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The C-RAN architecture has been prevailing in mobile networks for 5G and beyond. Along with the significant increase in the amount of mobile data, network operators must consider the spatio-temporal pattern of traffi c demand due to human mobility and lifestyles. It has been an important problem to efficiently deploy mobile networks avoiding the underutilization of cell capacities in off -peak times. To address this problem, in this paper we propose a concept of an adaptive C-RAN architecture toward the beyond 5G era. The proposed architecture enables flexible reconfi guration of the radio unit (RU) states and movable DU locations considering the changes in demand distribution. The DUs and RUs compose wireless relay fronthaul networks to forward fronthaul streams satisfying the strict latency requirements. This paper also proposes the joint scheduling algorithm to activate RUs, relocate DUs, and determine forwarding paths of fronthaul streams. It was confi rmed with computer simulations that mobile networks can be efficiently reconstructed with the proposed idea by activating/deactivating RUs and relocating/ migrating DUs. [ABSTRACT FROM AUTHOR]

The hidden terminal problem degrades the uplink system throughput of wireless local area network seriously. In this paper, we propose the optimum allocation (OA) scheme of the location-based virtual sector (VS) method, which solves the hidden terminal problem without massive overheads like request-to-send and clear-to-send (RTS/CTS) packets. The VS method forms sectors virtually to make short-distance mobile terminal (MT) groups using MTs’ location information. In the group, all MTs can sense the transmission of all other MTs. In the proposed method, rough time slot control is implemented for intersector control, which does not need a highly functional centralized controller. The proposal OA scheme of the VS method improves the fairness among MTs by optimizing active periods of VS according to the number of MTs in each VS. By computer simulations, we show that the proposed method can increase the system throughput from the RTS/CTS and improve fairness among MTs even in the condition that positioning error is 1/10 of cell radius. [ABSTRACT FROM AUTHOR]

Equal allocation of bandwidth and/or power may not be efficient for wireless multi-user networks with limited bandwidth and power resources. Optimal joint bandwidth and power allocation strategies for wireless multi-user networks with and without relaying are proposed in this paper for 1) the maximization of the sum capacity of all users; 2) the maximization of the worst user capacity; and 3) the minimization of the total power consumption of all users. It is shown that the proposed allocation problems are convex and, therefore, can be solved efficiently. Moreover, joint bandwidth and power allocation for admission control is considered. A suboptimal greedy search algorithm is developed to solve the admission control problem efficiently. Instructive analysis of the greedy search shows that it can achieve good performance, and the condition under which the greedy search is optimal is derived. The formal and in-depth analysis of the greedy search algorithm presented in this paper can serve as a benchmark for analyzing similar algorithms in other applications. The performance improvements offered by the proposed optimal joint bandwidth and power allocation are demonstrated by simulations. The advantages of the suboptimal greedy search algorithm for admission control are also shown in numerical results. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a self-directed adaptive phased array control method using the low-frequency part of the signal for a millimeter-wave wireless personal area network, which can reduce the hardware requirement and power consumption compared with those of the conventional digital beamforming method. The signal from each element antenna of the antenna array is phase shifted and down converted to the baseband and then divided into two paths. The first paths are low-pass filtered to extract the low-frequency part of the signals for beamforming control. The second paths from all antennas are combined in-phase in an analog domain and then sampled by two high-speed A/D converters for demodulation. A beamforming algorithm using the sampled low-frequency part of the signal is also proposed. The beamforming calculation time is established as a function of the signal-to-noise ratio, the bandwidth of the low-frequency part, and the required phase control accuracy. The calculated values match the measured results. Using the IEEE 802.15.3c specifications with an eight-element array antenna, the calculation time is less than \5~\mu\s for initial beam establishment and less than \30~\mu\s for beam tracking. Therefore, high-speed beamforming is possible while reducing the power consumption. [ABSTRACT FROM AUTHOR]

In cognitive networks, primary and secondary users (PUs and SUs) share the radio resource according to fair regulations. The goal of this paper is to introduce a new method to detect an unfair user (freeloader) that hides its radio signal under the noise floor in the presence of an active (either primary or secondary) user. The performance of the proposed technique is evaluated by theoretical analysis and computer simulations. The probability of detection is expressed, for constant false-alarm rates, as a function of both the active signal power and the background noise variance. The results show the effectiveness of the new monitoring algorithm in several operating cases. [ABSTRACT FROM PUBLISHER]

