Research On SC-FDMA Modem Algorithms For LTE Uplink System

Long Term Evolution(LTE) proposed by the 3GPP(3rd Generation Partnership Project) makes extensive technical innovations to enhance the overall system performance. Single-Carrier-Frequency-Division-Multiple-Access(SC-FDMA) with a low peak-average-ratio(PAPR) has been finally determined as the LTE uplink radio transmission scheme. Furthermore, the transmitted frames are assigned with an additional cyclic prefix(CP) to attenuate the inter-symbol interference(ISI) and inter-carrier interference(ICI) effectively. However, in some special communication scenarios, such as wide sea-surface and high-speed train, a phenomenon with an insufficient CP length will dramatically degrade the system performance. Based on the SC-FDMA scheme in LTE uplink, this paper focuses on the modulation and demodulation technologies. The main contributions are summarized as follows:1. By following LTE standard, a systematic simulation platform is established, which mainly includes the Turbo channel coding and decoding, SC-FDMA frame-forming, multipath channel modeling, frequency-offset estimation and correction, channel estimation and equalization compensation, etc.2. Considering the scenarios with sufficient CP length, the techniques on frequency-offset estimation, channel estimation and equalization are intensive discussed and verified. According to our results, pilot-based and CP-based algorithms are suitable for frequency-offset estimation; the DFT-based channel estimation algorithm gives the best performance among the considered three channel estimation algorithms, i.e., the LS-based, MMSE-based and DFT-based channel estimation algorithms; Similarly, three key equalization algorithms are studied in detail, including linear equalization, MMSE-based residual ISI cancellation(MMSE-RISIC) and decision-feedback frequency domain equalization(DF-FDE). MMSE-RISIC equalization algorithm can improve the performance of LTE uplink system.3. With the assumption of an insufficient CP length, this paper investigates several effective equalization compensation algorithms to improve the performance.On the one hand, from the view of time-domain equalization, several channel shorten algorithms are studied, including MSSNR, Z-domain channel shortening and an adaptive blind MERRY equalization. Results show that channel shortening is not a high-efficient algorithm for the considered SC-FDMA system.On the other hand, from the view of frequency-domain equalization, we proposed a MMSE-based DFE algorithm specifically for the SC-FDMA system based on extensive studies on MMSE equalization, hard-decision-based residual ISI cancellation(RISIC) and CP reconstruction. Simulations based on the SC-FDMA platform verified the efficiency of the proposed algorithm, which shows BER performance can be improved when the scenarioes with an insufficient CP length are considered.