Abstract
Analog radio-over-fiber (RoF) is a suitable technology for efficiently developing the cloud-RAN concept in fifth generation deployments based on long-term evolution advanced (LTE-A). Distortion and radiofrequency (RF) power amplifier gain should be taken into account in order to achieve the desired transmission power at the base station. Both mainly depend on several parameters that characterize the optical link, such as the RF input power and bias current. This paper analyzes the link performance due to variations on the traffic load as expected under real operation. In this paper, we show that it is possible in this scenario to adaptively choose the optimum RF input power to minimize the measured error vector magnitude and reduce the RF subsystem gain. Results show that this adaptation allows to relax the RF amplifier gain requirements up to 3-4 dB for medium load conditions.
Highlights
F UTURE 5G communications systems are based on new proposals which combine a more efficient use of the spectrum and the latest technological advances in signal processing, communications and networks
The Cloud Radio Access Network (C-RAN) concept will be applied [1] on 5G systems, where base station (BS) functionalities are split in two levels: a centralized baseband unit (BBU), of great capacity of computation which includes the Medium Access Control (MAC) and Physical (PHY) layers, and a set of distributed Remote Radio Head (RRH) units where RF transmission and reception are performed, which carry out the opto-electric and electro-optic conversions
Performance requirements are defined in the standard [7], where it is established that the error vector magnitude (EVM) of each E-UTRA carrier for different modulation schemes on Physical Downlink Shared Channel (PDSCH) should be better than 17.5% for Quadrature Phase Shift Keying (QPSK), 12.5% for 16QAM, 8% for 64QAM and 3.5% for 256QAM
Summary
F UTURE 5G communications systems are based on new proposals which combine a more efficient use of the spectrum and the latest technological advances in signal processing, communications and networks. In [5] an automatic input level controller was needed to achieve the best EVM performance of a downstream RF signal when, besides the optical fiber subsystem (FO), the high power amplifier (HPA) at the input of the antenna is explicitly considered. EVM degradation will be observed at the HPA output if the received power at the RRH drives the amplifier stage out of its linear operation range. These studies consider simplified hypothesis about the downlink LTE-A system operation.
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