Extensionless Adaptive Transmitter and Receiver Windowing of Beyond 5G Frames

Newer cellular communication generations are planned to allow asynchronous transmission of multiple numerologies (waveforms with different parameters) in adjacent bands, creating unavoidable adjacent channel interference. Most prior work on windowing assume additional extensions reserved for windowing, which does not comply with standards. Whether windowing should be applied at the transmitter or the receiver was not questioned. In this work, we propose two independent algorithms that are implemented at the transmitter and receiver, respectively. These algorithms estimate the transmitter and receiver windowing duration of each resource element (RE) with an aim to improve fair proportional network throughput. While doing so, we solely utilize the available extension that was defined in the standard and present standard-compliant algorithms that also do not require any modifications on the counterparts or control signaling. Furthermore, computationally efficient techniques to apply per-RE transmitter and receiver windowing to signals synthesized and analyzed using conventional cyclic prefix orthogonal frequency division multiplexing are derived and their computational complexities are analyzed. The spectrotemporal relations between optimum window durations at either side, as well as functions of the excess signal to noise ratios, the subcarrier spacings and the throughput gains provided over previous similar techniques are numerically verified.Comment: 15 pages, 2 algorithms, 3 tables, 11 figures (1 of which includes 3 subfigures) and 3 author biographies. Final version accepted for publication in IEEE Transactions on Vehicular Technolog

Reducing Precoder/Channel Mismatch and Enhancing Secrecy in Practical MIMO Systems Using Artificial Signals

Practical multiple-input-multiple-output (MIMO) systems depend on a predefined set of precoders to provide spatial multiplexing gain. This limitation on the flexibility of the precoders affects the overall performance. Here, we propose a transmission scheme that can reduce the effect of mismatch between users' channels and precoders. The scheme uses the channel knowledge to generate an artificial signal, which realigns the predefined precoder to the actual channel. Moreover, the scheme can provide an additional level of secrecy for the communication link. The performance of the proposed scheme is evaluated using bit-error rate (BER), error vector magnitude (EVM), and secrecy capacity. The results show a significant improvement for the legitimate user, along with a degradation for the eavesdropper.Comment: 4 pages, 5 figures. Accepted for publication in IEEE Communications Letter

Algorithms Enabling Communications in the Presence of Adjacent Channel Interference

