Long Term Evolution, also known as LTE, telecommunications networks consist of several frequency bands with related bandwidths. There are several LTE frequency bands that have been allocated throughout the world.
As different countries have different areas of the spectrum, it has been impossible to have a strong level of coordination from one country to another, and this has issues with roaming as well as the number of bans needed for handsets.
All frequency bands are allocated a number so it can be explained easily and its limits are known. The Long Term Evolution or LTE channel bandwidth also gets numbers. These numbers can be calculated from a simple defined formula. By having specific radio channels, they can coordinate globally to facilitate roaming.
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LTE bands for FDD and TDD
The spectrum requirements and the frequency band allocation for Long Term Evolution are different for FDD and TDD. Let’s take a look at the frequency band allocations:
FDD LTE Bands: FDD spectrum needs pair bands – one for the uplink and next one for the downlink. It is important that there is enough space between the top of the lower band and the bottom of the upper band in order to allow enough filtering. In addition, the uplink to downlink channel spacing should be enough to allow enough filtering to prevent the transmitted signal from entering the receiver as well as desensitizing it.
TDD LTE Bands: TDD transmissions need a single band, and the paired spectrum is not needed.
The different Long Term Evolution frequency allocations are allocated numbers. In the present scenario, the LTE bands between 1 & 22 are for paired spectrum, that is, FDD and LTE bands between 33 & 41 are for unpaired spectrum, that is, TDD.
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How Does It Work?
Long Term Evolution uses two types of air interfaces or radio links – one for downlink and one for uplink. By using these types of interfaces, LTE utilizes the optional way to make wireless connections that make a better-optimized network and better battery life on LTE devices.
When it comes to the downlink, LTE uses an orthogonal frequency division multiple access or OFDMA air interface as opposed to the CDMA that is code division multiple access as well as TDMA that is time division multiple access, air interfaces that have been using since 1990. What does it mean? OFDMA mandates that MIMO (multiple in, multiple out) is used. MIMO defines that devices have several connections to a single cell that enhances the stability of the connection and eliminates latency tremendously. It also maximizes the total throughput of a connection.
There are a number of benefits of MIMO on WiFi N routers as well as network adapters. MIMO allows 802.11n WiFi to reach speeds of up to 600Mbps. However, there is a disadvantage of MIMO as well. It works better the further apart the individual carrier antennae are. When it comes to smaller phones, the noise generated by the antennae being so close to each other will create LTE performance to drop.
WiMAX mandates the usage of MIMO since it uses OFDMA. In addition to the same, HSPA+, which uses W-CDMA for its interface, can use MIMO as well. Similarly, when it comes to the uplink, LTE uses the DFTS-OFDMA scheme to generate an SC-FDMA single. As opposed to regular OFDMA, SC-FDMA is ideal for uplink as it has a better peak-to-average power ratio over OFDMA for uplink. LTE-enabled devices do not have a strong single going back to the tower, so a lot of the advantages of normal OFDMA could be lost with a weak single.