Joint transmission (JT) in time-division-duplex code-division multiple-access (TDD-CDMA) systems can provide a low peak-to-average power ratio (PAPR) for single paths, but causing a high PAPR in multipath environments. To avoid the high PAPR, we propose a new approach to JT technique by selecting certain paths instead of all paths used in JT processing so that PAPR becomes lower. The path selection proposal involves two methods; path selection by taking certain paths from all paths and by taking paths having path gains above a certain threshold value. To enhance the effectiveness of the proposed techniques, we evaluate a combination of the proposed technique with the clipping technique. We evaluate both PAPR and bit error rate (BER) performance for the proposed techniques and its combination with the clipping technique. We compare the results of the proposed techniques with conventional JT technique and the combination techniques with clipping technique. From the results of computer simulation, we show that the proposed path selection techniques perform low PAPR and good BER performance compared to the conventional JT processing. We also show that the combination of proposed path selection technique and clipping performs low PAPR performance without severe BER degradation compared to the conventional clipping technique.

In this paper, a multi-cell joint channel estimation (JCE) method is proposed for the TD-SCDMA downlink. In the proposed multi-cell JCE approach, the received midambles from adjacent cells are jointly processed, rather than being treated as interference as in single cell channel estimation. By jointly processing all the received midambles, the user can simultaneously estimate the channel impulse responses (CIRs) for both its home cell and adjacent cells. If the received signal from adjacent cells has a delay, multi-cell JCE is still operable with slight adjustment in the midamble matrix, and the performance loss is also minor. The performance of multi-cell JCE is analyzed and evaluated by simulations. The results demonstrate that the proposed multi-cell JCE method can significantly improve the channel estimation accuracy. When the signal from each cell has similar power level, the mean square error (MSE) of the estimated CIRs for all cells is lower than 0.01. With more accurate CIRs from multi-cell JCE, multi-cell JD also yields better performance compared with the single cell channel estimation methods.