**16. Orthogonal Multilevel
Spreading Sequence Design**

Finite field transforms are offered as a new tool of spreading sequence
design. This approach exploits orthogonality

roperties of synchronous non-binary sequences defined over a complex finite
field. It is promising for channels supporting

a high signal-to-noise ratio. New digital multiplex schemes based on such
sequences have also been introduced,

which are multilevel Code Division Multiplex. These schemes termed Galois-field
Division Multiplex (GDM) are

based on transforms for which there exist fast algorithms. They are also
convenient from the hardware viewpoint

since they can be implemented by a Digital Signal Processor. A new Efficient-bandwidth
code-division-multiple-access

CDMA is introduced, which is based on multilevel spread spectrum sequences
over a Galois field.

The primary advantage of such schemes regarding classical multiple access
digital schemes is their better spectral efficiency.

Galois-Fourier transforms contain some redundancy and only cyclotomic coefficients
are needed to be transmitted

yielding compact spectrum requirements.

** **