ENERGY HARVESTING USING CYCLIC PREFIXED OFDMA

Abstract

Generally, in wireless systems, battery provides power needed by the receiver for performing signal processing on received signal and the life of this battery restricts the receiver performance. These mobile wireless systems communicate using RF signals. If it is possible to extract energy from RF signal, then the constraint on receiver performance due to battery life can be removed. Orthogonal Frequency Division Multiplexing (OFDM) is widely being used in cellular telecommunication standard LTE. It is also popular for indoor communica- tion standards like Wi-Fi (802.11a, 802.11c and more) and Wi-MAX. OFDM symbol structure consists of two parts: information and redundant portion called cyclic pre- x . At receiver, this cyclic pre x is completely discarded and it doesn't take part in any further signal processing. So, all the power used for it is being wasted. In this report, it is shown that if instead of discarding the cyclic pre x, we retrieve it and extract its energy then fully self-sustainable receivers (without the need of battery) are possible under certain conditions. Firstly, this report discusses the conditions under which self-sustainable trans- mission (partial or full) is possible. Then the dependence of level of self-sustainability on cyclic pre x size, number of sub-carriers and power budget is observed. We found the probability of full self-sustainability for di erent systems. At rst, all these re- sults are obtained for single user system, then extended for multiple user systems. It is shown that self-sustainability level decreases as number of users increases. In practical systems, pathloss (depends on distance between transmitter and receiver) and shadowing (di erent environment clutter for same transmitter and receiver distance) are present. We check what level of self-sustainability can be achieved for practical systems and we show that how it varies for di erent cellular systems with di erent number of users. Presence of cyclic pre x contributes spectral e ciency loss at transmitter, how- ever, we can exploit it for extracting energy. We show that at maximum (with highest possible cyclic pre x size), how much spectral e ciency loss occurs. A composite approach for OFDM transmission is de ned in which two indepen- dent signals are transmitted to receiver and is shown that second signal (CIA signal) does not contribute any interference to information signal and how it improves the level of self-sustainability.