Narrow-band internet of things physical random-access channel (NPRACH) receiver
A method of Narrow-band Internet of Things physical random-access channel (NPRACH) communication includes: transmitting, from a user equipment (UE), a Narrow-band Internet of Things (NB-IoT) Orthogonal Frequency-Division Multiple Access (OFDMA) symbol using a transmit inverse fast Fourier transform (Tx-IFFT) having a first length; processing, at lower physical layer (LPHY) of a baseband unit (BBU), the NB-IoT OFDMA symbol using a receive fast Fourier transform (Rx-FFT) having a second length different from the first length to generate an Rx-FFT output; sending, from the LPHY of the BBU to upper physical layer (UPHY) of the BBU, a selected number of values of the Rx-FFT output corresponding to desired resources block in the NB-IoT OFDMA symbol; filtering, at the UPHY, intercarrier interference (ICI) from the selected number of values of the Rx-FFT output; and reconstructing, at the UPHY, the NB-IoT OFDMA symbol.
1. A method of communicating using Orthogonal Frequency Division Multiplexing (OFDM), comprising:
transmitting, from an OFDM transmitter to an OFDM receiver, a signal for which the length of the transmit inverse fast Fourier transform (Tx-IFFT) at the OFDM transmitter and the length of the receive inverse fast Fourier transform (Rx-FFT) at the OFDM receiver are different, wherein the OFDM transmitter transmits values on only a subset of possible subcarriers;
determining, by an equalizer of the OFDM receiver, the values transmitted on the subset of subcarriers;
wherein:
the method is for Narrow-band Internet of Things (NB-IoT) physical random-access channel (NPRACH) communication;
the OFDM transmitter is a user equipment (UE) transmitting an NB-IoT Orthogonal Frequency-Division Multiple Access (OFDMA) symbol using a transmit inverse fast Fourier transform (Tx-IFFT) having a first length;
a baseband unit (BBU) comprises the OFDM receiver, wherein a lower physical layer (LPHY) of the BBU is configured to support at least LTE and processes the NB-IoT OFDMA symbol using a receive fast Fourier transform (Rx-FFT) having a second length different from the first length to generate an Rx-FFT output, and the NB-IoT OFDM symbol received at the LPHY has 8192 samples; and
the LPHY of the BBU sends to upper physical layer (UPHY) of the BBU a selected number of values of the Rx-FFT output corresponding to desired resources block in the NB-IoT OFDMA symbol;
processing, at the LPHY, the NB-IoT OFDM symbol using 2048-point FFT on LTE Physical Uplink Shared Channel block (LPB);
filtering, at the UPHY, intercarrier interference (ICI) from the selected number of values of the Rx-FFT output; and
reconstructing, at the UPHY, the NB-IoT OFDMA symbol.
2. The method according to claim 1 , wherein:
the LPHY is not configured to support NB-IoT standard.
3. The method according to claim 2 , wherein:
the UPHY comprises an equalizer for the filtering and an NPRACH detector for reconstructing the NB-IoT OFDMA symbol.
4. The method according to claim 2 , wherein the LPHY is configured to support one of Long-Term Evolution (LTE) or 5G New Radio (5G-NR) standard.
5. The method according to claim 3 , wherein the LPHY is configured to support one of Long-Term Evolution (LTE) or 5G New Radio (5G-NR) standard.
6. The method according to claim 1 , wherein
the LPHY sends 12 values from the Rx FFT output corresponding to subcarriers of resource block (RB) in the NB-IoT OFDMA symbol to the UPHY.
7. The method according to claim 1 , wherein a system model of the equalizer is represented by the equation
y i =A i x+n
where:
y i is the 12×1 vector of subcarriers of RB in the NB-IoT OFDMA symbol;
n is the additive white Gaussian noise (AWGN) with variance σ 2 ;
i is LPB index;
A i is 12×12 system matrix; and
x =H.*x
where H is a 12×1 frequency domain channel vector of the UE, and x is 12×1 vector corresponding to NB-IoT subcarriers.
8. The method according to claim 7 , wherein:
the LPHY is not configured to support NB-IoT standard.
9. The method according to claim 8 , wherein:
the UPHY comprises an equalizer for the filtering and an NPRACH detector for reconstructing the NB-IoT OFDMA symbol.
10. The method according to claim 8 , wherein the LPHY is configured to support one of Long-Term Evolution (LTE) or 5G New Radio (5G-NR) standard.
11. The method according to claim 9 , wherein the LPHY is configured to support one of Long-Term Evolution (LTE) or 5G New Radio (5G-NR) standard.
12. The method according to claim 7 , wherein
the LPHY sends 12 values from the Rx FFT output corresponding to subcarriers of resource block (RB) in the NB-IoT OFDMA symbol to the UPHY.