Intercell interference coordination (ICIC) techniques not only help improve cellular data coverage but allow more efficient use of a valuable wireless spectrum as well. This paper investigates soft frequency reuse (SFR), which is a form of ICIC, for long-term evolution (LTE) systems. By analyzing the throughput of the SFR scheme, we find that classifying cell-edge users and cell-center users is critical. Thus, we develop low-complexity decentralized SFR scheduling algorithms that include optimal user classification and balance throughput and fairness among multiusers. We also propose suboptimal methods to reduce computational complexity. Computer simulation demonstrates that gains of the proposed SFR algorithm can improve the fifth percentile user throughput by 26% while maintaining the same cell average throughput, compared with a non-ICIC system. [ABSTRACT FROM PUBLISHER]

Signal detection algorithms providing likelihood information for coded spatial-multiplexing multiple-input–multiple-output (MIMO) wireless communication systems pose a critical design challenge due to their prohibitively high computational complexity. In this paper, we present a low-complexity soft-output detection algorithm by adopting four implementation-friendly algorithm-level improvements to the fixed-complexity sphere decoder. More specifically, we introduce a reliability-dependent tree expansion approach and an on-demand list-size reduction scheme for low-cost candidate list generation. In terms of performance improvement, we apply an early bit-flipping strategy and utilize the \ell^1-norm distance representation. The algorithm is evaluated by computer simulations performed over Rayleigh flat fading channels and computational complexity analysis. Compared with the soft-output K-Best algorithm, the proposed algorithm saves at least 60% of the computations for detecting 4 \times 4 64-quadrature amplitude modulation (QAM) MIMO signal and, at the same time, provides better detection performance, making it a promising detection scheme for real-life hardware implementation. [ABSTRACT FROM PUBLISHER]

The aim of this study is to determine a robust prediction algorithm that can be used to correct the measured specific absorption rate (SAR) in a homogeneous phantom when its complex permittivity deviates from standardized reference values. Results are analyzed over a frequency range of 30-6000 MHz. Both measurements and numerical simulations are presented. Several antenna sizes and distances to the phantom are investigated so as to study a large range of SAR distributions. It is demonstrated that the prediction algorithm, while developed using dipole antennas, also works well for mobile telephone models. Employing the prediction algorithm reduces the SAR measurement uncertainty, thereby improving the reproducibility of SAR compliance assessment between laboratories. Another benefit of the algorithm is that it enables the use of broadband tissue-equivalent liquids, whose dielectric parameters are not currently within the tight tolerances of existing standards. The use of broadband liquids reduces the cost of SAR measurement. The method presented in this paper is of benefit to the IEEE 1528 and IEC 62209 measurement standards. [ABSTRACT FROM AUTHOR]

Finding the positions of nodes in an ad hoc wireless sensor network (WSN) with the use of the incomplete and noisy distance measurements between nodes as well as anchor position information is currently an important and challenging research topic. However, most WSN localization studies have considered that the anchor positions and the signal propagation speed are perfectly known which is not a valid assumption in the underwater and underground scenarios. In this paper, semi-definite programming (SDP) algorithms are devised for node localization in the presence of these uncertainties. The corresponding Cramér-Rao lower bound (CRLB) is also produced. Computer simulations are included to contrast the performance of the proposed algorithms with the conventional SDP method and CRLB. [ABSTRACT FROM AUTHOR]

In order to improve the performance of multicarrier code division multiple access (MC-CDMA) in the uplink channel, quasi-synchronous MC-CDMA with minimum-mean-square-error (MMSE)-based subcarrier-combining method is effective. However, conventional MMSE methods require a lot of pilot symbols for derivation of optimal weights. In this paper, in order to reduce the number of pilot symbols for uplink MC-CDMA systems, we propose a multistage recursive-least-square (MS-RLS) method for the derivation of the weights for the MMSE subcarrier combining. In the MS-RLS, the received symbols are stored in the buffer memory, and the RLS algorithm is repeatedly performed with a multistage structure by using the same pilot symbols. In this method, the weights and the inverse matrices of correlation matrices of the adjacent subcarriers are utilized for the initial values of the next-stage weight updating. Through computer simulation, we confirm that the performance of MC-CDMA in the uplink channel is improved by using the proposed MS-RLS method, even with short pilot symbols. [ABSTRACT FROM AUTHOR]

