Uplink System Research Articles

User Selection Criteria for Uplink Spatial Multiplexing MIMO Systems

We study in this paper multiuser uplink scheduling algorithms for Multiple-Input Multiple-Output (MIMO) systems, where the multiusers compete for the MIMO Channel and the scheduler selects one user at a time based on a certain criterion. Then the selected user spatially multiplexes his data over the transmit antennas. This spatial multiplexing (SM) scheme provides high data rates while the multiuser diversity obtained from scheduling improves the performance of the uplink system. At the receiver, the Vertical-Bell-Labs LAyered Space Time architecture (V-BLAST) is used to detect the information layers. The main contribution of this paper is proposing and comparing the performance of several scheduling criteria for MIMO uplink scheduling. In addition, novel V-BLAST capacity bounds based on random matrix theory is presented. Furthermore, we investigate suboptimal schedulers and compare their performance. The main results of this study show that the scheduler that maximizes the optimal MIMO capacity doesn't work well for a V-BLAST system. Instead, the optimal scheduler that maximizes the V-BLAST capacity is derived and analyzed. In addition, we look into scheduling for SM with sphere decoding and we find that in this case, using MIMO capacity as the scheduling criterion performs the best.

On-body calibration and processing for a combination of two radio-frequency personal exposimeters.

Two radio-frequency personal exposimeters (PEMs) worn on both hips are calibrated on a subject in an anechoic chamber. The PEMs' response and crosstalk are determined for realistically polarised incident electric fields using this calibration. The 50 % confidence interval of the PEMs' response is reduced (2.6 dB on average) when averaged over both PEMs. A significant crosstalk (up to a ratio of 1.2) is measured, indicating that PEM measurements can be obfuscated by crosstalk. Simultaneous measurements with two PEMs are carried out in Ghent, Belgium. The highest exposure is measured for Global System for Mobile Communication downlink (0.052 mW m(-2) on average), while the lowest exposure is found for Universal Mobile Telecommunications System uplink (0.061 μW m(-2) on average). The authors recommend the use of a combination of multiple PEMs and, considering the multivariate data, to provide the mean vector and the covariance matrix next to the commonly listed univariate summary statistics, in future PEM studies.

Asymptotic and Non-Asymptotic Analysis of Uplink Sum Rate for Relay-Assisted MIMO Cellular Systems

We consider uplink relay-assisted MIMO cellular systems with multiple relays deployed in each cell that perform the amplify-and-forward operations. We are interested in obtaining deterministic expressions for the ergodic sum rate of such systems. We first consider the large MIMO dimension scenario, and obtain two asymptotic sum rate expressions, corresponding to the cases of fixed number of users and large number of users, respectively. We then consider the case of arbitrary MIMO dimension and large number of users, and obtain an upper and lower bound that the sum rate lies in between with high probability. The bounds are tight when the number of users is large. Both single-cell and multi-cell systems are considered, where the latter assumes full base station cooperation. Numerical experiments show that these deterministic sum rate expressions match well with the Monte Carlo simulation results. Therefore they can be useful tools for the design and analysis of relay-assisted MIMO cellular systems.

Carrier frequency offset estimation for OFDMA uplink using null sub-carriers

Carrier synchronization in OFDMA uplink systems comprises estimation and compensation of carrier frequency offsets (CFOs) corresponding to different users. We propose a null sub-carrier-based CFO estimation algorithm for OFDMA uplink systems, employing generalized or sub-band sub-carrier allocation scheme. We analyze the effect of location and number of null sub-carriers on the performance of the algorithm, in the presence of multi-user interference (MUI) and channel frequency selectivity. We calculate the acquisition range of the proposed estimation algorithm and prove that the identifiability of CFO estimation is guaranteed in the presence of MUI and channel nulls. We also evaluate the computational complexity and the performance of the proposed estimation algorithm and, compare it with some of the existing approaches in the literature.

