Non-orthogonal multiple access (NOMA) combined with multiple-input multiple-output (MIMO) can greatly increase the system throughput, but it will cause additional interference. Generally, the interference can be elimi...
详细信息
Non-orthogonal multiple access (NOMA) combined with multiple-input multiple-output (MIMO) can greatly increase the system throughput, but it will cause additional interference. Generally, the interference can be eliminated by utilizing the precoding technology. The previous studies preferentially focused on the channel difference between users, and neglected the lowly correlated scenarios, leading to the decline of users' throughput. A low-complexity user matching and power allocation scheme is proposed for such scenarios. Firstly, users with higher channel correlations are matched, and the remaining users are matched in terms of channel difference. Furthermore, the objective function is established to maximize the system throughput while assuring users' quality of service (QoS). Eventually, with the objective function in the Karush-Kuhn-Tucker (KKT) conditions being solved, the power allocation factors are achieved. The simulation results quantify that the proposed scheme has an advantage over the conventional MIMO-NOMA scheme. (C) 2020 Elsevier B.V. All rights reserved.
Orthogonal space-time block codes (STBCs) are known to orthogonalise the multiple-input multiple-output (MIMO) wireless channel, thus reducing the space-time vector detection to a simpler scalar detection problem. The...
详细信息
Orthogonal space-time block codes (STBCs) are known to orthogonalise the multiple-input multiple-output (MIMO) wireless channel, thus reducing the space-time vector detection to a simpler scalar detection problem. The capacity of STBCs over correlated Rayleigh and Ricean flat-fading MIMO channels under different adaptive transmitting techniques is studied. Three adaptive schemes known as optimal power and rate allocation, total channel inversion with fixed rate policy and its truncated variant are studied. Taking into account the effect of channel correlation, closed-form expressions are obtained for the capacity of orthogonalised Rayleigh and Ricean MIMO channels under these adaptive transmission techniques in order to avoid Monte-Carlo simulations.
The outdated channel state information (CSI) at the transmitter and receiver, which is resulted from time variation of channels, is considered in multiple-input multiple-output systems employing maximal ratio combinin...
详细信息
The outdated channel state information (CSI) at the transmitter and receiver, which is resulted from time variation of channels, is considered in multiple-input multiple-output systems employing maximal ratio combining. Closed-form expressions for the cumulative distribution function of output signal-to-noise ratio and symbol error rate under time-varying channels are presented to evaluate the effect of outdated CSI. The analytical results are compared with Monte Carlo simulations and a good agreement is obtained.
In this paper, a fist sphere decoder is proposed for the joint detection of phase-shift keying (PSK) signals in uncoded Vertical Bell Laboratories Layered Space Time (V-BLAST) systems. The proposed decoder consists of...
详细信息
In this paper, a fist sphere decoder is proposed for the joint detection of phase-shift keying (PSK) signals in uncoded Vertical Bell Laboratories Layered Space Time (V-BLAST) systems. The proposed decoder consists of preprocessing stage and search stage. The preprocessing stage is based oil the enhancement of the ordering mean square error decision feedback equalizer (MMSE-DFE). Its role is to generate a tree structure Suitable for the search stage. The search stage relies on the depth-first brand-and-bound (BB) algorithm with "best-first" orders stored in lookup tables. Simulation results show that the proposed decoder is able to provide the system with the maximum likelihood (ML) performance at low complexity. (C) 2008 Elsevier B.V. All rights reserved.
A low-profile pattern reconfigurable multiple-input multiple-output (MIMO) antenna is demonstrated in this paper. The antenna element is composed of a rectangular monopole and two sets of parasitic strips loaded with ...
详细信息
A low-profile pattern reconfigurable multiple-input multiple-output (MIMO) antenna is demonstrated in this paper. The antenna element is composed of a rectangular monopole and two sets of parasitic strips loaded with PIN diodes. The parasitic strips can operate as a reflector or a director by switching the PIN diodes on or off. As a result, the element provides a bidirectional mode and two directional modes. The MIMO antenna consists of two elements, which are arranged opposite to each other. Two decoupling strips are introduced to improve the isolation between the elements. The simulation and measurement results illustrate that the proposed antenna has nine pattern configurations. The overlapped bandwidth of the nine modes is 10.6%, and the isolation is greater than 16.5 dB. Also, a good diversity performance is obtained.
In this paper, we study the degrees of freedom (DoF) region for the multiple-input multiple-output two-way X relay channel with asymmetric antenna setting. In this channel model, there are two groups of source nodes, ...
详细信息
In this paper, we study the degrees of freedom (DoF) region for the multiple-input multiple-output two-way X relay channel with asymmetric antenna setting. In this channel model, there are two groups of source nodes, each group contains two source nodes, every source node in one group exchanges independent messages with every source node in another group via a common relay node, and each node has a different number of antennas. First, we derive an outer bound of the DoF region by using the cut-set theorem and the genie-message approach. Then, we obtain an inner bound of the DoF region by proposing a new transmission scheme that collectively utilizes antenna deactivation, pairwise signal alignment, cyclic signal alignment, and generalized signal alignment techniques. In the case of symmetric data exchange, our inner bound coincides with the outer bound, and thus, our proposed transmission strategy is optimal. We also obtain the optimal sum DoF for the special case, where the source nodes within a same group are equipped with the same number of antennas. This paper provides new insights for the study of more complicated relay networks.
