Research On Compressing Envelope Fluctuations Of LTE Downlink Signals

Long Term Evolution(LTE), which is the 4th Generation(4G) technology standard, introduced Orthogonal Frequency Division Multiplexing(OFDM) technology and high-order Quadrature Amplitude Modulation(QAM) technology. Compared with the 2nd Generation(2G) and 3rd Generation(3G) communication standards, LTE provides higher spectral efficiency and stronger anti-multipath fading capability. But the introduction of OFDM technology and high-order QAM technology causes large envelope fluctuations of LTE signals, which makes peak value of LTE signals easy to come into the nonlinear zone of Radio Frequency(RF) amplifier and results in serious in-band signal distortion and spectral expansion.Now, Peak-to-average Power Ratio(PAPR) and cubic metric(CM) are two metrics, both of which are widely used for describing envelope fluctuations of multi-carrier signals. In this paper, there are two methods proposed for PAPR reduction and CM reduction respectively. The innovations of this research are as follows:Firstly, an algorithm based on Uncertainty Principle(UP) has been proposed to reduce the PAPR of LTE signals. Feasibility of utilizing UP to reduce the PAPR of LTE signals has been analyzed, according to which an efficient iterative algorithm has been proposed. Simulation results show that the PAPR of LTE signals can be effectively reduced and bit error rate performance can also be improved by this algorithm. And this algorithm can achieve about 4.7dB PAPR reduction compared with original signal when Complementary Cumulative Distribution Function(CCDF) equals 10-3. Besides, the Error Vector Magnitude(EVM) of signals processed by our algorithm is 0.028.Secondly, another method has been proposed to reduce CM via convex optimization. We first proposed an optimization model on the basis of CM, Adjacent Channel Leakage Ratio(ACLR) and EVM. Then customized interior-point method was proposed for the convex model after performing one convex conversion on this problem, which achieves minimum EVM when given CM and ACLR, and this method converges after 3 iterations. Simulation results show that after 3 iterations this method achieves 4.12 dB CM reduction when CCDF=10-3.The two methods proposed in this paper can both compress envelope fluctuations of LTE downlink signals on the condition of standards specified by 3rd Generation Partnership Project(3GPP), so the two proposed methods in this paper can be widely used.