In the 5thgeneration of mobile cellular systems, non-orthogonal multiple access (NOMA) is being considered as a potential candidate for uplink (UL) multiple access (MA) in addition to the basic orthogonal multiple access scheme in order to support various usage scenarios including small packet transmissions, support of a massive number of users, and low latency and high reliability services. Since for NOMA, multiple users transmit uplink data packet in the same time and frequency resource, it is difficult to accurately estimate the channel coefficients from reference signals, especially if the reference signal itself suffers from interference from other users. This paper proposes a novel channel estimation algorithm which utilizes iterative interference cancellation operation in a data-aided manner in reference signal. This iterative channel estimation algorithm with data-aided interference cancellation provides improved channel estimation and overall link level performance at NOMA receiver.

In the 5th generation of mobile cellular systems, non-orthogonal multiple access (NOMA) is being considered as a potential candidate for uplink (UL) multiple access (MA) in addition to the basic orthogonal multiple access scheme in order to support various usage scenarios including small packet transmissions, support of a massive number of users , and low latency and high reliability services. In this paper, two simple multiple access schemes, low code rate spreading (LCRS) and short-sequence-based spreading multiple access (SSMA), with corresponding use of advanced receivers, are analyzed, demonstrating system capacity improvements compared to orthogonal multiple access (OMA) scheme. The robustness and gain of non-orthogonal multiple access scheme over orthogonal approaches are maximized when the packet size is small and suitable code rate is guaranteed.

Recently introduced UE types, such as Machine Type Communications (MTC) devices, require extremely efficient power saving mechanisms to operate in harsh situations for a long period with limited charging opportunities. Typical MTC devices, e.g., meters or sensors, access the network very infrequently, once per a few days or even months, but they have to suppress their power consumption as much as possible to survive the period with batteries or internal power sources with limited generation capabilities. During the idle mode in which the activity of UE is minimal, UE has to periodically monitor a control channel, PDCCH, to receive paging messages or identify whether system information is updated. In the LTE/LTE-A nomenclature, such a period is called Discontinuous Reception (DRX) cycle. In this paper, we outline the envisioned gain in power consumption when longer DRX cycle is applied, and explain the procedures to enable longer DRX. We analyze the impact of introducing the feature on the operation of the networks, and provide a guideline to facilitate longer DRX.

Device to device (D2D) communication techniques is one of main themes for the next generation wireless communication techniques. Compared to traditional Wireless Wide Area Network (WAN) communication where all radio links are formed between a user equipment (UE) and a base station (eNB), D2D communication uses a direct link between two different UEs. In the standard organization, 3rd Generation Partnership Project (3GPP), there is an ongoing discussion to adopt the D2D communication in current Long Term Evolution Advanced (LTE-A) system. The main target use cases of the D2D in LTE system comprise public safety using direct communication and commercial services using proximal device discovery. Introduction of the D2D discovery inside LTE-A network bring some impacts to existing cellular operation by the in-bane emission property. This paper provides a promising way to support D2D discovery in LTE-A system and analyze the in-band emission impact of D2D discovery on current LTE-A operation. In order to minimize the impact, an eNB based open loop power control algorithm is proposed for D2D discovery. To see the performance of the proposed scheme, system-level simulation results are provided. Our results show that eNB based open loop power control algorithm alleviate the in-band emission impact significantly.

In this work, we propose a QPSK OFDM code that has both low peak to average power ratio and good bit error rate performance. We consider a Time-frequency Turbo Block code. This code is composed of the cosets of the first-order binary Reed-Muller (RM) code in the frequency domain, and Bose-Chaudhuri-Hocquenghem (BCH) code in the time domain. Our contributions are two-fold: 1) we introduce two encoding schemes that guarantee a PAPR of 3 dB for QPSK constellation, 2) we propose moderate complexity decoding procedures for these schemes. We evaluate the performance of the proposed schemes for the additive white Gaussian noise channel. Our code performs only slightly worse than the best known Turbo codes but has significantly lower PAPR. This gives a significant total power gain over the best known Turbo codes.

In this paper, we present an advanced solution for the long standing problem of large peak to average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. Although the design of low PAPR codewords has been extensively studied and the existence of asymptotically good codes with low PAPR is also proven, still no code has been constructed to satisfy all requirements. The main goal of the paper is to develop a coding scheme that not only generates low PAPR codewords, but it also performs relatively close to the Shannon limit. We achieve this goal by implementing a time-frequency turbo block coded OFDM. In this scheme, we design the frequency domain component to have a tightly bounded PAPR. The time domain component code is designed to obtain good performance while the decoding algorithm has reasonable complexity. Through comparative performance evaluation we show that utilizing the proposed method, we achieve considerable improvement in terms of PAPR while we slightly loose the performance compared to capacity achieving codes with similar overall block length.

Dual Bose-Ray-Chaudhuri (BCH) codes, despite their favorable peak to average power ratio (PAPR) properties, have not been used in coded orthogonal frequency division multiplexing (OFDM) systems. This is due to unavailability of a practical decoder and large performance gap to the Shannon limit. In this paper, we propose an advanced approach to solve the aforementioned problems. We construct a new code with favorable PAPR properties based on dual BCH codes and develop the associated maximum a posteriori (MAP) decoding algorithm. By exploiting this code as the frequency domain constituent code in a time-frequency turbo structure, we reduce the gap between the performance and Shannon limit while the bounded PAPR of OFDM symbols is guaranteed. By comparative performance evaluation we illustrate that the performance of this system is comparable with that of capacity approaching codes while it has 7 dB lower PAPR.