共查询到20条相似文献,搜索用时 31 毫秒
1.
By bilinearly transforming the rectangularly pulsed multicarrier basis signals, new basis sets containing full-response continuous basis signals are developed for constructing spectrally efficient orthogonal frequency-division multiplexing (OFDM) signals with or without cyclic prefix (CP) or zero padding (ZP). Both multiple-product and linear-combination formats are presented for these basis sets. In the multiple-product format, the developed full-response basis signals are shown to be zero-valued at interval edges, and thus can be used to construct continuous-phase OFDM signals. It is analytically shown that the constructed continuous-phase OFDM signals exhibit relatively small power spectral sidelobes which fall off as f-4, and can thus provide much higher spectral efficiency than the traditional rectangularly pulsed OFDM signal. In the linear-combination format, the proposed basis signals are shown to be the linear combinations of rectangularly pulsed multicarrier basis signals, and thereby allow for the efficient realization of fast Fourier transform (FFT). Specifically, a spectrally precoded signaling structure is developed in conjunction with inverse FFT and guard insertion to construct continuous-phase OFDM signals with or without CP or ZP. The corresponding spectral decoders are also developed to enable zero-forcing (ZF) demodulation for spectrally precoded OFDM. With the zero-forcing demodulation, the spectrally precoded OFDM schemes are shown to outperform in average error-rate characteristics the conventional rectangularly pulsed and correlatively coded OFDM schemes on various delay-spread channels 相似文献
2.
Hao-Ming Chen Char-Dir Chung 《Communications Letters, IEEE》2009,13(5):324-326
In this letter, we study the asymptotic spectral behavior of the spectrally precoded orthogonal frequency-division multiplexing (SP-OFDM) signal with arbitrary input statistics. It is shown that all constraints and spectral precoders previously developed for SP-OFDM with independent and identically distributed and zero-mean data provide fast decaying spectral sidelobes for SP-OFDM with arbitrary input statistics. 相似文献
3.
Recently, the precoded orthogonal frequency division multiplexing (OFDM) was proposed to show robustness to intersymbol interference channels with spectral nulls. However, due to inserting (M-K) zeros between each two sets of K consecutive information symbols, the average transmitting power of the precoded OFDM system reduces by 10 log10 (M/K) dB compared with the conventional OFDM system. Under the same points, inverse fast Fourier transformation (IFFT), the precoded OFDM system has a higher peak-to-average power ratio (PAPR) compared with the conventional OFDM system. This paper proposes a rotated precoder-based OFDM system robust to channel spectral nulls and with reduced PAPR. The rotated precoder makes the N-point IFFT with N/2 zeros padded. Since half of the information symbols for IFFT are zeros, we have the PAPR reduced by 10 log10 2≈3 dB approximately, compared with the conventional precoded OFDM system. We also show that the proposed OFDM system has the same bit error rate (BER) performance as the conventional precoded OFDM system. Both theoretical performance analysis and simulation results are presented to verify the correctness of our theory analysis. 相似文献
4.
Fast blind subspace channel estimation using circular property of the channel matrix is investigated for space–time block coded (STBC) multiple-input multiple-output orthogonal frequency division multiplexing (MIMO–OFDM) systems in this paper. The noise subspace computed from the correlation matrix of received signals requires a large number of symbols to converge in the subspace channel estimation. Using the circular property of the channel matrix, we propose both the cyclic repetition method (CRM) and the forward–backward method (FBM) to generate N times of equivalent signals for each STBC–OFDM symbol, respectively, where N is the size of FFT operation. With these equivalent symbols, the proposed CRM, FBM and CRM–FBM (CFBM) channel estimations can perform very well within a few OFDM symbols. The CRM, FBM and CFBM schemes are applicable to the CP-OFDM, ZP-OFDM and VC-OFDM systems, respectively. The identifiability of the subspace channel estimation is investigated that the channel matrix is determined up to two ambiguity matrices. Computer simulations demonstrate that the CRM-based, FBM-based and CFBM-based channel estimations have better performances than the conventional ones. 相似文献
5.
针对认知无线电系统中OFDM(orthogonal frequency division multiplexing)信号信噪比估计算法适用范围受限、复杂度高的问题,提出一种新的基于符号相关性的信噪比盲估计算法,算法首先通过扩展前缀相关性检测区间得到一个特征序列,然后通过小波消噪去除多径信道的影响,最后通过序列极大值极小值与信号功率及噪声方差的关系得到信噪比的估计值。仿真结果表明,本文算法能够实现对ZP-OFDM(zero-padding OFDM)信号信噪比的准确估计,同时在应用于CP-OFDM(cyclic-prefix OFDM)信噪比估计时适用范围更广、运算更为简便,更加适用于认知无线电系统。 相似文献
6.
