基于编码法降低MC-CDMA系统峰均比技术研究

分析了多载波码分多址（MC-CDMA）系统模型及扩频码序列性能,根据MC-CDMA系统特点,研究了采用GOLAY码、Gold码及Walsh码等不同扩频序列及不同序列长度对MC-CDMA系统峰均比的影响。仿真分析了序列长度为16、32及64位时MC-CDMA系统峰均比性能。     

A Low Complexity VCS Method for PAPR Reduction in Multicarrier Code Division Multiple Access

This paper investigates a peak to average power ratio (PAPR) reduction method in multicarrier code division multiple access (MC-CDMA) system. Variable code sets (VCS), a spreading codes selection scheme, can improve the PAPR property of the MC-CDMA signals, but this technique requires an exhaustive search over the combinations of spreading code sets. It is observed that when the number of active users increases, the search complexity will increase exponentially. Based on this fact, we propose a low complexity VCS (LC-VCS) method to reduce the computational complexity. The basic idea of LC-VCS is to derive new signals using the relationship between candidature signals. Simulation results show that the proposed approach can reduce PAPR with lower computational complexity. In addition, it can be blindly received without any side information.     

基于多相扩频码的MC-CDMA信号峰平比抑制方法研究

降低信号峰平比(PAPR)是多载波码分多址(MC-CDMA)系统的关键技术之一。该文推导了基于正交互补扩频码的MC-CDMA信号PAPR关系式;基于多相脉压码构造了可用于MC-CDMA系统的多相脉压扩频码集合;证明了多相脉压扩频码即为正交互补扩频码。仿真结果表明,各种输入信息调制方式下,大部分多相脉压扩频码比常用扩频码能进一步降低信号的PAPR,其中多电平调制方式下多相脉压扩频码的PAPR性能更优;在不同用户数情况下,多相脉压扩频码都是MC-CDMA系统扩频码的一个很好选择。     

A Low Complexity VCS Method for PAPR Reduction in Multicarrier Code Division Multiple Access

This paper investigates a peak to average power ratio (PAPR) reduction method in multicarrier code division multiple access (MC-CDMA) system. Variable code sets (VCS), a spreading codes selection scheme, can improve the PAPR property of the MC-CDMA signals, but this technique requires an exhaustive search over the combinations of spreading code sets. It is observed that when the number of active users increases, the search complexity will increase exponentially. Based on this fact, we propose a low complexity VCS (LC-VCS) method to reduce the computational complexity. The basic idea of LC-VCS is to derive new signals using the relationship between candidature signals. Simulation results show that the proposed approach can reduce PAPR with lower computational complexity. In addition, it can be blindly received without any side information.     

A joint cross-layer transmission design with time–frequency coded cooperation HARQ for underground coal mine MC-CDMA WSNs

In this paper, multicarrier code division multiple access (MC-CDMA) modulation is adapted to constitute wireless sensors to improve the monitoring performance of wireless sensor networks (WSNs) for underground coal mine. A subcarrier phase compensation algorithm based on selective mapping (SLM) is proposed to reduce the relatively high PAPR of MC-CDMA signal. To further improve the monitoring performance of the underground MC-CDMA WSNs, a joint cross-layer transmission with time–frequency coded cooperation hybrid automatic repeat request (HARQ) is also proposed. The proposed cross-layer transmission combines time–frequency coded cooperation of physical layer with HARQ of media access control (MAC) layer. In the proposed transmission, the cooperative sensor utilizes time–frequency coded cooperation method to retransmit the monitoring information of source sensor at each retransmission time to obtain the coding gain and spatial diversity gain. Simulation results show that the proposed joint cross-layer transmission for underground coal mine MC-CDMA WSNs based on SLM phase compensation has significantly reduced the PAPR of MC-CDMA signal and improved the monitor performance of the coal mine MC-CDMA WSNs.     

一种新的相位序列在选择性映射中的应用

正交频分复用（OFDM）和多载波码分多址（MC-CDMA）被广泛认为是未来4G通信的核心技术。但是,OFDM和MC-CDMA信号的高峰均功率比（PAPR）会引起非线性失真并导致误码率性能恶化,这已成为它们实用化的最大障碍。选择性映射（SLM）是一种能有效地降低系统PAPR方法,其中相位序列的选择直接影响降低PAPR的效果。提出将一种新的伪随机扰码作为选择性映射中的相位序列来降低OFDM和MC-CDMA系统的PAPR,仿真得出这种伪随机扰码序列能有效地降低系统的PAPR,且优于传统Walsh-Hadamard、Golay序列。     

M元多码MC-CDMA系统信号包络特性分析

针对扩频通信中的M元多码系统,结合OFDM技术特点,提出了一种新的M元多码MC-CDMA系统。在分析系统基本原理基础上,建立了系统信号模型,对系统发射信号包络特性进行了分析研究,推导出系统信号包络公式,讨论了系统多码分路数与系统包络以及系统PAPR的关系。对系统不同分路数情况下包络状态进行了仿真,结果表明M元多码MC-CDMA系统发射信号包络和PAPR受多码分路数以及扩频序列的影响。     

