Copyright 2019 Thomas Schwengler. A significantly updated and completed 2019 Edition is available.


Support independent publishing: Buy this book on Lulu.

Chapter 1
Wireless Communications

Modern telecommunications are one of the main application of electromagnetic theory (along with remote sensing and radars). The wireless telecommunications industry incredible advances in recent years are based on a mixture of well-known principles new new inventions and new practical implementations. This chapter introduces some aspects of wireless communications, including its spectrum landscape.

1.1 Brief History

Many textbooks begin with a good historical overview of wireless communications and excellent insights (see for further reading informative introductory chapters in refs. [368]). We do not chose to expand much on these historical aspects or radio communications, still a few statements might be interesting to recall on the major innovations in wireless technology.

1.1.1 Past

Early smoke signals and carrier pigeons may of course be considered as a form of wireless communications, but offer little modern interest. Early coding schemes, however, are more interesting: British scientist Robert Hooke invented large mobile panels coding the letters of the alphabet (1684). nd more elaborate schemes appear in the late 18th century, including the noteworthy optical telegraph invented by French physicist Claude Chappe (1791), transmitting coded words (rather than letters) over long distances; large signaling towers were developed in the following years into a large network over major cities in France and surrounding countries. These precursors to radio communications already emphasize some valuable points: 1) coding information is used for efficiency, 2) transmission works well in line of sight, and may suffer from outages due to obstructions, or even weather. In a sense these systems are rather reminiscent of current fixed wireless systems such as microwave, millimeter-wave, or infrared links.


PIC

Figure 1.1: Heinrich Hertz (1857-1894) and James Clerk Maxwell (1831-1879), physicists who laid the foundation of electromagnetic theory and its wireless applications.

True radio communications of course rely on electromagnetic waves, and build on the work of Maxwell and the experiments of Hertz. The first use of radio to transmit coded information was proposed by Tesla in the 1880’s, and the first radio communication systems were described in his papers around 1891. Nearly simultaneously, Marconi patented the telegraph and demonstrated to the world the usefulness of mobile communications with ships crossing the English Channel. These facts already emphasize the importance of some aspects of radio communications: 1) certain radio frequencies overcome line-of-sight obstructions and weather impediments, 2) mobility is the main application, 3) patent protection is paramount.


PIC

Figure 1.2: Nicola Tesla (1856-1943) and Guglielmo Marconi (1874-1937), wireless visionaries, pioneers, inventors. Their rivalry and the way history remembers their inventions, patents, and achievements is foretelling of important aspects of the wireless industry.

The next major advances in radio systems were developed during and after world war two, and benefitted from significant research around radar and remote sensing. Subsequently, different applications flourished: TV broadcasting in the 1940’s probably has the merit of introducing the first standardization of communications technology, leading to major television standards, (NTSC Color Standard in 1953, and recently ATSC Digital Standard in 2009). Standards have become very important in all aspects of wireless communications, and will be analyzed in more details further.

Cellular systems were devised by AT&T Bell Labs in the seventies. Continued improvements in standards and products provide increasing spectral efficiencies, lower prices, and wider consumer acceptance. Amazing growth occurred in the wireless industry during the 1980’s and 1990’s, which led to almost ubiquitous service availability and cheap service plans; some irrational exuberance in the industry also caused failures and bankruptcies around 2000 (such as excessive spectrum bidding, expensive satellite services, or some early broadband wireless initiatives).

1.1.2 Present

Current events and trends in the wireless industry are in constant evolution and their descriptions quickly become obsolete; still the following milestones are noteworthy:

The above points show a fast-paced change of landscape. The best sources of information for these data points are periodicals, publications, and websites that specialize in the trade. When searching them, always pay attention to publication dates, and beware not to use obsolete data; take very good care to search for a trustworthy and recent fact source.

