Berna Özbek

Feedback Strategies for Wireless Communication

This book explores the different strategies regarding limited feedback information. The book analyzes the impact of quantization and the delay of CSI on the performance. The author shows the effect of the reduced feedback information and gives an overview about the feedback strategies in the standards. This volume presents theoretical analysis as well as practical algorithms for the required feedback information at the base stations to perform adaptive resource algorithms efficiently and mitigate interference coming from other cells.

Adaptive Reduced Feedback Links for Distributed Power Allocation in Multicell MISO-OFDMA Networks

For multi-antenna Orthogonal Frequency-Division Multiple Access (OFDMA) based multicell networks, the channel state information (CSI) of all users is required to share among base stations in order to perform distributed power allocation. However, the amount of feedback increases with the number of users, base stations, subcarriers and antennas. Therefore, it is important to perform a selection at the user side to reduce the feedback load and the complexity of resource allocation. In this letter, we propose adaptive reduced feedback links by choosing the users based on their approximate signal to interference noise ratio (SINR) and their locations in the cell to satisfy users rate constraints. We illustrate the performance results of reduced feedback links by employing distributed resource allocation with link adaptation.

Hierarchical successive stream selection for heterogeneous network interference

This paper presents a hierarchical stream selection approach to deal with the interference in a heterogeneous network where different cell types are coexisting with each other to increase the sum capacity. Due to the variety of the transmit powers between the macro and small cells, interference levels are different. The proposed solution hierarchically selects the strongest streams of each cell with a contribution to the sum rate, while constructing the streams via singular value decomposition (SVD). In order to reduce the interference, the channel matrices of the remaining streams are projected orthogonally to the virtual transmit channel and virtual receive channel of the selected stream. The performance evaluations are obtained by considering different locations of small cells with respect to the macro cell. It is shown that the proposed method can dynamically select more streams in heterogeneous networks and achieve higher data rates compared to the existing algorithms.

Reduced feedback links for power minimization in distributed multicell OFDMA networks

In the next generation of multicell networks, adaptive resource allocation techniques will play an important role to improve both quality of service and spectral efficiency. In order to employ distributed power allocation for multicell Orthogonal Frequency-Division Multiple Access (OFDMA) networks, the channel state information (CSI) belonging to all users is required to share among base stations. However, the amount of feedback increases with the number of users, base stations and subcarriers. Therefore, it is important to perform a selection at the user side for multicell networks. In this paper, we propose reduced feedback links by choosing the users based on their approximate signal to interference noise ratio (SINR). The performance of the reduced feedback links are illustrated in multicell OFDMA systems.

Improved successive stream selection with quantized channel in heterogeneous networks

This paper focuses on different distortion metrics in order to analyze the influence of the imperfect channel state information (CSI) on the improved successive stream selection algorithm that manages the interference in a heterogeneous network. The presented approach initially selects the streams from the user of the pico cell, continuing with the strongest streams among the remaining streams that increase the sum rate and satisfy the constraint that at least one stream is selected from each user. In order to reduce the interference, the channel matrices of the remaining streams are projected orthogonally to the virtual transmit and receive channels of the selected stream. The impact of the quantization distortion on the precoding and postcoding design is examined. The performance of two distortion metrics which are the Chordal distance and the Euclidean distance are compared for different number of quantization bits. The performance evaluations are obtained by considering different locations of small cells with respect to the macro cell.

Sum capacity maximization in distributed multicell MISO-OFDMA systems with reduced feedback links

In this paper, we examine distributed and fair resource allocation for weighted sum multicell capacity maximization in multi-input single-output (MISO)-Orthogonal Frequency-Division Multiple Access (OFDMA) multicell systems with reduced feedback links. We apply zero forcing (ZF) precoding to reduce interference between the users in the same cell and then propose iterative distributed power allocation algorithm for the users with high signal-to-interference-plus-noise ratio (SINR) to reduce the interference between BSs. In order to perform distributed RA for MISO-OFDMA multicell systems, the channel state information (CSI) of all required links are fed back to all base stations. However, the feedback load increases with the number of users, base stations, subcarriers and antennas. Therefore, we propose a user selection algorithm at the receiver side to reduce the feedback load while providing CSI of the users with high SINR at the BSs. The performance results of the proposed algorithms are illustrated for multicell MISO-OFDMA systems in wireless channels.

Feedback channel designs for fair scheduling in MISO–OFDMA systems

In the next generation of wireless communication, adaptive resource allocation techniques will play an important role to improve quality of service and spectral efficiency. In order to employ adaptive fairness scheduling for multiple-input single-output (MISO) orthogonal frequency-division multiple access (OFDMA), the channel state information (CSI) belonging to all users is required at the base station. However, the amount of feedback increases with the number of users, transmit antennas and subchannels. Therefore, it is important to perform a user selection at the receiver side without cooperation among the users and to quantize the CSI. In this article, the reduced feedback channel designs are examined for MISO–OFDMA systems while providing fairness between the users. In order to reduce the feedback rate, we choose the users considering their norm and orthogonality properties as well as their location in the cell. In order to limit the feedback rate, channel direction information is quantized by designing a specific codebook thanks to the proposed criterion. We obtain an expression to determine the amount of required feedback information for MISO–OFDMA systems to support more than one beam per subchannel for a given number of users, subchannels and transmit antennas. The performance results of the reduced feedback channel designs are evaluated for fair scheduling in wireless channels.

Interference management for multiuser multiantenna OFDMA underlaying device-to-device communications

Underlaying device-to-device (D2D) transmission in cellular wireless systems is one of the promising transmission techniques for fifth generation (5G) and beyond 5G applications. Nevertheless, the interference between the D2D pairs, the interference from cellular users to D2D receivers and the interference that affects the cellular communications should be mitigated to increase the overall system performance. In this paper, we propose interference management techniques for D2D under-laying communications in multiuser multiantenna orthogonal frequency division multiple access (OFDMA) systems. Our goal is to increase the data rate of both the cellular users and D2D pairs by performing interference management in frequency, power and spatial dimensions. The performance evaluations illustrate the effectiveness of the proposed algorithm in terms of average data rate and average transmitted power for both cellular users and D2D pairs.

Dynamic Shared Spectrum Allocation for Underlaying Device-to-Device Communications

This article provides an overview on spectrum sharing in D2D underlaying communications for 5G and beyond 5G applications. Various spectrum sharing algorithms are summarized within a framework of underlaying D2D communications in cellular networks to increase spectrum efficiency. Dynamic spectrum sharing algorithms in the frequency, power, and spatial dimensions are proposed for underlaying D2D communications with both single antenna and multiple antennas at the base station. Performance evaluations show the effectiveness of the proposed algorithms in terms of average data rate per D2D pair.

On stream selection for interference alignment with limited feedback in heterogeneous networks

This paper presents a stream selection based interference alignment approach with imperfect channel state information for heterogeneous networks. The proposed solution constructs stream sequences by selecting only the strongest stream of each user where the first stream of the constructed stream sequences is associated to a pico user. While selecting the streams, the channel matrices of the unselected streams are projected orthogonally to the virtual transmit and receive channels of the selected stream in order to align the interference in the null space of these virtual channels. In addition, the influence of imperfect channel state information on the proposed algorithm is analysed. A bit allocation scheme is given by deriving an upper bound on the rate loss because of quantisation. The simulation results are carried out by considering various scenarios with different locations of pico cells at the cell edge regions of the macro cell. The performance results show that the proposed algorithm with the imperfect channel state information achieves higher performance than the existing algorithms. Copyright