnssrnsrnstrnstrnsrnsrnsstnnsrnnsrnnstnnstnnsnnnsrnasnna nnna nn nnt 7 4 DELaTIEDDOCHMENTS geesde ENEE ENEE eebe aaa aa 8 43 Application e CT 8 42 Technical e 9 5 AMOEHIEROGHMENT an tse igeseeebreggeuengeedehte sesch aa iaaa aaaea EENE NR ege hee dek Eet 10 6 WIRES VS WIRELESS i u uu a ebesteefeget SEENEN eEERdhE
13. a nAi r WSN Deployment Guideline Document Type Application Note 6 WIRES VS WIRELESS The notion of a wired link is a familiar one a cable joins two connectors and a link is made The link is normally broken by disconnection at either end or rarely if the intervening cable is broken perhaps by accident Thus the physical environment of a wired link e g the office usually plays little or no part in determining the state of the link For a radio link the situation is different There is no cable to act as a secure and reliable signal path The link must be made across free space through walls people and other obstructions This environment may be constantly changing such as in a busy working area with people moving around Furthermore the environment may already contain other wireless systems that seek to share the same airwaves as the system to be deployed In short in wireless system deployment there is usually little or no control over the deployment environment which can vary widely So what can be done to ensure that your network is deployed efficiently First consider listening to an FM radio Here you are enjoying the result of an established radio link deployment The engineers who built this system have used high towers on which they have located their transmit antennae They have engineered the system to ensure as much as is reasonably possible that the radio signal reaches you in good enough shape for clear audio r
14. e _ Pa Equation 1 ATN Px where R Achievable range in meters Free space wavelength in meters Ptx Transmitter power in Watts Prx Receiver sensitivity in Watts Using approximate values for typical Beanair RF Transceievr performance measurements we can calculate that equipping the satellites with standard RF Transceiver gives a range of around 700 meters Using high power RF Transceiver the increase in transmit power together with an improvement in receive sensitivity pushes this range up ten fold to nearly 7 kilometers The above calculations are based on free space radio wave propagation in a perfect vacuum and use antennae that are considered to be isotropic radiate equally in all directions In reality there are many real world issues that challenge these assumptions and a different result may be obtained Please consider the environnement before printing this document Page 14 37 Rethinking sensing technology Document version 1 2 WSN Deployment Guideline 8 ANTENNA OPTIONS Radio systems must both launch radio energy from their transmitter and capture energy from the airwaves into their receiver for this they use an antenna The correct choice and connection of the antenna is crucial to maximizing performance Thus this topic warrants detailed consideration The following table shows the antenna technology used on our products BeanGateway BeanGateway EcoSenso
15. e an antenna type which is appropriate for your network o If anode needs to receive and transmit signals in various directions use an antenna with low directivity Beanair recommends a half wave dipole antenna o If anode needs to receive and transmits signals only in a specific direction use an antenna with high directivity such as a Yagi antenna this solution is suitable for point to point links which require a large range v Refer to Section 9 2 for details v Ensure that the gains transmit power and receive sensitivity of your chosen antennae are sufficient to achieve the required range refer to Section 9 3 v Be sure to orientate the antennae such that their dominant polarisations are aligned particularly for point to point links see Section 9 4 v Where possible try to ensure an uninterrupted line of sight between nodes be aware that the following will reduce signal strength and quality vY Obstructions such as furniture and people absorb reflect and diffract radio waves v Walls floors and ceilings absorb and reflect radio waves the degree of absorption depends on the thickness structure and construction materials v Refer to Chapter 10 for details vif there is no line of sight between nodes be aware that multipath radio propagation through reflection and diffraction is vital to achieve radio communication you may be able to help produce a good multipath signal by positioning nodes such that their signal
16. eproduction They have considered walls trees hills and all manner of things that could be located between the transmit tower and you The fact that you are listening means they have deployed their network effectively The successful deployment of a wireless IEEE 802 15 4 network requires us to consider some of the same deployment issues as above but on a smaller physical scale The advice we give here is pragmatic and realistic acknowledging that a reliable system must be achieved within limited deployment time Please consider the environnement before printing this document Page 11 37 a Rethinking sensing technology Document version 1 2 f ea nAi r WSN Deployment Guideline Document Type Application Note 7 RADIO CHANNEL BASICS This chapter introduces some of the basic concepts of radio communication particularly those relevant to wireless networks 7 1 2 4 GHZ ISM BAND LIVING WITH YOUR NEIGHBOURS Beanair s Wireless sensors are designed to operate in the 2 4 GHz radio band which is available worldwide This band also known as an ISM Industrial Scientific and Medical band has rules which allow many different systems to use it at the same time An IEEE 802 15 4 network may have to share its frequency space with systems such as Wi Fi e g IEEE802 11b g wireless LAN video distribution Bluetooth and cordless telephones However the IEEE 802 15 4 protocol is well suited to shared band operation It has 1
