A circular phased array antenna that can generate orbital angular momentum (OAM) radio beams in the 10 GHz band is described. The antenna consists of eight inset-fed patch elements and a microstrip corporate feeding network. A full-wave electromagnetic simulator is used to aid the antenna design and theoretical simulations are confirmed by measurements.Introduction: Recently, orbital angular momentum (OAM) for radio communications has attracted much attention as it allows the possibility of transmitting multiple signals simultaneously at the same frequency, which may be used to increase channel capacity and potentially improve spectrum efficiency. The OAM characteristic was initially investigated and gave rise to many applications in the optical region [1,2]. In [3], an optical wireless link reached a data rate of 2.56 Tbit/s by using OAM beams. Recently, OAM was proposed for radio communications at lower frequencies [4,5]. The first laboratory experiments of OAM radio beam generation and detection were presented in [6]. In 2012, an OAM-based radio was demonstrated experimentally in a realworld setting, with two radio waves encoded with different OAM states and operating at the same frequency over a distance of 442 m [7].There are several methods that have been investigated for the generation of OAM radio beams. In [6], a discrete eight-step staircase nonfocusing phase reflector was used, where each staircase of the reflector introduced a discontinuous phase step of 2π/8 radians. The beam of OAM mode +1 was generated when a plane wave was reflected from the spiral reflector. Using a similar approach, a helicoidal parabolic antenna was fabricated and tested in [7]. Circular phased array antennas were predicted to generate OAM beams in [4,5,[8][9][10], and a timeswitched array was recently suggested to be an alternative option in [11]. For an N-element OAM circular phased array, all radiation elements are fed by the same signal but with an incremental phase shift. This inter-element phase shift can be calculated by 2πl/N, where the integer l is the OAM mode number, such that the phase will be incremented by 2πl radians in one geometrical rotation around the array axis. Hence, a 'twisted' radio beam at OAM mode l can be generated.To the authors' best knowledge, all previous published research relating to OAM generation by circular phased arrays has only considered numerical predictions. Hence, in this Letter, we present a practical 8-element circular phased array designed for OAM-based communications. The antenna structure, including the feeding network, is investigated based on both numerical and experimental methods, and the generation of an OAM radio beam is confirmed.

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A means of encoding and decoding data using wireless orbital angular momentum (OAM) modes is proposed and analysed. Source data symbols are used to select an OAM mode, which is generated using an 8-element circular array. A 2-element array is used to detect the mode by estimating the phase gradient of the received signal, and hence identifying the transmitted data symbol. The results are presented in terms of mode estimation error.

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Two empirical indoor‐to‐outdoor path loss models to facilitate femtocell network deployment are derived from continuous wave power measurements. A large set of indoor–outdoor transmitter locations in two residential streets in an urban setting and operating at 900 MHz, 2 GHz, 2.5 GHz and 3.5 GHz have been used to derive the model parameters by using singular value decomposition (SVD). The path loss models have been compared and validated against existing models as well as independent measurement data and good comparison is shown. The root mean square error of the residual path loss data obtained from the measurement data, which directly relates to the channel shadowing characteristics, is compared and validated with known results and has led to new model parameters being proposed. The expressions derived from the modelling can be used in system‐level simulators, as well as for shadowing interference analysis of two‐tier heterogeneous networks operating in indoor–outdoor scenarios at or close to the operating frequencies considered. In this study, the models extend the operating frequency range compared to related models and introduce SVD as a convenient means of deriving parameters from measured path loss data.

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It has been 20 years since the word ultrawideband has first been used in open literature. In these 20 years, ideas have been transformed into real products. Yet some might object that ultrawidebandhas not yet lived up to the promises of gigabit wireless. This review shows that despite some drawbacks, ultrawideband is not only needed because of the spectrum gridlock but it still can deliver its promises including gigabit wireless. To do so the gap between the potential, which is achievable, and the current performance must be closed. Thus, this review identifies some main issues of UWB (range, BER performance, data-rate, chip complexity and issues associated by strong narrowband interference). It shows that their reasons are well understood and addressed by erudite research which includes low complexity chip design, alternative modulation schemes, multiple antenna systems, UWB radio-over-fibre, higher band UWB and interferer detection and suppression techniques. A specific feature of this review is the cross-layer approach. The latest findings from different system layers, e.g., wave propagation, are linked to the system performance or complexity. Aims and structureThe ultrawideband wireless communication technology for civilian use has been subject to intensive scientific investigation for the last two decades. At the time of writing this article, the search for "ultrawideband" and "UWB" in IEEExplore TM gives 860 journal papers and 1560 conference papers between 1991 and 2011. This amount of scientific work has resulted in serious progress from theoretical considerations to real products in the market place. However, the intensity of research activities is not being reduced as there is still a gap between the theoretical potential and the actual performance of practical systems. The main objective of this paper is to show that this gap is well understood and how on-going research activities aim to close it.As the gap must be identified first, the paper begins with explanation of the need for ultrawideband wireless communication (Section 2.1) followed by brief summary of the history of the technology (Section 2.2) and its current situation, achievements and issues which are thought to be the reason for the existence of the gap (Section 2.3). Section 3 then introduces the current UWB regulations in the leading markets to provide more understanding for the framework of UWB systems and also to introduce some recent changes which for instance increased the need for development of efficient detect and avoid algorithms. Section 4 then identifies range, BER performance, data-rate, chip complexity and issues associated by strong narrowband interference as the most burning issues of current UWB. Section 5 then groups current research activities in six subsets, describes them and shows how these activities aim to address one or more issues listed in section 4.