Location Services with Riverbed Xirrus APPLICATION NOTE

Transcription

1 Location Services with Riverbed Xirrus APPLICATION NOTE

2 Introduction Indoor location tracking systems using Wi-Fi, as well as other shorter range wireless technologies, have seen a significant increase in adoption in recent years. Real Time Location Systems (RTLS) technology enables organizations to identify and track the physical location of users and devices in real time using the inherent properties of Radio Frequency (RF) waves. Wi-Fi technology, being widely deployed and relatively inexpensive, is uniquely positioned to deliver location information in support of a wide variety of use cases in retail stores, corporate offices, transportation hubs, educational institutions, and more. Riverbed Xirrus provides high-performance wireless solutions that support a unique, integrated location service that accurately determines the location of Wi-Fi devices in real-time without any additional equipment or cost. This document describes Riverbed Xirrus location services and outlines best practices for designing and deploying Wi-Fi networks for optimal results. page 2 of 18

3 Location Methodologies There are several methodologies that can be used to determine Wi-Fi client location. Some implementations might only use one methodology while more accurate systems implement a combination of several methodologies. Riverbed Xirrus uses a combination of these methods as described in a subsequent section. The most popular methods of locating mobile client devices are: 1. Cell of Origin 2. Distance-Based (Trilateration) 3. Angle of Arrival (Triangulation) Cell of Origin This method simply determines client location based on which access point (AP) a mobile client device is associated. It is by far the simplest way to estimate the approximate location of a mobile device as an existing Wi-Fi network can be used and no special algorithms or equipment are required. The primary disadvantage is accuracy, which directly correlates with the number of APs deployed. In addition, this method is subject to sticky clients that do not readily roam and may remain connected to an AP further away than another that is closer. To overcome this, the location can be provided by the AP that sees the highest signal strength from the client device, even if it is not associated with it. FIGURE 1. Location Methodologies: Cell of Origin page 3 of 18

4 Distance-Based (Trilateration) Trilateration is a method based on the distance between an AP and the client device. The most common way to determine distance is using the Received Signal Strength Indicator (RSSI), which measures the strength of the Wi-Fi signal seen from another device. For example, the signal from a client as seen at the AP. The stronger the signal strength, the closer the client, and vice versa. If the client device is seen by only one AP, then after estimating the distance, we can locate the client device anywhere on a circle around the AP. Of course, this is not very accurate. When a second AP is added to the equation, we can locate the client device at one of two points where the circles intersect. Adding a third AP to the equation allows a precise location for the client device to be determined at the intersection of the three circles. FIGURE 2. Location Methodologies: Distance-based Trilateration. Angle of Arrival Angle-based techniques locate the mobile client device by determining the angle at which the radio signal arrives at the receiving radio. Directional antennas on AP radios can calculate the angle and the position of a client device. When multiple radios with directional antennas are present, triangulation methods are used to determine the precise location of the mobile client device. page 4 of 18

5 In this drawing, directional antennas at two APs can be used to pinpoint the location of the mobile device. FIGURE 3. Location Methodologies: Angle of Arrival The Xirrus Location Solution Xirrus Wi-Fi solutions provide a number of unique capabilities and advantages in delivering location services compared with traditional AP solutions. These include: Distributed Compute: client location information is calculated directly in every AP instead of in a central appliance as with other solutions. This eliminates cost, complexity, and system failure points, which are described in more detail below. High-Density APs: unique multi-radio APs with 4 Wi-Fi radios provide more signal data points for locating clients per AP. Directional Antennas: high-density APs with directional antennas provide more precise location information since an indication of direction is derivable from signal strength data across multiple radios, in addition to distance. Xirrus APs are based on a distributed architecture with dedicated 2 or 4 core processors per AP. Location algorithm calculations are run in a coordinated fashion distributed across all the access points in the network. This eliminates the expensive central appliance in the data center required by other location systems. In addition, because the load is distributed across many APs, the system does not take a negative hit in performance when servicing lots of clients and so can deliver low latency location information updates in an ultra-scalable solution. The more access points in the network, the more processing power available to the location system. page 5 of 18

6 FIGURE 4. Client signal data is shared and location calculations are distributed among all APs The Xirrus solution uses a combination of the location methodologies discussed earlier in this document. If the client device is heard on more than one AP, trilateration is used to determine the client device location. If a client device is heard on only one AP, Angle of Arrival is used on multi-radio APs and Cell of Origin is used on 2 radio APs. The client data gathering interval is less than 5-seconds and this interval is configurable. The maximum data overhead on the network is very small at 2.5 bps per AP per client device assuming a 5-second data gathering interval. All communications are secure using https. Xirrus Positioning System (XPS) The Xirrus location solution makes results available in one of several ways. The Xirrus Positioning System (XPS) is designed to aggregate and publish location data from many APs. It supports up to 100,000 clients in a single system. APs upload location data to the XPS server via https. The XPS supports APIs that are used to integrate with and push location data to Xirrus Management System (XMS-Enterprise, XMS-Cloud) or third party applications. The XPS is delivered as a VMware appliance (.ova file). You must be running XMS-Enterprise version 8.0 or higher and APs must be running AOS version or higher. page 6 of 18

