2 research outputs found
Multimedia Transmission over Cognitive Radio Channels under Sensing Uncertainty
This paper studies the performance of hierarchical modulation-based
multimedia transmission in cognitive radio (CR) systems with imperfect channel
sensing results under constraints on both transmit and interference power
levels. Unequal error protection (UEP) of data transmission using hierarchical
quadrature amplitude modulation (HQAM) is considered in which high priority
(HP) data is protected more than low priority (LP) data. In this setting,
closed-form bit error rate (BER) expressions for HP data and LP data are
derived in Nakagami- fading channels in the presence of sensing errors.
Subsequently, the optimal power control that minimizes weighted sum of average
BERs of HP bits and LP bits or its upper bound subject to peak/average transmit
power and average interference power constraints is derived and a
low-complexity power control algorithm is proposed. Power levels are determined
in three different scenarios, depending on the availability of perfect channel
side information (CSI) of the transmission and interference links, statistical
CSI of both links, or perfect CSI of the transmission link and imperfect CSI of
the interference link. The impact of imperfect channel sensing decisions on the
error rate performance of cognitive transmissions is also evaluated. In
addition, tradeoffs between the number of retransmissions, the severity of
fading, and peak signal-to-noise ratio (PSNR) quality are analyzed numerically.
Moreover, performance comparisons of multimedia transmission with conventional
quadrature amplitude modulation (QAM) and HQAM, and the proposed power control
strategies are carried out in terms of the received data quality and number of
retransmissions.Comment: To appear in the IEEE Transactions on Signal Processin
DSAT-MAC : Dynamic Slot Allocation based TDMA MAC protocol for Cognitive Radio Networks
Cognitive Radio Networks (CRN) have enabled us to efficiently reuse the
underutilized radio spectrum. The MAC protocol in CRN defines the spectrum
usage by sharing the channels efficiently among users. In this paper we propose
a novel TDMA based MAC protocol with dynamically allocated slots. Most of the
MAC protocols proposed in the literature employ Common Control Channel (CCC) to
manage the resources among Cognitive Radio (CR) users. Control channel
saturation in case of large number of CR users is one of the main drawbacks of
the CCC based MAC protocols. In contrast with CCC based MAC protocols, DSAT-MAC
protocol is based on the TDMA mechanism, without using any CCC for control
information exchange. The channels are divided into time slots and CR users
send their control or data packets over their designated slot. The protocol
ensures that no slot is left vacant. This guarantees full use of the available
spectrum. The protocol includes the provision for Quality of Service, where
real-time and safety critical data is transmitted with highest priority and
least delay. The protocol also ensures a fair sharing of available spectrum
among the CR users, with the mechanism to regulate the transmission of
malicious nodes. Energy saving techniques are also presented for longer life of
battery operated CR nodes. Theoretical analysis and simulations over ns-2 of
the proposed protocol reveal that the protocol performs better in various CR
adhoc network applications.Comment: 19 pages, 20 figures, Initial work in proc. of the Ninth IEEE
International Conference on Wireless and Optical Communications Networks
(IEEE WOCN-2012), Indore, INDIA, 20-22 September, 201