Downlink performance analysis of a BPSK-based WCDMA usingconventional RAKE receivers with channel estimation

We consider the downlink of a Universal Mobile Telecommunication System terrestrial radio access-wideband code division multiple access (UTRA-WCDMA) system and we investigate the performance of the conventional RAKE receiver. A multipath slowly Rayleigh fading channel is assumed. For the purpose of channel tap weight estimation, a common control physical channel, that is either serial or parallel multiplexed with the dedicated physical channels, is used. The receiver sensitivity to imperfect knowledge of the path delays, to the number of pilot symbols, and to the power ratio of pilot to data channels is also investigated. The system performance is evaluated by means of bit-error rates (BERs) derived using quadratic forms and characteristic functions for a BPSK modulation. The mean-squared estimation error (MSEE) of the channel tap weights is also computed and compared to the classical Cramer-Rao lower bound (CRLB). The mutual interference between pilot and data symbols is taken into account     

WCDMA下行链路信道估计算法的性能分析及比较

在WCDMA／FDD第三代移动通信系统中，下行链路的信道估计有基于公共导频信道（CPICH）和基于时分复用导频符号两种方式。本文就分别基于这两种方式的信道估计算法进行了性能的分析和比较，并给出实现模型及仿真结果。     

多码CDMA系统中联合并行干扰抵消与迭代信道估计方法

本文针对多码CDMA系统提出了一种联合并行干扰抵消与迭代信道估计方法。该方法首先通过导频符号对信道进行估计，然后使用RAKE接收机后的软信息对信道参数进行修正，最后通过并行干扰抵消(PIC)去除多码干扰(MCI)。仿真结果表明，经过多次迭代后，该方法可显著地降低多码CDMA系统的误比特率平台。本文同时还给出了信道估计质量、码道数和PIC次数对多码CDMA系统性能的影响。     

Pilot Position Selection and Detection for Channel Estimation of SC-FDE

In this letter, we propose a simple pilot position selection/detection technique for channel estimation of single- carrier frequency domain equalization (SC-FDE). Unlike the conventional channel estimation techniques such as frequency domain superimposed pilot technique (FDSPT), the proposed scheme selects the pilot positions to minimize the distortion of original signals caused by the loss of useful data tones in frequency domain. The corresponding receiver structure is also presented, where the pilot positions are blindly detected and the distorted data symbols are iteratively reconstructed. Simulation results show that the proposed system gives better BER performance than the FDSPT and approaches the lower bound of SC-FDE.     

WCDMA系统中结合导频与信息码的信道估计方法

研究了快衰落环境中第三代移动通信空中接口WCDMA(FDD),基于时分复用的导频信号辅助衰落信道下的信道估计。提出了同时根据导频信号及数据信号估计信道参数的信道估计方法,该方法将信道估计分为根据导频信号和数据信号两部分进行并由其加权合并完成。计算了最小均方误差下的合并系数。仿真结果表明该方法能快速跟踪信道的衰落,有效地估计出各时隙中数据段的信道参数。利用该算法,尤其在高速运动情况下,接收机的性能可得到显著的改善。     

高速场景下基于叠加导频的迭代EKF信道估计方法

针对正交频分复用（Orthogonal Frequency Division Multiplexing,OFDM）系统在高速移动场景下时/频域选择性衰落（双选衰落）和非平稳特性给信道估计带来的技术挑战,本文采用导频与数据叠加的帧结构,提出一种基于基扩展模型（Basis Expansion Model,BEM）的迭代扩展卡尔曼滤波（iterative Extend-Kalman Filter,iEKF）信道估计方法.基于BEM信道模型且采用EKF信道估计方法可以联合估计出信道冲激响应（Channel Impulse Response,CIR）与时变的时域自相关系数,有效消除子载波间干扰（Inter Carrier Interference,ICI）.同时,为了进一步消除叠加导频位置处的数据符号干扰,我们提出将叠加位置处的数据和导频先解耦、后重构再进行迭代EKF的信道估计方法.仿真分析表明,相较传统叠加导频的信道估计方法和导频符号辅助调制（Pilot Symbol Assisted Modulation,PSAM）估计方法,本文提出的信道估计方法在高速场景特别是低信噪比的条件下,具有更高的估计精度,更强的鲁棒性及更大的吞吐量.     

