High-Rate Space-Time Coded Large MIMO Systems: Low-Complexity Detection and Channel Estimation

In this paper, we present a low-complexity algorithm for detection in high-rate, non-orthogonal space-time block coded (STBC) large-MIMO systems that achieve high spectral efficiencies of the order of tens of bps/Hz. We also present a training-based iterative detection/channel estimation scheme for such large STBC MIMO systems. Our simulation results show that excellent bit error rate and nearness-to-capacity performance are achieved by the proposed multistage likelihood ascent search (M-LAS) detector in conjunction with the proposed iterative detection/channel estimation scheme at low complexities. The fact that we could show such good results for large STBCs like 16x16 and 32x32 STBCs from Cyclic Division Algebras (CDA) operating at spectral efficiencies in excess of 20 bps/Hz (even after accounting for the overheads meant for pilot based training for channel estimation and turbo coding) establishes the effectiveness of the proposed detector and channel estimator. We decode perfect codes of large dimensions using the proposed detector. With the feasibility of such a low-complexity detection/channel estimation scheme, large-MIMO systems with tens of antennas operating at several tens of bps/Hz spectral efficiencies can become practical, enabling interesting high data rate wireless applications.Comment: v3: Performance/complexity comparison of the proposed scheme with other large-MIMO architectures/detectors has been added (Sec. IV-D). The paper has been accepted for publication in IEEE Journal of Selected Topics in Signal Processing (JSTSP): Spl. Iss. on Managing Complexity in Multiuser MIMO Systems. v2: Section V on Channel Estimation is update

A Low-Complexity Precoder for Large Multiuser MISO Systems

In this paper, we consider the problem of preceding in large multiuser MISO systems, where by 'large' we mean (i) large number of transmit antennas (N_t) at the base station of the order of tens to hundreds of transmit antennas, and (ii) large number of downlink users (N_u) of the order of tens to hundreds of users where each user has one receive antenna. Such large MISO systems will be of immense interest because of the high capacities (sum-rates) of the order of hundreds of bits/channel use possible in such systems. We propose a vector perturbation based low-complexity precoder, termed as norm descent search (NDS) precoder, which has a complexity of just O(N_uN_t) per information symbol. This low complexity attribute of the precoder is achieved by searching for the perturbation vector over a reduced search space. Interestingly, in terms of BER performance, the proposed precoder achieves increasingly better BER for increasing N_t, N_u, such that for large N_t, N_u it achieves near-exponential diversity with some SNR loss, thus making it suited for large MISO systems both in terms of complexity as well as performance. The results of uncoded/turbo-coded simulations without and with channel estimation errors are presented

Efficacy of Hyaluronic Acid Injections versus Steroid Injections on Painful Tendinopathies

Background: Tendinopathies are manifested by pain, swelling, and limited mobility functions. Corticosteroid injections have been a mainstay in the treatment of tendinopathy, and are widely used despite the controversy regarding their usefulness and safety. The peri-tendinous administration of hyaluronic acid (HA) has shown promising results in the management of tendinopathy. Objectives: The aim of the current study was to evaluate the efficacy of peri-tendinous injections of hyaluronic acid versus steroid injections on pain reduction in patients with painful tendinopathies. Patients and methods: A prospective study, including a total of 90 patients with tendinopathy who were recruited from the Rheumatology and Rehabilitation Outpatient Clinic at Sohag University Hospital. Demographic data including age, disease duration, and tendon affected were evaluated. Patients were divided into three groups, each group contained 30 patients. First group received peritendinous steroid injection, second group received peritendinous hyaluronic acid injection, and the third group received both peritendinous hyaluronic acid and steroid injections. Groups were compared using in visual analogue scale, tenderness and range of motion after one week, one month and after 3 months from injection. Results: Best improvement was seen in the group of combined hyaluronic acid and steroid; followed by the group of steroid injection alone, which showed early response better than hyaluronic acid alone. Conclusion: Local injection for tendinopathies by combined hyaluronic acid and steroid gives significantly better and more long standing effect compared to either hyaluronic acid or steroid alone. On the other hand, monotherapy showed non-significant difference between steroid and hyaluronic acid