ESTIMATION AND DESIGN OF MC-DS-CDMA FOR HYBRID CONCATENATED CODING IN HIGH SPEED VEHICULAR COMMUNICATION

The design of Multi Carrier Direct Sequence Code Division Multiple Access (MC-DS-CDMA) structure which generalizes serial and parallel concatenated code is investigated to this project. This model is ideal for designing various codes in the performance of both error floor and water floor region. We propose a concatenated code for transmitter block which is used for multi carrier direct sequence CDMA technique. Simulation results of MC-DS-CDMA uplink system using Cadence software shows the various parameters such as memory, Execution time and number of transient steps required for the Execution of MC-DS-CDMA uplink system was estimated and also power consumed was determined for each block in the transmitter. An improved concatenated code model is used for uplink mobile communication. Further system performance improvements can be obtained by concatenating inner code and outer code and the results of computer simulations demonstrate that the performance of the concatenated code was investigated.

Relay Selection and Subcarrier-Pair Based Energy-Efficient Resource Allocation for Multirelay Cooperative OFDMA Networks

Energy-efficient resource allocation is investigated for a relay-based multiuser cooperation orthogonal frequency division multiple access (OFDMA) uplink system with amplify-and-forward (AF) protocol for all relays. The objective is to maximize the total energy efficiency (EE) of the uplink system with consideration of some practical limitations, such as the individual power constraint for the users and relays and the quality of service (QoS) for every user. We formulate an energy-efficient resource allocation problem that seeks joint optimization of subcarrier pairing, relay selection, subcarrier assignment, and power allocation. Unlike previous optimization throughput models, we transform the considered EE problem in fractional form into an equivalent optimal problem in subtractive form, which is solved by using dual decomposition and subgradient methods. To reduce computation costs, we propose two low-complexity suboptimal schemes. Numerical studies are conducted to evaluate the EE of the proposed algorithms.

大规模天线系统中MRC解码法的性能分析

研究基于大规模天线上行系统，对接收端采用最大比合并(MRC)解码法的成对错误概率(PEP)进行了分析。假定信道慢平坦衰落，基站已知信道状态信息。第一，介绍了MRC解码器的解码方法；第二，基于此方法，推导了系统的PEP公式；第三，针对两种不同情况推导出PEP的渐近趋势。分析表明：1) 当天线数固定时，信噪比趋于无穷大所得到的PEP不为零；2) 当信噪比固定时，天线数趋于无穷大时PEP降为零。最后，讨论了能量尺度律(power scale law)。数值仿真证实了上述结论的正确性。Based on a massive multiple-input, multiple-output (MIMO) uplink system, the pair-wise error probability (PEP) of the maximal ratio combining (MRC) decoder on the receiver is analyzed. The channel is assumed to be slow flat fading, and the base station (BS) knows the instant channel state information. Firstly, the MRC decoder is defined for the system. Secondly, a formula calculating the PEP of the system with the decoder is derived. Thirdly, asymptotic analyses of the PEP based on two different situations are given. These analyses reveal facts: 1) The PEP cannot go to zero even when signal-to-noise (SNR) goes to infinity; 2) The PEP goes to zero when the number of antennas at BS is increased to infinity and SNR is fixed. Finally, power scale law on PEP is discussed. Numerical simulations firm the above conclusions.

基于FPGA的LTE系统信道估计算法 研究与设计

本论文从实现的角度对LTE系统信道估计算法进行了研究，对LS、MMSE等常用的信道估计算法进行了分析和MATLAB仿真；详细介绍了采用数字化后的MMSE算法实现的信道估计器电路结构，依照3GPP物理层标准，实现了基于FPGA的TD-LTE系统上行的信道估计算法电路。仿真结果表明，所提出的数字化MMSE算法模型系统在系统复杂度和信道估计效果上都较为优化。 From the point of view of implementation, channel estimation of LTE uplink is studied in the paper. Firstly, LS, MMSE and other commonly used channel estimation algorithm are analyzed and simulated by MATLAB. Secondly, channel estimator circuit structure adopting digital MMSE algorithm is described in detail. Then, in accordance with the 3GPP physical layer standards, based on FPGA, digital channel estimation algorithm of TD-LTE uplink system is implemented. The simulation results illustrate that the digital MMSE algorithm model system is optimal in both the complexity of the system and channel estimation effect.

