Data sensitivity is a key problem in the application of adaptive beamforming technology. Based on the analysis of the principle of fast time-domain analytical MVDR algorithm, the influence of the amplitude fluctuation of array signal on fast time-domain analytical MVDR beamforming algorithm is analyzed by using numerical simulation and sea test data. The results show that the amplitude fluctuation has little influence on the conventional beamforming algorithm, but has great influence on the fast time domain analytical MVDR algorithm, so the fast time domain analytical MVDR beamforming algorithm requires high channel consistency of each hydrophone.

A low complexity channel estimation scheme using data-dependent superimposed training (DDST) is proposed in this paper, where the pilots are inserted in more than one block, rather than the single block of the original DDST. Comparing with the original DDST (which improves the performance of channel estimation at the cost of huge computational overheads), the proposed DDST scheme improves the performance of channel estimation with only a slight increase in the consumption of computation resources. The optimal precoder is designed to minimize the data distortion caused by the rank-deficient precoding. The optimal pilots and placement are also provided to improve the performance of channel estimation. In addition, the impact of power allocation between the data and pilots on symbol detection is analyzed, the optimal power allocation scheme is derived to maximize the effective signal-to-noise ratio at the receiver. Simulation results are presented to show the computational advantage of the proposed scheme, and the advantages of the optimal pilots and power allocation scheme.

双向中继网络在提高频谱效率的同时会引入额外的自干扰,本文针对放大转发(AF)模式下双向多输入多输出(MIMO)中继网络中的自干扰抵消问题,从消除信道估计误差引入的剩余自干扰着手,提出一种采用信道独立预编码的盲干扰抵消(BIC)方案.新方案在源节点对信息进行行空间预编码,从而构建不依赖于MIMO信道矩阵的期望信号子空间和自干扰子空间,实现未知信道状态下自干扰抵消和期望信号分离,从而消除非理想信道估计带来的剩余自干扰信号.在此基础上,以最大化有效信噪比为目标设计最佳预编码,通过推导可达和速率的闭合表达式,分析不同方案下信道估计误差对可达和速率的影响.仿真结果表明,新方案在不同的信道估计误差下,能够实现完美自干扰消除,其检测性能和容量均优于基于信道估计的自干扰消除方案.

Additional self-interference is introduced in two-way relay network (TWRN) while spectral efficiency is increased. As for self-interference problem in amplify-and-forward (AF) modes, a kind of blind interference cancelation (BIC) scheme is employed. The scheme can realize self-interference cancellation and desired signal separation with unknown channel status information by signal precoding operating at transmitting node. In this way, the impact of residual self-interference caused by imperfect channel estimation on TWRN performance is eliminated. Based on this, the closed expression and asymptotic expression of the system outage probability (OP) under M-phase shift keying (MPSK) modulation is derived. Moreover, the influence of SOP performance with channel estimation error under different schemes is analyzed. The correctness of the theoretical derivation is verified by simulation comparison.

双向中继网络(two-way relay network,TWRN)在提高频谱效率的同时会引入额外的自干扰,针对放大转发模式下的自干扰抵消问题,从消除非理想信道估计带来的剩余自干扰着手,提出一种基于正交预编码的盲干扰抵消方案。新方案通过对端节点信号进行"右乘"正交预编码,将期望目标信号与自干扰信号映射到不依赖于信道状态信息的正交子空间,实现未知信道状态下自干扰抵消和期望信号分离,从而消除非理想信道估计带来的剩余自干扰对TWRN性能的影响,提高了系统的鲁棒性。在此基础上,通过推导平均误比特率(bit error rate,BER)的闭合表达式和渐进表达式,分析不同方案下信道估计误差对平均BER的影响,并通过仿真对比验证了理论推导的正确性。

针对放大转发(Amplify-and-Forward,AF)模式下的菱形中继网络,为了高效获取级联和单跳链路信道状态信息(Channel State Information,CSI),本文提出基于叠加训练的信道估计方案,以消除多址接入干扰和训练间互干扰为目标,进行最优的多训练序列设计.新方案将中继训练叠加到源训练序列上,通过对中继识别符号以及中继训练组进行联合优化设计,设计了一种基于频域循环移位的正交扩展序列组生成算法.为了消除非高斯复合噪声对单跳信道估计造成的严重干扰,进而提出中继噪声消除算法.该方案能够准确获取CSI,在端节点实现分集合并,有效提高符号检测性能.仿真实验对比了同类型的信道估计方案,分析验证了方案的有效性.

In this letter, we deal with the problem of individual channel estimation in amplify-and-forward (AF) relaying systems. A novel superimposed training (ST) scheme is proposed where the relay superimposes its own training sequence directly on top of the received data signal without bandwidth expansion. As a result, the training sequences from the source and relay nodes are independent of each other and can be viewed as a time-multiplexed (TM) mode in the proposed scheme, thus making it more flexible and robust in relay-training design. To remove the data-induced interference and relaying-propagated noise during channel estimation, a modified ST scheme is designed by discarding some relaying data to accommodate the relay-training sequence. Simulation results are presented to assess the performances of the proposed scheme and to obtain the optimal power allocation.