1.1.3 Future

“Prediction is very difficult, especially about the future.” (Attributed to Niels Bohr, Danish physicist, 1885–1962.) Nevertheless, most predictions show a continuing growing trend. The growth is based on continuing increase in data use in smart phones, tablets, as well as the proliferation of applications including in new areas such as the Internet of Things. We will investigate new standards and technologies that will lead us to better understand some of these wireless trends.

1.2 Spectrum

Spectrum is a very important notion for any wireless system: it refers to the range of frequencies used by the system’s electromagnetic waves; when several services use the same spectrum in the same location interferences occur that may be harmful to these services. Governments therefore step in and set rules and regulations for spectrum coordination.

1.2.1 Spectrum Use

Spectrum is a valuable resource for many applications such as radio communications (terrestrial and satellite), radar, remote sensing. Some applications require very quiet portions of spectrum (such as deep-space observations), others may share or reuse spectrum fairly aggressively. In all cases rules and regulations are in place for each spectrum bands, which will be reviewed further.

Different bands of spectrum benefit from very different properties. Lower spectrum generally propagates better through the atmosphere and through obstacles; it has been traditionally used for radio and TV broadcasting, and is excellent for mobile applications. Higher spectrum is more abundant and therefore used for higher throughput applications, but is much more attenuated by atmospheric particles and weather variations, and needs near line-of-sight conditions.

A wide range of spectrum is used in modern communications: megahertz (MHz) radio frequencies, gigahertz (GHz) microwaves and millimeter waves, and terahertz (THz) infrared lasers for free-space optics. Accurate study of radio waves at any given frequencies can be performed by studying electromagnetic fields properties: propagation, scattering, etc. Maxwell’s equations are used to determine wave characteristics in complex situations, but in many practical situation full-wave modeling is too complex and time consuming; instead the industry has been relying on simple approximations, rules, and models. We will see some of these models in chapter 3, but we start here with some high-level properties of radio frequencies.

Communication systems use diverse frequencies either in a wired mode (with a wave guide from transmitter to receiver such as coaxial cable, copper wires, or fiber), or in a wireless mode, which is our focus here. To summarize:

1.2.2 Atmospheric Effects

The earth atmosphere is a complex gaseous mixture and has various effects on radio propagation; the dominant effect is usually attenuation, though depolarization also occurs. Most wireless cellular system use frequencies below 6 GHz for good coverage, and are therefore not significantly affected by atmospheric variations. Weather conditions do have an impact on wireless cellular networks, but their effects are typically not dominant, and are usually not part of initial system design.

Above 6 GHz, atmospheric effects may be significant and must be taken into account in the design of a wireless system. This is especially important for the backhaul, which may rely on wireless links up to several tens of miles. (See 5.4.3).

Atmospheric absorption usually dominated by absorption by water vapor molecules or oxygen molecules; these molecules have specific frequencies of resonance that create some peaks of absorption around these frequencies. Water vapor has an absorption peak around 24 GHz and its multiples, and oxygen has it main peak at 60 GHz.

In addition to gaseous absorption, hydrometeors are also a severe cause of absorption. Heavy rain with large drop size has an especially severe impact. At 30 GHz for instance heavy 50-100 mm/hr precipitation causes 10-20dB/km attenuation, and will usually cause radio outages. This may be the case for LMDS (28 GHz) or point-to-point microwave links (6, 11, 18, 23 GHz). Refer to chapter 5 on backhaul for more details.

1.2.3 Duplexing

Communications require bidirectional exchange of information; in wireless communication, the two communications links are often referred to as uplink and downlink, or as forward and reverse link. The terms downlink and forward link refer to the transmission from a base station to a customer device like a mobile phone; uplink or reverse link refer to the transmission from the customer to the base station.

A fundamental aspect of a spectrum band is how it is used to provide both uplink and downlink communications; which is called duplexing. The two common duplexing schemes used for wireless communications are: time division and frequency division. Frequency Division Duplexing (FDD) uses two different bands of spectrum for uplink and downlink, these bands are said to be paired; one portion of the spectrum is reserved for uplink operations, the other for downlink. Time Division Duplexing (TDD) uses the same band for uplink and downlink, and uses different time slots to separate uplink from downlink traffic; the spectrum band is usually continuous, and is said to be unpaired; unlicensed spectrum usually uses TDD.

