Bluetooth channels and frequencies

Bluetooth radio interface, modulation, & channels

The Bluetooth radio interface has been designed to enable communications to be made reliably over short distances. The radio interface is relatively straightforward, although it has many attractive features. The Bluetooth radio interface supports a large number of channels and different power levels, as well as using reliable forms of modulation.

Bluetooth radio interface basics

Running in the 2.4 GHz ISM band, Bluetooth employs frequency hopping techniques with the carrier modulated using Gaussian Frequency Shift Keying (GFSK).

With many other users on the ISM band from microwave ovens to Wi-Fi, the hopping carrier enables interference to be avoided by Bluetooth devices. A Bluetooth transmission only remains on a given frequency for a short time, and if any interference is present the data will be re-sent later when the signal has changed to a different channel which is likely to be clear of other interfering signals. The standard uses a hopping rate of 1600 hops per second, and the system hops over all the available frequencies using a pre-determined pseudo-random hop sequence based upon the Bluetooth address of the master node in the network..

During the development of the Bluetooth standard it was decided to adopt the use of frequency hopping system rather than a direct sequence spread spectrum approach because it is able to operate over a greater dynamic range. If direct sequence spread spectrum techniques were used then other transmitters nearer to the receiver would block the required transmission if it is further away and weaker.

Bluetooth channels and frequencies

Bluetooth frequencies are all located within the 2.4 GHz ISM band. The ISM band typically extends from 2 400 MHz to 2 483.5 MHz (i.e. 2.4000 — 2.4835 GHz). The Bluetooth channels are spaced 1 MHz apart, starting at 2 402 MHz and finishing at 2 480 MHz. This can be calculated as 2401 + n, where n varies from 1 to 79.

This arrangement of Bluetooth channels gives a guard band of 2 MHz at the bottom end of the band and 3.5 MHz at the top.

In some countries the ISM band allocation does not allow the full range of frequencies to be used. In France, Japan and Spain, the hop sequence has to be restricted to only 23 frequencies because of the ISM band allocation is smaller.

There are also some Bluetooth frequency accuracy requirements for Bluetooth transmissions. The transmitted initial centre frequency must be within ±75 kHz from the receiver centre frequency. The initial frequency accuracy is defined as being the frequency accuracy before any information is transmitted and as such any frequency drift requirement is not included.

In order to enable effective communications to take place in an environment where a number of devices may receive the signal, each device has its own identifier. This is provided by having a 48 bit hard wired address identity giving a total of 2.815 x 10^14 unique identifiers.

Bluetooth modulation

The format originally chosen for Bluetooth in version 1 was Gaussian frequency shift keying, GFSK, however with the requirement for higher data rates two forms of phase shift keying were introduced for Bluetooth 2 to provide the Enhanced Data Rate, EDR capability.

Gaussian frequency shift keying: When GFSK is used for the chosen form of Bluetooth modulation, the frequency of the carrier is shifted to carry the modulation. A binary one is represented by a positive frequency deviation and a binary zero is represented by a negative frequency deviation. The modulated signal is then filtered using a filter with a Gaussian response curve to ensure the sidebands do not extend too far either side of the main carrier. By doing this the Bluetooth modulation achieves a bandwidth of 1 MHz with stringent filter requirements to prevent interference on other channels. For correct operation the level of BT is set to 0.5 and the modulation index must be between 0.28 and 0.35.

Phase shift keying: Phase shift keying is the form of Bluetooth modulation used to enable the higher data rates achievable with Bluetooth 2 EDR (Enhanced Data Rate). Two forms of PSK are used:

• π/4 DQPSK: This is a form of phase shift keying known as π/4 differential phase shift keying. It enables the raw data rate of 2 Mbps to be achieved.
• 8DPSK: This form of Bluetooth modulation is eight point or 8-ary phase shift keying. It is used when link conditions are good and it allows raw data rates of up to 3 Mbps to be achieved.

The enhanced data rate capability for Bluetooth modulation is implemented as an additional capability so that the system remains backwards compatible.

The Bluetooth modulation schemes and the general format do not lend themselves to carrying higher data rates. For Bluetooth 3, the higher data rates are not achieved by changing the format of the Bluetooth modulation, but by working cooperatively with an IEEE 802.11g physical layer. In this way data rates of up to around 25 Mbps can be achieved.

Bluetooth power levels

The transmitter powers for Bluetooth are quite low, although there are three different classes of output dependent upon the anticipated use and the range required.

Power Class 1 is designed for long range communications up to about 100m devices, and this has a maximum output power of 20 dBm.

Next is Power Class 2 which is used for what are termed for ordinary range devices with a range up to about 10m, with a maximum output power of 6 dBm.

Finally there is Power Class 3 for short range devices. Bluetooth class 3 supports communication only up to distances of about 10cm and it has a maximum output power of 0 dBm.

Power control is mandatory for Bluetooth Class 1, but optional for the others, although its use is advisable to conserve battery power. The appropriate power elvel can be chosen according to the RSSI, Received Strength Signal Indictor reading.

Class	Maximum power dBm	Power control capability
1	20	Mandatory
2	4	Optional
3	0	Optional

Summary of Bluetooth Power Classes

Bluetooth power level choice and RSSI

In order to conserve battery power, the lowest transmitted power level consistent with a reliable link should be chosen. Assuming that power level control is available, the power level is chosen according to an RSSI reading. If the RSSI indication falls below a given level, the Bluetooth power level can be increased to bring the RSSI level up to an accepted level.

The value of any RSSI figure is arbitrary as it is simply used to provide an indication of when the signal level and hence the transmitted power level needs to be increased or decreased.

