BWP Part-1

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BWP Basic 

Before we learn more about BWP first of all we learn what was the need to introduce BWP in NR:

BWP is a new concept introduced in 5G mainly to reduce the power consumption of the mobile phone as the 5G bandwidth is large upto 400MHz. Different numerology support different bandwidth size. Thus we can say that bandwidth part is a subset of the entire bandwidth.

The frequency of 5G are divided into two parts as per the range as defined in  38.101:

1) FR1(Frequency Range 1):

f < 6GHz(low frequency)

15kHz SCS:  Support 5,10,15,20,25,30,40,50 MHz bandwidth (Maximum PRB 270)

30kHz SCS: Support 5,10,15,20,25,30,40,50,60,70,80,90,100 MHz bandwidth (Maximum PRB 273)

60kHz SCS: Support 5,10,15,20,25,30,40,50,60,70,80,90,100 MHz bandwidth (Maximum PRB 135)

2) FR2 (Frequency Range 2):

 f > 6GHz(High frequency or millimeter wave(above 24 GHz)).

The bandwidth of FR2 can be 50MHz, 100MHz, 200MHz and 400MHz.

60kHz SCS: Support 50,100,200 MHz bandwidth (Maximum PRB 264)

120kHz SCS: Support 50,100,200,400 bandwidth (Maximum PRB 264)

240kHz SCS: Support 50,100,200,400 bandwidth (Maximum PRB 138)

In NR Minimum RB support is 24, maximum RB support is 275.

EX:

No of RB = (Channel Bandwidth – 2* Guard Bandwidth)/(12* Numerology)

                = (100*10^3- 2*845)/(12*30)

                =273PRB  

But as we know that, LTE was designed with a belief that all the devices are capable of working with a maximum carrier bandwidth of 20MHz.

This avoided several complications, for example, around the handling of the DC sub-carrier, while having a negligible impact on the device cost. 

It also allowed control channels to stretch the full carrier bandwidth to maximize frequency diversity.

Also, reception of very wide bandwidth can be costly in terms of device energy consumption compared to receiving a narrow bandwidth. So if the same approach is used like LTE, where the downlink control channels would occupy the full carrier bandwidth would significantly increase the power consumption of the device.

In 5G bandwidth can range minimum from5MHz to maximum 400MHz. High performance is require for the end user UE if  it’s support a maximum of 400MHz and this can be a disadvantage for reducing the cost of the UE. 


It is impossible for one UE to occupy the entire 400M bandwidth at the same instant. At the same time it will be undoubtedly waste of performance if the UE adopts the sampling rate corresponding to 400M bandwidth. Also, large bandwidth means high sampling rate and high sampling rate means high power consumption.

This same assumption that all devices are able to receive the full carrier bandwidth is not sensible as far as NR is concerned, given very wide carrier bandwidth supported.

Therefore, the means for handling different device capabilities in terms of bandwidth support must be included in the NR design.

So to overcome this a better approach is used in NR that is to use receiver bandwidth adaptation such  that the device can use a narrower bandwidth for monitoring control channels and to receive small to medium sized data transmissions and to open the full BW when a large amount of data is scheduled.

So basically BWPs (bandwidth parts) is defined in NR to handle these two aspects –

·        To support for devices not capable of receiving the full carrier BW

·        And receiver side BW adaption

Bandwidth part and its configuration:

Bandwidth part is a contiguous set of physical resource blocks with same subcarrier spacing and thus has the same numerology. 

The bandwidth part is abbreviated as BWP. A BWP is characterized by subcarrier spacing and cyclic prefix (numerology) and a set of consecutive resource blocks in the numerology of BWP, starting at a certain common resource block and can be configure flexibly.

                    

The bandwidth of the BWP must be greater than or equal to the SSB.

But it is not necessary that BWP include the SSB.

Stay tune to learn more about BWP ............


--Pinal Dobariya

Reference:

3gpp 38.213

3gpp 38.214 

3gpp 38.321

3gpp 38.331

https://arxiv.org/ftp/arxiv/papers/1712/1712.09724.pdf