在本論文中討論分集計畫的進一步結果。首先在本文前半部份，推導出分集碼差分相移鍵調變(DPSK)在相關性瑞雷衰落通道下的截止率，並且使用截止率作為碼價值計算，進而利用電腦搜尋即可搜尋到好的分集碼，並且拿它們與利用碼字錯誤機率當作碼價值計算所搜尋到的分集碼做比較。 此外，由於無線通訊中多重路徑效應會造成系統效能的嚴重衰退，因此在本文後半部份中研究分集系統中使用尋得的短碼在多重路徑效應影響下的表現，可以發現有很好的效能增益。 This thesis discusses more further results on diversity scheme. In the first place, a new way for searching diversity codes is proposed in the first half part of this thesis. A closed form formula is derived for the cutoff rate of diversity codes for differential phase modulation in correlated Rayleigh fading channels. Using the cutoff rate as the code metric figure (CMF), useful short diversity codes are found by computer search and compared with the conventional diversity codes that are searched by using the codeword error probability as the CMF. Furthermore, it is worthwhile noting that multipath effects in wireless communication systems can be a great detriment to system performance. In the second half part of this thesis, it is analytically shown that the diversity systems employing the searched short-blocklength codes can offer remarkable gain in error performance on the multipath effects.