基于虚导频和功控导频的OFDM信道估计

提出了一种基于虚导频和功控导频的OFDM信道估计方法。该方法通过选择可靠的解调数据符号作为虚导频，同时对导频采用功率控制，从而提高了信道估计的质量。计算机仿真结果显示，相对于传统方法，可以用较少的导频获得性能的改善。     

限幅OFDM的一种信道估计优化方法

在OFDM 系统中,限幅常用于抑制信号的峰平比,而限幅会引入额外的限幅噪声,以致干扰数据和导引符号,恶化传输性能.本文针对限幅OFDM系统,提出一种基于导引符号的限幅噪声消除算法.该算法在插入导引符号之前,滤除位于导引位置的限幅噪声,从而改善信道估计性能.在此基础上,本文还提出了利用迭代算法以进一步提高信道估计精确度.本文对所提出的限幅噪声消除算法及迭代算法进行了仿真验证,结果表明,新算法能够明显改善信道估计,优化传输性能.     

Doubly iterative receiver for block transmissions with EM-based channel estimation

Cyclic-prefix code division multiple access (CP-CDMA), multicarrier CDMA (MC-CDMA) and single carrier cyclic-prefix (SCCP) transmission are some schemes that could support the increasing demand of future high data rate applications. The linear and nonlinear equalizers used to detect the transmitted signal are always far from the Maximum-Likelihood (ML) detection bound. The block iterative generalized decision feedback equalizer (BI-GDFE) is an iterative and effective interference cancelation scheme which could provide near-ML performance yet with very low complexity. In order to deploy this scheme, the channel state information (CSI) must be available at the receiver. In practice, this information has to be estimated by using pilot and data symbols. This paper investigates the problem of channel estimation using the Expectation Maximization (EM) algorithm. The BI-GDFE provides the soft information of the transmitted signals to the EM-based algorithm in the form a combination of hard decision and a coefficient so-called the input-decision correlation (IDC). The resultant receiver becomes a doubly iterative scheme. To evaluate the performance of the proposed estimation algorithm, the Cramér-Rao Lower Bound (CRLB) is also derived. Computer simulations show that the bit error rate (BER) performance of the proposed receiver for joint channel estimation and signal detection can reach the performance of the BI-GDFE with perfect CSI.     

Bandwidth-efficient pilot-symbol-aided technique formultipath-fading channels

Pilot-symbol-aided (PSA) transmission is one of the effective methods to combat multipath-fading in digital mobile communications systems. In the PSA systems, redundant bandwidth and power are required to transmit the pilot symbols. We propose a novel fading estimation technique that requires a very low bandwidth redundancy in the PSA systems. The proposed technique uses simple linear interpolation on the pilot symbols and the detected data symbols to obtain the estimates of the channel fading effects. Monte Carlo computer simulation has been carried out to study the effects of the technique on the bit error rate performance of 16-ary quadrature amplitude modulation in the flat and the frequency-selective Rayleigh-fading channels corrupted with cochannel interference and additive white Gaussian noise. Results have shown that the proposed technique can, at the expense of a little power efficiency, significantly improve the bandwidth efficiency of the PSA systems using receivers with low complexity and latency     

An iterative maximum SINR receiver for multicarrier CDMA systems over a multipath fading channel with frequency offset

A robust iterative multicarrier code-division multiple-access (MC-CDMA) receiver with adaptive multiple-access interference (MAI) suppression is proposed for a pilot symbols assisted system over a multipath fading channel with frequency offset. The design of the receiver involves a two-stage procedure. First, an adaptive filter based on the generalized sidelobe canceller (GSC) technique is constructed at each finger to perform despreading and suppression of MAI. Second, pilot symbols assisted frequency offset estimation, channel estimation and a RAKE combining give the estimate of signal symbols. In order to enhance the convergence behavior of the GSC adaptive filters, a decisions-aided scheme is proposed, in which the signal waveform is first reconstructed and then subtracted from the input data of the adaptive filters. With signal subtraction, the proposed MC-CDMA receiver can achieve nearly the performance of the ideal maximum signal-to-interference-plus noise ratio receiver assuming perfect channel and frequency offset information. Finally, a low-complexity partially adaptive (PA) realization of the GSC adaptive filters is presented as an alternative to the conventional multiuser detectors. The new PA receiver is shown to be robust to multiuser channel estimation errors and offer nearly the same performance of the fully adaptive receiver.     

