Using Bluetooth on the phone

Bluetooth Low Energy (Bluetooth LE) is a wireless technology designed for low-data rate communication at ultra-low power. Every Bluetooth LE system consists of two elements: a peripheral that transmits an advertisement containing some useful information, and a central that receives and uses this information. In many cases, a connection between the peripheral and central device is created to exchange further information, but this is not always required.

The Dolby Conference Phone includes a Bluetooth LE module that conforms to Bluetooth Specification Version 4.0. Using Bluetooth APIs provided by the SDK, a phone can be configured to operate as a peripheral device that transmits a Bluetooth LE advertisement. This advertisement can be scanned by other Bluetooth LE-capable devices, such as mobile phones, to detect Dolby Conference Phones in their proximity.

This guide provides information for developers designing applications that detect the presence of nearby Dolby Conference Phones. It provides details about the format of the advertisement transmitted by the phone and the RF performance of the Bluetooth module. It is recommended that you read and understand the Bluetooth APIs in the SDK before reading this guide. Prior knowledge of Bluetooth is useful but not required.

Advertisement Format

Bluetooth advertisements transmitted by a Dolby Conference Phone can be used to signal its presence to nearby scanners. The contents of the advertisement are defined by the application within the constraints specified by the Bluetooth APIs in the SDK. Figure 1 illustrates how the Dolby Conference Phone uses Bluetooth: the Dolby Conference Phone acts as the peripheral and transmits an advertisement. The central device, typically a mobile phone, receives the advertisement.

Dolby Conference Phone advertisements are encapsulated as the payload of a non-connectable undirected advertising PDU (ADV_NONCONN_IND) as defined in Bluetooth Specification Version 4.0, Volume 0, Part B, Section 4.4 Low Energy Core Configuration or Section 4.5 Basic Rate and Low Energy Combined Configuration.

The user-defined part of the advertisement is encapsulated using the Manufacturer Specific Advertising Data structure defined in Bluetooth Specification Version 4.0, Volume 6, Part B, Section 2.3 Advertising Channel PDU.

Advertisement

A Bluetooth LE advertisement can be up to 31 bytes in length. On the Dolby Conference Phone, the first three bytes are used to indicate the features of the advertiser: general discoverable, Bluetooth LE host-only, non-connectable. These features are fixed and not accessible to the application. Of the remaining 28 bytes reserved for the advertisement, 4 bytes are used to indicate the length, type (Manufacturer Specific Advertising Data), and Dolby's manufacturer code (0x0309). The application-defined portion of the advertisement can consume, at most, 24 bytes. Detailed information about the structure and contents of the advertisement are provided in figure 2 and table 1.

Advertisements transmitted by a Dolby Conference Phone contain two parts:

  • UUID: A mandatory application-defined UUID that is 16-bits, 32-bits, or 128-bits in length.
  • Data: Optional data that is defined as an array of 8-bit integers. Maximum length of the array depends on the length of the UUID.

Figure 2 shows the structure and order of bytes in advertisements transmitted by the Dolby Conference Phone.

Table 1 describes the various fields that make up an advertisement with default values where appropriate.

Field NameDescriptionAccepted Values
AD LENGTHLength of type and data included in the advertisementVaries based on UUID and DATA. Calculated by firmware.
AD TYPEManufacturer Specific Advertising Data Structure0xFF
MFG IDDolby company identifier assigned and maintained by Bluetooth SIG0x0309
UUIDVariable length (16-bit, 32-bit, or 128-bit) unique identifierBig endian representation of application-defined identifier.
DATAVariable length (depending on length of UUID) additional dataOptional array of 8-bit integers defined by application.

Scan Response

Central devices may be configured to scan in one of two modes: passive and active. A central device operating in passive scanning mode receives only the payload shown in figure 2. A central device operating in active scanning mode, on the other hand, also receives a scan response in addition to the advertisement. The Dolby Conference Phone transmits its name, defined by configuration parameter Sip.Account.DisplayName, in the scan response. If Sip.Account.DisplayName is empty, a default name of the form DVCP-<serial_number> will be used for the scan response.

Note to iOS users

Dolby Conference Phone advertisements function like iBeacons. iOS applications access information embedded in iBeacons using CoreLocation APIs; raw advertisement data is not required. To read data embedded in a Dolby advertisement, iOS applications will need to use the CBCentralManager class and access the raw advertisement data.

RF Performance

Radio performance is a critical aspect of Bluetooth system design and must be considered when designing proximity-based applications. The sections that follow present the RF characteristics of the Bluetooth module on the Dolby Conference Phone. Use this information as a guide to tune signal thresholds used by your application to detect Dolby Conference Phones.

Radio Output Power

The Dolby Conference Phone is designed to transmit over relatively short distances; the Bluetooth module on the phone transmits at a constant output power of +10dbM.

