Gateway Supports 100 Connected Devices

The Enlighted network design guidelines limit the maximum number of connected devices per gateway (including plugloads) to 100 for lighting and energy applications. For real-time data applications such as Where app, which has higher bandwidth network use, limit the maximum number of devices per gateway to 50.  

For applications that use the Surface sensors, USB, for desk occupancy and ceiling sensors located in the same space, Enlighted recommends not more than 100 sensors per gateway. Refer to the Surface Sensor (SU-5i-USB) Design Guidelines.

A sensor can be configured as a hopper to broadcast messages to other fixtures in its range.   For configuring sensors as hoppers, refer to the article Configuring Sensors as Hoppers. See Network and IT Design Guidance for additional details on Gateways and Hopper guidelines.

The Enlighted Gateway is the intermediary device that aggregates wireless traffic between the network of Enlighted Smart Sensors and Manage servers located on-premise or in the cloud. Gateways communicate over IEEE 802.15.4 compliant wireless protocol.

This application note applies to the following models of Enlighted sensors:

  • Gen 5 Micro Sensor (SU-5E), High Bay Sensor (SU-5S-H), Ruggedized Sensor (SU-5S), 8-pin and 2-wire models
  • Compact Sensor (SU-4E, SU-3E-00)
  • Smart Sensor High Bay (SU-4S-H, SU-2O-00)
  • Ruggedized Sensor High and Low Bay (SU-4S-HRW/HRB/LRW/LRB) (RS-2O-S1/S2/H1/H2)
  • Two-wire Compact Sensor (CS-D2)
  • Two-wire Fixture Mount Sensor (FS-D22)

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Gateway Outdoor Antenna Selection Guidelines

The intention of this article is to provide a series of suggestions for relocating the antenna for a Gateway. It is Enlighted’s recommendation that for any antenna installation you work closely with your local contractor.

The Gateway should be put indoors because of its temperature rating. A Gateway located indoors ensures network security in addition to environmental issues. This article explains how to choose an antenna for use with the Enlighted Gateway in outdoor applications. The following are some of the factors to consider when selecting an outdoor antenna: antenna type, Ingress Protection code, electrical specifications, installation suggestions, and cable alternatives for connecting the Gateway to the antenna.

1.     Antenna Options

The choice of the antenna depends on the application range and the placement of the Enlighted sensors with respect to the antenna. Below is a detailed reference of what to look for when selecting an antenna to use with the Enlighted Gateway. The selected antenna should have a nominal impedance of 50 Ohms.

Please follow all antenna manufacturers installation instructions.

Note: All installations outside of North America should consider the guidelines presented in this document.

Omni-directional Antennas

Omni-directional antennas radiate uniformly in the entire Azimuth plane and, hence, can communicate with Enlighted sensors in all horizontal directions around the antenna (side to side). However, such antennas do not have equal radiations in vertical (up/down) directions. A representative plot of the radiation pattern of an omnidirectional Antenna is shown below:

Fig_1.png

Figure 1: (a) Radiation Pattern

Fig_2.png
Figure 2: (b) Application of a vertically oriented omnidirectional antenna

Frequency Range: The antenna should operate in the frequency range of 2400 MHz – 2483.5 MHz. While it is harmless to select an antenna with a wider frequency range of operation, an antenna with a narrower frequency range cannot meet the requirements. 

Gain: Every antenna is characterized by multiple electrical specifications, including “Gain” which has a unit of “dB” or “dBi”. When selecting an antenna, there are considerations to have in mind about the gain. We recommend selecting an antenna with a gain not lower than 2 dBi and not higher than 25 dBi. The gain of the antenna is directly correlated with the desired communications range. The following table provides a guide into how much higher antenna gain is required for extending the communication range in 10 m steps:

Table 1: Antenna Gain based on Communication Range

Desired Range Extension

Additional Gain Required

Absolute value of Antenna Gain (no cable loss)

Absolute value of Antenna Gain (assuming average cable loss of 2 dB)

From 20 m to 30 m

+3.5 dBi

-1.4 dBi or more

0.4 dBi or more

From 30 m to 40 m

+2.5 dBi

3.9 dBi or more

5.9 dBi or more

From 40 m to 50 m

+1.9 dBi

5.8 dBi or more

7.8 dBi or more

From 50 m to 60 m

+1.6 dBi

7.4 dBi or more

9.4 dBi or more

From 60 m to 70 m

+1.4 dBi

8.8 dBi or more

10.8 dBi or more

From 70 m to 80 m

+1.2 dBi

10 dBi or more

12 dBi or more

From 80 m to 90 m

+1 dBi

11 dBi or more

13 dBi or more

The range values calculated in the above table are theoretical and based on proper installation of the antenna with respect to the sensors.

