Performance analysis of cognitive hybrid satellite-terrestrial networks for futuristic wireless communications

Abstract

The explosion of mobile applications and their integration in various aspects of everyday life necessitates the deployment of modern wireless systems that can handle such exponentially rising data traffic. High-speed broadband access, high capacity, low signal latency, long battery lifetime, wide coverage, etc., are the most important requirements to be considered for deploying the next-generation communication net works. In this regard, hybrid satellite-terrestrial networks (HSTNs) have emanated as a promising and prevalent infrastructure for future wireless networks owing to their capability of providing high throughput with ubiquitous coverage. In HSTNs, satellite communication and terrestrial networks are incorporated to enable their po tential applications in the field of navigation, disaster relief, and broadcasting. The performance of HSTNs can be further enhanced while exploiting the cooperative communication techniques using amplify-and-forward (AF) and decode-and-forward (DF) based relaying protocols, which may extend the satellite coverage especially in the unpopulated and suburban areas. However, the static allocation of the frequency spectrum in traditional ways in HSTNs does not meet the requirements of future wireless networks. As such, in HSTNs, the spectral resources allocated to satellites get underutilized, whereas terrestrial spectral resources are becoming overutilized day by day due to the escalating growth in mobile data traffic. This eventually necessitates the efficient utilization of limited spectral resources. In this context, integrating the cognitive radio approach using underlay and overlay paradigms in HSTNs has become an efficient way of improving the spectrum utilization efficiency. This evokes a propitious architecture referred to as cognitive HSTN (CHSTN), which allows the simultaneous data transmissions of both primary satellite network and secondary terrestrial network over the same frequency band, subject to satisfying the quality-of-service (QoS) constraint at the primary user (PU). With such QoS restrictions from the PUs, it becomes challenging to improve the performance of sec ondary network. To address the design objectives of the future wireless networks, this thesis comprehensively investigates the performance of CHSTNs under the ap propriately modelled shadowed-Rician fading for the satellite links and Nakagami-m fading for the terrestrial links, by exploring the various spectral-efficient schemes. Firstly, we consider an overlay multiuser hybrid satellite-terrestrial spectrum sharing (OMHSTSS) system. Herein, we exploit both direct and relay links from a primary satellite source to multiple terrestrial users with the coexistence of a secondary transmitter-receiver pair on the ground. Based on an overlay approach, the secondary transmitter (ST) provides an AF-based relay cooperation to the pri mary satellite network that employs opportunistic scheduling of multiple users. The underlying user scheduling strategy is based on satisfying the criterion of minimal outage probability (OP) for the primary network, and eventually, exploring more op portunities of the spectrum sharing for the secondary terrestrial network. To assess the performance of this analytical framework, we proficiently derive the exact and asymptotic closed-form expressions of the OP for primary and secondary networks, and further highlight the corresponding achievable diversity orders. Consequently, it can be inferred that the achievable diversity order of the primary network directly depends on the number of PUs. We also discuss the power allocation policy to explore more opportunities for the secondary spectrum access. Then, we analyze the performance of an overlay CHSTN (OCHSTN) consisting of a primary satellite source-receiver pair and a secondary transmitter-receiver pair on the ground while taking into account the practical hardware impairments (HIs) at the user devices. Herein, we manifest analytically that, for the higher data rates, the HIs invoke ceiling effects which reprehensibly cap the fundamental capacity of the system. To mitigate the effect of HIs, we propose an adaptive relaying (AR) protocol for both AF and DF operations and compare its performance with the com petitive fixed relaying (FR) schemes. The proposed AR protocol efficiently utilizes the available spectrum resources to enhance the system performance. Hereby, we comprehensively analyze AR-based AF (AAF) and AR-based DF (ADF) operations by deriving the OP expressions for primary and secondary networks in the presence of HIs. We showcase that the ADF relaying is more robust and resilient to HIs when compared with AAF relaying. Further, based on the derived OP expressions for the primary network, we identify two important ceiling effects, namely, relay coopera tion ceiling (RCC) and direct link ceiling (DLC), and highlight their impacts on the system performance. We also provide the tolerable limit of HIs level for the given rate requirements. Next, we investigate the performance of an overlay multiuser cognitive satellite terrestrial network (OMCSTN) comprising a primary satellite source with its mul tiple terrestrial receivers and a secondary transmitter-receiver pair on the ground.