Search

Non terrestrial network (NTN) has been regarded as an important component of beyond 5G communication. The 3rd Generation Partnership Project (3GPP) has officially started studies on NTN for the purpose of integrating satellites with New Radio (NR) terrestrial networks. However, the NR defined orthogonal frequency division multiplexing (OFDM) waveform is susceptible to doubly selective fading and nonlinear distortions in the NTN uplink, thus leading to severe performance loss. In this paper, a type of block scalable OFDM (BS-OFDM) waveform is proposed, which has modified subcarrier and sub-symbol segmentation when compared to the conventional NR defined OFDM. With our proposed framework, block scalable discrete Fourier transform spread OFDM (BS-DFT-s-OFDM) and block scalable orthogonal time frequency space (BS-OTFS) can also be implemented. To obtain a comprehensive understanding of different waveforms, performance metrics concerning peak to average power ratio (PAPR), total degradation (TD), bit error rate (BER), and complexity are presented. The simulation results demonstrate that the proposed block scalable waveforms can obtain better performance and lower complexity than existing NR waveforms in different NTN uplink scenarios, and can therefore be promising candidate waveforms for NR NTN.

Orthogonal Frequency Division Multiplexing (OFDM) is considered as a strong candidate for future wireless communication because it is marked by its higher frequency multiplicity and greater immunity to multipath fading. However, the main drawback of OFDM is its high amplitude fluctuations measured by peak-to-average power ratio (PAPR), which leads to power inefficiency and requires expensive high power amplifier (HPA) with very good linearity. In this paper, we propose selected mapping (SLM) with predistortion technique to decrease the nonlinear distortion and to improve the power efficiency of the nonlinear HPA. In the proposed method SLM reduces the PAPR and improves the power efficiency, the predistorter improves the bit error rate (BER) performance of the system. The PAPR reduction is possible with SLM when compared with original OFDM. After reducing the PAPR with SLM the data goes into the HPA with and without predistorter. The BER performance curves of SLM method with or without predistorter shows that, predistorter operates more effectively in SLM method than original OFDM system. At 4 dB IBO (input backoff) the conventional method with predistorter achieves 1.8 dB SNR gain than conventional method without a predistorter and at 6 dB IBO the BER performance is towards the ideal linear amplifier. The proposed system will be evaluated for OFDM system in the presence of a nonlinear power amplifier.

In this paper, we propose a new Peak-to-Average Power Ratio (PAPR) reduction technique using a partial transmit sequence (PTS) combined with adaptive peak power reduction (APPR) methods. This technique is used in a system based on Orthogonal Frequency Division Multiplexing (OFDM). In order to reduce PAPR, the sequence of input data is rearranged by the PTS for the reduction of PAPR and then fed to the APPR process in the proposed system. The APPR method controls the peak level of the modulation signal by an adaptive algorithm. The proposed method shows the improvement on PAPR, on the power spectrum density (PSD) and on the high performance on bit error rate (BER) of an OFDM system.

In this paper, we propose the PAPR (peak to average power ratio) reduction methods of SLM (selected mapping), and PTS (partial transmit sequence) to decrease the nonlinear distortion and to improve the power efficiency of the nonlinear HPA (high power amplifier) in the multi-code CDMA (code division multiple access) system. The phase rotation factors transmitted as side information in PTS and SLM methods play an important role in the BER performance. So, we newly derive the theoretical BER equation when the effects of side information are considered in the multi-code CDMA communication system. Simulation results show that the PTS reduces the PAPR by about 2 dB while SLM can reduce by about 3 dB, compared with the original MC-CDMA when QPSK is used for 32 branches. Also, we find the BER performance of multi-code CDMA system with and without predistorter in front of the HPA. When predistorter is used, 3 dB IBO (input backoff) is required in SLM method, and 5 dB IBO in PTS method to closely match with the linear amplifier Without PAPR reduction method, more than 7 dB is required. Finally, we show that the simulation results are very close to the theoretical results. [ABSTRACT FROM AUTHOR]

Local Multipoint Distribution Service (LMDS) has the potential to become a viable alternative to coaxial cable, fiber and other wired and wireless technologies providing "last mile" communication services. A major obstacle, however, is the high equipment cost. While for example cable modems supporting two-way services are available for $200 to $300, LMDS modem providing similar services will cost over $1000. The major cost driver of LMDS equipment is the radio frequency (RF) unit, as Ka-band technology still is quite expensive. The modem design must minimize the overall architecture cost, and low-cost modems requiring an expensive architecture should not be used. The channel characteristics of LMDS systems are very different from those of fiber, coaxial cable, and lower frequency wireless links, major channel impairments being non-linear high power amplifier (HPA), high phase noise and high co-channel interference. Modems should therefore be developed specifically for LMDS systems. This report deals with the choice of coding and modulation schemes, the LMDS channel, and how the channel impairments should be overcome by digital signal processing algorithms.