Installation: We recommend that this antenna be mounted on a pole, such that it is not blocked by a wall or metallic object. Ideally, this antenna should be mounted at the center of the space where sensors are located and at the same elevation (height) level to maximize the communication range and take advantage of the omnidirectional radiation pattern of the antenna. The higher the antenna gain, the more sensitive the connection would be to height misalignments between the antenna and the sensors. Most omni-directional antennas must be mounted vertically such that the azimuth plane is perpendicular to the orientation of the antenna. The antenna should not be covered with any metallic covers or objects. 

Ground Plane Dependency: Some antennas are ground-plane dependent, while others are independent of a ground plane. If an antenna is ground-plane dependent, it works best with certain proximity to or clearance from a ground plane. Most off-the-shelf antennas are ground-plane independent; that is, they do not require a ground plane underneath to deliver high-quality RF signals. If an antenna requires a ground plane to deliver high-quality signals, a flat metallic plate can represent that ground plane. Please refer to the installation guide that comes with the antenna for the size of this plate and the proper connection to the antenna and/or distance from the antenna feed point. Ground-plane dependencies, if any, are clearly stated in technical datasheets.

IP Rating: IP-67 for outdoor applications, fiberglass random material recommended.

Figure 3 highlights the reference planes for the current omnidirectional antenna used for the Gateway.

Fig_3_1.pngFig_3.png

Figure 3: A representative plot for H and E plane pattern for current Gateway antenna

II.      Directional Antennas

While most applications require omnidirectional antennas, there are certain cases where the use of directional antennas may be more efficient. For example, if the antenna is backed by a solid wall and radiation is only desired towards one side, a directional antenna (such as an off-the-shelf patch antenna) can be selected.

Fig_4.png

Figure 4: A representative plot for the application of a directional antenna

The more directional an antenna is, the smaller the horizontal span of communication (θ) will be. As such, in applications where sensors are closely lined up in a line-of-sight configuration from the antenna as shown in Figure 5, a very directional antenna can be used. In such a case, the spread of the signal emerging from the antenna is quite narrow, which means that the antenna beam should be pointed directly towards the sensors.

Fig_5.png

Figure 5: A representative plot for the application of a highly directional antenna

The same ground plane dependency, gain, frequency range, and IP rating considerations discussed for omnidirectional antennas apply to directional antennas as well.

Installation: Directional antennas require more careful installation. Whereas omnidirectional antennas radiate quite uniformly in all azimuth directions, a directional antenna favors specific directions over the rest for radiating the signal. As such, each product should be installed such that the direction of radiation of the antenna points at the Enlighted sensors’ locations. Figure 6 shows the RF antenna pattern for a directional antenna.

Fig_6_1.pngFig_6_2.png

Figure 6: A representative plot for the application of a highly directional antenna

Distinctions Between Omni-directional and Directional Antennas:

  • Availability: Off-the-shelf antennas that have a gain of 20 dBi or higher mainly come in the form of “directional” antennas. While off-the-shelf omni-directional antennas are widely available, they tend to have gains lower than 18 dBi.
  • Installation: Omni-directional antennas have a donut-shaped radiation pattern, and they radiate the signal uniformly in the azimuth plane perpendicular to the axis of the antenna at the center of antenna axis. As such, height alignment is an important factor in installation of omni-directional antennas. Directional antennas, however, are somewhat less sensitive to height alignment. Instead, the azimuthal alignment becomes more important, as directional antennas do not radiate uniformly in the azimuth plane. There is a window if radiation identified by “3-dB beamwidth” or “half-power beamwidth” in the technical datasheet of the antenna, stated in degrees. It must be ensured during the installation that this window of radiation points towards the sensors. Detailed installation considerations are usually provided by the antenna supplier. In both cases, the higher the antenna gain, the more accurate the installation alignments need to be.
  • Gain vs Range or Cable Length: For the same communication range and cable length, a directional antenna must have a gain greater than an omni-directional counterpart by 3 dBi to guarantee a successful communication link (see Table IV for detailed information). This is due to the nonuniform radiation pattern discussed under installation considerations.
  • Practical Use: Omni-directional antennas are the best choice when a gain of 18 dBi or lower is needed (due to availability concerns), and sensors are in multiple horizontal directions with respect to the gateway. Directional antennas are the proper choice when a gain higher than 18 dBi is needed, and sensors are located only on one side of the gateway within a particular angular span that matched the “beamwidth” of the antenna.

