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標題: 直接序列分碼多工系統之多用者檢測
Multiuser Detection for Direct Sequence Code Division Multiple Access System
作者: 黃興隆
關鍵字: WMF;直接序列展瀕分碼多工;ZF-BLE;MMSE-BLE;ZF-BDFE;MMSE-BDFE;最小平方誤差等化器
出版社: 電機工程學系
在分碼多工系統,訊號經由時變多重路徑無線頻道來傳送,則碼際干擾及多重進接干擾將產生很大的影響。在傳統次理想接收器僅包含一組Matched filter,常常無法有效來排除這些干擾。 而一理想多使用者偵測器在現今又太複雜,因此在本論文中,我們將使用依Zero forcing 和最小平方誤差(MMSE)兩等化器為基礎,及其兩者包含回饋偵測決定值及不包含回饋偵測決定值,四種次理想偵測技術來作比較及說明。 這四種等化器均能對抗碼際干擾及多重路徑傳輸效應。而這些等化器當中,我們發現MMSE等化器的效能較Zero Forcing來的好,而有回饋偵測決定值方法較無回饋偵測值較佳。同時我們也比較這四種偵測方法在不同的展頻碼上,我們發現使用金碼(Gold Codes)較random codes較佳,而Walsh Hadamard codes為最差。

In code-division multiple-access (CDMA) systems transmitting over time-varying multi-path channels, both inter-symbol interference(ISI) and multiple-access interference (MAI) arise. The conventional sub-optimum receiver consisting of a band of matched filters is often inefficient because interference is treated as noise. The optimum multi-user detector is too complex to be implemented at present. In this paper, four sub-optimum detection techniques based on zero forcing (ZF) and minimum mean-square-error(MMSE) equalization with and without decision feedback(DF) are presented and compared. They combat both ISI and MAI. All four equalizers are independent of the size of the data symbol alphabet. It is shown that the performance of the MMSE equalizers is better than that of the corresponding ZF equalizers. Furthermore, the performance of the equalizers with DF is better than that of the corresponding equalizers without DF. On the other hand, we use the some different spreading codes like as randomly generating codes, Gold codes and Walsh Hadamard codes to compare with the performance using the detection techniques of ZF-BLE, MMSE-BLE, ZF-BDFE and MMSE-BDFE. We found the performance of used Gold codes is better than used Walsh Hadamard codes.
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