Improved Resource Allocation for TV White Space Network Based on Modified Firefly Algorithm

There is continued increased demand for dynamic spectrum access of TV White Spaces (TVWS) due to growing need for wireless broadband. Some of the use cases such as cellular (2G/3G/4G/5G) access to TVWS may have a high density of users that want to make use of TVWS. When there is a high density of secondary users (SUs) in a TVWS network, there is possibility of high interference among SUs that exceeds the desired threshold and also harmful interference to primary users (PUs). Optimization of resource allocation (power and spectrum allocation) is therefore necessary so as to protect PUs against harmful interference and to reduce the level of interference among SUs. Existing resource allocation optimization algorithms for a TVWS network ignore adjacent channel interference, interference among SUs or apply greedy algorithms which result in sub-optimal resource allocation. In this paper we propose an improved resource allocation algorithm based on continuous-binary firefly algorithm. Simulation is done using Matlab. Simulation results show that the proposed algorithm improves the SU sum throughput and SU signal to interference noise(SINR) ratio in the secondary network

Secondary spectrum usage in TV white space

Currently, the use of TV frequencies is exclusively license based with the area not covered by licensed TV transmitters being known as TV white space. In TV white space, the spectrum can be reused by a secondary user. This thesis studies how the TV white space can be used by a cellular system. The study addresses the problems of how the access to the spectrum is arranged, how the spectrum usage is constrained and how much capacity a secondary system will have. The access to TV white space can be arranged by using spectrum sensing or a geolocation database. This spectrum sensing relies on the performance of the signal detection algorithm. The detector has to operate in a fading environment where it should identify very low signal levels. In this thesis, the detector performance in a slow and fast fading environment is modeled. The model indicates that for a sufficiently long measurement time the impact of the fast fading can be averaged out. Unfortunately, simple single antenna-based detectors are not able to operate at a low enough signal-to-noise level. We propose a novel multi antenna-based detection algorithm that is specially designed to operate in a fading environment. TV white space is characterized by the amount of spectrum available for secondary usage. Because of the signal detection errors, a system using the sensing-based access is not able to use the entire available spectrum. This dissertation provides a method for estimating the spectrum utilization efficiency. The method illustrates how the detection error level affects the amount of available spectrum. One of the central questions studied in this thesis is how to describe the interference generated by the secondary transmitters. In the conventional model, the interference is computed as the sum of the interfering powers from individual transmitters. An alternative approach, pursued here, is to characterize the transmitter by its transmission power density per area. With such a model, the interference computation is done by integrating over the secondary system deployment area. The proposed method simplifies the interference estimation process. In data communication systems the spectrum attractiveness depends on the data rate the system can provide. Within the scope of this work, the achievable data rate is computed for a cellular system. Such computation is described as an optimization problem. The solution to this problem is found by searching for the optimal power allocation among the cochannels and the adjacent channels of a nearby TV transmitter

Interference control and radio spectrum allocation in shared spectrum access

With demands on the radio spectrum intensifying, it is necessary to use this scarce resource as efficiently as possible. One way forward is to apply flexible authorization schemes such as shared spectrum access. While such schemes are expected to make additional radio resource available and lower the spectrum access barriers, they also bring new challenges toward effectively dealing with the created extra interference which degrades the performance of networks, limiting the potential gains in a shared use of spectrum. In this thesis, to address the interference issue, different spectrum access schemes and deployment scenarios are investigated.  Firstly, we consider licensed shared access where database-assisted TV white space network architecture is employed to facilitate the controlled access of the secondary system to the TV band. The operation of the secondary system is allowed only if the quality of service experienced by the incumbent users is preserved. Furthermore, the secondary system should benefit itself from utilizing the TV band in licensed shared access mode. One challenge for efficient operation of the licensed secondary system is to control the cross-tier interference generated at the TV receiver, taking into account the self-interference in the secondary system.  Secondly, we consider co-primary shared access where multiple operators share a part of their spectrum. This can be done in two different operational levels, users and cells. The user level is done in the context of D2D communications where two users subscribed to different operators can transmit directly to each other. The cell level allows spectrum sharing between two small cells, e.g., indoor and outdoor small cells, in a dense urban environments. The main challenges for such scenarios are to manage the cross-tier interference generated by other users or cells subscribed to different operators, and to identify the amount of radio spectrum each operator contributes.  There are several approaches to reduce the risk of interference, but they often come at a high price in terms of complexity and signaling overhead. In this thesis, we aim to propose low complexity mechanisms that take interference control and radio spectrum allocation into account. The proposed mechanisms are based on tractable models which characterize the effects of the fundamental design parameters on the system behavior in shared spectrum access. The models are leveraged to capture the statistic of the aggregate interference and its effects on the performance metrics

