Wireless Communication Chips

Question 1

What are commonly available communication chips in smartphones?

Answer 1

• WiFi
• Cellular (CDMA)
• Bluetooth
• Near Field Communication (NFC)

Question 2

What are the factors affecting wireless system design?

Answer 2

• Frequency
• Signals encoding
• Antennas and propagation
• Multiple access mechanism
• Error correction

Question 3

What is frequency?

Answer 3

Wavelength = c/f c=speed of light

Question 4

How does Radio Transmitter work?

Answer 4

Digital Data (Bits) -> digital modulation -> analog baseband signal + radio carrier -> analog modulation -> output

Question 5

How does Radio Receiver work?

Answer 5

Radio carrier -> analog demodulation (-> output) -> analog baseband signal -> synchronization decision -> digital data

Question 6

Three Digital Modulation Techniques

Answer 6

• Amplitude Shift Keying (ASK)
• Frequency Shift Keying (FSK)
• Phase Shift Keying (PSK)

Question 7

What is ASK?

Answer 7

• Simple, low bandwidth requirements, and very susceptible to interference
• no amplitude for 0, some amplitude for 1

Question 8

What is FSK?

Answer 8

• Needs larger bandwidth

- Different frequency for 1 and 0

Question 9

What is PSK?

Answer 9

• More complex and robust against interference

- Phase difference for 1 and 0

Question 10

What does wireless communication systems consist of?

Answer 10

• Transmitters
• Antennas: radiates electromagnetic energy into air
• Receivers

Question 11

What are transceivers?

Answer 11

Transmitters and receivers on the same chip

Question 12

How does antennas work?

Answer 12

• Electrical conductor or system of conductors to send/receive RF signals
• Transmission/Reception - radiates/collects electromagnetic energy into/from space

Question 13

What are modes of antennas?

Answer 13

Omni Mode: nodes receive signals with gain G^o

Directional Mode: more gain in specified direction, G^d

Question 14

What is strength of signal?

Answer 14

Received power is proportional to 1/(d^2f^2)

Question 15

Why does attenuation matter?

Answer 15

• Received signal must have sufficient strength so circuitry in receiver can interpret signal
• Signal must maintain a level sufficiently higher than noise to be received without error

Question 16

How does Transmitters work?

Answer 16

• Oscillator
• Mixer
• Filter
• Amplifier

Question 17

Generation a 900 MHz signal from original signal at 300 MHz. Role of Oscillator?

Answer 17

Create a carrier wave of 600 MHz

Question 18

Generation a 900 MHz signal from original signal at 300 MHz. Role of Mixer?

Answer 18

Combines signal and oscillator to produce 900 MHz

Question 19

Generation a 900 MHz signal from original signal at 300 MHz. Role of Filter?

Answer 19

Select correct frequency

Question 20

Generation a 900 MHz signal from original signal at 300 MHz. Role of Amplifier?

Answer 20

Strengthen the signal before sending it over the air

Question 21

What are the signal propagation ranges?

Answer 21

• Transmission range
• Detection range
• Interference range

Question 22

What happens in Transmission range?

Answer 22

• Communication possible

- Low error rate

Question 23

What happens in detection range?

Answer 23

• Detection of signal possible

- No communication possible

Question 24

What happens in interference range?

Answer 24

• Signal may not be detected

- Signal adds to background noise

Question 25

What is receiving power influenced by?

Answer 25

• Shadowing
• Reflection at large obstacles
• Refraction depending on density of a medium
• Scattering at small obstacles
• Diffraction at edges
• Receiving power proportional to 1/d^2

Question 26

What is multi path propagation?

Answer 26

Signal can take different paths between sender and receiver due to reflection, scattering, and diffraction

• Time dispersion: signal is dispersed over time
• Signal reaches receiver directly and phase shifted

Question 27

What are the effects of mobility?

Answer 27

• Channel characteristics change over time and location: signal paths change, different delay variations, and different phase.
• Quick changes in power received
• Slow changes in average power received

Question 28

What are 4 dimensions of multiplexing?

Answer 28

• Space
• Time
• Frequency
• Code

Question 29

What does frequency multiplexing do?

Answer 29

Separate the spectrum into smaller frequency bands.

User gets a certain band of spectrum for the whole time

Question 30

Advantages and Disadvantages of Frequency Multiplexing

Answer 30

A: No dynamic coordination necessary
D: Waste of bandwidth if traffic is distributed unevenly and guard spaces needed

Question 31

What does time multiplexing do?

Answer 31

User gets the whole spectrum for a certain amount of time

Question 32

Advantages and Disadvantages of Time Multiplexing

Answer 32

A: Only one carrier in medium at any time
D: Precise synchronization necessary

Question 33

What does Time and Frequency Multiplexing do?

Answer 33

Combination of both methods.

A user gets a certain frequency band for a certain amount of time

Question 34

Advantages and Disadvantages of Time and Frequency Multiplexing

Answer 34

A: better protection against jamming and protection against frequency selective interference
D: Precise coordination required

Question 35

What does Code Multiplexing do?

Answer 35

Each user has a unique code.
All users share the same spectrum all the time
Implemented using spread spectrum technology

Question 36

Advantages and Disadvantages of Code Multiplexing

Answer 36

A: Bandwidth efficient, no coordination and synchronization necessary, and good protection against interference and jamming
D: Complex signal processing