Knowledge Center: B
An alphabetical glossary of terms related to Laird's embedded wireless modules.
Data transmission rate. The higher the rate the more bits per second transferred.
A beacon is a periodic packet that is sent out by the 802.11 AP to announce its presence, readiness, and SSID. A beacon period is the amount of time between these packets and is typically measured in Kilomicroseconds where one Ksec equals 1.024 microseconds.
Basically, a lower interval or period means faster detection of the AP, but it also means an increased use of airtime (and decreased throughput because of increased competition for the signal).
BG Channel Set is an SCU Global setting that indicates the 2.4 GHz channels that the radio scans when contemplating a roam to determine what access points are available. BG channel set options include:
Basic Input/Output System. BIOS is a program located in the ROM (read-only memory) that loads the bootstrap loader upon power up. Once the computer is on, the BIOS becomes an intermediary for the CPU and Input/Output devices.
Bitrate is the measurement of how much data is transmitted in a given amount of time from one location to another. It is generally measured in bits per second (bps), kilobits per second (Kbps), or megabits per second (Mbps).
Bluetooth is a proprietary open wireless technology designed for short-range wireless connections between devices. These connections are between fixed and mobile devices in a Wireless Personal Area Network (WPAN) with high levels of security.
Refers to the three levels of power for Bluetooth devices: Class 1, 2, and 3. The following table compares power and range of these three classes:
|BT Class||Maximum Power||Operating Range|
|Class 1||100 mW (20 dBm)||100 meters|
|Class 2||2.5 mW (4 dBm)||10 meters|
|Class 3||1 mW (0 dBm)||1 meter|
To communicate over the 100 meter range, a class 1 BT device is required at both ends. To communicate over the 10 meter range, a class 1 or class 2 device is required at both ends.
Note: Class 3 devices are uncommon due to their very limited range.
A feature of the latest version of Bluetooth hardware (Bluetooth 4.0) which enables low-volume, low-power data transmission over longer periods. This protocol enables longer battery life and easier implementation of Bluetooth communications in small devices.
A Bluetooth Low Energy implementation allows a client device to share small bits of data known as "statuses" repeatedly over long periods of time to a server. For example, a heart monitor can routinely update a server about a patient's vitals. Since this data is principally low in volume (much lower than Bluetooth's standard audio transmission), this device can operate intermittently in small bursts, dramatically increasing the device's power efficiency. A standard watch battery may last years in many Bluetooth Low Energy implementations.
Bluetooth Low Energy is not backwards compatible with all legacy Bluetooth hardware, though in many instances a firmware update may introduce this functionality to older systems.
In low energy operation, is Bluetooth range adversely affected?
Low power usage is achieved because of the topology change. In classic BT, a slave device must have its receiver ON all the time to catch an incoming connection; this means current draw of 25 mA most of the time. In BLE, the slave device chooses when to advertise that it can connect. This allows it to manage exactly how much energy to expend and when. At higher levels, classic BT is mainly used to relay bulk data. BLE utilizes a small database that resides in the chip and the BLE protocol (called GATT) acts like SQL to read and write to those data records. Hence, BLE is well suited for sensor-type applications where small blocks of data need to be transferred. BLE enables up to 512-byte chunks of data to be manipulated over the air.
What is an 'Advert' packet in BLE?
An advertising packet is only sent by the slave device and is akin to a simultaneous 'hello' message and invitation for an incoming connection. There are 4 types of advertising packets:
- Give data and allow no incoming connection - used to broadcast small blocks of data.
- Give data and only allow a peer to request one more packet of data
- Give data and invite connection from a specific address (i.e. a bonded/trusted relationship)
- Give data and invite connection from anyone - promiscuous usage
Although a slave can only be connected to one master, it is allowed to advertise types (1) and (2) while in a connection.
Does Bluetooth low energy feature a piconet as in classic BT?
Yes. A 'peripheral' device ( or slave) can have ONLY ONE 'central' device (or master). A central device can connect to many peripheral devices. Classic BT is limited to 7 peripherals because devices have a 3-bit address. BLE uses a 24-bit address, theoretically allowing millions of slave devices in a star configuration. In reality, hundreds of slave devices is more practical since each connection needs radio time and RAM. For example, with 100 slave connections each slave will only have the attention of the master for 10 ms in each second on average.
Do I need to enroll in Apple's MFi program to use BLE with an iPhone?
BLE is outside the scope of MFi. Apple has exposed an API that is free to use without an authentication chip.
What about other operating systems?
As of Android 4.1 (Jelly Bean), the Android BLE API and Windows 8 (both tablet and desktop versions) come with a built-in BLE stack.
The BLE module is going to be programmable using which version of BASIC?
The interface is somewhat akin to VisualBASIC of 2012 without the graphical user interface and the OOP. Like VBASIC, it is more structured and eliminates the need for line numbers. Laird has optimised performance for an embedded microcontroller with very limited memory resources in both FLASH and RAM.
How can my overall design be cheaper and quicker to prototype?
The BASIC on our BLE module means you can do all sorts of programming without the need for a toolchain, which eliminates the need for an external processor. The BLE module has an ARM Cortex processor running at 16 MHz from on-board flash (hence no wait states). Designing a product using an external PIC could compress development time from months to a few days.
If the slave advertises when it is available for receiving, how do the master and slave sync when data should be sent?
