UPTEC F17 052
Examensarbete 30 hp Oktober 2017
Data communication for near shore applications
Andreas Stetenfeldt
Teknisk- naturvetenskaplig fakultet UTH-enheten
Besöksadress:
Ångströmlaboratoriet Lägerhyddsvägen 1 Hus 4, Plan 0
Postadress:
Box 536 751 21 Uppsala
Telefon:
018 – 471 30 03
Telefax:
018 – 471 30 00
Hemsida:
http://www.teknat.uu.se/student
Abstract
Data communication for near shore applications
Andreas Stetenfeldt
The wave energy conversion concept developed at Uppsala University is based on a buoy at sea level that is connected to a linear generator on the sea bed. The movements of the buoy riding the waves gets converted into electricity by the reciprocal movements of the translator inside the generator.
To be able to compensate the negative impact of water level variations on power production, which is especially important at sites with high tidal range, a sea level compensation system to be placed on the buoy was developed. During development, the system used cellphone technology to communicate, which can be power
demanding and is dependent on adequate cellphone reception.
Since future wave power parks could be localized up to 10 km offshore, in rural areas of developing countries, a new approach is needed for communication with the sea level compensation system that is not dependent on cellphone reception at sea.
In this report, a review of the regulations for radio communication and radio equipment in Sweden, Spain, Nigeria, Ghana and India is presented together with research of different possibilities of communication. Moreover, a new system for sending commands and receiving telemetry have been developed and have been tested for basic functionality, range and power efficiency.
Due to differences in the countries regulations and uncertainties about conditions at the future sites of deployment, the programs in the system are to be easily adapted to function with different radios depending on the country of interest and the conditions at the site. Hence, a system layout have been proposed rather than a specific
communication solution.
The experimental setup developed has been tested over land with license free radios, over a range of 10km in the vicinity of Uppsala. In the test, 100% of the transmitted commands were received and acknowledged within three attempts. The new control system for the buoys reduced the energy consumption from the previous
development system by 90%.
ISSN: 1401-5757, UPTEC F17 052
Examinator: Tomas Nyberg
Ämnesgranskare: Cecilia Boström
Handledare: Irina Temiz
Svensk sammanfattning
V˚ agkraftkonceptet som utvecklats vid Uppsala universitet ¨ ar baserat p˚ a en boj vid vattenytan som ¨ ar kopplad till en linj¨ argenerator p˚ a havsbotten. N¨ ar bojen f¨ oljer v˚ agornas r¨ orelse ¨ overf¨ ors r¨ orelsen till en translator i generatorn, som d˚ a alstrar elektricitet.
F¨ or att kompensera f¨ or de negativa effekter p˚ a elproduktion som uppst˚ ar n¨ ar havs- niv˚ an f¨ or¨ andras, vilket ¨ ar s¨ arskillt viktigt p˚ a platser d¨ ar tidvattnet orsakar stora vari- ationer, s˚ a har ett kompensationssystem utvecklats som placeras p˚ a bojen. Under utvecklingen anv¨ andes mobiltelefonteknologi f¨ or att kommuniceria med systemet.
Denna teknologi kan vara energikr¨ avande och ¨ ar beroende av mobilt¨ ackning.
Framtida v˚ agkraftsparker kan komma att placeras upp till 10 km utanf¨ or kusten p˚ a landsbygden i utvecklingsl¨ ander. Ett alternativt s¨ att f¨ or att kommunicera med kom- pensationssystemet som inte ¨ ar beroende av mobilt¨ ackning ¨ ar d¨ arf¨ or ¨ onskat.
I den h¨ ar rapporten presenteras efterforskning g¨ allande radiokommunikation och radioutrustning i Sverige, Spanien, Nigeria, Ghana och Indien. Vidare presenteras m¨ ojliga l¨ osningar till kommunikation. Ett nytt system f¨ or att s¨ anda kommandon och ta emot telemetri har utvecklats och grundl¨ aggande test har genomf¨ orts med systemet.
D˚ a regleringen av radiokommunikation skiljer sig ˚ at bland de unders¨ okta l¨ anderna, och p˚ a grund av os¨ akerhet kring r˚ adande f¨ orh˚ allanden p˚ a de framtida placeringarna av v˚ agkraftsparker, s˚ a har systemet utveklats f¨ or att kunna anv¨ anda olika radio beroende p˚ a vilket land det anv¨ ands i samt de r˚ adande f¨ orh˚ allandena p˚ a plat- sen.
Det utvecklade testsystemet har testats ¨ over land med licensfri radio, p˚ a ett avst˚ and
av 10 km i utkanten av Uppsala. Vid testet mottogs och bekr¨ aftades 100% av de
s¨ anda kommandona inom tre f¨ ors¨ ok. Testsystemet reducerade ocks˚ a energif¨ orbruknin-
gen med 90% j¨ amf¨ ort med den l¨ osning som anv¨ ants vid utvecklingen av kompensa-
tionssystemet.
