Frequencies in the millimeter band that once were commercially unusable for communications purposes will be usable to support 5G and other networks, in large part because of advances in network architecture (small cells) and the ability to use sophisticated signal processing and antennas to recover useful signals that would have been quite difficult in an analog environment.
Facebook’s Project ARIES, presently in test mode, features a base station with 96 antennas, supporting 24 simultaneous streams. It is envisioned as a fixed wireless platform for Internet access.
Facebook so far has achieved 71 bps/Hz, and Facebook engineers are aiming for supplying 100 bps/Hz eventually.
By way of comparison, that would surpass the efficiency of Long Term Evolution and vastly outperform most other interfaces ever commercially deployed.
The issue is where the business models will work, taking into account signal loss characteristics of millimeter waves. Of course, we have some commercial experience with use of point-to-point communications. Even earlier-generation radios for point-to-point links could achieve distances of 3 km to 5 km (roughly two to three miles), assuming line of sight is possible.
Keep in mind that the engineering of fixed network local loops in the United States has been to keep access cables at 18,000 feet or less (three miles). Though foliage, buildings and other obstructions, plus typical weather conditions, will impose greater constraints on any single transmitting site, 28 GHz signals reach about as far as the design length for fixed network access lines.
The issue with today’s MIMO (multiple-input and multiple-output) antenna technology is how much better performance generally can be expected, and what per-unit costs for MIMO antenna systems used for 5G and other networks will be, in volume production.
Signal attenuation in the millimeter bands is non-linear, as is the case for optical communications, and generally increases as frequency increases. That noted, there are, in the millimeter radio bands frequencies that have better signal attenuation characteristics, as is the case for optical communications.
Optical attenuation is much better at 1300 nm and 1500 nm, for example, than at 1400 nm, which is why 1300 nm and 1550 nm are used for optical communication systems.
In a similar way, freespace attention of millimeter radio waves is better in the band between about at 26 GHz and 38 GHz, than at 40 GHZ, and far better than at 60 GHz, 120 GHZ or 325 GHz and 380 GHz.
In addition to 26 GHz and 38 GHz, better attenuation performance is found at about 80 GHz to 90 GHz and 210 GHz to 225 GHz.
The point is that millimeter wave communications, in conjunction with small cells, MIMO radios and fiber to the base stations, should be commercially viable for Internet access. The issue is not so much the revenue side of the business case but the cost of the solution, compared to others that are possible alternatives.
No comments:
Post a Comment