This paper details a new orthogonal-frequency-division-multiplexing (OFDM) modulator based on the use of a pseudorandom postfix (PRP)-OFDM and discusses low-complexity equalization and channel estimation/tracking architectures. The main property of this new modulation scheme is the ability to estimate and track the channel variations semi-blindly using order-one statistics of the received signal. Compared with known cyclic prefix OFDM (CP-OFDM) pilot-symbol-assisted modulation (PSAM) schemes, the pilot overhead is avoided: The channel estimation is performed based on the exploitation of pseudorandomly weighted postfix sequences replacing the guard interval contents of CP-OFDM. PRP-OFDM is shown to be of advantage if the target application requires 1) a minimum pilot overhead, 2) low-complexity channel tracking (e.g., high mobility context), and 3) adjustable receiver complexity/performance trade-offs (available due to the similarities of PRP-OFDM to the zero-padded OFDM (ZP-OFDM) modulation scheme) without requiring any feedback loop to the transmitter. 相似文献
7.
Jian Wang Jian Song Zhi-Xing Yang Lin Yang Jun Wang 《Broadcasting, IEEE Transactions on》2006,52(2):252-260
The performance of the orthogonal frequency division multiplexing (OFDM) systems may be severely deteriorated when passing through wireless channels with the spectral s. Zero-Padding (ZP) for the OFDM signal guarantees the symbol recovery regardless of the channel spectral s if complicated ZP-OFDM-MMSE equalizer is used. In this paper we first establish a connection between ZP-OFDM and DFT codes and then two novel signal reconstruction schemes, signal projection and low-complexity signal reconstruction, are presented to deal with the spectral s based on the frames theory. The simulation results demonstrate that significant performance improvement can be achieved using our proposed methods over the so-called ZP-OFDM overlap and add (ZP-OFDM OLA) scheme. 相似文献
8.
Xiang-Gen Xia 《Communications, IEEE Transactions on》2001,49(8):1363-1374
The performance of orthogonal frequency-division multiplexing (OFDM) systems may be degraded when intersymbol interference (ISI) channels have spectral nulls. Also, when ISI channels have many taps, the data rate overhead due to the insertion of the cyclic prefix is high. We first propose a precoded OFDM system that may improve the performance of the OFDM systems for spectral null channels. We also propose size K×x1 vector OFDM (VOFDM) systems that reduce the cyclic prefix length by K times compared to the conventional OFDM systems. The precoding scheme is simply to insert one or more zeros between each two sets of K consecutive information symbols, although it can be generalized to a general form. This precoding scheme may be able to remove the spectral nulls of an ISI channel without knowing the ISI channel. When no zero is inserted between each two sets of K consecutive information symbols and only each K consecutive symbols are blocked together, we obtain VOFDM systems. Both theoretical performance analysis and simulation results are presented. Finally, we compare the combination of the VOFDM systems and the unitary matrix modulation with the conventional OFDM systems and the phase-shift keying modulation, where both differential (noncoherent) and coherent modulations and demodulations are considered 相似文献
9.
A precoding scheme for DFT-based OFDM to suppress sidelobes 总被引:1,自引:0,他引:1
Renhui Xu Ming Chen 《Communications Letters, IEEE》2009,13(10):776-778
In spectrum pooling scenario, the spectral leakage of DFT-based OFDM signal can be divided into in-band-out-of-subband (IBOSB) radiation and out-of-band (OOB) radiation. A precoding scheme is proposed to suppress the IBOSB sidelobes. The precoding design is based on the generalized eigenvalue problem. Simulation results demonstrate that the proposed scheme can suppress the sidelobes significantly in contrast to the uncoded schemes. At the same time, the bit-error-rate (BER) performance of the precoded system over multipath fading channel is improved due to the frequency diversity. 相似文献
10.
Based on a novel class of orthogonal pulse pairs, a spectrally efficient full-response quadrature-quadrature phase-shift keying (Q/sup 2/PSK) signal format is proposed. The proposed full-response Q/sup 2/PSK signals can provide higher spectral compactness than conventional full-response Q/sup 2/PSK signal, minimum-shift keying signal and quadrature phase-shift keying signal. 相似文献
11.
This paper presents a Zadoff-Chu matrix transform (ZCMT) precoding based multicarrier orthogonal-frequency-division-multiplexing (OFDM) system to minimize the high peak-to-average power ratio (PAPR). In the proposed system, ZCMT kernel is applied to the constellation symbols which not only reduces PAPR but also improves bit-error-rate (BER) performance. The ZCMT precoded OFDM signals allow the radio-frequency high-power-amplifier (HPA) to operate near its saturation level, thus maximize the power efficiency. Extensive computer simulations have been performed to analyze the PAPR, BER and power-spectral-density (PSD). Simulation results show that the proposed system has excellent PAPR gain and BER performance with no spectral distortion. 相似文献
12.
