A distributed underlay channel assignment for cognitive cooperative ad hoc networks based on interfe

A Distributed Underlay Channel Assignment for Cognitive Cooperative ad hoc Networks Based on Interference Temperature
Shadi Ebrahimi Asl
Petropars Ltd. School of Electrical Engineering, Iran University of Science and Technology Tehran, Iran
where IT(fC,BC) is the IT in a channel with central frequency fC and bandwidth BC, P(fC,BC) is the average power in watts on the channel, S(fC,BC) is the power spectral density of P(fC,BC) and k is Boltzmann's constant ( 1.38 × 10 −23 Joules per Kelvin). Another problem for channel assignment in cognitive underlay transmission is achieving a good secondary capacity when high power primary signal is available in the host channel. Since cognitive users are generally low power radios in comparison with PUs, they receive the primary signal as high power interference. However, in this condition no modification is permitted to be exerted on the primary system. Thus, cognitive users must suppress the high power interference from the primary base station (PBS) to improve their achieved capacities. In [6][14], using adaptive array by secondary user has been proposed to reduce the interference between primary and secondary networks. Ref. [7] and [8] study performance of cognitive links with the assumption that a cognitive radio respectively knows or estimates the primary signal to subtract it from the total received signal. In this paper, we develop a single user and a multi user version of a Distributed Underlay Channel Assignment (DUCHA) algorithm in the downlink channel of a primary cell for a cognitive cooperative ad hoc network overlaid with a primary cell. We assume there is a mobile PU in the primary cell that transmits signal to the PBS on an uplink channel. In our proposed channel assignment scenario all cognitive channel applicants (CCHAs)
1 P ( f C , BC ) BC = IT ( f C , BC ) = kBC
∫ S( f
BC
C
, BC )df
kBC
,
(1)
Categories and Subject Descriptors
C.2.1 [COMPUTER-COMMUNICATION Wireless communication. NETWORKS]:
General Terms
Algorithms.
Keywords
Cognitive radio, Underlay transmission, Direct sequence spread spectrum, Jammer suppression.
1. INTRODUCTION
Cognitive radio has been introduced as a secondary user in a licensed host channel such that it produces no harmful interference to the primary user (PU) of that channel [1]. Accordingly, if a group of cognitive radios aim to use a common host channel they must use a channel assignment algorithm
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Bahman AbolhasFra bibliotekaniSchool of Electrical Engineering, Iran University of Science and Technology, Tehran, Iran
shadi_ebrahimiasl@ee.iust.ac.ir ABSTRACT
In this paper, we develop a single user and a multi user version of a Distributed Underlay Channel Assignment (DUCHA) algorithm for spectrum access to a downlink channel of a primary cell for a cognitive cooperative ad hoc network overlaid with the cell. We use direct sequence spread spectrum as a medium interface for cognitive links. We investigate performance of DUCHA algorithm in three spreading scenarios with regard to the bandwidth of the channel. Simulation results show that when there are 100 cognitive channel applicants and spreading factor is 100 the multi user DUCHA algorithm assigns the channel to an average 51.8 percent of channel applicants and in this case it achieves 22.57 bps/Hz spectral efficiency under high power interference from the primary base station of the cell. We show that in this condition the increased in-band and out of band interference temperatures are non-harmful and have values of respectively 22.48 dB and -0.99 dB.
99
that are interested in using the downlink channel first share their measured data in a common control channel. Then, each CCHA independently executes the proposed DUCHA algorithm to find the best set of qualified CCHAs for secondary transmissions. Two main criteria in DUCHA algorithm for selecting a CCHA for secondary transmission are: locating out of no-talk zone1 of the PU and producing an in-band IT which does not increase the total IT at the PU above a determined harmful level. In order to overcome the high power interference from the PBS to cognitive links we consider the signal from the PBS as a destructive noise jammer. We use direct sequence spread spectrum (DSSS) as a medium interface in cognitive links such that cognitive receivers are able to suppress this jamming signal by using suitable spreading factors. We investigate performance of the proposed DUCHA algorithm in three spreading scenarios. We show that in our proposed transmission scenario the proposed multi user DUCHA algorithm assigns the downlink channel of the primary system to 51.8 percent of CCHAs when there are 100 CCHAs in the cognitive network and spreading factor is 100 and also in this condition it achieves 22.57 bps/Hz spectral efficiency under high power interference from the PBS of the host channel. We show that in this condition the increased in-band and out of band IT are non-harmful and have values of respectively 22.48 dB and -0.99 dB. The rest of this paper is organized as follows. In Section II, we introduced our proposed Distributed Underlay Channel Assignment (DUCHA) algorithm. In Section III, we investigate performance of the proposed DUCHA algorithm in three spreading scenarios through computer simulations. Conclusions of this work are presented in Section IV. We use term secondary transmission and cognitive transmission interchangeably throughout this paper.