Filipe D. Cardoso

Fading depth dependence on system bandwidth in mobile communications - an analytical approximation

A simple and computationally inexpensive analytical approach is proposed for the evaluation of the dependence of short-term fading depth on system bandwidth and environmental characteristics. The approach, accounting for the maximum difference in propagation path length and having the Rice factor as a parameter, is derived by fitting simulated data from a model in the literature. Application examples are presented for GSM, UMTS, HIPERLAN, and mobile broadband systems (MBS), giving some insight into the fading depth observed under different conditions with regard to system bandwidth and environmental characteristics. Macro-, micro-, and picocell environments are considered. In the microcellular environment, the fading depth experienced by UMTS is below the one for GSM by 0.1 to 5.5 dB, while in the picocellular one, the difference between GSM and UMTS is not significant, being almost independent of environment characteristics. When considering HIPERLAN or systems with larger bandwidths, the fading depth, both in micro and picocellular environments, is smaller than the one verified by UMTS; however, there is an increased dependence on environmental characteristics. In the macrocellular environment, the fading depth experienced by UMTS is about 6 to 11 dB below the one for GSM. Hence, different short-term fading margins should be considered for each system and working environment.

Energy efficient transmission techniques for LTE

The goal of the European ICT Project EARTH is to enhance energy efficiency of current LTE cellular networks by 50 percent, enabling operators to provide more extensive coverage, namely to less densely populated areas, while ensuring high levels of efficiency, hence, reducing the carbon footprint. In order to achieve this objective, different strategies, at different levels, are being addressed. Energy efficient transmission techniques for LTE, proposed within the framework of EARTH, are addressed and discussed, with an emphasis on beamforming and MIMO. It is concluded that the strategic objective of EARTH is achievable. Combined MIMO mode selection, resource allocation, scheduling and precoding strategies will allow an energy consumption reduction of more than 50 percent in macro-cells. A reduction in MIMO power consumption of 91.7 percent (factor of 12) can be achieved in pico-cells.

MIMO gain and energy efficiency in LTE

Current 3GPP specifications for LTE include the use of MIMO as a key technology. MIMO can be seen from two different perspectives: if increased data rates are targeted, for a given value of SNR, one gets improved data transmission; however, from an energy efficiency viewpoint, lower values of SNR are needed for the same reference data rate, therefore, allowing the reduction of the transmitted power, while providing the same data rate as the one for SISO. In this paper, a framework for evaluating the possible benefit of using MIMO instead of SISO, from the expected SNR improvement viewpoint is proposed, and results for different environments are presented and discussed. The proposed evaluation methodology allows one to properly assess the expected benefits of MIMO, therefore, providing guidelines to enable a proper SISO/MIMO mode selection according to the required service data rate. The analysis being presented is based on existing 3GPP models for data rate versus SNR in LTE. Simulation results for the ETU70 3GPP channel model are provided. It is observed that, for given reference data rates, significant SNR improvements can be obtained. Maximum values of 7.1, 15.7 and 18.0 dB SNR reduction are obtained for 2×2, 4×4 and 8×8 MIMO configurations, compared to the SISO case, therefore, allowing a significant reduction of the transmitted power, while providing the same target data rate as the one for SISO.

Beamforming Strategies for Energy Efficient Transmission in LTE

The actual internet traffic growth is challenging the sustainability of mobile networks, therefore, the energy efficiency of the mobile communication infrastructure becomes a topic of particular relevance. Decreasing CO2 emissions and energy demands while expanding the mobile infrastructure to satisfy traffic demands is essential. In this paper the energy efficient use of beamforming techniques and active antennas, in which an advanced antenna is utilized to direct the transmitted signal in a narrow direction, is evaluated. Slow beamforming based on reconfigurable antennas, exploits medium/long term variations of traffic in order to save energy. Fast beamforming, on the contrary, is immediately following the traffic distribution and can even allow saving more energy. From simulations it is observed that, when compared to existing state-of-art bases base stations, in a dense urban environment reconfigurable beamforming allows a maximum gain of about 8%. Adaptive beamforming, allows an additional consumed power reduction of up to 40%. Hence, the overall power consumption reduction that can be achieved by combining these techniques can be as high as 50%.

OConS Supported on Demand Radio Resource Allocation for Virtual Connectivity

With the increase of mobile network utilisation, the virtualisation of wireless resources becomes an important issue in the overall Virtual Networks (VNets) process. In this paper, the On Demand Virtual Network Radio Resource Allocation (OnDemand VRRA) mechanism is proposed to take advantage of the set of shared resources available within a cluster of wireless resources from different Radio Access Technologies (RATs) for wireless virtualisation. Optimising resource utilisation satisfying the VNet contracted capacity is its main objective. Furthermore, the mechanism is modelled according to the Open Connectivity Services (OConS) architecture, in order to demonstrate the advantages of its use within the OConS framework. Simulation results show that the introduction of OnDemand VRRA allows supporting the minimum bandwidth requirement in a wireless cluster, composed of several physical base stations from different RATs. The percentage of operation out of contract (i.e., below the virtual operator’s contracted capacity) for a VNet with guaranteed minimum service is zero for a number of end users in the VNet up to 80% of the total, which is higher than in other circumstances. One also observes that VNets providing guaranteed services can achieve the contracted data rate independently of the number of end users in other VNets.

