Urban Channel Models for Smart City IoT-Networks Based on Empirical Measurements of

LoRa-links at 433 and 868MHz

Pascal Jorke, Stefan Bocker, Florian Liedmann, Christian WietfeldCommunication Networks Institute (CNI), TU Dortmund University, Germany

Email: {pascal.joerke, stefan.boecker, florian.liedmann, christian.wietfeld}@tu-dortmund.de

Abstract—The vision of Smart City is to enablenew use cases being overall connected. Consid-ering a large number of Internet of Things sen-sors and challenging channel characteristics, newtechnologies evolve facing these new challenges. Apromising solution to meet such requirements areLow Power Wide Area Networks. In this paper, aLoRa availability analysis is carried out to analyzeperformance of a Low Power Wide Area Networksrepresentative in the 433 MHz and 868 MHz ISMbands considering a Smart City Internet of Thingsscenario, resulting in signal ranges up to 5.8 km.Additional reliability measurements show that in-door and outdoor LoRa nodes are able to achievea Packet Delivery Rate of over 99% within a rangeof 4.8 km, depending on their installation side. Theresults of these measurements are compared withestablished empirical channel models. Due to theinsufficient prediction accuracy of the establishedmodels in the examined Smart City area of Dort-mund, Germany, two new path loss models forurban areas are presented for both the 868 MHzand 433 MHz frequency bands.

Index Terms—Smart City, LoRa, Range analy-sis, Path loss models

I. Introduction

With the sustained fast digitalization of everydaylife, existing communication technologies are facedwith new challenges. Upcoming scenarios like SmartWaste Management where all garbage cans in thecity inform the waste collection services if they needto be emptied, promise a better planning of services,making the city smarter. To meet resulting challengesof high scalability as well as low energy consumptionand high communication range for easy and low-costdeployment, new technologies have emerged, facingthe rising Internet of Things (IoT) with billions ofdevices being developed digitally. In doing so, theestablishment of suitable communication networksshould be handled quickly, simply and affordable.

To examine and evaluate the requirements deploy-ing an urbanized Smart City communication net-work, the TU Dortmund university has set up a LowPower Wide Area Network (LPWAN) in the city

of Dortmund, Germany, using LoRa as a networktechnology. LoRa modulation promises long lifetimeof battery powered end devices, low cost installationand high ranges with data rates between 0.3 kbit/sand 11 kbit/s [1]. Though the actual range dependson the data rate and frequency used as well as on thepropagation conditions found on the installation site.This paper focuses on the range and performanceevaluation considering a real world availability andreliability analysis in the urban area of Dortmund,comparing the results with established empirical pathloss models. Most LoRa installations are using the868 MHz band in Europe, which has significantly bet-ter propagation characteristics compared to the 2.4GHz ISM band. Additionally, LoRa systems are alsoavailable for the 433 MHz ISM band, which furtherreduces path loss, but comes with a reduced maximalequivalent isotropically radiated power (EIRP) of 10dBm in contrast to 14 dBm using 868 MHz. Thispaper examines both 433 MHz and 868 MHz systems,analyzing which system performs better.

For designing a Smart City communication sys-tem the knowledge of propagation characteristics isfundamental. Reducing the costs of a Smart Cityrollout, the number of LPWAN gateways should beas low as possible. For this purpose empirical pathloss models can be used to estimate the necessaryamount of gateways. Reflecting the measurementsamples of the availability analysis, the suitabilityof established empirical path loss models such asOkumura Hata, ITU Advanced, Winner+ and 3GPPSpatial Channel Model for narrow band LoRa signalswill be examined.

