Digital Signal Processing Reference
In-Depth Information
Chapter 4
Distributed Monitoring for Opportunistic
Radios
4.1 To Not Interfere
This chapter focuses on the monitoring challenge that is faced by opportunistic ra-
dios. First, the exact problem context of this chapter is introduced. Next, it is illus-
trated where this fits into the cognitive design flow introduced in Chap. 3. Finally,
some measurements are given to emphasize the complexity of this problem.
4.1.1 Problem Context
To solve the spectrum scarcity problem, the reuse of licensed spectrum when it is
locally not in use is receiving more and more attention. When such sharing is con-
sidered, it is very important that the secondary users adapt their transmission power
optimally so that they don't harm the primary user, but simultaneously maximize the
throughput of the secondary network. The straightforward approach for this prob-
lem is to adapt the transmission power based on local sensing or monitoring or make
use of a geolocation database information. The sensing puts significant sensitivity
requirements on the sensing device, and moreover requires taking into account large
design margins to account for worst-case fading and shadowing of the sensing de-
vice (see Fig.
4.1
). The database approach relaxes the sensitivity requirements, but
is a static approach that is expected to also consider significant margins.
To improve spatial planning of networks, this chapter introduces a distributed
and practical monitoring algorithm that
(a) relaxes the sensitivity requirements and hence allows for less expensive hard-
ware and more practical deployments,
(b) achieves optimal power allocation as a function of actual and arbitrary propaga-
tion conditions.
Moreover, it will be shown that the algorithm scales well and is robust against mea-
surement noise. Distributed or enhanced monitoring is an important enabler for an