Abbreviations
BER Bit error rate
EIRP Equivalent isotropic radiated power ERP Equivalent radiated power
ETSI European Telecommunications Standards Institute IoT Internet of things
ISM Industrial, scientific and medical
ITU International Telecommunication Union LPWAN Low power wide area network
M2M Machine to machine MCU Microcontroller unit
RPi Raspberry Pi
RSSI Received signal strength indication SCADA Supervisory control and data acquisition SLCS Sea level compensation system
SRD Short range device WEC Wave energy converter
Notation
dBd Antenna gain relative to half-wave dipole antenna dBi Antenna gain relative to isotropic antenna
dBm P dBm = 10 log 10 1mW P dBW P dBW = 10 log 10 P
UHF Ultra high frequency: 300 MHz - 3 GHz
VHF Very high frequency: 30 - 300 MHz
Contents
Abstract i
Svensk sammanfattning ii
Abbreviations iii
Notation iii
1 Introduction 1
1.1 Background . . . . 1
1.2 Thesis specifications . . . . 2
1.3 Assumptions and restrictions . . . . 2
1.4 Outline of the report . . . . 2
2 Technical background 3 2.1 Preceding approaches . . . . 3
2.2 Radio communication background . . . . 3
2.2.1 Free space loss . . . . 3
2.2.2 Ground wave propagation . . . . 4
2.2.3 Antenna . . . . 4
2.2.4 ERP and EIRP . . . . 5
2.2.5 Weather . . . . 5
2.2.6 Noise . . . . 5
2.2.7 Signal to noise ratio . . . . 5
2.2.8 Empirical prediction models . . . . 6
2.3 Organizations . . . . 6
2.3.1 International Telecommunication Union . . . . 6
2.3.2 European Telecommunications Standards Institute . . . . 7
3 Radio equipment background 8 3.1 General classifications . . . . 8
3.1.1 Licensed spectrum . . . . 8
3.1.2 License free spectrum . . . . 8
3.1.3 Integrated circuits & Radio modules . . . . 8
3.1.4 External radio . . . . 9
3.2 LPWAN . . . . 9
3.3 Available solutions . . . . 9
4 Regulatory background 11 4.1 Sweden . . . 11
4.2 Ghana . . . 12
4.3 Lagos, Nigeria . . . 12
4.4 Andaman Island, India . . . 13
4.5 Canaries Islands, Spain . . . 13
5 Design choices 14 5.1 Considerations . . . 14
5.1.1 Radio regulations . . . 14
5.1.2 Link budget . . . 15
5.1.3 Noise . . . 18
5.2 Chosen setup . . . 19
5.2.1 Hardware . . . 20
6 Implementation 21 6.1 Base station . . . 21
6.1.1 Database . . . 21
6.1.2 Base station main program . . . 22
6.2 Buoy control setup . . . 24
6.2.1 Buoy main program . . . 25
7 Experiments 27 7.1 System functionality . . . 27
7.2 Range test . . . 27
7.3 Energy consumption . . . 27
8 Results 29 8.1 System functionality . . . 29
8.2 Range test . . . 29
8.3 Energy consumption . . . 29
9 Discussion 30
10 Conclusions 31
11 Future work 31
References 32
1 Introduction
1.1 Background
The transition to a more sustainable electricity production calls for an extended harnessing of renewable energy sources. One of the renewable energy sources that has not been utilized for electricity production on a large-scale is wave energy. The global potential for wave energy is estimated to be 29 500 TWh/yr while estimations of practically recoverable potential varies from 2 to 5.5 TWh/yr [1].
Although the first patent for wave energy was filed in 1799, the technologies to harness wave energy is still maturing and today there are a multitude of concepts in varying states of development [1, 2].
One of these wave energy conversion concepts has been developed at Uppsala Uni- versity and is now being commercialized through the spin-off company Seabased Industry AB 1 , who are developing, building and deploying WECs in Sweden and abroad.
This conversion concept is based on a buoy at sea level that is connected to a linear generator on the sea bed. The movements of the buoy riding the waves gets converted into electricity by the reciprocal movements of a translator moving along a stator inside the generator. The WECs are connected to the power grid through a submerged substation in which the output voltage of the WECs is converted to the correct frequency, amplitude and phase of the power grid.
The WEC has been confirmed to work in Swedish waters, where the waves and tidal range are moderate but research has shown a substantially reduced power production efficiency with increased variations of the mean sea level [3, 4]. A shift of the mean sea level from the ideal, causes a corresponding shift of the translators work point.
This reduces the efficiency of the interaction between the translator and stator and it can cause the translator to reach the end points more frequently, causing more stress on the components.
To adapt the WEC for deployment where there are larger variations of the mean sea level, a sea level compensation system has been developed and tested at the Lysekil research site in Sweden [5, 6]. This system is placed on the buoy and can vertically adjust the mounting point of the line connecting the buoy to the translator, thus adjusting the translator work point.
The sea level compensation system uses solar panels and a battery to power its motor and additional hardware. To communicate, the system uses cellphone technology, which is both power demanding and dependent on adequate cellphone reception [7, 8].
Since deployment of wave power farms could be localized up to 10km offshore, in
rural areas in developing countries, a new approach is required to communicate with
the sea level compensation system, that is not dependent on cellphone reception at
sea.
1.2 Thesis specifications
The given specifications for the project were
• Investigate possible solutions for communication with the sea level compen- sator.
A suggested technology to investigate is LPWAN.
• Investigate the rules and regulations for radio communication in Ghana, Lagos, Andaman Island and Canaries Islands in the correct frequency bands.
• Based on the investigation, implement a test system with suitable hardware that can transmit and receive tidal data or just winch commands to the buoys.
• Test and confirm the functionality of the system under realistic conditions.
1.3 Assumptions and restrictions
To delimit the research, some assumptions and restrictions have been made through- out the work of the thesis. Some were also done due to the fact that the conditions on the possible future sites of use are largely unknown.
• Solutions depending on a network operator providing coverage of the area are not considered.
• The path from shore to the buoys at sea is considered to be passing over salt water, without obstructions along the path.
• For a radio placed on shore the antenna is assumed to be able to be mounted at 10 m or higher above ground and without surrounding clutter.
• The frequencies for radio communication are limited to the VHF and UHF bands.
Additionally, Sweden is added among the countries to investigate regulations for since the development takes place there as well.
1.4 Outline of the report
The report starts by covering earlier approaches for controlling the sea level com- pensator and by presenting some basic characteristics of radio communication in Section 2. This is followed by a presentation of radio equipment and some of its key features in Section 3. In Section 4 the regulatory background for radio communica- tion in the specified countries is presented.
