There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Wireless Communications

Mobile users' data rate and quality of service are limited by the fact that, within the duration of any given call, they experience severe variations in signal attenuation, thereby necessitating the use of some type of diversity. In this two-part paper, we propose a new form of spatial diversity, in which diversity gains are achieved via the cooperation of mobile users. Part I describes the user cooperation strategy, while Part II (see ibid., p.1939-48) focuses on implementation issues and performance analysis. Results show that, even though the interuser channel is noisy, cooperation leads not only to an increase in capacity for both users but also to a more robust system, where users' achievable rates are less susceptible to channel variations.

http://dns2.asia.edu.tw/~ysho/YSHO-English/2000%20Engineering/PDF/IEE%20Tra%20Com51,%201927.pdf

User cooperation diversity. Part I. System description

Multi-user MIMO offers big advantages over conventional point-to-point MIMO: it works with cheap single-antenna terminals, a rich scattering environment is not required, and resource allocation is simplified because every active terminal utilizes all of the time-frequency bins. However, multi-user MIMO, as originally envisioned, with roughly equal numbers of service antennas and terminals and frequency-division duplex operation, is not a scalable technology. Massive MIMO (also known as large-scale antenna systems, very large MIMO, hyper MIMO, full-dimension MIMO, and ARGOS) makes a clean break with current practice through the use of a large excess of service antennas over active terminals and time-division duplex operation. Extra antennas help by focusing energy into ever smaller regions of space to bring huge improvements in throughput and radiated energy efficiency. Other benefits of massive MIMO include extensive use of inexpensive low-power components, reduced latency, simplification of the MAC layer, and robustness against intentional jamming. The anticipated throughput depends on the propagation environment providing asymptotically orthogonal channels to the terminals, but so far experiments have not disclosed any limitations in this regard. While massive MIMO renders many traditional research problems irrelevant, it uncovers entirely new problems that urgently need attention: the challenge of making many low-cost low-precision components that work effectively together, acquisition and synchronization for newly joined terminals, the exploitation of extra degrees of freedom provided by the excess of service antennas, reducing internal power consumption to achieve total energy efficiency reductions, and finding new deployment scenarios. This article presents an overview of the massive MIMO concept and contemporary research on the topic.

/pdf/massive-mimo-for-next-generation-wireless-systems-1eydagg3js.pdf

Massive MIMO for next generation wireless systems

Multiuser diversity is a form of diversity inherent in a wireless network, provided by independent time-varying channels across the different users. The diversity benefit is exploited by tracking the channel fluctuations of the users and scheduling transmissions to users when their instantaneous channel quality is near the peak. The diversity gain increases with the dynamic range of the fluctuations and is thus limited in environments with little scattering and/or slow fading. In such environments, we propose the use of multiple transmit antennas to induce large and fast channel fluctuations so that multiuser diversity can still be exploited. The scheme can be interpreted as opportunistic beamforming and we show that true beamforming gains can be achieved when there are sufficient users, even though very limited channel feedback is needed. Furthermore, in a cellular system, the scheme plays an additional role of opportunistic nulling of the interference created on users of adjacent cells. We discuss the design implications of implementing. this scheme in a complete wireless system.

https://web.stanford.edu/~dntse/papers/oppbf_it.pdf

Opportunistic beamforming using dumb antennas

This paper presents a new approach to the soft detection of spatial data streams in MIMO channels in slow fading channels. We focus on high spectral efficiency bit interleaved coded modulation (BICM) MIMO OFDM system where, after serial to parallel conversion and per antenna coding, spatial data streams are simultaneously transmitted by using an antenna array. We propose a detection algorithm basing on the combination of linear and non linear detection techniques. The proposed algorithm orders the spatial streams as per V-BLAST ordering and then uses linear detectors as MMSE or zero forcing (ZF) to detect the streams which have seen good channel realizations and therefore enjoy higher signal-to-noise-ratios (SNRs). These streams after being detected are subsequently stripped off leading to the max log MAP detection of the streams which have seen comparatively poor realizations of the channel and consequently have lower SNRs. Unlike maximum likelihood (ML) detection, whose complexity is huge due to the need for enumerating all possible combinations of the transmitted constellation points, the proposed method has low complexity. The algorithm has a fully parallel structure, suitable for the implementation in parallel hardware. Numerical examples illustrate its performance on slow fading 3 × 3 and 4 × 4 complex MIMO channels.

Reduced complexity soft detection for BICM MIMO OFDM system

We describe a demonstration run on R2lab, an anechoic chamber located at Inria Sophia Antipolis, France. The demonstration consists in deploying a standalone 5G network in less than 5 minutes. All the network components (base station, subscriber management, serving and packet gateways, network traffic analyzers) were run automatically using the nepi-ng experiment orchestration tool. Download and upload performance to the Internet from a commercial phone located in the anechoic chamber are shown.

https://dl.acm.org/doi/pdf/10.1145/3123878.3132005

Deploy a 5G Network in Less Than 5 Minutes

Power control possibilities are explored for the downlink of a time-division duplex (TDD) CDMA system while employing three different kinds of multipath diversity combining schemes namely the RAKE, the pre-RAKE and the transmit antenna pre-selection. In the latter two, knowledge of the channel characteristics is employed at the base-station to provide maximum decoupling between users on the downlink. Performance of the these receivers is compared in a Rayleigh fading urban environment. It is shown that power control is absolutely indispensable in the latter two schemes and results in considerable performance gains as compared to the RAKE receiver.

/pdf/power-control-for-diversity-reception-in-time-division-2q6kycop7c.pdf

Power control for diversity reception in time-division duplex CDMA

In this paper, we study a communication system consisting of three end-nodes, e.g. a single transceiver base station (BS), one transmitting and one receiving user equipments (UEs), and a common two-way relay node (RN) wherein the full-duplex BS transmits to the receiving UE in downlink direction and receives from the transmitting UE in uplink direction with the help of the intermediate full-duplex RN. We call this system model as interference two-way relay channel (ITWRC) with three end-nodes. Information theoretic bounds corresponding this system model are derived and analyzed so as to better understand the potentials of exploiting RN in future communication systems. Specifically, achievable rate regions corresponding to decode-and-forward (DF) relaying with and without rate splitting, and partial-DF and compress-and-forward (pDF+CF) relaying strategies are derived.

Interference Two-Way Relay Channel with Three End-nodes

Performance of future wireless communication systems being interference limited, researchers are focusing on interference alignment, interference mitigation and interference suppression to diminish, manage or exploit these interferers. In this paper, we carry out the performance analysis of the recently proposed low complexity max log MAP detector and linear MMSE detector for interference suppression under the realistic conditions of correlated fading in cellular environment. We assume only receive correlation as base stations (BSs) due to their extended separation are likely to be uncorrelated. However the intricacy of realizing requisite antenna spacing in the mobile station (MS) combined with the lack of scattering would instigate the individual antennas at MS to be correlated. Employing moment generating function (MGF)-based approach, we derive upper bounds of coded pairwise error probability (PEP) and study the degrading effect of correlation on both the detectors.

/pdf/analysis-of-low-complexity-max-log-map-detector-and-mmse-3ul6k4a0dk.pdf

Raymond Knopp

Papers

Reduced complexity soft detection for BICM MIMO OFDM system

Deploy a 5G Network in Less Than 5 Minutes

Power control for diversity reception in time-division duplex CDMA

Interference Two-Way Relay Channel with Three End-nodes

Analysis of Low Complexity Max Log MAP Detector and MMSE Detector for Interference Suppression in Correlated Fading