We consider the uplink of a multicell multiuser single-input multiple-output system (MU-SIMO), where the channel experiences both small- and large-scale fading. The data detection is done by using ...the linear zero-forcing technique, assuming the base station (BS) has perfect channel state information of all users in its cell. We derive new exact analytical expressions for the uplink rate, the symbol error rate (SER), and the outage probability per user, as well as a lower bound on the achievable rate. This bound is very tight and becomes exact in the large-number-of-antenna limit. We further study the asymptotic system performance in the regimes of high signal-to-noise ratio (SNR), large number of antennas, and large number of users per cell. We show that, at high SNRs, the system is interference limited, and hence, we cannot improve the system performance by increasing the transmit power of each user. Instead, by increasing the number of BS antennas, the effects of interference and noise can be reduced, thereby improving system performance. We demonstrate that, with very large antenna arrays at the BS, the transmit power of each user can be made inversely proportional to the number of BS antennas while maintaining a desired quality of service. Numerical results are presented to verify our analysis.
It is well known that the performance of frequency-division-duplex (FDD) massive MIMO systems with i.i.d. channels is disappointing compared with that of time-division-duplex (TDD) systems, due to ...the prohibitively large overhead for acquiring channel state information at the transmitter (CSIT). In this paper, we investigate the achievable rates of FDD massive MIMO systems with spatially correlated channels, considering the CSIT acquisition dimensionality loss, the imperfection of CSIT and the regularized-zero-forcing linear precoder. The achievable rates are optimized by judiciously designing the downlink channel training sequences and user CSIT feedback codebooks, exploiting the multiuser spatial channel correlation. We compare our achievable rates with TDD massive MIMO systems, i.i.d. FDD systems, and the joint spatial division and multiplexing (JSDM) scheme, by deriving the deterministic equivalents of the achievable rates, based on the one-ring model and the Laplacian model. It is shown that, based on the proposed eigenspace channel estimation schemes, the rate-gap between FDD systems and TDD systems is significantly narrowed, even approached under moderate number of base station antennas. Compared to the JSDM scheme, our proposal achieves dimensionality-reduction channel estimation without channel pre-projection, and higher throughput for moderate number of antennas and moderate to large channel coherence block length, though at higher computational complexity.
In massive multiple-input-multiple-output base stations, power consumption and cost of the low-noise amplifiers (LNAs) can be substantial because of the many antennas. We investigate the feasibility ...of inexpensive, power efficient LNAs, which inherently are less linear. A polynomial model is used to characterize the nonlinear LNAs and to derive the second-order statistics and spatial correlation of the distortion. We show that, with spatial matched filtering (maximum-ratio combining) at the receiver, some distortion terms combine coherently, and that the signal-to-interference-and-noise ratio of the symbol estimates therefore is limited by the linearity of the LNAs. Furthermore, it is studied how the power from a blocker in the adjacent frequency band leaks into the main band and creates distortion. The distortion term that scales cubically with the power received from the blocker has a spatial correlation that can be filtered out by spatial processing and only the coherent term that scales quadratically with the power remains. When the blocker is in free-space line-of-sight and the LNAs are identical, this quadratic term has the same spatial direction as the desired signal, and hence cannot be removed by linear receiver processing.
It is now well known that employing channel adaptive signaling in wireless communication systems can yield large improvements in almost any performance metric. Unfortunately, many kinds of channel ...adaptive techniques have been deemed impractical in the past because of the problem of obtaining channel knowledge at the transmitter. The transmitter in many systems (such as those using frequency division duplexing) can not leverage techniques such as training to obtain channel state information. Over the last few years, research has repeatedly shown that allowing the receiver to send a small number of information bits about the channel conditions to the transmitter can allow near optimal channel adaptation. These practical systems, which are commonly referred to as limited or finite-rate feedback systems, supply benefits nearly identical to unrealizable perfect transmitter channel knowledge systems when they are judiciously designed. In this tutorial, we provide a broad look at the field of limited feedback wireless communications. We review work in systems using various combinations of single antenna, multiple antenna, narrowband, broadband, single-user, and multiuser technology. We also provide a synopsis of the role of limited feedback in the standardization of next generation wireless systems.
A robust nonlinear control is designed for stabilizing linear multi-input-multi-output systems. The presented control law homogenizes a linear system (without its transformation to a canonical form) ...with a specified degree and stabilizes it in a finite time (or with a fixed-time attraction to any compact set containing the origin) if the degree of homogeneity is negative (positive). The tuning procedure is formalized in an linear matrix inequalities (LMI) form. Performance of the approach is illustrated by numerical and experimental examples.
Phased array antennas in MIMO receiver Kozłowski, Sebastian; Yashchyshyn, Yevhen; Modelski, Józef
Journal of Telecommunications and Information Technology,
06/2023
1
Journal Article
Peer reviewed
Open access
In this paper, a computer simulation of a MIMO system comprising phased array antennas (PAA) in all receiving branches is presented. In order to examine the system performance under relatively ...realistic conditions, a ray-tracing simulator was applied to generate a baseband channel impulse response matrix H. A bit error rate (BER) of two systems utilizing different detection methods: V-BLAST and simple matrix inversion was examined in order to determine phased array antennas applicability. Results of an attempt to determine relationship between BER and properties of particular matrix H realization are also provided.
