first day!
going over syllabus
access to website: http://ee424:Morse@www.ece.uah.edu/~ljoiner/ee424

intro to digi comms
finite values in a given time interval
most important measure of perf is P(error)
ex: analog sensor, digital transmission, sensor outputs continuum of values, transmitter outputs 0s and 1s
sampler uses a pulse train to pull discrete time signals
quantizer rounds to acceptable values

pulse code modulation: positive or negative pulse for 1 or 0
alternatively, can use different amps, phases, or freqs of a sinusoid to get this into a higher freq
why is everything going digital? dig sigs easy to regen, flexibility in proc, lend to sig proc f()s protecting against interference and jamming, better utilization of spectrum

src encoder: removes redundant info, possible to xmit string of symbols, each selected from alphabet fo q symbols from output of redundant src by fewer than the avg of log2 q bits per symbol, yay for reducing bits/symbol, morse code is an example of this

encryption: comm privacy

channel encoder: adds controlled redundancy to allow for error detection and correction

data modulator: produces continuous waveform for transmission through analog channel, converts baseband sig to freq utilized on channel, 

spread spectrum modulator: adds additional level of mod, produces a spectrum for the xmitted sig that is much wider, first used by military to provide resistance to interference and jamming, provides a means for masking transmitted sig in packground noise in order to lower prob of intercept, provides resistance to sig interference from multiple xmission paths, permits access of common comm channels by more than one user(cell system), provides means for ranging, 

channel: medium that can convey the electric sigs at the transmitter output over a distance, typical chans: twisted pair, coax, fiber, RF link, chan behaves like a filter and corrupts signal with noise, attenuation increases with chan length, distortion because of physical phenomena such as freq dependent gains, multipath effects, and doppler shift
	noise made up of interfering sigs, internal (thermal motion of charged particles, random emission, diffusion/recombination of charged carriers) and external (interference by other chans, human made, natural noise)
BW - chan BW (range of freqs transmittable with reasonable fidelity), signal BW (range of freqs that exist in the signal itself)
chan bw must exceed sig bw for proper xmission
sig power - quality of transmission, more power diminishes SNR (ratio of sig power to noise power, determines success of xmission)
relationship between bw and pwr, can transmit with smaller bw, but get signal distortion, but can be mitigated with more pwr
chan capacity - theoretical capacity of a given channel assuming maximum possible utilization, for AWGN chan w/ finite bw, C = B*log2(1+SNR) in bps, arbitrarily low probability of error, can be increased by increasing BW or SNR
BW and SNR are somewhat linked, not independent
design tradeoffs - speed of xmission, accuracy of reception, reliability of equipment
cost params - complexity of equipment, channel bw, xmit power
components not under control - source, chan and chan characteristics, others
sesign focuses on building a xmitter and rx to optimize perf vs cost tradeoffs for a particular app