Eigenvalue-Decomposition-Precoded Ultra-Dense Non-Orthogonal Frequency-Division Multiplexing

Abstract

This paper proposes a novel ultra-dense nonorthogonal frequency-division multiplexing (NOFDM) transmission, where subcarrier spacing is set significantly lower than that of orthogonal frequency-division multiplexing (OFDM). In order to eliminate the detrimental effects of NOFDM-specific intercarrier interference and correlated additive noises, eigenvaluedecomposition-aided precoding is conceived. The classical capacity formula is extended to one supporting our precoded NOFDM scheme. Optimal power allocation (PA) is developed in order to maximize the derived capacity of the proposed scheme. Furthermore, truncated PA is developed to combat the limitations due to significantly low eigenvalues, which are specifically imposed by the proposed ultra-dense NOFDM. Through analytical and numerical results, we demonstrate that the proposed NOFDM schemes with optimal and truncated PA outperform the conventional NOFDM and the classical OFDM schemes.

Impact of Inter-Frame Interference on Eigendecomposition-Precoded Non-Orthogonal Frequency-Division Multiplexing

“…Such significantly small eigenvalues cannot be accurately calculated in the standard double-precision environment. The fraction of significantly small eigenvalues of the presented multi-frame NOFDM scheme was higher than that of the conventional single-frame EVD-NOFDM scheme ignoring the IFI effects [10]. Therefore, in the multi-frame scenario of the proposed scheme, the effects of ICI and IFI have to be carefully evaluated, unlike in the conventional single-frame scenario.…”

“…We derive the optimal power allocation coefficients q i (i = 0, • • • , N − 1) of the proposed scheme by maximizing the information rate of the proposed generalized EVD-NOFDM with the aid of the Lagrange multiplier method [10]. The upper MI limit of the proposed scheme is formulated as the sum of each substream's MI as follows:…”

“…To cancel the detrimental effects of ICI specific to NOFDM, several waveform precoding schemes have been developed [8]- [10]. In [8], a simple zero-forcing precoding method was used at a multiple-input multiple-output (MIMO) transmitter in a narrowband downlink scenario.…”

“…In [8], a simple zero-forcing precoding method was used at a multiple-input multiple-output (MIMO) transmitter in a narrowband downlink scenario. In [9], [10], eigendecomposition (EVD)-based precoding with power allocation was proposed to attain an ICI-free system model of parallel substreams. Also, in [10], an information-theoretic analysis was provided to show the achievable information rates of the NOFDM and EVD-NOFDM schemes.…”

“…In [9], [10], eigendecomposition (EVD)-based precoding with power allocation was proposed to attain an ICI-free system model of parallel substreams. Also, in [10], an information-theoretic analysis was provided to show the achievable information rates of the NOFDM and EVD-NOFDM schemes. It is predicted that the NOFDM with small subcarrier separation may increase the frame duration, hence suffering from the effects of inter-frame interference (IFI).…”