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.

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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.

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AhslructWhen estiniating the potential radiation liazard of a base station antenna systeni, one often relies on the atitenimfarrfield radialion pmtern. while /lie estimation oflen refers lo /he antenna near-fjeld zone. It ir widely accepted llial this leads to ovemtiination ofrhe.field amplitades. This work analyzes the typical sector aiitenna.widely wed in GSMsysteni. Antenna newfield distribution is calculated using NECZ, for varioiis con/;pratiom of antema installations. Analysis of the ontenno injree space ,shows that tlie overeslbnation only happens in the mainlobe. while in all other directions even iinderestimatioii can happen. Ftwtliermore, condirctive objects in close pro.rimity qf the antenna. like in widely-used mtdtiple-antenna configurations. can sign@onlly distort (he radiutian pattern in a generally unknown manner, leading to tinexpected higher anip1itade.s in the tinknow? dir.ections. For trtdy conservative, worst-case EMfjeld estimation, this shoiild be taken into accozint. The paper corichrdes ivitli some guidelines on using the mod(fied radiation pafteri?.for such estimation.