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This paper studies differential space-time modulation using diversity-encoded differential amplitude and phase shift keying (DAPSK) for the multiple-input multiple-output (MIMO) system over independent but not identically distributed (inid) time-correlated Rician fading channels. An asymptotic maximum likelihood (AML) receiver is developed for differentially detecting diversity-encoded DAPSK symbol signals by operating on two consecutive received symbol blocks sequentially. Based on Beaulieu’s convergent series, the bit error probability (BEP) upper bound is analyzed for the AML receiver over inid time-correlated Rician fading channels. Particularly, an approximate BEP upper bound of the AML receiver is also derived for inid time-invariant Rayleigh fading channels with large received signal-to-noise power ratios. By virtue of this approximate bound, a design criterion is developed to determine the appropriate diversity encoding coefficients for the proposed DAPSK MIMO system. Numerical and simulation results show that the AML receiver for diversity-encoded DAPSK is nearly optimum when the average received signal-to-noise power ratios are high and the channel is heavily correlated fading and can provide better error performance than conventional noncoherent MIMO systems when the effect of non-ideal transmit power amplification is taken into account. 相似文献
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We analyze the bit error rate (BER) performance of M-ary quadrature amplitude modulation (M-QAM) when using space-time block coding (STBC) along with packet combining triggered by automatic repeat request (ARQ) retransmission over multiple-input multiple-output (MIMO) fading channels. Specifically, adopting a log-likelihood ratio (LLR) based approach and considering the 16-QAM case of study, we provide an exact formulation for the aggregate LLR distribution in the case the STBC codeword can be transmitted twice, and derive the resulting BER. For higher number of retransmissions, an approximation of the error function is used to derive the LLR distributions and the system's ensuing BER. Considering different values of combined transmissions and M-QAM with possible constellation rearrangement (CoRe), validation of the proposed BER analytical model through simulations and assessment of the advantages of packet combining are provided for transmissions over additive white Gaussian noise (AWGN) channel and orthogonalized MIMO Rayleigh fading channels with different STBC mappings. 相似文献
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In this paper, the performance of multiuser CDMA systems with different space time code schemes is investigated over Nakagami
fading channel. Low-complexity multiuser receiver schemes are developed for space-time coded CDMA systems with perfect and
imperfect channel state information (CSI). The schemes can make full use of the complex orthogonality of space-time coding
to obtain the linear decoding complexity, and thus simplify the exponential decoding complexity of the existing scheme greatly.
Moreover, it can achieve almost the same performance as the existing scheme. Based on the bit error rate (BER) analysis of
the systems, the theoretical calculation expressions of average BER are derived in detail for both perfect CSI and imperfect
CSI, respectively. As a result, tight closed-form BER expressions are obtained for space-time coded CDMA with orthogonal spreading
code, and approximate closed-form BER expressions are attained for space-time coded CDMA with quasi-orthogonal spreading code.
Computer simulation for BER shows that the theoretical analysis and simulation are in good agreement. The results show that
the space-time coded CDMA systems have BER performance degradation for imperfect CSI. 相似文献
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Several standards such as IEEE 802.11a/g, IEEE 802.16, and the European Computer Manufacturers Association (ECMA) multiband orthogonal frequency division multiplexing (MB-OFDM) for high data-rate ultra-wideband employ bit-interleaved convolutionally coded multicarrier modulation over quasi-static fading channels. Motivated by the lack of appropriate error rate analysis techniques for this popular type of system and channel model, we present two novel analytical methods for bit error rate (BER) estimation of coded multicarrier systems operating over frequency-selective quasi-static channels with nonideal interleaving. In the first method, the approximate performance of the system is calculated for each realization of the channel, which is suitable for obtaining the outage BER performance (a common performance measure for, e.g., MB-OFDM systems). The second method assumes Rayleigh distributed frequency-domain subcarrier channel gains and knowledge of their correlation matrix, and can be used to directly obtain the average BER performance. Both methods are applicable to convolutionally coded interleaved multicarrier systems employing quadrature amplitude modulation, and are also able to account for narrowband interference (modeled as a sum of tone interferers). To illustrate the application of the proposed analysis, both methods are used to study the performance of a tone-interference-impaired MB-OFDM system. 相似文献
