A Brief Overview
Bluetooth systems operate in the
unlicensed Industrial-Scientific-Medical (ISM) radio band at 2.4 GHz. Low-power
RF transmission provides communication between devices over a range of 10 to100
meters.
Bluetooth enables ad-hoc
networking between eight devices without the need for any formal networking
infrastructure. The ad-hoc network which is created between the bluetooth
devices is called piconet. In a piconet one master device can actively communicate
with seven slave devices (limited by a 3 bit address), and up to 255 devices
could be part of piconet but inactive (parked state).
The devices which can paired to a
given bluetooth device is unlimited and practically limited by the amount of
memory a device has to store device MAC address and Link key(pairing key).
The bluetooth system uses
frequency hopping spread spectrum (FHSS) to combat interference and fading. The
ISM 2.4 GHz band is from 2400 to 2483.5 MHz and Bluetooth uses 79 radio
frequency channels in this band, starting at 2402MHz and continuing every 1 MHz.
it’s these frequency channels that Bluetooth technology is “hopping” over. The
signal switches carrier channels rapidly, at a rate of 1600 hops per second,
over a determined frequency-hopping pattern of channels. The basic
frequency-hopping pattern is a pseudo-random ordering of 79 channels
frequencies. Bluetooth system performance is further improved by having
adaptive frequency hopping where it identifies the channels with known interference
and marks them bad.
Power Classes
Bluetooth devices are classified into three power classes
based on their highest output power capabilities:
Power Class
|
Maximum Output Power
|
Distance
|
1
|
100 mW (20 dBm)
|
Bluetooth devices can transmit up to 100 meters
|
2
|
2.5 mW (4
dBm)
|
Bluetooth devices can transmit up to 10 meters
|
3
|
1 mW (0 dBm)
|
1 meter
|
Bluetooth versions
There are two factors which help distinguish between
different versions of the bluetooth:
·
Speed
·
Power consumption
Bluetooth 1.x:
Bluetooth version 1.x which used GFSK (Gaussian Frequency Shift Keying)
modulation technique and speed was capped at 1Mbps. This version of bluetooth
is also known as Basic Rate (BR mode). This was extensively used in speakers
and game controllers. This version had many limitations like less speed and
lack of data security.
Summary: If
someone refers Bluetooth as BR radio he is actually referring to bluetooth 1.x.
Bluetooth 2.x: Bluetooth
version 2.x replaced GFSK with p/4-DQPSK and 8DPSK modulation techniques which
used change in waveform’s phase as oppose to change in frequency to carry
information. This led to increase in speeds 2Mbps and 3Mbps respectively. The
Bluetooth Core Specification version 2.0 + EDR introduced Enhanced Data Rate
(EDR). EDR provides a set of additional packet types. Bluetooth 2.x also introduced secure simple
pairing to make Bluetooth more secure.
Summary: If
someone refers Bluetooth as BR/EDR radio he is actually referring to bluetooth
2.x.
Bluetooth 3.x : Bluetooth 3.x also known as a Bluetooth high
speed, improved data speed with addition of 802.11 for up to 24Mbps. 3.x added
concept of Alternate MAC Phy (AMP)
as a secondary controller in the
Bluetooth core system. So the BR/EDR radio would be used to perform discovery,
association, and connection establishment and connection maintenance and if both
devices support WiFi then data transfer would run over 802.11g
wireless connections in the 2.4GHz.
Summary:
Bluetooth 3.x refers to Bluetooth AMP (Alternate MAC Phy) which translates the
data packets [sent] from the Bluetooth stack, and sends these [out] over 802.11(WiFi).
Bluetooth version
1.x to 3.x also known as classic bluetooth suffered from
short battery life because of higher power consumption and were unusable for
IoT use.
Bluetooth 4.x: In order to meet increasing demand for
wireless connectivity for IoT devices, a new flavor of Bluetooth was introduced
known as Bluetooth Low Energy (BLE). BLE again returns to 1Mbps throughput
using GFSK just like BT 1.0.
