Centralized Radio Access Network Architecture Research Articles

Delay and Fairness Analysis of C-RAN for Single and Multi Scheduling Domain Strategies

Background: Centralized Radio Access Network (C-RAN) is the most promising network architecture for next-generation communication networks. It meets the need for flexibility on fronthaul as well as large bandwidth on backhaul of the network. All along, scheduling is very important for the transmission of information in an organized manner. C-RAN has not been studied with the scheduling domain strategies yet in the literature. Objective: In this work, packet transmission duration, overall transmission time, wait time, and fairness index parameters have been calculated and analysed for C-RAN architecture for two different scheduling domains. The total transmission cycle time parameter is calculated for the three upper functional split options of C-RAN. The overall transmission time is a parameter calculated for the entire uplink channel. Methods: To implement the network scenario, extensive scripting is done on MATLAB Editor for single scheduling domain (SSD) and multi-scheduling domain (MSD) for three higher functional split options of C-RAN. The data traffic generated in the network is considered random. Results: A closer examination of results reveals the advantages and disadvantages of both algorithms, as well as trade-offs between them. Conclusion: For quicker data transmission, SSD should be preferred whereas MSD should be preferred if multiple users want to access resources simultaneously. Lower functional split options of C-RAN require less transmission cycle time. The MSD technique is fairer than SSD.

Enhancing coordinated multi-point joint reception with dynamic bandwidth allocation

Coordinated Multipoint (CoMP) Joint Reception (JR) is a vital technology to mitigate uplink inter-cell interference (ICI) and can be facilitated by the centralized radio access network (C-RAN). In C-RAN architecture, base stations (BSs) are decoupled into the central unit (CU) and the distributed units (DUs). Meanwhile, a fronthaul (FH) is employed to connect CU and DUs. However, FH constructed by the time division multiplexing passive optical network (TDM-PON) significantly affects the performance of JR. The inherent polling mechanism of TDM-PON results in the asynchronous forwarding of JR data, which leads to high JR latency and a large amount of storage consumption. To alleviate the problem, we presented a novel dynamic bandwidth allocation (DBA) scheme, which classifies network data as JR and non-JR data and optimizes the data forwarding order of different types and DUs. A heuristic algorithm called Rearrange Sub-timeslot DBA (RS-DBA) was proposed to implement the DBA scheme. Simulation results indicate the proposed RS-DBA algorithm can reduce the average latency of JR data and storage resources consumption. In addition, the RS-DBA can make a better tradeoff between latency and efficiency.

A low cost PON-FSO based fronthaul solution for 5G CRAN architecture

The continuous growth in mobile network traffic driven by the extensive range of new user applications, for instance, interactive e-learning, social networking sites, remote medical service and machine-to-machine communication has pushed the mobile network operators to enhance their network capacity. The main solution to deal with this problem is to deploy thousands of low power small cell base stations through Centralized Radio Access Network (C-RAN) architecture. The C-RAN offers a green solution for the deployment of small cells with advanced wireless features such as coordinated multipoint, joint scheduling, and multi-radio access technology. However, the provision of fronthaul connections to these small cells at a reasonable cost is a big concern for mobile operators especially when fronthaul link requires high capacity. Therefore, in this work, we present the hybrid fronthaul approach for C-RAN architecture based on Passive Optical Network (PON) and Free Space Optics (FSO) to enhance flexibility and minimize deployment costs of fronthaul network. The paper aims to examine the Total Cost of Ownership (TCO) of fronthaul networks taking into account both capital expenditure and operational expenditure costs, moreover, the efficacy of our proposed model is also analyzed by using optisystem simulator. The proposed model, in terms of TCO, is compared with the standalone PON based fronthaul system in green field scenarios. The numerical results revealed that the hybrid PON-FSO based fronthaul solution can save up to 42.89% TCO associated with small cell fronthaul architecture.

