Channelization Sử dụng trực giao lây lan By lây lan, mỗi biểu tượng là XORed với tất cả các chip trong chuỗi trực giao (Walsh trình tự) được giao cho người sử dụng. Trình tự được xử lý và sau đó được truyền qua các kênh vật lý cùng với các biểu tượng lây lan khác. | 80-13321-1 X11 CDMA 120 - cdmaOne and CDMA2000 Concepts and Terminology Section 3 Codes in cdmaOne Qualcomm cdma university Channelization Example CDMA 120 Section 3-9 1 -1 User Input 1 0 0 1 1 Orthogonal niin Min sequence 0110 0110 0110 Tx Data 1001 0110 0110 0110 0110 1001 1001 1 -1 Channelization Using Orthogonal Spreading By spreading each symbol is XORed with all the chips in the orthogonal sequence Walsh sequence assigned to the user. The resulting sequence is processed and is then transmitted over the Physical Channel along with other spread symbols. In this figure a 4-digit code is used. The product of the user symbols and the spreading code is a sequence of digits that must be transmitted at 4 times the rate of the original encoded binary signal. 2002 QUALCOMM Incorporated 3-9 CDMA 120 - cdmaOne and CDMA2000 Concepts and Terminology 80-13321-1 X11 Section 3 Codes in cdmaOne Qualcomm cdma university Channelization Example continued CDMA 120 Section 3-10 Rx Data Correct Function 1001 0110 0110 0110 0110 0110 1001 0110 1001 0110 1111 0000 0000 1111 1111 1 0 0 1 1 1 -1 Recovery of Spread Symbols The receiver despreads the chips by using the same Walsh code used at the transmitter. Notice that under no-noise conditions the symbols or digits are completely recovered without any error. In reality the channel is not noise free but cdmaOne systems employ Forward Error Correction FEC techniques to combat the effects of noise and enhance the performance of the system. 2002 QUALCOMM Incorporated 3-10 CDMA 120 - cdmaOne and CDMA2000 Concepts and Terminology 80-13321-1 X11 Section 3 Codes in cdmaOne Qualcomm cdma university Channelization Example continued CDMA 120 Section 3-11 Rx Data Incorrect Function 1001 0101 1100 0110 0101 0011 0110 0101 0011 1001 1001 0101 0101 1100 1100 Recovery of Spread Symbols using Wrong Function When the wrong Walsh sequence is used for despreading the resulting correlation yields an
