how to send bits with signals
coding: signal sent directly on wire
- considerations
- signals are 0/1 - need freq transitions to decode (e.g., lots of 0s in a row can be confusing)
- clock recovery: map every 4 bits into 5 code bits w/o long runs
- signals are 0/1 - need freq transitions to decode (e.g., lots of 0s in a row can be confusing)
modulation: modulate carrier
- send baseband signals at higher frequencies for better propagation
- modulate by changing amplitude, freq, phase
terms
- bandwidth-delay product: amt of data in-flight
- BD = bandwidth (rate) * latency (delay)
- every analog signal has a bandwidth (transition speed) (diff from rate ver - affects rate of transitions of signals - how sharp the signal is)
limitations
- Nyquist = max symbol rate = 2 * bandwidth (transition speed)
- how many digital symbols can you cram into a signal with a given bandwidth (transition speed)
- Shannon Capacity - how much info can you communicate over a noisy channel
- channel capacity grows linearity with bandwidth (transition speed), logarithmically with signal-to-noise ratio
- bits/sec
- the rate which we can transmit data without loss given error correction