Device-to-device (D2D) communications was initially proposed in cellular networks as a new paradigm for enhancing network performance. The emergence of new applications such as content distribution and location-aware advertisement introduced new user cases for D2D communications in cellular networks. The initial studies showed that D2D communications has advantages such as increased spectral efficiency and reduced communication delay. However, this communication mode introduces complications in terms of interference control overhead and protocols that are still open research problems. The feasibility of D2D communications in Long-Term Evolution Advanced is being studied by academia, industry, and standardization bodies. To date, there are more than 100 papers available on D2D communications in cellular networks, but there is no survey on this field. In this paper, we provide a taxonomy based on the D2D communicating spectrum and review the available literature extensively under the proposed taxonomy. Moreover, we provide new insights into the over-explored and under-explored areas that lead us to identify open research problems of D2D communications in cellular networks.

https://eprints.networks.imdea.org/id/document/2488

A Survey on Device-to-Device Communication in Cellular Networks

Device-to-Device (D2D) communication was initially proposed in cellular networks as a new paradigm to enhance network performance. The emergence of new applications such as content distribution and location-aware advertisement introduced new use-cases for D2D communications in cellular networks. The initial studies showed that D2D communication has advantages such as increased spectral efficiency and reduced communication delay. However, this communication mode introduces complications in terms of interference control overhead and protocols that are still open research problems. The feasibility of D2D communications in LTE-A is being studied by academia, industry, and the standardization bodies. To date, there are more than 100 papers available on D2D communications in cellular networks and, there is no survey on this field. In this article, we provide a taxonomy based on the D2D communicating spectrum and review the available literature extensively under the proposed taxonomy. Moreover, we provide new insights to the over-explored and under-explored areas which lead us to identify open research problems of D2D communication in cellular networks.

Multiuser orthogonal frequency division multiplexing (MU-OFDM) is a promising technique for achieving high downlink capacities in future cellular and wireless local area network (LAN) systems. The sum capacity of MU-OFDM is maximized when each subchannel is assigned to the user with the best channel-to-noise ratio for that subchannel, with power subsequently distributed by water-filling. However, fairness among the users cannot generally be achieved with such a scheme. In this paper, a set of proportional fairness constraints is imposed to assure that each user can achieve a required data rate, as in a system with quality of service guarantees. Since the optimal solution to the constrained fairness problem is extremely computationally complex to obtain, a low-complexity suboptimal algorithm that separates subchannel allocation and power allocation is proposed. In the proposed algorithm, subchannel allocation is first performed by assuming an equal power distribution. An optimal power allocation algorithm then maximizes the sum capacity while maintaining proportional fairness. The proposed algorithm is shown to achieve about 95% of the optimal capacity in a two-user system, while reducing the complexity from exponential to linear in the number of subchannels. It is also shown that with the proposed resource allocation algorithm, the sum capacity is distributed more fairly and flexibly among users than the sum capacity maximization method.

/pdf/adaptive-resource-allocation-in-multiuser-ofdm-systems-with-441ykegom1.pdf

Adaptive resource allocation in multiuser OFDM systems with proportional rate constraints

From the Publisher:
Multi-carrier modulation, in particular orthogonal frequency division multiplexing (OFDM), has been successfully applied to a wide variety of digital communications applications for several years. Although OFDM has been chosen as the physical layer standard for a diversity of important systems, the theory, algorithms, and implementation techniques remain subjects of current interest. 

This book is intended to be a concise summary of the present state of the art of the theory and practice of OFDM technology. This book offers a unified presentation of OFDM theory and high speed and wireless applications. In particular, ADSL, wireless LAN, and digital broadcasting technologies are explained. 

It is hoped that this book will prove valuable both to developers of such systems, and to researchers and graduate students involved in analysis of digital communications, and will remain a valuable summary of the technology, providing an understanding of new advances as well as the present core technology.

/pdf/multi-carrier-digital-communications-theory-and-applications-15x93hdfw3.pdf

Multi-Carrier Digital Communications: Theory and Applications of OFDM

A system based on orthogonal frequency division multiple access (OFDMA) has been developed to deliver mobile broadband data service at data rates comparable to those of wired services, such as DSL and cable modems. We consider the resource allocation problem of assigning a set of subcarriers and determining the number of bits to be transmitted for each subcarrier in OFDMA systems. We compare simplicity, fairness and efficiency of our algorithm with the optimal and proposed suboptimal algorithms for varying values of delay spread, number of users and total power constraint. The results show that the performance of our approach is appealing and can be close to optimal. We also consider another resource allocation scheme in which there is no fixed QoS requirements per symbol but capacity is maximized.

