LTE Flavors in Unlicensed Spectrum


Guest post by Faris Alfarhan*

The unprecedented increase in demand for high-speed broadband requires a bundle of solutions to satisfy the demanded capacity. Unlicensed spectrum is increasingly considered by cellular operators, internet service providers, and businesses as part of solution set. Unlicensed spectrum cannot match the quality of licensed spectrum, as the interference profile is much more stochastic. However, unlicensed spectrum offers a complimentary solution to licensed carriers for operators, and an opportunity to cable companies and internet service providers – who typically don’t own any licensed spectrum – to deploy wireless networks and hotspots. Read more of this post

Millimeter Wave MIMO Systems for 5G Access Networks

Guest post by Faris Alfarhan*

Cellular NetworkConventionally, millimeter wave (mmW) frequency bands have been either largely overlooked or treated solely as real estate for wireless backhaul and personal indoor networks. That is mainly due to higher atmospheric attenuation loss, penetration losses, and increased absorption and scattering in rainy conditions. However, recent measurements indicate good outdoor short range coverage – of 200 meters on average – when using directive antenna beams, even when radio line of sight conditions are not met [1-3]. The propagation characteristics of mmW bands vary considerably depending on whether LOS or NLOS conditions are present. Since mmW signals experience low diffraction due to their small wavelength, LOS signals propagate in conditions similar to free space (a path loss exponent of 2 on average). NLOS signals, on the contrary, experience more significant losses and hence a pathloss exponent of 5.7 on average [3]. However, the NLOS pathloss exponent is significantly reduced when directing the Tx and Rx antenna beams towards each other. In order to overcome the increased pathloss at mmW frequencies, directional beamforming or beamsteering is used to generate narrow beams towards users. Since the required antenna size is inversely proportional to the operating frequency, mmW antenna arrays could encompass as much as 64-256 antenna elements at the base station and 4-12 elements on a mobile device. For example, the required antenna element length is about 0.5 cm at 28 GHz,whereas it is about 20 cm at 700 MHz. Figure 1 shows measurement results for the maximum coverage distance of a mmW systems operating at 28 GHz as a function of the pathloss exponent and the combined Tx-Rx antenna gains, where acceptable coverage is deemed to have an SNR of 10 dB and higher. Read more of this post