BER performance analysis of optical NOMA-OFDM system and its application in hybrid LIFI

Abstract

In optical wireless communication, data transfer between transmitter and receiver occurs wirelessly using visible light wave as carrier. Bit Error Rate (BER) is one of the most important performance measure of any communication system. In this thesis, performance of different optical Orthogonal Frequency Division Multiplexing (OFDM) modulation schemes such as Asymmetrically Clipped Optical OFDM (ACO-OFDM), DC Biased Optical OFDM (DCO-OFDM) and Asymmetrically Clipped DC Biased Optical OFDM (ADO-OFDM) is evaluated by measuring BER. Multiuser system has been evaluated considering Non Orthogonal Multiple Access (NOMA) scheme based on static and dynamic power allocation strategies. Static power allocation strategy such as Fixed Power Allocation (FPA) and dynamic power allocation strategies such as Gain Ratio Power Allocation (GRPA) and Normalized Gain Difference Power Allocation (NGDPA) have been considered for allocating power to users. The BER performances have been evaluated for both 2-user and 3-user systems. The ACO-OFDM shows the best BER performance among the three followed by DCO-OFDM and then ADO-OFDM modulation scheme. Fixed Power Allocation performs well in predefined user locations and controlled indoor environments. Dynamic power allocation strategy GRPA works well where users are largely separated from each other. On the other hand, NGDPA works well where users are distributed in a very closely packed manner. Also a hybrid Lifi – Wifi system has been simulated and its SNR profile has been evaluated in the indoor environment. Hybrid TDMA – NOMA has been used for resource allocation to users of this system and 16-QAM based DCO-OFDM has been used as optical modulation scheme. A priority based resource allocation technique has been introduced in Hybrid TDMA-NOMA multiple access scheme. Resources are allocated to users based on their prioritization set at the Access point (AP). The sharing of resources among users has been determined by grouping them into two clusters: priority and non-priority. The BER and sum rate performance of the proposed system have been evaluated considering 4-user which includes one priority user and three non priority users.