In this paper, a novel closed-form transmit beamforming scheme is proposed for multiple-input multiple-output (MIMO) wiretap channel. The proposed method follows the idea of maximizing signal-to-leakage-plus-noise rat...
详细信息
In this paper, a novel closed-form transmit beamforming scheme is proposed for multiple-input multiple-output (MIMO) wiretap channel. The proposed method follows the idea of maximizing signal-to-leakage-plus-noise ratio and does not need additional power allocation. An efficient approach is further developed to implement the generalized eigenvalue decomposition required by our method when n (r) < n (t) (n (t) , n (r) and n (e) denote the antenna numbers at the transmitter, the intended receiver and the eavesdropper, respectively), which has lower complexity than the existing approaches. Moreover, we identify some shortcomings of the generalized singular value decomposition (GSVD) based beamforming method, a common beamforming scheme for MIMO wiretap channel. Finally, simulation results show that the proposed method significantly outperforms GSVD-based method when n (e) < n (t) and has almost the same performance as GSVD-based method when n (e) a parts per thousand yen n (t) .
High-resolution and wide-swath (HRWS) imaging is highly desired in future synthetic aperture radar (SAR) systems. However, it is a contradictory requirement between high azimuth resolution and wide unambiguous swath c...
详细信息
High-resolution and wide-swath (HRWS) imaging is highly desired in future synthetic aperture radar (SAR) systems. However, it is a contradictory requirement between high azimuth resolution and wide unambiguous swath coverage in a traditional SAR system. This paper proposes a novel solution to realize HRWS imaging by resolving the range ambiguity through a phase coding technique. The phase coding is employed in both spatial channels and slow time pulses. By properly designing the coding scheme, it is possible to separate the echoes from multiple ambiguous range regions from each other in the spatial domain. For each particular range region, the corresponding optimized receive beampattern can be used to extract the desired echoes from the presumed range region and suppress the undesired echoes from other range-ambiguous regions. The residual range-ambiguous echoes are also addressed. Specifically, it is capable of further mitigating the residual range-ambiguous echoes by optimally designing the coding scheme and the transmit beampattern. In the final, a bank of imaging processors can be implemented to obtain the high-resolution images of these range regions, which can be synthesized into a whole HRWS SAR image of the scene of interest. Simulation results have demonstrated the effectiveness of the proposed method. (C) 2019 Elsevier B.V. All rights reserved.
In recent years, there has been significant interest in information-theoretic security techniques that encrypt physical layer signals. We have proposed chaos modulation, which has both physical layer security and chan...
详细信息
In recent years, there has been significant interest in information-theoretic security techniques that encrypt physical layer signals. We have proposed chaos modulation, which has both physical layer security and channel coding gain, as one such technique. In the chaos modulation method, the channel coding gain can be increased using a turbo mechanism that exchanges the log-likelihood ratio (LLR) with an external concatenated code using the max-log approximation. However, chaos modulation, which is a type of Gaussian modulation, does not use fixed mapping, and the distance between signal points is not constant;therefore, the accuracy of the max-log approximated LLR degrades under poor channel conditions. As a result, conventional methods suffer from performance degradation owing to error propagation in turbo decoding. Therefore, in this paper, we propose a new LLR clipping method that can be optimally applied to chaos modulation by limiting the confidence level of LLR and suppressing error propagation. For effective clipping on chaos modulation that does not have fixed mappings, the average confidence value is obtained from the extrinsic LLR calculated from the demodulator and decoder, and clipping is performed based on this value, either in the demodulator or the decoder. Numerical results indicated that the proposed method achieves the same performance as the one using the exact LLR, which requires complicated calculations. Furthermore, the security feature of the proposed system is evaluated, and we observe that sufficient security is provided.
A coherent multiple-input multiple-output architecture is proposed for optical wireless communications (OWCs) to mitigate atmospheric turbulence effects. Transmitter optical signals operate at distinct carrier frequen...
详细信息
A coherent multiple-input multiple-output architecture is proposed for optical wireless communications (OWCs) to mitigate atmospheric turbulence effects. Transmitter optical signals operate at distinct carrier frequencies to allow the received optical signals to be separately processed. The accumulated phase noise in each transmission branch can then be independently and electrically compensated. Based on the proposed architecture, several diversity combining techniques are used at the receiver end for system performance evaluation. Three different turbulence models are considered in this paper for different scintillation level ranges, including gamma-gamma turbulence, K-distributed turbulence, and negative exponential turbulence. Closed-form error rate expressions are derived using a series expansion approach. The diversity order in the gamma-gamma turbulence channel is found to depend only on the smaller channel parameter, while the K-distributed and negative exponential turbulence channels are found to have the same diversity order. The presented numerical results demonstrate substantial system performance improvement over single-link coherent OWC.
暂无评论