17. erent levels of confidence refer to the publication The Mobile Radio Propagation Channel by David Parsons Pentech Press 1992 ISBNO 7273 1316 9 Figure 9 plots node to node spacing versus confidence level for situations where there is no directional antenna and no line of sight present The plot uses typical values for the Beandevice AX 3D Wireless accelerometer Furthermore in Figure 9 scenarios are considered for traversing zero one and two floors The node to node spacings displayed in Figure 9 are very approximate However they do provide some guidelines for pre planning an installation if time permits If this is not feasible a simple approach of pacing out distances between nodes will bring rewards in terms of mesh reliability for information on mesh networks refer to Chapter 7 Please consider the environnement before printing this document Page 29 37 Rethinking sensing technology Document version 1 2 WSN Deployment Guideline Document Type Application Note 160 0 8 Indoor Node to node Spacing metres 200 00 60 65 70 75 80 85 90 95 100 Confidence Level High Pow er Module Traversing 0 Floors High Power Module Traversing 1 Floors Low Power Module Traversing 0 Floors rss High Pow er Module Traversing 2 Floors Low Power Module Traversing 1 Floors Figure 9 Node to Node spacing for v modules and confidence levels Page 30 37 Please consider
18. ials but a loss will be incurred as compared with freespace propagation Depending on the thickness moisture content and angle of incidence a wall may allow between 1 100 and of the radio power to pass through In radio terms this loss is significant but not a disaster However a metal panel or metallised glass window will not allow much radio power to pass through the vast majority of the incident power will be reflected as if the panel were a mirror beware that plasterboard is often backed with metal foil This can be a serious issue since losses can build up very quickly However some radio a Rethinking sensing technology Document version 1 2 Ge ea n Ai r WSN Deployment Guideline Document Type Application Note power may propagate through small holes apertures in the panel or around metal edges through the process of diffraction Thick layers of building material absorb a lot of radio energy for example very thick stone walls Such absorption also poses problems for overground to underground communication For particularly difficult environments it may be advisable to request advice on antenna types and placement from Beanair Support or external specialists An IEEE 802 15 4 wireless network will not work underwater In addition nodes operating in wet conditions i e in heavy rainfall may exhibit some degradation In most cases water droplets on or close to the antenna are more serious than
19. ice Such changes will nevertheless be incorporated into new editions of this document Copyright Transmittal reproduction dissemination and or editing of this document as well as utilization of its contents and communication thereof to others without express authorization are prohibited Offenders will be held liable for payment of damages All rights are reserved Copyright BeanAir GmBh 2015 Please consider the environnement before printing this document Page 4 37 a Rethinking sensing technology Document version 1 2 RAS az WSN Deployment Guideline Document Type Application Note 1 TECHNICAL SUPPORT For general contact technical support to report documentation errors and to order manuals contact BeanAir Technical Support Center BTSC at tech support beanair com For detailed information about where you can buy the BeanAir equipment software or for recommendations on accessories and components visit www beanair com To register for product news and announcements or for product questions contact BeanAir s Technical Support Center BTSC Our aim is to make this user manual as helpful as possible Please keep us informed of your comments and suggestions for improvements BeanAir appreciates feedback from the users Please consider the environnement before printing this document Page 5 37 Rethinking sensing technology Document version 1 2 WSN Deployment Guideline D