In this paper, we study the performance of spatial modulation (SM) multiple-input-multiple-output (MIMO) wireless systems over generic fading channels. More precisely, a comprehensive analytical ...framework to compute the average bit error probability (ABEP) is introduced, which can be used for any MIMO setup, for arbitrary correlated fading channels, and for generic modulation schemes. It is shown that, when compared with state-of-the-art literature, our framework 1) has more general applicability over generalized fading channels, 2) is, in general, more accurate as it exploits an improved union-bound method, and, 3) more importantly, clearly highlights interesting fundamental trends about the performance of SM, which are difficult to capture with available frameworks. For example, by focusing on the canonical reference scenario with independent identically distributed Rayleigh fading, we introduce very simple formulas that yield insightful design information on the optimal modulation scheme to be used for the signal constellation diagram, as well as highlight the different roles played by the bit mapping on the signal and spatial constellation diagrams. Numerical results show that, for many MIMO setups, SM with phase-shift-keying (PSK) modulation outperforms SM with quadrature-amplitude modulation (QAM), which is a result never reported in the literature. In addition, by exploiting asymptotic analysis, closed-form formulas of the performance gain of SM over other single-antenna transmission technologies are provided. Numerical results show that SM can outperform many single-antenna systems and that, for any transmission rate, there is an optimal allocation of the information bits onto spatial and signal constellation diagrams. Furthermore, by focusing on the Nakagami-fading scenario with generically correlated fading, we show that fading severity plays a very important role in determining the diversity gain of SM. In particular, the performance gain over single-antenna systems increases for fading channels less severe than Rayleigh fading, whereas it gets smaller for more severe fading channels. In addition, it is shown that the impact of fading correlation at the transmitter is reduced for less severe fading. Finally, analytical frameworks and claims are substantiated through extensive Monte Carlo simulations.
This letter proposes a two-port multiple-input-multiple-output smartphone antenna for frequency bands below 1 GHz, which is robust to user effects. The design is achieved by first analyzing the ...characteristic modes of a chassis that includes the large screen. Two modes predicted to be less affected by the user than other commonly used modes are selected. The modal currents and near-fields of the two desired modes then guide the design: The monopole-like mode introduced by the screen is tuned to resonance using shorting pins and selectively excited using the center feed location. The nonresonant loop mode is selectively excited for the first time by four inductive feeds added along the longer sides of the chassis, with proper phase shifts provided by a feeding network. The proposed antenna features isolation of above 19 dB and envelope correlation coefficient of below 0.12 in the considered scenarios. The measured bandwidth is above 15% for both ports, and the average radiation efficiency is 2 and 4.57 dB higher for two user scenarios with respect to a reference design. Moreover, no adaptive matching is needed as the impedance matching is robust to the user hand/head.
Cell-free Massive multiple-input multiple-output (MIMO) comprises a large number of distributed low-cost low-power single antenna access points (APs) connected to a network controller. The number of ...AP antennas is significantly larger than the number of users. The system is not partitioned into cells and each user is served by all APs simultaneously. The simplest linear precoding schemes are conjugate beamforming and zero-forcing. Max-min power control provides equal throughput to all users and is considered in this paper. Surprisingly, under max-min power control, most APs are found to transmit at less than full power. The zero-forcing precoder significantly outperforms conjugate beamforming. For zero-forcing, a near-optimal power control algorithm is developed that is considerably simpler than exact max-min power control. An alternative to cell-free systems is small-cell operation in which each user is served by only one AP for which power optimization algorithms are also developed. Cell-free Massive MIMO is shown to provide five- to ten-fold improvement in 95%-likely per-user throughput over small-cell operation.
The paper presents a technique to enhance the isolation between adjacent radiating elements that is common in densely packed antenna arrays. Such antennas provide frequency beam‐scanning capability ...needed in multiple‐input multiple‐output (MIMO) systems and synthetic aperture radars. The method proposed here uses a metamaterial decoupling slab (MTM‐DS), which is located between radiating elements, to suppress mutual coupling between the elements that would otherwise degrade the antenna efficiency and performance in both the transmit and receive mode. The proposed MTM‐DS consists of mirror imaged E‐shaped slits engraved on a microstrip patch with inductive stub. Measured results confirm over 9–11 GHz with no MTM‐DS the average isolation (S12) is −27 dB; however, with MTM‐DS the average isolation improves to −38 dB. With this technique the separation between the radiating element can be reduced to 0.66λ0, where λ0 is free space wavelength at 10 GHz. In addition, with this technique there is 15% improvement in operating bandwidth. At frequencies of high impedance match of 9.95 and 10.63 GHz the gain is 4.52 and 5.40 dBi, respectively. Furthermore, the technique eliminates poor front‐to‐back ratio encountered in other decoupling methods. MTM‐DS is also relatively simple to implement. Assuming adequate space is available between adjacent radiators the MTM‐DS can be fixed retrospectively on existing antenna arrays, which makes the proposed method versatile.
Key Points
A technique is presented to enhance isolation between adjacent radiating elements that are found in densely packed antenna arrays
The proposed method uses a metamaterial decoupling slab located between radiating elements to suppress mutual coupling between the elements
Over the antenna's operating frequency (9‐11 GHz) without MTM‐DS maximum isolation is ‐37 dB so with MTM‐DS it improves to ‐57 dB (35% growth)
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