Analog MIMO RoC Passive Relay for Indoor Deployments of Wireless Networks

Most of the indoor coverage issues arise from network deployments that are usually planned for outdoor scenarios. Moreover, the ever-growing number of devices with different Radio Access Technologies (RATs), expected for new 5G scenarios and to maintain compatibility with older cellular standards (mostly 3G/4G), worsen this situation thus calling for novel bandwidth-efficient, low-latency and cost-effective solutions for indoor coverage. To solve this problem, Centralized Radio Access Network (C-RAN) architectures have been proposed to provide dense and controlled coverage inside buildings. However, all-digital C-RAN solutions are complex and expensive when indoor layout constraints and device costs are considered. We discuss here an analog C-RAN architecture, referred to as Analog MIMO Radio-over-Copper (A-MIMO-RoC), that aims at distributing RF signals indoors over distances in the order of 50 m. The all-analog passive-only design presented here proves the feasibility of analog relaying of MIMO radio signals over LAN cables at frequency bandwidth values up to 400 MHz for multi-RAT applications. After asserting the feasibility of the A-MIMO-RoC platform, we present some experimental results obtained with the proposed architecture. These preliminary results show that the A-MIMO-RoC system is a valid solution towards the design of dedicated 4G/5G indoor wireless systems for the billions of buildings which nowadays still suffer from severe indoor coverage issues.

Joint User Scheduling and RRU Association for ODFMA-Based Networks With Inter-BBU Coordination

This paper investigates the joint user scheduling (US) and user association (UA) problem for OFDMA-based networks under the centralized radio access network (C-RAN) architecture. We first formulate the joint optimization problem for US and UA, which is intractable in its exact form, and therefore, we propose a corresponding upper bound problem, with much lower computational complexity, with the help of a novel continuous rate function. We show that the upper bound problem can be further converted into an equivalent convex optimization problem via geometric programming (GP) that can be solved with inter-baseband unit coordination, which is viable in the C-RAN architecture. Furthermore, we show that the solutions of the convex upper bound problem can be mapped into the solution space of the original joint US and UA problem with a small gap. As a practically implementable solution to the original problem, a heuristic-based scheduler has been developed to obtain quasi-optimal UA and US solutions for the uplink (UL) as well as the downlink (DL) transmissions. Through extensive numerical simulations, we verify that the performance of the proposed heuristic-based scheduler is quasi-optimal on both UL and DL.

Boosting Fronthaul Capacity: Global Optimization of Power Sharing for Centralized Radio Access Network

The limited fronthaul capacity imposes a challenge on the uplink of centralized radio access network (C-RAN). We propose to boost the fronthaul capacity of massive multiple-input multiple-output (MIMO) aided C-RAN by globally optimizing the power sharing between channel estimation and data transmission both for the user devices (UDs) and the remote radio units (RRUs). Intuitively, allocating more power to the channel estimation will result in more accurate channel estimates, which increases the achievable throughput. However, increasing the power allocated to the pilot training will reduce the power assigned to data transmission, which reduces the achievable throughput. In order to optimize the powers allocated to the pilot training and to the data transmission of both the UDs and the RRUs, we assign an individual power sharing factor to each of them and derive an asymptotic closed-form expression of the signal-to-interference-plus-noise for the massive MIMO aided C-RAN consisting of both the UD-to-RRU links and the RRU-to-baseband unit (BBU) links. We then exploit the C-RAN architecture's central computing and control capability for jointly optimizing the UDs' power sharing factors and the RRUs' power sharing factors aiming for maximizing the fronthaul capacity. Our simulation results show that the fronthaul capacity is significantly boosted by the proposed global optimization of the power allocation between channel estimation and data transmission both for the UDs and for their host RRUs. As a specific example of 32 receive antennas (RAs) deployed by RRU and 128 RAs deployed by BBU, the sum-rate of 10 UDs achieved with the optimal power sharing factors improves 33\% compared with the one attained without optimizing power sharing factors.