Multidimensional parallel combinatory transform domain communication system

Transform domain communication system is an adaptive anti‐interference system that can dynamically generate interference‐orthogonal waveforms. As a spread spectrum system, its low spectrum efficiency limits potential practical applications. In TDCS, cyclic code shift keying is an orthogonal modulation, whose symbols can be regarded as scalars in different dimensions. However, the constellation is restricted by signal time‐bandwidth product. In this study, extending constellation is proven to be a valid approach to improve spectrum efficiency. The combinatory of multidimensional vectors is designed mathematically to increase the variety of the scalars with the minimum orthogonality damage. On the basis of the design, an efficient modulation scheme, namely, multidimensional parallel combinatory transform domain communication system, is proposed, whose fundamental modulation symbols can be represented by the combinatory of a series of cyclic code shift keying symbols with phase shift keying modulation. Compared with the existing methods, multidimensional parallel combinatory transform domain communication system can achieve a considerably higher spectrum efficiency. The bit error rate performance is also improved to various extents. Theoretical spectrum efficiency and bit error rate of the proposed method are derived for additive white Gaussian noise and typical multipath fading channels. System with different spectral conditions and channel estimation methods is also simulated and analyzed to confirm the practical usability.     

Rake接收机中信道最大多普勒频移估计的一种新方法及其在信道估计中的应用

Ｒａｋｅ接收机是ＣＤＭＡ系统中实现多径分集接收的核心部件,而信道估计对其接收性能有很大影响。传统连续导频符号的信道估计是采用对固定区间的信道参数估计值进行平均的方法以抑制接收噪声。     

一种实用的基于导频的空时编码OFDM系统信道估计方法

该文研究了在多径衰落信道情况下的基于导频的空时编码OFDM系统的信道估计方法,包括基于DFT的LS,LMMSE算法,提出了一种实用的估计方法,该方法通过优化设计的导频符号避免了复杂的矩阵求逆计算,大大降低了LS,LMMSE算法的复杂度和运算量,在性能上接近理想信道信息情况下的性能。     

Pilot-symbol-assisted detection scheme for distributed orthogonal space-time block coding

In this letter, we investigate the effect of imperfect channel estimation on the performance of distributed space-time block codes (DSTBCs) with amplify-and-forward relaying. Exploiting the orthogonality of the underlying code, we derive a maximum likelihood metric conditioned on the channel estimate acquired through the insertion of pilot symbols. For a large number of pilot symbols, we demonstrate that the proposed decoding rule coincides with the so-called mismatched receiver. On the other hand, as the number of pilot symbols decreases, the proposed decoder converges to a non-coherent detector. Through Monte-Carlo simulations, we further demonstrate that the performance of the proposed scheme lies within 0.8dB of the genie receiver performance bound.     

通用滤波多载波通信系统中干扰抑制均衡算法

作为5G多载波技术强有力的候选对象,通用滤波多载波利用子带滤波技术抑制带外功率泄露,进而降低同步要求和获得更高的频谱效率。本文首先针对通用滤波多载波在慢时变多径信道下的性能进行了分析和研究;其次为消除多径信道所带来的干扰,提出了适用于该多载波系统的信道估计方案,该方案设计了具有重复样式的导频结构进行信道估计,复杂度低;最后针对通用滤波多载波在多径信道下容易遭受符号间干扰的问题,提出了基于干扰消除的Zero-Forcing均衡算法和基于迭代干扰消除的均衡算法,两种算法均能够在消除ISI的基础上进一步地消除ICI和IBI。仿真结果表明,本文提出的信道估计和均衡算法能有效消除通用滤波多载波技术在多径信道下所经受的ISI、ICI和IBI。      

