question: 5G uses millimeter waves, but why can't we just fit more devices on existing 3G/4G spectrum?
comment: Systems and network specialist here: Only certain frequencies are available for consumer electronics due to government use. Certain frequencies are also less stable and can be interfered with more easily, there must also be a somewhat large 'space' between frequencies, the same as a radio, when inbetween two stations you can often here a little of both. There are ways to improve the current network technologies however the receiving equipment is very expensive to replace and update so although phones and other devices that can be updated to accommodate new technologies often and for, the receivers can't be. There are different routing methods and bandwidth allocation algorithms that can be pushed about older hardware however users wouldn't really notice any major improvement unless the network is heavily congested in one particular area
passages: Large quantities of new spectrum (5G NR frequency bands) have been allocated to 5G in order to support its increased throughput requirements. For example, in July 2016, the U.S. Federal Communications Commission (FCC) freed up vast amounts of bandwidth in underused high-band spectrum for 5G. The Spectrum Frontiers Proposal (SFP) doubled the amount of millimeter-wave unlicensed spectrum to 14 GHz and created four times the amount of flexible, mobile-use spectrum the FCC had licensed to date. In March 2018, European Union lawmakers agreed to open up the 3.6 and 26 GHz bands by 2020.
   There are plans to use millimeter waves for 5G. Millimeter waves have shorter range than microwaves, therefore the cells are limited to smaller size; The waves also have trouble passing through building walls. Millimeter wave antennas are smaller than the large antennas used in previous cellular networks. They are only a few inches (several centimeters) long. Another technique used for increasing the data rate is massive MIMO (multiple-input multiple-output). Each cell will have multiple antennas communicating with the wireless device, received by multiple antennas in the device, thus multiple bitstreams of data will be transmitted simultaneously, in parallel. In a technique called "beamforming" the base station computer will continuously calculate the best route for radio waves to reach each wireless device, and will organize multiple antennas to work together as phased arrays to create beams of millimeter waves to reach the device.
   Section::::Other countries.
  
  In the 20th century, the International Telecommunication Union often held regional or global conferences with users and national regulatory agencies to fix allocation problems in select part of the radio spectrum.
  
  In Canada, Innovation, Science and Economic Development Canada manages spectrum re-allocations. However, due to the lack of spectrum crowding—except for the seven most populated cities—this has largely not been a political issue.
  
  At the November 2015 meeting of the World Radiocommunication Conference, companies wanting to use spectrum below 700 MHz for purposes other than broadcasting asked that countries be willing to offer spectrum for mobile broadband.
   5G can use higher frequencies than 4G, and as a result, some 5G signals are not capable of traveling large distances (over a few hundred meters), unlike 4G or lower frequency 5G signals. This requires placing 5G base stations every few hundred meters in order to utilize higher frequency bands. Also, these higher frequency 5G signals cannot easily penetrate solid objects, like cars, trees and walls, because of the nature of these higher frequency electromagnetic waves.
  
  Section::::Technology.:Massive MIMO.
   Implementations of Mobile WiMAX and first-release LTE are largely considered a stopgap solution that will offer a considerable boost until WiMAX 2 (based on the 802.16m spec) and LTE Advanced are deployed. The latter's standard versions were ratified in spring 2011, but are still far from being implemented.
   In the United States only, the two largest carriers are instead implementing 4G LTE in the 700 MHz band, which was reallocated from TV broadcasting during the DTV transition. TV stations were forced to move to lower UHF and even far worse VHF frequencies with poorer mobile TV and even regular terrestrial TV performance, because the 700 MHz band has better radio propagation characteristics that allow mobile phone signal to penetrate deeper into buildings with less attenuation than the 1700 MHz or 2100 MHz bands.
   Higher frequencies are a disadvantage when it comes to coverage, but it is a decided advantage when it comes to capacity. Picocells, covering e.g. one floor of a building, become possible, and the same frequency can be used for cells which are practically neighbors.
   MulteFire is another variant of LTE in unlicensed bands and has been proposed as a standalone version of LTE for small cells. This variant will use only the unlicensed spectrum as the primary and only carrier, and it will provide an opportunity for neutral hosts to deploy LTE in the future. The idea of standalone operation of LTE in unlicensed bands was originally proposed by a small minority of vendors in 3GPP but rejected by the network operators who wanted the technology to be reliant on their licensed spectrum holdings. This technology is now developed by the MuLTEfire Alliance.
  
