Multi-service Signal Multiplexing and Isolation for Physical-Layer Network Slicing (PNS)

Network slicing has been identified as one of the most important features for 5G and beyond to enable operators to utilize networks on an as-a-service basis and meet the wide range of use cases. In physical layer, the frequency and time resources are split into slices to cater for the services with individual optimal designs, resulting in services/slices having different baseband numerologies (e.g., subcarrier spacing) and / or radio frequency (RF) front-end configurations. In such a system, the multi-service signal multiplexing and isolation among the service/slices are critical for the Physical-Layer Network Slicing (PNS) since orthogonality is destroyed and significant inter-service/ slice-band-interference (ISBI) may be generated. In this paper, we first categorize four PNS cases according to the baseband and RF configurations among the slices. The system model is established by considering a low out of band emission (OoBE) waveform operating in the service/slice frequency band to mitigate the ISBI. The desired signal and interference for the two slices are derived. Consequently, one-tap channel equalization algorithms are proposed based on the derived model. The developed system models establish a framework for further interference analysis, ISBI cancelation algorithms, system design and parameter selection (e.g., guard band), to enable spectrum efficient network slicing

Channel Estimation and Optimal Pilot Signals for Universal Filtered Multi-Carrier (UFMC) Systems

We propose channel estimation algorithms and pilot signal optimization for the universal filtered multi-carrier (UFMC) system based on the comb-type pilot pattern. By considering the least square linear interpolation (LSLI), discrete Fourier transform (DFT), minimum mean square error (MMSE) and relaxed MMSE (RMMSE) channel estimators, we formulate the pilot signals optimization problem by minimizing the estimation MSE subject to the power constraint on pilot tones. The closed-form optimal solutions and minimum MSE are derived for LSLI, DFT, MMSE and RMMSE estimators

Efficient DCT-MCM Detection for Single and Multi-Antenna Wireless Systems

The discrete cosine transform (DCT) based multicarrier modulation (MCM) system is regarded as one of the promising transmission techniques for future wireless communications. By employing cosine basis as orthogonal functions for multiplexing each real-valued symbol with symbol period of T, it is able to maintain the subcarrier orthogonality while reducing frequency spacing to 1/(2T) Hz, which is only half of that compared to discrete Fourier transform (DFT) based multicarrier systems. In this paper, following one of the effective transmission models by which zeros are inserted as guard sequence and the DCT operation at the receiver is replaced by DFT of double length, we reformulate and evaluate three classic detection methods by appropriately processing the post-DFT signals both for single antenna and multiple-input multiple-output (MIMO) DCT-MCM systems. In all cases, we show that with our reformulated detection approaches, DCT-MCM schemes can outperform, in terms of error-rate, conventional OFDM-based systems

Performance analysis and optimization of DCT-based multicarrier system on frequency-selective fading channels

Regarded as one of the most promising transmission techniques for future wireless communications, the discrete cosine transform (DCT) based multicarrier modulation (MCM) system employs cosine basis as orthogonal functions for real-modulated symbols multiplexing, by which the minimum orthogonal frequency spacing can be reduced by half compared to discrete Fourier transform (DFT) based one. With a time-reversed pre-filter employed at the front of the receiver, interference-free one-tap equalization is achievable for the DCT-based systems. However, due to the correlated pre-filtering operation in time domain, the signal-to-noise ratio (SNR) is enhanced as a result at the output. This leads to reformulated detection criterion to compensate for such filtering effect, rendering minimum-mean-square-error (MMSE) and maximum likelihood (ML) detections applicable to the DCT-based multicarrier system. In this paper, following on the pre-filtering based DCT-MCM model that build in the literature work, we extend the overall system by considering both transceiver perfections and imperfections, where frequency offset, time offset and insufficient guard sequence are included. In the presence of those imperfection errors, the DCT-MCM systems are analysed in terms of desired signal power, inter-carrier interference (ICI) and inter-symbol interference (ISI). Thereafter, new detection algorithms based on zero forcing (ZF) iterative results are proposed to mitigate the imperfection effect. Numerical results show that the theoretical analysis match the simulation results, and the proposed iterative detection algorithms are able to improve the overall system performance significantly

A DHT-Based Multicarrier Modulation System with Pairwise ML Detection

This paper presents a complex-valued discrete multicarrier modulation (MCM) system based on the real-valued discrete Hartley transform (DHT) and its inverse (IDHT). Unlike the conventional discrete Fourier transform (DFT), the DHT cannot diagonalize multipath fading channels due to its inherent properties, and this results in mutual interference between subcarriers of the same mirror-symmetrical pair. We explore this interference pattern in order to seek an optimal solution to utilize channel diversity for enhancing the bit error rate (BER) performance of the system. It is shown that the optimal channel diversity gain can be achieved via pairwise maximum likelihood (ML) detection, taking into account not only the subcarrier's own channel quality but also the channel state information of its mirror-symmetrical peer. Performance analysis indicates that DHT-based MCM can mitigate fast fading effects by averaging channel power gains of each mirror-symmetrical pair of subcarriers. Simulation results show that the proposed scheme has a substantial improvement in BER over the conventional DFT-based MCM system

Interference analysis and power allocation in the presence of mixed numerologies

The flexibility in supporting heterogeneous services with vastly different technical requirements is one of the distinguishing characteristics of the fifth generation (5G) communication systems and beyond. One viable solution is to divide the system bandwidth into several bandwidth parts (BWPs), each having a distinct numerology optimized for a particular service. However, multiplexing of mixed numerologies over a unified physical infrastructure comes at the cost of induced interference. In this paper, we develop an analytical system model for inter-numerology interference (InterNI) analysis in orthogonal frequency-division multiplexing (OFDM) systems with and without filter processing in the presence of mixed numerologies. With the analytical model, the level of InterNI is quantified by the developed analytical metric, which is expressed as a function of several system parameters. This leads to an analysis and evaluation of these parameters for meeting a given distortion target. Moreover, a case study on power allocation utilizing the derived analysis is presented, where an optimization problem of maximizing the sum rate is formulated, and a solution is also provided. It is also demonstrated that a filtered-OFDM system better accommodates the coexistence of mixed numerologies. The proposed model provides an accurate analytical guidance for the multi-service design in 5G and beyond systems

