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采用多载波渊制的正交频分复用(OFDM)系统是未来移动通信系统的一个倍受关注的候选方案,它能减轻多径衰落环境的影响,提供高速率的数据传输。在OFDM系统中,传输频带被分为若干个相互重叠的子信道,这些子信道是两两正交的。发送数据经过串并变换后在这些子信道上并行传输。由于子信道 相似文献
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MIMO—OFDM系统信道估计中的最优导频设计 总被引:4,自引:1,他引:3
针对采用梳状导频的MIMO-OFDM系统信道估计问题,提出了一种新的最优导频设计方案,该方案的基本思想是不同发射天线中的导频位置相互正交,对应其他天线导频位置的子载波不被使用.对比传统的最优导频设计方法,所提方案有两个优点,一是它所需非传输信号的子载波数更少,用于传输信号的子载波增加,从而提高了系统频带的利用率.二是当OFDM频带两端设置保护频带时,系统存在一个极限保护频带宽度,在这个极限保护频带宽度范围内可以通过调整导频序列的初始位置来避免部分导频落入保护频带中,对比传统设计方法,此方案所允许的极限保护频带宽度更大.仿真实验验证了此设计方案的有效性. 相似文献
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MIMO-OFDM技术 总被引:5,自引:0,他引:5
多进多出(MIMO)系统在发射端和接收端分别设置多副发射天线和接收天线,采用MIMO技术可以提高信道容量和信道可靠性,降低误码率。正交频分复用(OFDM)是一种特殊的多载波传输方案,各子载波在整个符号周期上正交,各子载波信号频谱可以互相重叠,子载波正交复用技术大大减少了保护带宽,提高了频带利用率。MIMO-OFDM技术是OFDM与MIMO技术结合形成的一种新技术,该技术是在OFDM传输系统中采用阵列天线实现空间分集,提高了信号质量。MIMO-OFDM技术将成为下一代移动通信核心技术的解决方案。文中全面介绍了MIMO技术和OFDM技术及两者的结合,分析了实现MIMO-OFDM技术的关键,展望了发展前景。 相似文献
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多频带OFDM(正交频分复用)已作为支持高速、低功率和点对点无线通信UWB的重要解决方案。通过介绍多频带OFDM系统的原理,对多频带OFDM的UWB系统进行仿真研究。通过仿真得出多频带OFDM—UWB系统工作稳定,接收信号准确,并且能在短时间内减小功耗。 相似文献
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针对MIMO—OFDM系统的自适应调制技术进行分析,利用奇异值分解把MIMO—OFDM信道转化成一系列并行的子信道,然后将这些子信道按照信道增益从大到小的顺序排列。通过研究排序后信道增益的统计特性,提出了一种低复杂度的自适应传输方法来优化系统的发射功率。该方法通过固定排序后的子信道的功率和比特分配方案大大降低了复杂度。 相似文献
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Haruki Nishimura Mamiko Inamori Yukitoshi Sanada Mohammad Ghavami 《Wireless Personal Communications》2013,68(3):711-725
In impulse-radio or DS/SS UWB communications, a prerake scheme has been proposed to achieve path diversity while reducing computational complexity in a mobile terminal. On the other hand, in an OFDM system, fractional sampling (FS) has been proposed to achieve path diversity with a single antenna. However, in the FS-OFDM system, it is necessary to oversample a received signal that leads to larger power consumption in the terminal side. In this paper, a precoded transmit path diversity scheme in an OFDM system has been proposed. The proposed scheme can achieve path diversity without oversampling the received signal. 相似文献
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研究了高峰值传输速率时UWB系统的多址性能,对一种干扰抑制的OFDM传输方案进行了调整,提出了一种基于串行干扰抵消的两用户OFDM UWB多址方案.仿真结果显示所提出的方案可适度改善无纠错编码的OFDM UWB系统的误符号性能. 相似文献
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本文根据MB-OFDM-UWB系统的特点,提出了将OFDM技术和MSFH(多级跳频)技术结合的全部载波多址接入方案.该多址方案有二级构成,其中前一级使用OFDM,设计时参考了Multi-band OFDM Physical Proposal for IEEE 802.15 TaskGroup3a中的物理层建议,后一级采用跳频模块,并将基于余数域的多级跳频图案应用到该多址方案中,不仅大大减小了多用户碰撞的概率,而且有利于超宽带信号的生成.理论分析和仿真结果表明,基于OFDM和多级跳频结构的全部载波多址接入方案在系统容量、误比特率性能、抗干扰等方面具有诸多的优势.在8用户情况下,当系统误比特率为10~(-2)时,基于该结构的全载波方案比TH-PPM多址方案改善信噪比5dB左右. 相似文献
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Debarati Sen Saswat Chakrabarti R. V. Raja Kumar 《Wireless Personal Communications》2010,53(2):281-298
This article deals with a new energy based adaptive timing synchronization scheme (ATS) which estimates the symbol timing
information within two (2) OFDM symbols and updates the information with different frequency bands (adaptive in sense) in
a multi-band orthogonal frequency division multiplexing (MB-OFDM) based system. The new approach provides significant improvement
in system performance for high delay spread ultra-wideband (UWB) channel model (CM) environments where fast and low-complexity
timing synchronization is a critical issue. This paper also addresses a crucial aspect of UWB channel which is frequency dependent
delay characteristics. This effect contributes to different dispersion and timing shift of an UWB signal for different frequency
bands. In this work, the wideband channel delay characteristics are studied and delay parameters are found considerably different
over frequency bands 3.1–4.6 GHz. Based on this observation, the ATS which estimates and maintains the timing delays of each
band separately is presented. The performance of ATS algorithm is measured by mean-squared error (MSE), synchronization probability,
signal to interference ratio (SIR) reduction due to synchronization errors and bit error rate (BER) through the computer simulation
for several UWB CM environments CM2–CM4. Each of these UWB CMs is simulated for 100,000 noisy channel realizations for both
coded and uncoded MB-OFDM system. It is shown that ATS gives signal-to-noise ratio (SNR) improvement of 1.1 dB at BER of 1
× 10−3, 1.2 dB at BER of 2 × 10−4, and 0.7 dB at BER of 2 × 10−4 for CM4, CM3, and CM2 respectively for coded MB-OFDM system over a non-adaptive synchronization scheme [Yak et al., Proceedings
of IEEE PIMRC, Berlin, Germany, vol 1, pp 471–475, September 11–14, 2005]. 相似文献
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Debarati Sen Saswat Chakrabarti R. V. Raja Kumar 《Circuits, Systems, and Signal Processing》2009,28(6):993-1016
This paper presents a highly accurate frequency offset estimation algorithm for multi-band orthogonal frequency division multiplexing