  Section::::Controversy.
   Critics of 5G say that these millimeter wave frequencies used by 5G have not been extensively tested on the general public and some experts believe that more scientific research is required, even as millimeter wave technology has been used in technology such as radar for many decades.
   Section::::System standards.
  
  Section::::System standards.:IMT-2000 compliant 4G standards.
  
  As of October 2010, ITU-R Working Party 5D approved two industry-developed technologies (LTE Advanced and WirelessMAN-Advanced) for inclusion in the ITU's International Mobile Telecommunications Advanced program (IMT-Advanced program), which is focused on global communication systems that will be available several years from now.
  
  Section::::System standards.:IMT-2000 compliant 4G standards.:LTE Advanced.
   The study on NR within 3GPP started in 2015, and the first specification release was made available by the end of 2017. While the 3GPP standardization process was ongoing, industry had already begun efforts to implement infrastructure compliant with the draft standard, with the expectation that the first large scale commercial launch of 5G NR would occur in 2019.
  
  Section::::Frequency bands.
  
  The Frequency bands for 5G NR are being separated into two frequency ranges:
  
  BULLET::::1. Frequency Range 1 (FR1), including sub-6 GHz frequency bands
  
  BULLET::::2. Frequency Range 2 (FR2), including frequency bands in the mmWave range (20-60GHz)
  
  Section::::Network deployments.
   The first HPUE has been presented by the Finnish company Bittium Oyj formerly known as Elektrobit, together with Rohde & Schwarz at Mobile World Congress 2014. They implemented the test cases of 3GPP, to show that the use of HPUE does indeed not interfere with adjacent commercial LTE networks.
   Spectra used by various 5G proposals will be very near that of passive remote sensing such as by weather and Earth observation satellites, particularly for water vapor monitoring. Interference will occur and will potentially be significant without effective controls. An increase in interference already occurred with some other prior proximate band usages. Interference to satellite operations impairs numerical weather prediction performance with substantially deleterious economic and public safety impacts. The concerns prompted US Secretary of Commerce Wilbur Ross and NASA Administrator Jim Bridenstine in February 2019 to urge the FCC to delay some spectrum auction proposals, which was rejected. The chairs of the House Appropriations Committee and House Science Committee wrote separate letters to FCC chair Ajit Pai asking for further review and consultation with NOAA, NASA, and DoD, and warning of harmful impacts to national security. Acting NOAA director Neil Jacobs testified before the House Committee in May 2019 that 5G out-of-band emissions could produce a 30% reduction in weather forecast accuracy and that the resulting degradation in ECMWF model performance would have failed to predict the track and thus impact of Superstorm Sandy in 2012. The Navy in March 2019 wrote a memorandum warning of deterioration and made technical suggestions to control band bleed-over limits, for testing and fielding, and for coordination of the wireless industry and regulators with weather forecasting organizations.
   Conventional MIMO systems, known as point-to-point MIMO or collocated MIMO, require both the transmitter and receiver of a communication link to be equipped with multiple antennas. While MIMO has become an essential element of wireless communication standards, including IEEE 802.11n (Wi-Fi), IEEE 802.11ac (Wi-Fi), HSPA+ (3G), WiMAX (4G), and Long Term Evolution (4G), many wireless devices cannot support multiple antennas due to size, cost, and/or hardware limitations. More importantly, the separation between antennas on a mobile device and even on fixed radio platforms is often insufficient to allow meaningful performance gains. Furthermore, as the number of antennas is increased, the actual MIMO performance falls farther behind the theoretical gains.
   Like LTE in unlicensed spectrum, 5G NR will also support operation in unlicensed spectrum (NR-U). In addition to License Assisted Access (LAA) from LTE that enable carriers to use those unlicensed spectrum to boost their operational performance for users, in 5G NR it will support standalone NR-U unlicensed operation which will allow new 5G NR networks to be established in different environments without acquiring operational license in licensed spectrum, for instance for localized private network or lower the entry barrier for providing 5G internet services to the public.
  
  Section::::Concerns.
  
  Section::::Concerns.:Interference issues.
   BULLET::::- It may also be limited by local geographical or regulatory factors and weather conditions.
  
  BULLET::::- In addition there are timing limitations in some technologies (e.g., even in free space, GSM would be limited to 35 km, with 70 km being possible with special equipment)
  
  Generally, in areas where there are enough cell sites to cover a wide area, the range of each one will be set to:
   The other important advantage of the above-mentioned access techniques is that they require less complexity for equalization at the receiver. This is an added advantage especially in the MIMO environments since the spatial multiplexing transmission of MIMO systems inherently require high complexity equalization at the receiver.
  
