Overview

The evolving 802.11 WLAN technology has been chasing for higher speed. Consider the entire 802.11x family, starting from the legacy 802.11a/b/g, to the current-generation 802.11n and the upcoming 802.11ac, the supported, maximum speed has improved from 11Mbps to 600Mbps and 6.93Gbps correspondingly. As 802.11x races for higher speed, we believe that an equally important goal is its energy efficiency. In this project, we seek for the ideal technology which balances between speed and energy during the race, since faster transmission is typically achieved with larger power consumption and potentially higher energy cost.

Research Progress

EERA: Energy-based Rate Adaptation for 802.11n

Rate adaptation (RA) has been used to achieve high goodput. In this work, we explore to use RA for energy efficiency in 802.11n NICs. We show that current MIMO RA algorithms are not energy efficient for NICs despite ensuring high throughput. The fundamental problem is that, the high-throughput setting is not equivalent to the energy-efficient one. Marginal throughput gain may be realized at high energy cost. We propose EERA, an energy-based RA solution that trades off goodput for energy savings at NICs. Our experiments have confirmed its energy savings at NICs while keeping the cost at the device level and across clients acceptable.

CMES: Collaborative Energy Save for MIMO 802.11 Wireless Networks

This work experimentally studies the energy consumption of multiple-antenna MIMO 802.11 devices. Our measurements reveal an increase in power consumption and speed with the number of antennas. State of the art proposals have limitations to save energy in MIMO 802.11 networks. First, they focus on either maximizing speed or minimizing power consumption. Second, they only seek to minimize energy for the receiver side of mobile devices. As a result, they present limitations to utilize MIMO speed gains and to save energy in MIMO 802.11 infrastructure. To this end, we design Collaborative MIMO Energy Save (CMES), which seeks to identify the transmitterreceiver most energy efficient antenna setting, at runtime. Our experiments with commodity MIMO 802.11n testbeds confirm that CMES can provide energy savings in real scenarios.

What is Wrong/Right with IEEE 802.11n SMPS?

The IEEE 802.11n standard has proposed a new Spatial Multiplexing Power Save (SMPS) feature, which allows for a station to retain one active receive chain, to mitigate MIMO circuitry power consumption. But does it work in all cases? Our experiments reveal that SMPS may not always save power compared with multiple active chains at the receiver. Even when it does, it may be proven more energy hungry. In this work, we seek to uncover the "good", the "bad" and the "ugly" of SMPS using real experiments. We further devise a MIMO Receiver Energy Save (MRES) algorithm, which seeks to identify and set the most energy-efficient receive chain setting, by using a novel, low-overhead sampling scheme. Our prototype experiments show that, MRES outperforms SMPS with energy savings up to 37%.

Publication

Team Member

• Chunyi Peng  (Purdue University)
• Songwu Lu  (University of California, Los Angeles)
• Ioannis Pefkianakis  (Researcher, HP Lab)
• Suk-Bok Lee  (Faculty, Hanyang University, KR)
• Chi-Yu Li  (University of California, Los Angeles)

Research Support