Naveen Gupta

Outage analysis of cooperative OFDM relaying system with opportunistic spectrum sharing

In this paper, we analyze the outage performance of an opportunistic spectrum sharing protocol. In the proposed protocol if the primary system (licensed user) is incapable of supporting its target transmission rate, then secondary system (cognitive user) helps the primary system via two phase cooperative Orthogonal Frequency Division Multiplexing (OFDM) relaying. Secondary system acts as an Amplify & Forward (AF) relay by allocating some of its subcarriers to boost the performance of primary transmission whereas remaining subcarriers are used for secondary transmission. Simulation results demonstrate the outage probability with respect to primary transmit power for different sets of subcarriers in both direct & cooperation mode. Through simulation results it is proved that the primary outage probability with cooperation is less than outage probability with direct transmission. Results also demonstrate the outage probability for increasing distance between primary & secondary transmitter. As distance between primary & secondary transmitter increases outage probability increases.

A Cognitive Subcarriers Sharing Scheme for OFDM Based Decode and Forward Relaying System

This paper analyzes the performance of a proposed subcarriers sharing scheme. According to the scheme, secondary system helps the primary system via two phase Decode and Forward orthogonal frequency division multiplexing based relaying. If primary (licensed user) is unable to achieve its target rate then secondary transmitter (which is located within a critical distance from primary transmitter) will provide few subcarriers to primary receiver, to fulfill the requirement of the primary system and remaining subcarriers can be used by secondary (cognitive) system for its own data transmission. If secondary transmitter is located at or beyond the critical distance from primary transmitter then no spectrum sharing is possible. The analytic expression of outage probability of the primary and secondary system has been computed. Through theoretical and simulation results it has been shown that the primary outage probability with cooperation (while secondary transmitter acts a partial relay) is less than the outage probability for direct transmission. Therefore opportunistic spectrum sharing can be achieved by secondary system.

An Adaptive Subcarrier Sharing Scheme for OFDM-Based Cooperative Cognitive Radios

Incorporation of orthogonal frequency division multiplexing (OFDM) in cooperative cognitive radio network facilitates subcarrier sharing to achieve spatial diversity with opportunistic spectrum access. In addition, adaptive modulation has been adopted widely in wireless communication to improve spectral efficiency. Use of adaptive modulation for cooperative cognitive relaying transmission to maximize throughput under bit error rate (BER) constraint is an open issue. In this paper, we propose an adaptive subcarrier sharing scheme for OFDM-based cooperative cognitive radio system, wherein cognitive (secondary) system helps the primary system to achieve its target rate of communication in exchange for opportunistic spectrum sharing. Secondary transmitter uses adaptive mode of transmission to relay the primary signal with higher throughput while maintaining the BER constraint of primary system. At primary receiver, a BER-based selection combining scheme is employed to combine the signals received in two phases. Closed-form analytical expressions for BER and outage probability of primary and secondary system for a Rayleigh flat fading channel have been derived. Results show that the outage probability with the proposed scheme (for dissimilar modulation) outperforms direct transmission and conventional maximal ratio combining scheme (for similar modulation).

Rate and Outage Trade-Offs for OFDMA Based Device to Device Communication Frameworks

This paper presents the rate and outage tradeoffs for orthogonal frequency division multiple access-based device-to-device (D2D) communication frameworks, wherein multiple D2D users coexist with the cellular users in the same cell. Analytical expressions for outage probability for three D2D frameworks, namely underlay, overlay, and cooperative D2D (C-D2D) have been derived. Specifically, for underlay framework, a minimum value of angle

Subcarrier sharing scheme for overlay anc cooperative D2D communication in cellular networks

\theta

Cooperative Spectrum Sharing Using Transmit Antenna Selection for Cognitive Radio Systems

(an angle between a cellular link and D2D interference link) is derived, for which the target rate and outage probability constraint of both cellular and D2D users are satisfied. For overlay and C-D2D frameworks, an optimal subcarrier sharing scheme is proposed, which not only helps the cellular users to achieve the target quality-of-service but also helps the D2D users to communicate with each other. In addition to above, benefits involved in employing one framework over other have also been investigated. Our results show that for a higher outage probability constraint of the cellular user, the C-D2D framework outperforms the underlay and overlay frameworks.

Insights from the measurement results for adaptive and cooperative D2D communication framework

Device-to-device (D2D) is a new communication paradigm which has evolved recently to meet the capacity requirements of 4G/beyond 4G cellular networks. In a generic D2D framework, two cellular users living in close proximity can form a direct link for data transmission without routing it through the base station (BS). However control or signaling information between the users will still be carried out by the BS. In this paper, we augment the development of D2D communication by proposing an orthogonal frequency division multiplexing (OFDM) based subcarrier sharing scheme to facilitate D2D communication between cellular users. Analytical expressions for outage probability for two different D2D frameworks namely overlay and cooperative D2D have been derived. Through the obtained results, we can determine the exact number of subcarriers available for D2D communication while fulfilling the target rate and outage probability constraint of cellular system. It also has been shown that for low cellular outage constraint, overlay performs better than cooperative D2D whereas for high cellular outage constraint, the cooperative D2D framework completely outperforms the overlay D2D framework.

Testbed implementation and proof-of-concept demonstration for cooperative device-to-device communication framework

In this paper, a spectrum sharing scheme that utilizes the two-phase cooperative decode-and-forward relaying protocol is proposed. The cooperation between primary (i.e. licensed) and secondary (i.e. unlicensed) system helps in achieving the desired target rate for the primary system and spectrum access for cognitive (i.e. secondary) system. In the proposed scheme, secondary transmitter which is equipped with multiple antennas uses transmit antenna selection to improve the primary’s performance by reducing the interference level of secondary signal at primary receiver, while keeping the performance of secondary system unaffected. Closed form expressions for outage probability have been derived for both systems by varying transmit power level at secondary transmitter. The theoretical results have been compared with simulation results to validate the analysis done in this paper.