Transactions on Computational Science XXIX by Marina L. Gavrilova & C. J. Kenneth Tan

Author:Marina L. Gavrilova & C. J. Kenneth Tan
Language: eng
Format: epub
Publisher: Springer Berlin Heidelberg, Berlin, Heidelberg

Keywords

Cognitive radio networksSingle adaptive thresholdTwo adaptive thresholdsTwo detectorsCentralized spectrum sensing

1 Introduction

Nowadays, call drop is one of the major issues in wireless communication system. This happens due to the limited bandwidth, phenomena are known as “spectrum scarcity”. Only the licensed users (those who have assigned or allotted frequency band) do not affect from this. But the other unlicensed users or secondary users (SUs) face spectrum scarcity problem. To resolve such problem, Federal Communication Commission (FCC) analyzed this matter and concluded in their report that this problem arises due to the shortage of spectrum because numbers of users are increasing. Therefore, the solution is to choose another appropriate frequency band whose operational characteristics are similar to the mobile band. TV band is quite similar and 70% of TV band is unused, thus efficient utilization of TV band by mobile users reduce spectrum scarcity problem [1].

Further, in 1998, Dr. Joseph Mitola proposed 5G concepts to solve the spectrum underutilization problem. In 5G or cognitive radio networks, unlicensed users utilize PU frequency bands opportunistically and efficiently when PUs do not use the same.

There are four basic functions of CRN systems, spectrum sensing, spectrum sharing, spectrum mobility, and spectrum decision [2]. Spectrum sensing defines when the SU detects available vacant bands of PUs. Therefore, various sensing techniques have been introduced by researchers to sense licensed signal. Among all detectors, conventional-ED is one who is usually used due to its ease to implement and less complexity. But its performance degrades under low SNR values.

To improve detector performance at low SNR in [3] authors introduced two-stage detectors, energy detector in the first stage and the second stage is a cyclostationary detector. But detector has limitations, computationally more complex and required longer sensing time. Moreover, to minimize sensing time, in [4], authors presented adaptive spectrum sensing scheme, in which out of two stages only one stage’s detector perform sensing operation at a time. However, authors minimized sensing time but system complexity was there. Furthermore, in [5], authors presented adaptive sensing technique using energy detector (EDT-ASS). Here, authors discussed on cost-function and concluded about the primary user’s (PU’s) absence or presence.

In this paper, we optimize detection performance using multiple antennas with two detectors, two detectors ED_SAT and ED_TAT perform sensing operation simultaneously. Thresholds are adaptive that’s why chances of occurring sensing failure problem is negligible [6]. The output results of detectors go to decision device (DD) who takes final decision using OR-rule, if the output of DD is 1 shows frequency band is busy (H 1 ), otherwise free (H 0 ). The main difference between this paper and others [3, 4, & 5] are that none of these techniques focused on spectrum sensing failure [6], and fading problem. Adaptive threshold scheme reduces sensing failure problem while multiple antennas mitigate the fading problem.

We further propose CSS with multiple antennas based improved sensing detector (MA_ISD). In CSS, each CR user sends local decision (0 or 1 bit) to a common centralized node known as fusion center (FC). FC uses hard decision OR-rule to take a final decision.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.