To reduce power consumption, a
BLE device is kept in sleep mode most of the time. When an event occurs, the
device wakes and a short message is transferred to a gateway, PC, or
smartphone. Maximum/peak power consumption is less than 15 mA and the average
power consumption is about 1 μA. The active power consumption is reduced to a
tenth of the energy consumption of classic Bluetooth. In low duty cycle
applications, a button cell battery could provide 5-10 years of reliable
operation.
·
Bluetooth
4.1 : Following are the major
improvements at the heart of BT 4.1 specification
a.
Coexistence:
Bluetooth and LTE signals interfere degrading each other’s performance and
reducing battery life. Bluetooth 4.1 solves this issue by coordinating its
radio with 4G automatically so that there is no overlap and both can perform at
their maximum potential.
b.
Improved
data transfer: Bluetooth 4.1 devices are able to act as both endpoint and
hub simultaneously. This enables peripheral to peripheral communication, for
4.0 devices if one peripheral e.g. smartwatch has to talk to Mobile phone in
order to get data from your heart rate monitor. However with 4.1 devices
smartwatch can directly talk to heart rate monitor saving your phone’s battery.
c.
Smart
Connectivity: Rather than carry a fixed timeout period, Bluetooth 4.1 will
allow manufacturers to specify the reconnection timeout intervals for their
devices. This means devices can better manage their power and that of the
device they are paired to by automatically powering up and down based on a
bespoke power plan.
This is achieved through Low Duty Cycle Directed
Advertising. Low Duty Cycle directed
advertisement is designed for cases where a reconnection with a specific device
is required, but time is not the essence or it is not known if the central
device is in range or not.
·
Bluetooth
4.2
Several new
features were introduced in bluetooth core specification 4.2 release. The major
areas of improvement were:
a.
Low Energy
(LE) Data Packet Length Extension: Till BLE 4.1 LE controller could send
data channel packet data unit (PDU) with payloads of 27 bytes. With Data length
extension this payload size was increased to 251 bytes.
b.
LE secure
connections: LE Secure Connections is an enhanced security feature
introduced in Bluetooth v4.2. It uses a Federal Information Processing
Standards (FIPS) compliant algorithm called Elliptic Curve Diffie Hellman
(ECDH) for key generation.
c. Link Layer Privacy: The LE privacy
feature allows devices to periodically generate new address to use over the
air. This behavior greatly reduces the ability for a scanner to track
broadcasting Bluetooth low energy devices over a period of time.
d.
Link
Layer Extended Scanner Filter Policies: If the Link Layer supports the
Extended Scanner Filter policies, then the following modes shall also be
supported:
•
The Link Layer shall process advertising packets
only from devices in the White List. A connectable directed advertising packet
shall not be ignored if the Target is the scanner's device address or a
resolvable private address.
·
The Link Layer shall process all advertising
packets (i.e., the White List is not used). A connectable directed advertising
packet shall not be ignored if the Target is the scanner's device address or a
resolvable private address.
Summary:
Bluetooth 4.x added support of BLE to bluetooth specification. So devices which
only support BLE are called single mode devices and are branded as bluetooth
smart and dual mode devices which support both BLE and classic bluetooth are
branded as bluetooth smart ready. Bluetooth 4.0 /4.1 supported BLE data payload
as 27 bytes and BLE 4.2 upgraded PDU size to 251 bytes which led to throughput
increase by 10 times.