Newer cellular communication generations are planned to allow asynchronous transmission of multiple numerologies (waveforms with different parameters) in adjacent bands, creating unavoidable adjacent channel interference (ACI). Contemporary windowed-orthogonal frequency division multiplexing (W-OFDM) algorithms have limited ACI rejection capability under high delay spread and small fast Fourier transformation (FFT) sizes. CP is designed to be longer than the maximum excess delay (MED) of the channel to accommodate such algorithms in current standards. Most prior work on windowing assume additional extensions reserved for windowing, which does not comply with standards. The robustness of these algorithms can only be improved against these conditions by adopting additional extensions in a new backward incompatible standard. Whether windowing should be applied at the transmitter or the receiver was not questioned. Such extensions would deteriorate the performance of high mobility vehicular communication systems in particular. In this dissertation, algorithms that enable minimum, even insufficient guards are discussed to achieve the spectral efficiency and latency requirements of cellular communication systems beyond 5G. This leads to interference in both time and frequency domains. First, a partial-non-orthogonal multiple accessing (NOMA) scenario in which the desired user is experiencing both intersymbol interference (ISI) due to insufficient CP and ACI caused by asynchronous transmitters using non-orthogonal numerologies in adjacent bands is investigated. ISI and ACI depend on the power offset between desired and interfering users, the instantaneous channel impulse responses (CIRs) of interfering users and transmitter and receiver window functions. Therefore, joint and adaptive utilization of CP requires real-time calculation of ISI and ACI. Analytical expressions for expected ISI and ACI at each subcarrier of the desired user are derived to minimize their combination. Accordingly, an adaptive algorithm consisting of windowing each subcarrier at the receiver with window length that minimizes the combined interference at that subcarrier by optimally exchanging ISI and ACI is proposed. Interference reduction performances of current, outdated and average optimal window length raised cosine receiver windows are assessed and compared to fixed and no receiver windowing. Windowing reduces interference even when CP is shorter than the channel if window length is determined using the proposed design guidelines. Second, two independent algorithms are proposed that are implemented at the transmitter and receiver, respectively. These algorithms estimate the transmitter and receiver windowing duration of each RE with an aim to improve fair proportional network throughput. While doing so, solely the available extension that was defined in the standard is utilized. Presented standard-compliant algorithms also do not require any modifications on the counterparts or control signaling. Furthermore, computationally efficient techniques to apply per-RE transmitter and receiver windowing to signals synthesized and analyzed using conventional CP-OFDM are derived and their computational complexities are analyzed. The spectrotemporal relations between optimum window durations at either side, as well as functions of the excess SNRs, the subcarrier spacings and the throughput gains provided over previous similar techniques are numerically verified. Third, a low-complexity Hann receiver windowed-orthogonal frequency division multiplexing (RW-OFDM) scheme that provides resistance against ACI without requiring any ISI-free redundancies is presented. While this scheme is backward compatible with current and legacy standards and requires no changes to the conventionally transmitted signals, it also paves the way towards future spectrotemporally localized and efficient schemes suitable for higher mobility vehicular communications. A Hann window effectively rejects unstructured ACI at the expense of structured and limited inter-carrier interference (ICI) across data carriers. A simple maximum ratio combining (MRC)-successive interference cancellation (SIC) receiver is therefore proposed to resolve this induced ICI and receive symbols transmitted by standard transmitters currently in use. The computational complexity of the proposed scheme is comparable to that of contemporary RW-OFDM algorithms, while ACI rejection and BER performance is superior in both long and short delay spreads. Channel estimation using Hann RW-OFDM symbols is also discussed. Finally, the extension of this flexible signaling approach to other radio access technologies (RATs), such as characteristics that could be exploited in the cellular structure and application of these approaches to NOMAs schemes are discussed, and such an extension is exemplified using practical multiple-input-multiple-output (MIMO) systems. Practical MIMO systems depend on a predefined set of precoders to provide spatial multiplexing gain. This limitation on the flexibility of the precoders affects the overall performance. Here, we propose a transmission scheme that can reduce the effect of mismatch between users’ channels and precoders. The scheme uses the channel knowledge to generate an artificial signal, which realigns the predefined precoder to the actual channel. Moreover, the scheme can provide an additional level of secrecy for the communication link. The performance of the proposed scheme is evaluated using BER, EVM, and secrecy capacity. The results show a significant improvement for the legitimate user, along with a degradation for the eavesdropper

Adaptive windowing of insufficient CP for joint minimization of ISI and ACI beyond 5G

Using minimum, even insufficient guards are proposed to achieve the spectral efficiency and latency requirements of cellular communication systems beyond 5G. This leads to interference in both time and frequency domains. In this paper, a partial-non-orthogonal multiple accessing scenario in which the desired user is experiencing both intersymbol interference (ISI) due to insufficient cyclic prefix (CP) and adjacent channel interference (ACI) caused by asynchronous transmitters using non-orthogonal numerologies in adjacent bands is investigated. ISI and ACI depend on the power offset between desired and interfering users, the instantaneous channel impulse responses of interfering users and transmitter and receiver window functions. Therefore, joint and adaptive utilization of CP requires real-time calculation of ISI and ACI. Analytical expressions for expected ISI and ACI at each subcarrier of the desired user are derived to minimize their combination. Accordingly, an adaptive algorithm consisting of windowing each subcarrier at the receiver with window length that minimizes the combined interference at that subcarrier by optimally exchanging ISI and ACI is proposed. Interference reduction performances of current, outdated and average optimal window length raised cosine receiver windows are assessed and compared to fixed and no receiver windowing. Windowing reduces interference even when CP is shorter than the channel if window length is determined using the proposed design guidelines.Institute of Electrical and Electronics Engineers Inc.IEEE Communications Societ