Mobile positioning has drawn significant attention in recent years. Nonline-of-sight (NLOS) propagation error is the dominant error source in mobile positioning. Most previous research in this area has focused on NLOS identification and mitigation. In this paper, we investigate new positioning algorithms to take advantage of the NLOS propagation paths rather than canceling them. Based on a prior information about the NLOS path, a geometrical approach is proposed to estimate mobile location by using two NLOS paths. On top of this, the least-squares (LS)-based position estimation algorithm is developed to take multiple NLOS paths into account, and its performance in terms of root mean-square error (RMSE) is analyzed. A general LS algorithm considering both LOS and NLOS paths is also derived, and the maximum likelihood-based algorithm is presented to jointly estimate the mobile's and scatterers' positions. The Cramer-Rao lower bound on the RMSE is derived for the benchmark of the performance comparison. The performance of the proposed algorithms is evaluated analytically and is done via computer simulations. Numerical results demonstrate that the derived analytical results closely match the simulated results. [ABSTRACT FROM AUTHOR]

It has been well recognized that significant throughput gains can be leveraged in multiuser wireless communication systems by exploiting multiuser diversity with a smart scheduler. This scheduler collects channel state information (CSI) from all users and allocates the resources to the user(s) experiencing favorable channel conditions. However, for a frequency-division-duplex system with a large number of users, how to efficiently collect the required CSI will be a challenging task, especially when the feedback links are of limited capacity. In this paper, we propose a scheduling algorithm to exploit multiuser diversity with possibly imperfect one-bit channel state feedback. The basic idea is to define a threshold λ and let each user report one-bit information to the scheduler about the comparison between its measured channel fading level and λ. Correspondingly, the scheduler uses these feedback bits to classify all users into two sets and assigns the channel to one user belonging to the set experiencing favorable channel conditions. Several implementation schemes are developed by attacking the optimization of λ under different system configurations, covering both the case when the one-bit feedback is perfect and those when the one-bit feedback is imperfect. Computer simulations show that when the user number is large, say, more than ten users, the proposed scheduling supports significantly larger data rate over the round-robin scheduling, while in comparison with the optimum scheduling with complete CSI, the performance loss is limited if the one-bit feedback is of high reliability. In addition, our studies show that we can effectively enhance the robustness against feedback imperfectness by incorporating the feedback reliability into optimization of λ. [ABSTRACT FROM AUTHOR]

Recently, ultra wide-band (UWB) wireless communication technology, which provides high data transmission rates and is capable of linearly trading off between throughput and signal-to-noise ratio (SNR), has drawn much attention for short-range wireless networks. To fully exploit its desirable features and to minimize its interference with coexisting other systems requires knowledge of the SNRs at the receivers. In this paper, we propose an algorithm for estimating the pulse energy-to-noise ratio of an UWB signal through utilization of output samples from a correlator in the receiver and evaluate the performance of the proposed algorithm through computer simulation. A notable feature of the proposed algorithm is that it does not affect the effective throughput because the estimation process does not require any additional specific training signals. [ABSTRACT FROM AUTHOR]

A novel full rate space-time turbo trellis code, referred to as an assembled space-time turbo trellis code (ASTTTC), is presented in this paper. For this scheme, input information binary sequences are first encoded using two parallel concatenated convolutional encoders. The encoder outputs are split into four parallel streams and each of them is modulated by a QPSK modulator. The modulated symbols are assembled by a predefined linear function rather than punctured as in the standard schemes. This results in a lower code rate and a higher coding gain over time-varying fading channels. An extended two-dimensional (2-D) log-MAP (maximum a posteriori probability) decoding algorithm, which simultaneously calculates two a posteriori probabilities (APP), is developed to decode the proposed scheme. Simulation results show that, under the same conditions, the proposed code considerably outperforms the conventional space-time turbo codes over time-varying fading channels. [ABSTRACT FROM AUTHOR]

