Wireless Communication Chips Flashcards
What are commonly available communication chips in smartphones?
- WiFi
- Cellular (CDMA)
- Bluetooth
- Near Field Communication (NFC)
What are the factors affecting wireless system design?
- Frequency
- Signals encoding
- Antennas and propagation
- Multiple access mechanism
- Error correction
What is frequency?
Wavelength = c/f c=speed of light
How does Radio Transmitter work?
Digital Data (Bits) -> digital modulation -> analog baseband signal + radio carrier -> analog modulation -> output
How does Radio Receiver work?
Radio carrier -> analog demodulation (-> output) -> analog baseband signal -> synchronization decision -> digital data
Three Digital Modulation Techniques
- Amplitude Shift Keying (ASK)
- Frequency Shift Keying (FSK)
- Phase Shift Keying (PSK)
What is ASK?
- Simple, low bandwidth requirements, and very susceptible to interference
- no amplitude for 0, some amplitude for 1
What is FSK?
- Needs larger bandwidth
- Different frequency for 1 and 0
What is PSK?
- More complex and robust against interference
- Phase difference for 1 and 0
What does wireless communication systems consist of?
- Transmitters
- Antennas: radiates electromagnetic energy into air
- Receivers
What are transceivers?
Transmitters and receivers on the same chip
How does antennas work?
- Electrical conductor or system of conductors to send/receive RF signals
- Transmission/Reception - radiates/collects electromagnetic energy into/from space
What are modes of antennas?
Omni Mode: nodes receive signals with gain G^o
Directional Mode: more gain in specified direction, G^d
What is strength of signal?
Received power is proportional to 1/(d^2f^2)
Why does attenuation matter?
- 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
How does Transmitters work?
- Oscillator
- Mixer
- Filter
- Amplifier
Generation a 900 MHz signal from original signal at 300 MHz. Role of Oscillator?
Create a carrier wave of 600 MHz
Generation a 900 MHz signal from original signal at 300 MHz. Role of Mixer?
Combines signal and oscillator to produce 900 MHz
Generation a 900 MHz signal from original signal at 300 MHz. Role of Filter?
Select correct frequency
Generation a 900 MHz signal from original signal at 300 MHz. Role of Amplifier?
Strengthen the signal before sending it over the air
What are the signal propagation ranges?
- Transmission range
- Detection range
- Interference range
What happens in Transmission range?
- Communication possible
- Low error rate
What happens in detection range?
- Detection of signal possible
- No communication possible
What happens in interference range?
- Signal may not be detected
- Signal adds to background noise
What is receiving power influenced by?
- 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
What is multi path propagation?
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
What are the effects of mobility?
- 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
What are 4 dimensions of multiplexing?
- Space
- Time
- Frequency
- Code
What does frequency multiplexing do?
Separate the spectrum into smaller frequency bands.
User gets a certain band of spectrum for the whole time
Advantages and Disadvantages of Frequency Multiplexing
A: No dynamic coordination necessary
D: Waste of bandwidth if traffic is distributed unevenly and guard spaces needed
What does time multiplexing do?
User gets the whole spectrum for a certain amount of time
Advantages and Disadvantages of Time Multiplexing
A: Only one carrier in medium at any time
D: Precise synchronization necessary
What does Time and Frequency Multiplexing do?
Combination of both methods.
A user gets a certain frequency band for a certain amount of time
Advantages and Disadvantages of Time and Frequency Multiplexing
A: better protection against jamming and protection against frequency selective interference
D: Precise coordination required
What does Code Multiplexing do?
Each user has a unique code.
All users share the same spectrum all the time
Implemented using spread spectrum technology
Advantages and Disadvantages of Code Multiplexing
A: Bandwidth efficient, no coordination and synchronization necessary, and good protection against interference and jamming
D: Complex signal processing