Each duplexing scheme has advantages in some situations. FDD schemes tend to be slightly more spectrum efficient for symmetric traffic; they are typically preferred for long-range links such as private line and for voice communications (typically based on symmetrical standards: DS0, DS1, etc). FDD schemes allow simultaneous uplink and downlink transmission in paired bands of spectrum with enough separation to avoid interference.

TDD schemes are technically slightly less spectrum efficient since some quiet times are required between uplink and downlink traffic (at least greater than round-trip delay between the base and the furthest device); but they offer the great advantage of allowing dynamic changes in the amount of time (and therefore bandwidth) dedicated for uplink versus downlink, which may actually be a more spectral efficient solution for asymmetric or bursty data services. TDD schemes are therefore useful for small cells and LAN data applications.

FDD vs. TDD preferences sometimes give rise to endless arguments: one argument is that adaptive antenna systems (smart antennas) and MIMO systems require fast channel estimation and are better suited for TDD schemes (although efficient FDD adaptive system certainly have been demonstrated). Other considerations of cost of equipment are sometimes important to choose between TDD and FDD: FDD devices are typically more expensive to manufacture since frequency diplexers must be used to transmit and receive at the same time. To alleviate that cost, some cheaper devices use hybrid frequency division duplexing (H-FDD) in which they use paired spectrum like an FDD device (different transmit and receive bands), but are not capable of transmitting and receiving at the same time (like a TDD device). Although H-FDD may allow for cheaper devices, the drawback is a very inefficient use of the spectrum.

Practically duplexing choices are often determined by local spectrum rules and regulations: when regulators make spectrum available (e.g. for an auction), they announce if it is paired or unpaired, practically forcing the use of FDD or TDD (see for instance figure 1.9). Consequently most standards have TDD and FDD profiles to adapt to multiple regulatory environments, though sometimes not with the same time to market and equipment availability.

1.3 US Spectrum Landscape

In the US, spectrum is regulated by several government institutions: the National Telecommunications and Information Administration (NTIA) Office of Spectrum Management (OSM) for government and military use, the Federal Communications Commission (FCC) for commercial use.1 Some bands are also opened for license exempt use, and have contributed to the widespread of wireless LAN technologies like Wi-Fi.

1.3.1 Code of Federal Regulations

In the US, the Code of Federal Regulations (CFR) is the set of rules and regulations for federal administrative law governing anything from agriculture to public health, including telecommunications. The FCC rules around telecommunications (including spectrum) are under title 47 of that code, and are referred to as CFR title 47 [10]. Title 47 has multiple parts governing many spectrum bands and their different applications: amateur radios, satellite, microwave, cellular, etc. In particular part 101 deals with specific radio applications and is covered in chapter 5. Part 15 deals with unlicensed transmissions, from spurious emissions (1.4) to wireless communications in unlicensed bands detailed next.

1.3.2 Unlicensed Spectrum

The main bands for unlicensed (or license exempt) use in the United States are listed below. These bands are governed by different FCC rules; device power and EIRP are limited in order to alleviate interference concerns, and equipment must be approved by the FCC (mainly to verify power levels and emission masks).

Unused TV spectrum:
(below 698 MHz) TV channels 2 to 51. The FCC issued an order in 2008 to allow unlicensed use of TV “white spaces” (TVWS) left unused by TV broadcasters. The amount of spectrum at low frequency caused great enthusiasm, especially for rural environments, but was slow to roll out because of uncertainty around rules to avoid TV interferences.

