Filtered Orthogonal Frequency Division Multiplex Modulation Application For Fronthaul Network

The rapid development of mobile internet technology has driven various mobile apps for new types of business,as well as availability of faster traffic flows.Cloud Radio Access Networks(C-RAN)as an innovative new architecture,has attracted attention for its significant advantages in reducing energy consumption,lowering operational costs and performing load balance.In C-RAN,Base Band Units(BBUs)can be centralized in a pool location and be separated from the remote radio units(RRUs).With the separation,a main standard body called common public radio interface(CPRI)serves as the fronthaul that enables communication between BBUs and RRUs.However,the CPRI has notably drawbacks such as constant data stream regardless of the dynamically changing mobile traffic,stringent requirement on dedicated channels,and low flexibility and scalability.These shortcomings are key challenges to C-RAN realization and application in the future.To address the issue,China Mobile is introducing a promising fronthaul solution called Next Generation Fronthaul Interface(NGFI)that locates more functions inside the RRU,thus decreasing bandwidth requirements and achieving higher network utilization efficiency.Based on the above discussion,this paper proposes a multiintermediate frequency(multi-IF)fronthaul system based on Filtered Orthogonal Frequency Division Multiplexing(F-OFDM).While keeping the existing C-RAN's distributed base station architecture,the system assumes to place part of the signal processing functionality in RRU and implement multi-IF transmission scheme to reduce bandwidth requirements.F-OFDM-based structure can reduce a side lobe suppression of nearly up to 20 dB and thus significantly eliminating interference among adjacent signals.This helps to mitigate the inter-subcarrier and inter-symbol interference in the system and remarks the support for multi-users in uplink transmission.Also,the use of filtering reduces the level of out-of-band emission as well as guard band between IF signals,and increases the spectrum efficiency.In addition,to overcome the issue of high peak-to-average power ratio(PAPR)in multi-carrier signals that would affect modulation depth in device with linear behavior,this paper investigates existing researches and proposes a compensation solution based on uneven mapping.A series of experiments have been conducted to support the system proposed in this paper,including the downlink and uplink transmission that respectively identifies the impacts of variable IF bandwidths,transmission distance,and IF number have on transmission efficiency.The experiment results show that the optical power budget in a 20-km fiber link can reach 28 dB and receive 1:64 splitting ratio in the remote node.Compared with traditional OFDM analogue fronthaul system,the proposed system can boost bandwidth efficiency by 10%.In ideal situation the single-wavelength may achieve ~40.22-Gbps CPRI-equivalent rate.In addition,a point-topoint transmission experiment was performed to demonstrate the proposed method of reduction on PAPR.By comparing suppression effect and computational complexity with previous studies,the proposed technique realizes a low-complexity PAPR reduction.It increases modulation depth in linear device and reduce 2% of error vector magnitude in the transmission system,allowing signals to be compatible with higher modulation index in the same modulation system.