Performance Analysis of a Burst Transmission Mechanism Using Microsleep Operation for Green IEEE 802.11 WLANs +
Footnote †: journal: Applied Sciences  
[PERSON]  
1 Instituto de Computacao (IC), Universidade Estadual de Campinas (UNICAMP), Av. [PERSON] 1251, 13083-852 Campinas, SP, Brazil; [EMAIL_ADDRESS]  
[PERSON]  
1 Instituto de Computacao (IC), Universidade Estadual de Campinas (UNICAMP), Av. [PERSON] 1251, 13083-852 Campinas, SP, Brazil; [EMAIL_ADDRESS]  
[PERSON]  
2 Centre Tecnologic de Telecomunicacions de Catalunya (CTTC/CERCA), Parc Mediterrani de la Tecnologia (PMT) - Building B4, Av. [PERSON] 7, 08860 Castelldefels, Barcelona, Spain; [EMAIL_ADDRESS]  
Dipartimento di Ingegneria e Scienza dell'Informazione (DISI), Universita degli Studi di Trento (UNITN), Via Sommarive 9, 38123 Povo, Trento, Italy; [EMAIL_ADDRESS]  
[PERSON]  
3 Correspondence: [EMAIL_ADDRESS]; Tel. : +55-19-3521-5878  
The huge amount of WLAN traffic generated can cause devices to quickly drain their batteries due to the use of Wi-Fi. In continuous operation, an active Wi-Fi interface can consume more than 70% of the total energy in a smartphone when the screen is off, and can still consume 50% when the power save mode is enabled [3; 4; 5]. The reduction of such high energy consumption has been enabled by the definition of two Wi-Fi certified power save mechanisms that are based on the 802.11 Power Save Mode (PSM) and the 802.11e Automatic Power Save Delivery (APSD) [6]. In PSM and APSD, an 802.11 station (STA) can enter a low-power sleep state when no transmission and reception of data are expected on a shared wireless channel. However, when there is a large amount of data to either transmit or receive, an STA remains awake for a long period of time, since it needs to wait for its turn to transmit or receive data while other STAs occupy the channel. As a result, an STA wastes energy when it receives data sent to other STAs during waiting periods (i.e., overhearing). Such waiting periods of high energy waste in which data are sent to other STAs can be exploited to allow an STA to enter the sleep state, hence avoiding overhearing. This operation is called microsleep as it enables sleep periods in the order of tens, hundreds, or even thousands of microseconds. Microsleep was introduced in the 802.11n amendment by the Power Save Multi-Poll (PSMP) mechanism [6]. In addition, an extension of the PSMP microsleep was defined in the 802.11 ac Transmission Opportunity Power Save Mode (TXOP PSM) [6]. An overview of these and other power save mechanisms including microsleep [7; 8; 9; 10; 11; 12] is presented in Section 2. Microsleep has the potential to significantly increase the energy efficiency while maintaining the desired performance. It is particularly suited under high traffic loads and in dense WLANs with a large number of STAs connected to a single Access Point (AP) or to multiple overlapping APs. Such dense WLAN scenarios occur in Smart Homes, High Efficiency WLANs (HEWs), and the IoT [13]. In addition, microsleep operation can be combined with power save mechanisms designed for low traffic loads [14], such as PSM and APSD, to provide the highest STA energy efficiency across all possible traffic loads. Unfortunately, when existing mechanisms are employed, an STA is not able to frequently take advantage of microsleep due to the time delays and energy demands for the transitions to go to sleep and wake up. The duration and power consumption of these transitions depend on the hardware design and can be different for different STAs. For example, the transition time can be of some hundreds or few thousands of microseconds and there can be a peak of power consumption in a sleep to awake transition [15; 16; 17; 18; 19]. Moreover, microsleep is feasible only if a data transmission has longer duration than the awake and sleep transitions. In addition, the data transmission duration varies with the transmission data length and the Physical (PHY) data transmission rate employed.