The amount available varies by geographic area (and presence of broadcasters). Databases exist for white-space devices to determine which frequencies they can transmit on. See for instance the following URL’s:

Initial rules made channels 2-51 available for fixed service (except 3, 4, 37) up to 1W power output, 4 W EIRP as long as no TV signal is in the channel or adjacent channels. Antennas should be mounted outdoors (above 10m and below 30m). Channels 21-51 (except 37) are for personal/portable service, including mobile. Devices that use spectrum scanning and an Internet database can operate at 100 mW when no adjacent TV broadcast. Portable devices that only scan the are limited to 50 mW EIRP on all channels and 40 mW EIRP in an adjacent TV channel.

Subsequent actions restricted the amount of spectrum available for unlicensed use, and instead is planning on auctioning some of the precious spectrum (see 600 MHz section, 1.3.3). [11]


PIC

Figure 1.3: Unused TV channels are referred to as TV white spaces and are available for fixed and mobile use.

ISM 900 MHz:
(902-928 MHz) industrial, scientific, and medical band Maximum power up to 100 mW, devices.
ISM 2.4 GHz:
(2400-2483.5 MHz) industrial, scientific, and medical band. Maximum power up to 4 W, equivalent isotropically radiated power (EIRP). Additional limits on Peak power density (PSD) and out-of-band emissions.
UNII bands:
at 5 GHz, unlicensed national information & infrastructure (U-NII) bands are bands with power restrictions defined in part 15.407 as follows.

PIC

Figure 1.4: Unlicensed National Information and Infrastructure (U-NII) band was established in the US in 1997, later augmented in 2003, and new bands were proposed in 2013.

These various UNII bands are actually allocated on a primary basis to various services, either federal or commercial, such as aeronautical or maritime radionavigation, fixed satellite service, earth exploration, space research, which is why their license-exempt use has restrictions to avoid interferences.

Unlicensed PCS:
A 20 MHz band of spectrum between the uplink and downlink PCS spectrum (1910 to 1930 MHz) is reserved for unlicensed PCS voice and data use (CFR47 part 15.301 to 15.323). It is typically used for home devices such as DECT 6.0 cordless phones. An August 2014 FCC order requires equipment in that band to listen before transmit, and adopt a least-interfered access method.
Higher Bands:
Higher bands typically for point-to-point links at 24 GHz, 60 GHz, and infrared free-space optic are also unlicensed.

The 60 GHz band was recently extended from 57-64 GHz to now include 64-71 GHz (under part CFR 47, part 15.255) as part of an effort to provide more 5G spectrum [14]. Power levels are limited to 43 dBm indoor, and 82 dBm outdoor (minus 2 dB for every dB that the antenna gain is less than 51 dBi).

In summary the unlicensed spectrum landscape now contains: the busy but well established 900 MHz and 2.4 GHz ISM bands and a rich 775 MHz of unlicensed U-NII bands. This spectrum combines with powerful and ubiquitous wireless standards (like Wi-Fi 802.11n/ac/ax) to offer very powerful wireless solutions.

1.3.3 Licensed Spectrum

Different spectrum bands are made available for commercial use at different times. The spectrum bands listed in this section are interesting for US activities, they have a very different history and different rules. Many of the detailed band plans are available at www.fcc.gov under auctions.

Cellular and PCS spectrum:
The first US cellular spectrum, at 800 MHz, was given to interested operators in 1982 and 1986 to encourage rolling out mobile wireless systems. With the booming success of these cellular systems, the FCC decided to auction more spectrum, at 1900 MHz, referred to as PCS spectrum (for Personal Communication Services).

PIC

Figure 1.5: Cellular band plan at 800 MHz: two 20-MHz blocks (A and B) allocated by the FCC in 1982, augmented in 1986 (A* and B*).


PIC

Figure 1.6: PCS band plan: PCS spectrum was auctioned by the FCC in 1994-1996, different block sizes combined with spectrum caps encouraged newcomers in the industry.


PIC

Figure 1.7: AWS-1 band plan, pairs 1.7 GHz and 2.1 GHz spectrum, auctioned in 2006; later auctions AWS-2, 3, and 4 plan more nearby blocks.


