Downlink Power Control Scheme Research Articles

Power control of D2D communication based on quality of service assurance under imperfect channel information

In cellular networks, proximity users establish device-to-device(D2D) links directly under the control of base stations (BSs) for data exchange, and no base station forwarding is required. For the advantages such as lower transmission power, higher data transmission rate, D2D communication has been paid more and more attention. However, the environmental impact of introducing D2D shared spectrum resources has become a major challenge. This paper studies a robust downlink power control scheme with imperfect channel state information (CSI) in D2D communication system. In order to improve the system sum rates, this paper optimizes the transmitting power of D2D users (DUEs) and the base stations through geometric analysis and convex optimization while guaranteeing the quality-of-service (QoS) requirements for both DUEs and cellular users (CUEs). Because of the dynamic characteristics of wireless channel, it is difficult and expensive to acquire CSI without direct communication with BS. On this account, we consider channel uncertainty rather than perfect or instantaneous known CSI. Aiming at enhancing the system robustness, we formulate an outage-based robust optimization problem. The original deterministic the signal-to-interference-noise-ratio (SINR) constraints are substituted with the transformed probability constraints, which transforms the random channel gain into a deterministic one with outage threshold. The simulation results show that the power allocation based on the proposed algorithm can adapt to the complex channel environment and are with better robustness.

Energy-Efficient Activation and Uplink Transmission for Cellular IoT

Consider a large-scale cellular network in which base stations (BSs) serve massive Internet of Things (IoT) devices. Since IoT devices are powered by a capacity-limited battery, how to prolong their working lifetime is a paramount problem for the success of cellular IoT systems. This article proposes how to use BSs to manage the active and dormant operating modes of the IoT devices via downlink signaling in an energy-efficient fashion and how the IoT devices perform energy-efficient uplink power control to improve their uplink coverage. We first investigate the fundamental statistical properties of an activation signaling process induced by BSs that would like to activate the devices in their cells, which helps to derive the neat expressions of the true, false, and total activation probabilities that reveal joint downlink power control and BS coordination is an effective means to significantly improve the activation performance. We then propose an energy-efficient uplink power control for IoT devices which is shown to save power and ameliorate the uplink coverage probability at the same time. We also propose an energy-efficient downlink power control and BS coordination scheme, which is shown to remarkably improve the activation and uplink coverage performances at the same time.

Robust power control based on hierarchical game for hybrid access femtocell networks

Femtocell network is regarded as the potential and effective technique to improve the capacity and coverage of traditional cellular networks. One of the challenges is how to access the network and manage the interference among different users. Compared with other access strategies, hybrid access strategy allows femtocell base stations (FBSs) to provide preferential access to femtocell users (FUEs) while other users can access nearby FBS with specific restrictions. In this paper, a robust downlink power control scheme is studied in two-tier femtocell networks, where femtocells share the same frequency with macrocell. A hierarchical game framework that takes the different users' requirements into consideration is constructed. In addition, as the link gains are actually uncertain in dynamic environment, probabilistic constraints are used to describe the uncertainty. Then two sub-problems are obtained to maximise the sum rate of macrocell and femtocells, respectively and guarantee the quality of service (QoS) of different users. To tackle the nonlinear and nonconvex optimization problem, successive convex approximation is introduced. And the practical iterative power allocation algorithm is provided. Finally, numerical results show that the proposed scheme is effective in aspect of energy saving and QoS guarantee under dynamic environment.

Uplink impact analysis from TPC downlink enhancements

Abstract Slow downlink power control scheme of F-DPCH with TPC enhancements is reported to achieve the significant transmit power reduction in highly loaded cell scenario. When these TPC downlink enhancements from 300 Hz operation are applied, the same TPC commands at every 5-slot cycle are sent from Node B to control the transmit power of the uplink channel. Thus, it is necessary to investigate how these TPC enhancements can influence uplink performance, because the default TPC scheme is performed at 1500 Hz in both downlink and uplink. In this paper, the uplink impacts from TPC downlink enhancements will be analyzed through link simulations.