20. ixed network to communicate with one or a number of fixed nodes This situation can benefit from using a directive antenna if the antenna can be oriented correctly during installation However subject to a lower range performance this type of network can still use a nondirective antenna We recommend the use of half wavelength dipoles which at 2 45 GHz are relatively small antenna but effective performers Beandevice Ecosensor products are not adapted for long range applications We recommend to use BeanDevice ProcessSenor or SmartSensor products Please consider the environnement before printing this document Page 24 37 U E BeanAir 10 REFLECTIONS OBSTRUCTIONS AND MULTIPATH In a free space situation with no nearby obstructions radio waves have a clear path between two wireless network devices In reality this situation is only approximately possible when nodes are very close together perhaps several meters and there are no other structures nearby More often there are obstructions in the direct line of sight as well as structures around the devices giving rise to absorption of radio energy and multiple reflections This situation is illustrated in Figure 7 below Figure 7 A Simple Multipath Situation in a factory This situation is extremely complex and varies with the type of installation In fact radio waves will propagate through brick walls concrete floors and plasterboard partitions among other mater
21. ment Type Application Note 4 RELATED DOCUMENTS In addition to this User manual please consult the application notes amp technical notes mentioned below 4 1 APPLICATION NOTES Nom du document Produits concern s Description Please consider the environnement before printing this document Page 8 37 Rethinking sensing technology Document version 1 2 WSN Deployment Guideline 4 2 TECHNICAL NOTES Document name Concerned products Description Please consider the environnement before printing this document Page 9 37 le Le a Rethinking sensing technology Document version 1 2 7 D B WSN Deployment Guideline Document Type Application Note 5 AIM OF THE DOCUMENT The IEEE 802 15 4 wireless network standards have paved the way for a revolution in the implementation of PANs Personal Area Networks with the traditional wiring used to connect sensors and switches being replaced with radio links This wireless solution is hugely attractive in helping to reduce construction costs of new buildings For the majority of installations the siting of individual Beanair WSN will be done without expert radio knowledge This application note outlines the basic considerations and rules to enable successful installations in such cases Please consider the environnement before printing this document Page 10 37 a Rethinking sensing technology Document version 1 2 e e
22. n which by convention is defined as horizontal or vertical The range of the broadcast is optimised by using a receiving antenna with the same polarisation particularly when there is a line of sight or directional antennae are used The use of cross polarised antennae will result in reduced range Normally an antenna will have guidelines and or markings that show the dominant polarisation Where there is no line of sight polarisation becomes less important as signals reflected from different objects arrive with widely differing polarisations multipath propagation is described in Chapter 10 9 5 ANTENNA COMMISSIONING If we now look at the concept of directivity in terms of commissioning a wireless network there are two scenarios to consider v Non engineered A node is installed in a changing network in which the node is required to communicate with other nodes in various directions These directions may be known or unknown but they may also change with time as nodes are added or moved This scenario requires that all directions are covered by the antenna s radiation pattern and therefore the use of an antenna with low directivity such as the half wave dipole shown in Figure 5 Please consider the environnement before printing this document Page 23 37 a Rethinking sensing technology Document version 1 2 d D ea nAi r WSN Deployment Guideline Document Type Application Note v Engineered A node is installed in a f
23. nk We will now explore them and see their importance in a wireless network installation We will consider these concepts by taking the analogy to an audio system V Transmit Power This is similar to the power that is delivered to a speaker in a Hi Fi system the more power supplied the stronger the sound signal and the further it will travel and still be heard v Receive Sensitivity This is analogous to how well a person s hearing can detect the sound signal v Range This is equivalent to the maximum distance the sound signal can travel and still be intelligibly heard For example if the sound signal is a news report there is a distance from the speaker at which the sound can still be heard but beyond this limit the content of the report becomes indiscernible this distance defines the range For an IEEE 802 15 4 based radio link the radio transmit power is limited by the local regulatory radio regulations Beanair RF module is designed to comply with these regulations In radio terms the transmit power of a high power module is approximately 100 mW a hundred times that of a standard module which is 1 mW At the receive end of a radio link the minimum power level that can be detected is approximately 1 1000000000 of 1 mW 10 9 mW or 10 12 W Thus radio receivers require only a tiny amount of radio energy to discern a usable signal This factor is used to excellent effect in a radio network Due to the very small numbers involved