7 FIGURE 5. XPS sending location information to an application server Producing Location Results There are several ways to produce location results using the Xirrus solution. XMS Maps. You can view client location directly on floor plans via XMS-Enterprise and XMS-Cloud. FIGURE 6. View client locations in XMS maps. page 7 of 18

8 Direct from the AP. You can configure APs to send location data directly to a 3rd party system. FIGURE 7. APs send data to cloud-based 3rd party system via https. XPS server. You can configure APs to send location data to an XPS for aggregation before it is sent to another system. FIGURE 8. APs send location data to an XPS. page 8 of 18

9 The following screen capture shows client locations in XMS-Cloud during a live event. FIGURE 9. Client locations during a live event in XMS-Cloud Best Practices / Design Recommendations In a typical Wi-Fi network deployment, network architects design the placement of APs based on coverage, capacity, and channel reuse requirements. For location-aware environments, it is imperative to ensure that additional criteria are met to achieve high fidelity location tracking. It is quite unlikely an existing Wi-Fi network not originally designed for location services will provide accurate device location. The following section provides recommendations for Wi-Fi network design to achieve optimal accuracy using Riverbed Xirrus solutions. AP Selection Integrated location services are supported by the following series of Xirrus access points: XD, XR, XH, and XA with the exception of the X2-120 and XR-320 models. For XH and XA models that use external antennas, omnidirectional antennas must be used to achieve location accuracy. XD2 and XD4 model APs are generally recommended for most location service applications. The selection of which model will be based on the number of Wi-Fi clients you need to serve in the area. Higher device density areas are best served with the higher radio density XD4. For advice on specific model selection, speak with your Riverbed Xirrus sales team. page 9 of 18

10 AP Location If you are using an RF design tool (e.g. ibwave, AirMagnet, Ekahau), use Voice Overlay or an equivalent setting to design with location services in mind. This will typically place APs on your maps in a regular grid pattern. In general, the level of location accuracy will be determined by AP spacing. Best accuracy will be achieved by placing APs feet (11 15 meters) apart covering 1,225 2,500 sq. ft. ( sq. m) each. Place APs at regularly spaced intervals for best accuracy. In long hallways, stagger AP placements and avoid line of sight where possible. It is important to create a fence around the area in which you desire location data. Line the perimeter of the area covered with APs, then fill the interior area with regularly spaced APs following guidelines are given above to achieve appropriate trilateration. In multi-story buildings, stagger the locations of APs from floor-to-floor. Do not place APs directly above or below one another where possible. Keep all APs mounting heights around 10 feet (3 meters) where possible. Design AP coverage so that at least three APs are seen at a minimum signal level of -60dBm or greater in all areas of coverage. FIGURE 10. Best Practices: AP placement page 10 of 18

11 AP Orientation Some Xirrus AP models utilize directional internal antennas, in particular, multi-radio (4 or more radio) XD4 and XR-2000/4000 models. When APs with directional antennas are used in a network running location services, the orientation of the installed AP must be configured in the Xirrus management system to ensure location accuracy. Upon AP installation, for any 4 or more radio AP, record the direction the top face of the AP (the face with the LEDs) points as it is mounted (usually down) and its angular orientation. Document the angular orientation of the AP by noting the direction the 12 o clock position of the AP s top face points. The 12 o clock position is at the top when the Xirrus or Riverbed label in the middle of the AP reads right side up. FIGURE 11. Determining XD4 AP Orientation AP Configuration Design AP placement to provide -60 dbm or better Wi-Fi signal coverage throughout the entire area that is supporting location services. Stronger signal strengths typically result in higher location accuracy. Note: Wi-Fi signal strength is typically measured in dbm (the power ratio in decibels of the measured power referenced to one milliwatt). The signal strength is typically represented by negative numbers starting at So a signal measured at -50 dbm is stronger than one measured at -80 dbm. The number of APs deployed may require you to set smaller coverage cells by reducing AP radio power levels. You will need to balance between using too much power, which could result in co-channel interference between APs, and maintaining minimum -60 dbm signal strength in the coverage area. Xirrus APs use signal strength data received from client devices to calculate location. This signal strength information is collected from all radios that can hear a given client. Radios can provide Wi-Fi connectivity to clients, in which case they are set to a specific Wi-Fi channel, or run in monitor mode where they scan all channels. A certain percentage of radios in a network design should be set to monitor mode to provide the best location results. page 11 of 18

