SC-FDMA & OFDMA in LTE physical layer

This paper provides the introduction of LTE and the key components of its physical layer. These descriptions are simplified version of the detailed descriptions provided by 3gpp. In LTE, the OFDMA is used as downlink and SCFDMA as uplink modulation schemes; with OFDM as the basic building block. OFDMA is used for achieving high spectral efficiency in communication system; whereas, SC-FDMA for uplink multiple access scheme in LTE system. This paper evaluates the performance of SC-FDMA and OFDMA of LTE physical layer by considering different modulation schemes (BPSK, QPSK, 16QAM and 64QAM) on the basis of PAPR, BER and error probability. From the simulated results, it is observed that for a particular value of SNR, the BER increases for high order modulation (16- QAM and 64-QAM) in both OFDMA and SC-FDMA. However, the lower order modulation schemes (BPSK and QPSK) experience less BER at receiver; thus lower order modulations improve the system performance in terms of BER and SNR. In terms of bandwidth efficiency, the higher order modulation accommodates more data within a given bandwidth and is more bandwidth efficient as compared to lower order modulation. Thus, there exists a tradeoff between BER and bandwidth efficiency among these modulation schemes used in LTE. It is also observed that the error probability increases as order of modulation scheme increases. Therefore, the selection of modulation schemes in adaptive modulation is quite crucial based on these results.