Given this basis, the considerations, design choices, chosen setup and hardware for
the project are presented in Section 5. In Section 6 the implementation of the
chosen setup is explained in detail. Finally the experiments and results that verify
functionality are presented in Section 7 and 8 followed by discussion, conclusions
and recommendations for future work.
2 Technical background
2.1 Preceding approaches
The two preceding implementations of communication with the compensation sys- tem are both based on cellphone technology. A short presentation of the systems layout follows.
The prototype for the sea level compensation system developed at Uppsala Univer- sity was controlled by a CompactRIO programmable automation controller. The system used two communication systems, one GSM modem based for receiving commands and one based on a Raspberry Pi with a 3G modem for transferring measurements [7, 8]. Without the electro-mechanical system for adjusting the trans- lators work point active, the systems energy consumption was 15W. The estimated energy consumption of the electro-mechanical system at the Lysekil test site was 133 Wh/day [6].
The later project implementation of a control system was based on a Raspberry Pi with an unspecified Huawei USB Internet stick. The control program on the RPi is controlled through a secure shell connection or extracts commands from a file stored on an Internet cloud server. For each command the RPi flashes a program to a Arduino Uno which through a motor controller circuit executes the command [9].
Additionally, Seabased’s latest version of the controllers electro-mechanical system uses a motor controller circuit that is communicated by RS-232, together with a rotary encoder to determine position.
2.2 Radio communication background
Radio communication is dependent on physical limitations which need to be taken into account to achieve stable communication under given conditions. For terres- trial radio communications, the radiowaves interaction with the surroundings makes models too complex. Some key properties are presented bellow.
2.2.1 Free space loss
Radiowaves emitted by an isotropic antenna in free space will propagate uniformly in all directions. Thereby the power flux density, P , will decrease with distance from the transmitter and can be expressed
P = P t G t 4πd 2 = E 0 2
2η 0 (2.1)
where P t is the power transmitted, G t is the gain of the transmitting antenna, d is
the distance from the transmitting antenna, E 0 is the magnitude of the electric field
and η 0 is the free space intrinsic impedance [10].
The received signal power is dependent of the receiver antennas aperture area A e given by
A e = G r λ 2
4π (2.2)
where G r is the receiving antenna gain and λ is the wavelength [10].
Hence the signal strength P r in the receiver is dependent on the wavelength and can be expressed as
P r = P A e (2.3)
Combining equations (2.1) - (2.3) results in
P r = P t G t G r λ 2
(4πd) 2 (2.4)
and
P r = G r E 0 2 λ 2
8η 0 π (2.5)
The free space loss F SL, in decibel, is expressed by F SL dB = 10 log 10 P t P r
(2.6)
and for antennas with unity gain, the free space loss is then given by equation 2.7 [10].
F SL dB = 20 log 10 4πd λ
(2.7)
2.2.2 Ground wave propagation
The ground wave propagation, the propagation adjacent and parallel to the earth surface is dependent on the relative conductivity of the covered ground. For fre- quencies up to about 900 MHz, sea water can act as a good conductor and good ground wave propagation can be expected. The corresponding approximate cut of frequency for fresh water is 1.1 MHz and for dry ground 45 MHz [11].
2.2.3 Antenna
To reduce the transmission power needed or to improve the reception of signals, directive antennas are often used, concentrating the power in certain directions.
Directive antennas also have the benefit for receiving systems that surrounding noise
from outside the direction of the antennas main lobe gets attenuated.
2.2.4 ERP and EIRP
Equivalent radiated power is a measurement or transmitted power relative to a half wave dipole given by
ERP = P t G t
L t (2.8)
where P t is the power transmitted, G t is the gain of the transmitting antenna relative to a half-wave dipole antenna and L t is the losses in cable, connectors etc.
If instead a isotropic antenna is used for reference, the calculation gives the equiva- lent isotropic radiated power for the corresponding isotropic antenna gain G t [10].
2.2.5 Weather
Changes in weather and climate affects the wave propagation differently at different frequencies. For line-of-sight propagation in the VHF and UHF bands though, the effects of rain, fog, snow and hail are negligible or have low probability to occur [10].
2.2.6 Noise
Noise can come from multiple sources such as thermal, atmospheric, cosmic, and man-made. At different frequencies, antenna directions and at different locations the noise to be taken into consideration varies. For instance for the VHF and UHF bands, the galaxy, sky and sun noise is small and decrease with increased frequency [10] .
The thermal noise is equipment and temperature dependent and its maximum noise power N is given by
N = N 0 W = kT W (2.9)
where N 0 is the spectral density of the noise, k is Boltzmann’s constant, T is the components temperature and W is the bandwidth [11, 12].
2.2.7 Signal to noise ratio
To distinguish the received signal from present noise, the signal to noise ratio,SN R must be within the equipment limitations. The signal to noise ratio is given by
SN R = S N = P r
N (2.10)
where S = P r is the received signal power and N is the noise power in the re-
ceiver.
For digital communication, the quality measure E b /N 0 , a normalized version of signal to noise ratio, is also used as a quality measure. E b is bit energy and the equation is given by
E b N 0 = S
N W
R b (2.11)
where R b is the bit rate. The probability of bit errors versus E b /N 0 often shows a rapid degradation [11, 12].
