Orthogonal frequency-division multiplexing (OFDM) has been selected as a baseline waveform for long-term evolution (LTE) and fifth-generation new radio (5G NR). Fast-convolution (FC)-based frequency-domain signal processing has been recently considered as an effective tool for transmitter and receiver side subband filtering of OFDM-based waveforms. However, for the original continuous FC-based model, the filtering can, in general, be configured in time-direction only with the granularity of half subframe, corresponding to 7, 14, or 28 symbols with 15kHz, 30kHz, or 60kHz subcarrier spacing, respectively. In this paper, we present a symbol-synchronous FC-processing scheme flexibly allowing filter re-configuration with the time resolution equal to one OFDM symbol while supporting tight carrier-wise filtering for 5G NR in mixed-numerology scenarios with adjustable subcarrier spacings, center frequencies, and subband bandwidths, as well as providing co-existence with LTE. Proposed approach segments each stream of time-domain OFDM symbols into overlapping processing blocks of fixed size. Symbol synchronous processing is achieved by dynamically adjusting the overlap between the processing blocks while aligning the payload part of the processing blocks with the boundaries of the OFDM symbols. The proposed scheme is demonstrated to support the envisioned use cases of 5G NR and provide a flexible starting point for sixth generation (6G) development.

Cellular network based connectivity for high speed trains (HSTs) is subject to large carrier frequency offset (CFO) due to high Doppler shifts. Large CFO will cause losing orthogonality between OFDM subcarriers which leads to significant performance loss. In this paper, we compare two Doppler estimation methods for HST links to compensate and remove CFO effect in the receiver in the context of 5G New Radio (NR) and long term evolution (LTE) systems. The first considered method to estimate Doppler shifts in LTE systems is based on the cyclic prefix (CP). The second method considered in NR system context is based on the phase tracking reference signal (PTRS). Simulation results shown that NR PTRS based method has higher estimation accuracy compared to LTE CP based method. Moreover, NR PTRS based method has higher signal to noise ratio (SNR) gain to achieve considered link performance target which is set to 70% of the maximum achievable throughput in this study. Additionally, the uplink data channel performance studies shown that, for systems using two demodulation reference signal (DMRS) per subframe for channel estimation, LTE CP based method can support only QPSK modulation scheme. In this case, a significant performance improvement is observed when the number of DMRS symbols per subframe is increased up to four, while almost the same performance is observed in NR systems for both slot patterns. Therefore, NR systems using PTRS based method with two DMRS configuration per subframe can be used with lower system overhead. In addition, block error rate (BLER) performance results show that NR PTRS based method has superior performance compared to LTE CP based method. Overall, these results demonstrate that NR PTRS based Doppler estimation method is more suitable in HST use cases.

A common design of the random access procedure on the physical random access channel (PRACH) is required for the diverse usage scenarios in the fifth generation new radio (5G NR) mobile networks. Based on the latest 3GPP specifications and evaluation assumptions agreed for Release 16, the 2 step-RACH (2SR) enhancement, composed of the denoted MsgA and MsgB, not only reduces the latency but also the control-signalling overhead due to the reduced number of messages transmitted. The channel structure of MsgA comprises RACH preamble and data in the physical uplink shared channel (PUSCH) while MsgB combines the random access response and the contention resolution. This procedure should operate in local area (LA), medium range (MR) and wide area (WA) cells despite the lack of time alignment (TA) in the PUSCH part of MsgA. The demodulation performance degradation observed without time offset compensation at the base station (gNB), specially for MR or WA cells, highlight that practical gNB implementations relying in MAC control element-based TA command for PUSCH time alignment are not conceivable for 2SR. Furthermore, in the case that all preambles from multiple users (UEs) trying to perform the initial access are mapped to the same PUSCH physical resources, the associated data parts overlap and may result in unsuccessful decoding. There is therefore a trade-off between the collision probability of the PUSCH part of MsgA and the resource overhead for 2SR. This paper addresses the channel structure design of this procedure for the preamble and data parts of MsgA together with the receiver processing framework. The performance results suggest that using lower payload sizes provide higher resource utilization and allow more UEs to be multiplexed within the same PUSCH occasion. In addition, using different DMRS ports for UEs sharing same physical resources decrease the probability of failure in the decoding of the data part of MsgA while reduces the resource overhead for 2SR.

