5G NR Reference Point A And Bandwidth Parts
5G NR Reference Point A And Bandwidth Parts are two very important concepts. If you remember in LTE, all the devices are capable of decoding full carrier bandwidth. As the maximum carrier bandwidth is only 20MHz, it was okay to make all the devices with same capabilities. Also the carrier bandwidth are centered around the carrier frequency in LTE.
But in case of 5g we have large bandwidth. The maximum carrier bandwidth can be up to 400 MHz. It is not realistic to make all devices capable of receiving entire 400 MHz bandwidth because of cost factor. So, 5G NR devices may receive only part of the bandwidth. For efficient utilization of the carrier, the bandwidth received by the devices may not be centered around the carrier frequency.
Therefore in 5g there are concepts of NR reference point A and bandwidth part. These two parameters are needed by the Devices to decode data in NR.
5G NR Reference Point A
- Reference point A coincides with sub carrier 0 of common resource block 0 for all sub carrier spacing.
- Point A may be located outside the actual carrier.
- The reference point A act as a reference from where frequency structure can be described.
- After detecting the SSB, the devices gets the location of reference point A by decoding the broadcast system information (SIB1).
- All the physical resource blocks which transmit actual signals are located relative to this reference point.
5G NR Bandwidth Parts
LTE was designed assuming that all the devices would be capable of receiving full carrier bandwidth. It allows the control channels to span over the full carrier bandwidth to maximize the frequency diversity.
But same assumption that all devices would receive full carrier bandwidth is not reasonable in 5G NR. Reception of wide bandwidth can be costly in terms of power consumption compared to narrow bandwidth signal. So, 5G cannot have same approach as LTE where down link control channels span over whole carrier bandwidth.
Therefor a better approached was proposed for NR. This approach is receiver bandwidth adaptation. With this approach the device can monitor narrow bandwidth for control channels. It can also use narrow band to receive small to medium sized data and use full bandwidth when amount of data is large.
So to support these two aspects receiver bandwidth adaptation and device not capable of receiving full bandwidth, NR has introduced Bandwidth Parts.
The CORSET configuration information received from PBCH defines the initial bandwidth parts in the downlink
The initial active up link bandwidth part is obtained by decoding the broadcast system information(SIBs). These SIBs are scheduled by PDCCH.
