A Hierarchical Modulation Enabled SNR Allocable Delta-Sigma Digital Mobile Fronthaul System

Abstract

Internet of everything is being build up rapidly, which causes much higher requirements towards the flexibility of communication resources, especially the adaptivity of the fronthaul to various transmission distances and capacities. In this paper, we proposed a low-cost and spectrum efficient 5G fronthaul broadband connection solution that combines hierarchical modulation technology and delta-sigma modulation. The proposed scheme can double the number of accesses without occupying extra wavelengths. Moreover, such architecture can flexibly allocate the SNR of a group of remote radio units for different user requirement of transmission rate and reaches. Simulation results show that the proposed scheme can increase the access distance of the fronthaul network by 23% and the capacity by 16.7%. The feasibility of the solution is verified through a proof-of-concept experiment. After 20 km transmission, the OFDM-64QAM and -256QAM signal with a center frequency of 3.5 GHz and a bandwidth of 500 MHz can meet the EVM requirements of 8% and 3.5%, respectively. And when the 𝐑 𝑳𝑴 of the hierarchical PAM4 signal is 0.6, the ROP required by the most-significant bit branch can be reduced by ~1.5 dB.

The joint power-domain multiplexing and SSII mitigation scheme for IM DD downstream orthogonal frequency division multiple (OFDM-PON)

“…For an uncoded QAM-system, the equivalent SNR of ONU on subcarrier n is the SNR gap function  [27] which is used to ensure some QoS and is given by : 1 is the inverse standard Gaussian Q-function. However, the optimum power control in current NOMA protocols can only be obtained by exhaustive search [9][10][11], which does not suit for practical systems. According to SPC, the transmit power control consists of two parts: i) power division and ii) power allocation, where the former one determines the transmit power of each information stream; the latter one decides the mapping between information streams and signal layers.…”

“…Meanwhile, distinguishing from the fundamental time division multiple access (TDMA) and frequency division multiple access (FDMA), and code division multiple access (CDMA), the term "power-domain multiple access (PDMA)" was first proposed in [7], which is an initiative work using different transmit powers for multiuser access. PDM is well recognized as one of 5G techniques in terms of "non-orthogonal multiple access (NOMA)" protocol [8], which as a well-known high-capacity technique in future radio access and 5G system [9][10][11]. The NOMA protocols or PDM scheme offers greater spectrum efficiency and provide the method of power division to enable multiuser access.…”

Design Optimization of Feedforward Equalization for Mobile Fronthaul Based on Delta-Sigma Modulation With High-Order QAM Signals

“…Moreover, a unique advantage of the delta-sigma modulator is the functionalization of noise shaping which pushes the quantization noise out of the signal band [15]. Due to the aforementioned advantages, delta-sigma modulation technique has attracted extensive research interest and various study has been carried out such as the combination of hierarchical and delta-sigma modulations [16], ultra-high-order delta-sigma modulator [17] and novel feedback structures [18] to further improve the system performance and increase the transmission capacity in recent years. Nevertheless, to explore the benefits enabled by delta-sigma modulation, inter-symbol interference (ISI) needs to be eliminated via digital signal processing (DSP) since it's recognized as the main challenge to high-speed transmission systems.…”