Cell switch off technique combined with coordinated multi-point (CoMP) transmission for energy efficiency in beyond-LTE cellular networks

Due to the increased energy consumption of cellular access networks, energy efficiency of the systems should be considered jointly with spectral efficiency to obtain the overall performance metrics and trade-offs. Downlink coordinated multipoint (CoMP) joint transmission aided cell switch off schemes can mitigate inter-cell interference and increase energy efficiency by using the active cells to serve the users in the switched off cell. However, the performance of this newly proposed scheme is heavily dependent on the accuracy of the selected CoMP joint transmission set. In this paper, we model the multi-point channel estimation enabled via channel state information reference symbols (CSI-RS) introduced in 3GPP release 10 systems and simulate possible scenarios that would lead to inaccurate transmission set clustering: multi-point channel estimation errors and possible CoMP system delays due to CSI transfers, node processing delays and network topology limitations. In order to mitigate the effects of channel estimation errors and system delay, we propose a framework for multi- point channel estimation in CoMP systems using a time-varying interpolation filter which tracks each multipath delay tap separately for every measured point. Possible performance gains with different filter lengths are demonstrated. Simulation results are presented to show the effectiveness of the proposed scheme. In addition, proof of concept is provided for CoMP adaptive time-varying multi-point estimation filter designs, where the UEs which are being served by higher cluster degrees need to enlarge the estimation filter memory spans only for the points which are more likely to be included in the joint transmission set.

In recent years, energy efficiency (“greenness”) has become an important research topic in wireless networks. Environmental awareness and the increased cost of energy stimulate the research on this subject. In cellular networks, most of the power consumption takes place at the base stations (BSs). It is worth noting that the number of BSs has been steadily increasing since the 1G networks; moreover, this increase is expected to become even steeper in the foreseeable future with the advent of the small cell concept in the envisioned 5G networks. It is also worth noting that in cellular networks the traffic demand (load) in space and time is getting increasingly heterogeneous. As a result, parts of network will likely be lightly loaded at certain times. In such situations, it only makes sense to switch off as many BSs as possible without jeopardizing the key performance indicators. Although there in an increasing volume of literature on the cell switch-off (CSO) concept, to the best of our knowledge, there is no study which considers the user terminal (UT) power consumption as a key performance indicator, while the UT power efficiency indeed constitutes one of most important performance criterion in a mobile network. In many cases, switching off BSs for downlink energy efficiency may result in an uplink energy inefficiency, due to the fact that the UTs served by the switched off BSs will need to be connected to further away BSs. In this paper, we propose a heuristic CSO algorithm to achieve energy efficiency in the whole cellular network while taking into account the power consumption of UTs. We call the proposed algorithm as the user-aware CSO algorithm.

In this paper, a joint power and subcarrier optimization problem to minimize the network energy consumption with considerations of dynamic Coordinated Multipoint Transmission (CoMP) clustering, user quality of service (QoS) requirement and base station (BS) load is formulated for cell switch off in CoMP transmission scenario. Since the complexity of such optimization problem is prohibitive in practical application, following the manner of dynamic programming (DP), the original problem is decomposed to a sequence of sub-problems on cell switch off with dynamic CoMP clustering and system transmit power optimization. Then the Cluster Load Search, User Sum SINR and Cell Sum Load Based Clustering Schemes are proposed for cell switch off evaluation. The simulation results show that the proposed schemes achieve competitive network energy-efficient performance compared with benchmark optimization scheme while at the same time save up to 40% of the overall overhead.

Rajasthan power system has extensively grown in last 10 years due to potential of wind & solar power projects, construction of transmission system for formation of National Grid and for evacuation of large thermal power plants. Large number of 765 kV and 400 kV transmission lines have been constructed. Due to variability of wind and solar power generation, quantum and also direction of power flow on transmission lines is significantly changed. State Load Dispatch Center has instructed to switch off shunt capacitors from 6 pm to 6 am to control high voltage. This paper presents a comparative case study to control high voltage in power system by switching ON shunt reactors vs switching OFF shunt capacitors. Rajasthan power system has four 765 kV GSS, twenty-seven 400 kV GSS, one twenty-two 220 kV GSS and four fifty-two 132 kV GSS is selected to carry out simulation-based case study in MiPower software. Simulation model consists of 943 buses including 85 generator buses, 1142 transmission lines and 201 transformers. The daily routine grid operations without assessing the outcome or achievement level lead to create problems in power network. Shunt reactors are switched OFF at seven 400 kV grid sub stations where as to reduce high voltage shunt capacitor banks have been switched OFF. Case studies are carried out to observe the effect of switching ON shunt reactors to control high voltage instead of switching OFF shunt capacitors. Test network loading is about 10000 MW. The impact on voltage profile of buses, system losses, financial analysis, loadings of system elements is presented at last.

