  In the past few years we have witnessed the paradigm shift from static
spectrum allocation to dynamic spectrum access/sharing. Orthogonal
Frequency-Division Multiple Access (OFDMA) is a promising mechanism to
implement the agile spectrum access. However, in wireless distributed networks
where tight synchronization is infeasible, OFDMA faces the problem of
cross-band interference. Subcarriers used by different users are no longer
orthogonal, and transmissions operating on non-overlapping subcarriers can
interfere with each other. In this paper, we explore the cause of cross-band
interference and analytically quantify its strength and impact on packet
transmissions. Our analysis captures three key practical artifacts: inter-link
frequency offset, temporal sampling mismatch and power heterogeneity. To our
best knowledge, this work is the first to systematically analyze the cause and
impact of cross-band interference. Using insights from our analysis, we then
build and compared three mitigating methods to combat cross-band interference.
Analytical and simulation results show that placing frequency guardband at link
boundaries is the most effective solution in distributed spectrum sharing,
while the other two frequency-domain methods are sensitive to either temporal
sampling mismatch or inter-link frequency offset. We find that the proper
guardband size depends heavily on power heterogeneity. Consequently, protocol
designs for dynamic spectrum access should carefully take into account the
cross-band interference when configuring spectrum usage.