Therefore, this paper is organized as follows: Sec-tion II briefly outlines previous studies of LoRarange and performance analysis, while Section IIIintroduces LoRa as an emerging LPWAN technologyfor the IoT. In Section IV the Smart City scenarioof Dortmund as well as the measurement setup isintroduced, followed by presenting the results ofthe availability and reliability analysis in Section V.Finally a suitability analysis of path loss models is978-1-5386-3531-5/17/$31.00 c© 2017 European Union

Published in: 2017 IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC)DOI: 10.1109/PIMRC.2017.8292708

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examined in section VI, whose results are concludedin Section VII.

II. Related Work

In order to analyze the coverage of LoRa, theauthors in [2] provide real world measurements in themostly rural area of Oulu, Finland, using commer-cially available equipment. The measurements wereexecuted for scenarios when a node is located onland (attached on the roof rack of a car) or on water(attached to the radio mast of a boat), reporting theirdata to a base station.

In [3] the authors present a preliminary set ofmeasurements evaluating the performance of LoRain a high density urban area (Melbourne’s CentralBusiness District). The results show that loss freecommunication is assured only within a radius ofapproximately 200 meters from the base station andtotal loss of transmission occurs at around 600 me-ters, showing the high challenges of gateway instal-lations in high density urban areas. This paper alsouses a high building for the gateway installation, butin a medium density urban area, resulting in betterpropagation results up to 5.8 km.

The authors in [4] simulatively compare the cov-erage and capacity of SigFox, LoRa, GPRS and NB-IoT, using a real site deployment covering 8000 km2

in Northern Denmark using the positions of theTelenor cellular site grid hardware. The simulationbased analysis shows that all four technologies wereable to reach 99 percent outdoor coverage. Takingthese results into account, it is shown that cellularinstallation points are suitable for LoRa gateways,too, approving the installation site introduced in thispaper, as it is a cellular installation point as well.

III. LoRa: A long range IoT networksolution

With the increasing interest in IoT various tech-nologies are being developed to address the require-ments for the integration of intelligent devices, pur-posing low power consumption and wide area signalcoverage. This paper focuses on the requirements ofhigh coverage with respect to an easy and low costinstallation and operation.

As some of the LPWAN technologies are still underdevelopment, technologies like LoRa and SigFox arealready widely available on the market. Regardingto low cost operation, LoRa based networks shouldbe chosen over SigFox based networks, consideringthe need of a SigFox subscription for each device,resulting in running expenses for each connecteddevice [5]. Being able to set up a proprietary network,this paper focuses on the evaluation of a LoRa basedSmart City network.

When using LoRa, a distinction must be madebetween LoRa and LoRaWAN. While LoRaWANdescribes a full communication protocol mapping tothe second and third layer of the OSI model, LoRais the physical modulation used to transmit datafor high ranges [1]. LoRa modulates the signal us-ing a proprietary spread spectrum technique, whichspreads a narrow band input signal over a widerchannel bandwidth. The spreading of the spectrum isachieved by generating a chirp signal, that continu-ously varies in frequency, allowing distant receiversdecoding a severely attenuated signal several dBsbelow the noise floor.

The achievable data rate using LoRa modulationis based on the following factors:1) Spreading factor: To ensure an adaption of

data rate and signal range, various spreading factors(SF) between 7 and 12 are available, affecting thegradient of frequency variation and thus the energyper symbol. The higher the energy per chirp symbol,the higher the achieved signal range will be. Thougha higher spreading factor leads to a longer symboltransmit time, decreasing the overall data rate.[6]2) Bandwidth: LoRa based devices support band-

widths (BW) from 125 kHz up to 500 kHz [7].3) Coding Rate: To further improve the robustness

of the LoRa communication link, the devices imple-ment cyclic error coding performing forward errorcorrection. Such error coding incurs an additionaltransmit overhead, which depends on the chosencoding rate (CR) [7].

IV. Field Test Environment: Smart CityDortmund

The real world range analysis is performed in theurban area of Dortmund, Germany. Dortmund isinhabited by 600,000 people on an area of 280 km2,which leads to an average inhabitants density of 2143people per km2 [8]. Due to the definition of differentarea types [9] the real world range analysis presentedin this paper is based on a well urbanized area andthus a high attenuation is expected.

