Protection of primary users in dynamically varying radio environment: practical solutions and challenges

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.

Synchronization for NC-OFDM-based Cognitive Radio, robust against narrowband primary user

“…£-1 r(n) = L x(n-l)h(l)eJ 2 7r'"N' +v;;i eJ 2 7r jy + J'P+w(n), (3) 1=0 where h(l) is the lth path channel coefficient, v is the CFO nor malized to SCs spacing, and w(n) is a complex white Gaussian noise. The second component in (3) is the NBI characterized by power CJt, phase i.p and center frequency 1 as in [8].…”

“…A number of techniques has been proposed in order to reduce this interference even further, e.g. [3]- [5]. However no polices are in place to protect the CR transmission.…”

Reconfigurable wireless platforms for spectrally agile coexistence

“…In the case of MCM, and specifically with OFDM, the interference produced due to the sidelobe levels could be substantial, especially if operating in close proximity to other signals. Fortunately there exists a family of solutions that can reduce high sidelobe levels [8]. Several approaches presented in the literature include the following:…”

Low-Complexity Spectrum Shaping for OFDM-Based Cognitive Radio Systems

“…For example, when the coding rate is , every 3 received symbols, , , and , are converted to and as the decoded information symbols. Note that as high power values on the canceling tones may increase the peak-to-average power ratio (PAPR) [19], we may apply certain power constraints to the canceling tones.…”