The paradigm of wireless communications is shifting from data transfer to ubiquitous services. Perception of the surrounding environment has recently been highlighted as one of the key technologies enabling new applications, such as autonomous driving, extended reality, and healthcare. This movement gives a rise to an emerging concept of integrated sensing and communication (ISAC), where the distributed communication nodes, such as the base station and user devices, serve as probes for wide-area sensing, and the wideband radio signals are shared between communication and sensing. In recent years, a lot of effort has been directed towards the two main pillars of ISAC, i.e., self-localization of a node (positioning) and detection of device-free objects around the node (sensing). Nevertheless, only few of them have been implemented and brought up for real-world verification. This paper provides our latest efforts on validating the feasibility of wireless positioning and sensing. Through over-the-air measurement and processing in a 5G NR millimeter network with a commercial grade user equipment (UE), we demonstrate that the NR positioning and sensing techniques are mature enough to drive the evolution toward perceptive and cognitive wireless communications.

Integrated sensing and communication have drawn great research attention in recent years. Specifically, 5G mmWave has demonstrated its capabilities not only in high-speed communications but also in perceiving the physical environment. Apart from providing locationing services for user equipment (UE), 5G mmWave can also estimate the position of target objects that does not carry any equipment (i.e., device-free). Existing works of device-free wireless localization often employs a single monostatic radar or a few transceivers in fixed positions. In this work, we examine a cooperative sensing case, where multiple UEs cooperate with the infrastructure of transmit/receive points (TRPs) to jointly locate device-free objects. This new setting brings in new challenges for existing locationing algorithms as the number and the locations of the UEs and sensing targets are all dynamic. Our work proposes a novel procedure that uses visualization methods to jointly represent the information in the mmWave channel impulse responses and the locations of UEs and TRPs. We then introduce an end-to-end deep learning transformer architecture inspired by popular models in the computer vision domain to estimate the target objects’ locations from the visualizations. On a dataset generated using 3D ray-tracing simulations, our system can locate multiple device-free objects with an average error of 0.47 meters within a 20 meterby-40 meter experiment area.

Full-duplex (FD) millimeter-wave radios can increase the spectral efficiency and reduce the latency. In order to take an advantage of the FD technology, a self-interference (SI) needs to be suppressed. In this paper, we investigate the characteristics of SI in the 28 GHz band using over-the-air (OTA) measurements. Using our 28 GHz OTA FD platform, we investigate passive isolation with different antenna layouts and beam steering. We also use an intra-band carrier aggregation signal based on the fifth generation NR standard, and propose a nonlinear interference cancellation (NLIC) technique that works on a per-carrier component (CC) basis for multi-carrier systems. To deal with intermodulation distortion, we propose to include inter-CC terms for NLIC and confirm that the proposed FD and NLIC designs provide sufficient self-interference cancellation performance.

Full-duplex (FD) radios, which are expected to increase the spectral efficiency and reduce the latency, can help meet the ever-increasing capacity demands, in combination with the millimeter-wave (mmWave) band. In order to utilize the benefits of the FD technology, it is important to understand the characteristics of the self-interference (SI) in the mmWave band. In this paper, we study the impact of SI in the 60 GHz band and design self-interference cancellation (SIC) techniques. Using a 60 GHz hardware platform, we investigate passive SI isolation with beam steering. We also propose a nonlinear interference cancellation (NLIC) technique of feasible complexity with a limited number of kernels. Over-the-air link performance confirms that the proposed FD transceiver design provides sufficient SIC performances.

In cellular communications, user equipment (UE, i.e., mobile device)-side interference cancellation (IC) along with multicell coordinated scheduling can significantly reduce the effect of the downlink intercell interference. To aid UE-side IC, a study item, called network-assisted interference cancellation and suppression (NAICS), has been initiated for Long Term Evolution (LTE) Advanced Release 12. Among NAICS receivers, this paper considers a receiver with interference-aware successive decoding (IASD) capability, which is one of the most advanced UE-side IC techniques. The IASD achievable transmission rate is dependent on the interferer transmission rate. Thus, coordination among multiple cells for rate and UE selection would be necessary for the overall network performance enhancement. In this paper, we consider a single dominant interference model and propose an optimal single-user rate selection algorithm based on the belief-propagation framework. In the multi-user-per-cell case we propose several UE and rate selection algorithms and analyze their performance.

It has been generally believed that the multiple-input multiple-output channel capacity grows linearly with the size of antenna arrays. In terms of degrees of freedom, linear transmit and receive arrays of length L in a scattering environment of total angular spread \Ω\ asymptotically have \Ω\L degrees of freedom. In this paper, it is claimed that the linear increase in degrees of freedom may not be attained when scattered electromagnetic fields in the underlying scattering environment are statistically correlated. After introducing a model of correlated scattering, which is referred to as the colored scattering model, we derive a capacity upper bound, assuming that the channel is known perfectly at the receiver and in distribution at the transmitter. Unlike the uncorrelated case, the prelog factor of the capacity, i.e., the number of degrees of freedom, in the colored scattering channel is asymptotically limited by \Ω\·min{L, 1/ ΓI} where Γ is a parameter determining the extent of correlation. In other words, for very large arrays in the colored scattering environment, degrees of freedom can get saturated to an intrinsic limit rather than increasing linearly with the array size.