For the OFDM-based Amplify-and-Forward cooperative system, a novel relay-superimposed pilot strategy is proposed, where the source pilot symbols are frequency division multiplexed to estimate the cascaded channel while relay pilot sequence is superimposed onto the top of the cooperative data stream for second-hop channel estimation. This method avoids the loss of data rate for additional pilot subcarriers but results in the interference of unknown cooperative data. To remove the interference of cooperative data during the estimation of second-hop channel, the Cooperative Interference Cancelation scheme assisted by cooperative data from direct link is proposed. We derive the approximated lower bound for the MSE of second-hop channel estimation. Simulation results are presented to validate the performance of the proposed schemes.

In an amplify-and-forward (AF) cooperative relay network,the combined training scheme is proposed to acquire channel state information (CSI) of different links.The combined training mode consists time-division multiplexing (TM) training and superimposed training (ST),where the TM training is employed at source node to estimate the cascaded channel (S-R-D) while the relay training sequence is added on top of the information-beating received signal to estimate the second-hop channel (R-D).In order to improve the estimation performance of R-D link,a novel cooperative interference suppression (CIS) scheme is proposed to remove cooperative data interference using detected symbols of S-D links.The new scheme employs combined training mode to make the individual channel and cascaded channel estimated independently,decreasing the complexity of training sequence design.Simulation results are presented to validate the performance of the proposed schemes.

In this letter, we consider the inter-relay interference (IRI) problem for amplify-and-forward (AF) two-path successive relay networks. To reduce processing burden for IRI cancelation at the relay nodes, a novel precoding-based interference cancelation scheme based on row-space mapping is proposed, where a pair of orthogonal precoding matrices is alternately utilized to project the source data onto the null space of the received data that is independent of channel state information (CSI). By designing a combined decoding and re-encoding scheme, both the IRI signal and accumulated noise are perfectly suppressed at the relay nodes. Simulation results show that the proposed scheme is significantly better than the channel estimate based interference cancelation schemes.

In this paper, we investigate an individual channel estimation problem for multiple-input multiple-output (MIMO) two-way amplify-and-forward (AF) relay networks. To avoid self-interference during the estimation of the individual MIMO channels, a novel blind interference cancellation (BIC) approach is proposed based on an orthogonal preceding framework, where a pair of orthogonal precoding matrices is utilized at the source nodes. By designing an optimal decoding scheme, we propose to decompose the bidirectional transmission into a pair of unidirectional transmissions. Unlike most existing approaches, we make the practical assumption that the nonreciprocal MIMO channel and the mutual interference of multiple antennas are both taken into consideration. Under the precoding framework, we employ an orthogonal superimposed training strategy to obtain the individual MIMO channels. However, the AF strategy causes the noise at the terminal to be the sum of the local noise and the relay-propagated noise. To remove the relay-propagated noise during the estimation of the second-hop channel, a partial noise-nulling method is designed. We also derive a closed-form expression for the total mean square error (MSE) of the MIMO channel from which we compute the optimal power allocation. The simulation results demonstrate that the analytical and simulated curves match fully.

A novel orthogonal frequency-division multiplexing system using data-nulling superimposed pilots with subcarrier index modulation (SIM) is proposed, where the constellation modulation vector is first spread over all subcarriers using a precoding matrix, then the subcarriers activated by SIM are nulled and inserted by the superimposed pilots (SPs). As the nonzero subcarriers index of the SP is exploited to convey additional information using SIM, the SP not only completes channel estimation without a loss of bandwidth, but also transmits additional information. Two different blind pilot-detection techniques (BPDTs) (which detects the nonzero subcarriers index of the SP without any prior knowledge at the receiver) are designed to demodulate the information conveyed by the SP using SIM and extract the SP from the received signal to estimate channel state information. Monte Carlo simulation results show that the proposed BPDTs achieve good pilot detection performances, and the nonzero subcarrier index of the SP is effectively exploited to convey additional information.

In amplify-and-forward relay networks, accurate channel estimation of individual links is essential for coherent reception and optimal design. To acquire the channel state information of individual links, a novel in-band superimposed training is proposed, where relay superimposes its own training sequence directly on top of the information-bearing received data. As a result, the training sequences from the source and relay nodes are independent of each other, thus making it more flexible and robust in relay-training design. However, the proposed training scheme induces extra data interference that degrades the estimation performance. The authors first adopted the detected symbols to mitigate the data-induced interference during channel estimation. However, the estimation performance is degraded by the symbol detection error and relay propagated noise. To resolve this problem, the interference nulling at the relay is proposed, where some special frequency components of the received data are nulled prior to training superimposition. As a result, both the data-induced interference and relay propagated noise are totally removed during channel estimation. Simulation results are provided to assess the performance of the proposed schemes.

