Multiple Access Trade Study

The Personal Access Satellite System (PASS) strawman design uses a hybrid Time Division Multiple Access (TDMA)/Frequency Division Multiple Access (FDMA) implementation. TDMA is used for the forward direction (from Suppliers to Users), and FDMA for the return direction (from Users to Suppliers). An alternative architecture is proposed that will require minimal real time coordination and yet provide a fast access method by using random access Code Division Multiple Access (CDMA). The CDMA system issues are addressed such as connecting suppliers and users, both of whom may be located anywhere in the CONUS, when the user terminals are constrained in size and weight; and providing efficient traffic routing under highly variable traffic requirements. It is assumed that bandwidth efficiency is not of paramount importance. CDMA or Spread Spectrum Multiple Access (SSMA) communication is a method in which a group of carriers operate at the same nominal center frequency but are separable from each other by the low cross correlation of the spreading codes used. Interference and multipath rejection capability, ease of selective addressing and message screening, low density power spectra for signal hiding and security, and high resolution ranging are among the benefits of spread spectrum communications

Antenna Beam Coverage Concepts

The strawman Personal Access Satellite System (PASS) design calls for the use of a CONUS beam for transmission between the supplier and the satellite and for fixed beams for transmission between the basic personal terminal and the satellite. The satellite uses a 3 m main reflector for transmission at 20 GHz and a 2 m main reflector for reception at 30 GHz. There are several types of spot beams under consideration for the PASS system besides fixed beams. The beam pattern of a CONUS coverage switched beam is shown along with that of a scanning beam. A switched beam refers to one in which the signal from the satellite is connected alternatively to various feed horns. Scanning beams are taken to mean beams whose footprints are moved between contiguous regions in the beam's coverage area. The advantages and disadvantages of switched and/or scanning beams relative to fixed beams. The consequences of using switched/scanning in lieu of fixed beams in the PASS design and attempts are made to evaluate the listed advantages and disadvantages. Two uses of switched/scanning beams are examined. To illustrate the implications of switched beams use on PASS system design, operation at two beam scan rates is explored

Use of elliptical orbits for a Ka-band personal access satellite system

The use of satellites in elliptical orbits for a Ka-band personal communications system application designed to provide voice and data service within the continental U.S. is examined. The impact of these orbits on system parameters such as signal carrier-to-noise ratio, roundtrip delay, Doppler shift, and satellite antenna size is quantized for satellites in two elliptical orbits, the Molniya and the ACE orbits. The number of satellites necessary for continuous CONUS coverage has been determined for the satellites in these orbits. The increased system complexity brought about by the use of satellites at such altitudes is discussed

Multiple access capacity trade-offs for a Ka-band personal access satellite system

System capability is critical to the economic viability of a personal satellite communication system. Ka band has significant potential to support a high capacity multiple access system because of the availability of bandwidth. System design tradeoffs are performed and multiple access schemes are compared with the design goal of achieving the highest capacity and efficiency. Conclusions regarding the efficiency of the different schemes and the achievable capacities are given

A COMPARISON OF SERUM LEVELS OF 25-HYDROXY VITAMIN D IN PREGNANT WOMEN AT RISK FOR GESTATIONAL DIABETES MELLITUS AND WOMEN WITHOUT RISK FACTORS.

BACKGROUND: During pregnancy, Low serum 25-hydroxyvitamin-D [25(OH)D] concentration is even more critical. This deficiency leads to higher incidences of preeclampsia, gestational diabetes, preterm birth, bacterial vaginosis, and also affects the health of the infants. The aim of this study was to evaluate the relationships between serum levels of 25-hydroxyvitamin D (25[OH]D) and gestational diabetes mellitus (GDM) and differences in high-risk pregnant women and women without risk factors for GDM. METHODS: This cross sectional study including 155 pregnant women, who are still in the first trimester of pregnancy (less than 12 weeks gestation), were randomized to two groups of high and low risk for GDM. For these people, once at the gestational age less than 12 times a week and once at for 24 to 28 weeks of pregnancy, tests of FBS / BS / HbA1C / 25OHD / insulin / Ca / Albumin was requested. Besides, the OGTT test was performed with 75 g glucose at 24 and 28 weeks of pregnancy to diagnose GDM. RESULTS: Serum levels of 25(OH)D in the second trimester of pregnancy ng / ml (24.1 ± 39.5) was significantly lower than that of the first trimester ng / ml (25.9 ± 45.6) (p <0.001). But serum 25(OH)D levels in the first and second trimester of pregnancy was significantly different in women at high risk for GDM than women who had no risk factors (p =0.584 and p =0.99). Serum levels of 25(OH)D has an inverse and significant relationship with HbA1C at the beginning of pregnancy (p=0.007). In addition, a significant and inverse relationship was shown between serum levels of 25(OH)D in the second trimester with insulin (p=0.047) and blood sugar 2 hours after ingestion of 75 g glucose (p=0.045) at 24-28 weeks of gestation