Suggested Antenna Manufacturers:

Please note that omnidirectional antennas with a gain less than 18 dBi and directional antennas with a gain less than 20 dBi can generally be found off the shelf. Any antennas with higher gains tend to be custom designs, which will be more expensive and will have longer lead times.

2.     Coaxial Cable Options

To maximize the signal strength, the shortest possible cable must be used. Antenna cables are subject to signal degradation along the length of the cable, and as such, the longer the cable, the greater the signal loss. This results in a loss in the overall performance of the antenna. For applications that require long cables, higher-quality cables must be used to minimize the overall degradation, or higher gain antennas must be used to compensate for this degradation. The attenuation through a cable is normally characterized as dB/m or dB/ft. This number must be multiplied by the overall length of the cable to estimate the overall degradation. The following table provides recommendations for choosing cables in accordance with the required cable length. Cable impedance should be 50 ohms.

Table 2: Cable Loss

Cable Attenuation

Price per ft.

Application

Overall loss

Notes

0.55 dB/m or 0.17 dB/ft. (or less)

$

Short cable lengths, less than 20 ft.

2.5 dB for 15 ft. length

Usually identified as low loss cables

0.3 dB/m or 0.09 dB/ft. (or less)

$$

Medium cable lengths, between 20 ft. and 40 ft.

2.74 dB for 30 ft. length

Usually identified as low loss cables

0.2 dB/m or 0.06 dB/ft. (or less)

$$$

Long cable lengths, 40 ft. or more

2.44 dB for 40 ft. length

Usually identified as ultra-low loss cables

Choose the coaxial cable to meet the application requirements:

  • Outdoor
  • Outdoor/watertight
  • Indoor

Cable Examples: 

DISTRIBUTORS: DIGIKEY, MOUSER

$: AMPHENOL TIMES MICROWAVE SYSTEMS (LMR-240 or equivalent): Digikey PN 1946-1059-100-ND, Mouser PN 523-LMR-240

$$: AMPHENOL TIMES MICROWAVE SYSTEMS (LMR-400 or equivalent): Digikey PN 1946-1110-ND, Mouser PN 523-LMR-400

$$$: AMPHENOL TIMES MICROWAVE SYSTEMS (LMR-500 or equivalent): Digikey PN 1946-1143-250-ND, Mouser PN 523-LMR-400

The numbers listed in the last column of Table II for each cable quality/length can be added to the required antenna gain picked from Table I to compensate for signal degradation through the cable. For example, if a 50-meter (164 ft) communication range is needed, the third column of Table I specifies a minimum gain of 2.9 dBi for the antenna. If this antenna is then used with a 30 ft cable possessing attenuation characteristics consistent with the second row of Table II, the minimum required antenna gain increases to: 2.9 dBi + 2.74 dB = 5.64 dBi.

The above formula works best with the choice of omni-directional antennas. If the chosen antenna is directional, the user must be careful that the azimuthal angular span of the antenna beam labeled as θ in Figure 2 (often referred to as beamwidth in technical documents) is still large enough to cover the communication span of interest.

IP Rating: The cable should have IP-67 rating and/or be rated suitable for outdoor applications and broad temperature variations.