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This paper proposes a carrier frequency offset (CFO) estimation scheme for OFDM systems over fast fading channels. In the proposed scheme, exploiting the multiple preambles with the identical values, we estimate the CFO over fast fading channels. In particular, we improve the performance of the CFO estimator by applying the overlapped windows to preambles. Through simulations, we validate the proposed estimation scheme by showing the effectiveness of the proposed estimator. 相似文献
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空时分组码(STBC)由于具有较高的分集增益和简单的编译方法,从而得到普遍关注。但是它只适于频率平坦信道,而实际的信道多为频率选择性信道。丈中将考虑两种适用于频率选择性信道的空时分组码系统方案:OFDM-STBC和SC/FDE-STBC方案,即考虑空时分组码与正交频分复用或单载波频域均衡结合。通过对OFDM-STBC和SC/FDE-STBC系统性能仿真结果的比较和分析,表明SC/FDE-STBC方案要优于OFDM-STBC方案。此外,文中也给出一些细致的仿真性能的观察。 相似文献
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Orthogonal frequency division multiplexing (OFDM) systems are highly sensitive to carrier frequency offset (CFO), especially in doubly-selective fading environment. Cyclostationarity-based blind synchronization methods are appealing in high-data-rate applications and low signal-to-noise regions. However, the cyclostationarity has not been exploited for frequency synchronization of OFDM systems under doubly-selective fading channels. In this paper, we derive the close-form second order cyclic statistics of the received OFDM signal in presence of CFO, by modeling the doubly-selective fading channel with basis expansion model. Both transmitter-induced cyclostationarity and doubly-selective channel information are contained in the derived cyclic moments, and they are efficiently utilized for CFO estimation. Simulation results demonstrate that the proposed estimator provides significant improvements on frequency synchronization performance. 相似文献
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In MIMO systems, space-time block code (STBC) is good solution for improving system performance. Among the STBCs, coordinate interleaved orthogonal designs (CIODs) combined with QR-decomposition-based decision-feedback decoding (QR-DDF) allow achieving good performance for time-selective fading channels. However, half of entries in codeword matrix of CIODs are zeros. These zero entries result in high peak-to-average power ratio (PAPR) and also impose a severe constraint on hardware implementation of the code when turning off some of the transmitting antennas whenever a zero is transmitted. In this paper, we propose a new design of space-time block codes without zero entry in codeword matrix (NZE-STBCs) for time-selective fading channels. The main advantage of the proposed NZE-STBCs is that its peak-to-average ratio (PAPR) is 3 dB lower than that of CIODs, and its hardware implementation is also easier due to eliminating on-off switchers without sacrificing performance. Moreover, similar as CIODs, the proposed NZE-STBCs can use low complexity QR-DDF decoder over time-selective fading channels to enhance performance and reduce decoding complexity. Simulation results show that the proposed NZE-STBCs outperform CIODs for three transmit antennas while performing the same for two and four transmit antennas. 相似文献
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《Communications, IEEE Transactions on》2005,53(5):905-906
Bit Interleaved Time-Frequency Coded Modulation for OFDM Systems Over Time-Varying Channels Orthogonal frequency-division multiplexing (OFDM) is a promising technology in broadband wireless communications with its ability in transforming a frequency selective fading channel into multiple flat fading channels. However, the time-varying characteristics of wireless channels induce the loss of orthogonality among OFDM sub-carriers, which was generally considered harmful to system performance. In this paper, we propose a bit interleaved time–frequency coded modulation (BITFCM) scheme for OFDM to achieve both time and frequency diversity inherent in broadband time-varying channels. We will show that the time-varying characteristics of the channel are beneficial to system performance. Using the BITFCM scheme and for relatively low maximum normalized Doppler frequency, a reduced complexity Maximum Likelihood (ML) decoding approach is proposed to achieve good performance with low complexity as well. For high maximum normalized Doppler frequency, the inter-carrier interference (ICI) can be large and an error floor will be induced. To solve this problem, we propose two ICI mitigation schemes by taking advantage of the second order channel statistics and the complete channel information, respectively. It will be shown that both schemes can reduce the ICI significantly. 相似文献
