The impact of using multicode transmission in the WCDMA system

The multicode transmission scheme for achieving higher data rates in the WCDMA system is studied especially considering envelope variations and nonlinear power amplifiers. Results show that using three codes instead of a single code reduces the power efficiency of the power amplifier from about 40% down to 25% at a adjacent channel power ratio of -40 dB. However, by the introduction of a simple but very effective precoder it is possible to maintain the power efficiency of the amplifier at 40%. This precoder is a simple parity check code where the fourth bit is the parity of the three first bits. Assuming that four orthogonal spreading codes are used this precoder construction limits the envelope variations to that of a single code transmission thus allowing for the same output backoff of the power amplifier as for the single code transmission scheme. It is furthermore shown that the precoded scheme performs as well as the multicode scheme using three codes