Unit - 5

Applications of different RF bands

5.1 Applications of different RF bands: ranges

Wireless Radio frequency is any of the electromagnetic wave frequencies that lie in the range ranging from around 3 kHz-300 GHz, which comprise those frequencies used for radar signals or communications.

Radio frequency usually denotes to electrical rather than mechanical oscillations. But, mechanical RF systems do occur. Although RF is a rate of oscillation, the name RF or “radio frequency” are used as a substitute for radio to define the use of wireless communication, as different to communicate through electric wires.

Several types of wireless devices make use of radio frequency fields like Cordless & Cell phones, radio & TV broadcast stations, satellite communication systems, Bluetooth module and Wi-Fi, and also two-way radios all work in the RF spectrum.

In addition, other appliances, external communications, comprising garage-door openers and microwave ovens, function at radio frequencies. Some wireless devices such as, TV remote controls, computer mice, and some cordless computer keyboards operate at infrared frequencies, which have smaller electromagnetic wavelengths.

The term RF (Radio frequency) is measured in units called Hz (hertz), which denote the number of cycles/second when a radio signal is transmitted. One Hz (hertz) equals one cycle per second; radio waves range from 1,000 KHz to millions MHz to billions GHz of cycles per second. Microwaves are a kind of radio wave with higher frequencies. Radio frequencies (RF’s) are not visible to the human eye.

RF Spectrum Bands

The RF spectrum is separated into numerous ranges or bands. With the exemption of the low-frequency segment, every band denotes an increase of frequency similar to an order of magnitude. The following RF spectrum bands table shows the 8-bands in the RF spectrum, showing the ranges of frequency and bandwidth. The SHF (super high frequency) and EHF (extremely high frequency) bands are frequently referred to as the microwave spectrum.

The Main Features Affecting RF Module Performance

As with any other RF module, the RF module’s performance will depend on a number of factors. For instance, by increasing the power of a transmitter, a larger communication distance will be reached. But, this will also result in a higher electrical power drain on the transmitter (TX) device, which will root smaller operating life for battery-powered devices. Also, with a higher transmit power will make the system more disposed to interference with an extra RF device.

Correspondingly, increasing the sensitivity of the receiver will also rise the active communication range, but will also possibly cause an error due to interference with additional RF devices. The performance of the whole system may be enhanced by using corresponding antennas at each end of the communication link.

Lastly, the considered remote distance of any specific system is usually measured in an open-air line of sight outline without any interference, but frequently there will be problems like floors, walls, dense construction to grip the radio wave signals, so the current operational distance will in most real examples be less than specified.

Key takeaway

5.2 Brief about various applications of RF technology like WiFi, Bluetooth

WiFi

Bluetooth

5.3 Air traffic control

Although there are some variations, air traffic control communications infrastructure is divided into the following types:

 Tower (TWR)

 Approach (APP)

 Area Coverage (ACC)

 Oceanic

Whilst taxiing, the aircraft is under the control of the tower which controls the traffic on the ground at the airport. Once airborne, control is handed over to “approach” who manage air traffic into and out of the airport.

Finally, once clear of the airport, the aircraft is under the control of the “area coverage” service being handed over as it crosses airspaces of different authorities. If the flight is long-haul and involves crossing an ocean, then the aircraft leaves controlled airspace and controls its own flight path. There are agreed corridors and ATC services will be aware which flights are expected to leave and enter their airspace. Communications is still available to an aircraft over an ocean using satellite and/or HF systems but these are used by aircraft owners rather than the ATC providers. The sequence is then reversed as the aircraft approaches an airport.

Tower and Approach communications systems are located at the airport. An area coverage sector has a single control centre and remote radio sites. An area coverage sector may serve a single nation’s airspace, but for larger areas, the airspace is divided into sectors each with its own control centre. For example, the UK has two: Swanwick and Prestwick. A larger country will have more. A pilot remains tuned to a single frequency whilst in an area coverage sector and performs a hand-over to a new controller and new frequency as the aircraft moves to a new sector.

5.4 GPS navigation system

The global positioning satellite system has upgraded navigation and position for aircrafts, ships and majorly in surveying. The GPS satellite transmits L- band signals. There are many codes used in the transmission of signal. Initially coarse acquisition code (C/A) was made public and later P codes were used. The P codes were very helpful in military uses. The GPS systems are widely used as they provide exact location of GPS receiver.

