Abstract
The main OFDM drawbacks are Carrier Frequency Offset (CFO) and large Peak-to-Average Power Ratio (PAPR), which both degrade the Bit Error Rate (BER). Specifically, we consider here clipping or any other PAPR reduction method sufficient to prevent the nonlinear high-power amplifier from generating errors. Moreover, in small cells, the signal-to-noise ratio is large, while the small time dispersion allows the OFDM symbol cyclic prefix to prevent intersymbol interference. This retains the CFO to solely determine the BER and vice versa, enabling indirect estimation of CFO-induced phase distortion by simple BER testing. However, a particular problem is measuring very low BER values (generated by alike residual CFO), which could last a long time in order to acquire statistically enough errors. The test time can be drastically reduced if the noise margin is reduced in a controllable way, by adding the interfering signal to each subcarrier at the receiver. This approach is shown to enable efficient and accurate short-term BER (and so CFO phase error) testing.
Highlights
Carrier Frequency Offset (CFO) and large Peak-to-Average Power Ratio (PAPR) are the immanent and dominating impairments of Orthogonal Frequency-Division Multiplexing (OFDM), degrading the Bit Error Rate (BER)
CFO that we focus here can significantly degrade the orthogonality among the subcarriers, so paving the way to Inter-Carrier Interference (ICI) and consequent carrier lock errors, which shrinks the effective noise margin [1,2,3]
It is important to measure CFO, but the equipment needed for this purpose, such as the Vector Signal Analyzer (VSA) [4, 5], is rather complex and mostly available only at the test bench, which is not the case in many practical situations, in the network operator field service environment, where VSA is often not affordable but handheld instrumentation, such as BER testers, is common and widely available
Summary
Carrier Frequency Offset (CFO) and large Peak-to-Average Power Ratio (PAPR) are the immanent and dominating impairments of Orthogonal Frequency-Division Multiplexing (OFDM), degrading the Bit Error Rate (BER). In small cells, the signal is usually quite strong, implying that the signal-to-noise ratio (SNR) is large, while the small time dispersion allows the OFDM symbol cyclic prefix (CP) to prevent intersymbol interference (ISI) [12] This retains the CFO to solely determine the BER and vice versa, enabling indirect estimation of CFO by simple BER testing. Applying link abstraction principle, we can still use the above AWGN model but considering any nonAWGN distortion as an equivalent additive noise that would produce the same BER degradation This essentially shifts the BERðEb/N0Þ curve to the right for the adequate amount of Eb/N0, Figure 2.
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