Uplink vs Downlink | difference between Uplink and Downlink

The term uplink indicates transmissions from ground side towards cell tower and downlink indicates transmissions from cell tower towards ground side. Let us compare Uplink vs Downlink and derive difference between Uplink and Downlink.

This terms are usually used in wireless network. As we know wireless network is composed of two main parts viz. network side and mobile or fixed subscriber side. Network side houses network equipments such as base station (BTS) or Node-B or eNB. Network part also interfaces with PSTN, ISDN and PSDN (i.e. internet) in order to provide various services to the subscribers or users. Subscriber side houses mobile phone or smartphone with SIM card. The users can also use tablet or laptop to connect with network for data access. Here uplink refers to transmissions from subscribers side to the network and downlink refers to transmission from network to subscribers. Let us understand both uplink and downlink with respect to examples.

What is Uplink ?

It is used to indicate transmission route from one device to the other i.e. from mobile or fixed terminal to the network side. The frequency used for all the transmissions from Mobile Subscriber Unit (MS) to the Base Station (BS) (i.e. Node-B, eNB) is known as uplink frequency. The data transmission direction from MS to BS is called uplink direction. Let us understand term "uplink" with respect to different wireless technologies.

satellite vsat mesh configuration

As we know satellite communication is used to cover wide area of the earth. To provide ground connectivity with the satellite, VSATs and Hub or Earth stations are installed at various places on the earth after RF link budget estimation. The direction from VSATs to sallite is known as uplink and the direction from satellite to VSATs is known as downlink. 6GHz band frequency is used for uplink and 4GHz frequency band is used for downlink in C band satellite communication operation. 5925 MHz to 6425 MHz is uplink band where as 3700 to 4200 MHz is downlink band. Refer VSAT System Overview>>.

In GSM network, the packet transmission from MS to BTS is known as uplink where as from BTS to MS is known as downlink. In GSM frequency range from 890 MHz to 915 MHz is used as uplink frequency where as 935 MHz to 960 MHz is used as downlink frequency. Refer GSM system tutorial>>.

Uplink vs Downlink

What is Downlink ?

The frequency used for all the transmissions from Base Station to the Mobile Subscriber Unit (MS) is known as downlink frequency. The direction from BS to MSs is called downlink direction. TDD (Time Division Duplex) and FDD (Frequency Division Duplex) is used in combination with FDMA (Frequency Division Multiple Access) and TDMA (Time Division Multiple Access) in order to use the bandwidth effectively in wireless systems.

As mentioned above in C band satellite network, 3700 to 4200 MHz is used as downlink frequency band. In GSM, frequency range from 935 MHz to 960 MHz is used as downlink frequency range.

The RF unit called upconverter is used to convert baseband frequency to RF frequency for transmissions in the uplink side. The RF unit called downconverter is used to convert RF frequency to baseband frequency for receptions in the downlink side. The unit which does both teh uplink and downlink processing is known as Transceiver. Modem is used to interface with RF transceiver on one side and antenna is used on the other side.

In wireless system, these terms uplink and downlink are used to indicate channels (uplink channel, downlink channel) , frame structure (uplink frame, downlink frame), packets (uplink packet, downlink packet) and so on. Similarly in wired system, the transmissions from modem towards cable line is known as upstream direction where as from internet server towards modem/user terminal is known as downstream direction. From the above discussion we can easily derive difference between uplink and downlink terms.

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RF and Wireless Terminologies