Amount Of Feedback Information Research Articles

Limited Feedback-Based User Clustering for Non-Orthogonal Multiple Access in mmWave Systems

Non-orthogonal multiple access (NOMA) and mmWave are considered to be promising techniques for 5G and beyond cellular network communication systems. While the mmWave band provides a very wide under-utilized bandwidth, NOMA enhances the spectral efficiency compared to orthogonal multiple access (OMA). The combination of these two techniques could be considered as the key solution to the high required data rates in next-generation communication systems. The implementation of NOMA is studied and verified under an ideal condition with perfect knowledge of the channel state information (CSI) at the base station (BS). However, under the practical conditions, the fluctuation of the wireless channel makes perfect CSI unachievable at the BS. Hence, we proposed to use the angle of departure (AoD) as feedback information from UEs to the BS. We assume that, mobile users (UEs) perfectly estimate the channel by detecting the pilot signals. Then, UEs quantize the AoD and feed back to the BS. Finally, the BS uses the AoD to perform user clustering, power allocation and beamforming. To reduce the feedback overhead further, we proposed a user clustering algorithm which uses one-bit feedback to determine the change of the AoD. Numerical results demonstrate that the proposed NOMA system outperforms the conventional orthogonal multiple-access (OMA) system with the same amount of feedback information.

Exploring the Solution of Bionic Prosthesis Lacking Perceptual Feedback System: Using Invasive and Non-invasive Techniques

The bionic prosthesis is a more advanced research direction in the prosthesis, but there are still many shortcomings. One of them is the lack of an effective perceptual feedback system, which included the feedback of position, force, texture, roughness, temperature, and other environmental information, as well as the information perception ability of the prosthesis itself[1]. This defect limits the normal operation of the prosthesis and endanger the safety of users. By analyzing the sensory feedback mechanism of the human body, it is found in this paper, the main reason for the lack of an effective perceptual feedback system of the bionic prosthesis is that there is no structure connected with the internal nerves of the human body in the mechanical prosthesis. Therefore, the perceptual signals collected by artificial sensors cannot be transmitted to the cerebral cortex by invasive method, or lack specific in vitro devices to stimulate patients to produce specific perceptual feedback by non-invasive methods. At present, through the use of invasive and non-invasive technology, we have mastered the form of electrical stimulation, vibration stimulation, and other forms of perceptual feedback. Due to the larger amount of feedback information, shorter training time than other methods, non-invasive electrical stimulation feedback has become a promising research area in this field.

Adaptive Perturbation-Aided Opportunistic Hybrid Beamforming for mmWave Systems

In this paper, we propose an adaptive perturbation-aided opportunistic hybrid beamforming (AP-OHBF) scheme for temporally correlated millimeter wave (mmWave) channels. The basic idea is that the proposed scheme perturbs the channel parameters to track the channels of the scheduled mobile stations (MSs), whose channels are in favorable conditions, based on only the signal-to-interference-plus-noise ratio (SINR) information of MSs. Specifically, in each time slot, the proposed scheme makes random perturbations to the “best” known channel parameters in the memory, which corresponds to the maximum sum scheduling metric. Then the base station (BS) constructs the channel estimates from these parameters, which are subsequently used to generate the precoders. For data transmission, the BS adopts the successful perturbation, which achieves performance improvements. By contrast, if a perturbation results in performance degradation, it is discarded, whereas the precoders corresponding to the best-known parameters in the memory are instead used for transmission. Simulation results show that in mmWave channels, the proposed AP-OHBF scheme significantly improves the system throughput with respect to the conventional opportunistic beamforming schemes for the same amount of feedback information.

Hardware Implementation of the Joint Precoding Sub-System and MIMO Detection Preprocessor in IEEE 802.11n/ac WLAN

The compressed beamforming weights feedback is used in the MIMO-OFDM IEEE 802.11n/ac WLAN to reduce the amount of feedback information. The precoded sub-system at the receiver side of this system needs to perform singular value decomposition (SVD) on the estimated channel matrices at all sub-carriers, and to quantize the angles representing the right singular vectors to be fed back to the transmitter. Under the exemplary scenario of four antennas at the access point and two antennas at the station, our designed architecture for the precoding sub-system can compute the quantized angles fast enough to meet the requirement of the 80 MHz bandwidth transmission for the IEEE 802.11n/ac standard. Furthermore, by taking advantage of the SVD outputs, we demonstrate algorithmic complexity reduction for computing the preprocessing QRD for the tree search detectors. Surprisingly, although additional function to provide preprocessing QRD for future signal detection, our architecture for computing both SVD and QRD requires approximately the same amount of gates as one earlier architecture to compute the SVD only.

