Massive multiple-input multiple-output (MIMO) is a key technology to meet the user demands in performance and quality of services (QoS) for next generation communication systems. Due to a large number of antennas and radio frequency (RF) chains, complexity of the symbol detectors increased rapidly in a massive MIMO uplink receiver. Thus, the research to find the perfect massive MIMO detection algorithm with optimal performance and low complexity has gained a lot of attention during the past decade. A plethora of massive MIMO detection algorithms has been proposed in the literature. The aim of this paper is to provide insights on such algorithms to a generalist of wireless communications. We garner the massive MIMO detection algorithms and classify them so that a reader can find a distinction between different algorithms from a wider range of solutions. We present optimal and near-optimal detection principles specifically designed for the massive MIMO system such as detectors based on a local search, belief propagation and box detection. In addition, we cover detectors based on approximate inversion, which has gained popularity among the VLSI signal processing community due to their deterministic dataflow and low complexity. We also briefly explore several nonlinear small-scale MIMO (2-4 antenna receivers) detectors and their applicability in the massive MIMO context. In addition, we present recent advances of detection algorithms which are mostly based on machine learning or sparsity based algorithms. In each section, we also mention the related implementations of the detectors. A discussion of the pros and cons of each detector is provided.

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Massive MIMO Detection Techniques: A Survey

Among other things, a communication system comprising remote units and a controller is described. Each of the remote units comprises one or more radio frequency (RF) units to exchange RF signals with mobile devices. At least some of the RF signals comprise information destined for, or originating from, a mobile device. The controller comprises one or more modems and is connected to an external network. At least one of the modems is a baseband modem and is configured to pass first data corresponding to the information. The at least one of the modems is configured to perform real-time scheduling of the first data corresponding to the information. The controller is separated from the remote units by an intermediate network. The intermediate network comprises a switched Ethernet network over which second data corresponding to the information is carried in frames between the controller and the remote units.

Radio access networks

A distributed antenna system comprises a base transceiver station, a plurality of distributed antenna units and a signal routing apparatus. The base transceiver station has a plurality of output ports that generate a plurality of downlink signals having overlapping transmit frequencies and containing different communication content. The different communication content is directed toward each of a plurality of mobile units. The base transceiver station also has at least one uplink receive port that receives an uplink signal. The uplink signal includes communication content received from at least one of the mobile units. The plurality of distributed antenna units have coverage areas that are non-overlapping or only partially overlapping. The signal routing apparatus routes the downlink signals to the plurality of distributed antennas such that each of the plurality of downlink signals are transmitted by one or more of the distributed antennas and each distributed antenna only transmits one of the downlink signals.

Distributed antenna communications system

A method for deploying a wireless network in accordance with particular embodiments includes deploying one or more base stations configured to provide wireless connections between the one or more base stations and one or more endpoints. The method also includes deploying one or more remote transceivers configured to provide wireless connections between the one or more remote transceivers and one or more endpoints. The method further includes modifying at least one base station of the one or more base stations. The modified base station is configured to control the one or more remote transceivers. The method additionally includes modifying at least one remote transceiver of the one or more remote transceivers. The modified remote transceiver is configured to control the at least one remote transceiver without receiving control information from the at least one base station.

Method and apparatus for deploying a wireless network

We present joint multi-user beamforming (JMB), a system that enables independent access points (APs) to beamform their signals, and communicate with their clients on the same channel as if they were one large MIMO transmitter. The key enabling technology behind JMB is a new low-overhead technique for synchronizing the phase of multiple transmitters in a distributed manner. The design allows a wireless LAN to scale its throughput by continually adding more APs on the same channel. JMB is implemented and tested with both software radio clients and off-the-shelf 802.11n cards, and evaluated in a dense congested deployment resembling a conference room. Results from a 10-AP software-radio testbed show a linear increase in network throughput with a median gain of 8.1 to 9.4x. Our results also demonstrate that JMB's joint multi-user beamforming can provide throughput gains with unmodified 802.11n cards.

