Chapter 2 Flashcards
Layered Architecture (1)
- Makes system easier to understand.
Channel properties (4)
- Bit rate
- Delay
- Storage capacity
- Error rate
Bit rate (1)
- Number of bits per second
Delay (1)
How long does it take to get to the end?
Storage Capacity (2)
- How many bits can the channel hold at once
2. Capacity = BitRate * Delay
Error rate (1)
- Probability of bit flipping.
Twisted pair (2)
- Twisted because otherwise the cables would act as an antenna
- Bandwidth of 500 MHz
Coax Cable (1)
- Bandwidth in order of GHz
Optical Fiber (3)
- Uses light pulses to transmit bits.
- Receiver transforms light pulses in electric signals.
- Bandwidth in order of 100 GHz.
Radio frequencies (2)
- Can travel long distances
- Power of waves falls with distance from the source.
- f = 1 or 100 MHz based on AM or FM
Microwave (3)
- Needs line of sight because waves travel in straight lines.
- Do not travel through objects.
- f = 10Ghz
Baseband Transmission (4)
- Signal occupies frequencies from 0 to a max.
- NRZ
- Clock recovery problems
- Balanced signals.
Manchester encoding (1)
- XOR with the clock signal
NRZI (1)
- Codes 1 as transition and 0 as a non transition.
4B/5B (1)
- 4 bits are mapped into 5 bits so that no more than 3 consecutive 0 can appear.
Scrambling (1)
- Data is XOR with random sequence that is then XORed back from the receiver
Passband transmission (2)
- Signal is inside a certain frequency band which is shifted from the 0
- Data is sent by modulating phase frequency or amplitude.
- Frequency and phase are not independent so they canโt be modulated together.
Constellation diagram (3)
- Modulation of the signal is defined in amplitude and phase shift
- Phase shift is indicated by angle with x axis
- Amplitude defined by distance from origin
Nyquistโs theorem (1)
- Max data rate of a noiseless channel = 2. ๐ =2ร๐ต ร log2(๐)
Shannonโs theorem (2)
- Max data rate in noisy channel = ๐ = ๐ต ร log2(1+(๐/๐))
2. S/N = signal to noise radio, x db = 10^(x/10)
Multiplexing (1)
- Sending multiple signals on a single medium.
Simplex channels (1)
Only allow unidirectional data.
Duplex channels (1)
Allow data to pass through in both directions at the same time.
Half-duplex channels (1)
Allows data in both direction but not at the same time.
Frequency division Multiplexing FDM (2)
- Divides frequency spectrum in bands, each user can access a certain band.
- Guard bands are assigned to keep channels separated.
Time division multiplexing TDM (2)
- Users take turns to send data on a fixed schedule.
2. Guard time is used to protect against small time variations.
Code division multiplexing CDM (3)
- All stations send at the same time using the same frequencies.
- The receiver has to figure out who and what was sent.
CDM How ? ()
- Each station is assigned a bit sequence.
- When sending a 1 the station will send the sequence, when sending a 0 it will send the negation of the sequence.
- The sent sequences are added linearly.
- The receiver calculates the product between the sent sequence and the stations and then divides by n (size of the bit seqeunce)