The Research Of Pseudo Noise Code And Space-time Block Code In WCDMA

The third-generation communication standards have been admitted by ITU in 1985, and developed during the later twenty years. Nowadays, there are three famous editions used: WCDMA, CDMA2000 and TDS-CDMA, they are based on code division multiple access, and it comes true by spread spectrum. In fact, spread spectrum is that use PN code with high data rate to spread the transmit signal's spectrum, so the PN code used in the spread spectrum system. The important point of PN code is correlation, it reduces the interference between the channels as much as we can. In the spread spectrum, we use the good self-correlation but bad cross-correlation PN code. And using PN code can still demodulation signals correctly when power is lower interference or noise.But because CDMA is that found many code division channels on the same frequency, although PN code has good incorrelation , it's sure that the special channel be interfered by other channels, it is because that the cross-correlation of different users' PN code isn't zero, we also call it multiple access interference, one of the solution method is transmit diversity, the space-time block code is a new and effect diversity method, it can add the diversity gain of system, and simple in encode and decode.3GPP use space-time block code in the open loop diversity there are the close loop and the open loop in WCDMA and in the open loop every user has two different spread sequences, and it is a better diversity among some open loop diversity methods, but because of the amount of spread sequences, it has a little complex, and influence the system, but the open loop still has effect in high speech .This paper discuss the PN code and space-time block code, and simulate the open loop diversity in WCDMA, and get the conclusion that although interfered by spread sequences, the space-time block code has still improved the system.