Analysis of downlink power control and cooperation scheme for two‐tier heterogeneous cellular network

SummaryThe traditional cellular network cannot keep pace with the dramatic growth in data traffic due to exponentially increasing number of multimedia applications and mobile subscribers. Recently, femto base stations (FBSs) are deployed with the macro base station (MBS) tier for off‐loading the data traffic and to improve the indoor coverage of the heterogeneous cellular network. However, FBS deployment also increases the cross‐tier interference of the heterogeneous cellular network resulting in outage performance degradation of MBS tier. This work develops an analytical framework to limit the cross‐tier interference of MBS tier using power control scheme (PCS). The proposed PCS works on path loss inversion and location‐based power level rule for FBS. Moreover, a cooperation scheme and an association policy with MBS (CSAPM) are introduced to improve the outage performance of the FBS tier. Tools from the stochastic geometry are used for deriving the signal to interference and noise ratio outage probability, total outage probability, and area spectral efficiency (ASE) of MBS tier and FBS tier. Additionally, ASE maximization problem is formulated to evaluate the optimal density of FBSs. The effectiveness of the proposed PCS and CSAPM on outage performance and ASE are numerically demonstrated. It is noted from the results that the proposed CSAPM can compensate the loss in outage performance of FBS tier due to PCS. Finally, simulation results validate the analytical results.

Less Is More: Creating Spectrum Reuse Opportunities via Power Control for OFDMA Femtocell Networks

Femtocell is a promising technology which can significantly improve the spectrum efficiency and system capacity of wireless cellular networks. However, densely and randomly deployed femtocells may experience severe interfemtocell interference due to rough-and-tumble spectrum reuse with unconstrained transmit power. Different from traditional macrocell scenarios, there is no central controller available for femtocell networks. Moreover, a static planning scheme is not workable here due to random network topology. Based on game theory, we propose a sophisticated downlink power control scheme which creates more spectrum reuse opportunities among mutually interfering femtocells and enables a flexible spectrum reuse scheme. The power control problem is modeled as a generalized Nash equilibrium (NE) problem, and we employ variational inequality theory to analyze it. Existence and uniqueness properties of the NE solution are derived. Furthermore, a distributed channel-aware power control algorithm is proposed to create spectrum reuse opportunities for femtocells interfering each other. Numerical results suggest that a significant capacity improvement is acquired, and the NE point can be reached within a few iterations.

A downlink power control algorithm for long-term energy efficiency of small cell network

Recently, small cells have been densely deployed in hot spots and overlaid with macro cells in order to guarantee the quality of service for voluminous multimedia data. For a small cell network (SCN), the long-term energy efficiency is one of the most challenging issues for conserving energy while achieving link capacity over the air-interface. In this paper, we present a novel downlink power control scheme to maximize the long-term energy efficiency over a time division multiple access system, which includes multiple small cells and a central controller. Toward this goal, we formulate a long-term energy efficiency optimization problem by defining a long-term energy efficiency metric and performing an iterative algorithm to obtain optimal solutions in real-time via fast convergence. The simulation results show that the proposed metric is very effective at improving the long-term energy efficiency and conserving 8.1 % of the energy on average when compared to a conventional metric. In addition, it is verified that the proposed metric is more effective for an SCN, in particular, when the link capacity is severely degraded due to inter-cell interference.

Efficacy of coverage radius‐based power control scheme for interference mitigation in femtocells

A novel coverage radius-based downlink power control scheme to mitigate interference in densely deployed femtocells is presented. A femtocell access point (FAP) self-update algorithm is implemented, which determines the coverage radius of the femtocell with respect to its farthest served femtocell user equipment (FUE). Based on varying coverage radii, a max/min function is used to adjust the downlink transmit power value of a FAP. System-level simulations are performed to compare the performance of the presented scheme with the existing fixed coverage radius schemes. Even though the proposed scheme results in better cross-tier signal to interference plus noise ratio (SINR) values, due to a low co-tier SINR it is found that the efficacy of adaptive power control schemes based on the pilot power of a FAP is less significant if FUEs are located close to the neighbouring FAPs in densely deployed urban femtocells.

