Embedded Systems Software Training Center COPYRIGHT © 2012 DSR CORPORATION 802.15.x Wireless Technologies

Embedded Systems Software Training CenterEmbedded Systems Software Training Center

COPYRIGHT © 2012 DSR CORPORATIONCOPYRIGHT © 2012 DSR CORPORATION

802.15.x Wireless Technologies802.15.x Wireless Technologies

COPYRIGHT © 2012 DSR CORPORATIONCOPYRIGHT © 2012 DSR CORPORATION 22

Assumptions for Using this Teaching MaterialAssumptions for Using this Teaching Material

DSR and OTSL takes no responsibility about the problem which occurs as a result of applying the technical information written in this document in a commercial product, although the information is based on actualimplementation and our experiences, is reliable enough.

Agenda

Basic 802.15.x overview, RF basics

Bluetooth basics

Technical trend and application examples of Bluetooth

Historical necessity of Bluetooth

Architecture of Bluetooth

Co-existence issue of Bluetooth and Wi-Fi/ZB

Multi-Profile Issue


Objectives

Understand 802.15.x family basics

Understand Bluetooth basics and applications

Understand Bluetooth (comparison w/Wi-Fi/ZB) basic architecture

Understand Bluetooth most common issues.

Understand the difference between BT/ZB/Wi-Fi




Basic 802.15.x Overview, RF BasicsBasic 802.15.x Overview, RF Basics


RF Definition and CharacteristicsRF Definition and Characteristics

RF stands for Radio Frequency, but is often used in the sense for anything related with EM signals.

The main characteristics are:

Frequency: The number of times a signal goes through a complete “up and down” cycle in one second of time. It is measured in Hertz.

Amplitude: The difference between the maximum and the minimum value during one cycle. It is measured in Volts, and is related with the strength, or power, of the signal.

Phase: The phase corresponds to how far the signal is offset from a reference point.

N.B. For most digital data transfers, Phase-shifting keying (PSK) is used.


RF ExampleRF Example

The phase corresponds to how far the signal is offset from a reference point. As a convention, each cycle of the signal spans 360 degrees. For example, a signal might have a phase shift of 90 degrees, which means that the offset amount is one quarter (90/360 = 1/4) of the signal


Basic RF Terms (cont.)Basic RF Terms (cont.)

Power: In the RF world, power is commonly used to quantify a signal instead of amplitude; expressed in Watts.

Decibel: The decibel (abbreviated as dB) is a logarithmic expression of the ratio between the power, voltage, or current of two signals.

P = 10*lg(P2/P1) or P = 20*lg(E2/E1)

Chip Specific measurements:

LQI - Link Quality Indication

RSSI - Received signal strength indication


Basic RF TermsBasic RF Terms

Basic RF terms are:

Wavelength: The distance a radio wave will travel during one cycle.

λ=c/f λ - is the wave length, in meters

c - is the speed of light, 299793 m/s

f - is the frequency, in Hz



Bluetooth BasicsBluetooth Basics


Bluetooth wireless technology (BWT) was developed in 1994 at Ericsson in Sweden.

The original purpose of BWT was to eliminate the need for proprietary cable connections between devices such as PDAs and notebook PCs.

Although infrared communication existed at the time, it required line-of-sight contact. Therefore, Ericsson chose to use an inexpensive, low-power radio built into each device making it possible to wirelessly connect devices through walls and other nonmetallic materials.

After Ericsson began work on BWT, the concept blossomed into a radio technology that simultaneously connects several devices in a wireless personal area network (WPAN).

Bluetooth History


Naming Bluetooth

The Bluetooth SIG adopted the code name as a tribute to the tenth-century Viking king Harald Blåtand who peacefully united Denmark and Norway. Harald liked to eat blueberries, which gave his teeth the coloration that lead to the nickname "Bluetooth.”


Bluetooth Specs

Bluetooth is based on RF data transmissions

Radio Frequency is 2.4 GHz

Limited range (10-100m)

Low power consumption

Open and royalty-free specification


Bluetooth Applications

Cable replacement

Personal Area Networking

Multiplayer gaming

Location-based services

Social applications

Home

Enterprise

Identification


Bluetooth Versions

V1.0b and 1.1

Basic architecture, radio spec, basic protocols

V1.2

Faster connection, coexistence with WLAN, improved QoS, improved voice quality

V2.0+EDR

Faster data transfer: up to 2.18 Mbit/s (user data rate)

V3.0+HS

Power Optimization, improved security, enhanced power control, lower latency rates

V4.0+LE

Lower energy consumption

Bluetooth Trends

Enhancing routing capabilities

Power saving

Increasing speed



Bluetooth Protocols Stack


Radio: It is the layer where actual communication takes place.

