tailieunhanh - Cross Modulation in CDMA Mobile Phone Transceivers phần 2

IS-95 phát liên kết ngược lại điện thoại di động được hiển thị ở trên. Trong lĩnh vực số, một nguồn xung đồng hồ hai PN máy phát điện chuỗi (tiếng ồn giả ngẫu nhiên) được dựa trên IS-95. Mỗi sản lượng chip của các nguồn PN có 2 mẫu. Xuống mẫu 1 mẫu / chip và sau đó upsampled đến 4 mẫu mỗi chip với chèn không để tương thích với các giai đoạn sau của IS-95 FIR lọc. | 4 17 01 H IS-95 CDMA Mobile Phone Transmitter Page 11 The IS-95 reverse link mobile transmitter is shown above. In the numeric domain an impulse source clocks two PN pseudo random noise sequence generators that are based on IS-95. Each chip output of the PN source has 2 samples. It is down samples to 1 sample chip and then upsampled to 4 samples per chip with zero insertion in order to be compatible with the following stage IS-95 FIR filters. IS-95 defines the impulse response of these filters with 4 samples chip assuming the I and Q data inputs are an impulse stream. After the FIR filter the Q channel is delayed by Tchip 2 . by 2 samples for offset QPSK modulation. The I and Q signals are converted to time domain and QAM modulated on to a carrier at frequency ftx MHz. The out-of-band noise floor is flat and very high for the IS-95 transmitter. In order reduce the out-of-band noise floor and to reduce spectral leakage especially into the RX channel for cross modulation simulation the impulse response of the IS-95 FIR filters must be extended. This is done by cascading a raised cosine filter either in base band or at RF after increasing the sampling rate. The band width of the raised cosine filter must be carefully set so that it is not too narrow to degrade the IS-95 RHO factor and the MSE mean square error of IS-95 filter coefficients and at the same time fit the TX spectral template. Too wide a band width produces a step in the spectrum skirt out-ofband region has a step in the noise floor . 11 4 17 01 H RF Power Measurement in ADS Modulated RF input Agilent Technologies 1 sample output power in dBm Page 12 A model for gated RF power measurement is shown above. The output of an envelope detector is squared and integrated over the gated time between Tsave and Tstop . The CHOP block selects the gated region of the signal. Only one power measurement sample must be read at the output port. 12 4 17 01 H Cross Modulation simulated spectrum Page 13 The simulated .