24. ocument Type Application Note 2 VISUAL SYMBOLS DEFINITION Caution or Warning Alerts the user with important information about BeanAir wireless sensor networks WSN if this information is not followed the equipment software may fail or malfunction Danger This information MUST be followed if not you may damage the equipment permanently or bodily injury may occur Tip or Information Provides advice and suggestions that may be useful when installing BeanAir Wireless Sensor Networks Please consider the environnement before printing this document Page 6 37 a Rethinking sensing technology Document version 1 2 e ea nAi r WSN Deployment Guideline Document Type Application Note 3 ACRONYMS AND ABBREVIATIONS AES Advanced Encryption Standard CCA Clear Channel Assessment CSMA CA Carrier Sense Multiple Access Collision Avoidance GTS Guaranteed Time Slot kSps Kilo samples per second LLC Logical Link Control Lal Link quality indicator LDCDA Low duty cycle data acquisition MAC Media Access Control PAN Personal Area Network PER Packet error rate RF Radio Frequency SD Secure Digital SSD Smart shock detection WSN Wireless sensor Network Please consider the environnement before printing this document Page 7 37 Rethinking sensing technology Document version 1 2 WSN Deployment Guideline Docu
25. ons will be present in most 2 4 GHz radio paths When the path between two radio antennae is assessed the transmitted signal can follow many different paths to arrive at the receive antenna One path may be direct but other paths may involve multiple reflections from walls or metal obstructions These are multiple paths normally shortened to multipath This is a common experience in analogue TV systems where it can cause a ghost on a television image Where there is no line of sight it is multipath i e the scattered signal that propagates the radio energy and here multipath therefore provides a useful service However multipath gives rise to power fluctuations about an average value depending on location and in a busy area time This is illustrated in Figure 8 below which shows the variation in signal strength over time in a laboratory environment with people moving around In basic terms the strong signals regions or peaks are present when the multipath signals arrive in phase and add up this is known as constructive interference In the low signal regions nulls the multipath signals arrive out of phase and cancel each other out this is known as destructive interference Please consider the environnement before printing this document Page 27 37 Rethinking sensing technology Document version 1 2 Te 2 ea nAi r WSN Deployment Guideline Document Type Application Note a Oo e ae a oa
26. r ProcessSensor SmartSensor Antenna Indoor Outdoor product line product line product line Technology Re Antenna External Omnidirectional antenna with N Type plug External Omnidirectional antenna with RPSMA plug 8 1 PRODUCTS WITH EXTERNAL ANTENNA Beanair products range also includes RF connector and external antenna see Figure 2 Figure 2 1 Figure 2 2 below Page 15 37 Please consider the environnement before printing this document Le Rethinking sensing technology Document version 1 2 e WSN Deployment Guideline Figure 2 BeanDevice AN XX with N Type Antenna tte Se giDevice _ is Inchinometer Figure 2 2 BeanDevice HI INC Xrange with Radome antenna The available RF connectors include N type Radome Antenna and reverse polarity SMA These products offer a huge amount of flexibility in the choice and location of the antennae in a wireless network but we must be careful in our choices Some key points to bear in mind are Please consider the environnement before printing this document Page 16 37 a Rethinking sensing technology Document version 1 2 f ea nAi r WSN Deployment Guideline Document Type Application Note V Connectors The SMA RPSMA connector is a specialist RF connector designed to work well at the required 2 4 GHz frequency in fact special versions of this connector are available
27. rably higher cost Antennae of this type will give significantly more range but only in one direction and therefore are only really suitable for point to point links see Section 6 5 Another potential benefit is that the system is less susceptible to interfering signals from outside the main beam of the antenna Z axis Please consider the environnement before printing this document Page 21 37 a Rethinking sensing technology Document version 1 2 f e ea D I r WSN Deployment Guideline Document Type Application Note Figure 6 Yagi Antenna 9 3 ANTENNA GAIN Antenna gain is simply the antenna directivity taking into account any inefficiencies in the antenna and is usually expressed in dBi as for directivity see above Antenna inefficiencies can originate in the antenna structure itself as well as the RF feed and if fitted the cable to the antenna This becomes significant with very small antennae particularly ceramic types However for well engineered antennae with good RF feeds it is permissible to consider directivity and gain to be interchangeable Antennae with positive gains boost the range of the radio system in the direction that the gain is quoted Once again considering the case of the two satellites as described in Equation 1 if we now assume they have antennae with particular gains in the relevant directions then Equation 1 can be adjusted as shown below R fPxGi Go Equation 2 47 P