Baseband: It helps with setting up connections between devices. There is a 3-step inquiry

process:

1. Send ENQ message.

2. Discoverable device reply with ADDR and Clock.

3. Initiator reach device through paging signal.

Link Manager Protocol: It is involved in (with setup, detachment, or configuration of a link) exchanging

security-related messages; i.e., pairing, authentication, and encryption are exchanged by this layer.

Host Controller Interface (HCI): The HCI provides a command interface to the baseband controller and link

manager, and access to hardware status and control registers. Essentially, this interface provides a uniform method of accessing the Bluetooth baseband capabilities.

Bluetooth Protocols Stack (cont.)


Logical Link Control and Adaptation Protocol (L2CAP): Multiplexing – mixing messages from different senders before

transmitting in order to achieve high throughput. Segmentation and Reassembly – breaking input data into pieces

at one end and conjoining at receiving end. QoS – Quality of Service needed for that application. Group Management – similar to multicasting.

RFCOMM Protocol: The RFCOMM protocol provides emulation of serial ports over the

L2CAP protocol. The protocol is based on the ETSI standard TS 07.10.

Service Discovery Protocol (SDP): The service discovery protocol (SDP) provides a means for

applications to discover which services are available and to determine the characteristics of those available services.

Bluetooth Protocols Stack (cont.)

How Bluetooth Works

Bluetooth uses a radio technology which is called “frequency-hopping spread spectrum.” It works by chopping up the data that is being sent, and transmitting sections of it on up to 79 frequencies.

Spread-spectrum is good for several reasons. Firstly, the signals are very resistant to narrowband interference, which means the transmissions are more likely to reach their destination quickly and intact.

Spread-spectrum transmissions can share a frequency band with many types of conventional transmissions with minimal interference.

Spread-spectrum signals are also very difficult to intercept, making the technology relatively secure, except for some early security issues.


The Bluetooth SIG states, "Bluetooth profiles are general behaviors through which Bluetooth enabled devices communicate with other devices."

In order to connect to one another, devices that use Bluetooth technology must support and understand certain Bluetooth profiles. Bluetooth profiles define the possible applications and describe how Bluetooth technology is to be used for each specific device.

For example, the File Transfer profile is used to define how devices like a PDA will use Bluetooth Technology to transfer files to other devices like another PDA, cell phone, or computer.

Bluetooth Profiles


According to the Bluetooth SIG: At minimum, every Bluetooth profile includes information on the following issues:

Dependencies on other profiles.

Recommended user interface formats.

Particular parts of the Bluetooth protocol stack are used by the profile. To perform its functions, each profile uses particular options and parameters at each layer of the stack. This may include an outline of the required service record, if applicable.


Bluetooth Profiles


Bluetooth vs. WiFi vs. ZigBee vs. Others


Bluetooth 4.0

1. Lower energy consumption

2. Dual and single mode operation

3. Lower latency

4. And as a conseqence — wider market potential



Co-existence Issue of Wi-Fi and BluetoothCo-existence Issue of Wi-Fi and Bluetooth


Recommended Practice

The purpose of this recommended practice is to facilitate co-existence of IEEE 802.15 WPAN devices with selected other wireless devices operating in unlicensed frequency bands.


The implementation of antenna varies from:

Independent antenna type

Shared antenna type

WLANWLAN

Coexistence Coexistence controlcontrol

WPANWPAN WLANWLAN

Coexistence Coexistence controlcontrol

WPANWPAN

AntennaAntenna AntennaAntennaAntennaAntenna

Shared antenna typeShared antenna typeIndependent antenna typeIndependent antenna type

Antenna Type


Radio Waves Interference

There are different methods for avoiding interference of radio waves:

Using different bands for Wi-Fi / Bluetooth

“30cm rule” / “3m rule”

But there are some problems which cannot be solved by the methods above.

It is important to notify everyone of this information when developing wireless devices or software.


Interference with Wi-Fi and Bluetooth

It is well known that Bluetooth works in 2.4GHz band, that Wi-Fi works different bands by IEEE802.11b/g and IEEE802.11a/p, and that IEEE802.11n works in both 2.4GHz band and 5GHz band.

IEEE802.11b/gIEEE802.11b/g :: 2.4GHz

IEEE802.11a/pIEEE802.11a/p :: 5.15 ~ 5.35GHz, 5.47 ~ 5.725GHz

IEEE802.11n:IEEE802.11n: 2.4GHz 5.15 ~ 5.35GHz, 5.47 ~ 5.725GHz

As noted above, we can avoid interference between Bluetooth and Wi-Fi when we choose IEEE802.11a/p/n as Wi-Fi, because Bluetooth and Wi-Fi work in different bands.

