Unit - 5

Applications of different RF bands

Q1) Write the frequency band rages for various RF applications?

A1) The SHF (super high frequency) and EHF (extremely high frequency) bands are frequently referred to as the microwave spectrum.

Q2) What are the main features affecting RF module performance?

A2) 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.

Q3) Explain the Wi-Fi systems?

A3)

Q4) How is Bluetooth technology an application of RF?

A4)

Q5) What the infrastructure for ATC?

A5) 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.

Q6) What the RF challenges in ATC?

A6) Mitigating Co-Location Issues

The close proximity of multiple radios in a single site is probably the greatest challenge. Radios can interfere with each other in a number of ways which all have the effect of blocking or degrading channels.

Filtering

Filtering is perhaps the most obvious way of isolating radios operating at different frequencies. However, the congested ATC spectrum can often demand very high-Q filters operating at high RF power. For these reason cavity filters are the preferred choice. Cavity filters will often comprise two or three individual filters in series to obtain the required selectivity. Individual cavity filters can cost several hundred pounds each and take up significant rack space.

Circulators

Circulators are used in the ATC radio environment to ensure any interfering signals or reflected signal are prevented from flowing back into a transmitter. This protects the transmitter from the effects of a mismatched antenna but also prevents interfering signals from other transmitters entering the RF output of the transmitter where further unwanted signal frequencies can be generated by intermodulation.

Basic Radio Performance

Both cavity filters and circulators can be highly effective at allowing a number of radios to operate together within a congested part of the RF spectrum. However, both of these devices are expensive and would only be used when absolutely necessary. If the inherent performance of the radio can be optimised, the cost savings realised from having fewer filters and circulators can be considerable. This need to keep down the cost of associated costly components is one of the main drivers for the RF designer.

Receiver

There are several key ways in which the presence of signals on other channels can degrade the performance of an AM receiver. These are intermodulation, cross-modulation and de-sensitisation. They are all linked and usually have a fixed relationship between them but are considered and tested individually.

Intermodulation

Intermodulation occurs when two or more frequencies are incident upon any non-linear device. A classic frequency domain view of the process. Two unwanted signals at frequencies f1 and f2 produce a host of other signals at frequencies at the sum and differences of integer multiples of f1 and f2. The odd-order products are of most concern as they occupy channels close to the original signals. The third-order intermodulation products which are usually the closest and the largest signals as well as the fifth order which are the next closest and largest. There will be higher orders too getting progressively further away and weaker. The issue is that two signals generate further signals that can block other receiver channels rather than just those occupied by the transmitters themselves.

Cross-Modulation

Cross Modulation is a phenomenon that is most pronounced in AM systems (or signals with some AM component in them). This process occurs when a strong off-channel signal is incident upon a receiver front-end. The process can be visualised as the AM on the interfering signal causing small perturbations in the receiver gain as it swings between low and high power. These gain perturbations will modulate any wanted signal so transferring some of the AM from the interfering to the wanted signal. As with intermodulation, this effect can be reduced by improving the linearity of the receiver or attempting to reduce the level of the interfering signal through filtering.

 De-Sensitisation

A large signal can reduce the gain of a receiver so reducing its sensitivity to weaker signals. It is important to differentiate this phenomenon from that caused simply by noise from the interferer at the wanted frequency. Again, this type of degradation can be improved with enhanced linearity in the receiver or by attempting to reduce the level of the interfering signal with filtering.

Q7) Explain the position location of satellites used for communication?

A7) 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 1 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.

Q8) Explain block diagram of satellite communication?

A8) 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 2 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.

Q9) Explain 5G?

A9) 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

Q10) What is LTE and Wi-Fi compare them?

A10) 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. 

Comparison

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. 

Q11) Explain radio level aggregation?

A11) 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 (e.g., 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 (e.g., through ANDSF), user-based policies/preferences, etc. These policies may take into account various conditions (e.g., 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 (e.g., 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 (e.g., eNB).