PIC

Figure 1.8: New 600 MHz band plan under considerations. Different amount of spectrum may be cleared in different geographical locations, bands will be paired, and additional downlink blocks of spectrum may be available.


PIC

Figure 1.9: New 700 MHz band plan converts former TV channels 52 to 69 to different bands, of different sizes, some FDD, some TDD. These bands are auctioned for commercial use, a portion is reserved for public safety use.

TV bands at 600 MHz:
At the lower end of the spectrum, TV spectrum has been very interesting in recent years, including a recent proposal to auction spectrum between 600 MHz and 700 MHz (referred to as the 600 MHz band). Its repurpose (from TV to mobile communications) proposed a new approach: a reverse auction encouraging broadcasters to sell their spectrum, and a forward auction to sell the available spectrum to mobile providers. (See https://www.fcc.gov/wireless-telecommunications/auctions/auction-1000 ) [11]
UHF channels at 700 MHz:
With the migration of TV broadcasting to digital, some spectrum becomes available in the 700 MHz band (TV channels 52 to 69, 698-806 MHz). A portion of that spectrum is reserved for public safety services, while many blocks were offered in commercial auctions (44, 49, 60, 73, 92 between 2002 and 2011, the last one totaling $20 billion).
AWS at 1.7-2.1 GHz:
Advanced Wireless Services saw several auctions:
WCS at 2.3 GHz:
This small auction was mostly overlooked (auction 14, in 1997), and brought only $13.6 million for 30 MHz of spectrum (major bidders: Comcast, BellSouth, Metricom). That spectrum was designated very generically as Wireless Communication Service (WCS), and was left unused for a long time. It has become very interesting again since it corresponds to a band of interest for 802.16e, and has standard equipment for mobile WiMAX.
EBS and BRS at 2.5 GHz:
Formerly MMDS and ITFS, these spectrum bands are now referred to as Educational Broadband Services (EBS) and Broadband Radio Services (BRS). Sprint is the largest license holders in this band, which is well suited for 802.16e mobile WiMAX. Sprint started major efforts at the WiMAX forum in 2006 for its next generation “4G” network, creates a partnership with Clearwire in 2007, and announces investments in excess of $3 billion (mostly from cable operators) for 2009-2010 WiMAX rollout.

A new band plan was proposed by FCC to transition the old 6 MHz analog TV channels to 5.5 MHz channels. In 2006 broadband radio service (BRS) operators began filing their plans to initiate transitions of the 2.5 GHz band in various basic trading areas (BTAs) under the new rules adopted by the FCC in 2004.


PIC

Figure 1.10: New BRS and EBS band plan (formerly MMDS channels).

Citizen Broadband Radio Service (CBRS):
3.55-3.7 GHz introduces a new Spectrum Allocation System (SAS), that aims at using that spectrum more efficiently by proposing a 3-tier shared system. The first tier is for incumbents: federal and military use where and when needed. As a second tier, the SAS offers Priority Access Licenses (PAL), 10 MHz bands to be auctioned at county level or Partial Economic Areas (PAE) – but no more than seven PALs shall be assigned in any given area. The third and last tier is General Availability Access (GAA), which is an unlicensed use where no incumbent or PAL is used.

Power is regulated in several categories: Category A limited to 1 W (30 dBm) EIRP maximum in 10 MHz, Category B allows 10 W (47 dBm) EIRP in 10 MHz. End-user devices can transmit up to 23 dBm EIRP in 10 MHz – see the new part 96 for CFR 47 [10].

In addition existing non-exclusive licenses in the 3.65 GHz band are grandfathered until April 2020, and is otherwise reserved for GAA use. [13] Power in that grandfathered band is limited to 25 W EIRP maximum in 25 MHz (or 1 W in 1 MHz to keep same power spectral density), 1 W EIRP per 25 MHz maximum for mobile stations. (Also 150 km exclusion buffer zones were created around existing fixed satellite stations).

Rules around CBRS are still subject to change, and an auction (for PAL licenses) is expected in 2019.