This paper presents a reduced-complexity soft-input soft-output detection scheme, called iterative tree search detection for multiple-input multiple-output wireless communication systems employing turbo processing at the receiver. In this scheme, a reduced search space is selected with the aid of the M-algorithm, and QAM signal constellations with block partitionable labels are independent of the modulation order, as well as asymptotically linear in the number of transmit antennas. Results from computer simulations are presented which demonstrate the capability of the scheme to approach optimal performance at considerable reduced complexity. [ABSTRACT FROM AUTHOR]

Due to the use of variable length code (VLC), a single bit error in the discrete cosine transform (DCT)-based coded bit stream, such as 11.263, may propagate up to the end of the group of blocks (GOBs) or slice. In this paper, we propose an iterative error detection and correction algorithm for the slice mode of the H.263 bit stream. The visibly erroneous macroblocks (MBs) in the decoded frames are detected by checking a set of error detection conditions derived from the redundant information (such as neigh- boring MBs and inner-DC I block similarity measure) inherent within the frame. In each slice, the part of the bit stream before the first erroneous MB is decoded in the conventional manner. The remaining part after this MB is redecoded iteratively, skipping one bit at a time until a decodable subbit stream is found. In case an MB is nondecodable, it is replaced with gray level. Once all the slices are checked, the frame is reconstructed and again checked for erroneous MBs. This process is repeated until the decoder detects no more corrupted MB. The proposed step-by-step decoding technique limits the error into a few MBs only, which can easily be concealed by any error concealment technique. The simulation results demonstrate that our scheme can recover the corrupted frames under the bit error rates up to 1 % over binary symmetric channel (BSC), and improve the concealed picture quality by 4-6 dB over the conventional methods. [ABSTRACT FROM AUTHOR]

This paper proposes a two-phase hybrid algorithm for optimal placement of radioports. The placement strategy minimizes the dynamic range of the channel, and thus reduces the peak transmit power needed by a wireless handset. The performance of the proposed algorithm is compared with that of an exhaustive search, as well as with that of a simplex algorithm. Simulation results show that the two-phase hybrid algorithm, although suboptimal, outperforms the simplex algorithm with only a modest increase in computation time. It has the added advantage of being quite insensitive to the seed solution. [ABSTRACT FROM AUTHOR]

In this paper, the use of a crossed-dipole array is proposed in joint space-time channel estimation for asynchronous multipath direct sequence code division multiple access (DS-CDMA) systems. The polarization diversity offered by such an array, unlike linearly polarized arrays, is able to detect and estimate any arbitrary completely polarized signal path. By utilizing the polarization information inherent in the received signal to construct the polar-spatio-temporal array (polar-STAR) manifold vector, the accuracy and resolution of the polar-STAR parameters' estimation are significantly improved, and its signal detection capability is enhanced. To alleviate the need for a multidimensional search in the polarization space, a computationally efficient joint polarization-angle-delay channel parameter estimation algorithm is proposed for a "desired user" that operates in an asynchronous multiuser and multipath environment. The proposed algorithm, which can be seen as an application of MUSIC-type techniques, is based on combining a two-dimensional STAR-Subspace type technique with a set of analytical equations and is supported by representative examples and computer simulation studies. [ABSTRACT FROM AUTHOR]

In this paper, we propose a power-efficient and QoS (Quality of Service) -aware MAC (Medium Access Control) scheduling algorithm for Bluetooth scatternet. If the inter-piconet scheduler in a bridge node between piconets operates simply by the Round Robin (RR) policy, a number of time slots may be wasted due to the guard time for piconet switching and the exchange of POLL-NULL packets. To overcome the link wastage problem in Bluetooth scatternet scheduling, several algorithms have recently been proposed. Although they can provide all of the links of a bridge node with fair service opportunities, they may cause waste of wireless resources since different Bluetooth devices may have various traffic characteristics. In addition, since Bluetooth devices are often required to operate under limited battery capacity, the number of unnecessary piconet switching has to be minimized for the power-efficient operation of a Bluetooth scatternet. Therefore, we propose a mechanism to support the power-efficient operation of a Bluetooth scatternet while guaranteeing various QoS requirements of Bluetooth devices. The proposed algorithm is compliant with the current Bluetooth specification, and we demonstrate its improved performance via simulations. [ABSTRACT FROM AUTHOR]