Common Public Radio Interface Research Articles

Performance Evaluation of Ethernet-Based Mobile Fronthaul and Wireless CoMP in Split-PHY Processing

We experimentally evaluate the mobile fronthaul (MFH) optical bandwidth and wireless coordinated multipoint (CoMP) transmission and reception performance in Ethernet-based MFH with our proposed split-physical (PHY) processing (SPP). To reduce the MFH optical bandwidth, SPP redefines the base station (BS) functional split between the baseband unit (BBU) and the remote radio head (RRH) in a centralized/cloud radio access network (C-RAN) with a common public radio interface. The functional split point of SPP is between wireless channel coding and wireless modulation within the PHY layer functions. SPP employs its own CoMP joint transmission and reception schemes to achieve high wireless CoMP performance comparable to that in a conventional C-RAN while reducing the MFH optical bandwidth. Experimental results in the uplink and downlink show that SPP reduces the MFH optical bandwidth by over 90% compared to the conventional C-RAN. At the same time, SPP achieves wireless performance with a signal-to-noise ratio penalty of less than 2 dB compared to the conventional C-RAN in the uplink and outputs wireless signals identical to the wireless signal output in the conventional C-RAN in the downlink.

Near-lossless compression/decompression algorithms for digital data transmitted over fronthaul in C-RAN

The cloud radio access network (C-RAN) is not only a very important deployment solution for the future RAN but is also a core platform for network-centric advanced transmission techniques such as coordinated multi-point transmission and reception and the distributed antenna system. One of the main issues when implementing C-RAN at low cost and high efficiency is the need to reduce the implementation cost of the fronthaul and improve its usage efficiency. In order to achieve this, in this paper, near-lossless compression and decompression algorithms for digital data transported via fronthaul in C-RAN are proposed, where the compression is mainly achieved through the removal of various redundancies in wireless communication signals. Since the proposed algorithms significantly reduce the amount of data that should be transmitted via fronthaul while maintaining negligible in-band distortion in terms of error vector magnitude (EVM), we can actually reduce the number of transmission lines or enhance the utilization of them. In addition, they can be operated with a minimum compression ratio as well as a constant compression ratio; therefore, real-time processing and fronthaul data-muxing can be easily performed. Simulation results and comparisons have been carried out based on the 3rd generation partnership project long-term evolution system and the common public radio interface, which is a publicly available specification that is widely utilized to implement the fronthaul. Simulation results confirm that the proposed schemes can provide remarkable compression performance with a zero uncoded bit error rate and negligible signal distortion. Finally, the proposed schemes have various parameters that can be adjusted to meet given requirements such as latency, the compression ratio, EVM, complexity, and so on, and thus a smooth tradeoff between them can be achieved.

Resource Allocation Optimization for Time and Wavelength Division Multiplexing Passive Optical Network Enabled Mobile Fronthaul With Bitrate-Variable Compressed Common Public Radio Interface

Recently, a cloud radio access network (C-RAN) has been proposed as a candidate architecture for fifth-generation mobile communication. Fronthaul is a new segment in C-RAN. In this paper, we investigate the algorithms for resource allocation in time and wavelength division multiplexing passive optical network enabled front-haul. We formulate an integer nonlinear programming (INLP) model, considering the operation mode of the small cell. A heuristic method is also proposed based on an adaptive parallel genetic algorithm (GA). Three optimization objectives are considered when we implement the resource allocation schemes in the fronthaul: 1) minimize the total number of used wavelengths, 2) minimize the load imbalance of the fronthaul, and 3) minimize the amount of traffic influenced by fronthaul virtual topology change. The results show that INLP and adaptive parallel GA have good performance for resource allocation in the fronthaul. Wavelength resources can be significantly saved in different load scenarios, so that the load difference can be minimized with minimal topology adjustment. Furthermore, the adaptive parallel GA obtains more efficient resource allocation than the traditional GA with much less running time, which makes it applicable for the large-scale fronthaul network optimization with fast convergence.

Trade-Off Between Power and Bandwidth Consumption in a Reconfigurable Xhaul Network Architecture

The increasing number of wireless devices, the high required traffic bandwidth, and power consumption will lead to a revolution of mobile access networks, which is not a simple evolution of traditional ones. Cloud radio access network technologies are seen as promising solution in order to deal with the heavy requirements defined for 5G mobile networks. The introduction of the common public radio interface (CPRI) technology allows for a centralization in BaseBand unit (BBU) of some access functions with advantages in terms of power consumption saving when switching off algorithms are implemented. Unfortunately, the advantages of the CPRI technology are to be paid with an increase in required bandwidth to carry the traffic between the BBU and the radio remote unit (RRU), in which only the radio functions are implemented. For this reason, a tradeoff solution between power and bandwidth consumption is proposed and evaluated. The proposed solution consists of: 1) handling the traffic generated by the users through both RRU and traditional radio base stations (RBS) and 2) carrying the traffic generated by the RRU and RBS (CPRI and Ethernet flows) with a reconfigurable network. The proposed solution is investigated under the lognormal spatial traffic distribution assumption. After proposing resource dimensioning analytical models validated by simulation, we show how the sum of the bandwidth and power consumption may be minimized with the deployment of a given percentage of RRU. For instance we show how in 5G traffic scenarios this percentage can vary from 30% to 50% according to total traffic amount handled by a switching node of the reconfigurable network.

