Exploiting the increasing correlation of space constrained massive MIMO for CSI relaxation

In this paper, we explore low-complexity transmission in physically-constrained massive multiple-input multiple-output (MIMO) systems by means of channel state information (CSI) relaxation. In particular, we propose a strategy to take advantage of the correlation experienced by the channels of neighbour antennas when deployed in tightly packed antenna arrays. The proposed scheme is based on collecting CSI for only a subset of antennas during the pilot training stage and, subsequently, using averages of the acquired CSI for the remaining closely-spaced antennas. By doing this, the total number of radio frequency (RF) chains, for both CSI acquisition and data transmission, and the baseband signal processing are reduced, hence simplifying the overall system operation. At the same time, this impacts the quality of the channel estimation produced after the CSI acquisition process. To characterize this tradeoff, we explore the impact that the number of antennas with instantaneous CSI has on the performance, signal processing complexity, and energy efficiency of time-division duplex (TDD) systems. The analytical and simulation results presented in this paper show that the application of the proposed strategy in size-constrained antenna arrays is able to significantly enhance the energy efficiency against systems with full CSI availability, while approximately preserving their average performance

Cataract Surgery in Patients with Uveitis: Preoperative and Surgical Considerations

Cataract is one of the most frequent visual impairment complications of uveitis, accounting for up to 40% of the visual loss seen in these patients. In general, uveitis patients differ from the general cataract population in that they are younger and have a higher rate of comorbidities, however the rates of inflammatory sequelae vary markedly among uveitic entities. Cataract development may be influenced by the cause and duration of uveitis, the degree of inflammation control, and the use of corticosteroid therapy. Cataract surgery in patients with uveitis represents a serious challenge due to pre-existing ocular comorbidities that may limit the visual outcome and difficult the surgical procedure; the need for preoperative control of inflammation; and the efficacy of postoperative management to avoid immediate and late ocular complications. A detailed ophthalmologic exam prior to surgery is essential to know the status of pre-existing pathologic changes, adjust the medical therapy to achieve absolute control of inflammation, establish a surgical plan, and deliver an objective visual prognosis to the patient or the relatives. The key point to surgical success is the absolute control of inflammation, meaning no cells in the anterior chamber for at least 3 months prior to surgery. Today, minimally invasive phacoemulsification with acrylic foldable intraocular lens implantation is the standard of care for most patients with uveitis. It must be taken into consideration that higher rates of intraoperative and postoperative complications may occur. Vision-limiting pathology related to pre-existing uveitis complications are the major contributing factors for limited postoperative visual outcome

Efficient large scale antenna selection by partial switching connectivity

In this work we analyze the benefits of low-complexity radio frequency (RF) switching matrices (SMs) for antenna selection (AS) in large scale antenna systems (LSAS). The reduced RF complexity and insertion losses (ILs) are attained by limiting the number of internal connections in the SM, at the expense of a limited flexibility in the AS. The results presented in this paper demonstrate that partially-connected (PC) SMs outperform conventional fully-flexible (FF) alternatives due to their reduced ILs, which are characterized in this work

Power-efficient space shift keying transmission via semidefinite programming

Space shift keying (SSK) transmission is a low-complexity complement to spatial modulation (SM) that solely relies on a spatial-constellation diagram for conveying information. The achievable performance of SSK is determined by the channel conditions, which in turn define the minimum Euclidean distance (MED) of the symbols in the received SSK constellation. In this contribution we concentrate on improving the power efficiency of SSK transmission via symbol pre-scaling. Specifically, we pose a pair of related optimization problems for a) enhancing the MED at reception while satisfying a given power constraint at the transmitter, and b) reducing the transmission power required for achieving a given MED. The resultant optimization problems are NP-hard, hence they are subsequently reformulated and solved via semidefinite programming. The results presented demonstrate that the proposed pre-scaling strategies are capable of enhancing the attainable performance of conventional SSK, while simultaneously extending its applicability and reducing the complexity of the existing pre-scaling schemes