This letter investigates a power allocation problem in a downlink single-input single-output non-orthogonal multiple access (NOMA) system. Our goal is to maximize the sum rate of users subject to ...minimum user rate requirements. We rigorously prove the optimal user decoding order, and show that the sum rate maximization problem is convex, which guarantees the globally optimal solution. Numerical results validate the performance gain by the proposed NOMA compared with conventional schemes.
This paper studies energy efficient resource allocation for a machine-to-machine enabled cellular network with nonlinear energy harvesting, especially focusing on two different multiple access ...strategies, namely nonorthogonal multiple access (NOMA) and time division multiple access (TDMA). Our goal is to minimize the total energy consumption of the network via joint power control and time allocation while taking into account circuit power consumption. For both NOMA and TDMA strategies, we show that it is optimal for each machine type communication device (MTCD) to transmit with the minimum throughput, and the energy consumption of each MTCD is a convex function with respect to the allocated transmission time. Based on the derived optimal conditions for the transmission power of MTCDs, we transform the original optimization problem for NOMA to an equivalent problem which can be solved suboptimally via an iterative power control and time allocation algorithm. Through an appropriate variable transformation, we also transform the original optimization problem for TDMA to an equivalent tractable problem, which can be iteratively solved. Numerical results verify the theoretical findings and demonstrate that NOMA consumes less total energy than TDMA at low circuit power regime of MTCDs, while at high circuit power regime of MTCDs TDMA achieves better network energy efficiency than NOMA.
In this paper, we investigate the problems of sum power minimization and sum rate maximization for multi-cell networks with non-orthogonal multiple access. Considering the sum power minimization, we ...obtain closed-form solutions to the optimal power allocation strategy and then successfully transform the original problem to a linear one with a much smaller size, which can be optimally solved by using the standard interference function. To solve the nonconvex sum rate maximization problem, we first prove that the power allocation problem for a single cell is a convex problem. By analyzing the Karush-Kuhn-Tucker conditions, the optimal power allocation for users in a single cell is derived in closed form. Based on the optimal solution in each cell, a distributed algorithm is accordingly proposed to acquire efficient solutions. Numerical results verify our theoretical findings showing the superiority of our solutions compared with the orthogonal frequency division multiple access and broadcast channel.
Device-to-device (D2D) assisted offloading heavily depends on the participation of human users. The content preference and sharing willingness of human users are two crucial factors in the D2D ...assisted offloading. In this paper, with consideration of these two factors, the optimal content pushing strategy is investigated by formulating an optimization problem to maximize the offloading gain measured by the offloaded traffic. Users are placed into groups according to their content preferences and share content with intergroup and intragroup users at different sharing probabilities. Although the optimization problem is nonconvex, the closed-form optimal solution for a special case is obtained, when the sharing probabilities for intergroup and intragroup users are the same. Furthermore, an alternative group optimization (AGO) algorithm is proposed to solve the general case of the optimization problem. Finally, simulation results are provided to demonstrate the offloading performance achieved by the optimal pushing strategy for the special case and AGO algorithm. An interesting conclusion drawn is that the group with the largest number of interested users is not necessarily given the highest pushing probability. It is more important to give high pushing probability to users with high sharing willingness.
This letter proposes a nonparametric detector, termed as Gini Correlation (GC), to solve the classical problem of detecting deterministic signals buried in impulsive noise. With the help of the ...popular Middleton's Class-A impulsive noise (MCAN) model, we derive the expectation and variance of GC under alternative hypothesis and null hypothesis, which, along with the central limit theorem, are further employed for determining the detection probability and the detection threshold. The results show that the proposed detector possesses a constant false alarm rate property. Monte Carlo simulations verify not only the correctness of our theoretical findings but also the superiority of GC to other state-of-the-art methods in terms of receiver operating characteristic (ROC) curves and asymptotic relative efficiency (ARE) curves.
In this letter, we study the joint channel allocation and power control problem to maximize the energy efficiency (EE) of device-to-device (D2D) links in a D2D underlaid cellular network. Due to the ...location dispersion of D2D pairs and short-distance D2D transmission, it should be preferred that multiple D2D pairs can simultaneously share the resource with cellular users (CUs). To address the nonconvexity of the EE maximization problem, we divide the original problem into two subproblems and propose an iterative algorithm with low complexity to solve it. Simulation results show that the proposed algorithm converges rapidly and the EE of D2D links can be significantly improved compared with existing methods especially for an increasing number of CUs.
