The extreme multiple-input multiple-output (X-MIMO) framework is vital for 6G due to its capacity for extensive spatial multiplexing using numerous antenna ports. As antenna ports increase, the need for channel state information reference signals (CSI-RS) increases, leading to high overhead and energy usage, which limits data resources and performance gains. Although engaging all antennas ports for data transmission and reception reaps the high performance of X-MIMO, channel measurement from the reduced number of ports increases the efficiency. This study introduces a deep learning-based method for CSI reconstruction that reduces overhead in X-MIMO systems, called Transformer-based CSI feedback with subsampled CSI-RS (TS-CSI-RS). The TS-CSI-RS reconstructs the full-port channel information from undersampled measurement via Transformer. Simulations in a realistic channel environment show that TS-CSI-RS significantly reduces CSI-RS overhead (up to 75%) compared to conventional 5G systems, allowing spatial adaptation without activating all antenna ports for CSI measurement.

In modern wireless systems, the process of acquiring channel state information (CSI) has become increasingly important and challenging due to the conflicting needs of expanding antenna arrays and achieving high spectrum efficiency. Recent solutions leverage joint source and channel coding (JSCC) realized by an auto-encoder structure to enable a hybrid optimization of CSI compression and transmission, which shows great potential to improve the effectiveness of CSI feedback. However, the gap between research and realization is still big. This article proposes a comprehensive JSCC method for CSI feedback, including a technique solution for eliminating the impacts of residential fading and radio frequency ($\mathbf{R F}$) imperfections, and a protocol design to support the realization of the method in practical cellular systems. Furthermore, a hardware proof-ofconcept (PoC) platform was developed to validate the JSCC-based CSI feedback, and the results demonstrate the superiority of the method in realistic environments.

Since its introduction for long term evolution (LTE), vehicle-to-everything (V2X) communications have evolved to the recent new radio (NR)-based V2X with enhanced reliability, latency, capacity, and flexibility. One of the key features of NR V2X is the enabling of sidelink (SL) communications between user equipments (UEs) without any assistance from a base station (i.e. support of the out-of-coverage scenario). To this end, NR V2X supports SL resource allocation (RA) mode 2, in which a UE autonomously determines the subset of resources to use for data transmission while avoiding resource collision due to other UEs. This paper summarizes the resource sensing and selection (RSS) mechanisms for SL RA mode 2 specified in releases 16 and 17 of NR V2X. The critical aspect for RSS is the minimization of UE power consumption during resource sensing, which is caused by multiple blind decodings on the physical SL control channel. To address this issue, the effective number of blind decodings for conventional RSS is quantitatively analyzed to determine the potential enhancements required. Furthermore, an enhanced RA mode 2 procedure based on an intelligent partial-sensing (IPS) scheme is proposed to minimize the number of blind decodings. The proposed IPS utilizes a convolutional neural network-based physical channel-type classification model. Simulation and numerical results show that the throughput obtained with the proposed IPS scheme approximates that obtained via full sensing-based RA mode 2, while reducing the number of blind decodings by 90%.

This paper discusses a new 5G-Advanced duplex scheme called sub-band full-duplex (SBFD) and the details of implementing it for 5G TDD spectrum. The SBFD requires an advanced self interference cancellation (SIC) which is designed to handle extremely high level of cross link interference. Novel SIC techniques were designed for base stations (BSs) operating on 3.4 GHz with massive MIMO and on 26 GHz with multi-beam capability. By utilizing electromagnetic walls in conjunction with electromagnetic bandgap, an extremely high level of isolation between transmit and receive antennas is achieved. Residual interference is further removed using fractional nonlinear interference estimation in baseband. Two Proofs-of-Concepts (PoCs) have been implemented for feasibility verification. The first PoC was for a massive MIMO BS operating with 32 cross polarized antenna ports on 3.4 GHz and a bandwidth of 100 MHz. The second PoC was for a multi-beam BS with 256 antenna elements operating on 26 GHz and a bandwidth of 400 MHz. It was observed that the self-interference in SBFD can be suppressed in real time to a level of less than 0.7 dB over the RX noise floor for both 3.4 GHz and 26 GHz in an outdoor environment.

