Orthogonal Frequency Division Multiplexing (OFDM)

— The Peak-to-Average Power Ratio (PAPR) reduction in Orthogonal Frequency Division Multiplexing (OFDM) system has gained widespread attention during the last decade, leading to the development of several techniques for PAPR reduction. To benefit from these techniques while overcoming their inherent shortcomings, more recent work shows the use of hybrid variants of these techniques. In this paper, we present a brief overview of the hybrid techniques adapted for PAPR reduction. We also comment on the computational complexity and practicability of these approaches. Furthermore the paper covers a variety of hybrid techniques combining simple schemes e.g. clipping, companding and more complex schemes such as partial transmit sequence.

The demand for high-speed mobile wireless communications is rapidly growing. Orthogonal Frequency Division Multiplexing (OFDM) technology promises to be a key technique for achieving the high data capacity and spectral efficiency requirements for wireless communication systems in the near future. An Orthogonal Frequency Division Multiplexing (OFDM) scheme offers high spectral efficiency and better resistance to fading environments. In OFDM the data is modulated using multiple numbers of sub-carriers that are orthogonal to each other because of which the problems associated with other modulation schemes such as Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI) is reduced. This paper deals with the analysis of OFDM System utilizing different modulation techniques over Rayleigh, Rician and Additive White Gaussian Noise (AWGN) fading environments with the use of pilot aided arrangement and finally the results are conveyed. The aim of this thesis is to provide practical solutions for OFDM communication system by showing its better performance on different channel using different modulation technique. We applied different channel like AWGN, Rayleigh and Rician over OFDM system. We analyzed the performance of OFDM system regarding different channel. We analyzed the performance and showed the most suitable channel for OFDM communication system. Moreover, we also applied different modulation scheme over OFDM system to show which modulation technique is more efficient for OFDM system. Here we used BPSK, QPSK, 16-QAM and 64-QAM modulation technique. From our experiment we found that, among AWGN & the fading channels (Rayleigh & Rician), AWGN channel has less BER and P(e) than others. So we can say that, for OFDM system, AWGN channel is most suitable. We also found that, in all environments BPSK shows better performance than QPSK, 16QAM & 64QAM. When modulation level increased, corresponding BER & Probability of error P(e) also increased.

5G networks have to offer extremely high capacity for novel streaming applications. One of the most promising approaches is to embed large numbers of co-operating small cells into the macro-cell coverage area. Alternatively, optical wireless based technologies can be adopted as an alternative physical layer offering higher data rates. Visible light communications (VLC) is an emerging technology for future high capacity communication links (it has been accepted to 5GPP) in the visible range of the electromagnetic spectrum (~370–780 nm) utilizing light-emitting diodes (LEDs) simultaneously provide data transmission and room illumination. A major challenge in VLC is the LED modulation bandwidths, which are limited to a few MHz. However, myriad gigabit speed transmission links have already been demonstrated. Non line-of-sight (NLOS) optical wireless is resistant to blocking by people and obstacles and is capable of adapting its’ throughput according to the current channel state information. Concurrently, organic polymer LEDs (PLEDs) have become the focus of enormous attention for solid-state lighting applications due to their advantages over conventional white LEDs such as ultra-low costs, low heating temperature, mechanical flexibility and large photoactive areas when produced with wet processing methods. This paper discusses development of such VLC links with a view to implementing ubiquitous broadcasting networks featuring advanced modulation formats such as orthogonal frequency division multiplexing (OFDM) or carrier-less amplitude and phase modulation (CAP) in conjunction with equalization techniques. Finally, this paper will also summarize the results of the European project ICT COST IC1101 OPTICWISE (Optical Wireless Communications - An Emerging Technology) dealing VLC and OLEDs towards 5G networks.

This paper studies control format indicator (CFI) estimation methods in 4G-LTE communication systems. CFI is an essential control signal in LTE, and must be correctly detected at the receiver to avoid degraded system performance. The standard method of CFI detection involves the use of the Maximum Likelihood (ML) estimation criterion. Unfortunately, ML decoding performance relies on accurate channel estimation, and as a consequence may result in poor CFI decoding when channel estimates are poor. To improve CFI detection in severe fading channel conditions, a time-domain decision rule that requires no channel estimation, is proposed. Results show that when compared with the ML approach, the proposed method reduces the probability of CFI estimation error in the form of reduced block error rate.