The GPS satellite transmits two signals of frequencies L1 and L2. The L2 signals are modulated with 10.23 Mbps pseudorandom codes (PN) known as P code. The P codes are used in military positioning systems.

The GPS system consists of a clock which is synchronised with each clock on the receiving satellite. The GPS system provide two categories of service. The precise positioning service (PPS) and standard positioning service (SPS). In PPS receivers track P codes and C/A codes and are used in military. The SPS receiver track C/A codes, this service is used by general public.

The prerequisite requirement for GPS system is that there must be four satellites transmitting coded signal from known positions. The position location in GPS is done by defining the coordinates for GPS receiver and GPS satellite. A rectangular coordinate system is defined having centre of earth as its origin.

The axes are directed as Z-axis in North pole, Y-axis through 900 east meridian and X-axis through line of zero. The distance measured to satellite is denoted by I and is called as pseudo range.

Fig: Position Location of three satellites

The pseudo range can be measured as

PR = Ti x c

Ti = propagation time delay

C = velocity of EM wave.

Each satellite sends ephemeris data signal along with timing signals. The receiver calculates the coordinates satellite relative to centre of earth. The distance R is given as

R2 = (xA-xB)2 + (yA-yB)2 +(zA-zB)2

The ranging equations are given as

(X1-Ux)2 + (Y1-Uy)2 + (Z1-Uz)2 = (PR1 -c)2

(X2-Ux)2 + (Y2-Uy)2 + (Z2-Uz)2 = (PR2 -c)2

(X3-Ux)2 + (Y3-Uy)2 + (Z3-Uz)2 = (PR3 -c)2

(X4-Ux)2 + (Y4-Uy)2 + (Z4-Uz)2 = (PR4 -c)2

= receiver clock error

The value of can be added to GPS receiver so that time measurement is synchronized to standard GPS time. All GPS receivers are automatically in sync with any other GPS satellite anywhere in the world.

Key takeaway

The GPS satellite consists of two cesium clock and two rubidium clocks which are atomic clocks.

5.5 Satellite systems, mobile networks

Satellites are used to transfer information from one place to another using communication satellite on Earth’s orbit. Satellite communication began in 1957 and the first artificial satellite launched was Sputnik I by the USSR. The satellite communication can be one way as well. In this case the transmission of signal from the transmitter of first earth satellite and the receiver of the second earth satellite is in one direction.

In two-way communication the information is exchanged between the two earth stations. There are two uplinks and two downlinks required to achieve two ways communication.

The main elements of communication satellite are

i)                   Uplink

ii)                 Transponders

iii)              Downlink

The block diagram of satellite communication is shown below. A communication satellite is basically a R.F repeater.

Fig: Block Diagram of Satellite Communication

The uplink frequencies used are of range 5.9GHz-6.4GHz these frequencies are converted to lower frequencies and amplified. The mixers and local oscillators are used to convert the higher frequency uplink signals to lower frequency signals. The com satellite receives this signal amplifies it and then transmits it so that there is no interference in the uplink and down link signals.

The transponders provide the medium for two-way communication. The downlink frequency used for transmission is from the range of 3.7GHz to 4.2GHz. The number of transponders per satellite depends upon the task which the satellite needs to do. For television broadcast two transponders are used in a satellite.

Advantages

The advantages of satellite communication are

Applications

The applications of satellite communication are

Key takeaway

The satellites can be passive and active. The passive satellites just reflect back the signal to the earth as it is without any amplification. Due to this the signal received is weak. On other hand the active satellites amplify the transmitted signal before re-transmitting it to the earth and thus the received signal is of good strength.

Every user has a frequency range allocated for transmission so that interference can be avoided during communication.

5.6 Radio astronomy and remote sensing

CORF has a substantial interest in this proceeding, as it represents the interests of the scientific users of the radio spectrum, including users of the RAS and the EESS bands. Both RAS and EESS observers perform extremely important, yet vulnerable research d by scientists to study our universe. It was through the use of radio astronomy that scientists discovered the first planets outside the solar system, circling a distant pulsar. Measurements of radio spectral line emission have identified and characterized the birth sites of stars in our own galaxy, and the complex distribution and evolution of galaxies in the universe. Radio astronomy measurements have discovered ripples in the cosmic microwave background, generated in the early universe, which later formed the stars and galaxies we know today.