Efficient Mobile Fronthaul via DSP-Based Channel Aggregation

Mobile fronthaul is an important network segment that bridges wireless baseband units and remote radio units to support cloud radio access network. We review recent progresses on the use of frequency-division multiplexing to achieve highly bandwidth-efficient mobile fronthaul with low latency. We present digital signal processing (DSP) techniques for channel aggregation and deaggregation, frequency-domain windowing, adjacent channel leak age ratio reduction, and synchronous transmission of both the I/Q waveforms of wireless signals and the control words (CWs) used for control and management purposes. In a proof-of-concept experiment, we demonstrate the transmission of 48 20-MHz LTE signals with a common public radio interface (CPRI) equivalent data rate of 59 Gb/s, achieving a low round-trip DSP latency of <2 μs and a low mean error-vector magnitude (EVM) of ∼2.5% after fiber transmission. In a follow-up experiment, we further demonstrate the transmission of 32 20-MHz LTE signals together with CPRI-compliant CWs, corresponding to a CPRI-equivalent data rate of 39.32 Gb/s, in single optical wavelength channel that requires an RF bandwidth of only ∼1.6 GHz. After transmission over 5-km standard single-mode fiber, the CWs are recovered without error, while the LTE signals are recovered with an EVM of lower than 3%. Applying this technique to future 5G wireless networks with massive multiple-input multiple-output is also discussed. This efficient mobile fronthaul technique may find promising applications in future integrated fiber/wireless access networks to provide ultrabroadband access services.

Next Generation Mobile Fronthaul and Midhaul Architectures [Invited

Centralized processing is expected to bring about substantial benefits for wireless networks both on the technical side and on the economic side. While this concept is considered an important part of future radio access network architectures, it is more and more recognized that the current approach to fronthauling by employing the Common Public Radio Interface protocol will be inefficient for large-scale network deployments in many respects, and particularly for the new radio network generation 5G. In this paper, an overview is given of currently available optical fronthaul technologies, and of recently started activities toward more efficient and scalable solutions, and finally an outlook is given into which 5G specific service characteristics may further impact future backhaul, midhaul, and fronthaul networks.

Performance Evaluation of Mobile Front-Haul Employing Ethernet-Based TDM-PON With IQ Data Compression [Invited

In this paper, we experimentally and numerically evaluate the performance of a common public radio interface (CPRI) over a time division multiplexed passive optical network (TDM-PON) system for accommodating densely deployed small cells in centralized-radio-accessnetwork- based future radio access. A prototype of the CPRI over TDM-PON is developed by using Ethernet-based TDM-PON. Experimental results showed that its synchronization accuracy and latency meet the requirements of a mobile front-haul using CPRI by the implemented delay jitter reduction and low-latency bandwidth allocation techniques. An in-phase and quadrature (IQ) data compression technique is also implemented on the system to enable a higher accommodation of remote radio heads. Experiments confirmed that the compression technique meets open radio equipment interface standards in terms of latency and signal quality degradation. Numerical results showed that the technique with a 0.45 compression ratio increases the number of supportable remote radio heads from 3 to 7 for a mobile front-haul with a 100 μs latency limitation.

25-Gb/s TDM Optical Link Using EMLs for Mobile Fronthaul Network of LTE-A System

We propose and demonstrate a common public radio interface (CPRI)-compliant 25.2923-Gb/s mobile fronthaul network for long term evolution-advanced (LTE-A) systems. In order to meet the CPRI specifications and the stringent latency requirement of the LTE-A fronthaul network cost-effectively, we use the synchronous time-division-multiplexing, forward-error correction, and electrical equalization techniques. To enhance the cost-effectiveness, we also use an electroabsorption-modulated laser and exploit the possibility of using simple modulation formats such as the ON–OFF keying, electrical duobinary, and four-level pulse amplitude modulation. The performance of the proposed network is evaluated experimentally in terms of the tolerances to fiber dispersion and optical reflection.

A new C-RAN architecture based on RF signal soft-switching

Coordinated multi-point (CoMP) is known to be one of the key technologies for long-term evolution (LTE)-advanced systems. CoMP technology can improve system capacity and the quality of wireless communication services for users in LTE networks. However, in practice, the actual performance of CoMP technology is limited by the switching capacity of the backhaul network among distributed base stations as well as its latencies. In this paper, we propose a new cloud radio access network architecture based on RF signal soft-switching to solve this problem. Furthermore, we introduce a narrow-band parallel processing technique on a common public radio interface in downlink and uplink to reduce the volume of data as well as the latencies in the transmission process among base band units and remote radio units. By combining theoretical analysis with computer simulations, we show that the technique is valid both for downlink and uplink, i.e., it does not degrade the performance of downlink and uplink propagation between BBU pool and user equipments. Moreover, the computational time of the narrow-band parallel processing technique is less than that of the standard technique.

