Integrated Sensing and Communications (ISAC) is a new usage scenario for 6G. To enable studying ISAC solutions, standardization bodies such as European Telecommunications Standards Institute (ETSI) and Third Generation Partnership Project (3GPP) require specified ISAC channel models. 3GPP has been studying changes to the existing TR 38.901 channel models to model radio-frequency (RF) signal interactions between the transmitter, sensing target, receiver, and surrounding environment. In parallel, ETSI has been working on additional features to further support channel modelling for the rich variety of ISAC use cases envisioned in 6G. In this paper, we present an outline of the latest developments from industry and further provide an evaluation framework for assessing the models.

This paper provides an extensive analysis of Reliable and Available Wireless (RAW) enhancements and solutions needed to manage industrial environments more effectively. Starting from the description of a representative industrial use case, an analysis of gaps and promising new extensions is performed. Namely, the need to (i) support multi-domain operation, at both technology and administrative levels; (ii) integrate RAW with edge architectures; and, (iii) increase the mobility support in RAW networks. The identified gaps are indeed not yet tackled by the relevant standardization development organizations, mainly the Internet Engineering Task Force (IETF), and are thus object of our future work.

With massive deployment, multiple-input–multiple-output (MIMO) systems continue to take mobile communications to new heights, but the ever-increasing demands mean that there is a need to look beyond MIMO and pursue the next disruptive wireless technologies. Reconfigurable intelligent surface (RIS) is widely considered a key candidate technology block to provide the next generational leap. The first part of this article provides an updated overview of the conventional reflection-based RIS technology, which complements the existing literature to include active and semiactive RIS, and the synergies with cell-free massive MIMO (CF mMIMO). Then, we widen the scope to discuss the surface-wave-assisted RIS that represents a different design dimension in utilizing metasurface technologies. This goes beyond being a passive reflector and can use the surface as an intelligent propagation medium for superb radio propagation efficiency. The third part of this article turns the attention to the fluid antenna, a novel antenna technology that enables a diverse form of reconfigurability that can combine with RIS for ultrahigh capacity, power efficiency, and scalability. This article concludes with a discussion of the potential synergies that can be exploited between MIMO, RIS, and fluid antennas.

Reconfigurable intelligent surfaces (RIS) have the ability to steer the electromagnetic (EM) waves to a desired direction. This enables the improvement of the wireless link performance by allowing the illumination of receivers otherwise shadowed by buildings or hills. In this paper, a standards-compliant link-level simulator is developed to study the performance improvement offered by a RIS in 5G New Radio (NR) uplink operating at sub-6 GHz bands. At these frequencies the direct channel between the user and base station is rarely completely blocked, but given the stringent power restrictions of devices, the RIS is utilized for enhancing the coverage performance in the uplink direction. In the studied cases, the transmitter (TX) is close to the RIS and a line-of-sight (LoS) path between the TX and RIS is assumed. The channel between the TX and receiver (RX) is modeled as a non-line-of-sight (NLoS) channel with 5G NR clustered delay line A (CDL-A) profile. Both LoS and NLoS channels between the RIS and RX are considered. Under state-of-the-art system settings, the RIS is shown to increase the symbol error rate link performance by 6 dB. When the performance is measured with coded bit error rate, the performance gain in simulated cases is 1 dB. The coverage enhancement is measured with the throughput as a function of the distance between the TX and RX. The distance at which the maximum possible throughput can be achieved is increased about 5%. The coverage can be further extended if a lower than the maximum throughput is accepted.

In addition to CPRI, new functional splits have been defined in 5G creating diverse fronthaul transport bandwidth and latency requirements. These fronthaul requirements shall be fulfilled simultaneously together with the backhaul requirements by an integrated fronthaul and backhaul transport solution. In this paper, we analyze the technical challenges to achieve an integrated transport solution in 5G and propose specific solutions to address these challenges. These solutions have been implemented and verified with pre-commercial equipment. Our results confirm that an integrated fronthaul and backhaul transport dubbed Crosshaul can meet all the requirements of 5G fronthaul and backhaul in a cost-efficient manner.