Observations of supernovas have allowed us to witness the creation and distribution of heavy elements essential to the formation of planets like Earth, and of life itself. The EESS is a critical and unique resource for monitoring Earth’s global atmospheric and surface state. Satellite-based microwave remote sensing represents the only practical method of obtaining uniform-quality atmospheric and surface data encompassing the most remote oceans as well as densely populated areas of Earth. EESS data have contributed substantially to the study of meteorology, atmospheric chemistry, oceanography, and global change.

Currently, instruments operating in the EESS bands provide regular and reliable quantitative atmospheric, oceanic, and land measurements to support an extensive variety of scientific, commercial, and government (civil and military) data users. Applications of the data include aviation forecasts, hurricane and severe storm warning and tracking, seasonal and interannual climate forecasts, decadalscale monitoring of climate variability, medium-range forecasting, and studies of the ocean surface and internal structure, as well as many others. The emissions that radio astronomers’ study is extremely weak--a typical radio telescope receives only about one-trillionth of a watt from even the strongest cosmic source.

Because radio astronomy receivers are designed to pick up such remarkably weak signals, such facilities are therefore particularly vulnerable to interference from spurious and out-of-band emissions from licensed and unlicensed users of neighbouring bands, and those that produce harmonic emissions that fall into the RAS bands. Similarly, the emissions received by passive EESS radiometers in Earth orbit are weak by comparison with emissions from other services. In addition to the gains in scientific knowledge that result from radio astronomy and Earth sensing, CORF notes that such research enables technological developments that are of direct and tangible benefit to the public.

For example, radio astronomy techniques have contributed significantly to major advances in the following areas: --Computerized tomography (CAT scans) as well as other technologies for studying and creating images of tissue inside the human body; --Abilities to forecast earthquakes by very-long-baseline interferometric (VLBI) measurements of fault motions; and --Use of VLBI techniques in the development of wireless telephone geographic location technologies, which can be used in connection with the Commission’s “E911” requirements.

Continued development of new critical technologies enabled by passive scientific observation of the spectrum depends on scientists having continued access to interference-free spectrum. More directly, the underlying science undertaken by RAS and EESS observers cannot be performed without access to interference-free spectrum. Loss of such access constitutes a loss for the scientific and cultural heritage of all people, as well as for the practical civil and military applications arising from the information learned and the technologies developed.

5.7 5G technology

5G is the new technology in the field of cellular network. It is the technology with many advantages over the old generation of cellular networks. It is designed such that it will increase the speed, reduce error and make it more flexible for wireless communication. It can offer speeds up to 2Gbps.

Working of 5G 

This technology has improved architecture and also utilises the spectrum which was unused in 4G. The technology called Multiple input and multiple output abbreviated as MIMO is employed. This has many transmitters and receivers so that large data can be transferred. It is not just limited to new radio spectrum. It will have a software platform for networking. It will provide advancements in virtualization, cloud-based technology. The business process automation allows the 5G to be flexible enough to provide easy user access any time.5G networks can create software-defined subnetwork constructs known as network slices. These slices enable network administrators to dictate network functionality based on users and devices.

Advantage of 5G

5.8 LTE-WiFi

Long Term Evolution is a 4G wireless communication standard that’s designed to provide the fastest internet speeds for smartphones, tablets and other mobile devices. Unlike 3G that uses microwaves, 4G utilizes radio waves, which allows better area coverage and penetration through surfaces. 

To gain access, you need to have a mobile device that can run LTE and a reliable service provider that can provide data coverage in your area. Luckily, most smartphones can run 4G. However, performance still depends on your device. If you’re planning to upgrade your phone, take some time to read reviews so you can get the most out of your hard-earned money.  

WiFi is a networking protocol that provides internet connectivity within a fixed location. Similar to LTE, it also requires the services of a data provider, but its main difference is that it needs a router or another device that’s capable of wireless transmission. Once a router has been strategically set up at your home, it transmits data and sends out a signal for devices within its range. 

Key takeaway

LTE offers lightning-fast connection speed and is suited for dealing with high bandwidth applications on mobile devices. It can provide data transfer speeds between 100Mbps (100 megabits per second) to 1 Gbps (one gigabit per second). 

