Spreading sequences for multi-carrier CDMA systems

Multi and single carrier waveforms are utilized in cellular systems for high-speed data transmission. In The Fifth Generation (5G) system, several waveform techniques based on multi carrier waveforms are proposed. However, the Peak to Average Power Ratio (PAPR) is seen as one of the significant concerns in advanced waveforms as it degrades the efficiency of the framework. The proposed article documents the study, progress, and implementation of PAPR reduction algorithms for the 5G radio framework. We compare the PAPR algorithm performance for advanced and conventional waveforms. The simulation results reveal that the advanced Partial Transmission Sequence (PTS) and Selective Mapping (SLM) methods enhanced the throughput and gain of the 5G waveforms. Furthermore, we have also analyzed the performance of Orthogonal Time Frequency Space Modulation (OTFSM) based on a single carrier system and found that PAPR is significantly low and is best suited to fading environments. It is seen that the conventional algorithms lower the PAPR but increase the complexity. The proposed PTS and SLM have shown good performance with low computational complexity.

The variation of peak-to-average power ratio (PAPR) for different allocations of spreading code sequences in multi-carrier code division multiple access (MC-CDMA) and multi-carrier direct-sequence code division multiple access (MC-DS-CDMA) systems is investigated. The results show that for a small number of active users, the PAPR performance of an MC-CDMA system can be improved by careful allocation of the spreading code sequences to different users.

In this paper, a novel Peak-to-Average Power Ratio (PAPR) reduction method named cyclic-shifted scramble code (CSSC) method is proposed for multicarrier CDMA (MCCDMA) systems downlink. The proposed method utilizes the characteristics of multicarrier systems, i.e., if Inverse Fast Fourier Transform (IFFT) input sequence changes, the output waveform also changes. In CSSC method, a scramble code assigned to a base station is applied to user data symbols after cyclic-shift. Comparing PAPRs of IFFT outputs amongst different shifts of the scramble code, the shift minimizing PAPR is selected and the MC-CDMA signal with the minimum PAPR will be transmitted. The receiver can estimate the amount of phase shifts by correlating between the scramble code and the received signal component in the pilot channel. The numerical results showed that PAPR can be reduced by approximately 3 dB by CSSC method without BER performance degradation.

Multicarrier Code-Division Multiple Access (MC-CDMA) is a foreseen technique for future high data rate and high capacity multiuser wireless communications. However, the often large values of the Peak-to-Average Power Ratio (PAPR) of the transmitted signals pose a problem in multicarrier systems, because they can lead to nonlinear distortion at the High Power Amplifier (HPA) and a subsequent degradation of the system performance. In this paper, we propose a PAPR reduction scheme for MC-CDMA downlink systems based on the addition of peak reduction signals that borrow the spreading codes of idle users. The minimization of the PAPR can then be formulated as a Second-Order Cone Programming (SOCP) problem.

Complementary sequences are well studied in the communication field for their good correlation properties. Besides being used as spreading sequences, they can also be used for channel estimation, synchronization, reduction of peak-to-average power ratio of symbols, preamble design, sequence design, Target detection and so on. A recursive construction of complementary sequences based on orthogonal matrix and permutation matrix is proposed, which increases the number of complementary sequences in the set by increasing the number of their sub-sequences with the same sequences' length. Then the anti-interference performance of multi-carrier CDMA (MCCDMA) system based on complementary sequences is simulated, and the obtained results show that it has better anti-interference ability than traditional CDMA system.

Cognitive radio (CR) is considered nowadays as a strong candidate solution for the spectrum scarcity problem. On standards level, many cognitive radio standards have chosen Non-Contiguous Orthogonal Frequency Division Multiplexing (NC-OFDM) as their modulation scheme. Similar to OFDM, NC-OFDM suffers from the problem of having a high Peak to Average Power Ratio (PAPR). If not solved, either the transmitted signal will be distorted, which will cause interference to primary (licensed) users, or the effeciency of the power amplifier will be seriously degraded. The effect of the PAPR problem in NC-OFDM based cognitive radio networks is worse than normal OFDM systems. In this paper, we propose enhanced techniques to reduce the PAPR in NC-OFDM systems. We start by showing that combining two standard PAPR reduction techniques (interleaver-based and selective mapping) results in a lower PAPR than using them individually. Then, an “adaptive number of interleavers” will be proposed that achieves the same performance of conventional interleaver-based PAPR reduction while reducing the CPU time by 41.3%. Finally, adaptive joint interleaver with selective mapping is presented, and we show that it gives the same performance as conventional interleaver-based technique, with reduction in CPU time by a factor of 50.1%.

