Wireless Communication

Lecture 16 – BPSK, DPSK, QPSK, GMSK

BPSK: Binary Phase Shift Keying

where E = energy per bit, T = period of the bit, fc is the carrier frequency

DPSK: Differential Phase Shift Keying

Symbol stays the same if a “1” is transmitted, and changes if a “0” is transmitted.

OPSK: Orthogonal Phase Shift Keying:

QPSK: Quaternary Phase Shift Keying:

Constellations and higher-order modulations

Discuss the way that cos(A+B) leads to a nice way to represent this as a constellation of points in 2-D.

Show that this is easily extended to 8-PSK or 16-QAM.

Show that sequential numbering of 8-PSK or 16-QAM leads to unnecessarily high BER for a given SER.

Show how to gray code 16-QAM.

Show easy extensions to 16-APSK, 32-APSK for DVB-S2.

Discuss power backoff vs. distortion of APSK vs. QAM.

Show 64-APSK, 64-QAM, 128-cross-II, 256 QAM for cable.

Higher-order modulation trades:

Higher orders are more bandwidth efficient. Note that QPSK vs BPSK is a special case. M = 2^k bits per symbol, Rb = k*Rs

Higher orders are less power efficient. Show the minimum distance goes down given a fixed output power of the amplifier. Show BER curves.

Constellation Diagrams:

Plot magnitude and phase of each possible symbol

Information you can get from a constellation diagram:

· Increase dmin gives a decrease in BER

· Increase dimension (1D, 2D, 3D, etc.) increases bandwidth required

· Increase density increases BW efficiency and decreases power efficiency

GMSK