This LTE Tutorial Covers LTE Cell Search Procedure Used by UE

This LTE tutorial covers LTE Cell Search Procedure used by UE.
A cell search procedure is used by the UE to acquire time and frequency

synchronization with a LTE cell and UE detects the physical layer Cell ID
(PCI) of that cell. Two cell search procedures in LTE: initial synchronization
and detecting neighbor cells in preparation for handover LTE uses a
hierarchical cell search scheme similar to WCDMA
Step-1: After being powered on, UE tunes the RF and attempts to measure
the wideband received power (RSSI) for specific frequencies (channels as
commanded by higher layer) over a set of supported frequency bands one
after another and ranks those cells based on signal strength.
Step-2: Then it uses downlink synchronization channels i.e. locally stored P-

SS and S-SS to correlate with received one. UE first finds the primary
synchronization signal (PSS) which is located in the last OFDM symbol of first
time slot of the first and 5th sub-frames This enables UE to be synchronized
on sub-frame level.Primary Synchronization Signal helps for Slot Timing
Detection and Physical Layer ID (0,1,2) detection.
Step-3:: secondary synchronization symbols are also located in the same sub-
frame of P-SS but in the symbol before P-SS. From secondary SS, UE is able
to obtain physical layer cell identity group number (0 to 167) It helps for Radio
Frame Timing detection, find Physical Layer Cell ID, cyclic prefix length
detection, FDD or TDD detection. The same is depicted in the LTE cell
search procedure figure below.
Step-4: Once UE knows the PCI for a given cell, it also knows the location of
cell Reference signals - which are used for channel estimation, cell selection /
reselection and handover procedures. After channel estimation using
RS(reference signal), MMSE equalization is performed to remove the effect of
channel impairment from the received symbols.
This page describes LTE UE network entry procedure which covers cell
search procedure, system information decoding and random access
procedure as required for LTE UE to complete network entry with eNB.
The figure depicts all the process as required for LTE UE to camp on to LTE
compliant eNB or LTE cell. Step 1: LTE UE uses PSS and SSS to determine
physical layer cell identity (PCI) (1 out of 504).
For more visit our page on LTE UE cell search procedure.
Step 2: After cell search procedure is completed, LTE UE decodes following

using PBCH channel.
Master Information Block which is transmitted on BCH at the periodicity of
40ms, which is carrying system bandwidth, PHICH configuration, SFN number
of transmit antennas.
System Information Block Type 1 which is transmitted on DL-SCH at the

periodicity of 80ms, which is carrying PLMN IDs, tracking area code, cell
identity, access restrictions, scheduling information and more. SI-RNTI is used
on PDCCH to address System Information Block Type 1 and SI Messages.
Step 3 (a) : Random access procedure is intiated by UE by sending random
access preamble on PRACH. eNB responds with random access response on
PDSCH.
Step 3 (b) : The data transmission is scheduled on PUSCH. The contention

resolution is taken care by MAC and the same is intimated to UE by eNB on
DL-SCH.
This page describes difference between SC-FDMA and OFDM modulation

techniques.
SC-FDMA means Single Carrier Frequency Division Multiple Access
and OFDM means Orthogonal Frequency Division Multiplexing.
As shown in the figure in SC-FDMA one extra module DFT is added before
IFFT module in the transmitter chain and IDFT is added in the receiver chain.
This converts OFDM chain into SC-FDMA chain. Without this two modules the
chain is referred as OFDM transmit and receive chain.
SC-FDMA system usually will have low PAPR compare to OFDM system.
SC-FDMA system is less sensitive to frequency offset compare to OFDM

system.
SC-FDMA is widely used in LTE subscriber terminals in the transmit path and
its variant OFDMA is used in the eNodeB downlink(or receive path of LTE
subscribers). While OFDM is used in many broadband technologies such as
wimax-16d/16e, WLAN-11a/11n/11ac.
OFDM is referred as multicarrier modulation. It uses multiple rf carrier signals

at different frequencies which sends some of the bits on each of the assigned
channels. This seems to be similar to FDM but in the case of OFDM, total
subcarriers are divided into subchannels and these subchannels are mapped
to one single data/traffic source.

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This LTE Tutorial Covers LTE Cell Search Procedure Used by UE

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This LTE tutorial covers LTE Cell Search Procedure used by UE.

A cell search procedure is used by the UE to acquire time and frequency

Step-2: Then it uses downlink synchronization channels i.e. locally stored P-

Step 2: After cell search procedure is completed, LTE UE decodes following

System Information Block Type 1 which is transmitted on DL-SCH at the

Step 3 (b) : The data transmission is scheduled on PUSCH. The contention

This page describes difference between SC-FDMA and OFDM modulation

SC-FDMA system is less sensitive to frequency offset compare to OFDM

OFDM is referred as multicarrier modulation. It uses multiple rf carrier signals

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