Public Safety at 4.9 GHz:
In 2002, in the 4.9 GHz Order, the Commission designated 50 MHz in the 4.9 GHz band for exclusive public safety use. In many cases local governments control this spectrum, and opportunities exist around data services for emergency response or public safety systems (products often based on the Wi-Fi physical layer exist for that band).
Vehicle Communications at 5.9 GHz:
The FCC has modified some of the licensing and service rules it adopted in 2003 for dedicated short-range communications (DSRC) in the intelligent transportation systems (ITS) radio service in the 5.9 GHz band. Channel 172 (5.855-5.865 GHz) is reserved for “vehicle-to-vehicle safety communications for accident avoidance and mitigation, and safety of life and property applications,” the Commission said, while Channel 184 (5.915-5.925 GHz) is “for high-power, longer-distance communications to be used for public safety applications involving safety of life and property, including road intersection collision mitigation.”

That band is the area of focus of 802.11p, and may be an opportunity for public safety applications. Automobile industry has had most of the activity so far around smart cars and collision avoidance.

Higher Bands:
Higher microwave bands are available for licensing, either on a case-by-case basis (6, 11, 18, 23 GHz, and more recently 70, 80 GHz) or in wider geographical areas (LMDS at 28, 31, 38 GHz). These bands are traditionally used for high capacity fixed backhaul links and are investigated in chapter 5 .

More recently, bands above 24 GHz have been identified for mobile use as part of 5G. [14] Mobile rights are granted to existing license holders, license areas subdivided by county. FSS earth stations continue to share the band. LMDS and 39 GHz were regulated in part 101, and are now augmented with new mobile flexibility and moving under a new part 30 of 47 CFR [10] under the new denomination of Upper Microwave Flexible Use Service (UMFUS). Power is limited to 75 dBm per 100 MHz EIRP at the base station (average power of the sum of all antenna elements), 43 dBm EIRP for mobile, and 55 dBm for fixed transportable stations (such as in homes or cars).

The new 5G millimeter wave mobile bands are:

24 GHz
(24.25-24.45 and 24.75-25.25 GHz) Seven 100 MHz licenses,by PEA (auction 101, Nov 2018).
28 GHz
(27.5-28.35 GHz) Two 425 MHz licenses,by county (auction 102, Nov 2018).
39 GHz
(38.6-40 GHz) Seven 200 MHz licenses by PEA.
37 GHz
(37-38.6 GHz) Lower 600 MHz is Shared Access Licensee (SAL) with existing federal use; 37.6-38.6 GHz will be auctioned geographically in 200 MHz blocks by PEA, similar to 39 GHz (auction planned for 2019).
47 GHz
(47.2-48.2 GHz) 100 or 200 MHz channels – still to be determined (auction planned for 2019).

1.3.4 Geographical Areas

All the above licenses are auctioned in different areas: some are very large (Regional Economic Areas cover the continental US in only 6 service areas), while others are small (like the 416 Partial Economic Areas covering the US and territories). The various sizes are by design to allow large providers to bid on contiguous areas, while also letting small providers focus in local markets. The many FCC areas are detailed and mapped on the FCC website at www.fcc.gov/oet/maps/areas.

1.3.5 In Summary

The above sections show a fairly complex spectrum landscape in the US, with different bands coming from different use at different times; this overview shows the following points:

A final note: in some cases pre-existing systems may be operational at a given frequency, and bidders have to move these systems to another band before utilizing the spectrum they bid on. That requirement is called spectrum clearing, it can be time consuming and costly.

1.4 Emission Levels

Different spectrum bands have been identified by regulators for very different applications: some require high power (e.g. for long-haul communications), others on the contrary require very low power levels (e.g. for radars, or deep-space observations). Consequently regulations also have to deal with how much power is allowed in these bands, and how much can overflow into neighboring bands.

