In order to quantify the energy efficiency of a wireless network, the power consumption of the entire system needs to be captured. In this paper, the necessary extensions with respect to existing performance evaluation frameworks are discussed. The most important addendums of the proposed energy efficiency evaluation framework (E 3 F) are a sophisticated power model for various base station (BS) types, as well as large-scale long-term traffic models. The BS power model maps the RF output power radiated at the antenna elements to the total supply power of a BS site.The proposed traffic model emulates the spatial distribution of the traffic demands over large geographical regions, including urban and rural areas, as well as temporal variations between peak and off-peak hours. Finally, the E 3 F is applied to quantify the energy efficiency of the downlink of a 3GPP LTE radio access network. Index TermsEnergy efficiency, green radio, power & traffic model, system level energy efficiency simulations, energy aware radio and network technologies (EARTH)

Since the first cellular networks were trialled in the 1970s, we have witnessed an incredible wireless revolution. From 1G to 4G, the massive traffic growth has been managed by a combination of wider bandwidths, refined radio interfaces, and network densification, namely increasing the number of antennas per site. Due its cost-efficiency, the latter has contributed the most. Massive MIMO (multiple-input multiple-output) is a key 5G technology that uses massive antenna arrays to provide a very high beamforming gain and spatially multiplexing of users, and hence, increases the spectral and energy efficiency. It constitutes a centralized solution to densify a network, and its performance is limited by the inter-cell interference inherent in its cell-centric design. Conversely, ubiquitous cell-free Massive MIMO refers to a distributed Massive MIMO system implementing coherent user-centric transmission to overcome the inter-cell interference limitation in cellular networks and provide additional macro-diversity. These features, combined with the system scalability inherent in the Massive MIMO design, distinguishes ubiquitous cell-free Massive MIMO from prior coordinated distributed wireless systems. In this article, we investigate the enormous potential of this promising technology while addressing practical deployment issues to deal with the increased back/front-hauling overhead deriving from the signal co-processing.

This paper discusses how energy consumption can be significantly reduced in mobile networks by introducing discontinuous transmission (DTX) on the base station side. By introducing DTX on the downlink, or cell DTX, we show that it is possible to achieve significant energy reductions in an LTE network. Cell DTX is most efficient when the traffic load is low in a cell but even when realistic traffic statistics are considered the gains are impressive. The technology potential for a metropolitan area is shown to be 90% reduced energy consumption compared to no use of cell DTX. The paper also discusses different drives for the increased focus on energy efficient network operation and also provides insights on the impact of cell DTX from a life cycle assessment perspective.

Ubiquitous cell-free massive MIMO (multiple-input multiple-output) combines massive MIMO technology and usercentric transmission in a distributed architecture. All the access points (APs) in the network cooperate to jointly and coherently serve a smaller number of users in the same time-frequency resource. However, this coordination needs significant amounts of control signalling which introduces additional overhead, while data co-processing increases the back/front-haul requirements. Hence, the notion that the "whole world" could constitute one network, and that all APs would act as a single base station, is not scalable. In this study, we address some system scalability aspects of cell-free massive MIMO that have been neglected in literature until now. In particular, we propose and evaluate a solution related to data processing, network topology and power control. Results indicate that our proposed framework achieves full scalability at the cost of a modest performance loss compared to the canonical form of cell-free massive MIMO.Index Terms-Cell-free Massive MIMO, distributed wireless system, power control, spectral efficiency, system scalability. I. INTRODUCTIONCoordinated distributed wireless systems [1] leverage signal co-processing at multiple access points (APs) to guarantee high connectivity, reduce inter-cell interference and improve the user experience. Connectivity is enhanced thanks to the shorter AP-to-user distance; the joint coherent transmission from geographically distributed APs yields macro-diversity gain; and the coordination enables APs to select transmit strategies jointly (by sharing channel state information) in order to reduce inter-cell interference.Ubiquitous cell-free massive MIMO [2]-[4], where MIMO stands for multiple-input multiple-output, relies on these principles. However, it differs from prior coordinated distributed wireless systems such as network MIMO [5], [6], virtual MIMO [7], multi-cell MIMO cooperative networks [8] and coordinated multipoint with joint transmission (CoMP-JT) [9]- [11]. The performance of all the aforementioned frameworks, in their canonical forms, are limited by two factors: (i) the inter-cell (out-of-cluster) interference inherent in the static cell-centric transmission design [12]; (ii) the large amount of control signalling, channel state information (CSI) and data exchange, required for the coordination, that increases the back/front-hauling requirements and the overhead. These become more significant as the number of APs grows.Cell-free massive MIMO combines the benefits derived from using time division duplex (TDD) massive MIMO tech-

In this paper, A Parallel Combinatory-Orthogonal Frequency Division Multiplexing (PC-OFDM) system is proposed and analyzed. The proposed system selects at each symbol interval a subset of the available sub-carriers, and the selected sub-carriers are modulated by points from an M-PSK signal constellation. PC-OFDM systems can be designed to have lower Peak to Average Power Ratio (PAPR), higher bandwidth e ciency, and lower bit error probability on Gaussian channels compared to ordinary OFDM systems. A bit mapping procedure using the Johnson association together with a position algorithm for the PSK symbols is proposed. Good analytical approximations of the BER for PC-OFDM systems are derived for AWGN and Ricean fading channels, and extensive simulation results are presented.