A rank criterion for QAM space-time codes

Space-time coding has been studied extensively as a powerful error correction coding for systems with multiple transmit antennas. An important design goal is to maximize the level of space diversity that a code can achieve. Toward this goal, the only systematic algebraic coding theory so far is binary rank theory by Hammons and El Gamal (see ibid. vol. 46, p.524-42, 2000) for binary phase-shift keying (BPSK) modulated codes defined over binary field and quaternary phase-shift keying (QPSK) modulated codes defined over modulo four finite ring. To design codes with higher bandwidth efficiency, we develop an algebraic rank theory to ensure full space diversity for 2/sup 2k/ quadrature and amplitude modulated (QAM) codes for any positive integer k. The theory provides the most general sufficient condition of full space diversity so far. It includes the BPSK binary rank theory as a special case. Since the condition is over the same domain that a code is defined, the full space diversity code design is greatly simplified. The usefulness of the theory is illustrated in examples, such as analyses of existing codes, constructions of new space-time codes with better performance, including the full diversity space-time turbo codes.     

一种降低MC—CDMA系统峰均比的联合方法

文章提出了一种基于扩频码和选择性映射联合的方法来降低MC—CDMA系统的峰均比（PAPR）。首先对MC—CDMA系统的峰均比进行了理论推导,然后对选择性映射方法中的相位序列进行改进并选择了合适的扩频码,二者相结合来降低系统的峰均比。最后,在充分考虑系统的硬件资源消耗情况下,合理选取了相位序列的个数。通过性能仿真证明,该方法可以有效的降低系统的峰均比。     

降低MC-CDMA系统峰均功率比的SLM改进方法

多载波码分多址（MC-CDMA）被广泛认为是未来4G通信的核心技术,但MC-CDMA信号的高峰均功率比（PAPR）会引起非线性失真并导致误码率性能恶化。针对MC-CDMA系统的高峰均功率比的问题,对传统的选择性映射（SLM）算法进行改进。提出一种自适应选择复用帧数的选择性映射系统,在误码率满足一定条件的基础上,通过自适应选择复用帧数的算法选择出最适合系统的复用帧数的个数,使系统在复杂度较低的基础上仍能有效的降低信号的峰均功率比。仿真结果验证其有效性。     

New bound of algebraic immunity of a class of Boolean function

Algebraic immunity quantified the resistance of a Boolean function to the algebraic attack.Recently,Mesnager,et al showed that there were direct linked between the annihilators used in algebraic attacks and the coding theory.They showed that the lower bound of the algebraic immunity of Boolean functions could been derived from the minimum distance of the associated cyclic codes.An open problem proposed by Mesnager is settled with a detailed proof.Also,a lower bound of algebraic immunity of a class of Boolean functions will be introduced.     

On the computation and reduction of the peak-to-average power ratioin multicarrier communications

For any code C defined over an equal energy constellation, it is first shown that at any time instance, the problem of determining codewords of C with high peak-to-average power ratios (PAPR) in a multicarrier communication system is intimately related to the problem of minimum-distance decoding of C. Subsequently, a method is proposed for computing the PAPR by minimum-distance decoding of C at many points of time. Moreover an upper bound on the error between this computed value and the true one is derived. Analogous results are established for codes defined over arbitrary signal constellations. As an application of this computational method, an approach for reducing the PAPR of C proposed by Jones and Wilkinson (1996) is revisited. This approach is based on introducing a specific phase shift to each coordinate of all the codewords where phase shifts are independent of the codewords and known both to the transmitter and the receiver. We optimize the phase shifts offline by applying our method for computing the PAPR for the coding scenario proposed by the ETSI BRAN Standardization Committee. Reductions of order 4.5 dB can be freely obtained using the computed phase shifts. Examples are provided showing that most of the gain is preserved when the computed optimal phase shifts are rounded to quantenary phase-shift keying (PSK), 8-PSK, and 16-PSK type phase shifts     

An erasure-based scheme for reduction of PAPR in spatial multiplexing MIMO-OFDM using Reed-Solomon codes over GF(216 + 1)

In this paper, a novel erasure-based scheme which uses long Reed-Solomon (RS) codes over GF(65537) is proposed for the reduction of the peak-to-average power ratio (PAPR) in coded orthogonal frequency division multiplexing (OFDM). The motivation for using the field GF(65537) is to generate long code words (up to 65536 symbols in just one code word). Using long codes results in greater flexibility to search for low PAPR OFDM frames within the subsets of symbols of a code word because RS codes are maximum distance separable and any subset of a high enough number of symbols is sufficient for the recovery of data. Over this field, the lengths of code words are exponents of 2. Hence, low-complexity radix-2 fast Fourier transform can be exploited. RS codes are deployed for both PAPR reduction and error correction. Simulation results show that in similar PAPR reduction performances, the proposed scheme outperforms the previously reported work with RS codes in both error correction and computation complexity. The proposed scheme can be applied to both single-input single-output and multi-input multi-output systems.     