Filtered OFDM: an insight into intrinsic in-band interference and filter frequency response selectivity

The future mobile networks will face challenges in support of heterogeneous services over a unified physical layer, calling for a waveform with good frequency localization. Filtered orthogonal frequency division multiplexing (f-OFDM), as a representative subband filtered waveform, can be employed to improve the spectrum localization of orthogonal frequency-division multiplexing (OFDM) signal. However, the applied filtering operations will impact the performance in various aspects, especially for narrow subband cases. Unlike existing studies which mainly focus its benefits, this paper investigates two negative consequences inflicted on single subband f-OFDM systems: in-band interference and filter frequency response (FFR) selectivity. The exact-form expression for the in-band interference is derived, and the effect of FFR selectivity is analyzed for both single antenna and multiple antenna cases. The in-band interference-free and nearly-free conditions for f-OFDM systems are studied. A low-complexity blockwise parallel interference cancellation (BwPIC) algorithm and a pre-equalizer are proposed to tackle the two issues caused by the filtering operations, respectively. Numerical results show that narrower subbands suffer more performance degradation compared to wider bands. In addition, the proposed BwPIC algorithm effectively suppresses interference, and pre-equalized f-OFDM (pf-OFDM) considerably outperforms f- OFDM in both single antenna and multi-antenna systems

Resource allocation for mixed numerology NOMA

6G wireless networks will require the flexibility to accommodate an extremely diverse set of service types. Accommodating different quality of service (QoS) requirements for these service types necessitates the use of mixed numerologies, where services using different subcarrier spacings or symbol durations coexist in the same frequency band. Non-orthogonal multiple access (NOMA) techniques can potentially be used to accommodate users with different numerologies while also gaining the performance benefits associated with NOMA. To achieve the full performance benefits of a mixed numerology NOMA (MN-NOMA) system, resource allocation is paramount. However, the coexistence of mixed numerologies changes the nature of the interference that each user experiences. In this letter, we approach the problem of optimizing subcarrier and power allocation for maximizing the spectral efficiency of MN-NOMA. In particular, we propose a two-stage sub-optimal approach to solve this problem. Numerical results show that the proposed approach provides performance gains over existing benchmark schemes of up to 14% and 12% in spectral efficiency and fairness, respectively

Interference Analysis in Multi-Numerology OFDM Systems: A Continuous-Time Approach

Multi-numerology multi-carrier (MN-MC) techniques are considered as essential enablers for RAN slicing in fifth-generation (5G) communication systems and beyond. However, utilization of mixed numerologies breaks the orthogonality principle defined for single-numerology orthogonal frequency division multiplexing (SN-OFDM) systems with a unified subcarrier spacing. This leads to interference between different numerologies, i.e., inter-numerology interference (INI). This paper develops metrics to quantify the level of the INI using a continuous-time approach. The derived analytical expressions of INI in terms of mean square error (MSE) and error vector magnitude (EVM) directly reveal the main contributing factors to INI, which can not be shown explicitly in a matrix form INI based on discrete-time calculations. Moreover, the study of power offset between different numerologies shows a significant impact on INI, especially for high order modulation schemes. The finding in this paper provides analytical guidance in designing multi-numerology (MN) systems, for instance, developing resource allocation schemes and interference mitigation techniques

Multiplexing of Mixed Numerologies in OFDM/Filtered-OFDM Systems

The flexibility in supporting heterogeneous services with vastly different technical requirements is one of the distinguishing characteristics of the fifth generation (5G) communication systems and beyond. A generic framework is developed in this thesis to address the coexistence/isolation issues of mixing multiple services over a unified physical infrastructure, where the system bandwidth is divided into several bandwidth parts (BWPs), each being allocated a distinct numerology optimized for a particular service. However, multiplexing of mixed numerologies in the same carrier comes at the cost of induced inter-numerology interference (Inter-NI). The Inter-NI can be mitigated by performing additional filtering process on top of orthogonal frequency-division multiplexing (OFDM) waveform for each numerology, namely filtered OFDM or F-OFDM. The additional filtering operation makes transmitted signal better localized in the frequency domain but worse in the time domain, which in turn causes issues within numerology, such as intra-numerology interference (Inter-NI) and filter frequency response selectivity (FFRS). With the developed analysis framework, the problems within numerology and between different numerologies are analyzed, respectively. The issues of Intra-NI and FFRS are firstly analyzed within single numerology. An Intra-NI-free and a nearly-free condition for an F-OFDM system are discussed, and an algorithm on how to select the optimal cyclic redundancy (CR) length is presented. In addition, the impact of FFRS is analyzed for both single antenna and multiple antenna cases, and a pre-equalized F-OFDM (PF-OFDM) system is proposed to tackle the issue. The level of distortion, the Intra-NI and Inter-NI, is quantified by the developed analytical metrics, each of which is a function of several system parameters. Consequently, this leads to an analysis and evaluation of these parameters for meeting a given signal distortion target. A case study utilizing the offered analysis is also presented, where an optimization problem of power allocation is formulated, and a solution is also proposed in multi-numerology systems. It is also demonstrated that a F-OFDM system better addresses the coexistence/isolation problem of mixed numerologies. The work in this thesis provides an insightful analytical guidance for the multi-service design in 5G and beyond systems