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Uplink and Downlink Frequency

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • The process of transmitting data from the user device to wireless communication network infrastructure is called uplink.

  • The downlink process connects the satellite to the ground station receiver.

  • The uplink and downlink frequencies in satellite communication are separated by bandwidth, and the latter is lower than the former.

Uplink and Downlink Frequency

Ground-to-satellite (and vice-versa) data communication is enabled with the use of uplink and downlink frequency

Satellite-based infrastructure helps connect two locations that are miles apart. From the Earth’s surface, data is sent to the satellite station, then from the satellite station to the ground. Ground-to-satellite (and vice-versa) data communication is enabled with the use of uplink and downlink frequency. 

Bifurcation of the Wireless Communication Network

Any wireless communication network can be bifurcated into two parts.

  1. Network or operator side

  2. Subscriber or user side

The user is connected to the operator through devices such as smartphones, tablets, mobile phones, laptops, etc. We send and receive data through the devices that we hold; however, the wireless communication network is not just the handheld device. The wireless communication network is wide, with infrastructure based on either terrestrial or satellite systems.

Uplink Frequency

In wireless communication, the data received needs to be transmitted to the network infrastructure. In mobile and satellite communication networks, the data is transmitted to the network infrastructure from the user's device. The process of transmitting data from the user device to the wireless communication network infrastructure is called uplink, and the frequency associated with the uplink process is called uplink frequency. Uplink is analogous to upload or upstream.

Downlink Frequency

The downlink process refers to the data transfer from the network to the user or subscriber. The downlink process can be compared with either the download or downstream process where we get the data available in our device.

The table below gives the uplink and downlink descriptions of different wireless communication systems.

Wireless Communication

Uplink

Downlink

Satellite communication

In satellite communication, uplink frequency refers to the communication between the Earth station transmitter and the satellite. Data is transmitted from the ground station to the satellite at a specified frequency.

The downlink process connects the satellite to the ground station receiver. The downlink frequency is the frequency of the signal from the satellite to the ground station.

Radio communication

There is a global station and a radio station. The radio communication uplink service transmits the radio signals from the global station to the radio station. It can be either a radio station or a high-altitude platform.

The downlink frequency in radio communication is associated with signal transmission from the high-altitude platform or the radio station to the global station.

Mobile communication

Data transfer is from the mobile phone (portable station) to the mobile domain (base station).

In mobile communication, a method known as radio downlink is used to transfer the signals from mobile allocation to the end-user device for cell phones.

 

Why Are Uplink and Downlink Frequencies Different?

The uplink and downlink process of signal transmission utilizes only certain frequency bands specified by the International Telecommunication Union (ITU). For each band in satellite communication, there is an uplink frequency band and a downlink frequency bandwidth. As most satellites use the same antenna for both uplink and downlink, it is necessary to use different uplink and downlink frequencies to prevent the satellite receiver from jamming. The bandwidth separation between uplink and downlink frequencies enables the use of a single antenna in satellite communication, reducing the associated hardware used.

Range 

Uplink frequencies are typically greater than downlink frequencies. The range of uplink and downlink frequencies are selected in order to prevent the signal attenuation imparted by the atmosphere. With the increase in frequency, the signal loss increases, meaning high-power transmitters are required to establish reliable transmission. To reduce signal losses and address the incapability to accommodate high-power transmitters in lightweight satellites, a lower frequency is utilized for downlink compared to uplink.

Frequencies of Frequency Bands

Downlink frequencies are lower than uplink frequencies in satellite communication. This is different from other communication networks. For example, in GSM cellular networks, the uplink frequency ranges from 890 - 915 MHz, and the downlink frequency ranges from 935 MHz - 960 MHz. The uplink and downlink frequency ranges of certain frequency bands used for satellite communication are given in the table below.

Frequency Band

Uplink

Downlink

L

1.62 -1.66 GHz

1.52 - 1.55 GHz

C

5.9 - 6.4 GHz

3.7 - 4.2 GHz

Ku

14.0 - 14.5 GHz

11.7 - 12.2 GHz

Ka

27.5 - 31.0 GHz

17.7 - 21.2 GHz

As a cursory note, we can say uplink and downlink frequencies in satellite communication are separated by bandwidth, and the latter is lower than the former. Cadence’s suite of design and analysis tools can help you develop systems that utilize electromagnetic frequency bands such as satellite communication systems, microwave circuits, etc.

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