Test Setup

The characterization test uses the Dolby Conference Phone as an advertiser and records the strength of the received signal on two mobile devices. Relative Signal Strength Indicator (RSSI), the standard for measuring received radio signal power, is used to measure the signal strength on the receiving device.

Figure 3 shows the test setup used to characterize the radio performance of the Bluetooth module on the Dolby Conference Phone. All tests were conducted in a medium-sized, closed meeting room measuring 12ft x 16ft.

Two devices were used to receive the advertisement from the Dolby Conference Phone:

  • iPod touch running iOS version 9.3.5
  • HTC One M7 running Android 5.0.2

The nRF connect application from Nordic Semiconductor was used to record RSSI values on both devices.

Methodology

A Dolby Conference Phone transmitting a Bluetooth LE advertisement was placed in the center of the room. The two mobile devices were placed at varying distances and orientations respective to the Dolby Conference Phone. The orientation of the Dolby Conference Phone is indicated by a clock position. Figure 4 shows the various orientations of the Dolby Conference Phone used for the test.

At each position, RSSI values were recorded for 3 minutes. The Dolby Conference Phone advertises at 500ms intervals resulting in approximately 350 readings at each position. At the furthest test distance, the mobile devices were not in the Dolby Conference Phone's line of sight. At the shorter distances, the mobile devices were in the Dolby Conference Phone's line of sight.

Results

The tables below show the maximum, minimum, and average RSSI values recorded at 4ft, 8ft, and 16ft respectively, with the Dolby Conference Phone oriented at different positions. The hour indicates the end of the Dolby Conference Phone closest to the mobile device. For example, when the Dolby Conference Phone is oriented at 12 o'clock, the end marked 12 is closer to the mobile device. Figure 5 and figure 6 show a test setup with the Dolby Conference Phone at 12 o'clock and 3 o'clock respectively in relation to the receiving device.

Dolby Conference Phone at 12 o'clock

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4 feet8 feet16 feet

iPod touch (iOS)
(all measurements in dBm)
Max: -52
Min: -69
Avg: -58.58
Max: -52
Min: -77
Avg: -62.44
Max: -52
Min: -77
Avg: -59.73

HTC One (Android)
(all measurements in dBm)
Max: -49
Min: -64
Avg: -53.73
Max: -49
Min: -70
Avg: -55.58
Max: -49
Min: -70.50
Avg: -56.37
Dolby Conference Phone at 3 o'clock

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4 feet8 feet16 feet

iPod touch (iOS)
(all measurements in dBm)
Max: -50
Min: -78
Avg: -59.90
Max: -55
Min: -71
Avg: -61.29
Max: -53
Min: -82
Avg: -63.59

HTC One (Android)
(all measurements in dBm)
Max: -48
Min: -77
Avg: -55.96
Max: -53
Min: -77
Avg: -56.42
Max: -48
Min: -77
Avg: -57.28
Dolby Conference Phone at 6 o'clock

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4 feet8 feet16 feet

iPod touch (iOS)
(all measurements in dBm)
Max: -48
Min: -66
Avg: -58.31
Max: -50
Min: -74
Avg: -61.79
Max: -52
Min: -78
Avg: -61.54

HTC One (Android)
(all measurements in dBm)
Max: -48
Min: -79
Avg: -56.57
Max: -49
Min: -79
Avg: -56.82
Max: -48
Min: -79
Avg: -56.94
Dolby Conference Phone at 9 o'clock

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4 feet8 feet16 feet

iPod touch (iOS)
(all measurements in dBm)
Max: -54
Min: -84
Avg: -62.72
Max: -57
Min: -73
Avg: -70.80
Max: -49
Min: -85
Avg: -60.10

HTC One (Android)
(all measurements in dBm)
Max: -50
Min: -57
Avg: -53.73
Max: -49
Min: -61
Avg: -54.87
Max: -49
Min: -63
Avg: -54.40

Troubleshooting

This section contains information to help troubleshoot problems you may encounter when working with Bluetooth on the Dolby Conference Phone. The most likely error scenario you will encounter is a misconfigured Dolby Conference Phone that prevents advertisements. Table 6 lists the most likely causes and possible solutions.

More details about the specific errors described below are available in the Dolby Conference Phone Administrator’s guide.

POSSIBLE CAUSESOLUTION
CSAF application does not handle errors returned by device engineCheck syslog for error messages and check for errors in application code.
Dolby Conference Phone not configured to advertiseCheck if configuration parameter Dvms.Service.EnableBluetoothAdvertisement is true
Bluetooth module initialization failedOn the Dolby Conference Phone's user interface, tap Settings > ... > About > Status and check status of Bluetooth. If a red warning bubble is displayed, try rebooting the device. If the error persists, contact your Dolby representative.

References