Frequency-aware rate adaptation and MAC protocols

Abstract

There has been burgeoning interest in wireless technologies that can use wider frequency spectrum. Technology advances, such as 802.11n and ultra-wideband (UWB), are pushing toward wider frequency bands. The analog-to-digital TV transition has made 100-250 MHz of digital whitespace bandwidth available for unlicensed access. Also, recent work on WiFi networks has advocated discarding the notion of channelization and allowing all nodes to access the wide 802.11 spectrum in order to improve load balancing. This shift towards wider bands presents an opportunity to exploit frequency diversity. Specifically, frequencies that are far from each other in the spectrum have significantly different SNRs, and good frequencies differ across sender-receiver pairs.This paper presents FARA, a combined frequency-aware rate adaptation and MAC protocol. FARA makes three departures from conventional wireless network design: First, it presents a scheme to robustly compute per-frequency SNRs using normal data transmissions. Second, instead of using one bit rate per link, it enables a sender to adapt the bitrate independently across frequencies based on these per-frequency SNRs. Third, in contrast to traditional frequency-oblivious MAC protocols, it introduces a MAC protocol that allocates to a sender-receiver pair the frequencies that work best for that pair. We have implemented FARA in FPGA on a wideband 802.11-compatible radio platform. Our experiments reveal that FARA provides a 3.1× throughput improvement in comparison to frequency-oblivious systems that occupy the same spectrum.

A case for adaptive sub-carrier level power allocation in OFDMA networks

“…However, at a receiver, since each sub-carrier typically experiences a different fade (as seen both by our work and in prior related efforts such as [16]) the transmission rates that can be supported by the different sub-carriers can differ. Spatial and temporal diversity can further complicate the communications between a single sender and multiple receivers at different times.…”

“…Thus, poor received quality on a few sub-carriers can affect the supported transmission rate. To cope with this, Rahul et al [16], propose FARA, a scheme that supports per sub-carrier rate adaptation. While FARA provides gains over traditional rate-adaptation schemes, it does not address the problem of frequency-selectivity directly and does not utilize the available power budget efficiently.…”

TiM: Fine-Grained Rate Adaptation in WLANs

“…Many current works focus on evaluating channel SNR to estimate bitrate [24] [10] [18] [16]. In [16], it demonstrates to use different rate adaptive modulation schemes with varied frequency band. In [5], Camp et al propose a framework to evaluate rate adaptation schemes.…”

“…The widely used modulation schemes in WLANs are designed mainly in amplitude-phase domain, such as BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 16-QAM (Quadrature Amplitude Modulation) and 64-QAM. Based on this 2 Dimension (2D) scheme, TiM adds time dimension to make it into 3D.…”

A context-aware approach to wireless transmission adaptation

“…The introduction of SDR platforms provided rate adaptation protocols with sophisticated PHY-level information such as noise and signal levels [21], decoder confidence levels [24] and channel coherence time [10]. To best of our knowledge, energy and spectrum efficiency have not been addressed in an SDR setting.…”