On the feasibility of effective opportunistic spectrum access

Abstract

Dynamic spectrum access networks are designed to allow today's bandwidth hungry "secondary devices" to share spectrum allocated to legacy devices, or "primary users." The success of this wireless communication model relies on the availability of unused spectrum, and the ability of secondary devices to utilize spectrum without disrupting transmissions of primary users. While recent measurement studies have shown that there is sufficient underutilized spectrum available, little is known about whether secondary devices can efficiently make use of available spectrum while minimizing disruptions to primary users.In this paper, we present the first comprehensive study on the presence of "usable" spectrum in opportunistic spectrum access systems, and whether sufficient spectrum can be extracted by secondary devices to support traditional networking applications. We use for our study fine-grain usage traces of a wide spectrum range (20MHz-6GHz) taken at 4 locations in Germany, the Netherlands, and Santa Barbara, California. Our study shows that on average, 54% of spectrum is never used and 26% is only partially used. Surprisingly, in this 26% of partially used spectrum, secondary devices can utilize very little spectrum using conservative access policies to minimize interference with primary users. Even assuming an optimal access scheme and extensive statistical knowledge of primary user access patterns, a user can only extract between 20-30% of the total available spectrum. To provide better spectrum availability, we propose frequency bundling, where secondary devices build reliable channels by combining multiple unreliable frequencies into virtual frequency bundles. Analyzing our traces, we find that there is little correlation of spectrum availability across channels, and that bundling random channels together can provide sustained periods of reliable transmission with only short interruptions.

Building efficient spectrum-agile devices for dummies

“…Each sweep over the entire 1.6GHz bandwidth takes about 1.8s and captures 8,192 samples, with each sample spanning 200kHz. Although the measurement data does not capture channel usage patterns shorter than 1.8s, channel statistics have been shown to remain unchanged at shorter time scales [15]. This strongly suggests that we can expect such statistics to be present at sufficiently small time scales to make RODIN useful.…”

“…While this example deals with WiFi networks for clarity in exposition, the infeasibility of enhancing throughput by merely increasing bandwidth is also prevalent in non-WiFi networks. For example, a study of GSM usage patterns [15] shows that a wideband device cannot operate within the GSM band without some form of spectrum agility.…”

“…Hence, in order to sustain a 20MHz transmission, multiple discontiguous 1MHz (or narrower) channels have to be bonded together. Given that the correlation between the different channels is low [15], such a device can expect to continuously reconfigure its set of bonded channels to avoid primary user interference. The otherwise long outage duration that it faces, as shown in Fig.…”

A Wireless Spectrum Analyzer in Your Pocket

“…Authors in [18] have monitored a wide spectrum range (20MHz-6GHz) from three countries and reported that 54% of spectrum is never used and 26% is partially in use. Other work [10,21] has found substantial spectrum resources in TV whitespaces, and proposed different spectrum database designs to better predict vacant TV spectrum.…”

Learning and decision making with negative externality for opportunistic spectrum access

“…Although the existing dynamic spectrum access schemes have greatly improved the spectrum utilization efficiency, due to the mobility of nodes and the dynamics of the channel variation, the accuracy of players' decisions is limited and remains a challenge to fully utilize the scarce spectrum resources [12]. Nevertheless, players in a cognitive network are generally intelligent and able to optimize their performance.…”