In the case of WiFi users, maximum and minimum speeds may vary depending on the acquired plan. However, today’s WiFi standard lies between 10 and 25 Mbps. 

Both options are incredibly capable sources of internet connectivity, but it’s also important to know that speed can be affected by multiple factors. 

Since LTE is accessed through a mobile device, its range is virtually limitless. Whether you’re at home or in transit, you can surf the web at your convenience, as long as your provider covers the area, you’re in. 

5.9 Radio Level Aggregation (LWA)

LTE-WLAN aggregation (LWA) is a technology defined by the 3GPP. In LWA, a mobile handset supporting both LTE and Wi-Fi may be configured by the network to utilize both links simultaneously. It provides an alternative method of using LTE in unlicensed spectrum, which unlike LAA/LTE-U can be deployed without hardware changes to the network infrastructure equipment and mobile devices, while providing similar performance to that of LAA. Unlike other methods of using LTE and WLAN simultaneously (e.g., Multipath TCP), LWA allows using both links for a single traffic flow and is generally more efficient, due to coordination at lower protocol stack layers.

For a user, LWA offers seamless usage of both LTE and Wi-Fi networks and substantially increased performance. For a cellular operator, LWA simplifies Wi-Fi deployment, improves system utilization and reduces network operation and management costs. LWA can be deployed in collocated manner, where the eNB and the Wi-Fi AP or AC are integrated into the same physical device or in non-collocated manner, where the eNB and the Wi-Fi AP or AC are connected to the Internet traffic and the information transmitted with information and data protection by the sender does not accept the responsibility of the recipient to ensure that you have received this message in accordance with the disclaimer and privacy law to notify the sender via a standardized interface referred to as Xw. The latter deployment option is particularly suitable for the case when Wi-Fi needs to cover large areas and/or Wi-Fi services are provided by a 3rd party (e.g. a university campus), rather than a cellular operator.

LWA has been standardized by the 3GPP in Release-13. Release 14 Enhanced LWA (eLWA) adds support for 60 GHz band (802.11ad and 802.11ay aka WiGig) with 2.16 GHz bandwidth, uplink aggregation, mobility improvements and other enhancements.

Based on how the WLAN access is integrated in the operator network there are two categories:

 1) Core Network integration, in which the WLAN access is connected to the operator core network using either S2a or S2b interfaces) available in 3GPP networks since Release 8 and

2) RAN based integration in which the WLAN access is directly connected to RAN access nodes (eg. LWA or LWIP) available since Release 13.

 All of the above methods of integration assume a certain level of service continuity as well as the terminal devices being always under a licensed spectrum cellular coverage. When service continuity is not assumed the WLAN access it is said to be integrated through what is called Non-Seamless WLAN Offload (NSWO).

A terminal device may access either cellular or WLAN access or both. This procedure may be either network initiated or terminal initiated. When it is network initiated it may be either based on core network signaling (eg. NAS in the case of Network based IP flow mobility) or RAN based rules. Terminal based initiated procedures are based on either operator policies provided to the terminals (eg. through ANDSF), user-based policies/preferences, etc. These policies may take into account various conditions (eg. time, location, network load, access load, radio conditions, etc.) in determining both the access selection as well as traffic switching from one access to another.

In LTE - WLAN Aggregation (eg. LWA or LWIP) the WLAN access is directly connected to RAN access nodes and the access selection and traffic steering/splitting is done entirely under the control of the Radio Access Network node (eg. eNB).

References:

[1] Wireless Communications- Principles and Practice, T S Rappaport, Pearson Education India, Second Edition.

[2] Wireless Communication and Networks, Upen Dalal, Oxford university Press, First Edition, 2015.

[3] Wireless Communication and Networks 3G and Beyond, Iti Saha Misra, Tata

McGraw Hill Education Pvt. Ltd, Second Edition, 2009.

[4] Mobile Communication Engineering – Theory and Applications W C Y Lee, TMH Publication, Second Edition, 2008.

[5] Wireless Communication, Andrea Goldsmith, Cambridge University Press, 2005

[6] Fundamentals of Wireless Communication, David Tse and Pramod Viswanath,

Cambridge University Press, 2005