Bluetooth 5
New features in bluetooth core specification 5.0 release are
Ø
Multiple PHYs support
Bluetooth is a full protocol stack and
bottom most layer of the stack is known as physical layer commonly referred to
as PHY. Bluetooth 5 supports 3 different kind of PHYs:
o
LE 1M
PHY: It’s same PHY used in BT 4.x and uses GFSK (Gaussian Frequency
Shift Keying) and throughput available is 1Mega symbols/s. Its support is
mandatory in BT 5.
o
LE 2M
PHY: This PHY allows physical layer to operate at 2Mega symbols /sec and
thus allowing higher throughput. This PHY would allow use cases like Device
Firmware Upgrade (DFU) to be completed quickly.
o
LE
coded PHY: The LE coded PHYs use the 1M PHY rate but the actual payload
is coded either with 500kbps(S=2) 0r 125kbps(S=8) rate. Using the coded PHYs
improves the Rx sensitivity which also means the improved range. Typically, a
4-6 dB RX sensitivity improvement can be achieved using either the 500 kbps or
125 kbps PHY and this usually converts to a 2-4x range improvement. The
downside of the LE Coded PHY is of course that the TX and RX times are going to
be longer, which increase the average power consumption.
Ø
LE Advertising
Extensions
As shown below in
table, Bluetooth 4.x provided only three channels where a device could
advertise and payload for advertisements was limited to 27 bytes. Bluetooth 5
changes this significantly. First of all, the three advertisement channels are
going to remain exactly like in Bluetooth 4 for backwards compatibility and
interoperability, but they are now called primary advertisement channels. In
addition to the three primary advertisement channels, Bluetooth 5 devices can
use any of the remaining 37 data channels as secondary advertisement channels
to broadcast more data and offload the primary channels. The table below
summarizes the differences between Bluetooth 4 and 5 advertising channel
schemes.
Bluetooth
version
|
Advertising
channels
|
Payload
|
PHY
|
Bluetooth 4
|
3
|
0 - 31 B
|
1M
|
Bluetooth 5
|
3 Primary
37 Secondary |
0 - 31 B (Primary)
0 - 255 B (Secondary) |
1M, Coded (Primary)
1M, 2M Coded (Secondary) |
Ø
Slot availability mask
Bluetooth 5 introduced
the concept of Slot Availability Mask which will help to improve the
coexistence with other radio technologies on devices like smartphones.
Bluetooth 5 introduces a system called Slot
Availability Masks,
which allows Bluetooth to indicate the availability of its time slots and to
synchronize in an optimal manner with the use of the adjacent MWS (Mobile
Wireless Standard) bands.
Summary:
Bluetooth 5 slogan is “Go Faster, go Further”. Bluetooth 5 doubled its speed by
adding support of 2M PHY and increased its range by adding coded PHY. Both are
mutually exclusive you either get range
or speed at a time based on the PHY type configured at a given point of time.
Comparison table for various versions of bluetooth
BLUETOOTH
v2.1 |
BLUETOOTH
4.0
(LE) |
BLUETOOTH
5
(LE) |
|
Range
|
Up to 100 m
|
Up to 100 m
|
Up to 400 m
|
Max range
(free field) |
Around 100 m
(class 2 outdoors) |
Around 100 m
(outdoors) |
Around 1,000m
(outdoors) |
Frequency
|
2.402 – 2.481 GHz
|
2.402 – 2.481 GHz
|
2.402 - 2.481 GHz
|
Max data rate
|
1- 3 Mbit/s
|
1 Mbit/s
|
2 Mbit/s
|
Application
Throughput |
0.7-2.1 Mbit/s
|
Up to 305 kbit/s
|
Up to 1,360 kbit/s
|
Topologies
|
Point-to-point,
scatternet |
Point-to-point,
mesh network |
Point-to-point,
mesh network |
Network
Standard |
IEEE 802.15.1
|
IEEE 802.15.1
|
IEEE 802.15.1
|
Bluetooth Mesh
Mesh networking operates on
Bluetooth Low Energy (LE) and is compatible with core specification version 4.0
and higher. Only products designed to be upgradable can be enhanced in the
field to support mesh networking. Upgradeability is determined by several
factors, such as the amount of memory available in the Bluetooth chip.
Bluetooth mesh networking enables
many-to-many (m:m) device communications and is optimized for creating
large-scale device networks. It is ideally suited for building automation,
sensor network, asset tracking, and other IoT solutions that require tens,
hundreds or thousands of devices to communicate with one another.