Millimeter wave (mmWave) communications has gained considerable attention due to the availability of large bandwidths, which can be harnessed to meet the ever-increasing data rate demands. Directional beamforming combined with baseband precoding should be used owing to the high propagation losses encountered at mmWave frequencies. This is typically referred to as hybrid beamforming. In hybrid beamforming arrangements, the adjacent antenna elements are closely spaced, typically at half-wavelength spacing in order to compensate for the propagation losses. In this antenna array configuration, the mutual coupling between the adjacent antenna elements becomes significant and may limit the performance of the system. Therefore, in this paper, we propose a reduced-complexity near-optimal detection scheme, namely the so-called Element-based Lattice Reduction algorithm, for hybrid beamforming in mmWave communications and we investigate its performance in the presence of mutual coupling. We demonstrate that the mutual coupling affects the spatial correlation of the channels between the different antennas depending on the distance between the antenna elements, which has a direct effect on the achievable rate as well as bit error ratio (BER) performance of the system.

The Internet of Things (IoT) will support a massive number of devices, which will be connected to the wireless network. In the wireless IoT, the base station serves a wide variety of devices in the same time-frequency resource, where it is expected that the number of devices will be greater than the number of base station antennas. This results in a rank-deficient system. In this paper, we propose a minimum bit error ratio (MBER) precoder for rank-deficient MIMO systems in the context of the IoT, where the IoT devices are generally stationary. We invoke the particle swarm optimization (PSO) algorithm for solving the non-linearly constrained MBER problem and we show that the PSO assisted MBER precoder outperforms the conventional zero forcing and linear minimum mean squared error (LMMSE) precoders, which produce an error floor in these challenging rank-deficient scenarios.

Hybrid analog-digital beamforming has emerged as an important technique to enable millimeter wave (mmWave) communications in 5G radio access networks. With a two-stage hybrid beamforming procedure, where analog and digital precoders are determined separately and sequentially, the benefits attributed to digital precoding on top of analog beams could be quite marginal in some cases, as sparse propagation paths in a mmWave channel could be well captured by analog beams alone. By exploiting such characteristic, this paper proposes a digital precoder codebook resolution adaptation scheme, wherein a user device is able to determine the digital precoder resolution based on the gain in addition to analog beamforming, in order to reduce feedback overhead without significant performance degradation.

The millimeter wave (mmWave) frequency band offers substantial hitherto unused spectral resources for future wireless communication systems in order to meet the increasing capacity demand. However, mmWave frequencies suffer from high propagation losses, which may be mitigated by directional beamforming in addition to baseband precoding. This is usually referred to as hybrid beamforming. In this paper, we investigate the so-called discrete Fourier transform- mutually unbiased bases (DFT-MUB) aided codebook design conceived for limited-feedback mmWave systems, where the MUB aided codebook is applied in the baseband, while the DFT codebook is invoked for RF analog phase shifters. We demonstrate that our DFT- MUB codebook design performs similarly to the optimal digital precoding matrix, where the precoder is selected as the right singular matrix of the channel. However, our solution significantly reduces the search complexity in the baseband, while performing within 2.5 dB from the optimal digital precoder.

In this paper we propose a new cooperative video multicast strategy, the so called Coordinated Multiple Relays (CoMR). The strategy is based on an efficient one-to-many resource sharing technique which exploits the space diversity of the two hop topology. The proposed scheme ensures a) significant gain in terms of coverage provided by relay deployment, b) boosted Signal to Interference and Noise Ratios (SINRs) at the second phase of the two hop transmission due to the positive superposition of synchronous transmissions, and c) the flexibility to switch to non-cooperative mode whenever cooperation is no longer beneficial. The new scheme showed considerable enhancement of both system throughput and user fairness and noticeable improvement in terms of energy efficiency compared to the non-cooperative multicast scheme.