(MB-OFDM) systems effective for realistic ultra-wideband (UWB) environment. The proposed algorithm derives its estimates based
on phase differences in the received subcarrier signals of several successive OFDM symbols in the preamble. We consider different
carrier frequency offsets and different channel responses in different bands to keep the analysis and simulation compatible
for practical multi-band UWB scenario. Performance of the proposed algorithm is studied by means of bit error rate (BER) performance
of MB-OFDM system. In order to compare the variance of the synchronizer to that of the theoretical optimum, we derive the
Cramer–Rao lower bound (CRLB) of the estimation error variance and compare it with the simulated error variance both in additive
white Gaussian noise and UWB channel model (CM) environments, CM1–CM4. Next, we modify the estimation algorithm by proposing
a multi-band averaging frequency offset synchronization (MBAFS) scheme. We establish superior BER performance with MBAFS compared
to our first scheme. We calculate modified CRLB for MBAFS and compare it with simulation results for CM1–CM4. Both analysis
and simulation show that MBAFS algorithm can estimate the carrier frequency offset effectively and precisely in UWB fading
channels for MB-OFDM applications. We also analyze the computational complexity of both the proposed algorithms in order to
verify their feasibility of implementation in practical UWB receiver design. 相似文献
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In this letter, P × N-point IFFT is proposed to replace the N-point IFFT and analog frequency conversion in an Orthogonal Frequency Division Multiplexing (OFDM)-based Ultra-WideBand (UWB) system, and a new algorithm, named fast P × N-point IFFT, is designed to reduce the complexity of the P × N-point IFFT in the proposed scheme. 相似文献
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Low duty-cycle (LDC) algorithm is interference mitigation technique, which can reduce the average interference to the existing
radio systems by lowering pulse repetition interval or pulse occupation time. In this paper, the coexistence environment between
low data rate ultra wideband (UWB) communication system such as wireless sensor network and the existing wideband system using
orthogonal frequency division multiplexing (OFDM) such as 4th generation mobile cellular system (4G), worldwide interoperability
for microwave access (WiMAX), and field pickup unit (FPU) is considered. In order to analyze the interference mitigation capability
of LDC algorithm with impulse based UWB (LDC-UWB) system, the frame error rate (FER) of wideband OFDM system is examined for
two types of LDC-UWB system: the signal with random polarity such as binary pole signals and without random polarity such
as mono pole signals. We present that LDC algorithm is an efficient interference mitigation technique for low data rate UWB
communication via computer simulations regardless of definitions of transmitted energy of UWB communication system, and also
that the signal with random polarity is suitable for LDC-UWB system to mitigate interference to the other radio systems. We
further investigate the adequate duty-cycle of LDC-UWB system for each definition of transmitted power of UWB communication. 相似文献
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Siriwongpairat W.P. Weifeng Su Olfat M. Liu K.J.R. 《Signal Processing, IEEE Transactions on》2006,54(1):214-224
The emerging ultrawideband (UWB) system offers a great potential for the design of high speed short-range wireless communications. In order to satisfy the growing demand for higher data rates, one possible solution is to exploit both spatial and multipath diversities via the use of multiple-input multiple-output (MIMO) and proper coding techniques. In this paper, we propose a general framework to analyze the performance of multiband UWB-MIMO systems regardless of specific coding schemes. A combination of space-time-frequency (STF) coding and hopping multiband OFDM modulation is also proposed to fully exploit all of the available spatial and frequency diversities, richly inherent in UWB environments. We quantify the performance merits of the proposed scheme in case of Nakagami-m frequency-selective fading channels. Different from the conventional STF coded MIMO-OFDM system, the performance of the STF coded hopping multiband UWB does not depend on the temporal correlation of the propagation channel. We show that the maximum achievable diversity of multiband UWB-MIMO system is the product of the number of transmit and receive antennas, the number of multipath components, and the number of jointly encoded OFDM symbols. Interestingly, the diversity gain does not severely depend on the fading parameter m, and the diversity advantage obtained under Nakagami fading with arbitrary m parameter is almost the same as that obtained in Rayleigh fading channels. Finally, simulation results are presented to support the theoretical analysis. 相似文献