共查询到19条相似文献,搜索用时 187 毫秒
1.
该文设计了一种用于正交频分复用(OFDM)系统的新型保护间隔信号-导频后缀(Pilot Postfix, PP),并构建了采用比特交织编码调制-迭代解码(BICM-ID)技术的PP-OFDM系统。PP由OFDM符号中的频域导频符号进行逆傅氏变换(IFFT)生成,在接收端可与OFDM符号中的导频相干合并,从而提高信道估计性能。该文给出了相应的信道估计、均衡和BICM-ID算法,并通过研究信道估值误差带来的接收信号有效信噪比变化,给出了PP幅度优化设计方法。仿真表明:选取适当的PP大小后,PP-OFDM比循环前缀/补零后缀-OFDM(CP/ZP-OFDM)的信道估计性能更好,误包率更低。 相似文献
2.
3.
利用最大似然代价函数推导出了一种导频辅助的OFDM定时估计算法。在信道阶数未知情况下,对其导频采用循环前缀(CP)方式和补零(ZP)方式的性能做了比较分析。用ZP方式导频时,该算法克服了信道阶数未知时定时测度平台。仿真分析验证了本算法性能的优越性。 相似文献
4.
5.
提出了一种基于编码的OFDM系统的导频符号迭代辅助信道估计。利用信道解码器中的APP符号来形成虚拟的导频。与原有的信道估计算法相比,此种算法不仅在一般的信道条件下具有良好的性能,而且更加适合快变信道条件下的OFDM系统。仿真结果表明:提出的OFDM信道估计算法不仅可以给出精度较高的信道信息,而且近似达到EM信道估计的性能。 相似文献
6.
基于导频辅助的无循环前缀SFBC-OFDM系统 总被引:1,自引:0,他引:1
设计了一种基于导频辅助的无循环前缀空频分组编码-OFDM系统(Non-CP SFBC-OFDM).区别于传统的循环前缀空时分组编码-OFDM系统(CP STBC-OFDM),新系统发射端将块状导频序列和由空频分组编码构成的OFDM符号交替排布发射,并且每个OFDM符号前不再附加循环前缀,而接收端针对这一新的数据发射结构设计出一种基于干扰抵消的信号检测和信道估计联合递归算法.理论推导和仿真结果表明:相对于应用最小平方(LS)、迭代最小平方(iterative LS)的信道估计算法的循环前缀STBC-OFDM系统,引入联合递归算法的新系统可以得到更高的信息数据传输效率和更低的系统误比特率. 相似文献
7.
8.
本文提出了一种针对存在虚子载波的MIMO OFDM系统下基于均匀分布型的最优导频设计,该设计通过采用时域最小二乘信道估计(TD-LS-CE),且以数据子载波的频域信道响应的均方误差为准则,在最大化带宽效率的前提下,对各发送天线上均匀分布型的导频子载波进行功率最优化分配,并推导了其闭式解。最后,仿真结果表明该最优导频序列在MSE、BER性能方面均优于传统的移相正交导频序列和等功率分配的交错正交导频序列。 相似文献
9.
10.
OFDM/OQAM系统中联合迭代信道估计和信号检测 总被引:3,自引:2,他引:1
与基于复数域空间正交条件的传统正交频分复用系统(OFDM with Cyclic Prefix, CP-OFDM)有所不同,基于交错正交调制的正交频分复用系统(OFDM/Offset QAM, OFDM/OQAM)满足实数域空间严格正交条件。因此在多径衰落信道条件下,CP-OFDM系统中的信道估计方法会导致OFDM/OQAM系统严重的字符间干扰和载波间干扰。该文结合OFDM/OQAM系统结构特点,提出了一种基于迭代信道估计和信号检测算法。该算法通过信道估计器和接收到的信号互相交换信息,消除导频序列中的字符间干扰和载波间干扰,提高信道估计和信号检测的准确度。仿真分析结果表明,经过一定次数迭代处理后,OFDM/OQAM迭代信道估计性能趋近于理想信道估计性能。 相似文献
11.
Optimizing Pilot Locations Using Feedback in OFDM Systems 总被引:2,自引:0,他引:2
《Vehicular Technology, IEEE Transactions on》2009,58(6):2803-2814
12.
13.
We propose three different dynamic resource allocation algorithms using adaptive beamforming for multiple-input multiple-output (MIMO) OFDM systems, and investigate their performance over multipath fading channels under perfect and imperfect channel state information (CSI). These approaches involve the use of adaptive modulation, adaptive frequency-domain power allocation, and/or adaptive sub-channel allocation. By employing the proposed approaches in MIMO/OFDM systems, significant performance improvement can be achieved compared to the conventional adaptive antenna array based OFDM. The investigation of the effects of imperfect CSI reveals that the adaptive-modulation based approach is too sensitive to channel estimation errors, and that its performance is worse than the adaptive frequency-domain power allocation and/or adaptive sub-channel allocation approaches. The performance analysis also shows that combining adaptive power allocation with sub-channel allocation yields the best performance under imperfect CSI while being robust to channel estimation errors. 相似文献
14.