PAPR reduction in mobile WiMAX: a novel DST precoding based random interleaved OFDMA uplink system

Mobile WiMAX is a 3rd generation broadband wireless technology that enables the convergence of mobile and fixed broadband networks through a wide area radio-access. Since January 2007, the IEEE 802.16 working group has been developing a new amendment the IEEE 802.16 standard i.e. IEEE 802.16 m as an advanced air interface to meet the requirements of ITU-R/IMT-Advanced for 4G systems. The mobile WiMAX air interface adopts orthogonal frequency division multiple access (OFDMA) as multiple access technique for its uplink and downlink to improve signal performance affected by multipath distortion. All OFDMA based networks, including mobile WiMAX, experience the problem of high peak-to-average power ratio (PAPR). This paper presents a discrete-sine-transform precoding technique based random-interleaved OFDMA (RI-OFDMA) uplink system for PAPR reduction in mobile WiMAX. The PAPR of proposed system is analyzed with root-raised-cosine pulse shaping filter to keep out of band radiation low and to fulfill the spectrum mask requirements. Simulation results show that, the proposed system has low PAPR compared to the Hadamard transform precoded RI-OFDMA uplink systems and the conventional RI-OFDMA uplink systems.

Channel interpolation for LTE uplink systems with high mobility using Slepian sequences

Single Carrier Frequency Division Multiple Access (SC-FDMA) has been adopted for 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) uplink communication since it combines the low peak to average power ratio feature of single-carrier transmission systems with the multipath resistance and flexible frequency allocation of orthogonal frequency-division multiple access (OFDMA). Unfortunately, SC-FDMA transmission over time-varying multipath fading channels for very high speed environments the subcarrier orthogonality is destroyed giving rise to intercarrier interference (ICI) due to channel variation within an SC-FDMA symbol. This paper is, therefore, focused on the use of time-domain channel interpolator for LTE uplink systems in large Doppler spread scenarios to improve channel tracking performance. The resulting interpolation algorithm is based on the discrete prolate spheroidal wave functions (DPSWF) which is particularly well suited to represent the rapidly time-varying fading channel due to optimum finite time and frequency support feature. The variations of the channel taps are tracked first by a Kalman filter in time domain during training symbols. Then, a DPSWF based channel interpolator is applied to recover the time variation of channel taps between training symbols within two consecutive slots in a single subframe. The performance of the proposed interpolator is compared with a polynomial interpolator whose order is adjusted adaptively to achieve the best fit under particular user mobilities. Moreover, the analytical mean square error (MSE) performance of DPSWF is derived and compared with the simulations. The results show that the DPSWF represents the time-varying fading channel very effectively and the proposed algorithm has excellent channel estimation performance in high SNR even with a very small number of channel interpolation parameters employed in the algorithm.

A simple blind CFO estimate technique for a QO-STBC based MC-CDMA uplink system

We propose a simple technique for estimating the carrier frequency offset (CFO) of a quasi-orthogonal space–time block coding (QO-STBC) multicarrier code-division multiple-access (MC-CDMA) uplink system without the knowledge of channel state information in a multipath fading channel. Based on the intrinsic properties of the considered system, a useful multiply constrained minimum output energy (MCMOE) receiver is developed, and the CFO estimate is achieved by using a one-dimensional linear search, whose objective is to maximize the output power of the developed receiver. In addition, an alternative based on the Taylor series expansion technique is designed to avoid the exhaustive search. By feeding the CFO-compensated data back to the input of the MCMOE receiver, we use an iterative approach to further enhance the estimatorʼs performance. Numerical results have been conducted to demonstrate that the proposed CFO estimator provides an accurate estimate within a few times of iteration.

