Abstract
Abstract One of the primary objectives of deploying cognitive radio (CR) within a dynamic spectrum access (DSA) network is to ensure that the legacy rights of incumbent licensed (primary) transmissions are protected with respect to interference mitigation when unlicensed (secondary) communications are simultaneously operating within the same spectral vicinity. In this article, we present non-contiguous orthogonal frequency division multiplexing (NC-OFDM) as a promising and practical approach for achieving spectrally agile wireless data transmission that is suitable for secondary users (SUs) to access fragmented spectral opportunities more efficiently. Furthermore, a review of the current state-of-the-art is conducted with respect to methods specifically designed to protect the transmissions of the primary users (PUs) from possible interference caused by nearby SU transceivers employing NC-OFDM. These methods focus on the suppression of out-of-band (OOB) emissions resulting from the use of NC-OFDM transmission. To achieve the required OOB suppression, we present two practical approaches that can be employed in NC-OFDM, namely, the insertion of cancellation carriers and windowing. In addition to the theoretical development and proposed improvements of these approaches the computer simulation results of their performance are presented. Several real-world scenarios regarding the coexistence of both PU and SU signals are also studied using actual wireless experiments based on software-defined radio. These simulation and experimental results indicate that OOB suppression can be achieved under real-world conditions, making NC-OFDM transmission a viable option for CR usage in DSA networks.
Highlights
The idea of cognitive radio (CR) encompasses opportunistic and dynamic access to spectrum resources that might be available at a certain location and time
Note that the reference system for this definition, i.e., all subcarriers employed for data transmission, is prohibited from operating in the considered scenario, where the primary users (PUs) transmission protection is required and the secondary users (SUs) sidelobes have to be reduced. 4.1.1 Simulation results Below, we present the Monte Carlo simulation results using MATLAB and showing that our introduced modifications of the combined cancel lation carriers (CCs) and W method improves the overall performance of the noncontiguous orthogonal frequency division multiplexing (NC-orthogonal frequency division multiplexing (OFDM)) system in several ways
We have presented several methods for handling the OOB interference generated by N-continuous OFDM (NC)-OFDM SU transmissions, observing that this type of interference can be reduced down to a level required to protect the transmission quality of the PU signals
Summary
The idea of cognitive radio (CR) encompasses opportunistic and dynamic access to spectrum resources that might be available at a certain location and time. Let us derive a metric that indicates the potential throughput loss caused by introduction of CCs, windowing or the combination of CCs and W This throughput loss can be assessed in comparison to a system not employing any OOB interference reduction method, in which all subcarriers are occupied by the DCs. Note that the actual system throughput depends on the number of data subcarriers and on the power assigned to these subcarriers and the channel characteristic observed. This metric indicates only potential throughput loss that results from the information signal bandwidth reduction due to introduction of the CCs and window duration extension, assuming the same transmit power and channel quality at each subcarrier It is described by the following expression: γ⎞.
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