Power efficient 2 × 1 space–time block code system with antenna shuffling

A transmit antenna shuffling method is proposed for a power efficient 2 × 1 space–time block code (STBC) system. Unlike a conventional STBC system that has identical power amplifiers (PAs), an asymmetric STBC (A-STBC) transmitter considered in this Letter has two asymmetric PAs, i.e. low-power and high-PAs. Considering the asymmetric PAs, the authors propose an antenna shuffling method with 1-bit feedback to improve the power efficiency (PE) of the STBC system. Numerical results verify that the proposed A-STBC system with 1-bit feedback antenna shuffling achieves a better PE-and-rate tradeoff and the potential ability of the small amount of feedback information for the power efficient systems.

Decision dynamics of departure times: Experiments and modeling

A fundamental problem in traffic science is to understand user-choice behaviors that account for the emergence of complex traffic phenomena. Despite much effort devoted to theoretically exploring departure time choice behaviors, relatively large-scale and systematic experimental tests of theoretical predictions are still lacking. In this paper, we aim to offer a more comprehensive understanding of departure time choice behaviors in terms of a series of laboratory experiments under different traffic conditions and feedback information provided to commuters. In the experiment, the number of recruited players is much larger than the number of choices to better mimic the real scenario, in which a large number of commuters will depart simultaneously in a relatively small time window. Sufficient numbers of rounds are conducted to ensure the convergence of collective behavior. Experimental results demonstrate that collective behavior is close to the user equilibrium, regardless of different scales and traffic conditions. Moreover, the amount of feedback information has a negligible influence on collective behavior but has a relatively stronger effect on individual choice behaviors. Reinforcement learning and Fermi learning models are built to reproduce the experimental results and uncover the underlying mechanism. Simulation results are in good agreement with the experimentally observed collective behaviors.

Joint Lattice-Reduction-Aided Precoder Design for Multiuser MIMO Relay System

Lattice reduction (LR) has been used widely in conventional multiple-input multiple-output (MIMO) systems to enhance the performance. However, LR is hard to be applied to the relay systems which are important but more complicated in the wireless communication theory. This paper introduces a new viewpoint for utilizing LR in multiuser MIMO relay systems. The vector precoding (VP) is designed along with zero force (ZF) criterion and minimum mean square error (MMSE) criterion and enhanced by LR algorithm. This implementable precoder design combines nonlinear processing at the base station (BS) and linear processing at the relay. This precoder is capable of avoiding multiuser interference (MUI) at the mobile stations (MSs) and achieving excellent performance. Moreover, it is shown that the amount of feedback information is much less than that of the singular value decomposition (SVD) design. Simulation results show that the proposed scheme using the complex version of the Lenstra--Lenstra--Lovasz (LLL) algorithm significantly improves system performance.

Improved lattice reduction‐aided linear precoding in MIMO systems with limited feedback

An approach of scaling and shifting constellation for MIMO lattice reduction(LR)-aided precoding is proposed. The proposed scheme is beneficial to improve the performance in terms of both BER and ergodic capacity. The feedback is a Gaussian integer matrix in which the entries are preserved in a region with respect to modulo operation. Then, the amount of feedback information is reduced significantly. Simulation results show that the LR-aided precoding scheme using the improved version of the constellation apparently improves system performance.

8-PSK 성운을 이용하는 이중계층 차분 선부호화 기법의 성능 분석

LTE 및 LTE-A 시스템에서 8-PSK 성운을 알파벳으로 가지는 이중계층 차분 코드북을 제안한다. 인접하는 무선 채널의 시간 상관으로 선부호화 행렬은 천천히 변화하므로, 무선 채널 공간의 전체를 양자화 하지 않고, 시간 상관에 따른 채널 공간의 일부분의 차분 성분만을 양자화하여 피드백을 한다면, 기존과 동일한 크기의 코드북으로도 가상적으로는 코드북이 매우 커지는 효과를 얻을 수 있어 채널 용량이 증가한다. 특히 제안하는 코드북은 LTE release-8의 코드북 설계조건인 8-PSK 성운을 사용하는 동 이득 특성 및 이중 계층 코드북이 단일 계층 코드북을 포함하는 특성을 가지는 새로운 차분 코드북이다. 코드북 내 코드워드들의 인자들이 8-PSK 성운만을 사용하므로, 선부호화 및 복호 시에 계산량이 낮아지는 LTE 코드북의 장점을 그대로 유지할 수 있다. 또한 동 이득 성질은 상대적으로 저렴한 비선형 증폭기를 사용할 수 있는 장점이 있어 가격의 제한을 받는 단말기 설계에는 필수적인 요소이다. 컴퓨터 시뮬레이션을 통한 이중계층 선부호화 기법의 성능 분석에서, 동일한 피드백 비트 수를 갖는 같은 크기의 코드북에서 제안하는 차분 코드북은 정상상태에서 기존 LTE 코드북보다 최소 1.2dB 성능 향상을 보인다. Dual-layer differential codebook using 8-PSK (phase shift keying) constellation as its codeword elements, is proposed for Long term evolution (LTE) and/or LTE-Advanced systems. Due to the temporal correlation of the adjacent channel matrices, the consecutive precoding matrices are likely to be similar. This approach quantize only the differential information of the channel instead of the whole channel subspace, which virtually increase the codebook size to realize more accurate quantization of the channel. Especially, the proposed codebook has the same properties of LTE release-8 codebook that is, constant modulus, complexity reduction, and nested property. The mobile station can be designed by using less expensive non-linear amplifier utilizing constant modulus property. Computer simulations show that the capacity of the proposed dual-layer codebook performs almost 1.2dB better than those of any other non-differential codebooks with the same amount of feedback information.

