Fronthaul Network Modeling and Dimensioning Meeting Ultra-Low Latency Requirements for 5G

Abstract

Enabling the transport of fronthaul traffic in next generation cellular networks (5G) following the Cloud Radio Access Network (C-RAN) architecture requires re-designing the fronthaul network featuring high-capacity and ultra-low latency. With the aim of leveraging statistical multiplexing gains, infrastructure reuse and, ultimately, cost reduction, the research community are focusing on Ethernet-based packet-switch networks. To this end, we propose to use high queueing delay percentiles of G/G/1 queueing model as the key metric in fronthaul network dimensioning. Simulations reveal that that the Kingman's Exponential Law of Congestion provides accurate estimates on such delays for the particular case of aggregating a number of eCPRI fronthaul flows, namely functional splits IU and IID. We conclude that conventional 10G, 40G and 100G transponders can cope with multiple legacy 10-20 MHz radio channels with worstcase delay guarantees. Conversely, scaling to 40 and 100 MHz channels will require the introduction of 200G, 400G and even 1T high-speed transponders.

A Survey of the Functional Splits Proposed for 5G Mobile Crosshaul Networks

“…The exact location of this split is under discussion by 3GPP in [82]. Theoretical surveys: [5], [19], [25], [26], [28], [31], [32], [38], [41], [42], [43], [44], [45], [49] Simulations: [53], [61], [75], [83] Practical experiments: [50], [84], [85] In this split, the precoding and resource element mapper are included in the DU. The fronthaul link transports subframe symbols.…”

“…[75] simulates the throughput and total cost of ownership for split option 7-2 transported over a MWR fronthaul. The work in [83] evaluates the transmission of eCPRI over Ethernet. [63] observes that the transmission of 20 legacy 20 MHz LTE channels using such a functional split can be realized with 40 Gbps transponders, guaranteeing 99th delay percentiles below 9 μs.…”

Converged Analog Fiber-Wireless Point-to-Multipoint Architecture for eCPRI 5G Fronthaul Networks

“…The network setup follows the Option 7 I U split, meaning that it is still highly centralized but not as inefficient as the traditional Option 8 E split followed in CPRI. Option 7 split produces a Constant Bit Rate (CBR) stream of Ethernet packets between the BBU and the RRHs, and for a typical 2 × 2 MIMO RRH module the flow has a periodicity of 66.6 μs [11]. Depending on the bandwidth of the RRH channel, the fronthaul flow produces from 9000 bytes for 20 MHz access channels per period (1080 Mbit/s) up to 45000 bytes for 100 MHz 5G NR channels (5400 Mbit/s) [11].…”

“…Splits I U , I D , II D are located within the PHY layer and therefore correspond to Option 7, split E corresponds to Option 8 and is equivalent to the traditional split used by CPRI, while split D corresponds to Option 6 and below. By employing a higher functional split the fronthaul capacity requirement is effectively reduced: for instance, split I U halves the necessary capacity required by split E, whereas even higher splits reduce it even further [11]. However, these capacity gains come at the expense of centralization, leading to costlier RRH modules, whereas the necessity for high-speed PtP fronthaul connections remains.…”

Minimizing Delay in NFV 5G Networks by Means of Flexible Split Selection and Scheduling

“…In a nutshell, the main idea behind this paradigm shift is to move some of the functions that were traditionally placed at the base station to a central controller, which might be even deployed over general purpose computing nodes. However, fully centralized approaches may be unpractical in real networks, due to the high fronthaul capacity demand, which can only be met with fiber links [6] [7]. In light of it, different initiatives are proposing the re-design of the fronthaul [8], where different splitting configurations can be chosen.…”