Fred Richter

Energy Efficiency Aspects of Base Station Deployment Strategies for Cellular Networks

In the strive for lessening of the environmental impact of the information and communication industry, energy consumption of communication networks has recently received increased attention. Although cellular networks account for a rather small share of energy use, lowering their energy con- sumption appears beneficial from an economical perspective. In this regard, the deployment of small, low power base stations, alongside conventional sites is often believed to greatly lower the energy consumption of cellular radio networks. This paper investigates on the impact of deployment strategies on the power consumption of mobile radio networks. We consider layouts featuring varying numbers of micro base stations per cell in addition to conventional macro sites. We introduce the concept of area power consumption as a system performance metric and employ simulations to evaluate potential improvements of this metric through the use of micro base stations. The results suggest, that for scenarios with full traffic load, the use of micro base stations has a rather moderate effect on the area power consumption of a cellular network.

Energy Efficiency Improvements through Micro Sites in Cellular Mobile Radio Networks

Efforts to increase the energy efficiency of infor- mation and communication systems in general and cellular mobile radio networks in particular has recently gained mo- mentum. Besides positive environmental effects, lowering the energy consumption of mobile radio systems appears beneficial from an economical perspective. In this regard, the deployment of small, low power base stations, alongside conventional sites is often believed to greatly lower the energy consumption of cellular mobile radio networks. In this paper we investigate that matter in more detail from a deployment perspective. We evaluate potential improvements of the area power consumption achievable with network layouts featuring varying numbers of micro sites in addition to conventional macro sites for given system performance targets under full load conditions.

Traffic Demand and Energy Efficiency in Heterogeneous Cellular Mobile Radio Networks

Optimization of the energy efficiency is considered not only to positively contribute to the ecological assessment, but gains in importance from operators point of view as well, since energy costs for running a mobile radio network have an increasing share of the operational expenditure. From this perspective, the utilization of small, low power base stations is regarded as a promising strategy to enhance a networks throughput and to increase the energy efficiency. In this paper we investigate on the efficiency of homogeneous and heterogeneous networks consisting of a varying number of micro sites with regard to traffic load conditions.

Cellular Mobile Network Densification Utilizing Micro Base Stations

Energy efficiency in information and communications technology, and in cellular mobile radio networks in particular, is gaining in importance not only with regard to the ecological assessment. Reducing the power consumption of mobile radio systems has recently attracted attention of network operators as energy costs make up a vast portion of todays operational expenditure. In this regard, it is often talked of deploying small, low power base stations to significantly increase energy efficiency of cellular radio networks. In this paper we study the efficiency of deployment layouts featuring micro base stations in comparison with conventional pure macro systems by means of area power consumption and system throughput. We further introduce the notion of measuring energy efficiency by evaluating the ratio of achievable system throughput to power spent in the network.

Micro base stations in load constrained cellular mobile radio networks

Future cellular mobile radio networks will exhibit a much more dense base station deployment than 2nd or 3rd generation communications systems, particularly with regard to traffic coverage. Hence, a significant increase in power consumption of cellular networks can be expected. In order to counter this trend, energy efficiency of such networks should be increased considerably. Concerning energy efficiency, utilizing micro base stations with their smaller power consumption capabilities appear promising. In this paper we study various homogeneous and heterogeneous deployment strategies incorporating micro base stations with focus on energy efficiency represented by power consumption and throughput. Further, we deal with the impact of different load scenarios on energy efficiency of the various network topologies in more detail.

Energy saving and capacity gain of micro sites in regular LTE networks: downlink traffic layer analysis

We study the effect of deployment of low cost, low power micro base stations along with macro base stations on energy consumption and capacity of downlink LTE. [1] studied this problem, using spectral area efficiency as the performance metric. We show that the analysis proposed in [1] is inaccurate as the traffic layer specifications of LTE networks is not included in the analysis. We also investigate the effect of user association and frequency band allocation schemes on energy consumption and capacity of LTE networks. Specifically, we add the following three important elements to the analysis proposed in [1]: a traffic layer analysis that take both the physical and traffic layer specifications of LTE downlink into account; a threshold-based policy to optimally associate users to base stations; and an allocation scheme to better allocate the frequency band to macro and micro base stations. We investigate all combinations of these elements through numerical evaluation and observe that 1. there are important differences between traffic layer and physical layer analysis, 2. threshold-based user association policy improve the traffic capacity of the network by up to 33% without affecting the energy profile of the network, and 3. considerable energy saving and capacity gain can be achieved thought a careful allocation of the frequency band to macro and micro base stations. Finally, we determine the optimal network configuration and show that up to 46% saving in energy can be achieved compared to the case that no micro base stations are deployed in the network.

Base Station Placement Based on Force Fields

Network planning and optimization becomes more and more important in cellular mobile communications due to the growing complexity of the networks. Besides taking new key performance indicators into account such as energy efficiency, the augmented heterogeneity, caused by a variety of radio access technologies (e.g., 3G and beyond as well as WiFi) and network node types (e.g., micro and femto cells), leads to an exploding dimension of the planning process. On the other hand, the degrees of freedom increase as well, giving rise for new optimization techniques. In this paper a novel approach for optimizing cellular deployments is presented. The model is based on characterizing the interrelations (among base stations and between base stations and the environment) by force fields, motivated by the physics of multiple particles in a closed system. Further, an algorithm is proposed which tracks the trajectory of base station locations under the presence of forces, focusing on finding a balanced state with minimal net force. Also, it is elaborated on how to combine different force types in order to capture different quality aspects of a network.

SINR Balancing for the Multi-User Downlink under General Power Constraints

We address the problem of maximizing the minimum signal to interference and noise ratio of individual users via linear preceding in a multiuser downlink channel with multiple antennas at the transmitter and single antenna receivers. While previous research aimed at optimizing transmission under a total power constraint over all antennas, we provide a framework for solving the optimization under power constraints per arbitrary groups of antennas. The results include power constraints per antenna as well as a sum-power constraint as special cases. The scenario is motivated by recent interest in so called network- MIMO techniques where mobile terminals may be served by multiple base stations subjected to individual power constraints.

Transmitter-Based Minimization of Error Rates in the Downlink of Wireless Systems

Using CDMA technology, one has to contend with interference in frequency-selective channels caused by multipath propagation and fading. Transmitter-based methods such as zero forcing joint transmission and transmit Wiener filter only reduce the bit error rate indirectly and do not exploit the knowledge of the transmit data symbols. Nonlinear optimization strategies, e.g., the Constrained Minimum BER MUT approach, outperform such methods while the computational complexity prevents their implementation. In this paper, a spread-spectrum TDD-CDMA downlink transmission system with 4-QAM modulation is considered, whereas perfect channel knowledge both in the transmitter and the receiver is assumed. Deriving a convex optimization problem, an alternative solution method with considerable decrease of the complexity is proposed.