But because most of counter device of communication (PDA, mobile phone, hotspot AP, etc.) supports only 2.4GHz band of IEEE802.11b/g or IEEE802.11n, we should support 2.4GHz band in actual we should support 2.4GHz band in actual implementationimplementation.

In the future, when the main stream of Wi-Fi become IEEE802.11a/p and IEEE802.11n and when there is no need to support 2.4GHz band, it is considered that this method will be the best solution.


30cm Rule and 3m Rule

Even though there is no explicit mention about this in any clause, there are prerequisites in “IEEE802.15.2 Part 15.2”, which we call “30cm rule” and “3m rule”:

30cm rule30cm rule

When a Wi-Fi device and Bluetooth device are placed in the distance less than 30cm, both devices are under the influence of interference.

3m rule3m rule

When a Wi-Fi device and Bluetooth device are placed in the distance more than 3m, the influence of interference is very low.

These values (30cm, 3m) are only an indication and are the result of simulations in an anechoic chamber or open air. In the environment that is surrounded by a reflecting wall, such as the inside of automobiles, these values are considered to increase because of the reflection of radio waves.

WiFi BT

under 30cm

high interference

WiFi BT

over 3m

low interference


Automotive 3m Rule

The most simple solution is to connect to as distanced of an antenna from each other as possible with shielded cable from ECU.

In actual implementation, the cost of the shielded cable and the cost of designing a routing cable will be very high and it will be very hard or costly to design with the distance of 3m.

WiFi BT

ECU

shielded cable

antenna antennaas distanced as possible, over 3m if possible

Fig.-3 “3m rule” example in automotive


Co-existenece Mechanisms

There are two categories of coexistence mechanisms: collaborative and non-collaborative.

WLAN

WPAN

WLAN

WPAN

physical unit

wired connection

Implemented in one physical unit and communicating with each other by wired connection

Implemented in different physical unit and not communicating with each other by wired connection

Collaborative Non-collaborative


Collaborative and Non-Collaborative ExamplesName タイプ

① AWMA : Alternating wireless medium access collaborative

② PTA : Packet traffic arbitration collaborative

③ DIS : Deterministic interference suppression collaborative

④ AIS : Adaptive interference suppression non-collaborative

⑤ APS : Adaptive packet selection non-collaborative

⑥ PS-ACL : Packet scheduling for ACL links non-collaborative

⑦ PS-SCO : Packet scheduling for SCO links non-collaborative

⑧ AFH : Adaptive frequency-hopping non-collaborative


Collaborative Examples

1. AWMA

2. PTA

3. DIS3. DIS

WLAN time WPAN time WLAN timetime

TDMA (Time Division Multiple Access)

WLANPTA

ControllEntity

WPAN

TxRequest TxRequest

TxConfirm TxConfirm

Status Status

transversal filter

This is effective for mitigating interference, but it deteriorates voice streaming such as SCO.

This can avoid deterioration of voice streaming by giving increased priority to SCO. But ACL data transfer rate will decrease.

input output

(the same principle as noise and echo canceller)

This is effective for mitigating interference, but it needs high cost and much time for implementation.

Approximating the contribution of interference sources and removing them

Fig.-6 PTA image


Non-Collaborative Examples

4. AIS

5. APS

Adaptive filterDelay

Σ

Cancelling the interference signal by the prediction signal

RLSL filterRLSL filter

Throughput in application

HV1 HV2 HV3＞＞

DM1 DM3 DM5＞＞less influence of interference

more influence of interference

Selecting the packet type adaptively for the system that needs transfer rate

x(n)

y(n)

e(n) Approximation of the IEEE802.11 signal

Fig.-9 APS image

IEEE802.15.1 SCO packet type

IEEE802.15.1 ACL packet type

Prediction unwanted narrowband IEEE802.15.1 signal


Non-Collaborative Examples (cont.)

7. PS-SCO

8. AFH

packet to transmit

last Slave Rx : badlast Master Rx : bad

Slave Rx now : goodMaster Rx now : good

delay

This is the Adaptive Frequency Hopping in Bluetooth standard itself.

This method is used only for SCO transportation.

The packet type is converted from HV3 to EV1, and if the last frequency status of the starting packet slot is “bad,” the transmit packet is delayed until the start packet slot whose last frequency status is “good” is reached.

6. PS-ACL If the last frequency status of the packet slot is “bad,” the transmit packet is delayed until the packet slot whose last frequency status is “good” is reached.


