" Wireless " Learning in Telecom

Cell Search Procedure in LTE Thought of adding a small diagram, that explains the very important cell search procedure in LTE, which is the very first that any LTE UE will perform before initiating network entry procedure, For full explanation of cell search procedure Cell Search Procedure in LTE What is a cell search procedure? Who does this?  Why do we need this? How is this done? I will try to answer these questions related to the LTE cell search procedure. A cell search is nothing but a procedure that, any sniffer or a UE shall perform in order to get more details about the nearby eNodeB/cell. So this is the first step that a UE shall do, as soon as it is powered on. The cell search procedure, is the UE’s way of acquiring cell specific information and this, the UE has to perform once or several times based on the condition of the network. Basically the steps involved in cell search are as follows, after the UE is powered ON 1.  ...

What is  cyclic prefix or why do we need the CP in LTE or for that matter in any wireless/OFDM system? The answer lies in the name itself. Cyclic indicates that, the CP maintains the cyclic nature of something and prefix says it is added at the beginning. Basically, the CP is nothing but a portion of the signal itself, which is copied and added to the beginning of the signal. The below diagram should explain more about the same, Cyclic Prefix for LTE Why CP is added? Now to understand why CP is added, you should know the basics of FFT/IFFT or the significance of doing a FFT/IFFT over any signal. In LTE, for downlink, an IFFT is performed to realize the OFDM concept. Now, first place what does FFT does?What does IFFT does to a signal? If you take a FFT of a signal, you are basically taking the signal from time domain to frequency domain and for IFFT, it is the vice versa, i.e from frequency domain to time domain. Lets see what happens when we take a FFT of a...

Long Term Evolution (LTE) supports both FDD and TDD Duplex mode. The major difference in TDD and FDD is that in TDD system a single frequency is shared in time domain between Uplink  and Downlink where as in FDD separate frequencies are used for Uplink and Downlink transmission. A TDD frame structure is shown in below figure. 10 mili second radio frame consists of Downlink subframe, Uplink subframe and Special subframe. In TDD there are about 7 frame configurations, based on different DL/UL partition. Downlink/Uplink ratio can vary from 1/3 (Frame configuration = 0) to 8/1 (Frame configuration = 1). An operator can choose a specific TDD configuration depending on the service requirements Frame always starts with a Downlink subframe, used for advertising the frame descriptor information i.e. PCFICH and PDCCH. UE hence learns the frame structure in the subframe. 3rd frame is always used for Uplink transmission When switching from Downlink to Uplink, there is need for a Spe...

This article shall speak about the different data units in LTE, the terms used for describing the amount of data. The basic data units in LTE are as below, -->  Bits -->  Complex Symbols -->  Transport Block & Code Block --> Resource Element Group Bits The basic unit, in any digital communication system, a bit. Its a binary representation, in terms of 1 or 0. Even in LTE, the smallest data unit is a bit. The bits undergo various processing such as encoding, scrambling, modulation etc Complex Symbols A complex symbol, in LTE is nothing but a representation for a group of bits, when a bit or group of bits is digitally modulated using different modulation schemes such as QPSK, 16QAM or 64QAM, we get complex symbols. The symbols are complex numbers with different number of bits per symbol depending on the modulation scheme. Each complex symbol is mapped to a subcarrier in the LTE resource grid. Transport Block & Code Block A ...

I was asked by many engineers on PUCCH and PUSCH functionality and major difference. This thread describes PUCCH functionality and PUSCH functionality. I have tried to differentiate major difference between PUCCH and PUSCH where possible.After reading entire post reader can conclude PUCCH vs PUSCH. PUCCH :  The Physical Uplink Control Channel (PUCCH) is used to transfer Uplink Control Information (UCI). UCI can also be transferred using the PUSCH.  Please refer Different Channel State Information (CSI) Reporting Types. The release 8 and 9 versions of the 3GPP specifications do not allow an individual UE to transmit both the PUCCH and PUSCH during the same sub frame. For Release 8 and 9 if UE has application data or RRC signalling than UCI information transmitted via PUSCH. The release 10 version of the 3GPP specifications introduces the option to support simultaneous PUCCH and PUSCH transmission. 3GPP specify 7 PUCCH formats.Different...

Event Type Intrafrequency WCDMA Events Event 1A : Serving cell CPICH enters the reporting range Event 1B : Serving cell CPICH leaves the reporting range Event 1C : Neighbour Cell CPICH becomes better than the serving cell CPICH Event 1D : Change of best cell Event 1E : Serving cell CPICH becomes better than an absolute threshold Event 1F : Serving cell CPICH becomes worse than an absolute threshold Interfrequency WCDMA events Event 2A : Change of best frequency Event 2B : The estimated quality of the currently used frequency is below a certain threshold and the estimated quality of a non-used frequency is above a certain threshold Event 2C : The estimated quality of a non-used frequency is above a certain threshold Event 2D : The estimated quality of the currently used frequency is below a certain threshol Event 2E : The estimated quality of a non-used frequency is below a certain threshold Event 2F : The estimated quality of the currently used frequency is above a certain threshold I...