For the measurement of LoRa in the 868 MHz ISMband Pycom LoPy modules are used as LoRa nodesand gateway to determine the performance of theLoRa technology. For the analysis of LoRa’s 433 MHzcharacteristics the gateway uses a Dragino LoRa433 MHz/GPS Hat mounted on a Raspberry Pi. Al-though the regulations allow the transmission in the433 MHz ISM band with up to 10 dBm, the gatewaytransmits with 3 dBm due to hardware restrictions.The 433 MHz node uses an Adafruit Feather 32u4RFM96 433 MHz LoRa radio. Tables I and II listthe used parameters for the real world range andperformance analysis. Note that for the real worldmeasurement parameters are set to the most robust

Fig. 1: Installation site of Smart City LoRa Gateway antennas in 30 m height and fixed LoRa nodes A to F(left) as well as Pycom LoRa measurement node (middle) mounted on car (right).

communication link for the complete measurement,determining the maximum range of the installedLoRa based network.

TABLE I: LoRa 868 MHz parameters.

Characteristics Gateway NodeModule Pycom LoPy Pycom LoPyLoRa Chip Semtech SX1272 SX1272Antenna gain 4.15 dBi 2.2 dBiPing interval 15 secFrequency 869.5 MHz 869.5 MHzBandwidth 125 kHz 125 kHzTransmit Power 14 dBmModulation LoRa LoRaSpreading Factor 12 12Coding Rate 4/8 4/8

TABLE II: LoRa 433 MHz parameters.

Characteristics Gateway NodeModule Dragino LoRa

433 MHz/GPSAdafruitFeather 32u4

LoRa Chip Semtech SX1276 SX1276Antenna gain 0 dBi 3 dBiPing interval 6 secFrequency 433.3 MHz 433.3 MHzBandwidth 125 kHz 125 kHzTransmit Power 3 dBmModulation LoRa LoRaSpreading Factor 12 12Coding Rate 4/8 4/8

The LoRa gateways are placed on the roof ofa building in 30 m height on the campus of TUDortmund university (Fig. 1). For an extensive rangeanalysis the LoRa nodes are installed on the roofof a car in 1.7 m height, driving through Dortmund(Fig. 1).

In order to analyze the reliability of LoRa com-munication links several 868 MHz LoRa nodes wereplaced in the area of Dortmund for several days,receiving a ping signal from the gateway.

V. 433MHz and 868MHz Range Evaluation

The range analysis includes two parts. Firstlyan availability analysis is performed, using moving433 MHz and 868 MHz nodes to detect the LoRa sig-nal strength within Dortmund. Afterwards a secondanalysis is undertaken to determine the reliability ofLoRa packet transmissions to various fixed locations.

A. Availability analysis

The first part consists of multiple measurementruns using a car as a node moving through thenetwork which results in an availability map of theLoRa network consisting of 546 measurement pointsfor 868 MHz LoRa and 775 measurement points for433 MHz LoRa. The results are presented in Fig. 2and Fig. 3. The measured RSSI is cumulated in foursegments:

1) RSSI greater than -100 dBm which gives astrong signal with a high anticipated reliabilitytowards fading and interference effects.

2) RSSI between -100 dBm and -116 dBm. Accord-ing to [10] the additional building penetrationloss for basement installed antennas such assmart meters increases the expected path lossby 24 dB. In respect of the additional 24 dBattenuation this segment provides a sufficientsignal strength to reach LoRa transceivers in-stalled indoors and even installed in basements.

3) All measurement positions with a Receive Sig-nal Strength Indicator (RSSI) of less than−116 dBm down to -140 dBm (the lowest mea-sured RSSI for successful packet reception).

4) Sections in which no LoRa ping was available(blind spots).