Required Performance

The required performance of the application is not interference suppression; but is responsiveness, continuity, and throughput of the entire system.

And the required performance varies according to the usage scene of the application.

We discuss the “Part 15.2” method from the viewpoint of the performance items below:

Responsiveness

Continuity of streaming (such as SCO and VoIP)

Throughput of entire system


Interconnectability with CSR Chip and Other Silicon Manufacturers

There are many WLAN chips that implement the wired connectivity (3 wire/5 wire), mentioned as the collaborative system recommended by IEEE. But the signal timing properties (such as TxRequest, TxConfirm, MediumFree) vary by silicon manufacturer’s implementation. And the specification of Status signal also varies by silicon manufacturer’s implementation. So we cannot expect that the Bluetooth devices from CSR connected to other silicon manufacturer’s WLAN chip will work correctly when simply connected.

The WLAN devices that implement the “Par15.2” method as it is are older generation. Now the silicon manufacturers implement their own method for coexistence into their WLAN chip, and the implementation among silicon manufacturers is getting more and more different.

Especially in CSR, Broadcom, and Texas Instruments, they are working from single chip integration including GPS, FM, and so on, and are using PTA method that exchanges more information between WLAN subsystem and Bluetooth subsystem than existing PTA.

The “enhanced” PTA, as mentioned above, exchanges the scheduling data of predicted Tx/Rx packet, reduces interference by Rx packet, and powers-down the WLAN subsystem. As a result, it achieves a much higher performance of interference suppression than the original “Part 15.2”.

Considering the situation above, when implementing the collaborative mechanism of Bluetooth and WLAN, it is almost impossible to implement using the WLAN device and Bluetooth device from different silicon manufacturers.


Interconnectability with CSR Chip and Other Silicon Manufacturers (cont.)

Methods that meets required performance and can be implemented are as follows:

Devices from the same silicon manufacturer with collaborative mechanism

To realize coexisting system by using the WLAN device and Bluetooth device from the same silicon manufacturer and by using collaborative mechanism.

Devices from different silicon manufacturers with non-collaborative mechanism

To realize coexisting system by using the WLAN device and Bluetooth device from different silicon manufacturers and by using non-collaborative mechanism.

Combo device of WLAN and Bluetooth

To realize coexisting system by using one-chip system of WLAN subsystem and Bluetooth subsystem designed recently by major silicon manufacturer (such as CSR, Broadcom, Texas Instruments, etc.), and by using collaborative mechanism.


Conclusion: Collaborative MechanismConclusion: Collaborative Mechanism

1. Devices from the same silicon manufacturer with collaborative mechanism Features:

High reliability in behavior of collaborative mechanism (inter-connectability of coexistence signal line), because of devices from the same silicon manufacturer.

Consideration for implementation: At the master device, to use AWMA and PTA as a core method and to use DIS and AFH as selectable

options.

It is necessary to control dynamically the enable/disable of AWMA, configuration of WLAN/BT time length, and configuration of PTA priority, according to usage scene of application in order to get high performance.

At the slave device (such as a BT mobile phone, Wi-Fi PDA, etc.), select AIS as an option when there is strong interference between WLAN and Bluetooth.

There is a selectable antenna option that is a WLAN/BT independent type or a WLAN/BT shared type.

WLAN

BT

AWMAPTA

AISDISBT mobile

phone

AIS

shared antenna

independent antenna

master device

WLAN AP

In this collaborative mechanism, collision of only the Tx packet can be avoided.In the case that the WLAN Rx packet reaches a shared antenna when Bluetooth is transmitting the packet in WPAN time, WLAN loses this Rx packet.

Collaborative mechanism

required

optional


Conclusion: Non-Collaborative Mechanism

2. Devices from the different silicon manufacturers with non-collaborative mechanism Features:

If the performance of the WLAN device or PTA algorithm from the same silicon manufacturer do not meet the requirement of the application, the WLAN device from the other silicon manufacturer is selected and AFH runs on Bluetooth.

AFH can meet the basic coexistence mechanism, and there is a merit that the devices from different silicon manufacturers can be selected.

Because the situation that hopping table is WLAN in-band can be avoided by AFH, the interference can be avoided almost perfectly by only the non-collaborative mechanism.

Because Bluetooth application and Wi-Fi application can be run independently, it becomes easy to reuse the past resources of Bluetooth and Wi-Fi.

WLAN

BTAFH

AIS

AIS

independent antenna

WLAN APmaster device slave device

Collaborative mechanism

required

optional


Consideration for implementation:

Independent antennas are required:

Because WLAN/Bluetooth run independently, they cannot share an antenna.

