Transmission impairments
In any communication system, the received signal is never is identical to the transmitted one due to some transmission impairments. The quality of analog signals will deteriorate due to transmission impairments as given above.
Attenuation:
The strength of a signal decrease with the increase in distance travelled over a medium. Attenuation means loss of energy. When any signal travels over a medium or channel, it loses some of its energy in the form of heat in the resistance of the medium. Attenuation decides the signal to noise ratio hence the quality of received signal. Attenuation is given in decibels as:
Attenuation (dB) = 10log10 (Pout/Pin)
Where, Pin= Power at the sending end
Pout= Power at the receiving end
Distortion (Harmonic):
Another meaning of distortion is change in shape of the signal. This type of distortion is observed for the composite signals made by different frequencies. If the medium is not perfect, then all the frequency components present at the input will not only be equally attenuated and will not be proportionally delayed.
Noise:
When the data travels over a transmission medium, noise gets added to it. Noise is a major limiting factor in communication system performance. Noise can be categorized into four types as follows:
(i) Thermal noise (ii) Inter-modulation noise (iii) Cross talk (iv) Impulse noise
Date Rate Limits
We want developers to create compelling user experiences, but we also want the Nest service and devices to always be available for the user. Works with Nest products that make a large number of requests in a given period of time can impact service and device availability, so we apply rate limits. Rate limiting restricts the number of API calls for a given time period.
Types of rate limits
We have implemented two classes of rate limits. The first limits are per device or structure per hour. These limits are shared across all products, and are intended to prevent overutilization of devices. The second class of limits are per access token. These limits are designed to prevent overutilization of the Nest service.
Per device/structure limits
Every write to the data model requires the device to wake up and synchronize state. This can impact battery life, so we limit the number of writes to devices and structures. We also monitor the battery state of all devices. If they drop below a certain threshold, we will reject write requests until the battery has recharged.
Per access token limits
Each access token also has an associated rate limit. Establishing connections to the service incurs some overhead, so we limit the number of connections a product can make in a specific time period. If you’re using the Firebase client, you shouldn’t hit these limits, as a single connection can handle all communication over a long period of time.
For REST and REST Streaming calls, each access token has a limited number of calls. Data rate limits apply to read/write calls via REST, and on read calls via REST Streaming. To avoid errors, we recommend you limit requests to one call per minute, maximum.
Error response
When using the supported Firebase SDKs (Web, iOS, and Android), rate limit violations appear as an error status when attempting to set a value, and will have description error text in the response message. If using the REST or REST Streaming clients, you will receive a response code of 429 Too Many Requests.
Handling 307 redirects
When making REST or REST Streaming calls, your product will need to handle 307 redirects. Also known as URL forwarding, a 307 Temporary Redirect response provides a new URL for the browser to resubmit a request.
When a 307 redirect happens, you’ll need to make the call again with the new URL information. When you do this, you should cache the host and port number for use in future calls with that user/access token. Remember, each call counts toward the rate limit. Consider how your user is interacting with your product. Some users will press a button or choose a setting repeatedly, so if you make a call for every user action, it can impact rate limits very quickly. If a user makes a series of changes in rapid succession, you should only make an API call for the last (most recent) value.
Introduction To Wireless Communication
In the present days, wireless communication system has become an essential part of various types of wireless communication devices, that permits user to communicate even from remote operated areas. There are many devices used for wireless communication like mobiles. Cordless telephones, Zigbee wirelss technology, GPS, Wi-Fi, satellite television and wireless computer parts. Current wireless phones include 3 and 4G networks, Bluetooth and Wi-Fi technologies.
Types of Wireless Communication
The different types of wireless communication mainly include, IR wireless communication, satellite communication, broadcast radio, Microwave radio, Bluetooth, Zigbee etc.
Satellite Communication
Satellite communication is one type of self contained wireless communication technology, it is widely spread all over the world to allow users to stay connected almost anywhere on the earth. When the signal (a beam of modulated microwave) is sent near the satellite then, satellite amplifies the signal and sent it back to the antenna receiver which is located on the surface of the earth. Satellite communication contains two main components like the space segment and the ground segment.The ground segment consists of fixed or mobile transmission, reception and ancillary equipment and the space segment, which mainly is the satellite itself.
