Modeling OFDM irreducible BER with impact of CP length and CFO in multipath channel with small delay dispersion

Abstract

In this paper, we propose an analytical model for estimating the irreducible bit error ratio (BER) in multipath channel with small-extent delay dispersion, such as indoor, where the signal-to-noise ratio is high, implying dominance of intersymbol interference as error-generating mechanism. Both channel and overall orthogonal frequency-division multiplexing (OFDM) symbols are modeled stochastically, resulting with novel expression for the residual BER prediction that is shown to analytically distinguish power delay profiles with equal delay spreads but having different profile shapes. In addition, the model could simply accommodate insertion of cyclic prefix onto the OFDM symbol, providing a means for either testing adequacy of any applied (standard) cyclic prefix length or finding its optimal value as a compromise between the performance enhancement achieved by inserting cyclic prefix and the consequently added redundancy. Finally, the model was modified as to include the analysis of effects of subcarrier frequency inaccuracy or Doppler shift, by adding additional equivalent delay dispersion with equal effect on BER degradation, while considering the system virtually free of carrier frequency offset. All analytically achieved results and conclusions are tested and successfully verified by conducted extensive Monte Carlo simulations.

Suppressing the OFDM CFO‐Caused Constellation Symbol Phase Deviation by PAPR Reduction

“…Assuming distortionless transmission, ideally, a particular k-th original symbol̂, = , , can be extracted from the incoming overall OFDM symbol̂, at the receiver, by exploiting the orthogonality within the overall OFDM symbol time , as follows [1]:…”

“…With this regard, among various impairments that can degrade the physical layer transmission performance, let us consider one out of two major inherent weaknesses of OFDM systems-the CFO [1][2][3][4][5][6]. Although, strictly speaking, CFO is a random variable with certain distribution, it is always considered constant and equal for all subcarriers.…”

“…Accordingly, the graphs for the exemplar CFO values: 0 Hz, 5 Hz, 70 Hz, and 300 Hz [1], and unit observed symbol amplitude , are presented in Figures 2-3, following (27) for the rates of 13 and 18 Mbps, respectively.…”

“…Orthogonal Frequency-Division Multiplexing (OFDM) has become widely accepted due to its excellent transmission performance and high data rate under multipath fading conditions [1]. However, though OFDM performance has been subject to extensive investigations in the last two decades, specifically with regard to practical local area wireless networks (WiFi) and the fourth-generation (4G) mobile communication systems, the Long-Term Evolution (LTE) in particular [2][3][4], still it remains affected mainly by two OFDM drawbacks.…”

“…Therefore, utmost care is given to CFO estimation and compensation in OFDM wireless systems [6][7][8][9]. However, following the CFO compensation, still some residual CFO remains, which can degrade the OFDM transmission performance [1].…”