Fast Spectrum Shaping for Next-Generation Wireless Networks

Spectrum management and device coordination for dynamic spectrum access (DSA) networks have received significant research attention. However, current wireless devices have yet to fully embrace DSA networks due to the difficulties in realizing spectrum-agile communications. We address the practical hurdles and present solutions toward implementing DSA devices, answering an important question “what is a simple practical extension to current wireless devices that makes them spectrum-agile?” To this end, we propose RODIN, a general per-frame spectrum-shaping protocol that has the following features to support DSA in commercial off-the-shelf (COTS) wireless devices: direct manipulation of passband signals from COTS devices, fast FPGA-based spectrum shaping, and a novel preamble design for spectrum agreement. RODIN uses an FPGA-based spectrum shaper together with a preamble I-FOP to achieve per-frame spectrum shaping with a delay of under 10 μs.

1 Introduction

Dynamic spectrum access (DSA), or spectrum agility, has become a popular solution to the problem of spectrum scarcity in wireless networks [6]. New devices that are designed to use only a monolithic block of spectrum can no longer expect to increase throughput by simply increasing their bandwidth. In fact, the throughput of an 802.11n device operating at 40 MHz can even be lower than its throughput at 20 MHz when encountering a 20-MHz interference from another 802.11 g or 802.11n device [8], [22]. Numerous other studies [12], [18] have reported performance anomalies when rate or bandwidth is blindly increased in an attempt to wrest more throughput from an overcrowded spectrum. We can only expect such problems to compound with the introduction of 802.11ac that support up to 160-MHz bandwidth. While this example deals with Wi-Fi networks for clarity in exposition, the infeasibility of enhancing throughput by merely increasing bandwidth is also prevalent in non-Wi-Fi 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.