회전로크 구조의 차분 선부호화 기법의 성능 분석

LTE (long term evolution) 및 LTE-A (LTE-Advanced) 시스템에서는 폐회로 기반의 다중 안테나 기술이 적용되었으며, 최대 비 전송 방식 (maximum ratio transmission, MRT) 보다 성능은 감소되지만, 동 이득 (equal gain) 특성을 유지할 수 있는 동 이득 전송 (equal gain transmission, EGT) 코드북을 채택하고 있다. 본 논문에서는 LTE 및 LTE-A 시스템에서 사용되는 코드북보다 성능을 향상시킬 수 있는 차분 코드북을 제안한다. 특히 동 이득 특성을 그대로 유지하면서 LTE 시스템의 코드북 요구조건을 모두 만족시키는 코드북을 제안한다. 코드북을 구성하는 코드워드들의 인자들 (elements)이 8-PSK(phase-shift keying) 성운 (constellation) 만을 사용하므로, 선부호화 및 복호 시 계산량이 낮아지는 LTE 코드북의 장점을 그대로 유지할 수 있다. 동 이득 성질은 특히 상향 링크에서 첨두 전력 대 평균 전력비 (PAPR)에 상당한 영향을 미치므로 매우 중요하다. 본 논문에서는 각 송신 안테나에 동 이득을 유지하는 성질을 이용한 새로운 차분 코드북을 제안하고, 동작원리를 회전 로크 구조로 설명한다. 컴퓨터 시뮬레이션을 통한 성능 분석에서, 동일한 피드백 비트 수를 갖는 같은 크기의 코드북에서 제안하는 차분 코드북은 기존 LTE 코드북보다 최소 0.9dB 성능 향상을 보인다.

CSI Usage over Parallel Fading Channels under Jamming Attacks: A Game Theory Study

Consider a parallel channel with M independent flat-fading subchannels. There exists a smart jammer which has possession of a copy of perfect channel state information (CSI) measured and sent back by a receiver to its transmitter. Under this model, a class of two-person zero-sum games is investigated where either achievable mutual information rate or Chernoff bound is taken as the underlying pay-off function with the strategy space of each player determined by respective power control and hopping functions. More specifically, we have tackled and answered the following three fundamental questions. The first one is about whether the transmitter and jammer should hop or fully use all degrees of freedom over the entire parallel channels given the full CSI available to both of them, i.e. to hop or not to hop. The second question is about the impact of sending back CSI on system performance considering that the smart jammer can exploit CSI to further enhance its interference effects, i.e. to feedback or not to feedback. The last question is about whether the amount of feedback information can be reduced given the mutual restrictions between transmitter and jammer, i.e. when to feedback and when not to.

CHANNEL FEEDBACK SCHEDULING FOR WIRELESS COMMUNICATIONS

Opportunistic scheduling can significantly improve wireless network performance by exploiting the underlying channel condition. There has been a lot of work on opportunistic scheduling, but the problem of finding the right feedback mechanism to convey channel information has largely been untouched. In emerging multichannel systems, the per-channel feedback induces a substantial amount of feedback overhead and requires high computational complexity. To reduce the feedback overhead, we consider an opportunistic feedback strategy that activates the channel feedback opportunistically according to the channel condition. Then, we combine the opportunistic feedback with the best-n channel feedback scheme where a mobile user chooses the best n channels and transfers this information to the base station. We analyze the throughput and the amount of channel feedback information for proportionally fair opportunistic scheduling under Rayleigh fading i.i.d. channels. The numerical results confirm that our partial feedback schemes achieve a remarkable reduction in the amount of feedback information without significant throughput degradation, thereby saving the scarce wireless bandwidth and limited battery power.

Combination lock-like differential codebook for temporally correlated channels

A novel differential codebook, preserving inherent properties of 3GPP long-term evolution (LTE) codebooks, is proposed for temporally correlated channels. The steady-state achievable throughput performance of the proposed codebook shows at least 0.9 dB of SNR better than that of the conventional LTE codebook with the same amount of feedback information.