A comparison between different approaches for fading evaluation in wideband mobile communications

Existing systems, eg., UMTS and HIPERLAN, and others to appear in the future, are wideband ones; hence, the observed short-term fading depths are usually smaller than the ones obtained from the Rayleigh or Ricean distributions. Overestimating short-term fading margins, by considering those distributions, leads to shorter cells, or to higher transmitting powers, thus, higher interference. In this paper, one proposes a simple relationship between the physical and the geometrical environment properties, and the rms delay spread of the propagation channel, therefore, allowing one to use different model for evaluating the fading depth in a given environment. Using the proposed relationship, fading depth results from two different models are compared, and a good agreement is verified. Furthermore, since the presented models account for the influence of system bandwidth, hence, providing more accurate fading margins (e.g., the fading margins for UMTS are usually 2 to 10 dB below the ones obtained from Rayleigh or Ricean distributions), the proposed approach allows a better power budget evaluation, enabling the optimisation of existing networks, and better and less costly radio network planning of future ones.

Physical layer aware network architecture for the future internet

In this article, physical layer awareness in access, core, and metro networks is addressed, and a Physical Layer Aware Network Architecture Framework for the Future Internet is presented and discussed, as proposed within the framework of the European ICT Project 4WARD. Current limitations and shortcomings of the Internet architecture are driving research trends at a global scale toward a novel, secure, and flexible architecture. This Future Internet architecture must allow for the co-existence and cooperation of multiple networks on common platforms, through the virtualization of network resources. Possible solutions embrace a full range of technologies, from fiber backbones to wireless access networks. The virtualization of physical networking resources will enhance the possibility of handling different profiles, while providing the impression of mutual isolation. This abstraction strategy implies the use of well elaborated mechanisms in order to deal with channel impairments and requirements, in both wireless (access) and optical (core) environments.

A Time-Domain Based Approach for Short-Term Fading Depth Evaluation in Wideband Mobile Communication Systems

In this paper a time-domain technique for wideband fading depth evaluation, is proposed, which is applicable to both Line-of-Sight and Non-Line-of-Sight cases, and the probability functions of the wideband received power are derived, contributing for filling in the gap of short-term fading characterisation in wideband systems. Application examples for different systems, namely GSM, UMTS and HIPERLAN/2, working in different standard reference environments, are shown. As expected, it is observed that Rayleigh and Rice distributions are appropriate for evaluating the fading margins for GSM in some environments; nevertheless, for UMTS and HIPERLAN/2, fading margins are usually well below the ones obtained from considering these narrowband distributions, the differences reaching up to around 10 and 13 dB, respectively.A simple relationship between the physical and the geometrical environment properties, and the rms delay spread of the propagation channel is also proposed, establishing a relationship between two models independently derived by different authors. Using the proposed relationship, fading depth results from the proposed time-domain technique are compared with the ones for an environment-geometry based one, and a good agreement is verified. The difference in fading depth between both approaches is roughly below 2 dB.

Short-term fading depth dependence on antenna characteristics in wideband mobile communications

The use of directional antennas at the mobile terminal or the base station, and its influence on the observed values of short-term fading depth, is addressed. This influence is modelled through the variation of the Rice factor and the maximum difference in propagation path length among different arriving components, relative to the case when omnidirectional antennas are used. Expressions for the dependence of these parameters on the antenna beamwidth, for different statistical distributions for the angle-of-arrival of arriving waves, and different types of antennas are presented. For illustration, results on the fading depth observed by UMTS and HIPERLAN/2 in different environments are presented and discussed. Globally, when using directional antennas, fading depth reduction is observed in micro-cellular environments; in macro- and pico-cellular ones, fading depth degradation can occur depending on the environment and system characteristics.

Fading depth evaluation in mobile communications - from GSM to future mobile broadband systems

A technique for fading depth characterisation in wideband mobile communications systems is described. The approach, based on the eigenvalue decomposition technique, allows deriving the cumulative distribution functions of the received power for Rayleigh and Ricean fading channels. Application examples for different systems, namely GSM, UNITS, HIPERLAN and MBS, working within different environments, as proposed by standard-setting bodies, are shown in detail, and the results are discussed, giving a general insight into the fading depth behaviour. In the considered environments, the fading depth experienced by GSM is between 9.4 and 18.4 dB. The fading depth observed by UNITS is below the one for GSM by 2.1 to 10.3 dB. Regarding HIPERLAN, the observed fading depth is 2.6 to 4.9 dB below the one for UNITS. MBS experiences fading depths that are usually below 9.7 dB (a worst case of 10.6 dB is observed in city streets under NLoS). Since the observed fading depth depends on the system and environment characteristics, different fading margins should be considered for each system and working environment.