A Power-Saving and Robust Point Coordination Function for the Transmission of VoIP over 802.11

Abstract

Group-polling based schemes for the enhancement of the Point Coordination Function (PCF) in the 802.11 have been supposed to be the most efficient scheme for the transmission of VoIP frame. However, most of the group-polling schemes are not energy-efficient at all due to the fact that all the stations in this list must listen to the channel during all the transmissions belonging to this polling list. Furthermore, if some stations loss this grouppolling frame, it will result in many empty group slots leading to unstable system states. In this article, we propose a Power-Saving and Robust Point Coordination function (PSR-PCF) for the transmission of VoIP over 802.11. Any stations can set its wakeup timer and fall asleep according to the schedule information of the received group polling frame. In order to make this system more robust, we propose a chained-scheme, that is, the MAC address of next active station is piggybacked in the frame header of the uplink data frame to the AP with no additional overheads. Analysis shows that the energy consumption can be reduced by over 93.2% compared with that of ICF [20]. The number of active VoIP stations sustained can be up to about 260 without any data loss under the 802.11a with 54Mbps data rate. Whereas, in the same parameters of 802.11a, the PCF with the Round-Robin (RR) scheduler will have more than 10% data losses if the number of active VoIP stations is larger than 60.

A Review of Software-Defined WLANs: Architectures and Central Control Mechanisms

“…From the energy point of view, the 802.11 standards provide two mechanisms: power saving mode (PSM), and automatic power saving delivery (APSD). However, the efficiency of these algorithms reduces as network density increases [51], [52]. For example, the concurrent wake-up of multiple clients results in collision and higher energy consumption [53].…”

Analysis of an energy-efficient MAC protocol based on polling for IEEE 802.11 WLANs

“…In addition to the power saving features defined in the IEEE 802.11 Standards, power saving has received much attention in recent years [2]. Particularly related to this paper are the power saving mechanisms based on polling presented in [8]- [10]. These inspiring works propose different structures for the beacons.…”

“…In [8], the STAs of later order may consume more energy due to overhearing, whereas in [9] this problem is effectively addressed at the cost of certain throughput degradation. The work in [10] copes with the limitations of [8] and [9] in terms of robustness and reliability.…”

“…In its turn, GreenPoll [6] differs from the proposed schemes in [8]- [10] in the fact that STAs enable sleeping processes based only on the virtual carrier sense information attached to the transmitted beacon, control, and data packets. Therefore, GreenPoll can avoid explicit scheduling information attached to the beacons and overcome scalability limitations.…”

An energy-efficient point coordination function using bidirectional transmissions of fixed duration for infrastructure IEEE 802.11 WLANs

“…When the number of active stations is large, the last station must consume energy to overhear all the transmissions of all stations to and from the AP. To optimize energy consumption, a group-polling frame with the polling order of stations and their assigned transmission times was introduced in [13], where a station is in the doze state most of CFP, except for when it intends to transmit a data frame. In [7] the Unified Point Coordination Function (UPCF) was proposed, which defines a vector-list poll frame and a power-conserving scheduling so that PS stations can spend as less energy as possible during the polling activity.…”