In this paper, an advanced duplex scheme, referred to as cross division duplex (XDD), is proposed to use flexible downlink (DL) and uplink (UL) allocation in time division duplex (TDD) carrier. By implementing self-interference cancellation (SIC) functions at the base station, the proposed XDD enables to simultaneously operate UL and DL on different frequency subband in the same channel. To do so, both TDD's ability to efficiently handle asymmetric UL and DL traffic and frequency division duplexing's coverage and latency advantage can be achieved together. To verify the feasibility of XDD, a Proof-of-Concept is developed and self-interference can be removed almost perfectly with proper implementation of SIC without guardband between DL and UL subband. From evaluation results, UL coverage, as well as latency, was improved using a longer UL duty period in XDD. Based on XDD, in 5G-Advanced, a significantly higher resource utilization than the existing 5G will be possible.

Industrial-IoT (IIoT) is one of the key areas where 5G is expected to expand its application into. IIoT requires higher reliability as well as lower latency when compared to typical IoT services. In 3GPP, IIoT is supported as part of 5G utilizing many of the features that were introduced for ultra-reliable and low latency communication (URLLC). In this paper, two channel access mechanisms under consideration for 5G IIoT in 3GPP are studied; i) dynamic channel access mechanism known as LBE (load based equipment) and ii) semi-static channel access mechanism known as FBE (frame based equipment). Average latency performance is compared for the two mechanisms using mathematical analysis and numerical results based on 3GPP evaluation assumptions. It is observed that FBE is beneficial in a congested environment where the wireless channel is likely to be busy and LBE is useful in a non-congested environment where the wireless channel is not likely to be busy.

Faster-Than-Nyquist (FTN) is a technique that can improve the spectral efficiency of communication systems by making better use of available spectrum resources at the cost of inter-symbol interference (ISI) and inter-carrier interference (ICI). In this paper, we propose a hybrid signaling scheme for a practical application of FTN for MIMO transmission. We propose a new slot structure optimized for the hybrid signaling supporting both FTN signaling and orthogonal frequency division multiplexing (OFDM) signaling. Specifically, in the proposed slot structure, data transmission is based on the FTN signaling and the pilot transmission is based on the OFDM signaling. Numerical results confirm that the proposed signaling scheme has clear benefit over the systems employing only OFDM or FTN signaling.

In this paper, a compressed sensing based channel acquisition is proposed for beyond 5G systems where the single carrier waveform is used over the millimeter wave spectrum. The key idea of the proposed technique, 2-dimensional compressed channel recovery (2D-CCR), is to estimate channel impulse response based on randomly selected time-domain pilot samples transmitted in a localized portion of the bandwidth. As a result of 2D-CCR, channel information of full bandwidth can be acquired from compressed sensing without having to take the measurement on the entire bandwidth. From the numerical evaluations, it is observed that the proposed scheme outperforms conventional channel estimation schemes in terms of estimation accuracy.

A novel physical downlink control channel (PDCCH) blind decoding method based on demodulation reference signal (DMRS) detection is proposed to reduce the power consumption at user equipment (UE) for 5G New Radio (NR). In the proposed scheme, a UE performs energy detection for the DMRS in the search space before PDCCH blind decoding. Based on the information of the time/frequency location where the DMRS is detected, the UE can dynamically adjust PDCCH monitoring configuration. Such adjustment helps UE to minimize unnecessary blind decoding attempts depending on the data traffic. Evaluations show a significant power saving gain over the conventional methods.

This paper studies a hybrid automatic repeat and request (HARQ) mechanism for multicast/broadcast services in 5G New Radio (NR) systems. HARQ is widely used in unicast transmission to improve reliability and resource efficiency under the fading channel. However, for multicast/broadcast, it is difficult to apply conventional HARQ technology because the probability of retransmission becomes high as the number of receiver increases. In this paper, we propose a novel and efficient retransmission scheme, called outer code- based HARQ. After the initial transmission of a given data packet for multicast/broadcast, each receiver sends feedback information on how many code blocks (CBs) are broken instead of which CBs are broken. Then, for retransmission of the data, the transmitter generates parity CBs by using outer code such as Reed- Solomon (RS) or Raptor code and transmits the parity CBs after applying inner code such as low density parity check (LDPC) code. Numerical results show that the proposed scheme outperforms the conventional HARQ schemes, reducing more than 50% of retransmissions.