Multicarrier Waveform (MCW) has several advantages and plays a very important role in cellular systems. Fifth generation (5G) MCW such as Non-Orthogonal Multiple Access (NOMA) and Filter Bank Multicarrier (FBMC) are thought to be important in 5G implementation. High Peak to Average Power Ratio (PAPR) is seen as a serious concern in MCW since it reduces the efficiency of amplifier use in the user devices. The paper presents a novel Divergence Selective Mapping (DSLM) and Divergence Partial Transmission Sequence (D-PTS) for 5G waveforms. It is seen that the proposed D-SLM and PTS lower PAPR with low computational complexity. The work highlighted a combination of multi-data block partial transmit schemes along with tone reservation. In this, an overlapping factor is used to determine the number of data blocks for every group. Here, considering only those data blocks that have minimum signal power, the use of DSLM and DPTS are required to eliminate the segment’s peaks. Simulation results reveal that the suggested hybrid technique proves to be better than the conventional PTS scheme. Furthermore, the power saving performance of FBMC and NOMA is compared with the Orthogonal Frequency Division Multiplexing (OFDM) waveform.

Multi-Carrier CDMA (MC-CDMA) has been considered as a combination of the techniques of Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplex (OFDM). However, even until now, the efficient MC-CDMA scheme is still under study because of the inherent bugs in OFDM, such as the troubles caused by Multiple Access Interference (MAI) and Peak to Average Power Ratio (PAPR). In this paper, we present a novel two-dimensional spreading sequence named Two Dimensional Combined Complementary Sequence (TDC). If we take this kind of sequences as spreading codes, several prominent advantages can be achieved compared with traditional MC-CDMA. First, it can achieve MAI free in the multi-path transmission both in uplink and downlink. Second, it offers low PAPR value within 3 dB with a quite simple architecture. The last but not the least, the proposed MC-CDMA scheme turns out to be an efficient approach with high bandwidth efficiency, high spreading efficiency and flexible transmission rate enriched by a special shift-and-add modulation. Meanwhile, an algorithm that constructs TDC sequences is discussed in details. Based on above results, we can get the conclusion that the novel TDC sequences and corresponding MC-CDMA architecture have great potential for applications in next generation wireless mobile communications, which require high transmission rate in hostile and complicated channels.

Orthogonal frequency division multiplexing (OFDM) is a strong candidate for 4G wireless networks, due to its high data rate and ability to combat frequency selective fading. OFDM may be combined with multiple-input multiple-output (MIMO) to increase the diversity gain and system capacity over the time-variant frequency-selective channels. However, a major drawback of MIMO-OFDM system is that the transmitted signals on different antennas might exhibit high peak-to-average power ratio (PAPR). The high PAPR leads to nonlinear distortion of the high-power-amplifier (HPA) and results in inter-carrier-interference (ICI) plus out-of-band radiation. In this paper, we present a Zadoff-Chu matrix transform (ZCMT) based space-time-block-coded (STBC) MIMO-OFDM system with reduced PAPR. Extensive simulations have been performed to analyze the PAPR of the proposed system with root-raised-cosine (RRC) pulse shaping. Simulation results show that, ZCMT precoded STBC MIMO-OFDM system has low PAPR when compared to both the Walsh-Hadamard transform (WHT) precoded STBC MIMO-OFDM systems and the conventional STBC MIMO-OFDM systems.

The direct Fourier transform-spread OFDM (DFT-s-OFDM) and cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) are used for the end-to-end data transmission to support the 5G services and backward compatibility. Improving battery life has always been an important concern in 5G machine-to-machine (M2M) communication nodes. Efficient utilization of power amplifiers (PA) and inferior peak-to-average power ratio (PAPR) is helpful to achieve enhanced battery life. Filter bank multi-carrier (FBMC) multiplexing is an alternative to CP-OFDM that offers low PAPR with the benefits of CP removal. Another way to get low PAPR is single carrier OFDM (SC-FDMA). The transmission requirements between these services are different, which presents a challenge for waveform adaptability to PAPR issues. The DFT-s-OFDM technique is one of the choices to overcome the PAPR that is used in uplink scenarios. Apart from PAPR reduction, DFT-s-OFDM provides optimal use of nonlinear power amplifiers. In addition to PAPR analysis, spectral efficiency is also compared in the simulation results. Using parameters that adjust the cost of spectral efficiency, DFT-s-OFDM provides the extent of improvement in PAPR performance and bit error rate over traditional CP-OFDM, SC-FDMA, and FBMC against the noisy channel.KeywordsM2M5G (NR)PAPRBERSNROFDMCP-OFDMSC-FDMAFBMC DFT-s-OFDM

In a turbo coded orthogonal frequency-division multiplexing (TCOFDM) system, low peak-to-average power ratio (PAPR) can be achieved by selective-mapping (SLM). In this paper, we propose to generate multiple candidates used in SLM by employing the tail-biting bits in a tail-biting turbo code. In our method, no explicit side information is needed and no error propagation is observed. Low PAPR can also be achieved by distortion-based techniques such as deliberate clipping. Although SLM is originally proposed for PAPR reduction, we also apply a concept similar to SLM to clipping-based TCOFDM systems for improved bit error rate (BER). With these proposed techniques, a tail-biting TCOFDM system can achieve both low PAPR and low BER.

