Evaluation of Sigma-Delta-over-Fiber for High-Speed Wireless Applications

Future mobile communication networks aim to increase the communication speed,\ua0provide better reliability and improve the coverage. It needs to achieve all of these enhancements, while the number of users are increasing drastically. As a result, new base-station (BS) architectures where the signal processing is centralized and wireless access is provided through multiple, carefully coordinated remote radio heads are needed. Sigma-delta-over-fiber (SDoF) is a communication technique that can address both requirements and enable very low-complexity, phase coherent remote radio transmission, while transmitting wide-band communication signals with high quality. This thesis investigates the potential and limitations of SDoF communication links as an enabler for future mobile networks.In the first part of the thesis, an ultra-high-speed SDoF link is realized by using state-of-the-art vertical-cavity surface-emitting-lasers (VCSEL). The effects of VCSEL characteristics on such links in terms of signal quality, energy efficiency and potential lifespan is investigated. Furthermore, the potential and limitations of UHS-SDoF are evaluated with signals having various parameters. The results show that, low-cost, reliable, energy efficient, high signal quality SDoF links can be formed by using emerging VCSEL technology. Therefore, ultra-high-speed SDoF is a very promising technique for beyond 10~GHz communication systems.In the second part of the thesis, a multiple-input-multiple-output (MIMO) communication testbed with physically separated antenna elements, distributed-MIMO, is formed by multiple SDoF links. It is shown that the digital up-conversion, performed with a shared local-oscillator/clock at the central unit, provides excellent phase coherency between the physically distributed antenna elements. The proposed testbed demonstrates the advantages of SDoF for realizing distributed MIMO systems and is a powerful tool to perform various communication experiments in real environments.In general, SDoF is a solution for the downlink of a communication system, i.e. from central unit to remote radio head, however, the low complexity and low cost requirement of the remote radio heads makes it difficult to realize the uplinks of such systems. The third part of this thesis proposes an all-digital solution for realizing complementary uplinks for SDoF systems. The proposed structure is extensively investigated through simulations and measurements and the results demonstrate that it is possible realize all-digital, duplex, optical communication links between central units and remote radio heads.In summary, the results in this thesis demonstrate the potential of SDoF for wideband, distributed MIMO communication systems and proposes a new architecture for all-digital duplex communication links. Overall, the thesis shows that SDoF technique is powerful technique for emerging and future mobile communication networks, since it enables a centralized structure with low complexity remote radio heads and provides high signal quality

Sigma-Delta-over-Fiber for High-Speed Wireless Communication Systems

Future mobile communication networks aim to increase the communicationspeed, provide better reliability and improve the coverage. It needs to achieveall of these enhancements, while the number of users are increasing drastically.As a result, new base-station (BS) architectures where the signal processingis centralized and wireless access is provided through multiple, carefullycoordinated remote radio units are needed.The sigma-delta-over-fiber (SDoF) is a communication technique that canaddress both requirements and enable very low-complexity, phase coherentremote radio transmission, while transmitting wide-band communication signalswith high quality. This thesis investigates the potential and limitations of SDoFcommunication links as an enabler of future mobile networks.In the first part of the thesis, a multiple-input-multiple-output (MIMO)communication testbed with physically separated antenna elements, distributed-MIMO, is formed by multiple SDoF links. It is shown that the digital upconversion,performed with a shared local-oscillator/clock at the central unit,provides excellent phase coherency between the physically distributed antennaelements. Moreover, the same approach decreases the complexity and thepackage size of the antenna units\ua0significantly by moving the complexity of theBSs to a central unit. The implemented testbed is evaluated through variouscommunication experiments. The results show that distributing the antennaunits of a MIMO communication system can increase the coverage and signalquality.In the second part of the thesis, an ultra-high-speed SDoF (UHS-SDoF) linkis realized by using the state-of-the-art vertical-cavity surface-emitting-lasers(VCSEL). The effects of VCSEL characteristics on such links in terms of signalquality, energy efficiency and potential lifespan is investigated. Furthermore, thepotential and limitations of UHS-SDoF are evaluated with signals having variousparameters. The results show that, low-cost, reliable, energy efficient, highsignal quality SDoF links can be formed by using emerging VCSELs. Therefore,UHS-SDoF is a very promising technique for beyond 10 GHz communicationsystems.In conclusion, this thesis has showed that low-complexity, low-cost, andenergy efficient ultra-high speed communication links and distributed MIMOsystems can be implemented by employing SDoF

Localization With Distributed MIMO Using a High-Speed Sigma-Delta-Over-Fiber Testbed

Distributed MIMO (D-MIMO) with synchronized access points (APs) is a promising architecture for both communications and localization in 5G and beyond systems. In this letter, we develop a time-difference-of-arrival (TDOA)-based indoor localization system using a 2.35-GHz high-speed sigma-delta-over-fiber (SDoF) D-MIMO testbed with 40-MHz bandwidth, exploiting the fully synchronized nature of the APs. Experimental results over an area of size 100 m\ub2 demonstrate accuracies below 0.2 m and agree with the theoretical Cram\ue9r-Rao bounds (CRBs) at most measurement locations, indicating the localization capability of high-speed SDoF D-MIMO

Automatic Distributed MIMO Testbed for beyond 5G Communication Experiments

This paper demonstrates an automated testbed suitable for beyond-5G distributed MIMO experiments, where bandwidth, number of transmitters and precoding methods are flexible and configured through a central unit. This is based on an all-digital radio-over-fiber approach to communication through 12 fully coherent, low-complexity remote radio transmitters. An automated robot receiver is implemented to facilitate efficient communication data collection in realistic environments. Using the proposed system, co-located and distributed MIMO communication antenna configurations are compared in a real in-door environment. The results show that distributed MIMO provides more significantly more uniform power distribution and better overall MIMO capacity compared to co-located MIMO