This comment corrects a few errors found in the derivation of the maximum likelihood estimate of differential phase in the paper, "A Technique for Orthogonal Frequency Division Multiplexing Frequency Offset Correction." We show that the problem of differential phase estimation can be considered as an estimation problem in the presence of nuisance parameters, which does not satisfy strong ancillarity. The approach in the above paper to solve this problem can be understood as conditioning for elimination of nuisance parameters but without taking proper steps. After making corrections on the proof, it is demonstrated that the estimator in the above paper is inherently suboptimal and thus prior knowledge on the nuisance parameters, if available, can be utilized to further improve the estimation performance.

Blind adaptive I/Q imbalance compensation has become more popular during the last decade due to its simplicity and need for no training data. In existing work, it has been pointed out that a statistical property of a signal, which is referred to as the properness condition, can be used for blind I/Q imbalance compensation. In this letter, the equi-absolute variance condition as well as the properness condition are used to propose two blind adaptive I/Q imbalance compensation algorithms based on the well-known LMS and RLS adaptation algorithms. The performances of the proposed algorithms are evaluated through simulations, and it is shown that the proposed algorithms provide nice convergence behaviors and high image rejections.

In this paper, we consider a class of single-source multicast relay networks. We assume that all outgoing channels of a node in the network to its neighbors are orthogonal while the incoming signals from its neighbors can interfere with each other. We first focus on Gaussian relay networks with interference and find an achievable rate using a lattice coding scheme. We show that the achievable rate of our scheme is within a constant bit gap from the information theoretic cut-set bound, where the constant depends only on the network topology, but not on the transmit power, noise variance, and channel gains. This is similar to a recent result by Avestimehr, Diggavi, and Tse, who showed an approximate capacity characterization for general Gaussian relay networks. However, our achievability uses a structured code instead of a random one. Using the idea used in the Gaussian case, we also consider a linear finite-field symmetric network with interference and characterize its capacity using a linear coding scheme.

A new partial transmit sequence (PTS) technique for orthogonal frequency division multiplexing (OFDM) signals which does not require side information, is proposed. In the proposed method, the transmitter applies PTS to reduce the peak-to-average power ratio (PAPR) and does not send the side information on the PTS phase factors to the receiver. Based on the OFDM symbol structure having pilot subcarriers, the receiver jointly estimates the channel and PTS phase factors from the pilot subcarriers. The proposed technique inherently causes bit error rate (BER) loss depending on the PTS subgroup size. However, simulation results demonstrate that if the PTS subgroup size is carefully chosen, the proposed method can reduce the PAPR significantly with a negligible BER loss.

In this paper, a Gaussian two-way relay channel, where two source nodes exchange messages with each other through a relay, is considered. We assume that all nodes operate in full-duplex mode and there is no direct channel between the source nodes. We propose an achievable scheme composed of nested lattice codes for the uplink and structured binning for the downlink. Unlike conventional nested lattice codes, our codes utilize two different shaping lattices for source nodes based on a three-stage lattice partition chain, which is a key ingredient for producing the best gap-to-capacity results to date. Specifically, for all channel parameters, the achievable rate region of our scheme is within1/2bit from the capacity region for each user and its sum rate is within log3/2bit from the sum capacity.

Increasing the dwell time in two-dimensional frequency-time hypothesis testing is, in practical terms, one of the most effective ways for Assisted Global Navigation Satellite Systems (A-GNSS) and GNSS receivers to achieve higher sensitivity. In an asynchronous cellular network, however, a mobile terminal may have a non-negligible unknown clock drift rate error originating from the received cellular downlink signal. In such a case, increasing the dwell time may not necessarily result in the expected sensitivity improvement. In addition, a mobile terminal in a rich multipath environment may experience jitters in the code phase of the resolved first arrival path due to short-delay multipaths, which also degrades the sensitivity. In this paper, new decision variables using a lone or a pair of adjacent H_1 cells for code phase hypothesis testing and clock drift rate hypothesis testing are proposed to cope with the unknown code phase drift rate error and the effect of code phase jitter in a parallel acquisition system. The statistics of the proposed decision variables are analyzed in a Rayleigh fading channel, and the performances of the proposed decision variables are compared with that of the conventional decision variable.

Preamble-based cell identification (CID) schemes are derived for orthogonal frequency division multiplexing (OFDM) systems. They include the optimal schemes based on the Bayesian and the maximum likelihood (ML) approaches, a suboptimal scheme that is a simplification of the ML scheme, and a differential decoding-based scheme that does not require any channel information. The complexities and performances of these CID schemes are examined and compared to existing schemes. The differential decoding-based scheme performs like the suboptimal scheme for most practical channels of interest and outperforms existing schemes, yet it is simpler to implement than the others.

This paper considers a broadband cellular orthogonal frequency-division multiple-access (OFDMA) system with relay nodes operating in decode-and-forward and half-duplex mode. Two transmit resource allocation problems for sum-rate maximization are formulated for such a system. The first one is the optimization of subcarrier allocation with predetermined power assignment for each subcarrier, and the other is the joint optimization of power and subcarrier allocation. Since these problems can't be solved easily in direct forms, we make continuous relaxation and solve the dual problems using a subgradient method. Numerical results show that a remarkable increment in sum-rate is achieved, with the aid of relay nodes and sophisticated resource allocation, compared to a system without relay nodes.