This paper investigates a grant-free non-orthogonal multiple access (NOMA) system where massive number of users wake up and send data right away without performing a grant-based initial access procedure. Since no scheduling grant is used in this system, the base station (BS) does not know which user is transmitting on each resource. Also, due to the lack of an uplink (UL) timing control process, multiple user's signals are asynchronously received at the BS. This causes asynchronous interference, or multiuser inter-carrier and inter-symbol interference. We propose two ideas to address these two problems. We first propose an auxiliary preamble structure to successfully detect the user activity, even in the presence of a massive number of users. We, then, propose a modification to the interleave-division multiple access (IDMA) receiver to mitigate asynchronous interference. The simulation results show that the proposed scheme significantly improves the preamble detection performance and BER performance compared to the conventional schemes. Furthermore, we show that the proposed grant-free NOMA system can achieve much better performance than the grant-based NOMA system in terms of transmission time and signaling overhead.

Licensed band communication systems have recently begun trying to utilize unlicensed bands. Due to lack of coordination, however, this spectrum utilization results in strong interference to other unlicensed band equipment (UBE). This problem highlights the need for coexistence scenario that will prevent UBE performance degradation. In this paper, we propose a new access control mechanism for downlink cellular networks using the unlicensed band. First, we analyze the impact of the cellular networks on the UBE outage performance. Based on the analysis, we then obtain a decision threshold for the unlicensed band access control. In the proposed control mechanism, the decision threshold is adaptively controlled by considering the density of the UBE. The numerical results demonstrate that the proposed access control mechanism guarantees the UBE's target performance under various network circumstances.

Device to device (D2D) communication techniques is one of main themes for the next generation wireless communication techniques. Compared to traditional Wireless Wide Area Network (WAN) communication where all radio links are formed between a user equipment (UE) and a base station (eNB), D2D communication uses a direct link between two different UEs. In the standard organization, 3rd Generation Partnership Project (3GPP), there is an ongoing discussion to adopt the D2D communication in current Long Term Evolution Advanced (LTE-A) system. The main target use cases of the D2D in LTE system comprise public safety using direct communication and commercial services using proximal device discovery. Introduction of the D2D discovery inside LTE-A network bring some impacts to existing cellular operation by the in-bane emission property. This paper provides a promising way to support D2D discovery in LTE-A system and analyze the in-band emission impact of D2D discovery on current LTE-A operation. In order to minimize the impact, an eNB based open loop power control algorithm is proposed for D2D discovery. To see the performance of the proposed scheme, system-level simulation results are provided. Our results show that eNB based open loop power control algorithm alleviate the in-band emission impact significantly.

In this paper, an asymptotic distribution for the sum rate capacity is derived in zero-forcing beamforming (ZF-BF) based multiuser MIMO systems with a large number of base station (BS)antennas. By utilizing the characteristics of a large number of antennas and the central limit theorem, we prove that the asymptotic distribution for the sum rate capacity follows Gaussian distribution. Also we derive the mean and variance values for the asymptotic Gaussian distribution. Based on the asymptotic Gaussian distribution, we also obtain the outage probability for the sum rate capacity as a closed form. Simulation results show that the asymptotic Gaussian distribution is well follows the actual sum rate capacity, and the both asymptotic mean and variance value are also very accurate.

This paper analyzes the pilot power ratio (PPR) in multiuser multiple-input multiple-output (MU-MIMO) systems with a large number of receive antennas (M) at the base station (BS). We consider zero-forcing based MU-MIMO orthogonal frequency division multiplexing (OFDM) systems. Based on the deterministic uplink sum-rate approximation for imperfect channel state information, we can formulate the optimization problems in terms of the PPR to maximize the ergodic uplink sum-rate subject to the per-slot or per-symbol power constraint. Under the per-slot power constraint, the optimal PPR can be obtained in a closed form while under the per-symbol power constraint, we propose an iterative algorithm which generates a suboptimal PPR. Simulation results show that the proposed PPRs perform close to the optimal performance in terms of the sum-rate. Also, it is shown that the proposed PPRs outperform the equal power allocation. In particular, in the ZF-R based MU-MIMO OFDM system with 8 users and M=32 under the per-slot power constraint, the proposed PPR can achieve about 8bps/Hz performance gain compared to the equal power allocation.

The impact of inaccurate channel knowledge on the system performance of a cooperative multi-cell system is studied. Using optimization theory, we investigate the performance degradation due to optimizing the collaborative downlink transmit signals of multiple base stations (BSs) based on inaccurate channel knowledge. Two important sources of channel knowledge inaccuracy are considered: quantization and delay. Based on mathematical analysis, multi-cell systems with different levels of cooperation are numerically evaluated and compared.

