The trend toward using increasingly large arrays of antenna elements continues. However, fitting more antennas into the limited space available on user equipment (UE) within the currently popular Frequency Range 1 spectrum presents a significant challenge. This limitation constrains the capacity-scaling gains for end users, even when networks support a higher number of antennas. To address this issue, we explore a user-centric collaborative MIMO approach, termed UE-CoMIMO, which leverages several fixed or portable devices within a personal area to form a virtually expanded antenna array. This paper develops a comprehensive mathematical framework to analyze the performance of UE-CoMIMO. Our analytical results demonstrate that UE-CoMIMO can significantly enhance the system’s effective channel response within the current communication system without requiring extensive modifications. Further performance improvements can be achieved by optimizing the phase shifters on the expanded antenna arrays at the collaborative devices. These findings are corroborated by ray-tracing simulations. Beyond the simulations, we implemented these collaborative devices and successfully conducted over-the-air validation in a real 5G environment, showcasing the practical potential of UE-CoMIMO. Several practical perspectives are discussed, highlighting the feasibility and benefits of this approach in real-world scenarios.

In this paper, we consider superposition coding (SC) scheme in a multiple-input multiple-output (MIMO) broadcast channel when the transmitter obtains the channel state information (CSI) through user's quantized feedback. The algorithms for the base station (BS) scheduling, including users selection, power allocation among co-scheduled users, and precoding matrix assignment are investigated. We also derive bounds for the achievable rates of the SC scheme with quantized CSI feedback and imperfect user measurement being taken into account.

In this paper, two issues in assessing the performance of superposition coding (SC) in the downlink Long Term Evolution (LTE) are investigated. The first issue is the prediction of user's signal-to-interference-plus-noise ratio (SINR) at the scheduler based on the user's channel state information (CSI) feedback, when the actual transmission scheme is different from the scheme used for CSI computation. Prediction of the SINR value is needed for the assignment of the modulation order and the code rate. The second issue is with regards to the physical layer abstraction used for modeling the system-level performance of the SC scheme on the basis of the link-level simulation results. With the physical layer abstraction, the complexity of the system level simulation is reduced significantly.

Sequences with specific autocorrelation (AC) and cross-correlation (CC) properties are crucial components in radar and wireless communications. In this paper, we derive the theoretical bounds on the AC and CC for OFDM sequences with constraints of spectral nulls, e.g., the mandatory nulls on the DC sub-carrier and guardbands in OFDM systems. The bounds and trade-off limits are provided for the properties of sequences, including the peak AC and CC levels, the cardinality of the sequence set, the sequence length, and the temporal length of the low correlation zone. We also investigate the trade-offs of correlations among sequence sets. The presented trade-off limits can serve as guidelines for applications where the performance measures or design criteria are related to the peak AC and CC levels.

Multiple-input multiple-output (MIMO) technique provides capacity improvement which scales linearly with the number of antennas. However, such improvement cannot be realized in line-of-sight (LOS) environments due to lack of scattering. It had been proposed that if a mobile station can receive signal from multiple repeaters, the artificial multipath could render an equivalent high-rank end-to-end MIMO channel. In this paper, we study whether fixed-location repeaters can induce significant MIMO capacity gain throughout the coverage of a cell in a LOS environment. Our results indicate that, for a wide range of repeater locations and antenna parameters, the majority of the coverage area of a cell can support a high-order capacity scaling factor. We further show that for a capacity scaling factor of 2, the corresponding coverage consists of a small number of simply-connected areas. We present the expressions for the contour of these areas as a function of base station and repeater locations, antenna spacings, and antenna orientations.

Fountain codes are suitable for data transmission over binary erasure channels. When such codes are applied in live broadcast applications, due to the limited bandwidth and delay constraints, it is often convenient to treat the input media stream as a concatenation of short data blocks and to encode each block individually. However, the use of a small block size may result in poor coding efficiency. In this paper, we introduce an approach to enhance the coding efficiency by encoding over progressively more source bits. Our approach can be considered as a generalization of the expanding window fountain code concept. In addition, we provide an error analysis based on state generating functions. The state generating function is useful both as a performance evaluation tool and as a design criterion for the generalized expanding window codes.

Many communication and radar systems necessitate the use of sequences with desired autocorrelation (AC) and cross-correlation (CC) properties. This paper presents a systematic method based on the transform domain characterization of the AC and CC constraints to generate new families of sequences that meet the requirements. We demonstrate that some existing families can easily be generated by our approach. Our approach, however, renders new families of sequences with less constraints. The proposed approach is elementary and can easily be extended to synthesize two-dimensional arrays or even higher dimensional waveforms that possess the desired multidimensional correlation properties. A preamble structure based on our new sequence family is suggested and performance of frequency offset and channel estimation algorithms for a multiantenna orthogonal frequency-division multiplexing (OFDM) system that uses such a preamble is given.

Many communication and radar systems necessitate the use of sequences with desired autocorrelation (AC) and crosscorrelation (CC) properties. This paper presents a systematic method based on the frequency (transform) domain characterization of the AC and CC constraints to generate new families of sequences that meet the requirements. We demonstrate that some existing families can easily be generated by our approach. But our approach is more general for it renders new families of sequences with less constraint on the sequence's AC period. The proposed approach is elementary and can easily be extended to synthesize two-dimensional arrays that possess the desired two-dimensional correlation properties.