digitalmodulationbasics(编辑修改稿)

digitalmodulationbasics(编辑修改稿)内容摘要：

oving the carrier signal to obtain the original signal waveform • Detection – extracts the symbols from the waveform – Coherent detection – Noncoherent detection 29/01/2020 Property of R. Struzak 19 Coherent Detection • An estimate of the channel phase and attenuation is recovered. It is then possible to reproduce the transmitted signal and demodulate. • Requires a replica carrier wave of the same frequency and phase at the receiver. • The received signal and replica carrier are crosscorrelated using information contained in their amplitudes and phases. • Also known as synchronous detection 29/01/2020 Property of R. Struzak 20 Coherent Detection 2 • Carrier recovery methods include – Pilot Tone (such as Transparent Tone in Band) • Less power in the information bearing signal, High peaktomean power ratio – Carrier recovery from the information signal • . Costas loop • Applicable to – Phase Shift Keying (PSK) – Frequency Shift Keying (FSK) – Amplitude Shift Keying (ASK) 29/01/2020 Property of R. Struzak 21 NonCoherent Detection • Requires no reference wave。 does not exploit phase reference information (envelope detection) – Differential Phase Shift Keying (DPSK) – Frequency Shift Keying (FSK) – Amplitude Shift Keying (ASK) – Non coherent detection is less plex than coherent detection (easier to implement), but has worse performance. 29/01/2020 Property of R. Struzak 22 Geometric Representation • Digital modulation involves choosing a particular signal si(t) form a finite set S of possible signals. • For binary modulation schemes a binary information bit is mapped directly to a signal and S contains only 2 signals, representing 0 and 1. • For Mary keying S contains more than 2 signals and each represents more than a single bit of information. With a signal set of size M, it is possible to transmit up to log2M bits per signal. 29/01/2020 Property of R. Struzak 23 Geometric Representation 2 • Any element of set S can be represented as a point in a vector space whose coordinates are basis signals j(t) such that        210 ,。 ( = a r e or t hog ona l )1。 ( nor m a l i z a t i on )T he n ijiNi ij jjt t dt i jE t dts t s t  29/01/2020 Property of R. Struzak 24 Example: BPSK Constellation Diagram           12122c os 2 , c os 2。 0 e ne r gy pe r bi t。 bi t pe r i od F or t hi s si gna l se t , th e r e i s a si ngl e b a si c si gna l2 c os 2。 0 bbB P SK c c bbbbbcbbB P SKEES s t f t s t f t t TTTETt f t t TTSE                        11,bbt E t      Eb Eb Q I Constellation diagram 29/01/2020 Proper。