It is important to design a spectrum-efficient and power-efficient wireless communication system, which is the main design target in cellular and wireless communication engineering. Basically, to make it, the desired system must have a low peak-to-average power ratio (PAPR), low-level of out-of-band (OOB) power emission and can provide a high throughput. In this paper, we propose a high-throughput cellular communication system, namely Discrete Fourier Transform-Spread Windowing and Restructuring Orthogonal Frequency Division Multiplexing (DFT-Spread WR-OFDM), which has considerably low PAPR and low OOB power emission for upcoming next-generation beyond 5G (B5G) and 6G cellular communication systems. High PAPR is still one of the challenging issues for the MIMO-OFDM system. The proposed system is an effective arrangement of DFT-Spreading and windowing techniques to reduce PAPR and OOB power emission, respectively. Multiuser diversity is obtained using localized subcarrier mapping. We take advantages of spatial multiplexing to enhance the data throughput significantly. Additionally, frequency-domain equalization (FDE)-minimum mean squared error (MMSE) is used to combat the inter-symbol interference (ISI) effect. Simulation results verify that the suggested system considerably lowers PAPR and OOB power emission compared to the conventional systems. Furthermore, the proposed scheme shows better bit error rate (BER) performance over the MIMO Rayleigh fading channel environment. Simulation results also confirmed that the channel capacity of our suggested system is better than the conventional multi-carrier systems.

This paper addresses the power assignment problem in multicarrier code-division multiple-access (MC-CDMA) systems. The problem is formulated as finding the correct transmission power to achieve a desired quality of service (QoS), described by an objective signal-to-interference and noise ratio (SINR). First, the model of the MC-CDMA is described, and by considering a matched filter at the receiver, the SINR after data estimation is explicitly characterized. Due to the diversity in MC-CDMA systems, the power assignment problem is approached with a minimum norm perspective restricted to achieve a pre-defined objective SINR per user. Centralized and distributed solutions are presented in the paper. The distributed power allocation strategy is further extended to consider general controllers, and measurement and processing delays. Necessary conditions for closed-loop stability and convergence to the optimal minimum norm solution are derived by using the small-gain theorem. One advantage of the proposed methodology is that it can use power control strategies previously suggested for CDMA systems, as the Foschini-Miljanic scheme and LQ-control.

Single carrier frequency division multiple access (SC-FDMA) which utilizes single carrier modulation at the transmitter and frequency domain equalization at the receiver is a technique that has similar performance and essentially the same overall structure as those of an OFDMA system. One prominent advantage over OFDMA is that the SC-FDMA signal has lower peak-to-average power ratio (PAPR). SC-FDMA has drawn great attention as an attractive alternative to OFDMA, especially in the uplink communications where lower PAPR greatly benefits the mobile terminal in terms of the transmit power efficiency. SC-FDMA is currently a working assumption for the uplink multiple access scheme in 3GPP Long Term Evolution (LTE). To achieve low PAPR, a novel scheme, SC-OFDMA with super frame using intermediate mapping (SF-IFDMA), is proposed in this paper. In our proposed scheme, B frames with N subcarriers will be combined into one super frame, then SC-OFDM technique is applied to reduce the PAPR of the super frame, the super frame with lowered PAPR will finally be divided into B OFDM frames for the transmission. The combining and dividing process is equivalent to the concatenation process. The proposed scheme requires no side information and can significantly reduce PAPR while maintaining small number of subcarriers.

This paper presents a class of circular M-ary Amplitude-Phase Shift Keying (APSK) signaling techniques with high bandwidth efficiency and low peak-to-average power ratio (PAPR) suitable for systems using nonlinear power amplifiers to achieve high power efficiency. For nonlinear amplification, good performance requires not only high squared minimum distance to average power ratio (DPR) but also low PAPR. A search algorithm for M-ary APSK schemes using circular constellations suitable for nonlinear amplification with minimum PAPR and maximum DPR is developed. Results for 8-, 16-, 32-, 64- and 128-APSK signalling schemes are presented. The effects of bandlimiting filter sharpness on the PAPR are examined and considered in the development. The analytical and simulation results show that this class of circular M-ary APSK signals outperforms the square and cross M-ary QAM schemes.