Cell switch-off (CSO) is an important approach to reducing energy consumption in cellular networks during off-peak periods. CSO addresses the research question of which cells to switch off when. Whereas online CSO, based on immediate user demands and channel states, is problematic to implement and difficult to model, off-line CSO is more practical and tractable. Furthermore, it is known that regular cell layouts generally provide the best coverage and spectral efficiency, which leads us to prefer regular static (off-line) CSO. We introduce sector-based regular CSO patterns for the first time. We organize the existing and newly introduced patterns using a systematic nomenclature; studying 26 patterns in total. We compare these patterns in terms of energy efficiency and the average number of users supported, via a combination of analysis and simulation. We also compare the performance of CSO with two benchmark algorithms. We show that the average number of users can be captured by one parameter. Moreover, we find that the distribution of the number of users is close to Gaussian, with a tractable variance. Our results demonstrate that several patterns that activate only one out of three sectors are particularly beneficial; such CSO patterns have not been studied before.

With the exponential increase in mobile internet traffic driven by a new generation of wireless devices, future cellular networks face a great challenge to meet this overwhelming demand of network capacity. At the same time, the demand for higher data rates and the ever-increasing number of wireless users led to rapid increases in power consumption and operating cost of cellular networks. One potential solution to address these issues is to overlay small cell networks with macrocell networks as a means to provide higher network capacity and better coverage. However, the dense and random deployment of small cells and their uncoordinated operation raise important questions about the energy efficiency implications of such multi-tier networks. Another technique to improve energy efficiency in cellular networks is to introduce active/sleep (on/off) modes in macrocell base stations. In this paper, we investigate the design and the associated tradeoffs of energy efficient cellular networks through the deployment of sleeping strategies and small cells. Using a stochastic geometry based model, we derive the success probability and energy efficiency in homogeneous macrocell (single-tier) and heterogeneous K-tier wireless networks under different sleeping policies. In addition, we formulate the power consumption minimization and energy efficiency maximization problems, and determine the optimal operating regimes for macrocell base stations. Numerical results confirm the effectiveness of switching off base stations in homogeneous macrocell networks. Nevertheless, the gains in terms of energy efficiency depend on the type of sleeping strategy used. In addition, the deployment of small cells generally leads to higher energy efficiency but this gain saturates as the density of small cells increases. In a nutshell, our proposed framework provides an essential understanding on the deployment of future green heterogeneous networks.

The use of a segmented transducer for rib sparing in HIFU treatments

NoCs have become a critical component in many-core architectures. Usually, the preferred topology is the 2D-Mesh as it enables a tile-based layout significantly reducing the design effort. However, new emerging challenges such as power consumption need to be addressed. Looking at the NoC, routers and links not being used must be switched off, thus achieving large power savings. Topology and routing algorithm must be carefully designed as they may lack enough flexibility to switch off components for long periods of time.

The exponential increase in high rate traffic driven by the new generation of wireless services is expected to overload cellular network capacity in the near future. Femtocell networks have recently been proposed as an efficient and cost-effective solution to enhance cellular network capacity and coverage. However, dense and unplanned deployment of new Base Stations (BSs) and their uncoordinated operation may increase the system power consumption and rise co-channel interference. Thus, efficient schemes are essential for managing femtocell activity and improving the system performance. Classical cell switch off and discontinuous transmission (DTX) algorithms aim at improving the network Energy Efficiency (EE) in lightly loaded scenarios. In this paper, we propose a novel multi-cell architecture for Open Access femtocell networks, which also enables energy saving at medium and high loads without compromising the end-user performance.

Coordinated MultiPoint (CoMP) transmission / reception techniques have been adopted by the 3GPP community for LTE-Advanced (Long Term Evolution-Advanced) to increase spectral efficiency and cell-edge throughput. Energy efficiency (EE) was previously ignored by most research efforts and was not considered by 3GPP as an important performance indicator until very recently. EE concerns have spurred considerable research in recent years as they enable both energy consumption and CO2 reduction over conventional cellular systems. As the “green evolution” becomes a major trend, energy-efficient transmission becomes more and more important. In this paper we investigate energy efficiency i.e., the number of corrected bits that can be transmitted throughout the channel per joule of energy consumed of different downlink CoMP techniques in LTE-Advanced. In addition, we use system level simulation to evaluate the performance.