The results of the 868 MHz LoRa measurementshow that signal strength and availability of the net-work highly depends on the actual position. Withina radius of 1.4 km signal strength and availabilityare sufficient for reaching LoRa nodes in buildingsand even in basements. Though from ranges of morethan 2 km first blind spots can be found, causedby elevations and shadowing by obstacles. Despitethe blind spots the gateway ping can be receivedin ranges up to 5.8 km, depending on the elevationprofile.

Measurement of 433 MHz LoRa results in similarranges, yet with a slightly lower RSSI compared tothe 868 MHz measurements. Due to the lower trans-mit power the building penetration is more limited.Increasing the transmit power to its maximum of10 dBm will lead to a higher range and better indoorpenetration.

2 km 3 km 4 km 5 km 6 km1 km

RSSI > -100dBm

-116 dBm <= RSSI < -100 dBm(Basement penetration possible)

-140 dBm <= RSSI < -116 dBm(No basement penetration possible)

(No ping received)

LoRa Gateway

LoRa Node(Fixed Installation Point)

B

E FA

C

D

G

OutdoorPDR: 65.76%RSSI: -132 dBmSNR: -18 dB

Indoor (Ground floor)PDR: 2.27%RSSI: -140 dBmSNR: -21 dB

Indoor (3rd floor)PDR: 99.97%RSSI: -115 dBmSNR: -2 dB

Indoor (3rd floor)PDR: 91.78%RSSI: -133 dBmSNR: -14 dB

Indoor (4th floor)PDR: 100%RSSI: -101 dBmSNR: 6 dB

OutdoorPDR: 100%RSSI: -116 dBmSNR: -2 dB

OutdoorPDR: 100%RSSI: -111 dBmSNR: 1 dB

869.5 MHz

PS = 14 dBmGGateway = 4.15 dBiGNode = 2.2 dBiH

OutdoorPDR: 100%RSSI: -121 dBmSNR: -9 dB

Fig. 2: Range and reliability analysis of 868 MHz LoRa-Network for Smart City Scenario in Dortmund,Germany (Map: OpenStreetMap contributors, CC BY-SA).

B. Reliability analysis

The second part consists of nine typical IoT deviceinstallation points. These positions were used for longterm reliability measurements consisting of an aver-age of 4300 measurement pings per location. Fig. 2illustrates the results of the KPI’s Packet DeliveryRate (PDR), average RSSI and average Signal toNoise Ratio (SNR) of this long-term measurement.

Measurement installation points A, B, C, D andH result in a PDR of over 99% with good SNRfor both 433 MHz and 868 MHz links. Despite ofa distance up to 4.2 km, most of the pings weresuccessfully received. With regard to the elevationprofiles shown in Fig. 4 it has to be noted that allmeasurement points A, B, C, D and H have goodpropagation conditions. However, measurement pointF is positioned on the ground floor in the centraldistrict of Dortmund. This leads to a high signalattenuation, which results in a packet delivery rate ofonly 2% and a deficient SNR of -20 dB at 868 MHz.An adequate communication is not possible, whileno 433 MHz LoRa ping is received due to insufficientsignal strength. The reliability analysis of point Gresulted in a slightly better RSSI than with E, only 2of 3 packets could be received for the 868 MHz link.Taking the SNR into account, the average SNR is4 dB lower in position G with only 2 dB left to theminimum required SNR of -20 dB for LoRa signaldecoding [7], which results in the unsatisfactory PDRof 66% in F and thus an adequate communication isnot possible. Using 433 MHz for the communicationlink leads to an insufficient average SNR of -20 dBand thus only 1 of 4 packets could be received. Taking

the elevation profiles in Fig. 5 into account, the prop-agation to point F and G consists of less clearance,when buildings with typical heights of 8 to 10 mare considered, resulting in additional path loss. Thereliability analysis shows, that all indoor and outdoorinstallation points within a radius of 3 km have asufficient PDR of more than 90%, which is a goodresult considering the urban environment. The anal-ysis for installation points of ranges greater than 3 kmdepict that reliability highly depends on the elevationprofile as shown in Fig. 4 and Fig. 5. Comparing the433 MHz and the 868 MHz communication links withthe used hardware constellation the latter performsbetter at the edge of the coverage area while 433 MHzleads to a more reliable communication link whenused closer to the gateway. Finally, the reliabilitymeasurements show that, despite the sufficient signalstrength, a full packet delivery reliability can notbe guaranteed, but packet losses can occur due tointerference.

