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What is SC-FDMA and how it works in LTE?

What is SC-FDMA and how it works in LTE? One of the major drawbacks of an OFDMA system is, that the transformation of a complex symbol mapped sequence (e.g. BPSK, QPSK, etc.) onto a small set of subcarriers produces time sequences that have high PAPR (Peak-to-Average Power Ratio). PAPR is the ratio between the maximum … Read more

Inter-Symbol Interference in LTE

Inter-Symbol Interference in LTE Definition: ISI is a phenomenon in LTE where symbols transmitted over a communication channel overlap, causing distortion in the received signal. Causes: Multipath Propagation: Signals take multiple paths with different delays, leading to overlapping symbols. Time Dispersion: Variation in signal arrival times at the receiver contributes to ISI. Impact on LTE: … Read more

Constellation in LTE

Constellation in LTE In LTE (Long-Term Evolution), the term “constellation” typically refers to the modulation scheme used for transmitting data over the air interface. LTE uses Quadrature Amplitude Modulation (QAM) to encode multiple bits into a single symbol. The constellation diagram visually represents how the amplitude and phase of the modulated signals correspond to specific … Read more

OFDM implementation in Detail

A typical OFDM transmitter is shown on the following figure. To reduce the amount of RF hardware required for OFDM the modulation process is split into two parts. A first part uses the inverse discrete Fourier transform (IDFT) or one of its more efficient but equivalent implementations known as Inverse Fast Fourier Transform to modulate … Read more

Difference Between OFDM and FDM in LTE

FDM in LTE Conventional multi-carrier operation as it is used for FDM works simply by selecting a number of center frequencies – one for each carrier to be used. The center frequencies must be spaced. In fact there is a trade-off between minimizing interference between different carriers and using the total  bandwidth efficiently. In other … Read more

Pulse shaping and spectrum in LTE

RF engineering is a trade off between: required radio spectrum (bandwidth), speed of data transmission (bit rates) and complexity of implementation. The pulse form used to modulate complex data symbols to the radio carrier frequency is the major element of this story. Over the years several pulse forms and their associated pulse shaping filters have … Read more

Orthogonal Code Usage – Coding & Decoding in WCDMA

How Orthogonal Code works in WCDMA? 1.Coding By spreading, each symbol is multiplied with all the chips in the orthogonal sequence assigned to the user. The resulting sequence is processed and is then transmitted over the physical channel along with other spread symbols. In this figure, 4-digit codes are used. The product of the user … Read more

System information & DL-SCH data in LTE

System information 1920 bits or 1728 bits are to be transmitted for normal or extended CP resp.. The PBCH is transmitted every 40 ms. The bit scrambling depends on the cell id and is starting in radio frames 0, 4, 8 … . PBCH uses QPSK. I.e. 960 (864) symbols need to be allocated. Mapping … Read more

OFDMA Parameter for LTE

How Many OFDMA Parameter for LTE? Which is OFDMA Parameter for LTE ? The width of a Sub-carrier is 15 kHz whatever the bandwidth The bandwidths are: 1.4, 3, 5, 10, 15 and 20 MHz Note that in LA1.1, only 5, 10 MHz are implemented  The symbol duration is always the same whatever the bandwidth … Read more

Ways to transmit training symbols: preamble or pilot tones in Wimax

There are two ways to transmit training symbols: preamble or pilot tones. Preambles entail sending a certain number of training symbols prior to the user data symbols. In the case of OFDM, one or two preamble OFDM symbols are typical. Pilot tones involve inserting a few known pilot symbols among the subcarriers. Channel estimation in … Read more