Abstract
Multicarrier systems such as orthogonal frequency division (OFDM) are considered as a promising candidate for wireless networks that support high data rate communication. In this article, we investigate the perform-ance of a multiuser OFDM system under imperfect synchronization. Analytical results indicate that the SNR degrades as the average power of the channel impairments such as AWGN, carrier frequency offset due to Doppler frequency and fading gain is increased. The SNR degradation leads to imperfect synchronization and hence decreases the total number of subcarriers available for allocation. Monte Carlo analysis shows up to 22% loss in the number of allocatable subcarriers can be expected under a specific imperfect synchroniza-tion condition as compared to perfect synchronization. We utilize empirical modelling to characterize the available number of subcarriers as a Poisson random variable. In addition, we determine the percentage de-crease in the total number of allocatable subcarriers under varying channel parameters. The results indicate 19% decrease in the number of available subcarriers as average AWGN power is increased by 10dB; 44% decrease as the Doppler frequency is varied from 10Hz to 100Hz; and 56% decrease as the fading gain is varied from 0dB to -30dB.
Highlights
The growing demand for high-speed wireless communications has led to the investigation of spectrally effcient systems for downlink transmission in multicarrier systems [1]
Orthogonal Frequency Division Multiplexing (OFDM) based systems are sensitive to carrier frequency offset (CFO), which leads to the loss of orthogonality between the subcarriers and introduction of inter-channel interference (ICI) [4]
Since practical systems are subject to imperfect synchronization, the analysis indicates that determining the availability of subcarriers for transmission is essential in the optimization process of radio resource allocation for multiuser systems
Summary
The growing demand for high-speed wireless communications has led to the investigation of spectrally effcient systems for downlink transmission in multicarrier systems [1] Multicarrier systems such as Orthogonal Frequency Division Multiplexing (OFDM) enable the network to provide high data rate communication by using adaptive subcarrier allocation. The performance improvement is achieved when the system is based on perfect synchronization and the utilization of instantaneous channel information to adaptively allocate subcarriers. The number of allocatable subcarriers as compared to perfect synchronization decreases which translates to a decrease in the aggregate data rate for a given number of users, the BER performance of the system could be improved by avoiding allocation on subcarrriers that are not suitable for transmission.
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