/pdf/qos-aware-adaptive-resource-allocation-techniques-for-fair-4pul09hlcs.pdf

QoS aware adaptive resource allocation techniques for fair scheduling in OFDMA based broadband wireless access systems

Adaptive subcarrier allocation and adaptive modulation for multiuser orthogonal frequency division multiplexing (OFDM) is considered. The optimal subcarrier and bit allocation problems, that have been formulated in Wong et al., (1999), and Rhee et al., (2000), as nonlinear optimizations, are converted into linear ones and solved by integer programming (IP). A suboptimal approach that separately performs subcarrier allocation and bit loading is proposed. It is shown that subcarrier allocation in this approach can be optimized by the linear programming (LP) relaxation of the IP. Comparison through computer simulation indicates that performance of the suboptimal approach can be close to that of the optimal.

/pdf/on-the-use-of-linear-programming-for-dynamic-subchannel-and-rp8cm0mvbr.pdf

On the use of linear programming for dynamic subchannel and bit allocation in multiuser OFDM

An adaptive subcarrier allocation and an adaptive modulation for multiuser orthogonal frequency-division multiplexing (OFDM) are considered. The optimal subcarrier and bit allocation problems, which are previously formulated as nonlinear optimizations, are reformulated into and solved by integer programming (IP). A suboptimal approach that performs subcarrier allocation and bit loading separately is proposed. It is shown that the subcarrier allocation in this approach can be optimized by the linear-programming (LP) relaxation of IP, while the bit loading can be performed in a manner similar to a single-user OFDM. In addition, a heuristic method for solving the LP problem is presented. The LP-based suboptimal and heuristic algorithms are considerably simpler to implement than the optimal IP, plus their performances are close to those of the optimal approach

Use of linear programming for dynamic subcarrier and bit allocation in multiuser OFDM

An apparatus for adaptively modulating/demodulating signals in a multi-input multi-output (MIMO) system having a layered time-space architecture detector and a method thereof is disclosed. The apparatus includes: a bit and power allocation information calculator for deciding an equivalent channel gain in a reverse order of Vertical-Bell laboratories Space Time (V-BLAST) based on MIMO channel information feedbacked from a receiver and determining the number of bits and transmission power to be transmitted to each transmitting antenna by using the equivalent channel gain; and adaptive modulation means for modulating signal of each layer with corresponding modulation method based on the determined number of bits and transmitting power, controlling the transmitting power and transmitting the adaptively modulated signal through each transmitting antenna. The present invention can improve performance without increase of implementation complexity and easily expand to MIMO-OFDM system by adaptively modulating and demodulating signals in reverse order of conventional V-BLAST detection method.

Apparatus and method for adaptively modulating a signal by using a layered time-space detector in MIMO systems

An apparatus and method are provided for estimating a Carrier-to-Interference-and-Noise Ratio (CINR) in a communication system based on Orthogonal Frequency Division Multiplexing (OFDM) or Orthogonal Frequency Division Multiple Access (OFDMA). In the communication system, all base stations boost a power level for a preamble or pilot by B dB. Accordingly, a received signal power level and a received interference level are boosted by B dB, but a noise level is not boosted. Transmission power for a preamble or pilot interval is boosted as compared with that for the data interval. After an interference and noise level is estimated from a preamble or pilot, the interference and noise level estimate of the preamble or pilot is corrected by taking into account a boosting level of the preamble or pilot.

Apparatus and method for estimating a carrier-to-interference-and-noise ratio in a communication system

Adaptive modulation for multiple-input multiple-output (MIMO) systems with zero forcing (ZF) V-BLAST is considered. Motivated by the observation that the detection ordering of the original V-BLAST algorithm, called the forward ordering, is not suitable for adaptive modulation, a new detection ordering for V-BLAST-based adaptive modulation is proposed. This ordering, called the reverse ordering, selects the symbol corresponding to the minimum gain at each iteration, in contrast to the forward ordering which always gives priority to the maximum gain. The advantage of the reverse ordering over the forward ordering is demonstrated through analysis and simulation. It is shown that the reverse ordering can provide about 2 dB gain as compared with the forward ordering and almost comparable to the optimal ordering which is found through an exhaustive search. The V-BLAST based adaptive modulation with reverse ordering performs somewhat worse than the singular value decomposition (SVD) based method [G.G Raleigh et al., March 1998], but the former is shown to be considerably simpler to implement than the latter.

http://ieeexplore.ieee.org/iel5/8574/27185/01207792.pdf

In-Hyoung Kim

Papers

On the use of linear programming for dynamic subchannel and bit allocation in multiuser OFDM

Use of linear programming for dynamic subcarrier and bit allocation in multiuser OFDM

Apparatus and method for adaptively modulating a signal by using a layered time-space detector in MIMO systems

Apparatus and method for estimating a carrier-to-interference-and-noise ratio in a communication system

Adaptive modulation for MIMO systems with V-BLAST detection