Filtered OFDM (F-OFDM) can accommodate diverse service requirements by introducing additional filtering to OFDM and flexibly adapting the filter according to the service requirement. However, when block filtering is flexibly adapted per-subband, the regular resource grid could be violated. In this letter, we propose a solution to maintain the regular resource grid for F-OFDM. The proposed solution is two-fold: 1) it allocates guard bands inside the filter bandwidth which is kept independent of guard band; 2) it introduces timing advance according to the filter used. It is shown in practically relevant scenarios that the proposed solution, despite its simplicity, performs better than another more complex approach.

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This paper proposes a simple, but efficient solution to avoid a potential problem for filtered OFDM (F-OFDM) that may violate regular resource grid structure. F-OFDM is an extension of OFDM by additional per-subband filtering and a well-localized filter can be utilized to significantly lower the outof-band radiation that can mitigate interference in asynchronous access. Even with the filtering, additional guard bands that carry no data may be needed between the subbands for different users to keep the interference level sufficiently low. The required guard bandwidth may vary since various aspects should be taken into account such as interference power, modulation format or quality of service requirement. If the subbands are simply shifted to add the guard bands, the regular resource grid will be destroyed. One option to keep the regular resource grid while supporting flexible guard bands is to define several filters, each of which is optimized for each possible guard bandwidth. But this is rather complex. We propose a much simpler solution allocating the guard bands inside the filter bandwidth, which is kept independent of guard bandwidths. We show through detailed analytical and numerical analysis that the proposed solution performs even better than the more complex one in practically relevant interference scenarios.

This paper proposes a transparent spectral confinement approach for OFDM to enable multiplexing of multiple services with diverse requirements in one system band. Besides mobile broadband services, new service types like machine type and ultra-reliable low latency communications foreseen for future 5G systems set new requirements for the chosen waveform to support asynchronous access and multiplexing different numerologies. That is not best handled by OFDM as it is. Thus, various spectral confinement techniques have been proposed in the literature, which, however, require specific processing at both the transmitter and receiver. This tight link would increase signaling overheads to agree on both sides to apply certain respective processing. The transparent approach proposed in this paper decouples the tight link and thus keeps the system simple and robust. We show by means of numerical evaluations that OFDM with spectral confinement techniques like windowing or filtering at the transmitter, but without respective receiver processing, outperforms the conventional OFDM.

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