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

Modlic

2021

Sensors

Self Cite

This work is motivated by growing evidence that the standard Cyclic Prefix (CP) length, adopted in the Long Term Evolution (LTE) physical layer (PHY) specifications, is oversized in propagation environments ranging from indoor to typical urban. Although this ostensibly seems to be addressed by 5G New Radio (NR) numerology, its scalable CP length reduction is proportionally tracked by the OFDM symbol length, which preserves the relative CP overhead of LTE. Furthermore, some simple means to optimize fixed or introduce adaptive CP length arose from either simulations or models taking into account only the bit-oriented PHY transmission performance. On the contrary, in the novel crosslayer analytical model proposed here, the closed-form expression for the optimal CP length is derived such as to minimize the effective average codeblock length, by also considering the error recovery retransmissions through the layers above PHY—the Medium Access Control (MAC) and the Radio Link Control (RLC), in particular. It turns out that, for given protective coding, the optimal CP length is determined by the appropriate rms delay spread of the channel power delay profile part remaining outside the CP span. The optimal CP length values are found to be significantly lower than the corresponding industry-standard ones, which unveils the potential for improving the net throughput.

Section: Introductionmentioning

confidence: 99%

PHY, MAC, and RLC Layer Based Estimation of Optimal Cyclic Prefix Length

Modlic

2021

Sensors

Self Cite

“…The impact of CFO on the BER floor (considered to be determined just by the CFO) can be modeled by conventional AWGN link abstraction, for example, as the PAPR was shown to affect the CFO-induced phase distortion

of the k -th original (pre-OFDM) symbol, as a function of BER, with the CFO

as the parameter [ 18 ]. Inversing the relationship

, we obtain:

where Q [·] is a Gaussian tail function.…”

Section: Efficient Ofdm Ber Floor With Joint Near-optimal Time Sammentioning

confidence: 99%

Efficient Estimation of CFO-Affected OFDM BER Floor in Small Cells with Resource-Limited IoT End-Points

Modlic

2020

Sensors

Self Cite

Contemporary wireless networks dramatically enhance data rates and latency to become a key enabler of massive communication among various low-cost devices of limited computational power, standardized by the Long-Term Evolution (LTE) downscaled derivations LTE-M or narrowband Internet of Things (NB IoT), in particular. Specifically, assessment of the physical-layer transmission performance is important for higher-layer protocols determining the extent of the potential error recovery escalation upwards the protocol stack. Thereby, it is needed that the end-points of low processing capacity most efficiently estimate the residual bit error rate (BER) solely determined by the main orthogonal frequency-division multiplexing (OFDM) impairment–carrier frequency offset (CFO), specifically in small cells, where the signal-to-noise ratio is large enough, as well as the OFDM symbol cyclic prefix, preventing inter-symbol interference. However, in contrast to earlier analytical models with computationally demanding estimation of BER from the phase deviation caused by CFO, in this paper, after identifying the optimal sample instant in a power delay profile, we abstract the CFO by equivalent time dispersion (i.e., by additional spreading of the power delay profile that would produce the same BER degradation as the CFO). The proposed BER estimation is verified by means of the industry-standard LTE software simulator.

“…Recently, it has been shown how the maximal CFO-caused squared phase deviation and the instantaneous per-OFDM-symbol PAPR determine the transmission performance, essentially the BER [3]. Moreover, successful PAPR reduction (e.g., by clipping), which was shown to indi-rectly suppress the CFO-caused phase deviation, too [3], implies that BER degradation in this case practically remains solely determined by the CFO-induced phase deviation and vice versa. Consequently, as BER testing is simple with respect to complex modulation signal analysis, it comes out that in many practical situations we can estimate the residual CFO from BER, applying the link abstraction method.…”

Section: Ber-based Estimation Of Cfo-induced Peak Phase Deviationmentioning

confidence: 99%

“…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). Specifically, 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 finally shrinks the effective noise margin [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Practical BER-Based Estimation of Residual OFDM CFO by Reducing Noise Margin

Mihaljević

Wireless Communications and Mobile Computing

et al. 2020

Self Cite

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.