A slave will advertise a packet (up to 31 bytes) consisting of data seen as a broadcast. The packet contains header bits that effectively say "you can now connect to this radio within 150 microseconds and at this address". The central end (i.e. master), then requests a connection with parameters saying "I will poll you every X milliseconds" (ranging from a few to 4000). Once that connection is up, the peripheral end (i.e. slave) wakes up every X ms (as negotiated in the connection request) to see if data is to be exchanged over that pipe. The protocol used over that pipe to exchange data is called GATT protocol.
What security feaures does BLE have?
BLE uses pairing like classic BT. Data can be encrypted using AES (classic BT uses the SAFER+ algorithm) Link keys are still 128 bits long. AES is implemented by higher layers rather than in the baseband as in classic BT.
Do I still have to deal with profiles?
Yes, but they are simpler and only deal with typical usage scenarios like Pulse Rate monitors, temperature, and proximity.
Note: All of these involve data abstractions of 'some situation' and getting the data defining that abstraction over the air to a peer.
Can I have custom profiles?
Yes. And the BT SIG encourages you to submit those profiles for adoption via a streamlined procedure (not mandatory).
Do I need Bluetooth SIG approvals and certification?
Yes, but you will be able to inherit most if not all of these from our approvals and certifications.
Bluetooth profiles indicate the general functionality or minimum requirements that a Bluetooth-enabled device must support in order to communicae with another Bluetooth device in a specific user scenario. A Bluetooth profile must contain at least the following information:
Profiles make Bluetooth devices compatible enough to be able to connect with each other.
There are two types of Bluetooth profiles:
The Laird SCU currently supports the following Bluetooth profiles:
Generic Access Profile
Generic Object Exchange Profile
Serial Port Profile
Advanced Audio Distribution Profile
Audio/Video Remote Control Profile
Human Interface Device Profile
Object Push Profile
Note: It is referred to as 'push' because the transfers are always initiated by the sender (client) rather than the receiver (server).
Depends on GEOP.
Personal Area Networking Profile
Smart Ready and Smart devices carry out different roles in a BLE communications scheme. Based on typical applications for a BLE network there are also some characteristics that they commonly share. Bluetooth Smart devices act as peripherals to Smart Ready devices.
Bluetooth Smart (single-mode) devices are able to enjoy the power-saving features of low energy connections to a higher degree than Smart Ready devices. Because a Bluetooth Smart device will most often be used as a peripheral to another central device, the nature of its communications is simpler, quicker, and lower on power consumption. Smart devices are the information servers that transmit their status to a Smart Ready device.
A Bluetooth Smart Ready (dual-mode) device can be thought of as the master or host in a BLE transmission. They perform the central role in a BLE configuration. Even though Smart Ready devices perform the client-role action of initiating a connection, they have access to more resources and are theoretically capable of maintaining connections to over a million clients. Smart Ready devices are typically configured to acquire status data (known as an "attribute") from Bluetooth Smart devices, which the Smart Ready device can then use.
Because Bluetooth and Wi-Fi transmit in different ways using differing protocols, and because Bluetooth and 802.11b, 802.11g, and 802.11n-compliant devices operate in the same 2.4 GHz frequency band, they are mutual interferers. Because Bluetooth and Wi-Fi radios are often found in the same device, this interference can impact the performance and reliability of both wireless interfaces.
Interference may be addressed by isolating radios. Isolation may be achieved using one or a combination of domains: space (spatial isolation), time (temporal isolation), and frequency (frequency isolation). Bluetooth and Wi-Fi coexistence schemes use one of these three domains and, when properly implemented, allow for acceptable performance and reliability for co-located Bluetooth and Wi-Fi radios.
For coexistence with Bluetooth, the system must support simultaneous or packet traffic arbitrated operation of Wi-Fi with Bluetooth. The system must also provide a coexistence scheme compatible with or similar to 802.15.2 Coexistence with co-located Bluetooth.
The 802.15.2 standard provides for two main categories of Bluetooth coexistence mechanisms: Collaborative and Non-Collaborative.
With a collaborative coexistence mechanism, the wireless personal area network (WPANT) and the WLAN communicate and collaborate to minimize mutual interference.
With the 802.15.2 collaborative approach, the Bluetooth and the Wi-Fi radio "time slice", which means only one transmits at a time. To do this, the radios exchange information, or collaborate, regarding their transmitting status. They exchange this information using hardware connections (pins or wires) between the radios. The most common implementations are Two-Wire and Three-Wire coexistence.
With a non-collaborative coexistence mechanism, there is no method for the WPANT and the WLAN to communicate.
With the 802.15.2 non-collaborative approach, both the Wi-Fi and the Bluetooth radio are capable of simultaneous transmission. Because both wireless interfaces share the same 2.4 GHz operating band, a method must be used to minimize mutual interference when transmitting at the same time. One method of non-collaborative mechanisms is Adaptive Frequency Hopping (AFH)
Refer the following topics for additional information on Bluetooth coexistence:
Bluetooth Network Encapsulation Protocol.
Defines how packets from various networking protocols are encapsulated and sent directly over Bluetooth L2CAP (Logical Link Control and Adaption Layer Protocol).
Used by the PAN profile.
Boolean data is a type in which the values may only be one of two values. These are typically expressed as 1 and 0 (binary) in computers, but can be thought of abstractly as true/false or yes/no values.
A program that exists in the non-volatile memory and is executed automatically when the computer is powered on; used to load the operating system. Sometimes referred to as bootstrapping or boot loader. This program has been replaced in computers equipped with an Extensible Firmware Interface (EFI) and is part of the EFI BIOS.
When a device is in broadcast mode it is set to send out a signal but does not allow other devices to respond and does not receive.