This article will totally focus on SC-FDM and OFDM. The difference and their application in 5G communication.
The single carrier transmission means one Radio Frequency carrier is used to carry the information. Hence information in the form of bits is carried by one single RF carrier. OFDM also known as multicarrier transmission or modulation, uses multiple carrier signals at different frequencies. Sending some of the bits on each channel
OFDM and OFDMA subcarrier location
With standard OFDM the subcarrier allocations are fixed for each user and performance can suffer from narrowband fading and interference. OFDMA incorporates elements of Time Division Multiple Access (TDMA) so that the subcarriers can be allocated dynamically among the different users of the channel. The result is a more robust system with increased capacity. The capacity comes from the trunking efficiency gained by multiplexing low rate users onto a wider channel to provide dynamic capacity when needed, and the robustness comes from the ability to schedule users by frequency to avoid narrowband interference and multipath fading.
Let’s See the Block diagram of OFDM and SC-FDM
As shown in the above figure in SC-FDMA one extra module DFT is added before the IFFT module in the transmitter chain and IDFT is added in the receiver chain. This converts the OFDM chain to the SC-FDMA chain. Without these two modules, the chain is referred to as OFDM transmit and receive chain.
SC-FDMA system usually has low PAPR(Peak to Average Power Ratio) compare to the OFDM system.
SC-FDMA system is less sensitive to frequency offset compared to the OFDM system.
SC-FDMA is widely used in LTE subscriber terminals in the transmit path and variant OFDMA is used in the eNodeB downlink(or receive path of LTE subscriber).
OFDM is referred to 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 case of OFDM, total subcarriers are divided into subchannels and these subchannels are mapped to one single data/traffic source.
Q. What is the merit OFDM?
Ans: SC-FDMA has merits as mentioned above. OFDM also has many advantages compare to SC-FDMA.
Frequency selective fading will be able to affect a few of the subchannels/subcarriers and not the entire band.
OFDM overcomes the effect of ISI occurring mostly in the multipath channel environment.
Q. Why to reduce PAPR?
Ans: The PAPR stands for Peak to Average Power Ratio of a time-domain signal x(t). It is the ratio between maximum instantaneous power and its average power. It has been found that if PAPR is lower, power efficiency is higher and hence increase the battery usage for a long time.
Note: PAPR is directly proportional to the square of the number of carriers.
BER performance comparison of OFDM & SC-FDMA Using ZF(Zero Forcing) Equalizer.
The performance of SC-FDM & OFDM is approximately similar when we don’t consider the effect of channel or consider 1 tap channel in the system.
The performance of SC-FDMA is slightly better, compare to OFDM when we include the effect of the channel for MMSE case
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This Article contributed by Anil Kr Shaw.
Anil Kr Shaw post graduated from Indian Institute of Technology (IIT) Hyderabad with specialization in Communication & Signal Processing..
You may reach him on Linkedin : https://www.linkedin.com/in/anil-kr-shaw-wildmelophile/