An impulse postfix OFDM (IP-OFDM) system, which performs channel estimation in time-domain by exploiting the IP instead of pilot tones, has recently been proposed by Chang et al. Although the proposed system can achieve the enhanced bit error rate (BER) performance compared to that of conventional OFDM systems, there is an important peak-to-average power ratio (PAPR) issue of using the IP that needs to be resolved. In this letter, we propose decision criteria for determining the power boosting factor (PBF) of IP in practical IP-OFDM systems with a high power amplifier (HPA). The analysis is performed with two criteria, the complementary cumulative distribution function of signal PAPR and the input back-off to determine the PBF of IP. The best PBF can be the one which gives an equal power to the IP and the rest of the OFDM symbol. From the analytic results, however, the PBF maximizing the power of the IP out of the HPA turns out to be the best one due to the non-linearities of the HPA. Simulation results demonstrate the effectiveness of the proposed decision criteria for IP-OFDM systems. 相似文献
15.
Orthogonal frequency division multiplexing (OFDM) transmission equipped with multiple receive antennas constitutes a single‐input multiple‐output (SIMO) OFDM system. SIMO‐OFDM systems have been widely used in wireless communications. Compared to those approaches using training sequences, blind channel estimation methods for SIMO‐OFDM systems have the advantage of saving bandwidth and improving energy efficiency and system throughput. As far as blind channel identification is concerned, it is known that zero padding (ZP)‐based single‐input single‐output (SISO)‐OFDM systems have desirable features compared to conventional cyclic prefix (CP)‐based SISO‐OFDM systems. However, it is yet unknown whether ZP‐ or CP‐based SIMO‐OFDM systems are favourable for blind channel estimation. To investigate this problem, we first propose a short‐data effective method for blind channel estimation for ZP‐based SIMO‐OFDM systems. Then we analyse a number of issues surrounding blind channel estimation for ZP‐ and CP‐based SIMO‐OFDM systems. The issues brought up in the paper have not been discussed in the existing research. The significance of our investigation is that it provides a deep insight into blind channel estimation for ZP‐ and CP‐based SIMO‐OFDM systems. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
16.
本文研究数字地面电视DVB-T的OFDM传输系统接收端的同步。根据OFDM的原理特点和DVB-T标准,设计同步方案。该方案采用多载波(OFDM)系统时域插在循环保护间隔携带的冗余信息进行粗符号和分数频率偏移估计。该方案利用OFDM系统时域插入的保护间隔前缀所携带的冗余信息,进行粗符号同步和分数频率偏移估计。FFT后,再利用频域插入的连续导频进行整数频偏估计,及利用分散导频通过估计信道冲击响应,实现精符号同步。仿真表明,同步设计在加性高斯白噪声信道能达到最佳性能,在慢衰落Rayleigh信道下也有较好的性能。 相似文献
17.
Conventional time-varying (TV) channel estimation (CE) methods for OFDM systems need optimal evenly spaced pilots to track channel time variations in one symbol period and the inter-carrier interference (ICI) on pilots caused by Doppler spread are regarded as noise. For practical OFDMA systems, the required evenly spaced pilots are unsatisfied and the ICI on pilots increase estimation errors. In this letter, a TV CE method for practical OFDMA systems is proposed. The time variations of the frequency domain transmission function in one symbol period are approximated by a linear model in time-frequency blocks for each user. Time domain transformations are avoided and evenly spaced pilots are not required. Furthermore, the ICI on pilots are mitigated by correlative coding. Simulation results demonstrate the Symbol-Error-Rate (SER) and Mean-Square- Error (MSE) performances of the proposed OFDMA CE method over TV channels. 相似文献
18.
Orthogonal frequency division multiplexing (OFDM) with pilot symbol assisted channel estimation is a promising technique for high rate transmissions over wireless frequency-selective fading channels. In this paper, we analyze the symbol error rate (SER) performance of OFDM with M-ary phase-shift keying (M-PSK) modulation over Rayleigh-fading channels, in the presence of channel estimation errors. Both least-squares error (LSE) and minimum mean-square error (MMSE) channel estimators are considered. For prescribed power, our analysis not only yields exact SER formulas, but also quantifies the performance loss due to channel estimation errors. We also optimize the number of pilot symbols, the placement of pilot symbols, and the power allocation between pilot and information symbols, to minimize this loss, and thereby minimize SER. Simulations corroborate our SER performance analysis, and numerical results are presented to illustrate our optimal claims. 相似文献
19.
Wei-Chieh Huang Chih-Peng Li Hsueh-Jyh Li 《Vehicular Technology, IEEE Transactions on》2009,58(4):1731-1740
Channel estimation in multipath environments is typically performed using the pilot-symbol-assisted modulation (PSAM) scheme. However, the traditional PSAM scheme requires the use of dedicated pilot subcarriers and therefore leads to a reduction in the bandwidth utilization. Accordingly, this paper investigates a channel-estimation approach for orthogonal frequency-division multiplexing (OFDM) systems using a superimposed training (ST) scheme, in which the pilot symbols are superimposed onto the data streams prior to transmission. By using equally spaced pilot symbols of equal power and assuming that the number of pilots is larger than the channel order, it is shown that the channel-estimation performance is independent of the number of pilots used. The optimal ratio of the pilot symbol power to the total transmission power is analyzed to maximize the lower bound of the channel capacity. Overall, the current results show that the ST-based channel estimation schemes have a slightly poorer performance than the PSAM scheme but yield higher system capacity. 相似文献