Mutual interference in OFDM-based spectrum pooling systems

Abstract

Public mobile radio spectrum has become a scarce resource while wide spectral ranges are only rarely used. Here, a new strategy called spectrum pooling is considered. It aims at enabling public access to these spectral ranges without sacrificing the transmission quality of the actual license owners. Unfortunately, using OFDM modulation in a spectrum pooling system has some drawbacks. There is an interaction between the licensed system and the OFDM based rental system due to the non-orthogonality of their respective transmit signals. In this paper, this interaction is described mathematically providing a quantitative evaluation of the mutual interference that leads to an SNR loss in both systems. However, this interference can be mitigated by windowing the OFDM signal in the time domain or by the adaptive deactivation of adjacent subcarriers providing flexible guard bands between licensed and rental system. It is obvious that both approaches sacrifice bandwidth of the rental system. A quantitative comparison of both approaches is given as a tradeoff between interference reduction and throughput in the rental system.

Cognitive Radio Dynamic Access Techniques

“…Recently a method called Spectrum Pooling is reported [4]. In spectrum pooling public access to spectrum is provided without sacrificing the transmission quality of the actual LUs.…”

“…In spectrum pooling public access to spectrum is provided without sacrificing the transmission quality of the actual LUs. Multicarrier communication for CR has been suggested in [4]. The rationale is that any CR system needs to sense the spectrum, and this involves some sort of spectral analysis.…”

“…Since FFT can be used for the spectral analysis [5] and at the same time it can act as the demodulator of an OFDM, it has been suggested as a proper candidate for multicarrier-based CR systems. A number of short-comings of OFDM in its application in CR have been noted in [4] and solutions to them have been proposed. The carriers located at the LUs band are deactivated, The sidelobes are reduced by deactivating more carriers adjacent to LUs band.…”

“…Due to the depth and importance of the topics, each of the spectrum adaptation techniques is discussed separately in individual sections. Multi carrier adaptive OFDM with Fourier and Wavelet basis functions and its combination 4 Spectrum picture: f c is carrier frequency; B is operation band [11] with spectrum pooling are analyzed in Sect. 4.…”

“…A strategy which is called spectrum pooling is proposed in [4] where the public access is enabled to these bands without giving significant interference to the actual license owners. Spectrum pooling enables public access to spectral ranges of licensed frequency bands which are seldom used by overlaying a secondary RU to an existing LU.…”