Interference Localization for Uplink OFDMA Systems in Presence of CFOs

Multiple carrier frequency offsets (CFOs) present in the uplink of orthogonal frequency division multiple access (OFDMA) systems adversely affect subcarrier orthogonality and impose a serious performance loss. In this paper, we propose the application of time domain receiver windowing to concentrate the leakage caused by CFOs to a few adjacent subcarriers with almost no additional computational complexity. This allows us to approximate the interference matrix with a quasi-banded matrix by neglecting small elements outside a certain band which enables robust and computationally efficient signal detection. The proposed CFO compensation technique is applicable to all types of subcarrier assignment techniques. Simulation results show that the quasi-banded approximation of the interference matrix is accurate enough to provide almost the same bit error rate performance as that of the optimal solution. The excellent performance of our proposed method is also proven through running an experiment using our FPGA-based system setup.Comment: Accepted in IEEE WCNC 201

Analysis and mitigation of carrier frequency offset for uplink of OFDMA

Orthogonal Frequency Division Multiplexing (OFDM) is being used in many wireless standards because of its immunity to multipath fading, high spectral efficiency and simple implementation, making it suitable for high data rate multimedia wireless applications. One of the significant drawbacks of the OFDM is its sensitivity to Carrier Frequency Offset (CFO). CFO causes Inter Carrier Interference (ICI) between subcarriers and Multiple User Interference (MUI) at Uplink between different users. ICI and MUI at uplink cause significant degradation in the performance of the receiver, therefore, to improve the receiver performance up to acceptable level, compensation of the CFO becomes necessary. In this research, Suppression of MUI by Minimum Mean Squared Error (MMSE) Feedback Equalizer in frequency domain which was originally proposed for Single Carrier- Frequency Domain Multiple Access (SC-FDMA) has been studied for Uplink of Orthogonal Frequency Division Multiple Access (OFDMA). However, calculation of MUI power required in this algorithm for all users impose very high computational burden on the receiver. In the proposed Low Complexity MUI Suppression by MMSE Equalization for Uplink of OFDMA approximation to the calculation of MUI power is applied to reduce its complexity. Simulation result & calculated complexity show that proposed method obtains good performance with much lower complexity

Timing and Carrier Synchronization in Wireless Communication Systems: A Survey and Classification of Research in the Last 5 Years

Timing and carrier synchronization is a fundamental requirement for any wireless communication system to work properly. Timing synchronization is the process by which a receiver node determines the correct instants of time at which to sample the incoming signal. Carrier synchronization is the process by which a receiver adapts the frequency and phase of its local carrier oscillator with those of the received signal. In this paper, we survey the literature over the last 5 years (2010–2014) and present a comprehensive literature review and classification of the recent research progress in achieving timing and carrier synchronization in single-input single-output (SISO), multiple-input multiple-output (MIMO), cooperative relaying, and multiuser/multicell interference networks. Considering both single-carrier and multi-carrier communication systems, we survey and categorize the timing and carrier synchronization techniques proposed for the different communication systems focusing on the system model assumptions for synchronization, the synchronization challenges, and the state-of-the-art synchronization solutions and their limitations. Finally, we envision some future research directions

Clock Error Impact on NB-IoT Radio Link Performance

3GPP has recently addressed the improvements in Random Access Network (RAN) and specified some new technologies such as enhanced Machine Type Communication (eMTC) and Narrow Band – Internet of Things (NB-IoT) in its release 13 which is also known as LTE-Advanced Pro. These new technologies are addressed mainly to focus on development and deployment of cellular IoT services. NB-IoT is less complex and easily deployable through software upgradation and is compatible to legacy cellular networks such as GSM and 4G which makes it a suitable candidate for IoT. NB-IoT will greatly support LPWAN, thus, it can be deployed for Smart cities and other fields such as smart electricity, smart agriculture, smart health services and smart homes. The NB-IoT targets for low cost device, low power consumption, relaxed delay sensitivity and easy deployment which will greatly support above mentioned fields. This thesis work studies the clock error impact on the radio link performance for up-link transmission on the NB-IoT testbed based on Cloud-RAN using Software Defined Radios (SDR) on a LTE protocol stack. The external clock error is introduced to the network and performance issues are analyzed in the radio link. The analysis indicates packet drops up to 51% in the radio link through the study of received power, packet loss, retransmissions, BLER and SINR for different MCS index. The major performance issues depicted by the analysis are packet loss up to 51% and retransmission of packets up to 128 times for lower SINR and high clock errors. Also, clock errors produce CFO up to 1.25 ppm which results in bad synchronization between UE and eNodeB

Inter-carrier interference suppression in orthogonal frequency division multiple access (OFDMA) systems uplink

Ph.DDOCTOR OF PHILOSOPH