Nelson V. Silva

Design and Optimization of Flexible and Coding Efficient All-Digital RF Transmitters

All-digital transmitters are getting increased attention due to its closer proximity to the ideal software-defined radio (SDR) transmitter. In this paper we propose a new transmitter architecture that addresses two key limitations of current approaches, namely, the poor coding efficiency and the high quality factor requirements of the RF output reconstruction filter that significantly limit the practical usability and dissemination of these new flexible RF transmitters. The proposed architecture combines a maximum coding efficiency of 79.3% and a signal-to-noise ratio (SNR) of 50 dB, while maintaining the high flexibility inherent to the all-digital transmitters and where the RF output carriers operating in the microwave frequency range are generated inside a single field-programmable gate array (FPGA) device. The obtained results also show the feasibility and potential of using FPGA-based architectures for implementing digital RF transmitters.

Gigasample Time-Interleaved Delta-Sigma Modulator for FPGA-Based All-Digital Transmitters

This paper presents the architecture and implementation of an FPGA-based all digital transmitter with a baseband sampling rate of 1 GHz. Hardware complexity and operation frequency analysis are performed to find the best hardware topology to improve the transmitter performance. The used polyphase decomposition techniques for delta sigma modulators considerably improve the bandwidth and SNR figures of merit of state-of-the-art FPGA integrated RF transmitters. The experimental results obtained show the feasibility of this approach and the improvement in the signal modulator oversampling ratio, enabling higher bandwidth in all-digital transmitters.

Evaluation of pulse modulators for all-digital agile transmitters

All-digital transmitters are gaining increased access over the last years, mainly due to white space technology needs. In this paper a new FPGA-based multichannel multimode transmitter architecture is presented. The new configuration includes improvements in PWM and ΣΔ Modulators, which are designed in order to optimize important figures of merit for RF transmitters as coding efficiency, usable bandwidth and SNR. The high flexibility of this architecture allows to easily change the frequency of the carriers as also the spectral masks, making it suitable for using in cognitive radio-based applications.

A dynamically reconfigurable architecture enabling all-digital transmission for cognitive radios

The proliferation of different wireless standards pushes an additional research effort towards the development of new agile radios, capable of adapting its communication parameters in order to meet the channel conditions, network restrictions and user demands. This change in the wireless communications paradigm requires the development of new radios with very flexible physical layers. In this paper we present a new reconfigurable ΣΔ-based transmitter architecture supporting multichannel multimode data transmission. The high flexibility of this architecture enables a data transmission scenario where the frequencies of the carriers and the spectral masks can be easily changed through software, making this agile transmitter interesting for use in cognitive radio-based applications.

The OReK real-time micro kernel for FPGA-based systems-on-chip

This paper presents the features, architecture, application design flow and evaluation of the OReK real-time micro kernel, for integration on FPGA-based SoCs for applications running on embedded softcore or hardwired processors. The features of the OReK kernel include the combined support for heterogeneous task sets, predictable shared resources synchronization, task-based interrupt servicing and runtime policing of the timing constraints, making it appropriate to manage multimedia application tasks with different types of timing properties and requirements. OReK is compact, highly configurable and supported on three distinct FPGA embedded processor architectures with different levels of performance and implementation technologies.

Mobile fronthaul RoF transceivers for C-RAN applications

We address the development of mobile fronthaul (MFH) radio-over-fibre (RoF) transceivers with the capability to transport Digital RoF (D-RoF) signals for C-RAN applications. The coexistence of transport of D-RoF with legacy and the future Passive Optical Network (PON) systems, such as Next Generation PON 2 (NG-PON2) will be analysed. The preliminary experimental results of transmitting several D-RoF signals with high spectral efficiency and based on Sub-Carrier Multiplexing (SCM) techniques will be presented.

Evaluation of an FPGA-based Reconfigurable SoC for All-Digital Flexible RF Transmitters

In this paper an FPGA-based System-on-Chip (SoC) implementation of a flexible digital radio is presented and evaluated. The implemented transmitter is able to perform a direct up-conversion of a baseband signal to RF operating in the gigahertz frequency range as well as it enables the simultaneous transmission of two different carriers, each one having a different modulation, bandwidth, etc. The developed architecture is fully integrated into a single FPGA device and allows software programmability by including an embedded microprocessor for control operations. The high flexibility of this architecture allows to easily change the frequency of the carriers as also the spectral masks, making it interesting in the scope of white spaces exploration and for software radio-based applications.

Novel fine tunable multichannel all-digital transmitter

All-digital transmitters are gaining an increased research importance due to the unparalleled proliferation of dissimilar wireless standards and more recently due to the white space technology needs. In this paper, a new fine tunable multichannel transmitter is presented. This new architecture supports concurrent multi-rate, multi-band, multi-standard transmission and significantly minimizes the output frequencies restrictions of current approaches by allowing fine frequency tuning for channel selection. The obtained results show the feasibility and potential of FPGA-embedded RF transmitters where the use of polyphase datapaths substantially improves the SNR of the desired signals.

Implementation and Evaluation of a Low Latency and Resource Efficient Compression Method for Digital Radio Transport of OFDM Signals

This paper presents the implementation and evaluation of non-linear quantization compression techniques targeted to Orthogonal Frequency Division Multiplexing (OFDM) based wireless standards, such as Long Term Evolution (LTE) and 802.11. The motivation for the implementation of digital radio compression is the high bandwidth requirements associated to its transport, which has a critical impact in the cost of an optical transport network, such as the fronthaul networks in the context of Cloud-Radio Access Network (C-RAN) architectures. An important aspect that must be taken into account in the development of access networks, and C-RAN in particular, is the end-to-end latency, including the compression overhead, which must be compliant with the standard imposed limits. The compression algorithm implemented in the context of this work, in addition to achieve considerable compression ratios with acceptable Error Vector Magnitude (EVM) degradation, features a low latency and reduced hardware complexity. The EVM evaluation is based on two laboratorial setups: the first one devoted to the separate evaluation of the compression technique, and the second one based on a C- RAN-like testbed with the integration of a Common Public Radio Interface (CPRI) optical link and a power amplifier.

High spectral efficient and flexible multicarrier D-RoF modem using up to 1024-QAM modulation format

We propose a flexible optical SCM modem to transmit, with high spectral efficiency, mobile front-haul signals. The real time experimental results, demonstrate the multicarrier aggregation capacity of 3.6 Gbps based on four 1024-QAM D-RoF subcarriers and a 30km transmission reach.