LayeredCast -A Hybrid Peer-to-Peer Live Layered Video Streaming Protocol

Abstract-Peer-to-Peer overlay networks are an attractive foundation for video streaming. However, live Peer-to-Peer media streaming systems face many challenges such as bandwidth heterogeneity, node churn, and selfish nodes. Although many tree based and mesh based streaming protocols have been proposed, each has its own drawbacks such as unreliability and unfairness in tree based and long startup delay and complex scheduling in mesh based protocols. In this paper, we propose a new video streaming protocol called LayeredCast main features of which are: 1) Hybrid: Drawbacks of the simple approaches are compensated using a hybrid of mesh and tree overlays. 2) Layered Video: Provides an adaptive scheme to enhance the video quality using a layered video codec for heterogeneous clients. 3) QoS: LayeredCast scheduling aims at moving complexity of Multi-Service network core to the network clients application layer, thus providing better QoS over simple regular networks. LayeredCast&apos;s tree network pushes the base layer to all peers while the enhancement layers and missing base layer segments are pulled over a mesh network by peers with extra bandwidth using a new data-driven scheduling scheme. We have evaluated the performance of LayeredCast on an innovative simulation framework. Simulation results verify better performance of LayeredCast in term of decodable video frames over CoolStreaming, especially when network resources are limited

Iliac vein stenting in a patient with lower extremity swelling resulting from diffuse pelvic mass: A case report

We report a 66-year-old male patient with severe right lower extremity swelling resulting from diffuse pelvic mass with compression on right external iliac vein. The patient had papillary urothelial carcinoma of bladder seven years ago and radical cystectomy and ureterostomy was performed. Recurrence of malignancy had occurred five years after the operation. The patient had also bilateral diffuse lung metastasis. The external iliac vein had severe stenosis and invasion of pelvic mass into the vein was evident on venography. Venoplasty of external iliac vein was performed throughout the stenosis. A venous stent of 80 mm length and 12 mm diameter was introduced over the guidewire and deployed in the external iliac vein. Dramatic clinical response was evident since postoperative day two. Swelling of right lower extremity was resolved dramatically on three-month and six-month follow-up visits. We believe that endovascular venous recanalization of iliac veins is feasible and safe in patients with unresectable and diffuse pelvic masses

The Prevalence of Trauma Injuries From Neighboring Countries Transferred to Iran

Introduction: In recent years, the prevalence of attacks perpetrated by humans against other humans has increased worldwide. The injuries suffered by attack victims are severe and multi-organ. Iran’s neighboring countries have been the scenes of attacks in the recent past. This study assessed the type and severity of injuries sustained by victims transferred to Iran during the time period 2005-2007. Methods: This study was conducted on injured civilians transferred to hospitals in Iran. Data regarding cause of injury, type and severity of injuries, diagnostic-therapeutic interventions, and patient outcomes was collected and statistically analyzed using SPSS version 14 software. Results: In the studied time period, 214 attack victims were transferred to 3 Level 1 trauma centers in Iran. The mechanisms of injury were explosion in 130 cases, gunshot in 48, and other causes in the remaining victims. The mean Injury Severity Score (ISS) was 5.91 ± 4.54 (range = 1-34), and the median was 4; 109 cases (51%) had an ISS between 1 and 8, 73 cases (34%) were scored between 9 and 14, 15 cases (7%) were scored from 16 to 24, and 17 cases (8%) had an ISS ≥25. In terms of the number of injured organs, 42 patients (20%) had one, 124 (58%) had 2, 36 (17%) had 3, and 12 patients (5%) had 4 or more injured organs. Procedures included 86 orthopedic, 25 general surgical, 21 ear, nose, and throat (ENT), 18 plastic, 15 neurosurgical, and 10 ophthalmic operations; 25 patients received psychiatric counseling. The mean (±SD) hospital stay was 13.43 (±19.76) days (range = 1-230). Conclusion: The injury pattern in attacks is more severe and differs from other traumas. The medical team should have adequate knowledge in this respect to provide comprehensive healthcare