Special Issue on Massive MIMO

International audienceDemand for wireless communications is projected to grow by more than a factor of forty or more over the next five years. A potential technology for meeting this demand is Massive MIMO (also called Large-Scale Antenna Systems, Large-Scale MIMO, ARGOS, Full-Dimension MIMO, or Hyper-MIMO), a form of multi-user multipleantenna wireless which promises orders-of-magnitude improvements in spectral-efficiency over 4G technology, and accompanying improvements in radiated energy-efficiency. The distinguishing feature of Massive MIMO is that a large number of service-antennas - possibly hundreds or even thousands - work for a significantly smaller number of active autonomous terminals. Upsetting the traditional parity between service antennas and terminals in this manner is a game-changer: The simplest multiplexing pre-coding and de-coding algorithms can be nearly optimal, expensive ultra-linear forty-Watt power amplifiers are replaced by many low-power units, and the favorable action of the law of large numbers can greatly facilitate power-control and resource-allocation. Massive MIMO is still an emerging field. There are many unanswered theoretical questions and much remains to be done to obtain a reduction to practice. The six papers in this Special Issue are a sampling of the types of problems that are topics of active research. The papers logically fall into three categories: a) Acquisition of Channel State Information, b) Spatial Multiplexing Algorithms, and c) Massive Array Issues and Architectures

Safety and Complications of Double-Lumen Tunnelled Cuffed Central Venous Dialysis Catheters : Clinical and radiological perspective from a tertiary centre in Oman

Objectives: This study aimed to assess the technical success, safety and immediate and delayed complications of double-lumen tunnelled cuffed central venous catheters (TVCs) at the Sultan Qaboos University Hospital (SQUH), Muscat, Oman. Methods: This retrospective study took place between January 2012 and October 2013. The clinical records and radiological data of all patients who underwent ultrasound- and fluoroscopy-guided TVC placement at SQUH during the study period were reviewed. Demographic data and information regarding catheter placement, technical success and peri- and post-procedure complications (such as catheter-related infections or thrombosis) were collected. Results: A total of 204 TVCs were placed in 161 patients. Of these, 68 were female (42.2%) and 93 were male (57.8%). The mean age of the patients was 54.4 ± 17.3 years. The most common reason for catheter placement was the initiation of dialysis (63.4%). A total of 203 procedures were technically successful (99.5%). The right internal jugular vein was the most common site of catheter placement (74.9%). Mild haemorrhage which resolved spontaneously occurred in 11 cases (5.4%). No other complications were observed. Subsequent follow-up data was available for 132 catheters (65.0%); of these, thrombosis-related catheter malfunction was observed in 22 cases (16.7%) and catheter-related infection in 29 cases (22.0%). Conclusion: Radiological-guided placement of tunnelled haemodialysis catheters can be performed safely with excellent technical success. The success rate of catheter insertion at SQUH was favourable in comparison with other studies reported in the literature

Operative management and outcomes in patients with myxomas: A single-center experience

BackgroundCardiac myxoma is a rare cardiac tumor that may be asymptomatic or can cause embolization or intracardiac obstruction, leading to heart failure, sudden cardiac death, and arrhythmia. This study aims to report an 11-year experience of a single center in the management of cardiac myxoma.MethodThis study is a single-center retrospective case series. Eighty cases of cardiac myxoma were collected in Ibn Albitar's specialized center for cardiac surgery. Transthoracic echocardiography was used to make the preoperative diagnosis in all patients. The surgeries were undertaken through the standard approach of a median sternotomy. All four cardiac chambers were thoroughly explored for additional myxomas. The major objective of the operations was complete tumor resection.ResultThe mean age of the patients was 46.3 years. Females (67.5%) were predominant over males (32.5%). Shortness of breath was the most common symptom (86.25%). The left atrium was the most affected site (83.75%), followed by the right atrium (13.75%). Coronary artery bypass grafting was required as the secondary or associated intervention in 19 (23.75%) cases. The recurrence rate was 11.25%, with a mortality rate of 3.75%.ConclusionRecurrence and tumor embolism are risks of surgical intervention for myxoma. Good preparation using transthoracic echocardiography as a diagnostic tool and standard median sternotomy to complete resection of the tumors can decrease the rate of recurrence, embolism, and even mortality