PARR reduction of TD-SCDMA with Joint Transmission technique

Joint Detection (JD) technique is used to reduce intersymbol interference (ISI) and multiple access interference (MAI) in current downlink (DL) of Time-Division Synchronous Code-Division-Multiple-Access (TD-SCDMA). However, the technique requires significant calculation and channel estimator in mobile station (MS), causing complexity in MS. Using TDD features where received uplink channel impulse responses (CIRs) can be used in DL, Joint Transmission (JT) has been proposed. In JT, all of JD functions are removed into BS, thus a simple and low cost MS can be realized. However, studies of JT show that the JT increases transmission power. This may affect Peak to Average Power Ratio (PARR) of the system. For a single path case, our result shows that JT increases overall transmitted power as well as average transmitted power, leading to lower PARR. However, as JT multiplies CIRs with spreading codes before transmission, high PARR might be occurred in multipath case. To avoid high PARR, we propose a new approach of JT technique that can perform lower PARR even in multipath case. The proposed technique selects certain paths instead of all paths used in JT processing so that PARR becomes lower, while keeping good bid error rate (BER) performance.