12 Monitor radios can operate in either Dedicated or Timeshare mode. In Dedicated mode, the radio acts as a full-time monitor and scans all Wi-Fi channels continually. This mode provides the most frequent location data updates as users move through a facility. In Timeshare mode, the radio will spend part of its time servicing client devices and the rest of the time in monitor mode. This mode provides less frequent client location updates. For 2 radio access points, it is recommended to place one radio in Dedicated monitor mode on most APs with the second radio set to service users on 5GHz. On every third or fourth access point, the second radio should be set to 2.4GHz to support those type of devices. For 4 or more radio access points, it is recommended to place one radio in Dedicated monitor mode on all APs. The 3 other radios can then be set to a combination of 5GHz and 2.4GHz depending on coverage and client mix requirements. Summary Radio Frequency (RF) and its inherent physical properties can be used to track mobile users, providing meaningful applications that benefit both IT and end users. Wi-Fi is uniquely capable of providing accurate location tracking information if implemented correctly. Riverbed Xirrus provides a unique, highly scalable wireless solution with integrated capabilities to accurately locate and track Wi-Fi users and devices in real-time. When deploying a Xirrus location system, applying best practices in the design and deployment of the Wi-Fi network is important to ensure optimal accuracy and efficiency of the system. page 12 of 18

13 Appendix A Configuring Location Services in XMS-Cloud Go to the Floor Plans page in XMS-Cloud. FIGURE 12. Go to the Floor Plans page. Click the map of the building that you will be using location services at. FIGURE 13. Click the map where location services will be used. page 13 of 18

14 Click the arrowhead button to open the flyout window. FIGURE 14. Click the arrowhead button to open the flyout window. Click the Settings button. FIGURE 15. Click the Settings button. page 14 of 18

15 Select Yes to Would you like to enable Location Reporting? FIGURE 16. Select Yes to Would you like to enable Location Reporting. Click DONE to save this configuration. FIGURE 17. Click DONE to save the configuration setting. If you want to send location data to another server, such as a 3rd party system or the XPS, select Yes for Would you like to send location data to an external service?. page 15 of 18

16 FIGURE 18. Select Yes to send data to a different server for processing. Next, specify the data format you will be using. If using the Xirrus Positioning System, select XPS and enter the server s URL. For any other type of location system, select Other and fill out the fields provided. Provide a URL to forward data to, the forwarding time period in seconds, and a customer key if one is required. Then specify how often data is to be sent to the server in seconds. For Enable per radio data:, select Yes to enable the collection and uploading of visitor analytic data on a per-radio basis. APs will then send multiple data points for a client data is sent for each AP radio that sees a probe request from the client. Choose No to send data on a per-ap basis. Placing APs on Floor Plans Next place APs on floor plans where they are installed and properly orient them. After you have imported and configured your floor plans of the coverage areas, place the APs on the map. It is very important to be accurate in the location of the APs to ensure accurate client location. Once the APs are placed on the floor plan, set their up/down orientation. Most APs face down when installed on a ceiling. If you are using a 4 radio AP, set the Face Position angle. You should have recorded the orientation of the AP when it was installed. Do this by clicking on the AP icon, click the blue dot (which is the 12 o clock position), and rotate the AP to point in the correct direction. page 16 of 18

17 FIGURE 19. Set AP orientation and direction. Appendix B Configure XMS-Enterprise to work with XPS In XMS-Enterprise, go to Settings Application Location Server FIGURE 20. In XMS-Enterprise go to Location Server. page 17 of 18

18 Enter the XPS server IP address (ex. and the admin login credentials. This information gets configured in Profiles and pushed to the APs. FIGURE 21. Enter XPS server IP address. Learn More For more information on Riverbed Xirrus including customer stories, product information, and a free trial, visit us at Riverbed.com/Xirrus. World Headquarters Riverbed Xirrus 680 Folsom St., 6th Floor San Francisco, CA USA Tel: +1 (877) Sunnyvale Office Riverbed Xirrus 525 Almanor Ave., 5th Floor Sunnyvale, CA USA Tel: +1 (408) EMEA Office Riverbed Xirrus Maxis 1, 1st Floor Western Road, Bracknell Berkshire. RG12 1RT, UK Tel: Riverbed Technology, Inc. All rights reserved. Riverbed and any Riverbed product or service name or logo used herein are trademarks of Riverbed Technology. All other trademarks used herein belong to their respective owners. The trademarks and logos displayed herein may not be used without the prior written consent of Riverbed Technology or their respective owners. MS-466_XRS_WP_US_073018