Infrared Communication
Infrared wireless communication communicates information in a device or systems through IR radiation . IR is electromagnetic energy at a wavelength that is longer than that of red light. It is used for security control, TV remote control and short range communications. In the electromagnetic spectrum, IR radiation lies between microwaves and visible light. So, they can be used as a source of communication
For a successful infrared communication, a photo LED transmitter and a photo diode receptor are required. The LED transmitter transmits the IR signal in the form of non visible light, that is captured and saved by the photoreceptor. So the information between the source and the target is transferred in this way. The source and destination can be mobile phones, TVs, security systems, laptops etc supports wireless communication.
Broadcast Radio
The first wireless communication technology is the open radio communication to seek out widespread use, and it still serves a purpose nowadays. Handy multi channel radios permit a user to speak over short distances, whereas citizen’s band and maritime radios offer communication services for sailors. Ham radio enthusiasts share data and function emergency communication aids throughout disasters with their powerful broadcasting gear, and can even communicate digital information over the radio frequency spectrum.
Mostly an audio broadcasting service, radio broadcasts sound through the air as radio waves. Radio uses a transmitter which is used to transmit the data in the form of radio waves to a receiving antenna(Different Types of Antennas). To broadcast common programming, stations are associated with the radio N/W’s. The broadcast happens either in simulcast or syndication or both. Radio broadcasting may be done via cable FM, the net and satellites. A broadcast sends information over long distances at up to two megabits/Sec (AM/FM Radio).
Radio waves are electromagnetic signals, that are transmitted by an antenna.These waves have completely different frequency segments, and you will be ready to obtain an audio signal by changing into a frequency segment.
For example, you can take a radio station. When the RJ says you are listening to 92.7 BIG FM, what he really means is that signals are being broadcasted at a frequency of 92.7 megahertz, that successively means the transmitter at the station is periodic at a frequency of 92.700,000 Cycles/second.
When you would like to listen to 92.7 BIG FM, all you have to do is tune the radio to just accept that specific frequency and you will receive perfect audio reception.
Microwave Communication
Microwave wireless communication is an effective type of communication, mainly this transmission uses radio waves, and the wavelengths of radio waves are measured in centimeters. In this communication, the data or information can be transfers using two methods. One is satellite method and another one is terrestrial method.
Wherein satellite method, the data can be transmitted though a satellite, that orbit 22,300 miles above the earth. Stations on the earth send and receive data signals from the satellite with a frequency ranging from 11GHz-14GHz and with a transmission speed of 1Mbps to 10Mbps. In terrestrial method, in which two microwave towers with a clear line of sight between them are used, ensuring no obstacles to disrupt the line of sight. So it is used often for the purpose of privacy. The frequency range of the terrestrial system is typically 4GHz-6GHz and with a transmission speed is usually 1Mbps to 10Mbps.
Wi-Fi
Wi-Fi is a low power wireless communication, that is used by various electronic devices like smart phones, laptops, etc.In this setup, a router works as a communication hub wirelessly. These networks allow users to connect only within close proximity to a router. WiFi is very common in networking applications which affords portability wirelessly. These networks need to be protected with passwords for the purpose of security, otherwise it will access by others
Mobile Communication Systems
The advancement of mobile networks is enumerated by generations. Many users communicate across a single frequency band through mobile phones. Cellular and cordless phones are two examples of devices which make use of wireless signals. Typically, cell phones have a larger range of networks to provide a coverage.But, Cordless phones have a limited range. Similar to GPS devices, some phones make use of signals from satellites to communicate.
Bluetooth Technology
The main function of the Bluetooth technology is that permits you to connect a various electronic devices wirelessly to a system for the transferring of data.Cell phones are connected to hands free earphones, mouse, wireless keyboard. By using Bluetooth device the information from one device to another device. This technology has various functions and it is used commonly in the wireless communication market.
Advantages of Wireless Communication
- Any data or information can be transmitted faster and with a high speed
- Maintenance and installation is less cost for these networks.
- The internet can be accessed from anywhere wirelessly
- It is very helpful for workers, doctors working in remote areas as they can be in touch with medical centers.
Disadvantages of Wireless Communication
- An unauthorized person can easily capture the wireless signals which spread through the air.
- It is very important to secure the wireless network so that the information cannot be misused by unauthorized users
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