LTE physical Transmission Resources (2)-band, channel bandwidth, and frequency point number EARFCN

1. Frequency band (Band)

The so-called frequency band , refers to the wireless decoder in the specified degree of distortion and rated output power of the operating band width, refers to a frequency range or the width of the spectrum , that is, the minimum operating frequency of the wireless decoder to the maximum operating frequency range, The unit is Hz. For convenience, in LTE, a digital 1-43 is used to denote different bands (36101-v10.21.0 version protocol), thus referring to different frequency ranges.

Protocol 36101 Specifies the current band of all LTE, the frequency range of the band, and the LTE format, as shown in. It is important to note that the upper and lower frequency range of the band 1-32 is not overlapping, that is, the uplink and downlink transmit data in different frequency points, which is also called " paired band " (paired Frequency Band), Reserved for FDD use. The frequency range of the band 33-43 is consistent, and this frequency band is also known as the " non-paired band " (Unpaired Frequency Band) reserved for TDD use.

At present, China Mobile, Unicom, telecom three operators using the frequency band range as shown in the table below.

The distribution of TDD is as follows:

The allocation of FDD is as follows:

As can be seen from the Spectrum usage table of the above operators, the concentration in the 39-41 of these high frequency bands used as TDD format has both advantages and disadvantages. The advantage is that the other wireless standard is not used in high-frequency band, so less interference, at the same time because of high-frequency spectrum resource rich, but also can get more spectrum bandwidth; The drawback is fast attenuation. The current distribution of the spectrum resources in our country is shown in the table below (the table is derived from the fega of knowledge).

2 bandwidth (channel Bandwidth)

The channel bandwidth limits the allowable frequency through the upper and lower frequencies of the channel, or limits a frequency pass band. In a frequency band band, it is possible to flexibly allocate several different channel bandwidths. The LTE system supports flexible channel bandwidth and is available in 6 configurations, namely 1.4mhz,3mhz,5mhz,10mhz,15mhz,20mhz. The lower bandwidth of 1.4MHz and 3MHz allows for easy CDMA2000 use of the spectrum to be migrated to LTE while helping to facilitate the migration of GSM and TD-SCDMA to LTE. The purpose of a variety of bandwidth is to adapt to different frequency of the use of the scene, such as the frequency of the available bandwidth of less than 10MHz, then the LTE system can be configured to 5MHz use.

not all channel bandwidth can be used as a resource for transmitting data, and portions of the channel bandwidth are reserved for bandwidth protection , such as signaling. Take 20MHz bandwidth, for example, a RB occupies 12 sub-carriers, each sub-carrier is 15K, then 20MHz of bandwidth, if all used as the transmission of data RB, there can be 110. But when the actual spectrum is emitted, it is impossible to be a theoretical rectangular window, at two edges of the channel bandwidth, it is unavoidable to have hypotenuse (transmit signal power roll-off). In addition to all channel bandwidth beyond the 1.4MHz bandwidth, the RB block for transferring resources consumes 90% of the channel bandwidth , so for the actual 20MHz bandwidth, the RB resource that can be used to transmit data is 100.

The number of resource RB for each bandwidth used for data transfer is as follows:

The 3GPP also specifies the types of bandwidth that can be used in different bands, as shown in the following table. for the current mobile, unicom, telecommunications use of TDD band 39, 40, 41来 said that the bandwidth is 5MHz, 10MHz, 15MHz and 20MHz.

3. Carrier frequency point number (EARFCN)

In order to uniquely identify the frequency range of an LTE system, only using frequency bands and channel bandwidth are not qualified, such as the mobile band 40 accounted for the 50M frequency range, and LTE the largest channel bandwidth is 20M, then in this 50M range is no way to limit this 20M specifically in what position, This is the time to introduce new parameters: Carrier Center frequency FC(referred to as carrier frequency ).

It can be seen that the specific frequency range of the LTE system can be determined by the three values of band band, channel bandwidth bandwidth and carrier frequency FC. Because the carrier Frequency FC is a floating-point value, compared with the shaping type, it is not good for the transmission of the interface, so at the time of the protocol formulation, the carrier frequency point is used to represent the corresponding carrier frequencies FC.

Carrier frequency Point , also known as EARFCN, the full name is E-utra Absolute Radio Frequency channelnumber, absolute wireless frequency channel numbers, using 16bit representation, The range is 0-65535. Because the EARFCN is used to refer to the carrier Frequency FC, the two parameters must be one by one-corresponding and can be converted to each other. The relationship between the carrier Frequency FC and EARFCN is shown below, where Fdl and Ful respectively represent the downstream and upstream specific central carrier frequencies,Ndl and Nul Indicates the absolute frequency point number of the downstream and upstream respectively.

Examples of how to calculate: For example, the current LTE system is using the band 40, the carrier frequency is 2320MHz, then the table can be fdl_low=2300mhz,noffs_dl=38650,ful_low=2300mhz,noffs_ul=38650. Then substituting the formula (note that MHz does not turn into Hz at the time of Generation), you can get the carrier frequency number of the upper and lower line is 38850.

Reference documents:

(1) 3GPP TS 36.101 V10.21.0 (2015-12) User equipment (UE) radio transmission and reception

(2) "4G lte/lte-advanced for Mobile Broadband"

LTE physical Transmission Resources (2)-band, channel bandwidth, and frequency point number EARFCN