Coordinated multipoint (CoMP) transmission provides high theoretic gains in spectral efficiency with coherent joint transmission (JT) to multiple users. However, this requires accurate channel state information at the transmitter (CSIT) and also user groups with spatially compatible users. The aim of this paper is to use measured channels to investigate if significant CoMP gains can still be obtained with channel estimation errors. This turns out to be the case, but requires the combination of several techniques. We here focus on coherent downlink JT CoMP to multiple users within a cluster of cooperating base stations. The use of Kalman predictors is investigated to estimate the complex channel gains at the moment of transmission. It is shown that this can provide sufficient CSIT quality for JT CoMP even for long (>20 ms) system delays at 2.66 GHz at pedestrian velocities or, for lower delays, at 500 MHz, at vehicular velocities. A user grouping and resource allocation scheme that provides appropriate groups for CoMP is also suggested. It provides performance close to that obtained by exhaustive search at very low complexity, low feedback cost and very low backhaul cost. Finally, a robust linear precoder that takes channel uncertainties into account when designing the precoding matrix is considered. We show that, in challenging scenarios, this provides large gains compared with zero-forcing precoding. Evaluations of these design elements are based on measured channels with realistic noise and intercluster interference assumptions. These show that high JT CoMP gains can be expected, on average over large sets of user positions, when the above techniques are combined - especially in severely intracluster interference limited scenarios.

With the continuous increase of user requirement, the Information and Communication Technology (ICT) has developed rapidly. As a result, both capacity and coverage performances have been improved, and at the same time, the communication networks have been more energy-intensive. In order to improve the energy efficiency of cellular networks, the green communication must be realized in the future networks. In this article, we present a short survey on energy-efficient technology of cellular networks. Moreover, we classify them into three categories based on theirapplication scenarios: energy-efficient architectures, energy-efficient resource management and energy-efficient radio technologies. For the first scenario, the applications of relay, Coordinated Multiple Points (CoMP) and heterogeneous network are discussed in detail. For the second scenario, the switching off scheme will be introduced as an emphasis of this part. And for the third scenario, the Multiple-Input Multiple-Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) will be introduced as the representatives of the Energy-Efficient Radio Technologies. Finally, based on the technologies introduced above, a prospect forecast of the energy-efficient wireless cellular network is presented.

Green communications has received much attention recently. For cellular networks, the base stations (BSs) account for more than 50 percent of the energy consumption of the networks. Therefore, reducing the power consumption of BSs is crucial to enhance the energy efficiency of cellular networks. Meanwhile, the mobile data traffic is expected to increase exponentially. To accommodate the increasing data traffic with the limited radio frequency, enhancing the spectrum efficiency is critical for next generation cellular networks. In this paper, we propose an auction-based energy-spectrum trading scheme which exploits the cooperation between primary base stations (PBSs) and the secondary base stations (SBSs) to enhance the energy as well as spectrum efficiency of cellular networks. In the cooperation, by leveraging cognitive radio, PBSs share the licensed spectrum with SBSs, and the SBSs provide data service to the primary users under its coverage utilizing the shared bandwidth. The cooperation between PSBs and SBSs can significantly improve the energy and spectral efficiency of cellular networks. However, optimizing the bandwidth sharing between PBSs and SBSs is an NP-hard problem. Solving such problem using centralized algorithms is not computationally efficient, especially when considering a large number of PBSs and SBSs. Thus, we design an auction-based decentralized mechanism to enable the cooperation between PBSs and SBSs. Simulation results that demonstrated the performance and viability of the proposed decentralized mechanism.

In heterogeneous network several types of base station (BSs) are deployed to satisfying user traffic demands of future communication system and improve network performance. The coordinated multi point (CoMP) transmission technique is considered a key feature in future wireless network to improve both cell edge users throughput by exploiting interference. However, to provide CoMP transmission several BSs need to be active, which eventually increases network energy consumption. Therefore, there is need to investigate the effectiveness of CoMP technique for energy efficient communication, especially in heterogeneous network scenario, where different BSs have different characteristics. In this paper, we investigate the performance of wireless system in heterogeneous environment without and with CoMP. In particular, we analysed network outage with its energy consumption efficiency with varied coverage range. Mobiles are assumed to be connected to nearest BSs. Furthermore, we have also investigated energy efficiency vs. outage probability in terms of number of coordinating BSs for joint-transmission enabling sleep mode mechanism.

In this study, we investigate reference signal (RS) transmission schemes that aim to efficiently support coordinated multi-point (CoMP) transmission by providing improved channel estimation accuracy so that transmission parameters can be appropriately chosen on a cellular network. First, we investigate typical scenarios for transmission parameter selection with the widely used CoMP transmission and precoding schemes aligned with those considered for Long Term Evolution (LTE)-Advanced systems. Second, we investigate an RS transmission scheme that can provide accurate channel estimation even with severe inter-cell interference. Finally, we verify the performance benefit of the investigated scheme by a multi-cell link level evaluation. The results obtained indicate: 1) the investigated scheme improves block error rate performance compared to conventional schemes for fixed modulation and coding schemes (MCSs) allocation with a better precoding control accuracy on the LTE-Advanced system downlink and 2) the investigated scheme provides a throughput performance gain compared to conventional schemes for adaptive MCS allocation and coordinated beamforming.