Abstract-With the continuously increasing demand of cost effective, broadband wireless access, radio-over-fiber (RoF) starts to gain more and more momentum. Various techniques already exist, using analog (ARoF) or digitized (DRoF) radio signals over fiber. Each with their own advantages and disadvantages. By transmitting a sigma delta modulated signal over fiber (SDoF), a similar immunity to impairments as DRoF can be obtained while maintaining the low complexity of ARoF. This letter describes a detailed experimental comparison between ARoF and SDoF that quantifies the improvement in linearity and error vector magnitude (EVM) of SDoF over ARoF. The experiments were carried out using a 16QAM constellation with a baudrate from 20 to 125 Mbaud modulated on a central carrier frequency of 1 GHz. The sigma delta modulator (SDM) runs at 8 or 13.5 Gbps. A high speed VCSEL operating at 850 nm is used to transmit the signal over 200 m multimode fiber. The receiver amplifies the electrical signals and subsequently filters to recover the original RF-signal. Compared to ARoF, improvements exceeding 40 dB were measured on the third order intermodulation products when SDoF was employed, the EVM improves between 2.4 to 7.1 dB.
To achieve the massive device connectivity and high data rate demanded by 5G, wireless transmission with wider signal bandwidths and higher-order multiple-input multiple-output (MIMO) is inevitable. This work demonstrates a possible function split option for the next generation fronthaul interface (NGFI). The proof-of-concept downlink architecture consists of real-time sigma-delta modulated signal over fiber (SDoF) links in combination with distributed multi-user (MU) MIMO transmission. The setup is fully implemented using off-the-shelf and in-house developed components. A single SDoF link achieves an error vector magnitude (EVM) of 3.14% for a 163.84 MHz-bandwidth 256-QAM OFDM signal (958.64 Mbps) with a carrier frequency around 3.5 GHz transmitted over 100 m OM4 multi-mode fiber at 850 nm using a commercial QSFP module. The centralized architecture of the proposed setup introduces no frequency asynchronism among remote radio units. For most cases, the 2×2 MU-MIMO transmission has little performance degradation compared to SISO, 0.8 dB EVM degradation for 40.96 MHzbandwidth signals and 1.4 dB for 163.84 MHz-bandwidth on average, implying that the wireless spectral efficiency almost doubles by exploiting spatial multiplexing. A 1.4 Gbps data rate (720 Mbps per user, 163.84 MHz-bandwidth, 64-QAM) is reached with an average EVM of 6.66%. The performance shows that this approach is feasible for the high-capacity hot-spot scenario.
A new high-speed delta-sigma modulator (DSM) topology is proposed by cascading a bit reduction process with a multi-stage noise shaping MASH-1-1 DSM. This process converts the two-bit output sequence of the MASH-1-1 DSM to a singlebit sequence, merely compromising the DSM noise-shaping performance. Furthermore, the high clock frequency requirements are significantly relaxed by using parallel processing. This DSM topology facilitates the design of e.g. wideband software defined radio (SDR) transmitters and delta-sigma radio-over-fiber transmitters. Experimental results of the FPGA implementation show that the proposed low-pass DSM can operate at 21 GS/s, providing 520 MHz baseband bandwidth with 42.76 dB signal-to-noiseand-distortion ratio (SNDR) or 1.1 GHz bandwidth with 32.04 dB SNDR (based on continuous wave measurements). An all-digital transmitter based on this topology can generate 218.75 MBd 256-QAM over 200 m OM4 multimode fiber in real-time, with 7-GS/s sampling rate and an error vector magnitude below 1.89%.
The fifth generation (5G) cellular network is expected to include the millimeter wave spectrum, to increase base station density, and to employ higher-order multiple-antenna technologies. The centralized radio access network architectures combined with radio-over-fiber (RoF) links can be the key enabler to improve fronthaul networks. The sigma-delta modulated signal over fiber (SDoF) architecture has been proposed as a solution leveraging the benefits of both digitized and analog RoF. This work proposes a novel distributed antenna system using sigma-delta modulated intermediate-frequency signal over fiber (SDIFoF) links. The system has an adequately good optical bitrate efficiency and high flexibility to switch between different carrier frequencies. The SDIFoF link transmits a signal centered at a 2.5 GHz intermediate frequency over a 100 m multi-mode fiber and the signal is up-converted to the radio frequency (24-29 GHz) at the remote radio unit. An average error vector magnitude (EVM) of 6.40 % (-23.88 dB) is achieved over different carrier frequencies when transmitting a 300 MHz-bandwidth 64-QAM OFDM signal. The system performance is demonstrated by a 2×1 multiple-input single-output system transmitting 160 MHzbandwidth 64-QAM OFDM signals centered at 25 GHz. Owing to transmit diversity, an average gain of 1.12 dB in EVM is observed. This work also evaluates the performance degradation caused by asynchronous phase noise between remote radio units. The performance shows that the proposed approach is a competitive solution for the 5G downlink fronthaul network for frequency bands above 24 GHz.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.