Abstract
This paper details fronthaul optical links using sub-Nyquist sampling rate analog-to-digital converters (ADCs) for Beyond fifth generation (B5G) and 6G sub-THz massive multiple-input multiple-output (Ma-MIMO) beamforming. Unlike Common Public Radio Interface (CPRI) using high speed ADCs in current fronthaul link, the proposed scheme involves ADCs operating at sub-Nyquist sampling rate for each antenna element. Based on pre-allocated relative time delays, pre-processed orthogonal frequency-division multiplexing (OFDM) signals sent from a baseband unit (BBU) can be deaggregated to different Ma-MIMO OFDM signals by sub-Nyquist sampling rate ADCs. In experiments, we assume that each remote radio unit (RRU) is equipped with 32/64 antenna elements and 32/64 ADCs operating at 1/32 and 1/64 of the Nyquist sampling rate. Furthermore, the received Ma-MIMO OFDM signal is then up-converted to 100-GHz for wireless transmission and defined as Ma-MIMO RF OFDM signal. We simulate the 32/64 antenna elements transmission scenario by individually transmit and demodulate each Ma-MIMO RF OFDM signal with 32/64 times of point-to-point antenna transmission. The error vector magnitude (EVM) and signal-to-noise ratio (SNR) of each received Ma-MIMO RF OFDM signal are less than 8% and 26 dB, respectively. And the total received 64 Ma-MIMO RF OFDM signals will require line rate as high as 393.6374 Gb/s according to CPRI option-7. Notably, the proposed scheme reduces the requirement of sampling rate and enables all the Ma-MIMO OFDM signals at baseband without the insertion of guard band. Thus, the proposed scheme can reduce the complexity of signal deaggregation and power consumption in the demodulation process, leading to an improvement in cost efficiency.
Highlights
From 4G to 5G mobile technologies, the data traffic has been increased 1000-fold due to proliferation of connected devices [1], and this trend is expected to continue in the decade
After 10-km single mode fiber (SMF) transmission, each RF chain signal is down-sampled by 1/64 Nyquist-sampling rate to obtain massive multiple-input multipleoutput (Ma-MIMO) RF orthogonal frequencydivision multiplexing (OFDM) signal, and the error vector magnitude (EVM) of each RF chain is less than 8%
This paper proposed a novel Beyond 5G (B5G)/6G MFH links based on the DDM scheme with LSR-analog-to-digital converters (ADCs)
Summary
From 4G to 5G mobile technologies, the data traffic has been increased 1000-fold due to proliferation of connected devices [1], and this trend is expected to continue in the decade. Our proposed MFH enables all the Ma-MIMO RF OFDM signals at baseband without the insertion of guard band comparing with a general A-RoF system. In the RRU, the LSR-ADC divided the total OFDM signals into 64 Ma-MIMO RF OFDM signals according to corresponding delay time, and the electric spectrum is as shown in Fig. 4 (II). The band width of Ma-MIMO OFDM signal spectrum received by LSR-ADC would vary according to number of antennas. We can enlarge the number of antennas from 1 to responses generated by delays and the effect of spectral 64 without EVM penalty, which is suitable for integrated with
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