It may be important here to consider other electrical devices: in general they all emit electromagnetic radiations, wanted or not, sometimes guided (as in a DSL or cable modem), sometimes for wireless applications over an antenna. Consequently, the FCC has a minimum allowed emission level in all bands. Part 15 (of CFR title 47 [10]) deals with these spurious emissions of any device in any band; it deals mostly with fairly low power devices (typically less than 1mW devices). The unlicensed bands identified in 1.3.2 are also covered by part 15, and allow for reasonably high power levels, all other bands are strictly limited. Power limitations are set in terms of electric field strength at a certain distance from the device: typically at 3 meters 200 μV/m below 960 MHz, and 500 μV/m above. Outside of unlicensed bands, spurious or unwanted EIRP radiated are limited to less than -40 dBm, which is very low... (Note that there are however some provisions that “periodic” signals or “intermittent control” signals can be higher.)

To determine if a system radiates within the limits allowed by part 15, refer for instances to details in FCC document OET bulletin no. 63 [16], p. 29, which gives a commonly used approximation to relate radiated power (P in W), antenna gain (G relative to an isotropic source) and electric field strength (E in V/m) at a distance D:

           2
-PG-- = -E---
4πD2    120π
(1.1)

For the purpose of assessing limitations at a distance of 3 meters, the accepted relation is simply EIRP = PG = 0.3 E2 (where EIRP is in W, E in V/m). The relation can simply be converted to dB’s by: EIRP (dBm) = 24.77 + 20log(E(V/m)).

Other levels of emission important for good cohabitation of services are out of band emission levels. Technical specifications as well as local regulators address these my mandating a spectrum mask for adjacent bands.

1.5 International Spectrum Landscape

The complex US spectrum landscape is due in part to the fact that multiple government and commercial entities compete for a scarce and precious resource. It can easily be pictured how difficult such coordination might be on a worldwide basis. Such coordination attempts occur regularly at the World Radiocommunication Conference (WRC), a conference organized by the ITU where governments delegations and standards bodies provide contributions, studies, and discussions to attempt to harmonize worldwide use of spectrum. Progress and coordination is typically very slow to achieve at the WRC, as different countries have very different priorities and needs. Some levels of harmonization have been successful, which have allowed for instance global roaming services in 3G cellular bands. WRC 2015 also started identifying 5G bands, including in the millimeter band mentioned above, and some bands above 95 GHz that will be discussed further at WRC 2019.

In addition, different governments have different incentives to use spectrum efficiently. In the US, typical rules associated with a spectrum band are fairly technology agnostic: the FCC tends to be standard agnostic in order to allow all technologies and promote innovation; in other countries, governments sometimes mandate the use of certain standards in certain bands in order to enforce some minimal spectrum efficiency. (In the late 90’s for instance, IMT-2000 provided a family of 3G standards for third generation cellular systems; the European Union mandated that these standards could be used in newly created bands, whereas the US did not have any such requirements).

1.6 Homework

  1. Wireless technologies are evolving. (a) What are the advantages of digital wireless over analog? (b) What are the advantages of 3G technologies over 2G? (c) Research online source and summarize what the advantages of 4G are over 3G. Do not copy/paste entire paragraphs, instead summarize the important points, sort them in your mind and write them down, add personal thoughts and opinions. Cite your sources and list the URL’s you use. (d) In your opinion, what does 5G need to bring over 4G to be successful?

    Also, throughput this class and your professional career, please proof-read ; if you don’t have the patience to re-read your work, do not expect anyone else to.

