Long-term Evolution Advanced Signals Research Articles

Investigation of transmission performance in multi-IFoF based mobile fronthaul with dispersion-induced intermixing noise mitigation.

We demonstrate the improvement of the transmission performance based on intermixing noise mitigation techniques in a multiple intermediate-frequency-over-fiber (IFoF) based mobile fronthaul. The interaction between fiber chromatic dispersion and frequency chirp of the directly modulated laser generates the second-order distortion that degrades the performance of multi-IFoF transmission system. To avoid second-order distortion, we use intermediate frequency (IF) spacing optimization and octave-confined frequency plan schemes in which intermixing noise would be generated in the out of signal band and would not affect the quality of transmitted signal. For bandwidth efficient transmission of radio signal over mobile fronthaul link, we employ the dispersion compensation technique to suppress the intermixing noise sufficiently. For realization of the multi-IFoF based mobile fronthaul, we experimentally investigate the transmission performances of 48-, 72- and 144-IF carriers of the long term evolution-advanced (LTE-A) signals mapped with 64-quadrature amplitude modulation (QAM). It is clearly observed that the intermixing noise is suppressed owing to dispersion compensation technique and overall system performances are improved by IF spacing optimization and octave-confined frequency plan. As a result, we successfully transmit 144-IF carriers of the LTE-A signal with less than 8% error vector magnitude (EVM) over 20-km single-mode fiber (SMF) within only 3 GHz bandwidth.

Multiband LTE-A and 4-PAM Signals Over Large-Core Plastic Fibers for In-Home Networks

This letter presents the transmission of eight standard compliant 64-QAM long term evolution advanced (LTE-A) bands and 1.4 Gb/s 4-pulse amplitude modulation (PAM) signals over 20 m of 1 mm core diameter graded-index polymethyl methacrylate plastic optical fiber. The optical transceiver consists of a red light VCSEL and a p-i-n photodiode followed by a transimpedance amplifier. The LTE-A signals were transparently transmitted with the radio-over-fiber technique and without complex frequency conversion at the receiver side. A gain control technique in the digital domain was used to avoid entering the VCSEL saturation regime. Digital filtering was employed at the transmitter and receiver sides to improve the spectrum shaping of the 4-PAM and LTE-A signals. The proposed system offers a single infrastructure in-home solution capable of accommodating wired services as well as multiband LTE-A wireless services. Only low-cost components were considered in this letter in order to provide a reliable and inexpensive solution for high-capacity in-home networks.

Linear X‐band GaN HEMT transformer‐based Doherty power amplifier

An X-band gallium-nitride high electron mobility transistor (GaN HEMT) transformer-based Doherty power amplifier (TBD PA) module with a phase lineariser has been developed. The TBD PA uses Cree's 6 W GaN HEMT bare die and realised in seven-layer PCB. The proposed lineariser is employed before the TBD PA to compensate the phase distortion during the Doherty operation. The implemented TBD PA with 9.56 GHz continuous wave test shows a 38.5% power-added efficiency at 39.6 dBm output power. Linearity characterisation is also performed using 40 MHz bandwidth, two carriers aggregated long-term evolution-advanced signal and shows −35.4 dBc carrier aggregation evolved-universal terrestrial radio access adjacent channel leakage power ratio which is 7 dB enhanced after phase compensation.

Full-Duplex Transmission of LTE-A Carrier Aggregation Signal Over a Bidirectional Seamless Fiber-Millimeter-Wave System

We propose a flexible and high-performance fronthaul system for future mobile networks using a seamless combination of fiber-optic and millimeter-wave (MMW) systems. The proposed system employs a high-quality optical MMW signal generation at the transmitter and a stable and high-performance MMW self-homodyne detection at the receiver. In the downlink direction, successful transmission of intraband and interband carrier aggregation (CA) long-term evolution-advanced (LTE-A) signals over the system is experimentally confirmed. We also confirm satisfactory performance for the transmission over a fiber–wireless bridge using a cascade of the seamless system and a conventional radio-over-fiber (RoF) link. In the uplink direction, we successfully demonstrate the transmission of an intraband CA LTE-A signal over a cascade of a radio-on-radio and a RoF system. In addition, we confirm that the full-duplex transmission of LTE-A signals over the proposed bidirectional system does not experience performance degradation compared to the case with half-duplex transmission. The proposed system is a potential solution for mobile-signal transmission in future networks.

Improvement of the transmission performance in multi-IF-over-fiber mobile fronthaul by using tone-reservation technique

We demonstrate the improvement of the transmission performance based on tone-reservation technique in a multiple intermediate-frequency-over-fiber (IFoF) based mobile fronthaul. The tone-reservation technique can suppress nonlinear distortion by eliminating the high peak components of orthogonal frequency-division multiplexing (OFDM) signal. To prevent the regrowth of peak, we employ tone-reservation after multiplexing IF carriers. Furthermore, we use an out-of-band signal as the reserved tones to avoid any modification of a mobile signal. The impact of the number of IF carriers on peak-to-average power ratio (PAPR) characteristics is presented via numerical simulation. For the multi-IFoF based mobile fronthaul, we experimentally investigate the transmission performance of 36-IF carriers of the long term evolution-advanced (LTE-A) signals mapped with 64-quadrature amplitude modulation (QAM). It is clearly observed that the clipping-induced nonlinear distortion is dramatically suppressed by using tone-reservation. As a result, the transmission performance of 36-IF carriers of the LTE-A signal is improved by an error-vector-magnitude (EVM) of 4% (from 9.7% to 5.7%) after 20-km transmission.