Section: New Results

Green networking

Participants : Sara Alouf, Nicaise Choungmo Fofack, Delia Ciullo, Alain Jean-Marie.

Analysis of power saving in cellular networks with continuous connectivity

We have pursued our effort in the analysis of the continuous connectivity mode used in 4G cellular networks. Assuming Poisson traffic at each user, S. Alouf and V. Mancuso (Institute IMDEA Networks, Madrid, Spain) analyze the impact of 3GPP-defined power saving mechanisms on the performance of users with continuous connectivity. Each downlink mobile user's traffic is seen as $M/G/1$ queue, and the base station's downlink traffic as an $M/G/1PS$ queue with multiple classes and inhomogeneous vacations. The model is validated through packet-level simulations in [35] ; its results show that consistent power saving can be achieved in the wireless access network.

The case of web traffic is investigated in [13] where the same authors, with the participation of N. Choungmo Fofack, perform in addition a sensitivity analysis to assess the impact of model parameters on the performance and cost metrics. It is found that significant power save can be achieved while users are guaranteed to experience high performance. Important outcomes of this work include the need to limit the number of active users in a cell (to less than 350 users – reasonable for 3GPP LTE, 802.16 and HSPA networks) in order to limit the web page download time, and the need to limit the web page size as large pages can dramatically decrease the energy saving. A green attitude would be to design web sites with short pages having few embedded objects, enabling cellular operators to use reasonable power save parameters and yet achieve a dramatic cost economy at both base station and mobile user sides, without any quality degradation.

Analysis of base station sleep modes in cellular networks

D. Ciullo, L. Chiaraviglio (Inria project-team Mascotte ), M. Ajmone Marsan (Politecnico di Torino, Italy and Institute IMDEA Networks, Spain), M. Mellia and M. Meo (Politecnico di Torino, Italy) study in [78] base station sleep modes. Putting into sleep mode some base stations in periods of low traffic improves the energy efficiency of cellular access networks. Two schemes are considered whether the sleep mode is activated once per day or multiple times per day having progressively fewer active base stations. For both schemes, the optimal base station sleep times are identified according to the traffic. Considering real traffic traces, the study reveals that significant energy saving can be achieved, the actual value strongly depending on the traffic pattern. An important result is that most of the potential savings can be attained with a single daily sleep mode, avoiding the increased complexity coming from the use of multiple sleep modes per day.

Analysis of sleep modes in backbone networks

The case of backbone networks is considered in [86] where L. Chiaraviglio (Inria project-team Mascotte )), D. Ciullo, M. Mellia and M. Meo (Politecnico di Torino, Italy) formulate a theoretical model based on random graph theory. This model allows to estimate the potential gains achievable by adopting sleep modes in fixed networks where some devices consume energy proportionally to the handled traffic. Putting a given fraction of devices in sleep mode reduces the energy these consume but increases the energy consumed by the devices still active due to the additional load these have to handle. The model of [86] allows to predict how much energy can be saved in different scenarios. The results show that sleep modes can be successfully combined with load proportional solutions. However, if the static power consumption component is one order of magnitude less than the load proportional component, then sleep modes are no longer convenient. Thanks to random graph theory, this model gauges the impact of different properties of the network topology.