Scalable user selection in FDD massive MIMO

User subset selection requires full downlink channel state information to realize effective multi-user beamforming in frequency-division duplexing (FDD) massive multi-input multi-output (MIMO) systems. However, the channel estimation overhead scales with the number of users in FDD systems. In this paper, we propose a novel propagation domain-based user selection scheme, labeled as zero-measurement selection, for FDD massive MIMO systems with the aim of reducing the channel estimation overhead that scales with the number of users. The key idea is to infer downlink user channel norm and inter-user channel correlation from uplink channel in the propagation domain. In zero-measurement selection, the base-station performs downlink user selection before any downlink channel estimation. As a result, the downlink channel estimation overhead for both user selection and beamforming is independent of the total number of users. Then, we evaluate zero-measurement selection with both measured and simulated channels. The results show that zero-measurement selection achieves up to 92.5% weighted sum rate of genie-aided user selection on the average and scales well with both the number of base-station antennas and the number of users. We also employ simulated channels for further performance validation, and the numerical results yield similar observations as the experimental findings.

Design of miniaturized dual-polarized dipole antenna for 4G & sub-6 GHz 5G applications

Dual-polarization, enhanced gain and compact size is the basic need of the base station antennas whereas a modern communication system needs a wideband antenna which can cover both the LTE & 5G applications. In the present work, a cross dipole antenna is proposed for LTE & sub 6 GHz 5G frequency band for Base Station Antenna Applications. By introducing asymmetrically shaped pentagon slots in the dipole and open-loop dipole patches, wide impedance bandwidth of 1.65–4.05 GHz at a return loss of −14 dB are achieved for 4G & 5G applications. Two symmetric feeding lines orthogonal to each other have been used to obtain the dual-polarization. Also, a high stable gain of 7 ± 1 dBi & HPBW of 80 ± 5° was achieved over the entire operating band at both the ports due to the symmetric structure. The proposed antenna is compared for size and bandwidth with the structures already proposed in the literature and significant enhancement is observed to be used for Base station antennas.

A Review on 5G Sub-6 GHz Base Station Antenna Design Challenges

Modern wireless networks such as 5G require multiband MIMO-supported Base Station Antennas. As a result, antennas have multiple ports to support a range of frequency bands leading to multiple arrays within one compact antenna enclosure. The close proximity of the arrays results in significant scattering degrading pattern performance of each band while coupling between arrays leads to degradation in return loss and port-to-port isolations. Different design techniques are adopted in the literature to overcome such challenges. This paper provides a classification of challenges in BSA design and a cohesive list of design techniques adopted in the literature to overcome such challenges.

On Actual Maximum Exposure From 5G Multi-Column Radio Base Station Antennas for Electromagnetic Field Compliance Assessment

The traditional approach of radio frequency electromagnetic field exposure compliance assessment is highly conservative when applied to radio base station antennas implementing dynamic beamforming. In this paper, an analytical model based on the queuing theory with a hyper-exponential service distribution time is developed to assess the time-averaged actual maximum downlink exposure of 5G multi-column radio base station antennas by taking into account the effects of beam scanning over time in free space. Using the measured antenna radiation patterns, the 5G downlink antenna precoding codebook, and assuming a conservative user equipment distribution, the ratio of the actual maximum exposure to the theoretical maximum exposure with 100% traffic load and 75% time-division duplex downlink duty cycle is found to be less than 0.5 and 0.3 for four-transmitter and eight-transmitter radio base station antennas, respectively. These results show that assuming constant peak power transmission in a fixed direction leads to an overestimate of downlink exposure also from conventional antennas characterized by only a few transmitters in addition to massive multi-input multi-output products.