VI. Suitability analysis of path loss modelsfor 433MHz and 868MHz

After examining the availability of LoRa basedsignals, empirical path loss models for urban areaswill be analyzed on their suitability for LoRa basednetworks in urban areas. The output of the previ-ously presented availability analysis consists of 1321measurement samples, including the signal strengthof the received ping (RSSI) and the position ofeach sample. Considering the free space path lossmodel, the Okumura Hata Model [11], the ITU-Advanced Channel Model for Urban Macro NLOSAreas [11], the Winner+ Channel Models for Urban

2 km 3 km 4 km 5 km 6 km1 km

RSSI > -100dBm

-116 dBm <= RSSI < -100 dBm(Basement penetration possible)

-140 dBm <= RSSI < -116 dBm(No basement penetration possible)

(No ping received)

LoRa Gateway

LoRa Node(Fixed Installation Point)

B

E FA

C

D

G

Indoor (Ground floor)PDR: 0.00%RSSI: n.a.SNR: n.a.

Indoor (3rd floor)PDR: 100%RSSI: -123 dBmSNR: -7 dB

OutdoorPDR: 100%RSSI: -122 dBmSNR: -5 dB

OutdoorPDR: 100%RSSI: -117 dBmSNR: -4 dB

433.3 MHz

PS = 3 dBmGGateway = 0 dBiGNode = 3 dBiH

OutdoorPDR: 100%RSSI: -127 dBmSNR: -13 dB

OutdoorPDR: 27.03%RSSI: -137 dBmSNR: -20 dB

Indoor (4th floor)PDR: 100%RSSI: -107 dBmSNR: 5 dB

Indoor (3rd floor)PDR: 98.31%RSSI: -139 dBmSNR: -17 dB

Fig. 3: Range and reliability analysis of 433 MHz LoRa-Network for Smart City Scenario in Dortmund,Germany (Map: OpenStreetMap contributors, CC BY-SA).

Low attenuation due togood direct path conditions

80

100

120

140

Hei

ght

[m]

160

0 1 2 3 4 5Distance [km]

A (PDR = 100%)

B (PDR = 100%)

C (PDR = 100%)

D (PDR = 99.97%)

H (PDR = 100%)

Elevation ProfileDirect Path

PDR measured at 868 MHz

Fig. 4: Elevation profiles for antenna installationpositions with feasible communication link (A-D, H).

High attenuation due toinsufficient direct path conditions

80

100

120

140

Hei

ght

[m]

160

0 1 2 3 4 5Distance [km]

F (PDR = 2.27%)

G (PDR = 65.76%)

E (PDR = 91.78%)

Elevation ProfileDirect Path

PDR measured at 868 MHz

Fig. 5: Elevation profiles for antenna installationpositions with critical communication link (E-G).

Macro NLOS Areas [12], the 3GPP Spatial ChannelModel for Urban Macro Areas and the Oulu channelmodel proposed in [2], the path loss (PL) of themeasurement samples is determined as

PL = PTX −RSSI + GTX + GRX (1)

with the transmit power of the gateways PTX , thegain of the gateway antennas GTX and the gain ofthe node antennas GRX .

The path loss and the distance between gatewayand node is used to determine a regression curve forthe mean path loss:

PLmean = B + 10n log 10(d) (2)

with the distance d in km, the path loss intercept Band the path loss exponent n.