In this paper, we consider channel estimation for single-carrier block transmission over doubly selective fading channel, where basis expansion models are used to describe the time-varying channel. The affine precoding model is used as the transmission strategy, wherein the training sequence is added on the top of the precoded data prior to transmission. By enforcing a special form of orthogonality between training sequence and precoded matrix, we propose orthogonal superimposed training design for doubly selective channel that makes channel estimation decouple from symbol detection, and then the affine precoding model based on orthogonal polyphase sequence set is designed under the orthogonal conditions. To further improve the estimation performance, we exploited a joint iterative approach is used, where the detected symbols, to enhance the estimation performance. Simulations results show that the proposed scheme can yield better detection performance than the data-dependent superimposed training and can be competitive with time-multiplexed training scheme with higher bandwidth efficiency.

We consider the training design and channel estimation in the amplify-and-forward (AF) diamond relay network. Our strategy is to transmit the source training in time-multiplexing (TM) mode while each relay node superimposes its own relay training over the amplified received data signal without bandwidth expansion. The principal challenge is to obtain accurate channel state information (CSI) of second-hop link due to the multiaccess interference (MAI) and cooperative data interference (CDI). To maintain the orthogonality between data and training, a modified relay-assisted training scheme is proposed to migrate the CDI, where some of the cooperative data at the relay are discarded to accommodate relay training. Meanwhile, a couple of optimal zero-correlation zone (ZCZ) relay-assisted sequences are designed to avoid MAI. At the destination node, the received signals from the two relay nodes are combined to achieve spatial diversity and enhanced data reliability. The simulation results are presented to validate the performance of the proposed schemes.

In amplify-and-forward (AF) orthogonal frequency division multiplexing (OFDM)-based cooperative network,to acquire channel state information (CSI) of different links efficiently,channel estimation scheme based on combined superimposed training is proposed.In the new scheme,different pilots are superimposed onto the transmitted data at source nodes and relay nodes respectively while channel estimation of cascaded link (S→R→D) and single-hop link (R→D) are achieved at destination nodes using source pilots and relay pilots.In order to eliminate the severe interference for channel estimation induced by data sequence in the superimposed pilots scheme,a data-nulling superimposed pilots (DNSP) method with pre-processing at the transmitter is proposed for source pilots design.Moreover,a novel cooperative interference cancelation (CIC) method is employed for relay pilots design.The degradation on performance of R→D channel estimation induced by cooperative data is canceled with the detected symbols from S→D link while the information distortion is compensated and detecting performance is improved using iterative reconstruction.Simulation results are provided that the proposed scheme can eliminate the spending of bandwidth for pilots and approach the detecting performance of traditional frequency division multiplexing (FDM) schemes.

In amplify-and forward (AF) cooperative systems, accurate channel state information (CSI) for both the cascaded and individual links is essential for coherent combining to achieve spatial diversity. The combined superimposed training strategy(TM+ST) is proposed, where the time-multiplexed (TM) training scheme is employed at source node (SN) to estimate the cascaded channel(S-R-D) while relay-assisted training scheme is employed to extract the individual channel of R-D link at destination node (DN) without bandwidth expansion. The Data-Dependent Distortion (DDD) removed iteration scheme is presented to improve the estimation performance of R-D link. Compared with the traditional estimation strategy, the new approach is proposed to optimize the design of training, making individual channel and cascaded channel estimated independently, which improves the flexibility of the system design. Simulation results are presented that diversity combination can eliminate the symbol error floor and assess the performance of the proposed schemes.

In amplify and forward cooperative relaying system, the knowledge of individual channel state information (CSI) is essential for coherent decoding and optimal design. To assist in the estimation of the individual channels, we proposed an in-band pilot strategy, where some cooperative data at the relay are discarded to insert pilots that can be utilized to estimate the relay to destination link. The new cooperative strategy implies that relay not only helps the source to transmit cooperative data, meanwhile, assisting the destination to acquire the individual CSI at the cost of cooperative information. Although some useful data are lost due to insertion of in-band pilots, the detection performance can be maintained with a simple iterative reconstruction method. Furthermore, if the direct link is available, the received signals from both the source and the relay can be combined to achieve spatial diversity. Simulation results are presented to assess the performance of the proposed schemes.

本文介绍了QPSK信号产生和解调的相关原理.利用数字信号处理芯片运算速度快、可编程性能好、抗干扰能力强,能适合于实现复杂的算法的特点,结合CCS开发平台,完成了以汇编语言为基础的QPSK信号解调的DSP仿真.通过对比Matlab仿真和DSP仿真结果,验证设计的解调过程各项性能指标均达到设计的要求.

In this paper, we consider bandwidth efficient design and channel estimation over time-varying frequency-selective environments, where the basis expansion model (BEM) is used to describe the time-varying channel. Superimposed training based channel estimation based affine precoding model is designed, where the data interference is eliminated from received data prior to performing channel estimation, while the training sequence is completely out in the symbol detection. Simulations results show that the proposed scheme can yield better detection performance with high bandwidth efficiency.