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
Synchronization in LTE Mobile "Switch On" Primary and Secondary Synchronization Signals occupy 2 blocks of symbols per 10 ms (central 72 subcarriers for all channel bandwidths). An example is shown below for 72 subcarrier- (1.4 MHz) / single antenna case. During the initial cell search, the mobile station searches for the strongest cell. It then … Read more
Benefits of SC-FDMA Receiver in LTE Low Peak-to-Average Power Ratio (PAPR): SC-FDMA (Single-Carrier Frequency Division Multiple Access) exhibits a lower PAPR compared to other modulation schemes, reducing the demand for power amplifiers with high linearity. Improved Power Efficiency: Lower PAPR contributes to improved power efficiency, making SC-FDMA well-suited for mobile devices with limited battery capacity. … Read more
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
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
The price for the optimum subcarrier spacing is the sensitivity of OFDM to frequency errors. If the receiver’s frequency is some fractions of the subcarrier spacing (subcarrier bandwidth) then we encounter not only interference between adjacent carriers, but in principle between all carriers. This is known as Inter-Carrier Interference (ICI) and sometimes also referred to … Read more
OFDMA is essentially a hybrid of FDMA and TDMA: Users are dynamically assigned subcarriers (FDMA) in different time slots (TDMA) . The advantages of OFDMA start with the advantages of single-user OFDM in terms of robust multipath suppression and frequency diversity. In addition, OFDMA is a flexible multiple-access technique that can accommodate many users with … Read more
For channel estimation different types of reference signals are in use: – Cell specific reference signals. – MBSFN reference signals. – UE specific reference signals CELL-SPECIFIC REFERENCE SIGNALS These signals are transmitted for all non-MBSFN subframes only where subcarrier spacing is 15 kHz. In MBSFN subframes only the first 2 OFDM symbols can be used. … Read more
SC-FDMA utilizes single carrier modulation, DFT-spread orthogonal frequency multiplexing, and frequency domain equalization. LTE uses OFDMA on the DL. It allocates DL bandwidth to the user based on resource blocks, rather than individual subcarriers. When the signal is a combination of subcarriers, high amplitude power peaks can occur. The base stations power amplifiers are designed … Read more
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