Turbo encoding and decoding of Reed-Solomon codes through binary decomposition and self-concatenation

This paper presents a two-stage turbo-coding scheme for Reed-Solomon (RS) codes through binary decomposition and self-concatenation. In this scheme, the binary image of an RS code over GF(2/sup m/) is first decomposed into a set of binary component codes with relatively small trellis complexities. Then the RS code is formatted as a self-concatenated code with itself as the outer code and the binary component codes as the inner codes in a turbo-coding arrangement. In decoding, the inner codes are decoded with turbo decoding and the outer code is decoded with either an algebraic decoding algorithm or a reliability-based decoding algorithm. The outer and inner decoders interact during each decoding iteration. For RS codes of lengths up to 255, the proposed two-stage coding scheme is practically implementable and provides a significant coding gain over conventional algebraic and reliability-based decoding algorithms.     

Dynamic spreading code selection method for PAPR reduction inOFDM-CDMA systems with 4-QAM modulation

We present a new dynamic spreading code selection technique to obtain low peak-to-average-power ratio (PAPR) of an orthogonal frequency-division multiplexing code-division multiple-access (OFDM-CDMA) system with 4-QAM modulation for the down-link in mobile communication. In this method, initially, each user is assigned a low and a high PAPR spreading code, which allows selecting one when the system is operating. The spreading code of each user is dynamically selected so that total PAPR level of the whole user group present in the system is minimized. With the proposed technique, the PAPR level of a system with 10 users and 64 sub-carriers using 64 chip Walsh-Hadamard (WH) codes, can be limited to 15 dB while the worst case theoretical maximum could go up to 28.1 dB. Although 64 chip WH codes are employed to evaluate the performance it can be generalized to all other sets of spreading codes     

A construction of codes with exponential error bounds on arbitrarydiscrete memoryless channels

This correspondence proposes an explicit construction of codes achieving capacity for arbitrary discrete memoryless channels. The proposed code is obtained by concatenating variable inner codes and an algebraic geometry code. Further, we clarify that the proposed code achieves the error exponent obtained by Forney for concatenated codes     

SLM降低峰均功率比MC-CDMA系统的研究

多载波码分多址（MC-CDMA）被认为是移动通信领域最具前景的应用之一,但MC-CDMA信号的高峰均功率比（PAPR）会引起非线性失真并导致误码率性能恶化。选择性映射（SLM）算法是解决该问题的有效方法,但其计算复杂度较高。针对该问题,将SLM算法转化为全局优化问题,采用模拟退火算法（Simulated Annealing.SA）优良的迭代寻优能力,从而用较小的复杂度获得了具有较低峰均功率比。仿真结果验证其有效性。     

THE STUDY OF AN M-ARY MC-CDMA SYSTEM BASED ON CYCLIC SPREADING CODES ＆ PRE-EQUALIZATION

A novel fast despreading scheme for M-ary Multi-Carrier Code-Division Multiple Access (MC-CDMA) system is proposed based on cyclic spreading codes and pre-equalizer. In the transmitter, the M spreading codes of each user are generated by circularly shifting the prototype spreading code. A feedback pre-equalizer is employed to process the M-ary MCCDMA signal before transmitted. The received signal is multiplied by the Inverse Discrete Fourier Transform (IDFT) result of the mirror image code of the prototype spreading code, and then demodulated by Orthogonal Frequency-Division Multiplexing (OFDM) demodulator. Compared with the conventional M-ary MC-CDMA receiver, the proposed scheme increases bandwidth efficiency, meanwhile, it achieves M-ary despread spectrum and multi-carrier demodulation, which reduces computation complexity remarkably.     

THE STUDY OF AN M-ARY MC-CDMA SYSTEM BASED ON CYCLIC SPREADING CODES & PRE-EQUALIZATION

A novel fast despreading scheme for M-ary Multi-Carrier Code-Division Multiple Access (MC-CDMA) system is proposed based on cyclic spreading codes and pre-equalizer. In the transmitter, the M spreading codes of each user are generated by circularly shifting the prototype spreading code. A feedback pre-equalizer is employed to process the M-ary MCCDMA signal before transmitted. The received signal is multiplied by the Inverse Discrete Fourier Transform (IDFT) result of the mirror image code of the prototype spreading code, and then demodulated by Orthogonal Frequency-Division Multiplexing (OFDM) demodulator. Compared with the conventional M-ary MC-CDMA receiver, the proposed scheme increases bandwidth efficiency, meanwhile, it achieves M-ary despread spectrum and multi-carrier demodulation, which reduces computation complexity remarkably.