2.2.8 Empirical prediction models
Due to the complexity of the radiowave’s interaction with the surroundings, empiri- cal models can be used for estimations of pathloss or received signal power. Due to the models generalizations, tuning of the models with the use of measurements is a necessity [13]. One model, is the Okumura-Hata model [10], which is used for point to area prediction where the loss L for open area is given by
L dB = 28.61 + 44.49 log 10 (f M Hz ) − 13.82 log 10 (h B ) (2.12) + (44.9 − 6.55 log 10 (h B )) log 10 (d km ) − 4.78(log 10 (f M Hz )) 2 where d is the distance in km, f is the frequency in MHz and h B is the base station height. The model is valid for frequencies from 150 to 1500 MHz, distances from 1 to 20 km, base station antenna heights from 30 to 200 m and mobile antenna heights from 1 to 10 m.
2.3 Organizations
There are several important organizations, cooperation agencies and authorities de- veloping standards and regulations for radio communication and equipment. Two of them are presented below.
2.3.1 International Telecommunication Union
The International Telecommunication Union is an agency of the United Nations.
The ITU works, inter alia, with recommendations for technical standards and allo- cation of radio spectrum. The common allocation of radio spectrum helps countries with, for example, efficient spectral utilization. Standardizations for radio equip- ment also makes the equipment usable in many countries and enables manufacturers to act on the global market.
Although countries, generally, follow the ITU Radio Regulations, there is still room
for local variations in the spectral utilization. Furthermore, the world is divided
into three different ITU regions with differences, for example, in some frequency
allocation.
Two relevant recommendations are the ITU-R P.1546 and ITU-R P.372. The ITU- R P.1546 provides methods to estimate field strength for terrestrial transmission in the UHF band [14]. The ITU also provide a helpful MATLAB implementation of recommendation ITU-R P.1546-5 [15]. The ITU-R P.372 provides recommendations for radio noise estimations [16].
Apart from recommendations, the ITU also provides other useful publications such the relevant Handbook, Terrestrial land mobile radiowave propagation in the VHF/
UHF bands [13], to assist in implementing recommendations.
2.3.2 European Telecommunications Standards Institute
The European Telecommunications Standards Institute, is officially recognized by the European Union as a European Standards Organization.
”...ETSI produces globally-applicable standards for Information and Communica- tions Technologies (ICT), including fixed, mobile, radio, converged, broadcast and Internet technologies...” [17]
The countries to investigate, all except India, base parts of their radio regulations
on ETSI standards.
3 Radio equipment background
For IoT, SCADA and other M2M communication, there are possibilities from sim- ple solutions, acting as a wired serial connection between two nodes, to advanced networks with gateways receiving and transmitting on multiple frequencies simulta- neously.
This yields many types of radio solutions available to control the sea level compen- sator where some considerations and possibilities will be presented below.
3.1 General classifications
For this project, the radio equipment can be given two important classifications:
spectrum type and type of hardware. The spectrum type is divided into licensed and unlicensed and is dependent on the country of use. The hardware can be divided into integrated circuit, module and external. These types are presented below.
3.1.1 Licensed spectrum
A radio license for a fixed service, where the transmitter or transmitters are consid- ered stationary can be adapted in the licensing process to give a good functionality while not causing interference for others. Thus the benefits of using licensed fre- quencies are less interference from other radio traffic and, generally, the possibility to use a higher transmission power.
3.1.2 License free spectrum
Countries, usually, have license exceptions in certain frequency bands. These license free bands can be limited to specific types of use and have standards and limitations to follow. One such band is the global 2.4 GHz ISM band which in most countries can be used without license for wireless local area networks, Bluetooth and other applications. Since radio communication can be allowed as secondary use at fre- quencies such as the ISM bands, a requirement can be that the equipment must accept harmful interference caused by the primary users [18].
Hence the interference at some license free frequencies can vary with location, for instance, depending on proximity to ISM applications, but also with proximity to other users of the same or neighbouring frequencies.
3.1.3 Integrated circuits & Radio modules
There are lots of integrated circuits and modules on the market, available to enable
radio communication. One of the benefits of using these is that they are relatively
cheap since the circuit or module can be selected for a specific use, thus not paying for
any unnecessary functionality. Some of these are also pre-certified, thus simplifying
an eventual type approval of the final circuitry.
3.1.4 External radio
Many modern digital portable and mobile radios can be used both for audio and data but there are also radio modems intended for data communication only. Some manufacturers have their own data transfer protocols, signal modulations or net- work solutions, which limits the customers to their hardware. Others use open or proprietary standards.
3.2 LPWAN
LPWAN is used for wireless communication with low energy consumption for the network connected objects. This is achieved by using narrow bandwidth to concen- trate the transmission energy, low transmission power, relatively low data rates to increase the bit energy, and by few transmissions per connected object. The fre- quencies used are mostly within widespread license free subbands of the UHF band.
The UHF band allows for small antennas and a balance of relatively low noise and good propagation characteristics. The transmission range between two objects or an object to a base station or gateway vary from meters to more than ten kilometers depending on the technology used and the environmental conditions.
A wide area coverage is achieved either by sheer transmission range where the objects communicate directly with a gateway or by using mesh networks where intermedi- ate objects relay the transmissions from the sender to the gateway. For a larger areal coverage additional gateways are used. The spacing between gateways can have a direct impact on the objects energy consumption by affecting the required transmission power, data rate or intermediate retransmissions.
Apart from radio connectivity, a LPWAN requires protocols to regulate the physi- cal interaction and network structure. It may also require network infrastructure, gateways, network controllers, network servers and application servers. This chain of services and equipment can fully or in part be provided by different companies depending on technology.
There is a growing market of IoT and M2M communication without a dominating standard, in comparison with the widespread IEEE 802.11 standard for connecting computers, printers etc. The later can be to energy consuming for objects operating solely on batteries [19, 20, 21, 22, 23].
3.3 Available solutions
There are many manufacturers producing integrated radio circuits and/or modules
and there are also many that build modules or external radios based on other manu-
facturers or own circuits. Some of these only support basic functionality while other
can be used for communicating by protocols such as IEEE 802.15.4g, LoRaWAN,
ZigBee, Wireless M-Bus etc. Important features such as the frequency range, sensi-
tivity and output power varies considerably depending on the chosen solution and
its intended use.
