Increasing coverage and maximum CFO in DFT-s-OFDM for Machine-Type Communications

One of the growing fields of interest in cellular communications is Machine-Type Communications (MTC). MTC traffic can be characterized in many applications by very low bit rates while requiring a high degree of coverage and reliability. Studies on how to increase coverage and reduce device costs have been extensively performed in DFT-s-OFDM due to its lower peak-to-average power ratio. Among the drawbacks of using DFT-s-OFDM for MTC are the Carrier Frequency Offset (CFO) requirements (thus precluding the use of low-cost local oscillators) and poor performance when coverage is limited (thus precluding devices with low transmission power). A common approach for coverage enhancements is to reduce the signal bandwidth in order to increase the power spectral density, but this does not alleviate the frequency offset requirements. This paper proposes an alternative transmission scheme that increases coverage and supports larger frequency offsets compared to classical bandwidth reduction schemes in DFT-s-OFDM. Link-level simulations demonstrate the superiority of the proposed technique in terms of coverage and resilience against large frequency offsets, and put into question the traditional approach of reducing bandwidth for coverage improvements in OFDM systems.