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QC-LDPC码是一个十分重要的LDPC码研究分支。QC-LDPC码(准循环低密度奇偶校验码)是一类结构化的LDPC码,其校验矩阵H采用准循环方式构造,具有实现复杂度低的特点,易于硬件实现。大量研究人员认为,MIMO-OFDM技术将会成为4G的核心技术。将QC-LDPC码与MIMO-OFDM系统相结合,分析了在时变频率选择性衰落信道下的系统性能。仿真结果表明,在时变频率选择性衰弱信道下,QC-LDPC码与随机构造的LDPC码具有接近的系统性能。 相似文献
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In this paper, we propose and give the performance of a novel uplink system based on the combination of multi-carrier (MC),
code division multiple access (CDMA) and multiple input multiple output (MIMO) techniques. First, we describe the interests
of spread-spectrum multi-carrier multiple access (SS-MC-MA) scheme for uplink, especially compared to MC-CDMA. Classically,
with SS-MC-MA, each user spreads its data symbols on a specific subset of adjacent or multiplexed subcarriers, to facilitate
the channel estimation and reduce complexity at the reception. In order to compensate for the lack of frequency diversity
of SS-MC-MA with adjacent subcarriers, we first combine it with an orthogonal space-time block code (STBC) and demonstrate
the resulting spatial diversity gain. Then, we propose to allocate the subsets to the different users by applying a frequency
hopping pattern (FH). In that case, each user benefits from the frequency diversity linked to the total bandwidth as with
the multiplexed subcarriers solution, while keeping the advantages of the adjacent subcarriers solution. The gain provided
by the use of the frequency hopping is stressed on. Finally, the performance of this scheme is evaluated over realistic MIMO
channel with channel turbo coding for systems offering asymptotic spectrum efficiency of 1, 2, 3 and 4.5 bit/s/Hz. Thus, the
efficiency of the novel proposed STBC FH SS-MC-MA system as a very promising multiple access and modulation scheme for the
uplink of the future wideband wireless networks is successfully demonstrated. 相似文献
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本文讨论了空时分组码的自适应调制技术.在接收端分集合并后的等效信道模型下,通过对自适应STBC信道容量的讨论证明了随着天线数的增加,自适应调制的重要性降低.之后针对二发一收的低价分集系统,讨论了其STBC基础上的自适应调制技术,同时给出了离散功率离散速率自适应调制区间端点的封闭解. 相似文献
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在多输入输出(Multiple-Input Multiple-Output,MIMO)系统中提出一种块分组编码与VBLAST的联合编码方案,该方案对最先检测的2层数据流采用块分组编码,其余层采用垂直分层空时码(Vertical Bell Layered Space-Time Code,VBLAST)的编码方式,MIMO系统同时具有了空时分组码(Space Time Block Code,STBC)可以降低误码率的优点与VBLAST能够提高系统容量的优点。块分组编码将数据符号按层分块后交叉通过不同的天线对发射,数据流之间产生了一定交织效果,使编码获得了更好的分集增益,在接收端结合QR分解的最大似然解码算法进行解码。仿真结果表明该联合编码方案与传统的Alamouti编码和VBLAST的联合编码方案相比误码率性能有较大改善。 相似文献
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This paper deals with a blind channel estimation method for space-time coded block transmission system. By concatenating the
real part and imaginary part of the received signal to form an elongated vector, we derive an equivalent input–output system
model. Then channel state information (CSI) is blindly estimated using subspace method, utilizing only the redundancy inherent
in space-time block coding (STBC) and cyclic prefix (CP). The estimation ambiguity, which is common to all blind methods,
is analyzed in detail and we prove that there only exist four scalar indeterminacies. Three effective methods to eliminate
the ambiguities are also proposed. Compared with other blind channel estimation methods for space time systems, this method
needs neither redundant precoding nor oversampling, and thus has higher data rate. Besides, this method is robust to channel
order overestimation, which is effectively demonstrated by numerical simulations.
This work was supported by NSFC (60496310, 60672093), NSFJS(BK2005061) and BK2005061. 相似文献
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MIMO-OFDM技术是未来无线通信的关键技术之一.在性能上,不规则LDPC码是LDPC码中性能最优越的.基于IEEE802.16标准的MIMO-OFDM系统,研究了不规则LDPC码的性能,并与规则LDPC码性能比较.仿真结果表明,不规则码比规则码在MIMO-OFDM系统中有明显的优势. 相似文献
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Differential Space-Time Block Codes (DSTBC) do not require any radio channel measurement and channel state information neither
on the transmitter nor at the receiver side. Therefore, they are an attractive alternative to coherent Multiple-Input Multiple-output
(MIMO) systems. The classical technical proposal for differential techniques is based on M-ary phase shift keying (M-PSK)
modulation schemes for DSTBC (PSK-DSTBC). One advantage of this scheme is the constant envelop of the transmit signal, but
it is well known that higher-order PSK is less efficient due to the small distance between adjacent points in the constellation
diagram. Therefore, in this paper an alternative modulation technique for DSTBC is discussed, which is based on quadrature
amplitude modulation (QAM-DSTBC). The signal envelope of the transmit signal is not any more constant in this case. Therefore,
the technical challenge of integrating QAM into the DSTBC system design is to control the transmit power in order to avoid
an increase or a decrease in transmit power to some extreme values. The mechanism, which is used in this paper to control
the transmit power is based on an extension of the original QAM constellation diagram. The additional points, which are integrated
into the constellation diagram are used in this case for the mapping procedure to select one of the modulation symbols with
high or alternatively low signal power. This means for each single bit pattern there are almost always two modulation symbols
available in the mapping procedure one with low and one with high signal power, which gives the basis for a signal power control
algorithm. The resulting bit-error-rate (BER) performance of QAM-DSTBC is compared finally to the performance figures of the
original proposal of PSK-DSTBC.
相似文献
Hermann RohlingEmail: |
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