28. s reflect off a plane surface v When siting nodes the following factors are useful to bear in mind V It is normally beneficial to place nodes as high as possible unless there are obstructions to be avoided such as support beams and ceiling lights v If obstructions are unavoidable do not place a node near to an obscuring object since a close object obscures a larger solid angle V You can check the quality of radio communications in an installed network using the Network diagnostic feature provided by the BeanScape read the Beanscape User Manual for further informations y Wireless networks based on IEEE 802 15 4 can automatically select the frequency channel with least detected activity when sampled at system start up If you wish to use a pre configured channel you should first investigate the potential interference present in the Please consider the environnement before printing this document Page 35 37 a Rethinking sensing technology Document version 1 2 RAS al B ea nAi r WSN Deployment Guideline given operating environment using the Energy Scan feature provided by the BeanScape read the Beanscape User Manual for further information Please consider the environnement before printing this document Page 36 37
29. s 1992 ISBNO 7273 1316 9 The assumption here is that the height of the antenna while above local obstructions is much less than the distance between the antennae To achieve optimum range between two nodes in a wireless network the nodes should be located as high as possible off the ground floor Please consider the environnement before printing this document Page 31 37 fo Rethinking sensing technology Document version 1 2 WSN Deployment Guideline Document Type Application Note High gain antenna may not be permitted under some local radio regulations and guidance should be sought before using them with ISM band equipment Please consider the environnement before printing this document Page 32 37 a Rethinking sensing technology Document version 1 2 Cp i ea nAi r WSN Deployment Guideline Document Type Application Note 13 SHARING CHANNELS WITH OTHER RADIO SYSTEMS As mentioned earlier the ISM band at 2 4 GHz is used by a variety of radio system types To illustrate this issue Figure 12 below shows the situation with respect to the now prevalent WLAN Wireless Local Area Network systems Channel US WLAN IEEE 802 11b non overlapping 2442 2437 2400MH 2483 5MHz European WLAN IEEE 802 11b non overlapping i Channel 11 ha 13 44 17 18 49 IEEE 802 15 4 2400 MHz PHY 2405 2410 2415 2420 2425 2430 2435 2440 2445 2450 2455 2460 2465 2470 2475 2480
30. the environnement before printing this document a Rethinking sensing technology Document version 1 2 e ea nAi r WSN Deployment Guideline Document Type Application Note 12 POINT TO POINT LINK GUIDELINES A point to point or fixed link is by definition an engineered radio link It is designed to link two specific points and is always raised above or placed away from local obstructions Examples in everyday use include a DBS satellite dish in this case the dish antenna is carefully aligned with a geostationary satellite found at a specific bearing Ce Ah em Figure 9 Point to point Link In a wireless network it is reasonable to assume that the two radio nodes of a point to point link will be elevated on a roof or perhaps high up on a wall The nodes will also have directional antenna with a line of sight between them even though they may be separated by several kilometers In this situation the main concerns will be any buildings or other large obstructions in the path between the directional antenna and the height of the antenna above the ground Fixed link planners spend a lot of time working through these considerations However for links that have a range of less than approximately 10km it is possible to obtain some guidance from what is called the plane earth propagation model with Egli s empirical terrain factor refer to The Mobile Radio Propagation Channel by David Parsons Pentech Pres
31. the rain itself so care should be taken to ensure that enclosures shed water well Apart from a few situations it is very difficult to exclude ALL radio power from an area Thus a radio link can be made to work under most situations with some careful planning but there are many situations to consider and radio path losses vary widely For example v A large public building may have few obstructions between nodes but large amounts of metallic paneling that cause reflections V Asmall domestic installation may have numerous brick walls between nodes in individual rooms v An office building may have metallized dry wall partitions together with mezzanine ceilings V A system in an open air car park will enjoy relatively few obstructions and may benefit from elevated gantry sites Given the huge variation in situations many researchers have studied the effects of the environment on 2 4 GHz radio wave propagation The techniques used have varied from deterministic models using ray tracing techniques to statistical approaches using curve fitting to measured data These are used to determine the siting of individual radio devices The BeanScape our wirelesss sensor networks supervision software incorporates a wireless diagnostic tool used to perform radio link measurements PER estimation Link Quality Indicator specific to the installation before individual nodes are placed in their final positions This technique has been used widely for
