By Dr. Ernest Simo
4.0 Variable Length, Complex Walsh Codes Are Used
- To increase the number of usable Walsh codes, QPSK modulation is employed prior to spreading:
- Every two information bits are mapped into a QPSK symbol.
- As a result, the available number of Walsh Codes is increased by a factor of two relative to BPSK (pre-spreading) symbols.
- Every two information bits are mapped into a QPSK symbol.
- Furthermore, the Walsh code length varies to achieve different information bit rates.
- The forward link may be interference limited or Walsh code limited depending on the specific deployment and operating environment.
- When a Walsh code limit occurs, additional codes may be created by Multiplying Walsh codes by the masking functions.
- The codes created in this way are called Quasi-Orthogonal.
- When a Walsh code limit occurs, additional codes may be created by Multiplying Walsh codes by the masking functions.
CDMA Online Tech Talk
By Dr. Ernest Simo
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