2023 1 embedded systems chapter 5

Wireless communication▪ First Wireless Communication SystemMarconi’s Radio Transmitter Systemhttp://iwcmediaecology.pbworks.com/w/page/8480806/Guglielmo%20Marconi... Wireless communicati

➢ 1894, Oliver Lodge was the first to publicly demonstrate the transmission and detection of electromagnetic radiation

➢ 1895, Marconi first heard of wireless and He was fascinated➢ 1897, He formed theWireless Telegraph and Signal Co Ltd,

the first commercial development in the world

Wireless communication

▪ First Wireless Communication System

Marconi’s Radio Transmitter System

http://iwcmediaecology.pbworks.com/w/page/8480806/Guglielmo%20Marconi

Wireless communication

▪ RF – Radio Frequency (few kHz to 300GHz)

Wireless communication

▪ Half-Duplex RF System

▪ Operation mode of a radio

communication system in which each end can transmit and

receive, but not simultaneously.

▪ The communication is bi-directional over the same

frequency, but uni-directional for the duration of a message The devices need to be transceivers.

Wireless communication

▪ Full-Duplex RF System

▪ Radio system which each end can transmit and receive simultaneously.

▪ Typically use two frequencies as channel Each channel is used solely for transmitting (or receiving).

▪ Example: Cell phone, satellite communication,…

▪ Frequency Shift Keying (FSK)

▪ Less susceptible to noise ▪ Require larger bandwidth

▪ Phase Shift Keying (PSK)

▪ Less susceptible to noise, bandwidth efficient

▪ Require synchronization in phase and frequency

Wireless communication

Basis Elements of Wireless Communication System

Wireless communication

Avoiding Interference in ISM Band

▪ Spread Spectrum Technique: intentionally spread over a wide frequency range

▪ Resistant to noise and interference thus increasing the probability that the signal will be received correctly

▪ Unlikely to interfere with other signals even if they are transmitted on the same frequency

▪ Types of Spread Spectrum common in ISM bands : ▪ Direct Sequence Spread Spectrum ( DSSS )

▪ Frequency Hopping Spread Spectrum ( FHSS )

▪ Orthogonal Frequency Division Multiplexing ( OFDM )

Wireless communication

Direct Sequence Spread Spectrum

Wireless communication

Direct Sequence Spread Spectrum

▪ Advantage of DSSS: ▪ More bandwidth ▪ Data are encoded

▪ Low power density, noise-like signal

Wireless communication

Frequency Hopping Spread Spectrum

▪

Wireless communication

Orthogonal Frequency Division Multiplexing

▪

Wireless communication

Orthogonal Frequency Division Multiplexing

▪

Wireless communication

ISM band – 2.4 GHz

▪ ISM: Industrial, scientific and Medical ▪ ISM band: 2.4GHz-2.483GHz

▪ Getting more crowed day by day

▪ Why use this band?

BLUETOOTH

▪ Initiated by Ericsson Mobile in 1989

▪ Named as a king of Denmark in 900s, Harald Bluetooth ▪ Frequency band 2.402 GHz - 2.480 GHz

▪ Connection between devices, point to point/ multipoint

BLUETOOTH Addresses and Name

▪ Every Bluetooth device has a unique 48-bit address – MAC

address (Medium Access Control)

▪ Bluetooth devices can also have user-friendly names (presented to user to identify devices)

BLUETOOTH

▪ Version

BLUETOOTH

▪ Version

BLUETOOTH Low Energy (BLE)

▪ BLE aims to operate at very low power ▪ BLE compromises in data rate

▪ 1Mbps (theory) – 0.27Mbps (practical) ▪ BLE devices switch between sleeping and

working state to save energy

▪ BLE requires rapid connection, small package

BLE Direction Finding

▪ Direction Finding is feature of BLE 5.1 ▪ Enable positioning solution

▪ Old BLE rely on RSSI (Receive Signal Strength Indicator) ▪ New BLE knows the actual direction of signal

BLE MCU

▪ “Wireless Fidelity”

▪ Exchange data wirelessly in Wireless ▪ IEEE 802.11

▪ links two or more devices using some wireless distribution method, and provides a connection through an access point to the wider internet

▪ High Speed , wide range ( 50m indoor , 100m out door )

▪ Power consumption : chipsets 0.5-1w; wifi device 1-2w , router 4-5w ,

WIFI star network

• Same role devices • All connect to Hub

• Security

• Limited access

• Access IP (192.168.xxx)

▪ Consume very low power: 2.5-3 times more efficient than Bluetooth

▪ "optimized for the unique needs of remote monitoring and control

Zigbee Mesh Network

▪ Message can be transferred from any source to any destination.

▪ Every FDD (full function device) or Router can connect to its neighbors ▪ High reliability achieved through

multiple paths

Zigbee Mesh Network

Zigbee Architecture

Comparison

WEB SERVER

System Diagram

•Directly control system

•Make use of the hardware capability

•Limited by hardware and OS•Can’t remote control

• Difficult to access online database

WEB SERVER

System Diagram

• Not depend on OS

• Control/monitor system from anywhere •Use resource available on the internet

• Depend on wifi/internet • Can’t be very complex

•Show data, plot graph

•Simple algorithms/calculation

WEB SERVER

• What is the web server and its functions? • How to create a web server?

• How to communicate/transfer data between web server and devices • Why do we need an embedded system?

WEB SERVER

• Web server hosts a web site and provides reliable services for any requesting client.

• Web server communicate with clients via different protocols: TCP, UDP,…

WEB SERVER

https://ruslanspivak.com/lsbaws-part1/

HyperText Transfer Protocol (HTTP)

• HTTP is an asymmetric request-response client-server

• HTTP is a stateless protocol

HyperText Transfer Protocol (HTTP)

• HTTP client and server communicate by sending text messages• An HTTP message consist of a message header and an optional

message body, separated by a blank line

HTTP request message

• The request message syntax:

• Request-method-name: GET, POST, HEAD, OPTIONS • Request-Url: specify the resource requested

• HTTP version: HTTP/1.0 &HTTP/1.1

HTTP request message

• The request header syntax:

• request-header-name: request-header-value1, request-header-value2 • The request header syntax:

• name1=value1& name2=value2&…

HTTP response message

• Status line: HTTP ver status-code reason-phrase