Low power ring oscillator for IoT applications

In order to scale with the demand of higher data rates and improved spectral efficiency in next generation wireless communication systems, a large-scale multiple-input and multiple-output (MIMO) technology called massive MIMO has been proposed. In massive MIMO, appropriate signal-to-noise ratio (SNR) values can be achieved by the addition of base station (BS) antennas in place of increasing transmit power. Pilot-based channel estimation is widely used in conventional MIMO systems, where pilot signal sequences are sent from the user terminals (UTs) to the BS to estimate the channel. In massive MIMO-based cellular networks, channel estimation in a given cell will be impaired by the pilot signal sequences transmitted by users in other cells—rendering the addition of antennas or transmit power ineffective. This effect is called pilot contamination. Therefore, pilot-based channel estimation limits the performance of massive MIMO. Semi-blind and blind methods are alternatives to pilot-based channel estimation that perform channel estimation with short pilot signal sequences and without pilot signal sequences, respectively. Blind channel estimation is one of the promising solutions to the pilot contamination problem in massive MIMO. This paper compares, using MATLAB simulations of a cluster-based COST 2100 channel model, the performance of pilot-based, semi-blind, blind, and adaptive-blind channel estimation methods. The pilot contamination effect on different channel estimation methods and how channel estimation methods can be used to overcome pilot contamination are shown. Finally, an adaptive independent component analysis (ICA)-based channel estimation method, which outperforms conventional ICA in terms of computational complexity, is proposed.     

Detection of Channel Variations to Improve Channel Estimation Methods

In current digital communication systems, channel information is typically acquired by supervised approaches that use pilot symbols included in the transmit frames. Given that pilot symbols do not convey user data, they penalize throughput spectral efficiency, and transmit energy consumption of the system. Unsupervised channel estimation algorithms could be used to mitigate the aforementioned drawbacks although they present higher computational complexity than that offered by supervised ones. This paper proposes a simple decision method suitable for slowly varying channels to determine whether the channel has suffered a significant variation, which requires to estimate the matrix of the recently changed channel. Otherwise, a previous estimate is used to recover the transmitted symbols. The main advantage of this method is that the decision criterion is only based on information acquired during the time frame synchronization, which is carried out at the receiver. We show that the proposed criterion provides a considerable improvement of computational complexity for both supervised and unsupervised methods, without incurring in a penalization in terms of symbol error ratio. Specifically, we consider systems that make use of the popular Alamouti code. Performance evaluation is accomplished by means of simulated channels as well as making use of indoor wireless channels measured using a testbed.     

A Decision Aided CDMA Receiver with Partially Adaptive Decorrelating Multi-User Interference Cancellation

A CDMA receiver with enhanced multiple access interference (MAI) suppressionis proposed for a pilot symbols assisted system over multipath channels. Thedesign of the receiver involves the following procedure. First, blind adaptivecorrelators are constructed at different fingers based on the scheme ofgeneralized sidelobe canceller (GSC) to collect the multipath signals andsuppress MAI. A low-complexity partially adaptive (PA) realization of the GSCcorrelators is proposed which incorporates multi-user information for reducedrank processing. By a judiciously designed decorrelating procedure, a new GSCstructure is obtained in which the MAI are decorrelated and suppressedindividually. The next step is then a simple coherent combining of thecorrelator outputs with pilot aided channel estimation. Finally, furtherperformance enhancement is achieved by an iterative scheme in which the signalis reconstructed and subtracted from the GSC correlators input data, leadingto faster convergence of the receiver. The proposed low-complexity PA CDMAmulti-user receiver is shown to be robust to multipath fading and channelerrors, and achieve nearly the same performance of the ideal maximum SINR andMMSE receivers by using a small number of pilot symbols.     

基于多中继导频频分复用的协同通信系统信道估计算法

本文针对频率选择性衰落环境下结合正交频分复用技术的放大转发多中继协同通信系统,提出了基于导频频分复用的频域信道估计算法,包括最小二乘（LS）估计算法和线性最小均方误差（LMMSE）估计算法。理论分析和仿真结果表明,该算法不仅成功分辨了多中继协同通信系统的所有频域信道衰落系数,避免了各中继节点转发的导频符号在目的节点上的混叠干扰,而且减少了频域信道估计所需的导频符号数量和时隙周期长度,提高了协同通信系统的传输效率和频谱利用率,同时显著提高了信道估计的精度,降低了算法的复杂度,具有较高的实用价值。