LPWAN, IoT and M2M solutions, together with radio modems have been looked into. Among the LPWAN technologies the LoRaWAN was considered the most suitable and readily deployable for private networks but more complex than radio modems.
While, for instance, the Semtech SX1276 tranciever [24], capable to use with LoRa- WAN, can work on frequencies from 137 to 1020 MHz, the usable frequency band is narrower on the complete modules. The SX1276 is also capable of 20 dBm transmission power and -148 dBm sensitivity. The actual transmission power that can be used is, however, limited in the LoRaWAN specifications regional parameters [25], adapted to regulations in the region of use. The frequencies, specified maximum transmission power and data rates are listed in Table 3.1 for various parts of the world.
Table 3.1: LoRaWAN restrictions
Main region Frequency Tx Power Data rate European Union 863-870 MHz ISM 16 dBm 0.25-50 kbps USA & Canada 902-928 MHz ISM 30 dBm 0.98-21.9 kbps China 779-787 MHz ISM 12.15 dBm 0.25-50 kbps European Union 433 MHz ISM 12.15 dBm 0.25-50 kbps Australia 915-928 MHz ISM 30 dBm 0.25-21.9 kbps China 470-510 MHz ISM 19.15 dBm 0.25-5.47 kbps 923 MHz ISM 16 dBm 0.25-50 kbps South Korea 920-923 MHz ISM 14 dBm 0.25-5.47 kbps India 865-867 MHz ISM 30 dBm 0.25-50 kbps
Some of the radio modems looked into together with important properties are pre- sented below.
Table 3.2: Radio modems
Manufacturer Model Frequency Tx Power Sensitivity Data rate
Adeunis RF ARF7940BA 863-870 MHz 500 mW -120 dBm, BER 10
−32.4-57.6 kbps
Icom IC-F5122DD 136-174 MHz 25 W -4 dBµV, BER 1% 4.8/5.6 kbps
Icom IC-F6122DD 400-470 MHz 25 W -4 dBµV, BER 1% 4.8/5.6 kbps
Satel Satelline-Easy 330-420 MHz 1 W -114 dBm 19.2 kbps
403-473 MHz
Satel Satelline-Easy 869 869.4725- 1 W -111 dBm 19.2 kbps
869.6375 MHz 865-867 MHz
Schneider Electric Trio K series 2.4 GHz ISM 500 mW -108 dBm, BER 10
−632-256 kbps
4 Regulatory background
Since the frequency spectrum can be regarded as a natural resource, countries gov- ern it for revenue and efficient utilization. This includes planning and licensing of frequency bands and approval of radio equipment to ensure safety and compliance with regulations.
The scope for the thesis is to investigate what regulations apply at suitable frequen- cies and for equipment to use at these frequencies.
A brief presentation of the regulations for the specified countries is presented be- low.
4.1 Sweden
• Governed by
The Swedish Post and Telecom Authority
• Radio equipment regulations
Radio equipment is regulated under Swedish law with a transpose of EU di- rective 2014/53/EU [26, 27, 28].
• Radio license regulations
Generally a license is required for radio transmission [29]. However, there are many exceptions to the requirement [30, 31].
By implementation of mentioned EU directive, radio equipment with CE marking is allowed to be used. Among the license exceptions are the ones presented below.
433.05-434.79 MHz. Radiotransmitter for unspecified use. Maximum transmission power is 15 mW ERP. Duty cycle limit is 10%.
869.40-869.65 MHz. Radiotransmitter for unspecified use. Maximum transmission power is 500 mW ERP. Duty cycle limit is 10% if techniques for spectral access and mitigation of interference is not used.
2400.0-2483.5 MHz. Radiotransmitter for data transmission. Maximum transmis- sion power is 100 mW EIRP with a maximum spectral density of 100 mW/100kHz EIRP for frequency-hopping modulation and 10 mW/100 kHz for other modula- tions.
2400.0-2483.5 MHz. Radiotransmitter for unspecified use. Maximum transmission power is 25 mW EIRP.
For these license exceptions additional requirements, standards and specifications
are also applied.
4.2 Ghana
• Governed by
The National Communications Authority of Ghana
• Radio equipment regulations
All radio equipment need a type approval from the authority [32, 33].
• Radio license regulations
Frequencies for licensed use, together with applicable standards can be found in Annex 4 of the Type approval guidelines [33].
Upon payment of a fee there are frequency bands in Ghana that are allowed to be used for unlicensed non-ISM equipment as presented in Table 4.1 [34].
Table 4.1: Ghana M2M specifications
Authorized RF output Transmitter spurious Applicable radio Typical application types
frequencies power emissions standards
433.05-434.79 MHz ≤ 10 mW ERP ≥ 32 dB below carrier at FCC Part 15 Radio telemetry, telecomm and 3 m or EN 300 220-1 EN 300 220-1 system, Short range device 2.4000-2.4835 GHz ≤ 200 mW EIRP FCC Part 15§15.209 FCC Part 15§15.247 Wireless LAN only
EN 300 328 EN 300 328
5.250-5.350 GHz ≤ 1000 mW EIRP FCC Part 15§15.209 FCC Part 15§ Wireless LAN and
5.470-5.725 GHz 15.247 or 15.407 broadband access only
5.725-5.850 GHz
4.3 Lagos, Nigeria
• Radio equipment regulations
The Nigerian Communications Commission (NCC)
• Type approval
All radio equipment need a type approval from the NCC [35, 36].