Minimal Euclidean distance‐inspired optimal and suboptimal modulation schemes for vector OFDM system
In single‐input and single‐output (SISO) systems, the vector orthogonal frequency division multiplexing (VOFDM) has been proposed to reduce the cyclic prefix length, whereas the precoded OFDM has been proposed to overcome spectral‐null channels. However, VOFDM does not show robustness to spectral‐null channels, and the precoded OFDM system has expanded data rate. This work proposes the optimal and suboptimal modulation schemes in vector OFDM systems with knowledge of the channel impulse response (CIR) in order to reduce the bit error rate (BER). As the BER performance is determined by the diversity of the received vector symbols, the proposed modulation scheme mainly concerns the minimal Euclidean distance of all the possible received vector symbols. Through the analysis of the vector input and output equations, we derive the Euclidean distance of the received vector symbols. Then, we propose optimal and suboptimal modulation schemes in VOFDM system to overcome spectral‐null channels by improving the minimal Euclidean distance. Both theoretical performance analysis and simulation results are presented to show the robustness of our system. Finally, we conduct a compared performance analysis of the proposed VOFDM system, the conventional precoded OFDM system, and the conventional VOFDM system. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
13.
To efficiently use frequency resources, the next 6th generation mobile communication technology must solve the problem of out-of-band emission (OoBE) of cyclic prefix (CP) orthogonal frequency division multiplexing (OFDM), which is not solved in 5th generation technology. This study describes a new zero insertion technique to replace an existing filtering scheme to solve this internal problem in OFDM signals. In the development of the proposed scheme, a precoder with a two-dimensional structure is first designed by generating a two-dimensional mapper and using the specialty of each matrix. A spectral shaping technique based on zero insertion instead of a long filter is proposed, so it can be applied not only to long OFDM symbols, but also very short ones. The proposed method shows that the transmitted signal is completely blocked at the bandwidth boundaries of signals according to the current standards, and it is confirmed that the proposed scheme is ideal with respect to bit error rate (BER) performance because its BER is the same as that of CP-OFDM. In addition, the proposed scheme can transformed into a real time structure through vectorizing process with minimal complexity. 相似文献
14.
Manton J.H. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2002,48(5):1203-1206
Channels with spectral nulls are sometimes dubbed bad channels because they can cause poor performance in communication systems. This article investigates the validity of this intuition by studying the geometry of an orthogonal frequency-division multiplex (OFDM) system. It is shown that the subchannel attenuation coefficients form a natural coordinate system for describing finite-impulse response (FIR) channels in an OFDM framework. It is also shown that channels with spectral nulls are geometrically significant; they form the faces of the convex set of all subchannel attenuation coefficients. This novel perspective makes it immediately clear why the worst performance of a linearly precoded OFDM system is achieved over a channel having the greatest number of spectral nulls. The practical implications of these results are discussed 相似文献
15.
16.
Orthogonal frequency-division multiplexing (OFDM) has been considered as a strong candidate for next-generation wireless communication systems to achieve high rate data transmission in a mobile environment. However, the performance of OFDM systems may be degraded when inter-symbol interference (ISI) channels have spectral nulls, and the data rate overhead due to the insertion of cyclic prefix is high when ISI channels have many taps. Recently, the precoded OFDM systems and vector OFDM (VOFDM) systems were proposed to combat these two problems, respectively. We propose a novel modulated coded OFDM system with special precoder that is robust to spectral nulls and with reduced cyclic prefix length. The precoder can be easily formulated by channel coding and digital modulation. This precoding scheme uses the redundancy information introduced by channel coding (such as zeros inserted in precoded OFDM system). It is able to remove the spectral nulls of an ISI channel without knowing the ISI. Simulation results show that our proposed OFDM system performance is better than precoded OFDM and VOFDM system. 相似文献
17.
OFDM信号的频谱分析及应用PCC对系统的改进 总被引:1,自引:1,他引:0
使用极性交替的sinc信号表示OFDM系统的各个正交子载波,这样的表示方法与用多项式抵消编码技术(PCC)来消除载波间干扰(ICI)的作用相一致。传统的OFDM系统信号频率滚降慢、带外辐射大。文中通过对系统的频谱分析和计算机仿真,证实了PCC技术可以改善信号频谱,大幅度降低信号带外辐射。 相似文献
18.
《IEEE transactions on circuits and systems. I, Regular papers》2009,56(7):1360-1372
19.
This work considers noncoherently orthogonal signaling with full response digital phase modulation and focuses on the phase function shaping problem. A criterion for the phase function that ensures noncoherent orthogonality of the modulated signal over one symbol interval is introduced. Furthermore, a new family of phase modulated signals is presented. This new orthogonal modulation format lacks the well-known spectral lines of noncoherently orthogonal FSK and hence uses the power efficiently to convey information 相似文献
20.
A novel trellis-shaping design with both peak and average power reduction for OFDM systems 总被引:1,自引:0,他引:1
A new trellis shaping design is proposed for reducing the peak-to-average power ratio of the bandlimited orthogonal frequency-division multiplexing (OFDM) signals. The approach is based on recursive minimization of the autocorrelation sidelobes of an OFDM data sequence. A novel metric in conjunction with the Viterbi algorithm is devised. The performance of the trellis shaping depends on signal mapping strategy, and the two types of mapping, referred to as Type-I and Type-II, are proposed. The Type-I mapping has no capability of reducing the average power, but it can achieve a significant reduction of the peak-to-average power ratio. On the other hand, the Type-II mapping is designed to achieve both peak and average power reduction. The bit error probability of the system over an AWGN channel is evaluated based on the simulations, which confirms the effectiveness of the proposed scheme. 相似文献