Coaxial Cable Structure: A coaxial cable consists of a center conductor, an insulator (dielectric), an outer braided conductor, and a protective plastic layer, as shown in Figure 7. The amount of loss per unit length of a coaxial cable largely depends on the insulator. This insulator may be air, glass, or plastic (usually Teflon/PTFE). While air-dielectric cables provide minimal losses, they often come in the form of “rigid” coaxial cables. We recommend the use of semi-rigid or flexible coaxial cables, which often have a flexible polymer that functions as the insulator.

fig_7.jpg
Figure 7: General structure of a coaxial cable

3.     Long Cables

If the application requires the RF coaxial cable to be run over a large distance, the highest quality cables with minimal losses should be used. Table III provides insight into the communication range that can be expected from an 18 dBi omni-directional antenna based on the cable length. As longer cables are used, the wireless communication range of the system will decrease due to the signal degradation in the coaxial cable. As such, there exists a trade-off between the length of the cable and the range of wireless communication.

Table 3: Communication Range for Different Cable Lengths (Fixed Omni-Directional Antenna Gain of 18 dBi)

Cable length (highest quality cable)

Communication Range

50 ft

144 m, 472 ft

100 ft

102 m, 334 ft

150 ft

72 m, 236 ft

200 ft

51 m, 167 ft

250 ft

36 m, 118 ft

300 ft

25 m, 82 ft

350 ft

18 m, 59 ft

The same principle may also be stated in terms of the dependence between the antenna gain and cable length for a fixed communication range. For this analysis, we have used the communication range of a 2 dBi rubber ducky antenna with no cable (150’ or 46 m) as a reference. Table IV exhibits how a higher gain antenna is needed to maintain the same communication range as the cable length increases. Column I lists various cable lengths, assuming the choice of highest quality cables with minimal losses, while columns II and III show the required antenna gains for omni-directional and directional antennas, respectively. Note that a higher (+3 dBi) gain antenna should be used when choosing a directional antenna, such that the variations in gain are accounted for. This is not a concern for omni-directional antennas, as the gain value is uniform in the azimuth plane.

Table 4: Antenna Gain Required for Different Cable Lengths (Same Communication Range as the Rubber Ducky Antenna’s with 5 dBi gain (150’ or 46 m))

Cable Length (Highest Quality Cable)

Antenna Gain Needed (Omni-directional)

Antenna Gain Needed (Directional)

50 ft.

8 dBi

11 dBi

100 ft.

11 dBi

14 dBi

150 ft.

14 dBi

17 dBi

200 ft.

17 dBi

20 dBi

250 ft.

20 dBi

23 dBi

300 ft.

23 dBi

26 dBi

Note that the high-gain antenna options that can be used in combination with 250-300 ft long cables (last two rows) are likely to be custom antennas. Off-the-shelf antenna options tend to have gains lower than 18 dBi (omni-directional) or 20 dBi (directional).

4.     Coaxial Connector Adapters:

Please note that the mating cable for the Gateway requires a RP SMA connector at the Gateway termination. The other termination on the cable should be consistent with the type of connector on the antenna side, see Figure 8.

Fig_8.png

Figure 8: Connector mating between the cable and the Gateway/Antenna

Depending on the choice of the antenna and the cable, there may be a need for an adapter at one or both ends of the cable. There are several types of adapters to choose from, based on the connectors that are to be mated. Some examples of the adapter types and corresponding applications are listed in Table V.

Table 5: Adapter Types and Their Applications

Adapter type

Application notes

Example Models

Coaxial Connector N type, Male Pin To N type, Male Pin

To allow connection between two N type female Connectors

Amphenol RF, Part # 172122

Tab1_1.jpg

SMA Male to N-type Male

To allow connection between a female SMA connector and a female N-type connector

‎Wlaniot, Part # ‎WSF-01

Tab1_2.jpg

SMA Female-Female adapter

To allow connection between two male SMA connectors

‎RFAdapter, Part # RFA0322-CA

Tab1_3.png

SMA Male-Male adapter

To allow connection between two female SMA connectors

Linx Technologies Inc., Part #ADP-SMAM-SMAM-G

Tab1_4.jpg

The adapters used, if any, must also be rated for outdoor applications (IP-67 Rating).

5.     Coaxial Cable Installation

User must ensure that the antenna is connected to the coaxial cable before turning the Gateway on. Failure to do so can cause a reflection of energy at the open end of the coaxial cable back to the Gateway and damage the device. Once the coaxial cable is ready to use, connect one end to the Gateway (off), the other end to the antenna, and then turn the Gateway on.

