2023 1 embedded systems chapter 5

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

<small>➢ 1895, Marconi first heard of wireless and He was fascinated➢ 1897, He formed theWireless Telegraph and Signal Co. Ltd, </small>

<small>the first commercial development in the world</small>

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Wireless communication

▪ First Wireless Communication System

<b><small>Marconi’s Radio Transmitter System</small></b>

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Wireless communication

<b>▪ RF – Radio Frequency (few kHz to 300GHz)</b>

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Wireless communication

<b>▪ Half-Duplex RF System</b>

▪ Operation mode of a radio

communication system in which each end can transmit and

<b>receive, but not simultaneously.</b>

▪ The communication is bi-directional over the same

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

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Wireless communication

<b>▪ Full-Duplex RF System</b>

<b>▪ Radio system which each end can transmit and receive simultaneously.</b>

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

▪ Example: Cell phone, satellite communication,…

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<b>▪ Frequency Shift Keying (FSK)</b>

▪ Less susceptible to noise ▪ Require larger bandwidth

<b>▪ Phase Shift Keying (PSK)</b>

▪ Less susceptible to noise, bandwidth efficient

▪ Require synchronization in phase and frequency

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Wireless communication

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<b>Basis Elements of Wireless Communication System</b>

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Wireless communication

<b>Avoiding Interference in ISM Band </b>

▪ 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 )

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Wireless communication

<b>Direct Sequence Spread Spectrum </b>

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Wireless communication

<b>Direct Sequence Spread Spectrum </b>

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

▪ Low power density, noise-like signal

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Wireless communication

<b>Frequency Hopping Spread Spectrum </b>

▪

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Wireless communication

<b>Orthogonal Frequency Division Multiplexing </b>

▪

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Wireless communication

<b>Orthogonal Frequency Division Multiplexing </b>

▪

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Wireless communication

<b>ISM band – 2.4 GHz </b>

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

▪ Getting more crowed day by day

▪ Why use this band?

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<b>BLUETOOTH </b>

▪ 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

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<b>BLUETOOTH Addresses and Name</b>

<b>▪ Every Bluetooth device has a unique 48-bit address – MAC </b>

address (Medium Access Control)

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

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<b>BLUETOOTH </b>

▪ Version

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<b>BLUETOOTH </b>

▪ Version

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<b>BLUETOOTH Low Energy (BLE) </b>

▪ 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

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<b>BLE Direction Finding </b>

▪ 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

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<b>BLE MCU </b>

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▪ “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 ,

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<b>WIFI star network</b>

• Same role devices • All connect to Hub

• Security

• Limited access

• Access IP (192.168.xxx)

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<b>▪ Consume very low power: 2.5-3 times more efficient than Bluetooth. </b>

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

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<b>Zigbee Mesh Network</b>

▪ 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

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<b>Zigbee Mesh Network</b>

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<b>Zigbee Architecture</b>

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<b>Comparison </b>

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<b>WEB SERVER</b>

<b>System Diagram </b>

<small>•Directly control system</small>

<small>•Make use of the hardware capability</small>

<small>•Limited by hardware and OS•Can’t remote control</small>

<small>•</small> _{Difficult to access online database}

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<b>WEB SERVER</b>

<b>System Diagram </b>

<small>•</small> _{Not depend on OS}

<small>•</small> _{Control/monitor system from anywhere} <small>•Use resource available on the internet</small>

<small>•</small> _{Depend on wifi/internet} <small>•</small> _{Can’t be very complex}

<small>•Show data, plot graph</small>

<small>•Simple algorithms/calculation</small>

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<b>WEB SERVER</b>

• 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?

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<b>WEB SERVER</b>

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

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

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<b>WEB SERVER</b>

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<b>HyperText Transfer Protocol (HTTP)</b>

<i><b>• HTTP is an asymmetric request-response client-server</b></i>

• HTTP is a stateless protocol

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<b>HyperText Transfer Protocol (HTTP)</b>

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

<b>message body, separated by a blank line</b>

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<b>HTTP request message </b>

• 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

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<b>HTTP request message </b>

• The request header syntax:

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

• name1=value1& name2=value2&…

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<b>HTTP response message</b>

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

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