32. tions as a transmitter and is equally sensitive in all directions as a receiver The antenna radiation pattern is simply a sphere with directivity of unity in all directions as shown in Figure 4 It is not a real world antenna and exists only in theory Its significance is that it provides a reference point for all other antennae often antenna directivity and gain are specified in units of dBi which defines the relative directivity or gain of the real world antenna against the theoretical isotropic antenna 9 2 2 Halt Wave Dipole Antenna Figure 5 below shows the radiation pattern of a half wave dipole antenna for the BeanGateway Indoor antenna example Note that the dipole radiates in a similar way to the isotropic case close to the horizontal but has virtually no radiation at the vertical Please consider the environnement before printing this document Page 20 37 Le Rethinking sensing technology Document version 1 2 WSN Deployment Guideline Document Type Application Note Z axis Figure 5 Half Wave Dipole Antenna 9 2 3 Yagi Antenna The Yagi antenna is highly directive Figure 6 below shows its radiation pattern for the Telex 2 4 GHz WLAN antenna in this example Notice that there is a direction in which the antenna radiates with almost ten times the power of the isotropic antenna However this directivity comes at the expense of power radiated in other directions and for conside
33. to this isotropic case with the assumption that both antennae radiate the same total power integrated over all directions The directivity is expressed logarithmically in units of dBi decibels with the i indicating with reference to the isotropic antenna Thus a directivity of 20 dBi indicates that the antenna radiates 100 times more power than an isotropic antenna in the given direction Please consider the environnement before printing this document Page 19 37 a Rethinking sensing technology Document version 1 2 e ea nAi r WSN Deployment Guideline Document Type Application Note 9 2 ANTENNA ISSUES AND TYPES Wireless networks do not normally require the use of highly directive antennae but there are a number of properties of the antennae that must be considered These issues are summarized below V Asingle antenna must function well for all likely angles of arrival of radio energy from other nodes v The antenna must in most cases be small enough to be compatible with a small radio node V Local radio regulatory rules may restrict the size of the antenna by setting a limit on the allowed gain see Section 9 3 v Where an antenna can be oriented in a particular direction it is likely that its direction setting will not be very precise The main types of antenna are considered in the subsections below 9 2 1 Isotropic Antenna As already mentioned an isotropic antenna radiates equally in all direc
34. where R Achievable range in meters Free space wavelength in meters Ptx Transmitter power in Watts Prx Receiver sensitivity in Watts G1 and G2 Linear antenna gains for Satellite 1 and Satellite 2 respectively Often it is simpler to use decibel dB quantities which are routinely quoted in datasheets in this case Equation 2 is rewritten as Please consider the environnement before printing this document Page 22 37 D Rethinking sensing technology Document version 1 2 S ea Ai r WSN Deployment Guideline Document Type Application Note Ei g Pry Pr 20 R A x 10 A Equation 3 AT where R Achievable range in meters Free space wavelength in meters Ptx Transmitter power in dBm Prx Receiver sensitivity in dBm g1 and g2 Antenna gains for Satellite 1 and Satellite 2 in dBi respectively Note that range increases with higher antenna gain higher transmit power and better receiver sensitivity antenna datasheets quote peak gain in the most favorable direction so it is worth checking the radiation patterns to see how much variation in gain occurs in different directions 9 4 ANTENNA POLARISATION A radio transmission is linearly polarised that is the electric and magnetic fields in the radio waves are in fixed orthogonal planes each containing the direction of wave propagation This is because the transmitting antenna has a dominant polarizatio
35. wireless PBX equipment cordless telephones and professional proprietary radio systems It is assumed that a typical installation of a wireless network is unlikely to have the benefit of a detailed site survey or propagation modelling techniques The placing of individual nodes will be largely non engineered as they will normally be sensors or switches with positions determined by other factors Please consider the environnement before printing this document Page 26 37 a Rethinking sensing technology Document version 1 2 Ge ea n Ai r WSN Deployment Guideline Document Type Application Note 11 DEPLOYMENT GUIDELINES The following sections offer some guidelines as a starting point for planning purposes 11 1 GENERAL GUIDELINES One of the most important factors when placing any node is its height above its immediate environment As a general rule in buildings head height or above is preferred and the higher the better for maximizing range If nodes must be placed in positions very close to the floor such as a radiator thermostat then the range may be reduced by between 50 and 90 It is also important to consider the environment close to the antenna If possible avoid placing the node where there are obscuring objects such as metal pillars posts or signs near to the antenna a close object obscures a wider range of solid angle 11 2 MULTIPATH AND FADE MARGINS It is a fact of life that radio reflecti
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