8PSK的基本原理.pptVIP

Fundamentals of 8-PSK Kari Niemel? 18 Nov1998 Content Modulation Constellation Burst Structure Linear Amplifier Adjacent Channel Power Modulation Vector Error Efficiency Receiver Performance Notify: ETSI Specifications are not yet approved and definitions shown in these slides might be changed. Modulation The following block diagrams emphasizes key differences between GMSK and 8-PSK GMSK Modulator 8-PSK modulator Gray mapping: 3 bits per symbol and only one bit changes between adjacent symbols Pulse Shaping The modulating 8PSK symbols as represented by Dirac pulses excite a linear pulse shaping filter. This filter is a linearised GMSK pulse, i.e. the main component in a Laurent decomposition of the GMSK modulation. In GMSK rectangular frequency pulses are filtered by Gaussian pre-filter. Vector diagram and Envelope Peak to Average ratio is 3.2 dB Envelope variation (Max to Min) is about 16dB 90% of power is distributed between -10dB.. +3dB compared to mean power Burst structure Burst structure is similar with current GMSK burst, but term bit is replaced by symbol Training sequence has lower envelope variations Seamless switchover between timeslots Linearity Linearity of RF parts has high impact to 8-PSK system performance. Linearity can measured and depicted through AM/AM- and AM/PM- properties (S21 vs level) of RF device. AM/AM conversion AM/PM conversion Back-off and Power Decrease Back-off means head room for signal peaks. If head room is not adequate signal is highly distorted Back-off is counted from 1dB gain compression point. 1 dB compression point indicates input level where gain is dropped 1dB from maximum value. The term back-off is also used to define output power decrease e.g. back-off is defined from output compression. (back-off = power decrease +1 dB) Modulation Spectrum Modulation spectrum is impacted by nonlinearities of transmitter Spectral growth for two different transmitter with