• Radio license regulations
A license is required but there are license exceptions [35]
Nigeria has no sub-GHz license free bands. For the 2.4 GHz ISM band, radio
communication is allowed on a secondary, non-protected, non-interference and non-
exclusive basis. Furthermore, the network must be registered with the NCC and
its telecommunication equipment need to be type-approved by the NCC. The max-
imum transmission power is 100 mW EIRP and only spread spectrum modulation
is allowed [37].
4.4 Andaman Island, India
• Governed by
The Wireless Planning & Coordination Wing of the Ministry of Communica- tion & Information Technology
• Radio equipment regulations
It is prohibited to possess a wireless telegraphy apparatus without required licenses [38]. For the de-licensed frequency bands all equipment need a equip- ment type approval [39, 40].
• Radio license regulations
Generally a license is required for radio transmission. However, there are some de-licensed frequency bands [41].
The frequencies 865-867 MHz with 200 KHz carrier band width is exempted from licensing requirements for up to 4 W ERP.
4.5 Canaries Islands, Spain
• Governed by
The Ministry of Energy, Tourism and Digital Agenda
• Radio equipment regulations
Radio equipment is regulated under Spanish law with a transpose of EU di- rective 2014/53/EU. This makes CE marked radio equipment allowed to be used in Spain. [42].
• Radio license regulations
Generally, a license is required although there are exceptions [43, 44, 45, 46].
By the homogenization of regulations throughout the European Union, the specific frequencies listed for Sweden in Section 4.1 are also available for license free use in Spain. Spain has a stricter implementation of 2013/752/EU, which reduces the allowed transmission power as follows.
433.05-434.79 MHz. Radiotransmitter for unspecified use. Maximum transmission power is 10 mW.
2400-2483.5 MHz. Radiotransmitter for unspecified use. Maximum transmission power is 10 mW EIRP.
Additional requirements, standards and specifications are also applied.
5 Design choices
The main considerations to choose a communication solution to control the sea level compensator is
• RF regulations
Compliance with the countries different regulations regarding frequency, emit- ted power, equipment etc.
• Link budget
Many of the conditions on the intended sites of use are unknown. The possi- bility of shadowing from adjacent waves, cable losses, mounting height of an eventual base station antenna and polarization losses for the buoys antenna when the buoy moves around are all unknown. This all urges a generous link margin to provide functionality without prior measurements of path loss and surrounding noise.
• Security
The communication with the buoys needs to be secure to protection against misuse.
• Infrastructure
The site of use could be in locations where the quality of service for Internet connectivity and power supply could be low.
• Energy consumption
The controller and communication solution for the sea level compensator should, on a daily basis, consume substantially less energy than the electro- mechanical system as to not be a limiting factor.
5.1 Considerations
5.1.1 Radio regulations
The regulatory research for the relevant countries showed that to know the limita- tions at a licensed frequency, a license process needs to be initiated, with the author- ities adapting the requested license with regulations and the surrounding conditions.
Thus the only given conditions regarding radio regulations could be found among the unlicensed frequencies.
For the relevant countries the only overlapping license free frequencies found are in the 2.4 GHz ISM band where the transmission power is limited to 100 mW EIRP in Nigeria, Sweden and Spain [35, 31, 46, 47].
For increased transmission power, the frequencies 869.40–869.65 MHz are allowed
for unspecified use with 500 mW ERP in Sweden and Spain [31, 43]. This neighbors
the Indian exemption from license requirement for the frequencies 865-867 MHz
with 200 kHz carrier bandwidth and maximum 1 W transmitter power and 4 W
ERP. These frequencies does not align with any unlicensed frequencies in Ghana
as presented in table 4.1 or Nigeria, who do not have unlicensed frequencies sub-
GHz [37].
5.1.2 Link budget
The received power is estimated with the ITU MATLAB implementation presented in Section 2.3.1 and using the theory of Section 2.2.1.
The estimation can be seen in Figure 5.1, with the parameters for the estimations presented in Table 5.1. For comparison, the received power for a rural path over land is presented in Figure 5.2 and with free space propagation in Figure 5.3, for transmission power and antenna gain as in Table 5.1.
Table 5.1: Estimation parameters
Model parameter Short description Value Units
t Required time 50 %
heff Transmitter height 10 m
h2 Receiver height 3 m
R2 Clutter height 0 m
area Receiver terrain Sea
path c Path terrain Sea
q Location variability 1 %
PTx Transmitter ERP 500 mW
Receiver antenna gain 0 dB i
-100 -90
5
Distance [km]
-80
500
Power [dBm]
-70
Frequency [MHz]
1000 -60
-50
1500 2000 2500 10 -140
-120 -100 -80 -60 -40
Power [dBm]
Figure 5.1: Estimated power received over sea path
-140 -120
5
Distance [km]
-100
500
Power [dBm]
-80
Frequency [MHz]
1000 -60
-40
1500 2000 2500 10 -140
-120 -100 -80 -60 -40
Power [dBm]
Figure 5.2: Estimated power received over land path
-100
5 -80
Distance [km]
500 -60
Power [dBm]
Frequency [MHz]
-40
1000 -20
1500 2000 2500 10 -140
-120 -100 -80 -60 -40
Power [dBm]
Figure 5.3: Free-space power received
From the Figures 5.1 and 5.3 it can be seen that the ITU sea path estimation differs, not only in power but also in characteristics compared to the free space propagation.
By comparison of the land and sea path estimations, it is clear that the estimated loss is greater for the land path. Especially for the higher frequencies.
A comparison of the three methods at 10 km can be seen in Figure 5.4.
500 1000 1500 2000 2500 Frequency [MHz]
-140 -120 -100 -80 -60 -40
Power [dBm]
Sea path Land path Free space
Figure 5.4: Power received at 10km
In Figure 5.4 the land path estimation shows the greatest loss and the two terres- trial estimations both have a greater loss than the theoretical free space propaga- tion.