  In addition to improvements in these multiplexing systems, improved modulation techniques are being used. Whereas earlier standards largely used Phase-shift keying, more efficient systems such as 64QAM are being proposed for use with the 3GPP Long Term Evolution standards.
  
  Section::::Principal technologies in all candidate systems.:IPv6 support.
   BULLET::::- Increased spectrum flexibility: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz wide cells are standardized. (W-CDMA has no option for other than 5 MHz slices, leading to some problems rolling-out in countries where 5 MHz is a commonly allocated width of spectrum so would frequently already be in use with legacy standards such as 2G GSM and cdmaOne.)
   Another focus of research for 5G wireless is CO-MIMO. In CO-MIMO, clusters of base stations work together to boost performance. This can be done using macro diversity for improved reception of signals from handsets or multi-cell multiplexing to achieve higher downlink data rates. However, CO-MIMO requires high-speed communication between the cooperating base stations.
  
  Section::::History.
   In the mid-1990s, many cordless phone manufacturers started producing phones that used the lower and upper ends of the 33 centimeter band for communication between the handset and base. These phones, which are regulated by Part 15 of the FCC's regulations, have made amateur use of the upper and lower end of the 33 centimeter band somewhat tricky due to the number of these phones used by the general population. Part 15 devices, by law, must accept interference from any licensed radio service with which they share frequencies.
  
  Section::::History.:900 MHz wireless networking.
   Wireless requires bandwidth, and because of this, there would need to be enough of the spectrum obtained to sustain the bandwidth of the network. It also needs to be considered that upload links and downstream communication can require a difference amount of space. In the FCC News in 2005, it is mentioned that there needs to be enough spectrum to account for the unbalancing of broadband services. The service typically needs a larger amount of bandwidth for downstream than for upload links. Wireless will only work with adequate spectrum to support the initiative and the many devices, networks, and applications that it will run. President Obama has set a goal of freeing 500 MHz of the spectrum for any wireless device within a decade. The CTIA also supports this within the next ten years. The space would also need to be within the stronger part of the spectrum. According to the 112th United States Congress, the Public Safety Spectrum and Wireless Innovation Act calls for this to be within the 700 MHz D block spectrum for rural and urban areas and was originally requested to be done before the Digital TV transition. The 700 MHz D block refers to the portion of the spectrum between the following frequencies
   4G networks provide even higher bitrates and many architectural improvements, which are not necessarily visible to the consumer. The current 4G systems that are deployed widely are HSPA+, WIMAX and LTE. The latter two are pure packet based networks without traditional voice circuit capabilities. These networks provide voice services via VoIP.
   The new 5G wireless devices also have 4G LTE capability, as the new networks use 4G for initially establishing the connection with the cell, as well as in locations where 5G access is not available.
  
  5G can support up to a million devices per square kilometer, while 4G supports only up to 100,000 devices per square kilometer.
  
  Section::::Overview.:Usage scenario.
   National regulatory agencies, such as the Federal Communications Commission in the U.S., often address the need for more spectrum resources by permitting sharing of underutilized spectrum. For instance, billions of Wi-Fi and Bluetooth devices compete for access to the ISM bands. Smartphones, Wi-Fi routers, and smart home hubs frequently support Wi-Fi, Bluetooth, and other wireless technologies in the same device. SIC technology enables these devices to operate two radios in the same band at the same time. Spectrum sharing is a topic of great interest to the mobile phone industry as it begins to deploy 5G systems.
  
  Section::::Applications.:Cognitive radio.
   By 2009, it had become clear that, at some point, 3G networks would be overwhelmed by the growth of bandwidth-intensive applications, such as streaming media. Consequently, the industry began looking to data-optimized fourth-generation technologies, with the promise of speed improvements up to ten-fold over existing 3G technologies. The first two commercially available technologies billed as 4G were the WiMAX standard, offered in North America by Sprint, and the LTE standard, first offered in Scandinavia by TeliaSonera.
  
presuppositions: The existing 3G/4G spectrum has the capacity for more devices to fit on it.
corrections: The existing 3G/4G spectrum is less stable and can be interfered with more easily.
raw_presuppositions: The existing 3G/4G spectrum has the capacity for more devices to fit on it. The existing 3G/4G spectrum has the capacity for more devices to fit on it.
raw_corrections: The existing 3G/4G spectrum is less stable and can be interfered with more easily. The existing 3G/4G spectrum is less stable and can be interfered with more easily.