In this paper, the performance of orthogonal frequency division multiple access orthogonal frequency division multiple access (OFDMA) is studied in the context of the general multiuser multicarrier multiple-input multiple-output (MIMO) (M3) system for both uplink (UP) and downlink (DL) channels. The relationship between OFDMA and the optimal M3solution is investigated from an information theoretical point of view. Specifically, the necessary and sufficient conditions of OFDMA being the capacity-maximizing M3transmission scheme is derived. In addition, OFDMA optimality is explicitly analyzed in some special cases.

In this paper, a new slotted mode operation in a cdma2000 wireless system is proposed. The proposed operation is designed to support emerging services such as Push-To-Talk(PTT) that require low paging delay and low power consumption. The proposed operation tries to minimize the paging delay and maximize battery life while using the same amount energy as that of legacy reduced slot cycle mode with the assumption that the inter-arrival time of a PTT call follows an exponential distribution. In the performance analysis, it is shown that the average paging delay can be reduced or battery life can be reduced.

This paper studies the problem of efficient exploitation of the available bandwidth on the reverse link (RL) of cdma2000 1/spl times/EV-DV system. The objective is to maximize user throughput and to minimize packet delay while ensuring that forward link (FL) overhead is as low as possible. Two radio resource management (RRM) mechanisms, the time-scheduled (TS) scheme and the rate-controlled (RC) scheme, which can be used as the RRM schemes for the RL of 1/spl times/EV-DV are introduced and compared. It is shown that the RC scheme offers a better sector throughput through higher rise-over-thermal (RoT) utilization with less FL overhead, while the TS scheme outperforms the RC scheme in terms of packet delay through the capability of fast rate adaptation. In addition, a hybrid RRM scheme, namely rate control with quick start (RCQS) is introduced to combine the advantages of the TS and RC schemes. It is shown that the throughput and delay of the RCQS are comparable to those of the RC scheme the TS scheme, respectively.

The paper evaluates the performance of hybrid automatic repeat request (HARQ) for the code division multiple access (CDMA) reverse link in a power controlled scenario and assesses the effect of imperfect power control on HARQ. Analytical results on the performance of HARQ and the effect of imperfect power control are derived and verified using simulation in Rayleigh and Rician fading channels. Results show that HARQ provides robustness against imperfect power control.

This paper evaluates the performance of hybrid autonomous request (HARQ) for the cdma2000 reverse link in a power controlled scenario and assesses the effect of imperfect power control on HARQ. Analytical results on the performance of HARQ and the effect of imperfect power control are derived and verified using simulation in Rayleigh fading channels. Results show that HARQ provides robustness against imperfect power control.

The performance of an MC-CDMA system with carrier frequency offsets in correlated multipath fading is mathematically analyzed. The bit error rate is obtained from such analysis for the uplink Rayleigh fading channel. The derived results show that the performance of the MC-CDMA system is sensitive to the frequency offset, and the correlation of the subcarriers. That is, the performance degradation of the MC-CDMA system is caused by both carrier frequency offset and correlation among subcarriers. From the derived results, however, the performance degradation due to correlation among subcarriers is more severe than effect of frequency offset.

The effect of carrier frequency on the performance of an MC-CDMA (multi-carrier code division multiple access) system is considered. The bit error probability of the downlink of this system is analyzed taking into account the effect of frequency offset. This paper is focused on the derivation of the bit error probability mathematically. The derived results show that the performance of MC-CDMA is very sensitive even to a relatively minute degree of frequency offset. Parameters such as the degree of carrier offset, number of subcarriers, number of users, method of combining, and type of channel are varied so that the influence of each parameter can be assessed.

The effect of carrier frequency offset on the performance of an MC-CDMA (multi-carrier code division multiple access) system is considered. Bit error probability of the downlink of an MC-CDMA system is analyzed taking into account the effect of frequency offset. Derived results show that the performance of an MC-CDMA system is very sensitive even to a relatively small frequency offset. As a countermeasure against carrier frequency offset, pulse shaping is proposed and analyzed. Comparison of the proposed method using different pulse shapes to conventional MC-CDMA transmission scheme shows that a considerable degree of performance improvement is possible.