To investigate the influence of the transmitter height, additional estimations were made with the ITU MATLAB implementation with settings given in Table 5.1 and the distance set to 10km. The resulting estimate of received power can be seen in Figure 5.5.
-100 -95
50 -90 -85
Power [dBm]
40 500 -80 -75
1000
Height [m] Frequency [MHz]
30 20 2000 1500
10 2500 -140
-120 -100 -80 -60 -40
Power [dBm]
Figure 5.5: Estimated power received at 10km
From Figure 5.5 it can be seen that the transmitter height has a great impact on the received power, especially in the sub-GHz frequencies.
For a land path comparison, the estimation of the Okumura-Hata model and the
is set to 50 m, the reciever height to 1.5 m, the height of clutter surrounding the receiver to 1 m and the frequency to 869 MHz. Additional parameters are as given in Table 5.1.
2 4 6 8 10 12
Distance [km]
-130 -120 -110 -100 -90 -80 -70 -60
Power [dBm]
ITU-R P.1546 Okumura-Hata
Figure 5.6: Estimated power received at 869MHz
5.1.3 Noise
Under the specified conditions of rural areas the occurrence of man made noise is expected to be low and is not taken into consideration.
For the frequencies 30 MHz to 3 GHz, the atmospheric noise can be ignored but the galactic noise needs to be considered [13].
Based on the theory of Section 2.2.6, the maximal thermal noise power in the re- ceiver at 300 K is calculated. The estimated minimum galactic noise power is also calculated based on ITU recommendations for a lossless antenna.
The calculations are presented in Figure 5.7 where the external noise figure F a for 100 MHz is estimated to 3 dB and for 900 MHz to -15 dB [16].
In Figure 5.7, it can be seen that the selection of frequency and bandwidth dictates
the amount of noise to be expected in the system.
1 10 100 1000 Bandwidth [kHz]
-160 -150 -140 -130 -120 -110
Power [dBm]
Thermal
Galactic @ 900MHz Galactic @ 100MHz
Figure 5.7: Noise power
5.2 Chosen setup
To keep the energy consumption of the system on the buoy low, the functionality of the solution should be limited to receiving commands and sending acknowledgments and, possibly, telemetry. This approach moves most of the calculations and data management to a base station on a site with better conditions for power supply and Internet connectivity. It also enables simpler, more power efficient hardware to be used to control the sea level compensator than in previous implementations.
From the regulatory research in the specified countries, no specific frequency band could be found where a license could be guaranteed. Since the true link budget needed is also unknown, a more general approach was opted for, with a system that could be adapted to use different radios if needed, depending on the country of use and on the site conditions.
An overview of the envisioned setup is presented in Figure 5.8 where the lower boxed part is considered out of scope for the thesis.
Computer Radio Radio MCU
Compensator Management
Base station Buoy
Figure 5.8: Setup overview
The management in Figure 5.8 can then either represent that the base station com- puter calculates commands for the buoys sea level compensator from telemetry, tidal charts etc. or that the commands are produced off site and uploaded to the base station for transmission.
The unknown quality of service on site for a Internet connection prompts for a local buffer of future commands at the base station. Since the tide can be predicted, a buffer of commands can be stored in the base station in advance. The commands can then be transmitted to the buoys on time even if Internet connection is temporarily lost.
5.2.1 Hardware
For the chosen generic approach the hardware for the test system was selected for a stationary base station and a mobile buoy system. To enable mobility for testing, the buoy system is powered by a 12 V MC battery and a LCD-display is used to present received commands.
The key hardware is selected for ease of use, interoperability and to be suited for further test development. The radios were selected as suitable for testing with regard to sensitivity and estimations of Section 5.1. Given favorable conditions on the intended sites a transmission power of 500 mW could be sufficient and hence the radios were selected to comply with unlicensed use in EU countries Sweden and Spain.
The key hardware was selected as follows Base station computer
Raspberry pi 3 Model B [48]. A low-cost single board computer with USB ports, GPIO pins and ethernet port. It is capable of running a local database server and programs of a multitude of programming languages.
Buoy system MCU
Arduino Mega 2560 [49]. A ATmega2560 based development board with 4 hardware serial ports, 54 digital I/O pins and 16 analog input pins.
Radio
Adeunis RF ARF7940BA [50]. External radios that operate between 863 and
870 MHz. The radios are capable of 500 mW output power and -122 dBm sen-
sitivity at BER 10 −3 . They are interfaced by RS-232 or RS-485 and supports
power supply voltages from 4.5 to 36 VDC.
6 Implementation
The implementation of the test system can run on two different power schemes for evaluation of power efficiency but also to fit different test scenarios. One scheme,
”Always on”, where the system on the buoys are always in reception mode when not transmitting and another scheme, ”Power saving”, where the system is intended to be in a sleep mode most of the time. For the Power saving scheme the system periodically powers up the radio, transmits some telemetry and then enters reception mode for a short period of time before again entering sleep mode. By doing so the base station can, when receiving telemetry from a buoy, search the database for commands for that buoy and transmit those while it is in reception mode.
6.1 Base station
The intended use of the base station is to store future commands for the buoys in a database and when triggered, send the commands. The commands can be inserted into the database remotely. By using a local database server and storing commands in advance the functionality is less dependent on the quality of the base stations network connection. To reduce the required memory of the database, any telemetry from the buoys only get stored in the database for a limited time. For evaluation and long time storage, the historic data can be downloaded from the base stations database.
6.1.1 Database
The database used for the base station is presented in Figure 6.1. The telemetry considered for the test system is the height setting of the sea level compensator and the systems battery level. The database can also store buoy and system events for evaluation of performance together with system settings for future implementation.