Compactly packaged monolithic four-wavelength VCSEL array with 100-GHz wavelength spacing for future-proof mobile fronthaul transport.

We report a cost-effective transmitter optical sub-assembly using a monolithic four-wavelength vertical-cavity surface-emitting laser (VCSEL) array with 100-GHz wavelength spacing for future-proof mobile fronthaul transport using the data rate of common public radio interface option 6. The wavelength spacing is achieved using selectively etched cavity control layers and fine current adjustment. The differences in operating current and output power for maintaining the wavelength spacing of four VCSELs are <1.4 mA and <1 dB, respectively. Stable operation performance without mode hopping is observed, and error-free transmission under direct modulation is demonstrated over a 20-km single-mode fiber without any dispersion-compensation techniques.

Evolution of Wireline Transceiver Standards: Various, Most-Used Standards for the Bandwidth Demand

Thanks to the bandwidth demand explosion in data centers and telecommunication infrastructures, the data-rate growth for wireline transceivers has been consistently increasing at about 2×/4 yr, as shown in Figure 1. The most-used standards are listed. Peripheral component interconnect express is used ubiquitously in almost all chip-to-chip interfaces. Optical Internetworking Forum (OIF)/Common Electrical Interface (CEI) and Ethernet usually come hand-in-hand for backplanes [long-reach (LR)], chip-to-module [short-reach (SR), or in some standards, medium-reach (MR)] applications. Common Public Radio Interface (CPRI) is the specialized standard for the wireless radio head, connecting between the top of the cell tower to the bottom of the tower, mostly in optical medium. Passive-Optical-Network (PON) distinguishes itself for the burst mode requirement.

125-km Long Cavity Based on Self-Seeded RSOAs Colorless Sources for 2.5-Gb/s DWDM Networks

The laser behavior of reflective semiconductor optical amplifier self-seeded sources is investigated. 2.5-Gb/s transmission is realized with optical cavities of 10, 26, 100, and 125 km for access and metropolitan networks, realizing the longest amplified self-seeded external cavity laser. Moreover, Gigabit Ethernet, common public radio interface, and 2.5-Gb/s transmissions are experimented using amplified self-seeded reflective semiconductor optical amplifier wavelength division multiplexing passive optical networks systems. A field trial setup is exploited to test the system performance in terms of reach and optical budget.

LTE-Advanced 이동통신망 Fronthaul 구간을 위한 Radio over Fiber 시스템의 필요 전송용량 및 요구사항 분석

Since smart phones are widely used globally, the demand for high-speed mobile communications are increasing. To accommodate the increased communication demand, the next-generation mobile communication services such as LTE-Advanced are deployed. In the LTE-Advanced base stations, the base station schemes of Digital Unit (DU) and Radio Unit (RU) are widely used. Here, the link between DU and RU is called fronthaul link. In the current fronthaul link, a digital optical communication interface is used, which is called Common Public Radio Interface (CPRI). However, the CPRI link cannot support the increased mobile traffic efficiently. Therefore, in this paper, we investigate an alternative technology based on the Radio over Fiber (RoF) to accommodate the increased mobile traffic economically.

Recent Progress on C-RAN Centralization and Cloudification

This paper presents the latest progress on cloud RAN (C-RAN) in the areas of centralization and virtualization. A C-RAN system centralizes the baseband processing resources into a pool and virtualizes soft base-band units on demand. The major challenges for C-RAN including front-haul and virtualization are analyzed with potential solutions proposed. Extensive field trials verify the viability of various front-haul solutions, including common public radio interface compression, single fiber bidirection and wavelength-division multiplexing. In addition, C-RANs facilitation of coordinated multipoint (CoMP) implementation is demonstrated with 50%-100% uplink CoMP gain observed in field trials. Finally, a test bed is established based on general purpose platform with assisted accelerators. It is demonstrated that this test bed can support multi-RAT, i.e., Time-Division Duplexing Long Term Evolution, Frequency-Division Duplexing Long Term Evolution, and Global System for Mobile Communications efficiently and presents similar performance to traditional systems.

WDM-PON 전송을 이용한 4G 이동통신망 CPRI 링크의 시스템 요구규격 분석

Recently, base stations composed of digital unit (DU) and radio unit (RU) have been widely used in 4G mobile networks. To connect DU and RU, CPRI (common public radio interface) is usually used as the interface standard. This CPRI link is considered as one of the application markets for WDM-PON. In this paper, we analyzed the required specification of WDM-PON for the CPRI link of the 4G LTE-Advanced base station composed of DU and RU. This analysis is important to set a target goal of the development of WDM-PON system for 4G mobile networks.

We mast do something about it [base station design

Operators&apos; continuous pressure on low cost is turning cellular masts into commoditised, highly modular products. The emergence of third generation (3G) mobile telecoms systems is shaking up the traditional mobile industry. Most obvious to consumers is the the rise in services beyond voice, which their operators are eager to offer them. However, in the background, the whole industry is shifting and the companies that make and supply infrastructure equipment are being forced to go along with the change. The industry has risen to the challenge with two initiatives instigated by two groups of vendors -OBSAI (Open Basestation Architecture Initiative) and CPRI (Common Public Radio Interface).