In this paper we evaluate an energy-aware relay selection mechanism which exploits channel state information and the availability of buffers at relays to perform flexible relaying based on a backpressure-driven optimization model. This model ensures the maximization of the cell throughput while maintains the stability of backlog queues. Performance evaluation is conducted using a System Level Simulator (SLS) which is fully compliant with IEEE 802.16m and supports various relaying scenarios. The Below Roof Top (BRT) relaying scenario is considered in this work. A holistic and flexible energy framework is implemented to capture the energy consumption of the cellular network nodes. The model maps the RF output power radiated at the antenna elements of each node including relays on the network to the total supply power of the node equipment. Two derivatives of the proposed mechanism, half-duplex and full-duplex are proposed and evaluated. Results of the two derivatives on BRT relaying scenario revealed noticeable increases for both cell throughput and system energy efficiency of the cell-edge users compared to the conventional relaying protocol and the non cooperative scheme.

This paper investigates high order NonUniform Constellations (NUC) with constellation sizes of up to 4K-QAM for broadcasting over-the-air very high data rate services such as Ultra-High Definition TV (UHDTV). An iterative algorithm is proposed for fast convergence towards the optimal NUC at each Signal-to-Noise Ratio (SNR) operating point. Performance evaluation assuming DVB-T2 as a reference shows significant gains for NUC over uniform constellations, above 1 dB for orders higher than 256-QAM, and up to 2 dB with 4K-QAM. This gain in dB converts into a relative throughput gain of nearly 10% compared to DVB-T2 using 32k FFT size with LDPC code rate 1/2.

This paper addresses the problem of link quality prediction on a secondary frequency carrier from measurements on a primary carrier during a scanning interval in multi-carrier wireless networks. An MMSE linear predictor is proposed which makes use of the information available in particular on shadowing time and frequency correlation. Compared to state of the art, the proposed solution achieves a significant gain in accuracy of prediction, up to 2.2 dB in average RMSE for 30 kmh mobile speed and IEEE 802.16e maximum scanning interval duration of 1.275 sec. The accuracy gain decreases when the time increases or the mobile speed increases, but it always keeps positive, thus proving the superiority of the proposed solution as compared to state of the art.

This paper presents a system level simulator for the evaluation of WiMAX IEEE 802.16m technologies in a multi-cellular environment. This simulator is a quite powerful tool which allows quantifying the benefits of proposed air interface technologies on overall system performance using several metrics. As a case of study, the paper conducts performance evaluation of WiMAX IEEE 802.16m contiguous and distributed sub-channelization modes. The results obtained show a clear advantage for the distributed mode in term of system throughput but not in term of number of simultaneously active users. Similarly, many different cases of study can be further conducted using this simulation platform, which will yield crystal clear conclusions on the performance of WiMAX IEEE 802.16m system.

In this paper the combination of Transmit Antenna Selection with Linear Dispersion Code Selection is studied. Two optimization criteria are proposed (bit error rate minimization and throughput maximization). The performance of the proposed spatial link adaptation scheme is evaluated under low mobility environments concluding that maximum spatial diversity is achieved as well as a smooth transition between codes with low spatial multiplexing rate and high spatial diversity (suitable for low SNR), to codes with high multiplexing rate but low diversity order (suitable for high SNR) maximizing the overall system throughput.

Linear dispersion codes (LDCs) are capable of achieving a good trade-off between link throughput and link robustness in multiple input multiple output (MIMO) broadband wireless access systems. This is thanks to their efficient spreading of data across both time and space domains. This paper proposes a novel LDC design method utilising the unitary matrix theory along with a genetic algorithm (GA). The proposed design framework can produce LDCs attaining higher data rates and better error protection than various well-known MIMO schemes, such as the Alamouti space-time code and spatial multiplexing (SM).

This paper proposes new frequency-time schedulers for 3GPP/LTE-like system in the downlink. 3GPP/LTE DL is OFDMA-based with adaptive modulation and coding (AMC) and frequency-time scheduling to enhance spectral efficiency and aggregate system throughput. Time-frequency scheduling and AMC can be implemented jointly or separately i.e. sequentially AMC after scheduling. Two novel schedulers are proposed in this paper with respectively joint and separate implementation of scheduling and AMC. Through system level performance evaluation, results show that the first scheduler with separate AMC and scheduling implementation outperforms the second scheduler (with joint AMC implementation) in terms of trade off between fairness and capacity and implementation complexity.