ICACT20230155 Slide.15
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References
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ICACT20230155 Slide.14
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In this study, we addressed the practical problem of simultaneously satisfying both band-edge attenuation and EVM performance for NB-IoT gNB in the 3GPP NTN scenario A. Firstly, we are following 3GPP specification to generate standard NB-IoT gNB signal to compatible with real system implementation. Secondly, we used two-stage IFIR filtering approach to investigate whether a favourable tradeoff exists between the attenuation (C1) and EVM (C2) criteria. Finally, after designing and simulating numerous candidate IFIR filters, we selected IFIR#2 with an optimized 128-tap prototype filter as the final design, which not only can meet strict spectral band-edge attenuation for NTN but also maintain network operator requirements for link performance, Hence, we conclude that the proposed for the two-stage IFIR filter can successfully satisfy all the criteria and can implementation at standard NB-IoT system, Therefore, this study is a promising candidate for practical applications in NB-IoT over NTN.
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ICACT20230155 Slide.13
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IFIR#2 can not only suppress the band-edge spectrum, but also maintain acceptable EVM performance, and average EVM also meet the 3GPP specification.
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ICACT20230155 Slide.12
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The average EVM result is presented in Figure, which was obtained by feeding the filtered I/Q data into the commercial vector signal analysis (VSA) Keysight 89600 software.
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ICACT20230155 Slide.11
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Although IFIR#1 successfully met the C1 criterion, its edge EVM did not meet the C2 criterion (20.111%).
IFIR#2 successfully met both the C1 and C2 criteria. Furthermore, using IFIR#2 outperforms IFIR#1 according to the EVM analysis results. IFIR#2 can not only suppress the band-edge spectrum, but also maintain acceptable EVM performance.
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ICACT20230155 Slide.10
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The following are the two criteria that we used to choose the IFIR: (C1) having simulated band-edge attenuation 60 dB, (C2) having a band-edge EVM ¡Â 10%.
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ICACT20230155 Slide.09
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Using the two candidate prototype, we constructed two band-edge filters BF#1 and BF#2 by interpolating zeros. Finally, by cascading the 64-tap MF after BF#1 and BF#2
From the simulation results, one IFIR design was chosen for implementation.
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ICACT20230155 Slide.08
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The IFIR approach involves designing two cascaded low-pass filters (LPFs).
The first-stage filter is constructed by up-sampling (or interpolation with inserted zeros) the impulse response (IR) of a prototype filter (PF). Hence,the frequency response (FR) of the first-stage filter will be the replicated and compressed FR of PF.
the second-stage filter in the IFIR design is used to remove the replicated FR images except the low-pass part around the DC, and is thus called the masking filter (MF).
Figure shows the IFIR two-stage filtering structure.
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ICACT20230155 Slide.07
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In the NTN scenario A, to avoid interference with other GEO commercial services, the power spectrum of the relayed OFDMA signal should be strictly limited to be within a bandwidth of 200 kHz, which results in a serious challenge on the gNB side. For example, some GEO operators specify that the band-edge attenuation at 100 kHz from the center frequency should be larger than 60 dB. Therefore, the gNB for NTN scenario A requires more sophisticated output filtering before it transmit signal is sent to the gateway and GEO.
In addition to the band-edge suppression challenge that GEO operators face, another vital requirement should be considered by network operators, whose primary goal is to maintain an acceptable link performance. During the 3GPP conformance test, transmit signal quality was evaluated in terms of the EVM of the modulation constellation. For example, for QPSK constellation to be faithfully received, the EVM should be less than 17.5%
Hence, the filtered signal may exhibit severe EVM degradation at its outermost subcarrier as a result of spectral edge suppression. In this study, we addressed this challenge to achieve an implementable filter design with a favourable tradeoff between band-edge suppression and EVM performance.
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ICACT20230155 Slide.06
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the NB-IoT transmission scheme is the same as that of 4G Long-Term Evolution (LTE), which uses OFDMA for the downlink (DL) signal. Figure shows the NB-IoT DL signal frame structure, in which one radio frame consists of 10 subframes with a duration of 1 ms and each subframe consists of 14 OFDM symbols. For each OFDM symbol, 12 subcarriers spaced by 15 kHz can carry either a Zadoff–Chu synchronization signal (NPSS/NSSS) or a system/user information data channel (NPBCH/NPDCCH/NPDSCH) in QPSK modulation. Hence, the nominal DL signal bandwidth is 180 kHz, which coincides with that of the LTE resource block, and the baseband sampling rate of the generated I/Q signal samples is Fs = 1.92 Msps. In order to conform to the real application scenario, this paper will follow the 3GPP specification to generate the above gNB signals/channel for this research.
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ICACT20230155 Slide.05
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The NB-IoT NTN scenario considered in this study was the 3GPP NTN scenario A. As shown in Figure, the UE directly communicates with the GEO, and the gNB signal is relayed through the ground station gateway and GEO to the UE. In the scenario A, the GEO serves as a sky transponder to transparently relay the gNB and UE signals.
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ICACT20230155 Slide.04
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Over the last three decades, wireless terrestrial networks (TNs) have spread across the globe. However, some remote areas, such as mountains and oceans, remain difficult to cover by TNs. Therefore, non-terrestrial networks (NTNs) are a promising alternative to TNs for global coverage extension and are expected to play a key role in the beyond-5G or 6G era. In this study, we investigated the expected shift from the current narrowband Internet of Things (NB-IoT) over TNs to the emerging NB-IoT over NTNs. We also investigated some key technological issues from a physical layer perspective.
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ICACT20230155 Slide.03
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Over the last three decades, wireless terrestrial networks (TNs) have spread across the globe. However, some remote areas, such as mountains and oceans, remain difficult to cover by TNs. Therefore, non-terrestrial networks (NTNs) are a promising alternative to TNs for global coverage extension and are expected to play a key role in the beyond-5G or 6G era. In this study, we investigated the expected shift from the current narrowband Internet of Things (NB-IoT) over TNs to the emerging NB-IoT over NTNs. We also investigated some key technological issues from a physical layer perspective.
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ICACT20230155 Slide.02
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In 3GPP 5G narrowband Internet-of-Things (NB-IoT) non-terrestrial networks (NTNs) based on a satellite, a relayed gNodeB (gNB) base station orthogonal frequency-division multiple access (OFDMA) signal is required to meet the highly strict band-edge attenuation constraint and simultaneously maintain acceptable error vector magnitude (EVM) performance. Although these seem to be two conflicting goals, we pursued a favourable tradeoff between gNB band-edge attenuation and EVM by designing a two-stage interpolated finite-impulse response (IFIR) filter. We first follow the 3GPP NB-IoT specification to generate a standard gNB signal, and then we designed and optimized the filter for a relayed gNB signal and simulated its effectiveness. The proposed gNB TX design was not only verified through simulation, but also practically verified by the commercial vector signal analyser (VSA). Hence, this work can be realistically applied to standard NB-IoT signals, making it a critical enabling technology for converting the original NB-IoT TN to NTN and can help NTN operators to flexibly allocate channels, improve overall spectrum efficiency, and avoid waste of spectrum resources.
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ICACT20230155 Slide.01
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Outline
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ICACT20230155 Slide.00
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Hi everybody, my name is Cheng-Feng Li. My presentation topic is NB-IoT NTN Band-Edge Attenuation/EVM Trade Off with Real-System Verification.
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