Research On Power Amplifier Efficiency Improvement For Downlink TD-SCDMA

Following the construction of a large scale network of TD-SCDMA, The wireless industry currently pays more attention to the reduction of Capital Expenditure (CapEx) and Operating Expenditure (OpEx). Considering the benefits of network operators, the equipment manufacturers, in order to reduce the cost of the mobile network, bring forward a distributed base station solution. Then some new features, such as DPD and CFR, are added into the base station to further bring down the OpEx cost.The OpEx cost is directly related to the power amplifier (PA) efficiency in the base station. Currently, only a small proportion of the DC power is actually transformed to output power. The power amplifier efficiency is a function of the envelope of the downlink signal. TD-SCDMA signal has a high peak to average power ratio (PAR), therefore the envelope fluctuates strongly. This sets a restriction to the operating point of PA: in order to handle peaks in the signal, PA output back-off will de increased, which deviates it from its most efficient operating point, so affects the efficiency. CFR algorithm is used to reduce the PAR of downlink signal so as to decrease the PA output back-off, accordingly the efficiency can be increased. Another method of improving the efficiency of the PA is to use DPD algorithm. Rather than using CFR to reduce the dynamic range of the downlink signal, DPD algorithm fulfills the linearization of the PA. DPD is only discussed briefly in this thesis.There are several methods to implement CFR technique. This thesis discusses a PC-CFR method in details. After the introduction of the basic theory of the algorithm, a FPGA+DSP collaboration design is presented to implement the PC-CFR. Then the design is tested based on the 3GPP technical specifications combined with some empirical values. At last a plan is figured out to further improve the performance of the design.