Time is stored as 32-bit Unix time.
buoys
dbId onSiteId address commandType
typeId description
commands
buoyId time type ack
cHeight
buoyId time height height
buoyId time height
battery
buoyId time level buoyEvent
buoyId time type
systemEvent time type
settings id value
Figure 6.1: Database relational schema
6.1.2 Base station main program
The main program used in the base station computer is programmed in C++. Al-
though the two routines handling the communication with the buoys differ, they
can both be described by the flow chart of Figure 6.2 with the main difference being
the trigger which is further explained below.
Initialize
Trigger Command
in DB
Send command
Incoming radio
Update DB Sleep
no
no yes
no
yes
yes
Figure 6.2: Base station program, flow chart
A description of the base stations main program presented in the flow chart of Figure 6.2.
Initialize
Establishes connection with the radio and database.
Trigger
Always on
The trigger can be set to ”true” periodically (e.g. every 15min) and stay
”true” until there are no new commands to transmit.
Power saving
The trigger is ”true” after receiving a message and while there is new commands for that buoy.
The trigger is always ”blocked” for a short period of time after each sent command, to await acknowledgement or telemetry from the buoy.
Command in DB
Searches the database for messages to be sent in a given timespan relative to the current time. Either for one specific buoy or for all depending on power scheme.
Send command
The function sets the recipient address in the radio and sends the command. It
also increments the commands ”transmission attempt” counter in the database
and sets a trigger ”block” timer.
Incoming radio
Checks the radios buffer for incoming messages. If a message is received it gets validated and classified. The classifications are telemetry or acknowledgment of given command. The address to the sender of the message is also stored for triggering.
Update DB
If the message and the sender is valid the database is updated in accordance with the classification of the message.
Sleep
Since the loops are performed very quickly, the program ”sleeps” for short periods of time to reduce the CPU usage and to not perform supernumerary radio checks.
6.2 Buoy control setup
The buoy hardware consists of a MCU connected to a two-way radio and to the sea level compensator. The MCU runs a program, described in the following Section 6.2.1, to communicate with the base station and to control the sea level compen- sator.
The assembled test system to simulate the buoy control system can be seen in Figure 6.3. In the test system, the sea level compensator is replaced with a LCD display to show the received commands. The test system components are explained below.
A
B
C
D E
F
G
H
Figure 6.3: Simulated buoy test system in temporary mounting
A Arduino board
B Soldered perforated board with three voltage dividers, additional ground and 5V connections and a transistor with supplementary resistors. The voltage dividers are used to set the LCD display contrast and to enable readings of the battery and supply voltage. The transistor enables the Arduino to control the backlight of the LCD display.
C LCD display to present commands and battery voltage
D Adjustable switched voltage regulator with added screw connections E RS-232 shifter with D-Sub 9-pin female connector
F Power cable from battery G Serial cable to radio H Power cable to radio
6.2.1 Buoy main program
The flow chart of the program running on the MCU is presented in Figure 6.4 and as for the base station program it supports two power schemes, with the main difference being the sleep which is further explained bellow.
Initialize
Incoming radio
Valid command
Sleep?
Send telemetry Send
acknow- ledgement
Adjust height Delay
Sleep no
yes
no
no
yes
Figure 6.4: Buoy program, flow chart Initialize
Initializes communication with the radio and applies basic radio settings.
Incoming radio
Checks the radio buffer for incoming messages.
Valid command
The received command gets validated. The commands either requests teleme- try or adjustment of height.
Send acknowledgement
If height adjustment is requested the command is acknowledged.
Adjust height
The new height is sent to the sea level compensator.
Send telemetry
If telemetry is requested the measurements are performed and values sent. A transmission of telemetry is also performed after sleep.
Sleep?
Always on
The check always return ”false”.
Power saving
The check is validated as ”true” after a given period of active time.
Sleep
For power efficiency the radio and MCU can be set to sleep mode with reduced energy consumption.
Delay
A short delay is implemented to not request supernumerary radio checks.
7 Experiments
To evaluate the test system three experiments were performed with respect to func- tionality, range and energy consumption.
7.1 System functionality
To evaluate the the programs and system functionality the test system was tested over a short range with the radios at a minimum transmission power of 10 dBm.
7.2 Range test
Range testing in real world conditions was limited to the vicinity of Uppsala, Sweden.
Hence the test was not performed over open seawater but instead mainly over open farmland. The base station had during the test an approximate height advantage of 45m relative to the mobile buoy system.
The range test was performed running the ”always on” routine with new commands being sent approximately every 15 seconds. The base station radio was mounted on a fifth-storey balcony of house 1 at the Polacksbacken campus. The mobile buoy systems radio was placed with its antenna approximately 1.5 m above ground on different locations to test whether the transmissions were received. The base station setting was to attempt each command up to five times while the buoy system transmitted a single acknowledgement of valid commands. The radios were set to 27 dBm transmission power, 2.4 kbps data rate and frequency 869.525 MHz.
The main test was performed with the buoy system placed at a distance of 10 km from the base station as presented in Figure 7.1. The commands were evaluated from the base station database to confirm that they had been acknowledged and how many attempts had been required to do so.
En route to the predetermined main test site, short stops were made do confirm reception of a few commands. The reception was also tested at two locations at a greater range than the main site at a range of approximately 11.5 km, with the locations separated by a few hundred meters. These locations are labeled as points A and B in Figure 7.1.
7.3 Energy consumption
The energy consumption is calculated from measurements of the supply voltage and current. During the power measurement the backlight was turned off, the battery voltage was 12.4 V and the voltage regulator output was 9.02 V.
Since the buoys are to send only a few acknowledgements or updates a day, and
these transmissions only take a fraction of a second, the energy consumption during
transmissions is omitted.
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