Continuous phase modulation

Continuous phase modulation is a method for modulation of data commonly used in wireless modems.

It is used primarily because continuous phase modulation has good spectral efficiency for a noncoherent modulation technique, and is less expensive to produce and more power efficient than coherent modulation schemes.

Continuous phase modulation requires filtering to achieve good spectral efficiency. Most common filter choices are Gaussian or Raised cosine. Partial response filtering can be used for even better spectral efficiency, but requires more complexity in the demodulation process.

Excess bandwidth trades spectral efficiency for range, where a value of 0.707 typically results in optimal sensitivity, depending on filter response.

MSK is another name for CPM with an excess bandwidth of 1/2 and a linear phase tragectory.

GMSK is used by GSM in most of the world's 2nd generation cell phones. It is also used in 802.11 FHSS, Bluetooth, and many other proprietary wireless modems.

See also: Wireless modems Frequency Modulation GSM GMSK MSK