Distributed Massive MIMO via all-Digital Radio Over Fiber

A crucial challenge in the implementation of distributed massive multiple-input multiple-output (MIMO) architectures is to provide phase coherence while, at the same time, limit the complexity of the remote-radio heads (RRHs), which is important for cost-efficient scalability. To address this challenge, we present in this paper a phase-coherent distributed MIMO architecture, based on off-the-shelf, low-cost components. In the proposed architecture, up- and down-conversion are carried out at the central unit (CU). The RRHs are connected to the CU by means of optical fibers carrying oversampled radio-frequency (RF) 1-bit signals. In the downlink, the 1-bit signal is generated via sigma-delta modulation. At the RRH, the RF signal is recovered from the 1-bit signal through a bandpass filter and a power amplifier, and then fed to an antenna. In the uplink, the 1-bit signal is generated by a comparator whose inputs are the low-noise-amplified received RF signal and a suitably designed dither signal. The performance of the proposed architecture is evaluated with satisfactory results both via simulation and measurements from a testbed

Controversy and Consensus on Indications for Sperm DNA Fragmentation Testing in Male Infertility: A Global Survey, Current Guidelines, and Expert Recommendations

Purpose: Sperm DNA fragmentation (SDF) testing was recently added to the sixth edition of the World Health Organization laboratory manual for the examination and processing of human semen. Many conditions and risk factors have been associated with elevated SDF; therefore, it is important to identify the population of infertile men who might benefit from this test. The purpose of this study was to investigate global practices related to indications for SDF testing, compare the relevant professional society guideline recommendations, and provide expert recommendations. Materials and Methods: Clinicians managing male infertility were invited to take part in a global online survey on SDF clinical practices. This was conducted following the CHERRIES checklist criteria. The responses were compared to professional society guideline recommendations related to SDF and the appropriate available evidence. Expert recommendations on indications for SDF testing were then formulated, and the Delphi method was used to reach consensus. Results: The survey was completed by 436 experts from 55 countries. Almost 75% of respondents test for SDF in all or some men with unexplained or idiopathic infertility, 39% order it routinely in the work-up of recurrent pregnancy loss (RPL), and 62.2% investigate SDF in smokers. While 47% of reproductive urologists test SDF to support the decision for varicocele repair surgery when conventional semen parameters are normal, significantly fewer general urologists (23%; p=0.008) do the same. Nearly 70% would assess SDF before assisted reproductive technologies (ART), either always or for certain conditions. Recurrent ART failure is a common indication for SDF testing. Very few society recommendations were found regarding SDF testing. Conclusions: This article presents the largest global survey on the indications for SDF testing in infertile men, and demonstrates diverse practices. Furthermore, it highlights the paucity of professional society guideline recommendations. Expert recommendations are proposed to help guide clinicians

Different Digital Predistortion Techniques for Power Amplifier Linearization

Linearity and high efficiency are crucial requirements for any power amplifier. However, power amplifiers have high efficiency levels when they are in non-linear regions. To overcome this issue there have been many suggestions in literature, one of the most successful methods is digital predistortion method. Digital predistortion (DPD) method’s low resource usage and fairly easy algorithm draws a lot of researcher’s attention. Many different methods are suggested for DPD algorithms. Volterra series based methods draws even more attention due to its flexibility and easy implementation. However, deciding which method to use for DPD purposes is not completed even when Volterra series based method is chosen. There are many different Volterra series based methods which differ from each other. This paper examines 5 different Volterra based methods for DPD purposes and tests them in 2 different PAs with LTE signals. Also forward behavioral modelling performance of these 5 methods are also examined for each PA with same signals. In chapter 1 needed theoretical information is explained about power amplifier characteristics. In chapter 2, the five chosen methods are examined in detail and corresponding parameters are explained. In chapter 3, forward behavioral modelling setup and the way to model power amplifiers is explained. In chapter 4, setup and the digital predistortion algorithms are explained. In the 5th chapter the results of both behavioral modelling and DPD is shown and comments on the results are given

A Flexible Multi-Gbps Transmitter Using Ultra-High Speed Sigma- Delta-over- Fiber

Sigma-delta-over-fiber (SDoF) using high speed-low cost optical components for datacom enables high speed transmission at X-band. This paper examines the limitations of SDoF in terms of maximum frequencies and highest bit rates. Different modulation formats, symbol rates and carrier frequencies are investigated. A high speed 850 nm vertical-cavity surface-emiting-laser (VCSEL) is used as an optical source to transmit the optical signal over a 50 meter, OM4, multimode fiber (MMF). Error vector magnitude (EVM) less than 6% is achieved at a 12-GHz center frequency for a 8-Gbps QAM256 modulated signal

Evaluation of Distributed MIMO Communication Using a Low-Complexity Sigma-Delta-over-Fiber Testbed

Distributing the antennas of a base station is a method to increase the coverage and the capacity of a conventional, co-located MIMO communication system. However, physically separated antennas/access points (AP) creates a fundamental challenge of RF phase synchronization required for joint/coordinated transmission in distributed MIMO (D-MIMO) systems. In this paper we compare co-located-and distributed-MIMO wireless communication thru various measurements using a fully synchronized, low-complexity, twelve-channel testbed based on sigma-delta-over-fiber (SDoF). Single and multi-user measurements are performed in a laboratory environment and the error-vector-magnitude (EVM), the received power and signal-to-interference ratio (SIR) is calculated. We show that distributing the access points improves the received symbol EVM up to 1.6-dB and increases the coverage of the service area by delivering more uniform received power levels