Showing posts from April, 2020

cell selection part-1

Home                 LTE                NB-IoT               5G(NR-NSA) In this section, we will learn about cell selection basics for SA and LTE. What is cell selection? If a device is under circumstances where UE needs to be switched on or after UE has left RRC connected mode or UE returns to a coverage area, it sees many base stations around it. Many a times UE might be surrounded by multiple base stations from different operators. So from this many base stations, UE can register to only one cell. So to register to a specific cell UE goes through a dedicated process. This specific decision making process where UE decides to which cell to camp on is known as cell selection. Is the initial cell selection procedure reacquired in the case of NSA ? When UE is connected to MCG that time only cell selection procedure is reacquired. Note: ENDC cells (SCG) are not used for initial cell selection. What is the cell selection procedure for LTE and SA? Cell selectio

Reference signals Part-3

Home                 LTE                NB-IoT               5G(NR-NSA) In the previous section, we learn about the DMRS, TRS, SRS reference signals. in this section, we will learn the remaining reference signals:- PTRS: What is PTRS? Now next is PTRS, this reference signal is introduced in NR to enable compensation of oscillator phase noise. Usually, phase noise increases as a function of the oscillator carrier frequency. Thus PTRS can be utilized at high carrier frequencies such as mm wave to reduce phase noise. In an OFDM signal, one of the main degradations caused by phase noise is an identical phase rotation of all the subcarriers, called as common phase error or CPE. it is designed so as to have high density in the time domain   and   low density in the frequency domain, as the phase rotation produced by common phase error is identical for all subcarriers within an OFDM symbols, but there is low correlation of phase noise across OFDM symbols. This RS is UE

Reference signals Part-2

Home                 LTE                NB-IoT               5G(NR-NSA) In this section, we will learn about the different reference signals. Now in order to keep the transmissions contained within a slot without having to depend on other slots and beams as well as to increase the protocol efficiency NR introduces the following reference signals:- (QUS: what are the types of reference signals in NR (5G)?) Demodulation reference signal (DMRS) Sound reference signal (SRS) Tracking reference signal (TRS)          Phase tracking reference signal (PTRS) Channel state information reference signal (CSI-RS) Why are reference signal required? RS are required for the demodulation of user data and channel estimation. The reference signal transmission frequency is adaptive in NR. DMRS : (QUS: What is DMRS?) & (QUS: Can we transmit DMRS in DL and UL both direction in NR?) DMRS is used to evaluate the radio channel for demodulation. It is UE specific, confined in a sc

DC Carrier in NR_2

Home                 LTE                NB-IoT               5G(NR-NSA) In this article, we will learn the interview QUS and ANS of DC Carrier for NR and LTE and why it is needed. Why in LTE, Data is not transmitted on DC subcarrier? DC subcarrier is typically excluded in LTE because it can suffer interference from local oscillator leakage. Local oscillator leakage can impact the performance of the DC subcarrier. Why in NR, Data is transmitted on DC subcarrier? New Radio (NR) allows the DC subcarrier to be used based upon the assumption that modern transceivers are able to manage the impact of local oscillator leakage. For Different BWP, is it possible to configure DC subcarrier location? Yes, the network can configure different DC locations for different BWP. In Which message The device can find DC subcarrier location in the case of ENDC (NSA)? In RRC reconfigure msg for SCG addition (which is also known as CG-config) In Which message The device can find