5G Centralized Multi-Cell Scheduling for URLLC: Algorithms and System-Level Performance

We study centralized radio access network (C-RAN) with multi-cell scheduling algorithms to overcome the challenges for supporting ultra-reliable low-latency communications (URLLC) in the fifth-generation new radio (5G NR) networks. Low-complexity multi-cell scheduling algorithms are proposed for enhancing the URLLC performance. In comparison with the conventional distributed scheduling, we show that the C-RAN architecture can significantly reduce undesirable queuing delay of URLLC traffic. The gain of user scheduling with different metrics and the benefit of packet segmentation are analyzed. The performance of the proposed solutions is evaluated with an advanced 5G NR compliant system-level simulator with high degree of realism. The results show that the centralized multi-cell scheduling achieves up to 60% latency improvement over the traditional distributed scheduling while fulfilling the challenging reliability of URLLC. It is shown that segmentation brings additional performance gain for both centralized and distributed scheduling. The results also highlight the significant impact of channel- and delay-aware scheduling of URLLC payloads.

Rank-Based Low-Latency Scheduling for Maximum Fronthaul Accommodation in Bridged Network

Fronthaul bridged networks have attracted attention to transport time-sensitive fronthaul streams in the centralized radio access network (C-RAN) architecture. When the functional split is changed and time-division duplex (TDD) is employed in the C-RAN architecture, the data rate in fronthaul becomes variable and the global synchronization of fronthaul streams will occur. In this case, it is critical to reduce the queuing delay among fronthaul streams to efficiently accommodate a number of radio equipments in a bridged network. In this paper, we propose a novel rank-based queue scheduling method for achieving low-latency in a fronthaul bridged network. The proposed scheme considers the frame-level queuing delay caused by global synchronization with the TDD. The worst-case delay of fronthaul flows is minimized, and the number of accommodated fronthaul streams is maximized. We confirmed with computer simulations that the proposed scheme can minimize the worst case delay and increase the number of accommodated fronthaul streams.

Functional Split of Zero-Forcing Based Massive MIMO for Fronthaul Load Reduction

The evolution towards centralized radio access network (C-RAN) for 5G is driven by the need for improved network performance and reduced total-cost-of-ownership (TCO). In C-RAN, physically separated remote radio units (RRUs) and baseband units (BBUs) are connected via fronthaul (FH) links, which are capacity constrained. When base-station antennas are upgraded to support massive MIMO techniques, an intra PHY split between RRU and BBU becomes favorable to avoid the dramatic rate growth on the FH links. In this paper, we present a new uplink functional split alternative that decomposes the massive MIMO processing, on the basis of zero-forcing (ZF) equalization, into two phases: dimension-reduction phase and interference cancellation phase, which are implemented in RRU and BBU respectively. Compared with the traditional C-RAN architecture having all baseband processing in the BBU, the new scheme largely alleviates the FH load by reducing the number of FH streams to be equal to the number of MIMO user layers. Compared with an existing split that places all MIMO processing in RRU, the new scheme reduces the RRU complexity without compromising the post-processing performances.

Self-Seeded DWDM Solution for Fronthaul Links in Centralized-Radio Access Network

One of the requirements for the fronthaul segment in the Centralized-Radio Access Network architecture, is the capability to multiplex several fronthaul links on the same fiber by means of wavelength division multiplexing (WDM). In the self-seeded solutions, each transceiver creates its own wavelength carrier to form the transmitter source. Thus, this scenario seems suitable for fronthaul applications as there is no longer requirement to provide wavelength specific sources. Each transceiver automatically creates a laser field that tunes to the connection port of the optical multiplexer. An optical cavity is established between an optical reflector (Faraday Rotator Mirror) and the Reflective Semiconductor Optical Amplifier. Achieving a colorless transceiver would solve the inventory management problem for wavelength assignment that appears in the traditional WDM fronthaul systems. However, to our knowledge, no study has been done yet to show the performances of this technique on a real fronthaul link. In this paper we study and verify the compatibility of a self-seeded DWDM solution with the most critical fronthaul requirements: the data rate, the bit error rate, the jitter, the round trip delay and the radio frequency accuracy budget. Moreover, the quality of the end to end long term evolution (LTE) signal is measured in terms of error vector magnitude (EVM). The experiments are carried out for transmission up to 30 km, for different cavity lengths and different LTE modulation signals (QPSK, 16-QAM, 64-QAM).