Orthogonal frequency-division multiplexing (OFDM) has been selected as the basis for the fifth-generation new radio (5G NR) waveform developments. However, effective signal processing tools are needed for enhancing the OFDM spectrum in various advanced transmission scenarios. In earlier work, we have shown that fast-convolution (FC) processing is a very flexible and efficient tool for filtered-OFDM signal generation and receiver-side subband filtering, e.g., for the mixed-numerology scenarios of the 5G NR. FC filtering approximates linear convolution through effective fast Fourier transform (FFT)-based circular convolutions using partly overlapping processing blocks. However, with the continuous overlap-and-save and overlap-and-add processing models with fixed block-size and fixed overlap, the FC-processing blocks cannot be aligned with all OFDM symbols of a transmission frame. Furthermore, 5G NR numerology does not allow to use transform lengths shorter than 128 because this would lead to non-integer cyclic prefix (CP) lengths. In this article, we present new FC-processing schemes which solve or avoid the mentioned limitations. These schemes are based on dynamically adjusting the overlap periods and extrapolating the CP samples, which make it possible to align the FC blocks with each OFDM symbol, even in case of variable CP lengths. This reduces complexity and latency, e.g., in mini-slot transmissions and, as an example, allows to use 16-point transforms in case of a 12-subcarrier-wide subband allocation, greatly reducing the implementation complexity. On the receiver side, the proposed scheme makes it possible to effectively combine cascaded inverse and forward FFT units in FC-filtered OFDM processing. Transform decomposition is used to simplify these computations, leading to significantly reduced implementation complexity in various transmission scenarios. A very extensive set of numerical results is also provided, in terms of the radio-link performance and associated processing complexity.

This paper proposes a cyclic prefix (CP) free spectral efficiency frequency division multiplexing (SEFDM) wireless signal transmission and reception method based on alignment signal (AS). The method needs the cooperation of both the transmission and reception sides. At the transmitter, time-domain AS is designed to prevent inter-symbol interference (ISI) caused by multipath propagation in the received signal. At the receiver, the channel circularity convolution providing processing is used to enable high accurate frequency domain one-tap equaliser. The extensive computer simulation results under the 5G new radio (5G-NR) channel model, TDL-D, show that the AS aided SEFDM has similar bit error rate performance as CP-SEFDM without energy and latency cost on CP. The AS-SEFDM capability to mitigate the ISI and to enable the one-tap equaliser in SEFDM systems makes it a promising technique for future wireless communication systems.

Cyclic-prefix orthogonal frequency-division multiplexing (CP-OFDM) is a widely adopted modulation scheme for broadband wireless communication systems. The use of CP makes the scheme robust and facilitates simple and effective channel equalization since it makes the frequency-selective multipath fading to appear as flat-fading at subcarrier level. However, CP causes overhead in the spectrum efficiency and power efficiency. Various schemes have been proposed in the literature to avoid the use of CP or other forms of guard intervals (GIs) between OFDM symbols, but none of those has been fully satisfying. One recent proposal is based on adding a so-called alignment signal to GI-less OFDM signal in such a way that (i) intersymbol interference is avoided and (ii) the multipath channel effect appears as the cyclic convolution between the effective channel impulse response and each OFDM symbol. While assuming channel knowledge on the transmitter side, this approach allows basic OFDM signal processing to be used on the receiver side for channel estimation, equalization, and synchronization. In this work, we provide enhancements to the alignment signal structure and generation, which provide clear improvement in the link performance and reduce the complexity of transmitter processing. Also, new insights about the characteristics of alignment signal based CP-free OFDM waveforms are provided.

In cyclic-prefix orthogonal frequency-division multiplexing (CP-OFDM)-based radio access, the coexistence of different technologies without precise time-frequency synchronization is limited due to high out-of-band (OOB) emissions. Therefore, the spectrum enhancement techniques play a key role in relaxing the synchronization and power control requirements. This allows a higher degree of opportunistic spectrum use with minimized interference. In addition, all the transmitting devices have to fulfill specific transmitted signal quality requirements, including the maximum OOB radiated signal power. With the orthogonal frequency-division multiplexing (OFDM)-based radio access, some additional signal processing for improved spectrum containment is commonly needed to achieve these requirements. The filtering and time-domain windowing are two fundamentally different approaches for spectrum enhancement. The filtered OFDM (F-OFDM) provides better spectrum localization than the time-windowing schemes [such as windowed overlap-add (WOLA)], with the cost of higher complexity. This article introduces low-complexity solutions for spectrally enhanced narrowband OFDM transmitters based on the use of lookup tables (LUTs). The proposed LUT approach, requiring only memory units and a low number of additions, allows to avoid all computationally expensive operations in online transmitter processing, as it builds the transmitted signal by summing the stored partial waveforms optimized offline. In certain cases, completely multiplication- and summation-free designs are possible. The transmitters of narrowband Internet of Things (NB-IoT) devices are natural applications for the proposed LUT approach, as they require additional digital baseband signal processing to reach the emission requirements. It is shown that the proposed LUT schemes can provide significant savings in real-time computations of NB-IoT devices, while fulfilling the 3GPP requirements.

