Fourier-Optics Based Opto-Electronic Architectures for Simultaneous Multi-Band, Multi-Beam, and Wideband Transmit and Receive Phased Arrays

Abstract

Current trends in wireless communications require a Base Transceiver Station (BTS) to support an ever-increasing number of antennas, wider bandwidths, multiple frequency bands, and many simultaneous beams. This is a tall order when considering all-electronic implementations, especially when operating at high carrier frequencies. We describe here Fourier-optics based opto-electronic architectures that include analog and fully connected transmit (TX) and receive (RX) implementations that support simultaneous multiband, multi-beam phased arrays where optical up-and down-conversion are used to generate IF/RF and RF/IF, respectively, signals for simultaneous multi-user and multi-beam transmission and reception over a wide range of frequencies. The proposed lens-based architectures have the ability to transmit and receive multiple distinct beams simultaneously even when only analog beamforming is performed, thus greatly simplifying the tasks of cell search and initial access without having to resort to complex matrix-based beamforming networks. Additionally, lens-based TX and RX beamforming is performed in the analog optical domain with zero power consumption and negligible latency bounded only by the time the light takes to travel through the lens. Photonic signal processing also reduces the number of RF components required at the remote radio unit (RRU) and the number of costly and power-hungry high-performance analog-to-digital/digital-toanalog converters (ADCs/DACs) required. The optical subsystems are ultra-wideband and frequency agnostic as only the front-end components (antennas, amplifiers) are RF frequency/band specific. Therefore, a single photonic system design may be operated at any band and, furthermore, existing installations may be modified/upgraded to operate in different bands with minimal component replacements needed. Finally, the presented architectures provide near unlimited beam-bandwidth product (BBP) with minimal power requirements and no external cooling. Theoretical analysis and experimental confirmation of the proposed architecture will both be reported, including a receiver with a nominal BBP of 36 GHz with a prototype system that consumed less than 300 W, thus yielding a power efficiency of beam formation of 8 W/GHz, which is more than a 6× improvement over the current state of the art.INDEX TERMS beamforming, microwave photonics, optical coherent detection, radio-over-fiber, wireless communications, beam bandwidth product.

Analysis on current opto-electronic transmission research and its materials with new perspectives

“…Recent structural improvement of wireless transmission systems has greatly increased its transmission bandwidth and power efficiency both of which were considered drawbacks of wireless communication. Prather et al designed an opto-electronic architecture based on Fourier Optics consisting of analog that transmits and receives implementation using optical up/down conversion [6].…”

“…It was assessed to have low power consumption and negligible latency (optical beam performing using lens) and near unlimited beam-bandwidth product with no need for external cooling [6]. Their article pointed out some limitations.…”

“…Fully digital beam-forming solutions were limited by their high cost and power consumption 4. Microwave In-phase quadrature up-converters were restrained by power and phase imbalance and relatively narrow operating bandwidth [6]. To address these limitations, the article proposed an implementation design which includes a common optical module that reduces the count number of radio frequency (RF) components (new Base Transceiver Station architecture) [6].…”

“…Microwave In-phase quadrature up-converters were restrained by power and phase imbalance and relatively narrow operating bandwidth [6]. To address these limitations, the article proposed an implementation design which includes a common optical module that reduces the count number of radio frequency (RF) components (new Base Transceiver Station architecture) [6]. While adjusting the antenna array of the Base Transceiver Station to suit the frequency of radio bands improved wide-spectra, multi-band operation, photonic up/down conversion processed RF waveform of high quality as high frequency amplifiers and up-converting modulators of receiver functioned in series with transmitter's photo-diodes and electronic processing occurred only at a low intermediate frequency [6].…”

“…The following section recounts research of recent 5 years on wire or wireless transmission, in which comparative analysis is conducted between these two transmission approaches regarding their transmission rate, cost and coverage range to provide a comprehensive description of their current status and developing trends [6][7][8]. The third section introduces key indicators of opto-electric transmission performance and analyzes how they are influenced by external conditions.…”