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We develop blind data detectors for orthogonal frequency-division multiplexing (OFDM) systems over doubly selective channels by exploiting both frequency-domain and time-domain correlations of the received signal. We thus derive two blind data detectors: a time-domain data detector and a frequency-domain data detector. We also contribute a reduced complexity, suboptimal version of a time-domain data detector that performs robustly when the normalized Doppler rate is less than 3%. Our frequency-domain data detector and suboptimal time-domain data detector both result in integer least-squares (LS) problems. We propose the use of the V-BLAST detector and the sphere decoder. The time-domain data detector is not limited to the Doppler rates less than 3%, but cannot be posed as an integer LS problem. Our solution is to develop an iterative algorithm that starts from the suboptimal time-domain data detector output. We also propose channel estimation and prediction algorithms using a polynomial expansion model, and these estimators work with data detectors (decision-directed mode) to reduce the complexity. The estimators for the channel statistics and the noise variance are derived using the likelihood function for the data. Our blind data detectors are fairly robust against the parameter mismatch 相似文献
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该文提出了两种新的适用于时变信道下空时分组编码多用户系统的解码器设计方案。空时分组编码多用户系统下,传统的迫零(Zero Forcing, ZF)和最小均方误差(Minimum Mean Squared Error, MMSE)解码器设计均假定信道准静态衰落。信道时变时,这些传统解码器在解码某用户信号时引入符号间干扰(Inter-Symbol Interference, ISI),且这种干扰随信道时变增大而增加。基于此,该文设计了两种新的解码器,该解码器可显著降低信道时变的影响。仿真结果表明,随信噪比(Signal-to-Noise Ratio, SNR)增加,两种传统解码器均出现误码率性能平层,而新解码器获得了显著的性能改善。 相似文献
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Yan Li Pooi Yuen Kam 《Communications, IEEE Transactions on》2007,55(8):1640-1644
The performance analysis of space-time trellis codes over rapid nonselective Rayleigh fading channels with imperfect channel state information is considered. A pilot-symbol-assisted-modulation scheme is used for channel estimation. The parameters used in this scheme, i.e., pilot spacing and Wiener filter length are chosen in a tradeoff between estimation accuracy, transmission rate/pilot overhead, and receiver complexity. A simple maximum likelihood receiver for M-ary phase shift keying modulation is derived. An exact closed-form pairwise error probability (PEP) expression and explicit PEP bounds are presented. It is shown that the performance loss caused by channel estimation errors increases mainly with the channel fade rate. 相似文献
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Alamouti orthogonal space-time block code (Alamouti in IEEE J Sel Areas Commun 16(8):1451–1458, 1998) has been applied widely in wireless communication, e.g., IEEE 802.16e-2005 standard. In this paper, theoretical analysis of symbol error rate performance for Alamouti orthogonal space-time block code (AOSTBC) over time-selective fading channels with a zero-forcing linear receiver is derived. Firstly, a closed-form expression (i.e., not in integral form) is derived for the average symbol pair-wise error probability (SPEP) in time-selective frequency-nonselective independent identically distributed Rayleigh fading channels. Then, the SPEP is used to derive a tight upper bound (UB) for the symbol-error rate (SER) of AOSTBC via establishing algorithmic Bonferroni-type upper bound. Extensive simulation results show that the curves for the UB coincide with the simulated SER curves for various antenna configurations even at very low signal-to-noise ratio regimes. The UB thus can be used to accurately predict the performance of AOSTBC code over time-selective fading channels when a zero-forcing receiver is used. 相似文献
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在移动通信系统中,由于无线时变衰落信道的特点,使通信过程存在大量的不确定性,自适应方式在信道条件好时提高了传输速率或减小发送功率,在信道条件差时降低了速率或增大功率。通过仿真结果证明,根据信道的优劣情况进行自适应调制的系统在保持较低的误码率性能的同时,能提高了系统的传输速率,从而增强传输的可靠性并可提高频带利用率。 相似文献
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Robust Packet Video Transport Over Wireless Fading Channels Using a Joint Source-channel Coding Approach 总被引:2,自引:2,他引:0
In this paper, we address the problem of robust video transmission over wireless networks. Specifically, we consider packet
video transmission over wireless IP networks based on the RTP/UDP/IP protocol stack. Digital video delivered over wireless
networks is expected to suffer quality degradation from both packet loss and bit errors in the payload. In this paper, both
packet loss and bit errors in the payload are considered and the performance of a joint source-channel coding (JSCC) approach
employing forward error-correction (FEC) coding schemes for H.263 + video transmission is studied. Results indicate that
with an appropriate JSCC approach, FEC-based error-control techniques can significantly improve the packetization efficiency
for a given end-to-end quality requirement and lead to more acceptable video delivery quality over time-varying wireless networks.
Another important observation is that with a JSCC approach the fading effects of wireless links upon end-to-end video quality
are substantially decreased compared to a system without using channel coding, resulting in attractive robust performance
characteristics.
相似文献
Yong PeiEmail: |