With the emergence of new 5G radio networks, high-accuracy positioning solutions are becoming extensively more important for numerous 5G-enabled applications and radio resource management tasks. In this paper, we focus on 5G mm-wave systems, and propose a method for high-accuracy estimation of the User Equipment (UE) position and antenna orientation. Based on the sparsity of the mm-wave channel, we utilize a compressive sensing approach for estimating the departure and arrival angles as well as the time-of-arrival for each observed radio propagation path. After this, in order to obtain statistical descriptions of the unknown parameters, we analytically derive a set of sampling distributions, which enable utilization of an iterative Gibbs sampling method. As shown by the obtained simulation results, the proposed method is able to achieve centimeter-level positioning accuracy with degree-level orientation accuracy, even in the absence of a line-of-sight path.

This paper investigates the 5G new radio (NR) uplink (UL) performance with CP-OFDM and DFT-s-OFDM based waveforms. The effects of highly non-linear PA behavior, inter-allocation interference, and UL multi-user MIMO on the relative performance of these waveforms are addressed. It is shown that with relaxed EVM and inband emission requirements for CP-OFDM, the coverage limited operation can be improved to achieve better link budget than DFT-s-OFDM based UL without performance penalty in the multi-user uplink. For high-throughput user equipment, the assumed highly non-linear PA behavior restricts the CP-OFDM based transmit power, which may limit the coverage compared to DFT-s-OFDM based waveform in UL without multi-user MIMO support. In UL multi-user MIMO scenario the CP-OFDM based waveform provides clearly better link performance and achieves better link budget than DFT-s-OFDM based waveform. Within the multi-user MIMO UL scenario, the requirement for substantially better PA linearity in high-throughput cases is also observed.

By the introduction of the fifth generation (5G) mobile communication networks and its physical layer entitled as new radio (NR), the question of link performance in coexistence scenario between the 5G NR and fourth generation (4G) mobile communication networks based on long term evolution (LTE) has been raised. In this paper, we evaluate the uplink (UL) performance of 5G NR and LTE links operating within a common channel. The need for subcarrier shift in 5G NR UL similar to LTE UL is addressed and analyzed, and the effect of guard band (GB) in frequency domain between 5G NR and LTE is studied. It is shown that with a single physical resource block GB no subcarrier shifting is required in 5G NR, as long as the power control accuracy is sufficient, in which case LTE performance is unaffected. From the 5G NR performance point of view no GB is required.

We study positioning of high-speed trains in 5G new radio (NR) networks by utilizing specific NR synchronization signals. The studies are based on simulations with 3GPP-specified radio channel models including path loss, shadowing and fast fading effects. The considered positioning approach exploits measurement of Time-Of-Arrival (TOA) and Angle-Of-Departure (AOD), which are estimated from beamformed NR synchronization signals. Based on the given measurements and the assumed train movement model, the train position is tracked by using an Extended Kalman Filter (EKF), which is able to handle the non-linear relationship between the TOA and AOD measurements, and the estimated train position parameters. It is shown that in the considered scenario the TOA measurements are able to achieve better accuracy compared to the AOD measurements. However, as shown by the results, the best tracking performance is achieved, when both of the measurements are considered. In this case, a very high, sub-meter, tracking accuracy can be achieved for most (>75%) of the tracking time, thus achieving the positioning accuracy requirements envisioned for the 5G NR. The pursued high-accuracy and high-availability positioning technology is considered to be in a key role in several envisioned HST use cases, such as mission-critical autonomous train systems.

For the 5G new radio physical layer the CP-OFDM waveform has been chosen as the baseline for communications below 40 GHz. The requirement for multicarrier waveforms used for uplink is to achieve similar coverage as achieved by SC-FDMA in LTE uplink. In this paper, multiple candidate waveforms with enhanced CP-OFDM processing proposed for 5G incorporating realistic 3GPP compliant power amplifier model and peak clipping are evaluated in uplink transmission, and compared against SC-FDMA in terms of maximum average power amplifier output power and coded block error rate. It is shown that multicarrier waveforms have minor disadvantage in single-PRB transmission, but as the allocation size increases to encounter frequency selective fading the multicarrier waveforms provide similar or even improved link budget compared to SC-FDMA uplink. This implies that given the expected cell edge throughput requirements for 5G mobile broadband services and expected power amplifier development, enhanced CP-OFDM waveforms can achieve the uplink coverage requirement.

In this paper, subband filtered CP-OFDM and windowed CP-OFDM waveforms proposed for 5G new radio (NR) are compared to LTE-like downlink and uplink waveforms under different power amplifier (PA) models. The effects of subband filtering or windowing are evaluated in terms of out-of-band and inband emissions, average error vector magnitude (EVM) and maximum uplink PA output power when increasing the bandwidth efficiency from 90% to 97.2%. The evaluations include recently proposed PA models by 3GPP TSG-RAN WG1 for downlink and uplink. It is shown that the cost of increased bandwidth efficiency in fullband downlink transmission is mainly complexity increase required by the steeper channelization filter. On the other hand, the increased EVM caused by channel filter induced inter-symbol-interference may limit the usability of modulation 256-QAM and above. In uplink with fullband transmission using 64-QAM modulation, the spectral containment is not an issue because the required backoff with highly non-linear PA model limits the Tx power to a very low level independently of the maximum allocation size. In the 1 PRB uplink, increased bandwidth utilization decreases the maximum PA output power while increased backoff improves the inband ACLR.