Multiuser MIMO Transceiver Design for Uplink and Downlink with Imperfect CSI

This paper considers a joint linear transmitter and receiver design for multi-user multiple-input multiple-output (MU-MIMO) systems using total mean square error (TMSE) criterion, subject to a total transmit power constraint assuming imperfect channel state information. Both the uplink and downlink MU-MIMO systems, which is employed with improper constellations such as binary phase shift-keying and $$M$$ M -ary amplitude shift-keying are considered. A minimum TMSE design is formulated as a nonconvex optimization problem under a total transmit power constraint and the closed-form optimum linear precoder and decoder for both the downlink and uplink MU-MIMO systems with improper modulation are determined by solving this nonconvex optimization problem. A novel contribution in this paper is to derive a closed-form optimum linear precoder and decoder for both the downlink and uplink MU-MIMO systems with improper modulation by solving the nonconvex optimization problem under total power constraint. The simulation results show that the performance of the proposed design is improved over the previous design.

유도탄 원격통제를 위한 대역확산 상향링크 시스템 개발

본 논문은 비행중인 유도탄을 원격으로 통제하기 위한 대역확산 방식의 무선통신 상향링크 개발에 대하여 기술하였다. 낮은 피탐성과 높은 항재밍 능력을 갖으며 비행체의 초고속 이동 및 페이딩에 의한 위상 또는 주파수 옵셋으로 인한 성능열화를 최소화하기 위해 대역확산 부분 DBPSK 변조방식을 사용하였으며 통신지연시간을 줄이기 위해 고속 디지털신호처리 알고리즘을 설계하였다. 또한 통신채널 장애의 주요 원인이 되는 멀티패스 간섭을 최소화하기 위해 복수의 수신안테나를 사용하여 선택적 다이버시티를 구현하였으며 추가적으로 터보코드를 에러정정부호로 사용하여 양질의 데이터를 수신할 수 있도록 개발하였고 비행시험을 통하여 성능을 확인하였다.

Improved Performance of Mean Greedy Algorithm for Chunk Allocation in SC-FDMA Uplink Systems using Joint-User and Chunk-Based Allocation

In this paper, the problem of subcarrier allocation on chunk-by-chunk basis in SC-FDMA uplink systems is investigated. Improved mean enhanced greedy algorithms are proposed for performing joint-user and chunk-based allocation at each transmission time interval. Selection criteria based on spectral efficiency and fairness are also proposed to choose the final allocation at each transmission time interval. Simulation results show that when the number of users and the velocity of the users were varied, the improved algorithms that use selection criteria based on spectral efficiency and fairness could outperform the existing mean greedy algorithms that employ user-based allocation in terms of spectral efficiency and fairness. Moreover, the improved algorithms not only showed better performance but also had the same time complexity as the existing mean greedy algorithms.

An Iterative CFO Estimation Using MVDR Criterion for Interleaved OFDMA Uplink Systems

This letter presents an iterative carrier frequency offset (CFO) estimator based on the minimum variance distortionless response criterion for interleaved orthogonal frequency division multiple access uplink systems, without using specific training sequences. The proposed estimator iteratively searches for the correct CFO vector by minimizing the objective function using a first-order Taylor series approximation of the CFO vector with the one initially given. However, the proposed estimator is not only can estimate CFO, but also has less computational load. Several computer simulation results are provided for illustrating the effectiveness of the blind estimate approach.

Relay Selection and Resource Allocation for Multi-User Cooperative OFDMA Networks

The resource allocation problem is investigated for relay-based multi-user cooperative Orthogonal Frequency Division Multiple Access (OFDMA) uplink system, considering heterogeneous services. A quality of service (QoS) aware optimal relay selection, power allocation and subcarrier assignment scheme under a total power constraint is proposed. The relay selection, power allocation and subcarrier assignment problem is formulated as a joint optimization problem with the objective of maximizing the system throughput, which is solved by means of a two level dual decomposition and subgradient method. To further reduce the computational cost, two low-complexity suboptimal schemes are also proposed. The performance of the proposed schemes is demonstrated through computer simulations based on LTE-A network. Numerical results show that the proposed schemes support heterogeneous services while guaranteeing each user's QoS requirements with slight total system throughput degradation.