D5.2 - Evaluation of Selected Measurement-based Techniques

Deliverable D5.2 del projecte FARAMIRPreprin

Multiantenna Interference Mitigation Schemes and Resource Allocation for Cognitive Radio

Maximum and efficient utilization of available resources has been a central theme of research on various areas of science and engineering. Wireless communication is not an exception to this. With the rapid growth of wireless communication applications, radio frequency spectrum has become a valuable commodity. Supporting very high demands for data rate and throughput has become a challenging problem which requires innovative solutions. Dynamic spectrum sharing (DSS) based cognitive radio (CR) is envisioned as a promising technology for future wireless communication systems, such as fifth generation (5G) further development and sixth generation (6G). Extensive research has been done in the areas of CRs and it is considered to mitigate the spectral crowding problem by introducing the notion of opportunistic spectrum usage. Spectrum sensing, which enables CRs to identify spectral holes, is a critical component in CR technology. Furthermore, improving the efficiency of the radio spectrum use through spectrum sensing and dynamic spectrum access (DSA) is one of the emerging trends. In the first part of this thesis, we focus on enhancing the spectrum usage of CR’s using interference cancellation methods that provides considerable performance gains with realistic computational complexity, especially, in the context of the widely used multicarrier waveforms. The primary focus is on interference rejection combining (IRC) methods, applied to the black-space cognitive radio (BS-CR). Earlier studies on the BS-CR in the literature were focused on using CRs as repeaters for the primary transmitter to guarantee that the CR is not causing significant interference to nearby primary users’ receivers. This kind of approaches are transmitter-centric in nature. In this thesis, receiver-centric approaches such as multi-antenna diversity combining, especially enhanced IRC methods, are considered and evaluated. IRC methods have been widely studied and adopted in several practical wireless communication systems. We focus on developing such BS-CR schemes under strong interference conditions, which has not been studied in the CR literature so far. Spatial covariance matrix estimation under mobility and high carrier frequencies is found to be the most critical part of such scheme. Algorithms and methods to mitigate these effects are developed in this thesis and they are evaluated under realistic BS-CR receiver operating conditions. We use sample covariance estimation approach with silent gaps in the CR transmisison. Covariance interpolation between silent gaps improves greatly the robustness with time-varying channels. Good link performance can be reached with low mobility at carrier frequency considered for the TV white-spaced case. The proposed BS-CR scheme could be feasible at below 6 GHz frequencies with pedestrian mobilities. The second part of this thesis investigates the effect of radio frequency (RF) impairments on the performance of the cognitive wireless communication. There are various unavoidable imperfections, mainly due to the limitations of analog high-frequency transmitter and receiver circuits. These imperfections include power amplifier (PA) non-linearities, receiver nonlinearities, and carrier frequency offset (CFO), which are considered in this study. These effects lead to significant signal distortion and, as a result of this, the wireless link quality may deteriorate. In multicarrier communications such signal distortions may lead to additional interference, and it is important to evaluate their effects on spectrum sensing quality and on the performance of the proposed BS-CR scheme. This part of the thesis provides critical analysis and insights into such issues caused by RF imperfections and demonstrates the need for designing proper compensation techniques required to avoid/reduce such degradations. It is found that the transmitter’s PA nonlinearities affect in the same way as in basic OFDM systems and BS-CR receiver’s linearity requirements are similar to those for advanced DSP-intensive software defined radios. The CR receiver’s CFO with respect to the PU has the most critical effect. However, synchronizing the CR with the needed high accuracy is considered achievable due to the PU signal’s high-power level. The final part of the thesis briefly looks at alternate waveforms and techniques that can be used in CRs. The filter bank multicarrier (FBMC) waveforms are considered as an alternative to the widely used OFDM schemes. Here the core idea is interference avoidance, targeting to reduce the interference leakage between CRs and the primary systems, by means of using a waveform with good spectrum localization properties. FBMC system’s performance is compared with OFDM based system in the context of CRs. The performance is compared from a combined spectrum sensing and resource allocation point of view through simulations. It is found that well-localized CR waveforms improve the CR link capacity, but with poorly localized primary signals, these possibilities are rather limited