This paper investigates the application of fast-convolution (FC) filtering schemes for flexible and effective waveform generation and processing in the fifth generation (5G) systems. FC-based filtering is presented as a generic multimode waveform processing engine while, following the progress of 5G new radio standardization in the Third-Generation Partnership Project, the main focus is on efficient generation and processing of subband-filtered cyclic prefix orthogonal frequency-division multiplexing (CP-OFDM) signals. First, a matrix model for analyzing FC filter processing responses is presented and used for designing optimized multiplexing of filtered groups of CP-OFDM physical resource blocks (PRBs) in a spectrally well-localized manner, i.e., with narrow guardbands. Subband filtering is able to suppress interference leakage between adjacent subbands, thus supporting independent waveform parametrization and different numerologies for different groups of PRBs, as well as asynchronous multiuser operation in uplink. These are central ingredients in the 5G waveform developments, particularly at sub-6-GHz bands. The FC filter optimization criterion is passband error vector magnitude minimization subject to a given subband band-limitation constraint. Optimized designs with different guardband widths, PRB group sizes, and essential design parameters are compared in terms of interference levels and implementation complexity. Finally, extensive coded 5G radio link simulation results are presented to compare the proposed approach with other subband-filtered CP-OFDM schemes and time-domain windowing methods, considering cases with different numerologies or asynchronous transmissions in adjacent subbands. Also the feasibility of using independent transmitter and receiver processing for CP-OFDM spectrum control is demonstrated

Forthcoming fifth generation (5G) mobile networks need to support a wide variety of services, from mobile broadband (MBB) communications supporting up to 100 Gbps throughput and millisecond class latency to ultra-low power machine-to-machine (M2M) communications supporting very low bit rates and tens of years operation with single battery or operation together with new energy harvesting solutions. In this paper, we concentrate on the MBB aspect and consider two new OQAM-OFDM based waveform candidates proposed for 5G communications while noting the strict time latency requirements. Also, we compare different preamble designs used for channel estimation and show that some of the pseudo-pilot power maximizing interference approximation method based preamble designs are not suitable for communications with any nonlinear power amplifier (PA) model and that an ad-hoc random OQAM based preamble design performs well compared to specific optimized preamble designs.

The projected growth of mobile data traffic requires the 5G wireless systems to support at least 1000× larger area throughput than the existing 4G solutions. This requires ultra- dense local area networks combined with fast and flexible time division duplex based access to provide wide bandwidths for multi-gigabit peak data rates. In this paper, we focus on the system level performance characterization and evaluations of the recently proposed 5GETLA radio interface for centimeter-wave communications. We study the effects of interference tiers on the throughput and SINR distributions and show that broadcasted, omnidirectional information should be minimized and preferably combined with learning spectral reuse and interference canceling receivers. We also demonstrate the low latency provided by the new 5G radio interface design.

In this paper we introduce a new flexible time division duplexing based radio interface for future 5G small cell communications. We describe the benefits of the new design to achieve high energy efficiency, high spectral efficiency and low latency at the same time. We also compare our reference design against LTE-A assuming rank 8 DL SU-MIMO transmission and show that we our design can achieve more than 29% lower total overhead and up to 90% lower round trip time.

In this paper an iterative, interference cancelling receive structure for single carrier transmission using superimposed training is studied. We derive the analytical MSE limits for LMMSE channel estimator using perfect channel knowledge and show that the simulated values follow well the analytical ones. Then, we utilise these results to analyse the MSE performance of a combined ML-LMMSE chanel estimator structure, where the initial channel estimates are obtained from the ML channel estimator

In this paper, we study the performance of our single carrier receiver model using turbo coding and regular low density parity check (LDPC) coding. The single carrier receiver utilizes filter bank based frequency domain equalizer, which is then followed by a low complexity, iterative noise predictive decision feedback equalizer (NP-DFE). Furthermore, the average computation rate as a function of Eb/N0ratio is observed for different coding methods, thus characterizing the performance vs. complexity trade-offs in the considered receiver structure in terms of the channel coding. Clear performance benefits from the NP-DFE loop can be achieved and the averaged complexity increase in our system is tolerable in the Eb/N0range where frame error rates below 10-1are achieved. In addition, by fixing the maximum decoding complexity to be the same between turbo and LDPC codes, the performance of these codes is similar but the averaged complexity of the LDPC code saturates to a clearly lower level.