  2. (a) Estimate how far apart cellular systems were introduced from first to second to third to fourth generation. (Document your references that lead you to these dates). From these estimates, when would you anticipate fifth generation systems to be introduced? Explain why. (b) Research recent announcements of LTE, or LTE-advanced systems rolling out in the US; which one(s) correspond(s) best with your earlier predictions? Comment.
  3. This problem reviews and compares spectrum acquisition for the major bidders of the 2008 700 MHz auction (auction 73).
    1. Estimate the average price per MHz-pop of the 700 MHz auction held in 2008 for the top 4 bidders (Verizon Wireless, AT&T, Echostar, and Qualcomm) – use FCC published results (on www.fcc.gov);
    2. Summarize licenses and prices for the top four bidders;
    3. In your opinion, who got (1) the best coverage, (2) the most capacity, and (3) the best deal? – Justify and comment.
  4. Find and read recent FCC documents on Citizens Broadband Radio Service (CBRS).
    1. Summarize important aspects of this upcoming spectrum, including spectrum amount, proposed power limits, band plans, and possible geographic areas considered. Carefully reference FCC public notices, notices of proposed rulemaking, etc.
    2. What is the main novelty for CBRS in terms of sharing spectrum? Explain in details.
    3. Outline pros and cons of the sharing approach above, comparing it to a simple auction of all CBRS spectrum.
  5. Find and read recent FCC documents on upcoming auctions 101 and 102. Summarize important aspects of these upcoming auctions, including spectrum amount, band plans, and possible geographic areas considered. Carefully reference FCC documents.
  6. It is difficult to summarize spectrum ownership in the US for a number of reasons, mostly because wireless carriers own different size and geographic shapes throughout the country.
    1. Research online, although estimates are difficult, try to estimate the average spectrum ownership of the main three wireless carriers in the US. (Provide detailed references and dates for your sources; beware that old sources may no longer be accurate as spectrum deals happen often).
    2. One way to summarize ownership is to try to estimate MHz/pop. Find estimates (or calculate) MHz/pop ownership for the main three carriers. (Explain your estimates and calculations; be careful, some own more spectrum in populated areas so MHz/pop may vary)
    3. Research spectrum price estimates, explain in details how you would estimate the value of spectrum these there carriers own. (Use any recent estimate you can find on the Web, explain your assumption, calculate the estimated value).
  7. In the US, the FCC is standard agnostic; on the contrary the EU often mandates that one standard be used in a given band. Explain in a few statements each choice and describe the advantages of each approach.
  8. (This problem assumes some basic notions of link budget – refer to further chapters if necessary). We consider manufacturing a wireless device under the rules of part 15 (see 1.4). We want the device to operate in the PCS band (at 1.9 GHz) and remain under the part 15 power levels.
    1. What are the maximum transmitted electric fields and EIRP allowed for data communications? (Hint: find FCC OET bulletin no. 63 and examine maximum power levels allowed; ignore levels associated with periodic or intermittent control signals. See in particular formulas on p.29.)
    2. Assuming receiver devices require -90dBm received power for good communications level. What is the link budget allowed by such device? (Assume small antenna gains of 0dBi).
    3. Comparatively, a typical Wi-Fi link budget is around 100dB, and is commonly said to propagate around 300 feet. How far would our manufactured system propagate? (detail your assumptions, show your calculations.)
  9. You decide to go around your home to see what device may emit spurious radiations (around microwave oven, fridge, TV, etc.) You simply use a spectrum analyzer with an antenna and measure different power levels. You notice that 3 meters away from your new plasma TV, you can measure a little peak of approximately -89 dBm at 830 MHz, and only when the TV in on.
    1. In what band does that occur? Is this likely to interfere with a cellular handset? a cellular base station? Explain.
    2. FCC part 15 requires emissions in the 216-960 MHz band below 200 μV/m, 3 meters away from the device. In free space the electrical field E is equivalent to a received power density of: P=E2∕η0, where η0 = 377 Ω is the characteristic impedance of free space. A field strength of 200 μV/m corresponds to a measured power density of how many W/m2 and how many dBm/m2?
    3. To compare this to the measured power, one needs to estimate the effective area of the test device: we assume a simple dipole antenna of gain G=2.1 dBi What is its effective area? (See 3.2 for a relationship between gain and effective area).
    4. What is the FCC power limit (in W and dBm) 3m away from the TV? Is the TV part 15 compliant?

Copyright 2019 Thomas Schwengler. A significantly updated and completed 2019 Edition is available.


Support independent publishing: Buy this book on Lulu.