Taking the empirical path loss models into ac-count, it has to be noted, that variation in frequencyresults in a constant offset of the path loss [11].In order to increase the statistical relevance of themeasurement a mean path loss exponent is com-puted with respect of the path loss exponents of the868 MHz and 433 MHz measurements. To adapt thepath loss intercepts to the mean path loss exponent,the minimum mean error is computed, resulting inthe parameters shown in Table III.

TABLE III: Path loss parameters for Smart Cityscenario Dortmund [2].

Metric Oulu868 MHz

Dortmund868 MHz

Dortmund433 MHz

PL exponent 2.32 2.65 2.65PL intercept 128.95 132.25 126.50

The resulting path loss models for the Smart Cityscenario of Dortmund are finally shown in Fig. 6 andFig. 7 and can be used for Smart City Scenariossimilar to Dortmund. Due to the higher buildingdensity compared to Oulu, the path loss in Dortmundis steeper with increasing distance, though using the

lower frequency band of 433 MHz, the path loss is re-duced by 5.75 dB, which comes close to the expected6 dB frequency gain of the free space path loss model.

0.1 0.2 0.5 1.0 2.0 5.0

80

10

01

20

14

01

60

Path

loss

[d

B]

SamplesDortmund (Urban) path loss modelFree space path lossOulu (Suburban/Rural) path loss modelOkumura Hata (Large City)ITU Advanced (UMa NLOS)Winner+ (UMa NLOS)3GPP Spatial (Urban Macro)

Distance [km]

Fig. 6: Comparison of path loss models with mea-surement regression curve for 868 MHz LoRa.

0.1 0.2 0.5 1.0 2.0 5.0

80

10

01

20

14

01

60

Distance [km]

Path

loss

[d

B]

SamplesDortmund (Urban) path loss modelFree space path lossOulu path loss modelOulu (Suburban/Rural) path loss modelITU Advanced (UMa NLOS)Winner+ (UMa NLOS)3GPP Spatial (Urban Macro)

Fig. 7: Comparison of path loss models with mea-surement regression curve for 433 MHz LoRa.

VII. Conclusion

In this paper the authors present a range andperformance evaluation of a LoRa based Smart CityIoT network in the city of Dortmund, Germany.First, results of real world measurements with aLoRa gateway installed in 30 m height above groundare presented and discussed. An availability analysisshows that signal reception is possible in coverageareas up to 5.8 km range, considering blind spots withno reception starting from ranges of 2 km, caused byelevations and shadowing by obstacles. Determiningthe reliability of the LoRa network, 10 LoRa nodeswere placed in Dortmund for a long term measure-ment, resulting in 100% packet reception up to 4 kmrange and over 99% in over 4.8 km range, dependingon propagation path conditions. In the second partof this paper the measurement results are used toexamine the suitability of given empirical path loss

models for urban environments. It is determined,that the considered channel models are insufficientlypredicting the expected path loss. Therefore newpath loss models for 868 MHz and 433 MHz LoRaSmart City scenarios are proposed based on theextensive LoRa availability measurement. In futurework further LPWAN technologies like Tiny Meshand Weightless P as well as NB-IoT and eMTCwill be analyzed on their performance in Smart Cityscenarios like Dortmund. In this process the proposedchannel model will be verified for these technologies.

AcknowledgmentThis work has been carried out in the course of the federal state

of Northrhine-Westphalia and the “European Regional Develop-ment Fund” (EFRE) 2014-2020 in the course of the “CPS.HUBNRW” project under grant number EFRE-0400008, as well as theIdeal project, funded by the Federal Ministry for Economic Affairsand Energy (BMWi) under grant agreement no. 03ET7557A andwas supported by the research unit 1511 ”Protection and controlsystems for reliable and secure operations of electrical transmissionsystems”, funded by the German Research Foundation (DFG), aswell as within the Collaborative Research Center SFB 876“Provid-ing Information by Resource-Constrained Analysis”, project A4.

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