The Bluetooth specification does define a maximum bit error rate of 0.1% and this equates to a minimum requirement for the receive sensitivity of -70dBm. This figures for sensitivity then lead to the distances achievable for the different power levels, although today’s receivers are generally more sensitive than those that were used to baseline the specification at its launch..

The Bluetooth radio interface provides rugged physical layer without any unnecessary complications to carry the required data from one device to the next. With many devices being physically small and not having large battery capacity levels, the radio interface has been designed to keep power consumption low, while still providing the required capabilities.

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RF Wireless World

This page mentions List of BLE (Bluetooth Low Energy) channels. It covers BLE Advertising channels and BLE (Bluetooth Low Energy) Data channels.

Introduction:
• BLE (Bluetooth Low Energy) is the latest in the series of bluetooth standards published by Bluetooth SIG. The latest bluetooth version is 5.1 released after v4.2 and v5.0.
• The devices (Initiator i.e. master and Advertiser i.e. slave) communicates in point-to-point and broadcasts modes. using advertising channels and data channels.

The figure-1 depicts list of BLE (Bluetooth Low Energy) channels. Bluetooth operates in 2.4 GHz ISM Band. It spans from 2400 to 2483.5 MHz. BLE channels are spaced 1 MHz. Let us understand use or function of these BLE channels and their frequency values.

BLE Advertising channels

• It carry broadcast data for applications.
• It helps to discover slaves in order to connect with them.
• BLE devices use any of the following BLE advertising channels for transmission/reception of advertising packets of various types. These channels carry advertising channel PDUs.

BLE Data channels

• Once connection is established between master and slave, devices can send data to one another. This is achieved by exchanging data channel PDUs during scheduled connection events.
• Master and slave BLE devices use any of the following BLE data channels for the transmission/reception.

BLE Channel Number	Frequency Value
0	2404 MHz
1	2406 MHz
2	2408 MHz
3	2410 MHz
4	2412 MHz
5	2414 MHz
6	2416 MHz
7	2418 MHz
8	2420 MHz
9	2422 MHz
10	2424 MHz
11	2428 MHz
12	2430 MHz
13	2432 MHz
14	2434 MHz
15	2436 MHz
16	2438 MHz
17	2440 MHz
18	2442 MHz
19	2444 MHz
20	2446 MHz
21	2448 MHz
22	2450 MHz
23	2452 MHz
24	2454 MHz
25	2456 MHz
26	2458 MHz
27	2460 MHz
28	2462 MHz
29	2464 MHz
30	2466 MHz
31	2468 MHz
32	2470 MHz
33	2472 MHz
34	2474 MHz
35	2476 MHz
36	2478 MHz

References:-

➤BLUETOOTH CORE SPECIFICATION Version 5.1

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Bluetooth

Bluetooth is a wireless technology for creating personal area networks operating in the 2.4 GHz unlicensed band, with a default range of 10 meters.

• http://engineeringagenda.com/agenda/2013/09/bluetooth/ An introduction to Bluetooth
• http://www.eetimes.com/document.asp?doc_id=1200909 An introduction to debugging Bluetooth in embedded systems
• http://travisgoodspeed.blogspot.fr/2011/12/introduction-to-bluetooth-rfcomm.html Introduction to Bluetooth RFCOMM Reverse Engineering

Bluetooth radio [ edit ]

Bluetooth 2.0 uses frequencies between 2.4000 and 2.4835 GHz, and divides the band into 79 MHz channels (numbered 0-78), with frequency hopping at a rate of 1600 times per second. Channel 0 has a frequency centred at 2.4020 GHz, allowing a lower guard band of 2 MHz. Channel 78 has a frequency centred at 2.4800 GHz, allowing an upper guard band of 3.5 MHz. Bluetooth devices are divided into three classes, depending on their maximum transmitted power (and hence their maximum range):

Bluetooth connection [ edit ]

The number of Bluetooth® devices you can connect at the same time depends on the Bluetooth® devices.

There are three type of connections in Bluetooth:

• Single-slave: a point-to-point connection (only 2 Bluetooth units involved)
• Piconet: One Bluetooth unit acts as the master of the piconet, whereas the (up to seven active) others units acts as slaves.
• Scatternet: Multiple piconets with overlapping coverage areas form a scatternet.

Device icons [ edit ]

Shows the types of found Bluetooth® devices using icons.

Icon	Device
	DUALSHOCK™4 wireless controller or other controller	Yes
	PlayStation®Move motion controller	Yes
	Computer	Yes
	Mobile phone, smartphone	Yes
	Headset	Yes
	Speakers	Yes
	Mouse	Yes
	Keyboard	Yes
	Printer	Yes

Bluetooth Addressing [ edit ]

Each Bluetooth unit has a unique 48-bit address (BD_ADDR).

Company_assigned						Company_id
Lower Adress Part (24-bit) transmitted with every packet as part of the packet header						Upper Adress Part (8-bit)		Non-Significant Adress Part (16-bit) assigned publicly by the IEEE
lsbxxxx	xxxx	xxxx	xxxx	xxxx	xxxx	xxxx	xxxx	xxxx	xxxx	xxxx	xxxx msb

Class of Device/Service (CoD) [ edit ]

In practice, most Bluetooth clients scan their surroundings in two successive steps: they first look for all bluetooth devices around them and find out their «class». You can do this on Linux with the hcitool scan command. Then, they use SDP in order to check if a device in a given class offers the type of service that they want.

• Major Service Class: Audio (0x200000)
• Major Service Class: Capturing (0x80000)
• Major Service Class: Rendering (0x40000)

• Major Device Class : Computer (0x100)

(The dualshock 4 in a game controller mode has a class of Device/Service (CoD) of 0x002508.

Related Articles [ edit ]

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