This letter investigates the resource allocation and power control for both device-to-device (D2D) pairs and cellular users (CUs) in D2D communication underlaying single-cell cellular networks, where ...multiple D2D pairs can share the same resources with CUs. Our goal is to maximize the sum rate of D2D pairs subject to the rate requirements for all CUs and power requirements for both D2D pairs and the base station. We first give the optimal conditions for the resource allocation of D2D pairs and power control of CUs and then propose an iterative resource allocation and power control algorithm. Numerical results show that the proposed algorithm achieves higher sum rate of D2D pairs than the existing schemes.
Objectives
The risk factors for extraurothelial recurrence (EUR) after radical nephroureterectomy (RNU) in patients with upper urinary tract urothelial carcinoma (UTUC) are currently inconsistent and ...unclear. In this study, we aimed to identify these risk factors and develop a grading system for EUR.
Methods
We retrospectively analyzed 220 patients who underwent RNU for UTUC in our center from January 2009 to December 2020. Overall survival (OS) and extraurothelial recurrence-free survival (EURFS) were compared using the Kaplan–Meier curve with a log-rank test. Univariate and multivariate Cox regression models were applied to identify the independent risk factors related to EUR.
Results
The median follow-up period was 42 (range: 2–143) months. Of the 220 patients, 61 patients developed EUR in our cohort, which had worse survival outcome. Multivariate Cox regression analysis showed pathologic stage, lymph node (LN) status, lymphovascular invasion (LVI), Ki-67, neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR) were independent risk factors for EUR. The Kaplan–Meier curves revealed a significant difference in EUR among the three risk groups.
Conclusion
Our study suggests that pathologic stage, LN status, LVI, Ki-67, NLR, and PLR are independent risk factors for EUR in UTUC patients after RNU. The development of a grading system for EUR risk stratification may assist urologists in making clinical decisions regarding the management of UTUC.
We aimed to evaluate the effect of the timing of diagnostic ureteroscopy (URS) on intravesical recurrence (IVR) following radical nephroureterectomy (RNU).
The clinical data of 220 patients with ...upper tract urothelial carcinoma (UTUC) treated with RNU at our center from June 2010 to December 2020 were retrospectively analyzed. According to the timing of the URS, all patients were divided into three groups: the no URS group, the 1-session group (diagnostic URS immediately followed by RNU), and the 2-session group (RNU after diagnostic URS). Additionally, we analyzed IVR-free survival (IVRFS) using the Kaplan-Meier and Cox proportional regression methods.
The median follow-up period of these 220 patents was 41 (range: 2-143) months. Among them, 58 patients developed IVR following RNU. Kaplan-Meier curve displayed a significantly higher IVR rate in both treatment groups than in the no-URS group (
=0.025). In the subgroup of patients with renal pelvis cancer, the incidence of IVR was significantly higher in both treatment groups than in the group without URS (
=0.006). In univariate Cox proportional regression analysis, the two treatment groups were risk factors for IVR compared to the no-URS group
=0.027, hazard ratio (HR): 1.93, 95% confidence interval (CI): 1.08-3.46. The two-stage group (
=0.032, HR: 1.98, 95% CI: 1.08-3.65), positive urine pathology (
<0.001, HR: 8.12, 95% CI: 3.63-18.15), adjuvant chemotherapy (
<0.001, HR: 0.20, 95% CI: 0.10-0.38), and positive margin (
<0.0001, HR: 7.50, 95% CI: 2.44-23.08) were all identified as independent predictors in the multivariate.
This study revealed that delayed RNU following diagnostic URS may increase the risk of postoperative IVR in patients with UTUC, preoperatively positive uropathology, and positive surgical margin were risk factors for IVR after RNU, while early postoperative chemotherapy may effectively prevent IVR. Delay of RUN after URS could increase the risk of IVR.
To guarantee nonnegative signals in optical wireless communication systems, flipped orthogonal frequency division multiplexing (Flip-OFDM) transmits the positive and negative parts of the signal over ...two consecutive OFDM subframes (positive subframe and negative subfame, respectively). The conventional receiver for Flip-OFDM recovers the data by subtracting the negative subframe from the positive one. However, the signal analysis shows that the signals in the two subframes contain the information of the transmitted data and can be used together to decode the data. An iterative receiver is then proposed to improve the transmission performance of Flip-OFDM by exploiting the signals in both subframes. Simulation results show that the proposed iterative receiver provides significant signal-to-noise ratio gain over the conventional receiver. Moreover, the iterative receiver also outperforms the existing advanced receiver.
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