Narrowband Signal Detection in OFDM Systems Using Spectral Shaping Techniques

Abstract: Orthogonal Frequency Division Multiplexing (OFDM) allow data to be transmitted efficiently and reliably by using multiple orthogonal subcarriers. It provides robustness against noise and corruption in the channel. The channel can be either wired or wireless depending on the particular application. Due to the close spacing of subcarriers, OFDM is susceptible to corruption caused by various narrowband signals such as Narrowband Interference (NBI). Spectral shaping shapes the Power Spectral Density (PSD) in order to have certain properties. Spectral shaping might improve the effectiveness of OFDM and make it sustainable in the long run for applications beyond the 4th generation of mobile communications (4G) and Long Term Evolution (LTE). We make use of spectral null codes and load them onto OFDM subcarriers. Introducing narrowband signals in the channel degrades the system’s performance and also eliminates the designed spectral properties. From this observation we infer that some narrowband noise is present in the channel. Previously, carriers hit by NBI or other narrowband noise had to be switched off manually. We found that combining OFDM with spectral shaping allows the presence of Narrowband signals in the channel to be detected and conclusions can be drawn over the channel quality. This did not improve the system in terms of bit error rate performance

Optimised orthogonal frequency-division multiplexing based communication systems for wireless environments

Abstract: The demand for wireless access to the internet is constantly increasing and the applications such as social media, gaming and video require a high bandwidth connections. Mobile technologies are becoming more affordable and accessible. Existing telecommunications systems can be improved to ensure that it is sustainable for future generations. Orthogonal Frequency Division Multiplexing (OFDM) is a good candidate which is already used widely in wireless applications. It is robust against many of the multipath effects commonly encountered in wireless channels. It also makes efficient use of the limited radio spectrum. Certain parameters of the OFDM system have been investigated and recommendations on the optimal parameters are made in order to achieve the best bit error rate (BER) performance. These investigations have been conducted by designing a comprehensive and configurable simulation of the OFDM system, including an adapted modulator and demodulator and an accurate channel model. The guard interval is an important design consideration as it counters Inter Symbol Interference (ISI). The optimal length of the guard interval should be less than 25% of the total symbol length. As shorter guard interval results in more usable bandwidth. The choice of quadrature amplitude modulation (QAM) scheme to use is also an important one and the optimal design depends on the throughput requirements of the system. The number of subcarriers depends on the available bandwidth and the subcarrier spacing....M.Ing. (Electrical Engineering

Effects of spectral null codes on PAPR and BER performance in OFDM systems

Abstract: Spectral null codes has a wide range of applications, and it has been shown that the Power Spectral Density (PSD) of messages in Orthogonal Frequency Division Multiplexing (OFDM) systems can be shaped to have nulls at designed frequencies. Peak to average power ratio (PAPR) is a common problem with OFDM, resulting in power intensive and more expensive modulators which are not suitable for modern mobile devices with limited battery life. The use of PAPR reduction techniques in OFDM is crucial in order to make it compatible with modern devices. We investigate the effect of spectral null codes on the performance of the OFDM system. In particular we focus on the bit error rate performance (BER) and the PAPR performance. We show that the use of spectral null codes has no negative impact on either the BER or PAPR performance, as expected. We conclude that the spectral null coding technique may be used to shape the PSD in OFDM systems without causing any significant negative impact on performance

Draft genome sequences of Armillaria fuscipes, Ceratocystiopsis minuta, Ceratocystis adiposa, Endoconidiophora laricicola, E-polonica and Penicillium freii DAOMC 242723

The genomes of Armillaria fuscipes, Ceratocystiopsis minuta, Ceratocystis adiposa, Endoconidiophora laricicola, E. polonica, and Penicillium freii DAOMC 242723 are presented in this genome announcement. These six genomes are from plant pathogens and otherwise economically important fungal species. The genome sizes range from 21 Mb in the case of Ceratocystiopsis minuta to 58 Mb for the basidiomycete Armillaria fuscipes. These genomes include the first reports of genomes for the genus Endoconidiophora. The availability of these genome data will provide opportunities to resolve longstanding questions regarding the taxonomy of species in these genera. In addition these genome sequences through comparative studies with closely related organisms will increase our understanding of how these pathogens cause disease