Uplink Resource Management for Multiuser OFDM Video Transmission Systems: Analysis and Algorithm Design

We consider a multiuser OFDM system in which users want to transmit videos via a base station. The base station knows the channel state information (CSI) as well as the rate distortion (RD) information of the video streams and tries to allocate power and spectrum resources to the users according to both physical layer CSI and application layer RD information. We derive and analyze a condition for the optimal resource allocation solution in a continuous frequency response setting. The optimality condition for this cross layer optimization scenario is similar to the equal slope condition for conventional video multiplexing resource allocation. Based on our analysis, we design an iterative subcarrier assignment and power allocation algorithm for an uplink system, and provide numerical performance analysis with different numbers of users. Comparing to systems with either only physical layer or only application layer information available at the base station, our results show that the user capacity and the video PSNR performance can be increased significantly by using cross layer design. Bit-level simulations which take into account the imperfection of the video coding rate control, the variation of RD curve fitting, as well as channel errors, are presented.

Generalised grouped minimum mean‐squared error‐based multi‐stage interference cancellation scheme for orthogonal frequency division multiple access uplink systems with carrier frequency offsets

In uplink orthogonal frequency division multiple access (OFDMA) systems with carrier frequency offsets (CFOs), there always be a dilemma that high performance and low complexity cannot be obtained simultaneously. In this study, in order to achieve better trade-off between performance and complexity, the authors propose a grouped minimum mean squared error (G-MMSE)-based multi-stage interference cancellation (MIC) scheme. The first stage of the proposed scheme is a G-MMSE detector, where the signal is detected group by group using banks of partial MMSE filters. The signal group can be either user based or subcarrier based. Multiple novel interference cancellation (IC) units are serially concatenated with the G-MMSE detector. Reusing the filters in the G-MMSE detector significantly reduces the computational complexity in the subsequent IC units as shown by the complexity analysis. The performance of the proposed G-MMSE-MIC schemes are evaluated by theoretical analysis and simulation. The results show that the proposed schemes outperform other existing schemes with considerably low complexity.

On the PAPR Reduction in LTE-Advanced: Precoding-Based SLM–LOFDMA Uplink Systems

Peak-to-average power ratio (PAPR) reduction is still a major challenge in the orthogonal frequency division multiple-access (OFDMA) uplink systems. The sub-carrier mapping in OFDMA can be done in two modes, clustered or localized mode and distributed mode. The localized mode is more appropriate for the practical implementations than the distributed mode due to its low sensitivity against the imperfect power control, phase noise and inter-carrier interference. In this paper, we present two precoding-based PAPR reduction techniques: Zadoff–chu and generalized chirp-like precoding-based techniques for localized OFDMA uplink systems, respectively, for the upcoming 3 GPP long-term evolution-advanced standard. In addition, the traditional selected mapping (SLM) PAPR reduction technique is implemented with the proposed systems to reduce more PAPR. At clip rate of 10−3, computer simulation results show that the precoding-based PAPR reduction techniques can reduce the PAPR up to 6.5 dB and precoding-based SLM techniques can further reduce the PAPR up to 4.4 dB, respectively, with user sub-carriers M = 16 and system sub-carriers N = 64, for the QPSK modulation. The symbol-error rate performance of the proposed systems is also better than the conventional OFDMA uplink systems and the WHT-based systems.

Resource Allocation Method of Device-to-Device Communication

In this paper, we study D2D (Device-to-Device) communication underlying LTE-Advanced uplink system. Since D2D communication reuses uplink resources with cellular communication in this scenario, it’s hard to avoid the inference between D2D users and cellular users. If there is no restriction for D2D communication on using the whole uplink frequency band, it will have a strong negative impact on cellular communication. In order to overcome this shortage, we propose a resource allocation method that D2D users and cellular users use orthogonal frequency resources. This method will effectively reduce the inference between both kinds of communication. However, an obvious disadvantage of this method is no effective use of uplink resources. Based on this, we propose an optimized resource allocation method that a specific cellular user will be chosen to reuse the RBs (Resource Block) of D2D users. These ideas will be taken into system-level simulation, and from the results of simulation we can see that the optimized method has the ability to improve overall system performance and limit inference for cell-edge users.