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JMB: scaling wireless capacity with user demands

In this paper, a multiple-input-multiple-output (MIMO) extension for a third-generation (3G) wireless system is described. The integration of MIMO concepts within the existing UMTS standard and the associated space-time RAKE receiver are explained. An analysis is followed by a description of an actual experimental MIMO transmitter and receiver architecture, both realized on digital signal processors (DSPs) and FPGAs within a precommercial OneBTS base station. It uses four transmit and four receive antennas to achieve downlink data rates up to 1 Mb/s per user with a spreading factor of 32 and the UMTS chip rate of 3.84 MHz. Furthermore, different MIMO detectors are evaluated, comparing their performance and complexity. System performance is evaluated through simulations and indoor over-the-air measurements. Capacity and bit-error rate measurement results are presented.

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Prototype experience for MIMO BLAST over third-generation wireless system

Cellular signals or other wireless signals/messages are introduced into a building or to an outside location by transmitting packets corresponding to those signals over a data network and low cost cables to designated locations within the data network. Once the designated packets containing the signals reach the destination, they are then broadcast over the air to a terminal capable of receiving the wireless message. In a first embodiment, an in-building gigabit Ethernet network, such as that currently existing presently in many buildings, is used to distribute radio signals indoors. Instead of transmitting the radio signals over the air from a repeater connected to a base station, coded baseband signals generated by the coding processor (e.g., a CDMA Modem Unit) in the base station are packetized and sent over the Ethernet network to radio processing equipment and antennas distributed throughout the building. The radio processing equipment strips the packet headers from the baseband signal packets so those signals can be broadcast via the antennas to one or more mobile terminals.

Method and apparatus for cellular communication over data networks

A method and an apparatus for enabling a digital wireless service across a first and a second wireless communications environment is provided The method comprises translating a receive signal carried on a forward link and having a first carrier frequency in the first wireless communications environment from a first frequency band to a second frequency band different from the first frequency band The method further comprises translating a transmit signal carried on a reverse link and having a second carrier frequency in the first wireless communications environment from the second frequency band to the first frequency band In this way, a digital wireless service may be provided between a mobile station and at least one base station on the ground across two different wireless communications environments The method further comprises compensating Doppler shift separately for individual beams directed at a plurality of terrestrial base stations The method further comprises injecting an additional path delay to insure that the terrestrial base stations receive reverse link signals at substantially similar round trip time offsets and to reduce search windows for the terrestrial base stations In this way, a wireless communication system may enable in-flight use of a mobile station to communicate with one or more base stations on the ground

Enabling a digital wireless service for a mobile station across two different wireless communications environments

RadioStar is a novel system developed by Bell Labs to provide low cost, cellular wireless coverage primarily targeted for enterprises, public spaces, and residences. The underlying concept is to digitize the output radio signals of a base station and to transport these signals over a Gigabit Ethernet network to multiple low-cost radio frequency radiation points. The received signals are returned through the network to the base station. This paper presents the architecture, implementation, and demonstration of RadioStar. It is shown how handoffs and precise frequency synchronization and timing control over a Gigabit Ethernet network can be established in such a way that the most stringent requirements of cellular communication air interfaces are satisfied. By converging cellular signal transport onto Gigabit Ethernet data networks, RadioStar can achieve substantially lower hardware and installation costs, while providing higher performance, more flexibility, and better operation, administration, and maintenance than current solutions. RadioStar concepts are being used in the ClearFill Star in-building product developed by the RFS business division of Alcatel-Lucent and currently being deployed commercially.

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Arnold Siegel

Papers

Prototype experience for MIMO BLAST over third-generation wireless system

Method and apparatus for cellular communication over data networks

Enabling a digital wireless service for a mobile station across two different wireless communications environments

RADIOSTAR: Providing wireless coverage over Gigabit ethernet