Communication Systems I

CPE 313: Micro Processors and Interfacing

How can information flow frompoint A to point B?

Morse Code

Can you spell your name?

See http://morsecode.scphillips.com/jtranslator.html for a live demo

Morse Code in Hollywood

1996 Film

Fountain of Bits

How to transmit voice?

Speaker = Sound reproducer Mic = Sound transducerMax Frequency Range:

20-20,000 Hz

Electrical signal in a transmission line

How Are Phone Connected?

How are phone conversations connected?

Traditional Switched Network

Each conversation needs a dedicated line. Very expensive to build the network.

Using Multiplexing Techniques

Frequency Division Multiplexing (FDM)

Many connections can be multiplexed through a single line

Freqeuncy Channels

Traditional Telephone Lines Limitthe Sound Frequencies Transmitted

400 – 3,400 Hz

The bandwidth of this line is 3kHz

Can you think of

why?

Frequency Channels

If the main transmission line has a maximum bandwidth of 1MHz,How many concurrent phone connections can it carry?

What if we want to send digital data over the phone line?

Can it be done?010111001010111001

Digital to Analog Encoding

See http://www.iesmarenostrum.com/informatica/zmaterias/ral/flash/digit_modulation.swf for an interactive demo.

Example: A Traditional Modem

Modem Typical Maximum Speed

56Kbps

How data is sent with a traditional modem

Traditional Modem

Telephone Network

Home

Internet Gateway

DestinationPhone

Example II: ADSL Modem

ADSL

Why is ADSL much faster?

256 Channels of 4 kHz each

But What About the 4K Bandwidth Limitation?

Splitter ADSL Modem

DSLAM

Telephone Network

Data Network

Home

Digital Subscriber Line Access Multiplexer

How fast is ADSL?

ADSL = 256 x 4 kHz x 8 bits= 8 Mbps

ADSL2 = 12 Mbps

ADSL2+ = 25 Mbps

*ADSL2+ expands channel frequency from 1.1 to 2.2 MHz

Serial vs Parallel Transmission

Image © Quatec

Example of Serial Comm?

Example of Parallel Comm?

Which Mode is More Common?

Cost. Less cables. Smaller size. Simplicity. Keeping bits aligned in a high-

speed parallel line requires more complex electronics.

Serial

Why?

The Need for SpeedS

peed

Mbp

s

Synchronous vs Asynchronous

A B

A B

Synchronous uses a clock line

Asynchronous relies on a common clock on each side

Playing Catch with a Blind Receiver

If you are the blind catcher, which method would you choose?Method 1: Pitcher throws and sends a signalMethod 2: Pitcher throws every 10 seconds. No signal.

PitcherCatcher

RS-232 (Serial Communication) Baud Rate

Data bits

Start bit / Stop bits

Parity

RS-232 Pulses

Letter “V” ASCII = 86 (0101 01102)9600 bps, 8-N-1

Layout: Start Bit, Data Bits, Parity, Stop Bits

* Note: Rs-232 logic pulses are inverted

RS-232 Pulses

Letter “Y” ASCII = 89 (0101 10012)9600 bps, 8-Odd-1

Layout: Start Bit, Data Bits, Parity, Stop Bits

* Note: Rs-232 logic pulses are inverted

How about ASCII 255?

Layout: Start Bit, Data Bits, Parity, Stop Bits

The data transmission is unbalanced. Can cause transmission errors.

9600 bps, 8-N-1

Manchester Encoding (IEEE 802.3)

Bit 1 = Low to High

Bit 0 = High to Low

Example

Image: Wikipedia

Data = 255

Manchester Code

Encode the following transmissions using the Manchester standard

Letter “V” ASCII = 86 (0101 01102)

Letter “Y” ASCII = 89 (0101 10012)