  1. Connector Care and Tools: If RF connectors are disconnected and the device is off, cover with plastic caps to protect against mechanical/electrical damage:

Fig_9.png
Figure 9: Plastic Cap to Protect RF Connectors

If the coaxial cable is connected to the Gateway and the device is ON, but there is no antenna connected on the other end, use a 50-ohm termination should be used to terminate the cable. 50-ohm coaxial terminators should be chosen such that they are compatible with the coaxial cable connector. The following table provides some examples for matching the cable connector and the RF termination:

Table 6: Termination Types and Their Applications

Cable Connector (Examples) at the Antenna End

Termination (Matched Load) Needed

SMA Male Connector

SMA Female 50-ohm Termination

Tab2_1.png

SMA Female Connector

SMA Male 50-ohm Termination

Tab2_2.jpg

N-type Male Connector

N-type Female 50-ohm Termination

Tab2_3.1.jpgTab2_3.2.jpg

Tools: Use a torque wrench with the proper size/type to tighten/loosen RF connectors and adaptors. Break-over type torque wrenches are recommended, in which the maximum torque value is pre-set; these torque wrenches feature a unique pivoting joint that “breaks” when the pre-set torque force has been reached to prevent the damage of the RF connector through excessive force.

Fig_10_1.jpg Fig_10_2.jpg

Figure 10: Break-over type torque wrenches recommended to tighten/loosen RF connectors

  1. Tamper-Proofing: Based on the choice of RF connector, security sleeves are available to prevent mechanical tampering. The security sleeves potentially look like this:

Fig_11.jpg
Figure 11: Representative image of a security sleeve

Example: https://www.showmecables.com/tamper-proof-security-sleeve-for-f-type-connector

And a tool/wrench compatible with the sleeve model is usually needed for tightening/loosening of the sleeve, which would look like this:

Fig_12.jpg
Figure 12: Representative image of a tool/wrench compatible with the security sleeve

Examples: https://www.amazon.ca/Security-Connector-Gripping-Installing-Removing/dp/B07F1NCGH9/ref=pd_lpo_2?pd_rd_i=B07F1NCGH9&psc=1"

https://www.showmecables.com/tamper-proof-security-sleeve-tool-for-f-connector

 

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Wi-Fi Bridge for Gateway-to-Cloud Communications

In the standard Enlighted system architecture, each Gateway device connects to a PoE switch that is connected to the IT network. The Gateways securely communicate to the Manage in the Cloud (“EMC”) using HTTPS through the IT network.

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An alternative to the standard architecture for situations where the Cat 5 and PoE installation and cabling is not feasible, connect each Gateway to a Wireless Bridge that connects to the IT Wi-Fi network. Manage in the Cloud is reached, as before, through the IT network via HTTPS.

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Equipment

Each Enlighted Gateway will connect to the PoE+Data port of a TP-Link TL-POE150S PoE Injector (or equivalent); refer to TL-POE150S document.

The Data port of the PoE Injector will connect to an Aruba 501 Wireless Client Bridge (or equivalent); refer to Aruba 501 Wireless Client Bridge document.

Both devices would access nearby AC power.

Configuration

The Wireless Client Bridge acts as a client on the local Wi-Fi network. The IT Administrator can configure the Bridge to use the appropriate security protocols [WPA2-PSK/AES/TKIP/etc.] and credentials [802.1x, etc.] for the specific network. The Bridge Data Sheet lists the supported protocols.

The IT Network should be configured to allow the Gateways to connect to Manage in the Cloud. The ports needed for outbound connectivity include:

  • UDP Port 123 for NTP
  • TCP Port 443 for HTTPS

Open up one of these ports on the customer network.

Bandwidth

An Enlighted system used for Advanced Lighting Control consumes minimal Wireless LAN bandwidth because each Enlighted Sensor is self-sufficient in managing the fixture to which it is connected; there is no System Master or Lighting Controller or Zone Master device. Each Sensor makes measurements and takes actions independently of such supervision.

The traffic offered to the Wireless LAN primarily consists of historical sensor data periodically sent to Manage in the Cloud for analysis and report generation. For every 100 sensors, the Gateway consumes a maximum of 12kbps, with an average of 4kbps. This is a minuscule portion of the Wireless LAN capacity.

Note: The Enlighted system was specifically designed to not require a Controller or Master device, thereby eliminating the vast amount of traffic typical of competitive systems.

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