Changyo Han

Experimental demonstrations of next generation cost-effective mobile fronthaul with IFoF technique

We described next generation mobile fronthaul based on IFoF technique and theoretically estimated its system performances. Based on our analysis, we also experimentally demonstrated mobile fronthaul with 12 IF carriers on a single wavelength.

Mode- and wavelength-division multiplexed transmission using all-fiber mode multiplexer based on mode selective couplers.

We propose all-fiber mode multiplexer composed of two consecutive LP₁₁ mode selective couplers that allows for the multiplexing of LP₀₁ mode and two-fold degenerate LP₁₁ modes. We demonstrate WDM transmission of 32 wavelength channels with 100 GHz spacing, each carrying 3 modes of 120 Gb/s polarization division multiplexed quadrature phase shifted keying (PDM-QPSK) signal, over 560 km of few-mode fiber (FMF). Long distance transmission is achieved by 6×6 multiple-input multiple-output digital signal processing and modal differential group delay compensated link of FMF. The all-fiber mode multiplexer has considerable potential to be used in mode- and wavelength-division multiplexed transmission.

Linearity improvement of directly-modulated multi-IF-over-fibre LTE-A mobile fronthaul link using shunt diode predistorter

We demonstrate linearity improvement of directly-modulated multi-IF-over-fibre links using a simple shunt diode predistorter. We experimentally confirm that the predistorter is capable of suppressing third order intermodulation distortions of the link through two-tone test and 4-IF carrier-multiplexed LTE-A signal transmission.

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.

Performance Improvement of Multi-IFoF-Based Mobile Fronthaul Using Dispersion-Induced Distortion Mitigation With IF Optimization

Nowadays, there have been many research works on multiple-intermediate-frequency-over-fiber (multi-IFoF)-based mobile fronthaul link to accommodate explosive mobile data traffic. The performance of multi-IFoF transmission scheme is affected by fiber dispersion-induced second-order distortion in 1.5 μm. Thus, we derive an appropriate frequency plan to avoid the distortion. By utilizing the frequency plan, we successfully transmit 24-20-MHz long-term evolution advanced (LTE-A) signals over 60-km single-mode fiber (SMF) without any penalties from the distortion. We also show the transmission performance when transmitting larger number of IF carriers in the limited modulation bandwidth so the penalties from the distortion are inevitable. We confirm that 72- 20-MHz LTE-A carriers can be transmitted over 30-km SMF within only 1.5-GHz modulation bandwidth.

Experimental comparison of the multi-IF carrier generation methods in IF-over-fiber system using LTE signals

Radio-over-fiber technique utilized by multiple IF carrier transmission scheme is expected to be a cost-effective solution for next generation mobile fronthaul architecture. We have experimentally investigated and compared multi-IF carrier generation methods based on analog IQ modulation and digital IQ modulation by back-to-back EVM measurement using five 64-QAM-LTE carriers having 20 MHz bandwidth.

Impact of dispersion-induced second-order distortion in multi-IFoF-based mobile fronthaul link for C-RAN

We investigate effects of second-order distortion induced by chirp and dispersion in multi-IFoF-based mobile fronthaul links. We optimize frequency plan avoiding distortion, and successfully transmit multiple LTE-A signals over 60-km SMF without any dispersion compensation.

Experimental investigations of uplink transmission performances in a mobile fronthaul based on IFoF technique

We experimentally investigate an IFoF mobile fronthaul uplink, where 64-QAM mapped and 2 carrier aggregated 20 MHz LTE-A OFDM signals with 90 RBs are transmitted over SMF 20 km, achieving EVM variations below 1%.

Bandwidth efficient transmission of 96 LTE-A signals with 118-Gb/s CPRI-equivalent rate using 2-GHz frequency span and intermixing mitigation for mobile fronthaul

We experimentally demonstrate bandwidth efficient transmission of 96-IF carriers LTE-A signals with 118-Gb/s CPRI-equivalent rate using 2-GHz bandwidth and intermixing mitigation. After 20-km mobile fronthaul transmission, EVM is below 5% for entire IF carriers.

Effect of rotational misalignment in phase-plate based mode multiplexer

We experimentally investigate the optical signal-to-noise ratio penalty induced by the rotational misalignment of the phase plates in phase-plate based mode multiplexer.