Adaptive beamforming with dimension reduction in spatially correlated MISO channels

In this paper, we propose an adaptive beamforming scheme that generates the beam weight using dominant eigenvectors of the spatial covariance matrix. The number of eigenvectors used for the generation of beam weight is determined to maximize the signal-to-noise ratio (SNR) for given feedback constraints (e.g., the amount of feedback information and feedback delay). It is shown that the conventional limited feedback beamforming and eigen-beamforming are special cases of the proposed scheme. Simulation results show that the proposed beamforming scheme can effectively be applied to spatially correlated channels.

Transmit Equal Gain Precoding in Rayleigh Fading Channels

Precoding with limited feedback information can achieve satisfactory performance while the amount of feedback information is kept small. In this paper, we analyze the theoretical performance of equal gain precoder and find that its performance is at most 1.049 dB worse than the optimal precoder no matter how the number of transmit antennas increases. Moreover, we analyze the performance degradation of the equal gain precoder due to scalar quantization theoretically. The result shows that 2-3 bits per transmit antenna (excluding the first antenna) can achieve 0.5-0.25-dB performance gap compared with the same scheme without quantization. Furthermore, we found that the equal gain precoder in general can achieve comparable performance with the Grassmannian precoder in the same moderate feedback bits. Simulation results are provided to corroborate the theoretical results.

Product Development Task Planning Using Worth Flow Analysis

The acceleration of the product development cycle continues to be a significant challenge for manufacturing enterprises around the world. This paper describes a task planning method that minimizes the number of trial and error to reduce the development time for large-scale and complex products at the early stage of product development. The proposed method matches groups of product components and determines the development sequence for each component to minimize the amount of feedback information required across task groups. The method provides, as evaluation indices for task prioritization, the product-sum of engineering interaction among components and worth of each component, which the authors define as the “worth flow.” A generic hair dryer with simple mechanical structure serves as an example, illustrating that the proposed method contributes to the reduction in the amount of information required for setting the interface links by 65% compared with the conventional planning methods.

An Efficient Multimode Quantized Precoding Technique for MIMO Wireless Systems

Multimode quantized precoding (QP) can provide full diversity gain or high capacity gain by adapting the number of substreams, as well as the precoding matrix, according to the instantaneous channel condition with low-rate feedback. Conventional multimode QP (MM-QP), however, does not consider the adaptive rate allocation among substreams; thus, it cannot have the additional gain by adaptive modulation. Furthermore, it is computationally complex since exhaustive matrix inversions are required to determine the optimal mode. In this paper, we propose an efficient MM-QP system that improves the performance of a conventional system in terms of error rate and has a lower computational complexity than the conventional system. First, we define the rate-partitioning vector as the mode and control the rate among substreams and the number of substreams according to the channel instantaneous condition. Second, to reduce the computational complexity for the receiver to determine the optimal mode, the simplified mode-selection technique using estimates of the modal metric is proposed. In the proposed mode-selection technique, the optimal mode can be obtained by several multiplication and division operations. Finally, the mode-reduction technique eliminating the less-frequently used modes is proposed, which leads to a significant reduction of the feedback information with negligible performance loss. In numerical experiments, it was verified that the proposed MM-QP system gives a better error-rate performance than the conventional system, with much less computational complexity for the same amount of feedback information.

Semi-Distributed Resource Allocation Based on Multihop Equilibrium for Cellular OFDM-Relay Networks

A semi-distributed resource allocation scheme based on multihop equilibrium is proposed for OFDM-relay networks. This method aims to reduce the amount of feedback information from the relay nodes (RNs). Moreover, it utilizes radio resource by striking an efficient balance between the capacities of the BS-RN link and RN-MS link. Simulation results show that the proposed semi-distributed scheme achieves good performances in terms of throughputs and fraction of satisfied users.

The Capacity of Downlink Multiuser OFDM with Quality Based CSI Feedback

The capacity of multiuser OFDM systems can be maximized by allocating resources (subcarrier and power) to the user with the highest instantaneous channel gain. This assumes complete channel state information (CSI) at the transmitter, which is achieved by every user reporting its CSI for all subcarriers to the transmitter via feedback channel. In practice, due to the limited capacity of the feedback channel, the completeness of CSI may be severely restricted especially with a large number of users transmitting a large amount of feedback information. In order to reduce the amount of feedback information while preserving the maximal capacity, quality based CSI feedback (QCF) is proposed in this letter. The system capacity is derived with QCF and compared with that of full CSI feedback. The results show that QCF successfully reduces the amount of feedback information with little capacity loss.

Random Beamforming Using Iterative Power Allocation with Small Feedback Information and Low Latency

In this letter, we propose a new power allocation scheme for random unitary beamforming assuming a discrete transmission rate with a small amount of feedback information and low latency. Simulation results show that the proposed scheme can improve throughput compared to the conventional power allocation scheme.