Flexible radio access beyond 5G: A future projection on waveform, numerology, and frame design principles

WOS: 000411791700037To address the vast variety of user requirements, applications, and channel conditions, flexibility support is strongly highlighted for 5G radio access technologies (RATs). For this purpose, usage of multiple orthogonal frequency division multiplexing (OFDM) numerologies, i.e., different parameterization of OFDM-based subframes, within the same frame has been proposed in the third-generation partnership project discussions for 5G new radio. This concept will likely meet the current expectations in multiple service requirements to some extent. However, since the quantity of wireless devices, applications, and heterogeneity of user requirements will keep increasing toward the next decade, the sufficiency of the aforementioned flexibility consideration remains quite disputable for future services. Therefore, novel RATs facilitating much more flexibility are needed to address various technical challenges, e.g., power efficiency, massive connectivity, latency, spectral efficiency, robustness against channel dispersions, and so on. In this paper, we discuss the potential directions to achieve further flexibility in RATs beyond 5G, such as future releases of 5G and 6G. In this context, a framework for developing flexible waveform, numerology, and frame design strategies is proposed along with sample methods. We also discuss their potential role to handle various upper-level system issues, including the ones in orthogonal and nonorthogonal multiple accessing schemes and cellular networks. By doing so, we aim to contribute to the future vision of designing flexible RATs and to point out the possible research gaps in the related fields.U.S. National Science Foundation [ECCS-1609581]This work was supported by the U.S. National Science Foundation under Grant ECCS-1609581

Non-redundant OFDM receiver windowing for 5G frames and beyond

Contemporary receiver windowed-orthogonal frequency division multiplexing (RW-OFDM) algorithms have limited adjacent channel interference (ACI) rejection capability under high delay spread and small fast Fourier transformation (FFT) sizes. Cyclic prefix (CP) is designed to be longer than the maximum excess delay (MED) of the channel to accommodate such algorithms in current standards. The robustness of these algorithms can only be improved against these conditions by adopting additional extensions in a new backward incompatible standard. Such extensions would deteriorate the performance of high mobility vehicular communication systems in particular. In this paper, we present a low-complexity Hann RW-OFDM scheme that provides resistance against ACI without requiring any intersymbol interference (ISI)-free redundancies. While this scheme is backward compatible with current and legacy standards and requires no changes to the conventionally transmitted signals, it also paves the way towards future spectrotemporally localized and efficient schemes suitable for higher mobility vehicular communications. A Hann window effectively rejects unstructured ACI at the expense of structured and limited inter-carrier interference (ICI) across data carriers. A simple maximum ratio combining (MRC)-successive interference cancellation (SIC) receiver is therefore proposed to resolve this induced ICI and receive symbols transmitted by standard transmitters currently in use. The computational complexity of the proposed scheme is comparable to that of contemporary RW-OFDM algorithms, while ACI rejection and bit-error rate (BER) performance is superior in both long and short delay spreads. Channel estimation using Hann RW-OFDM symbols is also discussed.National Science Foundation (NSF

Innovative telecommunications training through flexible radio platforms

The everchanging telecommunication industry is in severe need of a highly skilled workforce to shape and deploy future generation communication systems. This article presents innovative telecommunication training that is designed to satisfy this need. The training focuses on hardware layers of the open systems interconnection model. It integrates theory, numerical modeling, and hardware implementation to ensure complete and long-lasting understanding. The key telecommunication concepts that are covered in the fundamental training phase are detailed along with best teaching practices. In addition, methods that enrich the learning experience, such as gamified microtasks and interactive use of daily telecommunication devices, are featured. The project development case studies that cultivate creative thinking and scientific interest are highlighted. Also, a well-established guideline to compose the teaching environment that emphasizes hands-on experience is provided. Therefore, the presented training can be exemplary to other institutions that share the same mission to educate the distinguished engineers of the future

Flexibility through hybrid waveforms

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