It is recommended that application looks-up the hopping table of AFH and refreshes the table before transmitting the SCO/VoIP packet:

Without doing this step, collision occurs at the start of SCO/VoIP and noise comes out.

It takes several seconds to look-up all channels. In order not to make users feel the device is locking, it is recommended to transmit by SCO some kind of electric sound while looking-up.

It is recommended to notify with some kind of electric sound while the hopping table is being refreshed when the WLAN channel changes.

In the specific example that the application does not use WLAN or Bluetooth, it is recommended that the application shuts down the unused device and that the application looks-up the AFH table if Bluetooth is in use.

By the explicit refreshing of the application’s AFH hopping table, the avoidance of in-band becomes more accurate and the avoidance of interference becomes more accurate.

Conclusion: Non-Collaborative Mechanism (cont.)


Conclusion: WLAN and Bluetooth Combo DeviceConclusion: WLAN and Bluetooth Combo Device

3. Combo device of WLAN and Bluetooth

Features:

Major silicon manufacturers such as CSR, Broadcom, Texas Instruments, etc., have released the one-chip device that includes WLAN, Bluetooth, GPS, FM and so on.

The device of each silicon manufacturer includes IEEE802.15.2 Part 15.2 collaborative algorithm. And each silicon manufacturer adds their own coexistence mechanisms:

For example, in the Broadcom device, the function is added that the device transmits to AP the packet that notifies that the device cannot receive the Rx packet, and avoids packet-loss by making Rx packet retained in the AP. A function is added that reduces battery consumption and reduces noise by power-down.

Each silicon manufacturer designs ICs for target application so users can select ICs for their specific application.

Consideration for implementation:

PTA logic varies by each silicon manufacturer and each target application. It is important to check the design concept of PTA logic in selection to achieve expected performance.

Comparison



Comparison (cont.)

As mentioned above, throughput / latency does not always improve by collaborative mechanism of “item 1 (collaborative mechanism)” or “item 3 (combo device).”

Throughput is assured to a certain level, but it is not the maximum throughput.

When “item 3” is adopted, throughput is higher than “item 1,” but it is lower than the maximum throughput yet.

It is impossible to always assure the streaming band by collaborative mechanism. On the other hand, collaborative mechanism is suitable for the application that does not use streaming for the purpose of assuring throughput to a certain level.

In the actual application in automobiles, because it is considered that voice streaming is essential for hands-free, collaborative mechanism is not so effective.

AFH is more effective than collaborative mechanism because:

The best performance can be expected in throughput / latency.

It is only possible to assure the quality of streaming such as SCO / VoIP by AFH.


Bluetooth Multi-Profile IssuesBluetooth Multi-Profile Issues

Profile1 andProfile2 areindividuallyqualified.

However, when two profiles are implemented into the same application,sometimesproblems occur.

Profile 1

Qualified

Profile 2

Qualified

Bluetooth SIGBluetooth SIGConformance testConformance test

Profile 1 + Profile 2

Problems occur

ApplicationApplicationImplementedImplemented

Profile1 + Profile2Profile1 + Profile2

Individually qualified !


CauseCause

Each profile has different rolls.

For the same profile, different rolls are implemented by different manufacturers.

When only one profile is working, no problems occur in most cases.

But when two profiles are working at the same time (during audio streaming, telephone calls), sometimes conflict or hang-up happens:

For example, H-company’s smart phone hangs up with E-company’s Bluetooth headset when telephone call occurs during audio streaming.

A2DP AVRCP

SRC SNK

HFPHSP

HFAG

Smart phone Bluetooth Headset

Manufactured and testedby different manufacturers

Case StudyCase Study

Real causes of the problem are:

Confliction between procedures

Timeout caused by interruption of other procedures

Request code conflict

Etc.

To solve the problem, we need to study multi-profile implementation cases.

We need to find out critical points where conflict shown above may occur.

The next step is to clarify the mixed procedure of mixed profile in each case and to standardize the mixed procedure.


Bluetooth SIG Multi-profile WGBluetooth SIG Multi-profile WG

According to the discussion described above, Bluetooth SIG sets up a Multi-profile working group (WG).

In WG, members study reported cases and discuss the proper procedure to avoid the problem.

The goal of the WG is to make a standard mixed procedure for typical cases.

Another goal is to design a Golden Unit for some specific cases to be used for Bluetooth SIG conformance testing.

4949COPYRIGHT © 2012 DSR CORPORATIONCOPYRIGHT © 2012 DSR CORPORATION

Documents

Embedded Systems Software Training Center COPYRIGHT © 2012 DSR CORPORATION 802.15.x Wireless Technologies