Optimization Models and Algorithms for Joint Uplink/Downlink UMTS Radio Network Planning With SIR-Based Power Control

Universal mobile telecommunication system (UMTS) networks should be deployed according to cost-effective strategies that optimize a cost objective and satisfy target quality-of-service (QoS) requirements. In this paper, we propose novel algorithms for joint uplink/downlink UMTS radio planning with the objective of minimizing total power consumption in the network. Specifically, we define two components of the radio planning problem: 1) continuous-based site placement and 2) integer-based site selection. In the site-placement problem, our goal is to find the optimal locations of UMTS base stations (BSs) in a certain geographic area with a given user distribution to minimize the total power expenditure such that a satisfactory level of downlink and uplink signal-to-interference ratio (SIR) is maintained with bounded outage constraints. We model the problem as a constrained optimization problem with SIR-based uplink and downlink power control scheme. An algorithm is proposed and implemented using pattern search techniques for derivative-free optimization with augmented Lagrange multiplier estimates to support general constraints. In the site-selection problem, we aim to select the minimum set of BSs from a fixed set of candidate sites that satisfies quality and outage constraints. We develop an efficient elimination algorithm by proposing a method for classifying BSs that are critical for network coverage and QoS. Finally, the problem is reformulated to take care of location constraints whereby the placement of BSs in a subset of the deployment area is not permitted due to, e.g., private property limitations or electromagnetic radiation constraints. Experimental results and optimal tradeoff curves are presented and analyzed for various scenarios.

An Efficient Distributed Power Control for Infeasible Downlink Scenarios--Global-Local Fixed-Point-Approximation Technique

In this paper, we present an efficient downlink power control scheme, for wireless networks, based on two key ideas: (i) global-local fixed-point-approximation technique (GLOFPAT) and (ii) bottleneck removal criterion (BRC). The proposed scheme copes with all scenarios including infeasible case where no power allocation can provide all multiple accessing users with target quality of service (QoS). For feasible case, the GLOFPAT efficiently computes a desired power allocation which corresponds to the allocation achieved by conventional algorithms. For infeasible case, the GLOFPAT offers valuable information to detect bottleneck users, to be removed based on the BRC, which deteriorate overall QoS. The GLOFPAT is a mathematically-sound distributed algorithm approximating desired power allocation as a unique fixed-point of an isotone mapping. The unique fixed-point of the global mapping is iteratively computed by fixed-point-approximations of multiple distributed local mappings, which can be computed in parallel by base stations respectively. For proper detection of bottleneck users, complete analysis of the GLOFPAT is presented with aid of the Tarski's fixed-point theorem. Extensive simulations demonstrate that the proposed scheme converges faster than the conventional algorithm and successfully increases the number of happy users receiving target QoS.

Performance study for a microcell hot spot embedded in CDMA macrocell systems

The code-division multiple-access (CDMA) system can provide more capacity than other systems, and the hierarchical layer of cells is required for system design. However, the problem is whether the same radio frequency (RF) channels used in a CDMA overlayed/underlayed macrocell and microcell structure also obtain a high capacity as in the homogeneous structure. We investigate the interference of uplink and downlink from both the microcell and macrocell under a hierarchical structure. A downlink power control scheme and two power control methods for the uplink are also considered. Performance measures such as blocking probability, C/I, capacity, and service hole area are also obtained by computer simulation. Besides, some extra efforts for a microcell are also noted, such as more power need to be transmitted by a microcell base station (BS) if the same RF channels are used in the hierarchical structure. The capacities of macrocell and microcell in the overlaying/underlaying structure are limited by the uplink and downlink, respectively. With downlink power control, the microcellular capacity can be increased. However, the combination of downlink power control for the microcell and C/I uplink power control for the macrocell causes the overall system capacity to significantly increase.